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Sample records for volcanic flank zone

Multi-stage volcanic island flank collapses with coeval explosive caldera-forming eruptions

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Hunt, James E.; Cassidy, Michael; Talling, Peter J.

2018-01-01

Volcanic flank collapses and explosive eruptions are among the largest and most destructive processes on Earth. Events at Mount St. Helens in May 1980 demonstrated how a relatively small (<5 km3) flank collapse on a terrestrial volcano could immediately precede a devastating eruption. The lateral collapse of volcanic island flanks, such as in the Canary Islands, can be far larger (>300 km3), but can also occur in complex multiple stages. Here, we show that multistage retrogressive lands...
Hazard Potential of Volcanic Flank Collapses Raised by New Megatsunami Evidence

Science.gov (United States)

Ramalho, R. S.; Winckler, G.; Madeira, J.; Helffrich, G. R.; Hipólito, A.; Quartau, R.; Adena, K.; Schaefer, J. M.

2015-12-01

Large-scale gravitational flank collapses of steep volcanic islands are hypothetically capable of triggering megatsunamis with highly catastrophic effects. Yet evidence for the existence and impact of collapsed-triggered megatsunamis and their run-up heights remains scarce and/or is highly contentious. Therefore a considerable debate still exists over the potential magnitude of collapse-triggered tsunamis and their inherent hazard. In particular, doubts still remain whether or not large-scale flank failures typically generate enough volume flux to result in megatsunamis, or alternatively operate by slow-moving or multiple smaller episodic failures with much lower tsunamigenic potential. Here we show that one of the tallest and most active oceanic volcanoes on Earth - Fogo, in the Cape Verde Islands - collapsed catastrophically and triggered a megatsunami with devastating near-field effects ~73,000 years ago. Our deductions are based on the recent discovery and cosmogenic 3He dating of tsunamigenic deposits - comprising fields of stranded megaclasts, chaotic conglomerates, and sand sheets - found on the adjacent Santiago Island, which attest to the impact of this megatsunami and document wave run-up heights exceeding 270 m. The evidence reported here implies that Fogo's flank failure involved at least one sudden and voluminous event that resulted in a megatsunami, in contrast to what has been suggested before. Our work thus provides another line of evidence that large-scale flank failures at steep volcanic islands may indeed happen catastrophically and are capable of triggering tsunamis of enormous height and energy. This new line of evidence therefore reinforces the hazard potential of volcanic island collapses and stands as a warning that such hazard should not be underestimated, particularly in areas where volcanic island edifices are close to other islands or to highly populated continental margins.
Multi-stage volcanic island flank collapses with coeval explosive caldera-forming eruptions.

Science.gov (United States)

Hunt, James E; Cassidy, Michael; Talling, Peter J

2018-01-18

Volcanic flank collapses and explosive eruptions are among the largest and most destructive processes on Earth. Events at Mount St. Helens in May 1980 demonstrated how a relatively small (300 km 3 ), but can also occur in complex multiple stages. Here, we show that multistage retrogressive landslides on Tenerife triggered explosive caldera-forming eruptions, including the Diego Hernandez, Guajara and Ucanca caldera eruptions. Geochemical analyses were performed on volcanic glasses recovered from marine sedimentary deposits, called turbidites, associated with each individual stage of each multistage landslide. These analyses indicate only the lattermost stages of subaerial flank failure contain materials originating from respective coeval explosive eruption, suggesting that initial more voluminous submarine stages of multi-stage flank collapse induce these aforementioned explosive eruption. Furthermore, there are extended time lags identified between the individual stages of multi-stage collapse, and thus an extended time lag between the initial submarine stages of failure and the onset of subsequent explosive eruption. This time lag succeeding landslide-generated static decompression has implications for the response of magmatic systems to un-roofing and poses a significant implication for ocean island volcanism and civil emergency planning.
Focused seismicity triggered by flank instability on Kīlauea's Southwest Rift Zone

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Judson, Josiah; Thelen, Weston A.; Greenfield, Tim; White, Robert S.

2018-03-01

Swarms of earthquakes at the head of the Southwest Rift Zone on Kīlauea Volcano, Hawai´i, reveal an interaction of normal and strike-slip faulting associated with movement of Kīlauea's south flank. A relocated subset of earthquakes between January 2012 and August 2014 are highly focused in space and time at depths that are coincident with the south caldera magma reservoir beneath the southern margin of Kīlauea Caldera. Newly calculated focal mechanisms are dominantly dextral shear with a north-south preferred fault orientation. Two earthquakes within this focused area of seismicity have normal faulting mechanisms, indicating two mechanisms of failure in very close proximity (10's of meters to 100 m). We suggest a model where opening along the Southwest Rift Zone caused by seaward motion of the south flank permits injection of magma and subsequent freezing of a plug, which then fails in a right-lateral strike-slip sense, consistent with the direction of movement of the south flank. The seismicity is concentrated in an area where a constriction occurs between a normal fault and the deeper magma transport system into the Southwest Rift Zone. Although in many ways the Southwest Rift Zone appears analogous to the more active East Rift Zone, the localization of the largest seismicity (>M2.5) within the swarms to a small volume necessitates a different model than has been proposed to explain the lineament outlined by earthquakes along the East Rift Zone.
Heat flow, morphology, pore fluids and hydrothermal circulation in a typical Mid-Atlantic Ridge flank near Oceanographer Fracture Zone

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Le Gal, V.; Lucazeau, F.; Cannat, M.; Poort, J.; Monnin, C.; Battani, A.; Fontaine, F.; Goutorbe, B.; Rolandone, F.; Poitou, C.; Blanc-Valleron, M.-M.; Piedade, A.; Hipólito, A.

2018-01-01

Hydrothermal circulation affects heat and mass transfers in the oceanic lithosphere, not only at the ridge axis but also on their flanks, where the magnitude of this process has been related to sediment blanket and seamounts density. This was documented in several areas of the Pacific Ocean by heat flow measurements and pore water analysis. However, as the morphology of Atlantic and Indian ridge flanks is generally rougher than in the Pacific, these regions of slow and ultra-slow accretion may be affected by hydrothermal processes of different regimes. We carried out a survey of two regions on the eastern and western flanks of the Mid-Atlantic Ridge between Oceanographer and Hayes fracture zones. Two hundred and eight new heat flow measurements were obtained along six seismic profiles, on 5 to 14 Ma old seafloor. Thirty sediment cores (from which porewaters have been extracted) have been collected with a Kullenberg corer equipped with thermistors thus allowing simultaneous heat flow measurement. Most heat flow values are lower than those predicted by purely conductive cooling models, with some local variations and exceptions: heat flow values on the eastern flank of the study area are more variable than on the western flank, where they tend to increase westward as the sedimentary cover in the basins becomes thicker and more continuous. Heat flow is also higher, on average, on the northern sides of both the western and eastern field regions and includes values close to conductive predictions near the Oceanographer Fracture Zone. All the sediment porewaters have a chemical composition similar to that of bottom seawater (no anomaly linked to fluid circulation has been detected). Heat flow values and pore fluid compositions are consistent with fluid circulation in volcanic rocks below the sediment. The short distances between seamounts and short fluid pathways explain that fluids flowing in the basaltic aquifer below the sediment have remained cool and unaltered
VOLCANIC TSUNAMI GENERATING SOURCE MECHANISMS IN THE EASTERN CARIBBEAN REGION

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George Pararas-Carayannis

2004-01-01

Full Text Available Earthquakes, volcanic eruptions, volcanic island flank failures and underwater slides have generated numerous destructive tsunamis in the Caribbean region. Convergent, compressional and collisional tectonic activity caused primarily from the eastward movement of the Caribbean Plate in relation to the North American, Atlantic and South American Plates, is responsible for zones of subduction in the region, the formation of island arcs and the evolution of particular volcanic centers on the overlying plate. The inter-plate tectonic interaction and deformation along these marginal boundaries result in moderate seismic and volcanic events that can generate tsunamis by a number of different mechanisms. The active geo-dynamic processes have created the Lesser Antilles, an arc of small islands with volcanoes characterized by both effusive and explosive activity. Eruption mechanisms of these Caribbean volcanoes are complex and often anomalous. Collapses of lava domes often precede major eruptions, which may vary in intensity from Strombolian to Plinian. Locally catastrophic, short-period tsunami-like waves can be generated directly by lateral, direct or channelized volcanic blast episodes, or in combination with collateral air pressure perturbations, nuéss ardentes, pyroclastic flows, lahars, or cascading debris avalanches. Submarine volcanic caldera collapses can also generate locally destructive tsunami waves. Volcanoes in the Eastern Caribbean Region have unstable flanks. Destructive local tsunamis may be generated from aerial and submarine volcanic edifice mass edifice flank failures, which may be triggered by volcanic episodes, lava dome collapses, or simply by gravitational instabilities. The present report evaluates volcanic mechanisms, resulting flank failure processes and their potential for tsunami generation. More specifically, the report evaluates recent volcanic eruption mechanisms of the Soufriere Hills volcano on Montserrat, of Mt. Pel
Geomorphological Approach for Regional Zoning In The Merapi Volcanic Area

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Langgeng Wahyu Santosa

2013-07-01

Full Text Available Geomorphologial approach can be used as the basic for identifying and analyzing the natural resources potentials, especially in volcanic landscape. Based on its geomorphology, Merapi volcanic landscape can be divided into 5 morphological units, i.e.: volcanic cone, volcanic slope, volcanic foot, volcanic foot plain, and fluvio-volcanic plain. Each of these morphological units has specific characteristic and natural resources potential. Based on the condition of geomorphology, the regional zoning can be compiled to support the land use planning and to maintain the conservation of environmental function in the Merapi Volcanic area.
Tectonics of ridge-transform intersections at the Kane fracture zone

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Karson, J. A.; Dick, H. J. B.

1983-03-01

The Kane Transform offsets spreading-center segments of the Mid-Atlantic Ridge by about 150 km at 24° N latitude. In terms of its first-order morphological, geological, and geophysical characteristics it appears to be typical of long-offset (>100 km), slow-slipping (2 cm yr-1) ridge-ridge transform faults. High-resolution geological observations were made from deep-towed ANGUS photographs and the manned submersible ALVIN at the ridge-transform intersections and indicate similar relationships in these two regions. These data indicate that over a distance of about 20 km as the spreading axes approach the fracture zone, the two flanks of each ridge axis behave in very different ways. Along the flanks that intersect the active transform zone the rift valley floor deepens and the surface expression of volcanism becomes increasingly narrow and eventually absent at the intersection where only a sediment-covered ‘nodal basin’ exists. The adjacent median valley walls have structural trends that are oblique to both the ridge and the transform and have as much as 4 km of relief. These are tectonically active regions that have only a thin (young volcanics passes laterally into median valley walls with a simple block-faulted character where only volcanic rocks have been found. Along strike toward the fracture zone, the youngest volcanics form linear constructional volcanic ridges that transect the entire width of the fracture zone valley. These volcanics are continuous with the older-looking, slightly faulted volcanic terrain that floors the non-transform fracture zone valleys. These observations document the asymmetric nature of seafloor spreading near ridge-transform intersections. An important implication is that the crust and lithosphere across different portions of the fracture zone will have different geological characteristics. Across the active transform zone two lithosphere plate edges formed at ridge-transform corners are faulted against one another. In the non
Estimating volume of deposits associated with landslides on volcanic landscapes in the SW flank of the volcano Pico de Orizaba, Puebla-Veracruz

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Gabriel Legorreta Paulín

2017-03-01

Full Text Available Landslides that occur along river systems are very common and have the potential to cause harm to human, to its infrastructure or affect their socio-economic activity. This dynamic is magnified in territories where morphological contrasts are very marked; as in the border between the mountains and subhorizontal land. This is especially true for volcanic terrains where volcanic activity can trigger voluminous landslides along stream systems by sector and flank collapse and where high seasonal rainfall on terrains covered by poorly consolidated materials produces small but hazardous landslides and debris flows that occur continually along stream systems during the volcanic repose periods. Those type of landslides can deliver volumes of hundreds and millions cubic meters that create a potentially hazardous situation for people and property down the valleys. The study of landslides in volcanic terrains through a Geographic Information System (GIS and under a geomorphological criterion, have allowed to develop a comprehensive methodology linked to the development of multi-temporal inventory, with susceptibility and volume estimation of displaced material. The aim of this research is to develop a method (protocol for landslide susceptibility and landslide volume assessment of potentially unstable volcanic landscapes in order to be helpful in mitigating landslide damages to human settlements. Pico de Orizaba volcano is the highest volcano in Mexico. The volcano has been affected by large flank collapse landslides throughout its geological history. These events have partially destroyed the cone as it happened in Bezymianny volcano and St. Elena volcano. In this volcano, the risk associated with landslide and debris flows, is increased by the growing of human settlements along the hillslopes and by the subsistence agriculture, and deforestation. This situation is favored by a volcanic calm that has lasted 147 years, approximate. These conditions create a
Topographic stress and catastrophic collapse of volcanic islands

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Moon, S.; Perron, J. T.; Martel, S. J.

2017-12-01

Flank collapse of volcanic islands can devastate coastal environments and potentially induce tsunamis. Previous studies have suggested that factors such as volcanic eruption events, gravitational spreading, the reduction of material strength due to hydrothermal alteration, steep coastal cliffs, or sea level change may contribute to slope instability and induce catastrophic collapse of volcanic flanks. In this study, we examine the potential influence of three-dimensional topographic stress perturbations on flank collapses of volcanic islands. Using a three-dimensional boundary element model, we calculate subsurface stress fields for the Canary and Hawaiian islands to compare the effects of stratovolcano and shield volcano shapes on topographic stresses. Our model accounts for gravitational stresses from the actual shapes of volcanic islands, ambient stress in the underlying plate, and the influence of pore water pressure. We quantify the potential for slope failure of volcanic flanks using a combined model of three-dimensional topographic stress and slope stability. The results of our analysis show that subsurface stress fields vary substantially depending on the shapes of volcanoes, and can influence the size and spatial distribution of flank failures.
A Volcanic Hydrogen Habitable Zone

International Nuclear Information System (INIS)

Ramirez, Ramses M.; Kaltenegger, Lisa

2017-01-01

The classical habitable zone (HZ) is the circular region around a star in which liquid water could exist on the surface of a rocky planet. The outer edge of the traditional N_2–CO_2–H_2O HZ extends out to nearly ∼1.7 au in our solar system, beyond which condensation and scattering by CO_2 outstrips its greenhouse capacity. Here, we show that volcanic outgassing of atmospheric H_2 can extend the outer edge of the HZ to ∼2.4 au in our solar system. This wider volcanic-hydrogen HZ (N_2–CO_2–H_2O–H_2) can be sustained as long as volcanic H_2 output offsets its escape from the top of the atmosphere. We use a single-column radiative-convective climate model to compute the HZ limits of this volcanic hydrogen HZ for hydrogen concentrations between 1% and 50%, assuming diffusion-limited atmospheric escape. At a hydrogen concentration of 50%, the effective stellar flux required to support the outer edge decreases by ∼35%–60% for M–A stars. The corresponding orbital distances increase by ∼30%–60%. The inner edge of this HZ only moves out ∼0.1%–4% relative to the classical HZ because H_2 warming is reduced in dense H_2O atmospheres. The atmospheric scale heights of such volcanic H_2 atmospheres near the outer edge of the HZ also increase, facilitating remote detection of atmospheric signatures.
A Volcanic Hydrogen Habitable Zone

Energy Technology Data Exchange (ETDEWEB)

Ramirez, Ramses M.; Kaltenegger, Lisa, E-mail: rmr277@cornell.edu [Carl Sagan Institute, Cornell University, Ithaca, NY (United States)

2017-03-01

The classical habitable zone (HZ) is the circular region around a star in which liquid water could exist on the surface of a rocky planet. The outer edge of the traditional N{sub 2}–CO{sub 2}–H{sub 2}O HZ extends out to nearly ∼1.7 au in our solar system, beyond which condensation and scattering by CO{sub 2} outstrips its greenhouse capacity. Here, we show that volcanic outgassing of atmospheric H{sub 2} can extend the outer edge of the HZ to ∼2.4 au in our solar system. This wider volcanic-hydrogen HZ (N{sub 2}–CO{sub 2}–H{sub 2}O–H{sub 2}) can be sustained as long as volcanic H{sub 2} output offsets its escape from the top of the atmosphere. We use a single-column radiative-convective climate model to compute the HZ limits of this volcanic hydrogen HZ for hydrogen concentrations between 1% and 50%, assuming diffusion-limited atmospheric escape. At a hydrogen concentration of 50%, the effective stellar flux required to support the outer edge decreases by ∼35%–60% for M–A stars. The corresponding orbital distances increase by ∼30%–60%. The inner edge of this HZ only moves out ∼0.1%–4% relative to the classical HZ because H{sub 2} warming is reduced in dense H{sub 2}O atmospheres. The atmospheric scale heights of such volcanic H{sub 2} atmospheres near the outer edge of the HZ also increase, facilitating remote detection of atmospheric signatures.
Geologic setting of the proposed West Flank Forge Site, California: Suitability for EGS research and development

Science.gov (United States)

Sabin, Andrew; Blake, Kelly; Lazaro, Mike; Blankenship, Douglas; Kennedy, Mack; McCullough, Jess; DeOreo, S.B.; Hickman, Stephen H.; Glen, Jonathan; Kaven, Joern; Williams, Colin F.; Phelps, Geoffrey; Faulds, James E.; Hinz, Nicholas H.; Calvin, Wendy M.; Siler, Drew; Robertson-Tait, Ann

2017-01-01

The proposed West Flank FORGE site is within the China Lake Naval Air Weapons Station (NAWS), China Lake, CA. The West Flank is west of the Coso geothermal field, an area of China Lake NAWS dominated by the Quaternary Coso volcanic field largely comprised of rhyolite domes and their volcaniclastic and epiclastic horizons. The largest dome flow complex, Sugarloaf Mountain, marks the northwestern margin of the geothermal field. The West Flank is situated due west of Sugarloaf. The geologic setting of the West Flank was determined from one deep well (83-11) drilled as a potential production hole in 2009. The bottom-hole temperature (BHT) of well 83-11 approaches 600 oF (315˚C), but flow tests demonstrate very low, non-commercial permeabilities. With the exception of the upper 600 feet of volcaniclastic alluvium, well 83-11 is completed in granitic basement. The West Flank possesses the primary attributes of a FORGE site: non-commercial permeability (geothermal fieldThe Coso Mountains host the Coso volcanic field and are within a right-releasing stepover between the dextral Airport Lake (ALF) and Little Lake fault zones (LLFZ) and the Wild Horse Mesa and Owens Valley faults. Two distinct fault populations have been identified at Coso: WNW-trending and antithetical, NE-trending strike-slip faults and N- to NNE-trending normal faults. These faults are both high permeability drilling targets at depth within the main (productive) geothermal field and they locally segment the field into distinct hydrothermal regimes. The West Flank may be segmented from the rest of the field by one such northerly trending fault. The overall minimum principal stress orientation in the main geothermal field varies from 103˚ to 108˚; however, the minimum horizontal principal stress in 83-11 is rotated to 081˚.
Venus - Limited extension and volcanism along zones of lithospheric weakness

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Schaber, G. G.

1982-01-01

Three global-scale zones of possible tectonic origin are described as occurring along broad, low rises within the Equatorial Highlands on Venus (lat 50 deg N to 50 deg S, long 60 deg to 310 deg). The two longest of these tectonic zones, the Aphrodite-Beta and Themis-Atla zones, extend for 21,000 and 14,000 km, respectively. Several lines of evidence indicate that Beta and Atla Regiones, located at the only two intersections of the three major tectonic zones, are dynamically supported volcanic terranes associated with currently active volcanism. Rift valleys south of Aphrodite Terra and between Beta and Phoebe Regiones are characterized by 75- to 100-km widths, raised rims, and extensions of only a few tens of kilometers, about the same magnitudes as in continental rifts on the earth. Horizontal extension on Venus was probably restricted by an early choking-off of plate motion by high crustal and upper-mantle temperatures, and the subsequent loss of water and an asthenosphere.
Forests of the tropical eastern Andean flank during the middle Pleistocene

NARCIS (Netherlands)

Cárdenas, M.L.; Gosling, W.D.; Pennington, R.T.; Poole, I.; Sherlock, S.C.; Mothes, P.

2014-01-01

Inter-bedded volcanic and organic sediments from Erazo (Ecuador) indicate the presence of four different forest assemblages on the eastern Andean flank during the middle Pleistocene. Radiometric dates (40Ar-39Ar) obtained from the volcanic ash indicate that deposition occurred between 620,000 and
Geophysical evidence for widespread reversely magnetised pyroclastics in the western Taupo Volcanic Zone (New Zealand)

International Nuclear Information System (INIS)

Soengkono, S.; Hochstein, M.P.; Smith, I.E.M.; Itaya, T.

1992-01-01

Low-altitude aeromagnetic data show that negative residual anomalies are widespread over the western Taupo Volcanic Zone, New Zealand. Paleomagnetic study of eight rhyolitic ignimbrite units and two lava flows which are exposed in this area, together with new K-Ar dates of four of the ignimbrite units, indicate that the two lava units and seven of the ignimbrite units were erupted during the Matuyama geomagnetic epoch (>0.73 Ma B.P.) and suggest that rhyolitic volcanism in the western Taupo Volcanic Zone began as early as 1.6 Ma B.P. These results provide the basis for an interpretation of our aeromagnetic data which confirms the hypothesis that the magnetic anomalies observed in the western Taupo Volcanic Zone are caused by widespread, thick, reversely magnetised pyroclastic and lava flows. Magnetic modelling also allows thickness estimates of the younger, normally magnetised cover rocks which reach a maximum thickness of the order of 0.5 km in the Mangakino area. The magnetic structure of these volcanic rocks defines approximately the lateral extent of the Mangakino Volcanic Centre. (author). 41 refs., 2 figs., 3 tabs
Gold-silver mining districts, alteration zones, and paleolandforms in the Miocene Bodie Hills Volcanic Field, California and Nevada

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Vikre, Peter G.; John, David A.; du Bray, Edward A.; Fleck, Robert J.

2015-09-25

The Bodie Hills is a ~40 by ~30 kilometer volcanic field that straddles the California-Nevada state boundary between Mono Lake and the East Walker River. Three precious metal mining districts and nine alteration zones are delineated in Tertiary-Quaternary volcanic and Mesozoic granitic and metamorphic rocks that comprise the volcanic field. Cumulative production from the mining districts, Bodie, Aurora, and Masonic, is 3.4 million ounces of gold and 28 million ounces of silver. Small amounts of mercury were produced from the Potato Peak, Paramount-Bald Peak, and Cinnabar Canyon-US 395 alteration zones; a native sulfur resource in the Cinnabar Canyon-US 395 alteration zone has been identified by drilling. There are no known mineral resources in the other six alteration zones, Red Wash-East Walker River, East Brawley Peak, Sawtooth Ridge, Aurora Canyon, Four Corners, and Spring Peak. The mining districts and alteration zones formed between 13.4 and 8.1 Ma in predominantly ~15–9 Ma volcanic rocks of the Bodie Hills volcanic field. Ages of hydrothermal minerals in the districts and zones are the same as, or somewhat younger than, the ages of volcanic host rocks.
Understanding Etna flank instability through numerical models

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Apuani, Tiziana; Corazzato, Claudia; Merri, Andrea; Tibaldi, Alessandro

2013-02-01

As many active volcanoes, Mount Etna shows clear evidence of flank instability, and different mechanisms were suggested to explain this flank dynamics, based on the recorded deformation pattern and character. Shallow and deep deformations, mainly associated with both eruptive and seismic events, are concentrated along recognised fracture and fault systems, mobilising the eastern and south-eastern flank of the volcano. Several interacting causes were postulated to control the phenomenon, including gravity force, magma ascent along the feeding system, and a very complex local and/or regional tectonic activity. Nevertheless, the complexity of such dynamics is still an open subject of research and being the volcano flanks heavily urbanised, the comprehension of the gravitative dynamics is a major issue for public safety and civil protection. The present research explores the effects of the main geological features (in particular the role of the subetnean clays, interposed between the Apennine-Maghrebian flysch and the volcanic products) and the role of weakness zones, identified by fracture and fault systems, on the slope instability process. The effects of magma intrusions are also investigated. The problem is addressed by integrating field data, laboratory tests and numerical modelling. A bi- and tri-dimensional stress-strain analysis was performed by a finite difference numerical code (FLAC and FLAC3D), mainly aimed at evaluating the relationship among geological features, volcano-tectonic structures and magmatic activity in controlling the deformation processes. The analyses are well supported by dedicated structural-mechanical field surveys, which allowed to estimate the rock mass strength and deformability parameters. To take into account the uncertainties which inevitably occur in a so complicated model, many efforts were done in performing a sensitivity analysis along a WNW-ESE section crossing the volcano summit and the Valle del Bove depression. This was
Frictional processes during flank motion at Mount Etna (Italy): experimental characterisation of slip on similar and dissimilar volcanic and sedimentary rocks.

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Rozanski, Wojciech; Lavallee, Yan; Kendrick, Jackie; Castagna, Angela; Mitchell, Thomas; Heap, Michael; Vinciguerra, Sergio; Hirose, Takehiro; Dingwell, Donald

2015-04-01

The edifice of Mount Etna (Italy) is structurally unstable, exhibiting a near continuous ESE seaward sliding along a set of faults due to interplay between regional tectonics, gravity instability and magma intrusion. Continuous seismic and ground deformation monitoring reveals the resulting large-scale flank motion at variable rates. The mechanisms controlling this faulting kinetic remains, however, poorly constrained. Examination of the fault zones reveals a range of rock types along the different fault segments: fresh and altered basalt, clay and limestone. As lithological contrasts can jeopardise the structural stability of an edifice, we experimentally investigate the frictional properties of these rocks using low- to high-velocity-rotary shear tests on similar and dissimilar rocks to better understand episodes of slow flank motion as well as rapid and catastrophic sector collapse events. The first set of experiments was performed at velocities up to 1.2 m/s and at normal stresses of 1.5 MPa, commensurate with depths of the contacts seen in the Etna edifice. Friction experiments on clay gouge shows the strong rate-weakening dependence of slip in this material as well as the release of carbon dioxide. Friction experiments on solid rocks show a wider range of mechanical behaviour. At high velocity (>0.6 m/s) volcanic rocks tend to melt whereas the clay and limestone do not; rather they decarbonate, which prevents the rock from achieving the temperature required for melting. Experiments on dissimilar rocks clearly show that composition of host rocks affects the composition and viscosity of the resultant frictional melt, which can have a dramatic effect on shear stress leading to fault weakening or strengthening depending on the combination of host rock samples. A series of low- to moderate-slip velocity experiments is now being conducted to complement our dataset and provide a more complete rock friction model applicable to Mount Etna.
Local stresses, dyke arrest and surface deformation in volcanic edificesand rift zones

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L. S. Brenner

2004-06-01

Full Text Available Field studies indicate that nearly all eruptions in volcanic edifices and rift zones are supplied with magma through fractures (dykes that are opened by magmatic overpressure. While (inferred dyke injections are frequent during unrest periods, volcanic eruptions are, in comparison, infrequent, suggesting that most dykes become arrested at certain depths in the crust, in agreement with field studies. The frequency of dyke arrest can be partly explained by the numerical models presented here which indicate that volcanic edifices and rift zones consisting of rocks of contrasting mechanical properties, such as soft pyroclastic layers and stiff lava flows, commonly develop local stress fields that encourage dyke arrest. During unrest, surface deformation studies are routinely used to infer the geometries of arrested dykes, and some models (using homogeneous, isotropic half-spaces infer large grabens to be induced by such dykes. Our results, however, show that the dyke-tip tensile stresses are normally much greater than the induced surface stresses, making it difficult to explain how a dyke can induce surface stresses in excess of the tensile (or shear strength while the same strength is not exceeded at the (arrested dyke tip. Also, arrested dyke tips in eroded or active rift zones are normally not associated with dyke-induced grabens or normal faults, and some dykes arrested within a few metres of the surface do not generate faults or grabens. The numerical models show that abrupt changes in Young's moduli(stiffnesses, layers with relatively high dyke-normal compressive stresses (stress barriers, and weak horizontal contacts may make the dyke-induced surface tensile stresses too small for significant fault or graben formation to occur in rift zones or volcanic edifices. Also, these small surface stresses may have no simple relation to the dyke geometry or the depth to its tip. Thus, for a layered crust with weak contacts, straightforward

Leakage of active crater lake brine through the north flank at Rincon de la Vieja volcano, northwest Costa Rica, and implications for crater collapse

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Kempter, K.A.; Rowe, G.L.

2000-01-01

de la Vieja. The distribution of thermal water types at Rincon de la Vieja strongly indicates that formation of the north-flank ACS waters is not due to mixing of shallow, steam-heated AS water with deep-seated NC water. More likely, hyper-acidic brines formed in the Active Crater area are migrating through permeable zones in the volcanic strata that make up the Active Crater's north flank. Dissolution and shallow subsurface alteration of north-flank volcanoclastic material by interaction with acidic lake brine, particularly in the more permeable tephra units, could weaken the already oversteepened north flank of the Active Crater. Sector collapse of the Active Crater, with or without a volcanic eruption, represents a potential threat to human lives, property, and ecosystems at Rincon de la Vieja volcano.
Radon measurements in the SE and NE flank of Mt. Etna (Italy)

International Nuclear Information System (INIS)

La Delfa, S.; Imme, G.; Lo Nigro, S.; Morelli, D.; Patane, G.; Vizzini, F.

2007-01-01

Soil Radon has been monitored at two fixed sites located in the northeastern and southeastern flank of Mt. Etna. In this study we report the comparison between in-soil Radon concentration trend recorded in the SE flank and that one recorded in the NE one, where an in-soil Radon detection system is operating since 2001. The aim of this work was to implement the investigation area finding a suitable radon detection site, in the south-east flank of Mt. Etna, in order to better understand possible links between Radon anomalies and volcano dynamic. Radon data collected in NE and SE sites were compared with the volcanic tremor, frequency of occurrence of earthquakes and seismic strain-release recorded at a fixed 3D digital seismic station placed in the NE site. Same general in-soil Radon trends and anomalies were found in both sites. These results have confirmed the suitability of the chosen southeastern site for the in-soil Radon monitoring at Mt. Etna. The comparison of the recorded Radon concentration anomalies with seismicity and volcanic tremor trends, has also verified a possible link with the volcanic activity, as observed in our previous published studies
Geologic map of the northeast flank of Mauna Loa volcano, Island of Hawai'i, Hawaii

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Trusdell, Frank A.; Lockwood, John P.

2017-05-01

SummaryMauna Loa, the largest volcano on Earth, has erupted 33 times since written descriptions became available in 1832. Some eruptions were preceded by only brief seismic unrest, while others followed several months to a year of increased seismicity.The majority of the eruptions of Mauna Loa began in the summit area (>12,000-ft elevation; Lockwood and Lipman, 1987); yet the Northeast Rift Zone (NERZ) was the source of eight flank eruptions since 1843 (table 1). This zone extends from the 13,680-ft-high summit towards Hilo (population ~60,000), the second largest city in the State of Hawaii. Although most of the source vents are farther than 30 km away, the 1880 flow from one of the vents extends into Hilo, nearly reaching Hilo Bay. The city is built entirely on flows erupted from the NERZ, most older than that erupted in 1843.Once underway, Mauna Loa's eruptions can produce lava flows that reach the sea in less than 24 hours, severing roads and utilities in their path. For example, lava flows erupted from the Southwest Rift Zone (SWRZ) in 1950 advanced at an average rate of 9.3 km per hour, and all three lobes reached the ocean within approximately 24 hours (Finch and Macdonald, 1953). The flows near the eruptive vents must have traveled even faster.In terms of eruption frequency, pre-eruption warning, and rapid flow emplacement, Mauna Loa poses an enormous volcanic-hazard threat to the Island of Hawai‘i. By documenting past activity and by alerting the public and local government officials of our findings, we can anticipate the volcanic hazards and substantially mitigate the risks associated with an eruption of this massive edifice.From the geologic record, we can deduce several generalized facts about the geologic history of the NERZ. The middle to the uppermost section of the rift zone were more active in the past 4,000 years than the lower part, perhaps due to buttressing of the lower east rift zone by Mauna Kea and Kīlauea volcanoes. The historical flows
Holocene tephra-fall deposits of southern and austral Andes volcanic zones (33-54oS): eruption recurrence

International Nuclear Information System (INIS)

Naranjo, J.A.; Polanco, E.; Lara, L; Moreno, H; Stern, C.R

2001-01-01

Radiometric 14 C dating is a very useful tool to study the chronostratigraphy of pyroclastic deposits. In addition, 14 C ages are essential parameters for the estimation of the recurrence time of the explosive volcanic activity. The origin, distribution and relative age of mappable Holocene tephra-fall deposits of the Southern Andes Volcanic Zone (SVZ) and Austral Andes Volcanic Zone (AVZ) from 33 o S-54 o S, were studied and their recurrence period is analysed (au)
Pucarilla-Cerro Tipillas volcanic complex: the oldest recognized caldera in the southeastern portion of central volcanic zone of Central Andes?

Energy Technology Data Exchange (ETDEWEB)

Guzman, Silvina; Petrinovic, Ivan [CONICET -IBIGEO. Museo de Cs. Naturales, Universidad de Salta, Mendoza 2 (4400), Salta (Argentina)], E-mail: guzmansilvina@gmail.com

2008-10-01

We recognize the most eastern and oldest collapse caldera structure in the southern portion of the Central Volcanic Zone of the Andes. A description of Middle-Upper Miocene successions related to explosive- effusive events is presented. The location of this centre close to Cerro Galn Caldera attests a recurrence in the volcanism between 12 and 2 Ma in this portion of the Altiplano - Puna Plateau.
Volcanic gas emissions and degassing dynamics at Ubinas and Sabancaya volcanoes; implications for the volatile budget of the central volcanic zone

Science.gov (United States)

Moussallam, Yves; Tamburello, Giancarlo; Peters, Nial; Apaza, Fredy; Schipper, C. Ian; Curtis, Aaron; Aiuppa, Alessandro; Masias, Pablo; Boichu, Marie; Bauduin, Sophie; Barnie, Talfan; Bani, Philipson; Giudice, Gaetano; Moussallam, Manuel

2017-09-01

Emission of volcanic gas is thought to be the dominant process by which volatiles transit from the deep earth to the atmosphere. Volcanic gas emissions, remain poorly constrained, and volcanoes of Peru are entirely absent from the current global dataset. In Peru, Sabancaya and Ubinas volcanoes are by far the largest sources of volcanic gas. Here, we report the first measurements of the compositions and fluxes of volcanic gases emitted from these volcanoes. The measurements were acquired in November 2015. We determined an average SO2 flux of 15.3 ± 2.3 kg s- 1 (1325-ton day- 1) at Sabancaya and of 11.4 ± 3.9 kg s- 1 (988-ton day- 1) at Ubinas using scanning ultraviolet spectroscopy and dual UV camera systems. In-situ Multi-GAS analyses yield molar proportions of H2O, CO2, SO2, H2S and H2 gases of 73, 15, 10 1.15 and 0.15 mol% at Sabancaya and of 96, 2.2, 1.2 and 0.05 mol% for H2O, CO2, SO2 and H2S at Ubinas. Together, these data imply cumulative fluxes for both volcanoes of 282, 30, 27, 1.2 and 0.01 kg s- 1 of H2O, CO2, SO2, H2S and H2 respectively. Sabancaya and Ubinas volcanoes together contribute about 60% of the total CO2 emissions from the Central Volcanic zone, and dominate by far the total revised volatile budget of the entire Central Volcanic Zone of the Andes.
Stability analysis of Western flank of Cumbre Vieja volcano (La Palma) using numerical modelling

Science.gov (United States)

Bru, Guadalupe; Gonzalez, Pablo J.; Fernandez-Merodo, Jose A.; Fernandez, Jose

2016-04-01

assessment. Carracedo, J.C, Badiola, E.R., Guillou, H., de La Nuez J., Pérez Torrado F.J., (2001) Geology and volcanology of La Palma and El Hierro, Western Canaries, Estud. Geol. 57 175- 273. Day S.J., J.C. Carracedo, H. Guillou, P. Gravestock, Recent structural evolution of the Cumbre Vieja volcano, La Palma, Canary Islands: volcanic rift zone reconfiguration as a precursor to volcano flank instability? J. Volcanol. Geotherm. Res. 94 (1999) 135- 167. González, P. J., Tiampo, K. F., Camacho, A. G., & Fernández, J. (2010). Shallow flank deformation at Cumbre Vieja volcano (Canary Islands): Implications on the stability of steep-sided volcano flanks at oceanic islands. Earth and Planetary Science Letters, 297(3), 545-557. Moss, J.L., McGuire, W.J., Page, D. (1999). Gruound deformation monitoring of a potential landslide al La Palma, Canary Islands. Prieto, J.F., Gonzalez, P.J.,Seco, A., Rodriguez-Velasco, G., Tunini,L., Perlock, P.A., Arjona, A., Aparicio, A., Camacho, A.G., Rundle, J.B., Tiampo, K.F., Pallero, J.L.G., Pospiech, S., Fernandez, J., 2009. Geodetic and structural research in La Palma Island, Canary Islands, Spain: 1992 - 2007 results. Pure Appl. Geophys. 66, 1461 - 1484. doi:10.1007/s00024-009-0505-2 Urgeles R., D.G. Masson, M. Canals, A.B. Watts, T. Le Bas, Recurrent large-scale landsliding on the west flank of La Palma, Canary Islands, J. Geophys. Res. 104 (B11) (1999) 25331-25348.
The Te Rere and Okareka eruptive episodes : Okataina Volcanic Centre, Taupo Volcanic Zone, New Zealand

International Nuclear Information System (INIS)

Nairn, I.A.

1992-01-01

The Te Rere and Okareka eruptive episodes occurred within the Okataina Volcanic Centre at c. 21 000 and 18 000 yr B.P., respectively. The widespread rhyolitic pumice fall deposits of Te Rere Ash (volume 5 km 3 ) and Okareka Ash (6 km 3 ) are only rarely exposed in near-source areas, and locations of their vent areas have been uncertain. New exposures and petrographic and chemical analyses show that the Te Rere episode eruptions occurred from multiple vents, up to 20 km apart, on the Haroharo linear vent zone. The Okareka episode eruptions occurred from vents since buried beneath the Tarawera volcanic massif. Eruption of the rhyolitic Okareka pumice fall was immediately preceded by a small basaltic scoria eruption, apparently from vents close to those for the following rhyolite eruptions. Dacitic mixed pumices scattered within the rhyolite pumice layers immediately overlying the scoria were formed by mixing of the basalt and rhyolite magmas. The Te Rere and Okareka pyroclastic eruptions were both followed by extrusion of voluminous rhyolite lavas. These eruptive episodes mark the commencement of growth of the present-day Haroharo and Tarawera volcanic complexes. (author). 27 refs., 14 figs., 6 tabs
Numerical Simulation of a Non-volcanic Hydrothermal System Caused by Formation of a High Permeability Fracture Zone

Science.gov (United States)

Oka, Daisuke; Ehara, Sachio; Fujimitsu, Yasuhiro

2010-05-01

Because in the Japanese islands the earth crust activity is very active, a disposal stratum for high-level radioactive waste produced by reprocessing the spent nuclear fuel from nuclear power plants will be selected in the tectonically stable areas in which the waste can be disposed underground safely for a long term and there is no influence of earthquakes, seismic activities, volcanic activities, upheaval, sedimentation, erosion, climate and global sea level change and so on, which causes the risk of the inflow of the groundwater to destroy the disposal site or the outflow to the ground surface. However, even if the disposal stratum in such condition will be chosen, in case that a new high permeability fracture zone is formed by the earthquake, and a new hydrothermal system may be formed for a long term (thousands or millions years) and the system may affect the disposal site. Therefore, we have to understand the feature of the non-volcanic hydrothermal system through the high permeability fracture zone. We estimated such influence by using HYDROTHERM Ver2.2 (Hayba & Ingebritsen, 1994), which is a three-dimensional numerical reservoir simulator. The model field is the northwestern part of Kego Fault, which was formed by a series of earthquakes called "the 2005 Fukuoka Prefecture Western Offshore Earthquakes" (the main shock of Mjma 7.0 on 20 March 2005) in Kyushu, Japan. The results of the numerical simulations show the development of a low temperature hydrothermal system as a new fracture zone is formed, in case that there is no volcanic heat source. The results of the simulations up to 100,000 years after formation of the fracture zone show that the higher heat flow and the wider and more permeable fracture zone accelerate the development of the hydrothermal system in the fracture zone. As a result of calculation of up to10 million years, we clarified the evolutional process of the non-volcanic hydrothermal system through the high permeability fracture zone. At
Surface deformation in volcanic rift zones

Science.gov (United States)

Pollard, D.D.; Delaney, P.T.; Duffield, W.A.; Endo, E.T.; Okamura, A.T.

1983-01-01

The principal conduits for magma transport within rift zones of basaltic volcanoes are steeply dipping dikes, some of which feed fissure eruptions. Elastic displacements accompanying a single dike emplacement elevate the flanks of the rift relative to a central depression. Concomitant normal faulting may transform the depression into a graben thus accentuating the topographic features of the rift. If eruption occurs the characteristic ridge-trough-ridge displacement profile changes to a single ridge, centered at the fissure, and the erupted lava alters the local topography. A well-developed rift zone owes its structure and topography to the integrated effects of many magmatic rifting events. To investigate this process we compute the elastic displacements and stresses in a homogeneous, two-dimensional half-space driven by a pressurized crack that may breach the surface. A derivative graphical method permits one to estimate the three geometric parameters of the dike (height, inclination, and depth-to-center) and the mechanical parameter (driving pressure/rock stiffness) from a smoothly varying displacement profile. Direct comparison of measured and theoretical profiles may be used to estimate these parameters even if inelastic deformation, notably normal faulting, creates discontinuities in the profile. Geological structures (open cracks, normal faults, buckles, and thrust faults) form because of stresses induced by dike emplacement and fissure eruption. Theoretical stress states associated with dilation of a pressurized crack are used to interpret the distribution and orientation of these structures and their role in rift formation. ?? 1983.
Fault propagation folds induced by gravitational failure and slumping of the Central Costa Rica volcanic range: Implications for large terrestrial and Martian volcanic edifices

International Nuclear Information System (INIS)

Borgia, A.; Burr, J.; Montero, W.; Morales, L.D.; Alvarado, G.E.

1990-01-01

Long sublinear ridges and related scarps located at the base of large volcanic structures are frequently interpreted as normal faults associated with extensional regional stress. In contrast, the ridges bordering the Central Costa Rica volcanic range (CCRVR) are the topographic expression of hanging wall asymmetric angular anticlines overlying low-angle thrust faults at the base of the range. These faults formed by gravitational failure and slumping of the flanks of the range due to the weight of the volcanic edifices and were perhaps triggered by the intrusion of magma over the past 20,000 years. These anticlines are hypothesized to occur along the base of the volcano, where the thrust faults ramp up toward the sea bottom. Ridges and scarps between 2,000 and 5,000 m below sea level are interpreted as the topographic expression of these folds. The authors further suggest that the scarps of the CCRVR and valid scaled terrestrial analogs of the perimeter scarp of the Martian volcano Olympus Mons. They suggest that the crust below Olympus Mons has failed under the load of the volcano, triggering the radial slumping of the flanks of the volcano on basal thrusts. The thrusting would have, in turn, formed the anticlinal ridges and scarps that surround the edifice. The thrust faults may extend all the way to the base of the Martian crust (about 40 km), and they may have been active until almost the end of the volcanic activity. They suggest that gravitational failure and slumping of the flanks of volcanoes is a process common to most large volcanic edifices. In the CCRVR this slumping of the flanks is a slow intermittent process, but it could evolve to rapid massive avalanching leading to catastrophic eruptions. Thus monitoring of uplift and displacement of the folds related to the slump tectonics could become an additional effective method for mitigating volcanic hazards
Heterogeneity in Subducting Slab Influences Fluid Properties, Plate Coupling and Volcanism: Hikurangi Subduction Zone, New Zealand

Science.gov (United States)

Eberhart-Phillips, D. M.; Reyners, M.; Bannister, S. C.

2017-12-01

Seismicity distribution and 3-D models of P- and S-attenuation (1/Q) in the Hikurangi subduction zone, in the North Island of New Zealand, show large variation along-arc in the fluid properties of the subducting slab. Volcanism is also non-uniform, with extremely productive rhyolitic volcanism localized to the central Taupo Volcanic zone, and subduction without volcanism in the southern North Island. Plate coupling varies with heterogeneous slip deficit in the northern section, low slip deficit in the central section, and high slip deficit (strong coupling) in the south. Heterogeneous initial hydration and varied dehydration history both are inferred to play roles. The Hikurangi Plateau (large igneous province) has been subducted beneath New Zealand twice - firstly at ca. 105-100 Ma during north-south convergence with Gondwana, and currently during east-west convergence between the Pacific and Australian plates along the Hikurangi subduction zone. It has an uneven downdip edge which has produced spatially and temporally localized stalls in subduction rate. The mantle wedge under the rhyolitic section has a very low Q feature centred at 50-125 km depth, which directly overlies a 150-km long zone of dense seismicity. This seismicity occurs below a sharp transition in the downdip extent of the Hikurangi Plateau, where difficulty subducting the buoyant plateau would have created a zone of increased faulting and hydration that spent a longer time in the outer-rise yielding zone, compared with areas to the north and south. At shallow depths this section has unusually high fracture permeability from the two episodes of bending, but it did not experience dehydration during Gondwana subduction. This central section at plate interface depths less than 50-km has low Q in the slab crust, showing that it is extremely fluid rich, and it exhibits weak plate coupling with both deep and shallow slow-slip events. In contrast in the southern section, where there is a large deficit in
Late Pleistocene flank collapse of Zempoala volcano (Central Mexico) and the role of fault reactivation

Science.gov (United States)

Arce, José Luis; Macías, Rodolfo; García Palomo, Armando; Capra, Lucia; Macías, José Luis; Layer, Paul; Rueda, Hernando

2008-11-01

Zempoala is an extinct Pleistocene (˜ 0.7-0.8 Ma) stratovolcano that together with La Corona volcano (˜ 0.9 Ma) forms the southern end of the Sierra de las Cruces volcanic range, Central Mexico. The volcano consists of andesitic and dacitic lava flows and domes, as well as pyroclastic and epiclastic sequences, and has had a complex history with several flank collapses. One of these collapses occurred during the late Pleistocene on the S-SE flank of the volcano and produced the Zempoala debris avalanche deposit. This collapse could have been triggered by the reactivation of two normal fault systems (E-W and NE-SW), although magmatic activity cannot be absolutely excluded. The debris avalanche traveled 60 km to the south, covers an area of 600 km 2 and has a total volume of 6 km 3, with a calculated Heim coefficient (H/L) of 0.03. Based on the textural characteristics of the deposit we recognized three zones: proximal, axial, and lateral distal zone. The proximal zone consists of debris avalanche blocks that develop a hummocky topography; the axial zone corresponds with the main debris avalanche deposit made of large clasts set in a sandy matrix, which transformed to a debris flow in the lateral distal portion. The deposit is heterolithologic in composition, with dacitic and andesitic fragments from the old edifice that decrease in volume as bulking of exotic clasts from the substratum increase. Several cities (Cuernavaca, Jojutla de Juárez, Alpuyeca) with associated industrial, agricultural, and tourism activities have been built on the deposit, which pose in evidence the possible impact in case of a new event with such characteristics, since the area is still tectonically active.
Relaxation of the south flank after the 7.2-magnitude Kalapana earthquake, Kilauea Volcano, Hawaii

Science.gov (United States)

Dvorak, John J.; Klein, Fred W.; Swanson, Donald A.

1994-01-01

An M = 7.2 earthquake on 29 November 1975 caused the south flank of Kilauea Volcano, Hawaii, to move seaward several meters: a catastrophic release of compression of the south flank caused by earlier injections of magma into the adjacent segment of a rift zone. The focal mechanisms of the mainshock, the largest foreshock, and the largest aftershock suggest seaward movement of the upper block. The rate of aftershocks decreased in a familiar hyperbolic decay, reaching the pre-1975 rate of seismicity by the mid-1980s. Repeated rift-zone intrusions and eruptions after 1975, which occurred within 25 km of the summit area, compressed the adjacent portion of the south flank, apparently masking continued seaward displacement of the south flank. This is evident along a trilateration line that continued to extend, suggesting seaward displacement, immediately after the M = 7.2 earthquake, but then was compressed during a series of intrusions and eruptions that began in September 1977. Farther to the east, trilateration measurements show that the portion of the south flank above the aftershock zone, but beyond the area of compression caused by the rift-zone intrusions and eruptions, continued to move seaward at a decreasing rate until the mid-1980s, mimicking the decay in aftershock rate. Along the same portion of the south flank, the pattern of vertical surface displacements can be explained by continued seaward movement of the south flank and development of two eruptive fissures along the east rift zone, each of which extended from a depth of ∼3 km to the surface. The aftershock rate and continued seaward movement of the south flank are reminiscent of crustal response to other large earthquakes, such as the 1966 M = 6 Parkfield earthquake and the 1983 M = 6.5 Coalinga earthquake.
Soil radon monitoring in the NE flank of Mt. Etna (Sicily)

International Nuclear Information System (INIS)

Imme, G.; La Delfa, S.; Lo Nigro, S.; Morelli, D.; Patane, G.

2006-01-01

Soil radon has been monitored at a fixed location on the northeastern flank of Mt. Etna, a high-risk volcano in Sicily. The aim of this study was to evaluate the effects of the recent volcanic activity on soil radon concentration. Continuous radon measurements have been performed since July 2001. While comparison between the trend in in-soil radon concentration and the acquired meteorological series (temperature, humidity and pressure) appear to confirm a general seasonal correlation, nevertheless particular anomalies suggest a possible dependence of the radon concentration on volcanic dynamics
Holocene tephrostratigraphy of southern Chiloé Continental (Andean southern volcanic zone; ~43°S), Chile

Science.gov (United States)

Lachowycz, S.; Smith, V. C.; Pyle, D. M.; Mather, T. A.

2012-12-01

The eruptive history of the volcanoes in the southern part of the Andean Southern Volcanic Zone (42.5-45°S) is very poorly constrained: only several late Quaternary eruptions have been identified, mostly from study of sparse roadcuts [1]. In this study, we further constrain the Holocene explosive eruption history around 43°S by identifying and analysing tephra layers preserved in a ~3.25m long peat core from Cuesta Moraga [2], ~35km east of Yanteles volcano. Cryptotephra was extracted following the method of [3], in addition to macrotephra; owing to the vicinity of the sampling site to the tephra sources, cryptotephra was found throughout the core stratigraphy, but was sufficiently variable in concentration that discrete layers were identifiable and attributed to specific eruptions. Chemical analysis of the glass by electron microprobe shows that the tephra layers originate from a number of volcanoes in the region. This new tephrostratigraphy improves our knowledge of the important history of explosive volcanism in this area, potentially tying the tephrostratigraphies of surrounding areas (e.g., [4]) and allowing improved evaluation of regional volcanic risk. [1] Naranjo, J.A.., and C. R. Stern, 2004. Holocene tephrochronology of the southernmost part (42°30'-45°S) of the Andean Southern Volcanic Zone. Revista geológica de Chile, 31, pp. 225-240. [2] Heusser, C.J., et al., 1992. Paleoecology of late Quaterary deposits in Chiloé Continental, Chile. Revista Chilena de Historia Natural, 65, pp. 235-245. [3] Blockley, S.P.E., et al., 2005. A new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments. Quaternary Science Reviews, 24, pp. 1952-1960. [4] Watt, S.F.L., et al., 2011. Holocene tephrochronology of the Hualaihue region (Andean southern volcanic zone, ~42°S), southern Chile. Quaternary International, 246, pp. 324-343.
Melt zones beneath five volcanic complexes in California: an assessment of shallow magma occurrences

Energy Technology Data Exchange (ETDEWEB)

Goldstein, N.E.; Flexser, S.

1984-12-01

Recent geological and geophysical data for five magma-hydrothermal systems were studied for the purpose of developing estimates for the depth, volume and location of magma beneath each area. The areas studied were: (1) Salton Trough, (2) The Geysers-Clear Lake, (3) Long Valley caldera, (4) Coso volcanic field, and (5) Medicine Lake volcano, all located in California and all selected on the basis of recent volcanic activity and published indications of crustal melt zones. 23 figs.
Dykes and structures of the NE rift of Tenerife, Canary Islands: a record of stabilisation and destabilisation of ocean island rift zones

Science.gov (United States)

Delcamp, A.; Troll, V. R.; van Wyk de Vries, B.; Carracedo, J. C.; Petronis, M. S.; Pérez-Torrado, F. J.; Deegan, F. M.

2012-07-01

Many oceanic island rift zones are associated with lateral sector collapses, and several models have been proposed to explain this link. The North-East Rift Zone (NERZ) of Tenerife Island, Spain offers an opportunity to explore this relationship, as three successive collapses are located on both sides of the rift. We have carried out a systematic and detailed mapping campaign on the rift zone, including analysis of about 400 dykes. We recorded dyke morphology, thickness, composition, internal textural features and orientation to provide a catalogue of the characteristics of rift zone dykes. Dykes were intruded along the rift, but also radiate from several nodes along the rift and form en échelon sets along the walls of collapse scars. A striking characteristic of the dykes along the collapse scars is that they dip away from rift or embayment axes and are oblique to the collapse walls. This dyke pattern is consistent with the lateral spreading of the sectors long before the collapse events. The slump sides would create the necessary strike-slip movement to promote en échelon dyke patterns. The spreading flank would probably involve a basal decollement. Lateral flank spreading could have been generated by the intense intrusive activity along the rift but sectorial spreading in turn focused intrusive activity and allowed the development of deep intra-volcanic intrusive complexes. With continued magma supply, spreading caused temporary stabilisation of the rift by reducing slopes and relaxing stress. However, as magmatic intrusion persisted, a critical point was reached, beyond which further intrusion led to large-scale flank failure and sector collapse. During the early stages of growth, the rift could have been influenced by regional stress/strain fields and by pre-existing oceanic structures, but its later and mature development probably depended largely on the local volcanic and magmatic stress/strain fields that are effectively controlled by the rift zone growth
Rapid response of a hydrologic system to volcanic activity: Masaya volcano, Nicaragua

Science.gov (United States)

Pearson, S.C.P.; Connor, C.B.; Sanford, W.E.

2008-01-01

Hydrologic systems change in response to volcanic activity, and in turn may be sensitive indicators of volcanic activity. Here we investigate the coupled nature of magmatic and hydrologic systems using continuous multichannel time series of soil temperature collected on the flanks of Masaya volcano, Nicaragua, one of the most active volcanoes in Central America. The soil temperatures were measured in a low-temperature fumarole field located 3.5 km down the flanks of the volcano. Analysis of these time series reveals that they respond extremely rapidly, on a time scale of minutes, to changes in volcanic activity also manifested at the summit vent. These rapid temperature changes are caused by increased flow of water vapor through flank fumaroles during volcanism. The soil temperature response, ~5 °C, is repetitive and complex, with as many as 13 pulses during a single volcanic episode. Analysis of the frequency spectrum of these temperature time series shows that these anomalies are characterized by broad frequency content during volcanic activity. They are thus easily distinguished from seasonal trends, diurnal variations, or individual rainfall events, which triggered rapid transient increases in temperature during 5% of events. We suggest that the mechanism responsible for the distinctive temperature signals is rapid change in pore pressure in response to magmatism, a response that can be enhanced by meteoric water infiltration. Monitoring of distal fumaroles can therefore provide insight into coupled volcanic-hydrologic-meteorologic systems, and has potential as an inexpensive monitoring tool.
Volcanic avalanche fault zone with pseudotachylite and gouge in French Massif Central

Science.gov (United States)

Bernard, Karine; van Wyk de Vries, Benjamin

2017-11-01

Structures and textures with sedimentological variations at different scales of the lithofacies assemblage help us to constrain the basal kinematic transition from non-depositional to depositional conditions during volcanic avalanche emplacement. In the well-exposed impact-sheared contact along volcanic avalanche fault zone in the French Massif Central, we observe how the granular textures of the pseudotachylite and fault gouge have recorded the propagation of shock wave with granular oscillatory stress. Sequential events of basal aggradation along avalanche fault zone have been established related to fractal D-values, temperature pressure regime and oscillatory stress during slow wave velocity. A typical lithofacies assemblage with a reverse grading shows the pseudotachylite and fault gouge. A cataclastic gradient is characterised by the fractal D-values from 2.7 in jigsaw breccias with pseudotachylite partial melt, to 2.6 in the polymodal gouge. Shock, brecciation and comminution produce cataclastic shear bands in the pseudotachylite and quartz microstructures along the basal contact of the volcanic debris-avalanche deposit. Gouge microstructures show granular segregation, cataclasis with antithetic rotational Riedel shear, and an arching effect between the Riedel shear bands. X-ray microtomography provided 3D microfabrics along the clastic vein in the sandy-gouge. From the available statistical dataset, a few equations have been developed implicating the same cataclastic origin with a co-genetic evolution of lithofacies. An impact wave during primary shear propagation may contribute to produce hydroclastic matrix, pseudotachylite partial melt and proximal gouge thixotropy with v 50m/s and a T < 654 °C. The interseismic period with oscillatory stress is related to crushed clasts and basaltic melt around 800 °C, Riedel shear bands with granular segregation along the fault gouge. The secondary shock by matrix-rich avalanche (ΔP = 10GPa, T ≥ 1000-1500 �

Volcanic hazards of the Idaho National Engineering Laboratory and adjacent areas

International Nuclear Information System (INIS)

Hackett, W.R.; Smith, R.P.

1994-12-01

Potential volcanic hazards are assessed, and hazard zone maps are developed for the Idaho National Engineering Laboratory (INEL) and adjacent areas. The basis of the hazards assessment and mapping is the past volcanic history of the INEL region, and the apparent similarity of INEL volcanism with equivalent, well-studied phenomena in other regions of active volcanism, particularly Hawaii and Iceland. The most significant hazards to INEL facilities are associated with basaltic volcanism, chiefly lava flows, which move slowly and mainly threaten property by inundation or burning. Related hazards are volcanic gases and tephra, and ground disturbance associated with the ascent of magma under the volcanic zones. Several volcanic zones are identified in the INEL area. These zones contain most of the volcanic vents and fissures of the region and are inferred to be the most probable sites of future INEL volcanism. Volcanic-recurrence estimates are given for each of the volcanic zones based on geochronology of the lavas, together with the results of field and petrographic investigations concerning the cogenetic relationships of INEL volcanic deposits and associated magma intrusion. Annual probabilities of basaltic volcanism within the INEL volcanic zones range from 6.2 x 10 -5 per year (average 16,000-year interval between eruptions) for the axial volcanic zone near the southern INEL boundary and the Arco volcanic-rift zone near the western INEL boundary, to 1 x 10 -5 per year (average 100,000-year interval between eruptions) for the Howe-East Butte volcanic rift zone, a geologically old and poorly defined feature of the central portion of INEL. Three volcanic hazard zone maps are developed for the INEL area: lava flow hazard zones, a tephra (volcanic ash) and gas hazard zone, and a ground-deformation hazard zone. The maps are useful in land-use planning, site selection, and safety analysis
Eruptive and environmental processes recorded by diatoms in volcanically-dispersed lake sediments from the Taupo Volcanic Zone, New Zealand

Science.gov (United States)

Harper, Margaret A.; Pledger, Shirley A.; Smith, Euan G. C.; Van Eaton, Alexa; Wilson, Colin J. N.

2015-01-01

Late Pleistocene diatomaceous sediment was widely dispersed along with volcanic ash (tephra) across and beyond New Zealand by the 25.4 ka Oruanui supereruption from Taupo volcano. We present a detailed analysis of the diatom populations in the Oruanui tephra and the newly discovered floras in two other eruptions from the same volcano: the 28.6 ka Okaia and 1.8 ka Taupo eruptions. For comparison, the diatoms were also examined in Late Pleistocene and Holocene lake sediments from the Taupo Volcanic Zone (TVZ). Our study demonstrates how these microfossils provide insights into the lake history of the TVZ since the Last Glacial Maximum. Morphometric analysis of Aulacoseira valve dimensions provides a useful quantitative tool to distinguish environmental and eruptive processes within and between individual tephras. The Oruanui and Okaia diatom species and valve dimensions are highly consistent with a shared volcanic source, paleolake and eruption style (involving large-scale magma-water interaction). They are distinct from lacustrine sediments sourced elsewhere in the TVZ. Correspondence analysis shows that small, intact samples of erupted lake sediment (i.e., lithic clasts in ignimbrite) contain heterogeneous diatom populations, reflecting local variability in species composition of the paleolake and its shallowly-buried sediments. Our analysis also shows a dramatic post-Oruanui supereruption decline in Cyclostephanos novaezelandiae, which likely reflects a combination of (1) reorganisation of the watershed in the aftermath of the eruption, and (2) overall climate warming following the Last Glacial Maximum. This decline is reflected in substantially lower proportions of C. novaezelandiae in the 1.8 ka Taupo eruption deposits, and even fewer in post-1.8 ka sediments from modern (Holocene) Lake Taupo. Our analysis highlights how the excellent preservation of siliceous microfossils in volcanic tephra may fingerprint the volcanic source region and retain a valuable record
Enrichments of the mantle sources beneath the Southern Volcanic Zone (Andes) by fluids and melts derived from abraded upper continental crust

DEFF Research Database (Denmark)

Holm, Paul Martin; Søager, Nina; Dyhr, Charlotte Thorup

2014-01-01

Mafic basaltic-andesitic volcanic rocks from the Andean Southern Volcanic Zone (SVZ) exhibit a northward increase in crustal components in primitive arc magmas from the Central through the Transitional and Northern SVZ segments. New elemental and Sr–Nd-high-precision Pb isotope data from the Quat......Mafic basaltic-andesitic volcanic rocks from the Andean Southern Volcanic Zone (SVZ) exhibit a northward increase in crustal components in primitive arc magmas from the Central through the Transitional and Northern SVZ segments. New elemental and Sr–Nd-high-precision Pb isotope data from...... mantle by means of subduction erosion in response to the northward increasingly strong coupling of the converging plates. Both types of enrichment had the same Pb isotope composition in the TSVZ with no significant component derived from the subducting oceanic crust. Pb–Sr–Nd isotopes indicate a major...
Miocene volcanism in the Oaş-Gutâi Volcanic Zone, Eastern Carpathians, Romania: Relationship to geodynamic processes in the Transcarpathian Basin

Science.gov (United States)

Kovacs, Marinel; Seghedi, Ioan; Yamamoto, Masatsugu; Fülöp, Alexandrina; Pécskay, Zoltán; Jurje, Maria

2017-12-01

We present the first comprehensive study of Miocene volcanic rocks of the Oaş-Gutâi Volcanic Zone (OGVZ), Romania, which are exposed in the eastern Transcarpathian Basin (TB), within the Eastern Alpine-Western Carpathian-Northern Pannonian (ALCAPA) block. Collision between the ALCAPA block and Europe at 18-16 Ma produced the Carpathian fold-and-thrust belt. This was followed by clockwise rotation and an extensional regime forming core complexes of the separated TB fragment. Based on petrographic and geochemical data, including Srsbnd Nd isotopic compositions and Ksbnd Ar ages, we distinguish three types of volcanic activity in the OGVZ: (1) early Miocene felsic volcanism that produced caldera-related ignimbrites in the Gutâi Mountains (15.4-14.8 Ma); (2) widespread middle-late Miocene intermediate/andesitic volcanism (13.4-7.0 Ma); and (3) minor late Miocene andesitic/rhyolitic volcanism comprising the Oraşu Nou rhyolitic volcano and several andesitic-dacitic domes in the Oaş Mountains (11.3-9.5 Ma). We show that magma evolution in the OGVZ was controlled by assimilation-fractional crystallization and magma-mixing processes within an interconnected multi-level crustal magmatic reservoir. The evolution of volcanic activity within the OGVZ was controlled by the geodynamics of the Transcarpathian Basin. The early felsic and late intermediate Miocene magmas were emplaced in a post-collisional setting and were derived from a mantle source region that was modified by subduction components (dominantly sediment melts) and lower crust. The style of volcanism within the eastern TB system exhibits spatial variations, with andesitic composite volcanoes (Gutâi Mountains) observed at the margins, and isolated andesitic-rhyolitic monogenetic volcanoes (Oaş Mountains) in the center of the basin.
Lava-flow hazard on the SE flank of Mt. Etna (Southern Italy)

Science.gov (United States)

Crisci, G. M.; Iovine, G.; Di Gregorio, S.; Lupiano, V.

2008-11-01

considering its elevation, location with respect to the volcanic edifice, and proximity to its main weakness zones. Similarly, different probabilities can be assigned to the simulated event types (combinations of durations and lava volumes, and to the effusion-rate functions considered). In such a way, an implicit assumption is made that the volcanic style will not dramatically change in the near future. Depending on adopted criteria for probability evaluation, different maps of lava-flow hazard can be compiled, by taking into account both the overlapping of the simulated lava flows and their assumed probabilities, and by finally ranking computed values into few relative classes. The adopted methodology allows to rapidly exploring changes in lava-flow hazard as a function of varying probabilities of occurrence, by simply re-processing the database of the simulations stored in the GIS. For Civil Protection purposes, in case of expected imminent opening of a vent in a given sector of the volcano, re-processing may help in real-time forecasting the presumable affected areas, and thus in better managing the eruptive crisis. Moreover, further simulations can be added to the GIS data base at any time new different event types were recognised to be of interest. In this paper, three examples of maps of lava-flow hazard for the SE flank of Mt. Etna are presented: the first has been realised without assigning any probability to the performed simulations, by simply counting the frequencies of lava flows affecting each site; in the second map, information on past eruptions is taken into account, and probabilities are empirically attributed to each simulation based on location of vents and types of eruption; in the third one, a stronger role is ascribed to the main SSE-trending weakness zone, which crosses the study area between Nicolosi and Trecastagni, associated with the right flank of the above-cited deep-seated deformation. Despite being only preliminary (as based on a sub-set of the
Electromagnetic exploration in high-salinity groundwater zones: case studies from volcanic and soft sedimentary sites in coastal Japan

Science.gov (United States)

Suzuki, Koichi; Kusano, Yukiko; Ochi, Ryota; Nishiyama, Nariaki; Tokunaga, Tomochika; Tanaka, Kazuhiro

2017-01-01

Estimating the spatial distribution of groundwater salinity in coastal plain regions is becoming increasingly important for site characterisation and the prediction of hydrogeological environmental conditions resulting from radioactive waste disposal and underground CO2 storage. In previous studies of the freshwater-saltwater interface, electromagnetic methods were used for sites characterised by unconsolidated deposits or Neocene soft sedimentary rocks. However, investigating the freshwater-saltwater interface in hard rock sites (e.g. igneous areas) is more complex, with the permeability of the rocks greatly influenced by fractures. In this study, we investigated the distribution of high-salinity groundwater at two volcanic rock sites and one sedimentary rock site, each characterised by different hydrogeological features. Our investigations included (1) applying the controlled source audio-frequency magnetotelluric (CSAMT) method and (2) conducting laboratory tests to measure the electrical properties of rock core samples. We interpreted the 2D resistivity sections by referring to previous data on geology and geochemistry of groundwater. At the Tokusa site, an area of inland volcanic rocks, low resistivity zones were detected along a fault running through volcanic rocks and shallow sediments. The results suggest that fluids rise through the Tokusa-Jifuku Fault to penetrate shallow sediments in a direction parallel to the river, and some fluids are diluted by rainwater. At the Oki site, a volcanic island on a continental shelf, four resistivity zones (in upward succession: low, high, low and high) were detected. The results suggest that these four zones were formed during a transgression-regression cycle caused by the last glacial period. At the Saijo site, located on a coastal plain composed of thick sediments, we observed a deep low resistivity zone, indicative of fossil seawater remnant from a transgression after the last glacial period. The current coastal
Timescales and conditions of crystallization in the Pokai and Chimpanzee Ignimbrites, Taupo Volcanic Zone, New Zealand

Science.gov (United States)

Connor, M.; Gualda, G. A.; Gravley, D. M.

2013-12-01

Silicic magmas give rise to explosive eruptions that are both of scientific and societal interest. The central Taupo Volcanic Zone in New Zealand has been volcanically active for 2 Ma and represents the most active volcanic area in the world today. Particularly intense volcanic activity took place as part of a flare-up event that occurred from ~340 to ~240 ka, when 7 large ignimbrite eruptions took place, as well as many smaller eruptions, which erupted a total of at least 3000 km3 of magma. This project seeks to identify the conditions and timescales over which magma bodies that gave rise to these ignimbrite eruptions evolved. We aim to understand how much of the tens of thousands of years between successive eruptions were characterized by the presence of large bodies of silicic magma within the crust, as well the magma distribution within the crust during those times. We focus on the Chimpanzee and Pokai ignimbrites, which together erupted ~150 km3 of magma. The Pokai ignimbrite erupted at ~275 ka, while the Chimpanzee ignimbrite (undated) erupted between ~320 and 275 ka. Pumice clasts from the Chimpanzee and Pokai ignimbrite were collected in the field. Pumice bulk densities were measured using a submersion technique. Quartz and plagioclase crystals were extracted through a crushing, sieving, and winnowing procedure. Whole crystals were hand-picked under a conventional microscope, mounted on epoxy, and polished to expose grain interiors. Grain mounts were analyzed under an SEM using back-scattered electron, cathodoluminescence (CL), and energy-dispersive x-ray (EDX) imaging. Bulk-densities vary from 0.42 to 0.81 g/cm3 for Pokai and between 0.52 and 0.64 g/cm3 for Chimpanzee pumice clasts. Plagioclase is the dominant crystal phase in both units. Several plagioclase crystals have inclusions of orthopyroxene, ilmenite, magnetite, and zircon, which in some cases form clusters. Quartz is rare but is present in pumice from both deposits. Both plagioclase and quartz
North Kona slump: Submarine flank failure during the early(?) tholeiitic shield stage of Hualalai Volcano

Science.gov (United States)

Lipman, P.W.; Coombs, M.L.

2006-01-01

The North Kona slump is an elliptical region, about 20 by 60 km (1000-km2 area), of multiple, geometrically intricate benches and scarps, mostly at water depths of 2000–4500 m, on the west flank of Hualalai Volcano. Two dives up steep scarps in the slump area were made in September 2001, using the ROV Kaiko of the Japan Marine Science and Technology Center (JAMSTEC), as part of a collaborative Japan–USA project to improve understanding of the submarine flanks of Hawaiian volcanoes. Both dives, at water depths of 2700–4000 m, encountered pillow lavas draping the scarp-and-bench slopes. Intact to only slightly broken pillow lobes and cylinders that are downward elongate dominate on the steepest mid-sections of scarps, while more equant and spherical pillow shapes are common near the tops and bases of scarps and locally protrude through cover of muddy sediment on bench flats. Notably absent are subaerially erupted Hualalai lava flows, interbedded hyaloclastite pillow breccia, and/or coastal sandy sediment that might have accumulated downslope from an active coastline. The general structure of the North Kona flank is interpreted as an intricate assemblage of downdropped lenticular blocks, bounded by steeply dipping normal faults. The undisturbed pillow-lava drape indicates that slumping occurred during shield-stage tholeiitic volcanism. All analyzed samples of the pillow-lava drape are tholeiite, similar to published analyses from the submarine northwest rift zone of Hualālai. Relatively low sulfur (330–600 ppm) and water (0.18–0.47 wt.%) contents of glass rinds suggest that the eruptive sources were in shallow water, perhaps 500–1000-m depth. In contrast, saturation pressures calculated from carbon dioxide concentrations (100–190 ppm) indicate deeper equilibration, at or near sample sites at water depths of − 3900 to − 2800 m. Either vents close to the sample sites erupted mixtures of undegassed and degassed magmas, or volatiles were resorbed from
Integrated geophysical and hydrothermal models of flank degassing and fluid flow at Masaya Volcano, Nicaragua

Science.gov (United States)

Sanford, Ward E.; Pearson, S.C.P.; Kiyosugi, K.; Lehto, H.L.; Saballos, J.A.; Connor, C.B.

2012-01-01

We investigate geologic controls on circulation in the shallow hydrothermal system of Masaya volcano, Nicaragua, and their relationship to surface diffuse degassing. On a local scale (~250 m), relatively impermeable normal faults dipping at ~60° control the flowpath of water vapor and other gases in the vadose zone. These shallow normal faults are identified by modeling of a NE-SW trending magnetic anomaly of up to 2300 nT that corresponds to a topographic offset. Elevated SP and CO2 to the NW of the faults and an absence of CO2 to the SE suggest that these faults are barriers to flow. TOUGH2 numerical models of fluid circulation show enhanced flow through the footwalls of the faults, and corresponding increased mass flow and temperature at the surface (diffuse degassing zones). On a larger scale, TOUGH2 modeling suggests that groundwater convection may be occurring in a 3-4 km radial fracture zone transecting the entire flank of the volcano. Hot water rising uniformly into the base of the model at 1 x 10-5 kg/m2s results in convection that focuses heat and fluid and can explain the three distinct diffuse degassing zones distributed along the fracture. Our data and models suggest that the unusually active surface degassing zones at Masaya volcano can result purely from uniform heat and fluid flux at depth that is complicated by groundwater convection and permeability variations in the upper few km. Therefore isolating the effects of subsurface geology is vital when trying to interpret diffuse degassing in light of volcanic activity.
Structural control of monogenetic volcanism in the Garrotxa volcanic field (Northeastern Spain) from gravity and self-potential measurements

Science.gov (United States)

Barde-Cabusson, S.; Gottsmann, J.; Martí, J.; Bolós, X.; Camacho, A. G.; Geyer, A.; Planagumà, Ll.; Ronchin, E.; Sánchez, A.

2014-01-01

We report new geophysical observations on the distribution of subsurface structures associated with monogenetic volcanism in the Garrotxa volcanic field (Northern Spain). As part of the Catalan Volcanic Zone, this Quaternary volcanic field is associated with the European rifts system. It contains the most recent and best preserved volcanic edifices of the Catalan Volcanic Zone with 38 monogenetic volcanoes identified in the Garrotxa Natural Park. We conducted new gravimetric and self-potential surveys to enhance our understanding of the relationship between the local geology and the spatial distribution of the monogenetic volcanoes. The main finding of this study is that the central part of the volcanic field is dominated by a broad negative Bouguer anomaly of around -0.5 mGal, within which a series of gravity minima are found with amplitudes of up to -2.3 mGal. Inverse modelling of the Bouguer data suggests that surficial low-density material dominates the volcanic field, most likely associated with effusive and explosive surface deposits. In contrast, an arcuate cluster of gravity minima to the NW of the Croscat volcano, the youngest volcano of this zone, is modelled by vertically extended low-density bodies, which we interpret as a complex ensemble of fault damage zones and the roots of young scoria cones. A ground-water infiltration zone identified by a self-potential anomaly is associated with a steep horizontal Bouguer gravity gradient and interpreted as a fault zone and/or magmatic fissure, which fed the most recent volcanic activity in the Garrotxa. Gravimetric and self-potential data are well correlated and indicate a control on the locations of scoria cones by NNE-SSW and NNW-SSE striking tectonic features, which intersect the main structural boundaries of the study area to the north and south. Our interpretation of the data is that faults facilitated magma ascent to the surface. Our findings have major implications for understanding the relationship
The role of viscous magma mush spreading in volcanic flank motion at Kīlauea Volcano, Hawai'i

NARCIS (Netherlands)

Plattner, C.; Amelung, F.; Baker, S.; Govers, R.; Poland, M.

2013-01-01

Multiple mechanisms have been suggested to explain seaward motion of the south flank of Kīlauea Volcano, Hawai'i. The consistency of flank motion during both waxing and waning magmatic activity at Kīlauea suggests that a continuously acting force, like gravity body force, plays a substantial role.
The effect of offset on fracture permeability of rocks from the Southern Andes Volcanic Zone, Chile

Science.gov (United States)

Pérez-Flores, P.; Wang, G.; Mitchell, T. M.; Meredith, P. G.; Nara, Y.; Sarkar, V.; Cembrano, J.

2017-11-01

The Southern Andes Volcanic Zone (SVZ) represents one of the largest undeveloped geothermal provinces in the world. Development of the geothermal potential requires a detailed understanding of fluid transport properties of its main lithologies. The permeability of SVZ rocks is altered by the presence of fracture damage zones produced by the Liquiñe-Ofqui Fault System (LOFS) and the Andean Transverse Faults (ATF). We have therefore measured the permeability of four representative lithologies from the volcanic basement in this area: crystalline tuff, andesitic dike, altered andesite and granodiorite. For comparative purposes, we have also measured the permeability of samples of Seljadalur basalt, an Icelandic rock with widely studied and reported hydraulic properties. Specifically, we present the results of a systematic study of the effect of fractures and fracture offsets on permeability as a function of increasing effective pressure. Baseline measurements on intact samples of SVZ rocks show that the granodiorite has a permeability (10-18 m2), two orders of magnitude higher than that of the volcanic rocks (10-20 m2). The presence of throughgoing mated macro-fractures increases permeability by between four and six orders of magnitude, with the highest permeability recorded for the crystalline tuff. Increasing fracture offset to produce unmated fractures results in large increases in permeability up to some characteristic value of offset, beyond which permeability changes only marginally. The increase in permeability with offset appears to depend on fracture roughness and aperture, and these are different for each lithology. Overall, fractured SVZ rocks with finite offsets record permeability values consistent with those commonly found in geothermal reservoirs (>10-16 m2), which potentially allow convective/advective flow to develop. Hence, our results demonstrate that the fracture damage zones developed within the SVZ produce permeable regions, especially within the
Nature, source and composition of volcanic ash in sediments from a fracture zone trace of Rodriguez Triple Junction in the Central Indian Basin

Digital Repository Service at National Institute of Oceanography (India)

Mascarenhas-Pereira, M.B.L.; Nath, B.N.; Borole, D.V.; Gupta, S.M.

Volcanic glasses associated with pumice, micro nodules and palagonite like lithic fragments were recovered from a volcanic terrain in a fracture zone defined as Rodriguez Triple Junction trace in the Central Indian Basin. Morphologically, the tephra...
The effect of giant lateral collapses on magma pathways and the location of volcanism.

Science.gov (United States)

Maccaferri, Francesco; Richter, Nicole; Walter, Thomas R

2017-10-23

Flank instability and lateral collapse are recurrent processes during the structural evolution of volcanic edifices, and they affect and are affected by magmatic activity. It is known that dyke intrusions have the potential to destabilise the flanks of a volcano, and that lateral collapses may change the style of volcanism and the arrangement of shallow dykes. However, the effect of a large lateral collapse on the location of a new eruptive centre remains unclear. Here, we use a numerical approach to simulate the pathways of magmatic intrusions underneath the volcanic edifice, after the stress redistribution resulting from a large lateral collapse. Our simulations are quantitatively validated against the observations at Fogo volcano, Cabo Verde. The results reveal that a lateral collapse can trigger a significant deflection of deep magma pathways in the crust, favouring the formation of a new eruptive centre within the collapse embayment. Our results have implications for the long-term evolution of intraplate volcanic ocean islands.
Obsidian sources of the Coromandel Volcanic Zone, nortthern New Zealand

International Nuclear Information System (INIS)

Moore, P.R.

2013-01-01

The Coromandel Volcanic Zone includes nine geographically discrete obsidian sources (Fanal, Awana, Te Ahumata, Cooks Beach, Hahei, Tairua, Whangamata, Maratoto and Waihi). Each has a distinctive chemical composition, and some can also be differentiated on the basis of visual characteristics of the obsidian. Chemically, the three northern sources (Fanal, Awana, Te Ahumata), constituting the 'Great Barrier Group', are distinguished by high Rb concentrations and a high Rb/Sr ratio. Obsidian from six of the sources is known to have been utilized by pre-European Maori for the manufacture of flake tools, but at present there is no evidence for exploitation of the Awana, Maratoto and Tairua deposits. (author). 54 refs., 5 figs., 2 tabs.
Soil radon concentration and volcanic activity of Mt. Etna before and after the 2002 eruption

International Nuclear Information System (INIS)

Imme, G.; La Delfa, S.; Lo Nigro, S.; Morelli, D.; Patane, G.

2006-01-01

Soil radon investigation, using a continuous measurement device, has been performed on Mt. Etna in order to observe possible anomalies due to seismic and/or volcanic activity. In October 2002 an eruptive event occurred. Measurements, performed on the NE flank, have shown a possible correlation between eruptive activity of the volcano and soil radon concentration anomaly. The study of the seismic activity recorded in the same flank has, also, allowed to characterize the volcano dynamics and to correlate it with the variations of radon. The obtained results seem to indicate a possible dependence on volcanic activity of the radon concentration
Seismological evidence for a sub-volcanic arc mantle wedge beneath the Denali volcanic gap, Alaska

Science.gov (United States)

McNamara, D.E.; Pasyanos, M.E.

2002-01-01

Arc volcanism in Alaska is strongly correlated with the 100 km depth contour of the western Aluetian Wadati-Benioff zone. Above the eastern portion of the Wadati-Benioff zone however, there is a distinct lack of volcanism (the Denali volcanic gap). We observe high Poisson's ratio values (0.29-0.33) over the entire length of the Alaskan subduction zone mantle wedge based on regional variations of Pn and Sn velocities. High Poisson's ratios at this depth (40-70 km), adjacent to the subducting slab, are attributed to melting of mantle-wedge peridotites, caused by fluids liberated from the subducting oceanic crust and sediments. Observations of high values of Poisson's ratio, beneath the Denali volcanic gap suggest that the mantle wedge contains melted material that is unable to reach the surface. We suggest that its inability to migrate through the overlying crust is due to increased compression in the crust at the northern apex of the curved Denali fault.
Fluids in volcanic and geothermal systems

Science.gov (United States)

Sigvaldason, Gudmundur E.

Mineral buffers control the composition of most volatile components of magmas and dissolved species in geothermal fluids. The only element which occurs in significant quantities in volcanic and geothermal fluids and is not controlled by mineral buffers is chlorine. It is argued that in absence of marine influence, geothermal fluids reflect the chlorine content of associated magmatic fluids. The chlorine content of oceanic volcanic rocks has a positive correlation with elements, which are believed to indicate a heterogenous source region. Since the source is generally believed to be the Earth's mantle, the implication is that the mantle is heterogenous with regard to chlorine and other volatiles. Such heterogeneities would have important consequences for genesis and distribution of ore. All major magma types of the oceanic environment occur in Iceland. Their spatial distribution is closely related to a volcanotectonic pattern, suggesting crustal control. A geophysical model of crustal accretion in a rift zone is used in conjunction with classical petrology to predict geochemical processes in a rift zone crust. The model has two kinematic parameters-drift rate and subsidence rate-which combined describe trajectories of mass particles deposited on the surface. When considering in conjunction with thermal gradients of the rift zone a series of metamorphic reactions and chemical fractionation processes are bound to occur, eventually resulting in a layering of the oceanic crust. The physical parameters result in a derived variable, rift zone residence time, which depends on the width of a rift zone. Long residence times in a wide rift zone lead to multistage recycling of material. Other properties of the model, based on geometric arrangement of productive fissure swarms within a rift zone, explain off-rift volcanism as directly related to rift zone processes, either as plate trapped magmatic domains or a transgressive thermal anomaly into an older crust. Off
Global time-size distribution of volcanic eruptions on Earth.

Science.gov (United States)

Papale, Paolo

2018-05-01

Volcanic eruptions differ enormously in their size and impacts, ranging from quiet lava flow effusions along the volcano flanks to colossal events with the potential to affect our entire civilization. Knowledge of the time and size distribution of volcanic eruptions is of obvious relevance for understanding the dynamics and behavior of the Earth system, as well as for defining global volcanic risk. From the analysis of recent global databases of volcanic eruptions extending back to more than 2 million years, I show here that the return times of eruptions with similar magnitude follow an exponential distribution. The associated relative frequency of eruptions with different magnitude displays a power law, scale-invariant distribution over at least six orders of magnitude. These results suggest that similar mechanisms subtend to explosive eruptions from small to colossal, raising concerns on the theoretical possibility to predict the magnitude and impact of impending volcanic eruptions.
Volcanism and associated hazards: the Andean perspective

Science.gov (United States)

Tilling, R. I.

2009-12-01

Andean volcanism occurs within the Andean Volcanic Arc (AVA), which is the product of subduction of the Nazca Plate and Antarctica Plates beneath the South America Plate. The AVA is Earth's longest but discontinuous continental-margin volcanic arc, which consists of four distinct segments: Northern Volcanic Zone, Central Volcanic Zone, Southern Volcanic Zone, and Austral Volcanic Zone. These segments are separated by volcanically inactive gaps that are inferred to indicate regions where the dips of the subducting plates are too shallow to favor the magma generation needed to sustain volcanism. The Andes host more volcanoes that have been active during the Holocene (past 10 000 years) than any other volcanic region in the world, as well as giant caldera systems that have produced 6 of the 47 largest explosive eruptions (so-called "super eruptions") recognized worldwide that have occurred from the Ordovician to the Pleistocene. The Andean region's most powerful historical explosive eruption occurred in 1600 at Huaynaputina Volcano (Peru). The impacts of this event, whose eruptive volume exceeded 11 km3, were widespread, with distal ashfall reported at distances >1000 km away. Despite the huge size of the Huaynaputina eruption, human fatalities from hazardous processes (pyroclastic flows, ashfalls, volcanogenic earthquakes, and lahars) were comparatively small owing to the low population density at the time. In contrast, lahars generated by a much smaller eruption (Colombia) killed about 25 000 people - the worst volcanic disaster in the Andean region as well as the second worst in the world in the 20th century. The Ruiz tragedy has been attributed largely to ineffective communications of hazards information and indecisiveness by government officials, rather than any major deficiencies in scientific data. Ruiz's disastrous outcome, however, together with responses to subsequent hazardous eruptions in Chile, Colombia, Ecuador, and Peru has spurred significant

Experimental constraints on forecasting the location of volcanic eruptions from pre-eruptive surface deformation

Science.gov (United States)

Guldstrand, Frank; Galland, Olivier; Hallot, Erwan; Burchardt, Steffi

2018-02-01

Volcanic eruptions pose a threat to lives and property when volcano flanks and surroundings are densely populated. The local impact of an eruption depends firstly on its location, whether it occurs near a volcano summit, or down on the flanks. Then forecasting, with a defined accuracy, the location of a potential, imminent eruption would significantly improve the assessment and mitigation of volcanic hazards. Currently, the conventional volcano monitoring methods based on the analysis of surface deformation assesses whether a volcano may erupt but are not implemented to locate imminent eruptions in real time. Here we show how surface deformation induced by ascending eruptive feeders can be used to forecast the eruption location through a simple geometrical analysis. Our analysis builds on the results of 33 scaled laboratory experiments simulating magma intrusions in a brittle crust, during which the intrusion-induced surface deformation was systematically monitored at high spatial and temporal resolution. In all the experiments, surface deformation preceding the eruptions resulted in systematic uplift, regardless of the intrusion shape. The analysis of the surface deformation patterns leads to the definition of a vector between the centre of the uplifted zone and the point of maximum uplift, which systematically acted as a precursor to the eruption’s location. The temporal evolution of this vector indicated the direction in which the subsequent eruption would occur and ultimately the location itself, irrespective of the feeder shapes. Our findings represent a new approach on how surface deformation on active volcanoes could be analysed and used prior to an eruption with a real potential to improve hazard mitigation.
Seismically active column and volcanic plumbing system beneath the island arc of the Izu-Bonin subduction zone

Czech Academy of Sciences Publication Activity Database

Špičák, Aleš; Vaněk, Jiří; Hanuš, Václav

2009-01-01

Roč. 179, č. 3 (2009), s. 1301-1312 ISSN 0956-540X Institutional research plan: CEZ:AV0Z30120515 Keywords : seismicity and tectonics * volcano seismology * subduction zone processes * volcanic arc processes * magma migration and fragmentation * Pacific Ocean Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.435, year: 2009
Quantitative volcanic susceptibility analysis of Lanzarote and Chinijo Islands based on kernel density estimation via a linear diffusion process

Science.gov (United States)

Galindo, I.; Romero, M. C.; Sánchez, N.; Morales, J. M.

2016-06-01

Risk management stakeholders in high-populated volcanic islands should be provided with the latest high-quality volcanic information. We present here the first volcanic susceptibility map of Lanzarote and Chinijo Islands and their submarine flanks based on updated chronostratigraphical and volcano structural data, as well as on the geomorphological analysis of the bathymetric data of the submarine flanks. The role of the structural elements in the volcanic susceptibility analysis has been reviewed: vents have been considered since they indicate where previous eruptions took place; eruptive fissures provide information about the stress field as they are the superficial expression of the dyke conduit; eroded dykes have been discarded since they are single non-feeder dykes intruded in deep parts of Miocene-Pliocene volcanic edifices; main faults have been taken into account only in those cases where they could modified the superficial movement of magma. The application of kernel density estimation via a linear diffusion process for the volcanic susceptibility assessment has been applied successfully to Lanzarote and could be applied to other fissure volcanic fields worldwide since the results provide information about the probable area where an eruption could take place but also about the main direction of the probable volcanic fissures.
Patterns of deformation and volcanic flows associated with lithospheric loading by large volcanoes on Venus

Science.gov (United States)

Mcgovern, Patrick J.; Solomon, Sean C.

1993-01-01

models of a volcanic load detached from the underlying lithosphere predict overthrusting and radial normal faulting at the volcano's edge. Such a mechanism for the formation of radial rift zones on Venus volcanoes would make such features analogous to structures on the flanks of volcanoes on Earth.
Carboniferous geology and uranium potential of the northeast flank of the Parana Basin and southwest flank of the Parnaiba Basin, Brazil

International Nuclear Information System (INIS)

Andrade, S.M. de; Camarco, P.E.N.

1984-01-01

The Carboniferous sequences of the northeast flank of the Parana Basin and those of the southwest flank of the Parnaiba Basin have been the subject of discussion and polemics for quite a long time, especially in terms of their stratigraphic relations and depositional environments. Thus, we reinforce our main objective, which is to furnish data for the definition of the uranium potential in these Carboniferous sediments, by adding recently acquired information that should aid in the clarification of the existing controversies. The Carboniferous along the northeast flank of the Parana Basin is represented by the Aquidauana Formation which has been informally divided into three members: lower, middle and upper members. The middle member, of marine origin, constitutes a prospective target for uranium and phosphate associations, in which sandstones interbedded with shales constitute the host rocks. On the other hand, the Carboniferous of the southwest margin of the Parnaiba Basin, which encompasses the Longa, Poti and Piaui Formations has shown very remote possibilities of uranium occurrences. The regional structural framework, as reflected by the Carboniferous rocks along both basin flanks, is characterized by homoclines cut by gravity faults. The faults along these weakness zones were occasionally intruded by basic rocks of Cretaceous age. Superimposed on the regional structure, open folds appear in the form of anticlines and domes. These folds are discontinuous structures resulting from uplift due to vertical stresses or result from differential subsidence along the limbs of the folds. (Author) [pt
TECTONIC VERSUS VOLCANIC ORIGIN OF THE SUMMIT DEPRESSION AT MEDICINE LAKE VOLCANO, CALIFORNIA

Energy Technology Data Exchange (ETDEWEB)

Mark Leon Gwynn

2010-05-01

Medicine Lake Volcano is a Quaternary shield volcano located in a tectonically complex and active zone at the transition between the Basin and Range Province and the Cascade Range of the Pacific Province. The volcano is topped by a 7x12 km elliptical depression surrounded by a discontinuous constructional ring of basaltic to rhyolitic lava flows. This thesis explores the possibility that the depression may have formed due to regional extension (rift basin) or dextral shear (pull-apart basin) rather than through caldera collapse and examines the relationship between regional tectonics and localized volcanism. Existing data consisting of temperature and magnetotelluric surveys, alteration mineral studies, and core logging were compiled and supplemented with additional core logging, field observations, and fault striae studies in paleomagnetically oriented core samples. These results were then synthesized with regional fault data from existing maps and databases. Faulting patterns near the caldera, extension directions derived from fault striae P and T axes, and three-dimensional temperature and alteration mineral models are consistent with slip across arcuate ring faults related to magma chamber deflation during flank eruptions and/or a pyroclastic eruption at about 180 ka. These results are not consistent with a rift or pull-apart basin. Limited subsidence can be attributed to the relatively small volume of ash-flow tuff released by the only known major pyroclastic eruption and is inconsistent with the observed topographic relief. The additional relief can be explained by constructional volcanism. Striae from unoriented and oriented core, augmented by striae measurements in outcrop suggest that Walker Lane dextral shear, which can be reasonably projected from the southeast, has probably propagated into the Medicine Lake area. Most volcanic vents across Medicine Lake Volcano strike north-south, suggesting they are controlled by crustal weakness related to Basin and
Tectonic versus volcanic origin of the summit depression at Medicine Lake Volcano, California

Energy Technology Data Exchange (ETDEWEB)

Mark Leon Gwynn

2010-05-01

Medicine Lake Volcano is a Quaternary shield volcano located in a tectonically complex and active zone at the transition between the Basin and Range Province and the Cascade Range of the Pacific Province. The volcano is topped by a 7x12 km elliptical depression surrounded by a discontinuous constructional ring of basaltic to rhyolitic lava flows. This thesis explores the possibility that the depression may have formed due to regional extension (rift basin) or dextral shear (pull-apart basin) rather than through caldera collapse and examines the relationship between regional tectonics and localized volcanism. Existing data consisting of temperature and magnetotelluric surveys, alteration mineral studies, and core logging were compiled and supplemented with additional core logging, field observations, and fault striae studies in paleomagnetically oriented core samples. These results were then synthesized with regional fault data from existing maps and databases. Faulting patterns near the caldera, extension directions derived from fault striae P and T axes, and three-dimensional temperature and alteration mineral models are consistent with slip across arcuate ring faults related to magma chamber deflation during flank eruptions and/or a pyroclastic eruption at about 180 ka. These results are not consistent with a rift or pull-apart basin. Limited subsidence can be attributed to the relatively small volume of ash-flow tuff released by the only known major pyroclastic eruption and is inconsistent with the observed topographic relief. The additional relief can be explained by constructional volcanism. Striae from unoriented and oriented core, augmented by striae measurements in outcrop suggest that Walker Lane dextral shear, which can be reasonably projected from the southeast, has probably propagated into the Medicine Lake area. Most volcanic vents across Medicine Lake Volcano strike north-south, suggesting they are controlled by crustal weakness related to Basin and
Geophysical expression of caldera related volcanism, structures and mineralization in the McDermitt volcanic field

Science.gov (United States)

Rytuba, J. J.; Blakely, R. J.; Moring, B.; Miller, R.

2013-12-01

The High Rock, Lake Owyhee, and McDermitt volcanic fields, consisting of regionally extensive ash flow tuffs and associated calderas, developed in NW Nevada and SE Oregon following eruption of the ca. 16.7 Ma Steens flood basalt. The first ash flow, the Tuff of Oregon Canyon, erupted from the McDermitt volcanic field at 16.5Ma. It is chemically zoned from peralkaline rhyolite to dacite with trace element ratios that distinguish it from other ash flow tuffs. The source caldera, based on tuff distribution, thickness, and size of lithic fragments, is in the area in which the McDermitt caldera (16.3 Ma) subsequently formed. Gravity and magnetic anomalies are associated with some but not all of the calderas. The White Horse caldera (15.6 Ma), the youngest caldera in the McDermitt volcanic field has the best geophysical expression, with both aeromagnetic and gravity lows coinciding with the caldera. Detailed aeromagnetic and gravity surveys of the McDermitt caldera, combined with geology and radiometric surveys, provides insight into the complexities of caldera collapse, resurgence, post collapse volcanism, and hydrothermal mineralization. The McDermitt caldera is among the most mineralized calderas in the world, whereas other calderas in these three Mid Miocene volcanic fields do not contain important hydrothermal ore deposits, despite having similar age and chemistry. The McDermitt caldera is host to Hg, U, and Li deposits and potentially significant resources of Ga, Sb, and REE. The geophysical data indicate that post-caldera collapse intrusions were important in formation of the hydrothermal systems. An aeromagnetic low along the E caldera margin reflects an intrusion at a depth of 2 km associated with the near-surface McDermitt-hot-spring-type Hg-Sb deposit, and the deeper level, high-sulfidation Ga-REE occurrence. The Li deposits on the W side of the caldera are associated with a series of low amplitude, small diameter aeromagnetic anomalies that form a continuous
Slab dehydration in Cascadia and its relationship to volcanism, seismicity, and non-volcanic tremor

Science.gov (United States)

Delph, J. R.; Levander, A.; Niu, F.

2017-12-01

The characteristics of subduction beneath the Pacific Northwest (Cascadia) are variable along strike, leading to the segmentation of Cascadia into 3 general zones: Klamath, Siletzia, and Wrangelia. These zones show marked differences in tremor density, earthquake density, seismicity rates, and the locus and amount of volcanism in the subduction-related volcanic arc. To better understand what controls these variations, we have constructed a 3D shear-wave velocity model of the upper 80 km along the Cascadia margin from the joint inversion of CCP-derived receiver functions and ambient noise surface wave data using 900 temporary and permanent broadband seismic stations. With this model, we can investigate variations in the seismic structure of the downgoing oceanic lithosphere and overlying mantle wedge, the character of the crust-mantle transition beneath the volcanic arc, and local to regional variations in crustal structure. From these results, we infer the presence and distribution of fluids released from the subducting slab and how they affect the seismic structure of the overriding lithosphere. In the Klamath and Wrangelia zones, high seismicity rates in the subducting plate and high tremor density correlate with low shear velocities in the overriding plate's forearc and relatively little arc volcanism. While the cause of tremor is debated, intermediate depth earthquakes are generally thought to be due to metamorphic dehydration reactions resulting from the dewatering of the downgoing slab. Thus, the seismic characteristics of these zones combined with rather sparse arc volcanism may indicate that the slab has largely dewatered by the time it reaches sub-arc depths. Some of the water released during earthquakes (and possibly tremor) may percolate into the overriding plate, leading to slow seismic velocities in the forearc. In contrast, Siletzia shows relatively low seismicity rates and tremor density, with relatively higher shear velocities in the forearc
New structural, hydrogeological and hydrothermal insights on Cumbre Vieja (La Palma, Canary Islands, Spain)

Science.gov (United States)

Barde-Cabusson, S.; Finizola, A.; Torres, P.; Víctor Villasante-Marcos, V.; Abella, R.; Aragó, S.; Berthod, C.; Ibarra, P.; Geyer Traver, A.

2013-12-01

Determining the link between shallow structure and volcanism is a topic of interest in Volcanology. We carried out a geophysical study devoted to the characterization of the major structural limits influencing volcanic hydrothermal activity and underground meteoric circulations in La Palma (Canary Islands). Since 1 Ma volcanic activity concentrates at the southern half of the island, on the Cumbre Vieja volcanic rift-zone. During the 1949 eruption a N-S fault system, facing west, developed in the summit area of Cumbre Vieja. This was interpreted as the surface expression of an incipient deformation zone on the western flank. The distribution of the recent activity and faulting indicate that a discontinuity may be present beneath the western flank of Cumbre Vieja, along which a future collapse may occur. Our study, which combines the application of self-potential and soil temperature measurements, provides new information to characterize and locate the limits guiding upward or downward fluid circulation and possibly associated to future failures and potential landslides on the Cumbre Vieja rift-zone. We found a clear asymmetry of the self-potential signal between the eastern and the western flanks of Cumbre Vieja. Strong infiltration of meteoric water seems to affect most of the summit axis while we observe poor variation in the self-potential values on the western flank. This could be explained by a constant thickness of the vadose zone on this flank, i.e., the presence of an impermeable layer at constant depth. This layer could correspond to the landslide interface associated to the previous Cumbre Nueva edifice destruction, on which Cumbre Vieja is currently growing. This constant self-potential pattern is interrupted by at least one other main infiltration zone, near Tajuya volcano, at 1200 m a.s.l. on the western flank, where field observation allowed identifying a small horst-graben system. However it is not clear if this fault system results from local
Classifcation of volcanic structure in mesozoic era in the Fuzhou-Shaoxing area

International Nuclear Information System (INIS)

Zhang Fengqi.

1989-01-01

The volcanic structure in the Fuzhou-Shaoxing area can be classified into IV grades: the grade I be the zone of volcanic activity; the grade II be the second zone of volcanic activity; the grade III be the positive, negative volcanic structure; the grade IV be volcanic conduit, volcanic crater, concealed eruption breccia pipe. Based on the geological situation in this area, the different types of volcanic structure are also dealt with. In the mean time, both the embossed type in the depression area and the depressed type in the embossed area in the volcanic basin are pointed out. It is of great advantage to Uranium mineralization
Geology of the Ugashik-Mount Peulik Volcanic Center, Alaska

Science.gov (United States)

Miller, Thomas P.

2004-01-01

The Ugashik-Mount Peulik volcanic center, 550 km southwest of Anchorage on the Alaska Peninsula, consists of the late Quaternary 5-km-wide Ugashik caldera and the stratovolcano Mount Peulik built on the north flank of Ugashik. The center has been the site of explosive volcanism including a caldera-forming eruption and post-caldera dome-destructive activity. Mount Peulik has been formed entirely in Holocene time and erupted in 1814 and 1845. A large lava dome occupies the summit crater, which is breached to the west. A smaller dome is perched high on the southeast flank of the cone. Pyroclastic-flow deposits form aprons below both domes. One or more sector-collapse events occurred early in the formation of Mount Peulik volcano resulting in a large area of debris-avalanche deposits on the volcano's northwest flank. The Ugashik-Mount Peulik center is a calcalkaline suite of basalt, andesite, dacite, and rhyolite, ranging in SiO2 content from 51 to 72 percent. The Ugashik-Mount Peulik magmas appear to be co-genetic in a broad sense and their compositional variation has probably resulted from a combination of fractional crystallization and magma-mixing. The most likely scenario for a future eruption is that one or more of the summit domes on Mount Peulik are destroyed as new magma rises to the surface. Debris avalanches and pyroclastic flows may then move down the west and, less likely, east flanks of the volcano for distances of 10 km or more. A new lava dome or series of domes would be expected to form either during or within some few years after the explosive disruption of the previous dome. This cycle of dome disruption, pyroclastic flow generation, and new dome formation could be repeated several times in a single eruption. The volcano poses little direct threat to human population as the area is sparsely populated. The most serious hazard is the effect of airborne volcanic ash on aircraft since Mount Peulik sits astride heavily traveled air routes connecting the U
Assessment of volcanic hazards, vulnerability, risk and uncertainty (Invited)

Science.gov (United States)

Sparks, R. S.

2009-12-01

A volcanic hazard is any phenomenon that threatens communities . These hazards include volcanic events like pyroclastic flows, explosions, ash fall and lavas, and secondary effects such as lahars and landslides. Volcanic hazards are described by the physical characteristics of the phenomena, by the assessment of the areas that they are likely to affect and by the magnitude-dependent return period of events. Volcanic hazard maps are generated by mapping past volcanic events and by modelling the hazardous processes. Both these methods have their strengths and limitations and a robust map should use both approaches in combination. Past records, studied through stratigraphy, the distribution of deposits and age dating, are typically incomplete and may be biased. Very significant volcanic hazards, such as surge clouds and volcanic blasts, are not well-preserved in the geological record for example. Models of volcanic processes are very useful to help identify hazardous areas that do not have any geological evidence. They are, however, limited by simplifications and incomplete understanding of the physics. Many practical volcanic hazards mapping tools are also very empirical. Hazards maps are typically abstracted into hazards zones maps, which are some times called threat or risk maps. Their aim is to identify areas at high levels of threat and the boundaries between zones may take account of other factors such as roads, escape routes during evacuation, infrastructure. These boundaries may change with time due to new knowledge on the hazards or changes in volcanic activity levels. Alternatively they may remain static but implications of the zones may change as volcanic activity changes. Zone maps are used for planning purposes and for management of volcanic crises. Volcanic hazards maps are depictions of the likelihood of future volcanic phenomena affecting places and people. Volcanic phenomena are naturally variable, often complex and not fully understood. There are
Hf isotope evidence for variable slab input and crustal addition in basalts and andesites of the Taupo Volcanic Zone, New Zealand

DEFF Research Database (Denmark)

Waight, Tod Earle; Troll, Valentin R.; Gamble, J.A.

2017-01-01

-Nd isotopes. Here we present new Hf isotope data for a selection of volcanic rocks and crustal lithologies fromthe Taupo Volcanic Zone (TVZ), NewZealand and propose that the scatter in Hf-Nd isotopes indicates heterogeneity in the parental magmas prior to interactions with crustal lithologies. The observed......, whereas younger lavas have probably interacted more with mid- to shallow crustal meta-sedimentary greywacke-argillite lithologies of the Permian to Cretaceous composite Torlesse Terrane. Hf-Nd isotopic compositions of meta-igneous granulite xenoliths from Mt. Ruapehu are consistent with previous...
Debris Avalanches and Debris Flows Transformed from Collapses in the Trans-Mexican Volcanic Belt, México.

Science.gov (United States)

Capra, L.; Macias, J.; Scott, K.; Abrams, M.; GarduÃ±o, V.

2001-12-01

Volcanoes of the Trans-Mexican Volcanic Belt (TMVB) have yielded numerous sector and flank collapses during Pleistocene and Holocene time. Sector collapses associated with magmatic activity have yielded debris avalanches with generally limited runout extent (e.g. Popocatépetl, Jocotitlán, and Colima volcanoes). In contrast, flank collapses (smaller failures not involving the volcano summit), both associated and unassociated with magmatic activity and correlated with intense hydrothermal alteration in ice-capped volcanoes, commonly have yielded highly mobile cohesive debris flows (e.g. Pico de Orizaba and Nevado de Toluca volcanoes). Collapse orientation in the TMVB is preferentially to the south and north-east, probably reflecting the tectonic regime of active E-W and NNW faults. The different mobilities of the flows transformed from collapses have important implications for hazard assessment. Both sector and flank collapse can yield highly mobile debris flows, but this transformation is more common in the case of the smaller failures. High mobility is related to factors such as water and clay content of the failed material, the paleotopography, and the extent of entrainment of sediment during flow (bulking). Both debris-avalanches and debris-flows are volcanic hazards that occur from both active volcanoes, as well as those that are inactive or dormant volcanoes, and may by triggered by earthquakes, precipitation, or simple gravity. There will be no precursory warning in such non-volcanic cases.
Ages of plains volcanism on Mars

Science.gov (United States)

Hauber, Ernst; Jagert, Felix; Broz, Petr

2010-05-01

Plain-style volcanism [1] is widespread in the Tharsis and Elysium volcanic provinces on Mars, [2,3]. Detailed images and topographic data reveal the morphology and topography of clusters of low shields and associated lava flows. The landforms of plains volcanism on Mars have all well-known terrestrial analogues in basaltic volcanic regions, such as Hawaii, Iceland, and in particular the Snake River Plains [4]. The very gentle flank slopes (J. (1981) Icarus, 45, 586-601. [3] Hodges C.A. and Moore H.J. (1994) Atlas of volcanic features on Mars: USGS Prof. Paper 1534, 194 p. [4] Hauber E. et al. (2009) J. Volcanol. Geotherm. Res. 185, 69-95. [5] Wilson L. et al. (2009) J. Volcanol. Geotherm. Res. 185, 28-46. [6] Vaucher, J. et al. (2009) Icarus 204, 418-442. [7] Baratoux D. et al. (2009) J. Volcanol. Geotherm. Res. 185, 47-68. [8] Bleacher J.E. et al. (2009) J. Volcanol. Geotherm. Res. 185, 96-102. [9] Ivanov B.A. (2001) Space Sci. Rev. 96, 87-104. [10] Hartmann W.H. and Neukum G. (2001) Space Sci. Rev. 96, 165-194 [11] Kneissl T. et al. (2010) LPS XVI, submitted. [12] Michael, G.G. and Neukum G. (2010) Earth Planet. Sci. Lett., in press. . [13] Malin M.C. et al. (2007) JGR 112, E05S04, doi: 10.1029/2006JE002808.
Discrete Element Simulations of Density-Driven Volcanic Deformation: Applications to Martian and Terrestrial Volcanoes

Science.gov (United States)

Farrell, L. L.; McGovern, P. J.; Morgan, J. K.

2008-12-01

We have carried out 2-D numerical simulations using the discrete element method (DEM) to investigate density-driven deformation in volcanic edifices on Earth (e.g., Hawaii) and Mars (e.g., Olympus Mons and Arsia Mons). Located within volcanoes are series of magma chambers, reservoirs, and conduits where magma travels and collects. As magma differentiates, dense minerals settle out, building thick accumulations referred to as cumulates that can flow ductilely due to stresses imparted by gravity. To simulate this process, we construct granular piles subject to Coulomb frictional rheology, incrementally capture internal rectangular regions to which higher densities and lower interparticle friction values are assigned (analogs for denser, weaker cumulates), and then bond the granular edifice. Thus, following each growth increment, the edifice is allowed to relax gravitationally with a reconfigured weak cumulate core. The presence and outward spreading of the cumulate causes the development of distinctive structural and stratigraphic patterns. We obtained a range of volcanic shapes that vary from broad, shallowly dipping flanks reminiscent of those of Olympus Mons, to short, steep surface slopes more similar to Arsia Mons. Edifices lacking internal cumulate exhibit relatively horizontal strata compared to the high-angle, inward dipping strata that develops within the cumulate-bearing edifices. Our simulated volcanoes also illustrate a variety of gravity driven deformation features, including regions of thrust faulting within the flanks and large-scale flank collapses, as observed in Hawaii and inferred on Olympus Mons. We also see significant summit subsidence, and of particular interest, distinct summit calderas. The broad, flat caldera and convex upward profile of Arsia Mons appears to be well-simulated by cumulate-driven volcanic spreading. In contrast, the concave upward slopes of Olympus Mons are more challenging to reproduce, and instead are attributed to volcanic
Exploring Microbial Processes with Thermal-Hydrological Models of the Eastern Flank of the Juan de Fuca Ridge

Science.gov (United States)

Weathers, T. S.; Fisher, A. T.; Winslow, D. M.; Stauffer, P. H.; Gable, C. W.

2017-12-01

The flanks of mid-ocean ridges experience coupled flows of fluid, heat, and solutes that are critical for a wide range of global processes, including the cycling of carbon and nutrients, which supports a vast crustal biosphere. Only a few ridge-flank sites have been studied in detail; hydrogeologic conditions and processes in the volcanic crust are best understood on the eastern flank of the Juan de Fuca Ridge. This area has been extensively explored with decades of drilling, submersible, observatory, and survey expeditions and experiments, including the first hole-to-hole tracer injection experiment in the ocean crust. This study describes the development of reactive transport simulations for this ridge-flank setting using three-dimensional coupled (thermal-hydrological) models of crustal-scale circulation, beginning with the exploration of tracer transport. The prevailing flow direction is roughly south to north as a result of outcrop-to-outcrop flow, with a bulk flow rate in the range of meters/year. However, tracer was detected 500 m south ("upstream") from the injection borehole during the first year following injection. This may be explained by local mixing and/or formation fluid discharge from the southern borehole during and after injection. The constraints and parameters required to fit the observed tracer behavior can be used as a basis for modeling reactive transport processes such as nutrient delivery or microbial community evolution as a function of fluid flow. For example, the sulfate concentration in fluid samples from Baby Bare outcrop ( 8 km south of the tracer transport experiment) was 17.8 mmol/kg, whereas at Mama Bare outcrop ( 8 km to north of the tracer transport experiment) the sulfate concentration was 16.3 mmol/mg. By integrating laboratory-derived sulfate reduction rates from microbial samples originating from Juan de Fuca borehole observatories into reactive transport models, we can explore the range of microbial activity that supports
Oxygen Isotopes in Intra-Back Arc Basalts from the Andean Southern Volcanic Zone

Science.gov (United States)

Parks, B. H.; Wang, Z.; Saal, A. E.; Frey, F. A.; Blusztajn, J.

2013-12-01

The chemical compositions of volcanic rocks from the Andean Southern Volcanic Zone (SVZ) reflect complex and dynamic interactions among the subducting oceanic lithosphere, the mantle wedge, and the overlying continental crust. Oxygen isotope ratios of olivine phenocrysts can be a useful means to identifying their relative contributions to the arc magmatism. In this study, we report high-precision oxygen-isotope ratios of olivine phenocrysts in a set of intra-back arc basalts from the SVZ. The samples were collected from monogenetic cinder cones east of the volcanic front (35-39 degrees S), and have been geochemically well-characterized with major and trace element contents, and Sr-Nd-Pb isotope compositions. Compared to lavas from the volcanic front, these intra-back arc lavas have similar radiogenic isotope, and a more alkalic and primitive (higher MgO content) chemical composition. We determined the oxygen-isotope ratios using the CO2-laser-fluorination method set up at the Department of Geology and Geophysics, Yale University following the techniques reported in Wang et al (2011). The samples were analyzed with standards of Gore Mountain Garnet (5.77×0.12‰ 1σ; Valley et al., 1995) and Kilbourne Hole Olivine (5.23×0.07‰ 1σ; Sharp, 1990) in order to account for minor changes in the vacuum line during analyses. The obtained δ18OSMOW values of olivine phenocrysts from the intra-back arc basalts vary from 4.98×0.01 to 5.34×0.01‰. This range, surprisingly, is similar to the δ18O values of olivines from mantle peridotites (5.2×0.2‰). Preliminary results indicate significant correlations of 87Sr/86Sr, 143Nd/144Nd and trace element ratios of the basaltic matrix with the δ18O values of olivine phenocrysts, indicating at least three components involved in the formation of the arc volcanism. By comparing the δ18O with the variations of major and trace element contents (e.g., MgO, TiO2 and Ni), and trace element ratios (e.g. Ba/Nb), we evaluate the effects
Petrography and geochemistry of lithic fragments in ignimbrites from the Mangakino Volcanic Centre : implications for the composition of the subvolcanic crust in western Taupo Volcanic Zone, New Zealand

International Nuclear Information System (INIS)

Krippner, S.J.P.; Briggs, R.M.; Wilson, C.J.N.; Cole, J.W.

1998-01-01

The Mangakino Volcanic Centre is the westernmost and oldest rhyolitic caldera volcano in the Taupo Volcanic Zone, North Island, New Zealand. The largest eruptions from Mangakino occurred in two periods of caldera-forming activity during the 1.68-1.53 Ma (Period I), and 1.21-0.95 Ma (Period IIA), producing several voluminous widespread welded and nonwelded ignimbrites and minor fall deposits. Other activity from Mangakino generated fall deposits and rhyolitic lava domes. Lithic fragments are common in all Mangakino ignimbrites (1-10 modal %), and consist of diverse lithologies including: rhyolite, dacite, andesite, and basaltic andesite lava, welded ignimbrite, tuff, volcanic breccia, biotite granite, granodiorite porphyry, siltstone, sandstone, greywacke, metagreywacke, metaconglomerate, biotite and hornblende-biotite schist. Lithic populations in Period I ignimbrites are dominated by andesite lavas, suggesting that there was a pre-existing andesite volcano in the Mangakino area, geochemically distinct from Titiraupenga and Pureora, the nearest roughly contemporaneous andesitic volcanoes. Later ignimbrites that erupted during Period IIA, contain predominantly rhyolitic lava lithics, implying that significant dome building activity occurred at Mangakino, which represented greater volumes of rhyolitic lava than previously described from the area. Petrographic, geochemical, and geophysical (density and magnetic susceptibility) data measured from the lithic fragments are used to propose a model for the shallow crust below Mangakino Volcanic Centre. This model postulates eruptions through a basement of Mesozoic biotite schists overlain by metagreywackes, a thin cover of Tertiary sandstones and siltsones, and an overlying volcanic succession of andesite, dacite and rhyolite lavas, welded ignimbrites, and lacustrine sediments. Ignimbrite eruptions incorporated comagmatic biotite granite fragments from the crystallised margins of the silicic magma chambers, and effectively

Mariner 9 photographs of small volcanic structures on Mars

Science.gov (United States)

Greeley, R.

1973-01-01

Surface features on the flanks of martian shield volcanoes photographed by Mariner 9 are identified as lava flow channels, rift zones, and partly collapsed lava tubes by comparisons with similar structures on the flanks of Mauna Loa shield volcano, Hawaii. From these identification, the composition of the martian lava flows in interpreted to be basaltic, with viscosities ranging from those of fluid pahoehoe to more viscous aa.
Database for volcanic processes and geology of Augustine Volcano, Alaska

Science.gov (United States)

McIntire, Jacqueline; Ramsey, David W.; Thoms, Evan; Waitt, Richard B.; Beget, James E.

2012-01-01

Augustine Island (volcano) in lower Cook Inlet, Alaska, has erupted repeatedly in late-Holocene and historical times. Eruptions typically beget high-energy volcanic processes. Most notable are bouldery debris avalanches containing immense angular clasts shed from summit domes. Coarse deposits of these avalanches form much of Augustine's lower flanks. This geologic map at 1:25,000 scale depicts these deposits, these processes.
Geochemical and geochronological constrains on the Chiang Khong volcanic rocks (northwestern Thailand) and its tectonic implications

Science.gov (United States)

Qian, Xin; Feng, Qinglai; Chonglakmani, Chongpan; Monjai, Denchok

2013-12-01

Volcanic rocks in northwestern Thailand exposed dominantly in the Chiang Khong area, are commonly considered to be genetically linked to the tectonic evolution of the Paleo-Tethyan Ocean. The volcanic rocks consist mainly of andesitic to rhyolitic rocks and are traditionally mapped as Permian-Triassic sequences. Our zircon U-Pb geochronological results show that two andesitic samples (TL-1-B and TL-31-B), are representative of the Doi Yao volcanic zone, and give a mean weighted age of 241.2±4.6 Ma and 241.7±2.9 Ma, respectively. The rhyolitic sample (TL-32-B1) from the Doi Khun Ta Khuan volcanic zone erupted at 238.3±3.8 Ma. Such ages indicate that Chiang Khong volcanic rocks erputed during the early Middle Triassic period. Seven samples from the Doi Yao and Doi Khun Ta Khuan zones exhibit an affinity to arc volcanics. Three rhyolitic samples from the Chiang Khong area have a geochemical affinity to both arc and syn-collisional volcanic rocks. The Chiang Khong arc volcanic rocks can be geochemically compared with those in the Lampang area in northern Thailand, also consistent with those in Jinghong area of southwestern Yunnan. This indicates that the Chiang Rai arc-volcanic zone might northwardly link to the Lancangjiang volcanic zone in southwestern China.
Rapid uplift in Laguna del Maule volcanic field of the Andean Southern Volcanic Zone (Chile) measured by satellite radar interferometry

Science.gov (United States)

Feigl, K.; Ali, T.; Singer, B. S.; Pesicek, J. D.; Thurber, C. H.; Jicha, B. R.; Lara, L. E.; Hildreth, E. W.; Fierstein, J.; Williams-Jones, G.; Unsworth, M. J.; Keranen, K. M.

2011-12-01

The Laguna del Maule (LdM) volcanic field of the Andean Southern Volcanic Zone extends over 500 square kilometers and comprises more than 130 individual vents. As described by Hildreth et al. (2010), the history has been defined from sixty-eight Ar/Ar and K-Ar dates. Silicic eruptions have occurred throughout the past 3.7 Ma, including welded ignimbrite associated with caldera formation at 950 ka, small rhyolitic eruptions between 336 and 38 ka, and a culminating ring of 36 post-glacial rhyodacite and rhyolite coulees and domes that encircle the lake. Dating of five post-glacial flows implies that these silicic eruptions occurred within the last 25 kyr. Field relations indicate that initial eruptions comprised modest volumes of mafic rhyodacite magma that were followed by larger volumes of high silica rhyolite. The post-glacial flare-up of silicic magmatism from vents distributed around the lake, is unprecedented in the history of this volcanic field. Using satellite radar interferometry (InSAR), Fournier et al. (2010) measured uplift at a rate of more than 180 mm/year between 2007 and 2008 in a round pattern centered on the west side of LdM. More recent InSAR observations suggest that rapid uplift has continued from 2008 through early 2011. In contrast, Fournier et al. found no measurable deformation in an interferogram spanning 2003 through 2004. In this study, we model the deformation field using the General Inversion of Phase Technique (GIPhT), as described by Feigl and Thurber (2009). Two different models fit the data. The first model assumes a sill at ~5 km depth has been inflating at a rate of more than 20 million cubic meters per year since 2007. The second model assumes that the water level in the lake dropped at a rate of 20 m/yr from January 2007 through February 2010, thus reducing the load on an elastic simulation of the crust. The rate of intrusion inferred from InSAR is an order of magnitude higher than the average rate derived from well-dated arc
Imaging an off-axis volcanic field in the Main Ethiopian Rift using 3-D magnetotellurics

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Huebert, J.; Whaler, K. A.; Fisseha, S.; Hogg, C.

2017-12-01

In active continental rifts, asthenospheric upwelling and crustal thinning result in the ascent of melt through the crust to the surface. In the Main Ethiopian Rift (MER), most volcanic activity is located in magmatic segments in the rift centre, but there are areas of significant off-axis magmatism as well. The Butajira volcanic field is part of the Silti Debre Zeyt Fault (SDZF) zone in the western Main Ethiopian Rift. It is characterized by densely clustered volcanic vents (mostly scoria cones) and by limited seismic activity, which is mainly located along the big border faults that form the edge of a steep escarpment. Seismic P-Wave tomography reveals a crustal low velocity anomaly in this area. We present newly collected Magnetotelluric (MT) data to image the electrical conductivity structure of the area. We deployed 12 LMT instruments and 27 broadband stations in the western flank of the rift to further investigate the along-rift and depth extent of a highly conductive region under the SDZF which was previously identified by MT data collected on the central volcano Aluto and along a cross-rift transverse. This large conductor was interpreted as potential pathways for magma and fluid in the crust. MT Stations were positioned in five NW-SE running 50 km long profiles, covering overall 100km along the rift and providing good coverage for a 3-D inversion of the data to image this enigmatic area of the MER.
Compartmentalization of the Coso East Flank geothermal field imaged by 3-D full-tensor MT inversion

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Lindsey, Nathaniel J.; Kaven, Joern; Davatzes, Nicholas C.; Newman, Gregory A.

2017-01-01

Previous magnetotelluric (MT) studies of the high-temperature Coso geothermal system in California identified a subvertical feature of low resistivity (2–5 Ohm m) and appreciable lateral extent (>1 km) in the producing zone of the East Flank field. However, these models could not reproduce gross 3-D effects in the recorded data. We perform 3-D full-tensor inversion and retrieve a resistivity model that out-performs previous 2-D and 3-D off-diagonal models in terms of its fit to the complete 3-D MT data set as well as the degree of modelling bias. Inclusion of secondary Zxx and Zyy data components leads to a robust east-dip (60†) to the previously identified conductive East Flank reservoir feature, which correlates strongly with recently mapped surface faults, downhole well temperatures, 3-D seismic reflection data, and local microseismicity. We perform synthetic forward modelling to test the best-fit dip of this conductor using the response at a nearby MT station. We interpret the dipping conductor as a fractured and fluidized compartment, which is structurally controlled by an unmapped blind East Flank fault zone.
The Elusive Evidence of Volcanic Lightning.

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Genareau, K; Gharghabi, P; Gafford, J; Mazzola, M

2017-11-14

Lightning strikes are known to morphologically alter and chemically reduce geologic formations and deposits, forming fulgurites. A similar process occurs as the result of volcanic lightning discharge, when airborne volcanic ash is transformed into lightning-induced volcanic spherules (LIVS). Here, we adapt the calculations used in previous studies of lightning-induced damage to infrastructure materials to determine the effects on pseudo-ash samples of simplified composition. Using laboratory high-current impulse experiments, this research shows that within the lightning discharge channel there is an ideal melting zone that represents roughly 10% or less of the total channel radius at which temperatures are sufficient to melt the ash, regardless of peak current. The melted ash is simultaneously expelled from the channel by the heated, expanding air, permitting particles to cool during atmospheric transport before coming to rest in ash fall deposits. The limited size of this ideal melting zone explains the low number of LIVS typically observed in volcanic ash despite the frequent occurrence of lightning during explosive eruptions.
Basaltic Diatreme To Root Zone Volcanic Processes In Tuzo Kimberlite Pipe (Gahcho Kué Kimberlite Field, NWT, Canada)

Science.gov (United States)

Seghedi, I.; Kurszlaukis, S.; Maicher, D.

2009-05-01

Tuzo pipe is infilled by a series of coherent and fragmental kimberlite facies types typical for a diatreme to root zone transition level. Coherent or transitional coherent kimberlite facies dominate at depth, but also occur at shallow levels, either as dikes or as individual or agglutinated coherent kimberlite clasts (CKC). Several fragmental kimberlite varieties fill the central and shallow portions of the pipe. The definition, geometry and extent of the geological units are complex and are controlled by vertical elements. Specific for Tuzo is: (1) high abundance of locally derived xenoliths (granitoids and minor diabase) between and within the kimberlite phases, varying in size from sub-millimeter to several tens of meters, frequent in a belt-like domain between 120-200 m depth in the pipe; (2) the general presence of CKC, represented by round-subround, irregular to amoeboid-shaped clasts with a macrocrystic or aphanitic texture, mainly derived from fragmentation of erupting magma and less commonly from previously solidified kimberlite, as well as recycled pyroclasts. In addition, some CKC are interpreted to be intersections of a complex dike network. This diversity attests formation by various volcanic processes, extending from intrusive to explosive; (3) the presence of bedded polymict wall- rock and kimberlite breccia occurring mostly in deep levels of the pipe below 345 m depth. The gradational contact relationships of these deposits with the surrounding kimberlite rocks and their location suggest that they formed in situ. The emplacement of Tuzo pipe involved repetitive volcanic explosions alternating with periods of relative quiescence causing at least partial consolidation of some facies. The volume deficit in the diatreme-root zone after each eruption was compensated by gravitational collapse of overlying diatreme tephra and pre-fragmented wall-rock xenoliths. Highly explosive phases were alternating with weak explosions or intrusive phases, suggesting
Volcanic gas impacts on vegetation at Turrialba Volcano, Costa Rica

Science.gov (United States)

Teasdale, R.; Jenkins, M.; Pushnik, J.; Houpis, J. L.; Brown, D. L.

2010-12-01

Turrialba volcano is an active composite stratovolcano that is located approximately 40 km east of San Jose, Costa Rica. Seismic activity and degassing have increased since 2005, and gas compositions reflect further increased activity since 2007 peaking in January 2010 with a phreatic eruption. Gas fumes dispersed by trade winds toward the west, northwest, and southwest flanks of Turrialba volcano have caused significant vegetation kill zones, in areas important to local agriculture, including dairy pastures and potato fields, wildlife and human populations. In addition to extensive vegetative degradation is the potential for soil and water contamination and soil erosion. Summit fumarole temperatures have been measured over 200 degrees C and gas emissions are dominated by SO2; gas and vapor plumes reach up to 2 km (fumaroles and gases are measured regularly by OVSICORI-UNA). A recent network of passive air sampling, monitoring of water temperatures of hydrothermal systems, and soil pH measurements coupled with measurement of the physiological status of surrounding plants using gas exchange and fluorescence measurements to: (1) identify physiological correlations between leaf-level gas exchange and chlorophyll fluorescence measurements of plants under long term stress induced by the volcanic gas emissions, and (2) use measurements in tandem with remotely sensed reflectance-derived fluorescence ratio indices to track natural photo inhibition caused by volcanic gas emissions, for use in monitoring plant stress and photosynthetic function. Results may prove helpful in developing potential land management strategies to maintain the biological health of the area.
The Santa Rita Shear Zone: Major Mesozoic deformation along the western flank of the White-Inyo Range, CA

Energy Technology Data Exchange (ETDEWEB)

Brudos, T.C.; Paterson, S.R. (Univ. of Southern California, Los Angeles, CA (United States). Dept. of Geological Sciences)

1993-04-01

The Santa Rita Shear Zone (SRSZ), briefly described by Ross (1967), deforms the western part of the 164 Ma Santa Rita Flat pluton (SRFP), located SSE of Big Pine, CA. The SRSZ comprises a subvertical zone of solid-state deformation (strike N15E) over an area at least 13 km long by 2--3 km wide. Exposure of the shear zone is limited to the north and west by overlying Quaternary volcanics and basin fill within the Late Cenozoic Owens Valley graben. The SRSZ is larger than its present outcrop extent: strain magnitudes are highest within the westernmost exposures. The SRSZ along this western margin is a continuous zone of deformation comprising a mm-scale solid-state foliation containing igneous feldspars flattened into ovals with > 10:1 aspect ratios. The authors have identified three dike phases within the SRFP: (1) minor NE-striking Phase 1 dikes, comprising cm-scale aplites; (2) widespread m-scale Phase 2 dikes, which strike N10E; and (3) m-scale NW-striking Phase 3 mafic dikes. The Phase 1 and Phase 3 dikes are pre- and post-tectonic respectively; observations described below indicate the Phase 2 dikes are syn- to post-deformation. Deformation becomes localized along the Phase 2 dikes -- which are parallel to the orientation of the main body of the shear zone. Solid-state fabrics imposed on the Phase 2 dikes formed at higher temperatures than those within the SRFP, and in the east the SRFP is deformed only within a few cm of the dikes. They surmise syntectonic emplacement of the dikes into dislocational surfaces within the SRSZ, followed by solid-state deformation of the cooling dikes. Several workers have suggested the dikes within the SRFP are part of the 148 Ma independence dike swarm (referring to the Phase 2 or 3 dikes). If correct, this correlation indicates a Jurassic age for the SRSZ. Radiometric analyses of the dikes are in progress.
Origin of three-armed rifts in volcanic islands: the case of El Hierro (Canary Islands)

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Galindo Jiménez, Inés; Becerril Carretero, Laura; Martí Molist, Joan; Gudmundsson, Agust

2015-04-01

Rifts zones in volcanic oceanic islands are common structures that have been explained through several theories/models. However, despite all these models it is as yet unclear whether it is the intense intrusive activity or the sector collapses that actually control the structural evolution and geometry of oceanic-island rift zones. Here we provide a new hypothesis to explain the origin and characteristics of the feeding system of oceanic-island rift zones based on the analysis of more than 1700 surface, subsurface (water galleries), and submarine structural data from El Hierro (Canary Islands). El Hierro's geological structure is primarily controlled by a three-armed rift-zone, the arms striking NE, WSW and S. Between the rift axes there are three valleys formed during huge landslides: El Golfo, El Julan, and Las Playas. Our results show: (1) a predominant NE-SW strike of structural elements, which coincides with the main regional trend of the Canary Archipelago as a whole; (2) a clear radial strike distribution of structural elements for the whole volcanic edifice (including submarine flanks) with respect to the centre of the island; (3) that the rift zones are mainly subaerial structures and do not propagate through the submarine edifice; (4) that it is only in the NE rift that structures have a general strike similar to that of the rift as a whole, and; (5) that in the W and S rifts there is not clear main direction, showing the structural elements in the W rift a fan distribution coinciding with the general radial pattern in the island as a whole. Based on these data, we suggest that the radial-striking structures reflect comparatively uniform stress fields that operated during the constructive episodes, mainly conditioned by the combination of overburden pressure, gravitational spreading, and magma-induced stresses. By contrast, in the shallower parts of the edifice, that is, the NE-SW, N-S and WNW-ESE-striking structures, reflect local stress fields related
Mariner 9 photographs of small-scale volcanic structures on Mars

Science.gov (United States)

Greeley, R.

1972-01-01

Surface features on the flanks of Martian shield volcanoes photographed by Mariner 9 are identified as lava flow channels, rift zones, and partly collapsed lava tubes by comparisons with similar structures on the flanks of Mauna Loa shield volcano, Hawaii. From these identifications, the composition of the Martian lava flows is interpreted to be basaltic, with viscosities ranging from those of fluid pahoehoe to more viscous aa.
Tectonic Constraints on the Evolution of Geothermal Systems in the Central Andean Volcanic Zone (CAVZ)

Science.gov (United States)

Veloso, E. E.; Tardani, D.; Aron, F.; Elizalde, J. D.; Sanchez-Alfaro, P.; Godoy, B.

2017-12-01

South of 19°S, geothermal fields and Pliocene-to-Holocene volcanic centers of the Central Andean Volcanic Zone are spatially associated with distinct, large-scale fault systems disrupting the volcanic arc, which control the architecture and dynamics of the fluids reservoirs at shallow crustal levels. Based on an extensive compilation of structural, lithological and isotopic data, and satellite imagery band-ratio analyses, we produced detailed maps of 13 areas comprising 19 identified and/or potential geothermal fields, to examine if particular local-scale tectonic configurations are associated to fluids migrating from different crustal levels. We defined three main tectonic environments according to the specific, kilometer-scale structural arrangement and its spatial relation to the geothermal surface manifestations. T1, dominated by left-lateral, pure strike-slip motion on a NW-trending duplex-like geometry with geothermal fields located along the faults - in turn distributed into five major subparallel zones cutting across the orogenic belt between ca. 20° and 27°S. T2, dominated by shortening on a series of N-trending thrust faults and fault-propagated folds, cut and displaced by the above mentioned NW-trending faults, with geothermal fields hosted at fault intersections and at fold hinges. And T3, characterized by transtension accommodated by NW-to-WNW-trending left-lateral/normal faults, with hot-springs lying along the fault traces. Interestingly, each of the independently defined tectonic environments has distinctive helium (in fluids) and strontium (in lavas) isotopic signatures and estimated geothermal reservoir temperatures. T1 shows a large 4He contribution, low 87Sr/86Sr ratio and temperatures varying between ca. 220°-310°C; T3 low 4He and high 87Sr/86Sr ratio and temperature (260°-320°C); T2 isotopic values fall between T1 and T3, yet showing the lowest (130°-250°C) temperatures. We suggest that these particular isotopic signatures are due to
GPS-derived coupling estimates for the Central America subduction zone and volcanic arc faults: El Salvador, Honduras and Nicaragua

Science.gov (United States)

Correa-Mora, F.; DeMets, C.; Alvarado, D.; Turner, H. L.; Mattioli, G.; Hernandez, D.; Pullinger, C.; Rodriguez, M.; Tenorio, C.

2009-12-01

We invert GPS velocities from 32 sites in El Salvador, Honduras and Nicaragua to estimate the rate of long-term forearc motion and distributions of interseismic coupling across the Middle America subduction zone offshore from these countries and faults in the Salvadoran and Nicaraguan volcanic arcs. A 3-D finite element model is used to approximate the geometries of the subduction interface and strike-slip faults in the volcanic arc and determine the elastic response to coupling across these faults. The GPS velocities are best fit by a model in which the forearc moves 14-16 mmyr-1 and has coupling of 85-100 per cent across faults in the volcanic arc, in agreement with the high level of historic and recent earthquake activity in the volcanic arc. Our velocity inversion indicates that coupling across the potentially seismogenic areas of the subduction interface is remarkably weak, averaging no more than 3 per cent of the plate convergence rate and with only two poorly resolved patches where coupling might be higher along the 550-km-long segment we modelled. Our geodetic evidence for weak subduction coupling disagrees with a seismically derived coupling estimate of 60 +/- 10 per cent from a published analysis of earthquake damage back to 1690, but agrees with three other seismologic studies that infer weak subduction coupling from 20th century earthquakes. Most large historical earthquakes offshore from El Salvador and western Nicaragua may therefore have been intraslab normal faulting events similar to the Mw 7.3 1982 and Mw 7.7 2001 earthquakes offshore from El Salvador. Alternatively, the degree of coupling might vary with time. The evidence for weak coupling indirectly supports a recently published hypothesis that much of the Middle American forearc is escaping to the west or northwest away from the Cocos Ridge collision zone in Costa Rica. Such a hypothesis is particularly attractive for El Salvador, where there is little or no convergence obliquity to drive the
Mainshock-Aftershocks Clustering Detection in Volcanic Regions

Science.gov (United States)

Garza Giron, R.; Brodsky, E. E.; Prejean, S. G.

2017-12-01

Crustal earthquakes tend to break their general Poissonean process behavior by gathering into two main kinds of seismic bursts: swarms and mainshock-aftershocks sequences. The former is commonly related to volcanic or geothermal processes whereas the latter is a characteristic feature of tectonically driven seismicity. We explore the mainshock-aftershock clustering behavior of different active volcanic regions in Japan and its comparison to non-volcanic regions. We find that aftershock production in volcanoes shows mainshock-aftershocks clustering similar to what is observed in non-volcanic areas. The ratio of volanic areas that cluster in mainshock-aftershocks sequences vs the areas that do not is comparable to the ratio of non-volcanic regions that show clustering vs the ones that do not. Furthermore, the level of production of aftershocks for most volcanic areas where clustering is present seems to be of the same order of magnitude, or slightly higher, as the median of the non-volcanic regions. An interesting example of highly aftershock-productive volcanoes emerges from the 2000 Miyakejima dike intrusion. A big seismic cluster started to build up rapidly in the south-west flank of Miyakejima to later propagate to the north-west towards the Kozushima and Niijima volcanoes. In Miyakejima the seismicity showed a swarm-like signature with a constant earthquake rate, whereas Kozushima and Niijima both had expressions of highly productive mainshock-aftershocks sequences. These findings are surprising given the alternative mechanisms available in volcanic systems for releasing deviatoric strain. We speculate that aftershock behavior might hold a relationship with the rheological properties of the rocks of each system and with the capacity of a system to accumulate or release the internal pressures caused by magmatic or hydrothermal systems.
Lichen Persistence and Recovery in Response to Varied Volcanic Disturbances

Science.gov (United States)

Nelson, P.; Wheeler, T. B.

2015-12-01

Volcanic eruptions produce many ecological disturbances that structure vegetation. While lichens are sensitive to disturbances, little is known about their responses to volcanic disturbances, except for colonization of lava. We examined lichen community responses through time to different disturbances produced by the May 1, 2008 eruption of Volcan Chaiten in south-central Chile. Pre-eruption vegetation near the volcano was old-growth Valdivian temperate rainforest dominated by closed-canopy Nothofagus sp... In 2012, we installed thirteen 1-acre plots across volcanic disturbance zones on which a time-constrained search was done for all macrolichen species, each of which was assigned an approximate log10 categorical abundance. We also installed a 0.2 m2 quadrat on two representative trees per plot for repeat photography of lichen cover. We remeasured at least one plot per disturbance zone in 2014 and re-photographed tree quadrats in 2013 and 2014. We then analyzed species composition and abundance differences among disturbance zones. In 2012, the blast (pyroclastic density flow), scorch (standing scorched forest at the edge of the blast) and deep tephra (>10 cm) zones had the lowest lichen species richness (5-13 species), followed by reference (unimpacted) and shallow (lichen species since 2012 while the light tephra and reference were essentially unchanged. Gravel rain, gravel rain + pumice and flooded forest plots all had about the same number of species in 2014 as 2012. Lichen colonization and growth in tree quadrats varied widely, from very little colonization in the blast to prolific colonization in the gravel rain + pumice zone. Lichen's varied responses to different volcanic disturbances were attributable to varying degrees of mortality and subsequent availability of substrate, quantity of light and removal of competitors. While sensitive to disturbance, lichens are apparently resilient to and can quickly recolonize after a variety of large, violent volcanic
Monitoring diffuse degassing in monogenetic volcanic field during seismic-volcanic unrest: the case of Tenerife North-West Rift Zone (NWRZ), Canary Islands, Spain

Science.gov (United States)

García, E.; Botelho, A. H.; Regnier, G. S. G.; Rodríguez, F.; Alonso Cótchico, M.; Melián, G.; Asensio-Ramos, M.; Padrón, E.; Hernández, P. A.; Pérez, N. M.

2017-12-01

Tenerife North-West Rift-Zone (NWRZ) is the most active volcano of the oceanic active volcanic island of Tenerife and the scenario of three historical eruptions (Boca Cangrejo S. XVI, Arenas Negras 1706 and Chinyero 1909). Since no visible degassing (fumaroles, etc.) at Tenerife NWRZ occurs, a geochemical monitoring program at Tenerife NWRZ was established mainly consisting on performing soil CO2 efflux surveys (50 surveys since 2000) to evaluate the temporal and spatial variations of soil CO2 efflux measurements and the diffuse CO2 emission rate. To do so, about 340 sampling sites were selected for each survey to obtain a homogeneous distribution after taking into consideration the local geology, structure, and accessibility. Measurements of soil CO2 efflux were performed in situ by means of a portable non-dispersive infrared sensor following the accumulation chamber method. The soil CO2 efflux values of the 2017 survey ranged from non-detectable to 46.6 g m-2 d-1. Statistical-graphical analysis of the 2017 data show two different geochemical populations; background (B) and peak (P) represented by 93.3% and 1.9% of the total data, respectively. The geometric means of the B and P populations are 2.4 and 19.1 g m-2 d-1, respectively. Most of the area showed B values while the P values were mainly observed at the N-W side of the volcanic rift. To estimate the diffuse CO2 emission in metric tons per day released from Tenerife NWRZ (75 km2) for the 2017 survey, we ran about 100 sGs simulations. The estimated 2017 diffuse CO2 output released to atmosphere by the Tenerife NWRZ volcano was 297 ± 13 t d-1. This 2017 diffuse CO2 emission rate value is relatively higher than the estimated background value (144 t d-1) and falls within the estimated background range (72 - 321 t d-1) observed for Tenerife NWRZ volcano during the 2000-2017 period. The observed temporal variation in the diffuse CO2 degassing output during this period does not seem to be driven by external
Caldera formation at Volcán Colima, Mexico, by a large large holocene volcanic debris avalanche

Science.gov (United States)

Luhr, James F.; Prestegaard, Karen L.

1988-12-01

About 4,300 years ago, 10 km 3 of the upper cone of ancestral Volcán Colima collapsed to the southwest leaving a horseshoe-shaped caldera 4 km in diameter. The collapse produced a massive volcanic debris avalanche deposit covering over 1550 km 2 on the southern flanks of the volcano and extending at least 70 km from the former summit. The avalanche followed a steep topographic gradient unobstructed by barriers, resulting in an unusually high area/volume ratio for the Colima deposit. The apparent coefficient of friction (fall height/distance traveled) for the Colima avalanche is 0.06, a low value similar to those of other large-volume deposits. The debris avalanche deposit contains 40-75% angular volcanic clasts from the ancestral cone, a small proportion of vesicular blocks that may be juvenile, and in distal exposures, rare carbonate clasts plucked from the underlying surface by the moving avalanche. Clasts range in size to over 20 m in diameter and are brecciated to different degrees, pulverized, and surrounded by a rock-flour matrix. The upper surface of the deposit shows prominent hummocky topography with closed depressions and surface boulders. A thick, coarse-grained, compositionally zoned scoria-fall layer on the upper northeastern slope of the volcano may have erupted at the time of collapse. A fine-grained surge layer is present beneath the avalanche deposit at one locality, apparently representing an initial blast event. Most of the missing volume of the ancestral volcano has since been restored at an average rate of 0.002 km 3/yr through repeated eruptions from the post-caldera cone. As a result, the southern slope of Volcán Colima may again be susceptible to collapse. Over 200,000 people are now living on primary or secondary deposits of the debris avalanche, and a repetition of this event would constitute a volcanic disaster of great magnitude. Ancestral Volcán Colima grew on the southern, trenchward flank of the earlier and larger volcano Nevado de
Hydrocarbon Reservoir Identification in Volcanic Zone by using Magnetotelluric and Geochemistry Information

Science.gov (United States)

Firda, S. I.; Permadi, A. N.; Supriyanto; Suwardi, B. N.

2018-03-01

The resistivity of Magnetotelluric (MT) data show the resistivity mapping in the volcanic reservoir zone and the geochemistry information for confirm the reservoir and source rock formation. In this research, we used 132 data points divided with two line at exploration area. We used several steps to make the resistivity mapping. There are time series correction, crosspower correction, then inversion of Magnetotelluric (MT) data. Line-2 and line-3 show anomaly geological condition with Gabon fault. The geology structure from the resistivity mapping show the fault and the geological formation with the geological rock data mapping distribution. The geochemistry information show the maturity of source rock formation. According to core sample analysis information, we get the visual porosity for reservoir rock formation in several geological structure. Based on that, we make the geological modelling where the potential reservoir and the source rock around our interest area.
Volcanic geology and eruption frequency, lower east rift zone of Kilauea volcano, Hawaii

Science.gov (United States)

Moore, Richard B.

1992-08-01

Detailed geologic mapping and radiocarbon dating of tholeiitic basalts covering about 275 km2 on the lower east rift zone (LERZ) and adjoining flanks of Kilauea volcano, Hawaii, show that at least 112 separate eruptions have occurred during the past 2360 years. Eruptive products include spatter ramparts and cones, a shield, two extensive lithic-rich tuff deposits, aa and pahoehoe flows, and three littoral cones. Areal coverage, number of eruptions and average dormant interval estimates in years for the five age groups assigned are: (I) historic, i.e. A D 1790 and younger: 25%, 5, 42.75; (II) 200 400 years old: 50%, 15, 14.3: (III) 400 750 years old: 20%, 54, 6.6; (IV) 750 1500 years old: 5%, 37, 20.8; (V) 1500 3000 years old: LERZ during the past 1500 years. Estimated volumes of the exposed products of individual eruptions range from a few tens of cubic meters for older units in small kipukas to as much as 0.4 km3 for the heiheiahulu shield. The average dormant interval has been about 13.6 years during the past 1500 years. The most recent eruption occurred in 1961, and the area may be overdue for its next eruption. However, eruptive activity will not resume on the LERZ until either the dike feeding the current eruption on the middle east rift zone extends farther down rift, or a new dike, unrelated to the current eruption, extends into the LERZ.

Gravitational, erosional and depositional processes on volcanic ocean islands: Insights from the submarine morphology of Madeira Archipelago

Science.gov (United States)

Quartau, Rui; Ramalho, Ricardo S.; Madeira, José; Santos, Rúben; Rodrigues, Aurora; Roque, Cristina; Carrara, Gabriela; Brum da Silveira, António

2018-01-01

The submarine flanks of volcanic ocean islands are shaped by a variety of physical processes. Whilst volcanic constructional processes are relatively well understood, the gravitational, erosional and depositional processes that lead to the establishment of large submarine tributary systems are still poorly comprehended. Until recently, few studies have offered a comprehensive source-to-sink approach, linking subaerial morphology with near-shore shelf, slope and far-field abyssal features. In particular, few studies have addressed how different aspects of the subaerial part of the system (island height, climate, volcanic activity, wave regime, etc.) may influence submarine flank morphologies. We use multibeam bathymetric and backscatter mosaics of an entire archipelago - Madeira - to investigate the development of their submarine flanks. Crucially, this dataset extends from the nearshore to the deep sea, allowing a solid correlation between submarine morphologies with the physical and geological setting of the islands. In this study we also established a comparison with other island settings, which allowed us to further explore the wider implications of the observations. The submarine flanks of the Madeira Archipelago are deeply dissected by large landslides, most of which also affected the subaerial edifices. Below the shelf break, landslide chutes extend downslope forming poorly defined depositional lobes. Around the islands, a large tributary system composed of gullies and channels has formed where no significant rocky/ridge outcrops are present. In Madeira Island these were likely generated by turbidity currents that originated as hyperpycnal flows, whilst on Porto Santo and Desertas their origin is attributed to storm-induced offshore sediment transport. At the lower part of the flanks (-3000 to -4300 m), where seafloor gradients decrease to 0.5°-3°, several scour and sediment wave fields are present, with the former normally occurring upslope of the latter
Seismically active column and volcanic plumbing system beneath the island arc of the Izu-Bonin subduction zone

Science.gov (United States)

Špičák, Aleš; Vaněk, Jiří; Hanuš, Václav

2009-12-01

A detailed spatio-temporal analysis of teleseismic earthquake occurrence (mb > 4.0) along the convergent margin of the Izu-Bonin-Mariana arc system reveals an anomalously high concentration of events between 27° and 30.5°N, beneath a chain of seamounts between Tori-shima and Nishino-shima volcanoes. This seismicity is dominated by the 1985/1986 earthquake swarm represented in the Engdahl-van der Hilst-Buland database by 146 earthquakes in the body wave magnitude range 4.3-5.8 and focal depth range 1-100 km. The epicentral cluster of the swarm is elongated parallel to the volcanic chain. Available focal mechanisms are consistent with an extensional tectonic regime and reveal nodal planes with azimuths close to that of the epicentral cluster. Earthquakes of the 1985/1986 swarm occurred in seven time phases. Seismic activity migrated in space from one phase to the other. Earthquake foci belonging to individual phases of the swarm aligned in vertically disposed seismically active columns. The epicentral zones of the columns are located in the immediate vicinity of seamounts Suiyo and Mokuyo, recently reported by the Japanese Meteorological Agency as volcanically active. The three observations-episodic character of earthquake occurrence, column-like vertically arranged seismicity pattern, and existence of volcanic seamounts at the seafloor above the earthquake foci-led us to interpret the 1985/1986 swarm as a consequence of subduction-related magmatic and/or fluid activity. A modification of the shallow earthquake swarm magmatic model of D. Hill fits earthquake foci distribution, tectonic stress orientation and fault plane solutions. The 1985/1986 deep-rooted earthquake swarm in the Izu-Bonin region represents an uncommon phenomenon of plate tectonics. The portion of the lithospheric wedge that was affected by the swarm should be composed of fractured rigid, brittle material so that the source of magma and/or fluids which might induce the swarm should be situated at a
Lithium, boron and chloride in volcanics and greywackes in Northland, Auckland and the Taupo Volcanic Zone

International Nuclear Information System (INIS)

Reyes, A.G.; Trompetter, W.J.

1998-01-01

During magmatic differentiation processes B preferentially partitions into the glassy mesostasis of rhyolite and andesite. The behaviour of Li, on the other hand, varies with the silica content of the rock. Lithium, B, Cl and water contents increase proportionally with the silica concentration of the volcanic rocks. Their relative proportions in andesites of the Taupo Volcanic Zone (TVZ) appear to reflect the nature of the underlying crust, the dip of the subducting slab and hence the depth and temperature of magma generation. The B/Li ratios of rhyolites associated with the northern Rotorua and Okataina eruptive centres yield lower B/Li ratios than those from Maroa and Taupo centres in the south, where the slab subducts at a shallower angle. Apparently, volcanics associated with a younger subduction event as in the TVZ, contain and retain more Cl, yielding lower Li/Cl ratios for the TVZ than Northland-Auckland basalts. The B/Li ratio of greywackes from the Torlesse terrane ( 1.4). In geothermal wells in Ngawha, hydrothermal alteration yields higher B/Li ratios of >2.8 for Waipapa terrane sedimentary rocks. The Li/Cl ratios for average South and North Island greywackes are similar and may reflect similar degrees of metamorphism. In general, the relative Li, B and Cl contents in greywackes are dictated by the composition of the detrital fragments, the clay fraction, the type of clays and the metamorphic grade. During hydrothermal alteration of rhyolite in the TVZ, Cl always partitions into solution while Li and B have an affinity for the rock. However, more Li remains in the rock than B at any given temperature. The distribution coefficients of Li and B between water and rock increase with increasing temperature. The partitioning of Li between rock and solution in TVZ hydrothermal systems is mainly dictated by temperature, whereas the mass distribution coefficient for B is related to the tectonic setting. An increase in relative Li of the rock is associated with the
Garnet pyroxenite from Nilgiri Block, southern India: Vestiges of a Neoarchean volcanic arc

Science.gov (United States)

Samuel, Vinod O.; Kwon, Sanghoon; Santosh, M.; Sajeev, K.

2018-06-01

Southern peninsular India preserves records of Late Neoarchean-Early Paleoproterozoic continental building and cratonization. A transect from the Paleoarchean Dharwar Craton to the Neoarchean arc magmatic complex in the Nilgiri Block across the intervening Moyar Suture Zone reveals an arc-accretionary complex composed of banded iron formation (BIF), amphibolite, metatuff, garnet-kyanite schist, metagabbro, pyroxenite and charnockite. Here we investigate the petrology, geochronology and petrogenesis of the pyroxenite and garnet-clinopyroxenite. The pyroxenite is mainly composed of orthopyroxene and clinopyroxene with local domains/pockets enriched in a clinopyroxene-garnet assemblage. Thermobarometric calculations and phase equilibria modeling suggest that the orthopyroxene- and clinopyroxene-rich domains formed at 900-1000 °C, 1-1.2 GPa whereas the garnet- and clinopyroxene-rich domains record higher pressure of about 1.8-2 GPa at similar temperature conditions (900-1000 °C). Zircon U-Pb SHRIMP dating show weighted mean 207Pb-206Pb age of 2532 ± 22 Ma, with metamorphic overgrowth at 2520 ± 27 Ma and 2478 ± 27 Ma. We propose a tectonic model involving decoupling and break-off of the oceanic plate along the southern flanks of the Dharwar Craton, which initiated oceanic plate subduction. Slab melting eventually built the Nilgiri volcanic arc on top of the over-riding plate along the flanks of the Dharwar Craton. Our study supports an active plate tectonic regime at the end of the Archean Era, aiding in the growth of paleo-continents and their assembly into stable cratons.
Flank pain

Science.gov (United States)

... how to do these exercises at home. Nonsteroidal anti-inflammatory drugs (NSAIDs) and physical therapy may be prescribed for flank pain caused by spinal arthritis. Antibiotics are used to treat most kidney infections. You ...
The Online GVP/USGS Weekly Volcanic Activity Report: Providing Timely Information About Worldwide Volcanism

Science.gov (United States)

Mayberry, G. C.; Guffanti, M. C.; Luhr, J. F.; Venzke, E. A.; Wunderman, R. L.

2001-12-01

over 60 volcanoes, with an average of 10 volcanoes discussed each week. Notable volcanic activity during November 2000-November 2001 included an eruption beginning on 6 February at Nyamuragira in the Democratic Republic of the Congo; it issued low-viscosity lava flows that traveled towards inhabited towns, and also produced ash clouds that adversely effected the health of residents and livestock near the volcano. Eruptions at Mayon in the Philippines on 24 June and 25 July caused local authorities to raise the alert to the highest level, close area airports, and evacuate thousands of residents near the volcano. Most recently a large flank eruption at Etna in Italy began on 17 July and gained worldwide attention as extensive lava flows threatened a small town and a tourist complex. While the information found in the Weekly Volcanic Activity Report, ranging from large eruptions to small precursory events, is of interest to the general public, it has also proven to be a valuable resource to volcano observatory staff, universities, researchers, secondary schools, and the aviation community.
Formation and evolution of mesozoic volcanic basins in Gan-Hang tectonic belt

International Nuclear Information System (INIS)

Zhang Xingpu

1999-01-01

The author mainly discusses the principle model for the formation and the evolution of Mesozoic volcanic basins in the Gan-Hang Tectonic Belt, and describes the distinct evolution features between the internal and external sites of volcanic basins, the natural relation between the down-warped, down-faulted, collapse volcanic basins and volcanic domes, the relationship between the formation of inter layered fractured zones of the volcanic cover and the evolution of volcanic basins
Diffuse CO2 degassing monitoring for the volcanic surveillance of Tenerife North-East Rift Zone (NERZ) volcano, Canary Islands

Science.gov (United States)

Rodríguez, F.; Thomas, G. E.; Wong, T.; García, E.; Melián, G.; Padron, E.; Asensio-Ramos, M.; Hernández, P. A.; Perez, N. M.

2017-12-01

The North East Rift zone of Tenerife Island (NERZ, 210 km2) is one of the three major volcanic rift-zones of the island. The most recent eruptive activity along the NERZ took place in the 1704-1705 period with eruptions of Siete Fuentes, Fasnia and Arafo volcanoes. Since fumarolic activity is nowadays absent at the NERZ, soil CO2 degassing monitoring represent a potential geochemical tool for its volcanic surveillance. The aim of this study is to report the results of the last CO2 efflux survey performed in June 2017, with 658 sampling sites. In-situ measurements of CO2 efflux from the surface environment of the NERZ were performed by means of a portable non-dispersive infrared spectrophotometer (NDIR) following the accumulation chamber method. To quantify the total CO2 emission, soil CO2 efflux spatial distribution maps were constructed using Sequential Gaussian Simulation (SGS) as interpolation method. The diffuse CO2 emission values ranged between 0 - 41.1 g m-2 d-1. The probability plot technique applied to the data allowed to distinguish two different geochemical populations; background (B) and peak (P) represented by 81.8% and 18.2% of the total data, respectively, with geometric means of 3.9 and 15.0 g m-2 d-1, respectively. The average map constructed with 100 equiprobable simulations showed an emission rate of 1,361±35 t d-1. This value relatively higher than the background average of CO2 emission estimated on 415 t d-1 and slightly higher than the background range of 148 t d-1 (-1σ) and 1,189 t d-1 (+1σ) observed at the NERZ. This study reinforces the importance of performing soil CO2 efflux surveys as an effective surveillance volcanic tool in the NERZ.
Geochemistry of volcanic ashes, thermal waters and gases ejected during the 1979 eruption of Ontake Volcano, Japan

International Nuclear Information System (INIS)

Sugiura, Tumomu; Sugisaki, Ryuichi; Mizutani, Yoshihiko; Kusakabe, Minoru.

1980-01-01

Ontake Volcano suddenly began to erupt on its south-western flank near the summit at 05sup(h)20sup(m) on Oct. 28, 1979, forming several new craters and ejecting large amounts of volcanic ash and steam. Up to that time, the volcano had been believed to be dormant, though there were weak geothermal activities at a part of the south-western flank of the volcano, Jigokudani. This paper reports some results obtained by preliminary examination of volcanic ashes, thermal waters and gases collected on and around Ontake Volcano during the early stage of eruptive activity. The volcanic ashes are homogeneous in chemical and mineralogical compositions, and similar in chemical composition to the pre-historic volcanic ashes. The ashes contain pyrite, anhydrite, cristobalite and clay minerals. The sulfur isotopic equilibrium temperature is estimated to be about 400 0 C for pyrite-anhydrite pairs in the volcanic ashes. The estimated temperature is apparently too high for the temperature of phreatic explosion. The interpretation of this isotopic data remains unsettled. The thermal waters collected from the boiling pools in craters are enriched in D and 18 O. The isotopic enrichment is probably caused by evaporation of water at the surface of boiling pool. The hydrogen and oxygen isotopic data also suggest that spring waters issuing around Ontake Volcano are meteoric in origin. Nigorigo Hot Spring, about 4 km north-west of Ontake Volcano, showed significant increase in the concentrations of major dissolved chemical components soon after the eruption, but since then no significant change in chemical and isotopic composition has been observed. (author)
The volcanism of the western part of the Los Frailes Meseta (Bolivia): a representative example of the Andean volcanism since the Upper Oligocene

International Nuclear Information System (INIS)

Leroy, L.; Jimenez, N.

1996-01-01

The Los Frailes Meseta (Bolivia) is one of the large tertiary ignimbritic fields of the inner volcanic arc from Central Andes (Central Volcanic Zone. CVZ), in contact zone between the Altiplano to the west and the Eastern Cordillera to the east. Field observations and mineralogical and geochemical studies (major and trace elements) lead to distinguish two types of volcanism in the western border to the Meseta. During the Middle Miocene and Pliocene, the volcanic activity can be subdivided into three pyroclastic emission cycles, the Larco, Coroma and Pliocene ignimbrites, the first two being separated by the Quechua 2 orogeny. All these ignimbrites are very similar and correspond to peraluminous rhyolites to rhyodacites. In the studies area, the Coroma cycle is the only one where an ignimbrite-less evolved resurgent dome association can be observed. Beside these ignimbrites, isolated small lava flows and domes overlay and/or intrude all the other formations. They are meta-aluminous lavas with a shoshonitic affinity. A quaternary age can be attributed to his second volcanism. These two volcanic types are well-known in the CVZ and are related to the different deformation stages, either compressional or extensional, which occur alternately in the Cordillera since 26 Ma. (authors). 61 refs., 12 figs., 3 tabs
Structural interpretation of El Hierro (Canary Islands) rifts system from gravity inversion modelling

Science.gov (United States)

Sainz-Maza, S.; Montesinos, F. G.; Martí, J.; Arnoso, J.; Calvo, M.; Borreguero, A.

2017-08-01

Recent volcanism in El Hierro Island is mostly concentrated along three elongated and narrow zones which converge at the center of the island. These zones with extensive volcanism have been identified as rift zones. The presence of similar structures is common in many volcanic oceanic islands, so understanding their origin, dynamics and structure is important to conduct hazard assessment in such environments. There is still not consensus on the origin of the El Hierro rift zones, having been associated with mantle uplift or interpreted as resulting from gravitational spreading and flank instability. To further understand the internal structure and origin of the El Hierro rift systems, starting from the previous gravity studies, we developed a new 3D gravity inversion model for its shallower layers, gathering a detailed picture of this part of the island, which has permitted a new interpretation about these rifts. Previous models already identified a main central magma accumulation zone and several shallower high density bodies. The new model allows a better resolution of the pathways that connect both levels and the surface. Our results do not point to any correspondence between the upper parts of these pathways and the rift identified at the surface. Non-clear evidence of progression toward deeper parts into the volcanic system is shown, so we interpret them as very shallow structures, probably originated by local extensional stresses derived from gravitational loading and flank instability, which are used to facilitate the lateral transport of magma when it arrives close to the surface.
Structural controls on fluid circulation at the Caviahue-Copahue Volcanic Complex (CCVC) geothermal area (Chile-Argentina), revealed by soil CO2 and temperature, self-potential, and helium isotopes

Science.gov (United States)

Roulleau, Emilie; Bravo, Francisco; Pinti, Daniele L.; Barde-Cabusson, Stéphanie; Pizarro, Marcela; Tardani, Daniele; Muñoz, Carlos; Sanchez, Juan; Sano, Yuji; Takahata, Naoto; de la Cal, Federico; Esteban, Carlos; Morata, Diego

2017-07-01

Natural geothermal systems are limited areas characterized by anomalously high heat flow caused by recent tectonic or magmatic activity. The heat source at depth is the result of the emplacement of magma bodies, controlled by the regional volcano-tectonic setting. In contrast, at a local scale a well-developed fault-fracture network favors the development of hydrothermal cells, and promotes the vertical advection of fluids and heat. The Southern Volcanic Zone (SVZ), straddling Chile and Argentina, has an important, yet unexplored and undeveloped geothermal potential. Studies on the lithological and tectonic controls of the hydrothermal circulation are therefore important for a correct assessment of the geothermal potential of the region. Here, new and dense self-potential (SP), soil CO2 and temperature (T) measurements, and helium isotope data measured in fumaroles and thermal springs from the geothermal area located in the north-eastern flank of the Copahue volcanic edifice, within the Caviahue Caldera (the Caviahue-Copahue Volcanic Complex - CCVC) are presented. Our results allowed to the constraint of the structural origin of the active thermal areas and the understanding of the evolution of the geothermal system. NE-striking faults in the area, characterized by a combination of SP, CO2, and T maxima and high 3He/4He ratios (up to 8.16 ± 0.21Ra, whereas atmospheric Ra is 1.382 × 10- 6), promote the formation of vertical permeability preferential pathways for fluid circulation. WNW-striking faults represent low-permeability pathways for hydrothermal fluid ascent, but promote infiltration of meteoric water at shallow depths, which dilute the hydrothermal input. The region is scattered with SP, CO2, and T minima, representing self-sealed zones characterized by impermeable altered rocks at depth, which create local barriers for fluid ascent. The NE-striking faults seem to be associated with the upflowing zones of the geothermal system, where the boiling process
Geochemical constraints on the relationship between the Miocene-Pliocene volcanism and tectonics in the Palaoco and Fortunoso volcanic fields, Mendoza Region, Argentina

DEFF Research Database (Denmark)

Dyhr, Charlotte Thorup; Holm, Paul Martin; Llambias, Eduardo J.

2013-01-01

New 40Ar/39Ar analyses constrain the formation of the volcanic succession of Sierra de Palaoco in the present back-arc of the Andean Southern Volcanic Zone (SVZ), near 36°S, to the Late Miocene and assigns them to the Huincán II Formation. The composition of major and trace elements, Sr, Nd and P...
Deformation at Krafla and Bjarnarflag geothermal areas, Northern Volcanic Zone of Iceland, 1993-2015

Science.gov (United States)

Drouin, Vincent; Sigmundsson, Freysteinn; Verhagen, Sandra; Ófeigsson, Benedikt G.; Spaans, Karsten; Hreinsdóttir, Sigrún

2017-09-01

The Krafla volcanic system has geothermal areas within the Krafla caldera and at Bjarnarflag in the Krafla fissure swarm, 9-km south of the Krafla caldera. Arrays of boreholes extract geothermal fluids for power plants in both areas. We collected and analyzed InSAR, GPS, and leveling data spanning 1993-2015 in order to investigate crustal deformation in these areas. The volcanic zone hosting the geothermal areas is also subject to large scale regional deformation processes, including plate spreading and deflation of the Krafla volcanic system. These deformation processes have to be taken into account in order to isolate the geothermal deformation signal. Plate spreading produces the largest horizontal displacements, but the regional deformation pattern also suggests readjustment of the Krafla system at depth after the 1975-1984 Krafla rifting episode. Observed deformation can be fit by an inflation source at about 20 km depth north of Krafla and a deflation source at similar depth directly below the Krafla caldera. Deflation signal along the fissure swarm can be reproduced by a 1-km wide sill at 4 km depth closing by 2-4 cm per year. These sources are considered to approximate the combined effects of vertical deformation associated with plate spreading and post-rifting response. Local deformation at the geothermal areas is well resolved in addition to these signals. InSAR shows that deformation at Bjarnarflag is elongated along the direction of the Krafla fissure swarm (∼ 4 km by ∼ 2 km) while it is circular at Krafla (∼ 5 km diameter). Rates of deflation at Krafla and Bjarnarflag geothermal areas have been relatively steady. Average volume decrease of about 6.6 × 105 m3/yr for Krafla and 3.9 × 105 m3/yr for Bjanarflag are found at sources located at ∼ 1.5 km depth, when interpreted by a spherical point source of pressure. This volume change represents about 8 × 10-3 m3/ton of the mass of geothermal fluid extracted per year, indicating important renewal
MED SUV TASK 6.3 Capacity building and interaction with decision makers: Improving volcanic risk communication through volcanic hazard tools evaluation, Campi Flegrei Caldera case study (Italy)

Science.gov (United States)

Nave, Rosella; Isaia, Roberto; Sandri, Laura; Cristiani, Chiara

2016-04-01

In the communication chain between scientists and decision makers (end users), scientific outputs, as maps, are a fundamental source of information on hazards zoning and the related at risk areas definition. Anyway the relationship between volcanic phenomena, their probability and potential impact can be complex and the geospatial information not easily decoded or understood by not experts even if decision makers. Focusing on volcanic hazard the goal of MED SUV WP6 Task 3 is to improve the communication efficacy of scientific outputs, to contribute in filling the gap between scientists and decision-makers. Campi Flegrei caldera, in Neapolitan area has been chosen as the pilot research area where to apply an evaluation/validation procedure to provide a robust evaluation of the volcanic maps and its validation resulting from end users response. The selected sample involved are decision makers and officials from Campanian Region Civil Protection and municipalities included in Campi Flegrei RED ZONE, the area exposed to risk from to pyroclastic currents hazard. Semi-structured interviews, with a sample of decision makers and civil protection officials have been conducted to acquire both quantitative and qualitative data. The tested maps have been: the official Campi Flegrei Caldera RED ZONE map, three maps produced by overlapping the Red Zone limit on Orthophoto, DTM and Contour map, as well as other maps included a probabilistic one, showing volcanological data used to border the Red Zone. The outcomes' analysis have assessed level of respondents' understanding of content as displayed, and their needs in representing the complex information embedded in volcanic hazard. The final output has been the development of a leaflet as "guidelines" that can support decision makers and officials in understanding volcanic hazard and risk maps, and also in using them as a communication tool in information program for the population at risk. The same evaluation /validation process
Investigation of the inner structure of La Crosa de Sant Dalmai maar (Catalan Volcanic Zone, Spain)

Science.gov (United States)

Bolós, Xavier; Barde-Cabusson, Stéphanie; Pedrazzi, Dario; Martí, Joan; Casas, Albert; Himi, Mahjoub; Lovera, Raúl

2012-12-01

La Crosa de Sant Dalmai volcano is the largest volcanic edifice of the Catalan Volcanic Zone (NE Spain). It is a very well preserved maar-type structure, 1.5 km in diameter, excavated at the contact between a hard substrate and a soft substrate formed by Palaeozoic granites and Pliocene and Quaternary gravels, respectively. In order to infer the uppermost inner structure of La Crosa de Sant Dalmai maar and to characterise its main geological and tectonic constraints, we have performed a multiparametric geophysical study including gravimetry, magnetometry, self-potential, and electrical resistivity tomography. The results obtained together with a field geology revision and additional geological data from two drill cores, provide a detailed picture of the post-eruptive maar infill sequence as well as of the uppermost part of the maar-diatreme structure. This information helps in understanding the origin and subsequent evolution of the volcano, which included an alternation of phreatomagmatic and Strombolian phases. Geophysical data show that the last Strombolian phase, which culminated with the formation of a scoria cone inside the maar, was associated with a NW-SE trending regional fault. The little erosion and degradation of the original tephra ring suggest a much younger age of La Crosa de Sant Dalmai maar than was previously stated.
Recurrence Rate and Magma Effusion Rate for the Latest Volcanism on Arsia Mons, Mars

Science.gov (United States)

Richardson, Jacob A.; Wilson, James A.; Connor, Charles B.; Bleacher, Jacob E.; Kiyosugi, Koji

2016-01-01

approach to the 29 volcanic vents, volcanism likely began around 200-300Ma then first peaked around 150Ma, with an average production rate of 0.4 vents per Myr (million years). The recurrence rate estimated including stratigraphic data is distinctly bimodal, with a second, lower peak in activity around 100Ma. Volcanism then waned until the final vents were produced 10-90Ma. Based on this model, volume flux is also bimodal, reached a peak rate of 1-8 cubic kilometers per million years by 150Ma and remained above half this rate until about 90Ma, after which the volume flux diminished greatly. The onset of effusive volcanism from 200-150Ma might be due to a transition of volcanic style away from explosive volcanism that emplaced tephra on the western flank of Arsia Mons, while the waning of volcanism after the 150Ma peak might represent a larger-scale diminishing of volcanic activity at Arsia Mons related to the emplacement of flank apron lavas.
Tectonic setting of the Tertiary volcanic rocks of the Olympic Peninsula, Washington

Science.gov (United States)

Cady, Wallace M.

1975-01-01

Lower and middle Eocene abyssal and Hawaiian type tholeiitic basalts form two accumulations that apparently were once far out on the east flank of the Juan de Fuca Ridge, within the Juan de Fuca plate. One of these (more than 15 km thick) is near the eastern and southeastern periphery of the Olympic Peninsula, and the other (about 5 km thick) is on the north. The tholeiites stratigraphically overlie and interfinger with Paleocene(?) and lower and middle Eocene marine turbidites and shales; one flow includes boulders that, like clasts in the sediments, were derived from the North American continental plate immediately to the east. The basalts are overlain stratigraphically by middle Eocene to middle Miocene clastic marine sedimentary rocks, which are in turn overlapped unconformably on the south and west by upper Miocene (?) and Pliocene, chiefly shallow-marine clastic rocks. These various peripheral rocks flank a middle or late Miocene structurally complex dome, or orocline convex to the east, in which originally east dipping and low angle late Eocene to late Miocene underthrusts are flexed. The outermost underthrust of the complex separates the chiefly volcanic peripheral rocks to the north, east, and south from stratigraphically correlative and comparable, though predominantly sedimentary, core rocks arranged in northwest trending arcuate belts or packets bounded by fault zones. Before underthrusting, and perhaps oroclinal folding connected with doming, the pre-middle Miocene section was possibly 150 to 200 km wide compared with the present Olympic Peninsula which is 120 km wide. The section accumulated on the ocean floor near the western margin of the continent, before and during subduction of the oceanic crust.
Recent and Hazardous Volcanic Activity Along the NW Rift Zone of Piton De La Fournaise Volcano, La Réunion Island

Science.gov (United States)

Walther, G.; Frese, I.; Di Muro, A.; Kueppers, U.; Michon, L.; Metrich, N.

2014-12-01

Shield volcanoes are a common feature of basaltic volcanism. Their volcanic activity is often confined to a summit crater area and rift systems, both characterized by constructive (scoria and cinder cones; lava flows) and destructive (pit craters; caldera collapse) phenomena. Piton de la Fournaise (PdF) shield volcano (La Réunion Island, Indian Ocean) is an ideal place to study these differences in eruptive behaviour. Besides the frequent eruptions in the central Enclos Fouqué caldera, hundreds of eruptive vents opened along three main rift zones cutting the edifice during the last 50 kyrs. Two short rift zones are characterized by weak seismicity and lateral magma transport at shallow depth (above sea level). Here we focus on the third and largest rift zone (15km wide, 20 km long), which extends in a north-westerly direction between PdF and nearby Piton des Neiges volcanic complex. It is typified by deep seismicity (up to 30 km), emitting mostly primitive magmas, testifying of high fluid pressures (up to 5 kbar) and large-volume eruptions. We present new field data (including stratigraphic logs, a geological map of the area, C-14 dating and geochemical analyses of the eruption products) on one of the youngest (~6kyrs) and largest lava field (Trous Blancs eruption). It extends for 24km from a height of 1800 m asl, passing Le Tampon and Saint Pierre cities, until reaching the coast. The source area of this huge lava flow has been identified in an alignment of four previously unidentified pit craters. The eruption initiated with intense fountaining activity, producing a m-thick bed of loose black scoria, which becomes densely welded in its upper part; followed by an alternation of volume rich lava effusions and strombolian activity, resulting in the emplacement of meter-thick, massive units of olivine-basalt alternating with coarse scoria beds in the proximal area. Activity ended with the emplacement of a dm-thick bed of glassy, dense scoria and a stratified lithic
Defining the Tristan-Gough Hotspot: High-Resolution 40Ar/39Ar Dating of Volcanism at Tristan da Cunha

Science.gov (United States)

Schnur, S.; Koppers, A. A. P.

2015-12-01

Explaining the spatial distribution of intra-plate volcanism is an important geologic problem. The Walvis Ridge is a uniquely-shaped hotspot trail in the South Atlantic that is not fully explained by the prevailing mantle plume paradigm. About halfway through its 130 Myr history, Walvis shows a morphological shift from a continuous ridge to a diffuse region of guyots arranged in two volcanic tracks. Recent volcanism at both Tristan da Cunha and Gough Island suggests these tracks are produced by two hotspots sourced from a single plume. However, the islands are located more than 400 km apart, which does not conform to our understanding of plumes as narrow, semi-stationary upwellings. It remains unclear which of the two islands better represents the current plume position. New ages from previously unstudied seamounts show that Tristan is younger than surrounding volcanism, whereas Gough appears to fit the local age progression (Schnur et al. 2014). Modern radiometric ages suggest the main island of Tristan may have been active for up to 1.3 ± 0.2 Myr (O'Connor and le Roex 1992). However, the seemingly older Inaccessible, Nightingale and Middle islands have yet to be reliably dated and could be up to 18 ± 4 Ma based on K-Ar ages (Miller in Baker et al. 1964). In order to confidently delineate the duration of volcanism at Tristan, we present the results of 29 new 40Ar/39Ar step-heating experiments on biotite, hornblende, plagioclase and groundmass separates from rocks collected on Inaccessible, Nightingale and Middle islands. Our results show that volcanism on all three islands is young, in most cases interpretations of plume dynamics. These results also show that magma was being supplied simultaneously to both Tristan and Gough over recent geologic time. Two possible explanations for this are that (1) there is a broad plume underlying the area, with focus points at Tristan and Gough or (2) hotspot magma is being focused at Tristan due to the nearby fracture zone

Compositional Differences between Felsic Volcanic Rocks from the ...

African Journals Online (AJOL)

Bheema

characteristics of the volcanic units, we describe the compositional differences ...... Geology and mineral resources of Somalia and surrounding regions. ... zone (Ethiopia) Journal of Volcanological and Geothermal Research, 80: 267-280.
Conditions for oceans on Earth-like planets orbiting within the habitable zone: importance of volcanic CO2 degassing

International Nuclear Information System (INIS)

Kadoya, S.; Tajika, E.

2014-01-01

Earth-like planets in the habitable zone (HZ) have been considered to have warm climates and liquid water on their surfaces if the carbonate-silicate geochemical cycle is working as on Earth. However, it is known that even the present Earth may be globally ice-covered when the rate of CO 2 degassing via volcanism becomes low. Here we discuss the climates of Earth-like planets in which the carbonate-silicate geochemical cycle is working, with focusing particularly on insolation and the CO 2 degassing rate. The climate of Earth-like planets within the HZ can be classified into three climate modes (hot, warm, and snowball climate modes). We found that the conditions for the existence of liquid water should be largely restricted even when the planet is orbiting within the HZ and the carbonate-silicate geochemical cycle is working. We show that these conditions should depend strongly on the rate of CO 2 degassing via volcanism. It is, therefore, suggested that thermal evolution of the planetary interiors will be a controlling factor for Earth-like planets to have liquid water on their surface.
Estimation of age of Dali-Ganis rifting and associated volcanic activity, Venus

Science.gov (United States)

Basilevsky, A. T.

1993-01-01

This paper deals with the estimation of age for the Dali and Ganis Chasma rift zones and their associated volcanism based on photogeologic analysis of stratigraphic relations of rift-associated features with impact craters which have associated features indicative of their age. The features are radar-dark and parabolic, and they are believed to be mantles of debris derived from fallout of the craters' ejecta. They are thought to be among the youngest features on the Venusian surface, so their 'parent' craters must also be very young, evidently among the youngest 10 percent of Venus' crater population. Dali Chasma and Ganis Chasma are a part of a system of rift zones contained within eastern Aphrodite and Atla Regio which is a significant component of Venus tectonics. The rifts of this system are fracture belts which dissect typical Venusian plains with rare islands of tessera terrain. The rift zone system consists of several segments following each other (Diane, Dali, Ganis) and forming the major rift zone line, about 10,000 km long, which has junctions with several other rift zones, including Parga Chasma Rift. The junctions are usually locations of rift-associated volcanism in the form of volcanic edifices (Maat and Ozza Montes) or plain-forming flows flooding some areas within the rift zones and the adjacent plains.
Evidence of magma recharge at Colli Albani (Italy), the volcanic district at the gates of Rome, from geodesy and gas geochemistry

Science.gov (United States)

Trasatti, E.; Marra, F.; Polcari, M.; Etiope, G.; Ciotoli, G.; Darrah, T.; Tedesco, D.; Stramondo, S.; Florindo, F.; Ventura, G.

2017-12-01

Colli Albani is in a rejuvenation stage and new, articulated dike-like magma storage zones are slowly forming below the western and southern flanks, with direct consequences for the volcanic hazard assessment at Rome.
Ductile extension of syn-magmatic lower crusts, with application to volcanic passive margins: the Ivrea Zone (Southern Alps, Italy)

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Bidault, Marie; Geoffroy, Laurent; Arbaret, Laurent; Aubourg, Charles

2017-04-01

Deep seismic reflection profiles of present-day volcanic passive margins often show a 2-layered lower crust, from top to bottom: an apparently ductile 12 km-thick middle-lower layer (LC1) of strong folded reflectors and a 4 km-thick supra-Moho layer (LC2) of horizontal and parallel reflectors. Those layers appear to be structurally disconnected and to develop at the early stages of margins evolution. A magmatic origin has been suggested by several studies to explain those strong reflectors, favoring mafic sills intrusion hypothesis. Overlying mafic and acidic extrusives (Seaward Dipping Reflectors sequences) are bounded by continentward-dipping detachment faults rooting in, and co-structurated with, the ductile part of the lower crust (LC1). Consequently the syn-rift to post-rift evolution of volcanic passive margins (and passive margins in general) largely depends on the nature and the properties of the lower crust, yet poorly understood. We propose to investigate the properties and rheology of a magma-injected extensional lower crust with a field analogue, the Ivrea Zone (Southern Alps, Italy). The Ivrea Zone displays a complete back-thrusted section of a Variscan continental lower crust that first underwent gravitational collapse, and then lithospheric extension. This Late Paleozoic extension was apparently associated with the continuous intrusion of a large volume of mafic to acid magma. Both the magma timing and volume, and the structure of the Ivrea lower crust suggest that this section represents an adequate analogue of a syn-magmatic in-extension mafic rift zone which aborted at the end of the Permian. Notably, we may recognize the 2 layers LC1 and LC2. From a number of tectonic observations, we reconstitute the whole tectonic history of the area, focusing on the strain field evolution with time, in connection with mafic magma injection. We compare those results with available data from extensional mafic lower crusts at rifts and margins.
Stratigraphy, age and correlation of middle Pleistocene silicic tephras in the Auckland region, New Zealand : a prolific distal record of Taupo Volcanic Zone volcanism

International Nuclear Information System (INIS)

Alloway, B.V.; Westgate, J.; Pillans, B.; Pearce, N.; Newnham, R.; Byrami, M.; Aarburg, S.

2004-01-01

Coastal sections in the Auckland region reveal highly carbonaceous and/or highly weathered clay-dominated cover-bed successions with numerous discrete distal volcanic ash (tephra) layers, fluvially reworked siliciclastic (tephric) deposits, and two widely distributed pyroclastic density current (PDC) deposits generated from explosive silicic volcanism within the Taupo Volcanic Zone (TVZ). The younger of the two PDC deposits (informally named Waiuku tephra) is glass-isothermal plateau fission-track (ITPFT) dated at 1.00 ± 0.03 Ma and occurs in a normal polarity interval interpreted as the Jaramillo Subchron. Waiuku tephra is correlated with Unit E sourced from the Mangakino Volcanic Centre of the TVZ. Waiuku tephra can be subdivided into two distinctive units enabling unequivocal field correlation: a lower stratified unit (dominantly pyroclastic surge with fall component) and an upper massive to weakly stratified unit (pyroclastic flow). At many sites in south Auckland, Waiuku tephra retains basal 'surge-like' beds (<1.4 m thickness). This provides clear evidence for primary emplacement and is an exceptional feature considering the c. 200 km this PDC has travelled from its TVZ source area. However, at many other Auckland sites, Waiuku tephra displays transitional sedimentary characteristics indicating lateral transformation from hot, gas-supported flow/surge into water-supported mass flow and hyperconcentrated flow (HCF) deposits. The older PDC deposit is dated at 1.21 ± 0.09 Ma, is enveloped by tephras that are ITPFT-dated at 1.14 ± 0.06 Ma (above) and 1.21 ± 0.06 Ma (below), respectively, and occurs below a short normal polarity interval (Cobb Mountain Subchron) at c. 1.19 Ma. This PDC deposit, correlated with Ongatiti Ignimbrite sourced from the Mangakino Volcanic Centre of TVZ, has laterally transformed from a gas-supported, fine-grained pyroclastic flow deposit at Oruarangi, Port Waikato, into a water-supported volcaniclastic mass flow deposit farther north
Geochemistry of volcanic series of Aragats province

International Nuclear Information System (INIS)

Meliksetyan, Kh.B.

2012-01-01

In this contribution we discuss geochemical and isotope characteristics of volcanism of the Aragats volcanic province and possible petrogenetical models of magma generation in collision zone of Armenian highland. We talk about combination of some specific features of collision related volcanism such as dry and high temperature conditions of magma generation, that demonstrate some similarities to intraplate-like petrogenesis and presence of mantle source enriched by earlier subductions, indicative to island-arc type magma generation models. Based on comprehensive analysis of isotope and geochemical data and some published models of magma generation beneath Aragats we lead to a petrogenetic model of origin of Aragats system to be a result of magma mixture between mantle originated mafic magma with felsic, adakite-type magmas
Remote Sensing and Geodetic Measurements for Volcanic Slope Monitoring: Surface Variations Measured at Northern Flank of La Fossa Cone (Vulcano Island, Italy

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Alessandro Bonforte

2013-05-01

Full Text Available Results of recent monitoring activities on potentially unstable areas of the NW volcano flank of La Fossa cone (Vulcano Island, Italy are shown here. They are obtained by integration of data by aerial photogrammetry, terrestrial laser scanning (TLS and GPS taken in the 1996–2011 time span. A comparison between multi-temporal models built from remote sensing data (photogrammetry and TLS highlights areas characterized by ~7–10 cm/y positive differences (i.e., elevation increase in the upper crown of the slope. The GPS measurements confirm these results. Areas characterized by negative differences, related to both mass collapses or small surface lowering, also exist. The higher differences, positive and negative, are always observed in zones affected by higher fumarolic activity. In the 2010–2012 time span, ground motions in the northern part of the crater rim, immediately above the upper part of observed area, are also observed. The results show different trends for both vertical and horizontal displacements of points distributed along the rim, with a magnitude of some centimeters, thus revealing a complex kinematics. A slope stability analysis shows that the safety factors estimated from these data do not indicate evidence of possible imminent failures. Nevertheless, new time series are needed to detect possible changes with the time of the stability conditions, and the monitoring has to go on.
Temperatures and isotopic evolution of silicic magmas, Taupo Volcanic Zone and Coromandel, New Zealand

International Nuclear Information System (INIS)

Blattner, P.; Rui-Zhong H.; Graham, I.J.; Houston-Eleftheriadis, C.

1996-01-01

A new set of oxygen and strontium isotope data on rhyolitic lavas and ignimbrites of the Taupo Volcanic Zone (TVZ) and the Coromandel Peninsula provides new limits for petrogenic models. For oxygen isotopes, the rock matrix is frequently altered, so that values for magma need to be phenocryst based. Within TVZ a trend towards more negative δ 1 8O values for more recent magmas appears likely (average before about 1 Ma and for Coromandel near 8.0 per mille; after 1 Ma near 7.5 per mille). This could indicate the gradual removal of supracrustal contaminants from the zones of magma accumulation and extrusion. Similar trends within Coromandel cannot yet be resolved. A generally positive correlation is found for oxygen and strontium isotopes of magmas. Most magmas have a limited range of isotopic values, which then becomes a fingerprint (e.g., the Mamaku, Matahina, and Waiotapu Ignimbrites). A narrow range of eruption temperatures of 880 ± 60 o C is derived from quartz-plagioclase fractionations of 0.98 ± 0.25 per mille δ 1 8O values of quartz and feldspar phenocrysts are sufficiently low to suggest interaction between surface water and magma. However, large negative oxygen isotope anomalies (such as known from Yellowstone), could be no more than partially concealed by the isotopically less depleted meteoric water of New Zealand, and have not yet been found in New Zealand. (authors). 45 refs., 6 figs., 3 tabs
Hybridization Capture Using Short PCR Products Enriches Small Genomes by Capturing Flanking Sequences (CapFlank)

DEFF Research Database (Denmark)

Tsangaras, Kyriakos; Wales, Nathan; Sicheritz-Pontén, Thomas

2014-01-01

, a non-negligible fraction of the resulting sequence reads are not homologous to the bait. We demonstrate that during capture, the bait-hybridized library molecules add additional flanking library sequences iteratively, such that baits limited to targeting relatively short regions (e.g. few hundred...... nucleotides) can result in enrichment across entire mitochondrial and bacterial genomes. Our findings suggest that some of the off-target sequences derived in capture experiments are non-randomly enriched, and that CapFlank will facilitate targeted enrichment of large contiguous sequences with minimal prior...
Late Holocene volcanism at Medicine Lake Volcano, northern California Cascades

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Donnelly-Nolan, Julie M.; Champion, Duane E.; Grove, Timothy L.

2016-05-23

Late Holocene volcanism at Medicine Lake volcano in the southern Cascades arc exhibited widespread and compositionally diverse magmatism ranging from basalt to rhyolite. Nine well-characterized eruptions have taken place at this very large rear-arc volcano since 5,200 years ago, an eruptive frequency greater than nearly all other Cascade volcanoes. The lavas are widely distributed, scattered over an area of ~300 km2 across the >2,000-km2 volcano. The eruptions are radiocarbon dated and the ages are also constrained by paleomagnetic data that provide strong evidence that the volcanic activity occurred in three distinct episodes at ~1 ka, ~3 ka, and ~5 ka. The ~1-ka final episode produced a variety of compositions including west- and north-flank mafic flows interspersed in time with fissure rhyolites erupted tangential to the volcano’s central caldera, including the youngest and most spectacular lava flow at the volcano, the ~950-yr-old compositionally zoned Glass Mountain flow. At ~3 ka, a north-flank basalt eruption was followed by an andesite eruption 27 km farther south that contains quenched basalt inclusions. The ~5-ka episode produced two caldera-focused dacitic eruptions. Quenched magmatic inclusions record evidence of intrusions that did not independently reach the surface. The inclusions are present in five andesitic, dacitic, and rhyolitic host lavas, and were erupted in each of the three episodes. Compositional and mineralogic evidence from mafic lavas and inclusions indicate that both tholeiitic (dry) and calcalkaline (wet) parental magmas were present. Petrologic evidence records the operation of complex, multi-stage processes including fractional crystallization, crustal assimilation, and magma mixing. Experimental evidence suggests that magmas were stored at 3 to 6 km depth prior to eruption, and that both wet and dry parental magmas were involved in generating the more silicic magmas. The broad distribution of eruptive events and the relative
Explosive Volcanic Activity at Extreme Depths: Evidence from the Charles Darwin Volcanic Field, Cape Verdes

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Kwasnitschka, T.; Devey, C. W.; Hansteen, T. H.; Freundt, A.; Kutterolf, S.

2013-12-01

Volcanic eruptions on the deep sea floor have traditionally been assumed to be non-explosive as the high-pressure environment should greatly inhibit steam-driven explosions. Nevertheless, occasional evidence both from (generally slow-) spreading axes and intraplate seamounts has hinted at explosive activity at large water depths. Here we present evidence from a submarine field of volcanic cones and pit craters called Charles Darwin Volcanic Field located at about 3600 m depth on the lower southwestern slope of the Cape Verdean Island of Santo Antão. We examined two of these submarine volcanic edifices (Tambor and Kolá), each featuring a pit crater of 1 km diameter, using photogrammetric reconstructions derived from ROV-based imaging followed by 3D quantification using a novel remote sensing workflow, aided by sampling. The measured and calculated parameters of physical volcanology derived from the 3D model allow us, for the first time, to make quantitative statements about volcanic processes on the deep seafloor similar to those generated from land-based field observations. Tambor cone, which is 2500 m wide and 250 m high, consists of dense, probably monogenetic medium to coarse-grained volcaniclastic and pyroclastic rocks that are highly fragmented, probably as a result of thermal and viscous granulation upon contact with seawater during several consecutive cycles of activity. Tangential joints in the outcrops indicate subsidence of the crater floor after primary emplacement. Kolá crater, which is 1000 m wide and 160 m deep, appears to have been excavated in the surrounding seafloor and shows stepwise sagging features interpreted as ring fractures on the inner flanks. Lithologically, it is made up of a complicated succession of highly fragmented deposits, including spheroidal juvenile lapilli, likely formed by spray granulation. It resembles a maar-type deposit found on land. The eruption apparently entrained blocks of MORB-type gabbroic country rocks with
40Ar/39Ar chronology of the McMurdo Volcanic Group at The Pleiades, Northern Victoria Land, Antarctica

International Nuclear Information System (INIS)

Esser, R.P.; Kyle, P.R.

2002-01-01

Fifteen samples from The Pleiades volcanic centre in northern Victoria Land, Antarctica, were dated using the 40 Ar/ 39 Ar furnace step-heating method. Ages range from 847 to 6 ka. Eight samples are <100 ka, showing that The Pleiades are very young. Three trachyte samples suggest eruptive activity started at c. 830 ka. An apparent increase in volcanic activity began at c. 100 ka, and at c. 65 ka a significant phase of cone building occurred at Mt Atlas, the largest volcanic cone at The Pleiades. At c. 45 ka, lava flows were erupted on the western flank of Mt Pleiones adjacent to Mt Atlas and near the summit of Alcyone Cone. The youngest activity (6 ± 6 ka) occurred at Taygete Cone, an endogenous dome of trachyte. The near-zero age for Taygete Cone is consistent with evidence of recent volcanism, including fresh hydrothermal activity and compositionally similar pumice lapilli scattered over parts of The Pleiades. (author). 6 refs., 3 figs., 1 tab
Magma reservoirs and neutral buoyancy zones on Venus - Implications for the formation and evolution of volcanic landforms

Science.gov (United States)

Head, James W.; Wilson, Lionel

1992-01-01

The production of magma reservoirs and neutral buoyancy zones (NBZs) on Venus and the implications of their development for the formation and evolution of volcanic landforms are examined. The high atmospheric pressure on Venus reduces volatile exsolution and generally serves to inhibit the formation of NBZs and shallow magma reservoirs. For a range of common terrestrial magma-volatile contents, magma ascending and erupting near or below mean planetary radius (MPR) should not stall at shallow magma reservoirs; such eruptions are characterized by relatively high total volumes and effusion rates. For the same range of volatile contents at 2 km above MPR, about half of the cases result in the direct ascent of magma to the surface and half in the production of neutral buoyancy zones. NBZs and shallow magma reservoirs begin to appear as gas content increases and are nominally shallower on Venus than on earth. For a fixed volatile content, NBZs become deeper with increasing elevation: over the range of elevations treated in this study (-1 km to +4.4 km) depths differ by a factor of 2-4. Factors that may account for the low height of volcanoes on Venus are discussed.
Conceptual model of volcanism and volcanic hazards of the region of Ararat valley, Armenia

Science.gov (United States)

Meliksetian, Khachatur; Connor, Charles; Savov, Ivan; Connor, Laura; Navasardyan, Gevorg; Manucharyan, Davit; Ghukasyan, Yura; Gevorgyan, Hripsime

2015-04-01

Armenia and the adjacent volcanically active regions in Iran, Turkey and Georgia are located in the collision zone between the Arabian and Eurasian lithospheric plates. The majority of studies of regional collision related volcanism use the model proposed by Keskin, (2003) where volcanism is driven by Neo-Tethyan slab break-off. In Armenia, >500 Quaternary-Holocene volcanoes from the Gegham, Vardenis and Syunik volcanic fields are hosted within pull-apart structures formed by active faults and their segments (Karakhanyan et al., 2002), while tectonic position of the large in volume basalt-dacite Aragats volcano and periphery volcanic plateaus is different and its position away from major fault lines necessitates more complex volcano-tectonic setup. Our detailed volcanological, petrological and geochemical studies provide insight into the nature of such volcanic activity in the region of Ararat Valley. Most magmas, such as those erupted in Armenia are volatile-poor and erupt fairly hot. Here we report newly discovered tephra sequences in Ararat valley, that were erupted from historically active Ararat stratovolcano and provide evidence for explosive eruption of young, mid K2O calc-alkaline and volatile-rich (>4.6 wt% H2O; amph-bearing) magmas. Such young eruptions, in addition to the ignimbrite and lava flow hazards from Gegham and Aragats, present a threat to the >1.4 million people (~ ½ of the population of Armenia). We will report numerical simulations of potential volcanic hazards for the region of Ararat valley near Yerevan that will include including tephra fallout, lava flows and opening of new vents. Connor et al. (2012) J. Applied Volcanology 1:3, 1-19; Karakhanian et al. (2002), JVGR, 113, 319-344; Keskin, M. (2003) Geophys. Res. Lett. 30, 24, 8046.
Conditions for oceans on Earth-like planets orbiting within the habitable zone: importance of volcanic CO{sub 2} degassing

Energy Technology Data Exchange (ETDEWEB)

Kadoya, S. [Department of Earth and Planetary Science, The University of Tokyo, Kiban Bldg. 408, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan); Tajika, E., E-mail: kadoya@astrobio.k.u-tokyo.ac.jp, E-mail: tajika@astrobio.k.u-tokyo.ac.jp [Department of Complexity Science and Engineering, The University of Tokyo, Kiban Bldg. 409, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561 (Japan)

2014-08-01

Earth-like planets in the habitable zone (HZ) have been considered to have warm climates and liquid water on their surfaces if the carbonate-silicate geochemical cycle is working as on Earth. However, it is known that even the present Earth may be globally ice-covered when the rate of CO{sub 2} degassing via volcanism becomes low. Here we discuss the climates of Earth-like planets in which the carbonate-silicate geochemical cycle is working, with focusing particularly on insolation and the CO{sub 2} degassing rate. The climate of Earth-like planets within the HZ can be classified into three climate modes (hot, warm, and snowball climate modes). We found that the conditions for the existence of liquid water should be largely restricted even when the planet is orbiting within the HZ and the carbonate-silicate geochemical cycle is working. We show that these conditions should depend strongly on the rate of CO{sub 2} degassing via volcanism. It is, therefore, suggested that thermal evolution of the planetary interiors will be a controlling factor for Earth-like planets to have liquid water on their surface.
The Geothermal Systems along the Watukosek fault system (East Java, Indonesia):The Arjuno-Welirang Volcanic Complex and the Lusi Mud-Eruption

Science.gov (United States)

Inguaggiato, Salvatore; Mazzini, Adriano; Vita, Fabio; Sciarra, Alessandra

2016-04-01

The Java Island is characterized by an intense volcanic activity with more then 100 active volcanoes. Moreover, this island is also known by the presence of many mud volcanoes and hydrothermal springs. In particular, in the 2006 several sudden hot mud eruptions, with fluids around 100° C, occurred in the NE side of the island resulting in a prominent eruption named Lusi (contraction of Lumpur Sidoarjo) located along the major Watukosek strike-slip fault zone. The Watukosek fault system, strikes from the Arjuno-Welirang volcanic complex, intersects Lusi and extends towards the NE of the Java island. Conversely of the normal mud eruptions (cold fluids emitted in a short time period of few days), the Lusi eruption was characterized by a persistent effusive hot fluids emissions for a long-time period of, so far, nearly a decade. Moreover, the isotopic composition of emitted gases like Helium showed a clear magmatic origin. For this reasons we decided to investigate the near Arjuno-Welirang complex located on the same strike-slip fault. Arjuno-Welirang is a twin strato-volcano system located in the East of Java along the Watukosek fault, at about 25 km SW respect to the Lusi volcano system. It features two main peaks: Arjuno (3339 masl) and Welirang (3156 masl). The last recorded eruptive activity took place in August 1950 from the flanks of Kawah Plupuh and in October 1950 from the NW part of the Gunung Welirang. This strato-volcano is characterized by a S-rich area, with high T-vent fumarole at least up to 220° C (and likely higher), located mainly in the Welirang crater. In addition, several hot springs vent from the flanks of the volcano, indicate the presence of a large hydrothermal system. During July 2015, in the framework of the Lusi Lab project (ERC grant n° 308126), we carried out a geochemical field campaign on the Arjuno-Welirang volcano hydrothermal system area, sampling water and dissolved gases from the thermal and cold springs located on the flanks of
Vesuvio civil protection exercise MESIMEX: survey on volcanic risk perception

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Tullio Ricci

2013-11-01

Full Text Available In October 2006 the European Civil Protection Exercise MESIMEX (Somma Vesuvio Mesimex – Major Emergency SIMulation Exercise on volcanic risk took place at Vesuvio, promoted by Campania Region and coordinated by the Italian Civil Protection Department. The exercise was focused on the preparedness phase for a major volcanic emergency in the area of Vesuvio. An evacuation of a sample of 1800 inhabitants from the Vesuvio Red Zone was also tested during the drill because the emergency plan ensures the complete evacuation of the population from the higher risk zone before the onset of the eruption. During that event a survey on volcanic risk perception was carried out on the evacuated population in order to compare the results with the ones coming from a previous similar survey, using the same questionnaire, carried out on a wider sample of residents in the Vesuvio Red Zone few months before MESIMEX exercise. The aim was to point out any differences in population’s attitude towards volcanic risk after having received detailed information on the emergency plan and on the hazards and risk related to the reactivation of Vesuvio, and experiencing the exercise. 463 questionnaires were distributed to the population evacuated from the 18 municipalities of the Red Zone and participating to the exercise. Main results in comparing data from MESIMEX survey with the Vesuvio previous one, put in evidence how the general level of Vesuvio residents’ trust remains quite low, indicating that a continuous and effective effort has to be done by both scientific community and Civil Protection Department. Particular attention should be paid in education and outreach activities and in involving people in risk mitigation procedures, also through more frequent exercises.
Neogene seismites and seismic volcanic rocks in the Linqu area, Shandong Province, E China

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Tian H.S.

2014-07-01

Full Text Available The Yishu Fault Zone runs through the centre of Shandong Province (E China; it is a deep-seated large fault system that still is active. Two volcanic faulted basins (the Shanwang and Linqu Basins in the Linqu area, west of the fault zone, are exposed to rifting, which process is accompanied by a series of tectonic and volcanic earthquakes with a magnitude of 5-8. Lacustrine sediments in the basins were affected by these earthquakes so that seismites with a variety of soft-sediment deformation structures originated. The seismites form part of the Shanwang Formation of the Linqu Group. Semi-consolidated fluvial conglomerates became deformed in a brittle way; these seismites are present at the base of the Yaoshan Formation. Intense earthquakes triggered by volcanic activity left their traces in the form of seismic volcanic rocks associated with liquefied-sand veins in the basalt/sand intercalations at the base of the Yaoshan Formation. These palaeo-earthquake records are dated around 14-10 Ma; they are responses to the intense tectonic extension and the basin rifting in this area and even the activity of the Yishu Fault Zone in the Himalayan tectonic cycle.
Contribution of the geophysical and radon techniques to characterize hydrogeological setting in the western volcanic zone of Yarmouk basin: Case study Deir El-Adas

International Nuclear Information System (INIS)

Al-Fares, W.; Soliman, E.; Al-Ali, A.

2009-01-01

The aim of this study is to illustrate the geophysical and radon techniques in characterizing ''at local scale'' a hydrogeological setting in the volcanic zone of Yarmouk basin. And to employ the obtained results to understand and explain similar hydrogeological situation related to particular subsurface geologic and tectonic structure. Based on the field observations and failed wells drilled at Deir El-Adas, and the occurrence of successful well out of that zone, all these reasons, have given us the incentive to verify and provide realistic explanation of this phenomena in the basaltic outcrops of Yarmouk basin. The interpretation of the vertical electrical surveys (VES), indicates to the presence of local faulted anticline structure of Palaeogene located under the volcanic outcrops. This structure has led to complex hydrogeological conditions, represented by limited recharge in this area which occurs through fractures and secondary faults in addition to the low direct precipitation. Piezometric map indicates to water divide in the north-west of Deir El-Adas related to the tectonic setting. Meanwhile, discharge map show low reproducibility of drilled wells in Deir El-Adas and its periphery. Due to limited radon data, it was difficult to draw concrete conclusions from this technique. (author)

Internal architecture, permeability structure, and hydrologic significance of contrasting fault-zone types

Science.gov (United States)

Rawling, Geoffrey C.; Goodwin, Laurel B.; Wilson, John L.

2001-01-01

The Sand Hill fault is a steeply dipping, large-displacement normal fault that cuts poorly lithified Tertiary sediments of the Albuquerque basin, New Mexico, United States. The fault zone does not contain macroscopic fractures; the basic structural element is the deformation band. The fault core is composed of foliated clay flanked by structurally and lithologically heterogeneous mixed zones, in turn flanked by damage zones. Structures present within these fault-zone architectural elements are different from those in brittle faults formed in lithified sedimentary and crystalline rocks that do contain fractures. These differences are reflected in the permeability structure of the Sand Hill fault. Equivalent permeability calculations indicate that large-displacement faults in poorly lithified sediments have little potential to act as vertical-flow conduits and have a much greater effect on horizontal flow than faults with fractures.
Crustal structure along the west flank of the Cascades, western Washington

Science.gov (United States)

Miller, K.C.; Keller, Gordon R.; Gridley, J.M.; Luetgert, J.H.; Mooney, W.D.; Thybo, H.

1997-01-01

Knowledge of the crustal structure of the Washington Cascades and adjacent Puget Lowland is important to both earthquake hazards studies and geologic studies of the evolution of this tectonically active region. We present a model for crustal velocity structure derived from analysis of seismic refraction/wide-angle reflection data collected in 1991 in western Washington. The 280-km-long north-south transect skirts the west flank of the Cascades as it crosses three tectonic provinces including the Northwest Cascades Thrust System (NWCS), the Puget Lowland, and the volcanic arc of the southern Cascades. Within the NWCS, upper crustal velocities range from 4.2 to 5.7 km s-1 and are consistent with the presence of a diverse suite of Mesozoic and Paleozoic metasediments and metavolcanics. In the upper 2-3 km of the Puget Lowland velocities drop to 1.7-3.5 km s-1 and reflect the occurrence of Oligocene to recent sediments within the basin. In the southern Washington Cascades, upper crustal velocities range from 4.0 to 5.5 km s-1 and are consistent with a large volume of Tertiary sediments and volcanics. A sharp change in velocity gradient at 5-10 km marks the division between the upper and middle crust. From approximately 10 to 35 km depth the velocity field is characterized by a velocity increase from ???6.0 to 7.2 km s-1. These high velocities do not support the presence of marine sedimentary rocks at depths of 10-20 km beneath the Cascades as previously proposed on the basis of magnetotelluric data. Crustal thickness ranges from 42 to 47 km along the profile. The lowermost crust consists of a 2 to 8-km-thick transitional layer with velocities of 7.3-7.4 km s-1. The upper mantle velocity appears to be an unusually low 7.6-7.8 km s-1. When compared to velocity models from other regions, this model most closely resembles those found in active continental arcs. Distinct seismicity patterns can be associated with individual tectonic provinces along the seismic transect. In
Volcanic ash in ancient Maya ceramics of the limestone lowlands: implications for prehistoric volcanic activity in the Guatemala highlands

Science.gov (United States)

Ford, Anabel; Rose, William I.

1995-07-01

In the spirit of collaborative research, Glicken and Ford embarked on the problem of identifying the source of volcanic ash used as temper in prehistoric Maya ceramics. Verification of the presence of glass shards and associated volcanic mineralogy in thin sections of Maya ceramics was straightforward and pointed to the Guatemala Highland volcanic chain. Considering seasonal wind rose patterns, target volcanoes include those from the area west of and including Guatemala City. Joint field research conducted in 1983 by Glicken and Ford in the limestone lowlands of Belize and neighboring Guatemala, 300 km north of the volcanic zone and 150 km from the nearest identified ash deposits, was unsuccessful in discovering local volcanic ash deposits. The abundance of the ash in common Maya ceramic vessels coupled with the difficulties of long-distance procurement without draft animals lead Glicken to suggest that ashfall into the lowlands would most parsimoniously explain prehistoric procurement; it literally dropped into their hands. A major archaeological problem with this explanation is that the use of volcanic ash occurring over several centuries of the Late Classic Period (ca. 600-900 AD). To accept the ashfall hypothesis for ancient Maya volcanic ash procurement, one would have to demonstrate a long span of consistent volcanic activity in the Guatemala Highlands for the last half of the first millennium AD. Should this be documented through careful petrographic, microprobe and tephrachronological studies, a number of related archaeological phenomena would be explained. In addition, the proposed model of volcanic activity has implications for understanding volcanism and potential volcanic hazards in Central America over a significantly longer time span than the historic period. These avenues are explored and a call for further collaborative research of this interdisciplinary problem is extended in this paper.
Volcanic geology and eruption frequency, São Miguel, Azores

Science.gov (United States)

Moore, Richard B.

1990-01-01

Six volcanic zones comprise São Miguel, the largest island in the Azores. All are Quaternary in age except the last, which is partly Pliocene. From west to east the zones are (1) the trachyte stratovolcano of Sete Cidades, (2) a field of alkali-basalt cinder cones and lava flows with minor trachyte, (3) the trachyte stratovolcano of Agua de Pau, (4) a field of alkali-basalt cinder cones and lava flows with minor trachyte and tristanite, (5) the trachyte stratovolcano of Furnas, and (6) the Nordeste shield, which includes the Povoação caldera and consists of alkali basalt, tristanite, and trachyte. New radiocarbon and K-Ar ages augment stratigraphic data obtained during recent geologic mapping of the entire island and provide improved data to interpret eruption frequency. Average dormant intervals for the past approximately 3000 years in the areas active during that time are about 400 years for Sete Cidades, 145 for zone 2, 1150 for Agua de Pau, and 370 for Furnas. However, the average dormant interval at Sete Cidades increased from 400 to about 680 years before each of the past two eruptions, and the interval at Furnas decreased from 370 to about 195 years before each of the past four eruptions. Eruptions in zone 4 occurred about once every 1000 years during latest Pleistocene and early Holocene time; none has occurred for about 3000 years. The Povoação caldera truncates part of the Nordeste shield and probably formed during the middle to late Pleistocene. Calderas formed during latest Pleistocene time at the three younger stratovolcanoes in the sequence: outer Agua de Pau (between 46 and 26.5 ka), Sete Cidades (about 22 ka), inner Agua de Pau (15.2 ka), and Furnas (about 12 ka). Normal faults are common, but many are buried by Holocene trachyte pumice. Most faults trend northwest or west-northwest and are related to the Terceira rift, whose most active segment on São Miguel passes through Sete Cidades and zone 2. A major normal fault displaces Nordeste
Electrical resistivity structure beneath the Hangai Dome, Mongolia: intraplate volcanism and deformation imaged with magnetotelluric data

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Comeau, M. J.; Becken, M.; Kaeufl, J.; Kuvshinov, A. V.; Kamm, J.; Grayver, A.; Demberel, S.; Usnikh, S. U.; Batmagnai, E.; Tserendug, S.

2017-12-01

The Hangai Dome in central Mongolia is characterized by intraplate volcanism on a high-elevation intra-continental plateau. Volcanism dates from the Oligocene to the Holocene and is thought to be coincident with the onset of the uplift of the Hangai Dome, indicating that the processes may be linked. However, the processes and driving mechanisms responsible for creating this region remain largely unexplained, due in part to a lack of high-resolution geophysical data over the area. An extensive magnetotelluric (MT) data set was collected over the Hangai Dome in 2016 and 2017, with broadband data (0.002 - 5,000 s) collected at a total of 294 sites. This data set consists of a large array ( 50 km site spacing) and several long ( 600 km) and dense ( 5 km site spacing) profiles that cross the uplifted Hangai Dome. Additionally, they cross the bounding faults of the Hangai block, the Bulnay fault in the north and the Bogd fault of the Gobi-Altai in the south, which have had several M>8 earthquakes in the past century. These MT data have been used to generate electrical resistivity models of the crust and upper mantle in this region. Anomalous, low resistivity ( 30 ohm-m) zones in the lower crust ( 25 - 50 km depth) are spatially associated with the surface expressions of volcanism and modern-day hydrothermal activity. These zones indicate the presence of local accumulations of fluids below the brittle-ductile transition zone. Interestingly, this feature terminates sharply at the South Hangai Fault Zone. Furthermore, lower resistivity pathways in the upper crust (0 - 25 km depth) connect the deeper features to the surface. This is prominently observed below the Hangai's youngest volcanic zones of Tariat/Khorgo and Chuluut, as well as the hot spring area of Tsenkher, near Tsetserleg. Additionally, an electrical signature can be associated with known fault zones and mineralized zones (such as the Bayankhongor mineral belt). An anomalous low-resistivity zone in the upper
Temperatures and isotopic evolution of silicic magmas, Taupo Volcanic Zone and Coromandel, New Zealand

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Blattner, P.; Rui-Zhong, Hu; Graham, I.J.; Houston-Eleftheriadis, C.

1996-01-01

A new set of oxygen and strontium isotope data on rhyolitic lavas and ignimbrites of the Taupo Volcanic Zone (TVZ) and the Coromandel Peninsula provides new limits for petrogenetic models. For oxygen isotopes, the rock matrix is frequently altered, so that values for magma need to be phenocryst based. Within TVZ a trend towards more negative delta 1 8 O values for more recent magmas appears likely (average before about 1 Ma and for Coromandel near 8.0 per thousand; after 1 Ma near 7.5 per thousand). This could indicate the gradual removal of supracrustal contaminants from the zones of magma accumulation and extrusion. Similar trends within Coromandel cannot yet be resolved. A generally positive correlation is found for oxygen and strontium isotopes of magmas. Most magmas have a limited range of isotopic values, which then becomes a useful fingerprint (e.g., the Mamaku, Matahina, and Waiotapu Ignimbrites). A narrow range of eruption temperatures of 880 plus or minus 60degC is derived from quartz-plagioclase fractionations of 0.98 plus or minus 0.25 per thousand delta 1 8 O for 15 magmas. Some delta 1 8 O values of quartz and feldspar phenocrysts are sufficiently low to suggest interaction between surface water and magma. However, large negative oxygen isotope anomalies (such as known from Yellowstone), could be no more than partially concealed by the isotopically less depleted meteoric water of New Zealand, and have not yet been found in New Zealand. (author). 45 refs., 3 tabs., 6 figs
Diffuse volcanic emissions of carbon dioxide from Vulcano Island, Italy.

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Baubron, J C; Allard, P; Toutain, J P

1990-03-01

RECENT investigations on Mount Etna (Sicily)(1-3) have revealed that volcanoes may release abundant carbon dioxide not only from their active craters, but also from their flanks, as diffuse soil emanations. Here we present analyses of soil gases and air in water wells on Vulcano Island which provide further evidence of such lateral degassing. Nearly pure carbon dioxide, enriched in helium and radon, escapes from the slopes of the Fossa active cone, adding a total output of 30 tonnes per day to the fumarolic crater discharge ( 180 tonnes CO(2) per day). This emanation has similar He/CO(2) and (13)C/(12)C ratios to those of the crater fumaroles (300%ndash;500 degrees C) and therefore a similar volcanic origin. Gases rich in carbon dioxide also escape at sea level along the isthmus between the Fossa and Vulcanello volcanic cones, but their depletion in both He and (13)C suggests a distinct source. Diffuse volcanic gas emanations, once their genetic link with central fumarole degassing has been demonstrated, can be used for continuous volcano monitoring, at safe distances from active craters. Such monitoring has been initiated at Vulcano, where soil and well emanations of nearly pure CO(2) themselves represent a threat to the local population.
Synthesis of gravity, magnetic and thermal studies at the Las Tres Virgenes geothermal zone, Baja California Sur, Mexico. Sintesis de los estudios de gravimetria, magnetometria y termometria en la zona geotermica de Las Tres Virgenes, Baja California Sur, Mexico

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Garcia Estrada, Gerardo (Departamento de Exploracion, Gerencia de Proyectos Geotermoelectricos de la Comision Federal de Electricidad, Morelia (Mexico)); Gonzalez Lopez, Macario (Residencia General de Cerro Prieto, Mexicali (Mexico))

1998-01-15

Las Tres Virgenes geothermal zone is located in the NE-SW central sector of a sigmoidal basin that regionally has a NW-SE trend. In the local deepest zone there is a NE-SE granodioritic basement horst acting as hydrologic barrier, that makes the fluids flow up. After moving in a direction parallel to the local horst, waters continue its regional SE-NW movement controlled by regional tectonics. The flanks of the granodioritic basement horst, and local N-S faulting act as fluid paths in the hydrothermal zone, but regional NW-SE regional faults determine the general flow direction. Both regional and local tectonics show magnetic evidences of the emplacement of magmatic bodies of intermediate to basic composition. Those along NW-SE trends are more noticeable but we consider they are not the present day heat source. Intermediate magmatism along NE-SW local trend seems to be less extensive but it is younger, so, we consider it constitutes the heat source of the hydrothermal system. Thermal data suggest that the heat source is located below the volcanic chain toward the S or SW of the wells, phenomena related with the general displacement of magmatism from NE to SW along the volcanic chain. However, recent intensive faulting permits a higher permeability in the northern sector in which there are slightly smaller temperatures but at shallower depths and with higher flow rates.
Neogene volcanism in Gutai Mts. (Eastern Carpathains: a review

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Marinel Kovacs

2003-04-01

Full Text Available Two types of volcanism developed in Gutâi Mts. (inner volcanic chain of Eastern Carpathians: a felsic, extensional/“back-arc” type and an intermediate, arc type. The felsic volcanism of explosive origin, consisting of caldera-related rhyolitic ignimbrites and resedimented volcaniclastics, had taken place during Early-Middle Badenian and Early Sarmatian. The intermediate volcanism, consisting of extrusive (effusive and explosive and intrusive activity, had developed during Sarmatian and Pannonian (13.4-7.0 Ma. It is represented by typical calc-alkaline series, from basalts to rhyolites. Lava flows of basaltic andesites and andesites are predominant, often emplaced in subaqueous environment. Extrusive domes, mainly composed of dacites, are associated to the andesitic volcanic structures. The intermediate volcanism, consisting of extrusive (effusive and explosive and intrusive activity, had developed during Sarmatian and Pannonian (13.4-7.0 Ma. It is represented by typical calc-alkaline series, from basalts to rhyolites. Lava flows of basaltic andesites and andesites are predominant, often emplaced in subaqueous environment. Extrusive domes, mainly composed of dacites, are associated to the andesitic volcanic structures. The geochemical study on the volcanic rocks shows the calc-alkaline character of both felsic and intermediate volcanism and typical subduction zones geochemical signatures for the intermediate one. The felsic volcanism shows affinities with subduction-related rocks as well. The main petrogenetic process in Gutâi Mts. was crustal assimilation, strongly constrained by trace element and isotope geochemistry.
Microsatellites grant more stable flanking genes

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Joukhadar Reem

2012-10-01

Full Text Available Abstract Background Microsatellites, or simple sequence repeats (SSRs, are DNA sequences that include tandem copies of specific sequences no longer than six bases. SSRs are ubiquitous in all genomes and highly mutable. Presentation of the hypothesis Results from previous studies suggest that flanking regions of SSR are exhibit high stability in a wide range of organisms. We hypothesized that the SSRs ability to discard weak DNA polymerases could be responsible for this unusual stability. . When the weak polymerases are being decayed over SSRs, the flanking sequences would have higher opportunity to be replicated by more stable DNA polymerases. We present evidence of the molecular basis of our hypothesis. Testing the hypothesis The hypothesis could be tested by examining the activity of DNA polymerase during and after a number of PCRs. The PCR reactions should be run with the same SSR locus possessing differences in the SSR length. The hypothesis could also be tested by comparing the mutational rate of a transferred gene between two transformations. The first one has a naked T-DNA (transferred DNA, while the second one has the same T-DNA flanked with two SSRs. Implications of the hypothesis In any transformation experiment, flanking the T-DNA fragment with SSR sequences would result in more stably transferred genes. This process would decrease the unpredictable risks that may occur because of the mutational pressure on this foreign segment.
Geologic structure and volcanic history of the Yanaizu-Nishiyama (Okuaizu) geothermal field, Northeast Japan

Energy Technology Data Exchange (ETDEWEB)

Mizugaki, Keiko [Geological Survey of Japan, Geothermal Research Dept., Higashi Tsukuba (Japan)

2000-04-01

The Yanaizu-Nishiyama geothermal field, also known as Okuaizu, supports a 65 MWe geothermal power station. It is located in the western part of Fukushima Prefecture, northeast Japan. This field is characterised by rhyolitic volcanism of about 0.3-0.2 Ma that formed Sunagohara volcano. Drillcore geology indicates that volcanism began with a caldera-forming eruption in the center of this field, creating a 2-km-diameter funnel-shaped caldera. Subsequently, a fault-bounded block including this caldera subsided to form a 5-km-wide lake that accumulated lake sediments. Post-caldera volcanism formed lava domes and intrusions within the lake, and deposited ash-flow tuffs in and around the lake. The hydrothermal system of this field is strongly controlled by subvertical faults that have no relation to the volcanism. The principal production zone occurs at a depth of 1.0-2.6 km within fractured Neogene formations along two northwest-trending faults to the southeast of the caldera. These faults also formed fracture zones in the lake sediments, but there was no apparent offset of the sediments. Stratigraphic studies suggest that post-caldera activities of Sunagohara volcano have migrated southeastward to the present high-temperature zone. The source magma of Sunagohara volcano may contribute to the thermal potential of this field. (Author)
Post-eruptive sediment transport and surface processes on unvegetated volcanic hillslopes - A case study of Black Tank scoria cone, Cima Volcanic Field, California

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Kereszturi, Gábor; Németh, Károly

2016-08-01

Conical volcanic edifices that are made up from lapilli to block/bomb pyroclastic successions, such as scoria cones, are widespread in terrestrial and extraterrestrial settings. Eruptive processes responsible for establishing the final facies architecture of a scoria cone are not well linked to numerical simulations of their post-eruptive sediment transport. Using sedimentological, geomorphic and 2D fragment morphology data from a 15-ky-old scoria cone from the Cima Volcanic Field, California, this study provides field evidence of the various post-eruptive sediment transport and degradation processes of scoria cones located in arid to semi-arid environments. This study has revealed that pyroclast morphologies vary downslope due to syn-eruptive granular flows, along with post-eruptive modification by rolling, bouncing and sliding of individual particles down a slope, and overland flow processes. The variability of sediment transport rates on hillslopes are not directly controlled by local slope angle variability and the flank length but rather by grain size, and morphological characteristics of particles, such as shape irregularity of pyroclast fragments and block/lapilli ratio. Due to the abundance of hillslopes degrading in unvegetated regions, such as those found in the Southwestern USA, granulometric influences should be accounted for in the formulation of sediment transport laws for geomorphic modification of volcanic terrains over long geologic time.
Plateau subduction, intraslab seismicity, and the Denali (Alaska) volcanic gap

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Chuang, Lindsay Yuling; Bostock, Michael; Wech, Aaron; Plourde, Alexandre

2018-01-01

Tectonic tremors in Alaska (USA) are associated with subduction of the Yakutat plateau, but their origins are unclear due to lack of depth constraints. We have processed tremor recordings to extract low-frequency earthquakes (LFEs), and generated a set of six LFE waveform templates via iterative network matched filtering and stacking. The timing of impulsive P (compressional) wave and S (shear) wave arrivals on template waveforms places LFEs at 40–58 km depth, near the upper envelope of intraslab seismicity and immediately updip of increased levels of intraslab seismicity. S waves at near-epicentral distances display polarities consistent with shear slip on the plate boundary. We compare characteristics of LFEs, seismicity, and tectonic structures in central Alaska with those in warm subduction zones, and propose a new model for the region’s unusual intraslab seismicity and the enigmatic Denali volcanic gap (i.e., an area of no volcanism where expected). We argue that fluids in the Yakutat plate are confined to its upper crust, and that shallow subduction leads to hydromechanical conditions at the slab interface in central Alaska akin to those in warm subduction zones where similar LFEs and tremor occur. These conditions lead to fluid expulsion at shallow depths, explaining strike-parallel alignment of tremor occurrence with the Denali volcanic gap. Moreover, the lack of double seismic zone and restriction of deep intraslab seismicity to a persistent low-velocity zone are simple consequences of anhydrous conditions prevailing in the lower crust and upper mantle of the Yakutat plate.
Self-potential anomalies in some Italian volcanic areas

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C. Silenziario

1996-06-01

Full Text Available The study of Self-Potential (SP space and time variations in volcanic areas may provide useful information on both the geometrical structure of the volcanic apparatuses and the dynamical behaviour of the feeding and uprising systems. In this paper, the results obtained on the islands of Vulcano (Eolian arc and Ponza (Pontine archipelago and on the Mt. Somma-Vesuvius complex are shown. On the island of Vulcano and on the Mt. Somma-Vesuvius apparatus areal SP surveys were performed with the aim of evidencing anomalies closely associated to the zones of major volcanic activity. On the island of Vulcano a profile across the fumaroles along the crater rim of the Fossa Cone was also carried out in order to have a direct relationship between fumarolic fracture migration and flow rate and SP anomaly space and time variations. The areal survey on the island of Ponza, which is considered an inactive area, is assumed as a reference test with which to compare the amplitude and pattern of the anomalies in the active areas. A tentative interpretation of the SP anomalies in volcanic areas is suggested in terms of electrokinetic phenomena, related to the movement of fluids of both volcanic and non-volcanic origin.
Petrology and geochronology of metamorphosed volcanic rocks and a middle Cretaceous volcanic neck in the east-central Sierra Nevada, California.

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Kistler, R.W.; Swanson, S.E.

1981-01-01

Metamorphosed Mesozoic volcanic rocks from the E-central Sierra Nevada range in composition from basalt to rhyolite and have ages, based on whole rock Rb-Sr and U-Pb zircon dating, of about 237- 224, 185, 163, 134, and 100Ma. The major plutons of the batholith in this area are of Triassic (215-200Ma) and Cretaceous (94-80Ma) ages. Initial 87Sr/86Sr values for the metamorphosed volcanic rocks of the area are in the range from 0.7042 to 0.7058 and are generally different from the values for the surrounding batholithic rocks (0.7056-0.7066). A circular, zoned granitic pluton, with an outcrop area of 2.5km2, similar in appearance to a ring dike complex, was apparently a conduit for some or possibly all of the middle-Cretaceous metamorphosed volcanic rocks exposed about 5km to the S in the western part of the Ritter Range. Samples from the metamorphosed volcanic rocks and the pluton yield a Rb/Sr whole rock isochron age of 99.9+ or -2.2Ma with an intitial 87Sr/86Sr of 0.7048+ or -0.00001. Major element variation diagrams of the pluton and volcanic rocks define coincident compositional trends. The ages of volcanic events relative to the ages of the major intrusive epochs and the major element and isotopic compositions of the volcanic rocks relative to the major plutons indicate that the volcanic rocks are not simply or directly related to the major plutons in the Sierra Nevada. -from Authors
Bookshelf faulting and transform motion between rift segments of the Northern Volcanic Zone, Iceland

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Green, R. G.; White, R. S.; Greenfield, T. S.

2013-12-01

Plate spreading is segmented on length scales from 10 - 1,000 kilometres. Where spreading segments are offset, extensional motion has to transfer from one segment to another. In classical plate tectonics, mid-ocean ridge spreading centres are offset by transform faults, but smaller 'non-transform' offsets exist between slightly overlapping spreading centres which accommodate shear by a variety of geometries. In Iceland the mid-Atlantic Ridge is raised above sea level by the Iceland mantle plume, and is divided into a series of segments 20-150 km long. Using microseismicity recorded by a temporary array of 26 three-component seismometers during 2009-2012 we map bookshelf faulting between the offset Askja and Kverkfjöll rift segments in north Iceland. The micro-earthquakes delineate a series of sub-parallel strike-slip faults. Well constrained fault plane solutions show consistent left-lateral motion on fault planes aligned closely with epicentral trends. The shear couple across the transform zone causes left-lateral slip on the series of strike-slip faults sub-parallel to the rift fabric, causing clockwise rotations about a vertical axis of the intervening rigid crustal blocks. This accommodates the overall right-lateral transform motion in the relay zone between the two overlapping volcanic rift segments. The faults probably reactivated crustal weaknesses along the dyke intrusion fabric (parallel to the rift axis) and have since rotated ˜15° clockwise into their present orientation. The reactivation of pre-existing rift-parallel weaknesses is in contrast with mid-ocean ridge transform faults, and is an important illustration of a 'non-transform' offset accommodating shear between overlapping spreading segments.
Post-Eocene volcanics of the Abazar district, Qazvin, Iran: Mineralogical and geochemical evidence for a complex magmatic evolution

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Asiabanha, A.; Bardintzeff, J. M.; Kananian, A.; Rahimi, G.

2012-02-01

The style of volcanism of post-Eocene volcanism in the Alborz zone of northern Iran is different to that of Eocene volcanism (Karaj Formation). Indeed, the volcanic succession of the Abazar district, located in a narrow volcanic strip within the Alborz magmatic assemblage, is characterized by distinct mineralogical and chemical compositions linked to a complex magmatic evolution. The succession was produced by explosive eruptions followed by effusive eruptions. Two main volcanic events are recognized: (1) a thin rhyolitic ignimbritic sheet underlain by a thicker lithic breccia, and (2) lava flows including shoshonite, latite, and andesite that overlie the first event across a reddish soil horizon. Plagioclase in shoshonite (An 48-92) shows normal zoning, whereas plagioclase in latite and andesite (An 48-75) has a similar composition but shows reverse and oscillatory zoning. QUILF temperature calculations for shoshonites and andesites yield temperatures of 1035 °C and 1029 °C, respectively. The geothermometers proposed by Ridolfi et al. (2010) and Holland and Blundy (1994) yield temperatures of 960 °C and 944 °C for latitic lava, respectively. The samples of volcanic rock show a typical geochemical signature of the continental arc regime, but the andesites clearly differ from the shoshonites, the latites and the rhyolites. The mineralogical and chemical characteristics of these rocks are explained by the following petrogenesis: (1) intrusion of a hot, mantle-depth mafic (shoshonitic) magma, which differentiated in the magma chamber to produce a latitic and then a rhyolitic liquid; (2) rhyolitic ignimbritic eruptions from the top of the magma chamber, following by shoshonitic and then latitic extrusions; (3) magma mingling between the latitic and andesitic magmas, as indicated by the occurrence of andesite clasts within the latite; and (4) andesitic effusions. The youngest volcanic events in the Alborz zone show a close chemical relationship with continental arc
Soil CO2 efflux measurement network by means of closed static chambers to monitor volcanic activity at Tenerife, Canary Islands

Science.gov (United States)

Amonte, Cecilia; García-Merino, Marta; Asensio-Ramos, María; Melián, Gladys; García-Hernández, Rubén; Pérez, Aaron; Hernández, Pedro A.; Pérez, Nemesio M.

2017-04-01

Tenerife (2304 km2) is the largest of the Canary Islands and has developed a central volcanic complex (Cañadas edifice), that started to grow about 3.5 My ago. Coeval with the construction of the Cañadas edifice, shield basaltic volcanism continued until the present along three rift zones oriented NW-SE, NE-SW and NS (hereinafter referred as NW, NE and NS respectively). Main volcanic historical activity has occurred along de NW and NE rift-zones, although summit cone of Teide volcano, in central volcanic complex, is the only area of the island where surface geothermal manifestations are visible. Uprising of deep-seated gases occurs along the aforementioned volcanic structures causing diffuse emissions at the surface environment of the rift-zones. In the last 20 years, there has been considerable interest in the study of diffuse degassing as a powerful tool in volcano monitoring programs. Diffuse degassing studies are even more important volcanic surveillance tool at those volcanic areas where visible manifestations of volcanic gases are absent. Historically, soil gas and diffuse degassing surveys in volcanic environments have focused mainly on CO2 because it is, after water vapor, the most abundant gas dissolved in magma. One of the most popular methods used to determine CO2 fluxes in soil sciences is based on the absorption of CO2 through an alkaline medium, in its solid or liquid form, followed by gravimetric, conductivity, or titration analyses. In the summer of 2016, a network of 31 closed static chambers was installed, covering the three main structural zones of Tenerife (NE, NW and NS) as well as Cañadas Caldera with volcanic surveillance porpoises. 50 cc of 0.1N KOH solution is placed inside the chamber to absorb the CO2 released from the soil. The solution is replaced weekly and the trapped CO2 is then analyzed at the laboratory by titration. The are expressed as weekly integrated CO2 efflux values. The CO2 efflux values ranged from 3.2 to 12.9 gṡm-2�
Morpho-structural evolution of a volcanic island developed inside an active oceanic rift: S. Miguel Island (Terceira Rift, Azores)

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Sibrant, A. L. R.; Hildenbrand, A.; Marques, F. O.; Weiss, B.; Boulesteix, T.; Hübscher, C.; Lüdmann, T.; Costa, A. C. G.; Catalão, J. C.

2015-08-01

The evolution of volcanic islands is generally marked by fast construction phases alternating with destruction by a variety of mass-wasting processes. More specifically, volcanic islands located in areas of intense regional deformation can be particularly prone to gravitational destabilisation. The island of S. Miguel (Azores) has developed during the last 1 Myr inside the active Terceira Rift, a major tectonic structure materializing the present boundary between the Eurasian and Nubian lithospheric plates. In this work, we depict the evolution of the island, based on high-resolution DEM data, stratigraphic and structural analyses, high-precision K-Ar dating on separated mineral phases, and offshore data (bathymetry and seismic profiles). The new results indicate that: (1) the oldest volcanic complex (Nordeste), composing the easternmost part of the island, was dominantly active between ca. 850 and 750 ka, and was subsequently affected by a major south-directed flank collapse. (2) Between at least 500 ka and 250 ka, the landslide depression was massively filled by a thick lava succession erupted from volcanic cones and domes distributed along the main E-W collapse scar. (3) Since 250 kyr, the western part of this succession (Furnas area) was affected by multiple vertical collapses; associated plinian eruptions produced large pyroclastic deposits, here dated at ca. 60 ka and less than 25 ka. (4) During the same period, the eastern part of the landslide scar was enlarged by retrogressive erosion, producing the large Povoação valley, which was gradually filled by sediments and young volcanic products. (5) The Fogo volcano, in the middle of S. Miguel, is here dated between ca. 270 and 17 ka, and was affected by, at least, one southwards flank collapse. (6) The Sete Cidades volcano, in the western end of the island, is here dated between ca. 91 and 13 ka, and experienced mutliple caldera collapses; a landslide to the North is also suspected from the presence of a
Permian to recent volcanism in northern sumatra, indonesia: a preliminary study of its distribution, chemistry, and peculiarities

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Rock, N. M. S.; Syah, H. H.; Davis, A. E.; Hutchison, D.; Styles, M. T.; Lena, Rahayu

1982-06-01

Sumatra has been a ‘volcanic arc’, above an NE-dipping subduction zone, since at least the Late Permian. The principal volcanic episodes in Sumatra N of the Equator have been in the Late Permian, Late Mesozoic, Palaeogene, Miocene and Quaternary. Late Permian volcanic rocks, of limited extent, are altered porphyritic basic lavas interstratified with limestones and phyllites. Late Mesozoic volcanic rocks, widely distributed along and W of the major transcurrent. Sumatra Fault System (SFS), which axially bisects Sumatra, include ophiolite-related spilites, andesites and basalts. Possible Palaeogene volcanic rocks include an altered basalt pile with associated dyke-swarm in the extreme NW, intruded by an Early Miocene (19 my) dioritic stock; and variable pyroxene rich basic lavas and agglomerates ranging from alkali basaltic to absarokitic in the extreme SW. Miocene volcanic rocks, widely distributed (especially W of the SFS), and cropping out extensively along the W coast, include calc-alkaline to high-K calc-alkaline basalts, andesites and dacites. Quaternary volcanoes (3 active, 14 dormant or extinct) are irregularly distributed both along and across the arc; thus they lie fore-arc of the SFS near the Equator but well back-arc farther north. The largest concentration of centres, around Lake Toba, includes the >2000 km3 Pleistocene rhyolitic Toba Tuffs. Quaternary volcanics are mainly calc-alkaline andesites, dacites and rhyolites with few basalts; they seem less variable, but on the whole more acid, than the Tertiary. The Quaternary volcanism is anomalous in relation to both southern Sumatra and adjacent Java/Bali: in southern Sumatra, volcanoes are regularly spaced along and successively less active away from the SFS, but neither rule holds in northern Sumatra. Depths to the subduction zone below major calc-alkaline volcanoes in Java/Bali are 160-210 km, but little over 100 km in northern Sumatra, which also lacks the regular K2O-depth correlations seen in

Managing the effects of accelerated glacial melting on volcanic collapse and debris flows: Planchon-Peteroa Volcano, Southern Andes

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Tormey, Daniel

2010-11-01

Glaciated mountains are among the most sensitive environments to climatic changes, and recent work has shown that large-scale glacial melting, including at the end of the Pleistocene, caused a significant increase in the incidence of large volcanic sector collapse and debris flows on then-active volcanoes. With current accelerated rates of glacial melting, glaciated active volcanoes are at an increasing risk of sector collapse, debris flow and landslide. These catastrophic events are Earth's most damaging erosion phenomenon, causing extensive property damage and loss of life. This paper illustrates these effects in well-studied settings, focusing on the end-Pleistocene to Holocene glaciovolcanic growth and destruction of the cone of the active volcano Planchon-Peteroa in the Andean Southern Volcanic Zone at latitude 35° 15' S, along the border between Chile and Argentina. The development of the volcano over the last 14,000 years illustrates how glacial melting and magmatic activity can trigger landslides and sector collapses. Planchon had a large sector collapse that produced a highly mobile and erosive debris avalanche 11,000 years BP, and other slope instabilities during the end-Pleistocene/early Holocene deglaciation. The summit amphitheater left after the sector collapse was subject to alternating periods of glaciation and melting-induced lake formation. Breaching of the moraine dams then formed lahars and landslides originating at the western edge of the summit amphitheater, and the deposits are preserved along the western flank of the volcano. Deep incision of moraine deposits further down the western slope of the volcano indicates that the lahars and landslides were water-rich and had high erosive power. As illustrated by Planchon-Peteroa, the interplay among glacial growth and melting, magmatic activity, and slope stability is complex, but must be accounted for in volcanic hazard assessment. Planchon-Peteroa currently has the southernmost temperate zone
129I in volcanic fluids: Testing for the presence of marine sediments in the Central American volcanic arc

International Nuclear Information System (INIS)

Snyder, Glen; Fehn, Udo

2000-01-01

The long half-life and the geochemical behavior of the 129 I system suggest that this cosmogenic radioisotope can contribute significantly to the understanding of processes associated with subduction zones and volcanic arc systems. Because iodine is not incorporated into igneous rocks, the age-signal associated with 129 I permits the determination of the origin of volatiles within arc volcanic systems. We report here results of a study to test the application of 129 I in fluids collected from hotsprings, crater lakes, fumaroles and geothermal wells from the Central American volcanic arc. Both the Momotombo geothermal field in Nicaragua and the Miravalles geothermal field in Costa Rica show 129 I/I ratios consistent with magmatic contributions from subducted marine pelagic sediments (minimum iodine ages of 25-30 Ma). In addition, several wells provide iodine isotopic ratios indicative of an older end-member, presumably located in the shallow crust (minimum iodine age = 65 Ma)
Modelling ground deformation patterns associated with volcanic processes at the Okataina Volcanic Centre

Science.gov (United States)

Holden, L.; Cas, R.; Fournier, N.; Ailleres, L.

2017-09-01

The Okataina Volcanic Centre (OVC) is one of two large active rhyolite centres in the modern Taupo Volcanic Zone (TVZ) in the North Island of New Zealand. It is located in a complex section of the Taupo rift, a tectonically active section of the TVZ. The most recent volcanic unrest at the OVC includes the 1315 CE Kaharoa and 1886 Tarawera eruptions. Current monitoring activity at the OVC includes the use of continuous GPS receivers (cGPS), lake levelling and seismographs. The ground deformation patterns preceding volcanic activity the OVC are poorly constrained and restricted to predictions from basic modelling and comparison to other volcanoes worldwide. A better understanding of the deformation patterns preceding renewed volcanic activity is essential to determine if observed deformation is related to volcanic, tectonic or hydrothermal processes. Such an understanding also means that the ability of the present day cGPS network to detect these deformation patterns can also be assessed. The research presented here uses the finite element (FE) modelling technique to investigate ground deformation patterns associated with magma accumulation and diking processes at the OVC in greater detail. A number of FE models are produced and tested using Pylith software and incorporate characteristics of the 1315 CE Kaharoa and 1886 Tarawera eruptions, summarised from the existing body of research literature. The influence of a simple ring fault structure at the OVC on the modelled deformation is evaluated. The ability of the present-day continuous GPS (cGPS) GeoNet monitoring network to detect or observe the modelled deformation is also considered. The results show the modelled horizontal and vertical displacement fields have a number of key features, which include prominent lobe based regions extending northwest and southeast of the OVC. The results also show that the ring fault structure increases the magnitude of the displacements inside the caldera, in particular in the
The tectonic origin of the Bay of Bengal and Bangladesh

Digital Repository Service at National Institute of Oceanography (India)

Talwani, M.; Desa, M.; Ismaiel, M.; Krishna, K.S.

direction for the Indian plate. 4. The 85°E Ridge was initially evolved as a fracture zone, and subsequently associated with volcanism. 5. The oceanic crust of the Western Basin of the Bay of Bengal is older than the crust of the Eastern Basin and Bangla... it a northern extension of the 86°E fracture zone, while Sar et al. [2009] suggested it could have a continental origin. Gibbons et al. [2013] inferred that the 85°E Ridge and the Kerguelen Fracture Zone formed as conjugate flanks of a 'leaky...
Right psoas abscess following right flank trauma: a case report ...

African Journals Online (AJOL)

This is a case of 15 year old boy who presented with three weeks history of right flank pain, two weeks history of fever and five days history of inability to walk well. There was history of right flank trauma a week before the onset of right flank pain. He had earlier presented in two different hospitals before he was brought to our ...
Volcanism Studies: Final Report for the Yucca Mountain Project

International Nuclear Information System (INIS)

Crowe, Bruce M.; Perry, Frank V.; Valentine, Greg A.; Bowker, Lynn M.

1998-01-01

This report synthesizes the results of volcanism studies conducted by scientists at the Los Alamos National Laboratory and collaborating institutions on behalf of the Department of Energy's Yucca Mountain Project. An assessment of the risk of future volcanic activity is one of many site characterization studies that must be completed to evaluate the Yucca Mountain site for potential long-term storage of high-level radioactive waste. The presence of several basaltic volcanic centers in the Yucca Mountain region of Pliocene and Quaternary age indicates that there is a finite risk of a future volcanic event occurring during the 10,000-year isolation period of a potential repository. Chapter 1 introduces the volcanism issue for the Yucca Mountain site and provides the reader with an overview of the organization, content, and significant conclusions of this report. The risk of future basaltic volcanism is the primary topic of concern including both events that intersect a potential repository and events that occur near or within the waste isolation system of a repository. Future volcanic events cannot be predicted with certainty but instead are estimated using formal methods of probabilistic volcanic hazard assessment (PVHA). Chapter 2 describes the volcanic history of the Yucca Mountain region (YMR) and emphasizes the Pliocene and Quaternary volcanic record, the interval of primary concern for volcanic risk assessment. The distribution, eruptive history, and geochronology of Plio-Quaternary basalt centers are described by individual center emphasizing the younger postcaldera basalt ( than about 7 x 10 -8 events yr -1 . Simple probability estimates are used to assess possible implications of not drilling aeromagnetic anomalies in the Amargosa Valley. The sensitivity of the disruption probability to the location of northeast boundaries of volcanic zones near the Yucca Mountain sit
Spatial and temporal variations of diffuse CO_{2} degassing at the N-S volcanic rift-zone of Tenerife (Canary Islands, Spain) during 2002-2015 period

Science.gov (United States)

Alonso, Mar; Ingman, Dylan; Alexander, Scott; Barrancos, José; Rodríguez, Fátima; Melián, Gladys; Pérez, Nemesio M.

2016-04-01

Tenerife is the largest of the Canary Islands and, together with Gran Canaria Island, is the only one with a central volcanic complex that started to grow at about 3.5 Ma. Nowadays the central complex is formed by Las Cañadas caldera, a volcanic depression measuring 16×9 km that resulted from multiple vertical collapses and was partially filled by post-caldera volcanic products. Up to 297 mafic monogenetic cones have been recognized on Tenerife, and they represent the most common eruptive activity occurring on the island during the last 1 Ma (Dóniz et al., 2008). Most of the monogenetic cones are aligned following a triple junction-shaped rift system, as result of inflation produced by the concentration of emission vents and dykes in bands at 120o to one another as a result of minimum stress fracturing of the crust by a mantle upwelling. The main structural characteristic of the southern volcanic rift (N-S) of the island is an apparent absence of a distinct ridge, and a fan shaped distribution of monogenetic cones. Four main volcanic successions in the southern volcanic rift zone of Tenerife, temporally separated by longer periods (˜70 - 250 ka) without volcanic activity, have been identified (Kröchert and Buchner, 2008). Since there are currently no visible gas emissions at the N-S rift, diffuse degassing surveys have become an important geochemical tool for the surveillance of this volcanic system. We report here the last results of diffuse CO2 efflux survey at the N-S rift of Tenerife, performed using the accumulation chamber method in the summer period of 2015. The objectives of the surveys were: (i) to constrain the total CO2 output from the studied area and (ii) to evaluate occasional CO2 efflux surveys as a volcanic surveillance tool for the N-S rift of Tenerife. Soil CO2 efflux values ranged from non-detectable up to 31.7 g m-2 d-1. A spatial distribution map, constructed following the sequential Gaussian simulation (sGs) procedure, did not show an
Pseudotachylyte formation in volcanic conduits: Montserrat vs. Mount St. Helens

Science.gov (United States)

Kendrick, J. E.; Lavallee, Y.; Petrakova, L.; Ferk, A.; Di Toro, G.; Hess, K.; Ferri, F.; Dingwell, D. B.

2012-12-01

Seismogenic fracture and faulting may result in non-equilibrium frictional melting of rock, which upon cooling and recrystallisation forms pseudotachylyte. In volcanic environments, the transition from endogenous to exogenous growth can be attributed to a shift in magma rheology into the brittle regime, and thus the ascent of high-viscosity magma can form discrete shear zones, comparable to tectonic faults, along conduit margins. Pseudotachylytes have, until now, rarely been noted in exogenous volcanic materials and seldom in active volcanic environments. This is despite the simultaneous occurrence of high pressures and differential stresses, which make high-viscosity magmas ideal candidates for the occurrence of frictional melting. Here, we compare the chemical, thermal, magnetic and structural properties of two candidate volcanic pseudotachylytes; one from Soufriere Hills (Montserrat) and one from Mount St. Helens (USA). Additionally, we present data from a set of high-velocity rotary shear experiments on the host materials of these natural pseudotachylytes in which melting was induced after just 10's of centimeters of slip at realistic extrusion velocities (0.4 - 1.6 ms-1) and low normal stresses (0.5-2 MPa). After 1-2 meters of slip a continuous melt layer formed, at which point friction decreased and the fault zone displayed slip-weakening behaviour. For volcanic conduits, this would facilitate temporarily elevated slip rates, or an increase in extrusion rate, and could cause transitions in dome morphology and eruption style. This study demonstrates that shear fracturing in magma or sliding along conduit margins can readily result in frictional melting. The conspicuous absence of pseudotachylytes in active volcanic environments is likely the result of exceptionally high background temperatures which precipitate near-equilibrium melting, thereby obviating one of the characteristic signatures of pseudotachylyte - glassy protomelts formed by selective melting of
Strontium isotopic ratios of Tertiary volcanic rocks of northeastern Honshu, Japan: implication for the spreading of the Japan Sea

International Nuclear Information System (INIS)

Kurasawa, Hajime; Konda, Tadashi.

1986-01-01

Strontium isotopic ratios of sixty-seven Tertiary volcanic rocks from the northeastern Honshu, Japan, were determined for the purpose of examining the genesis among the volcanic rocks. Two distince suites of volcanic rocks occur in the northeastern Honshu; the rocks older than 16 Ma (Monzen-Daijima Stege) of predominantly intermediate composition and the rocks younger than 16 Ma (Nishikurosawa-Funakawa Stege) with bimodal suite of mafic and felsic composition. Initial values of 87 Sr/ 86 Sr in the Teriary volcanic rocks from the northeastern Honshu, lie in the range from 0.7033 to 0.7068. High ( 87 Sr/ 86 Sr) I ratios are observed for the rocks older than 16 Ma from the Japan Sea side (H zone). It is noteworthy that the rocks younger than 16 Ma show significantly lower ( 87 Sr/ 86 Sr) I ratios in the Dewa Hill, Japan Sea coast and North Akita areas in the northeastern Honshu (L zone). The rocks younger than 16 Ma from the L zone can also be interpreted as having been originated as a mantle-diapir associated with the spreading of the Japan Sea basin. If the basaltic magma was formed from the diapir, the 87 Sr/ 86 Sr ratio would be close to the range from 0.7033 to 0.7037 as the low-Sr isotopic ratio zone (L zone) in the northeastern Honshu, Japan. (author)
Genesis of hydrothermal alterations using stable isotope geochemistry in Takestan area (Tarom zone

Directory of Open Access Journals (Sweden)

Batool Taghipou

2015-12-01

Full Text Available Hydrothermal alteration processes are extensively took place on volcanic and pyroclstics of Takestan area. Existence of abundant, deep fracturing and subvolcanic intrusions are enhanced extend hydrothermal alteration zones. The following alteration zones are determined: propylitic, argillic, advanced argillic and sillicic. There are outcropped and widespread in different size and limit. Formation of siliceous sinter, silicified tuffs with preserved primary sedimentary layering including pure mineralized alunite patches are most outstanding. Quartz, sussoritic plagioclase, chlorite, sericite and alunite are main mineral constituents in the volcanics. On the basis of geochemical data volcanic rocks are rhyolite, dacite, andesite, andesitic-basalt and basalt in composition. Acid-sulfate zone is the type of alteration in Tarom area and alunite is an index mineral of this zone. Results of 18O, D and 34S stable isotope geochemistry on altered minerals (muscovite, kaolinite and alunite, revealed that alteration fluids are magmatic in origin.
Flank Collapse Assessment At Kick-'em-Jenny Submarine Volcano (Lesser Antilles): A Combined Approach Using Modelling and Experiments

Science.gov (United States)

Dondin, F. J. Y.; Heap, M. J.; Robertson, R. E. A.; Dorville, J. F. M.; Carey, S.

2016-12-01

In the Lesser Antilles over 52 volcanic landslide episodes have been identified. These episodes serve as a testament to the hazard posed by volcanic landslides to a region composed of many islands that are small independent countries with vulnerable local economies. This study presents a relative slope stability analysis (RIA) to investigate the stability condition of the only active submarine volcano of the Lesser Antilles Arc: Kick-'em-Jenny Submarine Volcano (KeJ). Thus we hope to provide better constraint on the landslide source geometry to help mitigate volcanic landslide hazards at a KeJ. KeJ is located ca. 8 km north of Grenada island. KeJ lies within a collapse scar from a prehistorical flank collapse. This collapse was associated with a voluminous landslide deposit of about 4.4km3 with a 14 km runout. Numerial simulations showed that this event could generate a regional tsunami. We aim to quantify potential initial volumes of collapsed material using a RIA. The RIA evaluates the critical potential failure surface associated with factor of safety (Fs) inferior to unity and compares them to areas of deficit/surplus of mass/volume obtained from the comparison of an high resolution digital elevation model of the edifice with an ideal 3D surface. We use freeware programs VolcanoFit 2.0 and SSAP 4.7. and produce a 3D representation of the stability map. We report, for the first time, results of a Limit Equilibrium Method performed using geomechanical parameters retrieved from rock mechanics tests performed on two rock basaltic-andesite rock samples collected from within the crater of the volcano during the 1-18 November 2013 NA039 E/V Nautilus cruise. We performed triaxial and uniaxial deformation tests to obtain values of strength at the top and bottom of the edifice. We further characterized the permeability and P-wave velocity of the samples collected. The chosen internal structure for the model is composed of three bodies: (i) a body composed of basaltic
Holocene volcanic geology, volcanic hazard, and risk on Taveuni, Fiji

International Nuclear Information System (INIS)

Cronin, S.J.; Neall, V.E.

2001-01-01

The Holocene volcanic geology of Taveuni has been mapped in order to produce a volcanic hazard and risk assessment for the island. Taveuni is the third-largest island of the Fiji group and home to 14,500 people. At least cubic km 2.7 of olivine-alkali-basalt magma was erupted from over 100 events throughout the Holocene. Vents are concentrated along a northeast-striking rift zone that is parallel to other regional structural trends. There is an overall trend of younging southward along the rift. Holocene lavas and tephras are grouped within six newly defined eruptive periods, established on a basis of radiocarbon dating. Within these periods, 14 tephra layers, useful as local marker horizons, are recognised. At least 58% of Holocene eruptions produced lava flows, while almost all produced some tephra. Individual eruption event volumes ranged between 0.001 and cubic km 0.20 (dense rock equivalent). Many eruptions involved at least some phases of phreatic and/or phreato-magmatic activity, although dominant hydrovolcanic activity was limited to only a few events. A volcanic hazard map is presented, based on the Holocene geology map and statistical analyses of eruption recurrence. The highest levels of ground-based and near-vent hazards are concentrated along the southern portion of the island's rift axis, with the paths of initial lava flows predicted from present topography. Tephra fall hazards are based on eruption parameters interpreted from mapped Holocene tephra layers. Hawaiian explosive-style eruptions appear to be a dominant eruptive process, with prevailing low-level (<3 km) southeasterly winds dispersing most tephra to the northwestern quadrant. Vulnerable elements (population centres, infrastructure, and economy) on Taveuni have been considered in deriving a volcanic risk assessment for the island. A number of infrastructural and subdivision developments are either under way or planned for the island, driven by its highly fertile soils and availability of
Areal and time distributions of volcanic formations on Mars

International Nuclear Information System (INIS)

Katterfeld, G.N.; Vityaz, V.I.

1987-01-01

The analysis of igneous rock distribution has been fulfilled on the basis of the geomorphological map of Mars at scale 1:5,000,000, according to data obtained from interpretation of 1:2,000,000 scale pictures of Mariner 9, Mars 4, Mars 5, Viking 1 and 2. Areological areas are listed as having been distinguished as the stratigraphic basis for a martian time scale. The area of volcanic eruptions and the number of eruptive centers are calculated on 10 x 10 deg cells and for each areological eras. The largest area of eruptive happening at different times is related with Tharsis tectonic uplift. The study of distribution of igneous rock area and volcanic centers number on 10 deg sectors and zones revealed the concentration belts of volcanic formations
Areal and time distributions of volcanic formations on Mars

Science.gov (United States)

Katterfeld, G. N.; Vityaz, V. I.

1987-01-01

The analysis of igneous rock distribution has been fulfilled on the basis of the geomorphological map of Mars at scale 1:5,000,000, according to data obtained from interpretation of 1:2,000,000 scale pictures of Mariner 9, Mars 4, Mars 5, Viking 1 and 2. Areological areas are listed as having been distinguished as the stratigraphic basis for a martian time scale. The area of volcanic eruptions and the number of eruptive centers are calculated on 10 x 10 deg cells and for each areological eras. The largest area of eruptive happening at different times is related with Tharsis tectonic uplift. The study of distribution of igneous rock area and volcanic centers number on 10 deg sectors and zones revealed the concentration belts of volcanic formations.
Deformation of a Volcanic Edifice by Pore Pressurization: An Analog Approach

Science.gov (United States)

Hyman, D.; Bursik, M. I.

2015-12-01

Volcanic flank destabilization, preceded by pressurization-induced surface deformation or weakening, presents a significant hazard at stratovolcanoes with ample supply of magmatic volatiles or preexisting hydrothermal systems as in Bezymianny- and Bandai-type eruptions, respectively. Deformation is also an important sign of the nature of unrest at large calderas such as Long Valley, USA. Previous studies of volcanic inflation have focused primarily on the role of ascending magma. Relatively few studies have centered on surface deformation caused by pressurization from other volcanic fluids, including exsolved volatiles and pressurized hydrothermal systems. Most investigations of pore-pressurization have focused on numerical modelling of pore pressure transients. In analog experiments presented here, pore-filling fluids are injected into the base of a damp sand medium without exceeding dike propagating pressures, simulating the pressurization and bulk-permeable flow of volatile fluids through volcanic systems. The experiments examine surface deformation from a range of source depths and pressures as well as edifice geometries. 3D imaging is possible through use of the Microsoft® Kinect™ sensor, which allows for the generation of high-resolution, high frame rate, lab-scale Digital Elevation Models (DEMs). After initial processing to increase signal-to-noise ratio, surface deformation is measured using the DEM time-series generated by the Kinect™. Analysis of preliminary experiments suggests that inflation is possible up to approx. 10 % of pressure source depth. We also show that the Kinect™ sensor is useful in analog volcanological studies, an environment to which it is well-suited.
Reservoir Space Evolution of Volcanic Rocks in Deep Songliao Basin, China

Science.gov (United States)

Zheng, M.; Wu, X.; Zheng, M.; HU, J.; Wang, S.

2015-12-01

Recent years, large amount of natural gas has been discovered in volcanic rock of Lower Crataceous of Songliao basin. Volcanic reservoirs have become one of the important target reservoir types of eastern basin of China. In order to study the volcanic reservoirs, we need to know the main factors controlling the reservoir space. By careful obsercation on volcanic drilling core, casting thin sections and statistical analysis of petrophysical properties of volcanic reservoir in Songliao basin, it can be suggested that the igneous rock reservoir in Yingcheng formation of Lower Crataceous is composed of different rock types, such ad rohylite, rohylitic crystal tuff, autoclastic brecciation lava and so on. There are different reservoirs storage space in in various lithological igneous rocks, but they are mainly composed of primary stoma, secondary solution pores and fractures.The evolution of storage space can be divided into 3 stage: the pramary reservoir space,exogenic leaching process and burial diagenesis.During the evolution process, the reservoir space is effected by secondary minerals, tectonic movement and volcanic hydrothermal solution. The pore of volcanic reservoirs can be partially filled by secondary minerals, but also may be dissoluted by other chemical volcanic hydrothermal solution. Therefore, the favorable places for better-quality volcanic reservoirs are the near-crater facies of vocanic apparatus and dissolution zones on the high position of paleo-structures.
Hawaii's volcanoes revealed

Science.gov (United States)

Eakins, Barry W.; Robinson, Joel E.; Kanamatsu, Toshiya; Naka, Jiro; Smith, John R.; Takahashi, Eiichi; Clague, David A.

2003-01-01

Hawaiian volcanoes typically evolve in four stages as volcanism waxes and wanes: (1) early alkalic, when volcanism originates on the deep sea floor; (2) shield, when roughly 95 percent of a volcano's volume is emplaced; (3) post-shield alkalic, when small-volume eruptions build scattered cones that thinly cap the shield-stage lavas; and (4) rejuvenated, when lavas of distinct chemistry erupt following a lengthy period of erosion and volcanic quiescence. During the early alkalic and shield stages, two or more elongate rift zones may develop as flanks of the volcano separate. Mantle-derived magma rises through a vertical conduit and is temporarily stored in a shallow summit reservoir from which magma may erupt within the summit region or be injected laterally into the rift zones. The ongoing activity at Kilauea's Pu?u ?O?o cone that began in January 1983 is one such rift-zone eruption. The rift zones commonly extend deep underwater, producing submarine eruptions of bulbous pillow lava. Once a volcano has grown above sea level, subaerial eruptions produce lava flows of jagged, clinkery ?a?a or smooth, ropy pahoehoe. If the flows reach the ocean they are rapidly quenched by seawater and shatter, producing a steep blanket of unstable volcanic sediment that mantles the upper submarine slopes. Above sea level then, the volcanoes develop the classic shield profile of gentle lava-flow slopes, whereas below sea level slopes are substantially steeper. While the volcanoes grow rapidly during the shield stage, they may also collapse catastrophically, generating giant landslides and tsunami, or fail more gradually, forming slumps. Deformation and seismicity along Kilauea's south flank indicate that slumping is occurring there today. Loading of the underlying Pacific Plate by the growing volcanic edifices causes subsidence, forming deep basins at the base of the volcanoes. Once volcanism wanes and lava flows no longer reach the ocean, the volcano continues to submerge, while
Hemispherically Asymmetric Volcanic Forcing of Tropical Hydroclimate During the Last Millennium

Science.gov (United States)

Colose, Christopher M.; Legrande, Allegra N.; Vuille, Mathias

2016-01-01

Volcanic aerosols exert the most important natural radiative forcing of the last millennium. State-of-the-art paleoclimate simulations of this interval are typically forced with diverse spatial patterns of volcanic forcing, leading to different responses in tropical hydroclimate. Recently, theoretical considerations relating the intertropical convergence zone (ITCZ) position to the demands of global energy balance have emerged in the literature, allowing for a connection to be made between the paleoclimate simulations and recent developments in the understanding of ITCZ dynamics. These energetic considerations aid in explaining the well-known historical, paleoclimatic, and modeling evidence that the ITCZ migrates away from the hemisphere that is energetically deficient in response to asymmetric forcing. Here we use two separate general circulation model (GCM) suites of experiments for the last millennium to relate the ITCZ position to asymmetries in prescribed volcanic sulfate aerosols in the stratosphere and related asymmetric radiative forcing. We discuss the ITCZ shift in the context of atmospheric energetics and discuss the ramifications of transient ITCZ migrations for other sensitive indicators of changes in the tropical hydrologic cycle, including global streamflow. For the first time, we also offer insight into the large-scale fingerprint of water isotopologues in precipitation (delta sup 18 Op) in response to asymmetries in radiative forcing. The ITCZ shifts away from the hemisphere with greater volcanic forcing. Since the isotopic composition of precipitation in the ITCZ is relatively depleted compared to areas outside this zone, this meridional precipitation migration results in a large-scale enrichment (depletion) in the isotopic composition of tropical precipitation in regions the ITCZ moves away from (toward). Our results highlight the need for careful consideration of the spatial structure of volcanic forcing for interpreting volcanic signals in
Volcanism Studies: Final Report for the Yucca Mountain Project

Energy Technology Data Exchange (ETDEWEB)

Bruce M. Crowe; Frank V. Perry; Greg A. Valentine; Lynn M. Bowker

1998-12-01

This report synthesizes the results of volcanism studies conducted by scientists at the Los Alamos National Laboratory and collaborating institutions on behalf of the Department of Energy's Yucca Mountain Project. An assessment of the risk of future volcanic activity is one of many site characterization studies that must be completed to evaluate the Yucca Mountain site for potential long-term storage of high-level radioactive waste. The presence of several basaltic volcanic centers in the Yucca Mountain region of Pliocene and Quaternary age indicates that there is a finite risk of a future volcanic event occurring during the 10,000-year isolation period of a potential repository. Chapter 1 introduces the volcanism issue for the Yucca Mountain site and provides the reader with an overview of the organization, content, and significant conclusions of this report. The risk of future basaltic volcanism is the primary topic of concern including both events that intersect a potential repository and events that occur near or within the waste isolation system of a repository. Future volcanic events cannot be predicted with certainty but instead are estimated using formal methods of probabilistic volcanic hazard assessment (PVHA). Chapter 2 describes the volcanic history of the Yucca Mountain region (YMR) and emphasizes the Pliocene and Quaternary volcanic record, the interval of primary concern for volcanic risk assessment. The distribution, eruptive history, and geochronology of Plio-Quaternary basalt centers are described by individual center emphasizing the younger postcaldera basalt (<5 Ma). The Lathrop Wells volcanic center is described in detail because it is the youngest basalt center in the YMR. The age of the Lathrop Wells center is now confidently determined to be about 75 thousand years old. Chapter 3 describes the tectonic setting of the YMR and presents and assesses the significance of multiple alternative tectonic models. The Crater Flat volcanic zone is
The Role of Boron Chloride and noble gas isotope ratios in Taupo Volcanic Zone geothermal systems

International Nuclear Information System (INIS)

Hulston, J.R.

1995-01-01

The model of the geothermal system in which deep circulating groundwater con noble gases, at air saturated water concentrations, mixes with hot fluids of man origin at depth, is extended to include the effect of interaction of the ascending fluid with both solid and gaseous phases of basement (or other) rocks 'en route' the surface. It is demonstrated that this interaction is responsible for most of CO/sub 2/ in the Taupo Volcanic Zone (TVZ) geothermal systems. It is proposed th the modelling of this interaction might be accomplished by techniques similar to those used for the understanding of the oxygen isotope shift found in geothermal systems. The water rock interaction experiments of Ellis and Mahon (1964, 1967) provides some data on the kinetic rates for B and Cl dissolution from rocks like to be encountered in the geothermal system, but further information on the behaviour of B may be needed. If these problems can be overcome this modelling technique has promise for the estimation of the recharge of geothermal systems a hence the sustainability of these systems. (author). 17 refs., 4 figs

Volcanic history and petrography of the Pliocene Etrüsk Stratovolcano, E Turkey

Science.gov (United States)

Oyan, Vural; Keskin, Mehmet; Lebedev, Vladimir; Sharkov, Evgenii; Lustrino, Michele; Mattioli, Michele

2010-05-01

The Pliocene Etrusk volcano, with its 3100 m elevation and ~500 km2 area, is one of the major centers of the collision-related volcanism in E Anatolia. It is located in the northeast of Lake Van, sitting almost on the culmination of the "Lake Van dome" structure forming the vertex of the eastern Turkish high plateau (Sengor et al., 2008). A ~5-km-wide horseshoe-shaped caldera, open to the south, is located in the center of the volcano. Apart from two trace element analyses and two K/Ar dates, there are virtually no data available in the literature on this major eruption center. Our study intends to fill this gap with a detailed petrographical, geochemical and geochronological study. Our new K/Ar age determinations indicate that the main volcanic edifice of the Etrusk volcano was formed in period between 4.3 and 3.9 Ma, with the eruption of several intermediate to acid lavas from a central vent. This phase ended up with the formation of a small collapse caldera that produced pyroclastic material emplaced on the earlier lavas. The final impulse of the volcano activity from the Etrusk volcanic center was the eruption of a post-caldera rhyolitic lava flow from the southern flank of the volcano (~3.8-3.7 Ma). After about 2.7 Myr of magmatic quiescence, during the Quaternary time between ~1 and 0.43 Ma, basalts erupted from the SW flank of the Etrusk volcano. They were generated predominantly from a ~N-S extending fissure, as well as from a scoria cone (Karniyarik hill) and a maar-shaped volcanic center (i.e. Düzgeyikçukuru). Edifice-forming products of the Etrüsk stratovolcano are represented by sanidine-plagioclase-biotite-clinopyroxene-phyric trachytes and plagioclase-clinopyroxene-orthopyroxene-phyric trachyandesites containing sporadic olivine phenocrysts. K-feldspar is the most abundant mineral phase in trachitic lavas of the Etrüsk volcanic system. Post caldera lavas, on the other hand, have relatively more evolved compositions ranging from trachydacite to
Multiple edifice-collapse events in the Eastern Mexican Volcanic Belt: The role of sloping substrate and implications for hazard assessment

Science.gov (United States)

Carrasco-Nunez, Gerardo; Diaz-Castellon, Rodolfo; Siebert, L.; Hubbard, B.; Sheridan, M.F.; Rodriguez, Sergio R.

2006-01-01

The Citlalte??petl-Cofre de Perote volcanic chain forms an important physiographic barrier that separates the Central Altiplano (2500??masl) from the Gulf Coastal Plain (GCP) (1300??masl). The abrupt eastward drop in relief between these provinces gives rise to unstable conditions and consequent gravitational collapse of large volcanic edifices built at the edge of the Altiplano. Eastward sloping substrate, caused by the irregular configuration of the basement rocks, is the dominant factor that controls the direction of collapsing sectors in all major volcanoes in the region to be preferentially towards the GCP. These collapses produced voluminous debris avalanches and lahars that inundated the well-developed drainages and clastic aprons that characterize the Coastal Plain. Large catastrophic collapses from Citlalte??petl, Las Cumbres, and Cofre de Perote volcanoes are well documented in the geologic record. Some of the avalanches and transformed flows have exceptionally long runouts and reach the Gulf of Mexico traveling more than 120??km from their source. So far, no direct evidence has been found for magmatic activity associated with the initiation of these catastrophic flank-collapses. Apparently, instability of the volcanic edifices has been strongly favored by very intense hydrothermal alteration, abrupt topographic change, and intense fracturing. In addition to the eastward slope of the substrate, the reactivation of pre-volcanic basement structures during the Late Tertiary, and the E-W to ENE-SSW oriented regional stress regimes may have played an important role in the preferential movement direction of the avalanches and flows. In addition to magmatic-hydrothermal processes, high amounts of rainfall in the area is another factor that enhances alteration and eventually weakens the rocks. It is very likely that seismic activity may be the principal triggering mechanism that caused the flank collapse of large volcanic edifices in the Eastern Mexican Volcanic
Volcanic Supersites as cross-disciplinary laboratories

Science.gov (United States)

Provenzale, Antonello; Beierkuhnlein, Carl; Giamberini, Mariasilvia; Pennisi, Maddalena; Puglisi, Giuseppe

2017-04-01

Volcanic Supersites, defined in the frame of the GEO-GSNL Initiative, are usually considered mainly for their geohazard and geological characteristics. However, volcanoes are extremely challenging areas from many other points of view, including environmental and climatic properties, ecosystems, hydrology, soil properties and biogeochemical cycling. Possibly, volcanoes are closer to early Earth conditions than most other types of environment. During FP7, EC effectively fostered the implementation of the European volcano Supersites (Mt. Etna, Campi Flegrei/Vesuvius and Iceland) through the MED-SUV and FUTUREVOLC projects. Currently, the large H2020 project ECOPOTENTIAL (2015-2019, 47 partners, http://www.ecopotential-project.eu/) contributes to GEO/GEOSS and to the GEO ECO Initiative, and it is devoted to making best use of remote sensing and in situ data to improve future ecosystem benefits, focusing on a network of Protected Areas of international relevance. In ECOPOTENTIAL, remote sensing and in situ data are collected, processed and used for a better understanding of the ecosystem dynamics, analysing and modelling the effects of global changes on ecosystem functions and services, over an array of different ecosystem types, including mountain, marine, coastal, arid and semi-arid ecosystems, and also areas of volcanic origin such as the Canary and La Reunion Islands. Here, we propose to extend the network of the ECOPOTENTIAL project to include active Volcanic Supersites, such as Mount Etna and other volcanic Protected Areas, and we discuss how they can be included in the framework of the ECOPOTENTIAL workflow. A coordinated and cross-disciplinary set of studies at these sites should include geological, biological, ecological, biogeochemical, climatic and biogeographical aspects, as well as their relationship with the antropogenic impact on the environment, and aim at the global analysis of the volcanic Earth Critical Zone - namely, the upper layer of the Earth
Stratigraphy and structure of volcanic rocks in drill hole USW-G1, Yucca Mountain, Nye County, Nevada

International Nuclear Information System (INIS)

Spengler, R.W.; Byers, F.M. Jr.; Warner, J.B.

1981-01-01

Detailed subsurface studies in connection with the Nevada Nuclear Waste Storage Investigations program are being conducted to investigate the stratigraphic and structural features of volcanic rocks underlying Yucca Mountain, a volcanic highland situated along the western boundary of the Nevada Test Site in southern Nevada. As part of this continuing effort, drill hole USW-G1 was cored from 292 ft to a depth of 6000 ft from March to August 1980. The stratigraphic section is composed of thick sequences of ash-flow tuff and volcanic breccia interbedded with subordinate amounts of fine- to coarse-grained volcaniclastic rocks. All rocks are of Tertiary age and vary in composition from rhyolite to dacite. The 3005-ft level in the drill hole represents a significant demarcation between unaltered and altered volcanic rocks. For the most part, tuff units above 3005 ft appear devitrified and show little secondary alteration except within tuffaceous beds of Calico Hills, where the rock contains 60 to 80% zeolites. Below 3005 ft, most rocks show intermittent to pervasive alteration to clay minerals and zeolites. Examination of core for structural features revealed the presence of 61 shear fractures, 528 joints, and 4 conspicuous fault zones. Shear fractures mainly occurred in the Topopah Spring Member of the Paintbrush Tuff, flow breccia, and near fault zones. Nearly 88% of shear and joint surfaces show evidence of coatings. Approximately 40% of the fractures were categorized as completely healed. Rock quality characteristics as defined by the core index indicate that greater amounts of broken and lost core are commonly associated with (1) the densely welded zone of the Topopah Spring, (2) highly silicified zones, and (3) fault zones
Volcanic activity in the Acambay Graben: a < 25 Ka subplinian eruption from the Temascalcingo volcano and implications for volcanic hazard.

Science.gov (United States)

Pedrazzi, Dario; Aguirre Díaz, Gerardo; Sunyé Puchol, Ivan; Bartolini, Stefania; Geyer, Adelina

2016-04-01

The Trans-Mexican Volcanic Belt (TMVB) contains a large number of stratovolcanoes, some well-known, as Popocatepetl, Iztaccihuatl, Nevado de Toluca, or Colima and many others of more modest dimensions that are not well known but constitute the majority in the TMVB. Such volcanoes are, for example, Tequila, San Juan, Sangangüey, Cerro Culiacán, Cerro Grande, El Zamorano, La Joya, Palo Huerfano, Jocotitlán, Altamirano and Temascalcingo, among many others. The Temascalcingo volcano (TV) is an andesitic-dacitic stratovolcano located in the Trans-Mexican Volcanic Belt (TMVB) at the eastern part of the Acambay Graben (northwest portion of Estado de México). The TV is composed mainly by dacitic, porphyritic lavas, block and ash deposits and subordinate pumice fall deposits and ignimbrites (Roldán-Quintana et al., 2011). The volcanic structure includes a summit caldera that has a rectangular shape, 2.5×3.5 km, with the largest side oriented E-W, parallel to major normal faults affecting the edifice. The San Mateo Pumice eruption is one of the greatest paroxysmal episodes of this volcano with pumice deposits mainly exposed at the scarp of the Acambay-Tixmadeje fault and at the northern and northeastern flanks of TV. It overlies a paleosol dated at 25 Ka. A NE-trending dispersion was obtained from field data covering an area of at least 80 km2. These deposits overlie older lava flows and mud flows and are discontinuously covered and eroded by younger reworked deposits of Temascalcingo volcano. This event represents a highly explosive phase that generated a relatively thick and widespread pumice fallout deposit that may occur again in future eruptions. A similar eruption today would have a significantly impact in the region, overall due to the fact that there has been no systematic assessment of the volcanic hazard in any of the studies that have been conducted so far in the area. So, this is a pending and urgent subject that must be tackled without delay. Financed by
Low-pressure evolution of arc magmas in thickened crust: The San Pedro-Linzor volcanic chain, Central Andes, Northern Chile

Science.gov (United States)

Godoy, Benigno; Wörner, Gerhard; Kojima, Shoji; Aguilera, Felipe; Simon, Klaus; Hartmann, Gerald

2014-07-01

Magmatism at Andean Central Volcanic Zone (CVZ), or Central Andes, is strongly influenced by differentiation and assimilation at high pressures that occurred at lower levels of the thick continental crust. This is typically shown by high light to heavy rare earth element ratios (LREE/HREE) of the erupted lavas at this volcanic zone. Increase of these ratios with time is interpreted as a change to magma evolution in the presence of garnet during evolution of Central Andes. Such geochemical signals could be introduced into the magmas be high-pressure fractionation with garnet on the liquidus and/or assimilation from crustal rocks with a garnet-bearing residue. However, lavas erupted at San Pedro-Linzor volcanic chain show no evidence of garnet fractionation in their trace element patterns. This volcanic chain is located in the active volcanic arc, between 22°00‧S and 22°30‧S, over a continental crust ˜70 km thick. Sampled lavas show Sr/Y and Sm/Yb ratios Chile. We relate our geochemical observations to shallow crustal evolution of primitive magmas involving a high degree of assimilation of upper continental crust. We emphasize that low pressure AFC- (Assimilation Fractional Crystallization) type evolution of the San Pedro-Linzor volcanic chain reflects storage, fractionation, and contamination of mantle-derived magmas at the upper felsic crust (<40 km depth). The ascent of mantle-derived magmas to mid-crustal levels is related with the extensional regime that has existed in this zone of arc-front offset since Late-Miocene age, and the relatively thin portion of mafic lower crust observed below the volcanic chain.
Hybridization Capture Using Short PCR Products Enriches Small Genomes by Capturing Flanking Sequences (CapFlank)

DEFF Research Database (Denmark)

Tsangaras, Kyriakos; Wales, Nathan; Sicheritz-Pontén, Thomas

2014-01-01

nucleotides) can result in enrichment across entire mitochondrial and bacterial genomes. Our findings suggest that some of the off-target sequences derived in capture experiments are non-randomly enriched, and that CapFlank will facilitate targeted enrichment of large contiguous sequences with minimal prior...
Volcanic and Hydrothermal Activity of the North Su Volcano: New Insights from Repeated Bathymetric Surveys and ROV Observations

Science.gov (United States)

Thal, J.; Bach, W.; Tivey, M.; Yoerger, D.

2013-12-01

Bathymetric data from cruises in 2002, 2006, and 2011 were combined and compared to determine the evolution of volcanic activity, seafloor structures, erosional features and to identify and document the distribution of hydrothermal vents on North Su volcano, SuSu Knolls, eastern Manus Basin (Papua New Guinea). Geologic mapping based on ROV observations from 2006 (WHOI Jason-2) and 2011 (MARUM Quest-4000) combined with repeated bathymetric surveys from 2002 and 2011 are used to identify morphologic features on the slopes of North Su and to track temporal changes. ROV MARUM Quest-4000 bathymetry was used to develop a 10 m grid of the top of North Su to precisely depict recent changes. In 2006, the south slope of North Su was steeply sloped and featured numerous white smoker vents discharging acid sulfate waters. These vents were covered by several tens of meters of sand- to gravel-sized volcanic material in 2011. The growth of this new cone changed the bathymetry of the south flank of North Su up to ~50 m and emplaced ~0.014 km3 of clastic volcanic material. This material is primarily comprised of fractured altered dacite and massive fresh dacite as well as crystals of opx, cpx, olivine and plagioclase. There is no evidence for pyroclastic fragmentation, so we hypothesize that the fragmentation is likely related to hydrothermal explosions. Hydrothermal activity varies over a short (~50 m) lateral distance from 'flashing' black smokers to acidic white smoker vents. Within 2 weeks of observation time in 2011, the white smoker vents varied markedly in activity suggesting a highly episodic hydrothermal system. Based on ROV video recordings, we identified steeply sloping (up to 30°) slopes exposing pillars and walls of hydrothermal cemented volcaniclastic material representing former fluid upflow zones. These features show that hydrothermal activity has increased slope stability as hydrothermal cementation has prevented slope collapse. Additionally, in some places
Depleted arc volcanism in the Alboran Sea and shoshonitic volcanism in Morocco: geochemical and isotopic constraints on Neogene tectonic processes

Science.gov (United States)

Gill, R. C. O.; Aparicio, A.; El Azzouzi, M.; Hernandez, J.; Thirlwall, M. F.; Bourgois, J.; Marriner, G. F.

2004-12-01

Samples of volcanic rocks from Alborán Island, the Alboran Sea floor and from the Gourougou volcanic centre in northern Morocco have been analyzed for major and trace elements and Sr-Nd isotopes to test current theories on the tectonic geodynamic evolution of the Alboran Sea. The Alborán Island samples are low-K tholeiitic basaltic andesites whose depleted contents of HFS elements (˜0.5×N-MORB), especially Nb (˜0.2×N-MORB), show marked geochemical parallels with volcanics from immature intra-oceanic arcs and back-arc basins. Several of the submarine samples have similar compositions, one showing low-Ca boninite affinity. 143Nd/ 144Nd ratios fall in the same range as many island-arc and back-arc basin samples, whereas 87Sr/ 86Sr ratios (on leached samples) are somewhat more radiogenic. Our data point to active subduction taking place beneath the Alboran region in Miocene times, and imply the presence of an associated back-arc spreading centre. Our sea floor suite includes a few more evolved dacite and rhyolite samples with ( 87Sr/ 86Sr) 0 up to 0.717 that probably represent varying degrees of crustal melting. The shoshonite and high-K basaltic andesite lavas from Gourougou have comparable normalized incompatible-element enrichment diagrams and Ce/Y ratios to shoshonitic volcanics from oceanic island arcs, though they have less pronounced Nb deficits. They are much less LIL- and LREE-enriched than continental arc analogues and post-collisional shoshonites from Tibet. The magmas probably originated by melting in subcontinental lithospheric mantle that had experienced negligible subduction input. Sr-Nd isotope compositions point to significant crustal contamination which appears to account for the small Nb anomalies. The unmistakable supra-subduction zone (SSZ) signature shown by our Alboran basalts and basaltic andesite samples refutes geodynamic models that attribute all Neogene volcanism in the Alboran domain to decompression melting of upwelling asthenosphere
Unilateral flank ovariohysterectomy in guinea pigs (Cavia porcellus).

Science.gov (United States)

Rozanska, D; Rozanski, P; Orzelski, M; Chlebicka, N; Putowska, K

2016-11-01

To describe a simple, minimally invasive method of ovariohysterectomy via a unilateral flank approach in guinea pigs, for use in routine desexing of healthy female guinea pigs or treatment of ovarian cysts. The subjects of this retrospective study were 41 client-owned guinea pigs submitted for routine desexing or treatment of ovarian cysts. They included 16 healthy female guinea pigs aged 8-12 months (Group 1), and 15 females aged from 9 months to 3 years (Group 2), and 10 females aged from 3 to 7 years (Group 3) with different-sized ovarian cysts. Prior to surgery, the animals received clinical examination, blood testing (complete blood count and serum biochemistry profile) and examination of the abdomen using ultrasonography, to assess the condition of the reproductive tract and ensure the guinea pigs were fit for surgery. Ovariohysterectomy was performed via a unilateral flank incision made close to the erector spinae muscle starting approximately 1 cm caudal to the last rib. Both ovaries, uterine horns, and the uterine cervix were localised, ligated, and dissected through this unilateral retroperitoneal incision. Ovariohysterectomy was successfully completed via a single flank incision in 38/41 (93%) guinea pigs. Three guinea pigs with ovarian cysts from Group 3, which were >6 years old died during surgery due to circulatory and respiratory failure under anaesthesia. In the remaining 38 cases, surgery proceeded without complications. A further two guinea pigs from Group 3 were reluctant to move or eat for the first 3 days after surgery but recovered after provision of supportive care. All 38 animals fully recovered and wound healing was normal. This is the first report of ovariohysterectomy via a unilateral flank incision in guinea pigs. This approach is a simple, minimally invasive and safe alternative to the midline or bilateral flank approaches currently used for surgery of the reproductive tract in guinea pigs.
Initiation of long-term coupled microbiological, geochemical, and hydrological experimentation within the seafloor at North Pond, western flank of the Mid-Atlantic Ridge

Science.gov (United States)

Edwards, K.J.; Backert, N.; Bach, W.; Becker, K.; Klaus, A.; Griffin, Dale W.; Anderson, L.; Haddad, A.G.; Harigane, Y.; Campion, P.L.; Hirayama, H.; Mills, H.J.; Hulme, S.M.; Nakamura, K.; Jorgensen, S.L.; Orcutt, B.; Insua, T.L.; Park, Y.-S.; Rennie, V.; Salas, E.C.; Rouxel, O.; Wang, F.; Russel, J.A.; Wheat, C.G.; Sakata, K.; Brown, M.; Magnusson, J.L.; Ettlinger, Z.

2012-01-01

Integrated Ocean Drilling Program (IODP) Expedition 336 successfully initiated subseafloor observatory science at a young mid-ocean-ridge flank setting. All of the drilled sites are located in the North Pond region of the Atlantic Ocean (22??45'N, 46??05'W) in 4414-4483 m water depth. This area is known from previous ocean drilling and site survey investigations as a site of particularly vigorous circulation of seawater in permeable 8 Ma basaltic basement underlying a logged in Holes U1382A and U1383C. Upper oceanic crust in Hole U1382A, which is only 50 m west of Deep Sea Drilling Project (DSDP) Hole 395A, recovered 32 m of core between 110 and 210 meters below seafloor (mbsf). Core recovery in basement was 32%, yielding a number of volcanic flow units with distinct geochemical and petrographic characteristics. A unit of sedimentary breccia containing clasts of basalt, gabbroic rocks, and mantle peridotite was found intercalated between two volcanic flow units and was interpreted as a rock slide deposit. From Hole U1383C we recovered 50.3 m of core between 69.5 and 331.5 mbsf (19%). The basalts are aphyric to highly plagioclase-olivine-phyric tholeiites that fall on a liquid line of descent controlled by olivine fractionation. They are fresh to moderately altered, with clay minerals (saponite, nontronite, and celadonite), Fe oxyhydroxide, carbonate, and zeolite as secondary phases replacing glass and olivine to variable extents. In addition to traditional downhole logs, we also used a new logging tool for detecting in situ microbial life in ocean floor boreholes-the Deep Exploration Biosphere Investigative tool (DEBI-t). Sediment thickness was ???90 m at Sites U1382 and U1384 and varied between 38 and 53 m at Site U1383. The sediments are predominantly nannofossil ooze with layers of coarse foraminiferal sand and occasional pebble-size clasts of basalt, serpentinite, gabbroic rocks, and bivalve debris. The bottommost meters of sections cored with the advanced
Volcanic risk perception in the Campi Flegrei area

Science.gov (United States)

Ricci, T.; Barberi, F.; Davis, M. S.; Isaia, R.; Nave, R.

2013-03-01

The Campi Flegrei which includes part of the city of Naples, is an active volcanic system; its last eruption occurred in 1538 AD. More recently two significant crises occurred between 1969 and 72 and 1982-84 and were accompanied by ground movements (bradyseism) and seismic activity, forcing people of the town of Pozzuoli to be evacuated. Since 1984 development of a volcanic emergency plan has been underway. In 2000 Civil Protection published a risk map which defined the Red Zone, an area highly at risk from pyroclastic flows, which would need to be evacuated before an eruption. The first study to evaluate the volcanic risk perceptions of the people living within the Campi Flegrei area was completed in spring 2006, resulting in the largest sample ever studied on this topic except for one on Vesuvio area residents by Barberi et al. (2008). A 46 item questionnaire was distributed to 2000 of the approximately 300,000 residents of the Campi Flegrei Red Zone, which includes three towns and four neighborhoods within the city of Naples. A total of 1161 questionnaires were returned, for an overall response rate of 58%. Surveys were distributed to junior high and high school students, as well as to adult members of the general population. Results indicated that unlike issues such as crime, traffic, trash, and unemployment, volcanic hazards are not spontaneously mentioned as a major problem facing their community. However, when asked specific questions about volcanic risks, respondents believe that an eruption is likely and could have serious consequences for themselves and their communities and they are quite worried about the threat. Considering the events of 1969-72 and 1982-84, it was not surprising that respondents indicated earthquakes and ground deformations as more serious threats than eruptive phenomena. Of significant importance is that only 17% of the sample knows about the existence of the Emergency Plan, announced in 2001, and 65% said that they have not received
SYSTHESIS OF VOLCANISM STUDIES FOR THE YUCCA MOUNTAIN SITE CHARACTERIZATION PROJECT

International Nuclear Information System (INIS)

FV PERRY; GA CROWE; GA VALENTINE; LM BOWKER

1997-01-01

This report synthesizes the results of volcanism studies conducted by scientists at the Los Alamos National Laboratory and collaborating institutions on behalf of the Department of Energy's Yucca Mountain Project. Chapter 1 introduces the volcanism issue for the Yucca Mountain site and provides the reader with an overview of the organization, content, and significant conclusions of this report. The hazard of future basaltic volcanism is the primary topic of concern including both events that intersect a potential repository and events that occur near or within the waste isolation system of a repository. Future volcanic events cannot be predicted with certainty but instead are estimated using formal methods of probabilistic volcanic hazard assessment (PVHA). Chapter 2 describes the volcanic history of the Yucca Mountain region (YMR) and emphasizes the Pliocene and Quaternary volcanic record, the interval of primary concern for volcanic risk assessment. The distribution, eruptive history, and geochronology of Plio-Quaternary basalt centers are described by individual center emphasizing the younger postcaldera basalt ( -7 events per year. Bounding probability estimates are used to assess possible implications of not drilling aeromagnetic anomalies in the Arnargosa Valley and Crater Flat. The results of simulation modeling are used to assess the sensitivity of the disruption probability for the location of northeast boundaries of volcanic zones near the Yucca Mountain site. A new section on modeling of radiological releases associated with surface and subsurface magmatic activity has been added to chapter 6. The modeling results are consistent with past total system performance assessments that show future volcanic and magmatic events are not significant components of repository performance and volcanism is not a priority issue for performance assessment studies
File list: InP.Emb.50.AllAg.Embryonic_flank [Chip-atlas[Archive

Lifescience Database Archive (English)

Full Text Available InP.Emb.50.AllAg.Embryonic_flank mm9 Input control Embryo Embryonic flank SRX804059... http://dbarchive.biosciencedbc.jp/kyushu-u/mm9/assembled/InP.Emb.50.AllAg.Embryonic_flank.bed ...
Petrogenesis and tectonic implication of the Late Triassic post-collisional volcanic rocks in Chiang Khong, NW Thailand

Science.gov (United States)

Qian, Xin; Wang, Yuejun; Feng, Qinglai; Zi, Jian-Wei; Zhang, Yuzhi; Chonglakmani, Chongpan

2016-04-01

The volcanic rocks exposed within the Chiang Khong-Lampang-Tak igneous zone in NW Thailand provide important constraints on the tectonic evolution of the eastern Paleotethys ocean. An andesite sample from the Chiang Khong area yields a zircon U-Pb age of 229 ± 4 Ma, significantly younger than the continental-arc and syn-collisional volcanic rocks (ca. 238-241 Ma). The Chiang Khong volcanic rocks are characterized by low MgO (1.71-6.72 wt.%) and high Al2O3 (15.03-17.76 wt.%). They are enriched in LILEs and LREEs and depleted in HFSEs, and have 87Sr/86Sr (i) ratios of 0.7050-0.7065, εNd (t) of - 0.32 to - 1.92, zircon εHf (t) and δ18O values of 3.5 to - 11.7 and 4.30-9.80 ‰, respectively. The geochemical data for the volcanic rocks are consistent with an origin from the enriched lithospheric mantle that had been modified by slab-derived fluid and recycled sediments. Based on available geochronological and geochemical evidences, we propose that the Late Triassic Chiang Khong volcanic rocks are equivalent to the contemporaneous volcanic rocks in the Lancangjiang igneous zone in SW China. The formation of these volcanic rocks was possibly related to the upwelling of the asthenospheric mantle during the Late Triassic, shortly after slab detachment, which induced the melting of the metasomatized mantle wedge.
Thermal structure and geodynamics of subduction zones

Science.gov (United States)

Wada, Ikuko

The thermal structure of subduction zones depends on the age-controlled thermal state of the subducting slab and mantle wedge flow. Observations indicate that the shallow part of the forearc mantle wedge is stagnant and the slab-mantle interface is weakened. In this dissertation, the role of the interface strength in controlling mantle wedge flow, thermal structure, and a wide range of subduction zone processes is investigated through two-dimensional finite-element modelling and a global synthesis of geological and geophysical observations. The model reveals that the strong temperature-dependence of the mantle strength always results in full slab-mantle decoupling along the weakened part of the interface and hence complete stagnation of the overlying mantle. The interface immediately downdip of the zone of decoupling is fully coupled, and the overlying mantle is driven to flow at a rate compatible with the subduction rate. The sharpness of the transition from decoupling to coupling depends on the rheology assumed and increases with the nonlinearity of the flow system. This bimodal behaviour of the wedge flow gives rise to a strong thermal contrast between the cold stagnant and hot flowing parts of the mantle wedge. The maximum depth of decoupling (MDD) thus dictates the thermal regime of the forearc. Observed surface heat flow patterns and petrologically and geochemically estimated mantle wedge temperatures beneath the volcanic arc require an MDD of 70--80 km in most, if not all, subduction zones regardless of their thermal regime of the slab. The common MDD of 70--80 km explains the observed systematic variations of the petrologic, seismological, and volcanic processes with the thermal state of the slab and thus explains the rich diversity of subduction zones in a unified fashion. Models for warm-slab subduction zones such as Cascadia and Nankai predict shallow dehydration of the slab beneath the cold stagnant part of the mantle wedge, which provides ample fluid
Exceptional recurrence of flank destabilizations in the recent activity of the Colima volcanic complex, Mexico; Recurrence exceptionnelle de destabilisations de flanc dans l`activite recente du complexe volcanique du Colima, Mexique

Energy Technology Data Exchange (ETDEWEB)

Komorowski, J C [IPGP, (Mexico); Siebe, C [Institut de Geofisica, UNAM (Mexico); Rodriguez, S [Institut de Geologia, UNAM (Mexico); Cortes, A; Navarro, C; Gavilanes, J C

1997-12-31

This short paper reports on new {sup 14}C datings of debris flow units from the Nevado de Colima and Fuego de Colima volcanoes in Mexico. These new datings in connection with a detailed stratigraphic study in the deep canyons around the volcanoes has revealed an exceptional recurrence of flank destabilizations of the Fuego de Colima during the last 45000 years. The cumulated volume of debris in the whole Colima massif is estimated to 60-100 km{sup 3}. The correlation between Landsat satellite pictures and the distribution and age of the debris flows shows that both volcanoes are made of several post-destabilization remaining structures, and that both volcanoes were active and simultaneously collapsed 18500 years ago. The numerous fluvial-lacustrine sequences intercalated between the successive flows indicate that the debris flow were partially sedimented under water and could have led to catastrophic tsunamis towards the Pacific coast. Implications of this work are important because a population of more than 200000 inhabitants is living in a zone covered by several debris flows. (J.S.).
Exceptional recurrence of flank destabilizations in the recent activity of the Colima volcanic complex, Mexico; Recurrence exceptionnelle de destabilisations de flanc dans l`activite recente du complexe volcanique du Colima, Mexique

Energy Technology Data Exchange (ETDEWEB)

Komorowski, J.C. [IPGP, (Mexico); Siebe, C. [Institut de Geofisica, UNAM (Mexico); Rodriguez, S. [Institut de Geologia, UNAM (Mexico); Cortes, A.; Navarro, C.; Gavilanes, J.C.

1996-12-31

This short paper reports on new {sup 14}C datings of debris flow units from the Nevado de Colima and Fuego de Colima volcanoes in Mexico. These new datings in connection with a detailed stratigraphic study in the deep canyons around the volcanoes has revealed an exceptional recurrence of flank destabilizations of the Fuego de Colima during the last 45000 years. The cumulated volume of debris in the whole Colima massif is estimated to 60-100 km{sup 3}. The correlation between Landsat satellite pictures and the distribution and age of the debris flows shows that both volcanoes are made of several post-destabilization remaining structures, and that both volcanoes were active and simultaneously collapsed 18500 years ago. The numerous fluvial-lacustrine sequences intercalated between the successive flows indicate that the debris flow were partially sedimented under water and could have led to catastrophic tsunamis towards the Pacific coast. Implications of this work are important because a population of more than 200000 inhabitants is living in a zone covered by several debris flows. (J.S.).
Sequential assimilation of volcanic monitoring data to quantify eruption potential: Application to Kerinci volcano

Science.gov (United States)

Zhan, Yan; Gregg, Patricia M.; Chaussard, Estelle; Aoki, Yosuke

2017-12-01

Quantifying the eruption potential of a restless volcano requires the ability to model parameters such as overpressure and calculate the host rock stress state as the system evolves. A critical challenge is developing a model-data fusion framework to take advantage of observational data and provide updates of the volcanic system through time. The Ensemble Kalman Filter (EnKF) uses a Monte Carlo approach to assimilate volcanic monitoring data and update models of volcanic unrest, providing time-varying estimates of overpressure and stress. Although the EnKF has been proven effective to forecast volcanic deformation using synthetic InSAR and GPS data, until now, it has not been applied to assimilate data from an active volcanic system. In this investigation, the EnKF is used to provide a “hindcast” of the 2009 explosive eruption of Kerinci volcano, Indonesia. A two-sources analytical model is used to simulate the surface deformation of Kerinci volcano observed by InSAR time-series data and to predict the system evolution. A deep, deflating dike-like source reproduces the subsiding signal on the flanks of the volcano, and a shallow spherical McTigue source reproduces the central uplift. EnKF predicted parameters are used in finite element models to calculate the host-rock stress state prior to the 2009 eruption. Mohr-Coulomb failure models reveal that the shallow magma reservoir is trending towards tensile failure prior to 2009, which may be the catalyst for the 2009 eruption. Our results illustrate that the EnKF shows significant promise for future applications to forecasting the eruption potential of restless volcanoes and hind-cast the triggering mechanisms of observed eruptions.
Crustal-scale recycling in caldera complexes and rift zones along the Yellowstone hotspot track: O and Hf isotopic evidence in diverse zircons from voluminous rhyolites of the Picabo volcanic field, Idaho

Science.gov (United States)

Drew, Dana L.; Bindeman, Ilya N.; Watts, Kathryn E.; Schmitt, Axel K.; Fu, Bin; McCurry, Michael

2013-01-01

Rhyolites of the Picabo volcanic field (10.4–6.6 Ma) in eastern Idaho are preserved as thick ignimbrites and lavas along the margins of the Snake River Plain (SRP), and within a deep (>3 km) borehole near the central axis of the Yellowstone hotspot track. In this study we present new O and Hf isotope data and U–Pb geochronology for individual zircons, O isotope data for major phenocrysts (quartz, plagioclase, and pyroxene), whole rock Sr and Nd isotope ratios, and whole rock geochemistry for a suite of Picabo rhyolites. We synthesize our new datasets with published Ar–Ar geochronology to establish the eruptive framework of the Picabo volcanic field, and interpret its petrogenetic history in the context of other well-studied caldera complexes in the SRP. Caldera complex evolution at Picabo began with eruption of the 10.44±0.27 Ma (U–Pb) Tuff of Arbon Valley (TAV), a chemically zoned and normal-δ18O (δ18O magma=7.9‰) unit with high, zoned 87Sr/86Sri (0.71488–0.72520), and low-εNd(0) (−18) and εHf(0) (−28). The TAV and an associated post caldera lava flow possess the lowest εNd(0) (−23), indicating ∼40–60% derivation from the Archean upper crust. Normal-δ18O rhyolites were followed by a series of lower-δ18O eruptions with more typical (lower crustal) Sr–Nd–Hf isotope ratios and whole rock chemistry. The voluminous 8.25±0.26 Ma West Pocatello rhyolite has the lowest δ18O value (δ18Omelt=3.3‰), and we correlate it to a 1,000 m thick intracaldera tuff present in the INEL-1 borehole (with published zircon ages 8.04–8.35 Ma, and similarly low-δ18O zircon values). The significant (4–5‰) decrease in magmatic-δ18O values in Picabo rhyolites is accompanied by an increase in zircon δ18O heterogeneity from ∼1‰ variation in the TAV to >5‰ variation in the late-stage low-δ18O rhyolites, a trend similar to what is characteristic of Heise and Yellowstone, and which indicates remelting of variably hydrothermally altered tuffs

Determining Volcanic Deformation at San Miguel Volcano, El Salvador by Integrating Radar Interferometry and Seismic Analyses

Science.gov (United States)

Schiek, C. G.; Hurtado, J. M.; Velasco, A. A.; Buckley, S. M.; Escobar, D.

2008-12-01

From the early 1900's to the present day, San Miguel volcano has experienced many small eruptions and several periods of heightened seismic activity, making it one of the most active volcanoes in the El Salvadoran volcanic chain. Prior to 1969, the volcano experienced many explosive eruptions with Volcano Explosivity Indices (VEI) of 2. Since then, eruptions have decreased in intensity to an average VEI of 1. Eruptions mostly consist of phreatic explosions and central vent eruptions. Due to the explosive nature of this volcano, it is important to study the origins of the volcanism and its relationship to surface deformation and earthquake activity. We analyze these interactions by integrating interferometric synthetic aperture radar (InSAR) results with earthquake source location data from a ten-month (March 2007-January 2008) seismic deployment. The InSAR results show a maximum of 7 cm of volcanic inflation from March 2007 to mid-October 2007. During this time, seismic activity increased to a Real-time Seismic-Amplitude Measurement (RSAM) value of >400. Normal RSAM values for this volcano are earthquakes that occurred between March 2007 and January 2008 suggests a fault zone through the center of the San Miguel volcanic cone. This fault zone is most likely where dyke propagation is occurring. Source mechanisms will be determined for the earthquakes associated with this fault zone, and they will be compared to the InSAR deformation field to determine if the mid-October seismic activity and observed surface deformation are compatible.
Eruptive origins of a lacustrine pyroclastic succession: insights from the middle Huka Falls Formation, Taupo Volcanic Zone, New Zealand

International Nuclear Information System (INIS)

Cattell, H.J.; Cole, J.W.; Oze, C.; Allen, S.R.

2014-01-01

Current and ancestral lakes within the central Taupo Volcanic Zone (TVZ) provide depocentres for pyroclastic deposits, providing a reliable record of eruption history. These lakes can also be the source of explosive eruptions that directly feed pyroclast-rich density currents. The lithofacies characteristics of pyroclastic deposits allow discrimination between eruption-fed and resedimented facies. The most frequently recognised styles of subaqueous eruptions in the TVZ are shallow-water phreatomagmatic and phreatoplinian eruptions that form subaerial eruption columns. However, deeper source conditions (>150 m water depth) could generate subaqueous explosive eruptions that feed water-supported pyroclast-rich density currents, similar to neptunian eruptions. Such deep-water eruptions have not previously been recognised in the TVZ. Here we study a subsurface deposit, the middle Huka Falls Formation (MHFF), in the Wairakei-Tauhara geothermal fields (Wairakei-Tauhara), TVZ, which we interpret to be the product of a relatively deep-water pyroclastic eruption (150-250 m). The largely subsurface Huka Falls Formation records past sedimentary and volcaniclastic deposition in ancient Lake Huka. Deposits examined from eight drill cores reveal a lithic-rich lower unit, a middle volumetrically dominant pumice lapilli-tuff and an upper thinly bedded suspension-settled tuff unit. A coarse lithic lapilli-tuff within the lower unit is locally thick and coarse near well THM12, suggesting proximity to a source located beneath Lake Huka. This research provides an understanding of the origin of the MHFF deposit and offers insights for evaluating and interpreting the diversity of subaqueous volcanic lake deposits elsewhere. (author)
Flanking Variation Influences Rates of Stutter in Simple Repeats

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August E. Woerner

2017-11-01

Full Text Available It has been posited that the longest uninterrupted stretch (LUS of tandem repeats, as defined by the number of exactly matching repeating motif units, is a better predictor of rates of stutter than the parental allele length (PAL. While there are cases where this hypothesis is likely correct, such as the 9.3 allele in the TH01 locus, there can be situations where it may not apply as well. For example, the PAL may capture flanking indel variations while remaining insensitive to polymorphisms in the repeat, and these haplotypic changes may impact the stutter rate. To address this, rates of stutter were contrasted against the LUS as well as the PAL on different flanking haplotypic backgrounds. This study shows that rates of stutter can vary substantially depending on the flanking haplotype, and while there are cases where the LUS is a better predictor of stutter than the PAL, examples to the contrary are apparent in commonly assayed forensic markers. Further, flanking variation that is 7 bp from the repeat region can impact rates of stutter. These findings suggest that non-proximal effects, such as DNA secondary structure, may be impacting the rates of stutter in common forensic short tandem repeat markers.
Constraints of texture and composition of clinopyroxene phenocrysts of Holocene volcanic rocks on a magmatic plumbing system beneath Tengchong, SW China

Science.gov (United States)

Hu, Jun-Hao; Song, Xie-Yan; He, Hai-Long; Zheng, Wen-Qin; Yu, Song-Yue; Chen, Lie-Meng; Lai, Chun-Kit

2018-04-01

Understanding processes of magma replenishment in a magma plumbing system is essential to predict eruption potential of a dormant volcano. In this study, we present new petrologic and thermobarometric data for youngest lava flows from the Holocene Heikongshan volcano in the Tengchong area, SW China. Clinopyroxene phenocrysts from the trachytic lava flows display various textural/compositional zoning styles (i.e., normal, reverse and oscillatory). Such zoning patterns are indicative of an open magmatic plumbing system with multiphase magma replenishment and mixing, which were likely a key drive of the volcanic eruptions. Thermobarometric calculations of these zoned clinopyroxene phenocrysts yield crystallization pressures of 3.8-7.1 kbar (peak at 4.5-7.0 kbar), corresponding to a magma chamber at depths of 14-21 km. The calculated depths are consistent with the large low-resistivity body at 12-30 km beneath the Heikongshan volcano, implying that the magmatic plumbing system may still be active. Recent earthquakes in the Tengchong area suggest that the regional strike-slip faulting are still active, and may trigger future volcanic eruptions if the magma chamber(s) beneath the Tengchong volcanic field is disturbed, in spite of the volcanic quiescence since 1609 CE.
Experimental Constraints on Forecasting the Location of Volcanic Eruptions from Pre-eruptive Surface Deformation

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Frank Guldstrand

2018-02-01

Full Text Available Volcanic eruptions pose a threat to lives and property when volcano flanks and surroundings are densely populated. The local impact of an eruption depends firstly on its location, whether it occurs near a volcano summit, or down on the flanks. Then forecasting, with a defined accuracy, the location of a potential, imminent eruption would significantly improve the assessment and mitigation of volcanic hazards. Currently, the conventional volcano monitoring methods based on the analysis of surface deformation assesses whether a volcano may erupt but are not implemented to locate imminent eruptions in real time. Here we show how surface deformation induced by ascending eruptive feeders can be used to forecast the eruption location through a simple geometrical analysis. Our analysis builds on the results of 33 scaled laboratory experiments simulating the emplacement of viscous magma intrusions in a brittle, cohesive Coulomb crust under lithostatic stress conditions. The intrusion-induced surface deformation was systematically monitored at high spatial and temporal resolution. In all the experiments, surface deformation preceding the eruptions resulted in systematic uplift, regardless of the intrusion shape. The analysis of the surface deformation patterns leads to the definition of a vector between the center of the uplifted area and the point of maximum uplift, which systematically acted as a precursor to the eruption's location. The temporal evolution of this vector indicated the direction in which the subsequent eruption would occur and ultimately the location itself, irrespective of the feeder shapes. Our findings represent a new approach on how surface deformation on active volcanoes that are not in active rifts could be analysed and used prior to an eruption with a real potential to improve hazard mitigation.
New Data on the Composition of Cretaceous Volcanic Rocks of the Alazeya Plateau, Northeastern Yakutia

Science.gov (United States)

Tsukanov, N. V.; Skolotnev, S. G.

2018-02-01

This work presents new data on the composition of volcanics, developed within the Alazeya Plateau of the Kolyma-Indigirka fold area (Northeast Russia), which indicate essential differences in their composition and, accordingly, different geodynamic settings of the formation of rocks. The studied igneous rocks are subdivided into two groups. Volcanics of the first group of the Late Cretaceous age, which are represented by differentiated volcanic rock series (from andesitobasalts to dacites and rhyolites), were formed under island arc conditions in the continent-ocean transition zone. Volcanics of the second group are ascribed to the tholeiitic series and were formed under the other geodynamic setting, which is associated with the regime of extension and riftogenesis, manifested in the studied area probably at the later stage.
Atla Regio, Venus: Geology and origin of a major equatorial volcanic rise

Science.gov (United States)

Senske, D. A.; Head, James W., III

1992-01-01

Regional volcanic rises form a major part of the highlands in the equatorial region of Venus. These broad domical uplands, 1000 to 3000 km across, contain centers of volcanism forming large edifices and are associated with extension and rifting. Two classes of rises are observed: (1) those that are dominated by tectonism, acting as major centers for converging rifts such as Beta Regio and Alta Regio, and are termed tectonic junctions; and (2) those forming uplands characterized primarily by large-scale volcanism forming edifices. Western Eistla Regio and Bell Regio, where zones of extension and rifting are less developed. Within this second class of features the edifices are typically found at the end of a single rift, or are associated with a linear belt of deformation. We examine the geologic characteristics of the tectonic junction at Alta Regio, concentrating on documenting the styles of volcanism and assessing mechanisms for the formation of regional topography.
Pore Pressure Distribution and Flank Instability in Hydrothermally Altered Stratovolcanoes

Science.gov (United States)

Ball, J. L.; Taron, J.; Hurwitz, S.; Reid, M. E.

2015-12-01

Field and geophysical investigations of stratovolcanoes with long-lived hydrothermal systems commonly reveal that initially permeable regions (such as brecciated layers of pyroclastic material) can become both altered and water-bearing. Hydrothermal alteration in these regions, including clay formation, can turn them into low-permeability barriers to fluid flow, which could increase pore fluid pressures resulting in flank slope instability. We examined elevated pore pressure conditions using numerical models of hydrothermal flow in stratovolcanoes, informed by geophysical data about internal structures and deposits. Idealized radially symmetric meshes were developed based on cross-sectional profiles and alteration/permeability structures of Cascade Range stratovolcanoes. We used the OpenGeoSys model to simulate variably saturated conditions in volcanoes heated only by regional heat fluxes, as well as 650°C intrusions at two km depth below the surface. Meteoric recharge was estimated from precipitation rates in the Cascade Range. Preliminary results indicate zones of elevated pore pressures form: 1) where slopes are underlain by continuous low-permeability altered layers, or 2) when the edifice has an altered core with saturated, less permeable limbs. The first scenario might control shallow collapses on the slopes above the altered layers. The second could promote deeper flank collapses that are initially limited to the summit and upper slopes, but could progress to the core of an edifice. In both scenarios, pore pressures can be further elevated by shallow intrusions, or evolve over longer time scales under forcing from regional heat flux. Geometries without confining low-permeability layers do not show these pressure effects. Our initial scenarios use radially symmetric models, but we are also simulating hydrothermal flow under real 3D geometries with asymmetric subsurface structures (Mount Adams). Simulation results will be used to inform 3D slope
Deformation of volcanic materials by pore pressurization: analog experiments with simplified geometry

Science.gov (United States)

Hyman, David; Bursik, Marcus

2018-03-01

The pressurization of pore fluids plays a significant role in deforming volcanic materials; however, understanding of this process remains incomplete, especially scenarios accompanying phreatic eruptions. Analog experiments presented here use a simple geometry to study the mechanics of this type of deformation. Syrup was injected into the base of a sand medium, simulating the permeable flow of fluids through shallow volcanic systems. The experiments examined surface deformation over many source depths and pressures. Surface deformation was recorded using a Microsoft® Kinect™ sensor, generating high-spatiotemporal resolution lab-scale digital elevation models (DEMs). The behavior of the system is controlled by the ratio of pore pressure to lithostatic loading (λ =p/ρ g D). For λ 10, fluid expulsion from the layer was much faster, vertically fracturing to the surface with larger pressure ratios yielding less deformation. The temporal behavior of deformation followed a characteristic evolution that produced an approximately exponential increase in deformation with time until complete layer penetration. This process is distinguished from magmatic sources in continuous geodetic data by its rapidity and characteristic time evolution. The time evolution of the experiments compares well with tilt records from Mt. Ontake, Japan, in the lead-up to the deadly 2014 phreatic eruption. Improved understanding of this process may guide the evolution of magmatic intrusions such as dikes, cone sheets, and cryptodomes and contribute to caldera resurgence or deformation that destabilizes volcanic flanks.
Isotopic dating of the post-Alpine Neogene volcanism in the Betic Cordilleras, southern Spain

Energy Technology Data Exchange (ETDEWEB)

Nobel, F A; Rondeel, H E [Amsterdam Univ. (Netherlands). Geologisch Inst.; Andriessen, P A.M.; Hebeda, E H; Priem, H N.A. [Laboratorium voor Isotopen-Geologie, Amsterdam (Netherlands)

1981-06-01

The post-Alpine lamproitic volcanism in the Prebetic of the External Zone of the Betic Cordilleras of southern Spain is dated at 7.6-7.2 Ma by the K-Ar data from two richterites, two sanidines, a phlogopite and a whole-rock, and the fission-track analysis of an apatite. Biotite from a lava of the rhyolitic-dacitic suite in the post-orogenic Vera basin of the Internal Zone produces the same age. Phlogopite from a lamproitic (veritic) subvolcanic body in the Vera basin yields an age of about 8.6 Ma; as lavas belonging to the veritic suite reportedly overlie Late Messinian sediments, pointing to an age of less than about 5 Ma, this type of volcanism in the Vera basin must have been active over several million years.
SYSTHESIS OF VOLCANISM STUDIES FOR THE YUCCA MOUNTAIN SITE CHARACTERIZATION PROJECT

Energy Technology Data Exchange (ETDEWEB)

Perry, F. V.; Crowe, G. A.; Valentine, G. A.; Bowker, L. M.

1997-09-23

This report synthesizes the results of volcanism studies conducted by scientists at the Los Alamos National Laboratory and collaborating institutions on behalf of the Department of Energy's Yucca Mountain Project. Chapter 1 introduces the volcanism issue for the Yucca Mountain site and provides the reader with an overview of the organization, content, and significant conclusions of this report. The hazard of future basaltic volcanism is the primary topic of concern including both events that intersect a potential repository and events that occur near or within the waste isolation system of a repository. Future volcanic events cannot be predicted with certainty but instead are estimated using formal methods of probabilistic volcanic hazard assessment (PVHA). Chapter 2 describes the volcanic history of the Yucca Mountain region (YMR) and emphasizes the Pliocene and Quaternary volcanic record, the interval of primary concern for volcanic risk assessment. The distribution, eruptive history, and geochronology of Plio-Quaternary basalt centers are described by individual center emphasizing the younger postcaldera basalt (<5 Ma). The Lathrop Wells volcanic center is described in detail because it is the youngest basalt center in the YMR. The age of the Lathrop Wells center is now confidently determined to be about 75 thousand years old. Chapter 3 describes the tectonic setting of the YMR and presents and assesses the significance of multiple alternative tectonic models. The distribution of Pliocene and Quaternary basaltic volcanic centers is evaluated with respect to tectonic models for detachment, caldera, regional and local rifting, and the Walker Lane structural zone. Geophysical data are described for the YMR and are used as an aid to understand the distribution of past basaltic volcanic centers and possible future magmatic processes. Chapter 4 discusses the petrologic and geochemical features of basaltic volcanism in the YMR, the southern Great Basin and the
Lidar observations of stratospheric aerosol layer after the Mt. Pinatubo volcanic eruption

International Nuclear Information System (INIS)

Nagai, Tomohiro; Uchino, Osamu; Fujimoto, Toshifumi.

1992-01-01

The volcano Mt. Pinatubo located on the Luzon Island, Philippines, had explosively erupted on June 15, 1991. The volcanic eruptions such as volcanic ash, SO2 and H2O reached into the stratosphere over 30 km altitude by the NOAA-11 satellite observation and this is considered one of the biggest volcanic eruptions in this century. A grandiose volcanic eruption influences the atmosphere seriously and causes many climatic effects globally. There had been many impacts on radiation, atmospheric temperature and stratospheric ozone after some past volcanic eruptions. The main cause of volcanic influence depends on stratospheric aerosol, that stay long enough to change climate and other meteorological conditions. Therefore it is very important to watch stratospheric aerosol layers carefully and continuously. Standing on this respect, we do not only continue stratospheric aerosol observation at Tsukuba but also have urgently developed another lidar observational point at Naha in Okinawa Island. This observational station could be thought valuable since there is no lidar observational station in this latitudinal zone and it is much nearer to Mt. Pinatubo. Especially, there is advantage to link up these two stations on studying the transportation mechanism in the stratosphere. In this paper, we present the results of lidar observations at Tsukuba and Naha by lidar systems with Nd:YAG laser
Lidar Observations of Stratospheric Aerosol Layer After the Mt. Pinatubo Volcanic Eruption

Science.gov (United States)

Nagai, Tomohiro; Uchino, Osamu; Fujimoto, Toshifumi

1992-01-01

The volcano Mt. Pinatubo located on the Luzon Island, Philippines, had explosively erupted on June 15, 1991. The volcanic eruptions such as volcanic ash, SO2 and H2O reached into the stratosphere over 30 km altitude by the NOAA-11 satellite observation and this is considered one of the biggest volcanic eruptions in this century. A grandiose volcanic eruption influences the atmosphere seriously and causes many climatic effects globally. There had been many impacts on radiation, atmospheric temperature and stratospheric ozone after some past volcanic eruptions. The main cause of volcanic influence depends on stratospheric aerosol, that stay long enough to change climate and other meteorological conditions. Therefore it is very important to watch stratospheric aerosol layers carefully and continuously. Standing on this respect, we do not only continue stratospheric aerosol observation at Tsukuba but also have urgently developed another lidar observational point at Naha in Okinawa Island. This observational station could be thought valuable since there is no lidar observational station in this latitudinal zone and it is much nearer to Mt. Pinatubo. Especially, there is advantage to link up these two stations on studying the transportation mechanism in the stratosphere. In this paper, we present the results of lidar observations at Tsukuba and Naha by lidar systems with Nd:YAG laser.
Scientific Drilling in a Central Italian Volcanic District

Directory of Open Access Journals (Sweden)

Paola Montone

2007-09-01

Full Text Available The Colli Albani Volcanic District, located 15 km SE of Rome (Fig. 1, is part of the Roman Magmatic Province, a belt of potassic to ultra-potassic volcanic districts that developed along the Tyrrhenian Sea margin since Middle Pleistocene time (Conticelli and Peccerillo, 1992; Marra et al., 2004; Giordano et al., 2006 and references therein. Eruption centers are aligned along NW-SE oriented majorextensional structures guiding the dislocation of Meso-Cenozoic siliceous-carbonate sedimentary successions at the rear of the Apennine belt. Volcanic districts developed in structural sectors with most favorable conditions for magma uprise. In particular, the Colli Albani volcanism is located in a N-S shear zone where it intersects the extensional NW- and NE-trending fault systems. In the last decade, geochronological measurements allowed for reconstructions of the eruptive history and led to the classification as "dormant" volcano. The volcanic history may be roughly subdivided into three main phases marked by different eruptive mechanisms andmagma volumes. The early Tuscolano-Artemisio Phase (ca. 561–351 ky, the most explosive and voluminous one, is characterized by five large pyroclastic flow-forming eruptions. After a ~40-ky-long dormancy, a lesser energetic phase of activity took place (Faete Phase; ca. 308–250 ky, which started with peripheral effusive eruptions coupled with subordinate hydromagmatic activity. A new ~50-ky-long dormancypreceded the start of the late hydromagmatic phase (ca. 200–36 ky, which was dominated by pyroclastic-surge eruptions, with formation of several monogenetic or multiple maars and/or tuff rings.
The volcanism of the western part of the Los Frailes Meseta (Bolivia): a representative example of the Andean volcanism since the Upper Oligocene; Le volcanisme de la bordure occidentale de la Meseta de Los Frailes (Bolivie): un jalon representatif du volcanisme andin depuis l`Oligocene superieur

Energy Technology Data Exchange (ETDEWEB)

Leroy, L. [Nancy-1 Univ., 54 (France); Jimenez, N.

1996-12-31

The Los Frailes Meseta (Bolivia) is one of the large tertiary ignimbritic fields of the inner volcanic arc from Central Andes (Central Volcanic Zone. CVZ), in contact zone between the Altiplano to the west and the Eastern Cordillera to the east. Field observations and mineralogical and geochemical studies (major and trace elements) lead to distinguish two types of volcanism in the western border to the Meseta. During the Middle Miocene and Pliocene, the volcanic activity can be subdivided into three pyroclastic emission cycles, the Larco, Coroma and Pliocene ignimbrites, the first two being separated by the Quechua 2 orogeny. All these ignimbrites are very similar and correspond to peraluminous rhyolites to rhyodacites. In the studies area, the Coroma cycle is the only one where an ignimbrite-less evolved resurgent dome association can be observed. Beside these ignimbrites, isolated small lava flows and domes overlay and/or intrude all the other formations. They are meta-aluminous lavas with a shoshonitic affinity. A quaternary age can be attributed to his second volcanism. These two volcanic types are well-known in the CVZ and are related to the different deformation stages, either compressional or extensional, which occur alternately in the Cordillera since 26 Ma. (authors). 61 refs., 12 figs., 3 tabs.
Timing of the volcanism of the southern Kivu province: Implications for the evolution of the western branch of the East African rift system

International Nuclear Information System (INIS)

Pasteels, P.

1989-01-01

New K-Ar datings of a large rock sampling from the South Kivu volcanic province (Zaire, Rwanda, Burundi) are reported. No ages older than 10 Ma have been obtained. This result contrasts with older assumptions and puts severe constraints on the relations between volcanism and rift evolution. From 10 to 7.5 Ma tholeiitic volcanism predominates corresponding to an episode of fissural eruptions; from 7.5 to 5 Ma alkali basalts and their differentiates are mainly erupted in localized rifts. A culmination of activity occurs between 6.0 and 5.5 Ma ago. Pleistocene alkalic volcanism is restricted to localized areas. The transition from tholeiites to alkali-basaltic volcanism dated around 7.5 Ma would correspond to a major rifting phase which corresponds with the initiation of Lake Kivu Basin formation. The distribution of tholeiitic rocks in the central part of the rift, and predominantly alkalic rocks along the western active border fault, strengthens the idea that the former are associated with tension, the latter with vertical, possibly also strike-slip movements. Volcanism in the Western Rift is restricted to areas where tension occurs in a zone which is located between two zones of strike-slip. In the South Kivu area normal faults intersect strike-slip faults and this seems to have determined the location of volcanic activity. Magma formation is considered to be related with shear heating combined with adiabatic decompression in ascending diapirs. This implies heating at the lithosphere-asthenosphere boundary as a result of extension. Generation of tholeiitic or alkalic magmas is connected with the variable ascent velocity of mantle diapirs or with variable shear heating along the shear zone. Changes in both magma composition and intensity of volcanic activity with time are considered to be related to major phases of rift evolution. (orig.)
Platinum, palladium, and rhodium in volcanic and plutonic rocks from the Gravina-Nutzotin belt, Alaska

Science.gov (United States)

Page, Norman J; Berg, Henry C.; Haffty, Joseph

1977-01-01

The Gravina-Nutzotin belt of Middle (?) Jurassic to middle Cretaceous sedimentary and volcanic rocks in south and southeastern Alaska includes concentrically zoned ultramafic complexes known to contain platinum-group metals. Previous isotopic, petrologic, and geologic studies suggested a close relation in time and space between the volcanic rocks and the ultramafic complexes. Interpretation of 40 analyses for platinum, palladium, and rhodium in volcanic and plutonic rocks of the belt indicates a strong geochemical correlation between the two groups of rocks and is in support of their being cogenetic either from directly connected magma chambers and flows or indirectly by selective concentration processes from similar mantle material.
Asthenospheric flow and origin of volcanism in the Baikal rift area

NARCIS (Netherlands)

Lebedev, S.; Meier, T.; Hilst, R.D. van der

2006-01-01

The origin of low-volume, hotspot-like volcanism often observed in continental rift areas is debated, as is the nature of the flow in the mantle beneath. In this paper we assemble seismic constraints on the mantle flow below the Baikal Rift Zone. We combine new evidence from upper-mantle
Outline of tectonic geology of the cenozoic Pacific volcanic zone concerned with geothermal areas in the central America; Chubei ni okeru chinetsutai wo tomonau shinseidai Taiheiyo kazantai no chishitsu gaisetsu

Energy Technology Data Exchange (ETDEWEB)

Yamasaki, T [Kyushu University, Fukuoka (Japan); Matsumoto, Y [Yamaguchi University, Yamaguchi (Japan)

1994-09-16

For the purpose of technological cooperation on geothermal development, investigations and discussions have been given on the geological background in the geothermal areas in Central America where the Pacific volcanic zone stretches. The geology in Central America is divided largely into three geological structures distributed in a band form in the east-west direction. Among these structure, the Pacific Volcanic Province is a Caenozoic volcanic area ranging along the Pacific Ocean coast in the south-east direction, where young and active Quarternary volcanoes are lined straight over a distance of 1,400 km. The geological structure is such that continuously traceable rift valley or pit structure agrees with the array of volcanoes. The long and wide rift valley that governs this volcanic activity forms the base of the geothermal areas dotted in the above structure. Guatemala had been proceeding with a 24-MW power plant plan in Zunil, the most important point, but the construction has been delayed because of a landslide that caused impediment to the productive wells. The plant completion is now scheduled for 1995. El Salvador is the most advanced country in geothermal power generation, which operates three plants in the Ahuachapa geothermal area, with the output reaching 95 MW. The geothermal condition per production well is 110 tons per hour at 250{degree}C. Nicaragua had been successful in generating power of 70 KW with two plants in Momtombo by 1989. 22 refs., 8 figs., 4 tabs.
Petrology and oxygen isotope geochemistry of the Pucon ignimbrite - Southern Andean volcanic zone, Chile: Implications for genesis of mafic ignimbrites

International Nuclear Information System (INIS)

McCurry, Michael; Schmidt, Keegan

2001-01-01

Although mafic components of dominantly intermediate to silicic ignimbrites are rather common, voluminous, dominantly mafic ignimbrites are rare (e.g., Smith, 1979; cf. Freundt and Schmincke, 1995). Volcan Villarrica, the most active composite volcano in South America, located in the Southern Andean Volcanic Zone (SAVZ, Lopez-Escobar and Moreno, 1994a), has produced two such ignimbrites, respectively the Lican and Pucon Ignimbrites, in the last 14,000 years (Clavero, 1996). The two ignimbrites are low-Si andesite and basaltic-andesite to low-Si andesite, respectively, the former about twice as voluminous as the later (10 and 5 km 3 ). Eruption of the ignimbrites produced calderas respectively 5 and 2 km in diameter (Moreno, 1995; Clavero, 1996). In addition to its mafic bulk composition, the Pucon Ignimbrite (PI) is also distinguished by numerous xenolithic fragments among and also within magmatic pyroclasts. Many of these are fragments of granitoid rocks. Volcan Villarrica has also produced numerous smaller mafic ignimbrites and pyroclastic surge deposits, as well as dominantly basaltic fallout and lava flows (Lopez-Escobar and Moreno, 1994; Moreno, 1995; Clavero, 1996; Hickey-Vargas et al., 1989; Tormey et al., 1991). Reasons for the unusual style of mafic explosive activity at Volcan Villarrica are unclear. Clavero (1996), based upon an exemplary thesis-study of the physical volcanology and petrology of the PI, suggests it formed in response to a sequence of events beginning with injection of a shallow basaltic andesite magma chamber by hotter basaltic magma. In his model mixing and heat transfer between the two magmas initiated a violent Strombolian eruption that destabilized the chamber causing infiltration of large amounts of meteoric-water saturated country rocks. The Pucon Ignimbrite formed in response to subsequent phreatomagmatic interactions. In contrast, Lopez-Escobar and Moreno (1994) infer on geochemical grounds that volatiles leading to the explosive

Magma shearing and friction in the volcanic conduit: A crystal constraint

Science.gov (United States)

Wallace, P. A.; Kendrick, J. E.; Henton De Angelis, S.; Ashworth, J. D.; Coats, R.; Miwa, T.; Mariani, E.; Lavallée, Y.

2017-12-01

Magma shearing and friction processes in the shallow volcanic conduit are typical manifestations of strain localisation, which in turn can have an influential role on magma ascent dynamics. The thermal consequences of such events could drive the destabilisation of magma and thus dictate the style of activity at the surface. Shear heating and fault friction are prime candidates for the generation of significant quantities of heat. Here we use a combination of field and experimental evidence to investigate how crystals can act as sensitive recorders of both physical and chemical processes occurring in the shallow volcanic conduit. Spine extrusion during the closing of the 1991-95 eruption at Unzen volcano, Japan, provided the unique opportunity to investigate marginal shear zone formation, which preserves a relic of the deformation during magma ascent. Our results show that crystals can effectively act as a deformation marker during magma ascent through the viscous-brittle transition by accommodating strain in the form of crystal plasticity before fracturing (comminution). Electron backscatter diffraction (EBSD) reveals up to 40° lattice distortion of biotite phenocrysts in zones of high shear, with negligible plasticity further away. Plagioclase microlites display a systematic plastic response to an increase in shear intensity, as recorded by an increase in lattice distortion towards the spine margin of up to 9°. This localisation of strain within the shear zone is also accompanied by the destabilisation of hydrous mineral phases (i.e. amphibole), compaction of pores (23-13% Φ), glass devitrification and magnetic anomalies. The narrow zone of disequilibrium textures suggests the likely effect of a thermal input due to strain localisation being the contributing factor. These observations are complimented by high-temperature high-velocity rotary shear experiments which simulate the deformation evolution during shear. Hence, understanding these shallow volcanic
The link between great earthquakes and the subduction of oceanic fracture zones

Directory of Open Access Journals (Sweden)

R. D. Müller

2012-12-01

Full Text Available Giant subduction earthquakes are known to occur in areas not previously identified as prone to high seismic risk. This highlights the need to better identify subduction zone segments potentially dominated by relatively long (up to 1000 yr and more recurrence times of giant earthquakes. We construct a model for the geometry of subduction coupling zones and combine it with global geophysical data sets to demonstrate that the occurrence of great (magnitude ≥ 8 subduction earthquakes is strongly biased towards regions associated with intersections of oceanic fracture zones and subduction zones. We use a computational recommendation technology, a type of information filtering system technique widely used in searching, sorting, classifying, and filtering very large, statistically skewed data sets on the Internet, to demonstrate a robust association and rule out a random effect. Fracture zone–subduction zone intersection regions, representing only 25% of the global subduction coupling zone, are linked with 13 of the 15 largest (magnitude M_w ≥ 8.6 and half of the 50 largest (magnitude M_w ≥ 8.4 earthquakes. In contrast, subducting volcanic ridges and chains are only biased towards smaller earthquakes (magnitude < 8. The associations captured by our statistical analysis can be conceptually related to physical differences between subducting fracture zones and volcanic chains/ridges. Fracture zones are characterised by laterally continuous, uplifted ridges that represent normal ocean crust with a high degree of structural integrity, causing strong, persistent coupling in the subduction interface. Smaller volcanic ridges and chains have a relatively fragile heterogeneous internal structure and are separated from the underlying ocean crust by a detachment interface, resulting in weak coupling and relatively small earthquakes, providing a conceptual basis for the observed dichotomy.
Preliminary review and summary of the potential for tectonic, seismic, and volcanic activity at the Nevada Test Site defense waste disposal site

International Nuclear Information System (INIS)

Metcalf, L.A.

1983-03-01

A change from compressional to extensional tectonics, which occurred about 17 m.y. ago, marks the emergence of the present tectonic regime in the southern Great Basin. Crustal extension is continuing at the present time, oriented in a NW-SE direction in the NTS region. Concurrently with the onset of crustal extension a system of NW- and NE-trending shear zones developed, along which mutual offset has occurred. Present seismic and tectonic activity in the NTS region is concentrated along the intersections of the shear zones and in areas of deep basin formation. Natural historic seismicity of the NTS region has been low to moderate. Seismic hazard assessments suggest a maximum magnitude 6-7 earthquake, associated with a maximum peak acceleration of 0.7 to 0.9 g, is probable for the NTS. A return period of 12,700 to 15,000 y for the maximum peak acceleration indicates a relatively low seismic hazard. Silicic volcanism in the NTS region was active from 16 to 6 m.y. ago, followed by a transition to basaltic volcanism. The tectonic settings most favorable for Quaternary basaltic activity are areas of young basin-range extension, caldera ring fracture zones, and intersections of conjugate shear zones. Probability calculations for the Yucca Mountain waste repository result in a volcanic disruption hazard of 10 - 8 to 10 - 9 /y. This value is extremely low and is probably representative of the hazard at Frenchman Flat. However, due to its tectonic setting, Frenchman Flat may be an area conducive to future basaltic volcanism; further investigation is needed to properly assess volcanic hazard
Fault zone hydrogeology

Science.gov (United States)

Bense, V. F.; Gleeson, T.; Loveless, S. E.; Bour, O.; Scibek, J.

2013-12-01

Deformation along faults in the shallow crust (research effort of structural geologists and hydrogeologists. However, we find that these disciplines often use different methods with little interaction between them. In this review, we document the current multi-disciplinary understanding of fault zone hydrogeology. We discuss surface- and subsurface observations from diverse rock types from unlithified and lithified clastic sediments through to carbonate, crystalline, and volcanic rocks. For each rock type, we evaluate geological deformation mechanisms, hydrogeologic observations and conceptual models of fault zone hydrogeology. Outcrop observations indicate that fault zones commonly have a permeability structure suggesting they should act as complex conduit-barrier systems in which along-fault flow is encouraged and across-fault flow is impeded. Hydrogeological observations of fault zones reported in the literature show a broad qualitative agreement with outcrop-based conceptual models of fault zone hydrogeology. Nevertheless, the specific impact of a particular fault permeability structure on fault zone hydrogeology can only be assessed when the hydrogeological context of the fault zone is considered and not from outcrop observations alone. To gain a more integrated, comprehensive understanding of fault zone hydrogeology, we foresee numerous synergistic opportunities and challenges for the discipline of structural geology and hydrogeology to co-evolve and address remaining challenges by co-locating study areas, sharing approaches and fusing data, developing conceptual models from hydrogeologic data, numerical modeling, and training interdisciplinary scientists.
Magma-Tectonic Interactions along the Central America Volcanic Arc: Insights from the August 1999 Magmatic and Tectonic Event at Cerro Negro, Nicaragua

Science.gov (United States)

La Femina, P.; Connor, C.; Strauch, W.

2002-12-01

Volcanic vent alignments form parallel to the direction of maximum horizontal stress, accommodating extensional strain via dike injection. Roughly east-west extension within the Central America Volcanic Arc is accommodated along north-northwest-trending basaltic vent alignments. In Nicaragua, these alignments are located in a northwest-trending zone of dextral shear, with shear accommodated along northeast trending bookshelf faults. The recent eruption of Cerro Negro volcano, Nicaragua and Marabios Range seismic swarm revealed the interaction of these fault systems. A low energy (VEI 1), small volume (0.001 km3 DRE) eruption of highly crystalline basalt occurred at Cerro Negro volcano, Nicaragua, August 5-7, 1999. This eruption followed three tectonic earthquakes (each Mw 5.2) in the vicinity of Cerro Negro hours before the onset of eruptive activity. The temporal and spatial pattern of microseismicity and focal mechanisms of the Mw 5.2 earthquakes suggests the activation of northeast-trending faults northwest and southeast of Cerro Negro within the Marabios Range. The eruption was confined to three new vents formed on the southern flank of Cerro Negro along a preexisting north-northwest trending alignment; the El Hoyo alignment of cinder cones, maars and explosion craters. Surface ruptures formed > 1 km south and southeast of the new vents suggest dike injection. Numerical simulations of conduit flow illustrate that the observed effusion rates (up to 65 ms-1) and fountain heights (50-300 m) can be achieved by eruption of magma with little or no excess fluid pressure, in response to tectonic strain. These observations and models suggest that 1999 Cerro Negro activity is an excellent example of tectonically induced small-volume eruptions in an arc setting.
Applying geophysical surveys for studying subsurface geology of monogenetic volcanic fields: the example of La Garrotxa Volcanic Field (NE of Iberian Peninsula)

Science.gov (United States)

Bolós, Xavier; Barde-Cabusson, Stéphanie; Pedrazzi, Dario; Martí, Joan; Casas, Albert; Lovera, Raúl; Nadal-Sala, Daniel

2014-05-01

Improving knowledge of the shallowest part of the feeding system of monogenetic volcanoes and the relationship with the subsurface geology is an important task. We applied high-precision geophysical techniques that are self-potential and electrical resistivity tomography, for the exploration of the uppermost part of the substrate of La Garrotxa Volcanic Field, which is part of the European Cenozoic Rift System. Previous geophysical studies carried out in the same area at a less detailed scale were aimed at identifying deeper structures, and together constitute the basis to establish volcanic susceptibility in La Garrotxa. Self-potential study allowed identifying key areas where electrical resistivity tomography could be conducted. Dykes and faults associated with several monogenetic cones were identified through the generation of resistivity models. The combined results confirm that shallow tectonics controlling the distribution of the foci of eruptive activity in this volcanic zone mainly correspond to NNW-SSE and accessorily by NNE-SSW Neogene extensional fissures and faults and concretely show the associated magmatic intrusions. These studies show that previous alpine tectonic structures played no apparent role in controlling the loci of this volcanism. Furthermore, the results obtained show that the changes in eruption dynamics occurring at different vents located at relatively short distances in this volcanic area can be controlled by shallow stratigraphical, structural, and hydrogeological features underneath these monogenetic volcanoes. This study was partially funded by the Beca Ciutat d'Olot en Ciències Naturals and the European Commission (FT7 Theme: ENV.2011.1.3.3-1; Grant 282759: "VUELCO").
Sequential Assimilation of Volcanic Monitoring Data to Quantify Eruption Potential: Application to Kerinci Volcano, Sumatra

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Yan Zhan

2017-12-01

Full Text Available Quantifying the eruption potential of a restless volcano requires the ability to model parameters such as overpressure and calculate the host rock stress state as the system evolves. A critical challenge is developing a model-data fusion framework to take advantage of observational data and provide updates of the volcanic system through time. The Ensemble Kalman Filter (EnKF uses a Monte Carlo approach to assimilate volcanic monitoring data and update models of volcanic unrest, providing time-varying estimates of overpressure and stress. Although the EnKF has been proven effective to forecast volcanic deformation using synthetic InSAR and GPS data, until now, it has not been applied to assimilate data from an active volcanic system. In this investigation, the EnKF is used to provide a “hindcast” of the 2009 explosive eruption of Kerinci volcano, Indonesia. A two-sources analytical model is used to simulate the surface deformation of Kerinci volcano observed by InSAR time-series data and to predict the system evolution. A deep, deflating dike-like source reproduces the subsiding signal on the flanks of the volcano, and a shallow spherical McTigue source reproduces the central uplift. EnKF predicted parameters are used in finite element models to calculate the host-rock stress state prior to the 2009 eruption. Mohr-Coulomb failure models reveal that the host rock around the shallow magma reservoir is trending toward tensile failure prior to 2009, which may be the catalyst for the 2009 eruption. Our results illustrate that the EnKF shows significant promise for future applications to forecasting the eruption potential of restless volcanoes and hind-cast the triggering mechanisms of observed eruptions.
Park Volcanics, Murihiku Terrane, New Zealand : petrology, petrochemistry, and tectonic significance

International Nuclear Information System (INIS)

Coombs, D.S.; Cook, N.D.J.; Kawachi, Y.; Johnstone, R.D.; Gibson, I.L.

1996-01-01

The Late Triassic to Early Jurassic Park Volcanics Group comprises minor shallow intrusive and extrusive bodies emplaced during mainly marine sedimentation of the Murihiku Terrane, southern New Zealand. Gowan Andesite in western Southland and Glenham Porphyry andesites in eastern Southland are high-K andesites. Glassy examples have commonly lost K during alteration. Orthoclase contents of Or 3.6-3.7 in plagioclase phenocrysts at An 50 confirm the high-K nature of the melts at the time of phenocryst crystallisation. The Gowan andesites have higher Fe/Mg than the Glenham and related differences in minor element chemistry suggesting lower ∫O 2 during fractionation of the parent magma. Pinney Volcanics in western Southland are mostly high-K trachydacites but, like Glenham Porphyry, include minor rhyolite. Barnicoat Andesite in the Nelson area is medium-K olivine andesite, marginally tholeiitic in terms of its FeO*/MgO versus SiO 2 behaviour, but otherwise is typically calc-alkaline, as are the Gowan, Glenham, and Pinney. Analyses of pyroxenes (augites, orthopyroxenes, reaction rim and groundmass pigeonites) reveal xenocrysts recording an early stage of magma fractionation, slight iron enrichment in the andesite stage, and lowered Fe/Mg and increased Ca contents in augites of the most felsic rocks. Titanian tschermakite and titanian magnesio-tschermakite of deep-seated origin participated in fractionation leading to the Pinney Volcanics, and magnesio-hornblende, edenite, and biotite crystallised as minor late stage minerals following high-level emplacement of Gowan Andesite and siliceous Glenham Porphyry members. Low 87 Sr/ 86 Sr ratios (c. 0.7034-0.7037), REE and multi-element distribution patterns, and the mineralogical features collectively suggest fractionation of the andesites from parental basalt originating in an enriched mantle wedge above a subduction zone, with minimal contamination by continental crust. High-K andesites appear to be unknown in clearly
Volcanism on Io

Science.gov (United States)

Davies, Ashley Gerard

2014-03-01

Preface; Introduction; Part I. Io, 1610 to 1995: Galileo to Galileo: 1. Io, 1610-1979; 2. Between Voyager and Galileo: 1979-95; 3. Galileo at Io; Part II. Planetary Volcanism: Evolution and Composition: 4. Io and Earth: formation, evolution, and interior structure; 5. Magmas and volatiles; Part III. Observing and Modeling Volcanic Activity: 6. Observations: thermal remote sensing of volcanic activity; 7. Models of effusive eruption processes; 8. Thermal evolution of volcanic eruptions; Part IV. Galileo at Io: the Volcanic Bestiary: 9. The view from Galileo; 10. The lava lake at Pele; 11. Pillan and Tvashtar: lava fountains and flows; 12. Prometheus and Amirani: Effusive activity and insulated flows; 13. Loki Patera: Io's powerhouse; 14. Other volcanoes and eruptions; Part V. Volcanism on Io: The Global View: 15. Geomorphology: paterae, shields, flows and mountains; 16. Volcanic plumes; 17. Hot spots; Part VI. Io after Galileo: 18. Volcanism on Io: a post-Galileo view; 19. The future of Io observations; Appendix 1; Appendix 2; References; Index.
Statistical eruption forecast for the Chilean Southern Volcanic Zone: typical probabilities of volcanic eruptions as baseline for possibly enhanced activity following the large 2010 Concepción earthquake

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Y. Dzierma

2010-10-01

Full Text Available A probabilistic eruption forecast is provided for ten volcanoes of the Chilean Southern Volcanic Zone (SVZ. Since 70% of the Chilean population lives in this area, the estimation of future eruption likelihood is an important part of hazard assessment. After investigating the completeness and stationarity of the historical eruption time series, the exponential, Weibull, and log-logistic distribution functions are fit to the repose time distributions for the individual volcanoes and the models are evaluated. This procedure has been implemented in two different ways to methodologically compare details in the fitting process. With regard to the probability of at least one VEI ≥ 2 eruption in the next decade, Llaima, Villarrica and Nevados de Chillán are most likely to erupt, while Osorno shows the lowest eruption probability among the volcanoes analysed. In addition to giving a compilation of the statistical eruption forecasts along the historically most active volcanoes of the SVZ, this paper aims to give "typical" eruption probabilities, which may in the future permit to distinguish possibly enhanced activity in the aftermath of the large 2010 Concepción earthquake.
Compositional variations revealed by ASTER image analysis of the Viedma Volcano, southern Andes Volcanic Zone Variaciones composicionales reveladas mediante análisis de imágenes ASTER del volcán Viedma, Zona Volcánica Andina Austral

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Chiaki Kobayashi

2010-07-01

Full Text Available We conducted a lithological mapping of the Viedma volcano, one of five volcanoes in the Andean Austral Volcanic Zone (AVZ, using remote sensing techniques. We used data of the Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER sensor which is highly effective in geological research, to understand build-up processes and to deduce compositional variation of the Viedma volcano emerging from the South Patagonian ice field. The volcanic edifice was divided into bright parts that mainly compose the eastern flank of the volcano and dark parts at the central crater area based on the observation in visible and near infrared ranges. The SiO2 concentration was cal-culated using the bands in the visible and thermal infrared regions. The dark part and the bright part have approximately 51 wt% and 63 wt% average SiO2 content respectively, indicating that the exposures of the Viedma volcano have a wide variation in SiO2 concentration. Although, according to other authors, ejecta from the Viedma volcano have 64-66 wt% SiO2 and other AV Z volcanoes are essentially monolithologic dacite/andesite volcanoes, the edifice of the Viedma volcano appears to be composed mostly of basalts or older rocks/basement with low silica contents.Mediante el uso de técnica de sensoría remota se ha desarrollado un mapeo litológico del volcán Viedma, uno de los cinco volcanes de la Zona Volcánica Andina Austral (ZVA. Para este efecto, se ha utilizado el radiómetro ‘Advanced Spaceborne Thermal Emission and Reflection’ (ASTER que es muy efectivo en investigación geológica, para entender los procesos que han controlado la estructura y deducir las variaciones composi-cionales del volcán Viedma, que sobresale levemente de la superficie del campo de hielo Patagónico Sur. Sobre la base de la observación en el intervalo del espectro visible e infrarrojo cercano, en el edificio se distinguen partes brillantes que corresponden al flanco oriental del volcán y
Quaternary basaltic volcanism in the Payenia volcanic province, Argentina

DEFF Research Database (Denmark)

Søager, Nina

primitive basalts and trachybasalts but also more evolved samples from the retroarc region and the larger volcanoes Payún Matrú and Payún Liso are presented. The samples cover a broad range of compositions from intraplate lavas similar to ocean island basalts to arc andesites. A common feature found...... are isotopically similar to the Andean Southern Volcanic Zone arc rocks and their mantle source possibly resembled the source of South Atlantic N-MORB prior to addition of fluids and melts from the subduction channel. However, it must have been more enriched than the estimates of depleted upper mantle from...... the lithosphere is thinnest and possibly in areas of elevated mantle temperatures. The pyroxenite melts formed at deeper levels react with the surrounding peridotite and thereby changes composition leading to eruption of melts which experienced variable degrees of melt-peridotite interaction. This can presumably...
Interaction between climate, volcanism, and isostatic rebound in Southeast Alaska during the last deglaciation

Science.gov (United States)

Praetorius, Summer; Mix, Alan; Jensen, Britta; Froese, Duane; Milne, Glenn A.; Wolhowe, Matthew; Addison, Jason A.; Prahl, Fred

2016-01-01

Observations of enhanced volcanic frequency during the last deglaciation have led to the hypothesis that ice unloading in glaciated volcanic terrains can promote volcanism through decompression melting in the shallow mantle or a reduction in crustal magma storage time. However, a direct link between regional climate change, isostatic adjustment, and the initiation of volcanism remains to be demonstrated due to the difficulty of obtaining high-resolution well-dated records that capture short-term climate and volcanic variability traced to a particular source region. Here we present an exceptionally resolved record of 19 tephra layers paired with foraminiferal oxygen isotopes and alkenone paleotemperatures from marine sediment cores along the Southeast Alaska margin spanning the last deglacial transition. Major element compositions of the tephras indicate a predominant source from the nearby Mt. Edgecumbe Volcanic Field (MEVF). We constrain the timing of this regional eruptive sequence to 14.6–13.1 ka. The sudden increase in volcanic activity from the MEVF coincides with the onset of Bølling–Allerød interstadial warmth, the disappearance of ice-rafted detritus, and rapid vertical land motion associated with modeled regional isostatic rebound in response to glacier retreat. These data support the hypothesis that regional deglaciation can rapidly trigger volcanic activity. Rapid sea surface temperature fluctuations and an increase in local salinity (i.e., δ18Osw) variability are associated with the interval of intense volcanic activity, consistent with a two-way interaction between climate and volcanism in which rapid volcanic response to ice unloading may in turn enhance short-term melting of the glaciers, plausibly via albedo effects on glacier ablation zones.
Characterization of unsaturated zone hydrogeologic units using matrix properties and depositional history in a complex volcanic environment

Science.gov (United States)

Flint, Lorraine E.; Buesch, David C.; Flint, Alan L.

2006-01-01

Characterization of the physical and unsaturated hydrologic properties of subsurface materials is necessary to calculate flow and transport for land use practices and to evaluate subsurface processes such as perched water or lateral diversion of water, which are influenced by features such as faults, fractures, and abrupt changes in lithology. Input for numerical flow models typically includes parameters that describe hydrologic properties and the initial and boundary conditions for all materials in the unsaturated zone, such as bulk density, porosity, and particle density, saturated hydraulic conductivity, moisture-retention characteristics, and field water content. We describe an approach for systematically evaluating the site features that contribute to water flow, using physical and hydraulic data collected at the laboratory scale, to provide a representative set of physical and hydraulic parameters for numerically calculating flow of water through the materials at a site. An example case study from analyses done for the heterogeneous, layered, volcanic rocks at Yucca Mountain is presented, but the general approach for parameterization could be applied at any site where depositional processes follow deterministic patterns. Hydrogeologic units at this site were defined using (i) a database developed from 5320 rock samples collected from the coring of 23 shallow (deep (500–1000 m) boreholes, (ii) lithostratigraphic boundaries and corresponding relations to porosity, (iii) transition zones with pronounced changes in properties over short vertical distances, (iv) characterization of the influence of mineral alteration on hydrologic properties such as permeability and moisture-retention characteristics, and (v) a statistical analysis to evaluate where boundaries should be adjusted to minimize the variance within layers. Model parameters developed in this study, and the relation of flow properties to porosity, can be used to produce detailed and accurate
Volcanic systems of Iceland and their magma source

Science.gov (United States)

Sigmarsson, Olgeir

2017-04-01

Several active hot-spot volcanoes produce magma from mantle sources which composition varies on decadal time scale. This is probably best demonstrated by the recent work of Pietruszka and collaborators on Kilauea, Hawaii. In marked contrast, basalt lavas from volcanic system in Iceland located above the presumed centre of the Iceland mantle plume have uniform isotope composition over the last 10 thousand years. Volcanic systems are composed of a central volcano and a fissure swarm, or a combination of both and they represent a fundamental component of the neovolcanic zones in Iceland. Four such systems, those of Askja, Bárðarbunga, Kverkfjöll and Grímsvötn in central Iceland were chosen for investigation. The last three have central volcanoes covered by the Vatnajökull ice-sheet whereas part of their fissure swarms is ice-free. Tephra produced during subglacial eruptions together with lavas from the fissure swarms of Holocene age have been collected and analysed for Sr, Nd and Th isotope ratios. Those volcanic formations that can be univocally correlated to a given volcanic system display uniform isotope ratio but different from one volcanic system to another. An exception to this regularity is that Askja products have isotope ratios indistinguishable from those of Gímsvötn, but since these volcanic systems lies far apart their lava fields do not overlap. A practical aspect of these findings was demonstrated during the rifting event of Bárðarbunga and fissure eruption forming the Holuhraun lava field. Relatively low, O isotope ratios in these basalts and heterogeneous macrocrystal composition have been ascribed to important metabasaltic crustal contamination with or without crystal mush recycling. In that case a surprisingly efficient magma mixing and melt homogenization must have occurred in the past beneath the volcanic systems. One possibility is that during the rapid deglaciation much mantle melting occurred and melts accumulated at the mantle
Dispersed Volcanic Ash in Sediment Entering NW Pacific Ocean Subduction Zones: Towards a Regional Perspective

Science.gov (United States)

Scudder, R. P.; Murray, R. W.; Underwood, M.; Kutterolf, S.; Plank, T.; Dyonisius, M.; Arshad, M. A.

2011-12-01

Volcanic ash has long been recognized to be an important component of the global sedimentary system. Ash figures prominently in a number of sedimentary and petrophysical investigations, including how the fluid budget of subducting sediment will be affected by hydration/dehydration reactions. Additionally, many studies focus on discrete ash layers, and how to link their presence with volcanism, climate, arc evolution, biological productivity, and other processes. Less widely recognized is the ash that is mixed into the bulk sediment, or "dispersed" ash. Dispersed ash is quantitatively significant and is an under-utilized source of critical geochemical and tectonic information. Based on geochemical studies of ODP Site 1149, a composite of DSDP Sites 579 & 581, as well as IODP Sites C0011 & C0012 drilled during Expedition 322, we will show the importance of dispersed ash to the Izu-Bonin-Marianas, Kurile-Kamchatka and Nankai subduction zones. Initial geochemical analyses of the bulk sediment, as related to dispersed ash entering these subduction systems are presented here. Geochemical analysis shows that the characteristics of the three sites exhibit some variability consistent with observed lithological variations. For example, the average SiO2/Al2O3 ratios at Site 1149, Site C0011 and Site C0012 average 3.7. The composite of Sites 579 & 581 exhibits a higher average of 4.6. There are contrasts between other key major elemental indicators as well (e.g., Fe2O3). Ternary diagrams such as K2O-Na2O-CaO show that there are at least two distinct geochemical fields with Sites 1149, C0011 and C0012 clustering in one and Sites 579 & 581 in the other. Q-mode Factor Analysis was performed on the bulk sediment chemical data in order to determine the composition of potential end members of these sites. The multivariate statistics indicate that Site 1149 has 3-4 end members, consistent with the results of Scudder et al. (2009, EPSL, v. 284, pp 639), while each of the other sites
Multiple episodes of hydrothermal activity and epithermal mineralization in the southwestern Nevada volcanic field and their relations to magmatic activity, volcanism and regional extension

International Nuclear Information System (INIS)

Weiss, S.I.; Noble, D.C.; Jackson, M.C.

1994-01-01

Volcanic rocks of middle Miocene age and underlying pre-Mesozoic sedimentary rocks host widely distributed zones of hydrothermal alteration and epithermal precious metal, fluorite and mercury deposits within and peripheral to major volcanic and intrusive centers of the southwestern Nevada volcanic field (SWNVF) in southern Nevada, near the southwestern margin of the Great Basin of the western United States. Radiometric ages indicate that episodes of hydrothermal activity mainly coincided with and closely followed major magmatic pulses during the development of the field and together spanned more than 4.5 m.y. Rocks of the SWNVF consist largely of rhyolitic ash-flow sheets and intercalated silicic lava domes, flows and near-vent pyroclastic deposits erupted between 15.2 and 10 Ma from vent areas in the vicinity of the Timber Mountain calderas, and between about 9.5 and 7 Ma from the outlying Black Mountain and Stonewall Mountain centers. Three magmatic stages can be recognized: the main magmatic stage, Mountain magmatic stage (11.7 to 10.0 Ma), and the late magmatic stage (9.4 to 7.5 Ma)
The Park Volcanics Group : field relations of an igneous suite emplaced in the Triassic-Jurassic Murihiku Terrane, South Island, New Zealand

International Nuclear Information System (INIS)

Coombs, D.S.; Cook, N.D.J.; Campbell, J.D.

1992-01-01

flank collapse of a volcano lying beyond the present terrane boundary. In its unaltered condition, Barnicoat Andesite was an olivine two-pyroxene andesite, distinctly more tholeiitic than the Gowan and Glenham andesites. A previously reported occurrence of 'Park Intrusives' in the southern Taringatura Hills is discredited, as is the presence of Jurassic strata in that area. Weetwood Formation, in the eastern flanks of the Takitimu Mountains, is provisionally excluded from the Park Volcanics. Radiometric data indicate a Late Triassic or Early Jurassic age for the Gowan, Glenham, and Barnicoat andesites. Excluding the Pinney Volcanics, no more than 5 unequivocal volcanic events are recognised during more than 80 million years of sedimentation in the Murihiku Basin. A minimum volume of 7.5 km 3 is estimated for the Glenham Porphyry and about one-third of that figure for the Gowan Andesite. The volume of Pinney Volcanics and Barnicoat Andesite appears to be much less. Medium to high K 2 O in the Park Volcanics suggests that the locus of Murihiku sedimentation was a back-arc or possibly intra-arc rather than a fore-arc basin. (author). 46 refs., 11 figs., 1 tab
Uranium occurrences in the volcanic rocks of Upper Mahakam, east Kalimantan

International Nuclear Information System (INIS)

Djokolelono, S.; Agoes, E.

1988-01-01

The Kawat area, which is about 35 km 2 in size, is located in the Upper Mahakam region and is one of the areas being prospected in Kalimantan. It has already been covered by general, detailed and systematic prospection. The Kawat area formed a tectonical depression and was intercepted by the volcanic products of various episodes. The regional stratigraphy of this area, from the bottom upwards, is as follows: Unit 1: quartzite and ophiolitic green rock; Unit 2: black shale, sometimes with boulders of quartzite and radiolarite; Unit 3: massive conglomeratic sandstone, alternating with claystone and sandstone sequences; Unit 4: sandstone, siltstone and claystone, with an intercalation of volcanic rocks. Uraniferous occurrences are reflected by anomalous zones located in the volcanic facies of Unit 4, usually in aphanitic rhyolite. Mineralization consists of pitchblende associated with molybdenite and pyrite. Although the Kawat area is very remote, future development is of great interest. (author). 4 figs
Type of faulting and orientation of stress and strain as a function of space and time in Kilauea's south flank, Hawaii

Science.gov (United States)

Gillard, D.; Wyss, M.; Okubo, P.

1996-01-01

Earthquake focal mechanisms of events occurring between 1972 and 1992 in the south flank of Kilauea volcano, Hawaii, are used to infer the state of stress and strain as a function of time and space. We have determined 870 fault plane solutions from P wave first motion polarities for events with magnitudes ML ??? 2.5 and depth ranging between 6 and 12 km. Faulting is characterized by a mixture of decollement, reverse, and normal faults. Most large earthquakes with magnitude M 7 rupture the decollement plane, since it is the only surface large enough to generate magnitude 7 or larger earthquakes. The percentage of reverse faulting events is high compared to the decollement and normal faulting mechanisms for the period 1972-1983. The percentage of decollement type focal mechanisms becomes dominant after 1983. This pattern of faulting activity suggests that pressure was building up within Kilauea's rift zone prior to the 1983 Puu'Oo eruption. Overall, a single stress orientation with the maximum compressive stress oriented SE perpendicular to the rift and dipping at 45?? is compatible with the coeval existence of decollement, reverse, and normal faults. However, in a crustal volume east of longitude 155??10'W, we find a change of the orientation of ??1 from nearly horizontal to plunging 45?? SE occurring in 1979. This stress rotation suggests magma movements within the aseismic part of Kilauea's east rift zone. The strain and stress orientations are coaxial in the south flank except within the volume where the stress rotation is observed. We observe a change in the relationship between stress and strain directions caused either by the shifting of seismic activity from reverse faults to decollements, while stress stays constant, or by a rotation of stress, while strain remains constant. Assuming that the model of a noncohesive Coulomb wedge is appropriate for Kilauea's south flank, we find that high pore pressures are prevalent along the decollement and within the wedge

Geohazards (floods and landslides in the Ndop plain, Cameroon volcanic line

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Wotchoko Pierre

2016-07-01

Full Text Available The Ndop Plain, located along the Cameroon Volcanic Line (CVL, is a volcano-tectonic plain, formed by a series of tectonic movements, volcanic eruptions and sedimentation phases. Floods (annually and landslides (occasionally occur with devastating environmental effects. However, this plain attracts a lot of inhabitants owing to its fertile alluvial soils. With demographic explosion in the plain, the inhabitants (143,000 people tend to farm and inhabit new zones which are prone to these geohazards. In this paper, we use field observations, laboratory analyses, satellite imagery and complementary methods using appropriate software to establish hazard (flood and landslide maps of the Ndop Plain. Natural factors as well as anthropogenic factors are considered.
Geology and zircon fission track ages of volcanic rocks in the western part of Hoshino gold area, Fukuoka Prefecture, Japan

Energy Technology Data Exchange (ETDEWEB)

Belhadi, Ahmed; Himeno, Osamu; Watanabe, Koichiro; Izawa, Eiji [Kyushu Univ., Fukuoka (Japan). Faculty of Engineering

1999-12-01

The Hoshino gold area is located in the western part of the Hohi volcanic zone, northern Kyushu. Volcanic rocks in this area vary from andesitic rocks in the north to dacite and rhyolite in the South. The basement is constituted by metamorphic rocks of pre-Cretaceous age. The volcanic rocks of Pliocene age were subdivided into eight volcanic units. Seven fission track ages of zircons from five volcanic units have been determined, using the external detector method. The age data obtained, combined with some previously reported ages, show that two main volcanic activities have occurred in the area. The first volcanic activity took place around 4.3 Ma, and resulted into the deposition of the Hoshino Andesite and the Ikenoyama Conglomerate. The second main volcanism started around 3.5 Ma, and was characterized by the eruption of the Shakadake Andesite and the Reiganji Andesite at the early stage, then, by more acidic rocks of the Takeyama Andesite, the Hyugami Dacite and the Kuroki Rhyolite at the later stage. The main volcanism in the area ceased around 2.6 Ma. (author)
Mega-rings Surrounding Timber Mountain Nested Calderas, Geophysical Anomalies: Rethinking Structure and Volcanism Near Yucca Mountain (YM), Nevada

Science.gov (United States)

Tynan, M. C.; Smith, K. D.; Savino, J. M.; Vogt, T. J.

2004-12-01

Observed regional mega-rings define a zone ˜80-100 km in diameter centered on Timber Mountain (TM). The mega-rings encompass known smaller rhyolitic nested Miocene calderas ( ˜11-15 my, structural relationships. Mega-rings consist of arcuate faulted blocks with deformation (some remain active structures) patterns showing a genetic relationship to the TM volcanic system; they appear to be spatially associated and temporally correlated with Miocene volcanism and two geophysically identified crustal/upper mantle features. A 50+ km diameter pipe-like high velocity anomaly extends from crustal depth to over 200 km beneath TM (evidence for 400km depth to NE). The pipe is located between two ˜100 km sub-parallel N/S linear trends of small-magnitude earthquake activity, one extending through the central NV Test Site, and a second located near Beatty, NV. Neither the kinematics nor relational mechanism of 100km seismically active N/S linear zones, pipe, and mega-rings are understood. Interpreted mega-rings are: 1) Similar in size to larger terrestrial volcanic complexes (e.g., Yellowstone, Indonesia's Toba system); 2) Located in the region of structural transition from the Mohave block to the south, N/S Basin and Range features to the north, Walker Lane to the NW, and the Las Vegas Valley shear zone to the SE; 3) Associated with the two seismically active zones (similar to other caldera fault-bounded sags), the mantle high velocity feature, and possibly a regional bouguer gravity anomaly; 4) Nearly coincident with area hydrologic basins and sub-basins; 5) Similar to features described from terrestrial and planetary caldera-collapse studies, and as modeled in laboratory scaled investigations (ice melt, balloon/sand). Post Mid-Miocene basalts commonly occur within or adjacent to the older rhyolitic caldera moats; other basaltic material occurs marginal to both the outer rings of the interpreted mega-ring system and high velocity pipe. The YM repository may be situated in
Magma replenishment and volcanic unrest inferred from the analysis of VT micro-seismicity and seismic velocity changes at Piton de la Fournaise Volcano

Science.gov (United States)

Brenguier, F.; Rivemale, E.; Clarke, D. S.; Schmid, A.; Got, J.; Battaglia, J.; Taisne, B.; Staudacher, T.; Peltier, A.; Shapiro, N. M.; Tait, S.; Ferrazzini, V.; Di Muro, A.

2011-12-01

Piton de la Fournaise volcano (PdF) is among the most active basaltic volcanoes worldwide with more than one eruption per year on average. Also, PdF is densely instrumented with short-period and broad-band seismometers as well as with GPS receivers. Continuous seismic waveforms are available from 1999. Piton de la Fournaise volcano has a moderate inter-eruptive seismic activity with an average of five detected Volcano-Tectonic (VT) earthquakes per day with magnitudes ranging from 0.5 to 3.5. These earthquakes are shallow and located about 2.5 kilometers beneath the edifice surface. Volcanic unrest is captured on average a few weeks before eruptions by measurements of increased VT seismicity rate, inflation of the edifice summit, and decreased seismic velocities from correlations of seismic noise. Eruptions are usually preceded by seismic swarms of VT earthquakes. Recently, almost 50 % of seismic swarms were not followed by eruptions. Within this work, we aim to gather results from different groups of the UnderVolc research project in order to better understand the processes of deep magma transfer, volcanic unrest, and pre-eruptive magma transport initiation. Among our results, we show that the period 1999-2003 was characterized by a long-term increase of VT seismicity rate coupled with a long-term decrease of seismic velocities. These observations could indicate a long-term replenishment of the magma storage area. The relocation of ten years of inter-eruptive micro-seismicity shows a narrow (~300 m long) sub-vertical fault zone thus indicating a conduit rather than an extended magma reservoir as the shallow magma feeder system. Also, we focus on the processes of short-term volcanic unrest and prove that magma intrusions within the edifice leading to eruptions activate specific VT earthquakes that are distinct from magma intrusions that do not lead to eruptions. We thus propose that, among the different pathways of magma transport within the edifice, only one will
Mount Etna-Iblean volcanism caused by rollback-induced upper mantle upwelling around the Ionian slab edge : An alternative to the plume model

NARCIS (Netherlands)

Schellart, W. P.

Volcanism in Sicily (Italy) at Mount Etna (0.5 Ma to present) and the Iblean Plateau (ca. 7.0-1.1 Ma) remains enigmatic, because it is located in close proximity to, but is laterally offset from, the Calabrian subduction zone. Previous work suggests that the volcanism results from a plume or from
Mercury speciation, fluxes, and fate in the volcanically acidified fluids of Copahue volcano, Argentina

Science.gov (United States)

Kading, T.; Varekamp, J. C.; Andersson, M.; Balcom, P.; Mason, R. P.

2010-12-01

The behavior of mercury in volcanic acid springs and acidified rivers is poorly known, despite the potential impact this vector of contamination has on local surface and ground water quality. Mercury was measured in a volcanically acidified river system (pHvolcano, determined from river water flux measurements and Hg concentrations, was modest and varied between the 3/2008 and 3/2009 sampling campaigns resp. from 0.7 to 1.1 moles/year. The Hg:S ratio of the acid fluids was ~10-8, several orders of magnitude lower than that typically found in volcanic plumes and fumaroles. The small Hg flux and low Hg:S values suggest that the system is either inherently Hg-poor or has lost Hg through vapor loss deeper in the hydrothermal system. Support for the latter comes from high Hg concentrations in geothermal vents and mudpots on the flank of the mountain (24 - 55 ppm Hg). Mercury concentrations decreased conservatively downstream in the river as based on Hg/Cl and Hg/SO4. Non-conservative depletion occurs in the less acidic Lake Caviahue, suggesting that mercury is removed from the water column by sorption to organic matter or other phases. Mercury analyses of a short lake sediment core confirm this (Hg = 0.01 to 0.70 ppm). No evidence was found for preferential uptake of mercury by jarosite, schwertmannite, or goethite, although the latter two phases precipitate in the most distal and Hg-depleted section of the fluvial system.
Mitigation of Flanking Noise Transmission in Periodic Structures of Lightweight Elements

DEFF Research Database (Denmark)

Domadiya, Parthkumar Gandalal

through structural junctions and radiates into neighbouring rooms. To diminish the flanking transmission of sound, frames are usually designed with single or double studs or constructed with layers of foam or another viscoelastic material. This thesis is investigating the behaviour of flanking noise...... transmission in periodic structures of lightweight elements by employing various numerical, analytical and experimental methods. At first, three dimensional finite-element (FE) models of a Z-shaped lightweight panel structure based on various frame designs, inclusion of air and structural coupling between...... elements are considered for describing flanking noise transmission through panels. It is assumed that the ribs are fully fixed to the plates in case of various frame designs, and a parametric study is carried out on the centre panel with regard to various spacing between the ribs. Solid finite elements...
Flank tectonics of Martian volcanoes

International Nuclear Information System (INIS)

Thomas, P.J.; Squyres, S.W.; Carr, M.H.

1990-01-01

On the flanks of Olympus Mons is a series of terraces, concentrically distributed around the caldera. Their morphology and location suggest that they could be thrust faults caused by compressional failure of the cone. In an attempt to understand the mechanism of faulting and the possible influences of the interior structure of Olympus Mons, the authors have constructed a numerical model for elastic stresses within a Martian volcano. In the absence of internal pressurization, the middle slopes of the cone are subjected to compressional stress, appropriate to the formation of thrust faults. These stresses for Olympus Mons are ∼250 MPa. If a vacant magma chamber is contained within the cone, the region of maximum compressional stress is extended toward the base of the cone. If the magma chamber is pressurized, extensional stresses occur at the summit and on the upper slopes of the cone. For a filled but unpressurized magma chamber, the observed positions of the faults agree well with the calculated region of high compressional stress. Three other volcanoes on Mars, Ascraeus Mons, Arsia Mons, and Pavonis Mons, possess similar terraces. Extending the analysis to other Martian volcanoes, they find that only these three and Olympus Mons have flank stresses that exceed the compressional failure strength of basalt, lending support to the view that the terraces on all four are thrust faults
Soil gases and SAR measurements reveal hidden faults on the sliding flank of Mt. Etna (Italy)

Science.gov (United States)

Bonforte, Alessandro; Federico, Cinzia; Giammanco, Salvatore; Guglielmino, Francesco; Liuzzo, Marco; Neri, Marco

2013-02-01

From October 2008 to November 2009, soil CO2, radon and structural field surveys were performed on Mt. Etna, in order to acquire insights into active tectonic structures in a densely populated sector of the south-eastern flank of the volcano, which is involved in the flank dynamics, as highlighted by satellite data (InSAR). The studied area extends about 150 km2, in a sector of the volcano where InSAR results detected several lineaments that were not well-defined from previous geological surveys. In order to validate and better constrain these features with ground data evidences, soil CO2 and soil radon measurements were performed along transects roughly orthogonal to the newly detected faults, with measurement points spaced about 100 m. In each transect, the highest CO2 values were found very close to the lineaments evidenced by InSAR observations. Anomalous soil CO2 and radon values were also measured at old eruptive fractures. In some portions of the investigated area soil gas anomalies were rather broad over transects, probably suggesting a complex structural framework consisting of several parallel volcano-tectonic structures, instead of a single one. Soil gas measurements proved particularly useful in areas at higher altitude on Mt. Etna (i.e. above 900 m asl), where InSAR results are not very informative/are fairly limited, and allowed recognizing the prolongation of some tectonic lineaments towards the summit of the volcano. At a lower altitude on the volcanic edifice, soil gas anomalies define the active structures indicated by InSAR results prominently, down to almost the coastline and through the northern periphery of the city of Catania. Coupling InSAR with soil gas prospecting methods has thus proved to be a powerful tool in detecting hidden active structures that do not show significant field evidences.
Monitoring diffuse degassing in monogentic volcanic field during a quiescent period: the case of Cumbre Vieja (La Palma,Canary Islands, Spain)

Science.gov (United States)

Burns, F.; Cole, M.; Vaccaro, W.; Alonso Cótchico, M.; Melián, G.; Asensio-Ramos, M.; Padron, E.; Hernandez Perez, P. A.; Perez, N. M.

2017-12-01

Volcanic activity at La Palma (Canary Islands) in the last 123 ka has taken place exclusively at the southern part of the island, where Cumbre Vieja volcano, which is characterized by a main north-south rift zone 20 km long and up to 1950 m in elevation and covering an area of 220 km2 with vents located also at the northwest and northeast. Cumbre Vieja is the most active basaltic volcano in the Canaries with 7 historical eruptions being San Juan (1949) and Teneguía (1971) the most recent ones. Since no visible degassing (fumaroles, etc.) at Cumbre Vieja occurs, our geochemical program for the volcanic surveillance of Cumbre Vieja is mainly focused on diffuse degassing monitoring. Diffuse CO2 emission surveys are yearly performed in summer to minimize the influence of meteorological variations. About 570 sampling sites were selected for each survey to obtain a homogeneous distribution after taking into consideration the local geology, structure, and accessibility. Measurements of soil CO2 efflux were performed in situ by means of a portable non-dispersive infrared sensor following the accumulation chamber method. The soil CO2 efflux values of the 2017 survey ranged from non-detectable to 47.7 g m-2 d-1. Statistical-graphical analysis of the data show two different geocheleemical populations; background (B) and peak (P) represented by 98.2% and 1.8% of the total data, respectively. The geometric means of the B and P populations are 2.9 and 36.5 g m-2 d-1, respectively. Most of the area showed B values while the P values were mainly observed both flanks of the main N-S volcanic rift. To estimate the diffuse CO2 emission in metric tons per day released from Cumbre Vieja (220 km2) for the 2017 survey, we ran about 100 sGs simulations. The estimated 2017 diffuse CO2 output released to atmosphere by Cumbre Vieja was at 801 ± 27 t d-1, value relatively higher than the background average of CO2 emission estimated on 374 t d-1 and within the background range of 132 t d-1
Albari granodiorite - a typical calcalkaline diapir of volcanic arc stage from the Arabian Shield

Science.gov (United States)

Radain, Abdulaziz A.

Granodiorite rocks of the Arabian Shield are generally considered to be collision-related granitoids. However, there are some granodiorites that were formed during the volcanic arc stage. Major and trace elements studies are carried out on Albari diapiric granodiorite to reveal its tectonic environment. This intrusive rock type is common in the Taif arc province (Mahd adh Dhahab quadrangle) of the Asir microplate near the border of the southeast dipping subduction zone that ended up with arc-arc collision (Asir-Hijaz microplates) along the now known Bir Umq suture zone. The granodiorite exhibits a calcalkaline trend on ternary AFM and K 2ONa 2OCaO diagrams. Tectonic discrimination diagrams using multicationic parameters (R1 = 4Sill(Na+K)2(Fe+Ti); R2 = 6Ca+2Mg+Al), SiO 2-trace elements (Nb, Y, Rb), and Y versus Nb and Rb versus (Y+Nb) indicate a destructive active plate margin or volcanic arc stage tectonic environment. Albari calcalkaline granodiorite might have been derived directly from partial melting of subducted oceanic crust or overlying mantle contaminated with variable amounts of intermediate (quartz diorite, diorite, tonalite, trondhjemite) early and late volcanic arc-related plutonic country rocks.
Concurrent Preoperative Presence of Hydronephrosis and Flank Pain Independently Predicts Worse Outcome of Upper Tract Urothelial Carcinoma.

Science.gov (United States)

Yeh, Hsin-Chih; Jan, Hau-Chern; Wu, Wen-Jeng; Li, Ching-Chia; Li, Wei-Ming; Ke, Hung-Lung; Huang, Shu-Pin; Liu, Chia-Chu; Lee, Yung-Chin; Yang, Sheau-Fang; Liang, Peir-In; Huang, Chun-Nung

2015-01-01

To investigate the impact of preoperative hydronephrosis and flank pain on prognosis of patients with upper tract urothelial carcinoma. In total, 472 patients with upper tract urothelial carcinoma managed by radical nephroureterectomy were included from Kaohsiung Medical University Hospital Healthcare System. Clinicopathological data were collected retrospectively for analysis. The significance of hydronephrosis, especially when combined with flank pain, and other relevant factors on overall and cancer-specific survival were evaluated. Of the 472 patients, 292 (62%) had preoperative hydronephrosis and 121 (26%) presented with flank pain. Preoperative hydronephrosis was significantly associated with age, hematuria, flank pain, tumor location, and pathological tumor stage. Concurrent presence of hydronephrosis and flank pain was a significant predictor of non-organ-confined disease (multivariate-adjusted hazard ratio = 2.10, P = 0.025). Kaplan-Meier analysis showed significantly poorer overall and cancer-specific survival in patients with preoperative hydronephrosis (P = 0.005 and P = 0.026, respectively) and in patients with flank pain (P hydronephrosis and flank pain independently predicted adverse outcome (hazard ratio = 1.98, P = 0.016 for overall survival and hazard ratio = 1.87, P = 0.036 for and cancer-specific survival, respectively) in multivariate Cox proportional hazards models. In addition, concurrent presence of hydronephrosis and flank pain was also significantly predictive of worse survival in patient with high grade or muscle-invasive disease. Notably, there was no difference in survival between patients with hydronephrosis but devoid of flank pain and those without hydronephrosis. Concurrent preoperative presence of hydronephrosis and flank pain predicted non-organ-confined status of upper tract urothelial carcinoma. When accompanied with flank pain, hydronephrosis represented an independent predictor for worse outcome in patients with upper tract
Basalt microlapilli in deep sea sediments of Indian Ocean in the vicinity of Vityaz fracture zone

Digital Repository Service at National Institute of Oceanography (India)

Nath, B.N.; Iyer, S.D.

Two cores recovered from the flanks of Mid-India oceanic ridge in the vicinity of Vityaz fracture zone consist of discrete pyroclastic layers at various depths. These layers are composed of coarse-grained, angular basaltic microlapilli in which...
Revealing the hidden faults in the SE flank of Mt. Etna using radon in-soil gas measurement.

Science.gov (United States)

Johnová, K; Thinová, L; Giammanco, S

2014-07-01

Although there are many methods for investigating tectonic structures, many faults remain hidden, and they can endanger the life and property of people living along them. The slopes of volcanoes are covered with such hidden faults, near which strong earthquakes and gas releases can appear. Revealing hidden faults can therefore contribute significantly to the protection of people living in volcanic areas. In the study, seven different techniques were used for making measurements of in-soil radon concentrations in order to search for hidden faults on the SE flank of the Mt. Etna volcano. These reported methods had previously been proved to be useful tools for investigating fault structures. The main aim of the experiment presented here was to evaluate the usability of these methods in the geological conditions of the Mt. Etna region, and to find the best place for continual radon monitoring using a permanent station in the near future. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Detection of and response to a probable volcanogenic T-wave event swarm on the western Blanco Transform Fault Zone

Science.gov (United States)

Dziak, R.P.; Fox, C.G.; Embley, R.W.; Lupton, J.E.; Johnson, G.C.; Chadwick, W.W.; Koski, R.A.

1996-01-01

The East Blanco Depression (EBD), a pull-apart basin within the western Blanco Transform Fault Zone (BTFZ), was the site of an intense earthquake T-wave swarm that began at 1317Z on January 9, 1994. Although tectonically generated earthquakes occur frequently along the BTFZ, this swarm was unusual in that it was preceded and accompanied by periodic, low-frequency, long-duration acoustic signals, that originated from near the swarm epicenters. These tremor-like signals were very similar in character to acoustic energy produced by a shallow-submarine eruption near Socorro Island, a seamount several hundred km west of Baja, California. The ???69 earthquakes and ???400 tremor-like events at the EBD occurred sporadically, with two periods of peak activity occurring between January 5-16 and 27-31. The swarm-like character of the earthquakes and the similarity of the tremor activity to the Socorro eruption indicated that the EBD was undergoing an intrusion or eruption episode. On January 27, six CTD/rosette casts were conducted at the site. Water samples from two of the stations yielded anomalous 3He concentrations, with maxima at ???2800 m depth over the main basin. In June 1994 two camera tows within the basin yielded evidence of pillow-lava volcanism and hydrothermal deposits, but no conclusive evidence of a recent seafloor eruption. In September 1994, deployments of the U.S. Navy's Advanced Tethered Vehicle resulted in the discovery of an active hydrothermal mound on the flanks of a pillow-lava volcano. The hydrothermal mound consists of Fe-rich hydrothermal precipitate and bacterial mats. Temperatures to 60??C were measured 30 cm below the surface. This is the first discovery of active hydrothermal vents along an oceanic fracture zone. Although no conclusive evidence of volcanic activity associated with the T-wave event swarm was found during these response efforts, the EBD has been the site of recent seafloor eruptions. Copyright 1996 by the American Geophysical
Spatial Characteristics of Geothermal Spring Temperatures and Discharge Rates in the Tatun Volcanic Area, Taiwan

Science.gov (United States)

Jang, C. S.; Liu, C. W.

2014-12-01

The Tatun volcanic area is the only potential volcanic geothermal region in the Taiwan island, and abundant in hot spring resources owing to stream water mixing with fumarolic gases. According to the Meinzer's classification, spring temperatures and discharge rates are the most important properties for characterizing spring classifications. This study attempted to spatially characterize spring temperatures and discharge rates in the Tatun volcanic area, Taiwanusing indicator kriging (IK). First, data on spring temperatures and discharge rates, which were collected from surveyed data of the Taipei City Government, were divided into high, moderate and low categories according to spring classification criteria, and the various categories were regarded as estimation thresholds. Then, IK was adopted to model occurrence probabilities of specified temperatures and discharge rates in springs, and to determine their classifications based on estimated probabilities. Finally, nine combinations were obtained from the classifications of temperatures and discharge rates in springs. Moreover, the combinations and features of spring water were spatially quantified according to seven sub-zones of spring utilization. A suitable and sustainable development strategy of the spring area was proposed in each sub-zone based on probability-based combinations and features of spring water.The research results reveal that the probability-based classifications using IK provide an excellent insight in exploring the uncertainty of spatial features in springs, and can provide Taiwanese government administrators with detailed information on sustainable spring utilization and conservation in the overexploited spring tourism areas. The sub-zones BT (Beitou), RXY (Rd. Xingyi), ZSL (Zhongshanlou) and LSK (Lengshuikeng) with high or moderate discharge rates are suitable to supply spring water for tourism hotels.Local natural hot springs should be planned in the sub-zones DBT (Dingbeitou), ZSL, XYK
Volcanic impediments in the progressive development of pre-Columbian civilizations in the Ecuadorian Andes

Science.gov (United States)

Hall, Minard L.; Mothes, Patricia A.

2008-10-01

Archaeological investigations in Ecuador have proposed that there appear to be hiatus or anomalous jumps in the progressive development of pre-Columbian indigenous cultures, based upon the fact that their ceramics and tools demonstrate abrupt advances in their sophistication at several horizons in the soil profile. Because some of these horizons are clearly associated with volcanic ash layers, archaeologists have sought a causal relation with volcanism, that is, the eruptive events or their products severely interfered with the early inhabitants, resulting in their abandonment of certain areas. Geological studies of the young volcanoes in the Ecuadorian Andes carried out during the past two decades now allow us to make a more thorough evaluation of the role of volcanism during the Holocene. This contribution briefly describes the principal Holocene volcanic events and the distribution of the corresponding eruptive products found along the InterAndean Valley, from southern Colombia to central Ecuador. Only those events that were sufficiently large that they could have had a detrimental effect on the valley's early residents are discussed. Dacitic and rhyolitic ash flows, as well as numerous debris flows (lahars) have occurred frequently and their deposits cover many valleys and floodplains, where early inhabitants probably settled. The enormous Chillos Valley lahar, associated with the 4500 yBP eruption of Cotopaxi volcano, buried soils containing ceramics of the early Formative Period. However, the greatest impact upon mankind was probably not these short-lived violent events, but rather the burying of settlements and agricultural fields by ash fallout, the effect of which may have lasted hundreds of years. Ash fall layers are observed in pre-Columbian cultural horizons in the soil profile, occurring in the InterAndean Valley, the lower flanks of the Andes, and along Ecuador's Pacific coast, the oldest corresponding to the 5800 yBP eruption of Cotopaxi. This brief
Volcanic stratigraphy: A review

Science.gov (United States)

Martí, Joan; Groppelli, Gianluca; Brum da Silveira, Antonio

2018-05-01

Volcanic stratigraphy is a fundamental component of geological mapping in volcanic areas as it yields the basic criteria and essential data for identifying the spatial and temporal relationships between volcanic products and intra/inter-eruptive processes (earth-surface, tectonic and climatic), which in turn provides greater understanding of the geological evolution of a region. Establishing precise stratigraphic relationships in volcanic successions is not only essential for understanding the past behaviour of volcanoes and for predicting how they might behave in the future, but is also critical for establishing guidelines for exploring economic and energy resources associated with volcanic systems or for reconstructing the evolution of sedimentary basins in which volcanism has played a significant role. Like classical stratigraphy, volcanic stratigraphy should also be defined using a systematic methodology that can provide an organised and comprehensive description of the temporal and spatial evolution of volcanic terrain. This review explores different methods employed in studies of volcanic stratigraphy, examines four case studies that use differing stratigraphic approaches, and recommends methods for using systematic volcanic stratigraphy based on the application of the concepts of traditional stratigraphy but adapted to the needs of volcanological environment.
Friction in volcanic environments

Science.gov (United States)

Kendrick, Jackie E.; Lavallée, Yan

2016-04-01

Volcanic landscapes are amongst the most dynamic on Earth and, as such, are particularly susceptible to failure and frictional processes. In rocks, damage accumulation is frequently accompanied by the release of seismic energy, which has been shown to accelerate in the approach to failure on both a field and laboratory scale. The point at which failure occurs is highly dependent upon strain-rate, which also dictates the slip-zone properties that pertain beyond failure, in scenarios such as sector collapse and pyroclastic flows as well as the ascent of viscous magma. High-velocity rotary shear (HVR) experiments have provided new opportunities to overcome the grand challenge of understanding faulting processes during volcanic phenomena. Work on granular ash material demonstrates that at ambient temperatures, ash gouge behaves according to Byerlee's rule at low slip velocities, but is slip-weakening, becoming increasingly lubricating as slip ensues. In absence of ash along a slip plane, rock-rock friction induces cataclasis and heating which, if sufficient, may induce melting (producing pseudotachylyte) and importantly, vesiculation. The viscosity of the melt, so generated, controls the subsequent lubrication or resistance to slip along the fault plane thanks to non-Newtonian suspension rheology. The shear-thinning behaviour and viscoelasticity of frictional melts yield a tendency for extremely unstable slip, and occurrence of frictional melt fragmentation. This velocity-dependence acts as an important feedback mechanism on the slip plane, in addition to the bulk composition, mineralogy and glass content of the magma, that all influence frictional behaviour. During sector collapse events and in pyroclastic density currents it is the frictional properties of the rocks and ash that, in-part, control the run-out distance and associated risk. In addition, friction plays an important role in the eruption of viscous magmas: In the conduit, the rheology of magma is integral
The Origin of Widespread Long-lived Volcanism Across the Galapagos Volcanic Province

Science.gov (United States)

O'Connor, J. M.; Stoffers, P.; Wijbrans, J. R.; Worthington, T. J.

2005-12-01

40Ar/39Ar ages for rocks dredged (SO144 PAGANINI expedition) and drilled (DSDP) from the Galapagos Volcanic Province (Cocos, Carnegie, Coiba and Malpelo aseismic ridges and associated seamounts) show evidence of 1) increasing age with distance from the Galapagos Archipelago, 2) long-lived episodic volcanism at many locations, and 3) broad overlapping regions of coeval volcanism. The widespread nature of synchronous volcanism across the Galapagos Volcanic Province (GVP) suggests a correspondingly large Galapagos hotspot melting anomaly (O'Connor et al., 2004). Development of the GVP via Cocos and Nazca plate migration and divergence over this broad melting anomaly would explain continued multiple phases of volcanism over millions of years following the initial onset of hotspot volcanism. The question arising from these observations is whether long-lived GVP episodic volcanism is equivalent to `rejuvenescent' or a `post-erosional' phase of volcanism that occurs hundreds of thousands or million years after the main shield-building phase documented on many mid-plate seamount chains, most notably along the Hawaiian-Emperor Seamount Chain? Thus, investigating the process responsible for long-lived episodic GVP volcanism provides the opportunity to evaluate this little understood process of rejuvenation in a physical setting very different to the Hawaiian-Emperor Chain (i.e. on/near spreading axis versus mid-plate). We consider here timing and geochemical information to test the various geodynamic models proposed to explain the origin of GVP hotspot volcanism, especially the possibility of rejuvenated phases that erupt long after initial shield-building.

Status of volcanic hazard studies for the Nevada Nuclear Waste Storage Investigations. Volume II

International Nuclear Information System (INIS)

Crowe, B.M.; Wohletz, K.H.; Vaniman, D.T.; Gladney, E.; Bower, N.

1986-01-01

Volcanic hazard investigations during FY 1984 focused on five topics: the emplacement mechanism of shallow basalt intrusions, geochemical trends through time for volcanic fields of the Death Valley-Pancake Range volcanic zone, the possibility of bimodal basalt-rhyolite volcanism, the age and process of enrichment for incompatible elements in young basalts of the Nevada Test Site (NTS) region, and the possibility of hydrovolcanic activity. The stress regime of Yucca Mountain may favor formation of shallow basalt intrusions. However, combined field and drill-hole studies suggest shallow basalt intrusions are rare in the geologic record of the southern Great Basin. The geochemical patterns of basaltic volcanism through time in the NTS region provide no evidence for evolution toward a large-volume volcanic field or increases in future rates of volcanism. Existing data are consistent with a declining volcanic system comparable to the late stages of the southern Death Valley volcanic field. The hazards of bimodal volcanism in this area are judged to be low. The source of a 6-Myr pumice discovered in alluvial deposits of Crater Flat has not been found. Geochemical studies show that the enrichment of trace elements in the younger rift basalts must be related to an enrichment of their mantle source rocks. This geochemical enrichment event, which may have been metasomatic alteration, predates the basalts of the silicic episode and is, therefore, not a young event. Studies of crater dimensions of hydrovolcanic landforms indicate that the worst case scenario (exhumation of a repository at Yucca Mountain by hydrovolcanic explosions) is unlikely. Theoretical models of melt-water vapor explosions, particularly the thermal detonation model, suggest hydrovolcanic explosion are possible at Yucca Mountain. 80 refs., 21 figs., 5 tabs
Radioisotope distribution characteristics of the groundwater system in volcanic-type U deposits and isotope-dating estimation of the system

International Nuclear Information System (INIS)

Zhou Bingguan

1988-01-01

On the basis of groundwater sample measurements collected from the uranogenic belt of Mesozoic volcanic rocks in East China, the distribution characteristics of radioisotopes, including the total U content (CΣu), the activity of nuclides (Aui) or their activity ratio (ARu) and the relationship among the three ((Aui,ARu)=f(CΣu)), have been studied. Also, it is performed for radioactive water halos in the area to be divided into four various mineralization tendencies: (1) the convergent tendency of negative correlation, which has the genetic relationship with the primary U accumulation in volcanic rocks; (2) the scattered tendency of positive correlation, which is intimately related to epigenetic U mineralization in the supergene zone of volcanic rocks or in the sandstones; (3) the both positive and negative multiple-correlative tendency, which indicates that the primary volcanic-type U deposit has been leached and destroyed, and the secondary U enrichment has occurred within the supergene zone; (4) non-correlative tendency, which mainly results from increasing dispersion U. For the above recognitions, an evolution model for radioactive water halos related to this type of U deposit has been derived, and an attempt to estimate the radioisotopic age of the groundwater system also has been made. (author). 14 refs, 9 figs, 2 tabs
STRATIGRAPHY AND STURUCTURAL EVOLUTION OF PONTID/ANATOLID SUTURE ZONE IN NE ANATOLIA (BETWEEN OLTU-NARMAN

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Cevdet BOZKUŞ

1998-01-01

Full Text Available The rock units formed in Late Cretaceous to recent, outcrop in the investigated area. The oldest rock unit of the suture zone is a flysch (Alıcık formatıon of Upper Cretaceous (Santonıan-Maastrichtıan age containing volcanic intercalations. Ophiolitic melange tectonically set on the flysch. The initial emplacement of the ophioli- tic melange sheets in this area occur between Late Cretaceous and pre early Eocene. Lower-Midlle Eocene aged, fine grained continental to shallow marine sediments (Dağdibi formatıon cover all the units with an angular unconformity. On these sediments, Upper Eocene basic (basalt, basaltic andesite, tuff volcanics (Karataş formatıon are observed. Oligocene aged continental molasse sediments (Narman group which lie on the older units with an angular unconformity are; continental clastics, volcanic products and gypsum at the top displaying a thinning and fining upward motif of sequence. Pliocene-Pleistocene aged conglomerates represent river environments, cover all the units with an angular unconformity. Recent deposits are slope debris and alluvium. All the rocks exposed in the investigated area which take place Pontid /Anatolid suture zone and developed under the control of collisional tectonic processes of these two continents. In Upper Cretaceous age, the flysch is formed in a trench developed along a nortward dipping subductıon zone.. Ophiolitic melange which limits the suture zone at the south, is formed by slicing of oceanic crust and mixing of these slices with trench sediments by means of a tectono-sedimentary system.The collosion of Pontid/Anatolid continents (happened after Late Cretaceous and before Early Eocene. Lower-Mıddle Eocene (Ipresian-Lutetian aged continental, to shallow marine deposits were formed in an asimetric forearc molassic basin which developed along the suture zone. Oligocene aged continental deposits were developed together with volcanics in continental intermountain molassic
DISQUIETUDE ON THE EASTERN FLANK: AWAITING ALLIANCE RESPONSE

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Octavian Manea

2010-03-01

Full Text Available The absence of significant and tangible military defensive infrastructure on the Eastern flank generated over time a breach of credibility in the security guarantee provided by NATO under its Article 5 commitment. The main argument of the countries in the New Europe now is that, in order to be credible enough, and not just a paper guarantee, a collective defence commitment must be backed by “boots on the ground” and by military tangible logistics.While assuming this perspective, the present article looks at some of the alarm signals coming from the countries on NATO’s Eastern flank, trying to explain the feeling of insecurity perceived by the states in the region as well as the options available to the Euro-Atlantic community in order to engage in a much-needed process of strategic reassurance.
Economic method for helical gear flank surface characterisation

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Koulin, G.; Reavie, T.; Frazer, R. C.; Shaw, B. A.

2018-03-01

Typically the quality of a gear pair is assessed based on simplified geometric tolerances which do not always correlate with functional performance. In order to identify and quantify functional performance based parameters, further development of the gear measurement approach is required. Methodology for interpolation of the full active helical gear flank surface, from sparse line measurements, is presented. The method seeks to identify the minimum number of line measurements required to sufficiently characterise an active gear flank. In the form ground gear example presented, a single helix and three profile line measurements was considered to be acceptable. The resulting surfaces can be used to simulate the meshing engagement of a gear pair and therefore provide insight into functional performance based parameters. Therefore the assessment of the quality can be based on the predicted performance in the context of an application.
New Age and Geochemical Data From Seamounts in the Canary and Madeira Volcanic Provinces: A Contribution to the "Great Plume Debate"

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Geldmacher, J.; Hoernle, K.; van den Bogaard, P.; Duggen, S.; Werner, R.

2004-12-01

The role of hotspots (mantle plumes) in the formation of intraplate volcanic island and seamount groups is being increasingly questioned, in particular concerning the abundant and somewhat irregularly distributed island and seamount volcanoes off the coast of northwest Africa. However, new 40Ar/39Ar ages and Sr-Nd-Pb isotope geochemistry of volcanic rocks from two seamounts northeast of the Canary Islands and two northeast of the Madeira Islands provide new support for the plume hypothesis. The oldest ages of shield stage volcanism from seamounts and islands northeast of the Canary and Madeira Islands confirm progressions of increasing age to the northeast for both island/seamount chains consistent with northeast directed plate motion. Calculated angular velocities for the average movement of the African plate in both regions gave similar values of about 0.45\\deg plus/minus 0.05\\deg/Ma around a rotation pole located north of the Azores Islands. Furthermore, the curvature of the chains clearly deviates from the E-W orientation of fracture zones in the East Atlantic. A local control of surface volcanism by lithospheric zones of weakness, however, is likely for some E-W elongated seamounts and islands. The isotope geochemistry additionally confirms that the two volcanic provinces are derived from distinct sources, consistent with distinct mantle plumes having formed both volcanic groups. Conventional hotspot models, however, cannot easily explain the wide distribution of seamounts in the Canary region and the long history of volcanic activity at single volcanic centers (e.g. Dacia seamount, 47-4 Ma; Selvagen Islands, 30-3 Ma). A possible explanation could involve interaction of a Canary mantle plume with small-scale upper mantle processes such as edge driven convection at the edge of the NW African craton (e.g. King and Ritsema, 2000, Science 290, 1137-1140).
Structural control on arc volcanism: The Caviahue Copahue complex, Central to Patagonian Andes transition (38°S)

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Melnick, Daniel; Folguera, Andrés; Ramos, Victor A.

2006-11-01

This paper describes the volcanostratigraphy, structure, and tectonic implications of an arc volcanic complex in an oblique subduction setting: the Caviahue caldera Copahue volcano (CAC) of the Andean margin. The CAC is located in a first-order morphotectonic transitional zone, between the low and narrow Patagonian and the high and broad Central Andes. The evolution of the CAC started at approximately 4-3 Ma with the opening of the 20 × 15 km Caviahue pull-apart caldera; Las Mellizas volcano formed inside the caldera and collapsed at approximately 2.6 Ma; and the Copahue volcano evolved in three stages: (1) 1.2-0.7 Ma formed the approximately 1 km thick andesitic edifice, (2) 0.7-0.01 Ma erupted andesitic-dacitic subglacial pillow lavas, and (3) 0.01-0 Ma erupted basaltic-andesites and pyroclastic flows from fissures, aligned cones, and summit craters. Magma ascent has occurred along planes perpendicular to the least principal horizontal stress, whereas hydrothermal activity and hot springs also occur along parallel planes. At a regional scale, Quaternary volcanism concentrates along the NE-trending, 90 km long Callaqui-Copahue-Mandolegüe lineament, the longest of the southern volcanic zone, which is here interpreted as an inherited crustal-scale transfer zone from a Miocene rift basin. At a local scale within the CAC, effusions are controlled by local structures that formed at the intersection of regional fault systems. The Central to Patagonian Andes transition occurs at the Callaqui-Copahue-Mandolegüe lineament, which decouples active deformation from the intra-arc strike-slip Liquiñe-Ofqui fault zone to the south and the backarc Copahue-Antiñir thrust system.
The Dilemmas of Risk-Sensitive Development on a Small Volcanic Island

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Emily Wilkinson

2016-06-01

Full Text Available In the Small Islands Developing State (SIDS of St Vincent and the Grenadines in the Caribbean, the most destructive disasters in terms of human casualties have been the multiple eruptions of La Soufrière volcano situated in the north of St Vincent. Despite this major threat, people continue to live close to the volcano and national development plans do not include risk reduction measures for volcanic hazards. This paper examines the development options in volcanic SIDS and presents a number of conundrums for disaster risk management on the island of St Vincent. Improvements in monitoring of volcanic hazards and ongoing programmes to enhance communications systems and encourage community preparedness planning have increased awareness of the risks associated with volcanic hazards, yet this has not translated into more risk-informed development planning decisions. The current physical development plan in fact promotes investment in infrastructure in settlements located within the zone designated very high-hazard. However, this is not an anomaly or an irrational decision: severe space constraints in SIDS, as well as other historical social and economic factors, limit growth and options for low-risk development. Greater attention needs to be placed on developing measures to reduce risk, particularly from low-intensity hazards like ash, limiting where possible exposure to volcanic hazards and building the resilience of communities living in high-risk areas. This requires planning for both short- and longer-term impacts from renewed activity. Volcanic SIDS face multiple hazards because of their geography and topography, so development plans should identify these interconnected risks and options for their reduction, alongside measures aimed at improving personal preparedness plans so communities can learn to live with risk.
Volcanic features of Io

International Nuclear Information System (INIS)

Carr, M.H.; Masursky, H.; Strom, R.G.; Terrile, R.J.

1979-01-01

The volcanic features of Io as detected during the Voyager mission are discussed. The volcanic activity is apparently higher than on any other body in the Solar System. Its volcanic landforms are compared with features on Earth to indicate the type of volcanism present on Io. (U.K.)
Inherited discontinuities and fault kinematics of a multiphase, non-colinear extensional setting: Subsurface observations from the South Flank of the Golfo San Jorge basin, Patagonia

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Paredes, José Matildo; Aguiar, Mariana; Ansa, Andrés; Giordano, Sergio; Ledesma, Mario; Tejada, Silvia

2018-01-01

We use three-dimensional (3D) seismic reflection data to analyze the structural style, fault kinematics and growth fault mechanisms of non-colinear normal fault systems in the South Flank of the Golfo San Jorge basin, central Patagonia. Pre-existing structural fabrics in the basement of the South Flank show NW-SE and NE-SW oriented faults. They control the location and geometry of wedge-shaped half grabens from the "main synrift phase" infilled with Middle Jurassic volcanic-volcaniclastic rocks and lacustrine units of Late Jurassic to Early Cretaceous age. The NE-striking, basement-involved normal faults resulted in the rapid establishment of fault lenght, followed by gradual increasing in displacement, and minor reactivation during subsequent extensional phases; NW-striking normal faults are characterized by fault segments that propagated laterally during the "main rifting phase", being subsequently reactivated during succesive extensional phases. The Aptian-Campanian Chubut Group is a continental succession up to 4 km thick associated to the "second rifting stage", characterized by propagation and linkage of W-E to WNW-ESE fault segments that increase their lenght and displacement in several extensional phases, recognized by detailed measurement of current throw distribution of selected seismic horizons along fault surfaces. Strain is distributed in an array of sub-parallel normal faults oriented normal to the extension direction. A Late Cretaceous-Paleogene (pre-late Eocene) extensional event is characterized by high-angle, NNW-SSE to NNE-SSW grabens coeval with intraplate alkali basaltic volcanism, evidencing clockwise rotation of the stress field following a ∼W-E extension direction. We demonstrate differences in growth fault mechanisms of non-colinear fault populations, and highlight the importance of follow a systematic approach to the analysis of fault geometry and throw distribution in a fault network, in order to understand temporal-spatial variations
Magma-derived CO2 emissions in the Tengchong volcanic field, SE Tibet: Implications for deep carbon cycle at intra-continent subduction zone

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Zhang, Maoliang; Guo, Zhengfu; Sano, Yuji; Zhang, Lihong; Sun, Yutao; Cheng, Zhihui; Yang, Tsanyao Frank

2016-09-01

Active volcanoes at oceanic subduction zone have long been regard as important pathways for deep carbon degassed from Earth's interior, whereas those at continental subduction zone remain poorly constrained. Large-scale active volcanoes, together with significant modern hydrothermal activities, are widely distributed in the Tengchong volcanic field (TVF) on convergent boundary between the Indian and Eurasian plates. They provide an important opportunity for studying deep carbon cycle at the ongoing intra-continent subduction zone. Soil microseepage survey based on accumulation chamber method reveals an average soil CO2 flux of ca. 280 g m-2 d-1 in wet season for the Rehai geothermal park (RGP). Combined with average soil CO2 flux in dry season (ca. 875 g m-2 d-1), total soil CO2 output of the RGP and adjacent region (ca. 3 km2) would be about 6.30 × 105 t a-1. Additionally, we conclude that total flux of outgassing CO2 from the TVF would range in (4.48-7.05) × 106 t a-1, if CO2 fluxes from hot springs and soil in literature are taken into account. Both hot spring and soil gases from the TVF exhibit enrichment in CO2 (>85%) and remarkable contribution from mantle components, as indicated by their elevated 3He/4He ratios (1.85-5.30 RA) and δ13C-CO2 values (-9.00‰ to -2.07‰). He-C isotope coupling model suggests involvement of recycled organic metasediments and limestones from subducted Indian continental lithosphere in formation of the enriched mantle wedge (EMW), which has been recognized as source region of the TVF parental magmas. Contamination by crustal limestone is the first-order control on variations in He-CO2 systematics of volatiles released by the EMW-derived melts. Depleted mantle and recycled crustal materials from subducted Indian continental lithosphere contribute about 45-85% of the total carbon inventory, while the rest carbon (about 15-55%) is accounted by limestones in continental crust. As indicated by origin and evolution of the TVF
Inferring the effects of compositional boundary layers on crystal nucleation, growth textures, and mineral chemistry in natural volcanic tephras through submicron-resolution imaging

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Georg F. Zellmer

2016-09-01

Full Text Available Crystal nucleation and growth are first order processes captured in volcanic rocks and record important information about the rates of magmatic processes and chemical evolution of magmas during their ascent and eruption. We have studied glass-rich andesitic tephras from the Central Plateau of the Southern Taupo Volcanic Zone by electron- and ion-microbeam imaging techniques to investigate down to sub-micrometre scale the potential effects of compositional boundary layers (CBLs of melt around crystals on the nucleation and growth of mineral phases and the chemistry of crystal growth zones. We find that CBLs may influence the types of mineral phases nucleating and growing, and growth textures such as the development of swallowtails. The chemistry of the CBLs also has the capacity to trigger intermittent overgrowths of nanometre-scale bands of different phases in rapidly growing crystals, resulting in what we refer to as cryptic phase zoning. The existence of cryptic phase zoning has implications for the interpretation of microprobe compositional data, and the resulting inferences made on the conditions of magmatic evolution. Identification of cryptic phase zoning may in future lead to more accurate thermobarometric estimates and thus geospeedometric constraints. In future, a more quantitative characterization of CBL formation and its effects on crystal nucleation and growth may contribute to a better understanding of melt rheology and magma ascent processes at the onset of explosive volcanic eruptions, and will likely be of benefit to hazard mitigation efforts.
Geochronology, stratigraphy and geochemistry of Cambro-Ordovician, Silurian and Devonian volcanic rocks of the Saxothuringian Zone in NE Bavaria (Germany)—new constraints for Gondwana break up and ocean-island magmatism

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Höhn, Stefan; Koglin, Nikola; Klopf, Lisa; Schüssler, Ulrich; Tragelehn, Harald; Frimmel, Hartwig E.; Zeh, Armin; Brätz, Helene

2018-01-01

Stratigraphically well-defined volcanic rocks in Palaeozoic volcano-sedimentary units of the Frankenwald area (Saxothuringian Zone, Variscan Orogen) were sampled for geochemical characterisation and U-Pb zircon dating. The oldest rock suite comprises quartz keratophyre, brecciated keratophyre, quartz keratophyre tuff and basalt, formed in Upper Cambrian to Tremadocian time (c. 497-478 Ma). Basaltic volcanism continued until the Silurian. Quartz keratophyre shows post-collisional calc-alkaline signature, the Ordovician-Silurian basalt has alkaline signature typical of continental rift environments. The combined datasets provide evidence of Cambro-Ordovician bimodal volcanism and successive rifting until the Silurian. This evolution very likely resulted from break-up of the northern Gondwana margin, as recorded in many terranes throughout Europe. The position at the northern Gondwana margin is supported by detrital zircon grains in some tuffs, with typical Gondwana-derived age spectra mostly recording ages of 550-750 Ma and minor age populations of 950-1100 and 1700-2700 Ma. The absence of N-MORB basalt in the Frankenwald area points to a retarded break-off of the Saxothuringian terrane along a continental rift system from Uppermost Cambrian to Middle Silurian time. Geochemical data for a second suite of Upper Devonian basalt provide evidence of emplacement in a hot spot-related ocean-island setting south of the Rheic Ocean. Our results also require partial revision of the lithostratigraphy of the Frankenwald area. The basal volcanic unit of the Randschiefer Formation yielded a Tremadocian age and, therefore, should be attributed to the Vogtendorf Formation. Keratophyre of the Vogtendorf Formation, previously assigned to the Tremadoc, is most likely of Upper Devonian age.
Effect of the bases flanking an abasic site on the recognition of nucleobase by amiloride.

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Rajendran, Arivazhagan; Zhao, Chunxia; Rajendar, Burki; Thiagarajan, Viruthachalam; Sato, Yusuke; Nishizawa, Seiichi; Teramae, Norio

2010-06-01

We explain here the various non-covalent interactions which are responsible for the different binding modes of a small ligand with DNA. The combination of experimental and theoretical methods was used. The interaction of amiloride with thymine was found to depend on the bases flanking the AP site and different binding modes were observed for different flanking bases. Molecular modeling, absorption studies and binding constant measurements support for the different binding patterns. The flanking base dependent recognition of AP site phosphates was investigated by (31)P NMR experiments. The thermodynamics of the ligand-nucleotide interaction was demonstrated by isothermal titration calorimetry. The emission behavior of amiloride was found to depend on the bases flanking the AP site. Amiloride photophysics in the context of AP-site containing DNA is investigated by time-dependent density functional theory. Flanking bases affect the ground and excited electronic states of amiloride when binding to AP site, which causes flanking base-dependent fluorescence signaling. The various noncovalent interactions have been well characterized for the determination of nucleic acid structure and dynamics, and protein-DNA interactions. However, these are not clear for the DNA-small molecule interactions and we believe that our studies will bring a new insight into such phenomena. Copyright 2010 Elsevier B.V. All rights reserved.
Changes in shear-wave splitting before volcanic eruptions

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Liu, Sha; Crampin, Stuart

2015-04-01

We have shown that observations of shear-wave splitting (SWS) monitor stress-accumulation and stress-relaxation before earthquakes which allows the time, magnitude, and in some circumstances fault-plane of impending earthquakes to be stress-forecast. (We call this procedure stress-forecasting rather than predicting or forecasting to emphasise the different formalism.) We have stress-forecast these parameters successfully three-days before a 1988 M5 earthquake in SW Iceland, and identified characteristic anomalies retrospectively before ~16 other earthquakes in Iceland and elsewhere. SWS monitors microcrack geometry and shows that microcracks are so closely spaced that they verge on fracturing and earthquakes. Phenomena verging on failure in this way are critical-systems with 'butterfly wings' sensitivity. Such critical-systems are very common. The Earth is an archetypal complex heterogeneous interactive phenomenon and must be expected to be a critical-system. We claim this critical system as a New Geophysics of a critically-microcracked rock mass. Such critical systems impose a range of fundamentally-new properties on conventional sub-critical physics/geophysics, one of which is universality. Consequently it is expected that we observe similar stress-accumulation and stress-relaxation before volcanic eruptions to those before earthquakes. There are three eruptions where appropriate changes in SWS have been observed similar to those observed before earthquakes. These are: the 1996 Gjálp fissure eruption, Vatnajökull, Iceland; a 2001 flank eruption on Mount Etna, Sicily (reported by Francesca Bianco, INGV, Naples); and the 2010 Eyjafjajökull ash-cloud eruption, SW Iceland. These will be presented in the same normalised format as is used before earthquakes. The 1996 Gjálp eruption showed a 2½-month stress-accumulation, and a ~1-year stress-relaxation (attributed to the North Atlantic Ridge adjusting to the magma injection beneath the Vatnajökull Ice Cap). The
Attenuation and scattering tomography of the deep plumbing system of Mount St. Helens

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De Siena, Luca; Thomas, Christine; Waite, Greg P.; Moran, Seth C.; Klemme, Stefan

2014-01-01

We present a combined 3-D P wave attenuation, 2-D S coda attenuation, and 3-D S coda scattering tomography model of fluid pathways, feeding systems, and sediments below Mount St. Helens (MSH) volcano between depths of 0 and 18 km. High-scattering and high-attenuation shallow anomalies are indicative of magma and fluid-rich zones within and below the volcanic edifice down to 6 km depth, where a high-scattering body outlines the top of deeper aseismic velocity anomalies. Both the volcanic edifice and these structures induce a combination of strong scattering and attenuation on any seismic wavefield, particularly those recorded on the northern and eastern flanks of the volcanic cone. North of the cone between depths of 0 and 10 km, a low-velocity, high-scattering, and high-attenuation north-south trending trough is attributed to thick piles of Tertiary marine sediments within the St. Helens Seismic Zone. A laterally extended 3-D scattering contrast at depths of 10 to 14 km is related to the boundary between upper and lower crust and caused in our interpretation by the large-scale interaction of the Siletz terrane with the Cascade arc crust. This contrast presents a low-scattering, 4–6 km2 “hole” under the northeastern flank of the volcano. We infer that this section represents the main path of magma ascent from depths greater than 6 km at MSH, with a small north-east shift in the lower plumbing system of the volcano. We conclude that combinations of different nonstandard tomographic methods, leading toward full-waveform tomography, represent the future of seismic volcano imaging.
Debris avalanches and debris flows transformed from collapses in the Trans-Mexican Volcanic Belt, Mexico - behavior, and implications for hazard assessment

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Capra, L.; Macías, J. L.; Scott, K. M.; Abrams, M.; Garduño-Monroy, V. H.

2002-03-01

Volcanoes of the Trans-Mexican Volcanic Belt (TMVB) have yielded numerous sector and flank collapses during Pleistocene and Holocene times. Sector collapses associated with magmatic activity have yielded debris avalanches with generally limited runout extent (e.g. Popocatépetl, Jocotitlán, and Colima volcanoes). In contrast, flank collapses (smaller failures not involving the volcano summit), both associated and unassociated with magmatic activity and correlating with intense hydrothermal alteration in ice-capped volcanoes, commonly have yielded highly mobile cohesive debris flows (e.g. Pico de Orizaba and Nevado de Toluca volcanoes). Collapse orientation in the TMVB is preferentially to the south and northeast, probably reflecting the tectonic regime of active E-W and NNW faults. The differing mobilities of the flows transformed from collapses have important implications for hazard assessment. Both sector and flank collapse can yield highly mobile debris flows, but this transformation is more common in the cases of the smaller failures. High mobility is related to factors such as water content and clay content of the failed material, the paleotopography, and the extent of entrainment of sediment during flow (bulking). The ratio of fall height to runout distance commonly used for hazard zonation of debris avalanches is not valid for debris flows, which are more effectively modeled with the relation inundated area to failure or flow volume coupled with the topography of the inundated area.
Introduction to the structures and processes of subduction zones

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Zheng, Yong-Fei; Zhao, Zi-Fu

2017-09-01

Subduction zones have been the focus of many studies since the advent of plate tectonics in 1960s. Workings within subduction zones beneath volcanic arcs have been of particular interest because they prime the source of arc magmas. The results from magmatic products have been used to decipher the structures and processes of subduction zones. In doing so, many progresses have been made on modern oceanic subduction zones, but less progresses on ancient oceanic subduction zones. On the other hand, continental subduction zones have been studied since findings of coesite in metamorphic rocks of supracrustal origin in 1980s. It turns out that high-pressure to ultrahigh-pressure metamorphic rocks in collisional orogens provide a direct target to investigate the tectonism of subduction zones, whereas oceanic and continental arc volcanic rocks in accretionary orogens provide an indirect target to investigate the geochemistry of subduction zones. Nevertheless, metamorphic dehydration and partial melting at high-pressure to ultrahigh-pressure conditions are tectonically applicable to subduction zone processes at forearc to subarc depths, and crustal metasomatism is the physicochemical mechanism for geochemical transfer from the slab to the mantle in subduction channels. Taken together, these provide us with an excellent opportunity to find how the metamorphic, metasomatic and magmatic products are a function of the structures and processes in both oceanic and continental subduction zones. Because of the change in the thermal structures of subduction zones, different styles of metamorphism, metasomatism and magmatism are produced at convergent plate margins. In addition, juvenile and ancient crustal rocks have often suffered reworking in episodes independent of either accretionary or collisional orogeny, leading to continental rifting metamorphism and thus rifting orogeny for mountain building in intracontinental settings. This brings complexity to distinguish the syn
Electrical structure of Newberry Volcano, Oregon

Science.gov (United States)

Fitterman, D.V.; Stanley, W.D.; Bisdorf, R.J.

1988-01-01

From the interpretation of magnetotelluric, transient electromagnetic, and Schlumberger resistivity soundings, the electrical structure of Newberry Volcano in central Oregon is found to consist of four units. From the surface downward, the geoelectrical units are 1) very resistive, young, unaltered volcanic rock, (2) a conductive layer of older volcanic material composed of altered tuffs, 3) a thick resistive layer thought to be in part intrusive rocks, and 4) a lower-crustal conductor. This model is similar to the regional geoelectrical structure found throughout the Cascade Range. Inside the caldera, the conductive second layer corresponds to the steep temperature gradient and alteration minerals observed in the USGS Newberry 2 test-hole. Drill hole information on the south and north flanks of the volcano (test holes GEO N-1 and GEO N-3, respectively) indicates that outside the caldera the conductor is due to alteration minerals (primarily smectite) and not high-temperature pore fluids. On the flanks of Newberry the conductor is generally deeper than inside the caldera, and it deepens with distance from the summit. A notable exception to this pattern is seen just west of the caldera rim, where the conductive zone is shallower than at other flank locations. The volcano sits atop a rise in the resistive layer, interpreted to be due to intrusive rocks. -from Authors
Comparative lahar hazard mapping at Volcan Citlaltépetl, Mexico using SRTM, ASTER and DTED-1 digital topographic data

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Hubbard, Bernard E.; Sheridan, Michael F.; Carrasco-Nunez, Gerardo; Diaz-Castellon, Rodolfo; Rodriguez, Sergio R.

2007-01-01

In this study, we evaluated and compared the utility of spaceborne SRTM and ASTER DEMs with baseline DTED-1 “bald-earth” topography for mapping lahar inundation hazards from volcan Citlaltépetl, Mexico, a volcano which has had a history of producing debris flows of various extents. In particular, we tested the utility of these topographic datasets for resolving ancient valley-filling deposits exposed around the flanks of the volcano, for determining their magnitude using paleohydrologic methods and for forecasting their inundation limits in the future. We also use the three datasets as inputs to a GIS stream inundation flow model, LAHARZ, and compare the results.

Late Miocene marine tephra beds : recorders of rhyolitic volcanism in North Island, New Zealand

International Nuclear Information System (INIS)

Shane, P.; Black, T.; Eggins, S.; Westgate, J.

1998-01-01

A deep-sea sequence of 72 rhyolitic tephra beds, now exposed at Mahia Peninsula in the Hawke's Bay region of the east coast, North Island, New Zealand, provides a record of Late Miocene volcanism of the Coromandel Volcanic Zone (CVZ): the precursor to large-scale explosive volcanism of the Quaternary Taupo Volcanic Zone (TVZ). The geochemical signature of the glasses in the Miocene tephra has been protected from hydrothermal alteration and prolonged subaerial exposure that have affected proximal CVZ deposits. The tephra beds are primarily eruption-driven sediment gravity flows that have been emplaced into a trench-slope basin, some 300 km from active volcanoes. Their occurrence is consistent with long-distance fluvial transport followed by a point-source discharge into the deep-sea environment, and has no implications for the paleogeographic location of the basins relative to the volcanic arc. The tephra beds are calc-alkaline rhyolites with SiO 2 contents in the range 72-78 wt% (recalculated on a volatile-free basis), and are broadly similar to glassy rocks of the CVZ. Their major oxide, trace element, and REE compositions are indistinguishable from glasses of TVZ rhyolites. The trace element and REE compositional variability in the Late Miocene tephra beds, which were erupted over an estimated duration of c. 0.5-2.4 m.y. is no greater than that of large silicic eruptives of the last 350 ka, and is suggestive of a long-lived source and/or similar magmatic processes. However, the individual tephra beds are products of discrete homogeneous magma batches. New fission track ages of the Miocene tephra beds suggest the main period of volcaniclastic deposition occurred in the interval c. 9-7 Ma. This corresponds well with the initiation of rhyolitic volcanism in the CVZ at c. 10 Ma, and a major period of caldera formation that took place to c. 7 Ma. The ages suggest a sediment accumulation rate of between 0.23 and 1.2 m/ka (av. 0.4 m/ka), and a frequency of eruption of
Validation of gravity data from the geopotential field model for subsurface investigation of the Cameroon Volcanic Line (Western Africa)

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Marcel, Jean; Abate Essi, Jean Marcel; Nouck, Philippe Njandjock; Sanda, Oumarou; Manguelle-Dicoum, Eliézer

2018-03-01

Belonging to the Cameroon Volcanic Line (CVL), the western part of Cameroon is an active volcanic zone with volcanic eruptions and deadly gas emissions. The volcanic flows generally cover areas and bury structural features like faults. Terrestrial gravity surveys can hardly cover entirely this mountainous area due to difficult accessibility. The present work aims to evaluate gravity data derived from the geopotential field model, EGM2008 to investigate the subsurface of the CVL. The methodology involves upward continuation, horizontal gradient, maxima of horizontal gradient-upward continuation combination and Euler deconvolution techniques. The lineaments map inferred from this geopotential field model confirms several known lineaments and reveals new ones covered by lava flows. The known lineaments are interpreted as faults or geological contacts such as the Foumban fault and the Pan-African Belt-Congo craton contact. The lineaments highlighted coupled with the numerous maar lakes identified in this volcanic sector attest of the vulnerability of the CVL where special attention should be given for geohazard prevention.
Flank solar wind interaction. Annual report, June 1991-July 1992

International Nuclear Information System (INIS)

Moses, S.L.; Greenstadt, E.W.

1992-08-01

This report summarizes the results of the first 12 months of our program to study the interaction of the Earth's magnetosphere with the solar wind on the far flanks of the bow shock. This study employs data from the ISEE-3 spacecraft during its traversals of the Earth's magnetotail and correlative data from spacecraft monitoring the solar wind upstream. Our main effort to date has involved assembling data sets and developing new plotting programs. Two talks were given at the Spring Meeting of the American Geophysical Union describing our initial results from analyzing data from the far flank foreshock and magnetosheath. The following sections summarize our results
Long-range hazard assessment of volcanic ash dispersal for a Plinian eruptive scenario at Popocatépetl volcano (Mexico): implications for civil aviation safety

Science.gov (United States)

Bonasia, Rosanna; Scaini, Chiara; Capra, Lucia; Nathenson, Manuel; Siebe, Claus; Arana-Salinas, Lilia; Folch, Arnau

2014-01-01

Popocatépetl is one of Mexico's most active volcanoes threatening a densely populated area that includes Mexico City with more than 20 million inhabitants. The destructive potential of this volcano is demonstrated by its Late Pleistocene-Holocene eruptive activity, which has been characterized by recurrent Plinian eruptions of large magnitude, the last two of which destroyed human settlements in pre-Hispanic times. Popocatépetl's reawakening in 1994 produced a crisis that culminated with the evacuation of two villages on the northeastern flank of the volcano. Shortly after, a monitoring system and a civil protection contingency plan based on a hazard zone map were implemented. The current volcanic hazards map considers the potential occurrence of different volcanic phenomena, including pyroclastic density currents and lahars. However, no quantitative assessment of the tephra hazard, especially related to atmospheric dispersal, has been performed. The presence of airborne volcanic ash at low and jet-cruise atmospheric levels compromises the safety of aircraft operations and forces re-routing of aircraft to prevent encounters with volcanic ash clouds. Given the high number of important airports in the surroundings of Popocatépetl volcano and considering the potential threat posed to civil aviation in Mexico and adjacent regions in case of a Plinian eruption, a hazard assessment for tephra dispersal is required. In this work, we present the first probabilistic tephra dispersal hazard assessment for Popocatépetl volcano. We compute probabilistic hazard maps for critical thresholds of airborne ash concentrations at different flight levels, corresponding to the situation defined in Europe during 2010, and still under discussion. Tephra dispersal mode is performed using the FALL3D numerical model. Probabilistic hazard maps are built for a Plinian eruptive scenario defined on the basis of geological field data for the "Ochre Pumice" Plinian eruption (4965 14C yr BP
3-D interpretation of short-period magnetotelluric data at Furnas Volcano, Azores Islands

Science.gov (United States)

Hogg, C.; Kiyan, D.; Rath, V.; Byrdina, S.; Vandemeulebrouck, J.; Revil, A.; Viveiros, F.; Carmo, R.; Silva, C.; Ferreira, T.

2018-04-01

Accurate geophysical imaging of shallow subsurface features provides crucial constraints on understanding the dynamics of volcanic systems. At Furnas Volcano (Azores), intense circulation of volcanic fluids at depth leading to high CO2 outgassing and flank destabilization poses considerable threat to the local population. Presented is a novel 3-D electrical resistivity model developed from 39 magnetotelluric soundings that images the hydrothermal system of the Furnas Volcano to a depth of 1 km. The resistivity model images two conductive zones, one at 100 m and another at 500 m depth, separated by a resistive layer. The shallow conductor has conductivity less than 1 S m-1, which can be explained by clay mineral surface conduction with a mass fraction of at least 20 per cent smectite. The deeper conductor extends across the majority of the survey area. This deeper conductor is located at depths where smectite is generally replaced by chlorite and we interpret it as aqueous fluids near the boiling point and infer temperatures of at least 240 °C. The less conductive layer found between these conductors is probably steam-dominated, and coincides within the mixed-clay zone found in many volcanic hydrothermal systems.
Flux and genesis of CO2 degassing from volcanic-geothermal fields of Gulu-Yadong rift in the Lhasa terrane, South Tibet: Constraints on characteristics of deep carbon cycle in the India-Asia continent subduction zone

Science.gov (United States)

Zhang, Lihong; Guo, Zhengfu; Sano, Yuji; Zhang, Maoliang; Sun, Yutao; Cheng, Zhihui; Yang, Tsanyao Frank

2017-11-01

Gulu-Yadong rift (GYR) is the longest extensional, NE-SW-trending rift in the Himalayas and Lhasa terrane of South Tibet. Many volcanic-geothermal fields (VGFs), which comprise intense hot springs, steaming fissures, geysers and soil micro-seepage, are distributed in the GYR, making it ideal area for studying deep carbon emissions in the India-Asia continent subduction zone. As for the northern segment of GYR in the Lhasa terrane, its total flux and genesis of CO2 emissions are poorly understood. Following accumulation chamber method, soil CO2 flux survey has been carried out in VGFs (i.e., Jidaguo, Ningzhong, Sanglai, Tuoma and Yuzhai from south to north) of the northern segment of GYR. Total soil CO2 output of the northern GYR is about 1.50 × 107 t a-1, which is attributed to biogenic and volcanic-geothermal source. Geochemical characteristics of the volcanic-geothermal gases (including CO2 and He) of the northern GYR indicate their significant mantle-derived affinities. Combined with previous petrogeochemical and geophysical data, our He-C isotope modeling calculation results show that (1) excess mantle-derived 3He reflects degassing of volatiles related with partial melts from enriched mantle wedge induced by northward subduction of the Indian lithosphere, and (2) the crust-mantle interaction can provide continuous heat and materials for the overlying volcanic-geothermal system, in which magma-derived volatiles are inferred to experience significant crustal contamination during their migration to the surface.
Mass movement processes associated with volcanic structures in Mexico City

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Víctor Carlos Valerio

2012-11-01

Full Text Available Mexico City, one of the most populated areas of the world, has been affected by various hazards of natural origin, such as subsidence and cracking of the soil, seismicity, floods and mass movement processes (MMPs. Owing to the lack of space on the plain, in recent years urban growth has been concentrated particularly on the slopes of the surrounding mountain ranges, and this has significantly modified the dynamics of the relief as well as the hydrogeological conditions. The specific character of natural susceptibility to mass movements is strongly dependent on the geological–structural and morphological characteristics of the volcanic bodies that form the mountainous relief. This natural susceptibility, combined with the characteristics of vulnerability of the society, creates risk conditions that can generate severe consequences for the population and the economy. Hence, based on an inventory of mass movement processes comprising 95 data points, the present study aimed to achieve a zoning of the areas susceptible to these processes, as well as to characterize the mechanisms of instability in the volcanic structures that form the relief of the area in question. The results of this work clearly show the role of the lithology, the mode of emplacement and the morpho–structural characteristics of the volcanic structures, in the types of mass movement processes. In addition, it identifies the diverse activities of anthropogenic origin that favour slope instability in the zone: deforestation and burning of rubbish, felling of timber on the slopes for building infrastructure and dwellings, leakages of water, vibrations of vehicles, rotating machinery and the use of explosives in mining works, overloading the heads of the slopes, disturbance of the geohydrological regime, generation of rubbish tips, terracing of the slopes for cultivation, inadequate building regulations, and the use of counterproductive or ineffectual stabilization measures.
Wear evaluation of flank in burins of high speed steel modified with titanium ions

Science.gov (United States)

E Caballero, J.; V-Niño, E. D.

2017-12-01

This report shows the results obtained researching the flank wearing resistance performed by the high-speed steel (HSS) burins without any surface treatment (reference substrate) and others with surface treatment based on Titanium ions. The flank wearing was carried out by means of an industrial process by chip removal with repetitive tests of dry finished turning of AISI/SAE 1045 steel bars. The useful service life of the burins was evaluated according to ISO 3685:1993, and it was found that the burins treated with Titanium ions showed an increase in the flank wearing resistance with respect to the ones used as reference.
The Caucasian-Arabian segment of the Alpine-Himalayan collisional belt: Geology, volcanism and neotectonics

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E. Sharkov

2015-07-01

Full Text Available The Caucasian-Arabian belt is part of the huge late Cenozoic Alpine-Himalayan orogenic belt formed by collision of continental plates. The belt consists of two domains: the Caucasian-Arabian Syntaxis (CAS in the south and the EW-striking Greater Caucasus in the north. The CAS marks a zone of the indentation of the Arabian plate into the southern East European Craton. The Greater Caucasus Range is located in the south of the Eurasian plate; it was tectonically uplifted along the Main Caucasian Fault (MCF, which is, in turn, a part of a megafault extended over a great distance from the Kopetdag Mts. to the Tornquist-Teisseyre Trans-European Suture Zone. The Caucasus Mts. are bounded by the Black Sea from the west and by the Caspian Sea from the east. The SN-striking CAS is characterized by a large geophysical isostatic anomaly suggesting presence of mantle plume head. A 500 km long belt of late Cenozoic volcanism in the CAS extends from the eastern Anatolia to the Lesser and Greater Caucasus ranges. This belt hosts two different types of volcanic rocks: (1 plume-type intraplate basaltic plateaus and (2 suprasubduction-type calc-alkaline and shoshonite-latite volcanic rocks. As the CAS lacks signatures of subduction zones and is characterized by relatively shallow earthquakes (50–60 km, we suggest that the “suprasubduction-type” magmas were derived by interaction between mantle plume head and crustal material. Those hybrid melts were originated under conditions of collision-related deformation. During the late Cenozoic, the width of the CAS reduced to ca. 400 km due to tectonic “diffluence” of crustal material provided by the continuing Arabia-Eurasia collision.
Observations and modelling of inflation in the Lazufre volcanic region, South America

Science.gov (United States)

Pearse, J.; Lundgren, P.

2010-12-01

The Central Volcanic Zone (CVZ) is an active volcanic arc in the central Andes, extending through Peru, southwestern Bolivia, Chile, and northwestern Argentina [De Silva, 1989; De Silva and Francis, 1991]. The CVZ includes a number of collapsed calderas, remnants of catastrophic eruptions, which are now thought to be inactive. However, recent Interferometric Synthetic Aperture Radar (InSAR) observations [Pritchard and Simons, 2004] show surface deformation occurring at some of these large ancient volcanic regions, indicating that magma chambers are slowly inflating beneath the surface. The mechanisms responsible for the initiation and growth of large midcrustal magma chambers remains poorly understood, and InSAR provides an opportunity for us to observe volcanic systems in remote regions that are otherwise difficult to monitor and observe. The Lastarria-Cordon del Azufre ("Lazufre" [Pritchard and Simons, 2002]) volcanic area is one such complex showing recent deformation, with average surface uplift rates of approximately 2.5 cm/year [Froger et al., 2007; Ruch et al, 2008]. We have processed InSAR data from ERS-1/2 and Envisat in the Lazufre volcanic area, including both ascending and descending satellite tracks. Time series analysis of the data shows steady uplift beginning in about 2000, continuing into 2010. We use boundary-element elastic models to invert for the depth and shape of the magmatic source responsible for the surface deformation. Given data from both ascending and descending tracks, we are able to resolve the ambiguity between the source depth and size, and constrain the geometry of the inflating magma source. Finite element modelling allows us to understand the effect of viscoelasticity on the development of the magma chamber.
Tectonics control over instability of volcanic edifices in transtensional tectonic regimes

Science.gov (United States)

Norini, G.; Capra, L.; Lagmay, A. M. F.; Manea, M.; Groppelli, G.

2009-04-01

We present the results of analogue modeling designed to investigate the interactions between volcanic edifices and transtensional basement faulting. Three sets of experiments were run to account for three examples of stratovolcanoes in active transtensive tectonics regimes, the Nevado de Toluca and Jocotitlan volcanoes in Mexico, and the Mayon volcano in the Philippines. All these volcanoes show different behavior and relationship among volcanism, instability of the volcanic edifice, and basement tectonics. Field geological and structural data gave the necessary constrains to the models. The modeling apparatus consisted of a sand cone on a sheared basal layer. Injections of vegetable oil were used to model the rising of magma inside the deformed analogue cones. Set 1: In the case of a volcano directly on top of a basal transtensive shear producing a narrow graben, as observed on the Nevado de Toluca volcano, the analogue models reveal a strong control of the basement faulting on the magma migration path and the volcano instability. Small lateral collapses are directed parallel to the basal shear and affect a limited sector of the cone. Set 2: If the graben generated by transtensive tectonics is bigger in respect to the volcanic edifice and the volcano sits on one boundary fault, as in the case of Mayon volcano, the combined normal and transcurrent movements of the analogue basement fault generate a sigmoidal structure in the sand cone, inducing major sector collapses directed at approx 45° relative to the basement shear toward the downthrown block. Set 3: For volcanoes located near major transtensive faults, as the Jocotitlan volcano, analogue modelling shows an important control of the regional tectonics on the geometry of the fractures and migration paths of magma inside the cone. These structures render unstable the flanks of the volcano and promote sector collapses perpendicular to the basement shear and directed toward the graben formed by the transtensive
Groundwater circulations within a tropical humid andesitic volcanic watershed using the temperature as a tracer

Science.gov (United States)

Selles, Adrien; Violette, Sophie; Hendrayana, Heru

2014-05-01

Groundwater flow within volcano-detritic environment, is of prime importance to many human needs and activities, from the supply of clean drinking water to the extraction of hydrocarbons or geothermal energy. However, the heterogeneity of the geological formations makes difficult to quantify the groundwater spatial distribution. Moreover, its temporal variation in tropical humid regions is sometimes poorly known. For instance, the surronding of the Merapi volcano, in Central Java, Indonesia, is an area of high but seasonal rainfall, and extensive crop irrigation. It has a large population and a need to increase food and potable water supplies depending upon exploiting groundwater ressources. The stress on these resources increases with the intensification of the demography, the agricultural practices and the industrial exploitations. In order to implement a sustainable management of the water resources, the description of the groundwater circulations and the quantification of the resources is needed. A mutidisciplinary approach has been performed at the watershed scale, including geology, hydrogeochemistry and long term hydrogeological monitoring. The data synthesis and constisency have been confirm with a numerical model of physical processes. Based on a geological and geomorphological study, the hydrogeological watershed on the Eastern flank of the Merapi volcano is composed by an alternation of aquitards (mainly ashes, tuffs and clay) and aquifers (sand, gravel and boulders). The deep aquifers are agenced in conduit following the burried channel of the paleo-rivers. The eastern flank of Merapi provides excellent example of a volcanic-sedimentary environment. From 20 cold springs of 3 spring zones, sampled on 2 hydrological years (2011 to 2013), the study of the transfer into the saturated zone from upstream to downstream, given the geological context and topography, allows to estimate the role of supply from high and low altitudes to the recharge processes. The
Human platelet glycoprotein IX: An adhesive prototype of leucine-rich glycoproteins with flank-center-flank structures

International Nuclear Information System (INIS)

Hickey, M.J.; Williams, S.A.; Roth, G.J.

1989-01-01

The glycoprotein (GP) Ib-IX complex on the surface of human platelets functions as the von Willebrand factor receptor and mediates von Willebrand factor-dependent platelet adhesion to blood vessels. GPIX is a relatively small (M r , 17,000) protein that may provide for membrane insertion and orientation of the larger component of the complex. GPIb (M r , 165,000). Using antibody screening, the authors cloned a cDNA encoding GPIX from a human erythroleukemia cell cDNA library constructed in phage λgt11. Lacking a 5' untranslated region and start codon, the cDNA sequence includes 604 nucleotides, beginning with 495 bases at the 5' end coding for 165 amino acids, followed by a stop codon and 106 noncoding bases at the 3' end. By Northern blot analysis, the GPIX cDNA hybridizes with a single 1.0-kilobase species of platelet poly(A) + RNA. Translation of the cDNA sequence gives a predicted protein sequence beginning with a truncated putative signal sequence of 5 amino acids followed by a sequence of 17 amino acids matching that determined directly by Edman degradation of intact GPIX. GPIX contains a leucine-rich glycoprotein (LRG) sequence of 24 amino acids similar to conserved LRG sequences in GPIb and other proteins from humans, Drosophila, and yeast. The role of the flank-LRG center-flank structure in the evolution and function of the LRG proteins remains to be defined
Self-potential changes associated with volcanic activity. Short-term signals associated with March 9, 1998 eruption on La Fournaise volcano (Reunion Island)

Energy Technology Data Exchange (ETDEWEB)

Zlotniki, J. [UMR6530, Clermont-Ferrand (France); Institut de Physique du Globe de Paris, Laboratoire de Geomagnetisme, Paris (France); Le Mouel, J. L. [Institut de Physique du Globe de Paris, Laboratoire de Geomagnetisme, Paris (France); Sasai, Y. [Tokyo Univ., Tokyo (Italy). Earthquake Research Institute; Yvetot, P.; Ardisson, M. H. [UMR6524, Laboratoire de Geophysique d' Orleans, Orleans (France)

2001-04-01

After six years of quietness La Fournaise volcano entered into activity on March 9, 1998. Fissures opened gradually downwards on the northern flank of the cone. Two cones, Kapor and Krafft built, from which lava poured until September 1998. Several other vents opened during this eruption. Mappings, surveys, and continuous recordings of the Self-Potential have been performed on the volcano for twenty years. SP mappings disclose the variability of large scale SP anomalies due to the modification of the hydrothermal system over some ten years. Most of the eruptions take place along a Main Fracture Zone (MFZ), in which ground water flows prevail. SP measurements have also regularly been made on the northern flank of the cone, on a west-east profile crossing the MFZ. Between 1981 and 1992 an enlargement and a shift of the MFZ to the east are evidenced. In particular, the eastern fissural axis trending N35{sup 0}E could be related to the possible collapse of the east flank of the volcano. After a decrease between 1992 and 1997, the SP anomaly was enhanced again by the 1998 eruption. Short scale, about 250 m wide, 750 mV amplitude anomalies were superimposed on a large scale one, 2500 m wide, and about 250 mV in amplitude. For several years, continuous stations have been measuring the electric field along two directions, with a 20 s sampling, in order to record the genesis of SP signals associated with the volcanic activity. Oscillations belonging to the ULF band were evidenced several days before the 1988 eruption, some of them at 9 km from the summit. Their amplitude reached several tens mV/km. These oscillations sometimes present a phase lag from summit. Their amplitude reached several tens mV/km. These oscillations sometimes present a phase lag from one station to another; they progressively shift towards the location of the future effusive vents. The polarisation of the oscillations is similar to the polarisation of longer SP variations (1 h period or more) and are
Self-potential chenges associated with volcanic activity: Short-term signals associated with March 9, 1998 eruption on La Fournaise volcano (Reunion Island

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P. Yvetot

2001-06-01

Full Text Available After six years of quietness La Fournaise volcano entered into activity on March 9, 1998. Fissures opened gradually downwards on the northern flank of the cone. Two cones, Kapor and Krafft built, from which lava poured until September 1998. Several other vents opened during this eruption. Mappings, surveys, and continuous recordings of the Self-Potential have been performed on the volcano for twenty years. SP mappings disclose the variability of large scale SP anomalies due to the modification of the hydrothermal system over some ten years. Most of the eruptions take place along a Main Fracture Zone (MFZ in which ground water flows prevail. SP measurements have also regularly been made on the northern flank of the cone, on a west-east profile crossing the MFZ. Between 1981 and 1992 an enlargement and a shift of the MFZ to the east are evidenced. In particular, the eastern fissural axis trending N35°E could be related to the possible collapse of the east flank of the volcano. After a decrease between 1992 and 1997, the SP anomaly was enhanced again by the 1998 eruption. Short scale, about 250 m wide, 750 mV amplitude anomalies were superimposed on a large scale one, 2500 m wide, and about 250 mV in amplitude. For several years, continuous stations have been measuring the electric field along two directions, with a 20 s sampling, in order to record the genesis of SP signals associated with the volcanic activity. Oscillations belonging to the ULF band were evidenced several days before the 1988 eruption, some of them at 9 km from the summit. Their amplitude reached several tens mV/km. These oscillations sometimes present a phase lag from one station to another; they progressively shift towards the location of the future effusive vents. The polarisation of the oscillations is similar to the polarisation of longer SP variations (1 h period or more and are correlated with the structural anisotropy. Finally, during the last hours preceding the
Contrastive research of ionospheric precursor anomalies between Calbuco volcanic eruption on April 23 and Nepal earthquake on April 25, 2015

Science.gov (United States)

Li, Wang; Guo, Jinyun; Yue, Jianping; Yang, Yang; Li, Zhen; Lu, Deikai

2016-05-01

On April 23, 2015, the VEI4 (volcanic explosive index) Calbuco volcano abruptly erupted in Chile and the Mw7.9 Nepal earthquake occurred on April 25. In order to investigate the similarities and differences between total electron content (TEC) anomalies preceding these two types of geophysical activities, the TEC time series over preparation zones before the volcanic eruption and earthquake extracted from global ionosphere map were analyzed. We used sunspot numbers (SSN), Bz, Dst, and Kp indices to represent the solar-terrestrial environment and eliminate the effects of solar and geomagnetic activities on ionosphere by the sliding interquartile range method with the 27-day window. The results indicate that TEC-negative and -positive anomalies appeared in the 14th and 6th day before the eruption, respectively. The anomalies lasted about 4-6 h with a magnitude of 15-20 TECU. The TEC anomalies were also observed on the 14th and 6th day before the Nepal earthquake with a duration of 6-8 h, and the absolute magnitude of TEC anomalies was within 12-20 TECU. These findings indicate that the magnitude of TEC anomalies preceding volcanic eruption was larger, and the duration of TEC anomalies before the earthquake was longer, which may be associated with their particular physical mechanisms. The TEC anomalies before the Nepal earthquake in the Eastern hemisphere occurred in the afternoon local time, but those before the eruption were observed in the night local time. Peak regions of TEC anomalies did not coincide with the epicenters of geophysical activities, and the TEC anomalies also appeared in the magnetic conjugated region. Both the TEC anomalies in the preparation zone and conjugated region were distributed near the boundaries of equatorial anomaly zone and moved along the boundaries. In the moving process, sometimes the extent or magnitude of TEC anomalies in the conjugated region was larger than that in the preparation zone. Many more GPS stations and receivers
Method for Friction Force Estimation on the Flank of Cutting Tools

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Luis Huerta

2017-01-01

Full Text Available Friction forces are present in any machining process. These forces could play an important role in the dynamics of the system. In the cutting process, friction is mainly present in the rake face and the flank of the tool. Although the one that acts on the rake face has a major influence, the other one can become also important and could take part in the stability of the system. In this work, experimental identification of the friction on the flank is presented. The experimental determination was carried out by machining aluminum samples in a CNC lathe. As a result, two friction functions were obtained as a function of the cutting speed and the relative motion of the contact elements. Experiments using a worn and a new insert were carried out. Force and acceleration were recorded simultaneously and, from these results, different friction levels were observed depending on the cutting parameters, such as cutting speed, feed rate, and tool condition. Finally, a friction model for the flank friction is presented.
Emplacement controls for the basaltic-andesitic radial dikes of Summer Coon volcano and implications for flank vents at stratovolcanoes

Science.gov (United States)

Harp, A. G.; Valentine, G. A.

2018-02-01

Mafic flank eruptions are common events that pose a serious hazard to the communities and infrastructure often encroaching on the slopes of stratovolcanoes. Flank vent locations are dictated by the propagation path of their feeder dikes. The dikes are commonly thought to propagate either laterally from the central conduit or vertically from a deeper source. However, these interpretations are often based on indirect measurements, such as surface deformation and seismicity at active systems, and several studies at eroded volcanoes indicate the propagation paths may be more complex. We investigated the Oligocene age Summer Coon volcano (Colorado, USA), where erosion has exposed over 700 basaltic-andesitic radial dikes, to constrain the propagation directions, geometries, and spatial distributions of mafic dikes within a stratovolcano. The mean fabric angle of aligned plagioclase crystals was measured in oriented samples from the margins of 77 dikes. Of the 41 dikes with statistically significant flow fabrics, 85% had fabric angles that were inclined—plunging both inward and outward relative to the center of the volcano. After comparing fabric angles to those reported in other studies, we infer that, while most of the dikes with outward-plunging fabrics descended toward the flanks from a source within the edifice and near its axis, dikes with inward-plunging fabrics ascended through the edifice and toward the flanks from a deeper source. A possible control for the inclination of ascending dikes was the ratio between magma overpressure and the normal stress in the host rock. While higher ratios led to high-angle propagation, lower ratios resulted in inclined emplacement. Dikes crop out in higher frequencies within a zone surrounding the volcano axis at 2500 m radial distance from the center and may be the result of ascending dikes, emplaced at similar propagation angles, intersecting the current level of exposure at common distances from the volcano axis. The process
Sources of Quaternary volcanism in the Itasy and Ankaratra volcanic fields, Madagascar

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Rasoazanamparany, C.; Widom, E.; Kuentz, D. C.; Raharimahefa, T.; Rakotondrazafy, F. M. A.; Rakotondravelo, K. M.

2017-12-01

We present new major and trace element and Sr, Nd, Pb and Os isotope data for Quaternary basaltic lavas and tephra from the Itasy and Ankaratra volcanic fields, representing the most recent volcanism in Madagascar. Mafic magmas from Itasy and Ankaratra exhibit significant inter- and intra-volcanic field geochemical heterogeneity. The Itasy eruptive products range in composition from foidite to phonotephrite whereas Ankaratra lavas range from basanite to trachybasalts. Trace element signatures of samples from both volcanic fields are very similar to those of ocean island basalts (OIB), with significant enrichment in Nb and Ta, depletion in Rb, Cs, and K, and relatively high Nb/U and Ce/Pb. However, the Itasy volcanic rocks show enrichment relative to those of Ankaratra in most incompatible elements, indicative of a more enriched source and/or lower degrees of partial melting. Significant inter- and intra-volcanic field heterogeneity is also observed in Sr, Nd, Pb and Os isotope signatures. The Itasy volcanic rocks generally have less radiogenic Sr and Nd isotopic ratios but more radiogenic Pb isotopic signatures than the Ankaratra volcanic field. Together, the Itasy and Ankaratra volcanic rocks form a well-defined negative correlation in Sr vs. Pb isotopes that could be attributed to lithospheric contamination or variable degrees of mixing between distinct mantle sources. However, the lack of correlation between isotopes and indices of crustal contamination (e.g. MgO and Nb/U) are inconsistent with shallow lithospheric contamination, and instead suggest mixing between compositionally distinct mantle sources. Furthermore, although Sr-Pb isotope systematics are apparently consistent with mixing between two different sources, distinct trends in Sr vs. Nd isotopes displayed by samples from Itasy and Ankaratra, respectively, argue for more complex source mixing involving three or more sources. The current data demonstrate that although the Itasy and Ankaratra volcanic
Relationship between Diffuse CO2 Degassing and Volcanic Activity. Case Study of the Poás, Irazú, and Turrialba Volcanoes, Costa Rica

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Matthieu Epiard

2017-10-01

Full Text Available Active volcanoes exhibit diffuse gas emanations through the ground, the most abundant species of which is CO2. However, the relationship between diffuse degassing and volcanic activity is not often clear and some volcanoes may have low diffuse degassing levels despite having strong volcanic activity. The main goals of this study are to quantify diffuse CO2 degassing and determine whether patterns exist in relation to volcanic activity through the study of Turrialba, Poás, and Irazú, three active volcanoes in Costa Rica which are at different stages of activity. Structural controls of spatial distribution of diffuse degassing were also investigated. Measurement campaigns were conducted using the accumulation chamber method coupled with 10 cm depth ground temperature sampling with the aim of estimating the total diffuse CO2 degassing budget. The total amount of CO2 emitted diffusely by each volcano is ~113 ± 46 t/d over ~0.705 km2 for Turrialba, 0.9 ± 0.5 t/d for Poás over ~0.734 km2, 3.8 ± 0.9 t/d over ~0.049 km2 for Irazú's main crater, and 15 ± 12 t/d over 0.0059 km2 for Irazú's north flank. Turrialba and Poás volcano diffuse degassing budget represent about 10% of the whole gas output. Both volcanoes were in a transitional stage and the opening of new conduits may cause a loss in diffuse degassing and an increase of active degassing. Numerous diffuse degassing structures were also identified. At Turrialba, one of which was closely associated with the collapse of a crater wall in 2014 during the initiation of a new period of heightened eruptive activity. Similar structures were also observed on the outer slopes of the west crater, suggesting strong alteration and perhaps destabilization of the upper outer cone. Irazú's north flank is highly permeable and has experienced intense hydrothermal alteration.

Volcanic Processes and Geology of Augustine Volcano, Alaska

Science.gov (United States)

Waitt, Richard B.; Beget, James E.

2009-01-01

Augustine Island (volcano) in lower Cook Inlet, Alaska, has erupted repeatedly in late-Holocene and historical times. Eruptions typically beget high-energy volcanic processes. Most notable are bouldery debris avalanches containing immense angular clasts shed from summit domes. Coarse deposits of these avalanches form much of Augustine's lower flanks. A new geologic map at 1:25,000 scale depicts these deposits, these processes. We correlate deposits by tephra layers calibrated by many radiocarbon dates. Augustine Volcano began erupting on the flank of a small island of Jurassic clastic-sedimentary rock before the late Wisconsin glaciation (late Pleistocene). The oldest known effusions ranged from olivine basalt explosively propelled by steam, to highly explosive magmatic eruptions of dacite or rhyodacite shed as pumice flows. Late Wisconsin piedmont glaciers issuing from the mountainous western mainland surrounded the island while dacitic eruptive debris swept down the south volcano flank. Evidence is scant for eruptions between the late Wisconsin and about 2,200 yr B.P. On a few south-flank inliers, thick stratigraphically low pumiceous pyroclastic-flow and fall deposits probably represent this period from which we have no radiocarbon dates on Augustine Island. Eruptions between about 5,350 and 2,200 yr B.P. we know with certainty by distal tephras. On Shuyak Island 100 km southeast of Augustine, two distal fall ashes of Augustinian chemical provenance (microprobe analysis of glass) date respectively between about 5,330 and 5,020 yr B.P. and between about 3,620 and 3,360 yr B.P. An Augustine ash along Kamishak Creek 70 km southwest of Augustine dates between about 3,850 and 3,660 yr B.P. A probably Augustinian ash lying within peat near Homer dates to about 2,275 yr B.P. From before 2,200 yr B.P. to the present, Augustine eruptive products abundantly mantle the island. During this period, numerous coarse debris avalanches swept beyond Augustine's coast, most
Influence of margin segmentation and anomalous volcanism upon the break-up of the Hatton Bank rifted margin, west of the UK

Science.gov (United States)

Elliott, G. M.; Parson, L. M.

2007-12-01

The Hatton Bank margin, flanking the Iceland Basin is a widely cited example of a volcanic rifted margin. Prior to this study insights into the break-up history of the margin have been limited to profiles in the north and south, yet whilst valuable, the along margin tectono-magmatic variability has not been revealed. Over 5660 line km of high quality reflection seismic profiles with supplementary multibeam bathymetry were collected to support the UK's claim to Hatton region under the United Nations Convention on Law of the Sea (UNCLOS). Integration of this new data with existing profiles, allowed the margin to be divided into three segments, each of which are flanked by oceanic crust with a smooth upper surface and internal dipping reflectors. The southernmost segment is characterised by a series of inner and outer seaward dipping reflector (SDR) packages, which are separated by an outer high feature. The outer SDR are truncated by Endymion Spur, a chain of steep sided, late stage volcanic cones linked with necks. The central sector has no inner SDR package and is characterised by the presence of a highly intruded continental block, the Hatton Bank Block (HBB). The northern sector is adjacent to Lousy Bank, with a wider region of SDR recognised than to the south and a high amount of volcanic cones imaged. The variations in the distribution of the SDR's along the margin, the presence of the HBB and Endymion Spur all suggest that the break-up process was not uniform alongstrike. The division of the margin into three sectors reveals that structural segmentation played an important role in producing the variations along the margin. Break- up initiated in the south and progressed north producing the SDR packages witnessed, when the HBB was encountered the focus of break-up moved seaward of the block. The northern sector was closer to the Iceland Hotspot and hence a greater amount of volcanism is encountered. The smooth oceanic basement also indicates a high thermal flux
Three-dimensional interpretation of MT data in volcanic environments (computer simulation)

Energy Technology Data Exchange (ETDEWEB)

Spichak, V. [Geoelectromagnetic Research Institute RAS, Troitsk, Moscow (Russian Federation)

2001-04-01

The research is aimed, first, to find components of MT-fields and their transforms, which facilitate the imaging of the internal structure of volcanoes and, second, to study the detectability of conductivity variations in a magma chamber due to alterations of other physical parameters. The resolving power of MT data with respect to the electric structure of volcanic zones is studied using software developed by the author for three-dimensional (3D) numerical modeling, analysis and imaging. A set of 3D volcano models are constructed and synthetic MT data on the relief Earth's surface are analysed. It is found that impedance phases as well as in-phase and quadrature parts of the electric field type transforms enable the best imaging of the volcanic interior. The determinant impedance is, however, the most suitable for adequate interpretation of measurements carried out for the purpose of monitoring conductivity variations in a magma chamber. The way of removing the geological noise from the MT data by means of its upward analytical continuation to the artificial reference plane is discussed. Interpretation methodologies are suggested aimed at 3D imaging and monitoring volcanic interiors by MT data.
The hamster flank organ model: Is it relevant to man

International Nuclear Information System (INIS)

Franz, T.J.; Lehman, P.A.; Pochi, P.; Odland, G.F.; Olerud, J.

1989-01-01

The critical role that androgens play in the etiology of acne has led to a search for topically active antiandrogens and the frequent use of the flank organ of the golden Syrian hamster as an animal model. 17-alpha-propyltestosterone (17-PT) has been identified as having potent antiandrogenic activity in the hamster model, and this report describes its clinical evaluation. Two double-blind placebo controlled studies comparing 4% 17-PT in 80% alcohol versus vehicle alone were conducted. One study examined 17-PT sebosuppressive activity in 20 subjects. The second study examined its efficacy in 44 subjects having mild to moderate acne. A third study measured in vitro percutaneous absorption of 17-PT through hamster flank and monkey skin, and human face skin in-vivo, using radioactive drug. 17-PT was found to be ineffective in reducing either the sebum excretion rate or the number of inflammatory acne lesions. Failure of 17-PT to show clinical activity was not a result of poor percutaneous absorption. Total absorption in man was 7.7% of the dose and only 1.0% in the hamster. The sebaceous gland of hamster flank organ is apparently more sensitive to antiandrogens than the human sebaceous gland
Collision-induced post-plateau volcanism: Evidence from a seamount on Ontong Java Plateau

Science.gov (United States)

Hanyu, Takeshi; Tejada, Maria Luisa G.; Shimizu, Kenji; Ishizuka, Osamu; Fujii, Toshiyuki; Kimura, Jun-Ichi; Chang, Qing; Senda, Ryoko; Miyazaki, Takashi; Hirahara, Yuka; Vaglarov, Bogdan S.; Goto, Kosuke T.; Ishikawa, Akira

2017-12-01

Many seamounts on the Ontong Java Plateau (OJP) occur near the Stewart Arch, a topographic high that extends parallel to the North Solomon Trench along the southern margins of the plateau. Despite the thick sediment cover, several volcanic cones with strong acoustic reflection were discovered on the submarine flank of the Nuugurigia Seamount. From such volcanic cones, basalts were successfully sampled by dredging. Radiometric dating of basalts and ferromanganese encrustation indicate eruption age of 20-25 Ma, significantly younger than the 122 Ma main OJP plateau and post-plateau basalts. The age range coincides with the collision of the OJP with the Solomon Arc. The Nuugurigia basalts geochemically differ from any other rocks sampled on the OJP so far. They are alkali basalts with elevated Sr, low Zr and Hf, and Enriched Mantle-I (EMI)-like isotopic composition. Parental magmas of these alkali basalts may have formed by small-degree melting of peridotitic mantle impregnated with recycled pyroxenite material having enriched geochemical composition in the OJP's mantle root. We conclude that small-volume alkali basalts from the enriched mantle root migrated through faults or fractures caused by the collision along the Stewart Arch to form the seamount. Our results suggest that the collision of the OJP with the Solomon arc played an important role in the origin of similar post-plateau seamounts along the Stewart Arch.
Mantle and crustal contribution in the genesis of Recent basalts from off-rift zones in Iceland: Constraints from Th, Sr and O isotopes

Science.gov (United States)

Sigmarsson, Olgeir; Condomines, Michel; Fourcade, Serge

1992-05-01

Along the two volcanic off-rift zones in Iceland, the Sn˦fellsnes volcanic zone (SNVZ) and the South Iceland volcanic zone (SIVZ), geochemical parameters vary regularly along the strike towards the centre of the island. Recent basalts from the SNVZ change from alkali basalts to tholeiites where the volcanic zone reaches the active rift axis, and their 87Sr/ 86Sr and Th/U ratios decrease in the same direction. These variations are interpreted as the result of mixing between mantle melts from two distinct reservoirs below Sn˦fellsnes. The mantle melt would be more depleted in incompatible elements, but with a higher 3He/ 4He ratio ( R/Ra≈ 20) beneath the centre of Iceland than at the tip of the Sn˦fellsnes volcanic zone ( R/Ra≈ 7.5). From southwest to northeast along the SIVZ, the basalts change from alkali basalts to FeTi basalts and quartz-normative tholeiites. The Th/U ratio of the Recent basalts increases and both ( 230Th/ 232Th ) and δ 18O values decrease in the same direction. This reflects an important crustal contamination of the FeTi-rich basalts and the quartz tholeiites. The two types of basalts could be produced through assimilation and fractional crystallization in which primary alkali basaltic and olivine tholeiitic melts 'erode' and assimilate the base of the crust. The increasingly tholeiitic character of the basalts towards the centre of Iceland, which reflects a higher degree of partial melting, is qualitatively consistent with increasing geothermal gradient and negative gravity anomaly. The highest Sr isotope ratio in Recent basalts from Iceland is observed inÖr˦fajökull volcano, which has a 3He/ 4He ratio ( R/Ra≈ 7.8) close to the MORB value, and this might represent a mantle source similar to that of Mauna Loa in Hawaii.
An autochthonous geological model for the eastern Andes of Ecuador

Science.gov (United States)

Pratt, Warren T.; Duque, Pablo; Ponce, Miguel

2005-04-01

We describe a traverse across the Cordillera Real and sub-Andean Zone of Ecuador, poorly known areas with very little detailed mapping and very little age control. The spine of the Cordillera comprises deeply eroded Triassic and Jurassic plutons, the roots of a major arc, emplaced into probable Palaeozoic pelites and metamorphosed volcanic rocks. The W flank comprises a Jurassic (?) submarine basaltic-andesitic volcanic sequence, which grades up into mixed Jurassic/Cretaceous volcanic and sedimentary rocks of the Inter-Andean Valley. The sub-Andean Zone, on the E flank of the Cordillera, comprises a newly recognized Cretaceous basin of cleaved mudrocks, quartz arenites and limestones. East of the syndepositional Cosanga Fault, the Cretaceous basin thins into a condensed sequence that is indistinguishable from the rocks of the adjacent hydrocarbon-bearing Oriente Basin. The principal penetrative deformation of the Cordillera Real was probably latest Cretaceous/Palaeocene. It telescoped the magmatic belts, but shortening was largely partitioned into the pelites between plutons. The plutons suffered inhomogenous deformation; some portions completely escaped tectonism. The pelites conserve two foliations. The earliest comprises slaty cleavage formed under low- or sub-greenschist conditions. The later is a strong schistosity defined by new mica growth. It largely transposed and obliterated the first. Both foliations may have developed during a single progressive deformation. We find inappropriate recent terrane models for the Cordillera Real and sub-Andean Zone of Ecuador. Instead we find remarkable similarities from one side of the Cordillera to the other, including a common structural history. In place of sutures, we find mostly intrusive contacts between major plutons and pelites. Triassic to Cretaceous events occurred on the autochthonous western edge of the Archaean Guyana Shield. The latest Cretaceous-Paleocene deformation is interpreted as the progressive
ALVIN-SeaBeam studies of the Sumisu Rift, Izu-Bonin arc

Science.gov (United States)

Taylor, B.; Brown, G.; Fryer, P.; Gill, J. B.; Hochstaedter, A. G.; Hotta, H.; Langmuir, C. H.; Leinen, M.; Nishimura, A.; Urabe, T.

1990-10-01

Bimodal volcanism, normal faulting, rapid sedimentation, and hydrothermal circulation characterize the rifting of the Izu-Bonin arc at 31°N. Analysis of the zigzag pattern, in plan view, of the normal faults that bound Sumisu Rift indicates that the extension direction (080° ± 10°) is orthogonal to the regional trend of the volcanic front. Normal faults divide the rift into an inner rift on the arc side, which is the locus for maximum subsidence and sedimentation, and an outer rift further west. Transfer zones that link opposing master faults and/or rift flank uplifts further subdivide the rift into three segments along strike. Volcanism is concentrated along the ENE-trending transfer zone which separates the northern and central rift segments. The differential motion across the zone is accommodated by interdigitating north-trending normal faults rather than by ENE-trending oblique-slip faults. Volcanism in the outer rift has built 50-700 m high edifices without summit craters whereas in the inner rift it has formed two multi-vent en echelon ridges (the largest is 600 m high and 16 km long). The volcanism is dominantly basaltic, with compositions reflecting mantle sources little influenced by arc components. An elongate rhyolite dome and low-temperature hydrothermal deposits occur at the en echelon step in the larger ridge, which is located at the intersection of the transfer zone with the inner rift. The chimneys, veins, and crusts are composed of silica, barite and iron oxide, and are of similar composition to the ferruginous chert that mantles the Kuroko deposits. A 1.2-km transect of seven ALVIN heat flow measurements at 30°48.5'N showed that the inner-rift-bounding faults may serve as water recharge zones, but that they are not necessarily areas of focussed hydrothermal outflow, which instead occurs through the thick basin sediments. The rift basin and arc margin sediments are probably dominated by permeable rhyolitic pumice and ash erupted from submarine
Geophysical exploration on the subsurface geology of La Garrotxa monogenetic volcanic field (NE Iberian Peninsula)

Science.gov (United States)

Bolós, Xavier; Barde-Cabusson, Stéphanie; Pedrazzi, Dario; Martí, Joan; Casas, Albert; Lovera, Raúl; Nadal-Sala, Daniel

2014-11-01

We applied self-potential (SP) and electrical resistivity tomography (ERT) to the exploration of the uppermost part of the substrate geology and shallow structure of La Garrotxa monogenetic volcanic field, part of the European Neogene-Quaternary volcanic province. The aim of the study was to improve knowledge of the shallowest part of the feeding system of these monogenetic volcanoes and of its relationship with the subsurface geology. This study complements previous geophysical studies carried out at a less detailed scale and aimed at identifying deeper structures, and together will constitute the basis to establish volcanic susceptibility in La Garrotxa. SP study complemented previous smaller-scale studies and targeted key areas where ERT could be conducted. The main new results include the generation of resistivity models identifying dykes and faults associated with several monogenetic cones. The combined results confirm that shallow tectonics controlling the distribution of the foci of eruptive activity in this volcanic zone mainly correspond to NNW-SSE and accessorily by NNE-SSW Neogene extensional fissures and faults and concretely show the associated magmatic intrusions. These structures coincide with the deeper ones identified in previous studies, and show that previous Alpine tectonic structures played no apparent role in controlling the loci of this volcanism. Moreover, the results obtained show that the changes in eruption dynamics occurring at different vents located at relatively short distances in this volcanic area are controlled by shallow stratigraphical, structural and hydrogeological differences underneath these monogenetic volcanoes.
Full-Wave Ambient Noise Tomography of the Long Valley Volcanic Region (California)

Science.gov (United States)

Flinders, A. F.; Shelly, D. R.; Dawson, P. B.; Hill, D. P.; Shen, Y.

2017-12-01

In the late 1970s, and throughout the 1990s, Long Valley Caldera (California) experienced intense periods of unrest characterized by uplift of the resurgent dome, earthquake swarms, and CO2 emissions around Mammoth Mountain. While modeling of the uplift and gravity changes support the possibility of new magmatic intrusions beneath the caldera, geologic interpretations conclude that the magmatic system underlying the caldera is moribund. Geophysical studies yield diverse versions of a sizable but poorly resolved low-velocity zone at depth (> 6km), yet whether this zone is indicative of a significant volume of crystal mush, smaller isolated pockets of partial melt, or magmatic fluids, is inconclusive. The nature of this low-velocity zone, and the state of volcano's magmatic system, carry important implications for the significance of resurgent-dome inflation and the nature of associated hazards. To better characterize this low-velocity zone we present preliminary results from a 3D full-waveform ambient-noise seismic tomography model derived from the past 25 years of vertical component broadband and short-period seismic data. This new study uses fully numerical solutions of the wave equation to account for the complex wave propagation in a heterogeneous, 3D earth model, including wave interaction with topography. The method ensures that wave propagation is modeled accurately in 3D, enabling the full use of seismic records. By using empirical Green's functions, derived from ambient noise and modeled as Rayleigh surface waves, we are able to extend model resolution to depths beyond the limits of previous local earthquake studies. The model encompasses not only the Long Valley Caldera, but the entire Long Valley Volcanic Region, including Mammoth Mountain and the Mono Crater/Inyo Domes volcanic chain.
Subaqueous volcanism in the Etnean area: evidence for hydromagmatic activity and regional uplift inferred from the Castle Rock of Acicastello

Science.gov (United States)

Corsaro, R. A.; Cristofolini, R.

2000-01-01

The subalkaline rocks outcropping at the Acicastello Castle Rock, Catania, Sicily, and on its abrasion platforms, are related to the oldest Etnean volcanism (500-300 ka; [Gillot, P.Y., Kieffer, G., Romano, R., 1994. The evolution of Mount Etna in the light of potassium-argon dating. Acta Vulcanol. 5, 81-87.]). Here, submarine lavas with pillows closely packed onto each other are associated with heterogeneous and poorly sorted volcaniclastic breccia levels with sub-vertical sharp boundaries. The present-day attitude was previously interpreted as due to a local tilt [Di Re, M., 1963. Hyaloclastites and pillow-lavas of Acicastello (Mt. Etna). Bull. Volcanol. 25, 281-284.; Kieffer, G., 1985. Evolution structurale et dynamique d'un grand volcan polygenique: stades d'edification et activitè actuelle de l'Etna (Sicile). Clermont Ferrand IIDoctorat Etat Tesi, Clermont Ferrand II.], or to the seaward sliding of the entire eastern Etnean flank [Borgia, A., Ferrari, L., Pasquarè, G., 1992. Importance of gravitational spreading in the tectonic and volcanic evolution of Mount Etna. Nature 357, 231-235.], on the assumption of originally horizontal boundaries. On the contrary, our observations do not match the hypothesis of a significantly tilted succession and lead us to conclude that, apart from the strong regional uplift, the present Castle Rock exposure did not suffer any substantial change of its attitude.
Age of the Karakoram fault activation: 40Ar-39Ar geochronological study of Shyok suture zone in northern Ladakh, India

International Nuclear Information System (INIS)

Bhutani, Rajneesh; Pande, Kanchan; Desai, Nikhil

2003-01-01

Shyok volcanics, from the Shyok suture zone in northern Ladakh, ranging from basalts to andesites are analysed for 40 Ar- 30 Ar isotopic systematics by step heating experiment. All samples, collected along the Nubra river, in the vicinity of Karakoram fault zone, yielded disturbed age spectra, reflecting subsequent tectono-thermal events. However, consistency in the pattern of the age spectra, particularly at the low temperature steps, indicate a strong tectono-thermal event between ∼ 10 to ∼ 20 Ma ago. Mica-segregate from segregate from a sheared granite of Karakoram fault zone near village Murgi has yielded an excellent plateau age of 13.9 ± 0.1 Ma. This age of Karakoram fault activation explains the consistent but disturbed age spectra of Shyok volcanics within the vicinity of the fault zone. The Karakoram fault activation in Shyok suture zone is therefore synchronous with the extensional tectonic regime within the Tibetan plateau. (author)
The Western Arabian intracontinental volcanic fields as a potential UNESCO World Heritage site

Science.gov (United States)

Németh, Károly; Moufti, Mohammed R.

2017-04-01

considerred to be associated with dispersed intracontinental volcanic fields. In addition the nominated volcanic region also hosts the largest and youngest historic eruption (Al Madinah Eruption) in Western Saudi Arabia took place at 1256-AD, lasted 52 days and produced at least 0.29-km3 of pahoehoe-to-aa transitional lava fields that were emitted through a 2.3 km-long fissure and associated spatter-to-scoria cone complexes. The Western Arabian intracontinental volcanic fields provide the best exposed and most diverse type of intracontinental volcanic fields on Earth that also occupies the largest surface area. In addition, this chain of volcanic fields are also host significant archaeological and human occupation sites help to understand early human evolution as well as hosting several historic locations with high cultural heritage values. These generally intact and well-exposed volcanic zones hosting globally unique geoheritage sites can form the basis of complex geoeducational programs through the establishment of various volcanic geoparks in the region that can link together a UNESCO World Heritage Site on the basis of their global universal volcanic geoheritage values.
The Plio-Quaternary Volcanic Evolution of Gran Canaria Based on new Unspiked K-Ar ages and Magnetostratigraphy

Science.gov (United States)

Guillou, H.; Carracedo, J.; Perez Torrado, F.

2003-12-01

The combined use of radioisotopic dating, magnetostratigraphy and field geology is a powerful tool to provide reliable chronological frameworks of volcanic edifices. This approach has been used to investigate the last two stages of the volcanic evolution of Gran Canaria. Fifty samples were dated using the unspiked K-Ar method and had their magnetic polarity measured both in the field and in laboratory. Ages were compared to their stratigraphic positions and magnetic polarities before accepting their validity. The unspiked K-Ar chronology constrains the timing of lateral collapses, eruption rates and the contemporaneity of different volcano-magmatic stages at Gran Canaria. Our new data set modifies significantly the previous chronological framework of Gran Canaria, especially between 4 and 2.8 Ma. Based on these new ages, we can bracket the age of the multiple lateral collapses of the Roque Nublo stratovolcano flanks between 3.5 and 3.1 Ma .This time interval corresponds to a main period of volcanic quiescence. Calculated eruptive rates during the stratovolcano edification are about 0.1 km3/kyr which is significantly lower than the published estimates. The dating also reveals that the two main last stages are not separated by a major time gap, but that the early stages of the rift forming eruption and the vanishing activity of the Roque Nublo strato-volcano were contemporaneous for at least 600 kyrs. These results support that our combined approach provides a rapid first-pass and reliable geochronology. Nevertheless, this chronology can be amplified and made more precise where necessary through detailed Ar-Ar incremental-heating methods. Samples which should be investigated using this method are the oldest and youngest K-Ar dated flows of each volcanic stage, and samples from stratigraphic sections that hold potential to study the behaviour of the earth's magnetic field during reversals (Gauss-Gilbert transition, Olduvai and Reunion events).
Is there a geochemical link between volcanic and plutonic rocks in the Organ Mountains caldera?

Science.gov (United States)

Memeti, V.; Davidson, J.

2013-12-01

Results from separate volcanic and plutonic studies have led to inconsistent conclusions regarding the origins and thus links between volcanic and plutonic systems in continental arcs and the magmatic processes and time scales responsible for their compositional variations. Some have suggested that there is a geochemical and geochronological disconnect between volcanic and plutonic rocks and hence have questioned the existence of magma mush columns beneath active volcanoes. Investigating contemporary volcanic and plutonic rocks that are spatially connected is thus critical in exploring these issues. The ca. 36 Ma Organ Mountains caldera in New Mexico, USA, represents such a system exposing contemporaneous volcanic and plutonic rocks juxtaposed at the surface due to tilting during extensional tectonics along the Rio Grande Rift. Detailed geologic and structural mapping [1] and 40Ar/39Ar ages of both volcanics and plutons [2] demonstrate the spatial and temporal connection of both rock types with active magmatism over >2.5 myr. Three caldera-forming ignimbrites erupted within 600 kyr [2] from this system with a total erupted volume of 500-1,000 km3 as well as less voluminous pre- and post-caldera trachyte and andesite lavas. The ignimbrite sequence ranges from a crystal-poor, high-SiO2 rhyolite at the base to a more crystal-rich, low-SiO2 rhyolite at the top. Compositional zoning with quartz-monzonite at the base grading to syenite and alaskite at the top is also found in the Organ Needle pluton, the main intrusion, which is interpreted to be the source for the ignimbrites [1]. Other contemporaneous and slightly younger plutons have dioritic to leucogranitic compositions. We examined both volcanic and plutonic rocks with petrography and their textural variations with color cathodoluminescence, and used whole rock element and Sr, Nd and Pb isotope geochemistry to constrain magma compositions and origins. Electron microprobe analyses on feldspars have been completed to
U-Th age evidence from carbonate veins for episodic crustal deformation of Central Anatolian Volcanic Province

Science.gov (United States)

Karabacak, Volkan; Uysal, I. Tonguç; Ünal-İmer, Ezgi; Mutlu, Halim; Zhao, Jian-xin

2017-12-01

Central Anatolia represents one of the most outstanding examples of intraplate deformation related to both continental collision and back-arc extension generating non-uniformly distributed stress fields. In this study, we provide direct field evidence of various stress directions and investigate carbonate-filled fracture systems in the Central Anatolian Volcanic Province using U/Th geochronology and isotope geochemistry for evaluating the episodes of latest volcanic activity under regional stress. Field data reveal two independent fracture systems in the region. Successive fracture development has been controlled by two different volcanic eruption centers (Hasandağ Composite Volcano and Acıgöl Caldera). Trace element, and stable (C and O) and radiogenic (Sr) isotope compositions of carbonate veins indicate different fluid migration pathways for two different fracture systems. The U/Th age data for carbonate veins of two independent fracture systems indicate that the crustal deformation intensified during 7 episodic periods in the last 150 ka. The NNE-trending first fracture system was formed as a result of strain cycles in a period from 149 ± 2.5, through 91 ± 1.5 to 83 ± 2.5 ka BP. Subsequent deformation events represented by the ENE-trending second fracture zone have been triggered during the period of 53 ± 3.5, 44 ± 0.6 and 34 ± 1 ka BP before the first fracture zone resumed the activity at about 4.7 ± 0.15 ka BP. Although further studies are needed to evaluate statistical significance of age correlations, the periods of carbonate precipitation inferred from U-Th age distributions in this study are comparable with the previous dating results of surrounding volcanic eruption events.
Birth of two volcanic islands in the southern Red Sea

KAUST Repository

Xu, Wenbin

2015-05-26

Submarine eruptions that lead to the formation of new volcanic islands are rare and far from being fully understood; only a few such eruptions have been witnessed since Surtsey Island emerged to the south of Iceland in the 1960s. Here we report on two new volcanic islands that were formed in the Zubair archipelago of the southern Red Sea in 2011–2013. Using high-resolution optical satellite images, we find that the new islands grew rapidly during their initial eruptive phases and that coastal erosion significantly modified their shapes within months. Satellite radar data indicate that two north–south-oriented dykes, much longer than the small islands might suggest, fed the eruptions. These events occurred contemporaneously with several local earthquake swarms of the type that typically accompany magma intrusions. Earthquake activity has been affecting the southern Red Sea for decades, suggesting the presence of a magmatically active zone that has previously escaped notice.
PROPERTIES OF DENIZLI VOLCANICS AND POTENTIAL USING FOR CONCRETE PRODUCTION

Directory of Open Access Journals (Sweden)

Barış SEMİZ

2005-01-01

Full Text Available In this study, mineralogical, petrographical and chemical properties of volcanic rocks (Denizli Volcanics with basaltic trachyandesite composition which are located in southern of Denizli province have been investigated. Their physical and mechanical tests have been carried out on the samples to find out their performance both as an aggregate in concrete and as building stone in the construction sector. Unit weights, water absorption, porosity and uniaxial compressive strength of the tested samples are between 2250-2960 kg/m3, % 0.06-0.4, % 0.15-10.22 and 52.4-170.2 MPa, respectively. Average 28-day compressive strengths of the concrete are 94.44 MPa and the results fit the mineralogical and petrographical characteristics. There is a total of 2750 million ton probable reserve and it is an alternative aggregate to limestone which has already been produced in the region. High strength concrete production is vital for high quality construction especially in earthquake zones.
Volcano-tectonic evolution of a linear volcanic ridge (Pico-Faial Ridge, Azores Triple Junction) assessed by paleomagnetic studies

Science.gov (United States)

Silva, Pedro F.; Henry, Bernard; Marques, Fernando O.; Hildenbrand, Anthony; Lopes, Ana; Madureira, Pedro; Madeira, José; Nunes, João C.; Roxerová, Zuzana

2018-02-01

The morphology of volcanic oceanic islands results from the interplay between constructive and destructive processes, and tectonics. In this study, the analysis of the paleomagnetic directions obtained on well-dated volcanic rocks is used as a tool to assess tilting related to tectonics and large-scale volcano instability along the Pico-Faial linear volcanic ridge (Azores Triple Junction, Central-North Atlantic). For this purpose, 530 specimens from 46 lava flows and one dyke from Pico and Faial islands were submitted to thermal and alternating magnetic fields demagnetizations. Detailed rock magnetic analyses, including thermomagnetic analyses and classical high magnetic field experiments revealed titanomagnetites with different Ti-content as the primary magnetic carrier, capable of recording stable remanent magnetizations. In both islands, the paleomagnetic analysis yields a Characteristic Remanent Magnetization, which presents island mean direction with normal and reversed polarities in agreement with the islands location and the age of the studied lava flows, indicating a primary thermo-remanent magnetization. Field observations and paleomagnetic data show that lava flows were emplaced on pre-existing slopes and were later affected by significant tilting. In Faial Island, magmatic inflation and normal faults making up an island-scale graben, can be responsible for the tilting. In Pico Island, inflation related to magma intrusion during flow emplacement can be at the origin of the inferred tilting, whereas gradual downward movement of the SE flank by slumping processes appears mostly translational.
Investigating the consequences of urban volcanism using a scenario approach II: Insights into transportation network damage and functionality

Science.gov (United States)

Blake, Daniel M.; Deligne, Natalia I.; Wilson, Thomas M.; Lindsay, Jan M.; Woods, Richard

2017-06-01

Transportation networks are critical infrastructure in urban environments. Before, during and following volcanic activity, these networks can incur direct and indirect impacts, which subsequently reduces the Level-of-Service available to transportation end-users. Additionally, reductions in service can arise from management strategies including evacuation zoning, causing additional complications for transportation end-users and operators. Here, we develop metrics that incorporate Level-of-Service for transportation end-users as the key measure of vulnerability for multi-hazard volcanic impact and risk assessments. A hypothetical eruption scenario recently developed for the Auckland Volcanic Field, New Zealand, is applied to describe potential impacts of a small basaltic eruption on different transportation modes, namely road, rail, and activities at airports and ports. We demonstrate how the new metrics can be applied at specific locations worldwide by considering the geophysical hazard sequence and evacuation zones in this scenario, a process that was strongly informed by consultation with transportation infrastructure providers and emergency management officials. We also discuss the potential implications of modified hazard sequences (e.g. different wind profiles during the scenario, and unrest with no resulting eruption) on transportation vulnerability and population displacement. The vent area of the eruption scenario used in our study is located north of the Māngere Bridge suburb of Auckland. The volcanic activity in the scenario progresses from seismic unrest, through phreatomagmatic explosions generating pyroclastic surges to a magmatic phase generating a scoria cone and lava flows. We find that most physical damage to transportation networks occurs from pyroclastic surges during the initial stages of the eruption. However, the most extensive service reduction across all networks occurs 6 days prior to the eruption onset, largely attributed to the

SATURATED ZONE IN-SITU TESTING

Energy Technology Data Exchange (ETDEWEB)

P.W. REIMUS

2004-11-08

The purpose of this scientific analysis is to document the results and interpretations of field experiments that test and validate conceptual flow and radionuclide transport models in the saturated zone (SZ) near Yucca Mountain, Nevada. The test interpretations provide estimates of flow and transport parameters used in the development of parameter distributions for total system performance assessment (TSPA) calculations. These parameter distributions are documented in ''Site-Scale Saturated Zone Flow Model (BSC 2004 [DIRS 170037]), Site-Scale Saturated Zone Transport'' (BSC 2004 [DIRS 170036]), Saturated Zone Colloid Transport (BSC 2004 [DIRS 170006]), and ''Saturated Zone Flow and Transport Model Abstraction'' (BSC 2004 [DIRS 170042]). Specifically, this scientific analysis contributes the following to the assessment of the capability of the SZ to serve as part of a natural barrier for waste isolation for the Yucca Mountain repository system: (1) The bases for selection of conceptual flow and transport models in the saturated volcanics and the saturated alluvium located near Yucca Mountain. (2) Results and interpretations of hydraulic and tracer tests conducted in saturated fractured volcanics at the C-wells complex near Yucca Mountain. The test interpretations include estimates of hydraulic conductivities, anisotropy in hydraulic conductivity, storativities, total porosities, effective porosities, longitudinal dispersivities, matrix diffusion mass transfer coefficients, matrix diffusion coefficients, fracture apertures, and colloid transport parameters. (3) Results and interpretations of hydraulic and tracer tests conducted in saturated alluvium at the Alluvial Testing Complex (ATC) located at the southwestern corner of the Nevada Test Site (NTS). The test interpretations include estimates of hydraulic conductivities, storativities, total porosities, effective porosities, longitudinal dispersivities, matrix diffusion mass
SATURATED ZONE IN-SITU TESTING

International Nuclear Information System (INIS)

REIMUS, P.W.

2004-01-01

The purpose of this scientific analysis is to document the results and interpretations of field experiments that test and validate conceptual flow and radionuclide transport models in the saturated zone (SZ) near Yucca Mountain, Nevada. The test interpretations provide estimates of flow and transport parameters used in the development of parameter distributions for total system performance assessment (TSPA) calculations. These parameter distributions are documented in ''Site-Scale Saturated Zone Flow Model (BSC 2004 [DIRS 170037]), Site-Scale Saturated Zone Transport'' (BSC 2004 [DIRS 170036]), Saturated Zone Colloid Transport (BSC 2004 [DIRS 170006]), and ''Saturated Zone Flow and Transport Model Abstraction'' (BSC 2004 [DIRS 170042]). Specifically, this scientific analysis contributes the following to the assessment of the capability of the SZ to serve as part of a natural barrier for waste isolation for the Yucca Mountain repository system: (1) The bases for selection of conceptual flow and transport models in the saturated volcanics and the saturated alluvium located near Yucca Mountain. (2) Results and interpretations of hydraulic and tracer tests conducted in saturated fractured volcanics at the C-wells complex near Yucca Mountain. The test interpretations include estimates of hydraulic conductivities, anisotropy in hydraulic conductivity, storativities, total porosities, effective porosities, longitudinal dispersivities, matrix diffusion mass transfer coefficients, matrix diffusion coefficients, fracture apertures, and colloid transport parameters. (3) Results and interpretations of hydraulic and tracer tests conducted in saturated alluvium at the Alluvial Testing Complex (ATC) located at the southwestern corner of the Nevada Test Site (NTS). The test interpretations include estimates of hydraulic conductivities, storativities, total porosities, effective porosities, longitudinal dispersivities, matrix diffusion mass transfer coefficients, and colloid
Optimization of turning process through the analytic flank wear modelling

Science.gov (United States)

Del Prete, A.; Franchi, R.; De Lorenzis, D.

2018-05-01

In the present work, the approach used for the optimization of the process capabilities for Oil&Gas components machining will be described. These components are machined by turning of stainless steel castings workpieces. For this purpose, a proper Design Of Experiments (DOE) plan has been designed and executed: as output of the experimentation, data about tool wear have been collected. The DOE has been designed starting from the cutting speed and feed values recommended by the tools manufacturer; the depth of cut parameter has been maintained as a constant. Wear data has been obtained by means the observation of the tool flank wear under an optical microscope: the data acquisition has been carried out at regular intervals of working times. Through a statistical data and regression analysis, analytical models of the flank wear and the tool life have been obtained. The optimization approach used is a multi-objective optimization, which minimizes the production time and the number of cutting tools used, under the constraint on a defined flank wear level. The technique used to solve the optimization problem is a Multi Objective Particle Swarm Optimization (MOPS). The optimization results, validated by the execution of a further experimental campaign, highlighted the reliability of the work and confirmed the usability of the optimized process parameters and the potential benefit for the company.
Reconstruction of the eruptive activity on the NE sector of Stromboli volcano: timing of flank eruptions since 15 ka

NARCIS (Netherlands)

Calvari, S.; Branca, S.; Corsaro, R.A.; De Beni, E.; Miraglia, L.; Norini, G.; Wijbrans, J.R.; Boschi, E.

2011-01-01

A multidisciplinary geological and compositional investigation allowed us to reconstruct the occurrence of flank eruptions on the lower NE flank of Stromboli volcano since 15 ka. The oldest flank eruption recognised is Roisa, which occurred at ~15 ka during the Vancori period, and has transitional
Volcanic sulfur dioxide index and volcanic explosivity index inferred from eruptive volume of volcanoes in Jeju Island, Korea: application to volcanic hazard mitigation

Science.gov (United States)

Ko, Bokyun; Yun, Sung-Hyo

2016-04-01

Jeju Island located in the southwestern part of Korea Peninsula is a volcanic island composed of lavaflows, pyroclasts, and around 450 monogenetic volcanoes. The volcanic activity of the island commenced with phreatomagmatic eruptions under subaqueous condition ca. 1.8-2.0 Ma and lasted until ca. 1,000 year BP. For evaluating volcanic activity of the most recently erupted volcanoes with reported age, volcanic explosivity index (VEI) and volcanic sulfur dioxide index (VSI) of three volcanoes (Ilchulbong tuff cone, Songaksan tuff ring, and Biyangdo scoria cone) are inferred from their eruptive volumes. The quantity of eruptive materials such as tuff, lavaflow, scoria, and so on, is calculated using a model developed in Auckland Volcanic Field which has similar volcanic setting to the island. The eruptive volumes of them are 11,911,534 m3, 24,987,557 m3, and 9,652,025 m3, which correspond to VEI of 3, 3, and 2, respectively. According to the correlation between VEI and VSI, the average quantity of SO2 emission during an eruption with VEI of 3 is 2-8 × 103 kiloton considering that the island was formed under intraplate tectonic setting. Jeju Island was regarded as an extinct volcano, however, several studies have recently reported some volcanic eruption ages within 10,000 year BP owing to the development in age dating technique. Thus, the island is a dormant volcano potentially implying high probability to erupt again in the future. The volcanoes might have explosive eruptions (vulcanian to plinian) with the possibility that SO2 emitted by the eruption reaches stratosphere causing climate change due to backscattering incoming solar radiation, increase in cloud reflectivity, etc. Consequently, recommencement of volcanic eruption in the island is able to result in serious volcanic hazard and this study provides fundamental and important data for volcanic hazard mitigation of East Asia as well as the island. ACKNOWLEDGMENTS: This research was supported by a grant [MPSS
Diverse Eruptions at Approximately 2,200 Years B.P. on the Great Rift, Idaho: Inferences for Magma Dynamics Along Volcanic Rift Zones

Science.gov (United States)

Hughes, S. S.; Nawotniak, S. E. Kobs; Borg, C.; Mallonee, H. C.; Purcell, S.; Neish, C.; Garry, W. B.; Haberle, C. W.; Lim, D. S. S.; Heldmann, J. L.

2016-01-01

Compositionally and morphologically diverse lava flows erupted on the Great Rift of Idaho approximately 2.2 ka (kilo-annum, 1000 years ago) during a volcanic "flare-up" of activity following an approximately 2 ky (kiloyear, 1000 years) hiatus in eruptions. Volcanism at Craters of the Moon (COTM), Wapi and Kings Bowl lava fields around this time included primitive and evolved compositions, separated over 75 kilometers along the approximately 85 kilometers-long rift, with striking variability in lava flow emplacement mechanisms and surface morphologies. Although the temporal associations may be coincidental, the system provides a planetary analog to better understand magma dynamics along rift systems, including that associated with lunar floor-fractured craters. This study aims to help bridge the knowledge gap between ancient rift volcanism evident on the Moon and other terrestrial planets, and active rift volcanism, e.g., at Hawai'i and Iceland.
Flank wears Simulation by using back propagation neural network when cutting hardened H-13 steel in CNC End Milling

Science.gov (United States)

Hazza, Muataz Hazza F. Al; Adesta, Erry Y. T.; Riza, Muhammad

2013-12-01

High speed milling has many advantages such as higher removal rate and high productivity. However, higher cutting speed increase the flank wear rate and thus reducing the cutting tool life. Therefore estimating and predicting the flank wear length in early stages reduces the risk of unaccepted tooling cost. This research presents a neural network model for predicting and simulating the flank wear in the CNC end milling process. A set of sparse experimental data for finish end milling on AISI H13 at hardness of 48 HRC have been conducted to measure the flank wear length. Then the measured data have been used to train the developed neural network model. Artificial neural network (ANN) was applied to predict the flank wear length. The neural network contains twenty hidden layer with feed forward back propagation hierarchical. The neural network has been designed with MATLAB Neural Network Toolbox. The results show a high correlation between the predicted and the observed flank wear which indicates the validity of the models.
Flank wears Simulation by using back propagation neural network when cutting hardened H-13 steel in CNC End Milling

International Nuclear Information System (INIS)

Al Hazza, Muataz Hazza F; Adesta, Erry Y T; Riza, Muhammad

2013-01-01

High speed milling has many advantages such as higher removal rate and high productivity. However, higher cutting speed increase the flank wear rate and thus reducing the cutting tool life. Therefore estimating and predicting the flank wear length in early stages reduces the risk of unaccepted tooling cost. This research presents a neural network model for predicting and simulating the flank wear in the CNC end milling process. A set of sparse experimental data for finish end milling on AISI H13 at hardness of 48 HRC have been conducted to measure the flank wear length. Then the measured data have been used to train the developed neural network model. Artificial neural network (ANN) was applied to predict the flank wear length. The neural network contains twenty hidden layer with feed forward back propagation hierarchical. The neural network has been designed with MATLAB Neural Network Toolbox. The results show a high correlation between the predicted and the observed flank wear which indicates the validity of the models
Reconsidering Volcanic Ocean Island Hydrology: Recent Geophysical and Drilling Results

Science.gov (United States)

Thomas, D. M.; Pierce, H. A.; Lautze, N. C.

2017-12-01

Recent results of geophysical surveys and exploratory drilling in Hawaii have suggested that Hawaii's hydrogeology may be more complex than has been generally recognized. Instead of a more-or-less homogeneous pile of highly permeable eruptive basalts that are intermittently punctuated by volcanic dikes confined to calderas and rift zones, we are finding that dike compartmentalization is occurring outside of recognized rift zones, leading to significantly higher volumes of stored groundwater within the island. Analysis of recent geophysical surveys have shown local water table elevations that are substantially higher than can be accounted for by the high hydraulic conductivities of Hawaiian basalts. Recent diamond wireline drilling results have also shown that sub-horizontal variations in permeability, associated with significant changes in eruptive character (e.g. explosive vs effusive activity) are acting as significant perching and confining bodies over significant aerial extents and suggest that these features also contribute to increased storage of recharge. Not only is storage much higher than previously assumed, these features appear to impact subsurface groundwater flow in ways that are not accounted for in traditional methods of computing sustainable yields for near shore aquifers: where buried confining formations extend to depths well below sea level, higher elevation recharge is being intercepted and diverted to deep submarine groundwater discharge well below depths that are typically investigated or quantified. We will provide a summary of the recent geophysical survey results along with a revised conceptual model for groundwater circulation within volcanic ocean islands.
Plasma Transport at the Magnetospheric Flank Boundary. Final report

International Nuclear Information System (INIS)

Otto, Antonius

2012-01-01

Progress is highlighted in these areas: 1. Model of magnetic reconnection induced by three-dimensional Kelvin Helmholtz (KH) modes at the magnetospheric flank boundary; 2. Quantitative evaluation of mass transport from the magnetosheath onto closed geomagnetic field for northward IMF; 3. Comparison of mass transfer by cusp reconnection and Flank Kelvin Helmholtz modes; 4. Entropy constraint and plasma transport in the magnetotail - a new mechanism for current sheet thinning; 5. Test particle model for mass transport onto closed geomagnetic field for northward IMF; 6. Influence of density asymmetry and magnetic shear on (a) the linear and nonlinear growth of 3D Kelvin Helmholtz (KH) modes, and (b) three-dimensional KH mediated mass transport; 7. Examination of entropy and plasma transport in the magnetotail; 8. Entropy change and plasma transport by KH mediated reconnection - mixing and heating of plasma; 9. Entropy and plasma transport in the magnetotail - tail reconnection; and, 10. Wave coupling at the magnetospheric boundary and generation of kinetic Alfven waves
Force Modelling in Orthogonal Cutting Considering Flank Wear Effect

Science.gov (United States)

Rathod, Kanti Bhikhubhai; Lalwani, Devdas I.

2017-05-01

In the present work, an attempt has been made to provide a predictive cutting force model during orthogonal cutting by combining two different force models, that is, a force model for a perfectly sharp tool plus considering the effect of edge radius and a force model for a worn tool. The first force model is for a perfectly sharp tool that is based on Oxley's predictive machining theory for orthogonal cutting as the Oxley's model is for perfectly sharp tool, the effect of cutting edge radius (hone radius) is added and improve model is presented. The second force model is based on worn tool (flank wear) that was proposed by Waldorf. Further, the developed combined force model is also used to predict flank wear width using inverse approach. The performance of the developed combined total force model is compared with the previously published results for AISI 1045 and AISI 4142 materials and found reasonably good agreement.
The association between maternal hydronephrosis and acute flank pain during pregnancy: a prospective pilot-study.

Science.gov (United States)

Farr, Alex; Ott, Johannes; Kueronya, Verena; Margreiter, Markus; Javadli, Elchin; Einig, Sabrina; Husslein, Peter W; Bancher-Todesca, Dagmar

2017-10-01

Maternal hydronephrosis may cause flank pain during pregnancy. We aimed to investigate the association between maternal hydronephrosis and flank pain intensity. From 2014 to 2015, all consecutive women with singleton pregnancies, who presented at our tertiary center due to acute flank pain, were prospectively evaluated by renal ultrasonography and pain questionnaires. A visual analogue scale was used to assess pain intensity. The study had 90% power to detect a significant correlation between hydronephrosis and flank pain (Spearman's test). A total of 51 consecutive women with left-sided (13.7%), right-sided (64.7%) or bilateral (21.6%) pain were enrolled. The mean gestational age of these women, who presented due to their pain, was 27.5 ± 6.8 weeks at the time of consultation. The mean VAS score was 7.6 ± 2.2. In 43/51 (84.3%) women, hydronephrosis was found on renal sonograms. No correlation was found between the grade of hydronephrosis and pain intensity (p = 0.466; r= -0.28). Women delivered at a mean gestational age of 38.1 ± 2.4 weeks and their infants had a mean birthweight of 3138 ± 677 g. Hydronephrosis is a common finding among pregnant women with acute flank pain. The grade of hydronephrosis does not affect pain intensity. This study suggests normal pregnancy outcomes in these women.
Hydrothermal alteration, fumarolic deposits and fluids from Lastarria Volcanic Complex: A multidisciplinary study

OpenAIRE

Aguilera, Felipe; Layana, Susana; Rodríguez-Díaz, Augusto; González, Cristóbal; Cortés, Julio; Inostroza, Manuel

2016-01-01

A multidisciplinary study that includes processing of Landsat ETM+ satellite images, chemistry of gas condensed, mineralogy and chemistry of fumarolic deposits, and fluid inclusion data from native sulphur deposits, has been carried out in the Lastarria Volcanic Complex (LVC) with the objective to determine the distribution and characteristics of hydrothermal alteration zones and to establish the relations between gas chemistry and fumarolic deposits. Satellite image processing shows the pres...
Volcanic Alert System (VAS) developed during the (2011-2013) El Hierro (Canary Islands) volcanic process

Science.gov (United States)

Ortiz, Ramon; Berrocoso, Manuel; Marrero, Jose Manuel; Fernandez-Ros, Alberto; Prates, Gonçalo; De la Cruz-Reyna, Servando; Garcia, Alicia

2014-05-01

In volcanic areas with long repose periods (as El Hierro), recently installed monitoring networks offer no instrumental record of past eruptions nor experience in handling a volcanic crisis. Both conditions, uncertainty and inexperience, contribute to make the communication of hazard more difficult. In fact, in the initial phases of the unrest at El Hierro, the perception of volcanic risk was somewhat distorted, as even relatively low volcanic hazards caused a high political impact. The need of a Volcanic Alert System became then evident. In general, the Volcanic Alert System is comprised of the monitoring network, the software tools for the analysis of the observables, the management of the Volcanic Activity Level, and the assessment of the threat. The Volcanic Alert System presented here places special emphasis on phenomena associated to moderate eruptions, as well as on volcano-tectonic earthquakes and landslides, which in some cases, as in El Hierro, may be more destructive than an eruption itself. As part of the Volcanic Alert System, we introduce here the Volcanic Activity Level which continuously applies a routine analysis of monitoring data (particularly seismic and deformation data) to detect data trend changes or monitoring network failures. The data trend changes are quantified according to the Failure Forecast Method (FFM). When data changes and/or malfunctions are detected, by an automated watchdog, warnings are automatically issued to the Monitoring Scientific Team. Changes in the data patterns are then translated by the Monitoring Scientific Team into a simple Volcanic Activity Level, that is easy to use and understand by the scientists and technicians in charge for the technical management of the unrest. The main feature of the Volcanic Activity Level is its objectivity, as it does not depend on expert opinions, which are left to the Scientific Committee, and its capabilities for early detection of precursors. As a consequence of the El Hierro
Volcanic hazards to airports

Science.gov (United States)

Guffanti, M.; Mayberry, G.C.; Casadevall, T.J.; Wunderman, R.

2009-01-01

Volcanic activity has caused significant hazards to numerous airports worldwide, with local to far-ranging effects on travelers and commerce. Analysis of a new compilation of incidents of airports impacted by volcanic activity from 1944 through 2006 reveals that, at a minimum, 101 airports in 28 countries were affected on 171 occasions by eruptions at 46 volcanoes. Since 1980, five airports per year on average have been affected by volcanic activity, which indicates that volcanic hazards to airports are not rare on a worldwide basis. The main hazard to airports is ashfall, with accumulations of only a few millimeters sufficient to force temporary closures of some airports. A substantial portion of incidents has been caused by ash in airspace in the vicinity of airports, without accumulation of ash on the ground. On a few occasions, airports have been impacted by hazards other than ash (pyroclastic flow, lava flow, gas emission, and phreatic explosion). Several airports have been affected repeatedly by volcanic hazards. Four airports have been affected the most often and likely will continue to be among the most vulnerable owing to continued nearby volcanic activity: Fontanarossa International Airport in Catania, Italy; Ted Stevens Anchorage International Airport in Alaska, USA; Mariscal Sucre International Airport in Quito, Ecuador; and Tokua Airport in Kokopo, Papua New Guinea. The USA has the most airports affected by volcanic activity (17) on the most occasions (33) and hosts the second highest number of volcanoes that have caused the disruptions (5, after Indonesia with 7). One-fifth of the affected airports are within 30 km of the source volcanoes, approximately half are located within 150 km of the source volcanoes, and about three-quarters are within 300 km; nearly one-fifth are located more than 500 km away from the source volcanoes. The volcanoes that have caused the most impacts are Soufriere Hills on the island of Montserrat in the British West Indies
Uranium mineralization in tertiary volcanic rocks of the Los Frailes formation (Bolivia)

International Nuclear Information System (INIS)

Aparicio, A.

1981-01-01

The Los Frailes Formation, a 9000 km 2 area of Miocene-Pliocene age, contains uranium mineralization in acid tuffs, ignimbrites and lavas. Uranium also occurs in sedimentary rocks of various types and ages which outcrop in adjacent areas. So far the most extensive mineralization seems to be confined in volcanic pyroclastic rocks. Although the surface mineralization varies in grade from 0.01% to more than 2.5%, the average grade in the only deposit being mined (Cotaje) is 0.05% of U 3 O 8 . On the basis of the available data it is believed that certain leaching processes, during the last erosion cycle (Pliocene-Pleistocene) and under very humid conditions, brought about the mobilization of the uranium from the volcanic rocks in aqueous alkaline and calco-alkaline solutions circulating on the surface and underground. Uranium minerals were deposited, generally by chemical reduction, in tectonic zones and/or zones of high porosity. The common metallogenetic model in the western area, defined as the 'Sevaruyo uraniferous district', is exogenic and is characterized by epigenetic uranium occurrences and deposits formed by supergene enrichment. On the basis of their mechanism of formation, control of mineralization and mineral associations, these deposits are classified according to: those with strictly tectonic control, those with sedimentary control and those of mixed genetics. Recent discoveries in the eastern area of the volcanic complex give evidence of epigenetic mineralization, apparently linked with hypogene hydrothermal processes, in addition to exogenic mineralizations contained in rocks stratigraphically subjacent to the Los Frailes Formation. There is no intention of making an evaluation of the recently discovered resources since the studies and exploration are still at too early a stage to warrant prediction of their real potential. (author)
Magnetotelluric Investigation of the South Aegean Volcanic Arc, Greece

Science.gov (United States)

Kalisperi, Despina; Romano, Gerardo; Smirnov, Maxim; Kouli, Maria; Perrone, Angela; Makris, John P.; Vallianatos, Filippos

2014-05-01

The South Aegean Volcanic Arc (SAVA) is a chain of volcanic islands in the South Aegean resulting from the subduction of the African tectonic plate beneath the Eurasian plate. It extends from Methana, northwest, to the Island of Nisyros southeast (450 km total length). SAVA comprises a series of dormant and historically active volcanoes, with the most prominent to be Aegina, Methana, Milos, Santorini, Kolumbo, Kos and Nisyros. The aim of the ongoing research project "MagnetoTellurics in studying Geodynamics of the hEllenic ARc (MT-GEAR)" is to contribute to the investigation of the geoelectric structure of Southern Aegean, and particularly to attempt to image the Hellenic Subduction Zone. In this context, onshore magnetotelluric (MT) measurements were recently carried out on the central and eastern part of SAVA (Milos, Santorini, Nisyros and Kos Islands). Data were collected using two MT systems running simultaneously plus a remote reference station installed in Omalos plateau (Western Crete). Robust MT data analysis of the broad-band MT soundings and the resulting model of the conductivity structure of the South Aegean Volcanic Arc is presented. The research is co-funded by the European Social Fund (ESF) and National Resources under the Operational Programme 'Education and Lifelong Learning (EdLL) within the context of the Action 'Supporting Postdoctoral Researchers' in the framework of the project title "MagnetoTellurics in studying Geodynamics of the hEllenic ARc (MT-GEAR)".
Tectonic-Volcanic Interplay in the Dabbahu Segment of the Afar Rift from Cosmogenic 3He Constraints

Science.gov (United States)

Williams, A.; Pik, R.; Burnard, P.; Lahitte, P.; Yirgu, G.; Adem, M.

2008-12-01

The Afar Rift in Ethiopia is one of the only subaerial locations in the world where the transition from continental break-up to oceanic-spreading can be observed. Extension and volcanism in the Afar is concentrated in tectono-magmatic segments (TMS), similar in size and morphology to those that characterise spreading ridges. The Dabbahu TMS is the southernmost of the western Afar and has recently been the site of significant activity. A massive seismic event in late 2005, triggered by the injection of an 8-m wide dyke, heralded the onset of a new rifting period in the Dabbahu TMS. Volcanic activity associated with the periods of magma-driven extension, which have recurred at 4-8 mth intervals, has been both silicic (explosive) and basaltic (fissural). The most recent activity in the Afar thus testifies to the close interplay of tectonics and magmatism in rifting environments. In an effort to decipher the long-term structural and volcanic evolution of Dabbahu TMS we have employed the cosmogenic nuclide dating technique to provide chronological data for the segment. This method has advantages over other geochronological tools in that we can target both volcanic and tectonic surfaces of a few Kyr to several Myr age. Baddi Volcano, located off-axis on the western margin of the TMS, is a bimodal central stratovolcano typical of the Afar TMS. Late-stage basaltic lava flows cap an acidic base, which has been dated at 290 ± 4 ka using the K-Ar technique (Lahitte et al., 2003). Following preliminary sampling in 2007, we have determined a cosmogenic 3He age of 53.4 ± 3.7 ka from multiple samples from one of the basaltic flows on the NW flank of Baddi. These data show a significant time gap (240 Kyr) between the final phase of acidic volcanism and the onset of basaltic activity at the central volcanoes, presumably related to the rate of magma chamber replenishment. To test whether the spectacular shift to basaltic activity at 53 ka represents replenishment of the entire sub
Geochronology and petrology of OIB-type lavas from the central part of the Mexican Volcanic Belt

International Nuclear Information System (INIS)

Hasenaka, Toshiaki; Yoshida, Takeyoshi; Uto, Kozo; Uchiumi, Shigeru

1995-01-01

In Mexican Volcanic Belt, typical continental margin arc volcanic activities have occurred accompanying the subduction of Rivera Plate and Cocos Plate into North American Plate. It has been known by recent geochemical research that the oceanic island type magma which does not show the characteristic chemical composition of subduction zone has extruded. In order to investigate the relation of the development of volcanic belt in continental margin are with the change of wide area tectonics, and to impose important limit on magma formation models, it is important to know the state of production of oceanic island type magma in continental margin arc and the age of its activities. In this report, the results of the K-Ar age measurement for the oceanic island type lava produced in the middle of Mexican Volcanic Belt are shown, and the geochemical features of those samples are clarified. The state of production and the petrography of oceanic island type igneous rock samples are explained. The K-Ar age measurement experiment and the results are reported. The chemical composition of oceanic island type lava determined by photon activation process and fluorescent X-ray analysis is shown. (K.I.)
Catastrophic debris flows transformed from landslides in volcanic terrains : mobility, hazard assessment and mitigation strategies

Science.gov (United States)

Scott, Kevin M.; Macias, Jose Luis; Naranjo, Jose Antonio; Rodriguez, Sergio; McGeehin, John P.

2001-01-01

Communities in lowlands near volcanoes are vulnerable to significant volcanic flow hazards in addition to those associated directly with eruptions. The largest such risk is from debris flows beginning as volcanic landslides, with the potential to travel over 100 kilometers. Stratovolcanic edifices commonly are hydrothermal aquifers composed of unstable, altered rock forming steep slopes at high altitudes, and the terrain surrounding them is commonly mantled by readily mobilized, weathered airfall and ashflow deposits. We propose that volcano hazard assessments integrate the potential for unanticipated debris flows with, at active volcanoes, the greater but more predictable potential of magmatically triggered flows. This proposal reinforces the already powerful arguments for minimizing populations in potential flow pathways below both active and selected inactive volcanoes. It also addresses the potential for volcano flank collapse to occur with instability early in a magmatic episode, as well as the 'false-alarm problem'-the difficulty in evacuating the potential paths of these large mobile flows. Debris flows that transform from volcanic landslides, characterized by cohesive (muddy) deposits, create risk comparable to that of their syneruptive counterparts of snow and ice-melt origin, which yield noncohesive (granular) deposits, because: (1) Volcano collapses and the failures of airfall- and ashflow-mantled slopes commonly yield highly mobile debris flows as well as debris avalanches with limited runout potential. Runout potential of debris flows may increase several fold as their volumes enlarge beyond volcanoes through bulking (entrainment) of sediment. Through this mechanism, the runouts of even relatively small collapses at Cascade Range volcanoes, in the range of 0.1 to 0.2 cubic kilometers, can extend to populated lowlands. (2) Collapse is caused by a variety of triggers: tectonic and volcanic earthquakes, gravitational failure, hydrovolcanism, and

Long-range hazard assessment of volcanic ash dispersal for a Plinian eruptive scenario at Popocatépetl volcano (Mexico): implications for civil aviation safety

Science.gov (United States)

Bonasia, Rosanna; Scaini, Chirara; Capra, Lucia; Nathenson, Manuel; Siebe, Claus; Arana-Salinas, Lilia; Folch, Arnau

2013-01-01

Popocatépetl is one of Mexico’s most active volcanoes threatening a densely populated area that includes Mexico City with more than 20 million inhabitants. The destructive potential of this volcano is demonstrated by its Late Pleistocene–Holocene eruptive activity, which has been characterized by recurrent Plinian eruptions of large magnitude, the last two of which destroyed human settlements in pre-Hispanic times. Popocatépetl’s reawakening in 1994 produced a crisis that culminated with the evacuation of two villages on the northeastern flank of the volcano. Shortly after, a monitoring system and a civil protection contingency plan based on a hazard zone map were implemented. The current volcanic hazards map considers the potential occurrence of different volcanic phenomena, including pyroclastic density currents and lahars. However, no quantitative assessment of the tephra hazard, especially related to atmospheric dispersal, has been performed. The presence of airborne volcanic ash at low and jet-cruise atmospheric levels compromises the safety of aircraft operations and forces re-routing of aircraft to prevent encounters with volcanic ash clouds. Given the high number of important airports in the surroundings of Popocatépetl volcano and considering the potential threat posed to civil aviation in Mexico and adjacent regions in case of a Plinian eruption, a hazard assessment for tephra dispersal is required. In this work, we present the first probabilistic tephra dispersal hazard assessment for Popocatépetl volcano. We compute probabilistic hazard maps for critical thresholds of airborne ash concentrations at different flight levels, corresponding to the situation defined in Europe during 2010, and still under discussion. Tephra dispersal mode is performed using the FALL3D numerical model. Probabilistic hazard maps are built for a Plinian eruptive scenario defined on the basis of geological field data for the “Ochre Pumice” Plinian eruption (4965 14C
Volcanic Metal Emissions and Implications for Geochemical Cycling and Mineralization

Science.gov (United States)

Edmonds, M.; Mather, T. A.

2016-12-01

Volcanoes emit substantial fluxes of metals to the atmosphere in volcanic gas plumes in the form of aerosol, adsorbed onto silicate particles and even in some cases as gases.. A huge database of metal emissions has been built over the preceding decades, which shows that volcanoes emit highly volatile metals into the atmosphere, such as As, Bi, Cd, Hg, Re, Se, Tl, among others. Understanding the cycling of metals through the Solid Earth system has importance for tackling a wide range of Earth Science problems, e.g. (1) the environmental impacts of metal emissions; (2) the sulfur and metal emissions of volcanic eruptions; (3) the behavior of metals during subduction and slab devolatilization; (4) the influence of redox on metal behavior in subduction zones; (5) the partitioning of metals between magmatic vapor, brines and melts; and (6) the relationships between volcanism and ore deposit formation. It is clear, when comparing the metal composition and flux in the gases and aerosols emitted from volcanoes, that they vary with tectonic setting. These differences allow insights into how the magmatic vapor was generated and how it interacted with melts and sulfides during magma differentiation and decompression. Hotspot volcanoes (e.g. Kilauea, Hawaii; volcanoes in Iceland) outgas a metal suite that mirrors the sulfide liquid-silicate melt partitioning behaviors reconstructed from experiments (as far as they are known), suggesting that the aqueous fluids (that will later be outgassed from the volcano) receive metals directly from oxidation of sulfide liquids during degassing and ascent of magmas towards the surface. At arc volcanoes, the gaseous fluxes of metals are typically much higher; and there are greater enrichments in elements that partition strongly into vapor or brine from silicate melts such as Cu, Au, Zn, Pb, W. We collate and present data on volcanic metal emissions from volcanoes worldwide and review the implications of the data array for metal cycling
Resident perception of volcanic hazards and evacuation procedures

Directory of Open Access Journals (Sweden)

D. K. Bird

2009-02-01

Full Text Available Katla volcano, located beneath the Mýrdalsjökull ice cap in southern Iceland, is capable of producing catastrophic jökulhlaup. The Icelandic Civil Protection (ICP, in conjunction with scientists, local police and emergency managers, developed mitigation strategies for possible jökulhlaup produced during future Katla eruptions. These strategies were tested during a full-scale evacuation exercise in March 2006. A positive public response during a volcanic crisis not only depends upon the public's knowledge of the evacuation plan but also their knowledge and perception of the possible hazards. To improve the effectiveness of residents' compliance with warning and evacuation messages it is important that emergency management officials understand how the public interpret their situation in relation to volcanic hazards and their potential response during a crisis and apply this information to the ongoing development of risk mitigation strategies. We adopted a mixed methods approach in order to gain a broad understanding of residents' knowledge and perception of the Katla volcano in general, jökulhlaup hazards specifically and the regional emergency evacuation plan. This entailed field observations during the major evacuation exercise, interviews with key emergency management officials and questionnaire survey interviews with local residents. Our survey shows that despite living within the hazard zone, many residents do not perceive that their homes could be affected by a jökulhlaup, and many participants who perceive that their homes are safe, stated that they would not evacuate if an evacuation warning was issued. Alarmingly, most participants did not receive an evacuation message during the exercise. However, the majority of participants who took part in the exercise were positive about its implementation. This assessment of resident knowledge and perception of volcanic hazards and the evacuation plan is the first of its kind in
Orbital Evolution of Dust Particles in the Sublimation Zone near the Sun

Science.gov (United States)

Shestakova, L. I.; Demchenko, B. I.

2018-03-01

We have performed the calculations of the orbital evolution of dust particles from volcanic glass ( p-obsidian), basalt, astrosilicate, olivine, and pyroxene in the sublimation zone near the Sun. The sublimation (evaporation) rate is determined by the temperature of dust particles depending on their radius, material, and distance to the Sun. All practically important parameters that characterize the interaction of spherical dust particles with the radiation are calculated using the Mie theory. The influence of radiation and solar wind pressure, as well as the Poynting-Robertson drag force effects on the dust dynamics, are also taken into account. According to the observations (Shestakova and Demchenko, 2016), the boundary of the dust-free zone is 7.0-7.6 solar radii for standard particles of the zodiacal cloud and 9.1-9.2 solar radii for cometary particles. The closest agreement is obtained for basalt particles and certain kinds of olivine, pyroxene, and volcanic glass.
Volcanic signals in oceans

KAUST Repository

Stenchikov, Georgiy L.

2009-08-22

Sulfate aerosols resulting from strong volcanic explosions last for 2–3 years in the lower stratosphere. Therefore it was traditionally believed that volcanic impacts produce mainly short-term, transient climate perturbations. However, the ocean integrates volcanic radiative cooling and responds over a wide range of time scales. The associated processes, especially ocean heat uptake, play a key role in ongoing climate change. However, they are not well constrained by observations, and attempts to simulate them in current climate models used for climate predictions yield a range of uncertainty. Volcanic impacts on the ocean provide an independent means of assessing these processes. This study focuses on quantification of the seasonal to multidecadal time scale response of the ocean to explosive volcanism. It employs the coupled climate model CM2.1, developed recently at the National Oceanic and Atmospheric Administration\\'s Geophysical Fluid Dynamics Laboratory, to simulate the response to the 1991 Pinatubo and the 1815 Tambora eruptions, which were the largest in the 20th and 19th centuries, respectively. The simulated climate perturbations compare well with available observations for the Pinatubo period. The stronger Tambora forcing produces responses with higher signal-to-noise ratio. Volcanic cooling tends to strengthen the Atlantic meridional overturning circulation. Sea ice extent appears to be sensitive to volcanic forcing, especially during the warm season. Because of the extremely long relaxation time of ocean subsurface temperature and sea level, the perturbations caused by the Tambora eruption could have lasted well into the 20th century.
Earthquake and volcanic risks: issues for the Bataan Nuclear Power Plant

International Nuclear Information System (INIS)

Solidum, Dr. Renato U.

2009-01-01

The proposed re-commissioning of the mothballed Bataan Nuclear Power Plant (BNPP) has raised objections that include the perceived unsafe siting of the BNPP on Mt. Natib, a potentially active volcano, in an earthquake-prone region. This concern must be evaluated through thorough seismological, paleo-seismic, volcanological and engineering studies. The BNPP sits on Napot Point on the southwest foot slope of Mt. Natib, an andesitic to dacitic stratovolcano just 30 kms south of Mt. Pinatubo. Natib's evolution is poorly known, but involved at least 3 explosive summit eruptions that formed a 6 km-diameter coalescent caldera and a younger 2-km diameter caldera. Pyroclastic flows define the cone surface, and available age dating includes a ±27 ka 14C age for a deposit on the eastern flanks and an 11-18 ka relative dating for suspected pyroclastic deposits in Subic Bay (1). Whether these represent the most recent eruptions is uncertain. A detailed magmatic/eruptive history defining magmatic recharge and eruption recurrence rates, from which probabilities for future eruptive activity can be analyzed, will be necessary for quantifying volcanic risk. Furthermore, Natib,Pinatubo and adjacent Mariveles are part of the Luzon Arc and associated with ongoing subduction along the Manila Trench. Subduction earthquakes are common, but apart from these, seismic risk is also being attributted to tectonic structures inland that include reported on site faults inferred from drilling, basin faults seen in reflection profiles (1), the Subic Bay Fault Zone delineated by magmatic studies (2) and various lineaments inferred from satellite imageries. These, plus seismicity in the region are being argued as indicators of earthquake threat. However, much emphasis is given maximum seismic magnitudes rather than peak ground accelerations (PGAs), epicentral rather than focal sources,and the inference of faults/lineaments rather than paleoseismic evidence of recent faulting. Paleoseismic studies of
Autoradiographic localization of tritiated dihydrotestosterone in the flank organ of the albino hamster

International Nuclear Information System (INIS)

Lucky, A.W.; Eisenfeld, A.J.; Visintin, I.

1985-01-01

In the hamster flank organ, the growth of hair and growth of sebaceous glands are androgen-dependent functions. Although dihydrotestosterone (DHT) is known to be a potent stimulator of flank organ growth, there is no information about localization of DHT receptor sites in this organ. The purpose of this study was to use steroid autoradiography to localize DHT receptors in the hamster flank organ. Because steroid hormones are functional when translocated to nuclear receptors, nuclear localization by autoradiography defines receptor sites. In order to be able to visualize autoradiographic grains from radiolabeled androgens around hair follicles, albino hamsters were studied to avoid confusion between the grains and pigment granules which are abundant in the more common Golden Syrian hamster. Mature male hamsters castrated 24 hours earlier were given tritium-labeled dihydrotestosterone ( [ 3 H]DHT). Using the technique of thaw-mount steroid autoradiography, 4-micron unfixed frozen sections were mounted in the dark onto emulsion-coated glass slides and allowed to develop for 4-6 months. [ 3 H]DHT was found to be concentrated over sebocyte nuclei. The label was present peripherally as well as in differentiating sebocytes. There was no nuclear localization of [ 3 H]DHT in animals pretreated with excessive quantities of unlabeled DHT. Steroid metabolites of [ 3 H] DHT were assessed by thin-layer chromatography in paired tissue samples. Most of the label remained with DHT. Uptake was inhibited in the flank organ of hamsters pretreated with unlabeled DHT
Neoarchean history of the conjunction zone between the Belomorian mobile belt and the Karelian craton, Baltic shield: new isotopic data

International Nuclear Information System (INIS)

Alekseev, N.L.; Balaganskij, V.V.; Zinger, T.F.; Levchenkov, O.A.; Glebovitskij, V.A.; Makeev, A.F.; Yakovleva, S.Z.

2004-01-01

To study the neoarchean magmatism history of the conjunction zone between the Belomorian mobile belt and the Karelian craton one carried out U-Pb-isotope dating of volcanic zircons of the Kukas lake region. At the mentioned region one detected two pulses of the neoarchean volcanism that took place about 2877±45-2680.7±3.6 million years ago [ru
Mathematical description of tooth flank surface of globoidal worm gear with straight axial tooth profile

Science.gov (United States)

Połowniak, Piotr; Sobolak, Mariusz

2017-12-01

In this article, a mathematical description of tooth flank surface of the globoidal worm and worm wheel generated by the hourglass worm hob with straight tooth axial profile is presented. The kinematic system of globoidal worm gear is shown. The equation of globoid helix and tooth axial profile of worm is derived to determine worm tooth surface. Based on the equation of meshing the contact lines are obtained. The mathematical description of globoidal worm wheel tooth flank is performed on the basis of contact lines and generating the tooth side by the extreme cutting edge of worm hob. The presented mathematical model of tooth flank of TA worm and worm wheel can be used e.g. to analyse the contact pattern of the gear.
Surface heat flow and CO2 emissions within the Ohaaki hydrothermal field, Taupo Volcanic Zone, New Zealand

Science.gov (United States)

Rissmann, C.; Christenson, B.; Werner, C.; Leybourne, M.; Cole, J.; Gravley, D.

2012-01-01

Carbon dioxide emissions and heat flow have been determined from the Ohaaki hydrothermal field, Taupo Volcanic Zone (TVZ), New Zealand following 20a of production (116MW e). Soil CO2 degassing was quantified with 2663 CO2 flux measurements using the accumulation chamber method, and 2563 soil temperatures were measured and converted to equivalent heat flow (Wm -2) using published soil temperature heat flow functions. Both CO2 flux and heat flow were analysed statistically and then modelled using 500 sequential Gaussian simulations. Forty subsoil CO 2 gas samples were also analysed for stable C isotopes. Following 20a of production, current CO2 emissions equated to 111??6.7T/d. Observed heat flow was 70??6.4MW, compared with a pre-production value of 122MW. This 52MW reduction in surface heat flow is due to production-induced drying up of all alkali-Cl outflows (61.5MW) and steam-heated pools (8.6MW) within the Ohaaki West thermal area (OHW). The drying up of all alkali-Cl outflows at Ohaaki means that the soil zone is now the major natural pathway of heat release from the high-temperature reservoir. On the other hand, a net gain in thermal ground heat flow of 18MW (from 25MW to 43.3??5MW) at OHW is associated with permeability increases resulting from surface unit fracturing by production-induced ground subsidence. The Ohaaki East (OHE) thermal area showed no change in distribution of shallow and deep soil temperature contours despite 20a of production, with an observed heat flow of 26.7??3MW and a CO 2 emission rate of 39??3T/d. The negligible change in the thermal status of the OHE thermal area is attributed to the low permeability of the reservoir beneath this area, which has limited production (mass extraction) and sheltered the area from the pressure decline within the main reservoir. Chemistry suggests that although alkali-Cl outflows once contributed significantly to the natural surface heat flow (~50%) they contributed little (99% of the original CO 2
Geoethics implications in volcanic hazards in Argentina: 24 years of uninterrupted ash-fall

Science.gov (United States)

Rovere, Elizabeth I.; Violante, Roberto A.; Uber, Silvia M.; Vázquez Herrera, Marcelo

2016-04-01

The impact of falling ash reaches all human activities, has effects on human and animal health and is subject to climate and ecosystem of the affected regions. From 1991 until 2015 (24 years), more than 5 eruptions with VEI ≥ 4 in the Southern Volcanic Zone of the Andes occurred; pyroclastic, dust and volcanic ash were deposited (mostly) in Argentina. A recurring situation during eruptions of Hudson (1991), Chaiten (2008), Puyehue-Cordon Caulle (2011) and Calbuco (2015) volcanoes was the accumulation, storage and dump of volcanic ash in depressed areas, beaches, lakes, ditches, storm drains, areas of landfills and transfer stations. The issues that this practice has taken are varied: pollution of aquifers, changes in geomorphology and water courses, usually in "inconspicuous" zones, often in places where there are precarious population or high poverty settlements. The consequences are not immediate but the effects in the mid and long term bring serious drawbacks. On the contrary, a good example of intelligent management of the volcanic impact occurred many years before, during the eruption of Descabezado Grande (Quizapu) volcano in 1932. In that case, and as an example, the city of Trenque Lauquen, located nearly 770 km east of the volcano, decided a communitarian task of collection and burial of the ashfall in small areas, this was a very successful performance. The Quizapu ash plumes transported by the Westerlies (winds) covered with a blanket of volcanic ash the city, ashfall also reached the capital cities of Argentina (Buenos Aires) and Uruguay (Montevideo). Also, the bagging process of volcanic ash with reinforced plastics was an example of Good Practice in the management of the emergency. This allowed the entire affected community to take advantage of this "mineral resource" and contributes to achieving collective and participatory work leading to commercialization and sustainability of these products availed as fertilizers, granular base for ceramics and
Petrography and petrology of Quaternary volcanic rocks from Ghezel Ghaleh, northwest Qorveh

Directory of Open Access Journals (Sweden)

Alireza Bajelan

2014-10-01

Full Text Available Introduction In the east and northeast of Sanandaj in the Qorveh-Bijar-Takab axis, there are series of basaltic composition volcanoes with Quaternary age. The study area is part of the Sanandaj-Sirjan zone and is located between 47°52' and 47°57' E longitudes and 35°26 and '35°30' N latitudes. Due to the location of the volcanic cone on Pliocene clastic sediments and Quaternary travertine, the age of these volcanoes is considered to be Quaternary. The cones mostly consist of low scoria, ash, volcanic bombs, lapilli deposits and basaltic lava (Moein Vaziri and Aminsobhani, 1985. Petrological and geochemical studies have been carried out to evaluate Quaternary magmatism in the area and to determine the nature of the lithological characteristics, such as the evaluation of source rocks and magma type, degree of partial melting and the tectonic setting of Ghezel Ghaleh rocks (Moein Vaziri, 1997. Simplified geological map of the study area is characterized by ER-Mapper software. Materials and methods In the course of field studies in the region, 40 samples were taken, 30 thin sections were prepared and polished. XRD analyses were performed on some whole rock samples. All major, minor and trace elements were assessed by ICP-MS at Lab Weft Laboratory in Australia. Results Based on the classification of structural zones, the area is located in the Sanandaj-Sirjan zone, hundred kilometers away from the main Zagros thrust along the NW-SE direction. After early Cimmerian orogeny, andesitic volcanic activity took place (Moein Vaziri and Aminsobhani, 1985. A major secondary mineral in these rocks is iddingsite, formed by hydration and oxidation of the olivine (Shelley, 1993. According to SiO2 against Na2O + K2O (TAS diagram (Irvine and Baragar , 1971 and cationic R1 and R2 diagram (De La Roche et el., 1980, volcanic rocks of the area indicate alkaline series. Discussion To obtain more information on the tectonic setting of these rocks, the Zr/Y-Zr diagram
Metamorphic Perspectives of Subduction Zone Volatiles Cycling

Science.gov (United States)

Bebout, G. E.

2008-12-01

Field study of HP/UHP metamorphic rocks provides "ground-truthing" for experimental and theoretical petrologic studies estimating extents of deep volatiles subduction, and provides information regarding devolatilization and deep subduction-zone fluid flow that can be used to reconcile estimates of subduction inputs and arc volcanic outputs for volatiles such as H2O, N, and C. Considerable attention has been paid to H2O subduction in various bulk compositions, and, based on calculated phase assemblages, it is thought that a large fraction of the initially structurally bound H2O is subducted to, and beyond, subarc regions in most modern subduction zones (Hacker, 2008, G-cubed). Field studies of HP/UHP mafic and sedimentary rocks demonstrate the impressive retention of volatiles (and fluid-mobile elements) to depths approaching those beneath arcs. At the slab-mantle interface, high-variance lithologies containing hydrous phases such as mica, amphibole, talc, and chlorite could further stabilize H2O to great depth. Trench hydration in sub-crustal parts of oceanic lithosphere could profoundly increase subduction inputs of particularly H2O, and massive flux of H2O-rich fluids from these regions into the slab-mantle interface could lead to extensive metasomatism. Consideration of sedimentary N concentrations and δ15N at ODP Site 1039 (Li and Bebout, 2005, JGR), together with estimates of the N concentration of subducting altered oceanic crust (AOC), indicates that ~42% of the N subducting beneath Nicaragua is returned in the corresponding volcanic arc (Elkins et al., 2006, GCA). Study of N in HP/UHP sedimentary and basaltic rocks indicates that much of the N initially subducted in these lithologies would be retained to depths approaching 100 km and thus available for addition to arcs. The more altered upper part of subducting oceanic crust most likely to contribute to arcs has sediment-like δ15NAir (0 to +10 per mil; Li et al., 2007, GCA), and study of HP/UHP eclogites
A multidisciplinary system for monitoring and forecasting Etna volcanic plumes

Science.gov (United States)

Coltelli, Mauro; Prestifilippo, Michele; Spata, Gaetano; Scollo, Simona; Andronico, Daniele

2010-05-01

One of the most active volcanoes in the world is Mt. Etna, in Italy, characterized by frequent explosive activity from the central craters and from fractures opened along the volcano flanks which, during the last years, caused several damages to aviation and forced the closure of the Catania International Airport. To give precise warning to the aviation authorities and air traffic controller and to assist the work of VAACs, a novel system for monitoring and forecasting Etna volcanic plumes, was developed at the Istituto Nazionale di Geofisica e Vulcanologia, sezione di Catania, the managing institution for the surveillance of Etna volcano. Monitoring is carried out using multispectral infrared measurements from the Spin Enhanced Visible and Infrared Imager (SEVIRI) on board the Meteosat Second Generation geosynchronous satellite able to track the volcanic plume with a high time resolution, visual and thermal cameras used to monitor the explosive activity, three continuous wave X-band disdrometers which detect ash dispersal and fallout, sounding balloons used to evaluate the atmospheric fields, and finally field data collected after the end of the eruptive event needed to extrapolate important features of explosive activity. Forecasting is carried out daily using automatic procedures which download weather forecast data obtained by meteorological mesoscale models from the Italian Air Force national Meteorological Office and from the hydrometeorological service of ARPA-SIM; run four different tephra dispersal models using input parameters obtained by the analysis of the deposits collected after few hours since the eruptive event similar to 22 July 1998, 21-24 July 2001 and 2002-03 Etna eruptions; plot hazard maps on ground and in air and finally publish them on a web-site dedicated to the Italian Civil Protection. The system has been already tested successfully during several explosive events occurring at Etna in 2006, 2007 and 2008. These events produced eruption
The Volcanism Ontology (VO): a model of the volcanic system

Science.gov (United States)

Myer, J.; Babaie, H. A.

2017-12-01

We have modeled a part of the complex material and process entities and properties of the volcanic system in the Volcanism Ontology (VO) applying several top-level ontologies such as Basic Formal Ontology (BFO), SWEET, and Ontology of Physics for Biology (OPB) within a single framework. The continuant concepts in BFO describe features with instances that persist as wholes through time and have qualities (attributes) that may change (e.g., state, composition, and location). In VO, the continuants include lava, volcanic rock, and volcano. The occurrent concepts in BFO include processes, their temporal boundaries, and the spatio-temporal regions within which they occur. In VO, these include eruption (process), the onset of pyroclastic flow (temporal boundary), and the space and time span of the crystallization of lava in a lava tube (spatio-temporal region). These processes can be of physical (e.g., debris flow, crystallization, injection), atmospheric (e.g., vapor emission, ash particles blocking solar radiation), hydrological (e.g., diffusion of water vapor, hot spring), thermal (e.g., cooling of lava) and other types. The properties (predicates) relate continuants to other continuants, occurrents to continuants, and occurrents to occurrents. The ontology also models other concepts such as laboratory and field procedures by volcanologists, sampling by sensors, and the type of instruments applied in monitoring volcanic activity. When deployed on the web, VO will be used to explicitly and formally annotate data and information collected by volcanologists based on domain knowledge. This will enable the integration of global volcanic data and improve the interoperability of software that deal with such data.
Single nucleotide polymorphisms in the 5'-flanking region of the ...

African Journals Online (AJOL)

Prolactin (PRL), a polypeptide hormone synthesized and secreted by the animal's anterior pituitary gland, plays an important role in the regulation of mammalian lactation and avian reproduction. Considering the significant association between single nucleotide polymorphisms (SNPs) in the 5'-flanking region of PRL and ...
La structure, morphologie, et texture superficielle des dépôts d'avalanche de débris : cartographie de terrain, par télédétection et par modélisation analogique

OpenAIRE

Paguican, Engielle Mae

2012-01-01

Flank collapse generates avalanches and large landslides that significantly change the shape of a volcano and alter the surrounding landscape. Most types of volcanoes experience flank collapse at some point during their development. In the Philippines, for example, the numerous volcanoes with breached edifices belong to the cone, subcone, and massif morphometric classes. Debris avalanches occur frequently on both volcanic and non-volcanic terrains making it an important geologic event to cons...
Temporal and geochemical evolution of Miocene volcanism in the Andean back-arc between 36°S and 38°S and U-series analyses of young volcanic centers in the arc and back-arc, Argentina

DEFF Research Database (Denmark)

Dyhr, Charlotte Thorup

New 40Ar/39Ar, major and trace element, and Sr, Nd and Pb isotopic data for the c. 24-7 Ma volcanic rocks from the Andean back-arc (35°S – 38°S) in the Mendoza and Neuquén (Argentina) regions shed light on the Miocene evolution of the back-arc of the Southern Volcanic Zone. Incipient shallowing......-Sr-Pb isotopic compositions. The arc-like component that dominates the geochemistry of the Palaoco rocks is absent in both the Early Miocene and the Pliocene-Pleistocene in the same area. Young volcanic Provinces in the main arc, retro-arc and back-arc are further investigated by U-series analyses which confirm...... the fluid-enriched nature of arc-related rocks (U-excess are found in most rocks) and the more OIB-like nature of the Payún Matrú complex (Th-exsess is observed in all rocks). The fluid addition to the mantle source is modeled revealing timescales of 10 – 100 ka for the fluid enrichment. For the back...
Experimental study of the interplay between magmatic rift intrusion and flank instability with application to the 2001 Mount Etna eruption

KAUST Repository

Le Corvec, Nicolas

2014-07-01

Mount Etna volcano is subject to transient magmatic intrusions and flank movement. The east flank of the edifice, in particular, is moving eastward and is dissected by the Timpe Fault System. The relationship of this eastward motion with intrusions and tectonic fault motion, however, remains poorly constrained. Here we explore this relationship by using analogue experiments that are designed to simulate magmatic rift intrusion, flank movement, and fault activity before, during, and after a magmatic intrusion episode. Using particle image velocimetry allows for a precise temporal and spatial analysis of the development and activity of fault systems. The results show that the occurrence of rift intrusion episodes has a direct effect on fault activity. In such a situation, fault activity may occur or may be hindered, depending on the interplay of fault displacement and flank acceleration in response to dike intrusion. Our results demonstrate that a complex interplay may exist between an active tectonic fault system and magmatically induced flank instability. Episodes of magmatic intrusion change the intensity pattern of horizontal flank displacements and may hinder or activate associated faults. We further compare our results with the GPS data of the Mount Etna 2001 eruption and intrusion. We find that syneruptive displacement rates at the Timpe Fault System have differed from the preeruptive or posteruptive periods, which shows a good agreement of both the experimental and the GPS data. Therefore, understanding the flank instability and flank stability at Mount Etna requires consideration of both tectonic and magmatic forcing. Key Points Analyzing Mount Etna east flank dynamics during the 2001 eruption Good correlation between analogue models and GPS data Understanding the different behavior of faulting before/during/after an eruption © 2014. American Geophysical Union. All Rights Reserved.
Experimental study of the interplay between magmatic rift intrusion and flank instability with application to the 2001 Mount Etna eruption

KAUST Repository

Le Corvec, Nicolas; Walter, Thomas R.; Ruch, Joel; Bonforte, Alessandro; Puglisi, Giuseppe

2014-01-01

Mount Etna volcano is subject to transient magmatic intrusions and flank movement. The east flank of the edifice, in particular, is moving eastward and is dissected by the Timpe Fault System. The relationship of this eastward motion with intrusions and tectonic fault motion, however, remains poorly constrained. Here we explore this relationship by using analogue experiments that are designed to simulate magmatic rift intrusion, flank movement, and fault activity before, during, and after a magmatic intrusion episode. Using particle image velocimetry allows for a precise temporal and spatial analysis of the development and activity of fault systems. The results show that the occurrence of rift intrusion episodes has a direct effect on fault activity. In such a situation, fault activity may occur or may be hindered, depending on the interplay of fault displacement and flank acceleration in response to dike intrusion. Our results demonstrate that a complex interplay may exist between an active tectonic fault system and magmatically induced flank instability. Episodes of magmatic intrusion change the intensity pattern of horizontal flank displacements and may hinder or activate associated faults. We further compare our results with the GPS data of the Mount Etna 2001 eruption and intrusion. We find that syneruptive displacement rates at the Timpe Fault System have differed from the preeruptive or posteruptive periods, which shows a good agreement of both the experimental and the GPS data. Therefore, understanding the flank instability and flank stability at Mount Etna requires consideration of both tectonic and magmatic forcing. Key Points Analyzing Mount Etna east flank dynamics during the 2001 eruption Good correlation between analogue models and GPS data Understanding the different behavior of faulting before/during/after an eruption © 2014. American Geophysical Union. All Rights Reserved.

Volcanic signals in oceans

KAUST Repository

Stenchikov, Georgiy L.; Delworth, Thomas L.; Ramaswamy, V.; Stouffer, Ronald J.; Wittenberg, Andrew; Zeng, Fanrong

2009-01-01

Sulfate aerosols resulting from strong volcanic explosions last for 2–3 years in the lower stratosphere. Therefore it was traditionally believed that volcanic impacts produce mainly short-term, transient climate perturbations. However, the ocean
Focused volcanism and growth of a slow spreading segment (Mid-Atlantic Ridge, 35°N)

Science.gov (United States)

Rabain, Aline; Cannat, Mathilde; Escartín, Javier; Pouliquen, Gaud; Deplus, Christine; Rommevaux-Jestin, Céline

2001-02-01

Using off axis bathymetry, gravity and magnetic data, we studied the formation of a prominent seamount chain across segment OH1 (Mid-Atlantic Ridge, 35°N), and its relation to the past segmentation of the area. We also studied the size and shape of the seamounts to understand the processes leading to their formation. The chain is elongated in the spreading direction, and extends from the present day segment center to ˜6 Ma on both flanks. It coincides with a pronounced low in the residual mantle Bouguer gravity anomaly, suggesting thicker crust and thus more abundant magmatism than in surrounding areas. Magnetic anomalies are well defined over the seamount chain, consistent with formation on or near the axis. The seamounts within the chain are larger on average than those from other areas of the Mid-Atlantic Ridge, reflecting higher magma volumes and fluxes during eruptions. The distribution of seamounts suggests a focused magmatic source, located beneath the eastern side of the ridge axis, at a constant distance (˜45 km) from the Oceanographer transform fault. A V-shaped trend defines the southern end of OH1 and indicates that the segment propagated rapidly southwards, increasing in length from 50 to 90 km. The onset of propagation at ˜6 Ma coincided with the initiation of the volcanic chain, suggesting that magma supply at that time was focused at the end of the segment rather than at its center, as is typical for Mid-Atlantic Ridge segments. We propose that this unusual configuration is a consequence of the cold edge effect of the Oceanographer fracture zone. We also propose that enhanced and focused magmatism beneath the seamount chain may have caused the rapid southward propagation of OH1 over the past ˜6 Ma.
Geothermal waters from the Taupo Volcanic Zone, New Zealand: Li, B and Sr isotopes characterization

International Nuclear Information System (INIS)

Millot, Romain; Hegan, Aimee; Négrel, Philippe

2012-01-01

Chemical and isotopic data for 23 geothermal water samples collected in New Zealand within the Taupo Volcanic Zone (TVZ) are reported. Major and trace elements including Li, B and Sr and their isotopic compositions (δ 7 Li, δ 11 B, 87 Sr/ 86 Sr) were determined in high temperature geothermal waters collected from deep boreholes in different geothermal fields (Ohaaki, Wairakei, Mokai, Kawerau and Rotokawa geothermal systems). Lithium concentrations are high (from 4.5 to 19.9 mg/L) and Li isotopic compositions (δ 7 Li) are homogeneous, ranging between −0.5‰ and +1.4‰. In particular, it is noteworthy that, except for the samples from the Kawerau geothermal field having slightly higher δ 7 Li values (+1.4%), the other geothermal waters have a near constant δ 7 Li signature around a mean value of 0‰ ± 0.6 (2σ, n = 21). Boron concentrations are also high and relatively homogeneous for the geothermal samples, falling between 17.5 and 82.1 mg/L. Boron isotopic compositions (δ 11 B) are all negative, and display a range between −6.7‰ and −1.9‰. These B isotope compositions are in agreement with those of the Ngawha geothermal field in New Zealand. Lithium and B isotope signatures are in a good agreement with a fluid signature mainly derived from water/rock interaction involving magmatic rocks with no evidence of seawater input. On the other hand, Sr concentrations are lower and more heterogeneous and fall between 2 and 165 μg/L. The 87 Sr/ 86 Sr ratios range from 0.70549 to 0.70961. These Sr isotope compositions overlap those of the Rotorua geothermal field in New Zealand, confirming that some geothermal waters (with more radiogenic Sr) have interacted with bedrocks from the metasedimentary basement. Each of these isotope systems on their own reveals important information about particular aspects of either water source or water/rock interaction processes, but, considered together, provide a more integrated understanding of the geothermal systems from
Volcanism on Jupiter's moon Io and its relation to interior processes

Science.gov (United States)

Hamilton, Christopher

2013-04-01

agrees with predictions from asthensopheric-dominated tidal heating models, but the nearest neighbor analysis of hotspots (i.e., sites of active volcanism) and paterae (i.e., caldera-like volcano-tectonic depressions) reveals a random to uniform spatial organization. This suggests that Io may have an extensive subsurface magma reservoir with vigorous mantle convection, and/or a deep-mantle heating component, which reduces the amplitude of surface heat flux variations that would otherwise favor clustering. The tendency toward uniformity among volcanic systems may reflect their interaction through a process of magmatic lensing that focuses rising magma and inhibits volcanism in the surrounding capture zone. In summary, the distribution of volcanism on Io generally supports the presence of a globally extensive asthenosphere with local interactions occurring between volcanic systems, but a 30-60° eastward offset in the location of enhanced volcanism relative to predicted surface heat flux maxima cannot be explained by existing solid body tidal heating models. This may imply faster than synchronous rotation, state of stress controls on the locations of magma ascent, and/or a missing component in models of Io's interior, such as fluid tides generated within a globally extensive layer of interconnected partial melt.
Origins and exploration significance of replacement and vein-type alunite deposits in the Marysvale volcanic field, west central Utah.

Science.gov (United States)

Cunningham, C.G.; Rye, R.O.; Steven, T.A.; Mehnert, H.H.

1984-01-01

Alunite in the Marysvale volcanic field forms two (three are described) different types of deposits which contrast in appearance and conditions of origin: 1) Replacement deposits are generally fine-grained and formed by near-surface replacement of intermediate-composition volcanic rocks. The deposits form a bead necklace around a monzonite stock. Each deposit is zoned horizontally from alunitic cores to kaolinitic and propylitic envelopes and zoned vertically from pyrite/propylite upward through alunite/jarosite/hematite to a silica cap. Alunite does not extend below 100 m. Sulphur isotope ratios agree with derivation from underlying Mesozoic evaporites. 2) Natroalunite of 14-m.y. age crosscuts replacement-type alunite deposits. Its S-isotope ratios are comparable with those of pyrite in the volcanics. The Na may be from underlying Mesozoic halites. 3) Veins of coarse-grained alunite of 14-m.y. age filled extension fractures above a postulated stock. S-isotope ratios indicate a probable magmatic source. The contrasting properties of the Marysvale alunite deposits preclude any simple relation to ore deposits, but serve to refine interpretations based on other geological considerations. The replacement deposits are a logical near-surface result of skarn forming processes at depth around the monzonite stock. The vein- type deposits are a logical near-surface result of porphyry metallization in an underlying stock. -G.J.N.
Microgravity change as a precursor to volcanic activity

Science.gov (United States)

Rymer, Hazel

1994-07-01

In recent decades, systematic microgravity studies over some 20 active volcanoes in Central America, Iceland, Italy, Japan, Papua New Guinea and the USA have provided valuable data on sub-surface mass redistribution associated with volcanic activity. Concurrent data on ground deformation are essential to the unambiguous interpretation of gravity changes. In some instances, gravity and elevation vary along the free-air or Bouguer gradients, implying that there has been no sub-surface mass or density change, respectively. Where there are residual gravity changes after correction for elevation changes, magma movements in sub-surface chambers, feeder systems, vents and fissures (dykes) or water table variations are proposed. Although detailed interpretations depend on local circumstances and the calculations depend on source geometry, in general, the smallest residual gravity changes are associated with eruptions from volatile-poor basaltic vents and at extensional rift zones, whereas the highest residual values occur at explosive, subduction-related stratocones built from volatile-rich andesitic magma. The most intriguing, yet difficult, data to interpret derive from large-volume, infrequently erupting volcanic systems where caldera unrest is now becoming well documented and the ultimate hazards are most severe. Mass increases during inflation followed by limited mass loss during subsequent deflation typify these structures.
Cloning and characterization of the 5'-flanking region of the Ehox gene

International Nuclear Information System (INIS)

Lee, Woon Kyu; Kim, Yong-Man; Malik, Nasir; Ma Chang; Westphal, Heiner

2006-01-01

The paired-like homeobox-containing gene Ehox plays a role in embryonic stem cell differentiation and is highly expressed in the developing placenta and thymus. To understand the mechanisms of regulation of Ehox gene expression, the 5'-flanking region of the Ehox gene was isolated from a mouse BAC library. 5'-RACE analysis revealed a single transcriptional start site 130 nucleotides upstream of the translation initiation codon. Transient transfection with a luciferase reporter gene under the control of serially deleted 5'-flanking sequences revealed that the nt -84 to -68 region contained a positive cis-acting element for efficient expression of the Ehox gene. Mutational analysis of this region and oligonucleotide competition in the electrophoretic mobility shift assay revealed the presence of a CCAAT box, which is a target for transcription nuclear factor Y (NFY). NFY is essential for positive gene regulation. No tissue-specific enhancer was identified in the 1.9-kb 5'-flanking region of the Ehox gene. Ehox is expressed during the early stages of embryo development, specifically in Brain at 9.5 dpc, as well as during the late stages of embryo development. These results suggest that NFY is an essential regulatory factor for Ehox transcriptional activity, which is important for the post-implantation stage of the developing embryo
Flank gland-secreted putative chemosignals pertaining to photoperiod, endocrine states, and sociosexual behavior in golden hamsters

Directory of Open Access Journals (Sweden)

Ying-Juan LIU, Da-Wei WANG, Lixing SUN, Jin-Hua ZHANG, Jian-Xu ZHANG

2010-12-01

Full Text Available Behavioral studies have shown that flank glands are involved in chemical communication in golden hamsters Mesocricetus auratus but little chemical analysis has been conducted on volatiles arising from these glands. Using gas chromatography-mass spectrometry, we detected compounds from the flank glands of males, only eight of which were also produced in females. Based on these chemical data we performed a number of further experiments. By manipulating light we found that males exposed to short-photoperiods developed smaller flank glands than those exposed to long-photoperiods. Six flank gland volatiles reduced in relative abundance, which possibly coded for reproductive status of males of this seasonally breeding hamster species. Through dyadic encounters, we were able to induce the formation of dominant-subordinate relationships and show that two glandular compounds became high in relative abundance and may function as dominance pheromones. Castration eliminated all male-specific compounds resulting from flank glands, but bilateral ovariectomies only affected one compound in females. Once these ovariectomized females were treated with testosterone, their glandular compounds resembled those of males, suggesting these compounds are under the main control of androgen. Two female putative pheromones, tetradecanoic acid and hexadecanoic acid, were used in binary choice tests and were both found to attract males over females. Applying a solution of these pheromone compounds to adult males also suppressed their agonistic behavior [Current Zoology 56 (6: 800–812, 2010].
A mineralogical and granulometric study of Cayambe volcano debris avalanche deposit

Science.gov (United States)

Detienne, M.; Delmelle, P.; Guevara, A.; Samaniego, P.; Bustillos, J.; Sonnet, P.; Opfergelt, S.

2013-12-01

Volcano flank/sector collapse represents one of the most catastrophic volcanic hazards. Various volcanic and non-volcanic processes are known to decrease the stability of a volcanic cone, eventually precipitating its gravitational failure. Among them, hydrothermal alteration of volcanic rocks leading to clay mineral formation is recognized as having a large negative impact on rock strength properties. Furthermore, the presence of hydrothermal clays in the collapsing mass influences the behavior of the associated volcanic debris avalanche. In particular, clay-containing debris avalanches seem to travel farther and spread more widely than avalanches of similar volume but which do not incorporate hydrothermally-altered materials. However, the relationship between hydrothermal alteration, flank collapse and debris avalanche behavior is not well understood. The objective of this study is to better determine the volume and composition of hydrothermal clay minerals in the poorly characterized debris avalanche deposit (DAD) of Cayambe composite volcano, located in a densely populated area ~70 km northeast of Quito, Ecuador. Cayambe DAD originated from a sector collapse, which occurred less than 200 ka ago. The DAD is 10-20 m thick and has an estimated total volume of ~0.85 Km3. The H/L ratio (where H is the vertical drop and L is the travel distance of the avalanche) for Cayambe DAD is ~0.095, suggesting a high mobility. In the medial-distal zone, at 9-20 km from its source, the DAD consists of an unstratified and unsorted matrix supporting millimetric to metric clasts. It has a matrix facies (i.e. rich in particles DAD behaved as a cohesive debris flow. Analysis of 13 matrix samples reveals a large variability in particle size distribution. This may reflect poor mixing of the collapsed material during transport. The clay fraction content in the matrix ranges from 15 to 30 wt.%, and does not show a relationship with the sample position in the DAD. Mineralogical
Candidate constructional volcanic edifices on Mercury

OpenAIRE

Wright, J.; Rothery, D. A.; Balme, M. R.; Conway, S. J.

2018-01-01

[Introduction] Studies using MESSENGER data suggest that Mercury’s crust is predominantly a product of effusive volcanism that occurred in the first billion years following the planet’s formation. Despite this planet-wide effusive volcanism, no constructional volcanic edifices, characterized by a topographic rise, have hitherto been robustly identified on Mercury, whereas constructional volcanoes are common on other planetary bodies in the solar system with volcanic histories. Here, we descri...
Disruptive event analysis: volcanism and igneous intrusion

International Nuclear Information System (INIS)

Crowe, B.M.

1980-08-01

An evaluation is made of the disruptive effects of volcanic activity with respect to long term isolation of radioactive waste through deep geologic storage. Three major questions are considered. First, what is the range of disruption effects of a radioactive waste repository by volcanic activity. Second, is it possible, by selective siting of a repository, to reduce the risk of disruption by future volcanic activity. And third, can the probability of repository disruption by volcanic activity be quantified. The main variables involved in the evaluation of the consequences of repository disruption by volcanic activity are the geometry of the magma-repository intersection (partly controlled by depth of burial) and the nature of volcanism. Potential radionuclide dispersal by volcanic transport within the biosphere ranges in distance from several kilometers to global. Risk from the most catastrophic types of eruptions can be reduced by careful site selection to maximize lag time prior to the onset of activity. Certain areas or volcanic provinces within the western United States have been sites of significant volcanism and should be avoided as potential sites for a radioactive waste repository. Examples of projection of future sites of active volcanism are discussed for three areas of the western United States. Probability calculations require two types of data: a numerical rate or frequency of volcanic activity and a numerical evaluation of the areal extent of volcanic disruption for a designated region. The former is clearly beyond the current state of art in volcanology. The latter can be approximated with a reasonable degree of satisfaction. In this report, simplified probability calculations are attempted for areas of past volcanic activity
Edifice growth, deformation and rift zone development in basaltic setting: Insights from Piton de la Fournaise shield volcano (Réunion Island)

Science.gov (United States)

Michon, Laurent; Cayol, Valérie; Letourneur, Ludovic; Peltier, Aline; Villeneuve, Nicolas; Staudacher, Thomas

2009-07-01

The overall morphology of basaltic volcanoes mainly depends on their eruptive activity (effusive vs. explosive), the geometry of the rift zones and the characteristics of both endogenous and exogenous growth processes. The origin of the steep geometry of the central cone of Piton de la Fournaise volcano, which is unusual for a basaltic effusive volcano, and its deformation are examined with a combination of a detailed morphological analysis, field observations, GPS data from the Piton de la Fournaise Volcano Observatory and numerical models. The new caldera walls formed during the April 2007 summit collapse reveal that the steep cone is composed of a pyroclastic core, inherited from an earlier explosive phase, overlapped by a pile of thin lava flows. This suggests that exogenous processes played a major role in the building of the steep central cone. Magma injections into the cone, which mainly occur along the N25-30 and N120 rift zones, lead to an asymmetric outward inflation concentrated in the cone's eastern half. This endogenous growth progressively tilts the southeast and east flanks of the cone, and induces the development of a dense network of flank fractures. Finally, it is proposed that intrusions along the N120 rift zone are encouraged by stresses induced by magma injections along the N25-30 rift zone.
Teleseismic P and S wave attenuation constraints on temperature and melt of the upper mantle in the Alaska Subduction Zone.

Science.gov (United States)

Soto Castaneda, R. A.; Abers, G. A.; Eilon, Z.; Christensen, D. H.

2017-12-01

Recent broadband deployments in Alaska provide an excellent opportunity to advance our understanding of the Alaska-Aleutians subduction system, with implications for subduction processes worldwide. Seismic attenuation, measured from teleseismic body waves, provides a strong constraint on thermal structure as well as an indirect indication of ground shaking expected from large intermediate-depth earthquakes. We measure P and S wave attenuation from pairwise amplitude and phase spectral ratios for teleseisms recorded at 204 Transportable Array, Alaska Regional, and Alaska Volcano Observatory, SALMON (Southern Alaska Lithosphere & Mantle Observation Network) and WVLF (Wrangell Volcanics & subducting Lithosphere Fate) stations in central Alaska. The spectral ratios are inverted in a least squares sense for differential t* (path-averaged attenuation operator) and travel time anomalies at every station. Our preliminary results indicate a zone of low attenuation across the forearc and strong attenuation beneath arc and backarc in the Cook Inlet-Kenai region where the Aleutian-Yakutat slab subducts, similar to other subduction zones. This attenuation differential is observed in both the volcanic Cook Inlet segment and amagmatic Denali segments of the Aleutian subduction zone. By comparison, preliminary results for the Wrangell-St. Elias region past the eastern edge of the Aleutian slab show strong attenuation beneath the Wrangell Volcanic Field, as well as much further south than in the Cook Inlet-Kenai region. This pattern of attenuation seems to indicate a short slab fragment in the east of the subduction zone, though the picture is complex. Results also suggest the slab may focus or transmit energy with minimal attenuation, adding to the complexity. To image the critical transition between the Alaska-Aleutian slab and the region to its east, we plan to incorporate new broadband data from the WVLF array, an ongoing deployment of 37 PASSCAL instruments installed in 2016
Morphology, volcanism, and mass wasting in Crater Lake, Oregon

Science.gov (United States)

Bacon, C.R.; Gardner, J.V.; Mayer, L.A.; Buktenica, M.W.; Dartnell, P.; Ramsey, D.W.; Robinson, J.E.

2002-01-01

Crater Lake was surveyed nearly to its shoreline by high-resolution multibeam echo sounding in order to define its geologic history and provide an accurate base map for research and monitoring surveys. The bathymetry and acoustic backscatter reveal the character of landforms and lead to a chronology for the concurrent filling of the lake and volcanism within the ca. 7700 calibrated yr B.P. caldera. The andesitic Wizard Island and central-plattform volcanoes are composed of sequences of lava deltas that record former lake levels and demonstrate simultaneous activity at the two vents. Wizard Island eruptions ceased when the lake was ~80 m lower than at present. Lava streams from prominent channels on the surface of the central platform descended to feed extensive subaqueous flow fields on the caldera floor. The Wizard Island and central-platform volcanoes, andesitic Merriam Cone, and a newly discovered probable lava flow on the eastern floor of the lake apparently date from within a few hundred years of caldera collapse, whereas a small rhydacite dome was emplaced on the flank of Wizard Island at ca. 4800 cal. yr B.P. Bedrock outcrops on the submerged caldera walls are shown in detail and, in some cases, can be correlated with exposed geologic units of Mount Mazama. Fragmental debris making up the walls elsewhere consists of narrow talus cones forming a dendritic pattern that leads to fewer, wider ridges downslope. Hummocky topography and scattered blocks up to ~280 m long below many of the embayments in the caldera wall mark debris-avalanche deposits that probably formed in single events and commonly are affected by secondary failures. The flat-floored, deep basins contain relatively fine-grained sediment transported from the debris aprons by sheet-flow turbidity currents. Crater Lake apparently filled rapidly (ca. 400-750 yr) until reaching a permeable layer above glaciated lava identified by the new survey in the northeast caldera wall at ~1845 m elevation
L-Band Polarimetric SAR Signatures of Lava Flows in the Northern Volcanic Zone, Iceland

DEFF Research Database (Denmark)

Dierking, Wolfgang; Haack, Henning

1998-01-01

Studies of radar scattering signatures typical for lava surfaces are needed in order to interprete SAR images of volcanic terrain on the Earth and on other planets, and to establish a physical basis for the choice of optimal radar configurations for geological mapping. The authors focus on a study...... of different morphologic types within a flow. The largest contrasts are observed at cross-polarization. The phase difference between the VV- and HH-channels may provide information about a vegetation cover on the lava. The radar signal scattered from the flows is dominated by surface scattering contributions...
Hafnium at subduction zones: isotopic budget of input and output fluxes; L'hafnium dans les zones de subduction: bilan isotopique des flux entrant et sortant

Energy Technology Data Exchange (ETDEWEB)

Marini, J.Ch

2004-05-15

Subduction zones are the primary regions of mass exchanges between continental crust and mantle of Earth through sediment subduction toward the earth's mantle and by supply of mantellic magmas to volcanic arcs. We analyze these mass exchanges using Hafnium and Neodymium isotopes. At the Izu-Mariana subduction zone, subducting sediments have Hf and Nd isotopes equivalent to Pacific seawater. Altered oceanic crust has Hf and Nd isotopic compositions equivalent to the isotopic budget of unaltered Pacific oceanic crust. At Luzon and Java subduction zones, arc lavas present Hf isotopic ratios highly radiogenic in comparison to their Nd isotopic ratios. Such compositions of the Luzon and Java arc lavas are controlled by a contamination of their sources by the subducted oceanic sediments. (author)
Sensitivity of the Regional Climate in the Middle East and North Africa to Volcanic Perturbations

KAUST Repository

Dogar, Muhammad Mubashar; Stenchikov, Georgiy L.; Osipov, Sergey; Wyman, Bruce; Zhao, Ming

2017-01-01

The Middle East and North Africa (MENA) regional climate appears to be extremely sensitive to volcanic eruptions. Winter cooling after the 1991 Pinatubo eruption far exceeded the mean hemispheric temperature anomaly, even causing snowfall in Israel. To better understand MENA climate variability, the climate responses to the El Chichón and Pinatubo volcanic eruptions are analyzed using observations, NOAA/NCEP Climate Forecast System Reanalysis, and output from the Geophysical Fluid Dynamics Laboratory's High-Resolution Atmospheric Model (HiRAM). A multiple regression analysis both for the observations and the model output is performed on seasonal summer and winter composites to separate out the contributions from climate trends, El Niño Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Indian summer monsoon and volcanic aerosols. Strong regional temperature and precipitation responses over the MENA region are found in both winter and summer. The model and the observations both show that a positive NAO amplifies the MENA volcanic winter cooling. In boreal summer, the patterns of changing temperature and precipitation suggest a weakening and southward shift of the Intertropical Convergence Zone, caused by volcanic surface cooling and weakening of the Indian and West African monsoons. The model captures the main features of the climate response; however, it underestimates the total cooling, especially in winter, and exhibits a different spatial pattern of the NAO climate response in MENA compared to the observations. The conducted analysis sheds light on the internal mechanisms of MENA climate variability and helps to selectively diagnose the model deficiencies.
Sensitivity of the Regional Climate in the Middle East and North Africa to Volcanic Perturbations

KAUST Repository

Dogar, Muhammad Mubashar

2017-07-27

The Middle East and North Africa (MENA) regional climate appears to be extremely sensitive to volcanic eruptions. Winter cooling after the 1991 Pinatubo eruption far exceeded the mean hemispheric temperature anomaly, even causing snowfall in Israel. To better understand MENA climate variability, the climate responses to the El Chichón and Pinatubo volcanic eruptions are analyzed using observations, NOAA/NCEP Climate Forecast System Reanalysis, and output from the Geophysical Fluid Dynamics Laboratory\\'s High-Resolution Atmospheric Model (HiRAM). A multiple regression analysis both for the observations and the model output is performed on seasonal summer and winter composites to separate out the contributions from climate trends, El Niño Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Indian summer monsoon and volcanic aerosols. Strong regional temperature and precipitation responses over the MENA region are found in both winter and summer. The model and the observations both show that a positive NAO amplifies the MENA volcanic winter cooling. In boreal summer, the patterns of changing temperature and precipitation suggest a weakening and southward shift of the Intertropical Convergence Zone, caused by volcanic surface cooling and weakening of the Indian and West African monsoons. The model captures the main features of the climate response; however, it underestimates the total cooling, especially in winter, and exhibits a different spatial pattern of the NAO climate response in MENA compared to the observations. The conducted analysis sheds light on the internal mechanisms of MENA climate variability and helps to selectively diagnose the model deficiencies.
Sensitivity of the regional climate in the Middle East and North Africa to volcanic perturbations

Science.gov (United States)

Dogar, Muhammad Mubashar; Stenchikov, Georgiy; Osipov, Sergey; Wyman, Bruce; Zhao, Ming

2017-08-01

The Middle East and North Africa (MENA) regional climate appears to be extremely sensitive to volcanic eruptions. Winter cooling after the 1991 Pinatubo eruption far exceeded the mean hemispheric temperature anomaly, even causing snowfall in Israel. To better understand MENA climate variability, the climate responses to the El Chichón and Pinatubo volcanic eruptions are analyzed using observations, NOAA/National Centers for Environmental Prediction Climate Forecast System Reanalysis, and output from the Geophysical Fluid Dynamics Laboratory's High-Resolution Atmospheric Model. A multiple regression analysis both for the observations and the model output is performed on seasonal summer and winter composites to separate out the contributions from climate trends, El Niño-Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Indian summer monsoon, and volcanic aerosols. Strong regional temperature and precipitation responses over the MENA region are found in both winter and summer. The model and the observations both show that a positive NAO amplifies the MENA volcanic winter cooling. In boreal summer, the patterns of changing temperature and precipitation suggest a weakening and southward shift of the Intertropical Convergence Zone, caused by volcanic surface cooling and weakening of the Indian and West African monsoons. The model captures the main features of the climate response; however, it underestimates the total cooling, especially in winter, and exhibits a different spatial pattern of the NAO climate response in MENA compared to the observations. The conducted analysis sheds light on the internal mechanisms of MENA climate variability and helps to selectively diagnose the model deficiencies.
Successful flank appraisal with a horizontal well: a Niger Delta example

Energy Technology Data Exchange (ETDEWEB)

Ohanele, C.; Emelumadu, U.

1998-12-31

Case study of a horizontal well successfully drilled in 1994 by Shell Oil in the Niger Delta is described. The well was drilled with the objectives of improving drainage of the major D3.1 reservoir and appraising the poorly defined eastern flank for structure and fluid content of the overlying D3.0 sand. The well was optimized by 3D reservoir and hydrocarbon modeling of these reservoirs. Combining the development and appraisal objectives in one horizontal well proved to be the optimal solution, both from a cost as well as a production consideration. The well proved up over 50 MMstb of additional reserves. The structural flank proved to be significantly shallower than previously mapped and had a positive effect not only on the D3.0 reserves, but also on the the D3.1. 6 figs.

Comprehensive geophysical survey technique in exploration for deep-buried hydrothermal type uranium deposits in Xiangshan volcanic basin, China

International Nuclear Information System (INIS)

Ke, D.

2014-01-01

According to recent drilling results, uranium mineralization has been found underground more than 1000 m deep in the Xiangshan volcanic basin, in where uranium exploration has been carried out for over 50 years. This paper presents a comprehensive geophysical survey technique, including audio magnetotelluric method (AMT), high resolution ground magnetic and radon survey, which aim to prospect deep-buried and concealed uranium deposits in Xiangshan volcanic basin. Based on research and application, a comprehensive geophysical technique consisting of data acquisition, processing and interpretation has been established. Concealed rock and ore-controlling structure buried deeper than 1000 m can be detected by using this technique. Moreover, one kind of anti-interference technique of AMT survey is presented, which can eliminate the interference induced by the high-voltage power lines. Result of AMT in Xiangshan volcanic basin is demonstrated as high-low-high mode, which indicates there are three layers in geology. The upper layer with high resistivity is mainly the react of porphyroclastic lava. The middle layer with low resistivity is metamorphic schists or dellenite whereas the lower layer with high resistivity is inferred as granite. The interface between middle and lower layer is recognized as the potential zone for occurrence of uranium deposits. According to the corresponding relation of the resistivity and magnetic anomaly with uranium ore bodies, the tracing model of faults and interfaces between the different rocks, and the forecasting model of advantageous area for uranium deposits have been established. In terms of the forecasting model, some significant sections for uranium deposits were delineated in the west of the Xiangshan volcanic basin. As a result, some achievements on uranium prospecting have been acquired. High grade economic uranium ore bodies have been found in several boreholes, which are located in the forecasted zones. (author)
Evidence for magnocellular involvement in the identification of flanked letters

NARCIS (Netherlands)

Omtzigt, D.; Hendriks, A.W.C.J.; Kolk, H.H.J.

2002-01-01

Little is known about the role of the magno system in reading. One important hypothesis is that this system is involved in the allocation of attention. We reasoned that the presentation of a single letter automatically draws attention to this letter, whereas in the case of a flanked letter, an
Highly oxidising fluids generated during serpentinite breakdown in subduction zones.

Science.gov (United States)

Debret, B; Sverjensky, D A

2017-09-04

Subduction zones facilitate chemical exchanges between Earth's deep interior and volcanism that affects habitability of the surface environment. Lavas erupted at subduction zones are oxidized and release volatile species. These features may reflect a modification of the oxidation state of the sub-arc mantle by hydrous, oxidizing sulfate and/or carbonate-bearing fluids derived from subducting slabs. But the reason that the fluids are oxidizing has been unclear. Here we use theoretical chemical mass transfer calculations to predict the redox state of fluids generated during serpentinite dehydration. Specifically, the breakdown of antigorite to olivine, enstatite, and chlorite generates fluids with high oxygen fugacities, close to the hematite-magnetite buffer, that can contain significant amounts of sulfate. The migration of these fluids from the slab to the mantle wedge could therefore provide the oxidized source for the genesis of primary arc magmas that release gases to the atmosphere during volcanism. Our results also show that the evolution of oxygen fugacity in serpentinite during subduction is sensitive to the amount of sulfides and potentially metal alloys in bulk rock, possibly producing redox heterogeneities in subducting slabs.
Numerical modeling of magma-tectonic interactions at Pacaya Volcano, Guatemala

Science.gov (United States)

Wauthier, C.

2017-12-01

Pacaya Volcano is composed of several volcanic cones located along the southern rim of the Amatitlan caldera, approximately 25 km south of Guatemala City. It is a basaltic volcano located in the Central American Volcanic Arc. The shallow magma plumbing system at Pacaya likely includes at least three magma reservoirs: a very shallow ( 0.2-0.4 km depth) reservoir located below and possibly within the MacKenney cone, a 4 km deep reservoir located northwest of the summit, and a shallow dike-like conduit below the summit which fed the recent flank eruptions. Pacaya's western flank is slipping in a stick-slip fashion, and the instability seems associated with larger volume eruptions. Flank instability phases indeed occurred in 2010 and 2014 in coincidence with major intrusive and eruptive phases, suggesting a positive feedback between the flank motion and major intrusions. Simple analytical models are insufficient to fit the geodetic observations and model the flank processes and their mechanical interactions with the magmatic system. Here, numerical modeling approaches are used to characterize the 2014 flank deformation episode and magma-tectonic interactions.
Seismic attenuation structure beneath Nazca Plate subduction zone in southern Peru

Science.gov (United States)

Jang, H.; Kim, Y.; Clayton, R. W.

2017-12-01

We estimate seismic attenuation in terms of quality factors, QP and QS using P and S phases, respectively, beneath Nazca Plate subduction zone between 10°S and 18.5°S latitude in southern Peru. We first relocate 298 earthquakes with magnitude ranges of 4.0-6.5 and depth ranges of 20-280 km. We measure t*, which is an integrated attenuation through the seismic raypath between the regional earthquakes and stations. The measured t* are inverted to construct three-dimensional attenuation structures of southern Peru. Checkerboard test results for both QP and QS structures ensure good resolution in the slab-dip transition zone between flat and normal slab subduction down to a depth of 200 km. Both QP and QS results show higher attenuation continued down to a depth of 50 km beneath volcanic arc and also beneath the Quimsachata volcano, the northernmost young volcano, located far east of the main volcanic front. We also observe high attenuation in mantle wedge especially beneath the normal subduction region in both QP and QS (100-130 in QP and 100-125 in QS) and slightly higher QP and QS beneath the flat-subduction and slab-dip transition regions. We plan to relate measured attenuation in the mantle wedge to material properties such as viscosity to understand the subduction zone dynamics.
Vasopressin-dependent flank marking in golden hamsters is suppressed by drugs used in the treatment of obsessive-compulsive disorder

Directory of Open Access Journals (Sweden)

Messenger Tara

2001-08-01

Full Text Available Abstract Background Alterations in arginine vasopressin regulation and secretion have been proposed as one possible biochemical abnormality in patients with obsessive-compulsive disorder. In golden hamsters, arginine vasopressin microinjections into the anterior hypothalamus trigger robust grooming and flank marking, a stereotyped scent marking behaviors. The intensity and repetition of the behaviors induced by arginine vasopressin is somewhat reminiscent of Obsessive Compulsive Disorder in humans. The present experiments were carried out to test whether pharmacological agents used to alleviate obsessive compulsive disorder could inhibit arginine vasopressin-induced flank marking and grooming. Results Male golden hamsters were treated daily for two weeks with either vehicle, fluoxetine, clomipramine, or desipramine (an ineffective drug, before being tested for arginine vasopressin-induced flank marking and grooming. Flank marking was significantly inhibited in animals treated with fluoxetine or clomipramine but unaffected by treatment with desipramine. Grooming behavior was not affected by any treatment. Conclusion These data suggest that arginine vasopressin-induced flank marking may serve as an animal model for screening drugs used in the control of Obsessive Compulsive Disorder.
Imaging modalities and therapy options in patients with acute flank pain

International Nuclear Information System (INIS)

Grosse, A.; Grosse, C.

2014-01-01

The objective of this article is the description of imaging techniques for the evaluation of patients with acute flank pain and suspicion of urolithiasis and the impact of these techniques in the therapy management of patients with calculi. (orig.) [de
Late Cenozoic Samtskhe-Javakheti Volcanic Highland, Georgia:The Result of Mantle Plumes Activity

Science.gov (United States)

Okrostsvaridze, Avtandil

2017-04-01

intraplate volcanic ridge. Based on our studies, we assume that the Samtskhe-Javakheti volcanic highland is a result of full cycle mantle plume activity and not of by adiabatic decompression melting of the asthenosphere, as it is considered at present (Keskin, 2007). Therefore, we assume that this volcanic highland is a Northern marginal manifestation of the Eastern Africa-Red Sea -Anatolia mantle plume flow. If we accept this idea, then the Pliocene-Pleistocene Samtskhe-Javakheti volcanic highland is the youngest continental mantle plume formation of the Earth. REFERENCES Keskin M., 2007. Eastern Anatolia: a hotspot in a collision zone without a mantle plume. Geological Society of America, Special Paper 430, pp. 693 - 722. Okrostsavridze A., Popkhadze A., Kirkitadze G., 2016. Megavolcano in the Late Cenozoic Samtckhe-Javakheti Volcanic Province? In procceding of 6th workshop on Collapse Caldera, Hokkaido, Japan. p. 42-43.
Violent Explosive Eruptions in the Ararat Valley, Armenia and Associated Volcanic Hazards

Science.gov (United States)

Meliksetian, Khachatur; Savov, Ivan; Connor, Charles; Gevorgyan, Hripsime; Connor, Laura; Navasardyan, Gevorg; Manucharyan, Davit; Jrbashyan, Ruben; Ghukasyan, Yura

2016-04-01

The Anatolian-Armenian-Iranian volcanically active orogenic plateau is located in the collision zone between the Arabian and Eurasian plates. The majority of regional geodynamic and petrologic models of collision-related magmatism use the model proposed by Keskin (2003), where volcanism is driven by Neo-Tethyan slab break-off, however an updated model by Neill et al. (2015) and Skolbeltsyn et al.(2014) comprise break-off of two slabs. One of the significant (and understudied) features of the regionally extensive collision zone volcanism is the diversity of eruption styles and also the presence of large number of highly explosive (Plinian) eruptions with VEI≥5 during the Middle-Upper Pleistocene. Geological records of the Ararat depression include several generations of thick low aspect ratio Quaternary ignimbrites erupted from Aragats volcano, as well as up to 3 m thick ash and pumice fall deposit from the Holocene-historically active Ararat volcano. The Ararat tephra fall deposit is studied at 12 newly discovered outcrops covering an area ˜1000 km2. It is noteworthy, that the Ararat tephra deposits are loose and unwelded and observed only in cross-sections in small depressions or in areas where they were rapidly covered by younger, colluvium deposits, presumably of Holocene age. Therefore, the spatial extent of the explosive deposits of Ararat is much bigger but not well preserved due to rapid erosion. Whole rock elemental, isotope (Sr, Nd) and mineral chemistry data demonstrate significant difference in the magma sources of the large Aragats and Ararat stratovolcanoes. Lavas and pyroclastic products of Aragats are high K calc-alkaline, and nearly always deprived from H2O rich phases such as amphibole. In contrasts lavas and pyroclastic products from Ararat are medium K calc-alkaline and volatile-rich (>4.6 wt% H2O and amphibole bearing) magmas. Here we shall attempt to reveal possible geochemical triggers of explosive eruptions in these volcanoes and assess
Hafnium at subduction zones: isotopic budget of input and output fluxes

International Nuclear Information System (INIS)

Marini, J.Ch.

2004-05-01

Subduction zones are the primary regions of mass exchanges between continental crust and mantle of Earth through sediment subduction toward the earth's mantle and by supply of mantellic magmas to volcanic arcs. We analyze these mass exchanges using Hafnium and Neodymium isotopes. At the Izu-Mariana subduction zone, subducting sediments have Hf and Nd isotopes equivalent to Pacific seawater. Altered oceanic crust has Hf and Nd isotopic compositions equivalent to the isotopic budget of unaltered Pacific oceanic crust. At Luzon and Java subduction zones, arc lavas present Hf isotopic ratios highly radiogenic in comparison to their Nd isotopic ratios. Such compositions of the Luzon and Java arc lavas are controlled by a contamination of their sources by the subducted oceanic sediments. (author)
Using Volcanic Lightning Measurements to Discern Variations in Explosive Volcanic Activity

Science.gov (United States)

Behnke, S. A.; Thomas, R. J.; McNutt, S. R.; Edens, H. E.; Krehbiel, P. R.; Rison, W.

2013-12-01

VHF observations of volcanic lightning have been made during the recent eruptions of Augustine Volcano (2006, Alaska, USA), Redoubt Volcano (2009, Alaska, USA), and Eyjafjallajökull (2010, Iceland). These show that electrical activity occurs both on small scales at the vent of the volcano, concurrent with an eruptive event and on large scales throughout the eruption column during and subsequent to an eruptive event. The small-scale discharges at the vent of the volcano are often referred to as 'vent discharges' and are on the order of 10-100 meters in length and occur at rates on the order of 1000 per second. The high rate of vent discharges produces a distinct VHF signature that is sometimes referred to as 'continuous RF' radiation. VHF radiation from vent discharges has been observed at sensors placed as far as 100 km from the volcano. VHF and infrasound measurements have shown that vent discharges occur simultaneously with the onset of eruption, making their detection an unambiguous indicator of explosive volcanic activity. The fact that vent discharges are observed concurrent with explosive volcanic activity indicates that volcanic ejecta are charged upon eruption. VHF observations have shown that the intensity of vent discharges varies between eruptive events, suggesting that fluctuations in eruptive processes affect the electrification processes giving rise to vent discharges. These fluctuations may be variations in eruptive vigor or variations in the type of eruption; however, the data obtained so far do not show a clear relationship between eruption parameters and the intensity or occurrence of vent discharges. Further study is needed to clarify the link between vent discharges and eruptive behavior, such as more detailed lightning observations concurrent with tephra measurements and other measures of eruptive strength. Observations of vent discharges, and volcanic lightning observations in general, are a valuable tool for volcano monitoring, providing a
CO2 diffuse emission from maar lake: An example in Changbai volcanic field, NE China

Science.gov (United States)

Sun, Yutao; Guo, Zhengfu; Liu, Jiaqi; Du, Jianguo

2018-01-01

Numerous maars and monogenetic volcanic cones are distributed in northeast China, which are related to westward deep subduction of the Pacific Ocean lithosphere, comprising a significant part of the "Pacific Ring of Fire". It is well known that diffuse CO2 emissions from monogenetic volcanoes, including wet (e.g., maar lake) and dry degassing systems (e.g., soil diffuse emission, fault degassing, etc.), may contribute to budget of globally nature-derived greenhouse gases. However, their relationship between wet (e.g., maar lake) and concomitant dry degassing systems (e.g., soil diffuse emission, fault degassing, etc.) related to monogenetic volcanic field is poorly understood. Yuanchi maar, one of the typical monogenetic volcanic systems, is located on the eastern flank of Tianchi caldera in Changbai volcanic field of northeast China, which displays all of three forms of CO2 degassing including the maar lake, soil micro-seepage and fault degassing. Measurements of efflux of CO2 diffusion from the Yuanchi maar system (YMS) indicate that the average values of CO2 emissions from soil micro-seepage, fault degassing and water-air interface diffusion are 24.3 ± 23.3 g m- 2 d- 1, 39.2 ± 22.4 g m- 2 d- 1 and 2.4 ± 1.1 g m- 2 d- 1, respectively. The minimum output of CO2 diffuse emission from the YMS to the atmosphere is about 176.1 ± 88.3 ton/yr, of which 80.4% results from the dry degassing system. Degassing from the fault contributes to the most of CO2 emissions in all of the three forms of degassing in the YMS. Contributions of mantle, crust, air and organic CO2 to the soil gas are 0.01-0.10%, 10-20%, 32-36% and 48-54%, respectively, which are quantitatively constrained by a He-C isotope coupling calculation model. We propose that CO2 exsolves from the upper mantle melting beneath the Tianchi caldera, which migrates to the crustal magma chamber and further transports to the surface of YMS along the deep fault system. During the transportation processes, the emission
Volcanic risk and tourism in southern Iceland: Implications for hazard, risk and emergency response education and training

Science.gov (United States)

Bird, Deanne K.; Gisladottir, Gudrun; Dominey-Howes, Dale

2010-01-01

This paper examines the relationship between volcanic risk and the tourism sector in southern Iceland and the complex challenge emergency management officials face in developing effective volcanic risk mitigation strategies. An early warning system and emergency response procedures were developed for communities surrounding Katla, the volcano underlying the Mýrdalsjökull ice cap. However, prior to and during the 2007 tourist season these mitigation efforts were not effectively communicated to stakeholders located in the tourist destination of Þórsmörk despite its location within the hazard zone of Katla. The hazard zone represents the potential extent of a catastrophic jökulhlaup (glacial outburst flood). Furthermore, volcanic risk mitigation efforts in Þórsmörk were based solely on information derived from physical investigations of volcanic hazards. They did not consider the human dimension of risk. In order to address this gap and provide support to current risk mitigation efforts, questionnaire surveys were used to investigate tourists' and tourism employees' hazard knowledge, risk perception, adoption of personal preparedness measures, predicted behaviour if faced with a Katla eruption and views on education. Results indicate that tourists lack hazard knowledge and they do not adopt preparedness measures to deal with the consequences of an eruption. Despite a high level of risk perception, tourism employees lack knowledge about the early warning system and emergency response procedures. Results show that tourists are positive about receiving information concerning Katla and its hazards and therefore, the reticence of tourism employees with respect to disseminating hazard information is unjustified. In order to improve the tourism sector's collective capacity to positively respond during a future eruption, recommendations are made to ensure adequate dissemination of hazard, risk and emergency response information. Most importantly education campaigns
Petrography, mineral chemistry and geochemistry of post-ophiolitic volcanic rocks in the Ratouk area (south of Gazik, east of Iran

Directory of Open Access Journals (Sweden)

Zahra Vahedi Tabas

2017-11-01

Full Text Available Introduction Basaltic volcanoes are one of the volcanisms that have occurred in different parts of the world. The study of these lavas is important for petrologists, because they are seen in different tectonic settings and therefore diverse mechanisms affect their formation (Chen et al., 2007. Young volcanic rocks such as Quaternary basalts are one of latest products of magmatism in Iran that are related to deep fractures and active faults in Quaternary (Emami, 2000. The study area is located at 140km east of Birjand at Gazik 1:100000 geological map (Guillou et al., 1981 and have 60̊ 11' to 60̊ 15 '27" eastward longitude and 32̊ 33' 24" to 32̊ 39' 10" northward latitude. On the basis of structural subdivisions of Iran, this area is located in the northern part of the Sistan suture zone (Tirrul et al., 1983. Because of the importance of basaltic rocks in Sistan suture, this research is done with the aim of investigating the petrography and mineralogy of basaltic lavas, the nature of basaltic and intermediate magmatism and finally determination of tectonomagmatic regime. Materials and methods After field studies and sampling, 85 thin sections were prepared and carefully studied. Then ten samples with the lowest alteration were analyzed for major elements by inductively coupled plasma (ICP technologies and trace elements were analyzed using inductively coupled plasma mass spectrometry (ICP-MS, following a lithium metaborate/tetraborate fusion and nitric acid total digestion at the Acme laboratories, Vancouver, Canada. Electron probe micro analyses of clinopyroxene and olivine were done at the Iranian mineral processing research center (IMPRC by Cameca SX100 machine. X-ray diffraction analysis of minerals was done at the X-ray laboratory of the University of Birjand. Results In 60km south of GaziK at the east of the southern Khorasan province and the northern part of the Sistan suture zone, volcanic rocks with intermediate (Oligomiocene and
Impact of solar versus volcanic activity variations on tropospheric temperatures and precipitation during the Dalton Minimum

Science.gov (United States)

Anet, J. G.; Muthers, S.; Rozanov, E. V.; Raible, C. C.; Stenke, A.; Shapiro, A. I.; Brönnimann, S.; Arfeuille, F.; Brugnara, Y.; Beer, J.; Steinhilber, F.; Schmutz, W.; Peter, T.

2014-05-01

volcanic eruptions dominate the OHC changes in the deeper ocean and prevent its recovery during the DM. Finally, the simulations suggest that the volcanic eruptions during the DM had a significant impact on the precipitation patterns caused by a widening of the Hadley cell and a shift in the intertropical convergence zone.
Impact of solar vs. volcanic activity variations on tropospheric temperatures and precipitation during the Dalton Minimum

Science.gov (United States)

Anet, J. G.; Muthers, S.; Rozanov, E. V.; Raible, C. C.; Stenke, A.; Shapiro, A. I.; Brönnimann, S.; Arfeuille, F.; Brugnara, Y.; Beer, J.; Steinhilber, F.; Schmutz, W.; Peter, T.

2013-11-01

volcanic eruptions dominate the OHC changes in the deeper ocean and prevent its recovery during the DM. Finally, the simulations suggest that the volcanic eruptions during the DM had a significant impact on the precipitation patterns caused by a widening of the Hadley cell and a shift of the intertropical convergence zone.
Recurrence models of volcanic events: Applications to volcanic risk assessment

International Nuclear Information System (INIS)

Crowe, B.M.; Picard, R.; Valentine, G.; Perry, F.V.

1992-01-01

An assessment of the risk of future volcanism has been conducted for isolation of high-level radioactive waste at the potential Yucca Mountain site in southern Nevada. Risk used in this context refers to a combined assessment of the probability and consequences of future volcanic activity. Past studies established bounds on the probability of magmatic disruption of a repository. These bounds were revised as additional data were gathered from site characterization studies. The probability of direct intersection of a potential repository located in an eight km 2 area of Yucca Mountain by ascending basalt magma was bounded by the range of 10 -8 to 10 -10 yr -1 2 . The consequences of magmatic disruption of a repository were estimated in previous studies to be limited. The exact releases from such an event are dependent on the strike of an intruding basalt dike relative to the repository geometry, the timing of the basaltic event relative to the age of the radioactive waste and the mechanisms of release and dispersal of the waste radionuclides in the accessible environment. The combined low probability of repository disruption and the limited releases associated with this event established the basis for the judgement that the risk of future volcanism was relatively low. It was reasoned that that risk of future volcanism was not likely to result in disqualification of the potential Yucca Mountain site
Volcanic Plume Measurements with UAV (Invited)

Science.gov (United States)

Shinohara, H.; Kaneko, T.; Ohminato, T.

2013-12-01

Volatiles in magmas are the driving force of volcanic eruptions and quantification of volcanic gas flux and composition is important for the volcano monitoring. Recently we developed a portable gas sensor system (Multi-GAS) to quantify the volcanic gas composition by measuring volcanic plumes and obtained volcanic gas compositions of actively degassing volcanoes. As the Multi-GAS measures variation of volcanic gas component concentrations in the pumped air (volcanic plume), we need to bring the apparatus into the volcanic plume. Commonly the observer brings the apparatus to the summit crater by himself but such measurements are not possible under conditions of high risk of volcanic eruption or difficulty to approach the summit due to topography etc. In order to overcome these difficulties, volcanic plume measurements were performed by using manned and unmanned aerial vehicles. The volcanic plume measurements by manned aerial vehicles, however, are also not possible under high risk of eruption. The strict regulation against the modification of the aircraft, such as installing sampling pipes, also causes difficulty due to the high cost. Application of the UAVs for the volcanic plume measurements has a big advantage to avoid these problems. The Multi-GAS consists of IR-CO2 and H2O gas analyzer, SO2-H2O chemical sensors and H2 semiconductor sensor and the total weight ranges 3-6 kg including batteries. The necessary conditions of the UAV for the volcanic plumes measurements with the Multi-GAS are the payloads larger than 3 kg, maximum altitude larger than the plume height and installation of the sampling pipe without contamination of the exhaust gases, as the exhaust gases contain high concentrations of H2, SO2 and CO2. Up to now, three different types of UAVs were applied for the measurements; Kite-plane (Sky Remote) at Miyakejima operated by JMA, Unmanned airplane (Air Photo Service) at Shinomoedake, Kirishima volcano, and Unmanned helicopter (Yamaha) at Sakurajima
Integrating Volcanic Hazard Data in a Systematic Approach to Develop Volcanic Hazard Maps in the Lesser Antilles

Directory of Open Access Journals (Sweden)

Jan M. Lindsay

2018-04-01

Full Text Available We report on the process of generating the first suite of integrated volcanic hazard zonation maps for the islands of Dominica, Grenada (including Kick ‘em Jenny and Ronde/Caille, Nevis, Saba, St. Eustatius, St. Kitts, Saint Lucia, and St Vincent in the Lesser Antilles. We developed a systematic approach that accommodated the range in prior knowledge of the volcanoes in the region. A first-order hazard assessment for each island was used to develop one or more scenario(s of likely future activity, for which scenario-based hazard maps were generated. For the most-likely scenario on each island we also produced a poster-sized integrated volcanic hazard zonation map, which combined the individual hazardous phenomena depicted in the scenario-based hazard maps into integrated hazard zones. We document the philosophy behind the generation of this suite of maps, and the method by which hazard information was combined to create integrated hazard zonation maps, and illustrate our approach through a case study of St. Vincent. We also outline some of the challenges we faced using this approach, and the lessons we have learned by observing how stakeholders have interacted with the maps over the past ~10 years. Based on our experience, we recommend that future map makers involve stakeholders in the entire map generation process, especially when making design choices such as type of base map, use of colour and gradational boundaries, and indeed what to depict on the map. We also recommend careful consideration of how to evaluate and depict offshore hazard of island volcanoes, and recommend computer-assisted modelling of all phenomena to generate more realistic hazard footprints. Finally, although our systematic approach to integrating individual hazard data into zones generally worked well, we suggest that a better approach might be to treat the integration of hazards on a case-by-case basis to ensure the final product meets map users' needs. We hope that
Volcanic Hazards Associated with the NE Sector of Tacaná Volcano, Guatemala.

Science.gov (United States)

Hughes, S. R.; Saucedo, R.; Macias, J.; Arce, J.; Garcia-Palomo, A.; Mora, J.; Scolamacchia, T.

2003-12-01

Tacaná volcano, with a height of 4,030 m above sea level, straddles the southern Mexico/Guatemala border. Last active in 1986, when there was a small phreatic event with a duration of a few days, this volcano presents an impending hazard to over 250,000 people. The NE sector of the volcano reveals the violent volcanic history of Tacaná that may be indicative of a serious potential risk to the area. Its earliest pyroclastic history appears to consist of fall, flow, and surge deposits, together with lavas, that have formed megablocks within a series of old debris avalanche deposits. This sector collapse event is overlain by a sequence of pumice fall and ash flow deposits, of which the youngest, less-altered pumice fall deposit shows a minimum thickness of > 4 m, with a dispersal axis trending toward the NE. A second debris avalanche deposit, separated from the above deposits by a paleosoil, is dominated by megablocks of lava and scoriaceous dome material. The current topography around the northeastern flank of the volcano is determined by a third, and most recent debris avalanche deposit, a thick (> 20 m) sequence of six block and ash flows dated at around 16,000 years BP, each separated by 1-10 cm thick ash cloud surge deposit, together with secondary lahar deposits. These are followed by a at least 4 lava flows that extend 2 km down the flank of the volcano. It appears that the most recent pyroclastic event at Tacaná is also recorded in this sector of the volcano: above the block and ash flows occurs a > 1 m thick ash flow unit that can be seen at least 5 km from the vent. Lastly, the Santa Maria Ash fall deposit, produced in 1902, has capped most of the deposits at Tacaná.

Origin of the {sup 238}U-{sup 230}Th disequilibrium in magmas from subduction zones: the Arenal example; Origine du desequilibre {sup 238}U-{sup 230}TH dans les magmas des zones de subduction: exemple de l`Arenal

Energy Technology Data Exchange (ETDEWEB)

Villemant, B [Paris-6 Univ., 75 (France)

1997-12-31

The existence in some volcanic products of strong excess of {sup 238}U with respect to {sup 230}Th is one of the characteristics of volcanic arc magmas. These excesses are generally attributed to fluid additions inside mantellic sources before magma segregation, differentiation and eruption. These fluids should be linked to the dehydration of the subducted rocks. These hypotheses are essentially based on correlations between {sup 10}Be, {sup 87}Sr anomalies, Ba/La ratios and on the distribution of volcanic centers with respect to the subduction zone. Recent studies suggest an evolution of the composition of volcanic sources in Central America from a depleted mantle type (MORB) in the North (Nicaragua) to a less transformed enriched type (OIB) in the South (Costa Rica). The Arenal volcano belongs to a transition zone between these two types. The preliminary study of trace elements and {sup 238}U-{sup 230}Th disequilibria in recent volcanic products (1968-1993) indicates a more complex situation. At least two different mantle sources were successively involved characterized by different Th/La and La/Yb ratios and very different to the OIB type. Also most lavas are in equilibrium with {sup 238}U/{sup 232}Th ratios of about 1.2 to 1.3. However, in eruptive cycle, some lavas are characterized by a strong {sup 238}U excess with respect to {sup 230}Th with cannot be linked to the sources, even when modified by fluids in depth. These results are interpreted in terms of heterogeneities of mantle sources and low depths late interactions with hydrothermal fluids during eruptions. Abstract only. (J.S.). 2 refs.
Origin of the {sup 238}U-{sup 230}Th disequilibrium in magmas from subduction zones: the Arenal example; Origine du desequilibre {sup 238}U-{sup 230}TH dans les magmas des zones de subduction: exemple de l`Arenal

Energy Technology Data Exchange (ETDEWEB)

Villemant, B. [Paris-6 Univ., 75 (France)

1996-12-31

The existence in some volcanic products of strong excess of {sup 238}U with respect to {sup 230}Th is one of the characteristics of volcanic arc magmas. These excesses are generally attributed to fluid additions inside mantellic sources before magma segregation, differentiation and eruption. These fluids should be linked to the dehydration of the subducted rocks. These hypotheses are essentially based on correlations between {sup 10}Be, {sup 87}Sr anomalies, Ba/La ratios and on the distribution of volcanic centers with respect to the subduction zone. Recent studies suggest an evolution of the composition of volcanic sources in Central America from a depleted mantle type (MORB) in the North (Nicaragua) to a less transformed enriched type (OIB) in the South (Costa Rica). The Arenal volcano belongs to a transition zone between these two types. The preliminary study of trace elements and {sup 238}U-{sup 230}Th disequilibria in recent volcanic products (1968-1993) indicates a more complex situation. At least two different mantle sources were successively involved characterized by different Th/La and La/Yb ratios and very different to the OIB type. Also most lavas are in equilibrium with {sup 238}U/{sup 232}Th ratios of about 1.2 to 1.3. However, in eruptive cycle, some lavas are characterized by a strong {sup 238}U excess with respect to {sup 230}Th with cannot be linked to the sources, even when modified by fluids in depth. These results are interpreted in terms of heterogeneities of mantle sources and low depths late interactions with hydrothermal fluids during eruptions. Abstract only. (J.S.). 2 refs.
Reverse time migration of prism waves for salt flank delineation

KAUST Repository

Dai, Wei; Schuster, Gerard T.

2013-01-01

In this paper, we present a new reverse time migration method for imaging salt flanks with prism wave reflections. It consists of four steps: (1) migrating the seismic data with conventional RTM to give the RTM image; (2) using the RTM image as a reflectivity model to simulate source-side reflections with the Born approximation; (3) zero-lag correlation of the source-side reflection wavefields and receiver-side wavefields to produce the prism wave migration image; and (4) repeating steps 2 and 3 for the receiver-side reflections. An advantage of this method is that there is no need to pick the horizontal reflectors prior to migration of the prism waves. It also separately images the vertical structures at a different step to reduce crosstalk interference. The disadvantage of prism wave migration algorithm is that its computational cost is twice that of conventional RTM. The empirical results with a salt model suggest that prism wave migration can be an effective method for salt flank delineation in the absence of diving waves.
Reverse time migration of prism waves for salt flank delineation

KAUST Repository

Dai, Wei

2013-09-22

In this paper, we present a new reverse time migration method for imaging salt flanks with prism wave reflections. It consists of four steps: (1) migrating the seismic data with conventional RTM to give the RTM image; (2) using the RTM image as a reflectivity model to simulate source-side reflections with the Born approximation; (3) zero-lag correlation of the source-side reflection wavefields and receiver-side wavefields to produce the prism wave migration image; and (4) repeating steps 2 and 3 for the receiver-side reflections. An advantage of this method is that there is no need to pick the horizontal reflectors prior to migration of the prism waves. It also separately images the vertical structures at a different step to reduce crosstalk interference. The disadvantage of prism wave migration algorithm is that its computational cost is twice that of conventional RTM. The empirical results with a salt model suggest that prism wave migration can be an effective method for salt flank delineation in the absence of diving waves.
ACTIVITY AND Vp/Vs RATIO OF VOLCANO-TECTONIC SEISMIC SWARM ZONES AT NEVADO DEL RUIZ VOLCANO, COLOMBIA

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Londoño B. John Makario

2010-06-01

Full Text Available An analysis of the seismic activity for volcano-tectonic earthquake (VT swarms zones at Nevado del Ruiz Volcano (NRV was carried out for the interval 1985- 2002, which is the most seismic active period at NRV until now (2010. The swarm-like seismicity of NRV was frequently concentrated in very well defined clusters around the volcano. The seismic swarm zone located at the active crater was the most active during the entire time. The seismic swarm zone located to the west of the volcano suggested some relationship with the volcanic crises. It was active before and after the two eruptions occurred in November 1985 and September 1989. It is believed that this seismic activity may be used as a monitoring tool of volcanic activity. For each seismic swarm zone the Vp/Vs ratio was also calculated by grouping of earthquakes and stations. It was found that each seismic swarm zone had a distinct Vp/Vs ratio with respect to the others, except for the crater and west swarm zones, which had the same value. The average Vp/Vs ratios for the seismic swarm zones located at the active crater and to the west of the volcano are about 6-7% lower than that for the north swarm zone, and about 3% lower than that for the south swarm zone. We suggest that the reduction of the Vp/Vs ratio is due to degassing phenomena inside the central and western earthquake swarm zones, or due to the presence of microcracks inside the volcano. This supposition is in agreement with other studies of geophysics, geochemistry and drilling surveys carried out at NRV.
Determination of time- and height-resolved volcanic ash emissions and their use for quantitative ash dispersion modeling: the 2010 Eyjafjallajökull eruption

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A. Stohl

2011-05-01

Full Text Available The April–May, 2010 volcanic eruptions of Eyjafjallajökull, Iceland caused significant economic and social disruption in Europe whilst state of the art measurements and ash dispersion forecasts were heavily criticized by the aviation industry. Here we demonstrate for the first time that large improvements can be made in quantitative predictions of the fate of volcanic ash emissions, by using an inversion scheme that couples a priori source information and the output of a Lagrangian dispersion model with satellite data to estimate the volcanic ash source strength as a function of altitude and time. From the inversion, we obtain a total fine ash emission of the eruption of 8.3 ± 4.2 Tg for particles in the size range of 2.8–28 μm diameter. We evaluate the results of our model results with a posteriori ash emissions using independent ground-based, airborne and space-borne measurements both in case studies and statistically. Subsequently, we estimate the area over Europe affected by volcanic ash above certain concentration thresholds relevant for the aviation industry. We find that during three episodes in April and May, volcanic ash concentrations at some altitude in the atmosphere exceeded the limits for the "Normal" flying zone in up to 14 % (6–16 %, 2 % (1–3 % and 7 % (4–11 %, respectively, of the European area. For a limit of 2 mg m⁻³ only two episodes with fractions of 1.5 % (0.2–2.8 % and 0.9 % (0.1–1.6 % occurred, while the current "No-Fly" zone criterion of 4 mg m⁻³ was rarely exceeded. Our results have important ramifications for determining air space closures and for real-time quantitative estimations of ash concentrations. Furthermore, the general nature of our method yields better constraints on the distribution and fate of volcanic ash in the Earth system.
Seismic activity around and under Krakatau volcano, Sunda Arc: constraints to the source region of island arc volcanics

Czech Academy of Sciences Publication Activity Database

Špičák, Aleš; Hanuš, Václav; Vaněk, Jiří

2002-01-01

Roč. 46, č. 3 (2002), s. 545-565 ISSN 0039-3169 R&D Projects: GA ČR GA205/97/0898; GA AV ČR IAA3012002 Institutional research plan: CEZ:AV0Z3012916 Keywords : Krakatau * Sunda Strait seismicity * island arc volcanism * subduction * Wadati-Benioff zone Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 0.571, year: 2002
Deformation and seismic anisotropy of the subcontinental lithospheric mantle in NE Spain: EBSD data on xenoliths from the Catalan Volcanic Zone

Science.gov (United States)

Fernández-Roig, Mercè; Galán, Gumer; Mariani, Elisabetta

2017-02-01

Mantle xenoliths in Neogene-Quaternary basaltic rocks related to the European Cenozoic Rift System serve to assess the evolution of the subcontinental lithospheric mantle beneath the Catalan Volcanic Zone in NE Spain. Crystallographic preferred orientations, major element composition of minerals, and temperature and pressure estimates have been used to this end. The mantle consists of spinel lherzolites, harzburgites and subordinate websterites. Protogranular microstructures are found in all peridotites and websterites, but lherzolites also display finer-grained porphyroclastic and equigranular microstructures. The dominant olivine deformation fabric is [010] fiber, but subordinate orthorhombic and [100]-fiber types are also present, especially in porphyroclastic and equigranular lherzolites. The fabric strength (J index = 10.12-1.91), equilibrium temperature and pressure are higher in xenoliths with [010]-fiber fabric and decrease in those with orthorhombic and [100]-fiber type. Incoherence between olivine and pyroxene deformation fabric is mostly found in porphyroclastic and equigranular lherzolites. Seismic anisotropy, estimated from the crystal preferred orientations, also decreases (AVp = 10.2-2.60%; AVs max = 7.95-2.19%) in porphyroclastic and equigranular lherzolites. The olivine [010]-fiber fabric points to deformation by simple shear or transpression which is likely to have occured during the development of late-Hercynian strike-slip shear zones, and to subsequent annealing during late Hercynian decompression, Permian and Cretaceous rifting. Also, it cannot be excluded that the percolation of mafic magmas during these extensional events provoked the refertilization of the lithospheric mantle. However, no clear relationship has been observed between fabric strength and mineral mode and composition. Later transtensional deformation during late Alpine orogenesis, at higher stress and decreasing temperature and pressure, transformed the earlier fabric into
Presenting Numerical Modelling of Explosive Volcanic Eruption to a General Public

Science.gov (United States)

Demaria, C.; Todesco, M.; Neri, A.; Blasi, G.

2001-12-01

Numerical modeling of explosive volcanic eruptions has been widely applied, during the last decades, to study pyroclastic flows dispersion along volcano's flanks and to evaluate their impact on urban areas. Results from these transient multi-phase and multi-component simulations are often reproduced in form of computer animations, representing the spatial and temporal evolution of relevant flow variables (such as temperature, or particle concentration). Despite being a sophisticated, technical tool to analyze and share modeling results within the scientific community, these animations truly look like colorful cartoons showing an erupting volcano and are especially suited to be shown to a general public. Thanks to their particular appeal, and to the large interest usually risen by exploding volcanoes, these animations have been presented several times on television and magazines and are currently displayed in a permanent exposition, at the Vesuvius Observatory in Naples. This work represents an effort to produce an accompanying tool for these animations, capable of explaining to a large audience the scientific meaning of what can otherwise look as a graphical exercise. Dealing with research aimed at the study of dangerous, explosive volcanoes, improving the general understanding of these scientific results plays an important role as far as risk perception is concerned. An educated population has better chances to follow an appropriate behavior, i.e.: one that could lead, on the long period, to a reduction of the potential risk. In this sense, a correct divulgation of scientific results, while improving the confidence of the population in the scientific community, should belong to the strategies adopted to mitigate volcanic risk. Due to the relevance of the long term final goal of such divulgation experiment, this work represents an interdisciplinary effort, combining scientific expertise and specific competence from the modern communication science and risk
Origin of Holocene trachyte lavas of the Quetrupillán volcanic complex, Chile: Examples of residual melts in a rejuvenated crystalline mush reservoir

Science.gov (United States)

Brahm, Raimundo; Parada, Miguel Angel; Morgado, Eduardo; Contreras, Claudio; McGee, Lucy Emma

2018-05-01

The Quetrupillán Volcanic Complex (QVC) is a stratovolcano placed in the center of a NW-SE volcanic chain, between Villarrica volcano and Lanín volcano, in the Central Southern Volcanic Zone of the Andes. Its youngest effusive products are dominated by crystal-poor (most samples with differentiation at shallow depth (<1 kbar) and NNO-QFM oxidation conditions were obtained from initial melt compositions equivalent to the Huililco basalts, a small eruptive centre located ca. 12 km NE of the QVC main vent. Pyroxene-bearing crystal clots, locally abundant in the trachytes, were formed at 900-960 °C (±55 °C) and represent a dismembered crystal mush from which interstitial trachytic melts were extracted and transported upward before eruption. Heating of the crystal mush by a hotter magma recharge is inferred from complex zoned plagioclases formed at higher crystallization temperatures (50-90 °C) than those obtained from pyroxene. Ca-rich plagioclase overgrowths around more albitic cores, followed by an external rim of similar composition to the core are interpreted as restoration to the initial conditions of plagioclase crystallization after the mentioned heating event. Additionally, a late heating of up to 150 °C just prior to eruption is recorded by Fe-Ti oxide thermometry.
Zircon Geochronology (U-Pb), Petrography, Geochemistry and Radioisotopes of Bornaward Metarhyolites (Central Taknar Zone-Northwest of Bardaskan)

OpenAIRE

Reza Monazzami Bagherzadeh; Mohammad Hassan Karimpour; G. Lang Farmer; Charles R. Stern; Jose Francisco Santos; Sara Ribeiro; Behnam Rahimi; Mohammad Reza Haidarian Shahri

2016-01-01

Introduction The Bornaward area is located in the Northeastern Iran (in the Khorasan Razavi province) 28 km northwest of the city of Bardaskan at 57˚ 46΄ to 57˚ 52΄ N latitude and 35˚ 21΄ to 35˚ 24΄E longitude. The Taknar structural zone, situated in the North central Iranian micro continent, is part of the Lut block (Forster, 1978). The Taknar zone is an allochthonous block bounded by the Darouneh and Taknar major faults. Much of this zone consists of metarhyolite-rhyodacite volcanic rock...
Anomalously high porosity in subduction inputs to the Nankai Trough (SW Japan) potentially caused by volcanic ash and pumice

Science.gov (United States)

Huepers, A.; Ikari, M.; Underwood, M.; Kopf, A.

2013-12-01

At convergent margins, the sedimentary section seaward of the trench on the subducting oceanic lithosphere provides the source material for accretionary prisms and eventually becomes the host rock of the plate boundary megathrust. The mechanical properties of the sediments seaward of the subduction zone have therefore a first order control on subduction zone forearc mechanics and hydrogeology. At the Nankai Trough (SW Japan) the majority of sediment approaching the subduction zone is clay-rich. Scientific drilling expeditions in the framework of the Ocean Drilling Program (ODP) and the Integrated Ocean Drilling Program (IODP) have revealed an anomalous zone of high porosity in a major lithologic unit known as the Upper Shikoku Basin facies (USB), which is associated with elevated volcanic ash content and high amounts of silica in the interstitial water. The existence of the high porosity zone has previously been associated with advanced silica cementation, driven by the dual diagenetic transition of opal-A to opal-CT, and opal-CT to quartz. However, temperature estimates from recent drilling expeditions offshore the Kii peninsula reveal different in situ temperatures at the proposed diagenetic boundary in the Shikoku Basin. Furthermore, laboratory measurements using core samples from the USB show that cohesive strength is not elevated in the high porosity zone, suggesting that a process other than cementation may be responsible. The USB sediment is characterized by abundant volcanic ash and pumice, therefore the high porosity zone in the USB may be closely linked to the mechanical behavior of this phase. We conducted consolidation tests in the range 0.1 to 8 MPa effective vertical stress on artificial ash-smectite and pumice-smectite mixtures, as well as intact and remolded natural samples from the IODP Sites C0011 and C0012 to investigate the role of the volcanic constituent on porosity loss with progressive burial. Our results show that both remolded and intact
Surface heat flow and CO2 emissions within the Ohaaki hydrothermal field, Taupo Volcanic Zone, New Zealand

International Nuclear Information System (INIS)

Rissmann, Clinton; Christenson, Bruce; Werner, Cynthia; Leybourne, Matthew; Cole, Jim; Gravley, Darren

2012-01-01

Carbon dioxide emissions and heat flow have been determined from the Ohaaki hydrothermal field, Taupo Volcanic Zone (TVZ), New Zealand following 20 a of production (116 MW e ). Soil CO 2 degassing was quantified with 2663 CO 2 flux measurements using the accumulation chamber method, and 2563 soil temperatures were measured and converted to equivalent heat flow (W m −2 ) using published soil temperature heat flow functions. Both CO 2 flux and heat flow were analysed statistically and then modelled using 500 sequential Gaussian simulations. Forty subsoil CO 2 gas samples were also analysed for stable C isotopes. Following 20 a of production, current CO 2 emissions equated to 111 ± 6.7 T/d. Observed heat flow was 70 ± 6.4 MW, compared with a pre-production value of 122 MW. This 52 MW reduction in surface heat flow is due to production-induced drying up of all alkali–Cl outflows (61.5 MW) and steam-heated pools (8.6 MW) within the Ohaaki West thermal area (OHW). The drying up of all alkali–Cl outflows at Ohaaki means that the soil zone is now the major natural pathway of heat release from the high-temperature reservoir. On the other hand, a net gain in thermal ground heat flow of 18 MW (from 25 MW to 43.3 ± 5 MW) at OHW is associated with permeability increases resulting from surface unit fracturing by production-induced ground subsidence. The Ohaaki East (OHE) thermal area showed no change in distribution of shallow and deep soil temperature contours despite 20 a of production, with an observed heat flow of 26.7 ± 3 MW and a CO 2 emission rate of 39 ± 3 T/d. The negligible change in the thermal status of the OHE thermal area is attributed to the low permeability of the reservoir beneath this area, which has limited production (mass extraction) and sheltered the area from the pressure decline within the main reservoir. Chemistry suggests that although alkali–Cl outflows once contributed significantly to the natural surface heat flow (∼50%) they
Closer look at lunar volcanism

International Nuclear Information System (INIS)

Vaniman, D.T.; Heiken, G.; Taylor, G.J.

1984-01-01

Although the American Apollo and Soviet Luna missions concentrated on mare basalt samples, major questions remain about lunar volcanism. Lunar field work will be indispensable for resolving the scientific questions about ages, compositions, and eruption processes of lunar volcanism. From a utilitarian standpoint, a better knowledge of lunar volcanism will also yield profitable returns in lunar base construction (e.g., exploitation of rille or lava-tube structures) and in access to materials such as volatile elements, pure glass, or ilmenite for lunar industry
Volcanic alert system (VAS) developed during the 2011-2014 El Hierro (Canary Islands) volcanic process

Science.gov (United States)

García, Alicia; Berrocoso, Manuel; Marrero, José M.; Fernández-Ros, Alberto; Prates, Gonçalo; De la Cruz-Reyna, Servando; Ortiz, Ramón

2014-06-01

The 2011 volcanic unrest at El Hierro Island illustrated the need for a Volcanic Alert System (VAS) specifically designed for the management of volcanic crises developing after long repose periods. The VAS comprises the monitoring network, the software tools for analysis of the monitoring parameters, the Volcanic Activity Level (VAL) management, and the assessment of hazard. The VAS presented here focuses on phenomena related to moderate eruptions, and on potentially destructive volcano-tectonic earthquakes and landslides. We introduce a set of new data analysis tools, aimed to detect data trend changes, as well as spurious signals related to instrumental failure. When data-trend changes and/or malfunctions are detected, a watchdog is triggered, issuing a watch-out warning (WOW) to the Monitoring Scientific Team (MST). The changes in data patterns are then translated by the MST into a VAL that is easy to use and understand by scientists, technicians, and decision-makers. Although the VAS was designed specifically for the unrest episodes at El Hierro, the methodologies may prove useful at other volcanic systems.
Deformation and rupture of the oceanic crust may control growth of Hawaiian volcanoes.

Science.gov (United States)

Got, Jean-Luc; Monteiller, Vadim; Monteux, Julien; Hassani, Riad; Okubo, Paul

2008-01-24

Hawaiian volcanoes are formed by the eruption of large quantities of basaltic magma related to hot-spot activity below the Pacific Plate. Despite the apparent simplicity of the parent process--emission of magma onto the oceanic crust--the resulting edifices display some topographic complexity. Certain features, such as rift zones and large flank slides, are common to all Hawaiian volcanoes, indicating similarities in their genesis; however, the underlying mechanism controlling this process remains unknown. Here we use seismological investigations and finite-element mechanical modelling to show that the load exerted by large Hawaiian volcanoes can be sufficient to rupture the oceanic crust. This intense deformation, combined with the accelerated subsidence of the oceanic crust and the weakness of the volcanic edifice/oceanic crust interface, may control the surface morphology of Hawaiian volcanoes, especially the existence of their giant flank instabilities. Further studies are needed to determine whether such processes occur in other active intraplate volcanoes.
Lidar sounding of volcanic plumes

Science.gov (United States)

Fiorani, Luca; Aiuppa, Alessandro; Angelini, Federico; Borelli, Rodolfo; Del Franco, Mario; Murra, Daniele; Pistilli, Marco; Puiu, Adriana; Santoro, Simone

2013-10-01

Accurate knowledge of gas composition in volcanic plumes has high scientific and societal value. On the one hand, it gives information on the geophysical processes taking place inside volcanos; on the other hand, it provides alert on possible eruptions. For this reasons, it has been suggested to monitor volcanic plumes by lidar. In particular, one of the aims of the FP7 ERC project BRIDGE is the measurement of CO2 concentration in volcanic gases by differential absorption lidar. This is a very challenging task due to the harsh environment, the narrowness and weakness of the CO2 absorption lines and the difficulty to procure a suitable laser source. This paper, after a review on remote sensing of volcanic plumes, reports on the current progress of the lidar system.
Gas measurements from the Costa Rica-Nicaragua volcanic segment suggest possible along-arc variations in volcanic gas chemistry

Science.gov (United States)

Aiuppa, A.; Robidoux, P.; Tamburello, G.; Conde, V.; Galle, B.; Avard, G.; Bagnato, E.; De Moor, J. M.; Martínez, M.; Muñóz, A.

2014-12-01

Obtaining accurate estimates of the CO2 output from arc volcanism requires a precise understanding of the potential along-arc variations in volcanic gas chemistry, and ultimately of the magmatic gas signature of each individual arc segment. In an attempt to more fully constrain the magmatic gas signature of the Central America Volcanic Arc (CAVA), we present here the results of a volcanic gas survey performed during March and April 2013 at five degassing volcanoes within the Costa Rica-Nicaragua volcanic segment (CNVS). Observations of the volcanic gas plume made with a multicomponent gas analyzer system (Multi-GAS) have allowed characterization of the CO2/SO2-ratio signature of the plumes at Poás (0.30±0.06, mean ± SD), Rincón de la Vieja (27.0±15.3), and Turrialba (2.2±0.8) in Costa Rica, and at Telica (3.0±0.9) and San Cristóbal (4.2±1.3) in Nicaragua (all ratios on molar basis). By scaling these plume compositions to simultaneously measured SO2 fluxes, we estimate that the CO2 outputs at CNVS volcanoes range from low (25.5±11.0 tons/day at Poás) to moderate (918 to 1270 tons/day at Turrialba). These results add a new information to the still fragmentary volcanic CO2 output data set, and allow estimating the total CO2 output from the CNVS at 2835±1364 tons/day. Our novel results, with previously available information about gas emissions in Central America, are suggestive of distinct volcanic gas CO2/ST (= SO2 + H2S)-ratio signature for magmatic volatiles in Nicaragua (∼3) relative to Costa Rica (∼0.5-1.0). We also provide additional evidence for the earlier theory relating the CO2-richer signature of Nicaragua volcanism to increased contributions from slab-derived fluids, relative to more-MORB-like volcanism in Costa Rica. The sizeable along-arc variations in magmatic gas chemistry that the present study has suggested indicate that additional gas observations are urgently needed to more-precisely confine the volcanic CO2 from the CAVA, and from
Seismic evidence for deep fluid circulation in the overriding plate of subduction zones

Science.gov (United States)

Tauzin, B.; Reynard, B.; Bodin, T.; Perrillat, J. P.; Debayle, E.

2015-12-01

In subduction zones, non-volcanic tremors are associated with fluid circulations (Obara, 2002). Their sources are often located on the interplate boundary (Rogers and Dragert, 2003; Shelly et al, 2006; La Rocca, 2009), consistent with fluids released by the dehydration of subducted plates (Hacker et al., 2003). Reports of tremors in the overriding continental crust of several subduction zones in the world (Kao et al., 2005; Payero et al., 2008; Ide, 2012) suggest fluid circulation at shallower depths but potential fluid paths are poorly documented. Here we obtained seismic observations from receiver functions that evidence the close association between the shallow tremor zone, electrical conductivity, and tectonic features of the Cascadia overriding plate. A seismic discontinuity near 15 km depth in the crust of the overriding North American plate is attributed to the Conrad discontinuity. This interface is segmented, and its interruption is spatially correlated with conductive regions and shallow swarms of seismicity and non-volcanic tremors. These observations suggest that shallow fluid circulation, tremors and seismicity are controlled by fault zones limiting blocks of accreted terranes in the overriding plate (Brudzinski and Allen, 2007). These zones constitute fluid "escape" routes that may contribute unloading fluid pressure on the megathrust. Obara, K. (2002). Science, 296, 1679-1681. Rogers, G., & Dragert, H. (2003). Science, 300, 1942-1943. Shelly, D. R., et al. (2006). Nature, 442, 188-191. La Rocca, M., et al. (2009). Science, 323, 620-623. Kao, H., et al. (2005). Nature, 436, 841-844. Payero, J. S., et al. (2008). Geophysical Research Letters, 35. Ide, S. (2012). Journal of Geophysical Research: Solid Earth, 117. Brudzinski, M. R., & Allen, R. M. (2007). Geology, 35, 907-910.
Geophysical and geochemical constraints on the geodynamic origin of the Vrancea Seismogenic Zone Romania

Science.gov (United States)

Fillerup, Melvin A.

The Vrancea Seismogenic Zone (VSZ) of Romania is a steeply NW-dipping volume (30 x 70 x 200 km) of intermediate-depth seismicity in the upper mantle beneath the bend zone of the Eastern Carpathians. The majority of tectonic models lean heavily on subduction processes to explain the Vrancea mantle seismicity and the presence of a Miocene age calc-alkaline volcanic arc in the East Carpathian hinterland. However, recent deep seismic reflection data collected over the Eastern Carpathian bend zone image an orogen lacking (1) a crustal root and (2) dipping crustal-scale fabrics routinely imaged in modern and ancient subduction zones. The DRACULA I and DACIA-PLAN deep seismic reflection profiles show that the East Carpathian orogen is supported by crust only 30-33 km thick while the Focsani basin (foreland) and Transylvanian basin (hinterland) crust is 42 km and 46 km thick respectively. Here the VSZ is interpreted as the former Eastern Carpathian orogenic root which was removed as a result of continental lithospheric delamination and is seismically foundering beneath the East Carpathian bend zone. Because large volumes of calc-alkaline volcanism are typically associated with subduction settings existing geochemical analyses from the Calimani, Gurghiu, and Harghita Mountains (CGH) have been reinterpreted in light of the seismic data which does not advocate the subduction of oceanic lithosphere. CGH rocks exhibit a compositional range from basalt to rhyolite, many with high-Mg# (Mg/Mg+Fe > 0.60), high-Sr (>1000 ppm), and elevated delta-O18 values (6-8.7 /) typical of arc lavas, and are consistent with mixing of mantle-derived melts with a crustal component. The 143Nd/144Nd (0.5123-0.5129) and 87Sr/86Sr (0.7040-0.7103) ratios similarly suggest mixing of mantle and crustal end members to obtain the observed isotopic compositions. A new geochemical model is presented whereby delamination initiates a geodynamic process like subduction but with the distinct absence of subducted

An Angus/Argo study of the neovolcanic zone along the East Pacific rise from the Clipperton fracture zone to 12°N

Science.gov (United States)

Uchupi, E.; Schwab, W. C.; Ballard, R. D.; Cheminee, J. L.; Francheteau, J.; Hekinian, R.; Blackman, D. K.; Sigurdsson, H.

1988-09-01

Still photographs and video images collected along the Neovolcanic Zone of the East Pacific Rise from 10°15'N to 11°53'N show that recent volcanic sheet flows, possibly less than 100 years old, are superimposed on an older sediment-laden pillow terrane. This recent activity is restricted to a narrow zone that crosses two topographic highs at 10°55'N and 11°26'N and diminishes along-axis away from these highs. The association of recent sheet flows with older flows and collapse structures on the overlapping spreading centers at 11°45'N supports the evolutionary model for the occurrence and evolution of overlapping spreading centers by MacDonald and others (1986, 1988).
An Angus/Argo study of the neovolcanic zone along the East Pacific rise from the Clipperton fracture zone to 12°N

Science.gov (United States)

Uchupi, E.; Schwab, W.C.; Ballard, Richard D.; Cheminee, J.L.; Francheteau, Jean; Hekinian, R.; Blackman, D.K.; Sigurdsson, Haraldur

1988-01-01

Still photographs and video images collected along the Neovolcanic Zone of the East Pacific Rise from 10°15′N to 11°53′N show that recent volcanic sheet flows, possibly less than 100 years old, are superimposed on an older sediment-laden pillow terrane. This recent activity is restricted to a narrow zone that crosses two topographic highs at 10°55′N and 11°26′N and diminishes along-axis away from these highs. The association of recent sheet flows with older flows and collapse structures on the overlapping spreading centers at 11°45′N supports the evolutionary model for the occurrence and evolution of overlapping spreading centers by MacDonald and others (1986, 1988).
NATO’s Northeastern Flank: Emerging Opportunities for Engagement

Science.gov (United States)

2017-01-01

escalation concerns. Engagement should also stress the importance of Polish support for and capabilities toward addressing NATO’s southern flank...in their response to the Ukraine crisis.8 Some countries are either cowed by the Russian threat or genuinely less concerned about it than might be...no small part due to Hungary’s dependence on Russian gas exports, which heat the homes of most Hungarians. It is also, however, due to political
Crustal deformation and volcanism at active plate boundaries

Science.gov (United States)

Geirsson, Halldor

Most of Earth's volcanoes are located near active tectonic plate boundaries, where the tectonic plates move relative to each other resulting in deformation. Likewise, subsurface magma movement and pressure changes in magmatic systems can cause measurable deformation of the Earth's surface. The study of the shape of Earth and therefore studies of surface deformation is called geodesy. Modern geodetic techniques allow precise measurements (˜1 mm accuracy) of deformation of tectonic and magmatic systems. Because of the spatial correlation between tectonic boundaries and volcanism, the tectonic and volcanic deformation signals can become intertwined. Thus it is often important to study both tectonic and volcanic deformation processes simultaneously, when one is trying to study one of the systems individually. In this thesis, I present research on crustal deformation and magmatic processes at active plate boundaries. The study areas cover divergent and transform plate boundaries in south Iceland and convergent and transform plate boundaries in Central America, specifically Nicaragua and El Salvador. The study is composed of four main chapters: two of the chapters focus on the magma plumbing system of Hekla volcano, Iceland and the plate boundary in south Iceland; one chapter focuses on shallow controls of explosive volcanism at Telica volcano, Nicaragua; and the fourth chapter focuses on co- and post-seismic deformation from a Mw = 7.3 earthquake which occurred offshore El Salvador in 2012. Hekla volcano is located at the intersection of a transform zone and a rift zone in Iceland and thus is affected by a combination of shear and extensional strains, in addition to co-seismic and co-rifting deformation. The inter-eruptive deformation signal from Hekla is subtle, as observed by a decade (2000-2010) of GPS data in south Iceland. A simultaneous inversion of this data for parameters describing the geometry and source characteristics of the magma chamber at Hekla, and
Volcanic Hazards in Site Evaluation for Nuclear Installations

Energy Technology Data Exchange (ETDEWEB)

NONE

2012-10-15

This publication provides comprehensive and updated guidance for site evaluation in relation to volcanic hazards. It includes recommendations on assessing the volcanic hazards at a nuclear installation site, in order to identify and characterize, in a comprehensive manner, all potentially hazardous phenomena that may be associated with future volcanic events. It describes how some of these volcanic phenomena may affect the acceptability of the selected site, resulting in exclusion of a site or determining the corresponding design basis parameters for the installation. This Safety Guide is applicable to both existing and new sites, and a graded approach is recommended to cater for all types of nuclear installations. Contents: 1. Introduction; 2. Overview of volcanic hazard assessment; 3. General recommendations; 4. Necessary information and investigations (database); 5. Screening of volcanic hazards; 6. Site specific volcanic hazard assessment; 7. Nuclear installations other than nuclear power plants; 8. Monitoring and preparation for response; 9. Management system for volcanic hazard assessment; Annex I: Volcanic hazard scenarios; Annex II: Worldwide sources of information.
Regional stratigraphy, sedimentology, and tectonic significance of Oligocene-Miocene sedimentary and volcanic rocks, northern Baja California, Mexico

Science.gov (United States)

Dorsey, Rebecca J.; Burns, Beverly

1994-01-01

to viscous sediment gravity flows. Deposits of the Comondú Formation thin and fine systematically westward, from proximal volcanic conglomerate and breccia with thin basalt and andesite flows in the east, to distal volcaniclastic fluvial sandstone in the west. These proximal—distal relationships help to define the location and paleogeography of active arc-flanking volcaniclastic alluvial aprons of the Miocene magmatic arc in northern Baja California. A substantial late Miocene drop in regional base level (relative sea level) is best attributed to regional uplift caused by the renewal of magmatic and thermal activity in northern Baja California, which has continued to the present day.
Human renin 5'-flanking DNA to nucleotide-2750.

Science.gov (United States)

Smith, D L; Jeyapalan, S; Lang, J A; Guo, X H; Sigmund, C D; Morris, B J

1995-01-01

Renin is one of the most important factors in blood pressure and electrolyte regulation in mammals and the renin locus has been implicated in hypertension. To assist studies of promoter control we therefore determined the 5'-flanking sequence of the human gene (REN) to residue -2750 relative to the transcription start site (+1). Sites of homology to consensus sequences for binding of trans-acting factors involved in transcriptional control of other genes were identified, and functionality for two of these (a CRE and Pit-1 site) have so far been demonstrated.
Petrology, Magnetic susceptibility, Tectonic setting and mineralization associated with Plutonic and Volcanic Rocks, Eastern Bajestan and Taherabad, Iran

Directory of Open Access Journals (Sweden)

Malihe Ghoorchi

2009-09-01

Full Text Available Study area is located in district of Bajestan and Ferdows cities, NE of Iran. Structurally, this area is part of Lut block. The oldest exposed rocks, to the north of intrusive rocks and in Eastern Bajestan, are meta-chert, slate, quartzite, thin-bedded crystalline limestone and meta-argillite. The sedimentary units are: Sardar Formation (Carboniferous, Jamal Formation (Permian, Sorkh Shale and Shotori Formations (Triassic, carbonateous rocks (Cretaceous and lithostratigraphically equivalent to Kerman conglomerate (Cretaceous-Paleocene are exposed in this area. Based on relative age, magmatism in eastern Bajestan and Taherabad started after Late Cretaceous and it has been active and repeated during Tertiary time. At least, three episodes of volcanic activities are recognized in this area. The first stage was mainly volcanic flow with mafic composition and minor intermediate. The second episode was mainly intermediate in composition. The third stage was changed to acid-intermediate in composition. Since the plutonic rocks intruded the volcanic rocks, therefore they may be Oligo-Miocene age. Bajestan intrusive rocks are granite-granodiorite-quartz monzonite. Taherabad intrusive rocks are diorite-quartz diorite- monzonite-latite. Bajestan intrusive rocks are reduced type (ilmenite series and Taherabad intrusive rocks are oxidized type (magnetite series.Based on geochemical analysis including trace elements, REE and isotopic data, Bajestan intrusive rocks formed in continental collision zone and the magma has crustal origin. Taherabad intrusive rocks were formed in subduction zone and magma originated from oceanic crust. Taherabad intrusive rock has exploration potential for Cu-Au and pb.
Dating and source determination of volcanic rocks from Khunik area (South of Birjand, South Khorasan using Rb-Sr and Sm-Nd isotopes

Directory of Open Access Journals (Sweden)

Somayeh Samiee

2016-12-01

Full Text Available The Khunik area is located in the south of Birjand, Khorasan province, in the eastern margin of Lut block. Tertiary volcanic rocks have andesite to trachy-andesite composition. Dating analyzing by Rb-Sr method on plagioclase and hornblende as well as whole-rock isochron method was performed on pyroxene-hornblende andesite rock unit. On this basis the emplacement age is Upper Paleocene (58±11 Ma. These rocks have initial 87Sr/86Sr and εNd 0.7046-0.7049 and 2.16-3.12, respectively. According to isotopic data, volcanic rocks originated from depleted mantle and have the least crust contamination while it was fractionated. Geochemically, Khunik volcanic rocks have features typical of calk-alkaline to shoshonite and are metaluminous. Enrichment in LILEs and typical negative anomalies of Nb and Ti are evidences that the volcanic rocks formed in a subduction zone and active continental margin. Modeling suggests that these rocks were derived dominantly from 1–5% partial melting of a mainly spinel garnet lherzolite mantle source that is metasomatized by slab-derived fluid.
Geologic Map of the Bodie Hills Volcanic Field, California and Nevada: Anatomy of Miocene Cascade Arc Magmatism in the Western Great Basin

Science.gov (United States)

John, D. A.; du Bray, E. A.; Blakely, R. J.; Box, S.; Fleck, R. J.; Vikre, P. G.; Rytuba, J. J.; Moring, B. C.

2011-12-01

The Bodie Hills Volcanic Field (BHVF) is a >700 km2, long-lived (~9 Ma) but episodic, Miocene eruptive center in the southern part of the ancestral Cascade magmatic arc. A 1:50,000-scale geologic map based on extensive new mapping, combined with 40Ar/39Ar dates, geochemical data, and detailed gravity and aeromagnetic surveys, defines late Miocene magmatic and hydrothermal evolution of the BHVF and contrasts the subduction-related BHVF with the overlying, post-subduction, bimodal Plio-Pleistocene Aurora Volcanic Field (AVF). Important features of the BHVF include: Eruptions occurred during 3 major eruptive stages: dominantly trachyandesite stratovolcanoes (~14.7 to 12.9 Ma), mixed silicic trachyandesite, dacite, and rhyolite (~11.3 to 9.6 Ma), and dominantly silicic trachyandesite to dacite domes (~9.2 to 8.0 Ma). Small rhyolite domes were emplaced at ~6 Ma. Trachyandesitic stratovolcanoes with extensive debris flow aprons form the outer part of BHVF, whereas silicic trachyandesite to rhyolite domes are more centrally located. Geophysical data suggest that many BHVF volcanoes have shallow plutonic roots that extend to depths ≥1-2 km below the surface, and much of the Bodie Hills may be underlain by low density plutons presumably related to BHVF volcanism. BHVF rocks contain ~50 to 78% SiO2 (though few rocks have Bodie Hills at ~10 Ma, but the composition and eruptive style of volcanism continued unchanged for 2 Ma. However, kinematic data for veins and faults in mining districts suggest a change in the stress field from transtensional to extensional approximately coincident with cessation of subduction. The Bodie Hills are flanked to the east, north, and west by sedimentary basins that began to form in the late Miocene (locally >11 Ma). Fine to coarse sedimentary deposits within the BHVF include stream deposits in channels that cut across the hills and were partly filled by ~9.4 Ma Eureka Valley Tuff erupted 20 km to the northwest. Shallow dips and preservation of
Magnocellular involvement in flanked-letter identification relates to the allocation of attention

NARCIS (Netherlands)

Omtzigt, D.; Hendriks, A.W.C.J.

2004-01-01

To verify the hypothesis that the magnocellular system is important to flanked-letter identification [Neuropsychologia 40 (2002) 1881] because it subserves attention allocation, we conducted three letter-naming experiments in which we manipulated magnocellular involvement (colour vs. luminance
Update of map the volcanic hazard in the Ceboruco volcano, Nayarit, Mexico

Science.gov (United States)

Suarez-Plascencia, C.; Camarena-Garcia, M. A.; Nunez-Cornu, F. J.

2012-12-01

The Ceboruco Volcano (21° 7.688 N, 104° 30.773 W) is located in the northwestern part of the Tepic-Zacoalco graben. Its volcanic activity can be divided in four eruptive cycles differentiated by their VEI and chemical variations as well. As a result of andesitic effusive activity, the "paleo-Ceboruco" edifice was constructed during the first cycle. The end of this cycle is defined by a plinian eruption (VEI between 3 and 4) which occurred some 1020 years ago and formed the external caldera. During the second cycle an andesitic dome built up in the interior of the caldera. The dome collapsed and formed the internal caldera. The third cycle is represented by andesitic lava flows which partially cover the northern and south-southwestern part of the edifice. The last cycle is represented by the andesitic lava flows of the nineteenth century located in the southwestern flank of the volcano. Actually, moderate fumarolic activity occurs in the upper part of the volcano showing temperatures ranging between 20° and 120°C. Some volcanic high frequency tremors have also been registered near the edifice. Shows the updating of the volcanic hazard maps published in 1998, where we identify with SPOT satellite imagery and Google Earth, change in the land use on the slope of volcano, the expansion of the agricultural frontier on the east sides of the Ceboruco volcano. The population inhabiting the area is 70,224 people in 2010, concentrated in 107 localities and growing at an annual rate of 0.37%, also the region that has shown an increased in the vulnerability for the development of economic activities, supported by highway, high road, railroad, and the construction of new highway to Puerto Vallarta, which is built in the southeast sector of the volcano and electrical infrastructure that connect the Cajon and Yesca Dams to Guadalajara city. The most important economic activity in the area is agriculture, with crops of sugar cane (Saccharum officinarum), corn, and jamaica
Neotectonics of Graciosa island (Azores: a contribution to seismic hazard assessment of a volcanic area in a complex geodynamic setting

Directory of Open Access Journals (Sweden)

Ana Hipólito

2014-02-01

Full Text Available Graciosa is a mid-Pleistocene to Holocene volcanic island that lies in a complex plate boundary between the North American, Eurasian, and Nubian plates. Large fault scarps displace the oldest (Middle Pleistocene volcanic units, but in the younger areas recent volcanism (Holocene to Upper Pleistocene conceals the surface expression of faulting, limiting neotectonic observations. The large displacement accumulated by the older volcanic units when compared with the younger formations suggests a variability of deformation rates and the possibility of alternating periods of higher and lower tectonic deformation rates; this would increase the recurrence interval of surface rupturing earthquakes. Nevertheless, in historical times a few destructive earthquakes affected the island attesting for its seismic hazard. Regarding the structural data, two main fault systems, incompatible with a single stress field, were identified at Graciosa Island. Thus, it is proposed that the region is affected by two alternating stress fields. The stress field #1 corresponds to the regional stress regime proposed by several authors for the interplate shear zone that constitutes the Azorean segment of the Eurasia-Nubia plate boundary. It is suggested that the stress field #2 will act when the area under the influence of the regional stress field #1 narrows as a result of variations in the differential spreading rates north and south of Azores. The islands closer to the edge of the sheared region will temporarily come under the influence of a different (external stress field (stress field #2. Such data support the concept that, in the Azores, the Eurasia-Nubia boundary corresponds to a complex and wide deformation zone, variable in time.
Characterisation of Cements From Dominantly Volcanic Raw Materials of the Carpathian Bend Zone

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Halmagy Timea

2016-12-01

Full Text Available This paper presents the results of laboratory investigations regarding the production of cements from local raw materials, such as limestone from Varghis, gypsum from Nucsoara, basaltic scoria from Racosul de Jos, volcanic tuff from Racosul de Sus, diatomite from Filia, and red mud from Oradea. The raw mixtures, based on modified Bogue calculations, contain limestone, gypsum, and one or two of the above-mentioned materials. The cements resulted from clinker grinding in a laboratory gas furnace at 1260-1300 °C, with one hour at the peak temperatures, and were characterised for Blaine specific surface area, specific density, and mineral phases. Physico-mechanical properties, such as water content for normal consistency, setting time, soundness, and compressive strength were also determined. Results show that these cements contain belite, ferrite, calcium sulphoaluminate, anhydrite, and some minor compounds.
A porous flow model of flank eruptions on Mt. Etna: second-order perturbation theory

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N. Cenni

1997-06-01

Full Text Available A porous flow model for magma migration from a deep source within a volcanic edifice is developed. The model is based on the assumption that an isotropic and homogeneous system of fractures allows magma migration from one localized feeding dyke up to the surface of the volcano. The maximum level that magma can reach within the volcano (i.e., the «free surface» of magma, where fluid pressure equals the atmospheric pressure is reproduced through a second-order perturbation approach to the non-linear equations governing the migration of incompressible fluids through a porous medium. The perturbation parameter is found to depend on the ratio of the volumic discharge rate at the source (m3/s divided by the product of the hydraulic conductivity of the medium (m1/s times the square of the source depth. The second-order corrections for the free surface of Mt. Etna are found to be small but not negligible; from the comparison between first-order and second-order free surfaces it appears that the former is higher near the summit, slightly lower at intermediate altitudes and slightly higher far away from the axis of the volcano. Flank eruptions in the southern sector are found to be located in regions where the topography is actually lower than the theoretical free surface of magma. In this sector, modulations in the eruption site density correlate well with even minor differences between free surface and topography. In the northern and western sectors similar good fits are found, while the NE rift and the eastern sector seem to require mechanisms or structures respectively favouring and inhibiting magma migration.
Arsenic speciation and trace element analysis of the volcanic río Agrio and the geothermal waters of Copahue, Argentina

International Nuclear Information System (INIS)

Farnfield, Hannah R.; Marcilla, Andrea L.; Ward, Neil I.

2012-01-01

Surface water originating from the Copahue volcano crater-lake was analysed for total arsenic and four arsenic species: arsenite (iAs III ), arsenate (iAs V ), monomethylarsonic acid (MA V ) and dimethylarsinic acid (DMA V ) and other trace elements (Fe, Mn, V, Cr, Ni, Zn). A novel in-field technique for the preconcentration and separation of four arsenic species was, for the first time, used for the analysis of geothermal and volcanic waters. Total arsenic levels along the río Agrio ranged from T . The highest arsenic levels were recorded in the el Vertedero spring (3783 μg/l As T ) on the flank of the Copahue volcano, which feeds the acidic río Agrio. Arsenite (H 3 AsO 3 ) predominated along the upper río Agrio (78.9–81.2% iAs III ) but the species distribution changed at lago Caviahue and arsenate (H 2 AsO 4 − ) became the main species (51.4–61.4% iAs V ) up until Salto del Agrio. The change in arsenic species is potentially a result of an increase in redox potential and the formation of iron-based precipitates. Arsenic speciation showed a statistically significant correlation with redox potential (r = 0.9697, P = 0.01). Both total arsenic and arsenic speciation displayed a statistically significant correlation with vanadium levels along the river (r = 0.9961, P = 0.01 and r = 0.8488, P = 0.05, respectively). This study highlights that chemical speciation analysis of volcanic waters is important in providing ideas on potential chemical toxicity. Furthermore there is a need for further work evaluating how arsenic (and other trace elements), released in volcanic and geothermal streams/vents, impacts on both biota and humans (via exposure in thermal pools or consuming commercial drinking water). -- Highlights: ► Application of a novel field-based method for the separation of arsenic species in a volcanic surface water system. ► First arsenic speciation data for volcanic systems in the Andes (iAs V , iAs III , MA V , DMA V ). ► Total arsenic levels
Biophysical properties of regions flanking the bHLH-Zip motif in the p22 Max protein

International Nuclear Information System (INIS)

Pursglove, Sharon E.; Fladvad, Malin; Bellanda, Massimo; Moshref, Ahmad; Henriksson, Marie; Carey, Jannette; Sunnerhagen, Maria

2004-01-01

The Max protein is the central dimerization partner in the Myc-Max-Mad network of transcriptional regulators, and a founding structural member of the family of basic-helix-loop-helix (bHLH)-leucine zipper (Zip) proteins. Biologically important regions flanking its bHLH-Zip motif have been disordered or absent in crystal structures. The present study shows that these regions are resistant to proteolysis in both the presence and absence of DNA, and that Max dimers containing both flanking regions have significantly higher helix content as measured by circular dichroism than that predicted from the crystal structures. Nuclear magnetic resonance measurements in the absence of DNA also support the inferred structural order. Deletion of both flanking regions is required to achieve maximal DNA affinity as measured by EMSA. Thus, the previously observed functionalities of these Max regions in DNA binding, phosphorylation, and apoptosis are suggested to be linked to structural properties
Project Title: Geothermal Play Fairway Analysis of Potential Geothermal Resources in NE California, NW Nevada, and Southern Oregon: A Transition between Extension$-$Hosted and Volcanically$-$Hosted Geothermal Fields

Energy Technology Data Exchange (ETDEWEB)

McClain, James S. [Univ. of California, Davis, CA (United States). Dept. of; Dobson, Patrick [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Glassley, William [Univ. of California, Davis, CA (United States). Dept. of Earth and Planetary Sciences; Schiffman, Peter [Univ. of California, Davis, CA (United States). Dept. of Earth and Planetary Sciences; Zierenberg, Robert [Univ. of California, Davis, CA (United States). Dept. of Earth and Planetary Sciences; Zhang, Yingqi [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Conrad, Mark [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Siler, Drew [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Gasperikova, Erika [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Spycher, Nicolas F. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

2016-09-30

Final report for the UCD-LBNL effort to apply Geothermal Play Fairway Analysis to a transition zone between a volcanically-hosted and extensionally-hosted geothermal. The project focusses on the geothermal resources in northeastern California.
The origin of Mauna Loa's Nīnole Hills: Evidence of rift zone reorganization

Science.gov (United States)

Zurek, Jeffrey; Williams-Jones, Glyn; Trusdell, Frank A.; Martin, Simon

2015-01-01

In order to identify the origin of Mauna Loa volcano's Nīnole Hills, Bouguer gravity was used to delineate density contrasts within the edifice. Our survey identified two residual anomalies beneath the Southwest Rift Zone (SWRZ) and the Nīnole Hills. The Nīnole Hills anomaly is elongated, striking northeast, and in inversions both anomalies merge at approximately −7 km above sea level. The positive anomaly, modeled as a rock volume of ~1200 km3 beneath the Nīnole Hills, is associated with old eruptive vents. Based on the geologic and geophysical data, we propose that the gravity anomaly under the Nīnole Hills records an early SWRZ orientation, now abandoned due to geologically rapid rift-zone reorganization. Catastrophic submarine landslides from Mauna Loa's western flank are the most likely cause for the concurrent abandonment of the Nīnole Hills section of the SWRZ. Rift zone reorganization induced by mass wasting is likely more common than currently recognized.
Hazard map for volcanic ballistic impacts at El Chichón volcano (Mexico)

Science.gov (United States)

Alatorre-Ibarguengoitia, Miguel; Ramos-Hernández, Silvia; Jiménez-Aguilar, Julio

2014-05-01

The 1982 eruption of El Chichón Volcano in southeastern Mexico had a strong social and environmental impact. The eruption resulted in the worst volcanic disaster in the recorded history of Mexico, causing about 2,000 casualties, displacing thousands, and producing severe economic losses. Even when some villages were relocated after the 1982 eruption, many people still live and work in the vicinities of the volcano and may be affected in the case of a new eruption. The hazard map of El Chichón volcano (Macías et al., 2008) comprises pyroclastic flows, pyroclastic surges, lahars and ash fall but not ballistic projectiles, which represent an important threat to people, infrastructure and vegetation in the case of an eruption. In fact, the fatalities reported in the first stage of the 1982 eruption were caused by roof collapse induced by ashfall and lithic ballistic projectiles. In this study, a general methodology to delimit the hazard zones for volcanic ballistic projectiles during volcanic eruptions is applied to El Chichón volcano. Different scenarios are defined based on the past activity of the volcano and parameterized by considering the maximum kinetic energy associated with ballistic projectiles ejected during previous eruptions. A ballistic model is used to reconstruct the "launching" kinetic energy of the projectiles observed in the field. The maximum ranges expected for the ballistics in the different explosive scenarios defined for El Chichón volcano are presented in a ballistic hazard map which complements the published hazard map. These maps assist the responsible authorities to plan the definition and mitigation of restricted areas during volcanic crises.

Impact of Tropical Volcanic Eruptions on Hadley Circulation Using a High-Resolution AGCM

KAUST Repository

Dogar, Muhammad Mubashar

2018-03-31

The direct radiative effects of volcanic eruptions resulting in solar dimming, stratospheric warming, global surface cooling and reduction in rainfall are well documented. However, eruptions also cause indirect climatic impacts that are not well understood. For example, solar dimming induced by volcanic aerosols could cause changes in tropical Hadley circulation that in turn largely affect evaporation and precipitation patterns. Therefore, understanding the sensitivity of HC to volcanism is essential, as this circulation is directly related to precipitation changes in the tropics and with other large-scale circulations. Hence, to better understand the post-eruption sensitivity of HC and associated changes in the hydrologic cycle, simulations for the El Chichón and Pinatubo tropical eruptions were conducted using a high-resolution atmospheric model (HIRAM), effectively at 25 and 50 km grid spacing. The model simulated results are then compared with observational and reanalysis products. Both the model and observational analysis show posteruption weakening, shrinking and equatorward displacement of the updraft branch of HC caused by the equatorward shift of midlatitude jets and hemispheric land-sea thermal gradient. The Intertropical Convergence Zone (ITCZ) is tightly coupled to the rising branch of HC, hence, post-eruption weakening and equatorward displacement of HC cause weakening of ITCZ that adversely affects rainfall distribution in the monsoon-fed regions, especially the South Asian and African tropical rain-belt regions. The modelproduced post-eruption distribution of cloud contents suggests a southward shift of ITCZ. The HIRAM results are largely in agreement with the reanalysis, observations and previous studies indicating that this model performs reasonably well in reproducing the global and regional-scale dynamic changes caused by volcanic radiative forcing.
Impact of Tropical Volcanic Eruptions on Hadley Circulation Using a High-Resolution AGCM

KAUST Repository

Dogar, Muhammad Mubashar

2018-01-01

The direct radiative effects of volcanic eruptions resulting in solar dimming, stratospheric warming, global surface cooling and reduction in rainfall are well documented. However, eruptions also cause indirect climatic impacts that are not well understood. For example, solar dimming induced by volcanic aerosols could cause changes in tropical Hadley circulation that in turn largely affect evaporation and precipitation patterns. Therefore, understanding the sensitivity of HC to volcanism is essential, as this circulation is directly related to precipitation changes in the tropics and with other large-scale circulations. Hence, to better understand the post-eruption sensitivity of HC and associated changes in the hydrologic cycle, simulations for the El Chichón and Pinatubo tropical eruptions were conducted using a high-resolution atmospheric model (HIRAM), effectively at 25 and 50 km grid spacing. The model simulated results are then compared with observational and reanalysis products. Both the model and observational analysis show posteruption weakening, shrinking and equatorward displacement of the updraft branch of HC caused by the equatorward shift of midlatitude jets and hemispheric land-sea thermal gradient. The Intertropical Convergence Zone (ITCZ) is tightly coupled to the rising branch of HC, hence, post-eruption weakening and equatorward displacement of HC cause weakening of ITCZ that adversely affects rainfall distribution in the monsoon-fed regions, especially the South Asian and African tropical rain-belt regions. The modelproduced post-eruption distribution of cloud contents suggests a southward shift of ITCZ. The HIRAM results are largely in agreement with the reanalysis, observations and previous studies indicating that this model performs reasonably well in reproducing the global and regional-scale dynamic changes caused by volcanic radiative forcing.
Tectonic implications of the contrasting geochemistry of Damaran mafic volcanic rocks, South West Africa

International Nuclear Information System (INIS)

Miller, R.McG.

1983-01-01

Ortho-amphibolites occur in the southern and central parts of the north-east-trending branch of the Damara Orogen. The Matchless Member amphibolites are interbedded with quartzose mica schist. Mobility of Si, ΣFe, Mn, Mg, Ca, Na, K, P, CO 2 , H 2 O, Rb, Ba, Sr and possibly LREE and immobility of Co, V, Sc, Ga, Zr, Nb, Y and HREE are indicated during metamorphism and reaction with country rock. Central Zone amphibolites are alkaline. The stratigraphically lower amphibolites have a within-plate chemistry; their distribution and associated rock types indicate a continental origin. The Matchless amphibolites have an ocean-floor chemistry. The Damaran sedimentary and orogenic cycle was initiated by continental rifting in three parallel zones in which alkaline acid volcanics occur locally. Widespread subsidence of the rift zones and the intervening areas followed and led to deposition of carbonate and clastic rocks under shallow marine conditions. During renewed rifting, submarine, alkaline basic lavas were extruded. The Southern Margin Zone amphibolites are interbedded with continental slope mixtites and continental rise deep-water fans. Spreading led to continental breakup and the formation of oceanic crust
Petrology and geochemistry of volcanic rocks of Cheshmeh Khuri and Shekasteh Sabz areas, Khur, northwest of Birjand

Directory of Open Access Journals (Sweden)

Maryam Javidi Moghaddam

2016-09-01

Full Text Available Khur area is located in east of Iran and northwest of Birjand. The area comprises outcrops of Eocene to Oligocene volcanics with basaltic andesite to rhyolite composition, which were intruded by subvolcanic and intrusive bodies of granodiorite to gabbro. In the present work, petrogenesis of volcanic units in Cheshmeh Khuri and Shekasteh Sabz areas was studied, which are located in Khur area and these volcanics have most widespread in them. Rhyolite, dacite, andesite, trachyandesite and basaltic andesite units in Cheshmeh Khuri and trachyandesite unit in Shekasteh Sabz were identified. The main textures of these units are porphyritic, hialoporphyritic and microlitic and plagioclase, pyroxene, K-feldspar, hornblende, biotite and quartz are the main minerals. Volcanic units of Cheshmeh Khuri have characteristic of high-K Calc-alkaline. Enrichment of LREE relative to HREE and LILE to HFSE are important evidences that magma was formed in a magmatic belt of a subduction zone. Based on the initial 87Sr/86Sr of andesite and dacite, their magma has originated from partial melting of an enriched mantle and contaminated with the crust through its differentiation. Trachyandesites of Shekaste Sabz have characteristic of shoshonitic nature. These units are characterized by high FeOt/FeOt+MgO, K2O/Na2O and Zr>360 ppm, Y>39 ppm, and Ce> 100 ppm. Also, they are enrichment in REE particularly in LREE, depletion of Eu, strong enrichment in HFSE, and depletion in Ba and Sr. Therefore, trachyandesites of Shekaste Sabz belong to post collision volcanics.
How 210Pb dating gives information about volcanic radionuclides

International Nuclear Information System (INIS)

Whitehead, N.E.

1998-01-01

In lake sediments from the Taupo Volcanic Zone, the 1886 Tarawera tephra is often observed. The tephra contains unsupported 210 Pb which corresponds to its stratigraphic age, and shows that the 210 Pb has been adsorbed in its passage through the air, but not from the volatiles in the volcano itself which would be expected to contain the radionuclide. It is shown that only a small portion of the available 210 Pb in normal air was scavenged by the tephra. Sedimentation rates derived using the tephra were similar to those from 210 Pb dating. Some lakes showed excess 210 Pb inventories, ascribed to lake-bed geothermal activity. Contrary to expectation of increased erosion following deposition of an ash layer, sedimentation rates were less
The use of tree-rings and foliage as an archive of volcanogenic cation deposition

Energy Technology Data Exchange (ETDEWEB)

Watt, Sebastian F.L. [Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ (United Kingdom)]. E-mail: sebastian.watt@earth.ox.ac.uk; Pyle, David M. [Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ (United Kingdom); Mather, Tamsin A. [Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ (United Kingdom); Day, Jason A. [Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ (United Kingdom); Aiuppa, Alessandro [CFTA - Dipt. Chimica e Fisica della Terra e Applicazioni alle Georisorse, Universita degli Studi di Palermo, Via Archirafi 36, 90123 (Italy)

2007-07-15

Tree cores (Pinus nigra ssp. laricio) and leaves (Castanea sativa) from the flanks of Mount Etna, Sicily were analysed by ICP-MS to investigate whether volcanogenic cations within plant material provide an archive of a volcano's temporal and spatial depositional influence. There is significant compositional variability both within and between trees, but no systematic dendrochemical correlation with periods of effusive, explosive or increased degassing activity. Dendrochemistry does not provide a record of persistent but fluctuating volcanic activity. Foliar levels of bioaccumulated cations correspond to modelled plume transport patterns, and map short-term volcanic fumigation. Around the flanks of the volcano foliar variation is greater for volatile cations (Cs, Cd, Pb) than for lithophilic cations (Ba, Sr), consistent with trace-metal supply from volcanic aerosol during quiescent periods. - Dendrochemistry does not provide an archive of persistent volcanic activity.
The use of tree-rings and foliage as an archive of volcanogenic cation deposition

International Nuclear Information System (INIS)

Watt, Sebastian F.L.; Pyle, David M.; Mather, Tamsin A.; Day, Jason A.; Aiuppa, Alessandro

2007-01-01

Tree cores (Pinus nigra ssp. laricio) and leaves (Castanea sativa) from the flanks of Mount Etna, Sicily were analysed by ICP-MS to investigate whether volcanogenic cations within plant material provide an archive of a volcano's temporal and spatial depositional influence. There is significant compositional variability both within and between trees, but no systematic dendrochemical correlation with periods of effusive, explosive or increased degassing activity. Dendrochemistry does not provide a record of persistent but fluctuating volcanic activity. Foliar levels of bioaccumulated cations correspond to modelled plume transport patterns, and map short-term volcanic fumigation. Around the flanks of the volcano foliar variation is greater for volatile cations (Cs, Cd, Pb) than for lithophilic cations (Ba, Sr), consistent with trace-metal supply from volcanic aerosol during quiescent periods. - Dendrochemistry does not provide an archive of persistent volcanic activity
Earth's Largest Terrestrial Landslide (The Markagunt Gravity Slide of Southwest Utah): Insights from the Catastrophic Collapse of a Volcanic Field

Science.gov (United States)

Hacker, D. B.; Biek, R. F.; Rowley, P. D.

2015-12-01

The newly discovered Miocene Markagunt gravity slide (MGS; Utah, USA) represents the largest volcanic landslide structure on Earth. Recent geologic mapping of the MGS indicates that it was a large contiguous volcanic sheet of allochthonous andesitic mudflow breccias and lava flows, volcaniclastic rocks, and intertonguing regional ash-flow tuffs that blanketed an area of at least 5000 km2 with an estimated volume of ~3000 km3. From its breakaway zone in the Tushar and Mineral Mountains to its southern limits, the MGS is over 95 km long and at least 65 km wide. The MGS consists of four distinct structural segments: 1) a high-angle breakaway segment, 2) a bedding-plane segment, ~60 km long and ~65 km wide, typically located within the volcaniclastic Eocene-Oligocene Brian Head Formation, 3) a ramp segment ~1-2 km wide where the slide cuts upsection, and 4) a former land surface segment where the upper-plate moved at least 35 km over the Miocene landscape. The presence of basal and lateral cataclastic breccias, clastic dikes, jigsaw puzzle fracturing, internal shears, pseudotachylytes, and the overall geometry of the MGS show that it represents a single catastrophic emplacement event. The MGS represents gravitationally induced collapse of the southwest sector of the Oligocene to Miocene Marysvale volcanic field. We suggest that continuous growth of the Marysvale volcanic field, loading more volcanic rocks on a structurally weak Brian Head basement, created conditions necessary for gravity sliding. In addition, inflation of the volcanic pile due to multiple magmatic intrusions tilted the strata gently southward, inducing lateral spreading of the sub-volcanic rocks prior to failure. Although similar smaller-scale failures have been recognized from individual volcanoes, the MGS represents a new class of low frequency but high impact hazards associated with catastrophic sector collapse of large volcanic fields containing multiple volcanoes. The relationship of the MGS to
Magmatic evolution of Panama Canal volcanic rocks: A record of arc processes and tectonic change.

Directory of Open Access Journals (Sweden)

David W Farris

Full Text Available Volcanic rocks along the Panama Canal present a world-class opportunity to examine the relationship between arc magmatism, tectonic forcing, wet and dry magmas, and volcanic structures. Major and trace element geochemistry of Canal volcanic rocks indicate a significant petrologic transition at 21-25 Ma. Oligocene Bas Obispo Fm. rocks have large negative Nb-Ta anomalies, low HREE, fluid mobile element enrichments, a THI of 0.88, and a H2Ocalc of >3 wt. %. In contrast, the Miocene Pedro Miguel and Late Basalt Fm. exhibit reduced Nb-Ta anomalies, flattened REE curves, depleted fluid mobile elements, a THI of 1.45, a H2Ocalc of <1 wt. %, and plot in mid-ocean ridge/back-arc basin fields. Geochemical modeling of Miocene rocks indicates 0.5-0.1 kbar crystallization depths of hot (1100-1190°C magmas in which most compositional diversity can be explained by fractional crystallization (F = 0.5. However, the most silicic lavas (Las Cascadas Fm. require an additional mechanism, and assimilation-fractional-crystallization can reproduce observed compositions at reasonable melt fractions. The Canal volcanic rocks, therefore, change from hydrous basaltic pyroclastic deposits typical of mantle-wedge-derived magmas, to hot, dry bi-modal magmatism at the Oligocene-Miocene boundary. We suggest the primary reason for the change is onset of arc perpendicular extension localized to central Panama. High-resolution mapping along the Panama Canal has revealed a sequence of inward dipping maar-diatreme pyroclastic pipes, large basaltic sills, and bedded silicic ignimbrites and tuff deposits. These volcanic bodies intrude into the sedimentary Canal Basin and are cut by normal and subsequently strike-slip faults. Such pyroclastic pipes and basaltic sills are most common in extensional arc and large igneous province environments. Overall, the change in volcanic edifice form and geochemistry are related to onset of arc perpendicular extension, and are consistent with the
Quantifying the Plutonic to Volcanic Relationship Along the Puna Plateau: Implications for Cordilleran Plateau Evolution

Science.gov (United States)

Ward, K. M.; Delph, J. R.; Zandt, G.; Beck, S. L.; Ducea, M. N.

2016-12-01

Quantifying well constrained plutonic to volcanic (P:V) ratios is inherently difficult because the tectonic processes that exhume intrusive bodies rarely preserve their extrusive equivalents. Conversely, active magmatic systems that have well-preserved volcanic deposits require sophisticated geophysical or geochemical approaches to estimate their plutonic roots and even when these sophisticated approaches are available, it is not always clear what constitutes a plutonic volume. Further complicating the enigmatic plutonic to volcanic relationship is the highly episodic nature of pluton emplacement where magmatic flare-ups produce several orders of magnitude more magmatism when compared against magmatic lulls. Despite this inherent difficulty, a growing body of independently measured P:V ratios (e.g. seismic tomography, geomorphic modeling, geological mapping/dating, and Zircon age spectra modeling) suggests the contribution of magmatic addition as an uplift mechanism in Cordilleran systems is much larger than is currently accepted. However, it remains unclear if these studies can be generalized to represent type behavior in Cordilleran systems or result from the non-uniform sampling imposed by the ability to measure large P:V ratios in only a few select and potentially anomalous regions of the American Cordillera. To better examine the role of magmatic processes in building Cordilleran high plateaus, we image the crustal seismic shear-wave velocity for an 800 km section (20.5°-28°S) of the active South American Cordillera (Puna Plateau). When placed in the context of existing geological and geophysical datasets, our seismic model reveals numerous mid-crustal low-velocity zones that we unambiguously interpret as the plutonic underpinnings associated with the voluminous silicic volcanics of the Puna Plateau. These larger P:V ratios are consistent with recent thermomechanical modeling of granitic magma intrusions that support the existence of long-lived, partially
Magmatic evolution of Panama Canal volcanic rocks: A record of arc processes and tectonic change

Science.gov (United States)

Cardona, Agustin; Montes, Camilo; Foster, David; Jaramillo, Carlos

2017-01-01

Volcanic rocks along the Panama Canal present a world-class opportunity to examine the relationship between arc magmatism, tectonic forcing, wet and dry magmas, and volcanic structures. Major and trace element geochemistry of Canal volcanic rocks indicate a significant petrologic transition at 21–25 Ma. Oligocene Bas Obispo Fm. rocks have large negative Nb-Ta anomalies, low HREE, fluid mobile element enrichments, a THI of 0.88, and a H2Ocalc of >3 wt. %. In contrast, the Miocene Pedro Miguel and Late Basalt Fm. exhibit reduced Nb-Ta anomalies, flattened REE curves, depleted fluid mobile elements, a THI of 1.45, a H2Ocalc of arc basin fields. Geochemical modeling of Miocene rocks indicates 0.5–0.1 kbar crystallization depths of hot (1100–1190°C) magmas in which most compositional diversity can be explained by fractional crystallization (F = 0.5). However, the most silicic lavas (Las Cascadas Fm.) require an additional mechanism, and assimilation-fractional-crystallization can reproduce observed compositions at reasonable melt fractions. The Canal volcanic rocks, therefore, change from hydrous basaltic pyroclastic deposits typical of mantle-wedge-derived magmas, to hot, dry bi-modal magmatism at the Oligocene-Miocene boundary. We suggest the primary reason for the change is onset of arc perpendicular extension localized to central Panama. High-resolution mapping along the Panama Canal has revealed a sequence of inward dipping maar-diatreme pyroclastic pipes, large basaltic sills, and bedded silicic ignimbrites and tuff deposits. These volcanic bodies intrude into the sedimentary Canal Basin and are cut by normal and subsequently strike-slip faults. Such pyroclastic pipes and basaltic sills are most common in extensional arc and large igneous province environments. Overall, the change in volcanic edifice form and geochemistry are related to onset of arc perpendicular extension, and are consistent with the idea that Panama arc crust fractured during collision
The geochemistry of lithium-bearing geothermal water, Taupo Volcanic Zone, and shallow fluid processes in a very active silicic volcanic arc

Science.gov (United States)

Dean, A. S.; Hoskin, P. W.; Rudnick, R. L.; Liu, X.; Boseley, C.

2011-12-01

The Li abundances and isotopic systematics of Taupo Volcanic Zone (TVZ) geothermal fluids preserves a record of processes occurring within shallow portions of geothermal reservoirs as well as deeper portions of the arc crust. Understanding Li cycling and isotopic fractionation in TVZ geothermal systems contributes to a more refined understanding of physicochemical processes affecting New Zealand's geothermal resources. A comprehensive dataset of 73 samples was compiled, with samples collected from geothermal surface features (springs, spouters, geysers, etc.) and electric-power industry production wells, collectively representing18 geothermal fields across the breadth and width the TVZ. No comparable dataset of fluid analyses exists. Ion chromatography, AAS, and quadrupole ICP-MS analyses were done for Li, Cl-, SiO2, SO42- K, Na, Ca, Mg, B, Sr and Pb concentrations. Lithium abundance in geothermal fluids from the TVZ have a dataset-wide average of 5.9 mg/L and range 4 μg/L to 29 mg/L. The Li abundance and Li/Cl ratios for geothermal water and steam condensates vary systematically as a result of boiling, mixing, and water/rock reaction. Lithium abundance and Li/Cl ratios are, therefore, indicators of shallow (above 2.5 km) and locally variable reservoir processes. δ7Li analysis of 63 samples was performed at the University of Maryland, College Park. Data quality was controlled by measurement of L-SVEC as a calibration standard and by multiple analysis of selected samples. The average δ7Li value for TVZ geothermal fluids is -0.8%. Most δ7Li values for geothermal water fall within a small range of about -3% to+2% indicating similar processes are causing similar isotopic fractionation throughout the region. Considered together, Li aundances and δ7Li values, in combination with numerical models, indicate possible evolution pathways and water/rock reactions in TVZ geothermal systems. Models based on rocks and surface water analysis indicate that Li cycles and
Drilling into Rhyolitic Magma at Shallow depth at Krafla Volcanic Complex, NE-Iceland

Science.gov (United States)

Mortensen, A. K.; Markússon, S. H.; Gudmundsson, Á.; Pálsson, B.

2017-12-01

Krafla volcanic complex in NE-Iceland is an active volcano but the latest eruption was the Krafla Fires in 1975-1984. Though recent volcanic activity has consisted of basaltic fissure eruptions, then it is rhyolitic magma that has been intercepted on at least two occasions while drilling geothermal production wells in the geothermal field suggesting a layered magma plumbing system beneath the Krafla volcanic complex. In 2008 quenched rhyolitic glass was retrieved from the bottom of well KJ-39, which is 2865 m deep ( 2571 m true vertical depth). In 2009 magma was again encountered at an even shallower depth and in more than 2,5 km distance from the bottom of well KJ-39, but in 2009 well IDDP-1 was drilled into magma three times just below 2100 m depth. Only on the last occasion was quenched glass retrieved to confirm that magma had been encountered. In well KJ-39 the quenched glass was rhyolitic in composition. The glass contained resorbed minerals of plagioclase, clinopyroxene and titanomagnetite, but the composition of the glass resembles magma that has formed by partial melting of hydrated basalt. The melt was encountered among cuttings from impermeable, coarse basaltic intrusives at a depth, where the well was anticipated to penetrate the Hólseldar volcanic fissure. In IDDP-1 the quenched glass was also rhyolitic in composition. The glass contained less than 5% of phenocrysts, but the phenocryst assemblage included andesine plagioclase, augite, pigeonite, and titanomagnetite. At IDDP-1 the melt was encountered below a permeable zone composed of fine to coarse grained felsite and granophyre. The disclosure of magma in two wells at Krafla volcanic complex verify that rhyolitic magma can be encountered at shallow depth across a larger area within the caldera. The encounter of magma at shallow depth conforms with that superheated conditions have been found at >2000 m depth in large parts of Krafla geothermal field.
Hierarchical probabilistic regionalization of volcanism for Sengan region in Japan using multivariate statistical techniques and geostatistical interpolation techniques

International Nuclear Information System (INIS)

Park, Jinyong; Balasingham, P.; McKenna, Sean Andrew; Kulatilake, Pinnaduwa H. S. W.

2004-01-01

Sandia National Laboratories, under contract to Nuclear Waste Management Organization of Japan (NUMO), is performing research on regional classification of given sites in Japan with respect to potential volcanic disruption using multivariate statistics and geo-statistical interpolation techniques. This report provides results obtained for hierarchical probabilistic regionalization of volcanism for the Sengan region in Japan by applying multivariate statistical techniques and geostatistical interpolation techniques on the geologic data provided by NUMO. A workshop report produced in September 2003 by Sandia National Laboratories (Arnold et al., 2003) on volcanism lists a set of most important geologic variables as well as some secondary information related to volcanism. Geologic data extracted for the Sengan region in Japan from the data provided by NUMO revealed that data are not available at the same locations for all the important geologic variables. In other words, the geologic variable vectors were found to be incomplete spatially. However, it is necessary to have complete geologic variable vectors to perform multivariate statistical analyses. As a first step towards constructing complete geologic variable vectors, the Universal Transverse Mercator (UTM) zone 54 projected coordinate system and a 1 km square regular grid system were selected. The data available for each geologic variable on a geographic coordinate system were transferred to the aforementioned grid system. Also the recorded data on volcanic activity for Sengan region were produced on the same grid system. Each geologic variable map was compared with the recorded volcanic activity map to determine the geologic variables that are most important for volcanism. In the regionalized classification procedure, this step is known as the variable selection step. The following variables were determined as most important for volcanism: geothermal gradient, groundwater temperature, heat discharge, groundwater
The Massive Compound Cofre de Perote Shield Volcano: a Volcanological Oddity in the Eastern Mexican Volcanic Belt

Science.gov (United States)

Siebert, L.; Carrasco-Nunez, G.; Diaz-Castellon, R.; Rodriguez, J. L.

2007-12-01

Cofre de Perote volcano anchors the northern end of the easternmost of several volcanic chains orthogonal to the E-W trend of the Mexican Volcanic Belt (MVB). Its structure, geochemistry, and volcanic history diverge significantly from that of the large dominantly andesitic stratovolcanoes that have been the major focus of research efforts in the MVB. Andesitic-trachyandesitic to dacitic-trachydacitic effusive activity has predominated at Cofre de Perote, forming a massive low-angle compound shield volcano that dwarfs the more typical smaller shield volcanoes of the central and western MVB. The 4282-m-high volcano overlooking Xalapa, the capital city of the State of Veracruz, has a diameter of about 30 km and rises more than 3000 m above the coastal plain to the east. Repeated edifice collapse has left massive horseshoe-shaped scarps that truncate the eastern side of the edifice. Five major evolutionary stages characterize the growth of this compound volcano: 1) emplacement of a multiple-vent dome complex forming the basal structure of Cofre de Perote around 1.9-1.3 Ma; 2) construction of the basal part of the compound shield volcano from at least two main upper-edifice vents at about 400 ka; 3) effusion of the summit dome-like lavas through multiple vents at ca. 240 ka; 4) eruption of a large number of geochemically diverse, alkaline and calc-alkaline Pleistocene-to-Holocene monogenetic cones (likely related to regional volcanism) through the flanks of the Cofre de Perote edifice; 5) late-stage, large-volume edifice collapse on at least two occasions (ca. 40 ka and ca. 10 ka), producing long-runout debris avalanches that traveled to the east. An undated tephra layer from Cofre de Perote overlies deposits likely of the youngest collapse. Cofre de Perote is one of several volcanoes in the roughly N-S-trending chain that has undergone major edifice collapse. As with Citlaltepetl (Pico de Orizaba) and Las Cumbres volcanoes, Cofre de Perote was constructed at the
Flank wear analysing of high speed end milling for hardened steel D2 using Taguchi Method

Science.gov (United States)

Hazza Faizi Al-Hazza, Muataz; Ibrahim, Nur Asmawiyah bt; Adesta, Erry T. Y.; Khan, Ahsan Ali; Abdullah Sidek, Atiah Bt.

2017-03-01

One of the main challenges for any manufacturer is how to decrease the machining cost without affecting the final quality of the product. One of the new advanced machining processes in industry is the high speed hard end milling process that merges three advanced machining processes: high speed milling, hard milling and dry milling. However, one of the most important challenges in this process is to control the flank wear rate. Therefore a analyzing the flank wear rate during machining should be investigated in order to determine the best cutting levels that will not affect the final quality of the product. In this research Taguchi method has been used to investigate the effect of cutting speed, feed rate and depth of cut and determine the best level s to minimize the flank wear rate up to total length of 0.3mm based on the ISO standard to maintain the finishing requirements.
Conference on the Rehabilitation of Severely Damaged Land and Freshwater Ecosystems in Temperate Zones

CERN Document Server

Woodman, M

1978-01-01

This volume contains the papers presented at a conference on "The rehabilitation of severely damaged land and freshwater eco systems in temperate zones", held at Reykjavik, Iceland, from 4th to 11th July, 1976. The meeting was held under the auspices of the Ecosciences Panel of the N.A.T.O. Science Committee, and the organising expenses and greater part of the expenses of the speakers and chairmen were provided by N.A.T.O. The scientific programme was planned by M. W. Holdgate and M. J. Woodman, in consultation with numerous colleagues, and especially with the Administrative Director of the Conference in Iceland, Dr. Sturla Fridriksson. Iceland proved a particularly suitable location for such a Conference. Geologically, it is one of the youngest countries 1n the world, owing its origin to the up-welling of volcanic rock along the spreading zone of the mid-Atlantic ridge within the past 20 million years. Its structure, northern oceanic situation, recent glaciation and continuing volcanic activity make it dis...
Elements in the transcriptional regulatory region flanking herpes simplex virus type 1 oriS stimulate origin function.

Science.gov (United States)

Wong, S W; Schaffer, P A

1991-05-01

Like other DNA-containing viruses, the three origins of herpes simplex virus type 1 (HSV-1) DNA replication are flanked by sequences containing transcriptional regulatory elements. In a transient plasmid replication assay, deletion of sequences comprising the transcriptional regulatory elements of ICP4 and ICP22/47, which flank oriS, resulted in a greater than 80-fold decrease in origin function compared with a plasmid, pOS-822, which retains these sequences. In an effort to identify specific cis-acting elements responsible for this effect, we conducted systematic deletion analysis of the flanking region with plasmid pOS-822 and tested the resulting mutant plasmids for origin function. Stimulation by cis-acting elements was shown to be both distance and orientation dependent, as changes in either parameter resulted in a decrease in oriS function. Additional evidence for the stimulatory effect of flanking sequences on origin function was demonstrated by replacement of these sequences with the cytomegalovirus immediate-early promoter, resulting in nearly wild-type levels of oriS function. In competition experiments, cotransfection of cells with the test plasmid, pOS-822, and increasing molar concentrations of a competitor plasmid which contained the ICP4 and ICP22/47 transcriptional regulatory regions but lacked core origin sequences resulted in a significant reduction in the replication efficiency of pOS-822, demonstrating that factors which bind specifically to the oriS-flanking sequences are likely involved as auxiliary proteins in oriS function. Together, these studies demonstrate that trans-acting factors and the sites to which they bind play a critical role in the efficiency of HSV-1 DNA replication from oriS in transient-replication assays.
Arsenic speciation and trace element analysis of the volcanic rio Agrio and the geothermal waters of Copahue, Argentina

Energy Technology Data Exchange (ETDEWEB)

Farnfield, Hannah R. [ICP-MS Facility, Chemical Sciences, Faculty of Health and Medical Sciences, University of Surrey, Guildford, Surrey, GU2 7XH (United Kingdom); Marcilla, Andrea L. [Patagonia BBS, General Roca, Rio Negro (Argentina); Ward, Neil I., E-mail: n.ward@surrey.ac.uk [ICP-MS Facility, Chemical Sciences, Faculty of Health and Medical Sciences, University of Surrey, Guildford, Surrey, GU2 7XH (United Kingdom)

2012-09-01

Surface water originating from the Copahue volcano crater-lake was analysed for total arsenic and four arsenic species: arsenite (iAs{sup III}), arsenate (iAs{sup V}), monomethylarsonic acid (MA{sup V}) and dimethylarsinic acid (DMA{sup V}) and other trace elements (Fe, Mn, V, Cr, Ni, Zn). A novel in-field technique for the preconcentration and separation of four arsenic species was, for the first time, used for the analysis of geothermal and volcanic waters. Total arsenic levels along the rio Agrio ranged from < 0.2-3783 {mu}g/l As{sub T}. The highest arsenic levels were recorded in the el Vertedero spring (3783 {mu}g/l As{sub T}) on the flank of the Copahue volcano, which feeds the acidic rio Agrio. Arsenite (H{sub 3}AsO{sub 3}) predominated along the upper rio Agrio (78.9-81.2% iAs{sup III}) but the species distribution changed at lago Caviahue and arsenate (H{sub 2}AsO{sub 4}{sup -}) became the main species (51.4-61.4% iAs{sup V}) up until Salto del Agrio. The change in arsenic species is potentially a result of an increase in redox potential and the formation of iron-based precipitates. Arsenic speciation showed a statistically significant correlation with redox potential (r = 0.9697, P = 0.01). Both total arsenic and arsenic speciation displayed a statistically significant correlation with vanadium levels along the river (r = 0.9961, P = 0.01 and r = 0.8488, P = 0.05, respectively). This study highlights that chemical speciation analysis of volcanic waters is important in providing ideas on potential chemical toxicity. Furthermore there is a need for further work evaluating how arsenic (and other trace elements), released in volcanic and geothermal streams/vents, impacts on both biota and humans (via exposure in thermal pools or consuming commercial drinking water). -- Highlights: Black-Right-Pointing-Pointer Application of a novel field-based method for the separation of arsenic species in a volcanic surface water system. Black-Right-Pointing-Pointer First
Global volcanic emissions: budgets, plume chemistry and impacts

Science.gov (United States)

Mather, T. A.

2012-12-01

Over the past few decades our understanding of global volcanic degassing budgets, plume chemistry and the impacts of volcanic emissions on our atmosphere and environment has been revolutionized. Global volcanic emissions budgets are needed if we are to make effective use of regional and global atmospheric models in order to understand the consequences of volcanic degassing on global environmental evolution. Traditionally volcanic SO2 budgets have been the best constrained but recent efforts have seen improvements in the quantification of the budgets of other environmentally important chemical species such as CO2, the halogens (including Br and I) and trace metals (including measurements relevant to trace metal atmospheric lifetimes and bioavailability). Recent measurements of reactive trace gas species in volcanic plumes have offered intriguing hints at the chemistry occurring in the hot environment at volcanic vents and during electrical discharges in ash-rich volcanic plumes. These reactive trace species have important consequences for gas plume chemistry and impacts, for example, in terms of the global fixed nitrogen budget, volcanically induced ozone destruction and particle fluxes to the atmosphere. Volcanically initiated atmospheric chemistry was likely to have been particularly important before biological (and latterly anthropogenic) processes started to dominate many geochemical cycles, with important consequences in terms of the evolution of the nitrogen cycle and the role of particles in modulating the Earth's climate. There are still many challenges and open questions to be addressed in this fascinating area of science.

Las comunidades vegetales del Zacatonal Alpino de los volcanes Popocatépetl y Nevado de Toluca, Región Central de México.

NARCIS (Netherlands)

Almeida-Lenero, L.; Gimenez de Azcarate, J.; Cleef, A.M.; Gonzales Trapaga, A.

2004-01-01

This study of the zacatonal alpino zone of the volcanoes Popocatepetl (5452 in) and Nevado de Toluca (4690 m) in the central region of the Transmexican Volcanic Belt, is a follow-up of the study of ALMEIDA et al. (1994). This tropical alpine zacatonal represents the potential vegetation of the
Validating predictions made by a thermo-mechanical model of melt segregation in sub-volcanic systems

Science.gov (United States)

Roele, Katarina; Jackson, Matthew; Morgan, Joanna

2014-05-01

A quantitative understanding of the spatial and temporal evolution of melt distribution in the crust is crucial in providing insights into the development of sub-volcanic crustal stratigraphy and composition. This work aims to relate numerical models that describe the base of volcanic systems with geophysical observations. Recent modelling has shown that the repetitive emplacement of mantle-derived basaltic sills, at the base of the lower crust, acts as a heat source for anatectic melt generation, buoyancy-driven melt segregation and mobilisation. These processes form the lowermost architecture of complex sub-volcanic networks as upward migrating melt produces high melt fraction layers. These 'porosity waves' are separated by zones with high compaction rates and have distinctive polybaric chemical signatures that suggest mixed crust and mantle origins. A thermo-mechanical model produced by Solano et al in 2012 has been used to predict the temperatures and melt fractions of successive high porosity layers within the crust. This model was used as it accounts for the dynamic evolution of melt during segregation and migration through the crust; a significant process that has been neglected in previous models. The results were used to input starting compositions for each of the layers into the rhyolite-MELTS thermodynamic simulation. MELTS then determined the approximate bulk composition of the layers once they had cooled and solidified. The mean seismic wave velocities of the polymineralic layers were then calculated using the relevant Voight-Reuss-Hill mixture rules, whilst accounting for the pressure and temperature dependence of seismic wave velocity. The predicted results were then compared with real examples of reflectivity for areas including the UK, where lower crustal layering is observed. A comparison between the impedance contrasts at compositional boundaries is presented as it confirms the extent to which modelling is able to make predictions that are
Comparison of the diagenetic and reservoir quality evolution between the anticline crest and flank of an Upper Jurassic carbonate gas reservoir, Abu Dhabi, United Arab Emirates

Science.gov (United States)

Morad, Daniel; Nader, Fadi H.; Gasparrini, Marta; Morad, Sadoon; Rossi, Carlos; Marchionda, Elisabetta; Al Darmaki, Fatima; Martines, Marco; Hellevang, Helge

2018-05-01

This petrographic, stable isotopic and fluid inclusion microthermometric study of the Upper Jurassic limestones of an onshore field, Abu Dhabi, United Arab Emirates (UAE) compares diagenesis in flanks and crest of the anticline. The results revealed that the diagenetic and related reservoir quality evolution occurred during three phases, including: (i) eogenesis to mesogenesis 1, during which reservoir quality across the field was either deteriorated or preserved by calcite cementation presumably derived from marine or evolved marine pore waters. Improvement of reservoir quality was due to the formation of micropores by micritization of allochems and creation of moldic/intragranular pores by dissolution of peloids and skeletal fragments. (ii) Obduction of Oman ophiolites and formation of the anticline of the studied field was accompanied by cementation by saddle dolomite and blocky calcite. High homogenization temperatures (125-175 °C) and high salinity (19-26 wt% NaCl eq) of the fluid inclusions, negative δ18OVPDB values (-7.7 to -2.9‰), saddle shape of dolomite, and the presence of exotic cements (i.e. fluorite and sphalerite) suggest that these carbonates were formed by flux of hot basinal brines, probably related to this tectonic compression event. (iii) Mesogenesis 2 during subsidence subsequent to the obduction event, which resulted in extensive stylolitization and cementation by calcite. This calcite cement occluded most of the remaining moldic and inter-/intragranular pores of the flank limestones (water zone) whereas porosity was preserved in the crest. This study contributes to: (1) our understanding of differences in the impact of diagenesis on reservoir quality evolution in flanks and crests of anticlines, i.e. impact of hydrocarbon emplacement on diagenesis, and (2) relating various diagenetic processes to burial history and tectonic events of foreland basins in the Arabian Gulf area and elsewhere.
Transition of neogene arc volcanism in central-western Hokkaido, viewed from K-Ar ages, style of volcanic activity, and bulk rock chemistry

Energy Technology Data Exchange (ETDEWEB)

Hirose, Wataru; Iwasaki, Miyuki; Nakagawa, Mitsuhiro [Hokkaido Univ., Sapporo (Japan)

2000-02-01

Spatial and temporal variations in late Cenozoic volcanism of southwestern Hokkaido at the northern end of NE-Japan arc have been clarified by 261 K-Ar and 76 FT ages including 49 newly determined K-Ar ages, volcanic stratigraphy, physical volcanology and whole-rock geochemistry. Arc volcanism characterized by rocks with low-Ti and Nb, and by across-arc increase in K{sub 2}O content in these rocks has continued at least since 12 Ma. Based on volcanic stratigraphy, physical volcanology and whole-rock geochemistry, volcanism after 12 Ma can be subdivided into 4 stages, 12-5, 5-1.7, and 1.7-0 Ma. The volcanism from 12 Ma to 5 Ma extended northward widely compared with distribution of Quaternary arc volcanism (1.7-0 Ma). This suggests that the arc trench junction between Kuril and NE-Japan arc's trenches was located about 100 km northward from the present position. Since around 5 Ma until 1.7 Ma, different type of volcanism under local extension field, characterized by a group of monogenetic volcanoes of alkali basalt and shield volcanoes of calc-alkaline andesite, had occurred at northern end of the volcanic region (Takikawa-Mashike region). During and after this volcanism, the northern edge of arc volcanism in the area has migrated southward. This suggests that the trench junction has migrated about 100 km southward since {approx}5 Ma. The quaternary arc volcanism (1.7-0 Ma) has been restricted at the southern part of the region. The volcanism since 12 Ma might be influenced by oblique subduction of Pacific plate beneath Kuril arc, resulting in the formation of local back arc basin at the junction and to southward migration of the trench junction. (author)
Sr and Nd isotopic and trace element compositions of Quaternary volcanic centers of the Southern Andes

Science.gov (United States)

Futa, K.; Stern, C.R.

1988-01-01

Isotopic compositions of samples from six Quaternary volcanoes located in the northern and southern extremities of the Southern Volcanic Zone (SVZ, 33-46??S) of the Andes and from four centers in the Austral Volcanic Zone (AVZ, 49-54??S) range for 87Sr 86Sr from 0.70280 to 0.70591 and for 143Nd 144Nd from 0.51314 to 0.51255. The ranges are significantly greater than previously reported from the southern Andes but are different from the isotopic compositions of volcanoes in the central and northern Andes. Basalts and basaltic andesites from three centers just north of the Chile Rise-Trench triple junction have 87Sr 86Sr, 143Nd 144Nd, La Yb, Ba La, and Hf Lu that lie within the relatively restricted ranges of the basic magmas erupted from the volcanic centers as far north as 35??S in the SVZ of the Andes. The trace element and Sr and Nd isotopic characteristics of these magmas may be explained by source region contamination of subarc asthenosphere, with contaminants derived from subducted pelagic sediments and seawater-altered basalts by dehydration of subducted oceanic lithosphere. In the northern extremity of the SVZ between 33?? and 34??S, basaltic andesites and andesites have higher 87Sr 86Sr, Rb Cs, and Hf Lu, and lower 143Nd 144Nd than basalts and basaltic andesites erupted farther south in the SVZ, which suggests involvement of components derived from the continental crust. In the AVZ, the most primitive sample, high-Mg andesite from the southernmost volcanic center in the Andes (54??S) has Sr and Nd isotopic compositions and K Rb and Ba La similar to MORB. The high La Yb of this sample suggests formation by small degrees of partial melting of subducted MORB with garnet as a residue. Samples from centers farther north in the AVZ show a regionally regular northward increase in SiO2, K2O, Rb, Ba, Ba La, and 87Sr 86Sr and decrease in MgO, Sr, K Rb, Rb Cs, and 143Nd 144Nd, suggesting increasingly greater degrees of fractional crystallization and associated intra
Pancreatic Tail Cancer with Sole Manifestation of Left Flank Pain: A Very Rare Presentation

Directory of Open Access Journals (Sweden)

Hsing-Lin Lin

2008-06-01

Full Text Available Pancreatic cancer is sometimes called a “silent disease” because it often causes no symptoms in the early stage. The symptoms can be quite vague and various depending on the location of cancer in the pancreas. The anatomic site distribution is 78% in the head of the pancreas, 11% in the body, and 11% in the tail. Pancreatic cancer is rarely detected in the early stage, and it is very uncommon to diagnose pancreatic tail cancer during an emergency department visit. The manifestation of pancreatic tail cancer as left flank pain is very rare and has seldom been identified in the literature. We present a case of pancreatic tail cancer with the sole manifestation of dull left flank pain. Having negative findings on an ultrasound study initially, this female patient was misdiagnosed as having possible acute gastritis, urolithiasis or muscle strain after she received gastroendoscopy and colonofiberscopy. Her symptoms persisted for several months and she visited our emergency department due to an acute exacerbation of a persistent dull pain in the left flank area. Radiographic evaluation with computed tomography was performed, and pancreatic tail tumor with multiple metastases was found unexpectedly. We review the literature and discuss this rare presentation of pancreatic tail cancer.
Dynamics and Evolution of SO 2 Gas Condensation around Prometheus-like Volcanic Plumes on Io as Seen by the Near Infrared Mapping Spectrometer

Science.gov (United States)

Douté, Sylvain; Lopes, Rosaly; Kamp, Lucas W.; Carlson, Robert; Schmitt, Bernard; Galileo NIMS Team

2002-08-01

We analyze a series of spectral image cubes acquired by the Galileo Near Infrared Mapping Spectrometer (NIMS) over the Prometheus region of Io. We use SO 2 frost, a volatile compound ubiquitous on the surface, as a tracer to understand various thermodynamic and volcanic processes acting in this equatorial region. Here we develop a new method to derive, from the 12-wavelength NIMS products, the distribution and physical properties of solid SO 2. This method is based on the inversion of a bidirectional reflectance model on two observed spectral ratios sensitive to (1) the areal abundance of SO 2 and (2) its mean grain size. As a result, reliable and consistent maps of SO 2 abundance and granularity are obtained which can be correlated to distinguish four different physical units. The distribution of these SO 2 units indicates zones of condensation, metamorphism, and sublimation linked with the thermodynamic and volcanic processes of interest. Our maps depict equatorial plains undisturbed by any kind of vigorous volcanic activity over 35-40% of their surface. Elsewhere, 10-20% of the equatorial plains display abnormally low frost coverage which may imply the recent presence of positive thermal anomalies with temperatures in the range 110-200 K. Hot-spots such as Prometheus, Culann, Surya, and Tupan (to mention the most persistent) emit a great variety of gases, some of which will condense at Io's surface near their source regions. Associated fields of freshly condensed SO 2 are easily observed, and deposits of more refractory compounds with higher (e.g., S 8) or lower (e.g., NaCl) molecular weight must also be present (although their exact nature is unknown). Three different mechanisms of emission are proposed for the volatile compounds and supported by the distribution maps. These are (a) the interaction between flowing lava and preexisting volatile deposits on the surface, (b) direct degassing from the lava, an d (c) the eruption of a liquid aquifer from underground
An unusual manifestation of acute appendicitis with left flank pain

Directory of Open Access Journals (Sweden)

Roland Talanow, MD, PhD

2008-08-01

Full Text Available The author presents a case with an unusual presentation of early appendicitis. The patient presented initially with left sided flank pain. Workup for nephrolithiasis, including non-contrast CT of the abdomen and pelvis was negative for renal stones or hydronephrosis. After discharge, the patient presented one week later in the ED with right lower quadrant pain. Contrast enhanced CT of the abdomen revealed perforated appendicitis.
Changes in Bottom Water Physical Properties Above the Mid-Atlantic Ridge Flank in the Brazil Basin

Science.gov (United States)

Zhao, Jian; Thurnherr, Andreas M.

2018-01-01

Warming of abyssal waters in recent decades has been widely documented around the global ocean. Here repeat hydrographic data collected in 1997 and 2014 near a deep fracture zone canyon in the eastern Brazil Basin are used to quantify the long-term change. Significant changes are found in the Antarctic Bottom Water (AABW) within the canyon. The AABW in 2014 was warmer (0.08 ± 0.06°C), saltier (0.01 ± 0.005), and less dense (0.005 ± 0.004 kg m-3) than in 1997. In contrast, the change in the North Atlantic Deep Water has complicated spatial structure and is almost indistinguishable from zero at 95% confidence. The resulting divergence in vertical displacement of the isopycnals modifies the local density stratification. At its peak, the local squared buoyancy frequency (N2) near the canyon is reduced by about 20% from 1997 to 2014. Similar reduction is found in the basinwide averaged profiles over the Mid-Atlantic Ridge flank along 25°W in years 1989, 2005, and 2014. The observed changes in density stratification have important implications for internal tide generation and dissipation.
Volcanic risk: the responsibility of science in communication

Science.gov (United States)

Piccione, Caterina

2013-04-01

The knowledge of the places where we live comes both from the experience handed down from one generation to the other and from scientific knowledge. In some cases, natural risks are "invisible", such as earthquakes, in some other cases, natural risks are seemingly "invisible", such as a wall in danger of collapse or a valley in a flood zone. And besides all this, there is volcanic risk, where the power of the forces of nature appears in all its beauty and majesty. The possibility to see volcanoes, to perceive their changes, to observe them closely and the need to live with them, makes it very important for the population living in these areas to have an adequate knowledge of the risk, a knowledge that should be based on scientific research. In Italy the experience of the Istituto Nazionale di Geofisica e Vulcanologia in the Vesuvio area, in the Aeolian Islands and around Etna shows how vital it is to make people aware of volcanic risk. Thanks to the support of the scientific community, the population can develop the best possible coexistence with volcanoes and with the risk they represent. These are extreme situations, but they are the starting point for educational and informative activities continuing to evolve and upgrade in parallel to the availability of new technologies and media and the progress of research that INGV has been conducting for years through specific projects. The scientific community and individual researchers have the ethical duty to share with the community the knowledge on risk, a responsibility that becomes especially important in those areas affected by volcanic risk. It is from this educational action that depends on the awareness of the populations with regard to the risk they are exposed to, that results in a responsible behavior in case of emergency, and that becomes the main variable for the safety of communities coexisting with active volcanoes.
Volcanic Gases and Hot Spring Water to Evaluate the Volcanic Activity of the Mt. Baekdusan

Science.gov (United States)

Yun, S. H.; Lee, S.; Chang, C.

2017-12-01

This study performed the analysis on the volcanic gases and hot spring waters from the Julong hot spring at Mt. Baekdu, also known as Changbaishan on the North Korea(DPRK)-China border, during the period from July 2015 to August 2016. Also, we confirmed the errors that HCO3- concentrations of hot spring waters in the previous study (Lee et al. 2014) and tried to improve the problem. Dissolved CO2 in hot spring waters was analyzed using gas chromatograph in Lee et al.(2014). Improving this, from 2015, we used TOC-IC to analysis dissolved CO2. Also, we analyzed the Na2CO3 standard solutions of different concentrations using GC, and confirmed the correlation between the analytical concentrations and the real concentrations. However, because the analytical results of the Julong hot spring water were in discord with the estimated values based on this correlation, we can't estimate the HCO3-concentrations of 2014 samples. During the period of study, CO2/CH4 ratios in volcanic gases are gradually decreased, and this can be interpreted in two different ways. The first interpretation is that the conditions inside the volcanic edifice are changing into more reduction condition, and carbon in volcanic gases become more favorable to distribute into CH4 or CO than CO2. The second interpretation is that the interaction between volcanic gases and water becomes greater than past, and the concentrations of CO2which have much higher solubility in water decreased, relatively. In general, the effect of scrubbing of volcanic gas is strengthened during the quiet periods of volcanic activity rather than active periods. Meanwhile, the analysis of hot spring waters was done on the anion of acidic gases species, the major cations, and some trace elements (As, Cd, Re).This work was funded by the Korea Meteorological Administration Research and Development Program under Grant KMIPA 2015-3060.
Disruptive event analysis: volcanism and igneous intrusion

International Nuclear Information System (INIS)

Crowe, B.M.

1979-01-01

Three basic topics are addressed for the disruptive event analysis: first, the range of disruptive consequences of a radioactive waste repository by volcanic activity; second, the possible reduction of the risk of disruption by volcanic activity through selective siting of a repository; and third, the quantification of the probability of repository disruption by volcanic activity
The geothermal system of Caviahue-Copahue Volcanic Complex (Chile-Argentina): New insights from self-potential, soil CO2 degassing, temperature measurements and helium isotopes, with structural and fluid circulation implications.

Science.gov (United States)

Roulleau, Emilie; Bravo, Francisco; Barde-Cabusson, Stephanie; Pizarro, Marcela; Muños, Carlos; Sanchez, Juan; Tardani, Daniele; Sano, Yuji; Takahata, Naoto; de Cal, Federico; Esteban, Carlos

2016-04-01

Geothermal systems represent natural heat transfer engines in a confined volume of rock which are strongly influenced by the regional volcano-tectonic setting controlling the formation of shallow magmatic reservoirs, and by the local faults/fracture network, that permits the development of hydrothermal circulation cells and promote the vertical migration of fluids and heat. In the Southern Volcanic Zone of Chile-Argentina, geothermal resources occur in close spatial relationship with active volcanism along the Cordillera which is primarily controlled by the 1000 km long, NNE Liquiñe-Ofqui Fault Zone (LOFZ), an intra-arc dextral strike-slip fault system, associated with second-order intra-arc anisotropy of overall NE-SW (extensional) and NW-SE orientation (compressional). However there is still a lack of information on how fault network (NE and WNW strinking faults) and lithology control the fluid circulation. In this study, we propose new data of dense self-potential (SP), soil CO2 emanation and temperature (T) measurements within the geothermal area from Caviahue-Copahue Volcanic Complex (CCVC), coupled with helium isotopes ratios measured in fumaroles and thermal springs. We observe that inside the geothermal system the NE-striking faults, characterized by a combination of SP-CO2 and T maxima with high 3He/4He ratios (7.86Ra), promote the formation of high vertical permeability pathways for fluid circulation. Whereas, the WNW-striking faults represent low permeability pathways for hydrothermal fluids ascent associated with moderate 3He/4He ratios (5.34Ra), promoting the infiltration of meteoric water at shallow depth. These active zones are interspersed by SP-CO2- T minima, which represent self-sealed zones (e.g. impermeable altered rocks) at depth, creating a barrier inhibiting fluids rise. The NE-striking faults seem to be associated with the upflow zones of the geothermal system, where the boiling process produces a high vapor-dominated zone close to the
Timing and compositional evolution of Late Pleistocene to Holocene volcanism within the Harrat Rahat volcanic field, Kingdom of Saudi Arabia

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Stelten, M. E.; Downs, D. T.; Dietterich, H. R.

2017-12-01

Harrat Rahat is one of the largest ( 20,000 km2) of 15 active Cenozoic volcanic fields that stretch 3,000 km along the western Arabian Peninsula from Yemen to Syria. The Harrat Rahat volcanic field is 310 km long (N-S) by 75 km wide (E-W), and is dominated by alkalic basalts with minor hawaiite, mugearite, benmoreite, and trachyte eruptives. The timing of volcanism within greater Harrat Rahat is poorly constrained, but field relations and geochronology indicate that northern Harrat Rahat hosted the most recent eruptions. To better constrain the timing and compositional evolution of Harrat Rahat during this recent phase, we present 743 geochemical analyses, 144 40Ar/39Ar ages, and 9 36Cl exposure ages for volcanic strata from northernmost Harrat Rahat. These data demonstrate that volcanism has been ongoing from at least 1.2 Ma to the present, with the most recent eruption known from historical accounts at 1256 CE. Basalt has erupted persistently from 1.2 Ma to the present, but more evolved volcanism has been episodic. Benmoreite erupted at 1.1 Ma and between 550 to 400 ka. Trachytic volcanism has only occurred over the past 150 ka, with the most recent eruption at 5 ka. Aside from the well-documented basaltic eruption at 1256 CE, prior workers interpreted 6 additional basaltic eruptions during the Holocene. However, our 36Cl exposure ages demonstrate that these erupted between 60 to 13 ka. Interestingly, in the northern part of our field area, where the spatial density of volcanic vents is low, young volcanism (<150 ka) is dominated by basaltic eruptions. Conversely, young volcanism in the southern part of our field area, where volcanic vent density is high, is dominated by trachyte. This observation is consistent with a process wherein the time-integrated effects of basaltic influx into the crust in the south produced a mafic intrusive complex, through which younger basaltic magmas cannot ascend. Instead, these magmas stall and produce trachyte, likely through
National volcanic ash operations plan for aviation

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,; ,

2007-01-01

The National Aviation Weather Program Strategic Plan (1997) and the National Aviation Weather Initiatives (1999) both identified volcanic ash as a high-priority informational need to aviation services. The risk to aviation from airborne volcanic ash is known and includes degraded engine performance (including flameout), loss of visibility, failure of critical navigational and operational instruments, and, in the worse case, loss of life. The immediate costs for aircraft encountering a dense plume are potentially major—damages up to $80 million have occurred to a single aircraft. Aircraft encountering less dense volcanic ash clouds can incur longer-term costs due to increased maintenance of engines and external surfaces. The overall goal, as stated in the Initiatives, is to eliminate encounters with ash that could degrade the in-flight safety of aircrews and passengers and cause damage to the aircraft. This goal can be accomplished by improving the ability to detect, track, and forecast hazardous ash clouds and to provide adequate warnings to the aviation community on the present and future location of the cloud. To reach this goal, the National Aviation Weather Program established three objectives: (1) prevention of accidental encounters with hazardous clouds; (2) reduction of air traffic delays, diversions, or evasive actions when hazardous clouds are present; and (3) the development of a single, worldwide standard for exchange of information on airborne hazardous materials. To that end, over the last several years, based on numerous documents (including an OFCMsponsored comprehensive study on aviation training and an update of Aviation Weather Programs/Projects), user forums, and two International Conferences on Volcanic Ash and Aviation Safety (1992 and 2004), the Working Group for Volcanic Ash (WG/VA), under the OFCM-sponsored Committee for Aviation Services and Research, developed the National Volcanic Ash Operations Plan for Aviation and Support of the
Climatic impact of volcanic eruptions

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Rampino, Michael R.

1991-01-01

Studies have attempted to 'isolate' the volcanic signal in noisy temperature data. This assumes that it is possible to isolate a distinct volcanic signal in a record that may have a combination of forcings (ENSO, solar variability, random fluctuations, volcanism) that all interact. The key to discovering the greatest effects of volcanoes on short-term climate may be to concentrate on temperatures in regions where the effects of aerosol clouds may be amplified by perturbed atmospheric circulation patterns. This is especially true in subpolar and midlatitude areas affected by changes in the position of the polar front. Such climatic perturbation can be detected in proxy evidence such as decrease in tree-ring widths and frost rings, changes in the treeline, weather anomalies, severity of sea-ice in polar and subpolar regions, and poor grain yields and crop failures. In low latitudes, sudden temperature drops were correlated with the passage overhead of the volcanic dust cloud (Stothers, 1984). For some eruptions, such as Tambora, 1815, these kinds of proxy and anectdotal information were summarized in great detail in a number of papers and books (e.g., Post, 1978; Stothers, 1984; Stommel and Stommel, 1986; C. R. Harrington, in press). These studies lead to the general conclusion that regional effects on climate, sometimes quite severe, may be the major impact of large historical volcanic aerosol clouds.
Origin of seamount volcanism in northeast Indian Ocean with emphasis on Christmas Island

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Taneja, R.; O'Neill, C.; Rushmer, T. A.; Jourdan, F.; Blichert-Toft, J.; Turner, S.; Lackie, M. A.

2012-12-01

The Northeast Indian Ocean has been a central point of research in the recent past due to its intraplate geophysical and geochemical characteristics. It is dominated by sub-aerial volcanic islands and submerged guyots and two islands, namely, Cocos (Keeling) Island and Christmas Island. Christmas Island, the focus of this study, consists of limestone and mafic intraplate volcanics. The origin of most of the features in northeast Indian Ocean is not fully understood. Christmas Island has experienced multiple stages of intraplate volcanic activity as previously established by 40Ar/39Ar radioisotopic analyses of basalts from the island (Hoernl et al., 2011). Here, we present new 40Ar/39Ar ages where the rock samples from Waterfall Spring (WS), Ethel Beach (EB) & Dolly Beach (DB) on the east coast of the island yielded plateau and mini-plateau ages of 37.75±0.77 Ma, 37.10±0.66 Ma and 43.37±0.45 Ma respectively, whereas a sample from Flying Fish Cove (FFC) in the north of the island yielded a minimum age of 38.6±0.5 Ma. All these units are part of the Lower Volcanics Series. The samples from the west coast (Winifred Beach, WB) are younger with an age of 4.32 ± 0.17 Ma, and are part of the Upper Volcanic Series. This confirms two stages of volcanism at the island with a gap of around 38 Ma. The 40Ar/39Ar radioisotopic ages were overlayed on Gplates and seismic tomography models to determine its paleo motion. The present position of the island is 10.5°S, 105.5°E. During Eocene its reconstructed position was 30°S latitude. Seismic tomography models have highlighted a low velocity zone beneath the island during Eocene. Geochemically, the two volcanic suites (Upper & Lower) are mostly similar in their major and trace element composition. The majority of localities (WS, EB, and WB) are basanites; where as that from Dolly Beach is basaltic. The Dale's (west coast), are trachyte and appear evolved with high SiO2. They also have low Ba and Sr ~25ppm, whereas those from
MIGRATION OF SEISMIC AND VOLCANIC ACTIVITY AS DISPLAY OF WAVE GEODYNAMIC PROCESS

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Alexander V. Vikulin

2012-01-01

Full Text Available Publications about the earthquake foci migration have been reviewed. An important result of such studies is establishment of wave nature of seismic activity migration that is manifested by two types of rotational waves; such waves are responsible for interaction between earthquakes foci and propagate with different velocities. Waves determining long-range interaction of earthquake foci are classified as Type 1; their limiting velocities range from 1 to 10 cm/s. Waves determining short-range interaction of foreshocks and aftershocks of individual earthquakes are classified as Type 2; their velocities range from 1 to 10 km/s. According to the classification described in [Bykov, 2005], these two types of migration waves correspond to slow and fast tectonic waves. The most complete data on earthquakes (for a period over 4.1 million of years and volcanic eruptions (for 12 thousand years of the planet are consolidated in a unified systematic format and analyzed by methods developed by the authors. For the Pacific margin, Alpine-Himalayan belt and the Mid-Atlantic Ridge, which are the three most active zones of the Earth, new patterns of spatial and temporal distribution of seismic and volcanic activity are revealed; they correspond to Type 1 of rotational waves. The wave nature of the migration of seismic and volcanic activity is confirmed. A new approach to solving problems of geodynamics is proposed with application of the data on migration of seismic and volcanic activity, which are consolidated in this study, in combination with data on velocities of movement of tectonic plate boundaries. This approach is based on the concept of integration of seismic, volcanic and tectonic processes that develop in the block geomedium and interact with each other through rotating waves with a symmetric stress tensor. The data obtained in this study give grounds to suggest that a geodynamic value, that is mechanically analogous to an impulse
Morphology and Doping Level of Electropolymerized Biselenophene-Flanked 3,4- Ethylenedioxythiophene Polymer: Effect of Solvents and Electrolytes

International Nuclear Information System (INIS)

Agrawal, Vikash; Shahjad; Bhardwaj, Dinesh; Bhargav, Ranoo; Sharma, Gauri Datt; Bhardwaj, Ramil Kumar; Patra, Asit; Chand, Suresh

2016-01-01

Highlights: • Biselenophene-flanked 3,4-ethylenedioxythiophene polymer films were obtained by electrochemical polymerization. • Supporting electrolyte has significant effect on the doping level, whereas electropolymerized solvent has a major effect on morphology of the polymer films. • Optoelectronic properties and morphology of the electropolymerized films were studied. • Density functional theory (DFT) calculation has been made for optoelectronic properties. - Abstract: Biselenophene-flanked 3,4-ethylenedioxythiophene (EDOT) based polymer films were obtained by electrochemical polymerization. The effects of polymerization conditions such as supporting electrolytes and solvents on doping level, optical property and morphology of the polymer films were systematically studied. Interestingly, we found that polymer prepared by using different supporting electrolytes (TBAPF 6 , TBABF 4 and TBAClO 4 ) has significant effects on the doping level of the polymer films, whereas electropolymerized solvents (acetonitrile and dichloromethane) has no such effects on doping level. The polymer films show reversible dedoping and doping behavior upon treatment with hydrazine hydrate and iodine respectively. Biselenophene-flanked EDOT polymer shows a band gap of about 1.6 eV which is comparable to poly(3,4- ethylenedioxythiophene) (PEDOT) and parent polyselenophene, whereas fine-tuning of HOMO and LUMO energy levels has been found. In contrast, we observed that electropolymerized solvent has a major effect on morphology of the polymer films, while supporting electrolyte has very minor effects on the morphology. The surface morphologies of the polymer films were characterized by scanning electron microscope (SEM) and atomic force microscope (AFM) techniques. We also present an efficient synthesis of bisthiophene-flanked bridged EDOT (ETTE), and biselenophene-flanked bridged EDOT (ESeSeE), and their electrochemical polymerization, characterizations and throughout comparison
Modeling of Principal Flank Wear: An Empirical Approach Combining the Effect of Tool, Environment and Workpiece Hardness

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Mia, Mozammel; Al Bashir, Mahmood; Dhar, Nikhil Ranjan

2016-10-01

Hard turning is increasingly employed in machining, lately, to replace time-consuming conventional turning followed by grinding process. An excessive amount of tool wear in hard turning is one of the main hurdles to be overcome. Many researchers have developed tool wear model, but most of them developed it for a particular work-tool-environment combination. No aggregate model is developed that can be used to predict the amount of principal flank wear for specific machining time. An empirical model of principal flank wear (VB) has been developed for the different hardness of workpiece (HRC40, HRC48 and HRC56) while turning by coated carbide insert with different configurations (SNMM and SNMG) under both dry and high pressure coolant conditions. Unlike other developed model, this model includes the use of dummy variables along with the base empirical equation to entail the effect of any changes in the input conditions on the response. The base empirical equation for principal flank wear is formulated adopting the Exponential Associate Function using the experimental results. The coefficient of dummy variable reflects the shifting of the response from one set of machining condition to another set of machining condition which is determined by simple linear regression. The independent cutting parameters (speed, rate, depth of cut) are kept constant while formulating and analyzing this model. The developed model is validated with different sets of machining responses in turning hardened medium carbon steel by coated carbide inserts. For any particular set, the model can be used to predict the amount of principal flank wear for specific machining time. Since the predicted results exhibit good resemblance with experimental data and the average percentage error is <10 %, this model can be used to predict the principal flank wear for stated conditions.

Internal structure of the 85°E ridge, Bay of Bengal: Evidence for multiphase volcanism

Digital Repository Service at National Institute of Oceanography (India)

Ismaiel, M.; Krishna, K.S.; Srinivas, K.; Mishra, J.; Saha, D.

fragments 3 of Elan Bank and part of the present Kerguelen Plateau (Talwani et al., 2016). As a result, age of the oceanic floor in the Western Basin of the Bay of Bengal is older than the other parts. In southeastern quarter of the Bay of Bengal... interpreted as carbonate bank (Gopala Rao et al., 1997; Karuppuswamy, 2013), therefore, we too conjecture the lens shaped reflection free zone identified on our profiles as a carbonate bank, and this may have formed when the defunct volcanic structure...
Effect of Saw Palmetto Supplements on Androgen-Sensitive LNCaP Human Prostate Cancer Cell Number and Syrian Hamster Flank Organ Growth

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Alexander B. Opoku-Acheampong

2016-01-01

Full Text Available Saw palmetto supplements (SPS are commonly consumed by men with prostate cancer. We investigated whether SPS fatty acids and phytosterols concentrations determine their growth-inhibitory action in androgen-sensitive LNCaP cells and hamster flank organs. High long-chain fatty acids-low phytosterols (HLLP SPS ≥ 750 nM with testosterone significantly increased and ≥500 nM with dihydrotestosterone significantly decreased LNCaP cell number. High long-chain fatty acids-high phytosterols (HLHP SPS ≥ 500 nM with dihydrotestosterone and high medium-chain fatty acids-low phytosterols (HMLP SPS ≥ 750 nM or with androgens significantly decreased LNCaP cell number (n=3; p<0.05. Five- to six-week-old, castrated male Syrian hamsters were randomized to control (n=4, HLLP, HLHP, and HMLP SPS (n=6 groups. Testosterone or dihydrotestosterone was applied topically daily for 21 days to the right flank organ; the left flank organ was treated with ethanol and served as the control. Thirty minutes later, SPS or ethanol was applied to each flank organ in treatment and control groups, respectively. SPS treatments caused a notable but nonsignificant reduction in the difference between left and right flank organ growth in testosterone-treated SPS groups compared to the control. The same level of inhibition was not seen in dihydrotestosterone-treated SPS groups (p<0.05. Results may suggest that SPS inhibit 5α-reductase thereby preventing hamster flank organ growth.
Effect of Saw Palmetto Supplements on Androgen-Sensitive LNCaP Human Prostate Cancer Cell Number and Syrian Hamster Flank Organ Growth.

Science.gov (United States)

Opoku-Acheampong, Alexander B; Penugonda, Kavitha; Lindshield, Brian L

2016-01-01

Saw palmetto supplements (SPS) are commonly consumed by men with prostate cancer. We investigated whether SPS fatty acids and phytosterols concentrations determine their growth-inhibitory action in androgen-sensitive LNCaP cells and hamster flank organs. High long-chain fatty acids-low phytosterols (HLLP) SPS ≥ 750 nM with testosterone significantly increased and ≥500 nM with dihydrotestosterone significantly decreased LNCaP cell number. High long-chain fatty acids-high phytosterols (HLHP) SPS ≥ 500 nM with dihydrotestosterone and high medium-chain fatty acids-low phytosterols (HMLP) SPS ≥ 750 nM or with androgens significantly decreased LNCaP cell number (n = 3; p < 0.05). Five- to six-week-old, castrated male Syrian hamsters were randomized to control (n = 4), HLLP, HLHP, and HMLP SPS (n = 6) groups. Testosterone or dihydrotestosterone was applied topically daily for 21 days to the right flank organ; the left flank organ was treated with ethanol and served as the control. Thirty minutes later, SPS or ethanol was applied to each flank organ in treatment and control groups, respectively. SPS treatments caused a notable but nonsignificant reduction in the difference between left and right flank organ growth in testosterone-treated SPS groups compared to the control. The same level of inhibition was not seen in dihydrotestosterone-treated SPS groups (p < 0.05). Results may suggest that SPS inhibit 5α-reductase thereby preventing hamster flank organ growth.
Experimental Evaluation and Optimization of Flank Wear During Turning of AISI 4340 Steel with Coated Carbide Inserts Using Different Cutting Fluids

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Lawal, S. A.; Choudhury, I. A.; Nukman, Y.

2015-01-01

The understanding of cutting fluids performance in turning process is very important in order to improve the efficiency of the process. This efficiency can be determined based on certain process parameters such as flank wear, cutting forces developed, temperature developed at the tool chip interface, surface roughness on the work piece, etc. In this study, the objective is to determine the influence of cutting fluids on flank wear during turning of AISI 4340 with coated carbide inserts. The performances of three types of cutting fluids were compared using Taguchi experimental method. The results show that palm kernel oil based cutting fluids performed better than the other two cutting fluids in reducing flank wear. Mathematical models for cutting parameters such as cutting speed, feed rate, depth of cut and cutting fluids were obtained from regression analysis using MINITAB 14 software to predict flank wear. Experiments were conducted based on the optimized values to validate the regression equations for flank wear and 5.82 % error was obtained. The optimal cutting parameters for the flank wear using S/N ratio were 160 m/min of cutting speed (level 1), 0.18 mm/rev of feed (level 1), 1.75 mm of depth of cut (level 2) and 2.97 mm2/s palm kernel oil based cutting fluid (level 3). ANOVA shows cutting speed of 85.36 %; and feed rate 4.81 %) as significant factors.
The Ngorongoro Volcanic Highland and its relationships to volcanic deposits at Olduvai Gorge and East African Rift volcanism.

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Mollel, Godwin F; Swisher, Carl C

2012-08-01

The Ngorongoro Volcanic Highland (NVH), situated adjacent and to the east of Olduvai Gorge in northern Tanzania, is the source of the immense quantities of lava, ignimbrite, air fall ash, and volcaniclastic debris that occur interbedded in the Plio-Pleistocene sedimentary deposits in the Laetoli and Olduvai areas. These volcanics have proven crucial to unraveling stratigraphic correlations, the age of these successions, the archaeological and paleontological remains, as well as the source materials from which the bulk of the stone tools were manufactured. The NVH towers some 2,000 m above the Olduvai and Laetoli landscapes, affecting local climate, run-off, and providing varying elevation - climate controlled ecosystem, habitats, and riparian corridors extending into the Olduvai and Laetoli lowlands. The NVH also plays a crucial role in addressing the genesis and history of East African Rift (EAR) magmatism in northern Tanzania. In this contribution, we provide age and petrochemical compositions of the major NVH centers: Lemagurut, basalt to benmorite, 2.4-2.2 Ma; Satiman, tephrite to phonolite, 4.6-3.5 Ma; Oldeani, basalt to trachyandesite, 1.6-1.5 Ma; Ngorongoro, basalt to rhyolite, 2.3-2.0 Ma; Olmoti, basalt to trachyte, 2.0-1.8 Ma; Embagai, nephelinite to phonolite, 1.2-0.6 Ma; and Engelosin, phonolite, 3-2.7 Ma. We then discuss how these correlate in time and composition with volcanics preserved at Olduvai Gorge. Finally, we place this into context with our current understanding as to the eruptive history of the NVH and relationship to East African Rift volcanism. Copyright © 2011 Elsevier Ltd. All rights reserved.
Using Satellite Observations to Evaluate the AeroCOM Volcanic Emissions Inventory and the Dispersal of Volcanic SO2 Clouds in MERRA

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Hughes, Eric J.; Krotkov, Nickolay; da Silva, Arlindo; Colarco, Peter

2015-01-01

Simulation of volcanic emissions in climate models requires information that describes the eruption of the emissions into the atmosphere. While the total amount of gases and aerosols released from a volcanic eruption can be readily estimated from satellite observations, information about the source parameters, like injection altitude, eruption time and duration, is often not directly known. The AeroCOM volcanic emissions inventory provides estimates of eruption source parameters and has been used to initialize volcanic emissions in reanalysis projects, like MERRA. The AeroCOM volcanic emission inventory provides an eruptions daily SO2 flux and plume top altitude, yet an eruption can be very short lived, lasting only a few hours, and emit clouds at multiple altitudes. Case studies comparing the satellite observed dispersal of volcanic SO2 clouds to simulations in MERRA have shown mixed results. Some cases show good agreement with observations Okmok (2008), while for other eruptions the observed initial SO2 mass is half of that in the simulations, Sierra Negra (2005). In other cases, the initial SO2 amount agrees with the observations but shows very different dispersal rates, Soufriere Hills (2006). In the aviation hazards community, deriving accurate source terms is crucial for monitoring and short-term forecasting (24-h) of volcanic clouds. Back trajectory methods have been developed which use satellite observations and transport models to estimate the injection altitude, eruption time, and eruption duration of observed volcanic clouds. These methods can provide eruption timing estimates on a 2-hour temporal resolution and estimate the altitude and depth of a volcanic cloud. To better understand the differences between MERRA simulations and volcanic SO2 observations, back trajectory methods are used to estimate the source term parameters for a few volcanic eruptions and compared to their corresponding entry in the AeroCOM volcanic emission inventory. The nature of
Flanking sequence determination and event-specific detection of genetically modified wheat B73-6-1.

Science.gov (United States)

Xu, Junyi; Cao, Jijuan; Cao, Dongmei; Zhao, Tongtong; Huang, Xin; Zhang, Piqiao; Luan, Fengxia

2013-05-01

In order to establish a specific identification method for genetically modified (GM) wheat, exogenous insert DNA and flanking sequence between exogenous fragment and recombinant chromosome of GM wheat B73-6-1 were successfully acquired by means of conventional polymerase chain reaction (PCR) and thermal asymmetric interlaced (TAIL)-PCR strategies. Newly acquired exogenous fragment covered the full-length sequence of transformed genes such as transformed plasmid and corresponding functional genes including marker uidA, herbicide-resistant bar, ubiquitin promoter, and high-molecular-weight gluten subunit. The flanking sequence between insert DNA revealed high similarity with Triticum turgidum A gene (GenBank: AY494981.1). A specific PCR detection method for GM wheat B73-6-1 was established on the basis of primers designed according to the flanking sequence. This specific PCR method was validated by GM wheat, GM corn, GM soybean, GM rice, and non-GM wheat. The specifically amplified target band was observed only in GM wheat B73-6-1. This method is of high specificity, high reproducibility, rapid identification, and excellent accuracy for the identification of GM wheat B73-6-1.
Martian volcanism: A review

International Nuclear Information System (INIS)

Carr, M.H.

1987-01-01

Martian volcanism is reviewed. It is emphasized that lava plains constitute the major type of effusive flow, and can be differentiated by morphologic characteristics. Shield volcanoes, domes, and patera constitute the major constructional landforms, and recent work has suggested that explosive activity and resulting pyroclastic deposits may have been involved with formation of some of the small shields. Analysis of morphology, presumed composition, and spectroscopic data all indicate that Martian volcanism was dominantly basaltic in composition
Volcanic eruptions and solar activity

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Stothers, Richard B.

1989-01-01

The historical record of large volcanic eruptions from 1500 to 1980 is subjected to detailed time series analysis. In two weak but probably statistically significant periodicities of about 11 and 80 yr, the frequency of volcanic eruptions increases (decreases) slightly around the times of solar minimum (maximum). Time series analysis of the volcanogenic acidities in a deep ice core from Greenland reveals several very long periods ranging from about 80 to about 350 yr which are similar to the very slow solar cycles previously detected in auroral and C-14 records. Solar flares may cause changes in atmospheric circulation patterns that abruptly alter the earth's spin. The resulting jolt probably triggers small earthquakes which affect volcanism.
Petrology, Geochemistry and Tectonomagmatic Setting of Farmahin Volcanic Rocks (North of Arak

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Reza Zarei Sahamieh

2018-04-01

-J diagram located in the Mg-Fe-Ca (Quad field and in the 2Ti+Cr+AlVI vs. Na+AlIV diagram (Morimoto et al., 1988 located above on the Fe3+=0 line that indicate high oxygen fugacity during crystallization. Microscopic study on these rocks such as oscillatory zoning, resorption rims in plagioclase and the presence of basic inclusions suggest the occurrence of magmatic contamination on the parent magma. The presence of oxidized amfibool rims (in hornbelende as oxy hornbelende indicate the high temperature of the magma at the time of eruption. According to the classification diagrams such as total alkaline vs. SiO2 (Irvine and Baragar, 1971 TAS (Le Bas et al., 1986 and tectonic discrimination diagrams (Pearce et al., 1984 samples are plotted in sub-alkaline, basaltic-andesite, andesite, dacite and rhyodacite, subduction and volcanic arc fields, respectively. The geochemical diagrams such as AFM are used for the identification of magma series and show that the studied rocks are calc-alkaline and A/NK vs. The A/CNK diagram shows the metaluminous to peraluminous nature. Incompatible and LIL elements such as Ba, K and Rb enrichment show that the contamination of magma with continental crust has occurred. The similarity between the REE patterns in all of the collected samples in Alam Baghi, Vashaghan, Sarban and Ghermez Cheshmeh areas suggest the same source for all of the volcanic rocks. Discussion The tectonic setting diagrams show that these rocks belong to the continental margin which has been involved in a subduction zone. The position of the samples on the major elements vs. SiO2 diagrams indicate that magma differentiation has occurred. Spider diagrams show a positive anomalous in Rb and a negative anomalous in Nb and Ti This phenomenon shows a contamination between the magma and the crustal rocks (Rollinson, 1993. Also, MORB-normalized incompatible element patterns of the Farmahin area show that the parent magma has been contaminated. It appears that assimilation and
Evolution of Rajabasa Volcano in Kalianda Area and Its Vicinity, South Lampung Regency

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Sutikno Bronto

2014-06-01

Full Text Available DOI: 10.17014/ijog.v7i1.132Rajabasa Volcano (± 1281 m and Lampung Tuff, located in the South Lampung Regency, is the main point in order to understand the evolution of Quaternary volcanism in the area. A remote sensing analysis and field geologic work are the methods of the study. The volcanism began with the construction period of the Pre-Rajabasa composite cone which was followed by the destruction period of the cone to form the Pre-Rajabasa Caldera having ca. 25 km in diameter. The present Rajabasa Volcano, along with cones of flank eruptions and monogenesis, has appeared in the Pre-Rajabasa Caldera depression. Those volcanic activities are considered as the second construction period. During the first and the second construction periods, basaltic to andesitic lava flows, pyroclastic breccias, and tuffs were erupted. The Rajabasa eruption points moved in WNW - ESE direction, which were possibly controlled by a subsurface weak zone. The Pre-Rajabasa Caldera erupted voluminous Lampung Tuffs having rhyolite in composition, and they are considered as a combination of pyroclastic falls, flows, and surges, or pyroclastic density currents.
Using faults for PSHA in a volcanic context: the Etna case (Southern Italy)

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Azzaro, Raffaele; D'Amico, Salvatore; Gee, Robin; Pace, Bruno; Peruzza, Laura

2016-04-01

At Mt. Etna volcano (Southern Italy), recurrent volcano-tectonic earthquakes affect the urbanised areas, with an overall population of about 400,000 and with important infrastructures and lifelines. For this reason, seismic hazard analyses have been undertaken in the last decade focusing on the capability of local faults to generate damaging earthquakes especially in the short-term (30-5 yrs); these results have to be intended as complementary to the regulatory seismic hazard maps, and devoted to establish priority in the seismic retrofitting of the exposed municipalities. Starting from past experience, in the framework of the V3 Project funded by the Italian Department of Civil Defense we performed a fully probabilistic seismic hazard assessment by using an original definition of seismic sources and ground-motion prediction equations specifically derived for this volcanic area; calculations are referred to a new brand topographic surface (Mt. Etna reaches more than 3,000 m in elevation, in less than 20 km from the coast), and to both Poissonian and time-dependent occurrence models. We present at first the process of defining seismic sources that includes individual faults, seismic zones and gridded seismicity; they are obtained by integrating geological field data with long-term (the historical macroseismic catalogue) and short-term earthquake data (the instrumental catalogue). The analysis of the Frequency Magnitude Distribution identifies areas in the volcanic complex, with a- and b-values of the Gutenberg-Richter relationship representative of different dynamic processes. Then, we discuss the variability of the mean occurrence times of major earthquakes along the main Etnean faults estimated by using a purely geologic approach. This analysis has been carried out through the software code FISH, a Matlab® tool developed to turn fault data representative of the seismogenic process into hazard models. The utilization of a magnitude-size scaling relationship
Fine crustal and uppermost mantle S-wave velocity structure beneath the Tengchong volcanic area inferred from receiver function and surface-wave dispersion: constraints on magma chamber distribution

Science.gov (United States)

Li, Mengkui; Zhang, Shuangxi; Wu, Tengfei; Hua, Yujin; Zhang, Bo

2018-03-01

The Tengchong volcanic area is located in the southeastern margin of the collision zone between the Indian and Eurasian Plates. It is one of the youngest intraplate volcano groups in mainland China. Imaging the S-wave velocity structure of the crustal and uppermost mantle beneath the Tengchong volcanic area is an important means of improving our understanding of its volcanic activity and seismicity. In this study, we analyze teleseismic data from nine broadband seismic stations in the Tengchong Earthquake Monitoring Network. We then image the crustal and uppermost mantle S-wave velocity structure by joint analysis of receiver functions and surface-wave dispersion. The results reveal widely distributed low-velocity zones. We find four possible magma chambers in the upper-to-middle crust and one in the uppermost mantle. The chamber in the uppermost mantle locates in the depth range from 55 to 70 km. The four magma chambers in the crust occur at different depths, ranging from the depth of 7 to 25 km in general. They may be the heat sources for the high geothermal activity at the surface. Based on the fine crustal and uppermost mantle S-wave velocity structure, we propose a model for the distribution of the magma chambers.
[Effects of volcanic eruptions on human health in Iceland. Review].

Science.gov (United States)

Gudmundsson, Gunnar; Larsen, Guðrun

2016-01-01

Volcanic eruptions are common in Iceland and have caused health problems ever since the settlement of Iceland. Here we describe volcanic activity and the effects of volcanic gases and ash on human health in Iceland. Volcanic gases expelled during eruptions can be highly toxic for humans if their concentrations are high, irritating the mucus membranes of the eyes and upper respiratory tract at lower concentrations. They can also be very irritating to the skin. Volcanic ash is also irritating for the mucus membranes of the eyes and upper respiratory tract. The smalles particles of volcanic ash can reach the alveoli of the lungs. Described are four examples of volcanic eruptions that have affected the health of Icelanders. The eruption of Laki volcanic fissure in 1783-1784 is the volcanic eruption that has caused the highest mortality and had the greatest effects on the well-being of Icelanders. Despite multiple volcanic eruptions during the last decades in Iceland mortality has been low and effects on human health have been limited, although studies on longterm effects are lacking. Studies on the effects of the Eyjafjallajökul eruption in 2010 on human health showed increased physical and mental symptoms, especially in those having respiratory disorders. The Directorate of Health in Iceland and other services have responded promptly to recurrent volcanic eruptions over the last few years and given detailed instructions on how to minimize the effects on the public health. Key words: volcanic eruptions, Iceland, volcanic ash, volcanic gases, health effects, mortality. Correspondence: Gunnar Guðmundsson, ggudmund@landspitali.is.
Study of surface roughness and flank wear in hard turning of AISI 4140 steel with coated ceramic inserts

Energy Technology Data Exchange (ETDEWEB)

Das, Sudhansu Ranjan; Kuma, Amaresh [National Institute of Technology, Jamshedpur (India); Dhupal, Debabrata [Veer Surendra Sai University of Technology, Burla (India)

2015-10-15

This experimental investigation deals with dry hard turning of AISI 4140 steel using PVD-TiN coated Al{sub 2}O{sub 3}+TiCN mixed ceramic inserts. The combined effect of cutting parameters (cutting speed, feed and depth of cut) on performance characteristics such as surface roughness and flank wear is explored by Full factorial design (FFD) and analysis of variance (ANOVA). The results show that feed is the principal cutting parameter influencing surface roughness, followed by cutting speed. However, flank wear is affected by the cutting speed and interaction of feed-depth of cut, although depth of cut has not been found statistically significant, but flank wear is an increasing function of depth of cut. Observations are made on the machined surface, and worn tool by Scanning electron microscope (SEM) to establish the process. Abrasion was the major wear mechanism found during hard turning within the studied range. The effect of tool wear on surface roughness was also studied. The experimental data were analyzed to predict the optimal range of surface roughness and flank wear. Based on Response surface methodology (RSM), mathematical models were developed for surface roughness (Ra) and flank wear (VB) with 95% confidence level. Finally, under optimum cutting conditions (obtained by response optimization technique), tool life was evaluated to perform cost analysis for justifying the economic viability of coated ceramic inserts in hard turning. The estimated machining cost per part for TiN coated ceramic was found to be lower (Rs. 12.31) because of higher tool life (51 min), which results in the reduction of downtime and increase in savings.
Study of surface roughness and flank wear in hard turning of AISI 4140 steel with coated ceramic inserts

International Nuclear Information System (INIS)

Das, Sudhansu Ranjan; Kuma, Amaresh; Dhupal, Debabrata

2015-01-01

This experimental investigation deals with dry hard turning of AISI 4140 steel using PVD-TiN coated Al_2O_3+TiCN mixed ceramic inserts. The combined effect of cutting parameters (cutting speed, feed and depth of cut) on performance characteristics such as surface roughness and flank wear is explored by Full factorial design (FFD) and analysis of variance (ANOVA). The results show that feed is the principal cutting parameter influencing surface roughness, followed by cutting speed. However, flank wear is affected by the cutting speed and interaction of feed-depth of cut, although depth of cut has not been found statistically significant, but flank wear is an increasing function of depth of cut. Observations are made on the machined surface, and worn tool by Scanning electron microscope (SEM) to establish the process. Abrasion was the major wear mechanism found during hard turning within the studied range. The effect of tool wear on surface roughness was also studied. The experimental data were analyzed to predict the optimal range of surface roughness and flank wear. Based on Response surface methodology (RSM), mathematical models were developed for surface roughness (Ra) and flank wear (VB) with 95% confidence level. Finally, under optimum cutting conditions (obtained by response optimization technique), tool life was evaluated to perform cost analysis for justifying the economic viability of coated ceramic inserts in hard turning. The estimated machining cost per part for TiN coated ceramic was found to be lower (Rs. 12.31) because of higher tool life (51 min), which results in the reduction of downtime and increase in savings.
Hawaiian volcanic propagation and Hawaiian swell asymmetry : evidence of northwestward flow of the deep upper mantle

NARCIS (Netherlands)

Cox, RT

1999-01-01

Bathymetry and the geoid anomaly of the northern flank of the Hawaiian swell is broader and higher than the southern flank, and it is characterized by higher heat flow than the axis or southern flank. It is here proposed that the northern flank of the Hawaiian swell has been augmented by heat
Scanning mutagenesis of the amino acid sequences flanking phosphorylation site 1 of the mitochondrial pyruvate dehydrogenase complex

Directory of Open Access Journals (Sweden)

Nagib eAhsan

2012-07-01

Full Text Available The mitochondrial pyruvate dehydrogenase complex is regulated by reversible seryl-phosphorylation of the E1α subunit by a dedicated, intrinsic kinase. The phospho-complex is reactivated when dephosphorylated by an intrinsic PP2C-type protein phosphatase. Both the position of the phosphorylated Ser-residue and the sequences of the flanking amino acids are highly conserved. We have used the synthetic peptide-based kinase client assay plus recombinant pyruvate dehydrogenase E1α and E1α-kinase to perform scanning mutagenesis of the residues flanking the site of phosphorylation. Consistent with the results from phylogenetic analysis of the flanking sequences, the direct peptide-based kinase assays tolerated very few changes. Even conservative changes such as Leu, Ile, or Val for Met, or Glu for Asp, gave very marked reductions in phosphorylation. Overall the results indicate that regulation of the mitochondrial pyruvate dehydrogenase complex by reversible phosphorylation is an extreme example of multiple, interdependent instances of co-evolution.
Finite Element Analysis Of Influence Of Flank Wear Evolution On Forces In Orthogonal Cutting Of 42CrMo4 Steel

Directory of Open Access Journals (Sweden)

Madajewski Marek

2017-01-01

Full Text Available This paper presents analysis of flank wear influence on forces in orthogonal turning of 42CrMo4 steel and evaluates capacity of finite element model to provide such force values. Data about magnitude of feed and cutting force were obtained from measurements with force tensiometer in experimental test as well as from finite element analysis of chip formation process in ABAQUS/Explicit software. For studies an insert with complex rake face was selected and flank wear was simulated by grinding operation on its flank face. The aim of grinding inset surface was to obtain even flat wear along cutting edge, which after the measurement could be modeled with CAD program and applied in FE analysis for selected range of wear width. By comparing both sets of force values as function of flank wear in given cutting conditions FEA model was validated and it was established that it can be applied to analyze other physical aspects of machining. Force analysis found that progression of wear causes increase in cutting force magnitude and steep boost to feed force magnitude. Analysis of Fc/Ff force ratio revealed that flank wear has significant impact on resultant force in orthogonal cutting and magnitude of this force components in cutting and feed direction. Surge in force values can result in transfer of substantial loads to machine-tool interface.
Finite Element Analysis Of Influence Of Flank Wear Evolution On Forces In Orthogonal Cutting Of 42CrMo4 Steel

Science.gov (United States)

Madajewski, Marek; Nowakowski, Zbigniew

2017-01-01

This paper presents analysis of flank wear influence on forces in orthogonal turning of 42CrMo4 steel and evaluates capacity of finite element model to provide such force values. Data about magnitude of feed and cutting force were obtained from measurements with force tensiometer in experimental test as well as from finite element analysis of chip formation process in ABAQUS/Explicit software. For studies an insert with complex rake face was selected and flank wear was simulated by grinding operation on its flank face. The aim of grinding inset surface was to obtain even flat wear along cutting edge, which after the measurement could be modeled with CAD program and applied in FE analysis for selected range of wear width. By comparing both sets of force values as function of flank wear in given cutting conditions FEA model was validated and it was established that it can be applied to analyze other physical aspects of machining. Force analysis found that progression of wear causes increase in cutting force magnitude and steep boost to feed force magnitude. Analysis of Fc/Ff force ratio revealed that flank wear has significant impact on resultant force in orthogonal cutting and magnitude of this force components in cutting and feed direction. Surge in force values can result in transfer of substantial loads to machine-tool interface.

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