Sample records for volcanic units anisotropy

  1. Anisotropy of Anhysteretic Remanent Magnetization: A Tool To Estimate Trm Deviations In Volcanic Rocks (United States)

    Gattacceca, J.; Rochette, P.

    In order to assess the paleomagnetic direction deviations due to anisotropy in volcanic rocks, we studied the anisotropies of magnetic susceptibility (AMS), of anhysteretic remanent magnetization (AARM) and of thermoremanent magnetization (ATRM) of a set of Miocene pyroclastic rocks from Sardinia (Italy). The main magnetic carrier is pseudo-single domain titanomagnetite. AARM and ATRM were determined with a 3-position measurement scheme. The measurements show that there is no general relation between the degrees of AMS and ATRM (as this relation depends on the ti- tanomagnetite grain size spectrum), while the degree of AARM and ATRM are almost identical. Measuring the AMS is thus nearly irrelevant to quantitatively estimate TRM deviations due to anisotropy in volcanic rocks. Instead, measuring the AARM provides a reliable and relatively fast method to correct paleomagnetic direction deviations in volcanic rocks (inclination shallowing due to horizontal planar fabric in most cases). This is confirmed by a case study on a succession of four welded pyroclastic flows : an apparent paleosecular variation pattern is almost entirely explained by the effect of ATRM.

  2. Evidence for the development of permeability anisotropy in lava domes and volcanic conduits (United States)

    Farquharson, Jamie I.; Heap, Michael J.; Lavallée, Yan; Varley, Nick R.; Baud, Patrick


    The ease at which exsolving volatiles can migrate though magma and outgas influences the explosivity of a volcanic eruption. Volcanic rocks often contain discrete discontinuities, providing snapshots of strain localisation processes that occur during magma ascent and extrusion. Whether these features comprise pathways for or barriers to fluid flow is thus of relevance for volcanic eruption and gas emission modelling. We report here on nine discontinuity-bearing andesite blocks collected from Volcán de Colima, Mexico. We present a systematic porosity and permeability study of fifty cores obtained from the blocks collected, and interpret the genetic processes of the discontinuities through detailed microstructural examination. Bands in pumiceous blocks were inferred to be relicts of inhomogeneous bubble expansion which, despite significantly increasing porosity, do not markedly affect permeability. Other discontinuities in our blocks are interpreted to be shear strain-induced flow banding, cavitation porosity, and/or variably healed fractures. In each of these cases, an increase in permeability (up to around three orders of magnitude) was measured relative to the host material. A final sample contained a band of lower porosity than the host rock, characterised by variably infilled pores. In this case, the band was an order of magnitude less permeable than the host rock, highlighting the complex interplay between dilatant and densifying processes in magma. We therefore present evidence for significant permeability anisotropy within the conduit and/or dome of a volcanic system. We suggest that the abundance and distribution of strain localisation features will influence the escape or entrapment of volatiles and therefore the evolution of pore pressure within active volcanic systems. Using a simple upscaling model, we illustrate the relative importance of permeable structures over different lengthscales. Strain localisation processes resulting in permeability

  3. Magnetic anisotropy in rhyolitic ignimbrite, Snake River Plain: Implications for using remanent magnetism of volcanic rocks for correlation, paleomagnetic studies, and geological reconstructions (United States)

    Finn, David R.; Coe, Robert S.; Kelly, Henry; Branney, Michael; Knott, Thomas; Reichow, Marc


    Individual ignimbrite cooling units in southern Idaho display significant variation of magnetic remanence directions and other magnetic properties. This complicates paleomagnetic correlation. The ignimbrites are intensely welded and exhibit mylonite-like flow banding produced by rheomorphic ductile shear during emplacement, prior to cooling below magnetic blocking temperatures. Glassy vitrophyric lithologies commonly have discrepantly shallow remanence directions rotated closer to the orientation of the subhorizontal shear fabric when compared to the microcrystalline center of the same cooling unit. To investigate this problem, we conducted a detailed paleomagnetic and rock magnetic study of a vertical profile through a single ignimbrite cooling unit and its underlying baked soil. The results demonstrate that large anisotropy of thermal remanent magnetization correlates with large (up to 38°) deflections of the stable remanence direction. Anisotropy of magnetic susceptibility revealed no strong anisotropy. A strong lineation and deflection of the remanence declination suggest that rheomorphic shear above magnetic blocking temperatures is the dominant mechanism controlling the formation of the magnetic fabric, with compaction contributing to a lesser extent. Nucleation and growth of anisotropic fine-grained magnetite in volcanic glass at high temperatures after, and perhaps also during, emplacement is indicated by systematic variation of magnetic properties from the quickly chilled ignimbrite base to the interior. These properties include remanence directions, anisotropy, coercivity, susceptibility, strength of natural remanent magnetization, and dominant unblocking temperature. The microcrystalline ignimbrite center has a magnetic direction that is the same as the underlying baked soil and, therefore, is a more reliable recorder of the paleofield direction than the glassy margins of highly welded ignimbrites.

  4. Influence of anisotropy of magnetic susceptibility (AMS) on paleomagnetic sampling in volcanic glasses: a case study on rheomorphic ignimbrites of the Yellowstone hotspot-track, southern Idaho (United States)

    Finn, D.; Coe, R. S.; Murphy, J.; Bodiford, S.; Kelly, H.; Foster, S.; Spinardi, F.; Reichow, M. K.; Knott, T.; Branney, M. J.


    Large-scale explosive volcanism, associated with the Yellowstone hotspot, occurred in the central Snake River Plain between 12.5-8 Ma. It is characterized by unusually high-temperature, intensely welded, rheomorphic rhyolitic ignimbrites, typical of what is now known as 'Snake River (SR)-type volcanism'. Individual eruption volumes likely exceed 450 km3 but are poorly known due to the difficulty of correlating units between widely spaced (50-200 km) exposures along the north and south of the plain, when some occurred too close-spaced in time for radiometric resolution. Our goal is to use a combination of paleomagnetic, petrographic, chemical and field characterization to establish robust correlations, allowing us to develop a regional stratigraphy, and constrain ignimbrite eruption volumes and frequencies. This presentation focuses on how to sample rheomorphic, SR-type ignimbrites for paleomagnetic studies given the potential effects of hot, rheomorphic deformation. Individual SR-type ignimbrite cooling-units have an upper and lower glassy margins (vitrophyre) enclosing a lithoidal (microcrystalline) zone. We have sampled dozens of ignimbrites in detail and have observed that the lithoidal interiors are preferable to the glassy margins for paleomagnetic studies. We hypothesize that the glassy margins retain an anisotropic fabric related to emplacement compaction and/or shearing that affects their ability to accurately record the magnetic field during cooling. In the lithoidal interiors this anisotropic fabric was overprinted by continued grain growth and/or alteration and, therefore, may accurately record the paleomagnetic field. Paleomagnetic samples from vitrophyres generally have a higher anisotropy in magnetic susceptibility than lithoidal samples. The remanent magnetic directions recorded in samples with high anisotropy of magnetic susceptibility are often deflected away from the site mean and closer to the plane of easy magnetic susceptibility. Since the

  5. The United States national volcanic ash operations plan for aviation (United States)

    Albersheim, Steven; Guffanti, Marianne


    Volcanic-ash clouds are a known hazard to aviation, requiring that aircraft be warned away from ash-contaminated airspace. The exposure of aviation to potential hazards from volcanoes in the United States is significant. In support of existing interagency operations to detect and track volcanic-ash clouds, the United States has prepared a National Volcanic Ash Operations Plan for Aviation to strengthen the warning process in its airspace. The US National Plan documents the responsibilities, communication protocols, and prescribed hazard messages of the Federal Aviation Administration, National Oceanic and Atmospheric Administration, US Geological Survey, and Air Force Weather Agency. The plan introduces a new message format, a Volcano Observatory Notice for Aviation, to provide clear, concise information about volcanic activity, including precursory unrest, to air-traffic controllers (for use in Notices to Airmen) and other aviation users. The plan is online at While the plan provides general operational practices, it remains the responsibility of the federal agencies involved to implement the described procedures through orders, directives, etc. Since the plan mirrors global guidelines of the International Civil Aviation Organization, it also provides an example that could be adapted by other countries.

  6. Ultrasonic velocity and attenuation anisotropy of shales, Whitby, United Kingdom

    NARCIS (Netherlands)

    Zhubayev, A.; Houben, M.E.; Smeulders, D.M.J.; Barnhoorn, A.


    We have conducted ultrasonic experiments, between 0.3 and 1 MHz, to measure velocity and attenuation (Q−1) anisotropy of P- and S-waves in dry Whitby Mudstone samples as a function of stress. We found the degree of anisotropy to be as large as 70% for velocity and attenuation. The sensitivity of P-w

  7. Ultrasonic velocity and attenuation anisotropy of shales, Whitby, United Kingdom

    NARCIS (Netherlands)

    Zhubayev, Alimzhan; Houben, M.E.; Smeulders, David; Barnhoorn, A.


    We have conducted ultrasonic experiments, between 0.3 and 1 MHz, to measure velocity and attenuation (Q−1) anisotropy of P- and S-waves in dry Whitby Mudstone samples as a function of stress. We found the degree of anisotropy to be as large as 70% for velocity and attenuation. The sensitivity of P-w

  8. Anisotropy of Magnetic Susceptibility (AMS) of the Neogene Volcanic Succession at the Sierra Juarez - Las PintasVolcanic Province, Northeastern Baja California, Mexico: Preliminary Results (United States)

    Mendoza-Borunda, R.; Cañón-Tapia, E.; Suárez-Vidal, F.; Gradilla-Martínez, L.


    The Sierra Juarez-Las Pintas Volcanic Province is among the largest in northern Baja California. For this work, we focused on a bimodal volcanic succession of late Miocene age, composed of an extensive ignimbrite unit and few dispersed basaltic flows that crop out in central Sierra Juarez and northern Sierra Las Tinajas. The ignimbrite is zoned, composed by three distinctive members: a basal unwelded white tuff, a mid-section unwelded orange tuff, and an upper red welded tuff. The basaltic flows are olivine-rich. Samples were collected in five sites that define a NE-SW section across the Sierra Juarez Escarpment, in the western boundary of the so-called Gulf Extensional Province. In each of these sites a stratigraphic column composed of more than one geologic unit was sampled. The total number of analyzed cores is ca. 160. The preliminary results show vertical and lateral variations of the AMS of the ignimbrite that can be interpreted in terms of the local flow direction and processes of emplacement of these volcanic deposits. Such variations, in turn, are likely to reflect variations in the dynamics of the eruptive process that produced them. Although the AMS of all the rocks in this province display a complex set of orientations, in this work is shown that when examined in detail important clues concerning the geological evolution of the province can be obtained from these data.

  9. A detailed seismic anisotropy study during the 2011-2012 unrest period in the Santorini Volcanic Complex (United States)

    Kaviris, G.; Papadimitriou, P.; Kravvariti, Ph.; Kapetanidis, V.; Karakonstantis, A.; Voulgaris, N.; Makropoulos, K.


    The Santorini Volcanic Complex (SVC) is an area in the Southern Aegean (Greece) which has been characterized by low seismicity rates for the last decades, especially in the Santorini Caldera where they have been very low until 2010. This pattern changed completely in February 2011, when intense microseismic activity was initiated within the Caldera. During the manual analysis of the events, the shear-wave splitting phenomenon was observed, revealing the existence of an anisotropic upper crust in the SVC area. A detailed anisotropy study has been conducted using 231 events within the shear-wave window that fulfilled the selection criteria. The polarization direction of the fast shear-wave, the time-delay between the two split shear-waves and the source polarization direction were calculated after visual inspection, using both the polarigram and the hodogram representations. This procedure, applied for eight local stations, resulted in the determination of 340 splitting parameters. The obtained mean anisotropy directions are not homogeneous, revealing a complex regime in the activated area. Nevertheless, these results are explained by the APE model, related to the stress-sensitive behavior of fluid-saturated microcracked rocks. A detailed analysis of the temporal evolution of both the time-delay and anisotropy direction was carried out. The time-delays measured in the “band-1” window exhibit gradual increase and sudden drop that can be related to imminent bursts of seismicity, as well as to the major Mw = 5.1 and 5.2 events which took place about 40 km SW of Santorini on 26 and 27 January 2012, respectively. On the other hand, no significant temporal variations or 90° flips of the Sfast polarization direction were observed.

  10. Rock magnetism and magnetic anisotropy in folded sills and basaltic flows: A case study of volcanics from the Taimyr Peninsula, Northern Russia

    Institute of Scientific and Technical Information of China (English)

    ZHANG ShuWei; J. Harald WALDERHAUG; YANG YueJun


    Magnetic measurements were performed on apparently deformed igneous rocks of 23 sites from the southeastern part of the Taimyr Peninsula. Rock magnetism and reflected light microscopy analyses reveal that fine-grained titanomagnetites up to pure magnetites mainly carry the majority of magnetic fabrics in the sills, and that the slightly coarser Ti-poor or-medium titanomagnetites carry most mag-netic fabrics in the basaltic flows. Magnetic anisotropies were determined by applying anisotropy of low-field magnetic susceptibility (AMS) on 180 unheated samples and 128 samples that had been pre-viously heated to 600℃ during a paleomagnetic study to detect heating effects on the anisotropy of magnetic susceptibility (AMS) properties of volcanic rocks. Laboratory heating significantly affects anisotropy variations of these igneous rocks corresponding to the mineralogical changes during the heat treatment.

  11. Spatial Compilation of Holocene Volcanic Vents in the Western Conterminous United States (United States)

    Ramsey, D. W.; Siebert, L.


    A spatial compilation of all known Holocene volcanic vents in the western conterminous United States has been assembled. This compilation records volcanic vent location (latitude/longitude coordinates), vent type (cinder cone, dome, etc.), geologic map unit description, rock type, age, numeric age and reference (if dated), geographic feature name, mapping source, and, where available, spatial database source. Primary data sources include: USGS geologic maps, USGS Data Series, the Smithsonian Global Volcanism Program (GVP) catalog, and published journal articles. A total of 726 volcanic vents have been identified from 45 volcanoes or volcanic fields spanning ten states. These vents are found along the length of the Cascade arc in the Pacific Northwest, widely around the Basin and Range province, and at the southern margin of the Colorado Plateau into New Mexico. The U.S. Geological Survey (USGS) National Volcano Early Warning System (NVEWS) identifies 28 volcanoes and volcanic centers in the western conterminous U.S. that pose moderate, high, or very high threats to surrounding communities based on their recent eruptive histories and their proximity to vulnerable people, property, and infrastructure. This compilation enhances the understanding of volcano hazards that could threaten people and property by providing the context of where Holocene eruptions have occurred and where future eruptions may occur. Locations in this compilation can be spatially compared to located earthquakes, used as generation points for numerical hazard models or hazard zonation buffering, and analyzed for recent trends in regional volcanism and localized eruptive activity.

  12. Mechanism of formation of volcanic bombs: insights from a pilot study of anisotropy of magnetic susceptibility and preliminary assessment of analytical models (United States)

    Cañón-Tapia, Edgardo


    Volcanic bombs and achneliths are a special type of pyroclastic fragments formed by mildly explosive volcanic eruptions. Models explaining the general shapes of those particles can be divided in two broad categories. The most popular envisages the acquisition of shapes of volcanic bombs as the result of the rush of air acting on a fluid clot during flight, and it includes many variants. The less commonly quoted model envisages their shapes as the result of forces acting at the moment of ejection of liquid from the magma pool in the conduit, experiencing an almost negligible modification through its travel through air. Quantitative evidence supporting either of those two models is limited. In this work, I explore the extent to which the anisotropy of magnetic susceptibility (AMS) might be useful in the study of mechanisms of formation of volcanic bombs by comparing measurements made on two spindle and two bread-crusted bombs. The results of this pilot study reveal that the degree of anisotropy of spindle bombs is larger, and their principal susceptibility axes are better clustered than on bread-crusted bombs. Also, the orientation of the principal susceptibility axes is consistent with two specific models (one of the in-flight variants and the general ejection model). Consequently, the reported AMS measurements, albeit limited in number, indicate that it is reasonable to focus attention on only two specific models to explain the acquisition of the shapes of volcanic bombs. Based on a parallel theoretical assessment of analytical models, a third alternative is outlined, envisaging volcanic bomb formation as a two-stage process that involves the bursting of large ( m) gas bubbles on the surface of a magma pond. The new model advanced here is also consistent with the reported AMS results, and constitutes a working hypothesis that should be tested by future studies richer in data. Fortunately, since this work also establishes that AMS can be used to determine magnetic

  13. Field-trip guides to selected volcanoes and volcanic landscapes of the western United States (United States)



    The North American Cordillera is home to a greater diversity of volcanic provinces than any comparably sized region in the world. The interplay between changing plate-margin interactions, tectonic complexity, intra-crustal magma differentiation, and mantle melting have resulted in a wealth of volcanic landscapes.  Field trips in this guide book collection (published as USGS Scientific Investigations Report 2017–5022) visit many of these landscapes, including (1) active subduction-related arc volcanoes in the Cascade Range; (2) flood basalts of the Columbia Plateau; (3) bimodal volcanism of the Snake River Plain-Yellowstone volcanic system; (4) some of the world’s largest known ignimbrites from southern Utah, central Colorado, and northern Nevada; (5) extension-related volcanism in the Rio Grande Rift and Basin and Range Province; and (6) the eastern Sierra Nevada featuring Long Valley Caldera and the iconic Bishop Tuff.  Some of the field trips focus on volcanic eruptive and emplacement processes, calling attention to the fact that the western United States provides opportunities to examine a wide range of volcanological phenomena at many scales.The 2017 Scientific Assembly of the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) in Portland, Oregon, was the impetus to update field guides for many of the volcanoes in the Cascades Arc, as well as publish new guides for numerous volcanic provinces and features of the North American Cordillera. This collection of guidebooks summarizes decades of advances in understanding of magmatic and tectonic processes of volcanic western North America. These field guides are intended for future generations of scientists and the general public as introductions to these fascinating areas; the hope is that the general public will be enticed toward further exploration and that scientists will pursue further field-based research.

  14. Shear-wave velocity structure of the Tongariro Volcanic Centre, New Zealand: Fast Rayleigh and slow Love waves indicate strong shallow anisotropy (United States)

    Godfrey, Holly J.; Fry, Bill; Savage, Martha K.


    frequency range of 0.25-1 Hz. First-higher mode Love-waves are similarly slower than first-higher mode Rayleigh waves. This is incompatible with synthetic dispersion curves we calculate using isotropic, layered velocity models appropriate for Ruapehu and Tongariro, in which Love waves travel more quickly than Rayleigh waves of the same period. The Love-Rayleigh discrepancy is likely due to structures such as dykes or cracks in the vertical plane having increased influence on surface-wave propagation. However, several measurements at Ruapehu have Love-wave group velocities that are faster than Rayleigh-wave group velocities. The differences between the Love- and Rayleigh-wave dispersion curves also vary with the azimuth of the interstation path across Ruapehu and Tongariro Volcanoes. Significant azimuthal dependence of both Love and Rayleigh-wave velocities are also observed. This suggests azimuthal anisotropy within the volcanic structures, which coupled with radial anisotropy, makes the Vs structures of Ruapehu and Tongariro Volcanoes anisotropic with orthorhombic or lower order symmetry. We suggest that further work to determine three-dimensional volcanic structures should include provisions for such anisotropy.

  15. Anisotropy of magnetic susceptibility in welded tuffs: application to a welded-tuff dyke in the tertiary Trans-Pecos Texas volcanic province, USA (United States)

    Wolff, John A.; Ellwood, Brooks B.; Sachs, Scott D.


    Consideration of published anisotropy of magnetic susceptibility (AMS) studies on welded ignimbrites suggests that AMS fabrics are controlled by groundmass microlites distributed within the existing tuff fabric, the sum result of directional fabrics imposed by primary flow lineation, welding, and (if relevant) rheomorphism. AMS is a more sensitive indicator of fabric elements within welded tuffs than conventional methods, and usually yields primary flow azimuth estimates. Detailed study of a single densely welded tuff sample demonstrates that the overall AMS fabric is insensitive to the relative abundances of fiamme, matrix and lithics within individual drilled cores. AMS determinations on a welded-tuff dyke occurring in a choked vent in the Trans-Pecos Texas volcanic field reveals a consistent fabric with a prolate element imbricated with respect to one wall of the dyke, while total magnetic susceptibility and density exhibit axially symmetric variations across the dyke width. The dyke is interpreted to have formed as a result of agglutination of the erupting mixture on a portion of the conduit wall as it failed and slid into the conduit, followed by residual squeezing between the failed block and in situ wallrock. Irrespective of the precise mechanism, widespread occurrence of both welded-tuff dykes and point-welded, aggregate pumices in pyroclastic deposits may imply that lining of conduit walls by agglutionation during explosive volcanic eruptions is a common process.

  16. Preliminary overview map of volcanic hazards in the 48 conterminous United States (United States)

    Mullineaux, D.R.


    Volcanic eruptions and related phenomena can be expected to occur in the Western United States, and in some places are potentially hazardous enough to be considered in longe-range land-use planning. But the immediate risk from volcanic hazards is low because eruptions are so infrequent in the conterminous United States that few, if any, occur during any one person 1s lifetime. Furthermore, severely destructive effects of eruptions, other than extremely rare ones of catastrophic scale, probably would be limited to areas within a few tens of kilometers downvalley or downwind from a volcano. Thus, the area seriously endangered by any one eruption would be only a very small part of the Western United States. The accompanying map identifies areas in which volcanic hazards pose some degree of risk, and shows that the problem is virtually limited to the far western States. The map also shows the possible areal distribution of several kinds of dangerous eruptive events and indicates the relative likelihood of their occurrence at various volcanoes. The kinds of events described here as hazards are those that can occur suddenly and with little or no warning; they do not include long-term geologic processes. Table 1 summarizes the origin and some characteristics of potentially hazardous volcanic phenomena. The map is diagrammatic. It does not show the specific location of the next expected eruption , because such an event cannot be reliably predicted . Instead, the map shows general areas or zones that, over a long period of time, are relatively likely to be affected in one or more places by various kinds of hazardous volcanic events. However, only a small part of one of these areas would be affected by any single eruption.

  17. United States-Chile binational exchange for volcanic risk reduction, 2015—Activities and benefits (United States)

    Pierson, Thomas C.; Mangan, Margaret T.; Lara Pulgar, Luis E.; Ramos Amigo, Álvaro


    In 2015, representatives from the United States and Chile exchanged visits to discuss and share their expertise and experiences dealing with volcano hazards. Communities in both countries are at risk from various volcano hazards. Risks to lives and property posed by these hazards are a function not only of the type and size of future eruptions but also of distances from volcanoes, structural integrity of volcanic edifices, landscape changes imposed by recent past eruptions, exposure of people and resources to harm, and any mitigative measures taken (or not taken) to reduce risk. Thus, effective risk-reduction efforts require the knowledge and consideration of many factors, and firsthand experience with past volcano crises provides a tremendous advantage for this work. However, most scientists monitoring volcanoes and most officials delegated with the responsibility for emergency response and management in volcanic areas have little or no firsthand experience with eruptions or volcano hazards. The reality is that eruptions are infrequent in most regions, and individual volcanoes may have dormant periods lasting hundreds to thousands of years. Knowledge may be lacking about how to best plan for and manage future volcanic crises, and much can be learned from the sharing of insights and experiences among counterpart specialists who have had direct, recent, or different experiences in dealing with restless volcanoes and threatened populations. The sharing of information and best practices can help all volcano scientists and officials to better prepare for future eruptions or noneruptive volcano hazards, such as large volcanic mudflows (lahars), which could affect their communities.

  18. Seismic anisotropy and mantle dynamics beneath the central and western United States (United States)

    Yang, Bin

    Various tectonic features and the recent availability of high-quality broadband seismic data from the USArray and other seismic stations in the central and western United States (CWUS) provide a distinct opportunity to test different anisotropy-forming mechanisms. For the first part of the study, a total of 4138 pairs of well-defined shear wave splitting (SWS) parameters observed at 445 stations on the northern Great Plains show systematic spatial variations of anisotropic characteristics. Azimuthally invariant fast orientations subparallel to the absolute plate motion (APM) direction are observed at most of the stations on the Superior Craton and the southern Yavapai province, indicating that a single layer of anisotropy with a horizontal axis of symmetry is sufficient to explain the anisotropic structure. Based on the splitting measurements and previous results from seismic tomography and geodynamic modeling, we propose a model involving deflecting of asthenosphere flow by the bottom of the lithosphere and channeling flow by a zone of thinned lithosphere approximately along the northern boundary of the Yavapai province. The second part of the study created an up-to-date SWS database for CWUS in the area of 125° W to 90° W, 26° N to 52° N to upgrade a previous database [Liu et al., 2014]. A total of 7452 pairs of high-quality measurements recorded by 1202 digital broadband seismic stations (both permanent and portable seismic networks) over the period of 1989-2014 is obtained. The current version includes 23448 pairs of well-defined splitting parameters in three phases, i.e. PKS, SKKS and SKS. The dissertation is a combination of two journal papers published in 2014 and 2016, respectively.

  19. Overview of electromagnetic methods applied in active volcanic areas of western United States (United States)

    Skokan, Catherine K.


    A better understanding of active volcanic areas in the United States through electromagnetic geophysical studies received foundation from the many surveys done for geothermal exploration in the 1970's. Investigations by governmental, industrial, and academic agencies include (but are not limited to) mapping of the Cascades. Long Valley/Mono area, the Jemez volcanic field, Yellowstone Park, and an area in Colorado. For one example — Mt. Konocti in the Mayacamas Mountains, California — gravity, magnetic, and seismic, as well as electromagnetic methods have all been used in an attempt to gain a better understanding of the subsurface structure. In each of these volcanic regions, anomalous zones were mapped. When conductive, these anomalies were interpreted to be correlated with hydrothermal activity and not to represent a magma chamber. Electrical and electromagnetic geophysical methods can offer valuable information in the understanding of volcanoes by being the method which is most sensitive to change in temperature and, therefore, can best map heat budget and hydrological character to aid in prediction of eruptions.

  20. Paleomagnetic, Anisotropy of Magnetic Susceptibility, and 40AR/39AR Data from the Cienega Volcano, Cerros del Rio Volcanic Field, New Mexico (United States)

    Foucher, M. S.; Petronis, M. S.; Lindline, J.; Van Wyk de Vries, B.


    Cinder cone eruptions are typically interpreted to have formed by the ascension of magma through a simple conduit. Recent field work and laboratory studies on different excavated volcanoes around the world suggest that magma transport within cinder cones can involve a complex system of feeder geometries. We studied the Cienega volcano, a cinder cone in the Cerros del Rio volcanic field, northern New Mexico, in order to better understand the complexity and the evolution of volcanic plumbing systems in the development of cinder cone volcanoes. We hypothesized that cinder cone plumbing systems are inherently complex and involve numerous feeder geometries (e.g. dikes, sills) and flow patterns both towards and away from the central vent complex. The Cienega volcano comprises tephra fall deposits as well as several vents, multiple intrusions, and numerous lava flow sequences. We inspected the magmatic plumbing system using different laboratory methods including paleomagnetic, anisotropy of magnetic susceptibility (AMS), rock magnetic and thin section studies. We collected samples across each outcrop of the feeder system. The dikes are olivine porphyritic basalts with major clinopyroxene, calcic plagioclase feldspar, magnetite, and xenocrystic quartz. Most samples display a trachytic texture with plagioclase crystals showing a preferred orientation parallel to the dike margins. The magnetic information is held predominantly by a cubic phase magnetite with a low- to moderate-Ti composition of Single or Pseudo-Single Domain grains. The AMS results show various flow directions. Three of six dikes yielded magma flow directions away from the vent. The other dikes showed both a subvertical flow, which corresponds to the typical movement of magma in a dike originating from a deeper crustal level, and a downward flow direction. We concluded that magma initially flowed upward from the magma chamber until it encountered flow resistance. At this structural level (the current

  1. MODFLOW-2000, the U.S. Geological Survey modular ground-water model -- Documentation of the Model-Layer Variable-Direction Horizontal Anisotropy (LVDA) capability of the Hydrogeologic-Unit Flow (HUF) package (United States)

    Anderman, Evan R.; Kipp, K.L.; Hill, Mary C.; Valstar, Johan; Neupauer, R.M.


    This report documents the model-layer variable-direction horizontal anisotropy (LVDA) capability of the Hydrogeologic-Unit Flow (HUF) Package of MODFLOW-2000. The LVDA capability allows the principal directions of horizontal anisotropy to be different than the model-grid row and column directions, and for the directions to vary on a cell-by-cell basis within model layers. The HUF Package calculates effective hydraulic properties for model grid cells based on hydraulic properties of hydrogeologic units with thicknesses defined independently of the model layers. These hydraulic properties include, among other characteristics, hydraulic conductivity and a horizontal anisotropy ratio. Using the LVDA capability, horizontal anisotropy direction is defined for model grid cells within which one or more hydrogeologic units may occur. For each grid cell, the HUF Package calculates the effective horizontal hydraulic conductivity along the primary direction of anisotropy using the hydrogeologic-unit hydraulic conductivities, and calculates the effective horizontal hydraulic conductivity along the orthogonal anisotropy direction using the effective primary direction hydraulic conductivities and horizontal anisotropy ratios. The direction assigned to the model layer effective primary hydraulic conductivity is specified using a new data set defined by the LVDA capability, when active, to calculate coefficients needed to solve the ground-water flow equation. Use of the LVDA capability is illustrated in four simulation examples, which also serve to verify hydraulic heads, advective-travel paths, and sensitivities calculated using the LVDA capability. This version of the LVDA capability defines variable-direction horizontal anisotropy using model layers, not the hydrogeologic units defined by the HUF Package. This difference needs to be taken into account when designing model layers and hydrogeologic units to produce simulations that accurately represent a given field problem. This

  2. Pleistocene volcaniclastic units from North-Eastern Sicily (Italy): new evidence for calc-alkaline explosive volcanism in the Southern Tyrrhenian Sea (United States)

    Di Bella, Marcella; Italiano, Francesco; Sabatino, Giuseppe; Tripodo, Alessandro; Baldanza, Angela; Casella, Sergio; Pino, Paolo; Rasa', Riccardo; Russo, Selma


    A well-preserved volcaniclastic sequence crops out in Pleistocene marine sediments along the Tyrrhenian coastline of the Calabrian-Peloritani arc (Sicily, Italy), testifying the occurrence of Lower-Middle Pleistocene volcanic activity in Southern Tyrrhenian Sea. The presence of dominant highly vesicular and minor blocky glassy particles indicates that the volcanic clasts were originated by explosive events related to the ascent and violent emission of volatile-rich magmas accompanied by and/or alternated with hydromagmatic fragmentation due to magma-sea water interaction. Field investigations and sedimentological features of the studied volcaniclastic units suggest a deposition from sediment-water density flows. The chemical classification of the pumice clasts indicates prevalent rhyolitic and dacitic compositions with calc-alkaline to high-K calc-alkaline affinity. The geochemical features of immobile trace elements together with the presence of orthopyroxene are indicative of a provenance from an arc-type environment. The age (from 980-910 to 589 ka), the chemical composition and the evidence of subaerial explosive volcanic activity constrain the origin nature and temporal evolution of the arc-type volcanism in the Southern Tyrrhenian domain. Finally, the new information here provided contribute to a better understanding of the temporal geodynamic evolution of this sector of the Mediterranean domain.

  3. Vulnerability of shallow ground water and drinking-water wells to nitrate in the United States: Model of predicted nitrate concentration in shallow, recently recharged ground water -- Input data set for basalt and volcanic rocks (gwava-s_vrox) (United States)

    U.S. Geological Survey, Department of the Interior — This data set represents the presence or absence of basalt and volcanic rocks in the conterminous United States. The data set was used as an input data layer for a...

  4. Catastrophic volcanism (United States)

    Lipman, Peter W.


    Since primitive times, catastrophes due to volcanic activity have been vivid in the mind of man, who knew that his activities in many parts of the world were threatened by lava flows, mudflows, and ash falls. Within the present century, increasingly complex interactions between volcanism and the environment, on scales not previously experienced historically, have been detected or suspected from geologic observations. These include enormous hot pyroclastic flows associated with collapse at source calderas and fed by eruption columns that reached the stratosphere, relations between huge flood basalt eruptions at hotspots and the rifting of continents, devastating laterally-directed volcanic blasts and pyroclastic surges, great volcanic-generated tsunamis, climate modification from volcanic release of ash and sulfur aerosols into the upper atmosphere, modification of ocean circulation by volcanic constructs and attendent climatic implications, global pulsations in intensity of volcanic activity, and perhaps triggering of some intense terrestrial volcanism by planetary impacts. Complex feedback between volcanic activity and additional seemingly unrelated terrestrial processes likely remains unrecognized. Only recently has it become possible to begin to evaluate the degree to which such large-scale volcanic processes may have been important in triggering or modulating the tempo of faunal extinctions and other evolutionary events. In this overview, such processes are examined from the viewpoint of a field volcanologist, rather than as a previous participant in controversies concerning the interrelations between extinctions, impacts, and volcanism.

  5. Geomorphological Approach for Regional Zoning In The Merapi Volcanic Area

    Directory of Open Access Journals (Sweden)

    Langgeng Wahyu Santosa


    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.

  6. Volcanic hazards to airports (United States)

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


    , Tungurahua in Ecuador, Mt. Etna in Italy, Rabaul caldera in Papua New Guinea, Mt. Spurr and Mt. St. Helens in the USA, Ruapehu in New Zealand, Mt. Pinatubo in the Philippines, and Anatahan in the Commonwealth of the Northern Mariana Islands (part of the USA). Ten countries - USA, Indonesia, Ecuador, Papua New Guinea, Italy, New Zealand, Philippines, Mexico, Japan, and United Kingdom - have the highest volcanic hazard and/or vulnerability measures for airports. The adverse impacts of volcanic eruptions on airports can be mitigated by preparedness and forewarning. Methods that have been used to forewarn airports of volcanic activity include real-time detection of explosive volcanic activity, forecasts of ash dispersion and deposition, and detection of approaching ash clouds using ground-based Doppler radar. Given the demonstrated vulnerability of airports to disruption from volcanic activity, at-risk airports should develop operational plans for ashfall events, and volcano-monitoring agencies should provide timely forewarning of imminent volcanic-ash hazards directly to airport operators. ?? Springer Science+Business Media B.V. 2008.

  7. Radial anisotropy ambient noise tomography of volcanoes (United States)

    Mordret, Aurélien; Rivet, Diane; Shapiro, Nikolai; Jaxybulatov, Kairly; Landès, Matthieu; Koulakov, Ivan; Sens-Schönfelder, Christoph


    The use of ambient seismic noise allows us to perform surface-wave tomography of targets which could hardly be imaged by other means. The frequencies involved (~ 0.5 - 20 s), somewhere in between active seismic and regular teleseismic frequency band, make possible the high resolution imaging of intermediate-size targets like volcanic edifices. Moreover, the joint inversion of Rayleigh and Love waves dispersion curves extracted from noise correlations allows us to invert for crustal radial anisotropy. We present here the two first studies of radial anisotropy on volcanoes by showing results from Lake Toba Caldera, a super-volcano in Indonesia, and from Piton de la Fournaise volcano, a hot-spot effusive volcano on the Réunion Island (Indian Ocean). We will see how radial anisotropy can be used to infer the main fabric within a magmatic system and, consequently, its dominant type of intrusion.

  8. Elastic anisotropy of crystals

    Directory of Open Access Journals (Sweden)

    Christopher M. Kube


    Full Text Available An anisotropy index seeks to quantify how directionally dependent the properties of a system are. In this article, the focus is on quantifying the elastic anisotropy of crystalline materials. Previous elastic anisotropy indices are reviewed and their shortcomings discussed. A new scalar log-Euclidean anisotropy measure AL is proposed, which overcomes these deficiencies. It is based on a distance measure in a log-Euclidean space applied to fourth-rank elastic tensors. AL is an absolute measure of anisotropy where the limiting case of perfect isotropy yields zero. It is a universal measure of anisotropy applicable to all crystalline materials. Specific examples of strong anisotropy are highlighted. A supplementary material provides an anisotropy table giving the values of AL for 2,176 crystallite compounds.

  9. Volcanic gas (United States)

    McGee, Kenneth A.; Gerlach, Terrance M.


    In Roman mythology, Vulcan, the god of fire, was said to have made tools and weapons for the other gods in his workshop at Olympus. Throughout history, volcanoes have frequently been identified with Vulcan and other mythological figures. Scientists now know that the “smoke" from volcanoes, once attributed by poets to be from Vulcan’s forge, is actually volcanic gas naturally released from both active and many inactive volcanoes. The molten rock, or magma, that lies beneath volcanoes and fuels eruptions, contains abundant gases that are released to the surface before, during, and after eruptions. These gases range from relatively benign low-temperature steam to thick hot clouds of choking sulfurous fume jetting from the earth. Water vapor is typically the most abundant volcanic gas, followed by carbon dioxide and sulfur dioxide. Other volcanic gases are hydrogen sulfide, hydrochloric acid, hydrogen, carbon monoxide, hydrofluoric acid, and other trace gases and volatile metals. The concentrations of these gas species can vary considerably from one volcano to the next.

  10. Volcanic Catastrophes (United States)

    Eichelberger, J. C.


    The big news from 20th century geophysics may not be plate tectonics but rather the surprise return of catastrophism, following its apparent 19th century defeat to uniformitarianism. Divine miracles and plagues had yielded to the logic of integrating observations of everyday change over time. Yet the brilliant interpretation of the Cretaceous-Tertiary Boundary iridium anomaly introduced an empirically based catastrophism. Undoubtedly, decades of contemplating our own nuclear self-destruction played a role in this. Concepts of nuclear winter, volcanic winter, and meteor impact winter are closely allied. And once the veil of threat of all-out nuclear exchange began to lift, we could begin to imagine slower routes to destruction as "global change". As a way to end our world, fire is a good one. Three-dimensional magma chambers do not have as severe a magnitude limitation as essentially two-dimensional faults. Thus, while we have experienced earthquakes that are as big as they get, we have not experienced volcanic eruptions nearly as great as those preserved in the geologic record. The range extends to events almost three orders of magnitude greater than any eruptions of the 20th century. Such a calamity now would at the very least bring society to a temporary halt globally, and cause death and destruction on a continental scale. At maximum, there is the possibility of hindering photosynthesis and threatening life more generally. It has even been speculated that the relative genetic homogeneity of humankind derives from an evolutionary "bottleneck" from near-extinction in a volcanic cataclysm. This is somewhat more palatable to contemplate than a return to a form of Original Sin, in which we arrived at homogeneity by a sort of "ethnic cleansing". Lacking a written record of truly great eruptions, our sense of human impact must necessarily be aided by archeological and anthropological investigations. For example, there is much to be learned about the influence of

  11. 松辽盆地营城组火山岩冷却单元及地层结构分析%Volcanic Cooling Unit and Analysis of Stratigraphic Architecture of Yingcheng Formation in Songliao Basin

    Institute of Scientific and Technical Information of China (English)

    程日辉; 任延广; 沈艳杰; 许中杰


    火山岩冷却单元的识别是火山岩地层和岩相研究的重要环节.松辽盆地东南缘露头区和徐家围子断陷营城组火山岩剖面的剖析显示,冷却单元主要存在4种主要的单元类型:碎屑岩型、熔岩型、碎屑岩+熔岩型和熔岩+碎屑岩型.碎屑岩型和熔岩型是端元类型,分别反映蒸汽喷发和岩浆喷发的作用过程;碎屑岩+熔岩型是基本组合单元类型,反映蒸汽—岩浆喷发的连续作用过程;熔岩+碎屑岩型属于改造的或特殊机制的类型.冷却单元本身及其堆叠具有相的意义,是火山岩地层的基本成因地层单元,因此成为解释火山岩地层结构、了解形成与保存过程的重要基础.通过火山岩冷却单元识别与叠置分析,构建了松辽盆地徐家围子断陷营城组一段的地层结构.%The reorganization of volcanic cooling unit is a key to analyze volcanic stratigraphy am litho-facies. The study of the sections of Yingcheng Formation in Songliao basin shows that there an four types of cooling unit including pyroclastic, lava, pyroclastic + lava and lava + pyroclastic in th< outcrop of the southeast margin and Xujiaweizi fault depression. The type of pyroclastic is an end uni reflecting the processes of hydro explosion. The type of lava is another end unit reflecting the processe: of magma effusion. The type of pyroclastic + lava is a basic unit reflecting the consequent processes o hydro-magma eruption. The type of lava + pyroclastic is a reformed or special unit. Cooling unit itsel and its stacking contain meaning of litho-facies. The cooling unit is a genetic stratigraphic unit ii volcanic stratigraphy, which is fundamental to learn architecture, forming and preservation of volcanii strata. The recognition of volcanic cooling units and analysis of superimposition give a stratigraphii architecture of the First Member, Yingcheng Formation in Xujiaweizi of Songliao basin.

  12. Avoiding the Pitfalls of Anisotropy in Paleomagnetic Correlation of Snake River Plain Ignimbrites (United States)

    Finn, D. R.; Coe, R. S.; Kelly, H.; Murphy, J.; Reichow, M. K.; Knott, T.; Branney, M.


    Migration of the Yellowstone hotspot center tracks northeast along the central Snake River Plain (cSRP), leaving a succession of calderas, bimodal rhyolitic and basaltic volcanism, and crustal deformation. Large-scale explosive volcanism common to this province between 12.5-8 Ma is characterized by unusually high-temperature, intensely welded, rheomorphic rhyolitic ignimbrites, typical of what is now known as ';Snake River (SR)-type volcanism'. Individual eruption volumes likely exceed 450 km3 but are poorly known due to the difficulty of correlating units between widely spaced (50-200 km) exposures along the north and south of the plain. Radiometric dating does not have the resolution to identify the eruptive units. Our goal is to use a combination of paleomagnetic, petrographic, chemical and field characterization to establish robust correlations and better constrain eruption volumes and frequencies. Paleomagnetic correlation using the stable remanence, which is the focus of this presentation, has the advantage of very high temporal resolution of the order of centuries. This is due to the geologically rapid rate of geomagnetic secular variation and high accuracy to which extrusive rocks may record the instantaneous direction of the magnetic field. We have collected more than 1200 paleomagnetic samples from over 90 sites to help build a regional stratigraphy between the dozens of known ignimbrite units in the cSRP. During this process, however, we have found that the use of paleomagnetism is complicated by the large variation in the paleomagnetic direction that sometimes exists both within and between sub-lithologies of the same flow. Individual SR-type ignimbrite cooling-units have an upper and lower glassy margin (vitrophyre) enclosing a lithoidal (microcrystalline) zone. These vitrophyre lithologies often have a shallow paleomagnetic direction compared to the lithoidal lithologies. Here we present preliminary results from a detailed paleomagnetic and rock

  13. Volcanic hazard management in dispersed volcanism areas (United States)

    Marrero, Jose Manuel; Garcia, Alicia; Ortiz, Ramon


    Traditional volcanic hazard methodologies were developed mainly to deal with the big stratovolcanoes. In such type of volcanoes, the hazard map is an important tool for decision-makers not only during a volcanic crisis but also for territorial planning. According to the past and recent eruptions of a volcano, all possible volcanic hazards are modelled and included in the hazard map. Combining the hazard map with the Event Tree the impact area can be zoned and defining the likely eruptive scenarios that will be used during a real volcanic crisis. But in areas of disperse volcanism is very complex to apply the same volcanic hazard methodologies. The event tree do not take into account unknown vents, because the spatial concepts included in it are only related with the distance reached by volcanic hazards. The volcanic hazard simulation is also difficult because the vent scatter modifies the results. The volcanic susceptibility try to solve this problem, calculating the most likely areas to have an eruption, but the differences between low and large values obtained are often very small. In these conditions the traditional hazard map effectiveness could be questioned, making necessary a change in the concept of hazard map. Instead to delimit the potential impact areas, the hazard map should show the expected behaviour of the volcanic activity and how the differences in the landscape and internal geo-structures could condition such behaviour. This approach has been carried out in La Palma (Canary Islands), combining the concept of long-term hazard map with the short-term volcanic scenario to show the expected volcanic activity behaviour. The objective is the decision-makers understand how a volcanic crisis could be and what kind of mitigation measurement and strategy could be used.

  14. Supernovae anisotropy power spectrum

    CERN Document Server

    Ghodsi, Hoda; Habibi, Farhang


    We contribute another anisotropy study to this field of research using Supernovae Type Ia (SNe Ia). In this work, we utilise the power spectrum calculation method and apply it to both the current SNe Ia data and simulation. Our simulations are constructed with the characteristics of the upcoming survey of the Large Synoptic Survey Telescope (LSST), which shall bring us the largest SNe Ia collection to date. We make predictions for the amplitude of a possible dipole anisotropy or anisotropy in higher multipole moments that would be detectable by the LSST.

  15. A United Model for the cosmic ray energy spectra and anisotropy in the energy range 100 - 100 000 GeV

    CERN Document Server

    Zatsepin, V I; Sokolskaya, N V


    We propose a model where a supernova explodes in some vicinity of our solar system (some tens of parsecs) in the recent past (some tens of thousands years) with the energy release in cosmic rays of order of $ 10 ^ {51} $ erg. The flux from this supernova is added to an isotropic flux from other sources. We consider the case where the Sun's location is not in some typical for Our Galaxy average environment, but in the Local Superbubble about 100 pc across, in which the diffusion coefficient $D (E) = D_0 \\times E ^ {0.6} $, with the value of $ D_0 \\sim 10 ^ {25} cm^ 2 s^ {-1} $. We describe the energy dependence of the anisotropy of cosmic rays in the TeV region, together with the observed features of the energy spectrum of protons found in direct measurements. Our model provides a natural explanation to the hardening of the proton spectrum at 200 GeV, together with the observed steepening of the spectrum above 50 TeV.

  16. Volcanic hazard assessment in monogenetic volcanic fields


    Bartolini, Stefania


    [eng] One of the most important tasks of modern volcanology, which represents a significant socio-economic implication, is to conduct hazard assessment in active volcanic systems. These volcanological studies are aimed at hazard that allows to constructing hazard maps and simulating different eruptive scenarios, and are mainly addressed to contribute to territorial planning, definition of emergency plans or managing volcanic crisis. The impact of a natural event, as a volcanic eruption, can s...

  17. Paleomagnetic Evidence From Volcanic Units of Valsequillo Basin for the Laschamp Geomagnetic Excursion, and Implications for Early Human Occupation in Central Mexico (United States)

    Rocha, J.; Gogichaishvili, A.; Martin Del Pozzo, A.; Urrutia-Fucugauchi, J.; Soler, A. M.


    Alleged human and animal footprints were found within the upper bedding surfaces of the Xalnene volcanic ash layer that outcrops in Valsequillo basin, south of Puebla, Mexico (Gonzalez et al., Quaternary Science Reviews doi: 10.1016/j.quascirev, 2005). The ash has been dated to 40 ka by means of optically stimulated luminescence analysis. This was held as new evidence that America was colonized earlier. We carried out paleomagnetic and rock magnetic analysis of 18 Xalnene ash block and core samples collected at two distinct localities, and nineteen standard paleomagnetic cores belonging to nearby monogenetic volcanoes. Our data yield evidence that both volcanic lava flow and Xalnene ash were emplaced at during the Laschamp geomagnetic event spanning from about 45 to 39 ka. This interpretation indicates that Valsequillo probably remains one of the sites of early human occupation in the Americas, producing evidence of early arrival.

  18. Paleomagnetic and rock-magnetic study on volcanic units of the Valsequillo Basin: implications for early human occupation in central Mexico (United States)

    Goguitchaichvili, Avto; Pozzo, Ana Lillian Martin-Del; Rocha-Fernandez, Jose Luis; Urrutia-Fucugauchi, Jaime; Soler-Arechalde, Ana Maria


    Alleged human and animal footprints were found within the upper bedding surfaces of the Xalnene volcanic ash layer that outcrops in the Valsequillo Basin, south of Puebla, Mexico (Gonzalez et al, 2005). The ash has been dated at 40 ka by optically stimulated luminescence analysis, thereby providing new evidence that America was colonized earlier than the Clovis culture (about 13.5 Ma). We carried out paleomagnetic and rock magnetic analysis on 18 Xalnene ash block and core samples collected at two distinct localities and 19 standard paleomagnetic cores belonging to nearby monogenetic volcanoes. Our data provide evidence that both the volcanic lava flow and Xalnene ash were emplaced during the Laschamp geomagnetic event spanning from about 45 to 39 ka.

  19. Modeling elastic anisotropy in strained heteroepitaxy (United States)

    Krishna Dixit, Gopal; Ranganathan, Madhav


    Using a continuum evolution equation, we model the growth and evolution of quantum dots in the heteroepitaxial Ge on Si(0 0 1) system in a molecular beam epitaxy unit. We formulate our model in terms of evolution due to deposition, and due to surface diffusion which is governed by a free energy. This free energy has contributions from surface energy, curvature, wetting effects and elastic energy due to lattice mismatch between the film and the substrate. In addition to anisotropy due to surface energy which favors facet formation, we also incorporate elastic anisotropy due to an underlying crystal lattice. The complicated elastic problem of the film-substrate system subjected to boundary conditions at the free surface, interface and the bulk substrate is solved by perturbation analysis using a small slope approximation. This permits an analysis of effects at different orders in the slope and sheds new light on the observed behavior. Linear stability analysis shows the early evolution of the instability towards dot formation. The elastic anisotropy causes a change in the alignment of dots in the linear regime, whereas the surface energy anisotropy changes the dot shapes at the nonlinear regime. Numerical simulation of the full nonlinear equations shows the evolution of the surface morphology. In particular, we show, for parameters of the Ge0.25 Si0.75 on Si(0 0 1), the surface energy anisotropy dominates the shapes of the quantum dots, whereas their alignment is influenced by the elastic energy anisotropy. The anisotropy in elasticity causes a further elongation of the islands whose coarsening is interrupted due to facets on the surface.

  20. Modeling elastic anisotropy in strained heteroepitaxy. (United States)

    Dixit, Gopal Krishna; Ranganathan, Madhav


    Using a continuum evolution equation, we model the growth and evolution of quantum dots in the heteroepitaxial Ge on Si(0 0 1) system in a molecular beam epitaxy unit. We formulate our model in terms of evolution due to deposition, and due to surface diffusion which is governed by a free energy. This free energy has contributions from surface energy, curvature, wetting effects and elastic energy due to lattice mismatch between the film and the substrate. In addition to anisotropy due to surface energy which favors facet formation, we also incorporate elastic anisotropy due to an underlying crystal lattice. The complicated elastic problem of the film-substrate system subjected to boundary conditions at the free surface, interface and the bulk substrate is solved by perturbation analysis using a small slope approximation. This permits an analysis of effects at different orders in the slope and sheds new light on the observed behavior. Linear stability analysis shows the early evolution of the instability towards dot formation. The elastic anisotropy causes a change in the alignment of dots in the linear regime, whereas the surface energy anisotropy changes the dot shapes at the nonlinear regime. Numerical simulation of the full nonlinear equations shows the evolution of the surface morphology. In particular, we show, for parameters of the [Formula: see text] [Formula: see text] on Si(0 0 1), the surface energy anisotropy dominates the shapes of the quantum dots, whereas their alignment is influenced by the elastic energy anisotropy. The anisotropy in elasticity causes a further elongation of the islands whose coarsening is interrupted due to [Formula: see text] facets on the surface.

  1. Volcanic Reservoirs Permeability Prediction Using Multi-parameter Approach Based on Hydraulic Flow Units%基于流动单元用多参数方法预测火山岩渗透率

    Institute of Scientific and Technical Information of China (English)

    吴一雄; 张超谟; 李玮


    火山岩储层岩性变化快,矿物组分种类多,裂缝、溶孔发育,孔隙结构复杂,储层“四性”非匀质性强等特点为火山岩储层物性的定量评价带来了极大的困难.采用聚类分析方法,利用同一地区多口取心井的岩心数据进行地层流动单元的划分,在每一种流动单元下建立相应的渗透率模型.在未取心井中建立流动分层指标与多项测井参数的回归关系,为流动单元的划分建立判别函数.采用密度-核磁共振孔隙度方法确定火山岩储层有效孔隙度.用松辽盆地南部长岭、英台断陷深层火山岩储层数据对该方法进行验证,获得了较好的应用效果.%Fast changes of the volcanic reservoirs lithology,varieties of mineral components,development of fractures and dissolution pores,complexity of pore structures and strong non-homogeneity lead to the great difficulties in the volcanic reservoirs quantitative evaluation.We use core data of several wells in the same area to divide hydraulic flow units (HFU) of the formation,and establish the permeability model for each HFU by cluster analysis method.In the uncored wells,we establish regression relationship of hydraulic flow index (IFz) with several logging parameters to find the discriminant function for the division of HFU.We determine the effective porosity of the volcanic reservoirs by density-NMR porosity method.And then we verify this method with volcanic reservoir data in Changling,Yingtai fault depression of southern Songliao basin,the result of which is much better.

  2. [ReCl4(CN)2]2-: a high magnetic anisotropy building unit giving rise to the single-chain magnets (DMF)4MReCl4(CN)2 (M = Mn, Fe, Co, Ni). (United States)

    Harris, T David; Bennett, Miriam V; Clérac, Rodolphe; Long, Jeffrey R


    An S = 3/2, high-anisotropy building unit, trans-[ReCl(4)(CN)(2)](2-), representing the first paramagnetic complex with a mixture of just cyanide and halide ligands, has been synthesized through the reaction of (Bu(4)N)CN with ReCl(4)(THF)(2). This species is characterized in detail and employed in directing the formation of a series of one-dimensional coordination solids of formula (DMF)(4)MReCl(4)(CN)(2) (M = Mn (2), Fe (3), Co (4), Ni (5)). Variable-temperature dc magnetic susceptibility measurements demonstrate the presence of intrachain antiferromagnetic (2) and ferromagnetic (3-5) exchange coupling within these solids. In addition, probing the ac magnetic susceptibility as a function of both temperature and frequency reveals that all of the chain compounds exhibit slow relaxation of the magnetization. The relaxation time is shown to be thermally activated, with energy barriers to relaxation of Delta(tau) = 31, 56, 17, and 20 cm(-1) for 2-5, respectively. Notably, the field-dependent magnetization of the iron congener exhibits a significant hysteresis effect at low temperature, with a coercive field of H(C) = 1.0 T, thus demonstrating magnetlike behavior in this one-dimensional system. Finally, the magnetization dynamics of all solids occur within the finite-size regime, where the magnetic domain growth is limited due to physical defects along the chains within the crystals.

  3. Single-ion anisotropy and exchange interactions in the cyano-bridged trimers MnIII2MIII(CN)6 (MIII = Co, Cr, Fe) species incorporating [Mn(5-Brsalen)]+ units: an inelastic neutron scattering and magnetic susceptibility study

    DEFF Research Database (Denmark)

    Tregenna-Piggott, Philip L W; Sheptyakov, Denis; Keller, Lukas;


    expectations based on the unquenched orbital angular momentum of the [Fe(CN)(6)](3-) anion, giving rise to an M(s) approximately +/-9/2 ground state, isolated by approximately 11.5 cm(-1) from the higher-lying levels. The reported INS and magnetic data should now serve as a benchmark against which theoretical......The electronic structures of the compounds K[(5-Brsalen)(2)(H(2)O)(2)-Mn(2)M(III)(CN)(6)].2H(2)O (M(III) = Co(III), Cr(III), Fe(III)) have been determined by inelastic neutron scattering (INS) and magnetic susceptibility studies, revealing the manganese(III) single-ion anisotropy and exchange...... interactions that define the low-lying states of the Mn-M(III)-Mn trimeric units. Despite the presence of an antiferromagnetic intertrimer interaction, the experimental evidence supports the classification of both the Cr(III) and Fe(III) compounds as single-molecule magnets. The value of 17(2) cm(-1...

  4. Volcanic edifice alignment detection software in MATLAB: Test data and preliminary results for shield fields on Venus (United States)

    Thomson, Bradley J.; Lang, Nicholas P.


    The scarcity of impact craters on Venus make it difficult to infer the relative ages of geologic units. Stratigraphic methods can be used to help infer the relative ordering of surface features, but the relatively coarse resolution of available radar data means ambiguity about the timing of certain features is common. Here we develop a set of statistical tools in MATLAB to help infer the relative timing between clusters of small shield volcanoes and sets of fractures in the surrounding terrain. Specifically, we employed two variants of the two-point azimuth method to detect anisotropy in the distribution of point-like features. The results of these methods are shown to successfully identify anisotropy at two spatial scales: at the whole-field level and at scales smaller than a set fraction of the mean value. Initial results on the test cases presented here are promising, at least for volcanic fields emplaced under uniform conditions. These methods could also be used for detecting anisotropy in other point-like geologic features, such as hydrothermal vents, springs, and earthquake epicenters.

  5. Flow stress anisotropy

    DEFF Research Database (Denmark)

    Winther, G.


    stress Variation in the rolling plane, which may be as high as 20%, are presented. The traditional Taylor model is applied to the data to account for the effect of texture. However, texture effects alone are not enough to explain all of the observed anisotropy. New models which take the combined effects...... of texture and deformation microstructure into account are presented. The models are based on the Taylor and Sachs models but modified with an anisotropic critical shear stress to account for the effect of the microstructure. The agreement between experimental data and model predictions is definitely better...

  6. Volcanic signals in oceans

    KAUST Repository

    Stenchikov, Georgiy L.


    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.

  7. Magnetic anisotropy in nanostructures

    CERN Document Server

    Eisenbach, M


    method for solving the LDA Kohn-Sham equation. This extended code allows us to perform fully relativistic calculations to enable us to investigate the spin orbit coupling effects leading to anisotropies and potentially non collinear ordering of magnetic moments in these systems of magnetic inclusions in copper. With this approach we find that depending on the orientation of the atoms along the 100 or 110 direction in copper the ground state orientation of the magnetic moments in the chain is either perpendicular or parallel to the chain direction, when the magnetic dipolar interaction energy is added to the final ab initio result. In this thesis we investigate the effect of magnetic anisotropies in nanostructured materials. The main emphasis in our work presented here is on systems that have an underlying one dimensional structure, like nanowires or atomic chains. In a simple classical one dimensional model we show the rich ground state structure of magnetic orientations one might expect to find in such syste...

  8. Volcanic Rocks and Features (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Volcanoes have contributed significantly to the formation of the surface of our planet. Volcanism produced the crust we live on and most of the air we breathe. The...

  9. Seasonal anisotropy in handedness. (United States)

    Jones, Gregory V; Martin, Maryanne


    The preference for using either the left or the right hand has been linked to important human characteristics such as language lateralisation within the cerebral hemispheres, and evidence has been reported that the proportions of different types of handedness may be influenced by factors such as levels of maternal hormones and anxiety. Under such influences, it is possible in principle that distributions of handedness provide evidence of seasonal anisotropy, that is, variation in the direction of handedness for births in different parts of the year. The results of a number of studies are compared here, and shown to provide evidence of a significant tendency for the incidence of left-handed people to be higher among those born in the spring and ensuing months (March-July in the northern hemisphere) than among those born in the remainder of the year, at least among the male population.

  10. Ferromagnetic resonance of nanocrystal chains with competitive and cooperative anisotropy (United States)

    Koulialias, D.


    The formation of cellular magnetic dipoles by chain assemblies of nearly equidimensional, stable single domain magnetite nanocrystals aligned along their [111] easy axes is a common property encountered in many magnetotactic bacteria (MTB). The development of such dipoles permits the navigation of MTB along the geomagnetic field towards favourable habitats, a process also referred to as magnetotaxis. An important characteristic is the anisotropy within the chains, which mainly consists of the magnetocrystalline and the shape anisotropy. The two anisotropy contributions can be cooperative or competitive depending on the orientation with respect to the chain axis. The change in the relative orientation between the two anisotropy contributions caused by the Verwey transition TV, can be used to unambigously detect MTB and their fossil remains. Ferromagnetic resonance spectroscopy (FMR) is a well-established method to probe magnetic anisotropy in absolute units. Here, we use X- and Q-band FMR spectroscopy and numerical simulation to analyze the MTB species of Desulfovibrio magneticus RS-1 with elongated magnetosomes aligned along the [100] hard axis. In this special case, the magnetotaxis above TV is strongly affected by the shape anisotropy of the nanocrystals and it is competitive to the magnetocrystalline anisotropy. Below TV, the change of the easy axis [111] to [100] generates a cooperative system, which can be considered as the optimal case for magnetotaxis, i.e., shape and magnetocrystalline anisotropies are nearly parallel to the MTB chain axis. In summary, the nanocrystal assembly in RS-1 provides another step towards a better understanding of the physics behind magnetotaxis.

  11. Precambrian Lunar Volcanic Protolife

    Directory of Open Access Journals (Sweden)

    Jack Green


    Full Text Available Five representative terrestrial analogs of lunar craters are detailed relevant to Precambrian fumarolic activity. Fumarolic fluids contain the ingredients for protolife. Energy sources to derive formaldehyde, amino acids and related compounds could be by flow charging, charge separation and volcanic shock. With no photodecomposition in shadow, most fumarolic fluids at 40 K would persist over geologically long time periods. Relatively abundant tungsten would permit creation of critical enzymes, Fischer-Tropsch reactions could form polycyclic aromatic hydrocarbons and soluble volcanic polyphosphates would enable assembly of nucleic acids. Fumarolic stimuli factors are described. Orbital and lander sensors specific to protolife exploration including combined Raman/laser-induced breakdown spectrocsopy are evaluated.

  12. Secondary anisotropies of the CMB

    CERN Document Server

    Aghanim, Nabila; Silk, Joseph


    The Cosmic Microwave Background fluctuations provide a powerful probe of the dark ages of the universe through the imprint of the secondary anisotropies associated with the reionisation of the universe and the growth of structure. We review the relation between the secondary anisotropies and and the primary anisotropies that are directly generated by quantum fluctuations in the very early universe. The physics of secondary fluctuations is described, with emphasis on the ionisation history and the evolution of structure. We discuss the different signatures arising from the secondary effects in terms of their induced temperature fluctuations, polarisation and statistics. The secondary anisotropies are being actively pursued at present, and we review the future and current observational status.

  13. Polarization singularity anisotropy: determining monstardom

    CERN Document Server

    Dennis, Mark R


    C points, that is isolated points of circular polarization in transverse fields of varying polarization, are classified morphologically into three distinct types, known as lemons, stars and monstars. These morphologies are interpreted here according to two natural parameters associated with the singularity, namely the anisotropy of the C point, and the polarization azimuth on the anisotropy axis. In addition to providing insight into singularity morphology, this observation applies to the densities of the various morphologies in isotropic random polarization speckle fields.

  14. Lung problems and volcanic smog (United States)

    ... releases gases into the atmosphere. Volcanic smog can irritate the lungs and make existing lung problems worse. ... deep into the lungs. Breathing in volcanic smog irritates the lungs and mucus membranes. It can affect ...

  15. Volcanism and Oil & Gas In Northeast China

    Institute of Scientific and Technical Information of China (English)

    Shan Xuanlong


    Based on study on the relation with volcanic rock and oil & gas in Songliao Basin and Liaohe Basin in northeast China, author proposes that material from deep by volcanism enrichs the resources in basins, that heat by volcanism promotes organic matter transforming to oil and gas, that volcanic reservoir is fracture, vesicular, solution pore, intercrystal pore.Lava facies and pyroclastic facies are favourable reservoir. Mesozoic volcanic reservoir is majority of intermediate, acid rock,but Cenozoic volcanic reservoir is majority of basalt. Types of oil and gas pool relating to volcanic rock include volcanic fracture pool, volcanic unconformity pool, volcanic rock - screened pool, volcanic darpe structural pool.

  16. Marine mesocosm bacterial colonisation of volcanic ash (United States)

    Witt, Verena; Cimarelli, Corrado; Ayris, Paul; Kueppers, Ulrich; Erpenbeck, Dirk; Dingwell, Donald; Woerheide, Gert


    Volcanic eruptions regularly eject large quantities of ash particles into the atmosphere, which can be deposited via fallout into oceanic environments. Such fallout has the potential to alter pH, light and nutrient availability at local scales. Shallow-water coral reef ecosystems - "rainforests of the sea" - are highly sensitive to disturbances, such as ocean acidification, sedimentation and eutrophication. Therefore, wind-delivered volcanic ash may lead to burial and mortality of such reefs. Coral reef ecosystem resilience may depend on pioneer bacterial colonisation of the ash layer, supporting subsequent establishment of the micro- and ultimately the macro-community. However, which bacteria are involved in pioneer colonisation remain unknown. We hypothesize that physico-chemical properties (i.e., morphology, mineralogy) of the ash may dictate bacterial colonisation. The effect of substrate properties on bacterial colonisation was tested by exposing five substrates: i) quartz sand ii) crystalline ash (Sakurajima, Japan) iii) volcanic glass iv) carbonate reef sand and v) calcite sand of similar grain size, in controlled marine coral reef aquaria under low light conditions for six months. Bacterial communities were screened every month by Automated Ribosomal Intergenic Spacer Analysis of the 16S-23S rRNA Internal Transcribed Spacer region. Multivariate statistics revealed discrete groupings of bacterial communities on substrates of volcanic origin (ash and glass) and reef origin (three sands). Analysis of Similarity supported significantly different communities associated with all substrates (p=0.0001), only quartz did not differ from both carbonate and calcite sands. The ash substrate exhibited the most diverse bacterial community with the most substrate-specific bacterial operational taxonomic units. Our findings suggest that bacterial diversity and community composition during colonisation of volcanic ash in a coral reef-like environment is controlled by the

  17. Modeling volcanic ash dispersal

    CERN Document Server

    CERN. Geneva


    The assessment of volcanic fallout hazard is an important scientific, economic, and political issue, especially in densely populated areas. From a scientific point of view, considerable progress has been made during the last two decades through the use of increasingly powerful computational models and capabilities. Nowadays, models are used to quantify hazard...

  18. Magnetic anisotropy and porosity of Antarctic chondrites




    Magnetic susceptibility anisotropy and porosity were measured in eleven Antarctic meteorites. These meteorites are ordinary chondrites (H and L type) in various metamorphic stages. Large magnetic anisotropy has been observed in most of the chondrites. The foliation type of the anisotropy, inferred from the shape of the susceptibility ellipsoid indicates that a uniaxial compressional type deformation is responsible for the anisotropy. The degree of the anisotropy and the porosity do not correl...

  19. Anisotropy tuning with the Wilson flow

    CERN Document Server

    Borsanyi, S; Fodor, Z; Katz, S D; Krieg, S; Kurth, T; Mages, S; Schafer, A; Szabo, K K


    We use the Wilson flow to define the gauge anisotropy at a given physical scale. We demonstrate the use of the anisotropic flow by performing the tuning of the bare gauge anisotropy in the tree-level Symanzik action for several lattice spacings and target anisotropies. We use this method to tune the anisotropy parameters in full QCD, where we also exploit the diminishing effect of a well chosen smearing on the renormalization of the fermion anisotropy.

  20. Water in volcanic glass: From volcanic degassing to secondary hydration (United States)

    Seligman, Angela N.; Bindeman, Ilya N.; Watkins, James M.; Ross, Abigail M.


    have more bubbles per unit area (25-77 mm-2) than felsic tephra (736 mm-2) and thicker average bubble walls (0.07 mm) than felsic tephra (0.02 mm). We use a simplified diffusion model to quantify the hydration rate of vesicular glass as a function of the diffusivity of water and the average bubble wall thickness. Based on fits to our hydration rate data, we estimate the initial low-temperature diffusivity at 0.1 wt.% H2Ot in volcanic glass (mafic and felsic) to be on the order of 10-3 to 10-4 μm2/year and find that differences in hydration rates between mafic and felsic tephra can be attributed primarily to differences in vesicularity, although slightly slower hydration of basalt cannot be precluded. We also observe no consistent temporal difference in secondary meteoric water uptake in wet versus dry and hot versus cold climates.

  1. The Online GVP/USGS Weekly Volcanic Activity Report: Providing Timely Information About Worldwide Volcanism (United States)

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


    The awesome power and intricate inner workings of volcanoes have made them a popular subject with scientists and the general public alike. About 1500 known volcanoes have been active on Earth during the Holocene, approximately 50 of which erupt per year. With so much activity occurring around the world, often in remote locations, it can be difficult to find up-to-date information about current volcanism from a reliable source. To satisfy the desire for timely volcano-related information the Smithsonian Institution and US Geological Survey combined their strengths to create the Weekly Volcanic Activity Report. The Smithsonian's Global Volcanism Program (GVP) has developed a network of correspondents while reporting worldwide volcanism for over 30 years in their monthly Bulletin of the Global Volcanism Network. The US Geological Survey's Volcano Hazards Program studies and monitors volcanoes in the United States and responds (upon invitation) to selected volcanic crises in other countries. The Weekly Volcanic Activity Report is one of the most popular sites on both organization's websites. The core of the Weekly Volcanic Activity Report is the brief summaries of current volcanic activity around the world. In addition to discussing various types of volcanism, the summaries also describe precursory activity (e.g. volcanic seismicity, deformation, and gas emissions), secondary activity (e.g. debris flows, mass wasting, and rockfalls), volcanic ash hazards to aviation, and preventative measures. The summaries are supplemented by links to definitions of technical terms found in the USGS photoglossary of volcano terms, links to information sources, and background information about reported volcanoes. The site also includes maps that highlight the location of reported volcanoes, an archive of weekly reports sorted by volcano and date, and links to commonly used acronyms. Since the Weekly Volcanic Activity Report's inception in November 2000, activity has been reported at

  2. Developing International Guidelines on Volcanic Hazard Assessments for Nuclear Facilities (United States)

    Connor, Charles


    Worldwide, tremendous progress has been made in recent decades in forecasting volcanic events, such as episodes of volcanic unrest, eruptions, and the potential impacts of eruptions. Generally these forecasts are divided into two categories. Short-term forecasts are prepared in response to unrest at volcanoes, rely on geophysical monitoring and related observations, and have the goal of forecasting events on timescales of hours to weeks to provide time for evacuation of people, shutdown of facilities, and implementation of related safety measures. Long-term forecasts are prepared to better understand the potential impacts of volcanism in the future and to plan for potential volcanic activity. Long-term forecasts are particularly useful to better understand and communicate the potential consequences of volcanic events for populated areas around volcanoes and for siting critical infrastructure, such as nuclear facilities. Recent work by an international team, through the auspices of the International Atomic Energy Agency, has focused on developing guidelines for long-term volcanic hazard assessments. These guidelines have now been implemented for hazard assessment for nuclear facilities in nations including Indonesia, the Philippines, Armenia, Chile, and the United States. One any time scale, all volcanic hazard assessments rely on a geologically reasonable conceptual model of volcanism. Such conceptual models are usually built upon years or decades of geological studies of specific volcanic systems, analogous systems, and development of a process-level understanding of volcanic activity. Conceptual models are used to bound potential rates of volcanic activity, potential magnitudes of eruptions, and to understand temporal and spatial trends in volcanic activity. It is these conceptual models that provide essential justification for assumptions made in statistical model development and the application of numerical models to generate quantitative forecasts. It is a

  3. Basaltic ignimbrites in monogenetic volcanism: the example of La Garrotxa volcanic field (United States)

    Martí, J.; Planagumà, L. l.; Geyer, A.; Aguirre-Díaz, G.; Pedrazzi, D.; Bolós, X.


    Ignimbrites are pyroclastic density current deposits common in explosive volcanism involving intermediate and silicic magmas and in less abundance in eruptions of basaltic central and shield volcanoes. However, they are not widely described in association with monogenetic volcanism, where typical products include lava flows, scoria and lapilli fall deposits, as well as various kinds of pyroclastic density current deposits and explosion breccias. In La Garrotxa basaltic monogenetic volcanic field, part of the Neogene-Quaternary European rift system located in the northeast of the Iberian Peninsula, we have identified a particular group of pyroclastic density current deposits that show similar textural characteristics to silicic ignimbrites, indicating an overlap in transport and depositional processes. These deposits can be clearly distinguished from other pyroclastic density current deposits generated during phreatomagmatic phases that typically correspond to thinly laminated units with planar-to-cross-bedded stratification. The monogenetic ignimbrite deposits correspond to a few meters to several tens of meters thick units rich in lithic- and lapilli scoria fragments, with an abundant ash matrix, and internally massive structure, emplaced along valleys and gullies, with run-out distances up to 6 km and individual volumes ranging from 106 to 1.5 × 107 m3. The presence of flattened scoria and columnar jointing in some of these deposits suggests relatively high emplacement temperatures, coinciding with available paleomagnetic data that suggests an emplacement temperature around 450-500 °C. In this work, we describe the main characteristics of these pyroclastic deposits that were generated by a number of phreatomagmatic episodes. Comparison with similar deposits from silicic eruptions and previous examples of ignimbrites associated with basaltic volcanism allows us to classify them as `basaltic ignimbrites'. The recognition in monogenetic volcanism of such

  4. 1992-93 Results of geomorphological and field studies Volcanic Studies Program, Yucca Mountain Project

    Energy Technology Data Exchange (ETDEWEB)

    Wells, S.G.


    Field mapping and stratigraphic studies were completed of the Black Tank volcanic center, which represents the southwestern most eruptive center in the Cima volcanic field of California. The results of this mapping are presented. Contacts between volcanic units and geomorphic features were field checked, incorporating data from eight field trenches as well as several exposures along Black Tank Wash. Within each of the eight trenches, logs were measured and stratigraphic sections were described. These data indicate that three, temporally separate volcanic eruptions occurred at the Black Tank center. The field evidence for significant time breaks between each stratigraphic unit is the presence of soil and pavement-bounded unconformities.

  5. Exploring Hawaiian Volcanism (United States)

    Poland, Michael P.; Okubo, Paul G.; Hon, Ken


    In 1912 the Hawaiian Volcano Observatory (HVO) was established by Massachusetts Institute of Technology professor Thomas A. Jaggar Jr. on the island of Hawaii. Driven by the devastation he observed while investigating the volcanic disasters of 1902 at Montagne Pelée in the Caribbean, Jaggar conducted a worldwide search and decided that Hawai`i provided an excellent natural laboratory for systematic study of earthquake and volcano processes toward better understanding of seismic and volcanic hazards. In the 100 years since HVO's founding, surveillance and investigation of Hawaiian volcanoes have spurred advances in volcano and seismic monitoring techniques, extended scientists' understanding of eruptive activity and processes, and contributed to development of global theories about hot spots and mantle plumes.

  6. Exploring Hawaiian volcanism (United States)

    Poland, Michael P.; Okubo, Paul G.; Hon, Ken


    In 1912 the Hawaiian Volcano Observatory (HVO) was established by Massachusetts Institute of Technology professor Thomas A. Jaggar Jr. on the island of Hawaii. Driven by the devastation he observed while investigating the volcanic disasters of 1902 at Montagne Pelée in the Caribbean, Jaggar conducted a worldwide search and decided that Hawai‘i provided an excellent natural laboratory for systematic study of earthquake and volcano processes toward better understanding of seismic and volcanic hazards. In the 100 years since HVO’s founding, surveillance and investigation of Hawaiian volcanoes have spurred advances in volcano and seismic monitoring techniques, extended scientists’ understanding of eruptive activity and processes, and contributed to development of global theories about hot spots and mantle plumes.

  7. Giant dielectric anisotropy via homogenization

    CERN Document Server

    Mackay, Tom G


    A random mixture of two isotropic dielectric materials, one composed of oriented spheroidal particles of relative permittivity $\\epsilon_a$ and the other composed of oriented spheroidal particles of relative permittivity $\\epsilon_b$, was considered in the long wavelength regime. The permittivity dyadic of the resulting homogenized composite material (HCM) was estimated using the Bruggeman homogenization formalism. The HCM was an orthorhombic biaxial material if the symmetry axes of the two populations of spheroids were mutually perpendicular and a uniaxial material if these two axes were mutually aligned. The degree of anisotropy of the HCM, as gauged by the ratio of the eigenvalues of the HCM's permittivity dyadic, increased as the shape of the constituent particles became more eccentric. The greatest degrees of HCM anisotropy were achieved for the limiting cases wherein the constituent particles were shaped as needles or discs. In these instances explicit formulas for the HCM anisotropy were derived from t...

  8. Anisotropy in the deep Earth (United States)

    Romanowicz, Barbara; Wenk, Hans-Rudolf


    Seismic anisotropy has been found in many regions of the Earth's interior. Its presence in the Earth's crust has been known since the 19th century, and is due in part to the alignment of anisotropic crystals in rocks, and in part to patterns in the distribution of fractures and pores. In the upper mantle, seismic anisotropy was discovered 50 years ago, and can be attributed for the most part, to the alignment of intrinsically anisotropic olivine crystals during large scale deformation associated with convection. There is some indication for anisotropy in the transition zone, particularly in the vicinity of subducted slabs. Here we focus on the deep Earth - the lower mantle and core, where anisotropy is not yet mapped in detail, nor is there consensus on its origin. Most of the lower mantle appears largely isotropic, except in the last 200-300 km, in the D″ region, where evidence for seismic anisotropy has been accumulating since the late 1980s, mostly from shear wave splitting measurements. Recently, a picture has been emerging, where strong anisotropy is associated with high shear velocities at the edges of the large low shear velocity provinces (LLSVPs) in the central Pacific and under Africa. These observations are consistent with being due to the presence of highly anisotropic MgSiO3 post-perovskite crystals, aligned during the deformation of slabs impinging on the core-mantle boundary, and upwelling flow within the LLSVPs. We also discuss mineral physics aspects such as ultrahigh pressure deformation experiments, first principles calculations to obtain information about elastic properties, and derivation of dislocation activity based on bonding characteristics. Polycrystal plasticity simulations can predict anisotropy but models are still highly idealized and neglect the complex microstructure of polyphase aggregates with strong and weak components. A promising direction for future progress in understanding the origin of seismic anisotropy in the deep mantle

  9. Subdiffusion of volcanic earthquakes

    CERN Document Server

    Abe, Sumiyoshi


    A comparative study is performed on volcanic seismicities at Mt.Eyjafjallajokull in Iceland and Mt. Etna in Sicily, Italy, from the viewpoint of science of complex systems, and the discovery of remarkable similarities between them regarding their exotic spatio-temporal properties is reported. In both of the volcanic seismicities as point processes, the jump probability distributions of earthquakes are found to obey the exponential law, whereas the waiting-time distributions follow the power law. In particular, a careful analysis is made about the finite size effects on the waiting-time distributions, and accordingly, the previously reported results for Mt. Etna [S. Abe and N. Suzuki, EPL 110, 59001 (2015)] are reinterpreted. It is shown that spreads of the volcanic earthquakes are subdiffusive at both of the volcanoes. The aging phenomenon is observed in the "event-time-averaged" mean-squared displacements of the hypocenters. A comment is also made on presence/absence of long term memories in the context of t...

  10. Amazonian volcanism inside Valles Marineris on Mars (United States)

    Brož, Petr; Hauber, Ernst; Wray, James J.; Michael, Gregory


    The giant trough system of Valles Marineris is one of the most spectacular landforms on Mars, yet its origin is still unclear. Although often referred to as a rift, it also shows some characteristics that are indicative of collapse processes. For decades, one of the major open questions was whether volcanism was active inside the Valles Marineris. Here we present evidence for a volcanic field on the floor of the deepest trough of Valles Marineris, Coprates Chasma. More than 130 individual edifices resemble scoria and tuff cones, and are associated with units that are interpreted as lava flows. Crater counts indicate that the volcanic field was emplaced sometime between ∼0.4 Ga and ∼0.2 Ga. The spatial distribution of the cones displays a control by trough-parallel subsurface structures, suggesting magma ascent in feeder dikes along trough-bounding normal faults. Spectral data reveal an opaline-silica-rich unit associated with at least one of the cones, indicative of hydrothermal processes. Our results point to magma-water interaction, an environment of astrobiological interest, perhaps associated with late-stage activity in the evolution of Valles Marineris, and suggest that the floor of Coprates Chasma is promising target for the in situ exploration of Mars.

  11. Late Pleistocene ages for the most recent volcanism and glacial-pluvial deposits at Big Pine volcanic field, California, USA, from cosmogenic 36Cl dating (United States)

    Vazquez, Jorge A.; Woolford, Jeff M


    The Big Pine volcanic field is one of several Quaternary volcanic fields that poses a potential volcanic hazard along the tectonically active Owens Valley of east-central California, and whose lavas are interbedded with deposits from Pleistocene glaciations in the Sierra Nevada Range. Previous geochronology indicates an ∼1.2 Ma history of volcanism, but the eruption ages and distribution of volcanic products associated with the most-recent eruptions have been poorly resolved. To delimit the timing and products of the youngest volcanism, we combine field mapping and cosmogenic 36Cl dating of basaltic lava flows in the area where lavas with youthful morphology and well-preserved flow structures are concentrated. Field mapping and petrology reveal approximately 15 vents and 6 principal flow units with variable geochemical composition and mineralogy. Cosmogenic 36Cl exposure ages for lava flow units from the top, middle, and bottom of the volcanic stratigraphy indicate eruptions at ∼17, 27, and 40 ka, revealing several different and previously unrecognized episodes of late Pleistocene volcanism. Olivine to plagioclase-pyroxene phyric basalt erupted from several vents during the most recent episode of volcanism at ∼17 ka, and produced a lava flow field covering ∼35 km2. The late Pleistocene 36Cl exposure ages indicate that moraine and pluvial shoreline deposits that overlie or modify the youngest Big Pine lavas reflect Tioga stage glaciation in the Sierra Nevada and the shore of paleo-Owens Lake during the last glacial cycle.

  12. Flow stress anisotropy in aluminium

    DEFF Research Database (Denmark)

    Juul Jensen, D.; Hansen, N.


    The plastic anisotropy of cold-rolled high purity aluminum (99.996%) and commercially pure aluminum (99.6%) has been investigated. Sample parameters were the initial grain size and the degree of plastic strain (ϵ < 3.00). Flow stresses (0.2% offset) were measured at room temperature by uniaxial t...

  13. Learning to recognize volcanic non-eruptions (United States)

    Poland, Michael P.


    An important goal of volcanology is to answer the questions of when, where, and how a volcano will erupt—in other words, eruption prediction. Generally, eruption predictions are based on insights from monitoring data combined with the history of the volcano. An outstanding example is the A.D. 1980–1986 lava dome growth at Mount St. Helens, Washington (United States). Recognition of a consistent pattern of precursors revealed by geophysical, geological, and geochemical monitoring enabled successful predictions of more than 12 dome-building episodes (Swanson et al., 1983). At volcanic systems that are more complex or poorly understood, probabilistic forecasts can be useful (e.g., Newhall and Hoblitt, 2002; Marzocchi and Woo, 2009). In such cases, the probabilities of different types of volcanic events are quantified, using historical accounts and geological studies of a volcano's past activity, supplemented by information from similar volcanoes elsewhere, combined with contemporary monitoring information.

  14. Volcanism on Mars. Chapter 41 (United States)

    Zimbelman, J. R.; Garry, W. B.; Bleacher, J. E.; Crown, D. A.


    Spacecraft exploration has revealed abundant evidence that Mars possesses some of the most dramatic volcanic landforms found anywhere within the solar system. How did a planet half the size of Earth produce volcanoes like Olympus Mons, which is several times the size of the largest volcanoes on Earth? This question is an example of the kinds of issues currently being investigated as part of the space-age scientific endeavor called "comparative planetology." This chapter summarizes the basic information currently known about volcanism on Mars. The volcanoes on Mars appear to be broadly similar in overall morphology (although, often quite different in scale) to volcanic features on Earth, which suggests that Martian eruptive processes are not significantly different from the volcanic styles and processes on Earth. Martian volcanoes are found on terrains of different age, and Martian volcanic rocks are estimated to comprise more than 50% of the Martian surface. This is in contrast to volcanism on smaller bodies such as Earth's Moon, where volcanic activity was mainly confined to the first half of lunar history (see "Volcanism on the Moon"). Comparative planetology supports the concept that volcanism is the primary mechanism for a planetary body to get rid of its internal heat; smaller bodies tend to lose their internal heat more rapidly than larger bodies (although, Jupiter's moon Io appears to contradict this trend; Io's intense volcanic activity is powered by unique gravitational tidal forces within the Jovian system; see "Volcanism on Io"), so that volcanic activity on Mars would be expected to differ considerably from that found on Earth and the Moon.

  15. Volcanic Ash Nephelometer Probe Project (United States)

    National Aeronautics and Space Administration — Advanced dropsondes that could effectively be guided through atmospheric regions of interest such as volcanic plumes may enable unprecedented observations of...

  16. California's Vulnerability to Volcanic Hazards: What's at Risk? (United States)

    Mangan, M.; Wood, N. J.; Dinitz, L.


    California is a leader in comprehensive planning for devastating earthquakes, landslides, floods, and tsunamis. Far less attention, however, has focused on the potentially devastating impact of volcanic eruptions, despite the fact that they occur in the State about as frequently as the largest earthquakes on the San Andreas Fault Zone. At least 10 eruptions have occurred in the past 1,000 years—most recently in northern California (Lassen Peak 1914 to 1917)—and future volcanic eruptions are inevitable. The likelihood of renewed volcanism in California is about one in a few hundred to one in a few thousand annually. Eight young volcanoes, ranked as Moderate to Very High Threat [1] are dispersed throughout the State. Partially molten rock (magma) resides beneath at least seven of these—Medicine Lake Volcano, Mount Shasta, Lassen Volcanic Center, Clear Lake Volcanic Field, Long Valley Volcanic Region, Coso Volcanic Field, and Salton Buttes— causing earthquakes, toxic gas emissions, hydrothermal activity, and (or) ground deformation. Understanding the hazards and identifying what is at risk are the first steps in building community resilience to volcanic disasters. This study, prepared in collaboration with the State of California Governor's Office of Emergency Management and the California Geological Survey, provides a broad perspective on the State's exposure to volcano hazards by integrating mapped volcano hazard zones with geospatial data on at-risk populations, infrastructure, and resources. The study reveals that ~ 16 million acres fall within California's volcano hazard zones, along with ~ 190 thousand permanent and 22 million transitory populations. Additionally, far-field disruption to key water delivery systems, agriculture, utilities, and air traffic is likely. Further site- and sector-specific analyses will lead to improved hazard mitigation efforts and more effective disaster response and recovery. [1] "Volcanic Threat and Monitoring Capabilities

  17. Large Angular Scale Anisotropy in Cosmic Microwave Background Induced by Cosmic Strings

    Energy Technology Data Exchange (ETDEWEB)

    Allen, B.; Caldwell, R.R.; Shellard, E.P.; Stebbins, A.; Veeraraghavan, S. [Department of Physics, University of Wisconsin---Milwaukee, P.O. Box 413, Milwaukee, Wisconsin 53201 (United States)]|[University of Cambridge, Department of Applied Mathematics and Theoretical Physics, Silver Street, Cambridge CB3 9EW (United Kingdom)]|[NASA/Fermilab Astrophysics Center, P.O. Box 500, Batavia, Illinois 60510 (United States)]|[NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States)


    We simulate the anisotropy in the cosmic microwave background (CMB) induced by cosmic strings. By numerically evolving a network of cosmic strings we generate full-sky CMB temperature anisotropy maps. Based on 192 maps, we compute the anisotropy power spectrum for multipole moments l{le}20. By comparing with the observed temperature anisotropy, we set the normalization for the cosmic string mass per unit length {mu}, obtaining {ital G}{mu}/{ital c}{sup 2}=1.05{sub {minus}0.20}{sup +0.35}{times}10{sup {minus}6}, which is consistent with all other observational constraints on cosmic strings. We demonstrate that the anisotropy pattern is consistent with a Gaussian random field on large angular scales. {copyright} {ital 1996 The American Physical Society.}

  18. Pulsed recording of anisotropy and holographic polarization gratings in azo-polymethacrylates with different molecular architectures

    DEFF Research Database (Denmark)

    Forcén, Patricia; Oriol, Luis; Alcala, Rafael


    Recording of anisotropy and holographic polarization gratings using 532 nm, 4 ns light pulses has been carried out in thin films of polymers with the same azobenzene content (20 wt %) and different molecular architectures. Random and block copolymers comprising azobenzene and methylmethacrylate...... (MMA) moieties as well as statistical terpolymers with azobenzene, biphenyl, and MMA units have been compared in terms of recording sensitivity and stability upon pulsed excitation. Photoinduced anisotropy just after the pulse was significantly higher in the case of the block copolymers than in the two...... statistical copolymers. The stability of the recorded anisotropy has also been studied. While a stationary value of the photoinduced anisotropy (approximately 50% of the initial photoinduced value) is reached for the block copolymer, photoinduced anisotropy almost vanished after a few hours in the statistical...

  19. Volcanic Eruptions and Climate (United States)

    Robock, A.


    Large volcanic eruptions inject sulfur gases into the stratosphere, which convert to sulfate aerosols with an e-folding residence time of about one year. The radiative and chemical effects of these aerosol clouds produce responses in the climate system. Observations and numerical models of the climate system show that volcanic eruptions produce global cooling and were the dominant natural cause of climate change for the past millennium, on timescales from annual to century. Major tropical eruptions produce winter warming of Northern Hemisphere continents for one or two years, while high latitude eruptions in the Northern Hemisphere weaken the Asian and African summer monsoon. The Toba supereruption 74,000 years ago caused very large climate changes, affecting human evolution. However, the effects did not last long enough to produce widespread glaciation. An episode of four large decadally-spaced eruptions at the end of the 13th century C.E. started the Little Ice Age. Since the Mt. Pinatubo eruption in the Philippines in 1991, there have been no large eruptions that affected climate, but the cumulative effects of small eruptions over the past decade had a small effect on global temperature trends. The June 13, 2011 Nabro eruption in Eritrea produced the largest stratospheric aerosol cloud since Pinatubo, and the most of the sulfur entered the stratosphere not by direct injection, but by slow lofting in the Asian summer monsoon circulation. Volcanic eruptions warn us that while stratospheric geoengineering could cool the surface, reducing ice melt and sea level rise, producing pretty sunsets, and increasing the CO2 sink, it could also reduce summer monsoon precipitation, destroy ozone, allowing more harmful UV at the surface, produce rapid warming when stopped, make the sky white, reduce solar power, perturb the ecology with more diffuse radiation, damage airplanes flying in the stratosphere, degrade astronomical observations, affect remote sensing, and affect

  20. Lunar Pyroclastic Eruptions: Basin Volcanism's Dying Gasps (United States)

    Kramer, G. Y.; Nahm, A.; McGovern, P. J.; Kring, D. A.


    spatially isolated volcanic units, both confined within the central peak ring. One is a thin mare deposit to the north, and to the south is a 8.5 km long pyroclastic vent. The basin also a series of fractures, which exhibit complex cross-cutting relationships with each other and the basin floor materials, thereby offering clues about the timing of their formation. Some of these fractures widen as they cut across the uplifted peak ring, indicating that they are the surface manifestations of deep faulting and are younger. An orthogonal system of fractures in the southern basin floor outside of the peak ring is of particular interest because of its possible relationship to Schrodinger's basin volcanism. We are exploring the hypothesis that an expanding magma chamber once resided in this location, uplifted the basin floor, and formed these orthogonal fractures. Post-inflation, the reservoir was emptied via a propagating dike and sill complex that eventually surfaced at the location of the pyroclastic vent. [1] Saal et al. (2008) Nature; [2] Hauri et al. (2011) Science; [3] Saal et al. (2011) NASA Lunar Sci. Inst. Forum; [4] Delano (1986) JGR; [5] Head (1976) Rev. Geophys. Space Phys.; [6] McGovern & Litherland (2011) LPSC 42;McGovern et al. (2011) AGU Fall Session

  1. System of Volcanic activity

    Directory of Open Access Journals (Sweden)



    Full Text Available A comparison is made among the systems of B. G.
    Escher (3, of R. W. van Bemmelen (1 and that of the author (4. In this
    connection, on the basis of Esclier's classification, the terms of "constructiv
    e " and "destructive" eruptions are introduced into the author's system and
    at the same time Escher's concept on the possible relation between the depth
    of magma-chamber and the measure of the gas-pressure is discussed briefly.
    Three complementary remarks to the first paper (4 011 the subject of system
    of volcanic activity are added.

  2. Analysis of fractures in volcanic cores from Pahute Mesa, Nevada Test Site

    Energy Technology Data Exchange (ETDEWEB)

    Drellack, S.L. Jr.; Prothro, L.B.; Roberson, K.E. [and others


    The Nevada Test Site (NTS), located in Nye County, southern Nevada, was the location of 828 announced underground nuclear tests, conducted between 1951 and 1992. Approximately one-third of these tests were detonated near or below the water table. An unavoidable consequence of these testing activities was introducing radionuclides into the subsurface environment, impacting groundwater. Groundwater flows beneath the NTS almost exclusively through interconnected natural fractures in carbonate and volcanic rocks. Information about these fractures is necessary to determine hydrologic parameters for future Corrective Action Unit (CAU)-specific flow and transport models which will be used to support risk assessment calculations for the U.S. Department of Energy, Nevada Operations Office (DOE/NV) Underground Test Area (UGTA) remedial investigation. Fracture data are critical in reducing the uncertainty of the predictive capabilities of CAU-specific models because of their usefulness in generating hydraulic conductivity values and dispersion characteristics used in transport modeling. Specifically, fracture aperture and density (spacing) are needed to calculate the permeability anisotropy of the formations. Fracture mineralogy information is used qualitatively to evaluate diffusion and radionuclide retardation potential in transport modeling. All these data can best be collected through examination of core samples.

  3. Magnetic anisotropy of lecithin membranes. A new anisotropy susceptometer.


    Scholz, F.; Boroske, E; Helfrich, W.


    Cylindrical giant vesicles prepared from egg lecithin and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) are oriented in an external magnetic field and observed by phase contrast microscopy. The anisotropic part of the diamagnetic susceptibility of the lecithin membrane is determined from the distribution of angles between the magnetic field and the long cylinder axis due to thermal fluctuations. The anisotropy of DMPC is found to be larger by a factor of 2 than that of egg lecithin. This...

  4. Volcan Reventador's Unusual Umbrella (United States)

    Chakraborty, P.; Gioia, G.; Kieffer, S. W.


    In the past two decades, field observations of the deposits of volcanoes have been supplemented by systemmatic, and sometimes, opportunistic photographic documentation. Two photographs of the umbrella of the December 3, 2002 eruption of Volcan Reventador, Ecuador, reveal a prominently scalloped umbrella that is unlike any umbrella previously documented on a volcanic column. The material in the umbrella was being swept off a descending pyroclastic flow, and was, therefore, a co-ignimbrite cloud. We propose that the scallops are the result of a turbulent Rayleigh-Taylor (RT) instability with no precedents in volcanology. We ascribe the rare loss of buoyancy that drives this instability to the fact that the Reventador column fed on a cool co-ignimbrite cloud. On the basis of the observed wavelength of the scallops, we estimate a value for the eddy viscosity of the umbrella of 4000 ~m2/s. This value is consistent with a previously obtained lower bound (200 ~m2/s, K. Wohletz, priv. comm., 2005). We do not know the fate of the material in the umbrella subsequent to the photos. The analysis suggests that the umbrella was negatively buoyant. Field work on the co-ignimbrite deposits might reveal whether or not the material reimpacted, and if so, where and whether or not this material was involved in the hazardous flows that affected the main oil pipeline across Ecuador.

  5. Uranium series, volcanic rocks (United States)

    Vazquez, Jorge A.


    Application of U-series dating to volcanic rocks provides unique and valuable information about the absolute timing of crystallization and differentiation of magmas prior to eruption. The 238U–230Th and 230Th-226Ra methods are the most commonly employed for dating the crystallization of mafic to silicic magmas that erupt at volcanoes. Dates derived from the U–Th and Ra–Th methods reflect crystallization because diffusion of these elements at magmatic temperatures is sluggish (Cherniak 2010) and diffusive re-equilibration is insignificant over the timescales (less than or equal to 10^5 years) typically associated with pre-eruptive storage of nearly all magma compositions (Cooper and Reid 2008). Other dating methods based on elements that diffuse rapidly at magmatic temperatures, such as the 40Ar/39Ar and (U–Th)/He methods, yield dates for the cooling of magma at the time of eruption. Disequilibrium of some short-lived daughters of the uranium series such as 210Po may be fractionated by saturation of a volatile phase and can be employed to date magmatic gas loss that is synchronous with volcanic eruption (e.g., Rubin et al. 1994).

  6. Volcanic Eruptions and Climate (United States)

    LeGrande, Allegra N.; Anchukaitis, Kevin J.


    Volcanic eruptions represent some of the most climatically important and societally disruptive short-term events in human history. Large eruptions inject ash, dust, sulfurous gases (e.g. SO2, H2S), halogens (e.g. Hcl and Hbr), and water vapor into the Earth's atmosphere. Sulfurous emissions principally interact with the climate by converting into sulfate aerosols that reduce incoming solar radiation, warming the stratosphere and altering ozone creation, reducing global mean surface temperature, and suppressing the hydrological cycle. In this issue, we focus on the history, processes, and consequences of these large eruptions that inject enough material into the stratosphere to significantly affect the climate system. In terms of the changes wrought on the energy balance of the Earth System, these transient events can temporarily have a radiative forcing magnitude larger than the range of solar, greenhouse gas, and land use variability over the last millennium. In simulations as well as modern and paleoclimate observations, volcanic eruptions cause large inter-annual to decadal-scale changes in climate. Active debates persist concerning their role in longer-term (multi-decadal to centennial) modification of the Earth System, however.

  7. Magnetic, structural and geochronologic evidence bearing on volcanic sources and Oligocene Deformation of Ash Flow Tuffs, northeast Nevada (United States)

    Palmer, H. C.; MacDonald, W. D.; Hayatsu, A.


    Magnetic properties of mid-Tertiary volcanic rocks west of Jiggs in northeast Nevada were investigated for the purposes of interpreting igneous, structural, and tectonic processes in this part of the Basin and Range province. Anisotropy of magnetic susceptibility (AMS) patterns reflect flow fabrics and suggest previously unknown sources for these ash flow tuffs. Paleomagnetic and structural evidence suggest counterclockwise relative rotation of the southern part of the area with respect to the north. New stratigraphic, chemical and K-Ar isotopic data support these interpretations. Dacite to rhyolite ash flow tuffs of the Indian Well Formation were subdivided into two main units: the lower and predominant tuff of Jiggs (35.8-37.0 Ma) and the unconformably overlying but areally restricted tuff of Hackwood (30.8 Ma). The Jiggs unit has two polarities whereas the Hackwood has only a reversed polarity remanence. Together these units with tilt correction define a pole (92°E, 87°N, dp = 6°, dm = 8°) for approximately 30-37 Ma. This pole is concordant with coeval North American reference poles, indicating that this zone of approximately 30 km NS extent has not undergone significant vertical axis rotation relative to the North American reference. Andesite lavas of normal magnetic polarity and of 32.5-Ma age characterize the Diamond Hills immediately to the south. We interpret this region, from both structural evidence and discordant paleomagnetic direction, to have rotated approximately 25° counterclockwise relative to the Indian Well volcanic units to the north. The apparent rotation of the Diamond Hills is possibly the result of drag on the left-lateral Garcia fault which limits the Diamond Hills on the southwest. Analysis of AMS data suggests, by patterns of the K1 axes, two distinct sources for the Jiggs unit: a northern buried source and a central partially buried source. Lithologic evidence consistent with proximal vent facies is found near the latter source. An

  8. Where is magnetic anisotropy field pointing to?

    CERN Document Server

    Gutowski, Marek W


    The desired result of magnetic anisotropy investigations is the determination of value(s) of various anisotropy constant(s). This is sometimes difficult, especially when the precise knowledge of saturation magnetization is required, as it happens in ferromagnetic resonance (FMR) studies. In such cases we usually resort to `trick' and fit our experimental data to the quantity called \\emph{anisotropy field}, which is strictly proportional to the ratio of the searched anisotropy constant and saturation magnetization. Yet, this quantity is scalar, simply a number, and is therefore of little value for modeling or simulations of the magnetostatic or micromagnetic structures. Here we show how to `translate' the values of magnetic anisotropy constants into the complete vector of magnetic anisotropy field. Our derivation is rigorous and covers the most often encountered cases, from uniaxial to cubic anisotropy.

  9. Does Students' Source of Knowledge Affect Their Understanding of Volcanic Systems? (United States)

    Parham, Thomas L.; Cervato, Cinzia; Gallus, William; Larsen, Michael; Hobbs, Jon; Greenbowe, Thomas


    A recent survey of undergraduates at five schools across the United States indicates that many undergraduates feel that they have learned more about volcanic systems from Hollywood films and the popular media than they learned in the course of their precollegiate formal education. Scores on the Volcanic Concept Survey, an instrument designed to…

  10. Seismic lamination and anisotropy of the Lower Continental Crust (United States)

    Meissner, Rolf; Rabbel, Wolfgang; Kern, Hartmut


    Seismic lamination in the lower crust associated with marked anisotropy has been observed at various locations. Three of these locations were investigated by specially designed experiments in the near vertical and in the wide-angle range, that is the Urach and the Black Forrest area, both belonging to the Moldanubian, a collapsed Variscan terrane in southern Germany, and in the Donbas Basin, a rift inside the East European (Ukrainian) craton. In these three cases, a firm relationship between lower crust seismic lamination and anisotropy is found. There are more cases of lower-crustal lamination and anisotropy, e.g. from the Basin and Range province (western US) and from central Tibet, not revealed by seismic wide-angle measurements, but by teleseismic receiver function studies with a P-S conversion at the Moho. Other cases of lamination and anisotropy are from exhumed lower crustal rocks in Calabria (southern Italy), and Val Sesia and Val Strona (Ivrea area, Northern Italy). We demonstrate that rocks in the lower continental crust, apart from differing in composition, differ from the upper mantle both in terms of seismic lamination (observed in the near-vertical range) and in the type of anisotropy. Compared to upper mantle rocks exhibiting mainly orthorhombic symmetry, the symmetry of the rocks constituting the lower crust is either axial or orthorhombic and basically a result of preferred crystallographic orientation of major minerals (biotite, muscovite, hornblende). We argue that the generation of seismic lamination and anisotropy in the lower crust is a consequence of the same tectonic process, that is, ductile deformation in a warm and low-viscosity lower crust. This process takes place preferably in areas of extension. Heterogeneous rock units are formed that are generally felsic in composition, but that contain intercalations of mafic intrusions. The latter have acted as heat sources and provide the necessary seismic impedance contrasts. The observed

  11. Friction in volcanic environments (United States)

    Kendrick, Jackie E.; Lavallée, Yan


    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

  12. Magnetic field-dependent shape anisotropy in small patterned films studied using rotating magnetoresistance. (United States)

    Fan, Xiaolong; Zhou, Hengan; Rao, Jinwei; Zhao, Xiaobing; Zhao, Jing; Zhang, Fengzhen; Xue, Desheng


    Based on the electric rotating magnetoresistance method, the shape anisotropy of a Co microstrip has been systematically investigated. We find that the shape anisotropy is dependent not only on the shape itself, but also on the magnetization distribution controlled by an applied magnetic field. Together with micro-magnetic simulations, we present a visualized picture of how non-uniform magnetization affects the values and polarities of the anisotropy constants K1 and K2. From the perspective of potential appliantions, our results are useful in designing and understanding the performance of micro- and nano-scale patterned ferromagnetic units and the related device properties.

  13. Galactic foreground contribution to the BEAST CMB Anisotropy Maps

    CERN Document Server

    Mejia, J; Burigana, C; Childers, J; Figueiredo, N; Kangas, M; Lubin, P; Maino, D; Mandolesi, N; Marvil, J; Meinhold, P; O'Dwyer, I; O'Neill, H; Platania, P; Seiffert, M; Stebor, N; Tello, C A S; Villela, T; Wandelt, B; Wünsche, C A; Mej\\'{\\i}a, Jorge; Bersanelli, Marco; Burigana, Carlo; Childers, Jeff; Figueiredo, Newton; Kangas, Miikka; Lubin, Philip; Maino, Davide; Mandolesi, Nazzareno; Marvil, Josh; Meinhold, Peter; Dwyer, Ian O'; Neill, Hugh O'; Platania, Paola; Seiffert, Michael; Stebor, Nathan; Tello, Camilo; Villela, Thyrso; Wandelt, Benjamin; Wuensche, Carlos Alexandre


    We report limits on the Galactic foreground emission contribution to the Background Emission Anisotropy Scanning Telescope (BEAST) Ka- and Q-band CMB anisotropy maps. We estimate the contribution from the cross-correlations between these maps and the foreground emission templates of an H${\\alpha}$ map, a de-striped version of the Haslam et al. 408 MHz map, and a combined 100 $\\mu$m IRAS/DIRBE map. Our analysis samples the BEAST $\\sim10^\\circ$ declination band into 24 one-hour (RA) wide sectors with $\\sim7900$ pixels each, where we calculate: (a) the linear correlation coefficient between the anisotropy maps and the templates; (b) the coupling constants between the specific intensity units of the templates and the antenna temperature at the BEAST frequencies and (c) the individual foreground contributions to the BEAST anisotropy maps. The peak sector contributions of the contaminants in the Ka-band are of 56.5% free-free with a coupling constant of $8.3\\pm0.4$ $\\mu$K/R, and 67.4% dust with $45.0\\pm2.0$ $\\mu$K/...

  14. Volcanic studies at Katmai

    Energy Technology Data Exchange (ETDEWEB)


    The Continental Scientific Drilling Program (CSDP) is a national effort supported by the Department of Energy, the US Geological Survey, and the National Science Foundation. One of the projects proposed for the CSDP consists of drilling a series of holes in Katmai National Park in Alaska to give a third dimension to the model of the 1912 eruption of Novarupta, and to investigate the processes of explosive volcanism and hydrothermal transport of metals (Eichelberger et al., 1988). The proposal for research drilling at Katmai states that ``the size, youth, elevated temperature, and simplicity of the Novarupta vent make it a truly unique scientific target.`` The National Park Service (NPS), which has jurisdiction, is sympathetic to aims of the study. However, NPS wishes to know whether Katmai is indeed uniquely suited to the research, and has asked the Interagency Coordinating Group to support an independent assessment of this claim. NPS suggested the National Academy of Sciences as an appropriate organization to conduct the assessment. In response, the National Research Council -- the working arm of the Academy -- established, under the aegis of its US Geodynamics Committee, a panel whose specific charge states: ``The proposed investigation at Katmai has been extensively reviewed for scientific merit by the three sponsoring and participating agencies. Thus, the scientific merit of the proposed drilling at Katmai is not at issue. The panel will review the proposal for scientific drilling at Katmai and prepare a short report addressing the specific question of the degree to which it is essential that the drilling be conducted at Katmai as opposed to volcanic areas elsewhere in the world.``

  15. Quaternary basaltic volcanism in the Payenia volcanic province, Argentina

    DEFF Research Database (Denmark)

    Søager, Nina

    The extensive Quaternary volcanism in the Payenia volcanic province, Mendoza, Argentina, is investigated in this study by major and trace element analyses, Sr, Nd, Hf and Pb-isotopic analyses and Zr-Hf isotope dilution data on samples from almost the entire province. The samples are mainly...... in basalts from all the studied volcanic fields in Payenia is signs of lower crustal contamination indicating assimilation of, in some cases, large amounts of trace element depleted, mafic, plagioclase-bearing rocks. The northern Payenia is dominated by backarc basalts erupted between late Pliocene to late...

  16. Crustal stress and structure at Kīlauea Volcano inferred from seismic anisotropy (United States)

    Johnson, Jessica H.; Swanson, Donald; Roman, Diana C.; Poland, Michael P.; Thelen, Weston A.


    Seismic anisotropy, measured through shear wave splitting (SWS) analysis, can be indicative of the state of stress in Earth's crust. Changes in SWS at Kīlauea Volcano, Hawai‘i, associated with the onset of summit eruptive activity in 2008 hint at the potential of the technique for tracking volcanic activity. To use SWS observations as a monitoring tool, however, it is important to understand the cause of seismic anisotropy at the volcano throughout the eruptive cycle. To address this need, we analyzed SWS results from across Kīlauea in combination with macroscopic surface structures (mapped fractures, faults, and fissures) and stress orientations inferred from fault plane solutions. Seismic anisotropy seems to be due to pervasive aligned structures in most regions of the volcano. The upper East and Southwest Rift Zones, however, show a bimodality in stress and SWS, suggesting a stress discontinuity with depth, perhaps related to magma conduits that trend obliquely to the dominant structure. Other areas in and around Kīlauea Caldera display principal stresses of similar magnitudes, indicating that small stress perturbations can rotate the maximum horizontal compressive stress direction by up to 90°. In these locations, static structures generally control SWS, but dynamic conditions due to magmatic activity can override the structural control. Monitoring of SWS may therefore provide important signs of impending volcanism.

  17. Io. [theories concerning volcanic activity (United States)

    Johnson, T. V.; Soderblom, L. A.


    A report on the continuing investigation of Io is presented. Gravitational resonance is discussed as the cause of Io's volcanism, and the volcanic activity is explained in terms of sulfur chemistry. Theories concerning the reasons for the two main types of volcanic eruptions on Io are advanced and correlated with geographical features of the satellite. The sulfur and silicate models of the calderas are presented, citing the strengths and weaknesses of each. Problems of the gravitational resonance theory of Io's heat source are then described. Finally, observations of Io planned for the Galileo mission are summarized.

  18. Status of volcanism studies for the Yucca Mountain Site Characterization Project

    Energy Technology Data Exchange (ETDEWEB)

    Crowe, B.; Perry, F.; Murrell, M.; Poths, J.; Valentine, G.A. [Los Alamos National Lab., NM (United States); Wells, S. [Univ. of California, Riverside, CA (United States); Bowker, L.; Finnegan, K. [Univ. of Nevada, Las Vegas, NV (United States); Geissman, J.; McFadden, L.


    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. 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 Lathrop Wells volcanic center is described in detail because it is the youngest basalt center in the YMR. Chapter 3 describes the tectonic setting of the YMR and presents and assesses the significance of multiple alternative tectonic models. Geophysical data are described for the YMR and are used as an aid to understand the distribution of basaltic volcanic centers. Chapter 4 discusses the petrologic and geochemical features of basaltic volcanism in the YMR, the southern Great Basin and the Basin and Range province. The long time of activity and characteristic small volume of the Postcaldera basalt of the YMR result in one of the lowest eruptive rates in a volcanic field in the southwest United States. Chapter 5 summarizes current concepts of the segregation, ascent, and eruption of basalt magma. Chapter 6 summarizes the history of volcanism studies (1979 through early 1994), including work for the Yucca Mountain Site Characterization Project and overview studies by the state of Nevada and the Nuclear Regulatory Commission. Chapter 7 summarizes probabilistic volcanic hazard assessment using a three-part conditional probability model. Chapter 8 describes remaining volcanism work judged to be needed to complete characterization studies for the YMR. Chapter 9 summarizes the conclusions of this volcanism status report.

  19. Galaxy clusters and microwave background anisotropy

    CERN Document Server

    Quilis, V; Sáez, D


    Previous estimates of the microwave background anisotropies produced by freely falling spherical clusters are discussed. These estimates are based on the Swiss-Cheese and Tolman-Bondi models. It is proved that these models give only upper limits to the anisotropies produced by the observed galaxy clusters. By using spherically symmetric codes including pressureless matter and a hot baryonic gas, new upper limits are obtained. The contributions of the hot gas and the pressureless component to the total anisotropy are compared. The effects produced by the pressure are proved to be negligible; hence, estimations of the cluster anisotropies based on N-body simulations are hereafter justified. After the phenomenon of violent relaxation, any realistic rich cluster can only produce small anisotropies with amplitudes of order 10^{-7}. During the rapid process of violent relaxation, the anisotropies produced by nonlinear clusters are expected to range in the interval (10^{-6},10^{-5}). The angular scales of these anis...

  20. Quantitative assessment of diffusional kurtosis anisotropy. (United States)

    Glenn, G Russell; Helpern, Joseph A; Tabesh, Ali; Jensen, Jens H


    Diffusional kurtosis imaging (DKI) measures the diffusion and kurtosis tensors to quantify restricted, non-Gaussian diffusion that occurs in biological tissue. By estimating the kurtosis tensor, DKI accounts for higher order diffusion dynamics, when compared with diffusion tensor imaging (DTI), and consequently can describe more complex diffusion profiles. Here, we compare several measures of diffusional anisotropy which incorporate information from the kurtosis tensor, including kurtosis fractional anisotropy (KFA) and generalized fractional anisotropy (GFA), with the diffusion tensor-derived fractional anisotropy (FA). KFA and GFA demonstrate a net enhancement relative to FA when multiple white matter fiber bundle orientations are present in both simulated and human data. In addition, KFA shows net enhancement in deep brain structures, such as the thalamus and the lenticular nucleus, where FA indicates low anisotropy. Thus, KFA and GFA provide additional information relative to FA with regard to diffusional anisotropy, and may be particularly advantageous for the assessment of diffusion in complex tissue environments.

  1. Cemented Volcanic Soils, Martian Spectra and Implications for the Martian Climate (United States)

    Bishop, J. L.; Schiffman, P.; Drief, A.; Southard, R. J.


    Cemented volcanic crusts are studied to learn about their composition, formation processes, and implications for climate interactions with the surface on Mars. Such carbonate, sulfate and opal crusts may be present in cemented soil units on Mars.

  2. Magnetic Anisotropy in the Radula of Chiton

    Institute of Scientific and Technical Information of China (English)

    ZHAO Jian-Gao; QIAN Xia; LIU Wei; LIU Chuan-lin; ZHAN Wen-Shan


    Radular teeth of chitons were studied by using magnetic torque-meter and transmission electron microscopy (TEM). The magnetic torque curves give clear evidence of presence of strong uni-axial magnetic anisotropy. The easy axis is along the length direction of tongue-like radula. The TEM pattern shows that long chip-like magnetite nano-scaled particles packed in the radular teeth with both uni-axial shape anisotropy and magneto-crystalline anisotropy.

  3. Magnetic Anisotropy in the Radula of Chiton (United States)

    Zhao, Jian-Gao; Qian, Xia; Liu, Wei; Liu, Chuan-Lin; Zhan, Wen-Shan


    Radular teeth of chitons were studied by using magnetic torque-meter and transmission electron microscopy (TEM). The magnetic torque curves give clear evidence of presence of strong uni-axial magnetic anisotropy. The easy axis is along the length direction of tongue-like radula. The TEM pattern shows that long chip-like magnetite nano-scaled particles packed in the radular teeth with both uni-axial shape anisotropy and magneto-crystalline anisotropy.

  4. Statistical Anisotropy from Anisotropic Inflation

    CERN Document Server

    Soda, Jiro


    We review an inflationary scenario with the anisotropic expansion rate. An anisotropic inflationary universe can be realized by a vector field coupled with an inflaton, which can be regarded as a counter example to the cosmic no-hair conjecture. We show generality of anisotropic inflation and derive a universal property. We formulate cosmological perturbation theory in anisotropic inflation. Using the formalism, we show anisotropic inflation gives rise to the statistical anisotropy in primordial fluctuations. We also explain a method to test anisotropic inflation using the cosmic microwave background radiation (CMB).

  5. Formation of Magnetic Anisotropy by Lithography. (United States)

    Kim, Si Nyeon; Nam, Yoon Jae; Kim, Yang Doo; Choi, Jun Woo; Lee, Heon; Lim, Sang Ho


    Artificial interface anisotropy is demonstrated in alternating Co/Pt and Co/Pd stripe patterns, providing a means of forming magnetic anisotropy using lithography. In-plane hysteresis loops measured along two principal directions are explained in depth by two competing shape and interface anisotropies, thus confirming the formation of interface anisotropy at the Co/Pt and Co/Pd interfaces of the stripe patterns. The measured interface anisotropy energies, which are in the range of 0.2-0.3 erg/cm(2) for both stripes, are smaller than those observed in conventional multilayers, indicating a decrease in smoothness of the interfaces when formed by lithography. The demonstration of interface anisotropy in the Co/Pt and Co/Pd stripe patterns is of significant practical importance, because this setup makes it possible to form anisotropy using lithography and to modulate its strength by controlling the pattern width. Furthermore, this makes it possible to form more complex interface anisotropy by fabricating two-dimensional patterns. These artificial anisotropies are expected to open up new device applications such as multilevel bits using in-plane magnetoresistive thin-film structures.

  6. Surface magnetic anisotropy in amorphous alloys

    Energy Technology Data Exchange (ETDEWEB)

    Tejedor, M.; Rubio, H.; Elbaile, L.; Iglesias, R. (Univ. de Oviedo (Spain). Dept. de Fisica)


    The total in-plane magnetic anisotropy and the in-plane surface magnetic anisotropy constants have been measured in nearly-zero magnetostrictive amorphous ribbons in as-quenched state. The magnetostatic energy of a two-dimensional square-lattice of parallelepipeds or ellipsoids, whose dimensions are determined by the parameters characterizing the roughness, is evaluated. From the results obtained, they can conclude that the in-plane surface anisotropy can be magnetostatic in origin but it has little influence on the total in-plane magnetic anisotropy of the ribbon.

  7. Magnetic anisotropies in ultrathin bismuth iron garnet films

    Energy Technology Data Exchange (ETDEWEB)

    Popova, Elena, E-mail: [Groupe d' Etude de la Matière Condensée (GEMaC), CNRS/Université de Versailles-Saint-Quentin, 45 Avenue des Etats-Unis, 78035 Versailles (France); Franco Galeano, Andres Felipe [Laboratoire PROcédés, Matériaux et Energie Solaire (PROMES), CNRS/Université de Perpignan Via Domitia, 52 Avenue Paul Alduy, 66860 Perpignan (France); Deb, Marwan [Groupe d' Etude de la Matière Condensée (GEMaC), CNRS/Université de Versailles-Saint-Quentin, 45 Avenue des Etats-Unis, 78035 Versailles (France); Warot-Fonrose, Bénédicte [Centre d' Elaboration de Matériaux et d' Etudes Structurales (CEMES), CNRS, 29 rue Jeanne Marvig, 31055 Toulouse (France); Transpyrenean Associated Laboratory for Electron Microscopy (TALEM), CEMES-INA, CNRS–Universidad de Zaragoza (Spain); Kachkachi, Hamid [Laboratoire PROcédés, Matériaux et Energie Solaire (PROMES), CNRS/Université de Perpignan Via Domitia, 52 Avenue Paul Alduy, 66860 Perpignan (France); Gendron, François [Institut des NanoSciences de Paris (INSP), CNRS/Université Pierre et Marie Curie-Paris 6, 4 place Jussieu, Boîte courrier 840, 75252 Paris Cedex 05 (France); Ott, Frédéric [Laboratoire Léon Brillouin (LLB), CNRS/CEA, Bâtiment 563, CEA Saclay, 91191 Gif sur Yvette Cedex (France); and others


    Ultrathin bismuth iron garnet Bi{sub 3}Fe{sub 5}O{sub 12} films were grown epitaxially on (001)-oriented gadolinium gallium garnet substrates. Film thickness varied from two to three dozens of unit cells. Bi{sub 3}Fe{sub 5}O{sub 12} films grow pseudomorphically on substrates up to a thickness of 20 nm, and then a lattice relaxation occurs. Magnetic properties of the films were studied as a function of bismuth iron garnet thickness. The magnetization and cubic anisotropy decrease with decreasing film thickness. The uniaxial magnetocrystalline anisotropy is constant for all film thicknesses. For two unit cell thick films, the easy magnetization axis changes from in-plane to perpendicular to the plane direction. Such a reorientation takes place as a result of the competition of constant uniaxial perpendicular anisotropy with weakening film magnetization. - Highlights: ► Ultrathin Bi{sub 3}Fe{sub 5}O{sub 12} films were grown epitaxially on structure-matching substrates. ► Magnetic properties of Bi{sub 3}Fe{sub 5}O{sub 12} were studied down to the thickness of 2.5 nm. ► Reorientation of easy magnetization axis as a function of film thickness was observed.

  8. Volcanic eruptions observed with infrasound (United States)

    Johnson, Jeffrey B.; Aster, Richard C.; Kyle, Philip R.


    Infrasonic airwaves produced by active volcanoes provide valuable insight into the eruption dynamics. Because the infrasonic pressure field may be directly associated with the flux rate of gas released at a volcanic vent, infrasound also enhances the efficacy of volcanic hazard monitoring and continuous studies of conduit processes. Here we present new results from Erebus, Fuego, and Villarrica volcanoes highlighting uses of infrasound for constraining quantitative eruption parameters, such as eruption duration, source mechanism, and explosive gas flux.

  9. Los volcanes y los hombres


    García, Carmen


    Desde las entrañas de la tierra, los volcanes han creado la atmósfera, el agua de los océanos, y esculpido los relieves del planeta: son, pues, los zahoríes de la vida. Existen volcanes que los hombres explotan o cultivan, y otros sobre los cuales se han construido observatorios en los que se llevan a cabo avanzadas investigaciones científicas.

  10. Volcanic hazards and aviation safety (United States)

    Casadevall, Thomas J.; Thompson, Theodore B.; Ewert, John W.; ,


    An aeronautical chart was developed to determine the relative proximity of volcanoes or ash clouds to the airports and flight corridors that may be affected by volcanic debris. The map aims to inform and increase awareness about the close spatial relationship between volcanoes and aviation operations. It shows the locations of the active volcanoes together with selected aeronautical navigation aids and great-circle routes. The map mitigates the threat that volcanic hazards pose to aircraft and improves aviation safety.

  11. Volcanic Zone, New Zealand

    Directory of Open Access Journals (Sweden)

    Graham J. Weir


    Full Text Available A conceptual model of the Taupo Volcanic Zone (TVZ is developed, to a depth of 25 km, formed from three constant density layers. The upper layer is formed from eruption products. A constant rate of eruption is assumed, which eventually implies a constant rate of extension, and a constant rate of volumetric creation in the middle and bottom layers. Tectonic extension creates volume which can accomodate magmatic intrusions. Spreading models assume this volume is distributed throughout the whole region, perhaps in vertical dykes, whereas rifting models assume the upper crust is thinned and the volume created lies under this upper crust. Bounds on the heat flow from such magmatic intrusions are calculated. Heat flow calculations are performed and some examples are provided which match the present total heat output from the TVZ of about 4200 MW, but these either have extension rates greater than the low values of about 8 ± 4 mm/a being reported from GPS measurements, or else consider extension rates in the TVZ to have varied over time.

  12. Azimuthal anisotropy measurements by STAR

    Energy Technology Data Exchange (ETDEWEB)

    Yi, Li


    The recent study of centrality and transverse momentum (p{sub T}) dependence of inclusive charged hardron elliptic anisotropy (v{sub 2}) at midrapidity (|η|<1.0) in Au+Au collision at √(s{sub NN})=7.7,11.5,19.6,27, and39 GeV in STAR Beam Energy Scan program is presented. We show that the observed increase of inclusive v{sub 2} is mainly due to the average p{sub T} increase with energy. In Au+Au 200 GeV collisions, the triangular anisotropy (v{sub 3}) measurements highly depend on measurement methods; v{sub 3} is strongly dependent on Δη. The difference between two- and four-particle cumulants v{sub 2}{2} and v{sub 2}{4} for Au+Au and Cu+Cu collision at √(s{sub NN})=62.4 and 200 GeV is used to explore flow fluctuations. Furthermore, by exploiting the symmetry of average flow in pseudorapidity η about midrapidity, the Δη-dependent and independent components are separated using v{sub 2}{2} and v{sub 2}{4}.

  13. Geochemistry of the Lathrop Wells volcanic center

    Energy Technology Data Exchange (ETDEWEB)

    Perry, F.V.; Straub, K.T.


    Over 100 samples have been gathered from the Lathrop Wells volcanic center to assess different models of basalt petrogenesis and constrain the physical mechanisms of magma ascent in the Yucca Mountain region. Samples have been analyzed for major and trace-element chemistry, Nd, Sr and Ph isotopes, and mineral chemistry. All eruptive units contain olivine phenocrysts, but only the oldest eruptive units contain plagioclase phenocrysts. Compositions of minerals vary little between eruptive units. Geochemical data show that most of the eruptive units at Lathrop Wells defined by field criteria can be distinguished by major and trace-element chemistry. Normative compositions of basalts at Lathrop Wells correlate with stratigraphic position. The oldest basalts are primarily nepheline normative and the youngest basalts are exclusively hypersthene normative, indicating increasing silica saturation with time. Trace-element and major-element variations among eruptive units are statistically significant and support the conclusion that eruptive units at Lathrop Wells represent separate and independent magma batches. This conclusion indicates that magmas in the Yucca Mountain region ascend at preferred eruption sites rather than randomly.

  14. Strong crustal seismic anisotropy in the Kalahari Craton based on Receiver Functions

    DEFF Research Database (Denmark)

    Thybo, Hans; Soliman, Mohammad Youssof Ahmad; Artemieva, Irina


    Earlier seismic studies of the Kalahari Craton in southern Africa infer deformation of upper mantle by flow with fast direction of seismic anisotropy being parallel to present plate motion, and/or report anisotropy frozen into the lithospheric mantle. We present evidence for very strong seismic...... is uniform within tectonic units and parallel to orogenic strike in the Limpopo and Cape fold belts. It is further parallel to the strike of major dyke swarms which indicates that a large part of the observed anisotropy is controlled by lithosphere fabrics and macroscopic effects. The directions of the fast...... that the crust and lithospheric mantle may have been coupled since cratonisation. If so, the apparent match between mantle anisotropy and the present plate motion is coincidental....

  15. A search for small-scale anisotropy of PeV cosmic rays (United States)

    Zotov, M. Yu.; Kulikov, G. V.


    Recent results of Milagro, Tibet, ARGO-YBJ, and IceCube experiments on the small-scale anisotropy of Galactic cosmic rays (CRs) with energies from units up to a few hundred TeV arise a question on a possible nature of the observed phenomenon, as well as on the anisotropy of CRs at higher energies. An analysis of a small-scale anisotropy of CRs with energies at around PeV registered with the EAS MSU array presented in the article, reveals a number of regions with an excessive flux. A typical size of the regions varies from 3° up to 12°. We study correlation of these regions with positions of potential astrophysical sources of CRs and discuss a possible origin of the observed anisotropy.

  16. A Search for Small-Scale Anisotropy of PeV Cosmic Rays

    CERN Document Server

    Zotov, M Yu


    Recent results of Milagro, Tibet, ARGO-YBJ and IceCube experiments on the small-scale anisotropy of Galactic cosmic rays (CRs) with energies from units up to a few hundred TeV arise a question on a possible nature of the observed phenomenon, as well as on the anisotropy of CRs at higher energies. An analysis of a small-scale anisotropy of CRs with energies at around PeV registered with the EAS MSU array presented in the article, reveals a number of regions with an excessive flux. A typical size of the regions varies from 3 up to 12 degrees. We study correlation of these regions with positions of potential astrophysical sources of CRs and discuss a possible origin of the observed anisotropy.

  17. Strong crustal seismic anisotropy in the Kalahari Craton based on Receiver Functions

    DEFF Research Database (Denmark)

    Thybo, Hans; Soliman, Mohammad Youssof Ahmad; Artemieva, Irina


    Earlier seismic studies of the Kalahari Craton in southern Africa infer deformation of upper mantle by flow with fast direction of seismic anisotropy being parallel to present plate motion, and/or report anisotropy frozen into the lithospheric mantle. We present evidence for very strong seismic...... is uniform within tectonic units and parallel to orogenic strike in the Limpopo and Cape fold belts. It is further parallel to the strike of major dyke swarms which indicates that a large part of the observed anisotropy is controlled by lithosphere fabrics and macroscopic effects. The directions of the fast...... that the crust and lithospheric mantle may have been coupled since cratonisation. If so, the apparent match between mantle anisotropy and the present plate motion is coincidental....

  18. Measurements of the anisotropy in permalloy

    NARCIS (Netherlands)

    Eijkel, Kees J.


    A measurement system is described, which accurately determines the anisotropy field H/sub k/ and the orientation of the easy-axis in a permalloy film or in any material showing magnetization induced resistance anisotropy. An accuracy of 0.1% in H/sub k/ and 0.1 degrees in easy-axis orientation is re

  19. Detection and Classification of Volcanic Earthquakes/Tremors in Central Anatolian Volcanic Province (United States)

    Kahraman, Metin; Arda Özacar, A.; Bülent Tank, S.; Uslular, Göksu; Kuşcu, Gonca; Türkelli, Niyazi


    database to detect and classify the seismic source associated to volcanism, and identified events will be relocated and jointly interpreted with subsurface features detected by seismic imaging and MT. Keywords: Volcanic earthquakes, Central Anatolia Volcanic Province, seismic imaging, magnetotellurics Acknowledgements Continental Dynamics Central Anatolian Tectonics (CD-CAT) is supported by National Science Foundation, United States of America

  20. Optical and diamagnetic anisotropy of graphene oxide (United States)

    Exarhos, A. L.; Vora, P. M.; Lou, Z.; Johnson, A. T.; Kikkawa, J. M.


    We have recently shown that graphene oxide (GO) emits a broad photoluminescence (PL) band in both solid and aqueous preparations. The origin of this PL is not yet well understood, but for absorptive and emissive optical processes originating in the two dimensional GO plane, one expects an in-plane polarization. Studies of optical anisotropy can therefore help to clarify the origin of the PL. Here we use a method of optical nanomagnetometry (Torrens, et al, JACS 129, p. 252 (2007)) to extract these quantities, also determining the magnetic anisotropy. We find that when aqueous preparations of GO are placed in a magnetic field, diamagnetically induced alignment leads to marked linear polarization anisotropy of absorbance and photoluminescence. By taking six optical measurements at each magnetic field, we are able to extract the intrinsic polarization anisotropies of optical absorption and emission of GO flakes and to quantify the orbital diamagnetic anisotropy. We discuss how these quantities give insight into electronic delocalization in these systems.

  1. Anisotropy in solar wind plasma turbulence. (United States)

    Oughton, S; Matthaeus, W H; Wan, M; Osman, K T


    A review of spectral anisotropy and variance anisotropy for solar wind fluctuations is given, with the discussion covering inertial range and dissipation range scales. For the inertial range, theory, simulations and observations are more or less in accord, in that fluctuation energy is found to be primarily in modes with quasi-perpendicular wavevectors (relative to a suitably defined mean magnetic field), and also that most of the fluctuation energy is in the vector components transverse to the mean field. Energy transfer in the parallel direction and the energy levels in the parallel components are both relatively weak. In the dissipation range, observations indicate that variance anisotropy tends to decrease towards isotropic levels as the electron gyroradius is approached; spectral anisotropy results are mixed. Evidence for and against wave interpretations and turbulence interpretations of these features will be discussed. We also present new simulation results concerning evolution of variance anisotropy for different classes of initial conditions, each with typical background solar wind parameters.

  2. Descartes region - Evidence for Copernican-age volcanism. (United States)

    Head, J. W., III; Goetz, A. F. H.


    A model that suggests that the high-albedo central region of the Descartes Formation was formed by Copernican-age volcanism was developed from Orbiter photography, Apollo 12 multispectral photography, earth-based spectrophotometry, and thermal IR and radar data. The bright surface either is abundant in centimeter-sized rocks or is formed from an insulating debris layer overlying a surface with an abundance of rocks in the 1- to 20-cm size range. On the basis of these data, the bright unit is thought to be a young pyroclastic deposit mantling older volcanic units of the Descartes Formation. Since the Apollo 16 target point is only 50 km NW of the central part of this unit, evidence for material associated with this unique highland formation should be searched for in returned soil and rock samples.

  3. 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...... Pleistocene times. These basalts mark the end of a period of shallow subduction of the Nazca slab beneath the Payenia province and volcanism in the Nevado volcanic field apparently followed the downwarping slab in a north-northwest direction ending in the Northern Segment. The northern Payenia basalts...... the literature. The Nevado basalts have been modelled by 4-10 % melting of a primitive mantle added 1-5 % upper continental crust. In the southern Payenia province, intraplate basalts dominate. The samples from the Payún Matrú and Río Colorado volcanic fields are apparently unaffected by the subducting slab...

  4. The nature and origin of mineral coatings on volcanic rocks of the Black Mountain, Stonewall Mountain and Kane Springs Wash volcanic centers in southern Nevada (United States)

    Taranik, J. V.; Noble, D. D.; Hsu, L. C.; Hutsinpiller, A.


    Four LANDSAT thematic mapping scenes in southern Nevada were requested at two different acquisition times in order to assess the effect of vegetation on the signature of the volcanic units. The remote sensing data acquisition and analysis portion are nearly completed. The LANDSAT thematic mapping data is of good quality, and image analysis techniques are so far successful in delineating areas with distinct spectral characteristics. Spectrally distinct areas were correlated with variations in surface coating and lithologies of the volcanic rocks.

  5. Texture induced microwave background anisotropies

    Energy Technology Data Exchange (ETDEWEB)

    Borrill, Julian; Copeland, Edmund J.; Liddle, Andrew R.; Stebbins, Albert; Veeraraghavan, Shoba


    We use numerical simulations to calculate the cosmic microwave background anisotropy induced by the evolution of a global texture field, with special emphasis on individual textures. Both spherically symmetric and general configurations are analyzed, and in the latter case we consider field configurations which exhibit unwinding events and also ones which do not. We compare the results given by evolving the field numerically under both the expanded core (XCORE) and non-linear sigma model (NLSM) approximations with the analytic predictions of the NLSM exact solution for a spherically symmetric self-similar (SSSS) unwinding. We find that the random unwinding configuration spots' typical peak height is 60-75\\% and angular size typically only 10% of those of the SSSS unwinding, and that random configurations without an unwinding event nonetheless may generate indistinguishable hot and cold spots. A brief comparison is made with other work.

  6. Seepage Anisotropy of Heterogeneous Body

    Institute of Scientific and Technical Information of China (English)


    Ore dumps are heterogeneous bodies with anisotropic seepage characteristics because of the ore segregation.In an indoor experiment, a dump was constructed with three strata, where the horizontal and vertical seepage experiments were carried out.Horizontals flow are regarded as phreatic plan flows without penetration.Its seepage law satifies the Dupuit equation.With parallel lay seepage model, the equivalent seepage coefficient in the horizontal flow was obtained and was equivalent to the weighted mean of the seepage coefficient of each stratum.An unsaturated flow appeared in the vertical experiment, with a hydraulic gradient of 1.The vertical flow was equivalent to the seepage model that moved in vertical bedding; its equivalent seepage coefficient depended on the stratum with the minimum seepage coefficient.That the experiment showed clear anisotropy in a heterogeneous body was obvious with an anisotropic coefficient between 63 and 155, which is 25 to 100 times larger than that of a homogeneous body.

  7. CMB anisotropy science: a review

    CERN Document Server

    Challinor, Anthony


    The cosmic microwave background (CMB) provides us with our most direct observational window to the early universe. Observations of the temperature and polarization anisotropies in the CMB have played a critical role in defining the now-standard cosmological model. In this contribution we review some of the basics of CMB science, highlighting the role of observations made with ground-based and balloon-borne Antarctic telescopes. Most of the ingredients of the standard cosmological model are poorly understood in terms of fundamental physics. We discuss how current and future CMB observations can address some of these issues, focusing on two directly relevant for Antarctic programmes: searching for gravitational waves from inflation via B-mode polarization, and mapping dark matter through CMB lensing.

  8. Atmospheric chemistry in volcanic plumes. (United States)

    von Glasow, Roland


    Recent field observations have shown that the atmospheric plumes of quiescently degassing volcanoes are chemically very active, pointing to the role of chemical cycles involving halogen species and heterogeneous reactions on aerosol particles that have previously been unexplored for this type of volcanic plumes. Key features of these measurements can be reproduced by numerical models such as the one employed in this study. The model shows sustained high levels of reactive bromine in the plume, leading to extensive ozone destruction, that, depending on plume dispersal, can be maintained for several days. The very high concentrations of sulfur dioxide in the volcanic plume reduces the lifetime of the OH radical drastically, so that it is virtually absent in the volcanic plume. This would imply an increased lifetime of methane in volcanic plumes, unless reactive chlorine chemistry in the plume is strong enough to offset the lack of OH chemistry. A further effect of bromine chemistry in addition to ozone destruction shown by the model studies presented here, is the oxidation of mercury. This relates to mercury that has been coemitted with bromine from the volcano but also to background atmospheric mercury. The rapid oxidation of mercury implies a drastically reduced atmospheric lifetime of mercury so that the contribution of volcanic mercury to the atmospheric background might be less than previously thought. However, the implications, especially health and environmental effects due to deposition, might be substantial and warrant further studies, especially field measurements to test this hypothesis.

  9. Climatic impact of volcanic eruptions (United States)

    Rampino, Michael R.


    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.

  10. Anisotropy of the magnetic susceptibility of gallium (United States)

    Pankey, T.


    The bulk magnetic susceptibilities of single gallium crystals and polycrystalline gallium spheres were measured at 25??C. The following anisotropic diamagnetic susceptibilities were found: a axis (-0.119??0. 001)??10-6 emu/g, b axis (-0.416??0.002)??10 -6 emu/g, and c axis (-0.229??0.001) emu/g. The susceptibility of the polycrystalline spheres, assumed to be the average value for the bulk susceptibility of gallium, was (-0.257??0.003)??10-6 emu/g at 25??C, and (-0.299??0.003)??10-6 emu/g at -196??C. The susceptibility of liquid gallium was (0.0031??0.001) ??10-6 emu/g at 30??C and 100??C. Rotational diagrams of the susceptibilities in the three orthogonal planes of the unit cell were not sinusoidal. The anisotropy in the single crystals was presumably caused by the partial overlap of Brillouin zone boundaries by the Fermi-energy surface. The large change in susceptibility associated with the change in state was attributed to the absence of effective mass influence in the liquid state. ?? 1960 The American Institute of Physics.

  11. Petrogenesis of volcanic rocks that host the world-class Agsbnd Pb Navidad District, North Patagonian Massif: Comparison with the Jurassic Chon Aike Volcanic Province of Patagonia, Argentina (United States)

    Bouhier, Verónica E.; Franchini, Marta B.; Caffe, Pablo J.; Maydagán, Laura; Rapela, Carlos W.; Paolini, Marcelo


    We present the first study of the volcanic rocks of the Cañadón Asfalto Formation that host the Navidad world-class Ag + Pb epithermal district located in the North Patagonian Massif, Patagonia, Argentina. These volcanic and sedimentary rocks were deposited in a lacustrine environment during an extensional tectonic regime associated with the breakup of Gondwana and represent the mafic to intermediate counterparts of the mainly silicic Jurassic Chon Aike Volcanic Province. Lava flows surrounded by autobrecciated carapace were extruded in subaerial conditions, whereas hyaloclastite and peperite facies suggest contemporaneous subaqueous volcanism and sedimentation. LA-ICPMS Usbnd Pb ages of zircon crystals from the volcanic units yielded Middle Jurassic ages of 173.9 ± 1.9 Ma and 170.8 ± 3 Ma. In the Navidad district, volcanic rocks of the Cañadón Asfalto Formation show arc-like signatures including high-K basaltic-andesite to high-K dacite compositions, Rb, Ba and Th enrichment relative to the less mobile HFS elements (Nb, Ta), enrichment in light rare earth elements (LREE), Ysbnd Ti depletion, and high Zr contents. These characteristics could be explained by assimilation of crustal rocks in the Jurassic magmas, which is also supported by the presence of zircon xenocrysts with Permian and Middle-Upper Triassic ages (281.3 Ma, 246.5, 218.1, and 201.3 Ma) and quartz xenocrysts recognized in these volcanic units. Furthermore, Sr and Nd isotope compositions suggest a contribution of crustal components in these Middle Jurassic magmas. High-K basaltic andesite has initial 87Sr/86Sr ratios of 0.70416-0.70658 and ξNd(t) values of -5.3 and -4. High-K dacite and andesite have initial 87Sr/86Sr compositions of 0.70584-0.70601 and ξNd(t) values of -4,1 and -3,2. The range of Pb isotope values (206Pb/204Pb = 18.28-18.37, 207Pb/204Pb = 15.61-15.62, and 208Pb/204Pb = 38.26-38.43) of Navidad volcanic rocks and ore minerals suggest mixing Pb sources with contributions of

  12. Aurorae and Volcanic Eruptions (United States)


    Thermal-IR Observations of Jupiter and Io with ISAAC at the VLT Summary Impressive thermal-infrared images have been obtained of the giant planet Jupiter during tests of a new detector in the ISAAC instrument on the ESO Very Large Telescope (VLT) at the Paranal Observatory (Chile). . They show in particular the full extent of the northern auroral ring and part of the southern aurora. A volcanic eruption was also imaged on Io , the very active inner Jovian moon. Although these observations are of an experimental nature, they demonstrate a great potential for regular monitoring of the Jovian magnetosphere by ground-based telescopes together with space-based facilities. They also provide the added benefit of direct comparison with the terrestrial magnetosphere. PR Photo 21a/01 : ISAAC image of Jupiter (L-band: 3.5-4.0 µm) . PR Photo 21b/01 : ISAAC image of Jupiter (Narrow-band 4.07 µm) . PR Photo 21c/01 : ISAAC image of Jupiter (Narrow-band 3.28 µm) . PR Photo 21d/01 : ISAAC image of Jupiter (Narrow-band 3.21 µm) . PR Photo 21e/01 : ISAAC image of the Jovian aurorae (false-colour). PR Photo 21f/01 : ISAAC image of volcanic activity on Io . Addendum : The Jovian aurorae and polar haze. Aladdin Meets Jupiter Thermal-infrared images of Jupiter and its volcanic moon Io have been obtained during a series of system tests with the new Aladdin detector in the Infrared Spectrometer And Array Camera (ISAAC) , in combination with an upgrade of the ESO-developed detector control electronics IRACE. This state-of-the-art instrument is attached to the 8.2-m VLT ANTU telescope at the ESO Paranal Observatory. The observations were made on November 14, 2000, through various filters that isolate selected wavebands in the thermal-infrared spectral region [1]. They include a broad-band L-filter (wavelength interval 3.5 - 4.0 µm) as well as several narrow-band filters (3.21, 3.28 and 4.07 µm). The filters allow to record the light from different components of the Jovian atmosphere

  13. Geopulsation, Volcanism and Astronomical Periods

    Institute of Scientific and Technical Information of China (English)

    Yang Xuexiang; Chen Dianyou; Yang Xiaoying; Yang Shuchen


    Volcanism is mainly controlled by the intermittent release of energy in the earth. As far as the differential rotation of the earth's inner core is concerned, the Galactic Year may change the gravitational constant G, the solar radiative quantity and the moving speed of the solar system and affect the exchange of angular momentum between core and mantle as well as the energy exchange between crust and mantle. As a result, this leads to eruptions of superplumes and magma, and controls the energy flow from core - mantle boundary (CMB) to crust. When the earth' s speed decreases, it will release a huge amount of energy. They are the reason of the correspondence of the volcanic cycles one by one with the astronomical periods one by one. According to the astronomical periods, volcanic eruptions may possibly be predicted in the future.

  14. Volcanic eruptions and solar activity (United States)

    Stothers, Richard B.


    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.

  15. Geochemical study for volcanic surveillance

    Energy Technology Data Exchange (ETDEWEB)

    Panichi, C.; La Ruffa, G. [Consiglio Nazionale delle Ricerche, International Institute for Geothermal Research Ghezzano, PI (Italy)


    For years, geologists have been striving to reconstruct volcanic eruptions from the analysis of pyroclastic deposits and lava flows on the surface of the earth and in the oceans. This effort has produced valuable information on volcanic petrology and magma generation, separation, mixing, crystallisation, and interaction with water in phreatomagmatic and submarine eruptions. The volcanological process are tied to the dynamics of the earth's crust and lithosphere. The mantle, subducted oceanic crust, and continental crust contain different rock types and are sources of different magmas. Magmas consist primarily of completely or partially molten silicates containing volatile materials either dissolved in the melt or as bubbles of gas. The silicate and volatile portions affect the physical properties of magma and, therefore, the nature of a volcanic eruption.

  16. Models of volcanic eruption hazards

    Energy Technology Data Exchange (ETDEWEB)

    Wohletz, K.H.


    Volcanic eruptions pose an ever present but poorly constrained hazard to life and property for geothermal installations in volcanic areas. Because eruptions occur sporadically and may limit field access, quantitative and systematic field studies of eruptions are difficult to complete. Circumventing this difficulty, laboratory models and numerical simulations are pivotal in building our understanding of eruptions. For example, the results of fuel-coolant interaction experiments show that magma-water interaction controls many eruption styles. Applying these results, increasing numbers of field studies now document and interpret the role of external water eruptions. Similarly, numerical simulations solve the fundamental physics of high-speed fluid flow and give quantitative predictions that elucidate the complexities of pyroclastic flows and surges. A primary goal of these models is to guide geologists in searching for critical field relationships and making their interpretations. Coupled with field work, modeling is beginning to allow more quantitative and predictive volcanic hazard assessments.

  17. Anisotropy of rare-earth magnets

    Institute of Scientific and Technical Information of China (English)

    R.Skomski; D.J.Sellmyer


    Rare-earth intermetallics such as Nd2FeI4B and Sm-Co are widely used as high-performance permanent magnets,because they combine high magnetocrystalline anisotropy with reasonable magnetization and Curie temperature.The anisotropy is a combined effect of spin-orbit coupling and electrostatic crystal-field interactions.The main contribution comes from the rare-earth 4f electrons,which are well-screened from the crystalline environment but exhibit a strong spin-orbit coupling.In this limit,the magnetocrystalline anisotropy has a very transparent physical interpretation,the anisotropy energy essentially being equal to the energy of Hund's-rules 4f ion in the crystal field.The corresponding expression for the lowest-order uniaxial anisotropy constant K1 is used to discuss rare-earth substitutions,which have recently attracted renewed interest due to shifts in the rare-earth production and demand.Specific phenomena reviewed in this article are the enhancement of the anisotropy of Sm2Fe17 due to interstitial nitrogen,the use of Sm-Co magnets for high-temperature applications,and the comparison of rare-earth single-ion anisotropy with other single-ion and two-ion mechanisms.

  18. Recurrence models of volcanic events: Applications to volcanic risk assessment

    Energy Technology Data Exchange (ETDEWEB)

    Crowe, B.M. [Los Alamos National Lab., Las Vegas, NV (United States); Picard, R.; Valentine, G. [Los Alamos National Lab., NM (United States); Perry, F.V. [New Mexico Univ., Albuquerque, NM (United States)


    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{sup 2} area of Yucca Mountain by ascending basalt magma was bounded by the range of 10{sup {minus}8} to 10{sup {minus}10} yr{sup {minus}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.

  19. Controls on volcanism at intraplate basaltic volcanic fields (United States)

    van den Hove, Jackson C.; Van Otterloo, Jozua; Betts, Peter G.; Ailleres, Laurent; Cas, Ray A. F.


    A broad range of controlling mechanisms is described for intraplate basaltic volcanic fields (IBVFs) in the literature. These correspond with those relating to shallow tectonic processes and to deep mantle plumes. Accurate measurement of the physical parameters of intraplate volcanism is fundamental to gain an understanding of the controlling factors that influence the scale and location of a specific IBVF. Detailed volume and geochronology data are required for this; however, these are not available for many IBVFs. In this study the primary controls on magma genesis and transportation are established for the Pliocene-Recent Newer Volcanics Province (NVP) of south-eastern Australia as a case-study for one of such IBVF. The NVP is a large and spatio-temporally complex IBVF that has been described as either being related to a deep mantle plume, or upper mantle and crustal processes. We use innovative high resolution aeromagnetic and 3D modelling analysis, constrained by well-log data, to calculate its dimensions, volume and long-term eruptive flux. Our estimates suggest volcanic deposits cover an area of 23,100 ± 530 km2 and have a preserved dense rock equivalent of erupted volcanics of least 680 km3, and may have been as large as 900 km3. The long-term mean eruptive flux of the NVP is estimated between 0.15 and 0.20 km3/ka, which is relatively high compared with other IBVFs. Our comparison with other IBVFs shows eruptive fluxes vary up to two orders of magnitude within individual fields. Most examples where a range of eruptive flux is available for an IBVF show a correlation between eruptive flux and the rate of local tectonic processes, suggesting tectonic control. Limited age dating of the NVP has been used to suggest there were pulses in its eruptive flux, which are not resolvable using current data. These changes in eruptive flux are not directly relatable to the rate of any interpreted tectonic driver such as edge-driven convection. However, the NVP and other

  20. Field-trip guide to mafic volcanism of the Cascade Range in Central Oregon—A volcanic, tectonic, hydrologic, and geomorphic journey (United States)

    Deligne, Natalia I.; Mckay, Daniele; Conrey, Richard M.; Grant, Gordon E.; Johnson, Emily R.; O'Connor, Jim; Sweeney, Kristin


    The Cascade Range in central Oregon has been shaped by tectonics, volcanism, and hydrology, as well as geomorphic forces that include glaciations. As a result of the rich interplay between these forces, mafic volcanism here can have surprising manifestations, which include relatively large tephra footprints and extensive lava flows, as well as water shortages, transportation and agricultural disruption, and forest fires. Although the focus of this multidisciplinary field trip will be on mafic volcanism, we will also look at the hydrology, geomorphology, and ecology of the area, and we will examine how these elements both influence and are influenced by mafic volcanism. We will see mafic volcanic rocks at the Sand Mountain volcanic field and in the Santiam Pass area, at McKenzie Pass, and in the southern Bend region. In addition, this field trip will occur during a total solar eclipse, the first one visible in the United States in more than 25 years (and the first seen in the conterminous United States in more than 37 years).The Cascade Range is the result of subduction of the Juan de Fuca plate underneath the North American plate. This north-south-trending volcanic mountain range is immediately downwind of the Pacific Ocean, a huge source of moisture. As moisture is blown eastward from the Pacific on prevailing winds, it encounters the Cascade Range in Oregon, and the resulting orographic lift and corresponding rain shadow is one of the strongest precipitation gradients in the conterminous United States. We will see how the products of the volcanoes in the central Oregon Cascades have had a profound influence on groundwater flow and, thus, on the distribution of Pacific moisture. We will also see the influence that mafic volcanism has had on landscape evolution, vegetation development, and general hydrology.

  1. Effect of anisotropy on small magnetic clusters

    CERN Document Server

    Hucht, Alfred; Sil, Shreekantha; Entel, Peter; 10.1103/PhysRevB.84.104438


    The effect of dipolar interaction and local uniaxial anisotropy on the magnetic response of small spin clusters where spins are located on the vertices of icosahedron, cuboctahedron, tetrahedron and square geometry have been investigated. We consider the ferromagnetic and antiferromagnetic spin-1/2 and spin-1 Heisenberg model with uniaxial anisotropy and dipolar interaction and apply numerical exact diagonalization technique in order to study the influence of frustration and anisotropy on the ground state properties of the spin-clusters. The ground state magnetization, spin-spin correlation and several thermodynamic quantities such as entropy and specific heat are calculated as a function of temperature and magnetic field.

  2. Anisotropies of anhysteretic remanence and magnetic susceptibility of marly clays from Central Italy

    Directory of Open Access Journals (Sweden)

    L. Sagnotti


    Full Text Available Marly clays from an Upper Pliocene unit at Valle Ricca (Rorne were investigated for their Anisotropy of Anhysteretic Remanence (AAR and Anisotropy of Magnetic Susceptibility (AMS. The study of AAR was accomplished for the first time in ltaly, developing a suitable laboratory technique and adapting a standard statistical procedure. The comparison between anhysteretic remanence and magnetic susceptibility anisotropies discriminates the fabric of the ferromagnetic fraction from that of the paramagnetic matrix of the rock. The separation of fabric components was applied to distinguish subsequent geological processes that affected the total rock fabric. The results indicate that the clayey units are particularly suitable for the empirical investigation of fabric to strain relationship in weakly deformed rocks.

  3. Crust and upper-mantle seismic anisotropy variations from the coast to inland in central and Southern Mexico (United States)

    Castellanos, Jorge; Pérez-Campos, Xyoli; Valenzuela, Raúl; Husker, Allen; Ferrari, Luca


    Subduction zones are among the most dynamic tectonic environments on Earth. Deformation mechanisms of various scales produce networks of oriented structures and faulting systems that result in a highly anisotropic medium for seismic wave propagation. In this study, we combine shear wave splitting inferred from receiver functions and the results from a previous SKS-wave study to quantify and constrain the vertically averaged shear wave splitting at different depths along the 100-station MesoAmerican Subduction Experiment array. This produces a transect that runs perpendicular to the trench across the flat slab portion of the subduction zone below central and southern Mexico. Strong anisotropy in the continental crust is found below the Trans-Mexican Volcanic Belt (TMVB) and above the source region of slow-slip events. We interpret this as the result of fluid/melt ascent. The upper oceanic crust and the overlying low-velocity zone exhibit highly complex anisotropy, while the oceanic lower crust is relatively homogeneous. Regions of strong oceanic crust anisotropy correlate with previously found low Vp/Vs regions, indicating that the relatively high Vs is an anisotropic effect. Upper-mantle anisotropy in the southern part of the array is in trench-perpendicular direction, consistent with the alignment of type-A olivine and with entrained subslab flow. The fast polarization direction of mantle anisotropy changes to N-S in the north, likely reflecting mantle wedge corner flow perpendicular to the TMVB.

  4. A quantitative model for volcanic hazard assessment


    W. Marzocchi; Sandri, L.; Furlan, C


    Volcanic hazard assessment is a basic ingredient for risk-based decision-making in land-use planning and emergency management. Volcanic hazard is defined as the probability of any particular area being affected by a destructive volcanic event within a given period of time (Fournier d’Albe 1979). The probabilistic nature of such an important issue derives from the fact that volcanic activity is a complex process, characterized by several and usually unknown degrees o...

  5. Evidence for volcanism in NW Ishtar Terra, Venus (United States)

    Gaddis, L.; Greeley, Ronald

    Venera 15/16 radar data for an area in NW Ishtar Terra, Venus, show an area with moderate radar return and a smooth textured surface which embays low lying areas of the surrounding mountainous terrain. Although this unit may be an extension of the lava plains of Lakshmi Planum to the southeast, detailed study suggests a separate volcanic center in NW Ishtar Terra. Lakshmi Planum, on the Ishtar Terra highland, exhibits major volcanic and tectonic features. On the Venera radar image radar brightness is influenced by slope and roughness; radar-facing slopes (east-facing) and rough surfaces (approx. 8 cm average relief) are bright, while west-facing slopes and smooth surfaces are dark. A series of semi-circular features, apparently topographic depressions, do not conform in orientation to major structural trends in this region of NW Ishtar Terra. The large depression in NW Ishtar Terra is similar to the calderas of Colette and Sacajawea Paterae, as all three structures are large irregular depressions. NW Ishtar Terra appears to be the site of a volcanic center with a complex caldera structure, possibly more than one eruptive vent, and associated lobed flows at lower elevations. The morphologic similarity between this volcanic center and those of Colette and Sacajawea suggests that centralized eruptions have been the dominant form of volcanism in Ishtar. The location of this volcanic center at the intersection of two major compressional mountain belts and the large size of the calders (with an inferred large/deep magma source) support a crustal thickening/melting rather than a hot-spot origin for these magmas.

  6. Optical anisotropy of polyimide and polymethacrylate containing photocrosslinkable chalcone group in the side chain under irradiation of a linearly polarized UV light

    CERN Document Server

    Choi, D H


    Photocrosslinkable soluble polyimide and polymethacrylate compound were synthesized for studying the optically induced anisotropy of the thin films. Chalcone group was introduced into the side chain unit of two polymers. We observed a photodimerization behavior between the double bonds in the chalcone group and an optical anisotropy of these materials by irradiation of a linearly polarized UV light (LPL). Optical anisotropy of the thin film was also investigated by using polarized UV absorption spectroscopy.The dynamic property of optical anisotropy in photoreactive polyimide was compared to that in polymethacrylate containing chalcone group in the side chain.

  7. Volcanic forcing in decadal forecasts (United States)

    Ménégoz, Martin; Doblas-Reyes, Francisco; Guemas, Virginie; Asif, Muhammad; Prodhomme, chloe


    Volcanic eruptions can significantly impact the climate system, by injecting large amounts of particles into the stratosphere. By reflecting backward the solar radiation, these particles cool the troposphere, and by absorbing the longwave radiation, they warm the stratosphere. As a consequence of this radiative forcing, the global mean surface temperature can decrease by several tenths of degrees. However, large eruptions are also associated to a complex dynamical response of the climate system that is particularly tricky do understand regarding the low number of available observations. Observations seem to show an increase of the positive phases of the Northern Atlantic Oscillation (NAO) the two winters following large eruptions, associated to positive temperature anomalies over the Eurasian continent. The summers following large eruptions are generally particularly cold, especially over the continents of the Northern Hemisphere. Overall, it is really challenging to forecast the climate response to large eruptions, as it is both modulated by, and superimposed to the climate background conditions, largely driven themselves by internal variability at seasonal to decadal scales. This work describes the additional skill of a forecast system used for seasonal and decadal predictions when it includes observed volcanic forcing over the last decades. An idealized volcanic forcing that could be used for real-time forecasts is also evaluated. This work consists in a base for forecasts that will be performed in the context of the next large volcanic eruption.

  8. Experimental generation of volcanic lightning (United States)

    Cimarelli, Corrado; Alatorre-Ibargüengoitia, Miguel; Kueppers, Ulrich; Scheu, Bettina; Dingwell, Donald B.


    Ash-rich volcanic plumes that are responsible for injecting large quantities of aerosols into the atmosphere are often associated with intense electrical activity. Direct measurement of the electric potential at the crater, where the electric activity in the volcanic plume is first observed, is severely impeded, limiting progress in its investigation. We have achieved volcanic lightning in the laboratory during rapid decompression experiments of gas-particle mixtures under controlled conditions. Upon decompression (from ~100 bar argon pressure to atmospheric pressure), loose particles are vertically accelerated and ejected through a nozzle of 2.8 cm diameter into a large tank filled with air at atmospheric conditions. Because of their impulsive character, our experiments most closely represent the conditions encountered in the gas-thrust region of the plume, when ash is first ejected from the crater. We used sieved natural ash with different grain sizes from Popocatépetl (Mexico), Eyjafjallajökull (Iceland), and Soufrière Hills (Montserrat) volcanoes, as well as micrometric glass beads to constrain the influence of material properties on lightning. We monitored the dynamics of the particle-laden jets with a high-speed camera and the pressure and electric potential at the nozzle using a pressure transducer and two copper ring antennas connected to a high-impedance data acquisition system, respectively. We find that lightning is controlled by the dynamics of the particle-laden jet and by the abundance of fine particles. Two main conditions are required to generate lightning: 1) self-electrification of the particles and 2) clustering of the particles driven by the jet fluid dynamics. The relative movement of clusters of charged particles within the plume generates the gradient in electrical potential, which is necessary for lightning. In this manner it is the gas-particle dynamics together with the evolving particle-density distribution within different regions of

  9. Anisotropy and Corotation of Galactic Cosmic Rays

    CERN Document Server

    Amenomori, M; Bi, X J; Chen, D; Cui, S W; Danzengluobu; Ding, L K; Ding, X H; Feng Cun Feng; Zhaoyang Feng; Feng, Z Y; Gao, X Y; Geng, Q X; Guo, H W; He, H H; He, M; Hibino, K; Hotta, N; Haibing, H; Hu, H B; Huang, J; Huang, Q; Jia, H Y; Kajino, F; Kasahara, K; Katayose, Y; Kato, C; Kawata, K; Labaciren; Le, G M; Li, A F; Li, J Y; Lou, Y Q; Lü, H; Lu, S L; Meng, X R; Mizutani, K; Mu, J; Munakata, K; Nagai, A; Nanjo, H; Nishizawa, M; Ohnishi, M; Ohta, I; Onuma, H; Ouchi, T; Ozawa, S; Ren, J R; Saitô, T; Saito, T Y; Sakata, M; Sako, T K; Sasaki, T; Shibata, M; Shiomi, A; Shirai, T; Sugimoto, H; Takita, M; Tan, Y H; Tateyama, N; Torii, S; Tsuchiya, H; Udo, S; Wang, B; Wang, H; Wang, X; Wang, Y G; Wu, H R; Xue Liang; Yamamoto, Y; Yan, C T; Yang, X C; Yasue, S; Ye, Z H; Yu, G C; Yuan, A F; Yuda, T; Zhang, H M; Zhang, J L; Zhang, N J; Zhang, X Y; Zhang, Y; Zhaxisangzhu; Zhou, X X


    The intensity of Galactic cosmic rays is nearly isotropic because of the influence of magnetic fields in the Milky Way. Here, we present two-dimensional high-precision anisotropy measurement for energies from a few to several hundred teraelectronvolts (TeV), using the large data sample of the Tibet Air Shower Arrays. Besides revealing finer details of the known anisotropies, a new component of Galactic cosmic ray anisotropy in sidereal time is uncovered around the Cygnus region direction. For cosmic-ray energies up to a few hundred TeV, all components of anisotropies fade away, showing a corotation of Galactic cosmic rays with the local Galactic magnetic environment. These results have broad implications for a comprehensive understanding of cosmic rays, supernovae, magnetic fields, and heliospheric and Galactic dynamic environments.

  10. Cellulose and the Control of Growth Anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Tobias I. Baskin


    The authors research aims to understand morphogenesis, focusing on growth anisotropy, a process that is crucial to make organs with specific and heritable shapes. For the award, the specific aims were to test hypotheses concerning how growth anisotropy is controlled by cell wall structure, particularly by the synthesis and alignment of cellulose microfibrils, the predominant mechanical element in the cell wall. This research has involved characterizing the basic physiology of anisotropic expansion, including measuring it at high resolution; and second, characterizing the relationship between growth anisotropy, and cellulose microfibrils. Important in this relationship and also to the control of anisotropic expansion are structures just inside the plasma membrane called cortical microtubules, and the research has also investigated their contribution to controlling anisotropy and microfibril alignment. In addition to primary experimental papers, I have also developed improved methods relating to these objectives as well as written relevant reviews. Major accomplishments in each area will now be described.

  11. Elastic anisotropy of Earth's inner core. (United States)

    Belonoshko, Anatoly B; Skorodumova, Natalia V; Rosengren, Anders; Johansson, Börje


    Earth's solid-iron inner core is elastically anisotropic. Sound waves propagate faster along Earth's spin axis than in the equatorial plane. This anisotropy has previously been explained by a preferred orientation of the iron alloy hexagonal crystals. However, hexagonal iron becomes increasingly isotropic on increasing temperature at pressures of the inner core and is therefore unlikely to cause the anisotropy. An alternative explanation, supported by diamond anvil cell experiments, is that iron adopts a body-centered cubic form in the inner core. We show, by molecular dynamics simulations, that the body-centered cubic iron phase is extremely anisotropic to sound waves despite its high symmetry. Direct simulations of seismic wave propagation reveal an anisotropy of 12%, a value adequate to explain the anisotropy of the inner core.

  12. Magnetic anisotropies of rare-earth compounds (United States)

    Loewenhaupt, M.; Rotter, M.; Kramp, S.


    There are two kinds of magnetic anisotropy in rare-earth compounds: the single-ion anisotropy caused by the crystal field (CF) and the anisotropy of the two-ion interactions. Both types of anisotropy have to be considered to arrive at a consistent description of the magnetic properties of the orthorhombic intermetallic compound NdCu 2. From the analysis of NdCu 2 we can derive predictions for the type of ordering in other isostructural RCu 2 compounds, that agree well with experimental results: If the magnetic moments point into the crystallographic b-direction, an ordering wave vector of (2/3 0 0) is expected. If the moments are oriented perpendicular to b then the ordering wave vector is (2/3 1 0) .

  13. Microwave Background Anisotropies from Scaling Seed Perturbations

    CERN Document Server

    Durrer, R; Durrer, Ruth; Sakellariadou, Mairi


    We study microwave background anisotropies induced by scaling seed perturbations in a universe dominated by cold dark matter. Using a gauge invariant linear perturbation analysis, we solve the perturbation equations on super-horizon scales, for CMB anisotropies triggered by generic gravitational seeds. We find that perturbations induced by seeds -- under very mild restrictions -- are nearly isocurvature. Thus, compensation, which is mainly the consequence of physically sensible initial conditions, is very generic. We then restrict our study to the case of scaling sources, motivated by global scalar fields. We parameterize the energy momentum tensor of the source by ``seed functions'' and calculate the Sachs-Wolfe and acoustic contributions to the CMB anisotropies. We discuss the dependence of the anisotropy spectrum on the parameters of the model considered. Even within the restricted class of models investigated in this work, we find a surprising variety of results for the position and height of the first ac...

  14. Differentiation and volcanism in the lunar highlands: photogeologic evidence and Apollo 16 implications (United States)

    Trask, N.J.; McCauley, J.F.


    Materials of possible volcanic origin in the lunar highlands include (1) highland plains materials, (2) materials forming closely spaced hills in which summit furrows and chains of craters are common and (3) materials forming closely spaced hills (some of which parallel the lunar grid) on which summit furrows and chain craters are rare. The highland plains materials probably are basaltic lavas with less Fe and Ti than the mare plains materials. The two hilly units appear to consist of materials that, if volcanic, were more viscous in the molten state than any of the lunar plains units; thus these materials may be significantly enriched in felsic components. Most of the highland materials of possible volcanic origin formed after the Imbrium multi-ring basin but before mare material completed flooding parts of the moon; they therefore postdate accretion of the moon and may represent several episodes of premare volcanism. ?? 1972.

  15. Glass shards, pumice fragments and volcanic aerosol particles - diagenesis a recorder of volcanic activity? (United States)

    Obenholzner, J. H.; Schroettner, H.; Poelt, P.; Delgado, H.


    Detailed SEM/EDS studies of Triassic (Southern Alps, A, I, Sl) and Miocene (Mixteca Alta, Mexico) tuffs revealed that volcanic glass shards can be replaced by zeolites (analcite), chlorites and smectites preserving the shape of primary shards (1). The Triassic pyroclastic deposits have been incorporated in the pre-Alpine burial diagenesis, the Miocene pyroclastic deposits are bentonites. The volcanologist is impressed by the circumstances that million years old pyroclast relict textures can be sized. Shape parameters obtained by image analysis can be compared with much younger pyroclastic deposits (2). Both deposits have not been effected by shearing. The alteration of pumice fragments of Triassic age is not a simple replacement process. Intergrowth of different illites and chlorites and probably vesicle filling by SiO2 and subsequent overgrowth make a reconstruction sometimes difficult. These processes are accompanied by the formation of REE-, Y- and Zr-bearing minerals as well as with the alteration of zircons. Studies of recently erupted ash from Popocatepetl volcano reveal the presence of a variety of µm-sized contact-metamorphosed clasts being a part of the volcanic ash (3). Such clasts should be present in many older pyroclastic deposits, especially where volcanoes had been situated on massive sedimentary units providing contact metamorphism in the realm of a magma chamber or during magma ascent. Volcanic aerosol particles collected in 1997 from the passively degassing plume of Popocatepetl volcano revealed in FESEM/EDS analysis (H. Schroettner and P. Poelt) a wide spectrum of fluffy, spherical and coagulated spherical particles (µm-sized). Under pre-vacuum conditions they remained stable for ca. 3 years (3). In nature the fate of these particles in the atmosphere is unknown. Are there relicts in marine, lacustrine sediments and ice cores, which could be used as proxies of volcanic activity? (1) Obenholzner &Heiken,1999. Ann.Naturhist.Mus.Wien, 100 A, 13

  16. A Volcanic Hydrogen Habitable Zone (United States)

    Ramirez, Ramses M.; Kaltenegger, Lisa


    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 N2–CO2–H2O HZ extends out to nearly ∼1.7 au in our solar system, beyond which condensation and scattering by CO2 outstrips its greenhouse capacity. Here, we show that volcanic outgassing of atmospheric H2 can extend the outer edge of the HZ to ∼2.4 au in our solar system. This wider volcanic-hydrogen HZ (N2–CO2–H2O–H2) can be sustained as long as volcanic H2 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 H2 warming is reduced in dense H2O atmospheres. The atmospheric scale heights of such volcanic H2 atmospheres near the outer edge of the HZ also increase, facilitating remote detection of atmospheric signatures.

  17. Higher-order anisotropies in the Buda-Lund model: Disentangling flow and density field anisotropies

    Energy Technology Data Exchange (ETDEWEB)

    Loekoes, Sandor [Eoetvoes Lorand University, Budapest (Hungary); Csanad, Mate [Eoetvoes Lorand University, Budapest (Hungary); Stony Brook University, Stony Brook, NY (United States); Tomasik, Boris [Univerzita Mateja Bela, Banska Bystrica (Slovakia); Czech Technical University in Prague, FNSPE, Prague (Czech Republic); Csoergo, Tamas [Wigner RCP, Budapest (Hungary); KRF, Gyoengyoes (Hungary)


    The Buda-Lund hydro model describes an expanding ellipsoidal fireball, and fits the observed elliptic flow and oscillating HBT radii successfully. Due to fluctuations in energy depositions, the fireball shape however fluctuates on an event-by-event basis. The transverse plane asymmetry can be translated into a series of multipole anisotropy coefficients. These anisotropies then result in measurable momentum-space anisotropies, to be measured with respect to their respective symmetry planes. In this paper we detail an extension of the Buda-Lund model to multipole anisotropies and investigate the resulting flow coefficients and oscillations of HBT radii. (orig.)

  18. Higher order anisotropies in the Buda-Lund model -- disentangling flow and density field anisotropies

    CERN Document Server

    Lökös, Sándor; Csörgő, Tamás; Tomášik, Boris


    The Buda-Lund hydro model describes an expanding ellipsoidal fireball, and fits the observed elliptic flow and oscillating HBT radii successfully. Due to fluctuations in energy depositions, the fireball shape however fluctuates on an event-by-event basis. The transverse plane asymmetry can be translated into a series of multipole anisotropy coefficients. These anisotropies then result in measurable momentum-space anisotropies, to be measured with respect to their respective symmetry planes. In this paper we detail an extension of the Buda-Lund model to multipole anisotropies and investigate the resulting flow coefficients and oscillations of HBT radii.

  19. How Volcanism Controls Climate Change (United States)

    Ward, P. L.


    Large explosive volcanoes eject megatons of sulfur dioxide into the lower stratosphere where it spreads around the world within months and is oxidized slowly to form a sulfuric-acid aerosol with particle sizes that grow large enough to reflect and scatter solar radiation, cooling Earth ~0.5C for up to 3 years. Explosive eruptions also deplete total column ozone ~6% causing up to 3C winter warming at mid-latitudes over continents. Global cooling predominates. Extrusive, basaltic volcanoes deplete ozone ~6% but do not eject much sulfur dioxide into the lower stratosphere, causing net global warming. Anthropogenic chlorofluorocarbons (CFCs) deplete ozone ~3% for up to a century while each volcanic eruption, even small ones, depletes ozone twice as much but for less than a decade through eruption of halogens and ensuing photochemical processes. The 2010 eruption of Eyjafjallajökull, the 2011 eruption of Grímsvötn, plus anthropogenic CFCs depleted ozone over Toronto Canada 14% in 2012, causing an unusually warm winter and drought. Total column ozone determines how much solar ultraviolet energy with wavelengths between 290 and 340 nanometers reaches Earth where it is absorbed most efficiently by the ocean. A 25% depletion of ozone increases the amount of this radiation reaching Earth by 1 W m-2 for overhead sun and 0.25 W m-2 for a solar zenith angle of 70 degrees. The tropopause is the boundary between the troposphere heated from below by a sun-warmed Earth and the stratosphere heated from above by the Sun through photodissociation primarily of oxygen and ozone. The mean annual height of the tropopause increased ~160 m between 1980 and 2004 at the same time that northern mid-latitude total column ozone was depleted by ~4%, the lower stratosphere cooled ~2C, the upper troposphere warmed ~0.1C, and mean surface temperatures in the northern hemisphere rose ~0.5C. Regional total ozone columns are observed to increase as rapidly as 20% within 5 hours with an associated 5

  20. Friction anisotropy in boronated graphite

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, N., E-mail: [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam (India); Radhika, R. [Crystal Growth Centre, Anna University, Chennai (India); Kozakov, A.T. [Research Institute of Physics, Southern Federal University, Rostov-on-Don (Russian Federation); Pandian, R. [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam (India); Chakravarty, S. [UGC-DAE CSR, Kalpakkam (India); Ravindran, T.R.; Dash, S.; Tyagi, A.K. [Materials Science Group, Indira Gandhi Centre for Atomic Research, Kalpakkam (India)


    Graphical abstract: - Highlights: • Friction anisotropy in boronated graphite is observed in macroscopic sliding condition. • Low friction coefficient is observed in basal plane and becomes high in prismatic direction. • 3D phase of boronated graphite transformed into 2D structure after friction test. • Chemical activity is high in prismatic plane forming strong bonds between the sliding interfaces. - Abstract: Anisotropic friction behavior in macroscopic scale was observed in boronated graphite. Depending upon sliding speed and normal loads, this value was found to be in the range 0.1–0.35 in the direction of basal plane and becomes high 0.2–0.8 in prismatic face. Grazing-incidence X-ray diffraction analysis shows prominent reflection of (0 0 2) plane at basal and prismatic directions of boronated graphite. However, in both the wear tracks (1 1 0) plane become prominent and this transformation is induced by frictional energy. The structural transformation in wear tracks is supported by micro-Raman analysis which revealed that 3D phase of boronated graphite converted into a disordered 2D lattice structure. Thus, the structural aspect of disorder is similar in both the wear tracks and graphite transfer layers. Therefore, the crystallographic aspect is not adequate to explain anisotropic friction behavior. Results of X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy shows weak signature of oxygen complexes and functional groups in wear track of basal plane while these species dominate in prismatic direction. Abundance of these functional groups in prismatic plane indicates availability of chemically active sites tends to forming strong bonds between the sliding interfaces which eventually increases friction coefficient.

  1. Global Volcanism on Mercury at About 3.8 Ga (United States)

    Byrne, P. K.; Ostrach, L. R.; Denevi, B. W.; Head, J. W., III; Hauck, S. A., II; Murchie, S. L.; Solomon, S. C.


    Smooth plains occupy c. 27% of the surface of Mercury. Embayment relations, spectral contrast with surroundings, and morphologic characteristics indicate that the majority of these plains are volcanic. The largest deposits are located in Mercury's northern hemisphere and include the extensive northern plains (NP) and the Caloris interior and exterior plains (with the latter likely including basin material). Both the NP and Caloris deposits are, within statistical error, the same age (~3.8-3.9 Ga). To test whether this age reflects a period of global volcanism on Mercury, we determined crater size-frequency distributions for four smooth plains units in the planet's southern hemisphere interpreted to be volcanic. Two deposits are situated within the Beethoven and Tolstoj impact basins; two are located close to the Debussy and the Alver and Disney basins, respectively. Each deposit hosts two populations of craters, one that postdates plains emplacement and one that consists of partially to nearly filled craters that predate the plains. This latter population indicates that some time elapsed between formation of the underlying basement and plains volcanism, though we cannot statistically resolve this interval at any of the four sites. Nonetheless, we find that the age given by the superposed crater population in each case is ~3.8 Ga, and crater density values are consistent with those for the NP and Caloris plains. This finding supports a global phase of volcanism near the end of the late heavy bombardment of Mercury and may indicate a period of widespread partial melting of Mercury's mantle. Notably, superposition relations between smooth plains, degraded impact structures, and contractional landforms suggest that by this time interior cooling had already placed Mercury's lithosphere in horizontal compression, tending to inhibit voluminous dike-fed volcanism such as that inferred responsible for the NP. Most smooth plains units, including the Caloris plains and our

  2. Airborne volcanic ash; a global threat to aviation (United States)

    Neal, Christina A.; Guffanti, Marianne C.


    The world's busy air traffic corridors pass over or downwind of hundreds of volcanoes capable of hazardous explosive eruptions. The risk to aviation from volcanic activity is significant - in the United States alone, aircraft carry about 300,000 passengers and hundreds of millions of dollars of cargo near active volcanoes each day. Costly disruption of flight operations in Europe and North America in 2010 in the wake of a moderate-size eruption in Iceland clearly demonstrates how eruptions can have global impacts on the aviation industry. Airborne volcanic ash can be a serious hazard to aviation even hundreds of miles from an eruption. Encounters with high-concentration ash clouds can diminish visibility, damage flight control systems, and cause jet engines to fail. Encounters with low-concentration clouds of volcanic ash and aerosols can accelerate wear on engine and aircraft components, resulting in premature replacement. The U.S. Geological Survey (USGS), in cooperation with national and international partners, is playing a leading role in the international effort to reduce the risk posed to aircraft by volcanic eruptions.

  3. Mantle wedge dynamics from seismic anisotropy (Invited) (United States)

    Long, M. D.; Wirth, E. A.


    The mantle wedge above subducting slabs plays a critical role in many of the physical processes associated with subduction, including water transport into the upper mantle and the generation and transport of melts. Our understanding of mantle wedge dynamics is incomplete; in particular, the mantle flow field above subducting slabs remains poorly understood. Because seismic anisotropy is a consequence of deformation, observations of anisotropy (such as shear wave splitting and P-to-SH converted waves) can constrain the geometry of the wedge flow field. Additionally, because the presence of water (either in nominally anhydrous minerals or as hydrous phases) can have a large effect on anisotropic structure, a detailed understanding of mantle wedge anisotropy can help to constrain processes related to water cycling in subduction systems. We present a global, synoptic view of anisotropy observations in subduction zone mantle wedges, compiled from a large number of individual studies, with the goal of understanding the first-order controls on wedge anisotropy and flow patterns. This compilation allows us to explicitly test the predictions made by many different conceptual models for wedge anisotropy, as well as to explore the relationships between observed anisotropy parameters and other parameters that describe subduction. We find that no simple model can explain all of the trends observed in the global data set. Mantle wedge flow is likely controlled by a combination of downdip motion of the slab, trench migration, ambient mantle flow, small-scale convection, proximity to slab edges, and slab morphology, with the relative contributions of these in any given subduction system controlled by the subduction kinematics and mantle rheology. There is also a likely contribution from B-type olivine and/or serpentinite fabric in many subduction zones, governed by the local thermal structure and volatile distribution.

  4. Source mechanisms of volcanic tsunamis. (United States)

    Paris, Raphaël


    Volcanic tsunamis are generated by a variety of mechanisms, including volcano-tectonic earthquakes, slope instabilities, pyroclastic flows, underwater explosions, shock waves and caldera collapse. In this review, we focus on the lessons that can be learnt from past events and address the influence of parameters such as volume flux of mass flows, explosion energy or duration of caldera collapse on tsunami generation. The diversity of waves in terms of amplitude, period, form, dispersion, etc. poses difficulties for integration and harmonization of sources to be used for numerical models and probabilistic tsunami hazard maps. In many cases, monitoring and warning of volcanic tsunamis remain challenging (further technical and scientific developments being necessary) and must be coupled with policies of population preparedness. © 2015 The Author(s).

  5. Anomalous diffusion of volcanic earthquakes

    CERN Document Server

    Abe, Sumiyoshi


    Volcanic seismicity at Mt. Etna is studied. It is found that the associated stochastic process exhibits a subdiffusive phenomenon. The jump probability distribution well obeys an exponential law, whereas the waiting-time distribution follows a power law in a wide range. Although these results would seem to suggest that the phenomenon could be described by temporally-fractional kinetic theory based on the viewpoint of continuous-time random walks, the exponent of the power-law waiting-time distribution actually lies outside of the range allowed in the theory. In addition, there exists the aging phenomenon in the event-time averaged mean squared displacement, in contrast to the picture of fractional Brownian motion. Comments are also made on possible relevances of random walks on fractals as well as nonlinear kinetics. Thus, problems of volcanic seismicity are highly challenging for science of complex systems.

  6. Paleomagnetic data from the Trans-Mexican Volcanic Belt: implications for tectonics and volcanic stratigraphy (United States)

    Alva-Valdivia, L. M.; Goguitchaichvili, A.; Ferrari, L.; Rosas-Elguera, J.; Urrutia-Fucugauchi, J.; Zamorano-Orozco, J. J.


    We report a paleomagnetic and rock-magnetic study of Miocene volcanic rocks from the Trans-Mexican Volcanic Belt. A total of 32 sites (238 oriented samples) were collected from three localities: Queretaro, Guadalajara and Los Altos de Jalisco basaltic plateaux, which span from 11 to 7.5 Ma. Several rock-magnetic experiments were carried out in order to identify the magnetic carriers and to obtain information about their paleomagnetic stability. Microscopic observation of polished sections shows that the main magnetic mineral is Ti-poor titanomagnetite associated with exsolved ilmenite. Continuous susceptibility measurements with temperature yield in most cases reasonably reversible curves with Curie points close to that of magnetite. Judging from the ratios of hysteresis parameters, it seems that all samples fall in the pseudo-single domain (PSD) grain size region, probably indicating a mixture of multidomain (MD) and a significant amount of single domain (SD) grains. Based on our paleomagnetic and available radiometric data, it seems that the volcanic units have been emplaced during a relatively short time span of 1 to 2 My at each locality. The mean paleomagnetic directions obtained from each locality differ significantly from that expected for the Middle Miocene. The mean paleomagnetic direction calculated from 28 sites discarding those of intermediate polarity is I= 32.46°, D= 341.2°, k= 7.2 and a95= 11.6°. Comparison with the expected direction indicates some 20° anticlockwise tectonic rotations for the studied area, in accordance with the proposed left-lateral transtensional tectonic regime already proposed for this period.

  7. Volcanic mercury in Pinus canariensis (United States)

    Rodríguez Martín, José Antonio; Nanos, Nikos; Miranda, José Carlos; Carbonell, Gregoria; Gil, Luis


    Mercury (Hg) is a toxic element that is emitted to the atmosphere by both human activities and natural processes. Volcanic emissions are considered a natural source of mercury in the environment. In some cases, tree ring records taken close to volcanoes and their relation to volcanic activity over time are contradictory. In 1949, the Hoyo Negro volcano (La Palma-Canary Islands) produced significant pyroclastic flows that damaged the nearby stand of Pinus canariensis. Recently, 60 years after the eruption, we assessed mercury concentrations in the stem of a pine which survived volcano formation, located at a distance of 50 m from the crater. We show that Hg content in a wound caused by pyroclastic impacts (22.3 μg kg-1) is an order of magnitude higher than the Hg concentrations measured in the xylem before and after the eruption (2.3 μg kg-1). Thus, mercury emissions originating from the eruption remained only as a mark—in pyroclastic wounds—and can be considered a sporadic and very high mercury input that did not affect the overall Hg input in the xylem. In addition, mercury contents recorded in the phloem (9.5 μg kg-1) and bark (6.0 μg kg-1) suggest that mercury shifts towards non-living tissues of the pine, an aspect that can be related to detoxification in volcanism-adapted species.

  8. Recalibrated mariner 10 color mosaics: Implications for mercurian volcanism (United States)

    Robinson, M.S.; Lucey, P.G.


    Recalibration of Mariner 10 color image data allows the identification of distinct color units on the mercurian surface. We analyze these data in terms of opaque mineral abundance, iron content, and soil maturity and find color units consistent with the presence of volcanic deposits on Mercury's surface. Additionally, materials associated with some impact craters have been excavated from a layer interpreted to be deficient in opaque minerals within the crust, possibly analogous to the lunar anorthosite crust. These observations suggest that Mercury has undergone complex differentiation like the other terrestrial planets and the Earth's moon.

  9. The expected anisotropy in solid inflation

    Energy Technology Data Exchange (ETDEWEB)

    Bartolo, Nicola; Ricciardone, Angelo [Dipartimento di Fisica e Astronomia ' ' G. Galilei' ' , Università degli Studi di Padova, via Marzolo 8, I-35131, Padova (Italy); Peloso, Marco; Unal, Caner, E-mail:, E-mail:, E-mail:, E-mail: [School of Physics and Astronomy, University of Minnesota, 116 Church Street S.E., Minneapolis 55455 (United States)


    Solid inflation is an effective field theory of inflation in which isotropy and homogeneity are accomplished via a specific combination of anisotropic sources (three scalar fields that individually break isotropy). This results in specific observational signatures that are not found in standard models of inflation: a non-trivial angular dependence for the squeezed bispectrum, and a possibly long period of anisotropic inflation (to drive inflation, the ''solid'' must be very insensitive to any deformation, and thus background anisotropies are very slowly erased). In this paper we compute the expected level of statistical anisotropy in the power spectrum of the curvature perturbations of this model. To do so, we account for the classical background values of the three scalar fields that are generated on large (superhorizon) scales during inflation via a random walk sum, as the perturbation modes leave the horizon. Such an anisotropy is unavoidably generated, even starting from perfectly isotropic classical initial conditions. The expected level of anisotropy is related to the duration of inflation and to the amplitude of the squeezed bispectrum. If this amplitude is close to its current observational limit (so that one of the most interesting predictions of the model can be observed in the near future), we find that a level of statistical anisotropy F{sup 2} gives frozen and scale invariant vector perturbations on superhorizon scales.

  10. Submarine volcanoes along the Aegean volcanic arc (United States)

    Nomikou, Paraskevi; Papanikolaou, Dimitrios; Alexandri, Matina; Sakellariou, Dimitris; Rousakis, Grigoris


    The Aegean volcanic arc has been investigated along its offshore areas and several submarine volcanic outcrops have been discovered in the last 25 years of research. The basic data including swath bathymetric maps, air-gun profiles, underwater photos and samples analysis have been presented along the four main volcanic groups of the arc. The description concerns: (i) Paphsanias submarine volcano in the Methana group, (ii) three volcanic domes to the east of Antimilos Volcano and hydrothermal activity in southeast Milos in the Milos group, (iii) three volcanic domes east of Christiana and a chain of about twenty volcanic domes and craters in the Kolumbo zone northeast of Santorini in the Santorini group and (iv) several volcanic domes and a volcanic caldera together with very deep slopes of several volcanic islands in the Nisyros group. The tectonic structure of the volcanic centers is described and related to the geometry of the arc and the neotectonic graben structures that usually host them. The NE-SW direction is dominant in the Santorini and Nisyros volcanic groups, located at the eastern part of the arc, where strike-slip is also present, whereas NW-SE direction dominates in Milos and Methana at the western part, where co-existence of E-W disrupting normal faults is observed. The volcanic relief reaches 1100-1200 m in most cases. This is produced from the outcrops of the volcanic centers emerging usually at 400-600 m depth and ending either below sea level or at high altitudes of 600-700 m on the islands. Hydrothermal activity at relatively high temperatures observed in Kolumbo is remarkable whereas low temperature phenomena have been detected in the Santorini caldera around Kameni islands and in the area southeast of Milos. In Methana and Nisyros, hydrothermal activity seems to be limited in the coastal areas without other offshore manifestations.

  11. Geology, geochronology, and paleogeography of the southern Sonoma volcanic field and adjacent areas, northern San Francisco Bay region, California (United States)

    Wagner, D.L.; Saucedo, G.J.; Clahan, K.B.; Fleck, R.J.; Langenheim, V.E.; McLaughlin, R.J.; Sarna-Wojcicki, A. M.; Allen, J.R.; Deino, A.L.


    Recent geologic mapping in the northern San Francisco Bay region (California, USA) supported by radiometric dating and tephrochronologic correlations, provides insights into the framework geology, stratigraphy, tectonic evolution, and geologic history of this part of the San Andreas transform plate boundary. There are 25 new and existing radiometric dates that define three temporally distinct volcanic packages along the north margin of San Pablo Bay, i.e., the Burdell Mountain Volcanics (11.1 Ma), the Tolay Volcanics (ca. 10-8 Ma), and the Sonoma Volcanics (ca. 8-2.5 Ma). The Burdell Mountain and the Tolay Volcanics are allochthonous, having been displaced from the Quien Sabe Volcanics and the Berkeley Hills Volcanics, respectively. Two samples from a core of the Tolay Volcanics taken from the Murphy #1 well in the Petaluma oilfield yielded ages of 8.99 ?? 0.06 and 9.13 ?? 0.06 Ma, demonstrating that volcanic rocks exposed along Tolay Creek near Sears Point previously thought to be a separate unit, the Donnell Ranch volcanics, are part of the Tolay Volcanics. Other new dates reported herein show that volcanic rocks in the Meacham Hill area and extending southwest to the Burdell Mountain fault are also part of the Tolay Volcanics. In the Sonoma volcanic field, strongly bimodal volcanic sequences are intercalated with sediments. In the Mayacmas Mountains a belt of eruptive centers youngs to the north. The youngest of these volcanic centers at Sugarloaf Ridge, which lithologically, chemically, and temporally matches the Napa Valley eruptive center, was apparently displaced 30 km to the northwest by movement along the Carneros and West Napa faults. The older parts of the Sonoma Volcanics have been displaced at least 28 km along the RodgersCreek fault since ca. 7 Ma. The Petaluma Formation also youngs to the north along the Rodgers Creek-Hayward fault and the Bennett Valley fault. The Petaluma basin formed as part of the Contra Costa basin in the Late Miocene and was

  12. Interpreting Power Anisotropy Measurements in Plasma Turbulence

    CERN Document Server

    Chen, C H K; Horbury, T S; Schekochihin, A A


    A relationship between power anisotropy and wavevector anisotropy in turbulent fluctuations is derived. This can be used to interpret plasma turbulence measurements, for example in the solar wind. If fluctuations are anisotropic in shape then the ion gyroscale break point in spectra in the directions parallel and perpendicular to the magnetic field would not occur at the same frequency, and similarly for the electron gyroscale break point. This is an important consideration when interpreting solar wind observations in terms of anisotropic turbulence theories. Model magnetic field power spectra are presented assuming a cascade of critically balanced Alfven waves in the inertial range and kinetic Alfven waves in the dissipation range. The variation of power anisotropy with scale is compared to existing solar wind measurements and the similarities and differences are discussed.

  13. The expected anisotropy in solid inflation

    CERN Document Server

    Bartolo, Nicola; Ricciardone, Angelo; Unal, Caner


    Solid inflation is an effective field theory of inflation in which isotropy and homogeneity are accomplished via a specific combination of anisotropic sources (three scalar fields that individually break isotropy). This results in specific observational signatures that are not found in standard models of inflation: a non-trivial angular dependence for the squeezed bispectrum, and a possibly long period of anisotropic inflation (to drive inflation, the "solid" must be very insensitive to any deformation, and thus background anisotropies are very slowly erased). In this paper we compute the expected level of statistical anisotropy in the power spectrum of the curvature perturbations of this model. To do so, we account for the classical background values of the three scalar fields that are generated on large (superhorizon) scales during inflation via a random walk sum, as the perturbation modes leave the horizon. Such an anisotropy is unavoidably generated, even starting from perfectly isotropic classical initia...

  14. Psychophysics and the anisotropy of time. (United States)

    Riemer, Martin


    In psychophysics, experimental control over the presented stimuli is an important prerequisite. Due to the anisotropy of time, this prerequisite is not given in psychophysical experiments on time perception. Many important factors (e.g., the direction of perceived time flow) cannot be manipulated in timing experiments. The anisotropy of time is a peculiarity, which distinguishes the time dimension from other perceptual qualities. Here I summarize the anisotropy-related differences between the perception of time and the perception of other qualities. It is discussed to what extent these differences might affect results and interpretations in psychophysical experiments. In conclusion, I argue for a 'view from nowhen' on the psychophysical study of time perception. Copyright © 2015 Elsevier Inc. All rights reserved.

  15. CMB Anisotropies Total Angular Momentum Method

    CERN Document Server

    Hu, W; Hu, Wayne; White, Martin


    A total angular momentum representation simplifies the radiation transport problem for temperature and polarization anisotropy in the CMB. Scattering terms couple only the quadrupole moments of the distributions and each moment corresponds directly to the observable angular pattern on the sky. We develop and employ these techniques to study the general properties of anisotropy generation from scalar, vector and tensor perturbations to the metric and the matter, both in the cosmological fluids and from any seed perturbations (e.g.~defects) that may be present. The simpler, more transparent form and derivation of the Boltzmann equations brings out the geometric and model-independent aspects of temperature and polarization anisotropy formation. Large angle scalar polarization provides a robust means to distinguish between isocurvature and adiabatic models for structure formation in principle. Vector modes have the unique property that the CMB polarization is dominated by magnetic type parity at small angles and ...


    Energy Technology Data Exchange (ETDEWEB)



    Ferromagnetic nanocomposites, or ''exchange spring'' magnets, possess a nanoscaled microstructure that allows intergrain magnetic exchange forces to couple the constituent grains and alter the system's effective magnetic anisotropies. While the effects of the anisotropy alterations are clearly seen in macroscopic magnetic measurement, it is extremely difficult to determine the detailed effects of the system's exchange coupling, such as the interphase exchange length, the inherent domain wall widths or the effective anisotropies of the system. Clarification of these materials parameters may be obtained from the ''micromagnetic'' phenomenological model, where the assumption of magnetic reversal initiating in the magnetically-soft regions of the exchange-spring maqet is explicitly included. This approach differs from that typically applied by other researchers and allows a quantitative estimate of the effective anisotropies of an exchange spring system. Hysteresis loops measured on well-characterized nanocomposite alloys based on the composition Nd{sub 2}Fe{sub 14}B + {alpha}-Fe at temperatures above the spin reorientation temperature were analyzed within the framework of the micromagnetic phenomenological model. Preliminary results indicate that the effective anisotropy constant in the material is intermediate to that of bulk {alpha}-Fe and bulk Nd{sub 2}Fe{sub 14}B and increases with decreasing temperature. These results strongly support the idea that magnetic reversal in nanocomposite systems initiates in the lower-anisotropy regions of the system, and that the soft-phase regions become exchange-hardened by virtue of their proximity to the magnetically-hard regions.

  17. Hydraulic Conductivity Anisotropy of Heterogeneous Unsaturated Soils (United States)

    Sun, Dongmin; Zhu, Jianting


    The effects of saturation degree (or capillary pressure) on hydraulic conductivity anisotropy in unsaturated soils have not been fully understood. This study developed an approach based on a conceptualization of combining the neural network based pedo-transfer function (PTF) results with the thin layer concept to explore the capillary pressure-dependent anisotropy in relation to soil texture and soil bulk density. The main objective is to examine how anisotropy characteristics are related to the relationships between hydraulic parameters and the basic soil attributes such as texture and bulk density. The hydraulic parameters are correlated with the texture and bulk density based on the pedo-transfer function (PTF) results. It is demonstrated that non-monotonic behavior of the unsaturated soil anisotropy in relation to the capillary pressure is only observed when the saturated hydraulic conductivity and the shape parameter are both related to the mean particle diameter. When only one hydraulic parameter is related to the grain diameter or when both are not related to the same attribute simultaneously, the unsaturated soil anisotropy increases monotonically with the increasing capillary pressure head. Therefore, it is suggested that this behavior is mainly due to the coupled dependence of the layer saturated hydraulic conductivities and the shape factors on the texture and bulk density. The correlation between the soil grain diameter and bulk density decreases the anisotropy effects of the unsaturated layered soils. The study illustrates that the inter-relationships of soil texture, bulk density, and hydraulic properties may cause vastly different characteristics of anisotropic unsaturated soils.

  18. Effects of deglaciation on the petrology and eruptive history of the Western Volcanic Zone, Iceland (United States)

    Eason, Deborah E.; Sinton, John M.; Grönvold, Karl; Kurz, Mark D.


    New observations and geochemical analyses of volcanic features in the 170-km-long Western Volcanic Zone (WVZ) of Iceland constrain spatial and temporal variations in volcanic production and composition associated with the last major deglaciation. Subglacial eruptions represent a significant portion of the late Quaternary volcanic budget in Iceland. Individual features can have volumes up to ˜48 km3 and appear to be monogenetic. Subaqueous to subaerial transition zones provide minimum estimates of ice sheet thickness at the time of eruption, although water-magma interactions and fluctuating lake levels during eruption can lead to complex lithological sequences. New major and trace element data for 36 glacial and postglacial eruptive units, combined with observations of lava surface quality, passage zone heights, and 3He exposure ages of some glacial units, indicate a maximum in volcanic production in the WVZ during the last major ice retreat. Anomalously high volcanic production rates continue into the early postglacial period and coincide with significant incompatible element depletions and slightly higher CaO and SiO2 and lower FeO content at a given MgO. Subglacial units with strong incompatible element depletions also have lava surfaces that lack evidence of subsequent glaciation. These units likely formed after the onset of deglaciation, when rapidly melting ice sheets increased decompression rates in the underlying mantle, leading to anomalously high melting rates in the depleted upper mantle. This process also can explain the eruption of extremely depleted picritic lavas during the early postglacial period. These new observations indicate that the increased volcanic activity associated with glacial unloading peaked earlier than previously thought, before Iceland was completely ice free.

  19. Anisotropy of the Topopah Spring Member Tuff

    Energy Technology Data Exchange (ETDEWEB)

    Martin, R.J. III; Boyd, P.J.; Haupt, R.W. [New England Research, Inc., White River Junction, VT (United States); Price, R.H. [Sandia National Labs., Albuquerque, NM (United States)


    Mechanical properties of the tuffaceous rocks within Yucca Mountain are needed for near and far-field modeling of the potential nuclear waste repository. If the mechanical properties are significantly anisotropic (i.e., direction-dependent), a more complex model is required. Relevant data from tuffs tested in earlier studies indicate that elastic and strength properties are anisotropic. This scoping study confirms the elastic anisotropy and concludes some tuffs are transversely isotropic. An approach for sampling and testing the rock to determine the magnitude of the anisotropy is proposed.

  20. Mobility anisotropy of two-dimensional semiconductors (United States)

    Lang, Haifeng; Zhang, Shuqing; Liu, Zhirong


    The carrier mobility of anisotropic two-dimensional semiconductors under longitudinal acoustic phonon scattering was theoretically studied using deformation potential theory. Based on the Boltzmann equation with the relaxation time approximation, an analytic formula of intrinsic anisotropic mobility was derived, showing that the influence of effective mass on mobility anisotropy is larger than those of deformation potential constant or elastic modulus. Parameters were collected for various anisotropic two-dimensional materials (black phosphorus, Hittorf's phosphorus, BC2N , MXene, TiS3, and GeCH3) to calculate their mobility anisotropy. It was revealed that the anisotropic ratio is overestimated by the previously described method.

  1. Mobility anisotropy of two-dimensional semiconductors

    CERN Document Server

    Lang, Haifeng; Liu, Zhirong


    The carrier mobility of anisotropic two-dimensional (2D) semiconductors under longitudinal acoustic (LA) phonon scattering was theoretically studied with the deformation potential theory. Based on Boltzmann equation with relaxation time approximation, an analytic formula of intrinsic anisotropic mobility was deduced, which shows that the influence of effective mass to the mobility anisotropy is larger than that of deformation potential constant and elastic modulus. Parameters were collected for various anisotropic 2D materials (black phosphorus, Hittorf's phosphorus, BC$_2$N, MXene, TiS$_3$, GeCH$_3$) to calculate their mobility anisotropy. It was revealed that the anisotropic ratio was overestimated in the past.

  2. Remote Sensing of Volcanic ASH at the Met Office (United States)

    Marenco, F.; Kent, J.; Adam, M.; Buxmann, J.; Francis, P.; Haywood, J.


    The eruption of Eyjafjallajökull in 2010 has triggered the rapid development of volcanic ash remote sensing activities at the Met Office. Volcanic ash qualitative and quantitative mapping have been achieved using lidar on board the Facility for Airborne Atmospheric Measurements (FAAM) research aircraft, and using improved satellite retrieval algorithms. After the eruption, a new aircraft facility, the Met Office Civil Contingencies Aircraft (MOCCA), has been set up to enable a rapid response, and a network of ground-based remote sensing sites with lidars and sunphotometers is currently being developed. Thanks to these efforts, the United Kingdom (UK) will be much better equipped to deal with such a crisis, should it happen in the future.

  3. Self-limiting physical and chemical effects in volcanic eruption clouds (United States)

    Pinto, Joseph P.; Toon, Owen B.; Turco, Richard P.


    One-dimensional aerosol microphysical and photochemical models are used to study the chemistry of stratospheric volcanic clouds. The results indicate that the aerosol microphysical processes of condensation and coagulation produce larger particles as the SO2 injection rate is increased. Larger particles have a smaller optical depth per unit mass and settle out of the stratosphere at a faster rate than smaller ones, restricting the total number of particles in the stratosphere. The microphysical processes moderate the impact of volcanic clouds on the earth's radiation budget and climate, suggesting that volcanic effects may be self limiting. It is noted that the injection of HCl into the stratosphere, which could lead to large ozone changes, is limited by a cold trap effect in which HCl and water vapor condense on ash particles in the rising volcanic plume and fall out as ice.

  4. Fluorescence anisotropy of diphenylhexatriene and its cationic Trimethylamino derivative in liquid dipalmitoylphosphatidylcholine liposomes: opposing responses to isoflurane

    Directory of Open Access Journals (Sweden)

    Nelson Steven C


    Full Text Available Abstract Background The mechanism of action of volatile general anesthetics has not yet been resolved. In order to identify the effects of isoflurane on the membrane, we measured the steady-state anisotropy of two fluorescent probes that reside at different depths. Incorporation of anesthetic was confirmed by shifting of the main phase transition temperature. Results In liquid crystalline dipalmitoylphosphatidylcholine liposomes, isoflurane (7-25 mM in the bath increases trimethylammonium-diphenylhexatriene fluorescence anisotropy by ~0.02 units and decreases diphenylhexatriene anisotropy by the same amount. Conclusions The anisotropy data suggest that isoflurane decreases non-axial dye mobility in the headgroup region, while increasing it in the tail region. We propose that these results reflect changes in the lateral pressure profile of the membrane.

  5. Catastrophic volcanic collapse: relation to hydrothermal processes. (United States)

    López, D L; Williams, S N


    Catastrophic volcanic collapse, without precursory magmatic activity, is characteristic of many volcanic disasters. The extent and locations of hydrothermal discharges at Nevado del Ruiz volcano, Colombia, suggest that at many volcanoes collapse may result from the interactions between hydrothermal fluids and the volcanic edifice. Rock dissolution and hydrothermal mineral alteration, combined with physical triggers such as earth-quakes, can produce volcanic collapse. Hot spring water compositions, residence times, and flow paths through faults were used to model potential collapse at Ruiz. Caldera dimensions, deposits, and alteration mineral volumes are consistent with parameters observed at other volcanoes.

  6. Nephelometric Dropsonde for Volcanic Ash Project (United States)

    National Aeronautics and Space Administration — Advanced dropsondes that could effectively be guided through atmospheric regions of interest such as volcanic plumes could enable unprecedented observations of...

  7. Thermal vesiculation during volcanic eruptions (United States)

    Lavallée, Yan; Dingwell, Donald B.; Johnson, Jeffrey B.; Cimarelli, Corrado; Hornby, Adrian J.; Kendrick, Jackie E.; von Aulock, Felix W.; Kennedy, Ben M.; Andrews, Benjamin J.; Wadsworth, Fabian B.; Rhodes, Emma; Chigna, Gustavo


    Terrestrial volcanic eruptions are the consequence of magmas ascending to the surface of the Earth. This ascent is driven by buoyancy forces, which are enhanced by bubble nucleation and growth (vesiculation) that reduce the density of magma. The development of vesicularity also greatly reduces the ‘strength’ of magma, a material parameter controlling fragmentation and thus the explosive potential of the liquid rock. The development of vesicularity in magmas has until now been viewed (both thermodynamically and kinetically) in terms of the pressure dependence of the solubility of water in the magma, and its role in driving gas saturation, exsolution and expansion during decompression. In contrast, the possible effects of the well documented negative temperature dependence of solubility of water in magma has largely been ignored. Recently, petrological constraints have demonstrated that considerable heating of magma may indeed be a common result of the latent heat of crystallization as well as viscous and frictional heating in areas of strain localization. Here we present field and experimental observations of magma vesiculation and fragmentation resulting from heating (rather than decompression). Textural analysis of volcanic ash from Santiaguito volcano in Guatemala reveals the presence of chemically heterogeneous filaments hosting micrometre-scale vesicles. The textures mirror those developed by disequilibrium melting induced via rapid heating during fault friction experiments, demonstrating that friction can generate sufficient heat to induce melting and vesiculation of hydrated silicic magma. Consideration of the experimentally determined temperature and pressure dependence of water solubility in magma reveals that, for many ascent paths, exsolution may be more efficiently achieved by heating than by decompression. We conclude that the thermal path experienced by magma during ascent strongly controls degassing, vesiculation, magma strength and the effusive

  8. New Pliocene-Pleistocene 40Ar/ 39Ar ages fill in temporal gaps in the Nicaraguan volcanic record (United States)

    Saginor, Ian; Gazel, Esteban; Carr, Michael J.; Swisher, Carl C., III; Turrin, Brent


    The volcanic record of western Nicaragua documents a significant lull in volcanic activity that has persisted from the late Miocene (~ 7 Ma) to the formation of the modern volcanic front around 350 ka. This study fills this gap for the first time with samples collected in Northwest Nicaragua between Cosigüina and San Cristóbal volcanoes and with samples collected from the Nicaraguan Depression. We found two previously unknown volcanic units ranging from 3.6 to 1.3 Ma and the improved volcanic record allows us to reconstruct the geochemical evolution of the Nicaraguan arc. U/Th values increased by nearly threefold since the Miocene following the "carbonate crash" at 10 Ma, when dominantly carbonate sediment deposition shifted toward hemipelagic sediment deposition. This transition was thought to be abrupt, however our new data show that it took place gradually over the last 7 Ma. Northwest Nicaragua is a particularly interesting case study because it contains Middle Miocene volcanism on either side of the Nicaraguan Depression, the Coyol Formation (25-7 Ma) to the East and the Tamarindo Formation (14.7-11.7 Ma) to the West. The presence of Mid Miocene volcanism on either side of the Nicaraguan Depression has led to the hypothesis that the two coeval units, currently separated by ~ 100 km, were once connected and have since been separated by extension. Here, we present data suggesting that the Tamarindo and Coyol are geochemically distinct and therefore cannot be considered part of the same unit.

  9. Magma chamber processes in central volcanic systems of Iceland

    DEFF Research Database (Denmark)

    Þórarinsson, Sigurjón Böðvar; Tegner, Christian


    New field work and petrological investigations of the largest gabbro outcrop in Iceland, the Hvalnesfjall gabbro of the 6-7 Ma Austurhorn intrusive complex, have established a stratigraphic sequence exceeding 800 m composed of at least 8 macrorhythmic units. The bases of the macrorhythmic units......3 of clinopyroxene and magnetite indicative of magma replenishment. Some macrorhythmic units show mineral trends indicative of up-section fractional crystallisation over up to 100 m, whereas others show little variation. Two populations of plagioclase crystals (large, An-rich and small, less An...... olivine basalts from Iceland that had undergone about 20% crystallisation of olivine, plagioclase and clinopyroxene and that the macrorhythmic units formed from thin magma layers not exceeding 200-300 m. Such a "mushy" magma chamber is akin to volcanic plumbing systems in settings of high magma supply...

  10. Geochemical Characteristics and Metallogenesis of Volcanic Rocks as Exemplified by Volcanic Rocks in Ertix,Xinjiang

    Institute of Scientific and Technical Information of China (English)

    刘铁庚; 叶霖


    Volcanic rocks in Ertix,Xinjiang,occurring in the collision zone between the Siberia Plate and the Junggar Plate,are distributed along the Eritix River Valley in northern Xinjiang.The volcanic rocks were dated at Late Paleozoic and can be divided into the spilite-keratophyre series and the basalt-andesite series.The spilite-keratophyre series volcanic rocks occur in the Altay orogenic belt at the southwest margin of the Siberia Plate.In addition to sodic volcanic rocks.There are also associated potassic-sodic volcanic rocks and potassic volcanic rocks.The potassic-sodic volcanic rocks occur at the bottom of the eruption cycle and control the distribution of Pb and Zn deposits.The potassic volcanic rocks occur at the top of the eruption cycle and are associated with Au and Cu mineralizations.The sodic volcanic rocks occur in the middle stage of eruption cycle and control the occurrence of Cu(Zn) deposits.The basalt-andesite series volcanic rocks distributed in the North Junggar orogenic belt at the north margin of the Junggar-Kazakstan Plate belong to the potassic sodic volcain rocks.The volcanic rocks distributed along the Ulungur fault are relatively rich in sodium and poor in potassium and are predominated by Cu mineralization and associated with Au mineralization.Those volcanic rocks distributed along the Ertix fault are relatively rich in K and poor in Na,with Au mineralization being dominant.

  11. Three-dimensional phonon population anisotropy in silicon nanomembranes (United States)

    McElhinny, Kyle M.; Gopalakrishnan, Gokul; Holt, Martin V.; Czaplewski, David A.; Evans, Paul G.


    Nanoscale single crystals possess modified phonon dispersions due to the truncation of the crystal. The introduction of surfaces alters the population of phonons relative to the bulk and introduces anisotropy arising from the breaking of translational symmetry. Such modifications exist throughout the Brillouin zone, even in structures with dimensions of several nanometers, posing a challenge to the characterization of vibrational properties and leading to uncertainty in predicting the thermal, optical, and electronic properties of nanomaterials. Synchrotron x-ray thermal diffuse scattering studies find that freestanding Si nanomembranes with thicknesses as large as 21 nm exhibit a higher scattering intensity per unit thickness than bulk silicon. In addition, the anisotropy arising from the finite thickness of these membranes produces particularly intense scattering along reciprocal-space directions normal to the membrane surface compared to corresponding in-plane directions. These results reveal the dimensions at which calculations of materials properties and device characteristics based on bulk phonon dispersions require consideration of the nanoscale size of the crystal.

  12. Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy (United States)

    Ma, Q. L.; Zhang, X. M.; Miyazaki, T.; Mizukami, S.


    To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rare-earth system were rarely developed. Here, we develop a new type of ferrimagnetic superlattice exhibiting PMA based on abundant Heusler alloy families. The superlattice is formed by [MnGa/Co2FeAl] unit with their magnetizations antiparallel aligned. The effective anisotropy (Kueff) over 6 Merg/cm3 is obtained, and the SL can be easily built on various substrates with flexible lattice constants. The coercive force, saturation magnetization and Kueff of SLs are highly controllable by varying the thickness of MnGa and Co2FeAl layers. The SLs will supply a new choice for magnetic recording and spintronics memory application such as magnetic random access memory.

  13. Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy. (United States)

    Ma, Q L; Zhang, X M; Miyazaki, T; Mizukami, S


    To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rare-earth system were rarely developed. Here, we develop a new type of ferrimagnetic superlattice exhibiting PMA based on abundant Heusler alloy families. The superlattice is formed by [MnGa/Co2FeAl] unit with their magnetizations antiparallel aligned. The effective anisotropy (K(u)(eff)) over 6 Merg/cm(3) is obtained, and the SL can be easily built on various substrates with flexible lattice constants. The coercive force, saturation magnetization and K(u)(eff) of SLs are highly controllable by varying the thickness of MnGa and Co2FeAl layers. The SLs will supply a new choice for magnetic recording and spintronics memory application such as magnetic random access memory.

  14. Sedimentary responses to sub-aerial felsic volcanism from the Late Devonian-Early Carboniferous northern Macalister Synclinorium, southeastern Australia (United States)

    O'Halloran, G. J.; Gaul, A. J.


    Active sub-aerial volcanism has the capability to rapidly alter both the topographic and drainage characteristics of a landscape, and thus fundamentally influence resulting sedimentary facies. Relationships between sedimentation and volcanism are explored in this paper, via an investigation of the stratigraphy and early depositional history of the Upper Devonian volcano-sedimentary units of the northern Macalister Synclinorium, east-central Victoria. Complex interfingering relationships exist between sub-aerial felsic volcanic successions (Rose River Volcanics) and alluvial, fluvial and lacustrine sedimentary units (the Bindaree and Howitt Spur Formations). A depositional model is presented for these units, in which the Rose River Volcanics, an outflow (ignimbritic plateau) facies of the Tolmie caldera complex to the north, co-existed with a series of volcaniclastic alluvial fans and freshwater lakes. A dacitic volcanic centre (Refrigerator Gap Dacite) appears to have developed somewhat separately to the south, in the Jamieson River area. These lower successions of the northern Macalister Synclinorium record an episode of sedimentation in close proximity to an active felsic volcanic terrain, and in a landscape of significant topographic relief. The conglomerates of the Bindaree Formation, in particular, record the supply of abundant felsic volcanic detritus via high-gradient proximal alluvial stream systems. Comparisons can be made with sedimentological processes operating during deposition of overlying sedimentary successions, where influences by primary volcanic activity were less important. Well defined channel geometry successions and a diversification in clast and grain types within these younger units indicate ongoing headward erosion into metasedimentary basement rocks, and deposition within lower-gradient, higher-order stream systems.

  15. Anisotropy of Wood in the Microwave Region (United States)

    Ziherl, Sasa; Bajc, Jurij; Urankar, Bernarda; Cepic, Mojca


    Wood is transparent for microwaves and due to its anisotropic structure has anisotropic dielectric properties. A laboratory experiment that allows for the qualitative demonstration and quantitative measurements of linear dichroism and birefringence in the microwave region is presented. As the proposed experiments are based on the anisotropy (of…

  16. Effective anisotropy through traveltime and amplitude matching

    KAUST Repository

    Wang, Hui


    Introducing anisotropy to seismic wave propagation reveals more realistic physics of our Earth\\'s subsurface as compared to the isotropic assumption. However wavefield modeling, the engine of seismic inverse problems, in anisotropic media still suffers from computational burdens, in particular with complex anisotropy such as transversely isotropic (TI) and Orthorhombic anisotropy. We develop effective isotropic velocity and density models to package the effects of anisotropy such that the wave propagation behavior using these effective models approximate those of the original anisotropic model. We build these effective models through the high frequency asymptotic approximation based on the eikonal and transport equations. We match the geometrical behavior of the wave-fields, given by traveltimes, from the anisotropic and isotropic eikonal equations. This matching yields the effective isotropic velocity that approximates the kinematics of the anisotropic wavefield. Equivalently, we calculate the effective densities by equating the anisotropic and isotropic transport equations. The effective velocities and densities are then fed into the isotropic acoustic variable density wave equation to obtain cheaper anisotropic wavefields. We justify our approach by testing it on an elliptical anisotropic model. The numerical results demonstrate a good matching of both traveltime and amplitude between anisotropic and effective isotropic wavefields.

  17. Magnetic anisotropy in rare-earth metals

    DEFF Research Database (Denmark)

    Nielsen, Mourits; Bjerrum Møller, Hans; Lindgård, Per-Anker;


    The magnetic field dependence of the energy of long- wavelength magnons in Tb-10%Ho has been studied by inelastic neutron scattering. The results agree with the `frozen-lattice' model, provided that the second-order magnetoelastic effect is taken into account. The planar anisotropy is almost...

  18. Heterogeneity and anisotropy of Earth's inner core

    NARCIS (Netherlands)

    Deuss, Arwen


    Seismic observations provide strong evidence that Earth's inner core is anisotropic, with larger velocity in the polar than in the equatorial direction. The top 60-80 km of the inner core is isotropic; evidence for an innermost inner core is less compelling. The anisotropy is most likely due to alig

  19. Anisotropy of a cubic ferromagnet at criticality (United States)

    Kudlis, A.; Sokolov, A. I.


    Critical fluctuations change the effective anisotropy of cubic ferromagnet near the Curie point. If the crystal undergoes phase transition into orthorhombic phase and the initial anisotropy is not too strong, reduced anisotropy of nonlinear susceptibility acquires at Tc the universal value δ4*=2/v* 3 (u*+v*) where u* and v* are coordinates of the cubic fixed point on the flow diagram of renormalization group equations. In the paper, the critical value of the reduced anisotropy is estimated within the pseudo-ɛ expansion approach. The six-loop pseudo-ɛ expansions for u*, v*, and δ4* are derived for the arbitrary spin dimensionality n . For cubic crystals (n =3 ) higher-order coefficients of the pseudo-ɛ expansions obtained turn out to be so small that use of simple Padé approximants yields reliable numerical results. Padé resummation of the pseudo-ɛ series for u*, v*, and δ4* leads to the estimate δ4*=0.079 ±0.006 , indicating that detection of the anisotropic critical behavior of cubic ferromagnets in physical and computer experiments is certainly possible.

  20. Azimuthal anisotropy of jet quenching at LHC

    Indian Academy of Sciences (India)

    I P Lokhtin; S V Petrushanko; L I Sarycheva; A M Snigirev


    We analyze the azimuthal anisotropy of jet spectra due to energy loss of hard partons in quark–gluon plasma, created initially in nuclear overlap zone in collisions with non-zero impact parameter. The calculations are performed for semi-central Pb–Pb collisions at LHC energy.

  1. Heterogeneity and anisotropy of Earth's inner core

    NARCIS (Netherlands)

    Deuss, Arwen


    Seismic observations provide strong evidence that Earth's inner core is anisotropic, with larger velocity in the polar than in the equatorial direction. The top 60-80 km of the inner core is isotropic; evidence for an innermost inner core is less compelling. The anisotropy is most likely due to

  2. Plastic Anisotropy Prediction by Ultrasonic Texture Data


    Serebryany, V. N.


    The plastic anisotropy parameters (R coefficient and height of ears of the drawn cup) have been calculated from ultrasonic orientation distribution function (ODF) coefficients on the basis of Taylor theory for low carbon steel and aluminium alloy sheets. The ODF coefficients were defined by Sayers method and using the iterative procedure on the basis of measurement of bulk longitudinal and shear wave time delays.

  3. Magnetization of superparamagnetics in the state of mechanical anisotropy


    Ugulava, Archil; Chkhaidze, Simon; Kekutia, Shalva; Rostomashvili, Zurab


    The internal energy of magnetic anisotropy for some nanoparticles dominates over the thermal energy even at room temperature. Strong magnetic anisotropy of nanoparticles can significantly affect the process of magnetization of the magnetic fluid. This influence is substantial if the system of nanoparticles is in a state of mechanical anisotropy in which the anisotropy axes of the particles have the same direction. In this work, it is shown that the magnetization curve of the magnetic fluid in...

  4. Surface contribution to the anisotropy of magnetic nanoparticles


    Garanin, D. A.; Kachkachi, H.


    We calculate the contribution of the Neel surface anisotropy to the effective anisotropy of magnetic nanoparticles of spherical shape cut out of a simple cubic lattice. The effective anisotropy arises because deviations of atomic magnetizations from collinearity and thus the energy depends on the orientation of the global magnetization. The result is second order in the Neel surface anisotropy, scales with the particle volume and has cubic symmetry with preferred directions [+-1,+-1,+-1].

  5. Silicate melt inclusion evidence for extreme pre-eruptive enrichment and post-eruptive depletion of lithium in silicic volcanic rocks of the western United States: implications for the origin of lithium-rich brines (United States)

    Hofstra, Albert H.; Todorov, T.I.; Mercer, C.N.; Adams, D.T.; Marsh, E.E.


    To evaluate whether anatectic and/or highly fractionated lithophile element-enriched rhyolite tuffs deposited in arid lacustrine basins lose enough lithium during eruption, lithification, and weathering to generate significant Li brine resources, pre-eruptive melt compositions, preserved in inclusions, and the magnitude of post-eruptive Li depletions, evident in host rhyolites, were documented at six sites in the western United States. Each rhyolite is a member of the bimodal basalt-rhyolite assemblage associated with extensional tectonics that produced the Basin and Range province and Rio Grande rift, an evolving pattern of closed drainage basins, and geothermal energy or mineral resources. Results from the 0.8 Ma Bishop tuff (geothermal) in California, 1.3 to 1.6 Ma Cerro Toledo and Upper Bandelier tephra (geothermal) and 27.9 Ma Taylor Creek rhyolite (Sn) in New Mexico, 21.7 Ma Spor Mountain tuff (Be, U, F) and 24.6 Ma Pine Grove tuff (Mo) in Utah, and 27.6 Ma Hideaway Park tuff (Mo) in Colorado support the following conclusions. Melt inclusions in quartz phenocrysts from rhyolite tuffs associated with hydrothermal deposits of Sn, Mo, and Be are extremely enriched in Li (1,000s of ppm); those from Spor Mountain have the highest Li abundance yet recorded (max 5,200 ppm, median 3,750 ppm). Forty-five to 98% of the Li present in pre-eruptive magma was lost to the environment from these rhyolite tuffs. The amount of Li lost from the small volumes (1–10 km3) of Li-enriched rhyolite deposited in closed basins is sufficient to produce world-class Li brine resources. After each eruption, meteoric water leaches Li from tuff, which drains into playas, where it is concentrated by evaporation. The localized occurrence of Li-enriched rhyolites may explain why brines in arid lacustrine basins seldom have economic concentrations of Li. Considering that hydrothermal deposits of Sn, Mo, Be, U, and F may indicate potential for Li brines in nearby basins, we surmise that the

  6. Multi-scale characterization of topographic anisotropy (United States)

    Roy, S. G.; Koons, P. O.; Osti, B.; Upton, P.; Tucker, G. E.


    We present the every-direction variogram analysis (EVA) method for quantifying orientation and scale dependence of topographic anisotropy to aid in differentiation of the fluvial and tectonic contributions to surface evolution. Using multi-directional variogram statistics to track the spatial persistence of elevation values across a landscape, we calculate anisotropy as a multiscale, direction-sensitive variance in elevation between two points on a surface. Tectonically derived topographic anisotropy is associated with the three-dimensional kinematic field, which contributes (1) differential surface displacement and (2) crustal weakening along fault structures, both of which amplify processes of surface erosion. Based on our analysis, tectonic displacements dominate the topographic field at the orogenic scale, while a combination of the local displacement and strength fields are well represented at the ridge and valley scale. Drainage network patterns tend to reflect the geometry of underlying active or inactive tectonic structures due to the rapid erosion of faults and differential uplift associated with fault motion. Regions that have uniform environmental conditions and have been largely devoid of tectonic strain, such as passive coastal margins, have predominantly isotropic topography with typically dendritic drainage network patterns. Isolated features, such as stratovolcanoes, are nearly isotropic at their peaks but exhibit a concentric pattern of anisotropy along their flanks. The methods we provide can be used to successfully infer the settings of past or present tectonic regimes, and can be particularly useful in predicting the location and orientation of structural features that would otherwise be impossible to elude interpretation in the field. Though we limit the scope of this paper to elevation, EVA can be used to quantify the anisotropy of any spatially variable property.

  7. Pn Anisotropy in Old Pacific Lithosphere (United States)

    Shintaku, N.; Forsyth, D. W.; Weeraratne, D. S.


    Pn is the high frequency, scattered P phase guided for great distances within old oceanic lithosphere, which is also known as Po. Two arrays of ocean bottom seismometers were deployed on old (~150-160Ma) seafloor in the northwestern Pacific south of Shatsky Rise for the PLATE experiment (Pacific Lithosphere Anisotropy and Thickness Experiment). More than 5 or 6 Pn phases per day are recorded on these ocean bottom seismometers generated by earthquakes in western Pacific subduction zones during one year of deployment; we used 512 Pn phases from earthquakes with locations reported in routine bulletins. Each array was deployed on a separate limb of a magnetic bight, formed at a ridge-ridge-ridge triple junction. The spreading rates on both limbs were ~ 70mm/yr, and the current plate motion direction in the hotspot coordinate frame is WNW. Our overall goal is to identify the pattern of fossil anisotropy in the old oceanic lithosphere, and dynamically generated anisotropy in underlying asthenosphere using both body waves and surface waves. Using high frequency waves (3-10 Hz), we look at variations of Pn velocities as a function of backazimuth. In the western array, where the spreading direction is parallel to the absolute plate motion direction, we find clear Pn anisotropy with velocities varying from ~8.5 km/s in the spreading direction to ~ 8.0 km/s perpendicular to the spreading direction. However, in the eastern array where the fossil spreading direction is perpendicular to the current plate motion, the velocity variations as a function of backazimuth are much less obvious. This may be due to heterogeneity of anisotropy in the oceanic lithosphere, with the fast direction changing from the fossil direction at shallow levels to the absolute direction at greater depth.

  8. What does anisotropy measure? Insights from increased and decreased anisotropy in selective fiber tracts in schizophrenia.

    Directory of Open Access Journals (Sweden)

    Gabriel A De Erausquin


    Full Text Available Schizophrenia is a common, severe and chronically disabling mental illness of unknown cause. Recent MRI studies have focused attention on white matter abnormalities in schizophrenia using diffusion tensor imaging (DTI. Indices commonly derived from DTI include (a mean diffusivity, independent of direction, (b fractional anisotropy (FA or relative anisotropy (RA, (c axial diffusivity, and (d radial diffusivity. In cerebral white matter, contributions to these indices come from fiber arrangements, degree of myelination, and axonal integrity. Relatively pure deficits in myelin result in a modest increase in radial diffusivity, without affecting axial diffusivity and with preservation of anisotropy. Although schizophrenia is not characterized by gross abnormalities of white matter, it does involve a profound dysregulation of myelin-associated gene expression, reductions in oligodendrocyte numbers, and marked abnormalities in the ultrastructure of myelin sheaths. Since each oligodendrocyte myelinates as many as 40 axon segments, changes in the number of oligodendrocytes, and/or in the integrity of myelin sheaths, and/or axoglial contacts can have a profound impact on signal propagation and the integrity of neuronal circuits. Whereas a number of studies have revealed inconsistent decreases in anisotropy in schizophrenia, we and others have found increased fractional anisotropy in key subcortical tracts associated with the circuits underlying symptom generation in schizophrenia. We review data revealing increased anisotropy in dopaminergic tracts in the mesencephalon of schizophrenics and their unaffected relatives, and discuss the possible biological underpinnings and physiological significance of this finding.

  9. Cenozoic volcanic rocks of Saudi Arabia (United States)

    Coleman, R.G.; Gregory, R.T.; Brown, G.F.


    The Cenozoic volcanic rocks of Saudi Arabia cover about 90,000 km2, one of the largest areas of alkali olivine basalt in the world. These volcanic rocks are in 13 separate fields near the eastern coast of the Red Sea and in the western Arabian Peninsula highlands from Syria southward to the Yemen Arab Republic.

  10. Relationship between earthquake and volcanic eruption inferred from historical records

    Institute of Scientific and Technical Information of China (English)

    陈洪洲; 高峰; 吴雪娟; 孟宪森


    A large number of seismic records are discovered for the first time in the historical materials about Wudalianchi volcanic group eruption in 1720~1721, which provides us with abundant volcanic earthquake information. Based on the written records, the relationship between earthquake and volcanic eruption is discussed in the paper. Furthermore it is pointed that earthquake swarm is an important indication of volcanic eruption. Therefore, monitoring volcanic earthquakes is of great significance for forecasting volcanic eruption.

  11. The Glasma, Photons and the Implications of Anisotropy

    CERN Document Server

    McLerran, Larry


    We introduce distribution functions for quarks and gluons in the Glasma and discuss how they satisfy various relationships of statistical physics. We use these distributions to compute photon production in the early stages of heavy ion collisions. Photon rates satisfy geometric scaling, that is, the emission rate per unit area scales as a function of the saturation momenta divided by the transverse momentum of the photon. Photon distributions from the Glasma are steeper than those computed in the Thermalized Quark Gluon Plasma (TQGP). Both the delayed equilibration of the Glasma and a possible anisotropy in the pressure lead to slower expansion and mean times of photon emission of fixed energy are increased. This delayed emission might allow for larger photon elliptic flow.

  12. Lakshmi Planum: A distinctive highland volcanic province (United States)

    Roberts, Kari M.; Head, James W.

    Lakshmi Planum, a broad smooth plain located in western Ishtar Terra and containing two large oval depressions (Colette and Sacajawea), has been interpreted as a highland plain of volcanic origin. Lakshmi is situated 3 to 5 km above the mean planetary radius and is surrounded on all sides by bands of mountains interpreted to be of compressional tectonic origin. Four primary characteristics distinguish Lakshmi from other volcanic regions known on the planet, such as Beta Regio: (1) high altitude, (2) plateau-like nature, (3) the presence of very large, low volcanic constructs with distinctive central calderas, and (4) its compressional tectonic surroundings. Building on the previous work of Pronin, the objective is to establish the detailed nature of the volcanic deposits on Lakshmi, interpret eruption styles and conditions, sketch out an eruption history, and determine the relationship between volcanism and the tectonic environment of the region.

  13. Did intense volcanism trigger the first Late Ordovician icehouse? (United States)

    Buggisch, Werner; Joachimski, Michael M.; Lehnert, Oliver; Bergström, Stig M.; Repetski, John E.; Webers, Gerald F.


    Oxygen isotopes measured on Late Ordovician conodonts from Minnesota and Kentucky (United States) were studied to reconstruct the paleotemperature history during late Sandbian to Katian (Mohawkian–Cincinnatian) time. This time interval was characterized by intense volcanism, as shown by the prominent Deicke, Millbrig, and other K-bentonite beds. A prominent carbon isotope excursion (Guttenberg δ13C excursion, GICE) postdates the Millbrig volcanic eruptions, and has been interpreted to reflect a drawdown of atmospheric carbon dioxide and climatic cooling. The oxygen isotope record in conodont apatite contradicts this earlier interpretation. An increase in δ18O of 1.5‰ (Vienna standard mean ocean water) just above the Deicke K-bentonite suggests an abrupt and short-lived cooling that possibly initiated a first short-term glacial episode well before the major Hirnantian glaciation. The decrease in δ18O immediately after the mega-eruptions indicates warming before the GICE, and no cooling is shown in the GICE interval. The coincidence of the Deicke mega-eruption with a cooling event suggests that this major volcanic event had a profound effect on Late Ordovician (late Mohawkian) climate.

  14. Volcanism and associated hazards: the Andean perspective (United States)

    Tilling, R. I.


    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 (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 improvements in reducing volcano risk in the Andean region. But much remains to be done.

  15. Volcanism and associated hazards: The Andean perspective (United States)

    Tilling, R.I.


    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 (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 improvements in reducing volcano risk in the Andean region. But much remains to be done.

  16. Paleomagnetism of the Pleistocene Tequila Volcanic Field (Western Mexico) (United States)

    Rodríguez Ceja, M.; Goguitchaichvili, A.; Calvo-Rathert, M.; Morales-Contreras, J.; Alva-Valdivia, L.; Rosas Elguera, J.; Urrutia Fucugauchi, J.; Delgado Granados, H.


    This paper presents new paleomagnetic results from 24 independent cooling units in Tequila area (western Trans-Mexican Volcanic Belt). These units were recently dated by means of state-of-the-art 40Ar-39Ar method (Lewis-Kenedy et al., 2005) and span from 1130 to 150 ka. The characteristic paleodirections are successfully isolated for 20 cooling units. The mean paleodirection, discarding intermediate polarity sites, is I = 29.6°, D = 359.2°, k = 26, α95 = 7.1°, n = 17, which corresponds to the mean paleomagnetic pole position Plat = 85.8°, Plong = 84.3°, K = 27.5, A95 = 6.9°. These directions are practically undistinguishable from the expected Plestocene paleodirections, as derived from reference poles for the North American polar wander curve and in agreement with previously reported directions from western Trans-Mexican Volcanic Belt. This suggests that no major tectonic deformation occurred in studied area since early-middle Plestocene to present. The paleosecular variation is estimated trough the study of the scatter of virtual geomagnetic poles giving SF = 15.4 with SU = 19.9 and SL = 12.5 (upper and lower limits respectively). These values are consistent with those predicted by the latitude-dependent variation model of McFadden et al. (1991) for the last 5 Myr. The interesting feature of the paleomagnetic record obtained here is the occurrence of an intermediate polarity at 671± 13 ka which may correspond the worldwide observed Delta excursion at about 680-690 ka. This gives the volcanic evidence of this event. Two independent lava flows dated as 362± 13 and 354± 5 ka respectively, yield transitional paleodirections as well, probably corresponding to the Levantine excursion.

  17. Evidence of Multiple Flank Collapse at Volcan Baru, Panama (United States)

    Herrick, J. A.; Rose, W. I.


    Michigan Tech's Peace Corps Master's International program (PCMI) in Geological Hazards has enabled several long-term investigations of active volcanoes in Latin America. To contribute to volcanic hazard assessments in Panama and achieve the goals defined by the PCMI program, we developed this debris avalanche project to address outstanding questions regarding Volcan Baru's most devastating event - massive slope failure of the western flank. Relying on basic mapping tools as well as the 2007 USGS Open-File Report focusing on hazard assessments of Panama's youngest and potentially active volcano, identification of the debris avalanche deposits (DAD) required detailed field investigations to determine the limits of the units. Extending across an area larger than 600 km2, field strategies were developed based on outcrop exposures within drainages and road-cuts. Aerial photos and DEMs of Baru's nested craters were interpreted by earlier scientists as the remains of two collapsed flanks. The results from in-depth field traverses provide several important discoveries: paleosols and sharp contacts within the stratigraphy indicate multiple DAD, deeply weathered hummocks red-flag the deposits more than 50-km away from Baru's crater, and high-quality radiocarbon samples (up to 45-cm long fragments of entrained wood) lie in the distal reaches of the debris flow area. During the 2008-2009 field seasons, we received assistance from the University of Panama, Civil Protection, and Panama's National Institute of Geography. Support from local experts and feedback from professional scientists of the Smithsonian Institution and Costa Rica's Institute of Electricity were invaluable. The 2-year investment in volcanic hazard studies has brought together resources from several countries as well as fresh data that will benefit the residents and emergency management officials of Panama. Jigsaw fractured clasts lie within Volcan Baru's debris avalanche deposits more than 28 km south of the

  18. Importance of tropospheric volcanic aerosol for indirect radiative forcing of climate

    Directory of Open Access Journals (Sweden)

    A. Schmidt


    Full Text Available Observations and models have shown that continuously degassing volcanoes have a potentially large effect on the natural background aerosol loading and the radiative state of the atmosphere. Here, we use a global aerosol microphysics model to quantify the impact of these volcanic emissions on the cloud albedo radiative forcing under pre-industrial (PI and present-day (PD conditions. We find that volcanic degassing increases global annual mean cloud droplet number concentrations by 40% under PI conditions, but by only 10% under PD conditions. Consequently, volcanic degassing causes a global annual mean cloud albedo effect of −1.06 W m−2 in the PI era but only −0.56 W m−2 in the PD era. This non-equal effect is explained partly by the lower background aerosol concentrations in the PI era, but also because more aerosol particles are produced per unit of volcanic sulphur emission in the PI atmosphere. The higher sensitivity of the PI atmosphere to volcanic emissions has an important consequence for the anthropogenic cloud radiative forcing because the large uncertainty in volcanic emissions translates into an uncertainty in the PI baseline cloud radiative state. Assuming a −50/+100% uncertainty range in the volcanic sulphur flux, we estimate the annual mean anthropogenic cloud albedo forcing to lie between −1.16 W m−2 and −0.86 W m−2. Therefore, the volcanically induced uncertainty in the PI baseline cloud radiative state substantially adds to the already large uncertainty in the magnitude of the indirect radiative forcing of climate.

  19. Finite size effects on the magnetocrystalline anisotropy energy in Fe magnetic nanowires from first principles

    Energy Technology Data Exchange (ETDEWEB)

    Munoz, F. [Max-Planck-Institute fuer Mikrostrukturphysik (Germany); Romero, A. H. [CINVESTAV, Unidad Queretaro (Mexico); Mejia-Lopez, J., E-mail: [Facultad de Fisica, Pontificia Universidad Catolica de Chile (Chile); Moran-Lopez, J. L. [Universidad Nacional Autonoma de Mexico, Laboratorio Interdisciplinario, Departamento de Fisica, Facultad de Ciencias (Mexico)


    The geometric and the electronic structures, the magnetic moments, and the magnetocrystalline anisotropy energy of bcc-Fe nanowires with z-axis along the (110) direction are calculated in the framework of ab initio theories. In particular, we report a systematic study of free standing nanowires with geometries and sizes ranging from diatomic to 1 nm wide with 31 atoms per unit cell. We found that for nanowires with less than 14 atoms per unit cell, the ground-state structure is body-centered tetragonal. We also calculated the contributions of the dipolar magnetic energy to the magnetic anisotropy energy and found that in some cases, this contribution overcomes the magnetocrystalline part, determining thereby the easy axis direction. These results emphasize the importance and competition between both contributions in low dimensional systems.

  20. Magnetic anisotropy of grain boundaries in nanocrystalline Ni (United States)

    Bian, Q.; Niewczas, M.


    Temperature-dependent magnetic anisotropy due to grain boundaries in nanocrystalline Ni has been studied by simulating experimental magnetization data with the stochastic Landau-Lifshitz-Gilbert theory. In the model the grain boundary magnetic anisotropy energy is expressed as the sum of the uniaxial anisotropy and the cubic anisotropy, characterized by Kua and Kca anisotropy constants. By comparing the calculated magnetization with the experimental magnetization measurements at finite temperatures, the values of Kua and Kca can be determined. For nanocrystalline Ni it is found that with increasing temperature Kua decreases and Kca increases. At low temperatures Kua dominates the grain boundary anisotropy energy, whereas Kca is very small and it can be neglected. At room temperature Kua and Kca are of the same order with the corresponding ratio Kua /Kca ≈ 1.9 , both coefficients are much larger than the magnetocrystalline anisotropy constant.

  1. Perpendicular magnetic anisotropy of two-dimensional Rashba ferromagnets (United States)

    Kim, Kyoung-Whan; Lee, Kyung-Jin; Lee, Hyun-Woo; Stiles, M. D.


    We compute the magnetocrystalline anisotropy energy within two-dimensional Rashba models. For a ferromagnetic free-electron Rashba model, the magnetic anisotropy is exactly zero regardless of the strength of the Rashba coupling, unless only the lowest band is occupied. For this latter case, the model predicts in-plane anisotropy. For a more realistic Rashba model with finite band width, the magnetic anisotropy evolves from in-plane to perpendicular and back to in-plane as bands are progressively filled. This evolution agrees with first-principles calculations on the interfacial anisotropy, suggesting that the Rashba model captures energetics leading to anisotropy originating from the interface provided that the model takes account of the finite Brillouin zone. The results show that the electron density modulation by doping or an external voltage is more important for voltage-controlled magnetic anisotropy than the modulation of the Rashba parameter.

  2. Microwave Anisotropies from Texture Seeded Structure Formation

    CERN Document Server

    Durrer, R; Zhou, Z H


    The cosmic microwave anisotropies in a scenario of large scale structure formation with cold dark matter and texture are discussed and compared with recent observational results of the COBE satellite. A couple of important statistical parameters are determined. The fluctuations are slightly non gaussian. The quadrupole anisotropy is $1.5\\pm 1.2\\times 10^{-5}$ and the fluctuations on a angular scale of 10 degrees are $ (3.8\\pm 2.6)\\times 10^{-5}$. The COBE are within about one standard deviation of the typical texture + CDM model discussed in this paper. Furthermore, we calculate fluctuations on intermediate scales (about 2 degrees) with the result $\\De T/T(\\theta \\sim 2^o) = 3.9\\pm 0.8)\\times 10^{-5}$. Collapsing textures are modeled by spherically symmetric field configurations. This leads to uncertainties of about a factor of~2.

  3. Physics of the cosmic microwave background anisotropy

    CERN Document Server

    Bucher, Martin


    Observations of the cosmic microwave background (CMB), especially of its frequency spectrum and its anisotropies, both in temperature and in polarization, have played a key role in the development of modern cosmology and our understanding of the very early universe. We review the underlying physics of the CMB and how the primordial temperature and polarization anisotropies were imprinted. Possibilities for distinguishing competing cosmological models are emphasized. The current status of CMB experiments and experimental techniques with an emphasis toward future observations, particularly in polarization, is reviewed. The physics of foreground emissions, especially of polarized dust, is discussed in detail, since this area is likely to become crucial for measurements of the B modes of the CMB polarization at ever greater sensitivity.

  4. CMB anisotropies from primordial inhomogeneous magnetic fields

    CERN Document Server

    Lewis, A


    Primordial inhomogeneous magnetic fields of the right strength can leave a signature on the CMB temperature anisotropy and polarization. Potentially observable contributions to polarization B-modes are generated by vorticity and gravitational waves sourced by the magnetic anisotropic stress. We compute the corresponding CMB transfer functions in detail including the effect of neutrinos. The shear rapidly causes the neutrino anisotropic stress to cancel the stress from the magnetic field, suppressing the production of gravitational waves and vorticity on super-horizon scales after neutrino decoupling. A significant large scale signal from tensor modes can only be produced before neutrino decoupling, and the actual amplitude is somewhat uncertain. Plausible values suggest primordial nearly scale invariant fields of ~ 10^(-10)G today may be observable from their large scale tensor anisotropy. They can be distinguished from primordial gravitational waves by their non-Gaussianity. Vector mode vorticity sources B-m...

  5. Primordial anisotropies from cosmic strings during inflation (United States)

    Jazayeri, Sadra; Sadr, Alireza Vafaei; Firouzjahi, Hassan


    In this work, we study the imprint of an individual primordial cosmic string within a Hubble patch on the inflationary power spectrum. A straight cosmic string induces two distinct contributions to the curvature perturbations power spectrum. The first type of correction respects the translation invariance while violating isotropy. This generates quadrupolar statistical anisotropy in cosmic microwave background maps, which is constrained by the Planck data. The second contribution breaks both homogeneity and isotropy, generating a dipolar power asymmetry in the variance of temperature fluctuations with its amplitude falling on small scales. We show that the strongest constraint on the tension of primordial cosmic strings is obtained from the quadrupolar anisotropy and argue that the mass scale of the underlying theory responsible for the formation of the string cannot be much higher than the grand unified theory scale. The predictions for the diagonal and off-diagonal components of the cosmic microwave background angular power spectrum induced by the string are presented.

  6. Optical anisotropy in GaSe

    Energy Technology Data Exchange (ETDEWEB)

    Seyhan, A.; Karabulut, O.; Akinoglu, B.G.; Aslan, B.; Turan, R. [Department of Physics, Middle East Technical University, 06531, Ankara (Turkey)


    Optical anisotropy of the layer semiconductor GaSe has been studied by photoluminescence (PL) and Fourier Transform Infrared Spectroscopy (FTIR). The PL spectra are dominated by two closely positioned emission bands resulting from the free exciton and the bound exciton connected direct band edge of GaSe. Photoluminescence and transmission spectra of GaSe crystals have been measured for two cases in which the propagation vector k is perpendicular (k perpendicular to c) and parallel to the c-axis (k//c). Peak position of the PL emission band and the onset of the transmission have been found to be significantly different for these two cases. This observed anisotropy is related to anisotropic band structure and the selection rules for the optical absorption in layered GaSe. FTIR transmission spectrum is in good agreement with PL results. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  7. Results from the Wilkinson Microwave Anisotropy Probe

    CERN Document Server

    Komatsu, Eiichiro


    The Wilkinson Microwave Anisotropy Probe (WMAP) mapped the distribution of temperature and polarization over the entire sky in five microwave frequency bands. These full-sky maps were used to obtain measurements of temperature and polarization anisotropy of the cosmic microwave background with the unprecedented accuracy and precision. The analysis of two-point correlation functions of temperature and polarization data gives determinations of the fundamental cosmological parameters such as the age and composition of the universe, as well as the key parameters describing the physics of inflation, which is further constrained by three-point correlation functions. WMAP observations alone reduced the flat $\\Lambda$ cold dark matter ($\\Lambda$CDM) cosmological model (six) parameter volume by a factor of >68,000 compared with pre-WMAP measurements. The WMAP observations (sometimes in combination with other astrophysical probes) convincingly show the existence of non-baryonic dark matter, the cosmic neutrino backgrou...

  8. Anisotropy of transport in bulk Rashba metals (United States)

    Brosco, Valentina; Grimaldi, Claudio


    The recent experimental discovery of three-dimensional (3D) materials hosting a strong Rashba spin-orbit coupling calls for the theoretical investigation of their transport properties. Here we study the zero-temperature dc conductivity of a 3D Rashba metal in the presence of static diluted impurities. We show that, at variance with the two-dimensional case, in 3D systems, spin-orbit coupling affects dc charge transport in all density regimes. We find in particular that the effect of spin-orbit interaction strongly depends on the direction of the current, and we show that this yields strongly anisotropic transport characteristics. In the dominant spin-orbit coupling regime where only the lowest band is occupied, the conductivity anisotropy is governed entirely by the anomalous component of the renormalized current. We propose that measurements of the conductivity anisotropy in bulk Rashba metals may give a direct experimental assessment of the spin-orbit strength.


    Gonzalez, T.; Ortiz, I.


    Analysis and interpretation of gravimetric anomalies over the Occidental-Central Mexican Volcanic Belt, sheds new light on the subsurface structure of the Ixtlan de los Hervores, geothermal area. In Mexico, there are several geothermal areas that have been exploited commercially (Cerro Prieto, Los Azufres, Los Humeros, Tres Virgenes fields). However, there are many other known fields that have not been exploited. This is the case in the area of "Ixtlan de los Hervores" in the state of Michoacan. The analyzed region covers a rectangular area, aproximality from 20o N to 20.5° N and 102° W to 102.2°W. In the region there are thick basalt flows. The area is characterized by low and elongated hills formed by volcanic flows and on a smaller scale lacustrian sediments and major normal faults with a NW-SE direction particularly, the Ixtlan-Encinal fault which controls the trace of the Duero River and the Pajacuarán fault. The anomaly map was compared with the surface geology and the anomalies were correlated with major volcanic features, since our main interest was in mapping the subsurface faults and volcanic bodies. Two profiles were selected that cross major anomalies and the geothermal zone of Ixtlan. The Talwani algorithm for 2-D polygonal bodies has been used for calculating the theoretical anomalies. The proposed models adequately explain the main observed geological features. The models are made up of two lithostratigraphic units of volcanic rocks, represented by the Tertiary basalts, which adequately reflect the area's volcanic environment. These basaltic units, corresponding to different volcanic events were cut by the Ixtlan well. Both models reflect the existence of the Ixtlan-Encinal fault, the most important feature in the area which is also responsible for the existence of the geothermal area.

  10. Measurement of the thermopower anisotropy in iron arsenide

    Energy Technology Data Exchange (ETDEWEB)

    Fujii, T., E-mail: [Cryogenic Research Center, the University of Tokyo, 2-11-16 Yayoi, Bunkyo, Tokyo 113-0032 (Japan); Shirachi, T. [Department of Applied Physics, the University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Asamitsu, A. [Cryogenic Research Center, the University of Tokyo, 2-11-16 Yayoi, Bunkyo, Tokyo 113-0032 (Japan); Department of Applied Physics, the University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-8656 (Japan); Ashikaga Institute of Technology, 268-1 Omae, Ashikaga, Tochigi 326-8558 (Japan)


    Highlights: • In this study, in order to investigate the origin of the in-plane anisotropy, the in-plane anisotropy of the thermopower was measured for the detwined single crystals of BFe{sub 2}As{sub 2}. And, we found no anisotropy in the thermopower above T{sub AFO}, although there is a large anisotropy in the resistivity. This result gives evidence that the anisotropy in the resistivity arise from the anisotropy of the scattering time, and the energy dependence of the scattering time can be considered negligible. In the case of iron pnictides, the proposed orbital ordering more likely results in an anisotropy of electronic structure below T{sub AFO}, whereas the spin-nematic ordering leads to an anisotropy of electron scattering above T{sub AFO}. Therefore, our results suggest that nematicity above T{sub AFO} results from anisotropic magnetic scattering. - Abstract: We investigated the in-plane anisotropy of the thermopower and electrical resistivity on detwinned single crystals of BaFe{sub 2}As{sub 2}. The in-plane anisotropy of the resistivity was clearly observed far above the magnetostructural transition temperature T{sub AFO}. While, the thermopower showed the in-plane anisotropy only below T{sub AFO}. These results are associated with the different origin of the anisotropy above and below T{sub AFO}. Since the thermopower does not depend on the scattering time, the anisotropy of the resistivity above T{sub AFO} is considered to be due to the anisotropic scattering. On the other hand, the anisotropy in the thermopower below T{sub AFO} is ascribed to the reconstructed Fermi surface.

  11. Shape-induced anisotropy in antiferromagnetic nanoparticles


    H. Gomonay; Kondovych, S.; Loktev, V.


    High fraction of the surface atoms considerably enhances the influence of size and shape on the magnetic and electronic properties of nanoparticles. Shape effects in ferromagnetic nanoparticles are well understood and allow to set and control the parameters of a sample that affect its magnetic anisotropy during production. In the present paper we study the shape effects in the other widely used magnetic materials -- antiferromagnets, -- which possess vanishingly small or zero macroscopic magn...

  12. Pn anisotropy in Mesozoic western Pacific lithosphere (United States)

    Shintaku, Natsumi; Forsyth, Donald W.; Hajewski, Christina J.; Weeraratne, Dayanthie S.


    Pn is the high-frequency, scattered P phase guided for great distances within the old oceanic lithosphere. Two arrays of ocean bottom seismometers were deployed on old (150-160 Ma) seafloor in the northwestern Pacific south of Shatsky Rise for the Pacific Lithosphere Anisotropy and Thickness Experiment. We use Pn phases from 403 earthquakes during the 1 year of deployment to measure apparent velocities across the arrays. Each array was deployed on a separate limb of a magnetic bight, formed near a fast-spreading, ridge-ridge-ridge triple junction. Using high-frequency waves (5-10 Hz), we look at variations of Pn velocities as a function of azimuth. In the western array, we find Pn anisotropy with velocities ranging from ~8.7 km/s in the back azimuth (θ) direction of 310° to ~7.7 km/s at ~350°. In the eastern array, the velocity ranges from ~8.5 km/s in back azimuth direction of ~210° to ~7.7 km/s at 260° and ~310°. We observe rapid velocity changes with azimuth in the both arrays requiring sinusoidal variations of roughly equal amplitude as a function of both 2θ and 4θ, which is not expected for the orthorhombic symmetry of olivine or orthopyroxene. The fastest directions on the two limbs are roughly orthogonal to each other suggesting the dominance of fossil anisotropy, but the fast directions of the 2θ components are skewed counterclockwise from the spreading directions. We speculate that the rapid azimuthal variations may be caused by vertical stratification with changing anisotropy with depth in the oceanic lithosphere.

  13. Random anisotropy induced by structural disorder (United States)

    Martinez, B.; Labarta, A.; Badia, F.; Tejada, J.


    As a direct consequence of the structural disorder, inherent to the amorphous state, local electrostatic fields are highly irregular. Due to the interplay between those highly irregular local electrostatic fields and the aspherical 4f electron clouds of the rare earth atoms, local anisotropy axis, directed along directions that vary randomly in space, may be generated. These directions are determined by the local arrangement of atoms; therefore, some information about amorphous structure may be obtained through the study of the magnetization curve.

  14. The Role of Magmatic and Volcanic Loads in Generating Seaward Dipping Reflector Structures on Volcanic Rifted Margins (United States)

    Tian, X.; Buck, W. R.


    The largest volcanic constructs on Earth are the seismically imaged seaward dipping reflector (SDR) units found offshore of many rifted continental margins, including a large portion that border the Atlantic Ocean. There is considerable controversy over whether their formation requires large offset (i.e. 10s of km) normal faults or not. Although there is some evidence for faulting in association with SDRs, we here show that a wide range of SDRs structures can be produced solely by volcanic loading. To do this we first derive a simple analytic description of a particular type of volcanic construct. We assume that the increase in density when fluid magma in a dike solidifies provides load at the rift center onto the end of a lithospheric plate. Extrusives are assumed to form flat-topped layers that fill in the flexural depression produced by the load of the solidified dike. The thin-plate flexure approximation is used to calculate the deflections due to the vertical load. This simple model produces structures similar to the observed SDRs. Expressions for the maximum thickness of the volcanic pile and the dip of an individual SDR are derived in terms of the flexure parameter and material densities. Asymmetry of SDR units seen across some conjugate margins can be explained with this model if periodic offsets, or jumps of the center of magmatism are included. In addition, we developed a numerical model of lithospheric extension, magma intrusion and volcanism with a temperature dependent elasto-viscous and brittle-plastic rheology. Results of these 2D cross-sectional models with fixed thermal structure confirm the qualitative predictions of the analytic model without the simplified uniform plate assumption. Preliminary results suggest that the rapid subsidence of SDRs, inferred for some rifted margins, can occur if magma is supplied only to the brittle upper layer and the hot weak lower crust is thinned by stretching. This numerical approach may also allow us to test

  15. Geochronology of the volcanic rocks in the Lu-Zong basin and its significance

    Institute of Scientific and Technical Information of China (English)

    David; COOKE; Sebastien; MEFFRE


    The Lu-Zong (Lujiang-Zongyang) basin is one of the most important volcanic basins in the middle and lower reaches of the Yangtze River area, China. It comprises four shoshonitic volcanic units, which are, in an ascending order, the Longmenyuan, Zhuanqiao, Shuangmiao and Fushan Groups. The LA-ICP MS U-Pb zircon ages of the four units are: 134.8±1.8 Ma for the Longmenyuan Group, 134.1±1.6 Ma for the Zhuanqiao Group, 130.5±0.8 Ma for the Shuangmiao Group, and 127.1±1.2 Ma for the Fushan Group. The results indicate that all volcanic rocks in the Lu-Zong basin were formed in the Early Cretaceous from about 135 Ma to 127 Ma, lasting 8-10 Ma. There were no Jurassic volcanic activities in all the volcanic basins including the Lu-Zong basin in the middle and lower reaches of the Yangtze River area. This work has provided new chronological results for the further study and understanding of the tec- tonic, magmatic and metallogenic processes of eastern China in the Mesozoic.

  16. Geochronology of the volcanic rocks in the Lu-Zong basin and its significance

    Institute of Scientific and Technical Information of China (English)

    ZHOU TaoFa; FAN Yu; YUAN Feng; LU SanMing; SHANG ShiGui; David COOKE; Sebastien MEFFRE; ZHAO GuoChun


    The Lu-Zong (Lujiang-Zongyang) basin is one of the most important volcanic basins in the middle and lower reaches of the Yangtze River area, China. It comprises four shoshonitic volcanic units, which are,in an ascending order, the Longmenyuan, Zhuanqiao, Shuangmiao and Fushan Groups. The LA-ICP MS U-Pb zircon ages of the four units are: 134.8±1.8 Ma for the Longmenyuan Group, 134.1±1.6 Ma for the Zhuanqiao Group, 130.5±0.8 Ma for the Shuangmiao Group, and 127.1+1.2 Ma for the Fushan Group. The results indicate that all volcanic rocks in the Lu-Zong basin were formed in the Early Cretaceous from about 135 Ma to 127 Ma, lasting 8-10 Ma. There were no Jurassic volcanic activities in all the volcanic basins including the Lu-Zong basin in the middle and lower reaches of the Yangtze River area.This work has provided new chronological results for the further study and understanding of the tectonic, magmatic and metallogenic processes of eastern China in the Mesozoic.

  17. CMB anisotropies: Total angular momentum method (United States)

    Hu, Wayne; White, Martin


    A total angular momentum representation simplifies the radiation transport problem for temperature and polarization anisotropy in the cosmic microwave background (CMB). Scattering terms couple only the quadrupole moments of the distributions and each moment corresponds directly to the observable angular pattern on the sky. We develop and employ these techniques to study the general properties of anisotropy generation from scalar, vector, and tensor perturbations to the metric and the matter, both in the cosmological fluids and from any seed perturbations (e.g., defects) that may be present. The simpler, more transparent form and derivation of the Boltzmann equations brings out the geometric and model-independent aspects of temperature and polarization anisotropy formation. Large angle scalar polarization provides a robust means to distinguish between isocurvature and adiabatic models for structure formation in principle. Vector modes have the unique property that the CMB polarization is dominated by magnetic-type parity at small angles (a factor of 6 in power compared with 0 for the scalars and 8/13 for the tensors) and hence potentially distinguishable independent of the model for the seed. The tensor modes produce a different sign from the scalars and vectors for the temperature-polarization correlations at large angles. We explore conditions under which one perturbation type may dominate over the others including a detailed treatment of the photon-baryon fluid before recombination.

  18. Dynamical anisotropy of the optical propagation paths (United States)

    Arsenyan, Tatiana I.; Pisklin, Maksim V.; Suhareva, Natalia A.; Zotov, Aleksey M.


    Dynamics of laser beam intensity profile spatial modulations over a model tropospheric path with the controlled meteorological parameters was studied. Influence of the underlying surface temperature as well as the side wind load were considered. The increase of dynamic anisotropic disturbances saturation with the path length was observed. Spatio-temporal correlation characteristics of the directivity pattern in the signal beam registration plane were obtained. Proposed method of the experimental samples analysis on the base of chronogram with the following definition of the dynamic structure tensors array allows to estimate local and averaged projections of the flow velocities over the chosen spatio-temporal region and to restore their geometry in the zone of intersection with the signal beam. Additional characteristics suggested for the diagonalized local structure tensors such as local energy capacity and local structuredness are informative for the estimation of the inhomogeneities spatial dimensions, time of access through the section considered, the dynamics of energetic jets. The concepts of rotational and translational dynamic anisotropy are introduced to discriminate the types of the changes of the local ellipsoids axes orientation as well as their values. Rotational anisotropy shows itself in the changes of the local ellipsoids orientation, thus characterizing the illumination variation over the beam cross-section. Translational anisotropy describes the difference between the axes values for local ellipsoids.

  19. Effective surface anisotropy in polycrystalline ferromagnetic nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Holanda, J.; Campos, C.L.A.V.; Franca, C.A.; Padrón-Hernández, E., E-mail:


    Highlights: • Here we make a mixing of two models. A macroscopic and a microscopic model. • The principal idea in this paper is to write the free magnetic energy for a soft magnetic cylindrical nanowire and make the comparison with our previous models. • The model is tested to determine the effective constant in Ni nanowires. - Abstract: Here we express the effective surface anisotropy for soft ferromagnetic nanowires as the function of the micro-structural behaviors. Many papers about these systems determine the reversal modes for the magnetization to explain magnetic properties of the nanowires. Our previous works related morphological structure with magnetic properties. The principal idea in this paper is to write the free magnetic energy for a soft magnetic cylindrical nanowire and make the comparison with our previous models. In this way we include the macroscopic effective anisotropy due to the disordered atoms and ignoring other microstructure terms related in our previous works. From this idea and our last model to these systems, we made an association that permit to express the effective anisotropy in function of the principal morphological characteristics of nanowires. The model is tested to determine the numerical value of the mentioned constant in Ni nanowires obtained by electrodeposition in porous anodic aluminum oxide membranes using the Transmission Electron Microscopy.

  20. Anisotropy analyses of population distribution patterns

    Institute of Scientific and Technical Information of China (English)

    WANG Benyang; YU Shixiao; WANG Yongfan


    Direction-dependence,or anisotropy,of spatial distribution patterns of vegetation is rarely explored due to neglect of this ecological phenomenon and the paucity of methods dealing with this issue.This paper proposes a new approach to anisotropy analysis of spatial distribution patterns of plant populations on the basis of the data resampling technique (DRT) combined with Ripley's L index.Using the ArcView Geographic Information System (GIS) platform,a case study was carried out by selecting the population of Pinus massoniana from a needle- and broad-leaved mixed forest community in the Heishiding Nature Reserve,Guangdong Province.Results showed that the spatial pattern of the P massoniana population was typically anisotropic with different patterns in different directions.The DRT was found to be an effective approach to the anisotropy analysis of spatial patterns of plant populations.By employing resampling sub-datasets from the original dataset in different directions,we could overcome the difficulty in the direct use of current non-angular methods of pattern analysis.

  1. Anisotropy of ice Ih: Developement of fabric and effects of anisotropy on deformation (United States)

    Thorsteinsson, Throstur

    The anisotropy arising from preferred crystal orientation of ice I h is examined. To understand plastic anisotropy of polycrystalline materials it is necessary to examine the behavior at the single crystal level. Ice crystals have extremely strong plastic anisotropy that strongly influences the bulk behavior. There are several ways to relate single crystal deformation to the bulk behavior. Two approaches are used here. The first one is to assume a homogeneous stress throughout the bulk, which allows us to derive analytical relations between stress and strain rate. The anisotropy affects the strain rate-stress relationship significantly. For example strongly anisotropic ice, with a vertically symmetric fabric, can deform transversely to the applied stress in pure shear, be nearly undeformable in vertical compression, and shear easily in simple shear. The second approach takes the interaction between neighboring crystals into account, and recrystallization processes are also considered. Comparison of fabric evolution using the model and fabric from the GRIP ice core indicates that nearest neighbor interaction is necessary to explain observations. Quantification of the interaction is complicated by recrystallization processes. A consistent method of characterizing measured fabric is needed to verify models of fabric development. Here the elastic anisotropy of ice plays a central role, and relations between fabric and elastic wave velocities are used to characterize fabric. As always, several other methods are possible, but comparison indicates that sonic measurements give an accurate estimate for deformation effects from vertically symmetric fabric especially in simple shear. The deformation of the borehole at Dye 3, Greenland, has been measured with borehole inclinometry. Sonic velocity measurements done in the borehole allow us to model the deformation using an anisotropic flow law. Anisotropy alone cannot explain all the deformation. The additional processes

  2. Volcanic caves of East Africa - an overview

    Directory of Open Access Journals (Sweden)

    Jim W. Simons


    Full Text Available Numerous Tertiary to recent volcanoes are located in East Africa. Thus, much of the region is made up volcanic rock, which hosts the largest and greatest variety of East Africas caves. Exploration of volcanic caves has preoccupied members of Cave Exploration Group of East Africa (CEGEA for the past 30 years. The various publications edited by CEGEA are in this respect a treasure troves of speleological information. In the present paper an overview on the most important volcanic caves and areas are shortly reported.

  3. Toward Forecasting Volcanic Eruptions using Seismic Noise

    CERN Document Server

    Brenguier, Florent; Campillo, Michel; Ferrazzini, Valerie; Duputel, Zacharie; Coutant, Olivier; Nercessian, Alexandre


    During inter-eruption periods, magma pressurization yields subtle changes of the elastic properties of volcanic edifices. We use the reproducibility properties of the ambient seismic noise recorded on the Piton de la Fournaise volcano to measure relative seismic velocity variations of less than 0.1 % with a temporal resolution of one day. Our results show that five studied volcanic eruptions were preceded by clearly detectable seismic velocity decreases within the zone of magma injection. These precursors reflect the edifice dilatation induced by magma pressurization and can be useful indicators to improve the forecasting of volcanic eruptions.

  4. Volcanic Plume Measurements with UAV (Invited) (United States)

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


    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

  5. Optical anisotropy in packed isotropic spherical particles: indication of nanometer scale anisotropy in packing structure. (United States)

    Yamaguchi, Kohei; Inasawa, Susumu; Yamaguchi, Yukio


    We investigated the origin of birefringence in colloidal films of spherical silica particles. Although each particle is optically isotropic in shape, colloidal films formed by drop drying demonstrated birefringence. While periodic particle structures were observed in silica colloidal films, no regular pattern was found in blended films of silica and latex particles. However, since both films showed birefringence, regular film structure patterns were not required to exhibit birefringence. Instead, we propose that nanometer-scale film structure anisotropy causes birefringence. Due to capillary flow from the center to the edge of a cast suspension, particles are more tightly packed in the radial direction. Directional packing results in nanometer-scale anisotropy. The difference in the interparticle distance between radial and circumferential axes was estimated to be 10 nm at most. Nanometer-scale anisotropy in colloidal films and the subsequent optical properties are discussed.

  6. A Mars Analog for Wet-Based Glacial Alteration of Volcanic Terrains: Thermal Infrared Remote Sensing at Three Sisters, Oregon, U.S.A. (United States)

    Rutledge, A. M.; Scudder, N. A.; Horgan, B.; Rampe, E. B.


    This study characterizes wet-based glacial weathering products at a volcanic Mars analog site using thermal infrared remote sensing. Decorrelation stretches are used to examine the geographic relationships between compositional units.

  7. Fabrication of electrodeposited Co nanowire arrays with perpendicular anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Ge Shihui E-mail:; Ma Xiao; Li Chao; Li Wei


    Co nanowire arrays have been electrodeposited into polycarbonate membranes with nanosized pores at different voltages. By means of X-ray diffraction, electron diffraction, vibrating sample magnetometer, their microstructures and magnetic properties were investigated at full length. The sample prepared at -1.2 V, 250 mA/cm{sup 2} shows perpendicular anisotropy, but the one deposited at -1.0V, 125 mA/cm{sup 2} has no perpendicular anisotropy. This different magnetic behavior can be explained from their different microstructures. X-ray diffraction and electron diffraction evidence that the former sample is amorphous, and the latter is polycrystalline. In the polycrystalline sample, due to the competition of shape anisotropy and magnetocrystal anisotropy, the sample does not display perpendicular anisotropy. But magnetocrystal anisotropy is very small in amorphous sample, therefore, shape anisotropy plays a dominant role which leads to strong perpendicular anisotropy because of shape anisotropy. Furthermore, applying a magnetic field during deposition, Co grains will preferentially grow with c-axis along the wire axis, which also leads to strong perpendicular anisotropy.

  8. Volcanic Ash Advisory Database, 1983-2003 (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Volcanic ash is a significant hazard to aviation and can also affect global climate patterns. To ensure safe navigation and monitor possible climatic impact, the...

  9. Palaeoclimate: Volcanism caused ancient global warming (United States)

    Meissner, Katrin J.; Bralower, Timothy J.


    A study confirms that volcanism set off one of Earth's fastest global-warming events. But the release of greenhouse gases was slow enough for negative feedbacks to mitigate impacts such as ocean acidification. See Letter p.573

  10. Volcanics in the Gulf Coast [volcanicg (United States)

    U.S. Geological Survey, Department of the Interior — The volcanic provinces are modified after Plate 2, Principal structural features, Gulf of Mexico Basin (compiled by T.E. Ewing and R.F. Lopez) in Volume J, The...

  11. Volcanic rock properties control sector collapse events (United States)

    Hughes, Amy; Kendrick, Jackie; Lavallée, Yan; Hornby, Adrian; Di Toro, Giulio


    Volcanoes constructed by superimposed layers of varying volcanic materials are inherently unstable structures. The heterogeneity of weak and strong layers consisting of ash, tephra and lavas, each with varying coherencies, porosities, crystallinities, glass content and ultimately, strength, can promote volcanic flank and sector collapses. These volcanoes often exist in areas with complex regional tectonics adding to instability caused by heterogeneity, flank overburden, magma movement and emplacement in addition to hydrothermal alteration and anomalous geothermal gradients. Recent studies conducted on the faulting properties of volcanic rocks at variable slip rates show the rate-weakening dependence of the friction coefficients (up to 90% reduction)[1], caused by a wide range of factors such as the generation of gouge and frictional melt lubrication [2]. Experimental data from experiments conducted on volcanic products suggests that frictional melt occurs at slip rates similar to those of plug flow in volcanic conduits [1] and the bases of mass material movements such as debris avalanches from volcanic flanks [3]. In volcanic rock, the generation of frictional heat may prompt the remobilisation of interstitial glass below melting temperatures due to passing of the glass transition temperature at ˜650-750 ˚C [4]. In addition, the crushing of pores in high porosity samples can lead to increased comminution and strain localisation along slip surfaces. Here we present the results of friction tests on both high density, glass rich samples from Santaguito (Guatemala) and synthetic glass samples with varying porosities (0-25%) to better understand frictional properties underlying volcanic collapse events. 1. Kendrick, J.E., et al., Extreme frictional processes in the volcanic conduit of Mount St. Helens (USA) during the 2004-2008 eruption. J. Structural Geology, 2012. 2. Di Toro, G., et al., Fault lubrication during earthquakes. Nature, 2011. 471(7339): p. 494-498. 3

  12. Volcanism and associated hazards: the Andean perspective

    Directory of Open Access Journals (Sweden)

    R. I. Tilling


    Full Text Available 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 (<0.05 km3 in 1985 of Nevado del Ruiz (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

  13. About the Mechanism of Volcanic Eruptions

    CERN Document Server

    Nechayev, Andrei


    A new approach to the volcanic eruption theory is proposed. It is based on a simple physical mechanism of the imbalance in the system "magma-crust-fluid". This mechanism helps to explain from unified positions the different types of volcanic eruptions. A criterion of imbalance and magma eruption is derived. Stratovolcano and caldera formation is analyzed. High explosive eruptions of the silicic magma is discussed

  14. Episodic Volcanism and Geochemistry in Western Nicaragua (United States)

    Saginor, I.; Carr, M. J.; Gazel, E.; Swisher, C.; Turrin, B.


    The active volcanic arc in western Nicaragua is separated from the Miocene arc by a temporal gap in the volcanic record, during which little volcanic material was erupted. Previous work suggested that this gap lasted from 7 to 1.6 Ma, during which volcanic production in Nicaragua was limited or nonexistent. Because the precise timing and duration of this gap has been poorly constrained, recent fieldwork has focused on locating samples that may have erupted close to or even during this apparent hiatus in activity. Recent 40Ar/39Ar dates reveal pulses of low- level episodic volcanism at 7 Ma and 1 Ma between the active and Miocene arcs with current volcanism beginning ~350 ka. In addition, sampling from an inactive area between Coseguina and San Cristobal yielded two distinct groupings of ages; one of Tamarindo age (13 Ma) and the other around 3.5 Ma-the only samples of that age collected on-strike with the active arc. This raises the possibility the bases of the other active volcanoes contain lavas that are older than expected, but have been covered by subsequent eruptions. The Miocene arc differs from the active arc in Central America in several ways, with the latter having higher Ba/La and U/Th values due to increased slab input and changes in subducted sediment composition. Analysis of sample C-51 and others taken from the same area may shed light on the timing of this shift from high to low Ba/La and U/Th values. More importantly, it may help explain why the arc experienced such a dramatic downturn in volcanic production during this time. We also report 25 new major and trace element analyses that shed some light on the origins of these minor episodes of Nicaraguan volcanism. These samples are currently awaiting Sr and Nd isotopic analyses.

  15. Paleomagnetic Results of the Red Soil-Volcanic Rock Series of Yingfengling Section, Southern Leizhou Peninsula

    Institute of Scientific and Technical Information of China (English)

    王俊达; 梁池生


    The Yingfengling section composed of red soil and volcanic rocks can be distinguished into 8 stratigraphic units and 4 red soil-volcanic rock cycles. 64 paleomagnetic-orientated sam ples were collected from the bottom to the top of the section. Natural remanent magnetization and magnetic susceptibility were firstly measured. All the samples were stepwisely treated with thermal or/and alternating fields. Four clear polarity segments were recorded in the section.Compared with the geo-magnetic polarity scale, the section was formed since the late Olduvai subchron, about 1.37 Ma. B. P.

  16. Volcanic geomorphosites and geotourism in Las Cañadas del Teide National Park, Tenerife, Canary Islands, Spain (United States)

    Dóniz-Paéz, Javier; Becerra-Ramírez, Rafael; González-Cárdenas, Elena; Rodriguez, Fátima


    Geomorphosites and geoturism studies are increasing for the high scientific, societal, cultural, and aesthetic values of the relief. Volcanic areas are exciting targets for such studies for their geodiversity. The aim of these study is an inventory of volcanic geomorphosites and its relationship to geotourism. Las Cañadas del Teide National Park (LCTNP) is a volcanic complex area located in the central part of Tenerife island (Canary Islands, Spain). This area is a volcanic paradise rich in spectacular landforms: stratovolcanoes, calderas, cinder cones, craters, pahoehoe, aa, block and balls lavas, gullies, etc. The national park is registered in the world heritage list (UNESCO) in 2007 as a natural site. The LCTNP receives more than 2,5 million tourists per year and it has 21 main pahts and 14 secondary ones. For the selection of the geomophosites the LCTNP was divided into four geomorphological units (Teide-Pico Viejo stratovolcanoes, Las Cañadas Caldera wall, the bottom of Las Cañadas and the basaltic volcanic field) and each one of them is selected the most representative geomorphosites by its geodiversity, because of its geomorphological heritage, its landscapes and its tourist potential with the paths. All selected geomorphosites are within areas where public use is allowed in the park. The inventory classifies the 23 geomorphosites in two main categories: (a) direct volcanic with 17 geomorphosites (stratovolcanoes, domes, cinder cones, pahoehoe, aa and bloc lava flows, etc.) and (b) eroded volcanic landforms with 6 (wall of Las Cañadas caldera, talusees, foodplains, etc.). The Teide-Pico Viejo unit is which has more geomorphosites with 8 and the Las Cañadas wall unit possessing less with 5. The assessment evaluates the scientific, cultural/historical, and use values and helps to define priorities in site management. These geomorphosites demonstrate the volcanic history and processes of the LCTNP.

  17. Volcanic loading: The dust veil index

    Energy Technology Data Exchange (ETDEWEB)

    Lamb, H.H. [Univ. of East Anglia, Norwich (United Kingdom). Climatic Research Unit


    Dust ejected into the high atmosphere during explosive volcanic eruptions has been considered as a possible cause for climatic change. Dust veils created by volcanic eruptions can reduce the amount of light reaching the Earth`s surface and can cause reductions in surface temperatures. These climatic effects can be seen for several years following some eruptions and the magnitude and duration of the effects depend largely on the density or amount of tephra (i.e. dust) ejected, the latitude of injection, and atmospheric circulation patterns. Lamb (1970) formulated the Dust Veil Index (DVI) in an attempt to quantify the impact on the Earth`s energy balance of changes in atmospheric composition due to explosive volcanic eruptions. The DVI is a numerical index that quantifies the impact on the Earth`s energy balance of changes in atmospheric composition due to explosive volcanic eruptions. The DVI is a numerical index that quantifies the impact of a particular volcanic eruptions release of dust and aerosols over the years following the event. The DVI for any volcanic eruptions are available and have been used in estimating Lamb`s dust veil indices.

  18. Competing magnetic anisotropies in obliquely deposited thin permalloy film

    Energy Technology Data Exchange (ETDEWEB)

    Belyaev, B.A. [Siberian Federal University, 79, pr. Svobodnyi, Krasnoyarsk 660041 (Russian Federation); Kirensky Institute of Physics, Siberian Branch of the Russian Academy of Sciences, 50/38, Akademgorodok, Krasnoyarsk 660036 (Russian Federation); Reshetnev Siberian State Aerospace University, 31, pr. Imeni Gazety “Krasnoyarskii Rabochii”, Krasnoyarsk 660014 (Russian Federation); Izotov, A.V. [Siberian Federal University, 79, pr. Svobodnyi, Krasnoyarsk 660041 (Russian Federation); Kirensky Institute of Physics, Siberian Branch of the Russian Academy of Sciences, 50/38, Akademgorodok, Krasnoyarsk 660036 (Russian Federation); Solovev, P.N., E-mail: [Siberian Federal University, 79, pr. Svobodnyi, Krasnoyarsk 660041 (Russian Federation)


    Distribution of the magnetic anisotropy in thin film prepared by thermal vacuum oblique deposition of permalloy with small off-normal angle of incident in the presence of an external magnetic field has been studied by ferromagnetic resonance technique. On local area of the sample, a mutual compensation of near orthogonal in-plane uniaxial magnetic anisotropies induced by oblique deposition and by applied magnetic field has been found. Moreover, in addition to the uniaxial (twofold) magnetic anisotropy, fourfold and sixfold magnetic anisotropies have been observed in the sample. To explain the obtained high-order anisotropies, we assumed that the sample has exchange coupled adjacent regions or phases with different parameters of magnetic anisotropy. The results of the micromagnetic analysis of a two-layer model of the sample confirm the hypothesis.

  19. Extending Velocity Channel Analysis for Studying Turbulence Anisotropies

    CERN Document Server

    Kandel, Dinesh; Pogosyan, Dmitri


    We extend the analysis of the fluctuations in the velocity slices of Position-Position- Velocity (PPV) spectroscopic data from Doppler broadened lines, i.e. Velocity Channel Analysis (VCA) introduced by Lazarian & Pogosyan (2000), to study anisotropy of the underlying velocity and density turbulence statistics that arises from the presence of magnetic field. In particular, we study analytically how the measurable anisotropy of the statistics of the channel map fluctuations changes with the thickness of velocity channels. In agreement with the earlier VCA studies we find that the anisotropy of the thick channels reflects the anisotropy of the density field, while the relative contribution of density and velocity fluctuations to the thin velocity channels depends on the density spectral slope. We show that the anisotropies arising from Alfven, slow and fast modes are different, in particular, the anisotropy in PPV created by fast modes is opposite to that created by Alfven and slow modes and this can be use...

  20. CMB Spectral Distortions from the Scattering of Temperature Anisotropies


    Stebbins, Albert


    Thomson scattering of CMBR temperature anisotropies will cause the spectrum of the CMBR to differ from blackbody even when one resolves all anisotropies. A formalism for computing the anisotropic and inhomogeneous spectral distortions of intensity and polarization is derived in terms of Lorentz invariant central moments of the temperature distribution. The formalism is non-perturbative, requiring neither small anisotropies nor small metric or matter inhomogeneities; but it does assume cold el...

  1. Satellite Derived Volcanic Ash Product Inter-Comparison in Support to SCOPE-Nowcasting (United States)

    Siddans, Richard; Thomas, Gareth; Pavolonis, Mike; Bojinski, Stephan


    In support of aeronautical meteorological services, WMO organized a satellite-based volcanic ash retrieval algorithm inter-comparison activity, to improve the consistency of quantitative volcanic ash products from satellites, under the Sustained, Coordinated Processing of Environmental Satellite Data for Nowcasting (SCOPEe Nowcasting) initiative (http:/ nowcasting_en.php). The aims of the intercomparison were as follows: 1. Select cases (Sarychev Peak 2009, Eyjafyallajökull 2010, Grimsvötn 2011, Puyehue-Cordón Caulle 2011, Kirishimayama 2011, Kelut 2014), and quantify the differences between satellite-derived volcanic ash cloud properties derived from different techniques and sensors; 2. Establish a basic validation protocol for satellite-derived volcanic ash cloud properties; 3. Document the strengths and weaknesses of different remote sensing approaches as a function of satellite sensor; 4. Standardize the units and quality flags associated with volcanic cloud geophysical parameters; 5. Provide recommendations to Volcanic Ash Advisory Centers (VAACs) and other users on how to best to utilize quantitative satellite products in operations; 6. Create a "road map" for future volcanic ash related scientific developments and inter-comparison/validation activities that can also be applied to SO2 clouds and emergent volcanic clouds. Volcanic ash satellite remote sensing experts from operational and research organizations were encouraged to participate in the inter-comparison activity, to establish the plans for the inter-comparison and to submit data sets. RAL was contracted by EUMETSAT to perform a systematic inter-comparison of all submitted datasets and results were reported at the WMO International Volcanic Ash Inter-comparison Meeting to held on 29 June - 2 July 2015 in Madison, WI, USA (http:/ /cimss.ssec.wisc.edujmeetings/vol_ash14). 26 different data sets were submitted, from a range of passive imagers and spectrometers and

  2. Volcanic Eruption: Students Develop a Contingency Plan (United States)

    Meisinger, Philipp; Wittlich, Christian


    Dangerous, loud, sensational, exciting - natural hazards have what it takes to get students attention around the globe. Arising interest is the first step to develop an intrinsic motivation to learn about the matter and endure the hardships that students might discover along the way of the unit. Natural hazards thereby establish a close-knit connection between physical and anthropological geography through analyzing the hazardous event and its consequences for the people living in the affected area. Following a general principle of didactics we start searching right on our doorsteps to offer students the possibility to gain knowledge on the familiar and later transfer it to the unknown example. Even in Southwest Germany - a region that is rather known for its wine than its volcanic activity - we can find a potentially hazardous region. The "Laacher See" volcano (a caldera lake) in northern Rhineland-Palatinate is according to Prof. H.U. Schminke a "potentially active volcano" . Its activity can be proven by seismic activities, or experienced when visiting the lake's southeastern shore, where carbondioxid and sulphur gases from the underlying magma chamber still bubble up. The Laacher See is part of a range of volcanoes (classified from 'potentially active' to 'no longer active') of the East Eifel Volcanic Field. Precariously the Laacher See is located closely to the densely populated agglomerations of Cologne (NE, distance: 45 km) and the former capital Bonn (NE: 35km), as well as Koblenz (E: 24km) and the Rhine river. Apart from that, the towns of Andernach (E: 8km ± 30 000 inhabitants) and Mayen (SW: 11km ±20 000 inhabitants) and many smaller towns and villages are nearby due to economic reasons. The number of people affected by a possible eruption easily exceeds two million people considering the range as prime measurement. The underlying danger, as projected in a simulation presented by Prof. Schminke, is a lava stream running down the Brohltal valley

  3. Programming magnetic anisotropy in polymeric microactuators. (United States)

    Kim, Jiyun; Chung, Su Eun; Choi, Sung-Eun; Lee, Howon; Kim, Junhoi; Kwon, Sunghoon


    Polymeric microcomponents are widely used in microelectromechanical systems (MEMS) and lab-on-a-chip devices, but they suffer from the lack of complex motion, effective addressability and precise shape control. To address these needs, we fabricated polymeric nanocomposite microactuators driven by programmable heterogeneous magnetic anisotropy. Spatially modulated photopatterning was applied in a shape-independent manner to microactuator components by successive confinement of self-assembled magnetic nanoparticles in a fixed polymer matrix. By freely programming the rotational axis of each component, we demonstrate that the polymeric microactuators can undergo predesigned, complex two- and three-dimensional motion.

  4. Cosmology with cosmic microwave background anisotropy

    Indian Academy of Sciences (India)

    Tarun Sourdeep


    Measurements of CMB anisotropy and, more recently, polarization have played a very important role in allowing precise determination of various parameters of the `standard' cosmological model. The expectation of the paradigm of inflation and the generic prediction of the simplest realization of inflationary scenario in the early Universe have also been established - `acausally' correlated initial perturbations in a flat, statistically isotropic Universe, adiabatic nature of primordial density perturbations. Direct evidence for gravitational instability mechanism for structure formation from primordial perturbations has been established. In the next decade, future experiments promise to strengthen these deductions and uncover the remaining crucial signature of inflation - the primordial gravitational wave background.

  5. Adsorbate Azimuthal Orientation from Reflectance Anisotropy Spectroscopy (United States)

    Frederick, B. G.; Power, J. R.; Cole, R. J.; Perry, C. C.; Chen, Q.; Haq, S.; Bertrams, Th.; Richardson, N. V.; Weightman, P.


    We have determined the azimuthal orientation of an adsorbate on a metal surface from an intramolecular-transition-derived feature in reflectance anisotropy spectroscopy (RAS). Adsorption of 9-anthracene carboxylic acid onto p\\(2×1\\)O/Cu110 led to an ordered structure with a strong (2%), derivativelike feature at 4.5 eV. Fresnel theory predicts the measured intensity, functional behavior, and sense of the RAS signal for the molecule aligned along [110]. IR measurements confirm that the molecular plane is perpendicular to the surface and STM measurements support the azimuthal orientation. We reassign the sense of the clean Cu(110) surface RA spectrum.

  6. Altered Fractional Anisotropy in Early Huntington's Disease

    Directory of Open Access Journals (Sweden)

    Silky Singh


    Full Text Available Huntington's disease (HD is a dominantly inherited neurodegenerative disease best known for chorea. The disorder includes numerous other clinical features including mood disorder, eye movement abnormalities, cognitive disturbance, pendular knee reflexes, motor impersistence, and postural instability. We describe a mild case of HD early in the disease course with depression and subtle neurological manifestations. In addition, we review MRI and diffusion tensor imaging features in this patient. The bicaudate ratio, a measure of caudate atrophy, was increased. Fractional anisotropy values of the bilateral caudate and putamen were increased, signifying neurodegeneration of these structures in HD.

  7. A Backarc Basin Origin for the Eocene Volcanic Rocks North of Abbas Abad, East of Shahrud, Northeast Iran (United States)

    Khalatbari Jafari, M.; Mobasher, K.; Davarpanah, A.; Babaie, H.; La Tour, T.


    The region in northeastern Iran, bordered by the Miami fault and the Doruneh fault, mainly exposes the Eocene volcanic and Tertiary sedimentary rocks and sporadic outcrops of pre- Jurassic metamorphic rocks such as gneiss and mica-schist. We have divided the volcanic and volcanic-sedimentary rocks into six main units: E1 through the youngest E6. North of Abbas Abad, the Lower Eocene is conglomerate, sandstone, and red shale with lenses of nummulite-bearing limestone at the base, and dacitic lava (E1) at the top. The nummulites give an Early Eocene age for the limestone lenses. The E2 unit includes vesicular basalt, intercalated, intraformational conglomerate, and lenses of nummulite-bearing limestone. E3 is volcanic- sedimentary, and is made of green tuff, tuffite, shale, and nummulite bearing limestone. E4 includes basalt and vesicular trachy-basalt, and E5 is mostly sedimentary, made of tan marl, sandstone, shale, and lenses of Middle Eocene nummulite-bearing limestone. The E6 unit is the most extensive, with at least three levels of nummulite-bearing limestone lenses which give a Middle to Early Eocene age. The volcanic rocks of the E6 unit include few hundred meters of epiclastic to hyaloclastic breccia, with intercalations of lava at the base. These are overlain by four horizons of aphyric olivine basalt and basalt, and phyric trachy-andesite and trachy-basalt. The volume of the aphyric lavas decreases, and that of the phyric lavas increases upsection. The Eocene volcanic sequence is covered by turbidite; the marl washings give an Eocene-Oligocene age range. Chondrite-normalized multi-element plots indicate enrichment of the Eocene Abbas Abad volcanic rocks in the LILE elements, with variable ratios of La/Yb (4.36-19.33) and La/Sm (3.10-7.91). These plots show a gentle slope, and the volcanic rocks in the E1 to E4 units are less enriched than those in the E6 unit, probably reflecting the difference in the original source for the melt. The multi-element plots

  8. Theoretical Compton profile anisotropies in molecules and solids. VI. Compton profile anisotropies and chemical binding

    Energy Technology Data Exchange (ETDEWEB)

    Matcha, R.L.; Pettitt, B.M.


    An interesting empirical relationship between zero point Compton profile anisotropies (0) and nuclear charges is noted. It is shown that, for alkali halide molecules AB, to a good approximation (0) =N ln(Z/sub b//Z/sub a/).

  9. Molecular anisotropy effects in carbon K-edge scattering: depolarized diffuse scattering and optical anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Stone, Kevin H.


    Some polymer properties, such as conductivity, are very sensitive to short- and intermediate-range orientational and positional ordering of anisotropic molecular functional groups, and yet means to characterize orientational order in disordered systems are very limited. We demonstrate that resonant scattering at the carbon K-edge is uniquely sensitive to short-range orientation correlations in polymers through depolarized scattering at high momentum transfers, using atactic polystyrene as a well-characterized test system. Depolarized scattering is found to coexist with unpolarized fluorescence, and to exhibit pronounced anisotropy. We also quantify the spatially averaged optical anisotropy from low-angle reflectivity measurements, finding anisotropy consistent with prior visible, x-ray absorption, and theoretical studies. The average anisotropy is much smaller than that in the depolarized scattering and the two have different character. Both measurements exhibit clear spectral signatures from the phenyl rings and the polyethylene-like backbone. Discussion focuses on analysis considerations and prospects for using this depolarized scattering for studies of disorder in soft condensed matter.

  10. Molecular anisotropy effects in carbon K-edge scattering: Depolarized diffuse scattering and optical anisotropy (United States)

    Stone, Kevin H.; Kortright, Jeffrey B.


    Some polymer properties, such as conductivity, are very sensitive to short- and intermediate-range orientational and positional ordering of anisotropic molecular functional groups, and yet means to characterize orientational order in disordered systems are very limited. We demonstrate that resonant scattering at the carbon K edge is uniquely sensitive to short-range orientation correlations in polymers through depolarized scattering at high momentum transfers, using atactic polystyrene as a well-characterized test system. Depolarized scattering is found to coexist with unpolarized fluorescence and to exhibit pronounced anisotropy. We also quantify the spatially averaged optical anisotropy from low-angle reflectivity measurements, finding anisotropy consistent with prior visible, x-ray absorption, and theoretical studies. The average anisotropy is much smaller than that in the depolarized scattering and the two have different character. Both measurements exhibit clear spectral signatures from the phenyl rings and the polyethylenelike backbone. Discussion focuses on analysis considerations and prospects for using this depolarized scattering for studies of disorder in soft condensed matter.

  11. A Complete Treatment of CMB Anisotropies in a FRW Universe

    CERN Document Server

    Hu, W; White, M; Zaldarriaga, M; Hu, Wayne; Seljak, Uros; White, Martin; Zaldarriaga, Matias


    We generalize the total angular momentum method for computing Cosmic Microwave Background anisotropies to Friedman-Robertson-Walker (FRW) spaces with arbitrary geometries. This unifies the treatment of temperature and polarization anisotropies generated by scalar, vector and tensor perturbations of the fluid, seed, or a scalar field, in a universe with constant comoving curvature. The resulting formalism generalizes and simplifies the calculation of anisotropies and, in its integral form, allows for a fast calculation of model predictions in linear theory for any FRW metric. With this work, the perturbation theory of CMB temperature and polarization anisotropy formation through gravitational instability in an FRW universe may be considered complete.

  12. Computing magnetic anisotropy constants of single molecule magnets

    Indian Academy of Sciences (India)

    S Ramasesha; Shaon Sahoo; Rajamani Raghunathan; Diptiman Sen


    We present here a theoretical approach to compute the molecular magnetic anisotropy parameters, and for single molecule magnets in any given spin eigenstate of exchange spin Hamiltonian. We first describe a hybrid constant -valence bond (VB) technique of solving spin Hamiltonians employing full spatial and spin symmetry adaptation and we illustrate this technique by solving the exchange Hamiltonian of the Cu6Fe8 system. Treating the anisotropy Hamiltonian as perturbation, we compute the and values for various eigenstates of the exchange Hamiltonian. Since, the dipolar contribution to the magnetic anisotropy is negligibly small, we calculate the molecular anisotropy from the single-ion anisotropies of the metal centers. We have studied the variation of and by rotating the single-ion anisotropies in the case of Mn12Ac and Fe8 SMMs in ground and few low-lying excited states of the exchange Hamiltonian. In both the systems, we find that the molecular anisotropy changes drastically when the single-ion anisotropies are rotated. While in Mn12Ac SMM values depend strongly on the spin of the eigenstate, it is almost independent of the spin of the eigenstate in Fe8 SMM. We also find that the value is almost insensitive to the orientation of the anisotropy of the core Mn(IV) ions. The dependence of on the energy gap between the ground and the excited states in both the systems has also been studied by using different sets of exchange constants.

  13. Effects of anisotropy on the two-dimensional inversion procedure (United States)

    Heise, Wiebke; Pous, Jaume


    In this paper we show some of the effects that appear in magnetotelluric measurements over 2-D anisotropic structures, and propose a procedure to recover the anisotropy using 2-D inversion algorithms for isotropic models. First, we see how anisotropy affects the usual interpretation steps: dimensionality analysis and 2-D inversion. Two models containing general 2-D azimuthal anisotropic features were chosen to illustrate this approach: an anisotropic block and an anisotropic layer, both forming part of general 2-D models. In addition, a third model with dipping anisotropy was studied. For each model we examined the influence of various anisotropy strikes and resistivity contrasts on the dimensionality analysis and on the behaviour of the induction arrows. We found that, when the anisotropy ratio is higher than five, even if the strike is frequency-dependent it is possible to decide on a direction close to the direction of anisotropy. Then, if the data are rotated to this angle, a 2-D inversion reproduces the anisotropy reasonably well by means of macro-anisotropy. This strategy was tested on field data where anisotropy had been previously recognized.

  14. The study of the shape anisotropy in patterned permalloy films

    Institute of Scientific and Technical Information of China (English)

    Zhang Dong; Zhai Ya; Zhai Hong-Ru


    In this paper a systematic ferromagnetic resonance study shows that an in-plane magnetic anisotropy in the patterned micron octagon permalloy (Ni80Fe20) elements is mainly determined by the element geometry. The easy-axis is along the edge of the elements, and the hard-axis is along the diagonal. The shape anisotropy of the octagon elements is determined by square and equilateral octagon, and the theoretical calculation was studied on the shape anisotropy. The shape anisotropy of rectangular was calculated by using the same theory.

  15. Western Alborz Volcanic Rocks, a new Geochemical Viewpoint (United States)

    Ghorbani, M.


    Volcanic and pyroclastic rocks of Eocene age comprise vast outcrops of Alborz Mountain Range, a fold-thrusted structural unit extending across northern Iran for 2000 km in a curvilinear pattern. In his account of structural evolution of Iranian plateau, Berberian (1983; p. 55) ascribed these rocks to a subduction-type magmatism. Based on a tectonostratigraphic study, these rocks are attributed to an arc-type magmatism (Alavi; 1996, p. 29). Recently a new data set of major and trace element (including REE) analyses of volcanic rocks from western Alborz, some 50 km west of city of Qazvin, has been made available (Asiabanha, 2001). Careful examination of the data (i.e., those of basic-intermediate rocks) in present study revealed, for the first time, some geochemical characteristics which have important implications on the geodynamic synthesis of this structural unit. The rocks contain 50-60 wt% SiO2. They lie in the midalkaline-to-subalkaline domain of TAS diagram (Middlemost, 1997; p.216) and fall in the calcalkaline field of AFM diagram. The volcanic rocks display two distinct chondrite-normalized REE patterns, one is MREE-depleted while the other is a rather smooth uniform M-HREE pattern. These are called MREE-depleted and smooth M-HREE series. Basic rocks from the latter contain higher silica than the former (>53 vs. >50 wt%), yet they show lower incompatible elements (e.g., K and Rb) and HFSE contents. These features can not be explained by differentiation and might be interpreted as implying the involvement of two source regions. Chondrite-normalized trace element patterns of the MREE-depleted series is more akin to the island arc calcalkaline (IACA) basic rocks than the basic rocks from any other tectonic settings. However, island arc products, known for being depleted in HFSE relative to other incompatible elements, differ from the MREE-depleted series which is rich in both HFSE and incompatible elements. One may advocate the role of OIB-type mantle

  16. Age and duration of intra-oceanic arc volcanism built on a suprasubduction zone type oceanic crust in southern Neotethys, SE Anatolia

    Directory of Open Access Journals (Sweden)

    Fatih Karaoğlan


    Full Text Available The southeastern Anatolia comprises numbers of tectono-magmatic/stratigraphic units such as the metamorphic massifs, the ophiolites, the volcanic arc units and the granitoid rocks. All of them play important role for the late Cretaceous evolution of the southern Neotethys. The spatial and temporal relations of these units suggest the progressive development of coeval magmatism and thrusting during the late Cretaceous northward subduction/accretion. Our new U-Pb zircon data from the rhyolitic rocks of the wide-spread volcanic arc unit show ages of (83.1 ± 2.2–(74.6 ± 4.4 Ma. Comparison of the ophiolites, the volcanic arc units and the granitoids suggest following late Cretaceous geological evolution. The ophiolites formed in a suprasubduction zone (SSZ setting as a result of northward intra-oceanic subduction. A wide-spread island-arc tholeiitic volcanic unit developed on the top of the SSZ-type crust during 83–75 Ma. Related to regional plate convergence, northward under-thrusting of SSZ-type ophiolites and volcanic arc units was initiated beneath the Tauride platform (Malatya-Keban and followed by the intrusion of I-type calc-alkaline volcanic arc granitoids during 84–82 Ma. New U-Pb ages from the arc-related volcanic-sedimentary unit and granitoids indicate that under-thrusting of ophiolites together with the arc-related units beneath the Malatya-Keban platform took place soon after the initiation of the volcanic arc on the top of the SSZ-type crust. Then the arc-related volcanic-sedimentary unit continued its development and lasted at ∼75 Ma until the deposition of the late Campanian–Maastrichtian shallow marine limestone. The subduction trench eventually collided with the Bitlis-Pütürge massif giving rise to HP-LT metamorphism of the Bitlis massif. Although the development of the volcanic arc units and the granitoids were coeval at the initial stage of the subduction/accretion both tectono-magmatic units were

  17. The Early Andean Magmatic Province (EAMP): 40Ar/ 39Ar dating on Mesozoic volcanic and plutonic rocks from the Coastal Cordillera, northern Chile (United States)

    Oliveros, Verónica; Féraud, Gilbert; Aguirre, Luis; Fornari, Michel; Morata, Diego


    The Early Andean Magmatic Province (EAMP), consists of about 150 000 km 3 of volcanic and plutonic units in the Coastal Cordillera of northern Chile and southern Peru and represents a major magmatic Mesozoic event in the world, for which the precise age of the thick volcanic series was unknown. Thirty 40Ar/ 39Ar analyses were carried out on primary mineral phases of volcanic and plutonic rocks from northern Chile (18°30'-24°S). Reliable plateau and "mini plateau" ages were obtained on plagioclase, amphibole and biotite from volcanic and plutonic rocks, despite widespread strong alteration degree. In the Arica, Tocopilla and Antofagasta (700 km apart) regions, the ages obtained on lava flows constrain the volcanic activity between 164 and 150 Ma and no N-S migration of volcanism is observed. The uppermost lava flows of the volcanic sequence at the type locality of the La Negra Formation extruded at ca. 153-150 Ma, suggesting the end of the volcanic activity of the arc at that time. The oldest volcanic activity occurred probably at ca. 175-170 Ma in the Iquique area, although no plateau age could be obtained. The plutonic bodies of the same regions were dated between ca. 160 and 142 Ma, indicating that they were partly contemporaneous with the volcanic activity. At least one volcanic pulse around 160 Ma is evidenced over the entire investigated reach of the EAMP, according to the ages found in Arica, Tocopilla, Michilla and Mantos Blancos regions. The episodic emplacement of huge amounts of subduction related volcanism is observed throughout the whole Andean history and particularly during the Jurassic (southern Peru, northern Chile and southern Argentina). These events probably correspond to periodic extensional geodynamic episodes, as a consequence of particular subduction conditions, such as change of obliquity of the convergence, change in the subduction angle, slab roll back effect or lower convergence rate, that remain to be precisely defined.

  18. Venus volcanism - Classification of volcanic features and structures, associations, and global distribution from Magellan data (United States)

    Head, James W.; Crumpler, L. S.; Aubele, Jayne C.; Guest, John E.; Saunders, R. S.


    A classification and documentation of the range of morphologic features and structures of volcanic origin on Venus, their size distribution, and their global distribution and associations are presented based on a preliminary analysis of Magellan data. Some of the major questions about volcanism on Venus are addressed.

  19. Volcanic Supersites as cross-disciplinary laboratories (United States)

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


    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, 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

  20. Calibration of microbolometer infrared cameras for measuring volcanic ash mass loading (United States)

    Carroll, Russell C.

    Small spacecraft with thermal infrared (TIR) imaging capabilities are needed to detect dangerous levels of volcanic ash that can severely damage jet aircraft engines and must be avoided. Grounding aircraft after a volcanic eruption may cost the airlines millions of dollars per day, while accurate knowledge of volcanic ash density might allow for safely routing aircraft around dangerous levels of volcanic ash. There are currently limited numbers of satellites with TIR imaging capabilities so the elapsed time between revisits can be large, and these instruments can only resolve total mass loading along the line-of-sight. Multiple small satellites could allow for decreased revisit times as well as multiple viewing angles to reveal the three-dimensional structure of the ash cloud through stereoscopic techniques. This paper presents the design and laboratory evaluation of a TIR imaging system that is designed to fit within the resource constraints of a multi-unit CubeSat to detect volcanic ash mass loading. The laboratory prototype of this TIR imaging system uses a commercial off-the shelf (COTS) camera with an uncooled microbolometer sensor, two narrowband filters, a black body source and a custom filter wheel. The infrared imaging system detects the difference in attenuation of volcanic ash at 11 mum and 12 mum by measuring the brightness temperature at each band. The brightness temperature difference method is used to measure the column mass loading. Multi-aspect images and stereoscopic techniques are needed to estimate the mass density from the mass loading, which is the measured mass per unit area. Laboratory measurements are used to characterize the noise level and thermal stability of the sensor. A calibration technique is developed to compensate for sensor temperature drift. The detection threshold of volcanic ash density of this TIR imaging system is found to be from 0.35 mg/m3 to 26 mg/m3 for ash clouds that have thickness of 1 km, while ash cloud densities

  1. The Albano multiple-maar center (Rome, Italy): an active volcanic area since 70 ka (United States)

    Freda, C.; Gaeta, M.; Karner, D. B.; Marra, F.; Renne, P. R.; Scarlato, P.; Taddeucci, J.


    The Albano multiple-maar center hosted the most recent activity of the Alban Hills Volcanic District. The determination of its petrochemical characteristics and its geochronology is therefore of great importance in order to evaluate the status of this volcanic area and to assess the possible volcanic hazard for Rome. Despite the detailed 40Ar/39Ar geochronologic history of the products of its activity, relatively poor information on the stratigraphy and the petrology of this volcanic center exists. In order to develop a detailed chronostratigraphy, petrology, and a more thorough knowledge of the eruptive mechanisms that characterized the recent activity of the Albano center, a joint research project is being conducted by scientists from the Istituto Nazionale di Geofisica e Vulcanologia, the University of California at Berkeley, and the Berkeley Geochronology Center. Here we have studied the most complete stratigraphic section located within the northern crater rim of Albano, where most of the products are exposed. We have investigated proximal and distal outcrops, in order to correlate them to the units identified in the northern crater rim section. We will present our recently acquired geochronologic and petrochemical data, which indicates magma chamber recharge associated with this <70 ka volcanism.

  2. Subaqueous environment and volcanic evolution of the Late Cretaceous Chelopech Au-Cu epithermal deposit, Bulgaria (United States)

    Chambefort, Isabelle; Moritz, Robert


    A detailed field and petrographic study constrains the volcanic evolution and environment setting of the volcano-sedimentary-hosted Chelopech Cu-Au epithermal deposit, Bulgaria. Magmatic activity and associated high-sulfidation epithermal mineralization occurred at about 91 Ma in the Panagyurishte ore district of the Eastern European Banat-Timok-Srednogorie metallogenic belt. Volcanic and hydrothermal activity took place in a complex subaqueous setting, resulting in the intercalation of quartz sandstone with andesitic volcanic and volcaniclastic breccia. There are also hypabyssal andesite intrusion, phreatomagmatic breccia and interbeds of pyroclastic, oolithic and bioclastic rocks. The presence of altered cerebroid ooid-bearing sedimentary units characteristic of salty environment is in accordance with a lagoon environment predating the mineralization at Chelopech. Four principal stages of evolution for the Chelopech district are proposed based on field and petrographic observations. Initial volcanism occurred in a lake or in a coastal, shallow lagoon environment above crystalline basement. The Chelopech "phreatomagmatic" breccia and subsurface andesites were emplaced at this time. Subsequent hydrothermal activity produced the different hydrothermal breccia types, advanced argillic and quartz-phyllic alteration, and Au-Cu vein and replacement mineralization. The end of volcanism and hydrothermal activity was associated with opening of a pull-apart basin that covered the Chelopech environment with a sedimentary flysch. Tertiary compression faulting juxtaposed various rocks and tilted the ore deposit during the Alpine orogeny.

  3. Stratigraphy and Characterization of Volcanic Deposits on the Northwestern Flanks of Mt. Makiling, Laguna, Philippines (United States)

    Ybanez, R. L.; Bonus, A. A. B.; Judan, J. M.; Racoma, B. A.; Morante, K. A. M.; Balangue, M. I. R. D.


    Mt. Makiling is an inactive stratovolcano located in the province of Laguna. Semi-detailed geologic field mapping on the northwestern low-level flanks and apron of the volcano was conducted. Exposures reveal a volcanic terrain hosting a wide variety of volcanic rocks: lava flows, pyroclastic surges, pyroclastic flows, and tuff deposits. Stratigraphic logging of the volcanic deposits showed differences in occurrence of the deposit types as well as their characteristics. The pyroclastic flow deposits are found at the base of the column overlain by pyroclastic surges which were more common in the area. Capping the pyroclastic surges is a thin layer of tuffaceous units. Isolated deposits of lava flows of andesitic composition were mapped in the western flank of Mt. Makiling. These varying volcanic deposits are derived from different eruptive activities of Mt. Makiling, with at least three separate eruptive episodes indicated by the exposed deposits. Two separate explosive eruptions are marked by two different pyroclastic deposits, while an effusive episode, marked by andesitic lava flows, can also be identified. The pyroclastic surge deposit is uncharacteristically thick, around a hundred meters or more exposed, providing further questions as to the magnitude of past eruptions or the mechanism of pyroclastic material deposition around the volcano. Mt. Makiling, thus, has historically undergone different eruption types, but still releases generally the same material composition across varying deposits: intermediate or andesitic composition. This is consistent with the trend of Philippine volcanoes, and with the Macolod corridor which hosts this volcanic system.

  4. Contrasting origin of two clay-rich debris flows at Cayambe Volcanic Complex, Ecuador (United States)

    Detienne, M.; Delmelle, P.; Guevara, A.; Samaniego, P.; Opfergelt, S.; Mothes, P. A.


    We investigate the sedimentological and mineralogical properties of a debris flow deposit west of Cayambe Volcanic Complex, an ice-clad edifice in Ecuador. The deposit exhibits a matrix facies containing up to 16 wt% of clays. However, the stratigraphic relationship of the deposit with respect to the Canguahua Formation, a widespread indurated volcaniclastic material in the Ecuadorian inter-Andean Valley, and the deposit alteration mineralogy differ depending on location. Thus, two different deposits are identified. The Río Granobles debris flow deposit ( 1 km3) is characterised by the alteration mineral assemblage smectite + jarosite, and sulphur isotopic analyses point to a supergene hydrothermal alteration environment. This deposit probably derives from a debris avalanche initiated before 14-21 ka by collapse of a hydrothermally altered rock mass from the volcano summit. In contrast, the alteration mineralogy of the second debris flow deposit, which may itself comprise more than one unit, is dominated by halloysite + smectite and relates to a shallower and more recent (3200 m) volcanic soils. Our study reinforces the significance of hydrothermal alteration in weakening volcano flanks and in favouring rapid transformation of a volcanic debris avalanche into a clay-rich debris flow. It also demonstrates that mineralogical analysis provides crucial information for resolving the origin of a debris flow deposit in volcanic terrains. Finally, we posit that slope instability, promoted by ongoing subglacial hydrothermal alteration, remains a significant hazard at Cayambe Volcanic Complex.

  5. Volcanic Alert System (VAS) developed during the (2011-2013) El Hierro (Canary Islands) volcanic process (United States)

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


    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

  6. Electromagnetic Instabilities Excited by Electron Temperature Anisotropy

    Institute of Scientific and Technical Information of China (English)

    陆全明; 王连启; 周艳; 王水


    One-dimensional particle-in-cell simulations are performed to investigate the nonlinear evolution of electromagnetic instabilities excited by the electron temperature anisotropy in homogeneous plasmas with different parameters. The results show that the electron temperature anisotropy can excite the two right-hand electromagnetic instabilities, one has the frequency higher than Ωe, the other is the whistler instability with larger amplitude,and its frequency is below Ωe. Their dispersion relations are consistent with the prediction from the cold plasma theory. In the initial growth stage (prediction from linear theory), the frequency of the dominant mode (the mode whose amplitude is large enough) of the whistler wave almost does not change, but in the saturation stage the situation is different. In the case that the ratio of electron plasma frequency to cyclotron frequency is larger than 1, the frequency of the dominant mode of the whistler wave drifts from high to low continuously. However, for the case of the ratio smaller than 1, besides the original dominant mode of the whistler wave whose frequency is about 2.6ωe, another dominant mode whose frequency is about 1.55ωe also begins to be excited at definite time,and its amplitude increases with time until it exceeds the original dominant mode.

  7. Anisotropy and Heterogeneity Interaction in Shear Zones (United States)

    Dabrowski, M.; Schmid, D. W.


    Rocks are heterogeneous on many different scales and deformation may introduce a coexistence of heterogeneity and anisotropy in shear zones. A competent inclusion embedded in a laminated matrix is a typical example. Indisputably, the presence of a mechanical heterogeneity leads to a flow perturbation and consequently to a deflection of the lamination in its vicinity. Assuming a passive response of the matrix phase, the pattern formation around rigid objects has been modeled in two and three dimensions using analytical solutions. Yet, the laminas may be mechanically distinct, leading to an effectively anisotropic rheology of the matrix. The feedback of an evolving matrix structure on the inclusion motion cannot be precluded in this case. In our study elliptical inclusions of varying aspect ratios are embedded in a laminated linear viscous host and subject to a large simple shear deformation in finite element numerical simulations. Increasing the viscosity ratio of the weak and strong lamina significantly changes the pattern characteristics in the matrix. The structural evolution around an inclusion proves to have a major impact on the inclusion motion, leading to the stabilization of elongated inclusions at antithetic orientations. We provide a comparison of two different modeling approaches. In the first approach discrete layers are introduced in the matrix and the large strain evolution of individual minute layers is resolved. Next, the matrix is modeled as an anisotropic medium using an evolving director field that locally describes the anisotropy direction. The length scale of layering can be restored in this model using the micropolar medium formulation.

  8. Random magnetic anisotropy: Switching and coercivity behavior (United States)

    Creswell, A.; Paul, D. I.


    Starting from a Hamiltonian based on the random magnetic anisotropy model to describe the magnetic characteristics of amorphous materials such as TbFe2, we determine the low-temperature dependence of the coercivity as well as the magnetization dynamics of these materials. Our model features clusters, each characterized by its anisotropy direction. The exchange energy term entering the Hamiltonian is represented by an effective exchange interaction acting in the intercluster regions. Our Hamiltonian has a minimum in each of the two opposite hemispheres defined by the applied field. We derive the temperature-dependent coercivity by calculating the field necessary to have the one metastable minimum disappear. Our results agree well with experimental data for reasonable values of the parameters. We study the dynamics of the magnetization at 0 K by performing a numerical integration of the equations of motion derived from our Hamiltonian augmented by a Gilbert and Kelly damping term. The average magnetization of the material is reevaluated at each integration step in order for the mean-field approximation for exchange to remain physically meaningful. We obtain the time dependence of the magnetization, determine the switching fields and switching times, and study the influence of the exchange on the results.

  9. A fully covariant description of CMB anisotropies

    CERN Document Server

    Dunsby, P K S


    Starting from the exact non-linear description of matter and radiation, a fully covariant and gauge-invariant formula for the observed temperature anisotropy of the cosmic microwave background (CBR) radiation, expressed in terms of the electric ($E_{ab}$) and magnetic ($H_{ab}$) parts of the Weyl tensor, is obtained by integrating photon geodesics from last scattering to the point of observation today. This improves and extends earlier work by Russ et al where a similar formula was obtained by taking first order variations of the redshift. In the case of scalar (density) perturbations, $E_{ab}$ is related to the harmonic components of the gravitational potential $\\Phi_k$ and the usual dominant Sachs-Wolfe contribution $\\delta T_R/\\bar{T}_R\\sim\\Phi_k$ to the temperature anisotropy is recovered, together with contributions due to the time variation of the potential (Rees-Sciama effect), entropy and velocity perturbations at last scattering and a pressure suppression term important in low density universes. We a...

  10. CMB statistical anisotropy from noncommutative gravitational waves

    CERN Document Server

    Shiraishi, Maresuke; Ricciardone, Angelo; Arroja, Frederico


    Primordial statistical anisotropy is a key indicator to investigate early Universe models and has been probed by the cosmic microwave background (CMB) anisotropies. In this paper, we examine tensor-mode CMB fluctuations generated from anisotropic gravitational waves, parametrised by $P_h({\\bf k}) = P_h^{(0)}(k) [ 1 + \\sum_{LM} f_L(k) g_{LM} Y_{LM} (\\hat{\\bf k}) ]$, where $P_h^{(0)}(k)$ is the usual scale-invariant power spectrum. Such anisotropic tensor fluctuations may arise from an inflationary model with noncommutativity of fields. It is verified that in this model, an isotropic component and a quadrupole asymmetry with $f_0(k) = f_2(k) \\propto k^{-2}$ are created and hence highly red-tilted off-diagonal components arise in the CMB power spectra, namely $\\ell_2 = \\ell_1 \\pm 2$ in $TT$, $TE$, $EE$ and $BB$, and $\\ell_2 = \\ell_1 \\pm 1$ in $TB$ and $EB$. We find that B-mode polarisation is more sensitive to such signals than temperature and E-mode polarisation due to the smallness of large-scale cosmic varian...

  11. Anisotropy in thin Canning sheet metals (United States)

    Rees, D. W. A.


    The in-plane anisotropy of ductile sheet metal may be characterised by r-values within a uniform tensile strain range. In iow ductiiity material, tensile failure occurs by the formation of an inciined groove within which the plasticity is localised. Under these conditions, where lateral and axial displacements cannot determine an r-value reliably, the inclination of the local groove is used. Anisotropy is characterised from an orthotropic yield criterion within three r-values, found from tension tests at 0^{circ}, 45^{circ} and 90^{circ} to the roll. Application to bi-axial stress states are made from elliptical bulge forming. The theory may reprcduce the pressure-height curves and pole strain paths provided an equivalence exists between flow curves from tension and bulge tests. Otherwise, the circular bulge test is better for providing the hardening parameters and fracture strain for use in in biaxial stress applications. There appears to be no advantage in using other non-quadratic yield criteria except by the addition of linear and cubic terms.

  12. Anisotropy Studies with the Pierre Auger Observatory

    CERN Document Server

    Santos, E M


    An anisotropy signal for the arrival directions of ultra-high energy cosmic rays (UHECR) of more than 99% confidence level was established using data collected by the Pierre Auger Observatory. Cosmic rays with energy above $\\sim 6 \\times 10^{19}$ eV show a correlation with the positions of extragalactic nearby active galactic nuclei (AGN), being maximum for sources at less than $\\sim$100 Mpc and angular separation of a few degrees. The evolution of the correlation signal with the energy shows that the departure from anisotropy coincides with the flux suppression observed in the spectrum, being therefore consistent with the hypothesis that the correlated events have their origin in extragalactic sources close enough to avoid significant interaction with the cosmic microwave background (the Greisen-Zatsepin-Kuz'min effect). Even though the observed signal cannot unambiguously identify AGNs as the production sites of UHECRs, the potential sources have to be distributed in a similar way. A number of additional st...

  13. The nature versus nurture of anisotropies

    CERN Document Server

    Hu, W


    With the rapidly growing number of cosmic microwave background measurements on various scales, there is real hope that the number of acceptable models for structure formation will be limited to a very few in the near future. Yet any given model can always be saved by introducing and tuning extraneous free parameters. To better understand this question of ``nature versus nurture'' for temperature fluctuations, it is useful to know not only the general features of anisotropy predictions but also their causes. Extracting the physical content of our other works, we present here a {\\it simple} account of cosmic microwave background anisotropies on all scales. In particular, we show that analytic approximations can trace the structure of the so-called ``Doppler peaks,'' which arise due to the {\\it adiabatic} oscillations in the photon-baryon fluid. We also show how the finite thickness of the last scattering surface and the Silk damping mechanism can be described in a unified way by photon diffusion. In order to pr...

  14. Texture and anisotropy analysis of Qusaiba shales

    KAUST Repository

    Kanitpanyacharoen, Waruntorn


    Scanning and transmission electron microscopy, synchrotron X-ray diffraction, microtomography and ultrasonic velocity measurements were used to characterize microstructures and anisotropy of three deeply buried Qusaiba shales from the Rub\\'al-Khali basin, Saudi Arabia. Kaolinite, illite-smectite, illite-mica and chlorite show strong preferred orientation with (001) pole figure maxima perpendicular to the bedding plane ranging from 2.4-6.8 multiples of a random distribution (m.r.d.). Quartz, feldspars and pyrite crystals have a random orientation distribution. Elastic properties of the polyphase aggregate are calculated by averaging the single crystal elastic properties over the orientation distribution, assuming a nonporous material. The average calculated bulk P-wave velocities are 6.2 km/s (maximum) and 5.5 km/s (minimum), resulting in a P-wave anisotropy of 12%. The calculated velocities are compared with those determined from ultrasonic velocity measurements on a similar sample. In the ultrasonic experiment, which measures the effects of the shale matrix as well as the effects of porosity, velocities are smaller (P-wave maximum 5.3 km/s and minimum 4.1 km/s). The difference between calculated and measured velocities is attributed to the effects of anisotropic pore structure and to microfractures present in the sample, which have not been taken into account in the matrix averaging. © 2011 European Association of Geoscientists & Engineers.

  15. Results from the Wilkinson Microwave Anisotropy Probe (United States)

    Komatsu, E.; Bennett, Charles L.; Komatsu, Eiichiro


    The Wilkinson Microwave Anisotropy Probe (WMAP) mapped the distribution of temperature and polarization over the entire sky in five microwave frequency bands. These full-sky maps were used to obtain measurements of temperature and polarization anisotropy of the cosmic microwave background with the unprecedented accuracy and precision. The analysis of two-point correlation functions of temperature and polarization data gives determinations of the fundamental cosmological parameters such as the age and composition of the universe, as well as the key parameters describing the physics of inflation, which is further constrained by three-point correlation functions. WMAP observations alone reduced the flat ? cold dark matter (Lambda Cold Dark Matter) cosmological model (six) parameter volume by a factor of > 68, 000 compared with pre-WMAP measurements. The WMAP observations (sometimes in combination with other astrophysical probes) convincingly show the existence of non-baryonic dark matter, the cosmic neutrino background, flatness of spatial geometry of the universe, a deviation from a scale-invariant spectrum of initial scalar fluctuations, and that the current universe is undergoing an accelerated expansion. The WMAP observations provide the strongest ever support for inflation; namely, the structures we see in the universe originate from quantum fluctuations generated during inflation.

  16. Anisotropy and Crystalline Structure in Polyaniline Films (United States)

    Minto, C. D. G.; Vaughan, A. S.


    Films of polyaniline -- camphor sulphonic acid cast from m-cresol exhibit transport properties characteristic of a material stradelling the metal/insulator transition. This improvement in properties over traditional methods of polyaniline production has been suggested as being caused by the macromolecule adopting an expanded coil configuration in this solvent. Such films have been shown to be semi--crystalline and are presumed to be completely isotropic. We present here new results which demonstrate that such films are in fact appreciably aligned. X-ray scattering is utilised to expose the presence of molecular anisotropy within such films, the polymers forming a stacked structure with the molecules preferentially oriented parallel to the plane of the film. Similar measurements confirm that the molecules are randomly oriented within this plane. Such alignment considerably improves the transport properties. Anisotropy and the crystalline structure within these films, those cast from chloroform and those using the isolated enantiomeric counter ion are quantified and discussed. The results demonstrate that improved transport properties have arisen as a result of both polymer--solvent interactions and as a result of improved chain alignment.

  17. Scanning anisotropy parameters in complex media

    KAUST Repository

    Alkhalifah, Tariq Ali


    Parameter estimation in an inhomogeneous anisotropic medium offers many challenges; chief among them is the trade-off between inhomogeneity and anisotropy. It is especially hard to estimate the anisotropy anellipticity parameter η in complex media. Using perturbation theory and Taylor’s series, I have expanded the solutions of the anisotropic eikonal equation for transversely isotropic (TI) media with a vertical symmetry axis (VTI) in terms of the independent parameter η from a generally inhomogeneous elliptically anisotropic medium background. This new VTI traveltime solution is based on a set of precomputed perturbations extracted from solving linear partial differential equations. The traveltimes obtained from these equations serve as the coefficients of a Taylor-type expansion of the total traveltime in terms of η. Shanks transform is used to predict the transient behavior of the expansion and improve its accuracy using fewer terms. A homogeneous medium simplification of the expansion provides classical nonhyperbolic moveout descriptions of the traveltime that are more accurate than other recently derived approximations. In addition, this formulation provides a tool to scan for anisotropic parameters in a generally inhomogeneous medium background. A Marmousi test demonstrates the accuracy of this approximation. For a tilted axis of symmetry, the equations are still applicable with a slightly more complicated framework because the vertical velocity and δ are not readily available from the data.

  18. Automatic semi-continuous accumulation chamber for diffuse gas emissions monitoring in volcanic and non-volcanic areas (United States)

    Lelli, Matteo; Raco, Brunella; Norelli, Francesco; Virgili, Giorgio; Continanza, Davide


    Since various decades the accumulation chamber method is intensively used in monitoring activities of diffuse gas emissions in volcanic areas. Although some improvements have been performed in terms of sensitivity and reproducibility of the detectors, the equipment used for measurement of gas emissions temporal variation usually requires expensive and bulky equipment. The unit described in this work is a low cost, easy to install-and-manage instrument that will make possible the creation of low-cost monitoring networks. The Non-Dispersive Infrared detector used has a concentration range of 0-5% CO2, but the substitution with other detector (range 0-5000 ppm) is possible and very easy. Power supply unit has a 12V, 7Ah battery, which is recharged by a 35W solar panel (equipped with charge regulator). The control unit contains a custom programmed CPU and the remote transmission is assured by a GPRS modem. The chamber is activated by DataLogger unit, using a linear actuator between the closed position (sampling) and closed position (idle). A probe for the measure of soil temperature, soil electrical conductivity, soil volumetric water content, air pressure and air temperature is assembled on the device, which is already arranged for the connection of others external sensors, including an automatic weather station. The automatic station has been tested on the field at Lipari island (Sicily, Italy) during a period of three months, performing CO2 flux measurement (and also weather parameters), each 1 hour. The possibility to measure in semi-continuous mode, and at the same time, the gas fluxes from soil and many external parameters, helps the time series analysis aimed to the identification of gas flux anomalies due to variations in deep system (e.g. onset of volcanic crises) from those triggered by external conditions.

  19. Mean anisotropy of homogeneous Gaussian random fields and anisotropic norms of linear translation-invariant operators on multidimensional integer lattices

    Directory of Open Access Journals (Sweden)

    Phil Diamond


    Full Text Available Sensitivity of output of a linear operator to its input can be quantified in various ways. In Control Theory, the input is usually interpreted as disturbance and the output is to be minimized in some sense. In stochastic worst-case design settings, the disturbance is considered random with imprecisely known probability distribution. The prior set of probability measures can be chosen so as to quantify how far the disturbance deviates from the white-noise hypothesis of Linear Quadratic Gaussian control. Such deviation can be measured by the minimal Kullback-Leibler informational divergence from the Gaussian distributions with zero mean and scalar covariance matrices. The resulting anisotropy functional is defined for finite power random vectors. Originally, anisotropy was introduced for directionally generic random vectors as the relative entropy of the normalized vector with respect to the uniform distribution on the unit sphere. The associated a-anisotropic norm of a matrix is then its maximum root mean square or average energy gain with respect to finite power or directionally generic inputs whose anisotropy is bounded above by a≥0. We give a systematic comparison of the anisotropy functionals and the associated norms. These are considered for unboundedly growing fragments of homogeneous Gaussian random fields on multidimensional integer lattice to yield mean anisotropy. Correspondingly, the anisotropic norms of finite matrices are extended to bounded linear translation invariant operators over such fields.

  20. Contribution of individual interfaces in the MgO/Co/Pd trilayer to perpendicular magnetic anisotropy upon annealing

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Minseok; Kim, Sanghoon; Ko, Jungho; Hong, Jongill, E-mail: [Materials Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of)


    The contribution of each interface of the MgO/Co/Pd trilayer to the perpendicular magnetic anisotropy (PMA) was studied by changing chemical and crystalline structures through annealing. We found that volumetric anisotropy in the MgO/Co/Pd trilayer was significantly increased due to enhanced magnetoelastic anisotropy caused by stress built up most likely at the MgO/Co interface during annealing. When the trilayer was annealed at 400 °C, the alloy formation at the Co/Pd interface additionally increased the volumetric anisotropy. Our x-ray magnetic circular dichroism study supported that those structural modifications led to an increase in the orbital moment through spin-orbit coupling (SOC) along the film normal two times larger than that of the as-deposited trilayer, thereby enhancing PMA greatly. Our experimental results prove that the Co/Pd interface, rather than the MgO/Co interface, plays an essential role in inducing strong PMA in the trilayer. The precise investigation of annealing effect on both volumetric and interfacial anisotropies can provide a methodological solution to improve the SOC of the trilayer that can serve as the core unit of spintronic devices.

  1. Evidence for Noachian flood volcanism in Noachis Terra, Mars, and the possible role of Hellas impact basin tectonics (United States)

    Rogers, A. D.; Nazarian, A. H.


    Spectral and imaging data sets from Mars Reconnaissance Orbiter and Mars Odyssey, as well as spectral and topographic data from Mars Global Surveyor, are used to understand the origin of in-place rock units found in the intercrater plains and Hellas circumferential graben floors of Noachis Terra, Mars. The rocky units are interpreted as effusive volcanic plains on the basis of broad areal extent, structural competence, association with topographic lows, distinct mineralogy from regolith, and lack of sedimentary textures or minerals associated with aqueous processes. Some rocky expanses contain at least two compositionally distinct units. The relatively light-toned unit exhibits a higher plagioclase/pyroxene ratio than the lower, dark-toned unit. Both units exhibit ~10% olivine enrichment compared to surrounding regolith. These units are heavily degraded and exhibit crater model ages between ~3.80 and 4.0 Ga, making these some of the oldest preserved volcanic plains accessible by remote sensing. They are found in association with Hellas ring structures, where the westward extent of these rocky units is limited to the outermost ring structure. Fracturing associated with the Hellas impact may have enabled magmas to ascend from the base of the crust in the circum-Hellas region. Identification of these units as volcanic materials extends previous estimates for volume of outgassed volatiles. Though the estimated volcanic volume increase is minor, the local effects could have been significant. The role of multi-ring impact basins in providing a spatial control on Martian highlands volcanism and subsurface mineralization may have been underestimated in the past.

  2. The structural architecture of the Los Humeros volcanic complex and geothermal field, Trans-Mexican Volcanic Belt, Central Mexico (United States)

    Norini, Gianluca; Groppelli, Gianluca; Sulpizio, Roberto; Carrasco Núñez, Gerardo; Davila Harris, Pablo


    The development of geothermal energy in Mexico is a very important goal, given the presence of a large heat anomaly, associated with the Trans-Mexican Volcanic Belt, the renewability of the resource and the low environmental impact. The Quaternary Los Humeros volcanic complex is an important geothermal target, whose evolution involved at least two caldera events, that alternated with other explosive and effusive activity. The first caldera forming event was the 460 ka eruption that produced the Xaltipan ignimbrite and formed a 15-20 km wide caldera. The second collapse event occurred 100 ka with the formation of the Zaragoza ignimbrite and a nested 8-10 km wide caldera. The whole volcano structure, the style of the collapses and the exact location of the calderas scarps and ring faults are still a matter of debate. The Los Humeros volcano hosts the productive Los Humeros Geothermal Field, with an installed capacity of 40 MW and additional 75 MW power plants under construction. Recent models of the geothermal reservoir predict the existence of at least two reservoirs in the geothermal system, separated by impermeable rock units. Hydraulic connectivity and hydrothermal fluids circulation occurs through faults and fractures, allowing deep steam to ascend while condensate flows descend. As a consequence, the plans for the exploration and exploitation of the geothermal reservoir have been based on the identification of the main channels for the circulation of hydrothermal fluids, constituted by faults, so that the full comprehension of the structural architecture of the caldera is crucial to improve the efficiency and minimize the costs of the geothermal field operation. In this study, we present an analysis of the Los Humeros volcanic complex focused on the Quaternary tectonic and volcanotectonics features, like fault scarps and aligned/elongated monogenetic volcanic centres. Morphostructural analysis and field mapping reveal the geometry, kinematics and dynamics of

  3. Role of volcanism in climate and evolution

    Energy Technology Data Exchange (ETDEWEB)

    Axelrod, D.I.


    Several major episodes of Tertiary explosive volcanism coincided with sharply lowered temperature as inferred from oxygen-isotope composition of foraminiferal tests in deep-sea cores. At these times, fossil floras in the western interior recorded significant changes. Reductions in taxa that required warmth occurred early in the Paleogene. Later, taxa that demand ample summer rain were reduced during a progressive change reflecting growth of the subtropic high. Other ecosystem changes that appear to have responded to volcanically induced climatic modifications include tachytely in Equidae (12 to 10 m.y. B.P.), rapid evolution of grasses (7 to 5 m.y. B.P.), evolution of marine mammals, and plankton flucuations. Although Lake Cretaceous extinctions commenced as epeiric seas retreated, the pulses of sharply lowered temperature induced by explosive volcanism, together with widespread falls of volcanic ash, may have led to extinction of dinosaurs, ammonites, cycadeoids, and other Cretaceous taxa. earlier, as Pangaea was assembled, Permian extinctions resulted not only from the elimination of oceans, epeiric seas, and shorelines, and the spread of more-continental climates, bu also from the climatic effects of major pulses of global volcanism and Gondwana glaciation.

  4. Volcanic activity: a review for health professionals. (United States)

    Newhall, C G; Fruchter, J S


    Volcanoes erupt magma (molten rock containing variable amounts of solid crystals, dissolved volatiles, and gas bubbles) along with pulverized pre-existing rock (ripped from the walls of the vent and conduit). The resulting volcanic rocks vary in their physical and chemical characteristics, e.g., degree of fragmentation, sizes and shapes of fragments, minerals present, ratio of crystals to glass, and major and trace elements composition. Variability in the properties of magma, and in the relative roles of magmatic volatiles and groundwater in driving an eruption, determine to a great extent the type of an eruption; variability in the type of an eruption in turn influences the physical characteristics and distribution of the eruption products. The principal volcanic hazards are: ash and larger fragments that rain down from an explosion cloud (airfall tephra and ballistic fragments); flows of hot ash, blocks, and gases down the slopes of a volcano (pyroclastic flows); "mudflows" (debris flows); lava flows; and concentrations of volcanic gases in topographic depressions. Progress in volcanology is bringing improved long- and short-range forecasts of volcanic activity, and thus more options for mitigation of hazards. Collaboration between health professionals and volcanologists helps to mitigate health hazards of volcanic activity.

  5. Recurrence rate and magma effusion rate for the latest volcanism on Arsia Mons, Mars (United States)

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


    Magmatism and volcanism have evolved the Martian lithosphere, surface, and climate throughout the history of Mars. Constraining the rates of magma generation and timing of volcanism on the surface clarifies the ways in which magma and volcanic activity have shaped these Martian systems. The ages of lava flows on other planets are often estimated using impact crater counts, assuming that the number and size-distribution of impact craters per unit area reflect the time the lava flow has been on the surface and exposed to potential impacts. Here we show that impact crater age model uncertainty is reduced by adding stratigraphic information observed at locations where neighboring lavas abut each other, and demonstrate the significance of this reduction in age uncertainty for understanding the history of a volcanic field comprising 29 vents in the 110-km-diameter caldera of Arsia Mons, Mars. Each vent within this caldera produced lava flows several to tens of kilometers in length; these vents are likely among the youngest on Mars, since no impact craters in their lava flows are larger than 1 km in diameter. First, we modeled the age of each vent with impact crater counts performed on their corresponding lava flows and found very large age uncertainties for the ages of individual vents, often spanning the estimated age for the entire volcanic field. The age model derived from impact crater counts alone is broad and unimodal, with estimated peak activity in the field around 130 Ma. Next we applied our volcano event age model (VEAM), which uses a directed graph of stratigraphic relationships and random sampling of the impact crater age determinations to create alternative age models. Monte Carlo simulation was used to create 10,000 possible vent age sets. The recurrence rate of volcanism is calculated for each possible age set, and these rates are combined to calculate the median recurrence rate of all simulations. Applying this approach to the 29 volcanic vents, volcanism

  6. Reorientation of magnetic anisotropy in obliquely sputtered metallic thin films

    NARCIS (Netherlands)

    Lisfi, A.; Lodder, J.C.; Wormeester, H.; Poelsema, B.


    Reorientation in the magnetic anisotropy as a function of film thickness has been observed in Co-Ni and Co thin films, obliquely sputtered on a polyethylene terephthalate substrate at a large incidence angle (70°). This effect is a consequence of the low magnetocrystalline anisotropy of the films (f

  7. Tuning the Magnetic Anisotropy at a Molecule-Metal Interface

    DEFF Research Database (Denmark)

    Bairagi, K.; Bellec, A.; Repain, V.


    We demonstrate that a C60 overlayer enhances the perpendicular magnetic anisotropy of a Co thin film, inducing an inverse spin reorientation transition from in plane to out of plane. The driving force is the C60/Co interfacial magnetic anisotropy that we have measured quantitatively in situ...

  8. Effects of Surface Anisotropy on Magnetic Vortex Core


    Pylypovskyi, Oleksandr V.; Sheka, Denis D.; Kravchuk, Volodymyr P.; Gaididei, Yuri


    The vortex core shape in the three dimensional Heisenberg magnet is essentially influenced by a surface anisotropy. We predict that depending of the surface anisotropy type there appears barrel- or pillow-shaped deformation of the vortex core along the magnet thickness. Our theoretical study is well confirmed by spin-lattice simulations.


    Energy Technology Data Exchange (ETDEWEB)

    Esquivel, A. [Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Apartado Postal 70-543, 04510 México D.F., México (Mexico); Lazarian, A. [Astronomy Department, University of Wisconsin–Madison, 475 N. Charter Street, Madison, WI (United States); Pogosyan, D., E-mail:, E-mail:, E-mail: [Physics Department, University of Alberta, Edmonton, AB (Canada)


    Turbulence in the interstellar medium is anisotropic due to the ubiquitous magnetic fields. This anisotropy depends on the strength of the magnetic field and leaves an imprint on observations of spectral line maps. We use a grid of ideal magnetohydrodynamic simulations of driven turbulence and produce synthetic position–position–velocity maps to study the turbulence anisotropy in velocity channels of various resolutions. We found that the average structure function of velocity channels is aligned with the projection of the magnetic field on the plane of the sky. We also found that the degree of such anisotropy increases with the magnitude of the magnetic field. For thick velocity channels (low velocity resolution), the anisotropy is dominated by density, and the degree of anisotropy in these maps allows one to distinguish sub-Alfvénic and super-Alfvénic turbulence regimes, but it also depends strongly on the sonic Mach number. For thin channels (high velocity resolution), we find that the anisotropy depends less on the sonic Mach number. An important limitation of this technique is that it only gives a lower limit on the magnetic field strength because the anisotropy is related only to the magnetic field component on the plane of the sky. It can, and should, be used in combination with other techniques to estimate the magnetic field, such as the Fermi-Chandrasekhar method, anisotropies in centroids, Faraday rotation measurements, or direct line-of-sight determinations of the field from Zeeman effect observations.

  10. Anisotropy Spectra for Enantiomeric Differentiation of Biomolecular Building Blocks

    DEFF Research Database (Denmark)

    Evans, Amanda C.; Meinert, Cornelia; Bredehoft, Jan H.;


    light. This chapter will: (1) present the theory and configuration of anisotropy spectroscopy; (2) explain experimentally recorded anisotropy spectra of selected chiral biomolecules such as amino acids; and (3) discuss the relevance of these spectra for the investigation of the origin of the molecular...

  11. National volcanic ash operations plan for aviation (United States)

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    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

  12. CMB statistical anisotropy from noncommutative gravitational waves

    Energy Technology Data Exchange (ETDEWEB)

    Shiraishi, Maresuke; Ricciardone, Angelo [Dipartimento di Fisica e Astronomia ' ' G. Galilei' ' , Università degli Studi di Padova, via Marzolo 8, I-35131, Padova (Italy); Mota, David F. [Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315 Oslo (Norway); Arroja, Frederico, E-mail:, E-mail:, E-mail:, E-mail: [INFN, Sezione di Padova, via Marzolo 8, I-35131, Padova (Italy)


    Primordial statistical anisotropy is a key indicator to investigate early Universe models and has been probed by the cosmic microwave background (CMB) anisotropies. In this paper, we examine tensor-mode CMB fluctuations generated from anisotropic gravitational waves, parametrised by P{sub h}(k) = P{sub h}{sup (0)}(k) [ 1 + ∑{sub LM} f{sub L}(k) g{sub LM} Y{sub LM} ( k-circumflex )], where P{sub h}{sup (0)}(k) is the usual scale-invariant power spectrum. Such anisotropic tensor fluctuations may arise from an inflationary model with noncommutativity of fields. It is verified that in this model, an isotropic component and a quadrupole asymmetry with f{sub 0}(k) = f{sub 2}(k) ∝ k{sup -2} are created and hence highly red-tilted off-diagonal components arise in the CMB power spectra, namely ℓ{sub 2} = ℓ{sub 1} ± 2 in TT, TE, EE and BB, and ℓ{sub 2} = ℓ{sub 1} ± 1 in TB and EB. We find that B-mode polarisation is more sensitive to such signals than temperature and E-mode polarisation due to the smallness of large-scale cosmic variance and we can potentially measure g{sub 00} = 30 and g{sub 2M} = 58 at 68% CL in a cosmic-variance-limited experiment. Such a level of signal may be measured in a PRISM like experiment, while the instrumental noise contaminates it in the Planck experiment. These results imply that it is impossible to measure the noncommutative parameter if it is small enough for the perturbative treatment to be valid. Our formalism and methodology for dealing with the CMB tensor statistical anisotropy are general and straightforwardly applicable to other early Universe models.

  13. Ozone depletion following future volcanic eruptions (United States)

    Eric Klobas, J.; Wilmouth, David M.; Weisenstein, Debra K.; Anderson, James G.; Salawitch, Ross J.


    While explosive volcanic eruptions cause ozone loss in the current atmosphere due to an enhancement in the availability of reactive chlorine following the stratospheric injection of sulfur, future eruptions are expected to increase total column ozone as halogen loading approaches preindustrial levels. The timing of this shift in the impact of major volcanic eruptions on the thickness of the ozone layer is poorly known. Modeling four possible climate futures, we show that scenarios with the smallest increase in greenhouse gas concentrations lead to the greatest risk to ozone from heterogeneous chemical processing following future eruptions. We also show that the presence in the stratosphere of bromine from natural, very short-lived biogenic compounds is critically important for determining whether future eruptions will lead to ozone depletion. If volcanic eruptions inject hydrogen halides into the stratosphere, an effect not considered in current ozone assessments, potentially profound reductions in column ozone would result.

  14. Time-related variation of volatile contents of Western Ghats volcanic formations, Deccan, India (United States)

    Marzoli, Andrea; Callegaro, Sara; Baker, Don R.; De Min, Angelo; Renne, Paul R.


    Deccan volcanism in India covered more than 1 million square km and reached a maximum thickness of about 3 km, as presently preserved in the Western Ghats volcanic lava piles. Volcanic activity started at about 66.4 Ma (Jawhar formation) and ended at about 65.5 Ma (Mahabaleshwar unit; Renne et al., 2015). Deccan volcanism straddled the Cretaceous-Paleogene boundary (ca. 66.0 Ma) and possibly contributed to the end-Cretaceous mass extinction event through emission of gases such as SO2, CO2, Cl, F that may have triggered global climate changes. Severe pollution by volcanic gases is supported by the high S and Cl contents (up to 1400 and up to 900 ppm, respectively; Self et al., 2008) measured in a few olivine- and plagioclase-hosted melt inclusions from the Jawhar, Neral, and Thakurvadi Formations (early lava flows, ca. 66.3-66.4 ± 0.1 Ma; Renne et al., 2015) and by magmatic S contents (up to 1800 ppm; Callegaro et al., 2014) calculated from S measurements in clinopyroxenes from the Mahabaleshwar unit (ca. 65.5 ± 0.1; Schoene et al., 2015). Here, we present new analyses of S, Cl, and F, obtained by ion-probe and synchrotron light micro-fluorescence analyses on clinopyroxenes and plagioclase phenocrysts from ?al? lava flow units of the Western Ghats. The volatile contents of the host magmas have been calculated from recently published clinopyroxene/basalt partition coefficients. These new data will describe the time-related variation of volatile elements hosted and eventually emitted by Deccan lavas and shed light on their environmental impact. References: Callegaro S. et al. (2014). Geology 42, 895-898. Renne P.R. et al. (2015). Science 350, 76-78. Schoene B. et al. (2015). Science 347, 192-184. Self S. et al. (2008). Science 319, 1654-1657.

  15. Carrier-dependent magnetic anisotropy of Gd-adsorbed graphene (United States)

    Lu, Yuan; Zhou, Tie-ge; Shao, Bin; Zuo, Xu; Feng, Min


    Using first-principles calculation based on density functional theory, we study the magnetic anisotropy of Gd-adsorbed graphene and its dependence on carrier accumulation. We show that carrier accumulation not only impacts the magnitude of magnetic anisotropy but also switches its sign. Hole accumulation enhances the perpendicular anisotropy up to ˜16 meV per Gd atom, while electron accumulation switches the anisotropy from perpendicular to in-plane direction. Moreover, we find that the first order perturbation of spin-orbit coupling interaction induces a pseudo-gap at Γ for the perpendicular magnetization, which leads to the the anomalous magnetic anisotropy for the neutral composite. Our findings pave the way for magneto-electric materials based on rare-earth-decorated graphene for voltage-controlled spintronics.

  16. Tuning the Magnetic Anisotropy at a Molecule-Metal Interface. (United States)

    Bairagi, K; Bellec, A; Repain, V; Chacon, C; Girard, Y; Garreau, Y; Lagoute, J; Rousset, S; Breitwieser, R; Hu, Yu-Cheng; Chao, Yen Cheng; Pai, Woei Wu; Li, D; Smogunov, A; Barreteau, C


    We demonstrate that a C(60) overlayer enhances the perpendicular magnetic anisotropy of a Co thin film, inducing an inverse spin reorientation transition from in plane to out of plane. The driving force is the (60)/Co interfacial magnetic anisotropy that we have measured quantitatively in situ as a function of the (60) coverage. Comparison with state-of-the-art ab initio calculations show that this interfacial anisotropy mainly arises from the local hybridization between (60) p(z) and Co d(z(2)) orbitals. By generalizing these arguments, we also demonstrate that the hybridization of (60) with a Fe(110) surface decreases the perpendicular magnetic anisotropy. These results open the way to tailor the interfacial magnetic anisotropy in organic-material-ferromagnet systems.

  17. Carrier-dependent magnetic anisotropy of Gd-adsorbed graphene

    Directory of Open Access Journals (Sweden)

    Yuan Lu


    Full Text Available Using first-principles calculation based on density functional theory, we study the magnetic anisotropy of Gd-adsorbed graphene and its dependence on carrier accumulation. We show that carrier accumulation not only impacts the magnitude of magnetic anisotropy but also switches its sign. Hole accumulation enhances the perpendicular anisotropy up to ∼16 meV per Gd atom, while electron accumulation switches the anisotropy from perpendicular to in-plane direction. Moreover, we find that the first order perturbation of spin-orbit coupling interaction induces a pseudo-gap at Γ for the perpendicular magnetization, which leads to the the anomalous magnetic anisotropy for the neutral composite. Our findings pave the way for magneto-electric materials based on rare-earth-decorated graphene for voltage-controlled spintronics.

  18. Perpendicular magnetic anisotropy of Co85Cr15/Pt multilayers

    Institute of Scientific and Technical Information of China (English)

    Pol Hwang; Baohe Li; Tao Yang; Zhonghai Zhai; Fengwu Zhu


    The CoCr/Pt bilayers and (CoCr/Pt)20 multilayers with Pt underlayer were prepared by DC magnetron sputtering. The effects of prepared condition on perpendicular magnetic anisotropy were investigated. The results show that the thickness of Pt underlayer has a great effect on the microstructure and perpendicular magnetic anisotropy of CoCr/Pt bilayers and (CoCr/Pt)20 multilayers.When the thickness of Pt underlayer increases, Pt(111) and CoCr(002) peaks of both CoCr/Pt bilayers and (CoCr/Pt)20 multilayers increase and the bilayer periodicity of the multilayers is improved. The effective magnetic anisotropy of (CoCr/Pt)20 multilayers with Pt underlayer was much larger than that of CoCr/Pt bilayers. The (CoCr/Pt)20 multilayers has a stronger perpendicular magnetic anisotropy than that of CoCr/Pt bilayers. This is ascribed to the interface magnetic anisotropy of the multilayers.

  19. Tropical Volcanic Soils From Flores Island, Indonesia

    Directory of Open Access Journals (Sweden)



    Full Text Available Soils that are developed intropical region with volcanic parent materials have many unique properties, and high potential for agricultural use.The purpose of this study is to characterize the soils developed on volcanic materials from Flores Island, Indonesia,and to examine if the soils meet the requirements for andic soil properties. Selected five soils profiles developed fromandesitic volcanic materials from Flores Island were studied to determine their properties. They were compared intheir physical, chemical and mineralogical characteristics according to their parent material, and climatic characteristicdifferent. The soils were developed under humid tropical climate with ustic to udic soil moisture regimes withdifferent annual rainfall. The soils developed from volcanic ash parent materials in Flores Island showed differentproperties compared to the soils derived from volcanic tuff, even though they were developed from the sameintermediary volcanic materials. The silica contents, clay mineralogy and sand fractions, were shown as the differences.The different in climatic conditions developed similar properties such as deep solum, dark color, medium texture, andvery friable soil consistency. The soils have high organic materials, slightly acid to acid, low to medium cationexchange capacity (CEC. The soils in western region have higher clay content and showing more developed than ofthe eastern region. All the profiles meet the requirements for andic soil properties, and classified as Andisols order.The composition of sand mineral was dominated by hornblende, augite, and hypersthenes with high weatherablemineral reserves, while the clay fraction was dominated by disordered kaolinite, and hydrated halloysite. The soilswere classified into subgroup as Thaptic Hapludands, Typic Hapludands, and Dystric Haplustands

  20. Ages of plains volcanism on Mars (United States)

    Hauber, Ernst; Jagert, Felix; Broz, Petr


    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 (Ga - 2.9 Ga). Our results indicate that Late Amazonian volcanism is more widespread in Tharsis than previously recognized. Based on our results it appears possible that Mars is volcanologically not dead yet. Ongoing work investigates the volumes of erupted products and implications for the outgassing history and atmospheric evolution of Mars. [1] Greeley R. (1982) JGR 87, 2705-2712. [2] Plescia 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.

  1. The role of phreatomagmatism in a Plio-Pleistocene high-density scoria cone field: Llancanelo Volcanic Field (Mendoza), Argentina (United States)

    Risso, Corina; Németh, Károly; Combina, Ana María; Nullo, Francisco; Drosina, Marina


    The Plio-Pleistocene Llancanelo Volcanic Field, together with the nearby Payun Matru Field, comprises at least 800 scoria cones and voluminous lava fields that cover an extensive area behind the Andean volcanic arc. Beside the scoria cones in the Llancanelo Field, at least six volcanoes show evidence for explosive eruptions involving magma-water interaction. These are unusual in the context of the semi-arid climate of the eastern Andean ranges. The volcanic structures consist of phreatomagmatic-derived tuff rings and tuff cones of olivine basalt composition. Malacara and Jarilloso tuff cones were produced by fallout of a range of dry to wet tephra. The Malacara cone shows more evidence for a predominance of wet-emplaced units, with a steep slump-slope characterized by many soft-sediment deformation structures, such as: undulating bedding planes, truncated beds and water escape features. The Piedras Blancas and Carapacho tuff rings resulted from explosive eruptions with deeper explosion loci. These cones are hence dominated by lapilli tuff and tuff units, emplaced mainly by wet and/or dry pyroclastic surges. Carapacho is the only centre that appears to have started with phreatomagmatic eruptions, with lowermost tephra being rich in non-volcanic country rocks. The presence of deformed beds with impact sags, slumping textures, asymmetrical ripples, dunes, cross- and planar lamination, syn-volcanic faulting and accretionary lapilli beds indicate an eruption scenario dominated by excessive water in the transportational and depositional regime. This subordinate phreatomagmatism in the Llancanelo Volcanic Field suggests presence of ground and/or shallow surface water during some of the eruptions. Each of the tuff rings and cones are underlain by thick, fractured multiple older lava units. These broken basalts are inferred to be the horizons where rising magma interacted with groundwater. The strong palagonitization at each of the phreatomagmatic cones formed hard beds

  2. Hydrogeomorphic effects of explosive volcanic eruptions on drainage basins (United States)

    Pierson, Thomas C.; Major, Jon J.


    Explosive eruptions can severely disturb landscapes downwind or downstream of volcanoes by damaging vegetation and depositing large volumes of erodible fragmental material. As a result, fluxes of water and sediment in affected drainage basins can increase dramatically. System-disturbing processes associated with explosive eruptions include tephra fall, pyroclastic density currents, debris avalanches, and lahars—processes that have greater impacts on water and sediment discharges than lava-flow emplacement. Geo-morphic responses to such disturbances can extend far downstream, persist for decades, and be hazardous. The severity of disturbances to a drainage basin is a function of the specific volcanic process acting, as well as distance from the volcano and magnitude of the eruption. Postdisturbance unit-area sediment yields are among the world's highest; such yields commonly result in abundant redeposition of sand and gravel in distal river reaches, which causes severe channel aggradation and instability. Response to volcanic disturbance can result in socioeconomic consequences more damaging than the direct impacts of the eruption itself.

  3. Statistical anisotropy in the inflationary universe

    CERN Document Server

    Shtanov, Yuri


    During cosmological inflation, quasiclassical perturbations are permanently generated on super-Hubble spatial scales, their power spectrum being determined by the fundamental principles of quantum field theory. By the end of inflation, they serve as primeval seeds for structure formation in the universe. At early stages of inflation, such perturbations break homogeneity and isotropy of the inflationary background. In the present paper, we perturbatively take into account this quasiclassical background inhomogeneity of the inflationary universe while considering the evolution of small-scale (sub-Hubble) quantum modes. As a result, the power spectrum of primordial perturbations develops statistical anisotropy, which can subsequently manifest itself in the large-scale structure and cosmic microwave background. The statistically anisotropic contribution to the primordial power spectrum is predicted to have almost scale-invariant form dominated by a quadrupole. Theoretical expectation of the magnitude of this anis...

  4. Texture-induced microwave background anisotropies

    Energy Technology Data Exchange (ETDEWEB)

    Borrill, J.; Copeland, E.J.; Liddle, A.R.; Stebbins, A.; Veeraraghavan, S. (School of Mathematical and Physical Sciences, University of Sussex, Falmer, Brighton BN1 9QH (United Kingdom) Blackett Laboratory, Imperial College of Science and Technology, Prince Consort Road, London SW7 2BZ (United Kingdom) NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laoratory, Batavia, Illinois 60510 (United States) NASA Goddard Space Flight Center, Code 685, Greenbelt, Maryland 20771 (United States) Steward Observatory, University of Arizona, Tucson, Arizona 85721 (United States))


    We use numerical simulations to calculate the cosmic microwave background anisotropy induced by the evolution of a global texture field, with special emphasis on individual textures. Both spherically symmetric and general configurations are analyzed, and in the latter case we consider field configurations which exhibit unwinding events and also ones which do not. We compare the results given by evolving the field numerically under both the expanded core (XCORE) and nonlinear [sigma] model (NLSM) approximations with the analytic predictions of the NLSM exact solution for a spherically symmetric self-similar (SSSS) unwinding. We find that the random unwinding configuration spots' typical peak height is 60--75 % and angular size typically only 10% of those of the SSSS unwinding, and that random configurations without an unwinding event nonetheless may generate indistinguishable hot and cold spots. A brief comparison is made with other work.

  5. Anisotropy of light propagation in human skin (United States)

    Nickell, Stephan; Hermann, Marcus; Essenpreis, Matthias; Farrell, Thomas J.; Krämer, Uwe; Patterson, Michael S.


    Using spatially resolved, steady state diffuse reflectometry, a directional dependence was found in the propagation of visible and near infrared light through human skin in vivo. The skin's reduced scattering coefficient µ's varies by up to a factor of two between different directions of propagation at the same position. This anisotropy is believed to be caused by the preferential orientation of collagen fibres in the dermis, as described by Langer's skin tension lines. Monte Carlo simulations that examine the effect of partial collagen fibre orientation support this hypothesis. The observation has consequences for non-invasive diagnostic methods relying on skin optical properties, and it could be used non-invasively to determine the direction of lines of cleavage in order to minimize scars due to surgical incisions.

  6. Rational approach to anisotropy of sand (United States)

    Wu, Wei


    The paper presents a constitutive model for the three-dimensional deformation-strength behaviour of inherently anisotropic sand. Based on non-linear tensorial functions, the model is developed without recourse to the concepts in plasticity theory such as yield surface and plastic potential. Benefited from the fact that no decomposition of strain into elastic and plastic parts is assumed, a unified treatment of anisotropic behaviour of deformation and strength is achieved. Anisotropy is characterized by a vector normal to the bedding plane. The extension of the constitutive model is furnished by incorporating the vector under consideration of the principle of objectivity and the condition of material symmetry. Distinct features of the model are its elegant formulation and its simple structure involving few material parameters. Model performance and comparison with experiments show that the model is capable of capturing the salient behaviour of anisotropic sand.

  7. PAPPA: Primordial Anisotropy Polarization Pathfinder Array

    CERN Document Server

    Kogut, A; Fixsen, D; Hinshaw, G F; Limon, M; Moseley, S H; Phillips, N; Sharp, E; Wollack, E J; U-Yen, K; Cao, N; Stevenson, T; Hsieh, W; Devlin, M; Dicker, S; Semisch, C; Irwin, K


    The Primordial Anisotropy Polarization Pathfinder Array (PAPPA) is a balloon-based instrument to measure the polarization of the cosmic microwave background and search for the signal from gravity waves excited during an inflationary epoch in the early universe. PAPPA will survey a 20 x 20 deg patch at the North Celestial Pole using 32 pixels in 3 passbands centered at 89, 212, and 302 GHz. Each pixel uses MEMS switches in a superconducting microstrip transmission line to combine the phase modulation techniques used in radio astronomy with the sensitivity of transition-edge superconducting bolometers. Each switched circuit modulates the incident polarization on a single detector, allowing nearly instantaneous characterization of the Stokes I, Q, and U parameters. We describe the instrument design and status.

  8. Pseudo exchange bias due to rotational anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Ehrmann, A., E-mail: [Faculty of Engineering and Mathematics, Bielefeld University of Applied Sciences, 33619 Bielefeld (Germany); Komraus, S.; Blachowicz, T.; Domino, K. [Institute of Physics – Center for Science and Education, Silesian University of Technology, 44-100 Gliwice (Poland); Nees, M.K.; Jakobs, P.J.; Leiste, H. [Karlsruhe Nano Micro Facility (KNMF), Karlsruhe Institute of Technology (KIT), 76344 Eggenstein-Leopoldshafen (Germany); Mathes, M.; Schaarschmidt, M. [ACCESS e. V., 57072 Aachen (Germany)


    Ferromagnetic nanostructure arrays with particle dimensions between 160 nm and 400 nm were created by electron-beam lithography. The permalloy structures consist of rectangular-shaped walls around a square open space. While measuring their magnetic properties using the Magneto-Optical Kerr Effect (MOKE), in some angular regions an exchange bias (EB) seemed to appear. This paper gives an overview of possible reasons for this “pseudo exchange bias” and shows experimentally and by means of micromagnetic simulations that this effect can be attributed to unintentionally measuring minor loops. - Highlights: • Pseudo exchange bias can be found in square Py nanorings of different dimensions. • Pseudo exchange bias stems from unintentionally measuring minor loops. • New approach in explaining “real” exchange bias effect in coupled FM/AFM systems. • Theoretical base to explain other measurements of a rotational anisotropy.

  9. CMB Anisotropies from a Gradient Mode

    CERN Document Server

    Mirbabayi, Mehrdad


    A pure gradient mode must have no observable dynamical effect at linear level. We confirm this by showing that its contribution to the dipolar power asymmetry of CMB anisotropies vanishes, if Maldacena's consistency condition is satisfied. To this end, the existing second order Sachs-Wolfe formula in the squeezed limit is extended to include a gradient in the long mode and to account for the change in the location of the last scattering surface induced by this mode. At second order, a gradient mode generated in Single-field inflation is shown to induce a quadrupole moment. For instance in a matter-dominated model it is equal to 5/18 times the square of the linear gradient part. This quadrupole can be cancelled by superposing a quadratic perturbation. The result is shown to be a non-linear extension of Weinberg's adiabatic modes: a long-wavelength physical mode which looks locally like a coordinate transformation.

  10. Constraining the onset of flood volcanism in Isle of Skye Lava Field, British Paleogene Volcanic Province (United States)

    Angkasa, Syahreza; Jerram, Dougal. A.; Svensen, Henrik; Millet, John M.; Taylor, Ross; Planke, Sverre


    In order to constrain eruption styles at the onset of flood volcanism, field observations were undertaken on basal sections of the Isle of Skye Lava Field, British Paleogene Volcanic Province. This study investigates three specific sections; Camus Ban, Neist Point and Soay Sound which sample a large area about 1500 km2 and can be used to help explain the variability in palaeo-environments at the onset of flood volcanism. Petrological analysis is coupled with petrophysical lab data and photogrammetry data to create detailed facies models for the different styles of initiating flood basalt volcanism. Photogrammetry is used to create Ortho-rectified 3D models which, along with photomontage images, allow detailed geological observations to be mapped spatially. Petrographic analyses are combined with petrophysical lab data to identify key textural variation, mineral compositions and physical properties of the volcanic rocks emplaced during the initial eruptions. Volcanism initiated with effusive eruptions in either subaerial or subaqueous environments resulting in tuff/hyaloclastite materials or lava flow facies lying directly on the older Mesozoic strata. Volcanic facies indicative of lava-water interactions vary significantly in thickness between different sections suggesting a strong accommodation space control on the style of volcanism. Camus Ban shows hyaloclastite deposits with a thickness of 25m, whereas the Soay Sound area has tuffaceous sediments of under 0.1m in thickness. Subaerial lavas overly these variable deposits in all studied areas. The flood basalt eruptions took place in mixed wet and dry environments with some significant locally developed water bodies (e.g. Camus Ban). More explosive eruptions were promoted in some cases by interaction of lavas with these water bodies and possibly by local interaction with water - saturated sediments. We record key examples of how palaeotopography imparts a primary control on the style of volcanism during the

  11. Volcanic Pipe of the Namuaiv Mountain

    Directory of Open Access Journals (Sweden)

    Vladimir K. Karzhavin


    Full Text Available This research was aimed at reconstructing thermodynamic conditions required for the studied mineral assemblages to be created and exist in nature. The results of the investigations confirm to the recent ideas about an important, even leading, role of temperature, pressure and dioxide carbon in diamond formation in volcanic pipers. The results of this theoretical research allows assuming that one of the reasons for the absence of diamonds in the Namuaiv Mountain volcanic pipe may lie in the increased content of water and oxidizing environmental conditions of their formation

  12. Volcanic Eruptions and Climate: Outstanding Research Issues (United States)

    Robock, Alan


    Large volcanic eruptions inject sulfur gases into the stratosphere, which convert to sulfate aerosols with an e-folding residence time of about one year. The radiative and chemical effects of this aerosol cloud produce responses in the climate system. Based on observations after major eruptions of the past and experiments with numerical models of the climate system, we understand much about their climatic impact, but there are also a number of unanswered questions. Volcanic eruptions produce global cooling, and are an important natural cause of interannual, interdecadal, and even centennial-scale climate change. One of the most interesting volcanic effects is the "winter warming" of Northern Hemisphere continents following major tropical eruptions. During the winter in the Northern Hemisphere following every large tropical eruption of the past century, surface air temperatures over North America, Europe, and East Asia were warmer than normal, while they were colder over Greenland and the Middle East. This pattern and the coincident atmospheric circulation correspond to the positive phase of the Arctic Oscillation. While this response is observed after recent major eruptions, most state-of-the-art climate models have trouble simulating winter warming. Why? High latitude eruptions in the Northern Hemisphere, while also producing global cooling, do not have the same impact on atmospheric dynamics. Both tropical and high latitude eruptions can weaken the Indian and African summer monsoon, and the effects can be seen in past records of flow in the Nile and Niger Rivers. Since the Mt. Pinatubo eruption in the Philippines in 1991, there have been no large eruptions that affected climate, but the cumulative effects of small eruptions over the past decade have had a small effect on global temperature trends. Some important outstanding research questions include: How much seasonal, annual, and decadal predictability is possible following a large volcanic eruption? Do

  13. Tellurium in active volcanic environments: Preliminary results (United States)

    Milazzo, Silvia; Calabrese, Sergio; D'Alessandro, Walter; Brusca, Lorenzo; Bellomo, Sergio; Parello, Francesco


    Tellurium is a toxic metalloid and, according to the Goldschmidt classification, a chalcophile element. In the last years its commercial importance has considerably increased because of its wide use in solar cells, thermoelectric and electronic devices of the last generation. Despite such large use, scientific knowledge about volcanogenic tellurium is very poor. Few previous authors report result of tellurium concentrations in volcanic plume, among with other trace metals. They recognize this element as volatile, concluding that volcanic gases and sulfur deposits are usually enriched with tellurium. Here, we present some results on tellurium concentrations in volcanic emissions (plume, fumaroles, ash leachates) and in environmental matrices (soils and plants) affected by volcanic emissions and/or deposition. Samples were collected at Etna and Vulcano (Italy), Turrialba (Costa Rica), Miyakejima, Aso, Asama (Japan), Mutnovsky (Kamchatka) at the crater rims by using common filtration techniques for aerosols (polytetrafluoroethylene filters). Filters were both eluted with Millipore water and acid microwave digested, and analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Volcanic ashes emitted during explosive events on Etna and Copahue (Argentina) were analyzed for tellurium bulk composition and after leaching experiments to evaluate the soluble fraction of tellurium. Soils and leaves of vegetation were also sampled close to active volcanic vents (Etna, Vulcano, Nisyros, Nyiragongo, Turrialba, Gorely and Masaya) and investigated for tellurium contents. Preliminary results showed very high enrichments of tellurium in volcanic emissions comparing with other volatile elements like mercury, arsenic, thallium and bismuth. This suggests a primary transport in the volatile phase, probably in gaseous form (as also suggested by recent studies) and/or as soluble salts (halides and/or sulfates) adsorbed on the surface of particulate particles and ashes. First

  14. Emplacement Scenarios for Volcanic Domes on Venus (United States)

    Glaze, Lori S.; Baloga, Steve M.; Stofan, Ellen R.


    One key to understanding the history of resurfacing on Venus is better constraints on the emplacement timescales for the range of volcanic features visible on the surface. A figure shows a Magellan radar image and topography for a putative lava dome on Venus. 175 such domes have been identified with diameters ranging from 19 - 94 km, and estimated thicknesses as great as 4 km. These domes are thought to be volcanic in origin and to have formed by the flow of viscous fluid (i.e., lava) on the surface.

  15. Volcanic air pollution hazards in Hawaii (United States)

    Elias, Tamar; Sutton, A. Jeff


    Noxious sulfur dioxide gas and other air pollutants emitted from Kīlauea Volcano on the Island of Hawai‘i react with oxygen, atmospheric moisture, and sunlight to produce volcanic smog (vog) and acid rain. Vog can negatively affect human health and agriculture, and acid rain can contaminate household water supplies by leaching metals from building and plumbing materials in rooftop rainwater-catchment systems. U.S. Geological Survey scientists, along with health professionals and local government officials are working together to better understand volcanic air pollution and to enhance public awareness of this hazard.

  16. Nanomagnets with high shape anisotropy and strong crystalline anisotropy: perspectives on magnetic force microscopy. (United States)

    Campanella, H; Jaafar, M; Llobet, J; Esteve, J; Vázquez, M; Asenjo, A; del Real, R P; Plaza, J A


    We report on a new approach for magnetic imaging, highly sensitive even in the presence of external, strong magnetic fields. Based on FIB-assisted fabricated high-aspect-ratio rare-earth nanomagnets, we produce groundbreaking magnetic force tips with hard magnetic character where we combine a high aspect ratio (shape anisotropy) together with strong crystalline anisotropy (rare-earth-based alloys). Rare-earth hard nanomagnets are then FIB-integrated to silicon microcantilevers as highly sharpened tips for high-field magnetic imaging applications. Force resolution and domain reversing and recovery capabilities are at least one order of magnitude better than for conventional magnetic tips. This work opens new, pioneering research fields on the surface magnetization process of nanostructures based either on relatively hard magnetic materials-used in magnetic storage media-or on materials like superparamagnetic particles, ferro/antiferromagnetic structures or paramagnetic materials.

  17. Theoretical Compton profile anisotropies in molecules and solids. IV. Parallel--perpendicular anisotropies in alkali fluoride molecules

    Energy Technology Data Exchange (ETDEWEB)

    Matcha, R.L.; Pettitt, B.M.; Ramirez, B.I.; McIntire, W.R.


    Calculations of Compton profiles and parallel--perpendicular anisotropies in alkali fluorides are presented and analyzed in terms of molecular charge distributions and wave function character. It is found that the parallel profile associated with the valence pi orbital is the principal factor determining the relative shapes of the total profile anisotropies in the low momentum region.

  18. Geomagnetic imprint of the Persani volcanism (United States)

    Besutiu, Lucian; Seghedi, Ioan; Zlagnean, Luminita; Atanasiu, Ligia; Popa, Razvan-Gabriel; Pomeran, Mihai; Visan, Madalina


    The Persani small volume volcanism is located in the SE corner of the Transylvanian Depression, at the north-western edge of the intra-mountainous Brasov basin. It represents the south-easternmost segment of the Neogene-Quaternary volcanic chain of the East Carpathians. The alkaline basalt monogenetic volcanic field is partly coeval with the high-K calc-alkaline magmatism south of Harghita Mountains (1-1.6 Ma). Its eruptions post-dated the calc-alkaline volcanism in the Harghita Mountains (5.3-1.6 Ma), but pre-dated the high-K calc-alkaline emissions of Ciomadul volcano (1.0-0.03 Ma). The major volcanic forms have been mapped in previous geological surveys. Still, due to the small size of the volcanoes and large extent of tephra deposits and recent sediments, the location of some vents or other volcanic structures has been incompletely revealed. To overcome this problem, the area was subject to several near-surface geophysical investigations, including paleomagnetic research. However, due to their large-scale features, the previous geophysical surveys proved to be an inappropriate approach to the volcanological issues. Therefore, during the summers of 2014 and 2015, based on the high magnetic contrast between the volcanic rocks and the hosting sedimentary formations, a detailed ground geomagnetic survey has been designed and conducted, within central Persani volcanism area, in order to outline the presence of volcanic structures hidden beneath the overlying deposits. Additionally, information on the rock magnetic properties was also targeted by sampling and analysing several outcrops in the area. Based on the acquired data, a detailed total intensity scalar geomagnetic anomaly map was constructed by using the recent IGRF12 model. The revealed pattern of the geomagnetic field proved to be fully consistent with the direction of magnetisation previously determined on rock samples. In order to enhance the signal/noise ratio, the results were further processed by

  19. Paleomagnetism from Deception Island (South Shetlands archipelago, Antarctica), new insights into the interpretation of the volcanic evolution using a geomagnetic model (United States)

    Oliva-Urcia, B.; Gil-Peña, I.; Maestro, A.; López-Martínez, J.; Galindo-Zaldívar, J.; Soto, R.; Gil-Imaz, A.; Rey, J.; Pueyo, O.


    Deception Island shows the most recent exposed active volcanism in the northern boundary of the Bransfield Trough. The succession of the volcanic sequence in the island is broadly divided into pre- and post-caldera collapse units although a well-constrained chronological identification of the well-defined successive volcanic episodes is still needed. A new paleomagnetic investigation was carried out on 157 samples grouped in 20 sites from the volcanic deposits of Deception Island (South Shetlands archipelago, Antarctic Peninsula region) distributed in: (1) volcanic breccia (3 sites) and lavas (2 sites) prior to the caldera collapse; (2) lavas emplaced after the caldera collapse (10 sites); and (3) dikes cutting pre- and the lowermost post-caldera collapse units (5 sites). The information revealed by paleomagnetism provides new data about the evolution of the multi-episodic volcanic edifice of this Quaternary volcano, suggesting that the present-day position of the volcanic materials is close to their original emplacement position. The new data have been combined with previous paleomagnetic results in order to tentatively propose an age when comparing the paleomagnetic data with a global geomagnetic model. Despite the uncertainties in the use of averaged paleomagnetic data per volcanic units, the new data in combination with tephra occurrences noted elsewhere in the region suggest that the pre-caldera units (F1 and F2) erupted before 12,000 year BC, the caldera collapse took place at about 8300 year BC, and post-caldera units S1 and S2 are younger than 2000 year BC.

  20. Origin of magnetization-induced anisotropy of magnetic films

    Institute of Scientific and Technical Information of China (English)

    Jin Han-Min; Chong-Oh Kim; Taek-Dong Lee; Hyo-Jin Kim


    It is proposed that the magnetization-induced anisotropy of magnetic films of cubic crystal structure originates from the anisotropy of atomic pair ordering, shape anisotropy, and strain anisotropy resulting from the constraint of the magnetostriction strain imposed on the film by the substrate. Calculated are the three anisotropy constants and their sum K vs temperature for Ni, Fe, and 55%Ni-Fe films; the room temperature (RT) constants vs the substrate temperature Tt during deposition or annealing after deposition for Ni and 50%Ni-Co films; the RT constants vs composition fraction for Fe-Ni films with Tt = RT, 250℃ and 450℃, Co-Ni films at Tt = RT, 100℃ and 320℃, and Fe-Co films with Tt = RT and 300℃; the spread of RT K vs composition fraction for Fe-Ni films; and RT △K/K vs composition fraction for Fe-Ni and Co-Ni films, where △K denotes the variation of K of the film that is detached from its substrate. The calculated curves well accord with the measurements. The irrelevancy of K to the substrate material and the fast kinetics of the annealing in a field applied in the direction of the hard axis are explained reasonably.The anisotropies of Fe and Ni films originate mainly from the shape anisotropy and the strain anisotropy, respectively. The major anisotropy component in many cases depends not only on composition fraction but also on Tt . For example, the RT anisotropy of 40-70%Ni-Fe films, when Tt is RT, mostly comes from the anisotropy of atomic pair ordering while it stems mostly from the shape anisotropy when Tt is 450 ℃. The most important cause of the spread in values of K is the spread of the intrinsic anisotropic stresses superimposed on the intrinsic isotropic planar stress. It is suggested that the field cooling induced magnetic anisotropy originating from the induced crystal texture observed in the bulk alloys is also a major origin for Co and Co-rich alloy films of hexagonal crystal structure.

  1. Daytime Thermal Anisotropy of Urban Neighbourhoods: Morphological Causation

    Directory of Open Access Journals (Sweden)

    E. Scott Krayenhoff


    Full Text Available Surface temperature is a key variable in boundary-layer meteorology and is typically acquired by remote observation of emitted thermal radiation. However, the three-dimensional structure of cities complicates matters: uneven solar heating of urban facets produces an “effective anisotropy” of surface thermal emission at the neighbourhood scale. Remotely-sensed urban surface temperature varies with sensor view angle as a consequence. The authors combine a microscale urban surface temperature model with a thermal remote sensing model to predict the effective anisotropy of simplified neighbourhood configurations. The former model provides detailed surface temperature distributions for a range of “urban” forms, and the remote sensing model computes aggregate temperatures for multiple view angles. The combined model’s ability to reproduce observed anisotropy is evaluated against measurements from a neighbourhood in Vancouver, Canada. As in previous modeling studies, anisotropy is underestimated. Addition of moderate coverages of small (sub-facet scale structure can account for much of the missing anisotropy. Subsequently, over 1900 sensitivity simulations are performed with the model combination, and the dependence of daytime effective thermal anisotropy on diurnal solar path (i.e., latitude and time of day and blunt neighbourhood form is assessed. The range of effective anisotropy, as well as the maximum difference from nadir-observed brightness temperature, peak for moderate building-height-to-spacing ratios (H/W, and scale with canyon (between-building area; dispersed high-rise urban forms generate maximum anisotropy. Maximum anisotropy increases with solar elevation and scales with shortwave irradiance. Moreover, it depends linearly on H/W for H/W < 1.25, with a slope that depends on maximum off-nadir sensor angle. Decreasing minimum brightness temperature is primarily responsible for this linear growth of maximum anisotropy. These

  2. Abstracts for the October 2012 meeting on Volcanism in the American Southwest, Flagstaff, Arizona (United States)

    Lowenstern, Jacob B.


    Though volcanic eruptions are comparatively rare in the American Southwest, the States of Arizona, Colorado, New Mexico, Nevada, and Utah host Holocene volcanic eruption deposits and are vulnerable to future volcanic activity. Compared with other parts of the western United States, comparatively little research has been focused on this area, and eruption probabilities are poorly constrained. Monitoring infrastructure consists of a variety of local seismic networks, and ”backbone“ geodetic networks with little integration. Emergency response planning for volcanic unrest has received little attention by either Federal or State agencies. On October 18–20, 2012, 90 people met at the U.S. Geological Survey campus in Flagstaff, Arizona, providing an opportunity for volcanologists, land managers, and emergency responders to meet, converse, and begin to plan protocols for any future activity. Geologists contributed data on recent findings of eruptive ages, eruption probabilities, and hazards extents (plume heights, ash dispersal). Geophysicists discussed evidence for magma intrusions from seismic, geodetic, and other geophysical techniques. Network operators publicized their recent work and the relevance of their equipment to volcanic regions. Land managers and emergency responders shared their experiences with emergency planning for earthquakes. The meeting was organized out of the recognition that little attention had been paid to planning for or mitigation of volcanic hazards in the American Southwest. Moreover, few geological meetings have hosted a session specifically devoted to this topic. This volume represents one official outcome of the meeting—a collection of abstracts related to talks and poster presentations shared during the first two days of the meeting. In addition, this report includes the meeting agenda as a record of the proceedings. One additional intended outcome will be greater discussion and coordination among emergency responders, geologists

  3. On anisotropy function in crystal growth simulations using Lattice Boltzmann equation

    CERN Document Server

    Younsi, Amina


    In this paper, we present the ability of the Lattice Boltzmann (LB) equation, usually applied to simulate fluid flows, to simulate various shapes of crystals. Crystal growth is modeled with a phase-field model for a pure substance, numerically solved with a LB method in 2D and 3D. This study focuses on the anisotropy function that is responsible for the anisotropic surface tension between the solid phase and the liquid phase. The anisotropy function involves the unit normal vectors of the interface, defined by gradients of phase-field. Those gradients have to be consistent with the underlying lattice of the LB method in order to avoid unwanted effects of numerical anisotropy. Isotropy of the solution is obtained when the directional derivatives method, specific for each lattice, is applied for computing the gradient terms. With the central finite differences method, the phase-field does not match with its rotation and the solution is not any more isotropic. Next, the method is applied to simulate simultaneous...

  4. Magneto-optical investigation of the shape anisotropy of individual micron-sized magnetic elements (United States)

    Sebastian, T.; Conca, A.; Wolf, G.; Schultheiss, H.; Leven, B.; Hillebrands, B.


    In this work, the anisotropy of individual microstructured magnetic elements has been investigated. The investigated elements are of elliptical shape with different sizes and aspect ratios (AR), structured from a 5-nm-thick permalloy (Ni80 Fe20) film. For the measurements, a new magneto-optical Kerr effect (MOKE) magnetometer was used. To allow for the investigation of individual microstructured elements, a micro-focused probing laser beam (spatial resolution ≈1μm) has been combined with a self-stabilizing positioning system of high accuracy, including a rotating unit. Hysteresis loops can be taken for varying orientation of the symmetry axes of the magnetic elements relative to the applied field. For the characterization of the anisotropy, the coercive field as a function of the magnetization direction is extracted from the corresponding hysteresis loops. These results make a quantitative and systematic study of the influence of the shape anisotropy on the magnetic behavior of microstructures possible. The experimental data has been compared to an extended Stoner-Wohlfarth model.

  5. Geology and geochemistry of palaeoproterozoic low-grade metabasic volcanic rocks from Salumber area, Aravalli Supergroup, NW India

    Indian Academy of Sciences (India)

    L S Shekhawat; M K Pandit; D W Joshi


    The Palaeoproterozoic Aravalli Supergroup in Salumber region includes a basal unit of metabasic volcanic rocks (Salumber volcanic rocks) overlain by a volcaniclastic/conglomerate one. Although these volcanic rocks have been metamorphosed to green-schist facies, some primary volcanic features are still preserved. This metabasic volcanic sequence can be further differentiated on the basis of textural variations, and the mineral assemblages are: (a) oligoclase + actinolite + chlorite + epidote; and (b) oligoclase + hornblende+ chlorite + biotite + Fe-Ti oxides. The SiO2 content ranges from ∼47.7 to 55.8% and MgO from ∼4.2 to 12.8%. Geochemical characteristics allow their subdivision into high Mg and Fe tholeiites. Inverse relationship of MgO with silica, alkalis and Zr is generally consistent with fractionation mechanism, also suggested by a change in colour of the rocks from dark greenish to light greenish towards the upper parts of the sequence. These metabasic volcanic rocks are enriched in incompatible trace elements and LREE (La = 30 − 40 × chondrite, Lu = 2 − 5 × chondrite), and demonstrate affinity mainly with MORB and within plate settings in geochemical tectonic discrimination schemes. The geochemical characteristics suggest a complex evolutionary history envisaging derivation of the melt from an enriched heterogeneous lithospheric source.

  6. Petrographic and geochemical characterization of the Triassic and Jurassic magmatic and volcanic rocks of southeastern Ecuador (United States)

    Villares, Fabián; Eguez, Arturo; Yanez, Ernesto


    Formely, the subandean zone in the southeastern Ecuador involved large volcanic and magmatic rocks included in the Misahualli Formation and Zamora batholith, both as expression of the Jurassic cal-alcaline volcanic arc. The aim of the project carried out by the INIGEMM (Instituto Nacional de Investigación Geológico Minero Metalúrgico) was discriminate the volcanic products including a continuous set going from basalts to ryolithes and volcanoclastic rocks. Geochemical characterization was done using representative 16 whole - rock chemical analysis. The oldest rocks of the investigated area called Pachicutza Unit, include greenish to black, massive basalts and basaltic andesites, locally showing pillows structures. The texture is aphanitic to microporphyritic with slight crystal growth of plagioclase and pyroxenes. The Unit include also local pyroclastic breccias and tuffs showing variable skarnification related to the intrusion of the jurassic Zamora Batholith. Two samples of basalts show tholeiitic affinity, corresponding to an N- MORB, probably representing an early stage in opening of a regional Triassic rift reported since Colombia to Peru in the Andes. These geochemical characteristics are similar to the amphibolites of Monte Olivo Unit in the Real Cordillera. The Jurassic large volcanic assembly of the Misahualli Formation was also differenciated. Basal volcanics include green, subporphyritic andesites and volcanic breccias possibly generated at an early stage of the volcanic arc, caused by a change of extensive to compressive regime. Continental volcano sedimentary and sedimentary rock were discriminate as Nueva Esperanza and Suarez Units, respectively. The volcanosedimentary sequence include massive to laminate tuffs and tuffites of intermediate composition. The sediments of the Suarez Unit include dominant conglomerats and sandstones of fluvial domain. The regional volcanic sequence is completed by the Las Peñas Unit that includes aphanitic to

  7. Payenia volcanic province, southern Mendoza, Argentina

    DEFF Research Database (Denmark)

    Søager, Nina; Holm, Paul Martin; Llambias, Eduardo Jorge


    The Pleistocene to Holocene Payenia volcanic province is a backarc region of 60,000 km2 in Mendoza, Argentina, which is dominated by transitional to alkaline basalts and trachybasalts. We present major and trace element compositions of 139 rocks from this area of which the majority are basaltic...

  8. Monogenetic volcanism: personal views and discussion (United States)

    Németh, K.; Kereszturi, G.


    Monogenetic volcanism produces small-volume volcanoes with a wide range of eruptive styles, lithological features and geomorphic architectures. They are classified as spatter cones, scoria (or cinder) cones, tuff rings, maars (maar-diatremes) and tuff cones based on the magma/water ratio, dominant eruption styles and their typical surface morphotypes. The common interplay between internal, such as the physical-chemical characteristics of magma, and external parameters, such as groundwater flow, substrate characteristics or topography, plays an important role in creating small-volume volcanoes with diverse architectures, which can give the impression of complexity and of similarities to large-volume polygenetic volcanoes. In spite of this volcanic facies complexity, we defend the term "monogenetic volcano" and highlight the term's value, especially to express volcano morphotypes. This study defines a monogenetic volcano, a volcanic edifice with a small cumulative volume (typically ≤1 km3) that has been built up by one continuous, or many discontinuous, small eruptions fed from one or multiple magma batches. This definition provides a reasonable explanation of the recently recognized chemical diversities of this type of volcanism.

  9. Is volcanic phenomena of fractal nature? (United States)

    Quevedo, R.; Lopez, D. A. L.; Alparone, S.; Hernandez Perez, P. A.; Sagiya, T.; Barrancos, J.; Rodriguez-Santana, A. A.; Ramos, A.; Calvari, S.; Perez, N. M.


    A particular resonance waveform pattern has been detected beneath different physical volcano manifestations from recent 2011-2012 period of volcanic unrest at El Hierro Island, Canary Islands, and also from other worldwide volcanoes with different volcanic typology. This mentioned pattern appears to be a fractal time dependent waveform repeated in different time scales (periods of time). This time dependent feature suggests this resonance as a new approach to volcano phenomena for predicting such interesting matters as earthquakes, gas emission, deformation etc. as this fractal signal has been discovered hidden in a wide typical volcanic parameters measurements. It is known that the resonance phenomenon occurring in nature usually denote a structure, symmetry or a subjacent law (Fermi et al., 1952; and later -about enhanced cross-sections symmetry in protons collisions), which, in this particular case, may be indicative of some physical interactions showing a sequence not completely chaotic but cyclic provided with symmetries. The resonance and fractal model mentioned allowed the authors to make predictions in cycles from a few weeks to months. In this work an equation for this waveform has been described and also correlations with volcanic parameters and fractal behavior demonstration have been performed, including also some suggestive possible explanations of this signal origin.

  10. Organic Entrainment and Preservation in Volcanic Glasses (United States)

    Wilhelm, Mary Beth; Ojha, Lujendra; Brunner, Anna E.; Dufek, Josef D.; Wray, James Joseph


    Unaltered pyroclastic deposits have previously been deemed to have "low" potential for the formation, concentration and preservation of organic material on the Martian surface. Yet volcanic glasses that have solidified very quickly after an eruption may be good candidates for containment and preservation of refractory organic material that existed in a biologic system pre-eruption due to their impermeability and ability to attenuate UV radiation. Analysis using NanoSIMS of volcanic glass could then be performed to both deduce carbon isotope ratios that indicate biologic origin and confirm entrainment during eruption. Terrestrial contamination is one of the biggest barriers to definitive Martian organic identification in soil and rock samples. While there is a greater potential to concentrate organics in sedimentary strata, volcanic glasses may better encapsulate and preserve organics over long time scales, and are widespread on Mars. If volcanic glass from many sites on Earth could be shown to contain biologically derived organics from the original environment, there could be significant implications for the search for biomarkers in ancient Martian environments.

  11. Monitoring and forecasting Etna volcanic plumes

    Directory of Open Access Journals (Sweden)

    S. Scollo


    Full Text Available In this paper we describe the results of a project ongoing at the Istituto Nazionale di Geofisica e Vulcanologia (INGV. The objective is to develop and implement a system for monitoring and forecasting volcanic plumes of Etna. Monitoring is based at present by multispectral infrared measurements from the Spin Enhanced Visible and Infrared Imager on board the Meteosat Second Generation geosynchronous satellite, visual and thermal cameras, and three radar disdrometers able to detect ash dispersal and fallout. Forecasting is performed by using automatic procedures for: i downloading weather forecast data from meteorological mesoscale models; ii running models of tephra dispersal, iii plotting hazard maps of volcanic ash dispersal and deposition for certain scenarios and, iv publishing the results on a web-site dedicated to the Italian Civil Protection. Simulations are based on eruptive scenarios obtained by analysing field data collected after the end of recent Etna eruptions. Forecasting is, hence, supported by plume observations carried out by the monitoring system. The system was tested on some explosive events occurred during 2006 and 2007 successfully. The potentiality use of monitoring and forecasting Etna volcanic plumes, in a way to prevent threats to aviation from volcanic ash, is finally discussed.

  12. Western Eisila Regio, Venus - Radar properties of volcanic deposits (United States)

    Campbell, Bruce A.; Campbell, Donald B.


    The 1988 Arecibo Observatory dual-polarization radar images are presented for Western Eisila Regio, Venus. The polarization information and Pioneer-Venus Orbiter reflectivity and altimetry data are analyzed for volcanic deposits on two 400-500 km radius constructs, Sif and Gula Montes. Many of the large effusive deposits studied appear to require superposed flows or multiple vents to explain the observed progression of roughness along their length. High Fresnel reflectivity material may be present along the summit region of Gula Mons and in an embayed tessera-like region to the N. Radar-dark units on the flanks of Sif Mons are inferred to be pyroclastic deposits, but radar-dark features near the summits of both edifices are more consistent with very smooth lava flows. Higher spatial resolution Magellan data will be useful in testing these predictions.

  13. Impact of Volcanic Activity on AMC Channel Operations (United States)



  14. Implications of volcanic erratics in Quaternary deposits of North Greenland

    DEFF Research Database (Denmark)

    Funder, Svend Visby; Larsen, Ole


    Erratic boulders, petrographically similar to the volcanics exposed around Kap Washington, are found on islands and along the coast much further to the east. Isotopic measurements on two such boulders show that these volcanic rocks are of the same age as the Kap Washington volcanics. The regional...

  15. Halogen Chemistry in Volcanic Plumes (Invited) (United States)

    Roberts, Tjarda


    Volcanoes release vast amounts of gases and particles in the atmosphere. Volcanic halogens (HF, HCl, HBr, HI) are co-emitted alongside SO2, and observations show rapid formation of BrO and OClO in the plume as it disperses into the troposphere. The development of 1D and Box models (e.g. PlumeChem) that simulate volcanic plume halogen chemistry aims to characterise how volcanic reactive halogens form and quantify their atmospheric impacts. Following recent advances, these models can broadly reproduce the observed downwind BrO/SO2 ratios using "bromine-explosion" chemistry schemes, provided they use a "high-temperature initialisation" to inject radicals (OH, Cl, Br and possibly NOx) which "kick-start" the low-temperature chemistry cycles that convert HBr into reactive bromine (initially as Br2). The modelled rise in BrO/SO2 and subsequent plateau/decline as the plume disperses downwind reflects cycling between reactive bromine, particularly Br-BrO, and BrO-HOBr-BrONO2. BrCl is produced when aerosol becomes HBr-depleted. Recent model simulations suggest this mechanism for reactive chlorine formation can broadly account for OClO/SO2 reported at Mt Etna. Predicted impacts of volcanic reactive halogen chemistry include the formation of HNO3 from NOx and depletion of ozone. This concurs with HNO3 widely reported in volcanic plumes (although the source of NOx remains under question), as well as observations of ozone depletion reported in plumes from several volcanoes (Mt Redoubt, Mt Etna, Eyjafjallajokull). The plume chemistry can transform mercury into more easily deposited and potentially toxic forms, for which observations are limited. Recent incorporation of volcanic halogen chemistry in a 3D regional model of degassing from Ambrym (Vanuatu) also predicts how halogen chemistry causes depletion of OH to lengthen the SO2 lifetime, and highlights the potential for halogen transport from the troposphere to the stratosphere. However, the model parameter-space is vast and

  16. Holocene explosive volcanism of the Jan Mayen (island) volcanic province, North-Atlantic (United States)

    Gjerløw, Eirik; Haflidason, H.; Pedersen, R. B.


    The volcanic island Jan Mayen, located in the Norwegian-Greenland Sea, hosts the active stratovolcano of Beerenberg, the northernmost active subaerial volcano in the world. At least five eruptions are known from the island following its discovery in the 17th century, but its eruptive history prior to this is basically unknown. In this paper two sediment cores retrieved close to Jan Mayen have been studied in detail to shed light on the Holocene history of explosive volcanism from the Jan Mayen volcanic province. Horizons with elevated tephra concentrations were identified and tephra from these was analysed to determine major element chemistry of the tephra. The tephra chemistry was used to provide a link between the two cores and the land based tephra records from Jan Mayen Island. We managed to link two well-developed tephra peaks in the cores by their geochemical composition and age to Jan Mayen. One of these peaks represents the 1732 AD eruption of Eggøya while the other peak represents a previously undescribed eruption dated to around 10.3 ka BP. Two less prominent tephra peaks, one in each core, dated to approximately 2.3 and 3.0 ka BP, also have a distinct geochemical character linking them to Jan Mayen volcanism. However, the most prominent tephra layer in the cores located close to Jan Mayen and numerous other cores along the Jan Mayen ridge is the 12.1 ka BP Vedde Ash originating from the Iceland volcanic province. We find that the Holocene volcanism on Jan Mayen is much less explosive than volcanism in Iceland, and propose that either low amounts of explosive volcanic activity from the summit region of Beerenberg or small to absent glacier cover on Beerenberg is responsible for this.

  17. Laboratory measurements of the viscous anisotropy of olivine aggregates. (United States)

    Hansen, L N; Zimmerman, M E; Kohlstedt, D L


    A marked anisotropy in viscosity develops in Earth's mantle as deformation strongly aligns the crystallographic axes of the individual grains that comprise the rocks. On the basis of geodynamic simulations, processes significantly affected by viscous anisotropy include post-glacial rebound, foundering of lithosphere and melt production above subduction zones. However, an estimate of the magnitude of viscous anisotropy based on the results of deformation experiments on single crystals differs by three orders of magnitude from that obtained by grain-scale numerical models of deforming aggregates with strong crystallographic alignment. Complicating matters, recent experiments indicate that deformation of the uppermost mantle is dominated by dislocation-accommodated grain-boundary sliding, a mechanism not activated in experiments on single crystals and not included in numerical models. Here, using direct measurements of the viscous anisotropy of highly deformed polycrystalline olivine, we demonstrate a significant directional dependence of viscosity. Specifically, shear viscosities measured in high-strain torsion experiments are 15 times smaller than normal viscosities measured in subsequent tension tests performed parallel to the torsion axis. This anisotropy is approximately an order of magnitude larger than that predicted by grain-scale simulations. These results indicate that dislocation-accommodated grain-boundary sliding produces an appreciable anisotropy in rock viscosity. We propose that crystallographic alignment imparts viscous anisotropy because the rate of deformation is limited by the movement of dislocations through the interiors of the crystallographically aligned grains. The maximum degree of anisotropy is reached at geologically low shear strain (of about ten) such that deforming regions of the upper mantle will exhibit significant viscous anisotropy.

  18. Crustal radial anisotropy beneath Cameroon from ambient noise tomography (United States)

    Ojo, Adebayo Oluwaseun; Ni, Sidao; Li, Zhiwei


    To increase the understanding of crustal deformation and crustal flow patterns due to tectonic processes in Cameroon, we study the lateral variability of the crustal isotropic velocity and radial anisotropy estimated using Ambient Noise Tomography (ANT). Rayleigh and Love wave Noise Correlation Functions (NCFs) were retrieved from the cross-correlation of seismic ambient noise data recorded in Cameroon, and phase velocities at periods of 8 to 30 s were measured to perform surface wave tomography. Joint inversion of Rayleigh and Love wave data for isotropic velocity models could not fit the observed dispersions simultaneously. We attribute the Love-Rayleigh discrepancy to the presence of radial anisotropy in the crust and estimated its magnitude. Our 3-D radial anisotropic model reveals the spatial variation of strong to weak positive (Vsh > Vsv) and negative (Vsv > Vsh) radial anisotropy in the crust. We observe negative radial anisotropy in the upper crust that is associated mainly with the location of a previously reported mantle plume. The anisotropy could be attributed to the vertical alignment of fossil microcracks or metamorphic foliations due to the upwelling of plume material. A strong positive radial anisotropy is centered at the location of an inferred boundary between the Congo Craton and the Oubanguides Belt that might be related to the preferred orientation of crustal anisotropic minerals associated with shearing in this fault zone. The middle crust is characterized by a widespread negative radial anisotropy that is likely caused by the flow-induced alignment of anisotropic minerals that crystallized during magma intrusion. The magnitude of the radial anisotropy varies systematically from predominantly negative in the middle crust to positive in the lower crust. The imaged patterns of the isotropic velocity and radial anisotropy are consistent with previous studies and agree with regional tectonics.

  19. The Geologic Basis for Volcanic Hazard Assessment for the Proposed High-Level Radioactive Waste Repository at Yucca Mountain, Nevada

    Energy Technology Data Exchange (ETDEWEB)

    F. Perry


    Studies of volcanic risk to the proposed high-level radioactive waste repository at Yucca Mountain have been ongoing for 25 years. These studies are required because three episodes of small-volume, alkalic basaltic volcanism have occurred within 50 km of Yucca Mountain during the Quaternary. Probabilistic hazard estimates for the proposed repository depend on the recurrence rate and spatial distribution of past episodes of volcanism in the region. Several independent research groups have published estimates of the annual probability of a future volcanic disruption of the proposed repository, most of which fall in the range of 10{sup -7} to 10{sup -9} per year; similar conclusions were reached. through an extensive expert elicitation sponsored by the Department of Energy in 1995-1996. The estimated probability values are dominated by a regional recurrence rate of 10{sup -5} to 10{sup -6} volcanic events per year (equating to recurrence intervals of several hundred thousand years). The recurrence rate, as well as the spatial density of volcanoes, is low compared to most other basaltic volcanic fields in the western United States, factors that may be related to both the tectonic history of the region and a lithospheric mantle source that is relatively cold and not prone to melting. The link between volcanism and tectonism in the Yucca Mountain region is not well understood beyond a general association between volcanism and regional extension, although areas of locally high extension within the region may control the location of some volcanoes. Recently, new geologic data or hypotheses have emerged that could potentially increase past estimates of the recurrence rate, and thus the probability of repository disruption. These are (1) hypothesized episodes of anomalously high strain rate, (2) hypothesized presence of a regional mantle hotspot, and (3) new aeromagnetic data suggesting as many as twelve previously unrecognized volcanoes buried in alluvial-filled basins near

  20. Volcanic lake systematics II. Chemical constraints (United States)

    Varekamp, J.C.; Pasternack, G.B.; Rowe, G.L.


    A database of 373 lake water analyses from the published literature was compiled and used to explore the geochemical systematics of volcanic lakes. Binary correlations and principal component analysis indicate strong internal coherence among most chemical parameters. Compositional variations are influenced by the flux of magmatic volatiles and/or deep hydrothermal fluids. The chemistry of the fluid entering a lake may be dominated by a high-temperature volcanic gas component or by a lower-temperature fluid that has interacted extensively with volcanic rocks. Precipitation of minerals like gypsum and silica can strongly affect the concentrations of Ca and Si in some lakes. A much less concentrated geothermal input fluid provides the mineralized components of some more dilute lakes. Temporal variations in dilution and evaporation rates ultimately control absolute concentrations of dissolved constituents, but not conservative element ratios. Most volcanic lake waters, and presumably their deep hydrothermal fluid inputs, classify as immature acid fluids that have not equilibrated with common secondary silicates such as clays or zeolites. Many such fluids may have equilibrated with secondary minerals earlier in their history but were re-acidified by mixing with fresh volcanic fluids. We use the concept of 'degree of neutralization' as a new parameter to characterize these acid fluids. This leads to a classification of gas-dominated versus rock-dominated lake waters. A further classification is based on a cluster analysis and a hydrothermal speedometer concept which uses the degree of silica equilibration of a fluid during cooling and dilution to evaluate the rate of fluid equilibration in volcano-hydrothermal systems.

  1. International Database of Volcanic Ash Impacts (United States)

    Wallace, K.; Cameron, C.; Wilson, T. M.; Jenkins, S.; Brown, S.; Leonard, G.; Deligne, N.; Stewart, C.


    Volcanic ash creates extensive impacts to people and property, yet we lack a global ash impacts catalog to organize, distribute, and archive this important information. Critical impact information is often stored in ephemeral news articles or other isolated resources, which cannot be queried or located easily. A global ash impacts database would improve 1) warning messages, 2) public and lifeline emergency preparation, and 3) eruption response and recovery. Ashfall can have varying consequences, such as disabling critical lifeline infrastructure (e.g. electrical generation and transmission, water supplies, telecommunications, aircraft and airports) or merely creating limited and expensive inconvenience to local communities. Impacts to the aviation sector can be a far-reaching global issue. The international volcanic ash impacts community formed a committee to develop a database to catalog the impacts of volcanic ash. We identify three user populations for this database: 1) research teams, who would use the database to assist in systematic collection, recording, and storage of ash impact data, and to prioritize impact assessment trips and lab experiments 2) volcanic risk assessment scientists who rely on impact data for assessments (especially vulnerability/fragility assessments); a complete dataset would have utility for global, regional, national and local scale risk assessments, and 3) citizen science volcanic hazard reporting. Publication of an international ash impacts database will encourage standardization and development of best practices for collecting and reporting impact information. Data entered will be highly categorized, searchable, and open source. Systematic cataloging of impact data will allow users to query the data and extract valuable information to aid in the development of improved emergency preparedness, response and recovery measures.

  2. Space Radar Image of Pinacate Volcanic Field, Mexico (United States)


    This spaceborne radar image shows the Pinacate Volcanic Field in the state of Sonora, Mexico, about 150 kilometers (93 miles) southeast of Yuma, Arizona. The United States/Mexico border runs across the upper right corner of the image. More than 300 volcanic vents occur in the Pinacate field, including cinder cones that experienced small eruptions as recently as 1934. The larger circular craters seen in the image are a type of volcano known as a 'maar', which erupts violently when rising magma encounters groundwater, producing highly pressurized steam that powers explosive eruptions. The highest elevations in the volcanic field, about 1200 meters (4000 feet), occur in the 'shield volcano' structure shown in bright white, occupying most of the left half of the image. Numerous cinder cones dot the flanks of the shield. The yellow patches to the right of center are newer, rough-textured lava flows that strongly reflect the long wavelength radar signals. Along the left edge of the image are sand dunes of the Gran Desierto. The dark areas are smooth sand and the brighter brown and purple areas have vegetation on the surface. Radar data provide a unique means to study the different types of lava flows and wind-blown sands. This image was acquired by Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) onboard the space shuttle Endeavour on April 18, 1994. The image is 57 kilometers by 48 kilometers (35 miles by 30 miles) and is centered at 31.7 degrees north latitude, 113.4 degrees West longitude. North is toward the upper right. The colors are assigned to different radar frequencies and polarizations of the radar as follows: red is L-band, horizontally transmitted and received; green is L-band, horizontally transmitted, vertically received; and blue is C-band, horizontally transmitted, vertically received. SIR-C/X-SAR, a joint mission of the German, Italian, and United States space agencies, is part of NASA's Mission to Planet Earth.

  3. Effects of surface anisotropy on magnetic vortex core

    Energy Technology Data Exchange (ETDEWEB)

    Pylypovskyi, Oleksandr V., E-mail: [Taras Shevchenko National University of Kiev, 01601 Kiev (Ukraine); Sheka, Denis D. [Taras Shevchenko National University of Kiev, 01601 Kiev (Ukraine); Kravchuk, Volodymyr P.; Gaididei, Yuri [Institute for Theoretical Physics, 03143 Kiev (Ukraine)


    The vortex core shape in the three dimensional Heisenberg magnet is essentially influenced by a surface anisotropy. We predict that depending of the surface anisotropy type there appears barrel- or pillow-shaped deformation of the vortex core along the magnet thickness. Our theoretical study is well confirmed by spin–lattice simulations. - Highlights: • The shape of magnetic vortex core is essentially influenced by SA (surface anisotropy). • We predict barrel- or pillow-shaped deformation of the vortex depending on SA. • The variational approach fully describes the vortex core deformation. • We performed spin–lattice simulations to detect SA influence on the vortex core.

  4. Complete treatment of CMB anisotropies in a FRW universe (United States)

    Hu, Wayne; Seljak, Uroš; White, Martin; Zaldarriaga, Matias


    We generalize the total angular momentum method for computing cosmic microwave background anisotropies to Friedmann-Robertson-Walker (FRW) spaces with arbitrary geometries. This unifies the treatment of temperature and polarization anisotropies generated by scalar, vector and tensor perturbations of the fluid, seed, or a scalar field, in a universe with constant comoving curvature. The resulting formalism generalizes and simplifies the calculation of anisotropies and, in its integral form, allows for a fast calculation of model predictions in linear theory for any FRW metric.

  5. Cubic versus spherical magnetic nanoparticles: the role of surface anisotropy. (United States)

    Salazar-Alvarez, G; Qin, J; Sepelák, V; Bergmann, I; Vasilakaki, M; Trohidou, K N; Ardisson, J D; Macedo, W A A; Mikhaylova, M; Muhammed, M; Baró, M D; Nogués, J


    The magnetic properties of maghemite (gamma-Fe2O3) cubic and spherical nanoparticles of similar sizes have been experimentally and theoretically studied. The blocking temperature, T(B), of the nanoparticles depends on their shape, with the spherical ones exhibiting larger T(B). Other low temperature properties such as saturation magnetization, coercivity, loop shift or spin canting are rather similar. The experimental effective anisotropy and the Monte Carlo simulations indicate that the different random surface anisotropy of the two morphologies combined with the low magnetocrystalline anisotropy of gamma-Fe2O3 is the origin of these effects.

  6. CPO-induced seismic anisotropy in UHP eclogites

    Institute of Scientific and Technical Information of China (English)


    Ultrahigh-pressure (UHP) eclogites often show strong plastic deformation and anisotropy of seismic properties. We report in this paper the seismic velocity and anisotropy of eclogite calculated from the crystallographic preferred orientations (CPOs) of constituent minerals (garnet, omphacite, quartz and rutile) and single crystal elastic properties. We also compared the calculated results with the measured results in similar eclogites. Our results suggest that (1) Except that garnet is a seismically quasi-isotropic mineral, omphacite, quartz, coesite and rutile all have strong seismic anisotropies (AVp = 23.0%―40.9%, Max. AVs = 18.5%―47.1%). They are the major sources for anisotropy in eclogite. The average seismic velocities are fast in garnet and rutile, moderate in omphacite and coesite, and slow in quartz. (2) The deformed eclogites have the maximum Vp (8.33―8.75 km/s) approximately parallel to foliation and lineation, the minimum Vp (8.25―8.62 km/s) approximately normal to foliation and lineation and the Vp anisotropies of 1.0―1.7%. Their Vs are 4.93―4.97 km/s. The corresponding maximum anisotropies (0.73%―1.78%) of Vs are at 45° to both foliation and lineation and the minimum anisotropies at positions normal to lineation on the foliation plane. The Vs1 polarization planes are approximately parallel to foliation. The mean Vp and Vs of eclogite under UHP peak metamorphism conditions (P = 3―5 GPa, T = 900―1100℃) are estimated to be 3.4%―7.2% and 6.3%―12.1% higher than those at ambient pressure and temperature conditions, respectively. (3) Omphacite component dominates the anisotropy of eclogite while garnet component reduces the anisotropy and increases the seismic velocities. Quartz component has a small effect on the anisotropy but reduces the seismic velocities of eclogite. The effect of rutile component is negligible on seismic properties of eclogite due to its trivial volume fraction. (4) The increase of volume fraction of omphacite

  7. Review of the anisotropy working group at UHECR-2012

    Directory of Open Access Journals (Sweden)

    Ivanov A.


    Full Text Available The study of ultra-high energy cosmic rays (UHECRs has recently experienced a jump in statistics as well as improved instrumentation. This has allowed a better sensitivity in searching for anisotropies in the arrival directions of cosmic rays. In this written version of the presentation given by the inter-collaborative “Anisotropy Working Group” at the International Symposium on Future Directions in UHECR physics at CERN in February 2012, we report on the current status for anisotropy searches in the arrival directions of UHECRs.

  8. Texture induced magnetic anisotropy in Fe3O4 films (United States)

    Liu, Er; Huang, Zhaocong; Zheng, Jian-Guo; Yue, Jinjin; Chen, Leyi; Wu, Xiumei; Sui, Yunxia; Zhai, Ya; Tang, Shaolong; Du, Jun; Zhai, Hongru


    This letter reports a free energy density model for textured films in which the related physical concept and expression of magneto-texture anisotropy energy are presented. The structural characterization and out-of-plane angular dependence ferromagnetic resonance of strongly textured Fe3O4 films were systematically investigated. We found that the typical free energy density model for polycrystalline film cannot be applied to the textured films. With the introduction of magneto-texture anisotropy energy in the free energy density model for thin films, we simulated and quantitatively determined the competing anisotropies in (111)-textured Fe3O4 films.

  9. Canonical Transform Method for Treating Strongly Anisotropy Magnets

    DEFF Research Database (Denmark)

    Cooke, J. F.; Lindgård, Per-Anker


    An infinite-order perturbation approach to the theory of magnetism in magnets with strong single-ion anisotropy is given. This approach is based on a canonical transformation of the system into one with a diagonal crystal field, an effective two-ion anisotropy, and reduced ground-state corrections....... A matrix-element matching procedure is used to obtain an explicit expression for the spin-wave energy to second order. The consequences of this theory are illustrated by an application to a simple example with planar anisotropy and an external magnetic field. A detailed comparison between the results...

  10. A Theoretical Diagnosis on Light Speed Anisotropy from GRAAL Experiment

    CERN Document Server

    Lingli, Zhou


    The light speed anisotropy, i.e., the variation of the light speed with respect to direction in an "absolute" reference frame, is a profound issue in physics. The one-way experiment, performed at the GRAAL facility of the European Synchrotron Radiation Facility (ESRF) in Grenoble, reported results on the light speed anisotropy by Compton scattering of laser photons on high-energy electrons. We show in this paper that the azimuthal distribution of the GRAAL experiment data can be elegantly reproduced by a new theory of Lorentz invariance violation or space-time anisotropy, based on a general principle of physical independence of the mathematical background manifold.

  11. Anisotropies of Gravitational Wave Backgrounds: A Line Of Sight Approach

    CERN Document Server

    Contaldi, Carlo R


    In the weak field regime, gravitational waves can be considered as being made up of collisionless, relativistic tensor modes that travel along null geodesics of the perturbed background metric. We work in this geometric optics picture to calculate the anisotropies in gravitational wave backgrounds resulting from astrophysical and cosmological sources. Our formalism yields expressions for the angular power spectrum of the anisotropies. We show how the anisotropies are sourced by intrinsic, Doppler, Sachs-Wolfe, and Integrated Sachs-Wolfe terms in analogy with Cosmic Microwave Background photons.

  12. Engineering Curvature-Induced Anisotropy in Thin Ferromagnetic Films (United States)

    Tretiakov, Oleg A.; Morini, Massimiliano; Vasylkevych, Sergiy; Slastikov, Valeriy


    We investigate the effect of large curvature and dipolar energy in thin ferromagnetic films with periodically modulated top and bottom surfaces on magnetization behavior. We predict that the dipolar interaction and surface curvature can produce perpendicular anisotropy which can be controlled by engineering special types of periodic surface structures. Similar effects can be achieved by a significant surface roughness in the film. We demonstrate that, in general, the anisotropy can point in an arbitrary direction depending on the surface curvature. Furthermore, we provide simple examples of these periodic surface structures to show how to engineer particular anisotropies in thin films.

  13. Growth of Co Nanomagnet Arrays with Enhanced Magnetic Anisotropy (United States)

    Fernández, Laura; Ilyn, Maxim; Magaña, Ana; Vitali, Lucia; Ortega, José Enrique


    A trigon structure formed by submonolayer gadolinium deposition onto Au(111) is revealed as a robust growth template for Co nanodot arrays. Scanning Tunneling Microscopy and X‐Ray Magnetic Circular Dichroism measurements evidence that the Co nanoislands behave as independent magnetic entities with an out‐of‐plane easy axis of anisotropy and enhanced magnetic anisotropy values, as compared to other self‐organized Co nanodot superlattices. The large strain induced by the lattice mismatch at the interface between Co and trigons is discussed as the main reason for the increased magnetic anisotropy of the nanoislands. PMID:27711268

  14. Solitary structures with ion and electron thermal anisotropy

    CERN Document Server

    Khusroo, Murchana


    Formation of electrostatic solitary structures are analysed for a magnetised plasma with ion and electron thermal anisotropies. The ion thermal anisotropy is modelled with the help of the Chew-Goldberger-Low (CGL) double adiabatic equations of state while the electrons are treated as inertia-less species with an anisotropic bi-Maxwellian velocity distribution function. A negative electron thermal anisotropy $(T_{e\\perp}/T_e{\\parallel}>1)$ is found to help form large amplitude solitary structures which are in agreement with observational data.

  15. Local seismic hazard assessment in explosive volcanic settings by 3D numerical analyses (United States)

    Razzano, Roberto; Pagliaroli, Alessandro; Moscatelli, Massimiliano; Gaudiosi, Iolanda; Avalle, Alessandra; Giallini, Silvia; Marcini, Marco; Polpetta, Federica; Simionato, Maurizio; Sirianni, Pietro; Sottili, Gianluca; Vignaroli, Gianluca; Bellanova, Jessica; Calamita, Giuseppe; Perrone, Angela; Piscitelli, Sabatino


    This work deals with the assessment of local seismic response in the explosive volcanic settings by reconstructing the subsoil model of the Stracciacappa maar (Sabatini Volcanic District, central Italy), whose pyroclastic succession records eruptive phases ended about 0.09 Ma ago. Heterogeneous characteristics of the Stracciacappa maar (stratification, structural setting, lithotypes, and thickness variation of depositional units) make it an ideal case history for understanding mechanisms and processes leading to modifications of amplitude-frequency-duration of seismic waves generated at earthquake sources and propagating through volcanic settings. New geological map and cross sections, constrained with recently acquired geotechnical and geophysical data, illustrate the complex geometric relationships among different depositional units forming the maar. A composite interfingering between internal lacustrine sediments and epiclastic debris, sourced from the rim, fills the crater floor; a 45 meters thick continuous coring borehole was drilled in the maar with sampling of undisturbed samples. Electrical Resistivity Tomography surveys and 2D passive seismic arrays were also carried out for constraining the geological model and the velocity profile of the S-waves, respectively. Single station noise measurements were collected in order to define natural amplification frequencies. Finally, the nonlinear cyclic soil behaviour was investigated through simple shear tests on the undisturbed samples. The collected dataset was used to define the subsoil model for 3D finite difference site response numerical analyses by using FLAC 3D software (ITASCA). Moreover, 1D and 2D numerical analyses were carried out for comparison purposes. Two different scenarios were selected as input motions: a moderate magnitude (volcanic event) and a high magnitude (tectonic event). Both earthquake scenarios revealed significant ground motion amplification (up to 15 in terms of spectral acceleration

  16. Volcanism on Io: New insights from global geologic mapping (United States)

    Williams, D.A.; Keszthelyi, L.P.; Crown, D.A.; Yff, J.A.; Jaeger, W.L.; Schenk, P.M.; Geissler, P.E.; Becker, T.L.


    We produced the first complete, 1:15M-scale global geologic map of Jupiter's moon Io, based on a set of monochrome and color Galileo-Voyager image mosaics produced at a spatial resolution of 1km/pixel. The surface of Io was mapped into 19 units based on albedo, color and surface morphology, and is subdivided as follows: plains (65.8% of surface), lava flow fields (28.5%), mountains (3.2%), and patera floors (2.5%). Diffuse deposits (DD) that mantle the other units cover ???18% of Io's surface, and are distributed as follows: red (8.6% of surface), white (6.9%), yellow (2.1%), black (0.6%), and green (???0.01%). Analyses of the geographical and areal distribution of these units yield a number of results, summarized below. (1) The distribution of plains units of different colors is generally geographically constrained: Red-brown plains occur >??30?? latitude, and are thought to result from enhanced alteration of other units induced by radiation coming in from the poles. White plains (possibly dominated by SO2+contaminants) occur mostly in the equatorial antijovian region (??30??, 90-230??W), possibly indicative of a regional cold trap. Outliers of white, yellow, and red-brown plains in other regions may result from long-term accumulation of white, yellow, and red diffuse deposits, respectively. (2) Bright (possibly sulfur-rich) flow fields make up 30% more lava flow fields than dark (presumably silicate) flows (56.5% vs. 43.5%), and only 18% of bright flow fields occur within 10km of dark flow fields. These results suggest that secondary sulfurous volcanism (where a bright-dark association is expected) could be responsible for only a fraction of Io's recent bright flows, and that primary sulfur-rich effusions could be an important component of Io's recent volcanism. An unusual concentration of bright flows at ???45-75??N, ???60-120??W could be indicative of more extensive primary sulfurous volcanism in the recent past. However, it remains unclear whether most bright

  17. Texture and anisotropy of ferroelectric bismuth titanate (United States)

    Jones, Jacob Leo

    Ferroelectric bismuth titanate, Na0.5Bi4.5 Ti4O15, is a piezoelectric ceramic used as an electromechanical sensor in high temperature environments (T piezoelectric constant, d33, is relatively low in randomly oriented ceramics. Crystallographic texturing is often employed to increase the piezoelectric constant because the spontaneous polarization axes of the grains are better aligned. This research distinguishes between the crystallographic texture induced to the grains from tape casting and crystallographic texture induced to the ferroelectric domains from electrical poling. Novel quantitative approaches describe texture of both types independently using conventional and synchrotron X-ray sources as well as time-of-flight neutron diffraction with multiple detectors. Furthermore, methods are developed to describe the combined effect of a ferroelectric texture superimposed on a paraelectric texture. Texture of the paraelectric crystallographic axes was induced by novel processing approaches. An alternative to using plate-shaped template particles was developed utilizing calcined powder. Paraelectric texture develops from particle settling and strong surface energy anisotropy during sintering. The 00l textures induced from this process are on the order of two to four multiples of a random distribution. These textures create property anisotropies between the casting plane and normal directions of 6.4 and 5.7 in piezoelectric d33 constant and remanent polarization, respectively. Texture of the ferroelectric crystallographic axes was induced by electrical poling at different temperatures and in different orientations. Ceramics with an initial paraelectric texture can exhibit greater change in the domain volume fractions during electrical poling than randomly oriented ceramics. This is demonstrated by applying novel quantitative approaches to reflection X-ray spectra from many sample directions. Because orthorhombic Na0.5Bi 4.5Ti4O15 has two ferroelectric domains that

  18. Search for giant magnetic anisotropy in transition-metal dimers on defected hexagonal boron nitride sheet (United States)

    Li, J.; Wang, H.; Hu, J.; Wu, R. Q.


    Structural and magnetic properties of many transition-metal dimers embedded in a defected hexagonal boron nitride monolayer are investigated through density functional calculations to search for systems with magnetic anisotropy energies (MAEs) larger than 30meV. In particular, Ir-Ir@Dh-BN is found to have both large MAE (˜126 meV) and high structural stability against dissociation and diffusion, and it hence can serve as magnetic unit in spintronics and quantum computing devices. This giant MAE mainly results from the spin orbit coupling and the magnetization of the upper Ir atom, which is in a rather isolated environment.

  19. Exchange bias for ferromagnetic/antiferromagnetic bilayers with the uniaxial anisotropy being misaligned with the exchange anisotropy

    Institute of Scientific and Technical Information of China (English)

    BAI YuHao; YUN GuoHong


    Using the principle of minimal energy and S-W model, the exchange bias for ferromagnetic/antiferromagnetic bilayers has been investigated when the uniaxial anisotropy is misaligned with the exchange anisotropy. According to the relation between the energy of the bilayer and the orientation of ferromagnetic magnetization, it is found that the bilayer will be in the monostable state or bistable state when the external field is absent in the initial magnetization state. The monostable state or bistable state of the bilayer, which determines the angular dependence of exchange bias directly, is controlled by the competition between the exchange anisotropy and uniaxial anisotropy. When the applied field is parallel to the intrinsic easy axes and intrinsic hard axes, one of the switching fields of the hysteresis loop shows an abrupt change, while the other keep continuous by analyzing the magnetization reversal processes. Consequently, the exchange bias field and the coercivity will show a jump phenomenon.The numerical calculations indicate that both the magnitude and direction of the exchange anisotropy will significantly affect the angular dependence of exchange bias. The jump phenomenon of exchange bias is an intrinsic property of the bilayer, which is dependent on the interracial exchange-coupling constant, the orientation of the exchange anisotropy, the thickness and uniaxial anisotropy constant of the ferromagnetic layer.

  20. Exchange bias for ferromagnetic/antiferromagnetic bilayers with the uniaxial anisotropy being misaligned with the exchange anisotropy

    Institute of Scientific and Technical Information of China (English)


    Using the principle of minimal energy and S-W model,the exchange bias for ferromagnetic/antiferro-magnetic bilayers has been investigated when the uniaxial anisotropy is misaligned with the exchange anisotropy. According to the relation between the energy of the bilayer and the orientation of ferro-magnetic magnetization,it is found that the bilayer will be in the monostable state or bistable state when the external field is absent in the initial magnetization state. The monostable state or bistable state of the bilayer,which determines the angular dependence of exchange bias directly,is controlled by the competition between the exchange anisotropy and uniaxial anisotropy. When the applied field is parallel to the intrinsic easy axes and intrinsic hard axes,one of the switching fields of the hysteresis loop shows an abrupt change,while the other keep continuous by analyzing the magnetization reversal processes. Consequently,the exchange bias field and the coercivity will show a jump phenomenon. The numerical calculations indicate that both the magnitude and direction of the exchange anisotropy will significantly affect the angular dependence of exchange bias. The jump phenomenon of exchange bias is an intrinsic property of the bilayer,which is dependent on the interfacial exchange-coupling constant,the orientation of the exchange anisotropy,the thickness and uniaxial anisotropy constant of the ferromagnetic layer.

  1. The cause and source of melting for the most recent volcanism in Tibet: A combined geochemical and geophysical perspective (United States)

    Wei, Feixiang; Prytulak, Julie; Xu, Jiandong; Wei, Wei; Hammond, James O. S.; Zhao, Bo


    We investigate the youngest volcanic activity on the Tibetan Plateau by combining observations from petrologic, geochemical and seismic tomography studies. Recent (from 2.80 Ma to present) post-collisional potassium-rich lavas from the Ashikule Volcanic Basin (AVB) in northwestern Tibet are characterised by remarkably enriched light rare earth elements (LREE) relative to heavy rare earth elements (HREE), and enriched large ion lithophile element (LILE) relative to high field strength elements (HFSE). Strontium and neodymium isotopic compositions are surprisingly restricted, and show little evidence for mixing or crustal contamination, despite the thick crust upon which they are erupted. Geochemical characteristics indicate a homogeneous source, highly enriched in trace elements, which is most consistent with derivation from long-lived subcontinental lithospheric mantle (SCLM). P-wave anisotropy tomography documents a gap between the north-subducting Indian slab and south-subducting Tarim slab directly beneath the AVB. We propose that volcanism in northwestern Tibet is associated with the progressive closure of this gap, during which shear heating of the SCLM can generate localised melting, with deep-seated faults providing a mechanism for erupted lavas to escape large-scale crustal contamination and fractionation in magma reservoirs. Thus, shear heating may provide an explanation for the restricted range of radiogenic isotope compositions from a SCLM source that should be, by its nature, heterogeneous on a large scale.

  2. Volcanic and glacial evolution of Chachani-Nocarane complex (Southern Peru) deduced from the geomorphologic map. (United States)

    Alcalá, J.; Zamorano, J. J.; Palacios, D.


    The Chachani-Nocarane (16°11'S; 71°31'W; 6.057 m asl) is a large volcanic complex located in the western Central-Andean Cordillera, South of Peru. The date of the last eruption is not known and there are no registers of recent volcanic activity. The complex is shaped by glacial forms belonging to different phases, and periglacial forms (several generations of rock glaciers) which alternate with volcanic forms. The aim of this research is to establish the glacio-volcanic evolution of the volcanic complex Chachani-Nocarane. In order to do so, a detailed 1:20.000 scale geomorphological map was elaborated by integrating the following techniques: interpretation of the 1:35.000 scale aerial photographs (Instituto Geográfico Nacional de Perú, 1956) and the analysis of satellite images (Mrsid; NASA, 2000). Finally, the cartography was corrected though field work campaigns. Through the geomorphologic analysis of the landforms and their relative position, we have identified twelve phases, seven volcanic and five glacial phases. The most ancient volcanic phase is locate to the north area of the study area and correspond with Nocarane and Chingana volcanoes, alignment NW-SE. Above those ensemble the rest of the large delimited geomorphological units overlap. The most recent is located to the SW and consists of a complex series of domes, lava cones and voluminous lavas. Within the glacial phases, the most ancient one is related to the Last Glacial Maximum during the Pleistocene. Over this period, glaciers formed moraines from 3150 to 3600 m asl. The most recent glacier pulsation corresponds to the Little Ice Age (LIA). The moraines related to that event are the closest to the summits, located between 5.100 and 5.300 m asl, and they represent the last trace of glacial activity on the volcanic complex. Currently, this tropical mountain does not have glaciers. The only solid-state water reserves are found in the form of permafrost, as shown by various generations of rock

  3. Using Spatial Density to Characterize Volcanic Fields on Mars (United States)

    Richardson, J. A.; Bleacher, J. E.; Connor, C. B.; Connor, L. J.


    We introduce a new tool to planetary geology for quantifying the spatial arrangement of vent fields and volcanic provinces using non parametric kernel density estimation. Unlike parametricmethods where spatial density, and thus the spatial arrangement of volcanic vents, is simplified to fit a standard statistical distribution, non parametric methods offer more objective and data driven techniques to characterize volcanic vent fields. This method is applied to Syria Planum volcanic vent catalog data as well as catalog data for a vent field south of Pavonis Mons. The spatial densities are compared to terrestrial volcanic fields.

  4. Relationship between electrical conductivity anisotropy and fabric anisotropy in granular materials during drained triaxial compressive tests: a numerical approach (United States)

    Niu, Qifei; Revil, André; Li, Zhaofeng; Wang, Yu-Hsing


    The anisotropy of granular media and its evolution during shearing are important aspects required in developing physics-based constitutive models in Earth sciences. The development of relationships between geoelectrical properties and the deformation of porous media has applications to the monitoring of faulting and landslides. However, such relationships are still poorly understood. In this study, we first investigate the definition of the electrical conductivity anisotropy tensor of granular materials in presence of surface conductivity of the grains. Fabric anisotropy is related to the components of the fabric tensor. We define an electrical anisotropy factor based on the Archie's exponent second-order symmetric tensor m of granular materials. We use numerical simulations to confirm a relationship between the evolution of electrical and fabric anisotropy factors during shearing. To realize the simulations, we build a virtual laboratory in which we can easily perform synthetic experiments. We first simulate drained compressive triaxial tests of loose and dense granular materials (porosity 0.45 and 0.38, respectively) using the discrete element method. Then, the electrical conductivity tensor of a set of deformed synthetic samples is computed using the finite-difference method. The numerical results show that shear strains are responsible for a measurable anisotropy in the bulk conductivity of granular media. The observed electrical anisotropy response, during shearing, is distinct for dense and loose synthetic samples. Electrical and fabric anisotropy factors exhibit however a unique linear correlation, regardless of the shear strain and the initial state (porosity) of the synthetic samples. The practical implication of this finding confirms the usefulness of the electrical conductivity method in studying the fabric tensor of granular media. This result opens the door in using time-lapse electrical resistivity to study non-intrusively the evolution of anisotropy

  5. Submarine Volcanic Morphology of Santorini Caldera, Greece (United States)

    Nomikou, P.; Croff Bell, K.; Carey, S.; Bejelou, K.; Parks, M.; Antoniou, V.


    Santorini volcanic group form the central part of the modern Aegean volcanic arc, developed within the Hellenic arc and trench system, because of the ongoing subduction of the African plate beneath the European margin throughout Cenozoic. It comprises three distinct volcanic structures occurring along a NE-SW direction: Christianna form the southwestern part of the group, Santorini occupies the middle part and Koloumbo volcanic rift zone extends towards the northeastern part. The geology of the Santorini volcano has been described by a large number of researchers with petrological as well as geochronological data. The offshore area of the Santorini volcanic field has only recently been investigated with emphasis mainly inside the Santorini caldera and the submarine volcano of Kolumbo. In September 2011, cruise NA-014 on the E/V Nautilus carried out new surveys on the submarine volcanism of the study area, investigating the seafloor morphology with high-definition video imaging. Submarine hydrothermal vents were found on the seafloor of the northern basin of the Santorini caldera with no evidence of high temperature fluid discharges or massive sulphide formations, but only low temperature seeps characterized by meter-high mounds of bacteria-rich sediment. This vent field is located in line with the normal fault system of the Kolumbo rift, and also near the margin of a shallow intrusion that occurs within the sediments of the North Basin. Push cores have been collected and they will provide insights for their geochemical characteristics and their relationship to the active vents of the Kolumbo underwater volcano. Similar vent mounds occur in the South Basin, at shallow depths around the islets of Nea and Palaia Kameni. ROV exploration at the northern slopes of Nea Kameni revealed a fascinating underwater landscape of lava flows, lava spines and fractured lava blocks that have been formed as a result of 1707-1711 and 1925-1928 AD eruptions. A hummocky topography at

  6. Insight of the fusion behavior of volcanic ash: Implications for Volcanic ash Hazards to Aircraft Safety (United States)

    Song, Wenjia; Hess, Kai-Uwe; Küppers, Ulrich; Scheu, Bettina; Cimarelli, Corrado; Lavallée, Yan; Sohyun, Park; Gattermann, Ulf; Müller, Dirk; Dingwell, Donald Bruce


    The interaction of volcanic ash with jet turbines during via ingestion of ash into engines operating at supra-volcanic temperatures is widely recognized as a potentially fatal hazard for jet aircraft. In the past 12 years, more than 60 modern jet airplanes, mostly jumbo jets, have been damaged by drifting clouds of volcanic ash that have contaminated air routes and airport facilities. Seven of these encounters are known to have caused in flight loss of engine power to jumbo jets carrying a total of more than 2000 passengers. The fusibility of volcanic ash is believed to impact strongly its deposition in the hotter parts of jet engines. Despite this, explicit investigation of ash sintering using standardized techniques is in its infancy. Volcanic ash may vary widely in its physical state and chemical composition between and even within explosive volcanic eruptions. Thus a comparative study of the fusibility of ash which involves a standard recognized techniques would be highly desirable. In this work, nine samples of fine ash, deposited from co-pyroclastic offrom nine different volcanoes which cover a broad range of chemical composition, were investigated. Eight of them were collected from 2001-2009 eruptions. Because of the currently elevated level of eruptive activity and its potential hazards to aircraft safety and the remaining one sample was collected from a 12,121 ± 114 yr B.P. eruption. We used the method of accessing the behavior of deposit-forming impurities in high temperature boiler plants on the basis of observations of the change in shape and size of a cylindrical coal ash to study the fusion phenomena as well as determine the volcanic ash melting behavior by defining four characteristic temperatures (shrinkage temperature, deformation temperature, hemispherical temperature, and flow temperature) by means of heating microscope instrument and different thermal analysis methods. Here, we find that there are similar sticking ability and flow behavior of

  7. Loop quantum cosmology: Anisotropies and inhomogeneities (United States)

    Wilson-Ewing, Edward

    In this dissertation we extend the improved dynamics of loop quantum cosmology from the homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker space-times to cosmological models which allow anisotropies and inhomogeneities. Specifically, we consider the cases of the homogeneous but anisotropic Bianchi type I, II and IX models with a massless scalar field as well as the vacuum, inhomogeneous, linearly polarized Gowdy T3 model. For each case, we derive the Hamiltonian constraint operator and study its properties. In particular, we show how in all of these models the classical big bang and big crunch singularities are resolved due to quantum gravity effects. Since the Bianchi models play a key role in the Belinskii, Khalatnikov and Lifshitz conjecture regarding the nature of generic space-like singularities in general relativity, the quantum dynamics of the Bianchi cosmologies are likely to provide considerable intuition about the fate of such singularities in quantum gravity. In addition, the results obtained here provide an important step toward the full loop quantization of cosmological space-times that allow generic inhomogeneities; this would provide falsifiable predictions that could be compared to observations.

  8. Twinning anisotropy of tantalum during nanoindentation

    Energy Technology Data Exchange (ETDEWEB)

    Goel, Saurav, E-mail: [School of Mechanical and Aerospace Engineering, Queen' s University, Belfast, BT9 5AH (United Kingdom); Beake, Ben [Micro Materials Limited, Willow House, Yale Business Village, Ellice Way, Wrexham LL13 7YL (United Kingdom); Dalton Research Institute, Manchester Metropolitan University, Manchester, M15GD (United Kingdom); Chan, Chi-Wai [School of Mechanical and Aerospace Engineering, Queen' s University, Belfast, BT9 5AH (United Kingdom); Haque Faisal, Nadimul [School of Engineering, Robert Gordon University, Garthdee Road, Aberdeen AB10 7GJ (United Kingdom); Dunne, Nicholas [School of Mechanical and Aerospace Engineering, Queen' s University, Belfast, BT9 5AH (United Kingdom)


    Unlike other BCC metals, the plastic deformation of nanocrystalline Tantalum (Ta) during compression is regulated by deformation twinning. Whether or not this twinning exhibits anisotropy was investigated through simulation of displacement-controlled nanoindentation test using molecular dynamics (MD) simulation. MD data was found to correlate well with the experimental data in terms of surface topography and hardness measurements. The mechanism of the transport of material was identified due to the formation and motion of prismatic dislocations loops (edge dislocations) belonging to the 1/2〈111〉 type and 〈100〉 type Burgers vector family. Further analysis of crystal defects using a fully automated dislocation extraction algorithm (DXA) illuminated formation and migration of twin boundaries on the (110) and (111) orientation but not on the (010) orientation and most importantly after retraction all the dislocations disappeared on the (110) orientation suggesting twinning to dominate dislocation nucleation in driving plasticity in tantalum. A significant finding was that the maximum shear stress (critical Tresca stress) in the deformation zone exceeded the theoretical shear strength of Ta (Shear modulus/2π~10.03 GPa) on the (010) orientation but was lower than it on the (110) and the (111) orientations. In light of this, the conventional lore of assuming the maximum shear stress being 0.465 times the mean contact pressure was found to break down at atomic scale.

  9. $\\Lambda$-inflation and CMB anisotropy

    CERN Document Server

    Lukash, V N


    We explore a broad class of three-parameter inflationary models, called the cosmic gravitational waves consistent with the Harrison-Zel'dovich spectrum of primordial cosmological perturbations, the non-power-law wing-like spectrum of matter density perturbations, high efficiency of these models to meet current observational tests, and others. We show that a parity contribution of the gravitational waves and adiabatic density perturbations into the large-scale temperature anisotropy, T/S $\\sim 1$, is a common feature of are reached in models where (i) the local spectrum shape of density perturbations is flat or slightly red ($n_S{}_\\sim^< 1$), and (ii) the residual potential energy of the inflaton is near the GUT scale ($V_0^{{1/4}} \\sim 10^{16} GeV$). The conditions to find large T/S in the paradigm of cosmic inflation and the relationship of T/S to the ratio of the power spectra, $r$, and to the inflationary $\\gamma$ and Hubble parameters, are discussed. We argue that a simple estimate, T/S$\\simeq 3r\\sime...

  10. Studies of anisotropy of iron based superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Murphy, Jason A. [Iowa State Univ., Ames, IA (United States)


    To study the electronic anisotropy in iron based superconductors, the temperature dependent London penetration depth, Δλ(T), have been measured in several compounds, along with the angular dependent upper critical field, Hc2(T). Study was undertaken on single crystals of Ba(Fe1-xCox)2As2 with x=0.108 and x=0.127, in the overdoped range of the doping phase diagram, characterized by notable modulation of the superconducting gap. Heavy ion irradiation with matching field doses of 6 T and 6.5 T respectively, were used to create columnar defects and to study their effect on the temperature Δλ(T). The variation of the low-temperature penetration depth in both pristine and irradiated samples was fitted with a power-law function Δλ(T) = ATn. Irradiation increases the magnitude of the pre-factor A and decreases the exponent n, similar to the effect on the optimally doped samples. This finding supports the universal s ± scenario for the whole doping range.

  11. Anisotropy in the Interaction of Ultracold Dysprosium

    CERN Document Server

    Kotochigova, Svetlana


    The nature of the interaction between ultracold atoms with a large orbital and spin angular momentum has attracted considerable attention. It was suggested that such interactions can lead to the realization of exotic states of highly correlated matter. Here, we report on a theoretical study of the competing anisotropic dispersion, magnetic dipole-dipole, and electric quadrupole-quadrupole forces between two dysprosium atoms. Each dysprosium atom has an orbital angular momentum L=6 and magnetic moment $\\mu=10\\mu_B$. We show that the dispersion coefficients of the ground state adiabatic potentials lie between 1865 a.u. and 1890 a.u., creating a non-negligible anisotropy with a spread of 25 a.u. and that the electric quadrupole-quadrupole interaction is weak compared to the other interactions. We also find that for interatomic separations $R< 50\\,a_0$ both the anisotropic dispersion and magnetic dipole-dipole potential are larger than the atomic Zeeman splittings for external magnetic fields of order 10 G to ...

  12. Patchy polymer colloids with tunable anisotropy dimensions. (United States)

    Kraft, Daniela J; Hilhorst, Jan; Heinen, Maria A P; Hoogenraad, Mathijs J; Luigjes, Bob; Kegel, Willem K


    We present the synthesis of polymer colloids with continuously tunable anisotropy dimensions: patchiness, roughness, and branching. Our method makes use of controlled fusion of multiple protrusions on highly cross-linked polymer particles produced by seeded emulsion polymerization. Carefully changing the synthesis conditions, we can tune the number of protrusions, or branching, of the obtained particles from spheres with one to three patches to raspberry-like particles with multiple protrusions. In addition to that, roughness is generated on the seed particles by adsorption of secondary nucleated particles during synthesis. The size of the roughness relative to the smooth patches can be continuously tuned by the initiator, surfactant, and styrene concentrations. Seed colloids chemically different from the protrusions induce patches of different chemical nature. The underlying generality of the synthesis procedure allows for application to a variety of seed particle sizes and materials. We demonstrate the use of differently sized polyNIPAM (poly-N-isopropylacrylamide), as well as polystyrene and magnetite filled polyNIPAM seed particles, the latter giving rise to magnetically anisotropic colloids. The high yield together with the uniform, anisotropic shape make them interesting candidates for use as smart building blocks in self-assembling systems.

  13. Nanoscale magnetic ratchets based on shape anisotropy (United States)

    Cui, Jizhai; Keller, Scott M.; Liang, Cheng-Yen; Carman, Gregory P.; Lynch, Christopher S.


    Controlling magnetization using piezoelectric strain through the magnetoelectric effect offers several orders of magnitude reduction in energy consumption for spintronic applications. However strain is a uniaxial effect and, unlike directional magnetic field or spin-polarized current, cannot induce a full 180° reorientation of the magnetization vector when acting alone. We have engineered novel ‘peanut’ and ‘cat-eye’ shaped nanomagnets on piezoelectric substrates that undergo repeated deterministic 180° magnetization rotations in response to individual electric-field-induced strain pulses by breaking the uniaxial symmetry using shape anisotropy. This behavior can be likened to a magnetic ratchet, advancing magnetization clockwise with each piezostrain trigger. The results were validated using micromagnetics implemented in a multiphysics finite elements code to simulate the engineered spatial and temporal magnetic behavior. The engineering principles start from a target device function and proceed to the identification of shapes that produce the desired function. This approach opens a broad design space for next generation magnetoelectric spintronic devices.

  14. CMB anisotropies from a gradient mode (United States)

    Mirbabayi, Mehrdad; Zaldarriaga, Matias


    A linear gradient mode must have no observable dynamical effect on short distance physics. We confirm this by showing that if there was such a gradient mode extending across the whole observable Universe, it would not cause any hemispherical asymmetry in the power of CMB anisotropies, as long as Maldacena's consistency condition is satisfied. To study the effect of the long wavelength mode on short wavelength modes, we generalize the existing second order Sachs-Wolfe formula in the squeezed limit to include a gradient in the long mode and to account for the change in the location of the last scattering surface induced by this mode. Next, we consider effects that are of second order in the long mode. A gradient mode Φ = qṡx generated in Single-field inflation is shown to induce an observable quadrupole moment. For instance, in a matter-dominated model it is equal to Q = 5(qṡx)2/18. This quadrupole can be canceled by superposition of a quadratic perturbation. The result is shown to be a nonlinear extension of Weinberg's adiabatic modes: a long-wavelength physical mode which looks locally like a coordinate transformation.

  15. Microstructural, Magnetic Anisotropy, and Magnetic Domain Structure Correlations in Epitaxial FePd Thin Films with Perpendicular Magnetic Anisotropy (United States)

    Skuza, J. R.; Clavero, C.; Yang, K.; Wincheski, B.; Lukaszew, R. A.


    L1(sub 0)-ordered FePd epitaxial thin films were prepared using dc magnetron sputter deposition on MgO (001) substrates. The films were grown with varying thickness and degree of chemical order to investigate the interplay between the microstructure, magnetic anisotropy, and magnetic domain structure. The experimentally measured domain size/period and magnetic anisotropy in this high perpendicular anisotropy system were found to be correlated following the analytical energy model proposed by Kooy and Enz that considers a delicate balance between the domain wall energy and the demagnetizing stray field energy.

  16. Electrical charging of ash in Icelandic volcanic plumes

    CERN Document Server

    Aplin, Karen L; Nicoll, Keri A


    The existence of volcanic lightning and alteration of the atmospheric potential gradient in the vicinity of near-vent volcanic plumes provides strong evidence for the charging of volcanic ash. More subtle electrical effects are also visible in balloon soundings of distal volcanic plumes. Near the vent, some proposed charging mechanisms are fractoemission, triboelectrification, and the so-called "dirty thunderstorm" mechanism, which is where ash and convective clouds interact electrically to enhance charging. Distant from the vent, a self-charging mechanism, probably triboelectrification, has been suggested to explain the sustained low levels of charge observed on a distal plume. Recent research by Houghton et al. (2013) linked the self-charging of volcanic ash to the properties of the particle size distribution, observing that a highly polydisperse ash distribution would charge more effectively than a monodisperse one. Natural radioactivity in some volcanic ash could also contribute to self-charging of volcan...

  17. Axisymmetric equilibria with pressure anisotropy and plasma flow

    CERN Document Server

    Evangelias, Achilleas


    In this Master thesis we investigate the influence of pressure anisotropy and incompressible flow of arbitrary direction on the equilibrium properties of magnetically confined, axisymmetric toroidal plasmas. The main novel contribution is the derivation of a pertinent generalised Grad-Shafranov equation. This equation includes six free surface functions and recovers known Grad-Shafranov-like equations in the literature as well as the usual static, isotropic one. The form of the generalised equation indicates that pressure anisotropy and flow act additively on equilibrium. In addition, two sets of analytical solutions, an extended Solovev one with a plasma reaching the separatrix and an extended Hernegger-Maschke one for a plasma surrounded by a fixed boundary possessing an X-point, are constructed, particularly in relevance to the ITER and NSTX tokamaks. Furthermore, the impacts both of pressure anisotropy, through an anisotropy function assumed to be uniform on the magnetic surfaces, and plasma flow, via the...

  18. Is the magnetic anisotropy proportional to the orbital moment?

    Energy Technology Data Exchange (ETDEWEB)

    Skomski, R; Kashyap, A; Enders, A


    The relation between orbital moment and magnetic anisotropy is investigated by model calculations, which show that only a part of the spin-orbit coupling contributes to the anisotropy. A large part of the anisotropy energy, about 50% for iron series elements and nearly 100% for rare-earths, is stored in the nonrelativistic part of the Hamiltonian. A feature important for x-ray magnetic circular dichroism is that the orbital moment of heavy atoms rotates with the spin moment, whereas in light atoms, the orbital moment is recreated in each different direction. In the discussion, we consider three examples of current interest in different areas of magnetism, namely, spin-orbit coupling in Gd3+ and Eu2+, surface anisotropy of Nd2Fe14B, and multiferroic magnetization switching using rare-earths. (C) 2011 American Institute of Physics. [doi:10.1063/1.3562445

  19. Effects of electron temperature anisotropy on proton mirror instability evolution (United States)

    Ahmadi, Narges; Germaschewski, Kai; Raeder, Joachim


    Proton mirror modes are large amplitude nonpropagating structures frequently observed in the magnetosheath. It has been suggested that electron temperature anisotropy can enhance the proton mirror instability growth rate while leaving the proton cyclotron instability largely unaffected, therefore causing the proton mirror instability to dominate the proton cyclotron instability in Earth's magnetosheath. Here we use particle-in-cell simulations to investigate the electron temperature anisotropy effects on proton mirror instability evolution. Contrary to the hypothesis, electron temperature anisotropy leads to excitement of the electron whistler instability. Our results show that the electron whistler instability grows much faster than the proton mirror instability and quickly consumes the electron-free energy so that there is no electron temperature anisotropy left to significantly impact the evolution of the proton mirror instability.

  20. Limits on the ions temperature anisotropy in turbulent intracluster medium

    CERN Document Server

    Santo-Lima, R; Pino, E M de Gouveia Dal; Lazarian, A


    Turbulence in the weakly collisional intracluster medium of galaxies (ICM) is able to generate strong thermal velocity anisotropies in the ions (with respect to the local magnetic field direction), if the magnetic moment of the particles is conserved in the absence of Coulomb collisions. In this scenario, the anisotropic MHD turbulence shows a very different statistical behaviour from the isotropic (standard) one and is unable to amplify seed magnetic fields, in disagreement with previous cosmological MHD simulations which are able to explain the observed magnetic fields in the ICM. On the other hand, temperature anisotropy can also drive kinetic instabilities which grow faster near the ions kinetic scales. Observations from the solar wind suggest that these micro- instabilities scatter the ions, thus relaxing the anisotropy. This work aims to compare this relaxation rate with the growth rate of the anisotropies driven by the turbulence. We employ quasilinear theory to estimate the scattering rate provided by...

  1. Optical Anisotropy and Molecular Orientation of Neutralized Curdlan Gels

    National Research Council Canada - National Science Library

    Yasuyuki Maki; Hideki Okamura; Toshiaki Dobashi


    Curdlan gels were prepared by dialyzing its alkaline solutions in HCl solutions, and its optical anisotropy and molecular orientation in the gel were investigated by birefringence and small-angle X-ray scattering (SAXS...

  2. Microstructure, Slip Systems and Yield Stress Anisotropy in Plastic Deformation

    DEFF Research Database (Denmark)

    Winther, Grethe; You, Ze Sheng; Lu, Lei

    The highly anisotropic microstructures in nanotwinned copper produced by electrodeposition provide an excellent opportunity to evaluate models for microstructurally induced mechanical anisotropy. A crystal plasticity model originally developed for the integration of deformation induced dislocation...

  3. Low-temperature magnetic anisotropy in micas and chlorite

    DEFF Research Database (Denmark)

    Biedermann, Andrea R.; Bender Koch, Christian; Lorenz, Wolfram E A;


    of magnetic susceptibility. Because diamagnetic and paramagnetic susceptibility are both linearly dependent on field, separation of the anisotropic contributions requires understanding how the degree of anisotropy of the paramagnetic susceptibility changes as a function of temperature. Note that diamagnetic...... of approximately 6.3-8.7 for individual samples of muscovite, phlogopite and chlorite on cooling from RT to 77 K and between 11.2 and 12.4 for biotite. A decrease in temperature enhances the paramagnetic anisotropy in a mineral. Biotite exhibits a relatively stronger enhancement due to the onset of magnetic......Phyllosilicates, such as micas and chlorite, are common rock-forming minerals and often show preferred orientation in deformed rocks. In combination with single-crystal anisotropy, this leads to anisotropy of physical properties in the rock, such as magnetic susceptibility. In order to effectively...

  4. Tuning Exchange Anisotropy of Exchange-Biased System

    Institute of Scientific and Technical Information of China (English)

    XU Yan; HU Jing-Guo; R.L.Stamps


    Exchange anisotropy in FM/AFM bilayers has given a lot of static magnetization properties such as enhanced coercivity and magnetization loop shifts.These phenomena are primarily from the effective anisotropies intro-duced into a ferromagnet by exchange coupling with a strongly anisotropic antiferromagnet.These effective anisotropies can also be used to explain the dynamic consequences of exchange-biased bilayers.In this article,the dynamic con-sequences such as exchange-induced susceptibility,exchange-induced permeability,and the corresponding domain wall characteristics in the exchange-biased structures of ferromagnet/antiferromagnetl/antiferromagnet2 are studied.The results show that the second antiferromagnetic layer can largely affect the dynamic consequences of exchange-biased bilayers.Especially in the ease of critical temperature,the effects become more obvious.Practically,the exchange anisotropy of biased bilayer system can be tuned by exchange coupling with the second antiferromagnetic layer.

  5. Polarimetric investigation of materials with both linear and circular anisotropy

    DEFF Research Database (Denmark)

    Naydenova, I.; Nikolova, L.; Todorov, T.;


    We investigate light propagation through materials with both linear and circular anisotropy and find the relation of the amplitude and polarization transfer functions to the four anisotropic characteristics: linear circular birefringence, and linear and circular dichroism. We determine these four...

  6. Effects of electron temperature anisotropy on proton mirror instability evolution

    CERN Document Server

    Ahmadi, Narges; Raeder, Joachim


    Proton mirror modes are large amplitude nonpropagating structures frequently observed in the magnetosheath. It has been suggested that electron temperature anisotropy can enhance the proton mirror instability growth rate while leaving the proton cyclotron instability largely unaffected, therefore causing the proton mirror instability to dominate the proton cyclotron instability in Earth's magnetosheath. Here, we use particle-in-cell simulations to investigate the electron temperature anisotropy effects on proton mirror instability evolution. Contrary to the hypothesis, electron temperature anisotropy leads to excitement of the electron whistler instability. Our results show that the electron whistler instability grows much faster than the proton mirror instability and quickly consumes the electron free energy, so that there is no electron temperature anisotropy left to significantly impact the evolution of the proton mirror instability.

  7. CoTaZr/Pd multilayer with perpendicular magnetic anisotropy

    Directory of Open Access Journals (Sweden)

    Yong Chang Lau


    Full Text Available We report a novel perpendicularly magnetized thin film [Co91.5Ta4.5Zr4/Pd]5 multilayer, which exhibits strong perpendicular magnetic anisotropy when grown on 5 nm of Pd and Ru seed layers. The Pd-seeded multilayer annealed at 300 °C shows an effective uniaxial anisotropy constant, Keff = 1.1 MJ m−3, with an anisotropy field as high as 1.6 T. The perpendicular anisotropy is sustained on annealing at 400 °C for 1 h. X-ray diffraction on multilayers with 30 repeats suggests that the use of amorphous CoTaZr reduces the stress of the stack, compared to [Co/Pd] multilayer.

  8. Friction Anisotropy: A unique and intrinsic property of decagonal quasicrystals

    Energy Technology Data Exchange (ETDEWEB)

    Mulleregan, Alice; Park, Jeong Young; Salmeron, Miquel; Ogetree, D.F.; Jenks, C.J.; Thiel, P.A.; Brenner, J.; Dubois, J.M.


    We show that friction anisotropy is an intrinsic property of the atomic structure of Al-Ni-Co decagonal quasicrystals and not only of clean and well-ordered surfaces that can be prepared in vacuum [J.Y. Park et al., Science (2005)]. Friction anisotropy is manifested both in nanometer size contacts obtained with sharp atomic force microscope (AFM) tips as well as in macroscopic contacts produced in pin-on-disc tribometers. We show that the friction anisotropy, which is not observed when an amorphous oxide film covers the surface, is recovered when the film is removed due to wear. Equally important is the loss of the friction anisotropy when the quasicrystalline order is destroyed due to cumulative wear. These results reveal the intimate connection between the mechanical properties of these materials and their peculiar atomic structure.

  9. Dark matter electron anisotropy. A universal upper limit

    Energy Technology Data Exchange (ETDEWEB)

    Borriello, Enrico [Universita ' ' Federico II' ' , Napoli (Italy). Dipt. di Scienze Fisiche; INFN, Sezione di Napoli (Italy); Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Maccione, Luca [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Cuoco, Alessandro [Oskar Klein Centre for Cosmoparticle Physics, Stockholm (Sweden)


    Indirect searches of particle Dark Matter (DM) with high energy Cosmic Rays (CR) are affected by large uncertainties, coming both from the DM side, and from poor understanding of the astrophysical backgrounds. We show that, on the contrary, the DM intrinsic degree of anisotropy in the arrival directions of high energy CR electrons and positrons does not suffer from these unknowns. Furthermore, if contributions from possible local sources are neglected, the intrinsic DM anisotropy sets the maximum degree of total anisotropy. As a consequence, if some anisotropy larger than the DM upper bound is detected, its origin could not be ascribed to DM, and would constitute an unambiguous evidence for the presence of astrophysical local discrete sources of high energy electrons and positrons. The Fermi-LAT will be able to probe such scenarios in the next years. (orig.)

  10. Anisotropy signature in extended images from reverse-time migration

    KAUST Repository

    Sava, Paul


    Reverse-time migration can accurately image complex geologic structures in anisotropic media. Extended images at selected locations in the earth, i.e. at common-image-point gathers (CIPs), carry enough information to characterize the angle-dependent illumination and to provide measurements for migration velocity analysis. Furthermore, inaccurate anisotropy leaves a distinctive signature in CIPs, which can be used to evaluate anisotropy through techniques similar to the ones used in conventional wavefield tomography.

  11. Cosmic microwave background anisotropies seeded by incoherent sources

    CERN Document Server

    Riazuelo, A; Riazuelo, Alain; Deruelle, Nathalie


    The cosmic microwave background anisotropies produced by active seeds, such as topological defects, have been computed recently for a variety of models by a number of authors. In this paper we show how the generic features of the anisotropies caused by active, incoherent, seeds (that is the absence of acoustic peaks at small scales) can be obtained semi-analytically, without entering into the model dependent details of their formation, structure and evolution.

  12. Spatially frustrated S = 1 Heisenberg antiferromagnet with single ion anisotropy (United States)

    Pires, A. S. T.


    Using the SU(3) Schwinger boson formalism, I study the S = 1 square lattice Heisenberg antiferromagnet, at zero temperature, with spatially anisotropic nearest-neighbor couplings frustrated by a next-nearest neighbor interaction and single ion anisotropy. The phase diagram at zero temperature is presented. My calculations show two magnetically ordered phases separated by a quantum-disordered region for all values of the anisotropy.

  13. Ice-Templated W-Cu Composites with High Anisotropy


    Röthlisberger, André; Häberli, Sandra; Galinski, Henning; Dunand, David C.; Spolenak, Ralph


    Controlling anisotropy in self-assembled structures enables engineering of materials with highly directional response. Here, we harness the anisotropic growth of ice walls in a thermal gradient to assemble an anisotropic refractory metal structure, which is then infiltrated with Cu to make a composite. Using experiments and simulations, we demonstrate on the specific example of tungsten-copper composites the effect of anisotropy on the electrical and mechanical properties. The results are com...

  14. Anisotropies in the HI gas distribution toward 3C 196 (United States)

    Kalberla, P. M. W.; Kerp, J.


    Context. The local Galactic Hi gas was found to contain cold neutral medium (CNM) filaments that are aligned with polarized dust emission. These filaments appear to be dominated by the magnetic field and in this case turbulence is expected to show distinct anisotropies. Aims: We use the Galactic Effelsberg-Bonn Hi Survey (EBHIS) to derive 2D turbulence spectra for the Hi distribution in direction to 3C 196 and two more comparison fields. Methods: Prior to Fourier transform we apply a rotational symmetric 50% Tukey window to apodize the data. We derive average as well as position angle dependent power spectra. Anisotropies in the power distribution are defined as the ratio of the spectral power in orthogonal directions. Results: We find strong anisotropies. For a narrow range in position angle, in direction perpendicular to the filaments and the magnetic field, the spectral power is on average more than an order of magnitude larger than parallel. In the most extreme case the anisotropy reaches locally a factor of 130. Anisotropies increase on average with spatial frequency as predicted by Goldreich & Sridhar (1995, ApJ, 438, 763), at the same time the Kolmogorov spectral index remains almost unchanged. The strongest anisotropies are observable for a narrow range in velocity and decay with a power law index close to -8/3, almost identical to the average isotropic spectral index of -2.9 <γ< -2.6. Conclusions: Hi filaments, associated with linear polarization structures in LOFAR observations in direction to 3C 196, show turbulence spectra with marked anisotropies. Decaying anisotropies appear to indicate that we witness an ongoing shock passing the Hi and affecting the observed Faraday depth.

  15. Modeling plasma pressure anisotropy's effect on Saturn's global magnetospheric dynamics (United States)

    Tilley, M.; Harnett, E. M.; Winglee, R.


    A 3D multi-fluid, multi-scale plasma model with a complete treatment of plasma pressure anisotropy is employed to study global magnetospheric dynamics at Saturn. Cassini has observed anisotropies in the Saturnian magnetosphere, and analyses have showed correlations between anisotropy and plasma convection, ring current structure and intensity, confinement of plasma to the equatorial plane, as well as mass transport to the outer magnetosphere. The energization and transport of plasma within Saturn's magnetosphere is impactful upon the induced magnetic environments and atmospheres of potentially habitable satellites such as Enceladus and Titan. Recent efforts to couple pressure anisotropy with 3D multi-fluid plasma modeling have shown a significant move towards matching observations for simulations of Earth's magnetosphere. Our approach is used to study the effects of plasma pressure anisotropy on global processes of the Saturnian magnetosphere such as identifying the effect of pressure anisotropy on the centrifugal interchange instability. Previous simulation results have not completely replicated all aspects of the structure and formation of the interchange 'fingers' measured by Cassini at Saturn. The related effects of anisotropy, in addition to those mentioned above, include contribution to formation of MHD waves (e.g. reduction of Alfvén wave speed) and formation of firehose and mirror instabilities. An accurate understanding of processes such as the interchange instability is required if a complete picture of mass and energy transport at Saturn is to be realized. The results presented here will detail how the inclusion of a full treatment of pressure anisotropy for idealized solar wind conditions modifies the interchange structure and shape of the tail current sheet. Simulation results are compared to observations made by Cassini.

  16. Seismic anisotropy and heterogeneity in the crust beneath southeast Australia from ambient noise tomography (United States)

    Rawlinson, N.; Arroucau, P.; Young, M.; Salmon, M.; Kennett, B. L. N.


    . In the latter case, spatial resolution is decreased to offset the need for the additional parameters necessary to describe azimuthal anisotropy (since heterogeneity and anisotropy trade-off against each other). A comparison of the two results shows that the long wavelength heterogeneity of the two models are similar. In particular, the low velocity region associated with the vast intracratonic Murray Basin, the elevated velocities that closely correlate with outcropping igneous and metamorphic rocks of the Southern Highlands, and the lower velocities that underpin the Newer Volcanics in western Victoria. However, there is a pronounced velocity low beneath the northeast part of the Murray Basin that is present in the anisotropic model but not the isotropic model; interestingly, this appears to correlate with a region of weak anisotropy. The most striking feature of the anisotropic models - for periods 5 s and above - is the dominant alignment of the fast axis of anisotropy in the N-S direction, with magnitudes exceeding 4%. This orientation correlates closely with the dominant geological fabric of the Palaeozoic orogens, and is consistent with a prevailing direction of compression that was perpendicular to the proto-Pacific margin of Gondwana.

  17. Magnetic anisotropy and spin reorientation in U{sub 2}Co{sub 15}Si{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Tereshina, E.A. [Institute of Physics, Academy of Sciences, Na Slovance 2, Prague 18221 (Czech Republic) and Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, Prague 12116 (Czech Republic)]. E-mail:; Andreev, A.V. [Institute of Physics, Academy of Sciences, Na Slovance 2, Prague 18221 (Czech Republic); Institute of Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577 (Japan); Koyama, K. [Institute of Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577 (Japan); Shiokawa, Y. [Institute of Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577 (Japan); Satoh, I. [Institute of Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577 (Japan); Watanabe, K. [Institute of Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577 (Japan)


    Field and temperature dependencies of the magnetization measured along the principal axes of a U{sub 2}Co{sub 15}Si{sub 2} single crystal show that this compound is a ferromagnet with a spontaneous magnetic moment of 14.8 {mu} {sub B} per formula unit (at 4.2 K), located in the basal plane of the hexagonal crystal structure. A strong easy-plane magnetic anisotropy (K {sub 1}=-0.97 MJ m{sup -3} at 4.2 K) is attributed to the U sublattice because Lu{sub 2}Co{sub 15}Si{sub 2} exhibits easy-axis anisotropy with K {sub 1}=0.42 MJ m{sup -3}. The easy-plane anisotropy of U{sub 2}Co{sub 15}Si{sub 2} transforms to a cone of easy axes above 270 K. The magnetization vector approaches the c-axis at 350 K, and the compound has easy c-axis anisotropy up to the Curie temperature T {sub C}=601 K.

  18. Changes in reflectance anisotropy of wheat crop during different phenophases (United States)

    Lunagaria, Manoj M.; Patel, Haridas R.


    The canopy structure of wheat changes significantly with growth stages and leads to changes in reflectance anisotropy. Bidirectional reflectance distribution function characterises the reflectance anisotropy of the targets, which can be approximated. Spectrodirectional reflectance measurements on wheat crop were acquired using a field goniometer system. The bidirectional reflectance spectra were acquired at 54 view angles to cover the hemispheric span up to 60° view zenith. The observations were made during early growth stages till maturity of the crop. The anisotropy was not constant for all wavelengths and anisotropic factors clearly revealed spectral dependence, which was more pronounced in near principal plane. In near infrared, wheat canopy expressed less reflectance anisotropy because of higher multiple scattering. The broad hotspot signature was noticeable in reflectance of canopy whenever view and solar angles were close. Distinct changes in bidirectional reflectance distribution function were observed during booting to flowering stages as the canopy achieves more uniformity, height and head emergence. The function clearly reveals bowl shape during heading to early milking growth stages of the crop. Late growth stages show less prominent gap and shadow effects. Anisotropy index revealed that wheat exhibits changes in reflectance anisotropy with phenological development and with spectral bands.

  19. In-plane anisotropy of 1545 aluminum alloy sheet

    Institute of Scientific and Technical Information of China (English)

    PENG Yong-yi; YIN Zhi-min; YANG Jin; DU Yu-xuan


    The microstructures and the tensile mechanical properties in the rolling plane of 1545 aluminum alloy sheet at different orientations with respect to the rolling direction were studied by means of tensile test,X-ray diffractometer(XRD),optical microscope and transmission electron microscope.The in-plane anisotropy of tensile mechanical properties was calculated and the inverse pole figures of the rolling plane,transversal section and longitudinal section were obtained by Harris method.The results show that the 1545 Al alloy sheet has remarkable in-plane anisotropy of mechanical properties and the main texture component is{110}texture.On the basis of the model that regards the sheet containing only{110}texture as a monocrystal,the relationship of in-plane anisotropy and the anisotropy of crystallography was analyzed.The study shows that it is the combined effects of the anisotropy of crystallography and microstructures that cause the in-plane anisotropy of mechanical properties,but the main cause is the crystallographic texture.

  20. Anisotropy of eddy variability in the global ocean (United States)

    Stewart, K. D.; Spence, P.; Waterman, S.; Sommer, J. Le; Molines, J.-M.; Lilly, J. M.; England, M. H.


    The anisotropy of eddy variability in the global ocean is examined in geostrophic surface velocities derived from satellite observations and in the horizontal velocities of a 1/12° global ocean model. Eddy anisotropy is of oceanographic interest as it is through anisotropic velocity fluctuations that the eddy and mean-flow fields interact dynamically. This study is timely because improved observational estimates of eddy anisotropy will soon be available with Surface Water and Ocean Topography (SWOT) altimetry data. We find there to be good agreement between the characteristics and distributions of eddy anisotropy from the present satellite observations and model ocean surface. In the model, eddy anisotropy is found to have significant vertical structure and is largest close to the ocean bottom, where the anisotropy aligns with the underlying isobaths. The highly anisotropic bottom signal is almost entirely contained in the barotropic variability. Upper-ocean variability is predominantly baroclinic and the alignment is less sensitive to the underlying bathymetry. These findings offer guidance for introducing a parameterization of eddy feedbacks, based on the eddy kinetic energy and underlying bathymetry, to operate on the barotropic flow and better account for the effects of barotropic Reynolds stresses unresolved in coarse-resolution ocean models.

  1. Magnetic anisotropies of (Ga,Mn)As films and nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Hoffmann, Frank


    In this work the magnetic anisotropies of the diluted magnetic semiconductor (Ga,Mn)As were investigated experimentally. (Ga,Mn)As films show a superposition of various magnetic anisotropies which depend sensitively on various parameters such as temperature, carrier concentration or lattice strain. However, the anisotropies of lithographically prepared (Ga,Mn)As elements differ significantly from an unpatterned (Ga,Mn)As film. In stripe-shaped structures this behaviour is caused by anisotropic relaxation of the compressive lattice strain. In order to determine the magnetic anisotropies of individual (Ga,Mn)As nanostructures a combination of ferromagnetic resonance and time-resolved scanning Kerr microscopy was employed in this thesis. In addition, local changes of the magnetic anisotropy in circular and rectangular structures were visualized by making use of spatially resolved measurements. Finally, also the influence of the laterally inhomogeneous magnetic anisotropies on the static magnetic properties, such as coercive fields, was investigated employing spatially resolved static MOKE measurements on individual (Ga,Mn)As elements. (orig.)

  2. Physical modelling of elastic anisotropy in porous media

    Energy Technology Data Exchange (ETDEWEB)

    Furre, Anne-Kari


    During the last decades, anisotropy has become increasingly interesting in hydrocarbon prospecting. Knowledge of anisotropy in the subsurface can improve reservoir production and data interpretation. This thesis presents experimental studies of three different artificial anisotropic media: layered materials, isotropic matrix with stress-induced fractures, and layered media with controlled crack patterns at an oblique angle relative to layering. Layered media were constructed by varying grain size distributions for different layers, which resulted in acoustic and permeability anisotropy. The thin layer materials could be described by Backus modelling provided the wavelength was much larger than the layer periods. Frequency dependent scattering was observed for waves travelling normal to the layers. Saturated wave velocities were consistent with transverse isotropic Biot theory, but because the permeability anisotropy was small, no flow dependent attenuation anisotropy was observed. When sandstones were cemented under stress and then released, to simulate a vertical core or uplift process, predominantly horizontal cracks developed in the samples. On reloading to the cementing stress level, the velocities were below the initial values, which supports the theories of crack growth. In further triaxial tests on the same material a stress-dependent anisotropy occurred similar to what is often seen in natural samples taken from large depths. 70 refs., 200 figs., 56 tabs.

  3. Colossal anisotropy of the magnetic properties of doped lithium nitrodometalates

    Energy Technology Data Exchange (ETDEWEB)

    Antropov, Vladimir P [Ames Laboratory; Antonov, Victor N [Ames Laboratory


    We present a first-principles investigation of the electronic structure and physical properties of doped lithium nitridometalates Li2(Li1-xMx)N (LiMN) with M = Cr, Mn, Fe, Co, and Ni. The diverse properties include the equilibrium magnetic moments, magneto-crystalline anisotropy, magneto-optical Kerr spectra, and x-ray magnetic circular dichroism. We explain the colossal magnetic anisotropy in LiFeN by its unique electronic structure which ultimately leads to a series of unusual physical properties. The most unique property is a complete suppression of relativistic effects and freezing of orbital moments for in-plane orientation of the magnetization. This leads to the colossal spatial anisotropy of many magnetic properties including energy, Kerr, and dichroism effects. LiFeN is identified as an ultimate single-ion anisotropy system where a nearly insulating state can be produced by a spin orbital coupling alone. A very nontrivial strongly fluctuating and sign changing character of the magnetic anisotropy with electronic 3d-atomic doping is predicted theoretically. A large and highly anisotropic Kerr effect due to the interband transitions between atomic-like Fe 3d bands is found for LiFeN. A giant anisotropy of the x-ray magnetic circular dichroism for the Fe K spectrum and a very weak one for the Fe L2,3 spectra in LiFeN are also predicted.

  4. Limits on the ions temperature anisotropy in turbulent intracluster medium

    Energy Technology Data Exchange (ETDEWEB)

    Santos-Lima, R. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany); Potsdam Univ. (Germany). Inst. fuer Physik und Astronomie; Univ. de Sao Paulo (Brazil). Inst. de Astronomia, Geofisica e Ciencias Atmosfericas; Yan, H. [Deutsches Elektronen-Synchrotron (DESY), Zeuthen (Germany); Potsdam Univ. (Germany). Inst. fuer Physik und Astronomie; Gouveia Dal Pino, E.M. de [Univ. de Sao Paulo (Brazil). Inst. de Astronomia, Geofisica e Ciencias Atmosfericas; Lazarian, A. [Wisconsin Univ., Madison, WI (United States). Dept. of Astronomy


    Turbulence in the weakly collisional intracluster medium of galaxies (ICM) is able to generate strong thermal velocity anisotropies in the ions (with respect to the local magnetic field direction), if the magnetic moment of the particles is conserved in the absence of Coulomb collisions. In this scenario, the anisotropic pressure magnetohydrodynamic (AMHD) turbulence shows a very different statistical behaviour from the standard MHD one and is unable to amplify seed magnetic fields, in disagreement with previous cosmological MHD simulations which are successful to explain the observed magnetic fields in the ICM. On the other hand, temperature anisotropies can also drive plasma instabilities which can relax the anisotropy. This work aims to compare the relaxation rate with the growth rate of the anisotropies driven by the turbulence. We employ quasilinear theory to estimate the ions scattering rate due to the parallel firehose, mirror, and ion-cyclotron instabilities, for a set of plasma parameters resulting from AMHD simulations of the turbulent ICM. We show that the ICM turbulence can sustain only anisotropy levels very close to the instabilities thresholds. We argue that the AMHD model which bounds the anisotropies at the marginal stability levels can describe the Alfvenic turbulence cascade in the ICM.

  5. Analysis of North Sky Cosmic Ray Anisotropy with Atmospheric Neutrinos (United States)

    Wills, Elizabeth; IceCube Collaboration


    Since the discovery of Cosmic Ray anisotropy, no experiment has definitively discovered the source of this unexpected phenomenon. Studying the cosmic rays' neutral daughter particles with pointing capabilities, like neutrinos, could shed new light. This can be done at two levels; a source which produces cosmic rays must also produce high energy astrophysical neutrinos, and low energy atmospheric neutrinos are made when the cosmic rays interact with the atmosphere. This analysis focuses on atmospheric neutrinos detected by IceCube, a Cherenkov detector instrumenting a kilometer cubed of glacial ice at the South Pole. The anisotropy and its energy dependence have been studied in the Southern sky using atmospheric muons by IceCube. In the North, gamma ray detectors, such as HAWC, and Argo-YBJ, have observed this anisotropy in cosmic ray showers. Thus far, no single- detector full-sky map exists of the anisotropy. Using IceCube's neutrino data, we can complement these studies with an exploration of the northern sky anisotropy at higher energies of cosmic rays. This could bring us much closer to understanding the complete picture of this anisotropy across energy levels and the whole sky.

  6. Characterization of optical anisotropy in quantum wells under compressive anisotropic in-plane strain (United States)

    Biermann, Mark L.; Walters, Matthew; Diaz-Barriga, James; Rabinovich, W. S.


    Anisotropic in-plane strain in quantum wells leads to an optical polarization anisotropy that can be exploited for device applications. We have determined that for many anisotropic compressive strain cases, the dependence of the optical anisotropy is linear in the strain anisotropy. This result holds for a variety of well and barrier materials and widths and for various overall strain conditions. Further, the polarization anisotropy per strain anisotropy varies as the reciprocal of the energy separation of the relevant hole sub-bands. Hence, a general result for the polarization anisotropy per strain anisotropy is avialable for cases of compressive anisotropic in-plane strain.

  7. Characterization of optical anisotropy in quantum wells under compressive anisotropic in-plane strain

    Energy Technology Data Exchange (ETDEWEB)

    Biermann, Mark L [Physics Department, 566 Brownson Rd., U.S. Naval Academy, Annapolis, MD 21402 (United States); Walters, Matthew [Physics Department, 566 Brownson Rd., U.S. Naval Academy, Annapolis, MD 21402 (United States); Diaz-Barriga, James [Physics Department, 566 Brownson Rd., U.S. Naval Academy, Annapolis, MD 21402 (United States); Rabinovich, W S [Naval Research Laboratory, Code 5652, 4555 Overlook Ave. SW, Washington, DC 20375-5320 (United States)


    Anisotropic in-plane strain in quantum wells leads to an optical polarization anisotropy that can be exploited for device applications. We have determined that for many anisotropic compressive strain cases, the dependence of the optical anisotropy is linear in the strain anisotropy. This result holds for a variety of well and barrier materials and widths and for various overall strain conditions. Further, the polarization anisotropy per strain anisotropy varies as the reciprocal of the energy separation of the relevant hole sub-bands. Hence, a general result for the polarization anisotropy per strain anisotropy is available for cases of compressive anisotropic in-plane strain.

  8. The variation of linewidth in exchange coupled bilayer films with stress anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Lei [Inner Mongolia Key Lab of Nanoscience and Nanotechnology and School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021 (China); Rong, Jianhong, E-mail: [Inner Mongolia Key Lab of Nanoscience and Nanotechnology and School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021 (China); Yun, Guohong, E-mail: [Inner Mongolia Key Lab of Nanoscience and Nanotechnology and School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021 (China); College of Physics and Electronic Information, Inner Mongolia Normal University, Hohhot 010022 (China); Wang, Dong; Bao, Lingbo [Inner Mongolia Key Lab of Nanoscience and Nanotechnology and School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021 (China)


    The frequency linewidth and the field linewidth in ferromagnetic/antiferromagnetic bilayer films with stress anisotropy have been investigated by using ferromagnetic resonance method. The effects of the stress anisotropy for in-plane anisotropy, weak and strong perpendicular anisotropy on linewidth are observed. It is found that the frequency and the field linewidth all increase for in-plane and weak perpendicular anisotropy, as the stress anisotropy field increases. And furthermore, the stress anisotropy field affects obviously the frequency and the field linewidth for unsaturation field.

  9. Quaternary volcanism in the Acambay graben, Mexican Volcanic Belt: Re-evaluation for potential volcanic danger in central Mexico (United States)

    Aguirre-Diaz, G. J.; Pedrazzi, D.; Lacan, P.; Roldan-Quintana, J.; Ortuňo, M.; Zuniga, R. R.; Laurence, A.


    The Mexican Volcanic Belt (MVB) is best known for the major active stratovolcanoes, such as Popocatépetl, Citlaltépetl and Colima. The most common stratovolcanoes in this province are modest-size cones with heights of 800 to 1000 m. Examples are Tequila, Sangangüey, Las Navajas, Culiacán, La Joya, El Zamorano, Temascalcingo and Altamirano; these last two were formed within the Acambay Graben in central MVB. The Acambay graben (20 x 70 km) is 100 km to the NW of Mexico City, with E-W trending seismically active normal faults; in particular the Acambay-Tixmadejé fault related to a mB =7 earthquake in 1912. Within the graben there are many volcanic structures, including calderas, domes, cinder cones and stratovolcanoes; Temascalcingo and Altamirano are the largest, with about 800 and 900 m heights, respectively. Temascalcingo is mostly composed of dacitic lavas and block and ash flow deposits. Includes a 3 x 2.5 km summit caldera and a magmatic sector collapse event with the associated debris avalanche deposit. 14C ages of 37-12 ka correspond to the volcano's latest phases that produced pyroclastic deposits. A major plinian eruption formed the San Mateo Pumice with an age of <20 Ka. Altamirano volcano is poorly studied; it is andesitic-dacitic, composed of lavas, pyroclastic flow deposits, and pumice fallouts. Morphologically is better preserved than Temascalcingo, and it should be younger. 14C ages of 4.0-2.5 ka were performed in charcoal within pyroclastic flow deposits that apparently were erupted from Altamirano. An undated 3 m thick pumice fallout on the flanks of Altamirano volcano could be also Holocene. It represents a major explosive event. The relatively young ages found in volcanic deposits within the Acambay graben raise the volcanic danger level in this area, originally thought as an inactive volcanic zone. The two major volcanoes, Temascalcingo and Altamirano, should be considered as dormant volcanoes that could restart activity at any time. We

  10. Noise-induced variability of volcanic extrusions (United States)

    Alexandrov, D. V.; Bashkirtseva, I. A.; Ryashko, L. B.


    Motivated by important physical applications, we study a non-linear dynamics of volcanic extrusions on the basis of a simple pressure-mass flow model. We demonstrate that the deterministic phase portrait represents either the bulbous-type curves or closed paths stretched to their left depending on the initial conditions. The period of phase trajectories therewith increases when the pressure drop between the conduit top and bottom compensates the lava column pressure in it. Stochastic forcing changes the system dynamics drastically. We show that a repetitive scenario of volcanic behaviour with intermittency of stochastic oscillations of different extrusion amplitudes and frequencies appears in the presence of noises. As this takes place, the mean values of interspike intervals characterizing the system periodicity have a tendency to grow with increasing the noise intensity. The probability distribution functions confirming this dynamic behaviour are constructed.

  11. Triggering of volcanic eruptions by large earthquakes (United States)

    Nishimura, Takeshi


    When a large earthquake occurs near an active volcano, there is often concern that volcanic eruptions may be triggered by the earthquake. In this study, recently accumulated, reliable data were analyzed to quantitatively evaluate the probability of the occurrence of new eruptions of volcanoes located near the epicenters of large earthquakes. For volcanoes located within 200 km of large earthquakes of magnitude 7.5 or greater, the eruption occurrence probability increases by approximately 50% for 5 years after the earthquake origin time. However, no significant increase in the occurrence probability of new eruptions was observed at distant volcanoes or for smaller earthquakes. The present results strongly suggest that new eruptions are likely triggered by static stress changes and/or strong ground motions caused by nearby large earthquakes. This is not similar to the previously presented evidence that volcanic earthquakes at distant volcanoes are remotely triggered by surface waves generated by large earthquakes.

  12. Obsidian hydration dating of volcanic events (United States)

    Friedman, I.; Obradovich, J.


    Obsidian hydration dating of volcanic events had been compared with ages of the same events determined by the 14C and KAr methods at several localities. The localities, ranging in age from 1200 to over 1 million yr, include Newberry Craters, Oregon; Coso Hot Springs, California; Salton Sea, California; Yellowstone National Park, Wyoming; and Mineral Range, Utah. In most cases the agreement is quite good. A number of factors including volcanic glass composition and exposuretemperature history must be known in order to relate hydration thickness to age. The effect of composition can be determined from chemical analysis or the refractive index of the glass. Exposure-temperature history requires a number of considerations enumerated in this paper. ?? 1981.

  13. Volcanic ash impacts on critical infrastructure (United States)

    Wilson, Thomas M.; Stewart, Carol; Sword-Daniels, Victoria; Leonard, Graham S.; Johnston, David M.; Cole, Jim W.; Wardman, Johnny; Wilson, Grant; Barnard, Scott T.


    Volcanic eruptions can produce a wide range of hazards. Although phenomena such as pyroclastic flows and surges, sector collapses, lahars and ballistic blocks are the most destructive and dangerous, volcanic ash is by far the most widely distributed eruption product. Although ash falls rarely endanger human life directly, threats to public health and disruption to critical infrastructure services, aviation and primary production can lead to significant societal impacts. Even relatively small eruptions can cause widespread disruption, damage and economic loss. Volcanic eruptions are, in general, infrequent and somewhat exotic occurrences, and consequently in many parts of the world, the management of critical infrastructure during volcanic crises can be improved with greater knowledge of the likely impacts. This article presents an overview of volcanic ash impacts on critical infrastructure, other than aviation and fuel supply, illustrated by findings from impact assessment reconnaissance trips carried out to a wide range of locations worldwide by our international research group and local collaborators. ‘Critical infrastructure’ includes those assets, frequently taken for granted, which are essential for the functioning of a society and economy. Electricity networks are very vulnerable to disruption from volcanic ash falls. This is particularly the case when fine ash is erupted because it has a greater tendency to adhere to line and substation insulators, where it can cause flashover (unintended electrical discharge) which can in turn cause widespread and disruptive outages. Weather conditions are a major determinant of flashover risk. Dry ash is not conductive, and heavy rain will wash ash from insulators, but light rain/mist will mobilise readily-soluble salts on the surface of the ash grains and lower the ash layer’s resistivity. Wet ash is also heavier than dry ash, increasing the risk of line breakage or tower/pole collapse. Particular issues for water

  14. The Zuni-Bandera Volcanic Field, NM: An Analog for Exploring Planetary Volcanic Terrains (United States)

    Bleacher, J. E.; Garry, W. B.; Zimbelman, J. R.; Crumpler, L. S.; Aubele, J. C.


    The Zuni-Bandera volcanic field, near Grants, New Mexico, is comprised of volcanic deposits from several basaltic eruptions during the last million years. This vent field exhibits a diverse group of coalesced lava flows and displays well-preserved volcanic features including a’a and pahoehoe flows, collapsed lava tubes, cinder cones and low shields. The McCartys flow is a 48-km long inflated basalt flow and is the youngest in the field at around 3000 years old. Over the last three years we have used the Zuni-Bandera volcanic field, and the McCartys flow in particular, as a terrestrial analog for exploring planetary volcanic fields, and understanding the role of lava sheet inflation in flow field development. We have conducted three different styles of analog tests, 1) basic field science focused on understanding lava sheet inflation, 2) mission operations tests related to EVA design and real-time modification of traverse plans, and 3) science enabling technology tests. The Zuni-Bandera field is an ideal location for each style of analog test because it provides easy access to a diverse set of volcanic features with variable quality of preservation. However, many limitations must also be considered in order to maximize lessons learned. The McCartys flow displays well-preserved inflation plateaus that rise up to 15 m above the surrounding field. The preservation state enables textures and morphologies indicative of this process to be characterized. However, the pristine nature of the flow does not compare well with the much older and heavily modified inflated flows of Mars and the Moon. Older flows west of McCartys add value to this aspect of analog work because of their degraded surfaces, development of soil horizons, loose float, and limited exposure of outcrops, similar to what might be observed on the Moon or Mars. EVA design tests and science enabling technology tests at the Zuni-Bandera field provide the opportunity to document and interpret the relationships

  15. Anisotropy of magnetic susceptibility (AMS) data from Miocene ignimbrites in the Goldfield, Gold Point, and Beatty areas, western Great Basin, and their bearing on ignimbrite emplacement mechanisms during concurrent tectonism (United States)

    Fitter, T.; Geissman, J. W.; Jackson, J.


    As part of an ongoing and multifaceted project to better understand the history of Neogene right-lateral displacement transfer system in the southernmost Walker Lane area, we have collected paleomagnetic and anisotropy of magnetic susceptibility (AMS) data from outflow facies of regionally extensive mid-Miocene ignimbrites that originated from the Timber Mountain caldera complex and the upper Miocene Tuff of Slate Ridge, whose source remains less clear. With an area that extends from north Goldfield to west of Beatty, Nevada, we have obtained data from 277 sites, with 8 to 20 independent samples collected as drilled cores from each site. Most of our sampling is concentrated in the Slate Ridge to Gold Mountain areas, south of Gold Point, where these Miocene volcanic rocks have been deformed during the development of a regional, NNW-dipping detachment system. Preliminary AMS results for sites in the Tuff of Slate Ridge east of Gold Point show well imbricated fabrics, which, after correction for the orientation of compaction fabrics considered to represent the paleohorizontal, yield a general transport direction to the northwest (e.g., site GP211, with K3 trend of 313.0° and plunge of 61.4° (confidence angles (CA) = 9.9/5.7) and a source direction (K1 trend) of 129.2° and plunge of 28.6° (CA = 40.9/5.7, based on n=12 specimens). An average of data from seven sites in the Tuff of Slate Ridge in this area (n = 104) specimens yields a similar estimated transport direction of ~ 338° and a K1 trend to the origin of ~146°. Average bulk susceptibility (Km) from these seven sites is 5.03E-03 (SI volume units) and a degree of anisotropy (Pj) of 1.013. Most sites in the Timber Mountain sequence show well-imbricated fabrics (e.g., site GP02, yields an estimated transport direction of 9.5° and plunge of 82.4° (CA = 4.1/3.3) and a direction to the source of 145.9° and plunge of 5.5° (CA = 19.6/4.1, n=40 specimens). An average of data from four sites southeast of Gold

  16. Volcanic alert system (VAS) developed during the 2011-2014 El Hierro (Canary Islands) volcanic process (United States)

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


    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.

  17. Durham, North Carolina, Students Study Martian Volcanism (United States)


    This image of the wall of a graben a depressed block of land between two parellel faults in Tyrrhena Terra, in Mars' ancient southern highlands, was taken by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) at 0914 UTC (4:14 a.m. EST) on February 6, 2008, near 17.3 degrees south latitude, 95.5 degrees east longitude. CRISM's image was taken in 544 colors covering 0.36-3.92 micrometers, and shows features as small as 35 meters (115 feet) across. The region covered is just over 10 kilometers (6.2 miles) wide at its narrowest point. This image was part of an investigation planned by students in four high schools in Durham, North Carolina. The students are working with the CRISM science team in a project called the Mars Exploration Student Data Teams (MESDT), which is part of NASA's Mars Public Engagement Program and Arizona State University's Mars Education Program. Starting with a medium-resolution map of the area, taken as part of CRISM's 'multispectral survey' campaign to map Mars in 72 colors at 200 meters (660 feet) per pixel, the students identified a key rock outcrop to test their hypothesis that the irregular depression was formed by Martian volcanism. They provided the coordinates of the target to CRISM's operations team, who took a high-resolution image of the site. The Context Imager (CTX) accompanied CRISM with a 6 meter (20 feet) per pixel, high-resolution image to sharpen the relationship of spectral variations to the underlying surface structures. The Durham students worked with a mentor on the CRISM team to analyze the data, and presented their results at the 39th Lunar and Planetary Science Conference, held in League City, Texas, on March 10-14, 2008. The upper panel of the image shows the location of the CRISM data and the surrounding, larger CTX image, overlain on an image mosaic taken by the Thermal Emission Imaging System (THEMIS) on Mars Odyssey. The mosaic has been color-coded for elevation using data from the Mars Orbiter Laser

  18. Durham, North Carolina, Students Study Martian Volcanism (United States)


    This image of the wall of a graben a depressed block of land between two parellel faults in Tyrrhena Terra, in Mars' ancient southern highlands, was taken by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) at 0914 UTC (4:14 a.m. EST) on February 6, 2008, near 17.3 degrees south latitude, 95.5 degrees east longitude. CRISM's image was taken in 544 colors covering 0.36-3.92 micrometers, and shows features as small as 35 meters (115 feet) across. The region covered is just over 10 kilometers (6.2 miles) wide at its narrowest point. This image was part of an investigation planned by students in four high schools in Durham, North Carolina. The students are working with the CRISM science team in a project called the Mars Exploration Student Data Teams (MESDT), which is part of NASA's Mars Public Engagement Program and Arizona State University's Mars Education Program. Starting with a medium-resolution map of the area, taken as part of CRISM's 'multispectral survey' campaign to map Mars in 72 colors at 200 meters (660 feet) per pixel, the students identified a key rock outcrop to test their hypothesis that the irregular depression was formed by Martian volcanism. They provided the coordinates of the target to CRISM's operations team, who took a high-resolution image of the site. The Context Imager (CTX) accompanied CRISM with a 6 meter (20 feet) per pixel, high-resolution image to sharpen the relationship of spectral variations to the underlying surface structures. The Durham students worked with a mentor on the CRISM team to analyze the data, and presented their results at the 39th Lunar and Planetary Science Conference, held in League City, Texas, on March 10-14, 2008. The upper panel of the image shows the location of the CRISM data and the surrounding, larger CTX image, overlain on an image mosaic taken by the Thermal Emission Imaging System (THEMIS) on Mars Odyssey. The mosaic has been color-coded for elevation using data from the Mars Orbiter Laser

  19. Minerogenesis of volcanic caves of Kenya.

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    Rossi Antonio


    Full Text Available Kenya is one of the few countries in which karst cavities are scarce with respect to volcanic ones, which are widespread throughout the whole country. The great variability in lava composition allowed the evolution of very different cavities, some of which are amongst the largest lava tubes of the world. As normal for such a kind of cave, the hosted speleothems and cave minerals are scarce but important from the minerogenetic point of view. Anyway up to present no specific mineralogical research have been carried out therein. During the 8th International Symposium on Volcanospeleology, held in Nairobi in February 1998, some of the most important volcanic caves of Kenya have been visited and their speleothems and/or chemical deposits sampled: most of them were related to thick guano deposits once present inside these cavities. Speleothems mainly consisted of opal or gypsum, while the deposits related to guano often resulted in a mixture of sulphates and phosphates. The analyses confirmed the great variability in the minerogenetic mechanisms active inside the volcanic caves, which consequently allow the evolution of several different minerals even if the total amount of chemical deposit is scarce. Among the observed minerals kogarkoite, phillipsite and hydroxyapophyllite, must be cited because they are new cave minerals not only for the lava tubes of Kenya, but also for the world cave environment. The achieved results are compared with the available random data from previous literature in order to allow an updated overview on the secondary cave minerals of Kenya.

  20. A cryptoendolithic community in volcanic glass. (United States)

    Herrera, Aude; Cockell, Charles S; Self, Stephen; Blaxter, Mark; Reitner, Joachim; Thorsteinsson, Thorsteinn; Arp, Gernot; Dröse, Wolfgang; Tindle, Andrew G


    Fluorescent in situ hybridization (FISH) and 16S rDNA analysis were used to characterize the endolithic colonization of silica-rich rhyolitic glass (obsidian) in a barren terrestrial volcanic environment in Iceland. The rocks were inhabited by a diverse eubacterial assemblage. In the interior of the rock, we identified cyanobacterial and algal 16S (plastid) sequences and visualized phototrophs by FISH, which demonstrates that molecular methods can be used to characterize phototrophs at the limits of photosynthetically active radiation (PAR). Temperatures on the surface of the dark rocks can exceed 40 degrees C but are below freezing for much of the winter. The rocks effectively shield the organisms within from ultraviolet radiation. Although PAR sufficient for photosynthesis cannot penetrate more than approximately 250 mum into the solid rock, the phototrophs inhabit cavities; and we hypothesize that by weathering the rock they may contribute to the formation of cavities in a feedback process, which allows them to acquire sufficient PAR at greater depths. These observations show how pioneer phototrophs can colonize the interior of volcanic glasses and rocks, despite the opaque nature of these materials. The data show that protected microhabitats in volcanic rocky environments would have been available for phototrophs on early Earth.

  1. Venus volcanism: initial analysis from magellan data. (United States)

    Head, J W; Campbell, D B; Elachi, C; Guest, J E; McKenzie, D P; Saunders, R S; Schaber, G G; Schubert, G


    Magellan images confirm that volcanism is widespread and has been fimdamentally important in the formation and evolution of the crust of Venus. High-resolution imaging data reveal evidence for intrusion (dike formation and cryptodomes) and extrusion (a wide range of lava flows). Also observed are thousands of small shield volcanoes, larger edifices up to several hundred kilometers in diameter, massive outpourings of lavas, and local pyroclastic deposits. Although most features are consistent with basaltic compositions, a number of large pancake-like domes are morphologically similar to rhyolite-dacite domes on Earth. Flows and sinuous channels with lengths of many hundreds of kilometers suggest that extremely high effusion rates or very fluid magmas (perhaps komatiites) may be present. Volcanism is evident in various tectonic settings (coronae, linear extensional and compressional zones, mountain belts, upland rises, highland plateaus, and tesserae). Volcanic resurfacing rates appear to be low (less than 2 Km(3)/yr) but the significance of dike formation and intrusions, and the mode of crustal formation and loss remain to be established.

  2. Venus volcanism: Initial analysis from Magellan data (United States)

    Head, J.W.; Campbell, D.B.; Elachi, C.; Guest, J.E.; Mckenzie, D.P.; Saunders, R.S.; Schaber, G.G.; Schubert, G.


    Magellan images confirm that volcanism is widespread and has been fundamentally important in the formation and evolution of the crust of Venus. High-resolution imaging data reveal evidence for intrusion (dike formation and cryptodomes) and extrusion (a wide range of lava flows). Also observed are thousands of small shield volcanoes, larger edifices up to several hundred kilometers in diameter, massive outpourings of lavas, and local pyroclastic deposits. Although most features are consistent with basaltic compositions, a number of large pancake-like domes are morphologically similar to rhyolite-dacite domes on Earth. Flows and sinuous channels with lengths of many hundreds of kilometers suggest that extremely high effusion rates or very fluid magmas (perhaps komatiites) may be present. Volcanism is evident in various tectonic settings (coronae, linear extensional and compressional zones, mountain belts, upland rises, highland plateaus, and tesserae). Volcanic resurfacing rates appear to be low (less than 2 km3/yr) but the significance of dike formation and intrusions, and the mode of crustal formation and loss remain to be established.

  3. Texture and anisotropy in ferroelectric lead metaniobate (United States)

    Iverson, Benjamin John

    Ferroelectric lead metaniobate, PbNb2O6, is a piezoelectric ceramic typically used because of its elevated Curie temperature and anisotropic properties. However, the piezoelectric constant, d33, is relatively low in randomly oriented ceramics when compared to other ferroelectrics. Crystallographic texturing is often employed to increase the piezoelectric constant because the spontaneous polarization axes of grains are better aligned. In this research, crystallographic textures induced through tape casting are distinguished from textures induced through electrical poling. Texture is described using multiple quantitative approaches utilizing X-ray and neutron time-of-flight diffraction. Tape casting lead metaniobate with an inclusion of acicular template particles induces an orthotropic texture distribution. Templated grain growth from seed particles oriented during casting results in anisotropic grain structures. The degree of preferred orientation is directly linked to the shear behavior of the tape cast slurry. Increases in template concentration, slurry viscosity, and casting velocity lead to larger textures by inducing more particle orientation in the tape casting plane. The maximum 010 texture distributions were two and a half multiples of a random distribution. Ferroelectric texture was induced by electrical poling. Electric poling increases the volume of material oriented with the spontaneous polarization direction in the material. Samples with an initial paraelectric texture exhibit a greater change in the domain volume fraction during electrical poling than randomly oriented ceramics. In tape cast samples, the resulting piezoelectric response is proportional to the 010 texture present prior to poling. This results in property anisotropy dependent on initial texture. Piezoelectric properties measured on the most textured ceramics were similar to those obtained with a commercial standard.

  4. Frequency dispersion of the magnetic anisotropy field in metallic magnetic films with the plane anisotropy of electrical conductivity

    Energy Technology Data Exchange (ETDEWEB)

    Zimin, A.B.; Kornev, Y.V.; Sementsova, T.M.; Sidorenkov, V.V.


    Presence of the frequency dispersion of the field of induced single axis magnetic anisotropy and the angular position of the axis of easy magnetization in the film plane has been determined in metallic magnetic films with plane anisotropy of electrical conductivity. Theoretical dependences have been obtained which given satisfactory agreement with experimental data for cobalt and permalloy films prepared by sputtering on glass substrates and using the incident molecular beam under an angle with the substrate.

  5. Application of the anisotropy field distribution method to arrays of magnetic nanowires


    De La Torre Medina, Joaquin; Darques, Michaël; Piraux, Luc; Encinas, Armando


    The applicability of the anisotropy field distribution method and the conditions required for an accurate determination of the effective anisotropy field in arrays of magnetic nanowires have been evaluated. In arrays of magnetic nanowires that behave as ideal uniaxial systems having only magnetostatic contributions to the effective anisotropy field, i.e., shape anisotropy and magnetostatic coupling, the method yields accurate values of the average anisotropy field at low-moderate dipolar coup...

  6. Morphology, volcanism, and mass wasting in Crater Lake, Oregon (United States)

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


    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

  7. Integrating volcanic gas monitoring with other geophysical networks in Iceland (United States)

    Pfeffer, Melissa A.


    The Icelandic Meteorological Office/Icelandic Volcano Observatory is rapidly developing and improving the use of gas measurements as a tool for pre- and syn-eruptive monitoring within Iceland. Observations of deformation, seismicity, hydrological properties, and gas emissions, united within an integrated approach, can provide improved understanding of subsurface magma movements. This is critical to evaluate signals prior to and during volcanic eruptions, issue timely eruption warnings, forecast eruption behavior, and assess volcanic hazards. Gas measurements in Iceland need to be processed to account for the high degree of gas composition alteration due to interaction with external water and rocks. Deeply-sourced magmatic gases undergo reactions and modifications as they move to the surface that exercise a strong control on the composition of surface emissions. These modifications are particularly strong at ice-capped volcanoes where most surface gases are dissolved in glacial meltwater. Models are used to project backwards from surface gas measurements to what the magmatic gas composition was prior to upward migration. After the pristine magma gas composition has been determined, it is used together with fluid compositions measured in mineral hosted melt inclusions to calculate magmatic properties to understand magma storage and migration and to discern if there have been changes in the volcanic system. The properties derived from surface gas measurements can be used as input to models interpreting deformation and seismic observations, and can be used as an additional, independent observation when interpreting hydrological and seismic changes. An integrated approach aids with determining whether observed hydro/geological changes can be due to the presence of shallow magma. Constraints on parameters such as magma gas content, viscosity and compressibility can be provided by the approach described above, which can be utilized syn-eruptively to help explain

  8. On the origin of the anisotropy observed beneath the westernmost Mediterranean region (United States)

    Diaz, Jordi


    The Iberian Peninsula and Northern Morocco region provides an excellent opportunity to investigate the origin of subcrustal anisotropy. Following the TopoIberia-Iberarray experiment, anisotropic properties have been explored in a dense network of 60x60 km spaced broad-band stations, resulting in more than 300 sites investigated over an area extending from the Bay of Biscay to the Sahara platform and covering more than 6000.000 km2. The rather uniform N100°E FPD retrieved beneath the Variscan Central Iberian Massif is consistent with global mantle flow models taking into account contributions of surface plate motion, density variations and net lithosphere rotation. The origin of this anisotropy is hence globally related to the lattice preferred orientation of mantle minerals generated by mantle flow at asthenospheric depths, although significant regional variations are observed. The anisotropic parameters retrieved from single events providing high quality data show significant differences for stations located in the Variscan units of NW Iberia, suggesting that the region includes multiple anisotropic layers or complex anisotropy systems have to be considered there. The rotation of the FDE along the Gibraltar arc following the curvature of the Rif-Betic chain has been interpreted as an evidence of mantle flow deflected around the high velocity slab beneath the Gibraltar Arc. Beneath the SW corner of Iberia and the High Atlas zone, small delay times and inconsistent FPD have been detected, suggesting the presence of vertical mantle flow affecting the anisotropic structure of the asthenosphere. Future developments will include a better integration with the anisotropic estimations provided by Pn tomography and, in particular, with those arising from surface wave tomographic inversions using TopoIberia-Ibearray results. Additionally, the contribution of crustal anisotropy could be estimated from the analysis of receiver functions. The detailed knowledge on the

  9. Comparison of Low Cost Miniature Spectrometers for Volcanic SO2 Emission Measurements

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    Euripides P. Kantzas


    Full Text Available Miniature ultraviolet USB coupled spectrometers have become ubiquitously applied over the last decade for making volcanic SO2 emission rate measurements. The dominantly applied unit has recently been discontinued however, raising the question of which currently available devices should now be implemented. In this paper, we consider, and make recommendations on this matter, by studying a number of inexpensive compact spectrometers in respect of measurement performance and thermal behaviour. Of the studied units, the Avaspec demonstrated the best prospects for the highest time resolution applications, but in the majority of cases, we anticipate users likely preferring the less bulky USB2000+s.

  10. Comparison of Low Cost Miniature Spectrometers for Volcanic SO2 Emission Measurements (United States)

    Kantzas, Euripides P.; McGonigle, Andrew J. S.; Bryant, Robert G.


    Miniature ultraviolet USB coupled spectrometers have become ubiquitously applied over the last decade for making volcanic SO2 emission rate measurements. The dominantly applied unit has recently been discontinued however, raising the question of which currently available devices should now be implemented. In this paper, we consider, and make recommendations on this matter, by studying a number of inexpensive compact spectrometers in respect of measurement performance and thermal behaviour. Of the studied units, the Avaspec demonstrated the best prospects for the highest time resolution applications, but in the majority of cases, we anticipate users likely preferring the less bulky USB2000+s. PMID:22412310

  11. Crustal and tectonic controls on large-explosive volcanic eruptions (United States)

    Sheldrake, Tom; Caricchi, Luca


    Quantifying the frequency-Magnitude (f-M) relationship for volcanic eruptions is important to estimate volcanic hazard. Furthermore, understanding how this relationship varies between different groups of volcanoes can provide insights into the processes that control the size and rate of volcanic events. Using a Bayesian framework, which allows us to conceptualise the volcanic record as a series of individual and unique time series, associated by a common group behaviour, we identify variations in the size and rate of volcanism in different volcanic arcs. These variations in behaviour are linked to key parameters that include the motion of subduction, rate of subduction, age of the slab and thickness of the crust. The effects of these parameters on volcanism are interpreted in terms of variations in mantle productivity and the thermal efficiency of magma transfer in arc crustal systems. Understanding the link between subduction architecture, heat content of magmatic systems, and volcanic activity will serve to improve our capacity to quantify volcanic hazard in regions with limited geological and historical records of volcanic activity.

  12. Neogene volcanism in Gutai Mts. (Eastern Carpathains: a review

    Directory of Open Access Journals (Sweden)

    Marinel Kovacs


    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.

  13. Global volcanic emissions: budgets, plume chemistry and impacts (United States)

    Mather, T. A.


    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.

  14. Volcanic unrest in Kenya: geological history from a satellite perspective (United States)

    Robertson, E.; Biggs, J.; Edmonds, M.; Vye-Brown, C.


    The East African Rift (EAR) system is a 5,000 km long series of fault bounded depressions that run from Djibouti to Mozambique. In the Kenyan Rift, fourteen Quaternary volcanoes lie along the central rift axis. These volcanoes are principally composed of trachyte pyroclastics and trachyte and basaltic lavas forming low-angle multi-vent edifices. Between 1997 and 2008, geodetic activity has been observed at five Kenyan volcanoes, all of which have undergone periods of caldera collapse and explosive activity. We present a remote-sensing study to investigate the temporal and spatial development of volcanic activity at Longonot volcano. High-resolution mapping using ArcGIS and an immersive 3D visualisation suite (GeovisionaryTM) has been used with imagery derived from ASTER, SPOT5 and GDEM data to identify boundaries of eruptive units and establish relative age in order to add further detail to Longonot's recent eruptive history. Mapping of the deposits at Longonot is key to understand the recent geological history and forms the basis for future volcanic hazard research to inform risk assessments and mitigation programs in Kenya. Calderas at Kenyan volcanoes are elliptical in plan view and we use high-resolution imagery to investigate the regional stresses and structural control leading to the formation of these elliptical calderas. We find that volcanoes in the central and northern segments of the Kenyan rift are elongated nearly parallel to the direction of least horizontal compressive stress, likely as a reflection of the direction of the plate motion vector at the time of caldera collapse. The southern volcanoes however are elongated at an acute angle to the plate motion vector, most likely as a result of oblique opening of the Kenyan rift in this region.

  15. "Canary Islands, a volcanic window in the Atlantic Ocean": a 7 year effort of public awareness on volcano hazards and risk management (United States)

    Rodríguez, Fátima; Calvo, David; Pérez, Nemesio M.; Padrón, Eleazar; Melián, Gladys; Padilla, Germán; Barrancos, José; Hernández, Pedro A.; Asensio-Ramos, María; Alonso, Mar


    "Canary Islands: A volcanic window in the Atlantic Ocean" is an educational program born from the need to inform and educate citizens residing in the Canary Islands on the various hazards associated to volcanic phenomena. The Canary Islands is the only territory of Spain that hosts active volcanism, as is shown by the 16 historical eruptions that have occurred throughout this territory, being the last one a submarine eruption taking place on October 12, 2011, offshore El Hierro Island. In the last 7 years, ITER as well as INVOLCAN have been performing an educative program focused on educating to the population about the benefits of a volcanic territory, volcanic hazards, how to reduce volcanic risk and the management of volcanic risk in the Canary Islands. "Canary Islands: A volcanic window in the Atlantic Ocean" consists of three units, the first two dedicated to the IAVCEI/UNESCO videos "Understanding Volcanic Hazards" and "Reducing Volcanic Risk" and the third one dedicated to the management of volcanic risk in the Canary Islands, as well as some other aspects of the volcanic phenomena. Generally the three units are shown consecutively on Tuesday, Wednesday and Thursday. This educative program has been roaming all around the 88 municipalities of the archipelago since this initiative started in 2008. The total number of attendees since then amounts to 18,911 people. The increase of assistance was constant until 2011, with annual percentages of 7.8, 17.1 and 20.9 respectively, regarding to ratio assistant/municipality. Despite the heterogeneity of the audience, the main audience is related to aged people of 45 years and older. This could be related to the memories of the recent eruptions occurred at La Palma Island in 1949 and 1971. It is important to point out that many of those people attending the educative program are representatives of local government (i.e. civil protection). Regarding the interest of the audience, the educational program attendees have

  16. The anatomy of a cinder cone: preliminary paleomagnetic, rock magnetic, structural, and petrologic data from the La Cienega volcano, Cerros del Rio volcanic field, northern New Mexico (United States)

    Petronis, M. S.; Foucher, M.; Lineline, J.; Van Wyk de Vries, B.


    The Cerros del Rio volcanic field is one of several middle Pliocene to Pleistocene basaltic volcanic fields of the axial Rio Grande Rift in central and northern New Mexico. It is a monogenetic volcanic field that comprises about 60 cinder-spatter cones, occupies ~ 700 km2, and ranges in age from 2.7 Ma to 1.1 Ma. Eruptive centers are typically central vent volcanoes, ranging from low-relief shields to steep-sided, breached cinder and spatter cone remnants. They represent short eruptive events that likely were derived from rapidly evolving reservoir-conduit systems. Mining activity has exposed the volcanic plumbing system of the Cienega Mine cinder cone, just west of Santa Fe, NM. Here, geologists from France and USA have been investigating the exposed roots of this eviscerated Pliocene volcano to investigate magma conduit geometry, magma flow structures, and eruption patterns. We are testing models for magma transport and volcano construction using a variety of field and laboratory tools. Common models of volcanic construction envision the magma feeder as a dike or pipe-like conduit transporting molten rock from a deep reservoir to the eruptive vent. We posit that small volcanic pluming systems are inherently more complex and actually involve numerous feeder geometries throughout the volcano lifespan. Our preliminary work suggests that the simple exteriors of some cinder cones hide a long life and complex history, both of which would change the appreciation of the related volcanic hazards in active systems. The Cienega Mine cinder cone consists of several meter- to decimeter-wide intrusions that connect to eruptive centers. These intrusions show a continuity of brittle to ductile structures from their margins to interiors. We have collected samples across each intrusion as well as along strike for anisotropy of magnetic susceptibility (AMS) and petrographic analysis in order to establish magma flow patterns. AMS results yield a remarkably consistent dataset that

  17. Oxygen Isotope Character of the Lake Owyhee Volcanic Field, Oregon (United States)

    Blum, T.; Strickland, A.; Valley, J. W.


    Oxygen isotope analyses of zircons from lavas and tuffs from the Lake Owyhee Volcanic Field (LOVF) of east central Oregon unequivocally demonstrate the presence of mid-Miocene low-δ18O magmas (δ18Ozrc<4.7 ‰). Despite the growing data set of low-δ18O melts within, and proximal to, the Snake River Plain (SRP) Large Igneous Province, debate persists regarding both the mechanisms for low-δ18O magma petrogenesis, and their relative influence in the SRP. The LOVF is associated with widespread silicic volcanism roughly concurrent with the eruption of the Steens-Columbia River Basalt Group between ~17-15Ma. Silicic activity in the LOVF is limited to 16-15Ma, when an estimated 1100km3 of weakly peralkaline to metaluminous rhyolitic lavas and ignimbrites erupted from a series of fissures and calderas. Geographically, the LOVF overlaps the Oregon-Idaho Graben (OIG), and straddles the 87Sr/86Sr= 0.704 line which, together with the 0.706 line to the east, delineate the regional transition from the North American Precambrian continental crust to the east to younger Phanerozoic accreted terranes to the west. Here we report high accuracy ion microprobe analyses of δ18O in zircons using a 10-15μm spot, with average spot-to-spot precision ±0.28‰ (2SD), to investigate intra-grain and intra-unit δ18Ozrc trends for LOVF rhyolites. Due to its high closure temperature, chemical and physical resistance, and slow oxygen diffusion rates, zircon offers a robust record of magmatic oxygen isotope ratios during crystallization and provides constraints on the petrogenesis of Snake River Plain (SRP) low-δ18O melts. Individual zircons from LOVF rhyolites show no evidence of core-rim δ18O zoning, and populations exhibit ≤0.42‰ (2SD) intra-unit variability. Unit averages range from 2.2 to 4.3‰, with the lowest values in caldera-forming ignimbrites, but all units show evidence of crystallization from low-δ18O melts. Quartz and feldspar analyses by laser fluorination (precision

  18. Multiple episodes of hydrothermal activity and epithermal mineralization in the southwestern Nevada volcanic field and their relations to magmatic activity, volcanism and regional extension

    Energy Technology Data Exchange (ETDEWEB)

    Weiss, S.I.; Noble, D.C.; Jackson, M.C. [Univ. of Nevada, Reno, NV (United States)] [and others


    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).

  19. Anisotropy spectra for enantiomeric differentiation of biomolecular building blocks. (United States)

    Evans, A C; Meinert, C; Bredehöft, J H; Giri, C; Jones, N C; Hoffmann, S V; Meierhenrich, U J


    All biopolymers are composed of homochiral building blocks, and both D-sugars and L-amino acids uniquely constitute life on Earth. These monomers were originally enantiomerically differentiated under prebiotic conditions. Particular progress has recently been made in support of the photochemical model for this differentiation: the interaction of circularly polarized light with racemic molecules is currently thought to have been the original source for life's biological homochirality. The differential asymmetric photoreactivity of particular small molecules can be characterized by both circular dichroism and anisotropy spectroscopy. Anisotropy spectroscopy, a novel derivative of circular dichroism spectroscopy, records the anisotropy factor g = Δε/ε as a function of the wavelength. Anisotropy spectroscopy promisingly affords the wavelength-dependent determination of the enantiomeric excess (ee) inducible into chiral organic molecules by photochemical irradiation with circularly polarized light. Anisotropy spectra of small molecules therefore provide unique means for characterizing the different photochemical behaviors between enantiomers upon exposure to various wavelengths of circularly polarized light. This chapter will: (1) present the theory and configuration of anisotropy spectroscopy; (2) explain experimentally recorded anisotropy spectra of selected chiral biomolecules such as amino acids; and (3) discuss the relevance of these spectra for the investigation of the origin of the molecular homochirality observed in living organisms. This review describes a new chiroptical technique that is of significance for advances in asymmetric photochemistry and that is also highly relevant for the European Space Agency Rosetta Mission, which will determine enantiomeric excesses (ees) in chiral organic molecules in cometary ices when it lands on Comet 67P/Churyumov-Gerasimenko in November 2014.

  20. Characterization of the velocity anisotropy of accreted globular clusters (United States)

    Bianchini, P.; Sills, A.; Miholics, M.


    Galactic globular clusters (GCs) are believed to have formed in situ in the Galaxy as well as in dwarf galaxies later accreted on to the Milky Way. However, to date, there is no unambiguous signature to distinguish accreted GCs. Using specifically designed N-body simulations of GCs evolving in a variety of time-dependent tidal fields (describing the potential of a dwarf galaxy-Milky Way merger), we analyse the effects imprinted on the internal kinematics of an accreted GC. In particular, we look at the evolution of the velocity anisotropy. Our simulations show that at early phases, the velocity anisotropy is determined by the tidal field of the dwarf galaxy and subsequently the clusters will adapt to the new tidal environment, losing any signature of their original environment in a few relaxation times. At 10 Gyr, GCs exhibit a variety of velocity anisotropy profiles, namely, isotropic velocity distribution in the inner regions and either isotropy or radial/tangential anisotropy in the intermediate and outer regions. Independent of an accreted origin, the velocity anisotropy primarily depends on the strength of the tidal field cumulatively experienced by a cluster. Tangentially anisotropic clusters correspond to systems that have experienced stronger tidal fields and are characterized by higher tidal filling factor, r50/rj ≳ 0.17, higher mass-loss ≳ 60 per cent and relaxation times trel ≲ 109 Gyr. Interestingly, we demonstrate that the presence of tidal tails can significantly contaminate the measurements of velocity anisotropy when a cluster is observed in projection. Our characterization of the velocity anisotropy profiles in different tidal environments provides a theoretical benchmark for the interpretation of the unprecedented amount of three-dimensional kinematic data progressively available for Galactic GCs.

  1. Cluster Analysis of vents in monogenetic volcanic fields, Lunar Crater Volcanic Field (Nevada) (United States)

    Tadini, A.; Cortes, J. A.; Valentine, G. A.; Johnson, P. J.; Tibaldi, A.; Bonali, F. L.


    Monogenetic volcanic fields pose a serious risk to human activities and settlements due to their high occurrence around the world and because of the type of eruptive activity that they exhibit. The need of adequate tools to better undertake volcanic hazard assessment for volcanic fields, especially from a spatial point of view, is of key importance at the time of mitigate such hazard. Among these tools, a better understanding of the spatial distribution of cones and vents and any structural/tectonical relationship are essential to understand the plumbing system of the field and thus help to predict the likelihood location of future eruptions. In this study we have developed a spatial methodology, which is the combination of various methodologies developed for volcanic textures and other clustering goals [1,2], to study the clustering of volcanic vents and their relation with structural features from satellite images. The methodology first involves the statistical identification and removal of spatial outliers using a predictive elliptical area [2] and the generation of randomly distributed points in the same predictive area. A comparison of the Near Neighbor Distance (NND) between the generated data and the data measured in a volcanic field is used to determine whether the vents are clustered or not. If the vents are clustered, a combination of hierarchical clustering and K-means [3] is then used to identify the clusters and their related vents. Results are then further constrained with the study of lineaments and other structural features that can be affected and related with the clusters. The methodology was tested in the Lunar Crater Volcanic Field, Nevada (USA) and successfully has helped to identify tectonically controlled lineaments from those that are resultant of geomorphological processes such the drainage control imposed by the cone clusters. Theoretical approaches has been developed before to constrain the plumbing of a volcanic field [4], however these

  2. Space-time distribution of ignimbrite volcanism in the southern SMO: From Eocene to Pliocene (United States)

    Nieto-Obregon, J.; Aguirre-Diaz, G. J.


    A distinct variation in the age of the ignimbrites of the Sierra Madre Occidental (SMO) is observed in the southern portion, which includes the area between Tepic, Nayarit (-105° W) and Aguascalientes, Ags (-102° W). Older, high-grade ignimbrites are Eocene and occur as scattered outcrops. These are in turn covered by a widespread and voluminous sequence of high-grade ignimbrites and silicic to intermediate lavas that ranges in age from Middle Oligocene to Middle Miocene. The peak of this ignimbrite volcanism was at about 21 Ma to 22 Ma, but there is evidence showing that it initiated since about 30 Ma and ended at about 17.5 Ma. This ignimbrite and lava sequence is in turn covered by another series of lavas, predominantly mafic to intermediate, in the southern part of the area. This latest volcanism represents the initiation of the Mexican Volcanic Belt. Ignimbrite volcanism apparently initiated at the NE part of the study area, and migrated to the SW with time, that is from the area Presa Calles to the valley of Bolaños. Isotopic ages reported on these rocks, cluster in various groups reflecting the time evolution of volcanism. Rocks older than 30 Ma tend to occur on the raised blocks of Sierra de El Laurel and Northern Sierra de Morones, in the eastern part of the area. The interval from 30 to 20 Ma comprises a discontinuous set of ages that are concentrated in the blocks of Southern Sierra de Morones, Tlaltenango, Bolaños and the area around Cinco Minas-San Pedro Analco-Hostotipaquillo. An apparent gap of ages occurs between 12 to 18 Ma, followed by a predominantly mafic volcanism scattered mainly to the south of the area, that represents the transition of SMO to MVB. Finally mafic volcanism of the MVB of 3 to 4 Ma is present in the south, in the area excavated on the vicinity of Rio Grande de Santiago. A similar migration pattern has been reported in general for the whole SMO by Aguirre-Diaz and Labarthe-Hernandez (2003), from NE Chihuahua to SW Nayarit

  3. Improving volcanic ash predictions with the HYSPLIT dispersion model by assimilating MODIS satellite retrievals (United States)

    Chai, Tianfeng; Crawford, Alice; Stunder, Barbara; Pavolonis, Michael J.; Draxler, Roland; Stein, Ariel


    Currently, the National Oceanic and Atmospheric Administration (NOAA) National Weather Service (NWS) runs the HYSPLIT dispersion model with a unit mass release rate to predict the transport and dispersion of volcanic ash. The model predictions provide information for the Volcanic Ash Advisory Centers (VAAC) to issue advisories to meteorological watch offices, area control centers, flight information centers, and others. This research aims to provide quantitative forecasts of ash distributions generated by objectively and optimally estimating the volcanic ash source strengths, vertical distribution, and temporal variations using an observation-modeling inversion technique. In this top-down approach, a cost functional is defined to quantify the differences between the model predictions and the satellite measurements of column-integrated ash concentrations weighted by the model and observation uncertainties. Minimizing this cost functional by adjusting the sources provides the volcanic ash emission estimates. As an example, MODIS (Moderate Resolution Imaging Spectroradiometer) satellite retrievals of the 2008 Kasatochi volcanic ash clouds are used to test the HYSPLIT volcanic ash inverse system. Because the satellite retrievals include the ash cloud top height but not the bottom height, there are different model diagnostic choices for comparing the model results with the observed mass loadings. Three options are presented and tested. Although the emission estimates vary significantly with different options, the subsequent model predictions with the different release estimates all show decent skill when evaluated against the unassimilated satellite observations at later times. Among the three options, integrating over three model layers yields slightly better results than integrating from the surface up to the observed volcanic ash cloud top or using a single model layer. Inverse tests also show that including the ash-free region to constrain the model is not

  4. Comenditic and pantelleritic ash-flow tuffs from Volcan Las Navajas, Nayarit, Mexico

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, S.A.; Hebre, J.A.


    Two distinctive ash-flow tuffs occur around the base of Volcan Las Navajas, a Pleistocene trachyte - peralkaline rhyolite center located in the northwestern segment of the Mexican Volcanic belt. The lower ash-flow unit is locally up to 65 m thick, is lithic rich and contains pumice blocks of comenditic rhyolite. The unit is not extensively exposed, and thus its areal extent and volume cannot be determined. Its chemical characteristics and stratigraphic relationship to other products erupted from Las Navajas suggest that it is related to the formation of the older of the two calderas which occur on Las Navajas. Unconformably overlying this unwelded ash-flow is a pantelleritic airfall pumice unit which is locally welded. This airfall unit is conformably overlain by a welded as-flow tuff that contains fiamme of pantelleritic composition (72 %SiO/sub 2/, 8% FeO*, 900 ppm Zr, agpaitic index of 1.7) as well as pumice blocks that show evidence of various degrees of mixing between pantellerite and trachyte. This suggests eruption from a chemically zoned magma chamber. This unit is locally up to 20 m thick, although its top has been removed by erosion. It is found on all sides of Las Navajas except on the south where it may be covered by Volcan Sanganguey, a Pleistocene to Recent calc-alkaline volcano. The welded ash-flow has been dated by K - Ar at 0.2+/-0.1 m.y. Stratigraphically and chemically this ash-flow appears to be related to the formation of younger of the two calderas.

  5. More diversity for volcanism: Ceres' Ahuna Mons from Dawn's Framing Camera data (United States)

    Ruesch, Ottaviano; Platz, Thomas; Schenk, Paul M.; McFadden, Lucy Ann; Castillo-Rogez, Julie; Quick, Lynnae C.; Byrne, Shane; Preusker, Frank; O'Brien, David P.; Schmedemann, Nico; Williams, David A.; Li, Jian-Yang; Bland, Michael T.; Hiesinger, Harald; Kneissl, Thomas; Neesemann, Adrian; Schaefer, Michael; Pasckert, Jan Hendrik; Schmidt, Britney E.; Buczkowski, Debra; Sykes, Mark V.; Nathues, Andreas; Roatsch, Thomas; Hoffmann, Martin; Raymond, Carol; Russell, Christopher T.


    In the last decades, the exploration of planets and moons by spacecraft revealed a variety of volcanic expressions. The recent visit to dwarf planet Ceres by the Dawn spacecraft is shedding light on a possible new, compositionally different volcanism falling into the cryovolcanism field. The dwarf planet's properties, i.e., low bulk density, low internal temperatures and volatile-rich composition relative to terrestrial planets, would only generate melts composed of brines. On the other hand, Ceres' carbonate- and clay-rich surface mineralogy suggests a cryovolcanism different from that of water-ice dominated icy satellites.The Dawn Framing Camera (FC) provides a complete global dataset for photo-geological investigations of Ceres, including a 35 m/pixel visible coverage, a 135 m/pixel multi-spectral coverage, and a 135 m/pixel global digital elevation model from stereo-photogrammetry. Domical landforms up to a few kilometers in elevation and tens of kilometers in diameter (referred to as tholi and montes) are found scattered across Ceres' surface. Ahuna Mons is a 4-km topographic high distinct in its shape and morphology from other topographic features on Ceres. The mountain consists of two morphological units: a flank unit of unconsolidated material and a fractured (i.e., consolidated) summit unit. Steep slopes at the angle of repose characterize the flank unit, whereas the summit unit has a convex shape. The flank and summit morphologies and the morphometry of the mountain can be explained by the formation of a cryovolcanic dome, analogous to a silicic volcanic dome found on terrestrial planets. Albedo and crater size-frequency distribution measurements from FC imagery reveal geologically-recent activity on Ahuna Mons, occurring sometime within the last few hundreds Myr. The characteristics of and implications for this possible cryomagma for Ceres thermal and chemical evolution will be discussed.

  6. Late Neogene-Recent uplift of the Cabo de Gata volcanic province, Almerı´a, SE Spain (United States)

    Martín, José M.; Braga, Juan C.; Betzler, Christian


    Cabo de Gata is a Miocene volcanic province in the Betic Cordillera in southeastern Spain. The distribution of coastal deposits in the successive marine sedimentary units overlying the last volcanic episode (about 7.5 Ma old) has been used to reconstruct the post-volcanic palaeogeographic evolution of the region during the Late Neogene. The current elevation of well-dated shoreline marker rocks has been used to estimate uplift amount and rates. Since the late Tortonian, a N45°E-aligned (the strike of the Carboneras fault system) topographic relief was emergent in the Cabo de Gata region. The extension and height of this island increased throughout the late Neogene. Smaller, independent islands were emergent and finally became connected to the main island during the Messinian. The Carboneras and Agua Amarga Pliocene sub-basins were the last two marine basins prior to the final emergence of the region. Since the last volcanic eruption (ca. 7.5 Ma), maximum uplift of sedimentary rocks in Cabo de Gata has taken place on the western margin of the N45°E-aligned palaeorelief. The altitude of the shoreline marker rocks in the successive sedimentary units decreases eastwards to the present-day coast and northwards of the Rambla del Plomo. Uplift rates since deposition remain nearly constant for the successive Messinian rocks and decrease slightly for the lower Pliocene outcrops. Most of the uplift took place before the Pliocene while the main island enlarged. Uplift amounts and rates since deposition of the upper Neogene sedimentary units in the Cabo de Gata area are similar to the ones estimated for laterally equivalent units in the eastern Betic basins (approximately 50 m/Ma). Despite its volcanic nature and the occurrence of the Carboneras fault system, the Cabo de Gata probably became elevated as a consequence of regional uplift in connection with the rest of the Betic Cordillera.

  7. The Yucca Mountain probabilistic volcanic hazard analysis project

    Energy Technology Data Exchange (ETDEWEB)

    Coppersmith, K.J.; Perman, R.C.; Youngs, R.R. [Geomatrix Consultants, Inc., San Francisco, CA (United States)] [and others


    The Probabilistic Volcanic Hazard Analysis (PVHA) project, sponsored by the U.S. Department of Energy (DOE), was conducted to assess the probability of a future volcanic event disrupting the potential repository at Yucca Mountain. The PVHA project is one of the first major expert judgment studies that DOE has authorized for technical assessments related to the Yucca Mountain project. The judgments of members of a ten-person expert panel were elicited to ensure that a wide range of approaches were considered for the hazard analysis. The results of the individual elicitations were then combined to develop an integrated assessment of the volcanic hazard that reflects the diversity of alternative scientific interpretations. This assessment, which focused on the volcanic hazard at the site, expressed as the probability of disruption of the potential repository, will provide input to an assessment of volcanic risk, which expresses the probability of radionuclide release due to volcanic disruption.

  8. Assessing volcanic hazard at Yucca Mountain using expert judgment

    Energy Technology Data Exchange (ETDEWEB)

    Coppersmith, K.J.; Perman, R.C. [Geomatrix Consultants, Inc., San Francisco, CA (United States); Nesbit, J. [Department of Energy, Las Vegas, NV (United States)] [and others


    A study to assess the probability of a future volcanic event disrupting the potential repository at Yucca Mountain, termed the Probabilistic Volcanic Hazard Analysis (PVHA) project, is being sponsored by the U.S. Department of Energy (DOE). This assessment, which is focused on the volcanic hazard at the site, expressed as the probability of disruption of the potential repository, will eventually provide input to an assessment of volcanic risk, which expresses the probability of radionuclide release due to volcanic disruption. To ensure that a wide range of approaches are considered in the hazard analysis, judgments of members of an expert panel will be elicited. The results of the individual elicitations will be combined to develop an integrated assessment of the volcanic hazard that reflects the diversity of scientific interpretations. This paper outlines the hazard model components and the procedures for eliciting expert judgments.

  9. Volcanic geology of Admiralty Bay, King George Island, Antarctica

    Institute of Scientific and Technical Information of China (English)

    邢光福; 王德滋; 金庆民; 沈渭洲; 陶奎元


    At Admiralty Bay of central King George Island, Keller Peninsula, Ullman Spur and Point Hennequin are main Tertiary volcanic terranes. Field investigation and isotopic datings indicate that, there occurred three periods of eruptions ( three volcanic cycles) and accompanying N-toward migration of the volcanic center on Keller Peninsula. After the second period of eruptions, the crater collapsed and a caldera was formed, then later eruptions were limited at the northern end of the peninsula and finally migrated to Ullman Spur. Thus Keller Peninsula is a revived caldera, and its volcanism migrated toward E with time. Point Hennequin volcanism happened more or less simultaneously with the above two areas, but has no clear relation in chemical evolution with them, frequently it belongs to another independent volcanic center.

  10. Supervolcanoes within an ancient volcanic province in Arabia Terra, Mars. (United States)

    Michalski, Joseph R; Bleacher, Jacob E


    Several irregularly shaped craters located within Arabia Terra, Mars, represent a new type of highland volcanic construct and together constitute a previously unrecognized Martian igneous province. Similar to terrestrial supervolcanoes, these low-relief paterae possess a range of geomorphic features related to structural collapse, effusive volcanism and explosive eruptions. Extruded lavas contributed to the formation of enigmatic highland ridged plains in Arabia Terra. Outgassed sulphur and erupted fine-grained pyroclastics from these calderas probably fed the formation of altered, layered sedimentary rocks and fretted terrain found throughout the equatorial region. The discovery of a new type of volcanic construct in the Arabia volcanic province fundamentally changes the picture of ancient volcanism and climate evolution on Mars. Other eroded topographic basins in the ancient Martian highlands that have been dismissed as degraded impact craters should be reconsidered as possible volcanic constructs formed in an early phase of widespread, disseminated magmatism on Mars.

  11. Volcanic ash plume identification using polarization lidar: Augustine eruption, Alaska (United States)

    Sassen, Kenneth; Zhu, Jiang; Webley, Peter W.; Dean, K.; Cobb, Patrick


    During mid January to early February 2006, a series of explosive eruptions occurred at the Augustine volcanic island off the southern coast of Alaska. By early February a plume of volcanic ash was transported northward into the interior of Alaska. Satellite imagery and Puff volcanic ash transport model predictions confirm that the aerosol plume passed over a polarization lidar (0.694 mm wavelength) site at the Arctic Facility for Atmospheric Remote Sensing at the University of Alaska Fairbanks. For the first time, lidar linear depolarization ratios of 0.10 – 0.15 were measured in a fresh tropospheric volcanic plume, demonstrating that the nonspherical glass and mineral particles typical of volcanic eruptions generate strong laser depolarization. Thus, polarization lidars can identify the volcanic ash plumes that pose a threat to jet air traffic from the ground, aircraft, or potentially from Earth orbit.

  12. Petrography and chemical evidence for multi-stage emplacement of western Buem volcanic rocks in the Dahomeyide orogenic belt, southeastern Ghana, West Africa (United States)

    Nude, Prosper M.; Kwayisi, Daniel; Taki, Naa A.; Kutu, Jacob M.; Anani, Chris Y.; Banoeng-Yakubo, Bruce; Asiedu, Daniel K.


    The volcanic rocks of the Buem Structural Unit in the Dahomeyide orogenic belt of southeastern Ghana, constitute a unique assemblage among the monocyclic sedimentary formations of this structural unit. Representative volcanic rock samples were collected from the Asukawkaw, Bowiri-Odumase and Nkonya areas which form a roughly north-south trend. The volcanic rocks comprise spherulitic, amygdaloidal, vesicular, phyric and aphyric varieties. Whole rock geochemistry shows that these volcanic rocks exhibit both alkaline and subalkaline characteristics. The alkaline varieties are relatively enriched in REE and incompatible trace element concentrations, similar to OIB; the subalkaline varieties show E-MORB and N-MORB REE and incompatible element characteristics. The rocks have low La/Nb (<1), low K/Nb (<450) and high Nb/U (averagely 47.3) values, suggesting no significant effect of crustal contamination. The key characteristics of these volcanic rocks are the distinct petrography and geochemistry, shown from the three separate localities, which may suggest source fractionation at different depths or modes of emplacement. The association of volcanic rocks of OIB, E-MORB and N-MORB affinities, with no significant crustal contamination, may suggest mantle derived magma that may have been related to rifting event and eventual emplacement at the eastern passive margin of the West African Craton.

  13. Mid Miocene volcanism in Nicaragua and implications for the formation of the Nicaraguan Depression (United States)

    Saginor, I.; Gazel, E.; Carr, M. J.


    Northwest Nicaragua contains Mid Miocene volcanism on either side of the Nicaraguan Depression consisting of portions of the Coyol Formation to the East and the Tamarindo Formation to the West. The Tamarindo Formation is a narrow band of basaltic to andesitic lavas interlayered with thick ignimbrite deposits and volcaniclastic sediments that parallel Nicaragua’s Pacific coast to the west of the modern volcanic front with ages from 14.7-11.7 Ma. The Coyol represents primarily Miocene volcanism from 25-7 Ma and lies east of the active front. The presence of Mid Miocene volcanism on either side of the Nicaraguan Depression has led to speculation that the two coeval units, which are currently separated by almost 100km, were once connected and have since been separated by extension. Here, we present data that show the Tamarindo and Coyol are geochemically distinct and therefore cannot be considered part of the same unit. First, the Tamarindo has lower La/Yb values than Coyol, which suggests that the Tamarindo was formed by a higher degree of partial melting, assuming that mantle source compositions are similar for both units. In addition, the Tamarindo has higher Zr/Nb values than Coyol, which are indicative of High Field Strength Element (HFSE) depletion common in arc volcanics. Because the degree of partial melting and HFSE depletion is expected to increase towards the trench, both Tamarindo’s La/Yb and Zr/Nb values are consistent with its being emplaced closer to the trench than Coyol and the presence of these two units of Mid-Miocene age on opposite sides of the Nicaraguan Depression cannot be used as proof of significant extension. In addition, currently available data do not show the significant crustal thinning and large-scale structural surface features that would be expected if the Tamarindo and Coyol were once connected and later separated by extension. Fault displacement along the Nicaraguan Depression is insufficient to accommodate this extension and

  14. Zircon U-Pb Age Determination of Volcanic Eruptions in Lutao and Lanyu in the Northern Luzon Magmatic Arc

    Directory of Open Access Journals (Sweden)

    Wen-Yu Shao


    Full Text Available This paper reports for the first time zircon U-Pb ages of volcanic rocks and sands from Lutao and Lanyu, two islets off SE Taiwan in the north Luzon arc. The samples include (1 seven andesites from four volcanic units and three river/beach sands from Lutao and (2 five basaltic andesites from four volcanic units and two river/beach sands from Lanyu. The Lutao andesites contain abundant magmatic zircons, aging from ~1.54 to ~1.24 Ma for individual sample, which yielded an overall mean 206Pb/238U age of 1.31 ±± 0.03 Ma (n = 190, MSWD = 2.6. This is slightly older than, or broadly coincident with, a mean 206Pb/238U age of 1.23 ±± 0.03 Ma (n = 103, MSWD = 1.9 given by detrital zircons from the three sands. The Lanyu volcanics appear to have less abundant magmatic zircons, aging from ~2.72 to ~2.35 Ma for individual sample, which yielded an overall mean 206Pb/238U age of 2.61 ±± 0.13 Ma (n = 11, MSWD = 1.8. This accords with a mean 206Pb/238U age of 2.69 ±± 0.11 Ma (n = 34, MSWD = 4.7 obtained by detrital zircons from the two sands. The age data suggest that in Lutao and Lanyu the major volcanic eruptions occurred at ~1.3 and ~2.6 Ma, respectively. Moreover, volcanic samples from both islets contain various amounts of older inherited zircons, ~11% in Lutao and up to ~82% in Lanyu, which together with detrital zircons from the sands show main age peaks at ~150 Ma and ~1.9 and ~2.5 Ga, consistent with the notion for a _ continental crust involved in the genesis of the northern Luzon magmatic arc.

  15. Structural model of the Northern Latium volcanic area constrained by MT, gravity and aeromagnetic data

    Directory of Open Access Journals (Sweden)

    P. Gasparini


    Full Text Available The results of about 120 magnetotelluric soundings carried out in the Vulsini, Vico and Sabatini volcanic areas were modeled along with Bouguer and aeromagnetic anomalies to reconstruct a model of the structure of the shallow (less than 5 km of depth crust. The interpretations were constrained by the information gathered from the deep boreholes drilled for geothermal exploration. MT and aeromagnetic anomalies allow the depth to the top of the sedimentary basement and the thickness of the volcanic layer to be inferred. Gravity anomalies are strongly affected by the variations of morphology of the top of the sedimentary basement, consisting of a Tertiary flysch, and of the interface with the underlying Mesozoic carbonates. Gravity data have also been used to extrapolate the thickness of the neogenic unit indicated by some boreholes. There is no evidence for other important density and susceptibility heterogeneities and deeper sources of magnetic and/or gravity anomalies in all the surveyed area.

  16. Petrography, Geochemistry and Petrogenesis of Volcanic Rocks, NW Ghonabad, Iran

    Directory of Open Access Journals (Sweden)

    Sedigheh Zirjanizadeh


    Full Text Available Introduction The study area is located in NW Gonabad, Razavi Khorasan Province, northern Lut block and eastern Iran north of the Lut Block. Magmatism in NW Gonabad produced plutonic and volcanic rock associations with varying geochemical compositions. These rocks are related to the Cenozoic magmatic rocks in Iran and belong to the Lut Block volcanic–plutonic belt. In this study, petrogenesis of volcanic units in northwest Gonabad was investigated. The volcanic rocks are andesites/trachyandesites, rhyolites, dacites/ rhyodacites and pyroclastics.These rocks show porphyritic, trachytic and embayed textures in phenocrysts with plagioclase, sanidine and quartz (most notably in dacite and rhyolite, hornblende and rare biotite. The most important alteration zones are propylitic, silicification and argillic.Four kaolinite- bearing clay deposits have been located in areas affectedby hydrothermal alteration of Eocene rhyolite, dacite and rhyodacite. Analytical techniques Five samples were analyzed for major elements by wavelength dispersive X-ray fluorescence (XRF and six samples were analyzed for trace elements using inductively coupled plasma-mass spectrometry (ICP-MS in the Acme Laboratories, Vancouver (Canada.Sr and Nd isotopic compositions were determined for four whole-rock samples at the Laboratório de GeologiaIsotópica da Universidade de Aveiro, Portugal. Results Petrography. The rocks in this area are consist of trachyte, andesite/ trachyandesite, dacite/ rhyodacite, principally as ignimbrites and soft tuff. The textures of phenocrysts are mainly porphyritic, glomerophyric, trachytic and embayed textures in plagioclase, hornblende and biotite. The groundmasses consist of plagioclase and fine-grainedcrystals of hornblende. Plagioclase phenocrysts and microlitesare by far the most abundant textures in andesite - trachyandesites (>25% and in size from 0.01 to 0.1mm. Euhedral to subhedral hornblende phenocrysts areabundant (3-5%and 0.1 to 0

  17. The α-β phase transition in volcanic cristobalite.


    Damby, D. E.; Llewellin, E.W.; Horwell, C. J.; Williamson, B.J.; Najorka, J; Cressey, G.; Carpenter, M.A.


    Cristobalite is a common mineral in volcanic ash produced from dome-forming eruptions. Assessment of the respiratory hazard posed by volcanic ash requires understanding the nature of the cristobalite it contains. Volcanic cristobalite contains coupled substitutions of Al3+ and Na+ for Si4+; similar co-substitutions in synthetic cristobalite are known to modify the crystal structure, affecting the stability of the α and β forms and the observed transition between them. Here, for the first time...

  18. Distinguishing volcanic lithology using Self-Organizing Map

    Institute of Scientific and Technical Information of China (English)


    Self-Organizing Map is an unsupervised learning algorithm. It has the ability of self-organization,self-learning and side associative thinking. Based on the principle it can identified the complex volcanic lithology. According to the logging data of the volcanic rock samples, the SOM will be trained, The SOM training results were analyzed in order to choose optimally parameters of the network. Through identifying the logging data of volcanic formations, the result shows that the map can achieve good application effects.




    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 over...

  20. The `Strawberry Volcanic Field' of Northeastern Oregon: Another Piece of the CRB Puzzle? (United States)

    Steiner, A. R.; Streck, M. J.


    The Mid to Late Miocene Strawberry Volcanics field (SVF) located along the southern margin of the John Day valley of NE Oregon, comprise a diverse group of volcanic rocks ranging from basalt to rhyolite. The main outcrop area of the SVF (3,400 km2) is bordered by units from the Columbia River Basalt Group (CRBG), with the main CRB units to the north, the Picture Gorge Basalt to the east and Steens Basalt to the south. The geographic position and age of the Strawberry Volcanics make a genetic relationship to CRB volcanism likely, yet little is known about this diverse volcanic field. This research aims at refining the stratigraphic and age relationships as well as the petrology and geochemistry of magmas associated with the SVF. Previous investigations (e.g. Robyn, 1977) found that the SVF was active between 20 to 10 Ma with the main pulse largely being coeval with the 15 Ma CRBG eruptions. Lavas and tuffs from the SVF are calc-alkaline with low FeO*/MgO (~ 2.56 wt. %), high Al2O3 (~ 16.4 wt. %), low TiO2 (~ 1.12 wt.%), and span the entire compositional range from basalt to rhyolite (47-78 wt. % SiO2) with andesite as the dominant lithology. Basaltic lavas from the SVF have compositional affinities to earlier Steens Basalt, and some trace element concentrations and ratios are indistinguishable from those of CRBG lavas (e.g. Zr, Ba, Sr, and Ce/Y). Andesites are calc-alkaline, but contrary to typical arc (orogenic) andesites, SVF andesites are exceedingly phenocryst poor (Strawberry Volcanics are largely the product of hot-spot related basaltic magmas interacting with the continental crust. The range in compositions from calc-alkaline andesite to rhyolite may be attributed to the hybridization of mantle-derived and crustal melts, with the more evolved compositions reflecting greater proportions of crustally derived material and/or higher degrees of differentiation. Furthermore, since the earliest SVF eruption is 3 Ma older than the proposed onset of the CRBG (~ 17 Ma

  1. Magnetic anisotropy of ultrafine 316L stainless steel fibers (United States)

    Shyr, Tien-Wei; Huang, Shih-Ju; Wur, Ching-Shuei


    An as-received 316L stainless steel fiber with a diameter of 20 μm was drawn using a bundle drawing process at room temperature to form ultrafine stainless steel fibers with diameters of 12, 8, and 6 μm. The crystalline phases of the fibers were analyzed using the X-ray diffraction (XRD) profile fitting technique. The grain sizes of γ-austenite and α‧-martensite were reduced to nanoscale sizes after the drawing process. XRD analysis and focused ion beam-scanning electron microscope observations showed that the newly formed α‧-martensitic grains were closely arrayed in the drawing direction. The magnetic property was measured using a superconducting quantum interference device vibrating sample magnetometer. The magnetic anisotropy of the fibers was observed by applying a magnetic field parallel and perpendicular to the fiber axis. The results showed that the microstructure anisotropy including the shape anisotropy, magnetocrystalline anisotropy, and the orientation of the crystalline phases strongly contributed to the magnetic anisotropy.

  2. A Investigation of the Elastic and Dielectric Anisotropy of Paper. (United States)

    Fleischman, Elmer Henry, Jr.

    This investigation was undertaken to learn more about the way in which fiber orientation and drying restraint affect the elastic and dielectric properties in all three principal directions of paper. It was found that both variables affect the in -plane elastic anisotropy by similar magnitudes. What was surprising, however, was that wet straining has the greatest effect in the z-direction. The z-direction stiffness was reduced 50% as a result of only a moderate 2.4% wet strain in the plane of the sheet. On the other hand, the dielectric anisotropy was affected very little by wet straining. In fact, the dielectric results could be explained in terms of mixture theories. The anisotropy in the dielectric constant when measured at microwave frequencies could largely be explained as being the result of fiber orientation alone without having to assume that the fiber has an anisotropic dielectric constant. From comparison of the elastic and dielectric results, it may be concluded that the mechanism by which wet straining enhances the elastic anisotropy does not involve a large fiber orientation in the direction of wet straining. From a practical standpoint, one could use the dielectric anisotropy measured at microwave frequencies as a measure of the fiber orientation distribution in the sheet. On the basis of the results presented here, this measurement should be quite insensitive to any stresses imposed on the sheet as it dries.

  3. Origin of azimuthal seismic anisotropy in oceanic plates and mantle (United States)

    Becker, Thorsten W.; Conrad, Clinton P.; Schaeffer, Andrew J.; Lebedev, Sergei


    Seismic anisotropy is ubiquitous in the Earth's mantle but strongest in its thermo-mechanical boundary layers. Azimuthal anisotropy in the oceanic lithosphere and asthenosphere can be imaged by surface waves and should be particularly straightforward to relate to well-understood plate kinematics and large-scale mantle flow. However, previous studies have come to mixed conclusions as to the depth extent of the applicability of paleo-spreading and mantle flow models of anisotropy, and no simple, globally valid, relationships exist. Here, we show that lattice preferred orientation (LPO) inferred from mantle flow computations produces a plausible global background model for asthenospheric anisotropy underneath oceanic lithosphere. The same is not true for absolute plate motion (APM) models. A ˜200 km thick layer where the flow model LPO matches observations from tomography lies just below the ˜1200 °C isotherm of a half-space cooling model, indicating strong temperature-dependence of the processes that control the development of azimuthal anisotropy. We infer that the depth extent of shear, and hence the thickness of a relatively strong oceanic lithosphere, can be mapped this way. These findings for the background model, and ocean-basin specific deviations from the half-space cooling pattern, are found in all of the three recent and independent tomographic models considered. Further exploration of deviations from the background model may be useful for general studies of oceanic plate formation and dynamics as well as regional-scale tectonic analyses.

  4. Performance of ERNE in particle flux anisotropy measurement

    Directory of Open Access Journals (Sweden)

    E. Riihonen

    Full Text Available The HED particle detector of the ERNE experiment to be flown on the SOHO spacecraft is unique compared to the earlier space-born detectors in its high directional resolution (better than 2°, depending on the track inclination. Despite the fixed view cone due to the three-axis stabilization of the spacecraft, the good angular and temporal resolution of the detector provides a new kind of opportunity for monitoring in detail the development of the anisotropies pertaining, for example, to the onset of SEP events, or passage of shock fronts related to gradual events. In order to optimize the measurement parameters, we have made a preflight simulation study of the HED anisotropy measurement capabilities. The purpose was to prove the feasibility of the selected measurement method and find the physical limits for the HED anisotropy detection. The results show HED to be capable of detecting both strong anisotropies related to impulsive events, and smoother anisotropies associated with gradual events.

  5. Scaling of coercivity in a 3d random anisotropy model

    Energy Technology Data Exchange (ETDEWEB)

    Proctor, T.C., E-mail:; Chudnovsky, E.M., E-mail:; Garanin, D.A.


    The random-anisotropy Heisenberg model is numerically studied on lattices containing over ten million spins. The study is focused on hysteresis and metastability due to topological defects, and is relevant to magnetic properties of amorphous and sintered magnets. We are interested in the limit when ferromagnetic correlations extend beyond the size of the grain inside which the magnetic anisotropy axes are correlated. In that limit the coercive field computed numerically roughly scales as the fourth power of the random anisotropy strength and as the sixth power of the grain size. Theoretical arguments are presented that provide an explanation of numerical results. Our findings should be helpful for designing amorphous and nanosintered materials with desired magnetic properties. - Highlights: • We study the random-anisotropy model on lattices containing up to ten million spins. • Irreversible behavior due to topological defects (hedgehogs) is elucidated. • Hysteresis loop area scales as the fourth power of the random anisotropy strength. • In nanosintered magnets the coercivity scales as the six power of the grain size.

  6. Phenomenological description of anisotropy effects in some ferromagnetic superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Shopova, Diana V., E-mail: [TCCM Research Group, Institute of Solid State Physics, Bulgarian Academy of Sciences, BG-1784 Sofia (Bulgaria); Todorov, Michail D. [Department of Applied Mathematics and Computer Science, Technical University of Sofia, 1000 Sofia (Bulgaria)


    We study phenomenologically the role of anisotropy in ferromagnetic superconductors UGe{sub 2}, URhGe, and UCoGe for the description of their phase diagrams. We use the Ginzburg–Landau free energy in its uniform form as we will consider only spatially independent solutions. This is an expansion of previously derived results where the effect of Cooper-pair and crystal anisotropies is not taken into account. The three compounds are separately discussed with the special stress on UGe{sub 2}. The main effect comes from the strong uniaxial anisotropy of magnetization while the anisotropy of Cooper pairs and crystal anisotropy only slightly change the phase diagram in the vicinity of Curie temperature. The limitations of this approach are also discussed. - Highlights: • Anisotropic Landau energy for description of ferromagnetic superconductors is proposed. • Meissner phases are described with their existence and stability conditions. • The application of the model to UGe{sub 2} is discussed. • The limitations to apply the model for description of experimental data are explained.

  7. Anisotropy vs chemical composition at ultra-high energies

    CERN Document Server

    Lemoine, Martin


    This paper proposes and discusses a test of the chemical composition of ultra-high energy cosmic rays that relies on the anisotropy patterns measured as a function of energy. In particular, we show that if one records an anisotropy signal produced by heavy nuclei of charge Z above an energy E_{thr}, one should record an even stronger (possibly much stronger) anisotropy at energies >E_{thr}/Z due to the proton component that is expected to be associated with the sources of the heavy nuclei. This conclusion remains robust with respect to the parameters characterizing the sources and it does not depend at all on the modelling of astrophysical magnetic fields. As a concrete example, we apply this test to the most recent data of the Pierre Auger Observatory. Assuming that the anisotropy reported above 55EeV is not a statistical accident, and that no significant anisotropy has been observed at energies 10^{45}Z^{-2}erg/s. Using this bound in conjunction with the above conclusions, we argue that the current PAO data...

  8. Concepts for integrating plastic anisotropy into metal forming simulations

    Energy Technology Data Exchange (ETDEWEB)

    Raabe, D.; Roters, F. [Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf (Germany). Abt. fuer Mikrostrukturphysik; Klose, P.; Engl, B.; Imlau, K.P.; Friedel, F. [Research and Development, Quality Engineering, and Materials Testing, Thyssen Krupp Stahl AG, Duisburg (Germany)


    Modern metal forming and crash simulations are usually based on the finite element method. Aims of such simulations are typically the prediction of the material shape, failure, and mechanical properties during deformation. Further goals lie in the computer assisted lay-out of manufacturing tools used for intricate processing steps. Any such simulation requires that the material under investigation is specified in terms of its respective constitutive behavior. Modern finite element simulations typically use three sets of material input data, covering hardening, forming limits, and anisotropy. The current article is about the latter aspect. It reviews different empirical and physically based concepts for the integration of the elastic-plastic anisotropy into metal forming finite element simulations. Particular pronunciation is placed on the discussion of the crystallographic anisotropy of polycrystalline material rather than on aspects associated with topological or morphological microstructure anisotropy. The reviewed anisotropy concepts are empirical yield surface approximations, yield surface formulations based on crystallographic homogenization theory, combinations of finite element and homogenization approaches, the crystal plasticity finite element method, and the recently introduced texture component crystal plasticity finite element method. The paper presents the basic physical approaches behind the different methods and discusses engineering aspects such as scalability, flexibility, and texture update in the course of a forming simulation. (orig.)

  9. Anisotropies in the HI gas distribution toward 3C196

    CERN Document Server

    Kalberla, P M W


    The local Galactic HI gas was found to contain cold neutral medium (CNM) filaments that are aligned with polarized dust emission. These filaments appear to be dominated by the magnetic field and in this case turbulence is expected to show distinct anisotropies. We use the Galactic Effelsberg--Bonn HI Survey (EBHIS) to derive 2D turbulence spectra for the HI distribution in direction to 3C196 and two more comparison fields. Prior to Fourier transform we apply a rotational symmetric 50% Tukey window to apodize the data. We derive average as well as position angle dependent power spectra. Anisotropies in the power distribution are defined as the ratio of the spectral power in orthogonal directions. We find strong anisotropies. For a narrow range in position angle, in direction perpendicular to the filaments and the magnetic field, the spectral power is on average more than an order of magnitude larger than parallel. In the most extreme case the anisotropy reaches locally a factor of 130. Anisotropies increase on...

  10. Melting Behavior of Volcanic Ash relevant to Aviation Ash Hazard (United States)

    Song, W.; Hess, K.; Lavallee, Y.; Cimarelli, C.; Dingwell, D. B.


    Volcanic ash is one of the major hazards caused by volcanic eruptions. In particular, the threat to aviation from airborne volcanic ash has been widely recognized and documented. In the past 12 years, more than 60 modern jet airplanes, mostly jumbo jets, have been damaged by drifting clouds of volcanic ash that have contaminated air routes and airport facilities. Seven of these encounters are known to have caused in-flight loss of engine power to jumbo jets carrying a total of more than 2000 passengers. The primary cause of engine thrust loss is that the glass in volcanic ash particles is generated at temperatures far lower than the temperatures in the combustion chamber of a jet engine ( i.e. > 1600 oC) and when the molten volcanic ash particles leave this hottest section of the engine, the resolidified molten volcanic ash particles will be accumulated on the turbine nozzle guide vanes, which reduced the effective flow of air through the engine ultimately causing failure. Thus, it is essential to investigate the melting process and subsequent deposition behavior of volcanic ash under gas turbine conditions. Although few research studies that investigated the deposition behavior of volcanic ash at the high temperature are to be found in public domain, to the best our knowledge, no work addresses the formation of molten volcanic ash. In this work, volcanic ash produced by Santiaguito volcano in Guatemala in November 8, 2012 was selected for study because of their recent activity and potential hazard to aircraft safety. We used the method of accessing the behavior of deposit-forming impurities in high temperature boiler plants on the basis of observations of the change in shape and size of a cylindrical coal ash to study the sintering and fusion phenomena as well as determine the volcanic ash melting behavior by using characteristic temperatures by means of hot stage microscope (HSM), different thermal analysis (DTA) and Thermal Gravimetric Analysis (TGA) to

  11. Distribution and characteristics of volcanic reservoirs in China

    Institute of Scientific and Technical Information of China (English)

    HUANG Yulong; WANG Pujun; CHEN Shuming


    About forty productive oil/gas fields hosted in volcanic reservoirs have been found since 1957 in fourteen basins of China. They can be simply subdivided into two groups, the east and the west. Reservoir volcanic rocks of the east group are predominantly composed of Late Jurassic to Early Cretaceous rhyolite and Tertiary basalt, preferred being considered as rift type volcanics developed in the circum-Pacific tectonic regime. Those of the west are Permo-Carboniferous intermediate/basic volcanic rocks, being island-arc type ones developed in paleo-Asian Ocean tectonic regime.

  12. The volcanic and tectonic history of Enceladus (United States)

    Kargel, J.S.; Pozio, S.


    Enceladus has a protracted history of impact cratering, cryo-volcanism, and extensional, compressional, and probable strike-slip faulting. It is unique in having some of the outer Solar System's least and most heavily cratered surfaces. Enceladus' cratering record, tectonic features, and relief elements have been analyzed more comprehensively than done previously. Like few other icy satellites, Enceladus seems to have experienced major lateral lithospheric motions; it may be the only icy satellite with global features indicating probable lithospheric convergence and folding. Ridged plains, 500 km across, consist of a central labyrinthine ridge complex atop a broad dome surrounded by smooth plains and peripheral sinuous ridge belts. The ridged plains have few if any signs of extension, almost no craters, and an average age of just 107 to 108 years. Ridge belts have local relief ranging from 500 to 2000 m and tend to occur near the bottoms of broad regional troughs between swells. Our reanalysis of Peter Thomas' (Dermott, S. F., and P. C. Thomas, 1994, The determination of the mass and mean density of Enceladus from its observed shape, Icarus, 109, 241-257) limb profiles indicates that high peaks, probably ridge belts, also occur in unmapped areas. Sinuous ridges appear foldlike and are similar to terrestrial fold belts such as the Appalachians. If they are indeed folds, it may require that the ridged plains are mechanically (perhaps volcanically) layered. Regional topography suggests that folding may have occurred along zones of convective downwelling. The cratered plains, in contrast to the ridged plains, are heavily cratered and exhibit extensional structures but no obvious signs of compression. Cratered plains contain a possible strike-slip fault (Isbanir Fossa), along which two pairs of fractures seem to have 15 km of right-lateral offset. The oldest cratered plains might date from shortly after the formation of the saturnian system or the impact disruption and

  13. Exceptional Volumes of Rejuvenated Volcanism in Samoa (United States)

    Konter, J. G.; Jackson, M.; Storm, L.


    The internal structure of within-plate volcanoes is typically compared to the stages of volcanic evolution in Hawaii. In Samoa, these stages show some differences with the Hawaiian model, in terms of the duration, volume and geochemical composition of the stages. Particularly, the rejuvenated stage of volcanism in Samoa is significantly more voluminous, with increasing geographic coverage with age, completely repaving the island of Savai’i. This unusual outpouring of rejuvenated lavas has previously been proposed to be related to the tectonic setting, near the northern terminus of the Tonga Trench. Therefore, Samoan volcanism might be caused by lithospheric fracturing, a mantle plume, or potentially a combination of the two. We collected new samples from a deeply eroded canyon on Savai’i to determine a time evolution of the transition from shield to eventual rejuvenated lavas. The canyon exposes several hundred meters of lavas, and we collected samples about 200m vertically down into the canyon. These samples are dominantly olivine basalts, and their Pb isotope compositions fall within the compositional field of young rejuvenated lavas on Savai’i and Upolu. This canyon section, therefore, represents a minimum thickness for the rejuvenated lavas of 200m. Assuming eruption of rejuvenated lavas only occurred subaerially, with a universal thickness of 200m, the new data suggest more than one percent of the volume of Savai’i consists of rejuvenated lavas. This is an order of magnitude greater than the largest relative volumes in Hawaii (Kauai), and implies a different cause for rejuvenated volcanism in Samoa. Another feature that suggests different processes may be important is the transition between the shield and rejuvenated stage. Although Samoan volcanoes do not seem to erupt exactly the same rock types as characteristic Hawaiian post-shield stage lavas, there is a definite shift to more evolved compositions (including trachytes) during the later stages of

  14. Automatic landslides detection on Stromboli volcanic Island (United States)

    Silengo, Maria Cristina; Delle Donne, Dario; Ulivieri, Giacomo; Cigolini, Corrado; Ripepe, Maurizio


    Landslides occurring in active volcanic islands play a key role in triggering tsunami and other related risks. Therefore, it becomes vital for a correct and prompt risk assessment to monitor landslides activity and to have an automatic system for a robust early-warning. We then developed a system based on a multi-frequency analysis of seismic signals for automatic landslides detection occurring at Stromboli volcano. We used a network of 4 seismic 3 components stations located along the unstable flank of the Sciara del Fuoco. Our method is able to recognize and separate the different sources of seismic signals related to volcanic and tectonic activity (e.g. tremor, explosions, earthquake) from landslides. This is done using a multi-frequency analysis combined with a waveform patter recognition. We applied the method to one year of seismic activity of Stromboli volcano centered during the last 2007 effusive eruption. This eruption was characterized by a pre-eruptive landslide activity reflecting the slow deformation of the volcano edifice. The algorithm is at the moment running off-line but has proved to be robust and efficient in picking automatically landslide. The method provides also real-time statistics on the landslide occurrence, which could be used as a proxy for the volcano deformation during the pre-eruptive phases. This method is very promising since the number of false detections is quite small (landslide increases. The final aim will be to apply this method on-line and for a real-time automatic detection as an improving tool for early warnings of tsunami-genic landslide activity. We suggest that a similar approach could be also applied to other unstable non-volcanic also slopes.

  15. Volcanic hazard assessment at Deception Island (United States)

    Bartolini, S.; Sobradelo, R.; Geyer, A.; Martí, J.


    Deception Island is the most active volcano of the South Shetland Islands (Antarctica) with more than twenty eruptions recognised over the past two centuries. The island was formed on the expansion axis of the Central Bransfield Strait and its evolution consists of constructive and destructive phases. A first a shield phase was followed by the construction of a central edifice and formation of the caldera with a final monogenetic volcanism along the caldera rim. The post-caldera magma composition varies from andesitic-basaltic to dacitic. The activity is characterised by monogenetic eruptions of low volume and short duration. The eruptions show a variable degree of explosivity, strombolian or phreatomagmatic, with a VEI 2 to 4, which have generated a wide variety of pyroclastic deposits and lavas. It is remarkable how many phases of phreatic explosive eruptions are associated to the emission of large ballistic blocks. Tephra record preserved in the glacier ice of Livingston Island or in marine sediments show the explosive power of the phreatomagmatic phases and the wide dispersal of its finest products in a great variety of directions of the prevailing winds. Also it is important to highlight the presence of different lahar deposits associated with some of these eruptions. In this contribution we present the guidelines to conduct a short-term and long-term volcanic hazard assessment at Deception Island. We apply probabilistic methods to estimate the susceptibility, statistical techniques to determine the eruption recurrence and eruptive scenario, and reproduce the effects of historical eruptions too. Volcanic hazard maps and scenarios are obtained using a Voris-based model tool (Felpeto et al., 2007) in a free Geographical Information System (GIS), a Quantum GIS.

  16. Structural significance of the south Tyrrhenian volcanism (United States)

    Gaudiosi, G.; Musacchio, G.; Ventura, G.; de Astis, G.


    The southern part of the Tyrrhenian Sea represents a transition from ocenic- (the Tyrrhenian Sea) to continental-domain (the Calabrian Arc) and is affected by active calkalkaline to potassic volcanism (the Eolian Islands). Active extensional tectonics, coupled with the general upwelling of northern Sicily and Calabria continental crust, coexists with active subduction of the Ionian Plate beneath the Calabrian Arc. This has been interpreted as the result of the detachment of the slab beneath the Calbrian Arc. Present-day tectonics is characterized by NE-SW normal faults and NNW- SSE dextral oblique-slip faults. The normal faults form the major peri- Tyrrhenian basins. Refraction and high resolution onshore-offshore wide-angle-reflection profiles, as well as potential field modeling, provide a 3D image of the Moho. Short wave-length undulations characterize the Moho beneath the Aeolian Arch. The major upraise is about 6 km, beneath the Aeolian active volcanic area, and affects all the crustal boundaries. Another sharp crustal thinning is observed beneath the gulf of Patti at the south-eastern edge of the Tyrrhenian basin. We suggest that the graben-like structure, occurring along the Salina-Lipari-Vulcano islands and oriented at high angles to the trench, is lithospheric and can be followed down to Moho depths. NNW-SSE dextral oblique-slip faults, like the Tindari Letojanni fault system, control the Salina-Lipari-Vulcano portion of the Aeolian volcanism and connect the oceanic crust of the Marsili Basin to the Malta Escarpment, through the Etna volcano. Across this lineament seismicity changes from mostly shallow to the west, to deep intra- slab to the east.

  17. Volcanism/tectonics working group summary

    Energy Technology Data Exchange (ETDEWEB)

    Kovach, L.A. [Nuclear Regulatory Commission, Washington, DC (United States); Young, S.R. [Center for Nuclear Waste Regulatory Analyses, San Antonio, TX (United States)


    This article is a summary of the proceedings of a group discussion which took place at the Workshop on the Role of Natural Analogs in Geologic Disposal of High-Level Nuclear Waste in San Antonio, Texas on July 22-25, 1991. The working group concentrated on the subject of the impacts of earthquakes, fault rupture, and volcanic eruption on the underground repository disposal of high-level radioactive wastes. The tectonics and seismic history of the Yucca Mountain site in Nevada is discussed and geologic analogs to that site are described.

  18. Volcanic hazards on the Island of Hawaii (United States)

    Mullineaux, Donal Ray; Peterson, Donald W.


    Volcanic hazards on the Island of Hawaii have been determined to be chiefly products of eruptions: lava flows, falling fragments, gases, and particle-and-gas clouds. Falling fragments and particle-and-gas clouds can be substantial hazards to life, but they are relatively rare. Lava flows are the chief hazard to property; they are frequent and cover broad areas. Rupture, subsidence, earthquakes, and sea waves (tsunamis) caused by eruptions are minor hazards; those same events caused by large-scale crustal movements, however, are major hazards to both life and property. Volcanic hazards are greatest on Mauna Loa and Kilauea, and the risk is highest along the rift zones of those volcanoes. The hazards are progressively less severe on Hualalai, Mauna Kea, and Kohala volcanoes. Some risk from earthquakes extends across the entire island, and the risk from tsunamis is high all along the coast. The island has been divided into geographic zones of different relative risk for each volcanic hazard, and for all those hazards combined. Each zone is assigned a relative risk for that area as a whole; the degree of risk varies within the zones, however, and in some of them the risk decreases gradationally across the entire zone. Moreover, the risk in one zone may be locally as great or greater than that at some points in the zone of next higher overall risk. Nevertheless, the zones can be highly useful for land-use planning. Planning decisions to which the report is particularly applicable include the selection of kinds of structures and kinds of land use that are appropriate for the severity and types of hazards present. For example, construction of buildings that can resist a lava flow is generally not feasible, but it is both feasible and desirable to build structures that can resist falling rock fragments, earthquakes, and tsunamis in areas where risk from those hazards is relatively high. The report can also be used to select sites where overall risk is relatively low, to