quantification of the microstructural evolution of polycrystalline fabrics using fame application to in situ deformation of ice abstract in geology glaciology and material science new technological advances result in an ever increasing amount of data and datasets in particular when in situ experiments are conducted rapid rigorous and reliable statistical treatment is needed to allow researchers to access these large datasets for further analysis here we present fame fabric analyser based microstructure evaluation a suite of matlab scripts that utilize the matlab open source toolboxes mtex and polylx optional for rapid quantification of thin section data the data has been collected using an automated fabric analyser at a spatial resolution of 5 m pixel from the dataset grain maps are reconstructed and grain and grain boundary statistics are determined the same scripts calculate orientation density distribution diagrams and eigenvalues of the orientation tensor in the case of 2d in situ plane strain deformation experiments on polycrystalline heavy water d2o a matlab script based batch analysis for each deformation step was performed fame offers the possibility to generate movie files that combine optical data with c axes orientation data and grain statistics application of the presented scripts to analyse in situ deformation experiments of polycrystalline ice shows the value of rigorous quantification of the microstructural evolution data for process oriented research

microstructure and fabric development in ice lessons learned from in situ experiments and implications for understanding rock evolution abstract in this contribution we present a review of the evolution of microstructures and fabric in ice based on the review we show the potential use of ice as an analogue for rocks by considering selected examples that can be related to quartz rich rocks advances in our understanding of the plasticity of ice have come from experimental investigations that clearly show that plastic deformation of polycrystalline ice is initially produced by basal slip interaction of dislocations play an essential role for dynamic recrystallization processes involving grain nucleation and grain boundary migration during the steady state flow of ice to support this review we describe deformation in polycrystalline standard water ice and natural ice samples summarize other experiments involving bulk samples and use in situ plane strain deformation experiments to illustrate the link between microstructure and fabric evolution rheological response and dominant processes most terrestrial ice masses deform at low shear stresses by grain size insensitive creep with a stress exponent n 3 however from experimental observations it is shown that the distribution of plastic activity producing the microstructure and fabric is initially dominated by grain boundary migration during hardening primary creep followed by dynamic recrystallization during transient creep secondary creep involving new grain nucleation with further cycles of grain growth and nucleation resulting in near steady state creep tertiary creep the microstructural transitions and inferred mechanism changes are a function of local and bulk variations in strain energy i e dislocation densities with surface grain boundary energy being secondary except in the case of static annealing as there is a clear correspondence between the rheology of ice and the high temperature deformation dislocation creep regime of polycrystalline quartz we suggest that lessons learnt from ice deformation can be used to interpret polycrystalline quartz deformation different to quartz ice allows experimental investigations at close to natural strain rate and through in situ experiments offers the opportunity to study the dynamic link between microstructural development rheology and the identification of the dominant processes

calderas a planetary perspective caldera bearing volcanoes are the largest volcanic edifices on a planet and are expressions of long lived near surface magma chambers on earth only three morphological classes of calderas are common shield calderas e g mauna loa hawaii stratocone calderas e g crater lake oregon and ash flow calderas e g valles caldera new mexico each of these classes has a characteristic caldera size magma type and tectonic location no calderas have been recognized on the moon or mercury but mars has large shield calderas as well as the unique highland patera calderas the latter may represent an explosive ultramafic style of volcanism unlike any volcanic activity in modern earth history radar images suggest that venus has at least one large caldera bearing shield volcano and possible calderas of other types jupiter s satellite io has abundant large shieldlike calderas but no shield massifs the number and variety of calderas on a planet may be proportional to planet mass consistent with a previous suggestion that volcanic complexity increases with planet size io is an exception but heating in io is generated tidally rather than by the decay of radioactive elements so that its calderas are not related to its size the occurrence of shield volcanoes on four solar system bodies suggests that thermal and tectonic mechanisms i e hot spots giving rise to construction of shield mountains and associated collapsed summits are basic processes in planetary geology hot spot volcanism is expected to be most important on planets lacking plate tectonics on earth large shields have lifetimes of only a few million years but on mars large shields may have been active for 1 5 109 years shield calderas on earth are smaller than 20 km in diameter but known or suspected shield calderas on mars venus and io have considerably larger diameters assuming that caldera diameters are related to magma chamber diameters and depths magma chambers on other planets are significantly larger and or deeper than their counterparts on earth terrestrial magma chambers are small because terrestrial shield volcanoes are small in comparison to shields on mars and venus and terrestrial shields are small because the earth s mobile plates move growing shields away from their deep sources thus distributing magma along a narrow chain rather than piling it up around a central vent finally the long lava flows of mars are also explained if the volume of erupted magma has any simple relation to magma chamber volume

deformations and inferred stress field for ellipsoidal sources at long valley california 1975 1982 ground deformation and seismicity observed from 1975 to the present support the existence of magma beneath the central part of long valley caldera california constraints on the source geometry are obtained from deformation modeling of uplift and trilateration data over the period 1975 1982 the deformation data are modeled with an elastic half space incorporating an ellipsoidally shaped magma chamber under uniform pressure the hilton creek fault and the south moat fault the best fit to the deformation data indicates a nearly spherically shaped source beneath the central part of the caldera at a depth of 9 5 1 km however significant deviations of some horizontal displacement data suggest that movements along the faults are probably more complicated than the assumed dislocations the predicted normal stress on the vertical south moat fault plane varies from weak tension above 4 km depth to strong compression below that depth and the shear stress is right lateral in the eastern half and left lateral in the western half of the fault it is unlikely that such a stress field could trigger slip movement on the fault tangential stress at the surface of the magma chamber has a maximum tension near its intersection with the south moat fault it is possible that the 1983 earthquake swarms in the south moat were triggered by shallow magma intrusions beneath the south moat of the caldera a narrow prolate ellipsoidal source which produces about the same uplift as the spherical source model leads to a horizontal tensile stress that is about 1 order of magnitude higher in the region directly above the source however the crack opening location for magma injection is at the top of the source in this case and would not be related to the seismicity in 1983

seismic and geodetic progression of the 2018 summit caldera collapse of kīlauea volcano abstract the 2018 eruption of k lauea volcano hawai i resulted in a major collapse of the summit caldera along with an effusive eruption in the lower east rift zone the caldera collapse comprised 62 highly similar collapse cycles of strong ground deformation and earthquake swarms that ended with a magnitude 5 collapse event and one partial cycle that did not end with a collapse event we analyzed geodetic and seismic data to better understand how the caldera collapse progressed over 3 months of activity focusing on the cyclical activity we identified 3 main phases of collapse initial ring fault activation and small explosions phase 1 an eastward shift in activity and freeing of the central piston phase 2 and a recoupling of the piston to the reservoir followed by relatively steady behavior until the eruption s end phase 3 additionally we observed geodetic evidence of tangential motion from the localization of the main ring fault phase 2 and the formation of a major peripheral ring fault on the eastern side of the collapse caldera during phase 3 both geodetic and seismic parameters suggest that the collapse may have had an eastward component of motion after the ring fault system had formed the cyclical seismic and geodetic parameters show no obvious signs that the collapse was coming to an end with the only notable change being a significant increase in the ratio of cyclical displacement to co collapse displacement observed during the last complete cycle on gnss stations outside the caldera region

a model for deformation in long valley california 1980 1983 geodetic data collected in long valley california from 1975 through 1983 define a pattern of uplift and strain which is evidently associated with a sequence of earthquakes occurring in may 1980 and subsequent swarm activity continuing until the present we have constructed a model to explain the deformation observed since may 1980 in terms of inflation of two subsurface magma chambers faulting in the south moat region of the caldera and slip on the hilton creek fault the most significant new feature of the model is the shallow magma chamber at 5 km depth located a few hundred meters to the east of the casa diablo hot spring area inflation of this chamber causes stresses which show consistency with various aspects of the seismicity in the south moat of the caldera calculations of stress across vertical planes over the magma chamber can be used together with failure criteria to estimate the inflation volume at which the rock layers intervening between the chamber and the surface will fail by extensional fracture

reanalysis of s to p amplitude ratios for gross attenuation structure long valley caldera california because of the strong interest in the magmatism and volcanism at long valley caldera eastern california and because of recent significant improvements in our knowledge of the caldera velocity structure and earthquake locations i have reanalyzed the local earthquake s to p amplitude ratio data of sanders 1984 for the gross three dimensional attenuation structure of the upper 10 km of long valley caldera the primary goals of the analysis are to provide more accurate constraints on the depths of the attenuation anomalies using improved knowledge of the ray locations and an objective inversion procedure the new image of the high s wave attenuation anomaly in the west central caldera suggests that the top of the principal anomaly is at 7 km depth which is 2 km deeper than previously determined because of poor resolution in much of the region some of the data remain unsatisfied by the final attenuation model this unmodeled data may imply unresolved attenuation anomalies perhaps small anomalies in the kilometer or two just above the central caldera anomaly and perhaps a larger anomaly at about 7 km depth in the northwest caldera or somewhere beneath the mono craters the central caldera s wave attenuation anomaly has a location similar to mapped regions of low teleseismic p wave velocity crustal inflation reduced density and aseismicity strongly suggesting magmatic association

shear wave anisotropy and stress direction in and near long valley caldera california 1979 1988 we observed shear wave splitting birefringence for two temporary surface deployments of three component digital seismographs that were in place before and after m 6 earthquakes near the long valley caldera california in one of these deployments the data sample precedes the large events of the may 1980 mammoth lakes earthquake sequence by 6 months and cover the two most active months of the may 1980 aftershock sequence one of the stations wit from this deployment was reoccupied with identical instrumentation in 1988 another deployment preceded the 1986 chalfant valley mainshock by 2 days and recorded events for 6 days the polarization of the faster shear wave changes from n30 w at mammoth to due north at chalfant valley and in both cases is parallel to the strike of nearby surface faults and to the mean direction of p axes determined from focal mechanism groupings observations from nearby stations yield fast directions nearly at 23 from each other and time separations of fast and slow shear waves show considerable station to station variation showing no correlation with earthquake station distance or earthquake depth these observations suggest that the observed anisotropy results primarily from near station presumably shallow effects rather than from widespread aligned microcracks the records at long valley station wit show a slight variation of average fast shear wave polarization from 1979 to 1980 but with the limited amount of data available this difference is not statistically significant time separation measurements of up to 0 48 s at station wit yield estimates of 15 30 velocity anisotropy among the highest reported for local earthquakes secular variation in the time separation of fast and slow shear waves between events recorded at station wit in 1979 and 1980 is swamped by the scatter in the data if it is present the five events recorded in 1988 showed similar s wave polarizations and time separations to those in 1980 but there are not enough events for a statistical comparison unlocated events at long valley station mrs show a slight increase in time separation after the may 1980 m 6 0 earthquakes but the increase is not statistically significant

conductive heat flux in vc 1 and the thermal regime of valles caldera jemez mountains new mexico over 5 of heat in the western united states is lost through quaternary silicic volcanic centers including the valles caldera in north central new mexico these centers are the sites of major hydrothermal activity and upper crustal metamorphism metasomatism and mineralization producing associated geothermal resources we present new heat flow data from valles caldera core hole 1 vc 1 drilled in the southwestern margin of the valles caldera thermal conductivities were measured on 55 segments of core from vc 1 waxed and wrapped to preserve fluids these values were combined with temperature gradient data to calculate heat flow above 335 m which is probably unsaturated heat flow is 247 16 mw m 2 the only deep temperature information available is from an uncalibrated commercial log made 19 months after drilling gradients derived from uncalibrated temperature logs and conductivities are inversely correlated between 335 and 737 m indicating a conductive thermal regime and component heat fluxes over three depth intervals 335 539 m 549 628 m and 628 737 m are in excellent agreement with each other with an average of 504 15 mw m 2 temperature logs to 518 m depth with well calibrated temperature sensors result in a revised heat flow of 463 15 mw m we use shallow thermal gradient data from 75 other sites in and around the caldera to interpret the thermal regime at the vc 1 site a critical review of published thermal conductivity data from the valles caldera yields an average thermal conductivity of 1 w m 1 k 1 for the near surface tuffaceous material and we assume that shallow gradient values c km 1 are approximately numerically equal to heat flow mw m 2 heat loss from the caldera is asymmetrically distributed with higher values 400 mw m 2 or higher concentrated in the west southwestern quadrant of the caldera this quadrant also contains the main drainage from the caldera and the youngest volcanism associated with the caldera we interpret the shallow thermal gradient data and the thermal regime at vc 1 to indicate a long lived hydrothermal and magmatic system in the southwestern valles caldera that has been maintained through the generation of shallow magma bodies during the long postcollapse history of the caldera high heat flow at the vc 1 site is interpreted to result from hot water circulating below the base of the core hole and we attribute the lower heat flow in the unsaturated zone to hydrologic recharge

modeling of surface deformation in volcanic areas the 1970 1972 and 1982 1984 crises of campi flegrei italy campi flegrei is a densely inhabited volcanic area within a caldera 12 14 km in diameter immediately west of naples italy in 1970 1972 and in 1982 1984 campi flegrei experienced considerable ground surface deformation producing a bulge about 3 5 m high at its peak in the two inflation episodes the point of maximum uplift did not change coinciding with the caldera center about which the displacements exhibited radial symmetry the 1982 1984 uplift was accompanied by considerable seismic activity gravity changes have been interpreted as reflecting the occurrence of a subvertical magmatic intrusion volcanological petrological and geophysical data point to the existence of a shallow magma chamber just beneath the center of the caldera we assume that the observed surface displacements are the response of an essentially elastic medium to a pressure increase in the magma chamber static deformation is calculated by using a finite element method assuming axial symmetry around a vertical axis through the caldera center the role played by various components of the model geometry boundary conditions elastic properties is analyzed it is shown that models assuming uniform elasticity are inadequate therefore the major volcanotectonic features as well as the influence of temperature and pressure on the elastic properties are taken into account the results of various more complex models are presented it is suggested that a progressively fractured zone whose size and shape depend also on the possible occurrence of magmatic intrusions may explain the observed surface displacements and the other data collected at campi flegrei it is suggested that the 1970 1972 uplift was possibly accompanied by larger scale changes in the stress field

elasto plastic modeling of volcano ground deformation abstract elasto plastic models for pressure sources in heterogeneous domain were constructed to describe assess and interpret observed deformation in volcanic regions we used the finite element method fem to simulate the deformation in a 3d domain partitioned to account for the volcano topography and the heterogeneous material properties distribution firstly we evaluated the extent of a heated zone surrounding the magmatic source calculating the temperature distribution by a thermo mechanical numerical model secondly we included around the pressurized magma source an elasto plastic zone whose dimension is related to the temperature distribution this elasto plastic model gave rise to deformation comparable with that obtained from elastic and viscoelastic models but requiring a geologically satisfactory pressure we successfully applied the method to review the ground deformation accompanying the 1993 1997 inflation period on mt etna the model considerably reduces the pressure of a magma chamber to a few tens of mpa to produce the observed surface deformation results suggest that the approach presented here can lead to more accurate interpretations and inferences in future modeling based assessments of volcano deformation

development and maintenance mechanism for the semiannual oscillation of the north pacific upper level circulation abstractthe north south semiannual oscillation sao of the north pacific jet stream part of the atmospheric sao in the northern hemisphere can be well depicted by the semiannual component of the monthly mean eddy streamfunction expressed by the semiannual eddy streamfunction budget the dynamic processes develop and maintain the sao including the adjustment between vorticity advection and convergence of vorticity flux of the monthly mean mode and the convergence of transient vorticity flux an empirical orthogonal function analysis of these dynamic processes shows an east west elongated cyclonic anticyclonic cell of the semiannual eddy streamfunction anomaly which appears in january and july october and april south of the siberia alaska landmass the maximum minimum adjustment processes by the monthly mean mode and the maximum minimum feedback impact of transient activity on the sao occur in december and june september and march a month ahead of the maximum minimum north south sao of th

subsurface structural features of the saline range and adjacent regions of eastern california as interpreted from isostatic residual gravity anomalies new gravity data indicate a large unexpected anomaly in the saline range and other anomalies in neighboring ranges and valleys of eastern california residual gravity anomalies calculated by subtracting the field due to an airy model of isostatic compensation show the effects of lateral density contrasts in the upper crust a well defined negative gravity anomaly is centered over the saline range and connects the eureka valley and saline valley gravity minima apparently the saline range is a thin veneer of young volcanic material lying on a major alluvium filled basin connected on the north with eureka valley and on the south with saline valley we suggest that the basin formed in a pull apart zone that filled with low density alluvium and became the site of voluminous pliocene volcanic eruptions the age of this depression predates volcanism of the saline range dated at about 4 ma other significant anomalies are as follows 1 an offset in the owens valley fault at lat 37 01 n appears in the isostatic residual gravity data and marks the western end of a major gravity depression that continues across the inyo mountains at papoose flat the gravity depression suggests that the papoose flat pluton is larger than suggested by its surface exposure and may extend on the order of 10 km below the topographic surface 2 a density boundary trends west northwest across the inyo batholith and proterozoic and paleozoic rocks of the white mountains this trend is anomalous to exposed geologic structures and may reflect a structural boundary buried at relatively shallow depth 3 a large gravity low unexpected on the basis of exposed geologic features is in the eastern sierra nevada southwest of the town of lone pine

quasi geostrophic diagnosis of the monsoon depression of 5 8 july 1979 abstract quasi geostrophic diagnosis of the fields of vertical motion and streamfunction tendency based on wind analysis was undertaken for the monsoon depression of 5 8 july 1979 a uniquely well observed case during summer monex wind analysis in terms of streamfunction and velocity potential was performed for data averaged in three layers of equal pressure depth front 1000 to 100 mb the thermal stratification near the depression above 850 mb was approximately moist adiabatic the wind analyses showed that the basic zonal currents westerly in the lower troposphere and easterly in the middle levels weakened as the depression formed central vorticity increased rapidly on 5 6 july to a magnitude three times the coriolis parameter the center tilted toward the southwest with elevation the quasi geostrophic omega equation was solved at the interfaces between layers for a range of stabilities from the full dry adiabatic value to 1 of it ascent west of the center for the near neutral stability was

a systematic approach to the interpretation of magnetotelluric data in volcanic environments with applications to the quest for magma in long valley california magnetotelluric mt data in long valley california are principally sensitive to the complex structure in the rocks filling the caldera while the overall shapes of the sounding curves are set by the deep crustal structure and mantle the lateral variations of that response can be entirely explained using structure of the upper 1600 m a conductive body at depths from 1350 to 1600 m is present in the northern southern and western moats and beneath the resurgent dome this conductor effectively masks structures at intermediate depths we believe that this conductor represents fractured bishop tuff within the caldera and possibly graphitic metasediments beneath it electrical logs from wells penetrating these formations are used to corroborate our interpretation a large conductive 5 ohm m body of magma is precluded by the mt data the response to a spherical chamber of 4 km radius at a depth of 10 km is several times larger than the mismatch between our modeled and observed sounding curves small 2 km radius isolated pockets of magma may be present however we have developed a systematic approach to interpreting mt data in a complex volcanic environment we clustered sites on the basis of similar responses to perceive patterns in spite of severe distortions by local heterogeneity our model was built from the surface downward incorporating other published geophysical surveys and a time domain electromagnetic survey released by unocal three dimensional modeling was employed from the start and our interpretation was based primarily upon the phases this systematic approach of stripping off the known shallow structure in order to study the intermediate and deeper structure was quite successful an important finding of our study is that the phase is sensitive to shallow 1350 m three dimensional structure even at frequencies of 0 01 hz three dimensional modeling simply cannot be avoided in complex geological environments

inversion for p and s wave attenuation structure long valley caldera california p and s wave amplitude data from digital three component seismograms of local earthquakes recorded on a temporary seismic array have been used to tomographically invert for the three dimensional attenuation structure in the upper crust of long valley caldera california differential attenuation q 1 values are obtained through the use of a spectral ratio technique that minimizes the site effect on the spectral ratios the spectral ratios are inverted for q 1 using the lsqr algorithm zones of high positive p wave q 1 greater p wave attenuation are observed at a depth of 4 5 km beneath the east flank of mammoth mountain and at 6 8 km beneath the southwestern edge of the resurgent dome a region of positive s wave q 1 is seen at 7 8 km beneath the southern edge of the resurgent dome whereas at 6 7 km the s wave results are near average the region of positive s wave q 1 at 7 8 km beneath the resurgent dome may indicate the roof of a magmatic system the positive p wave q 1 at 4 5 km beneath mammoth mountain and 6 8 km beneath the resurgent dome may be due to the presence of a compressible fluid such as supercritical water these zones may represent some of the source regions for the long valley geothermal system

thermomechanical evolution of a thinned continental lithosphere under compression implications for the pyrenees in order to demonstrate the interactions between plate boundary forces and preexisting zones of weakness and how those control the localization of continental deformation inside the lithosphere the thermomechanical evolution of an initially thinned and thermally perturbed continental lithosphere in compression was analyzed within the framework of the pyrenees while a concensus exists as to the shallow structures the extent and geometry of deformation at depth have been the subject of great controversy the thermomechanical implications of recent geological hypotheses on the initial state prior to the compression recently derived from balanced cross section reconstructions are here quantified and compared to the recent ecors deep seismic reflection profile across the pyrenees a thermomechanical model based on finite elastoplastic viscoplastic deformations has therefore been formulated using phenomenological constitutive equations derived from experimental studies the thermally coupled problem is solved by an appropriate vertical two dimensional plane strain finite element approximation in those models most of the shortening is accommodated inside a local zone of intense plastic shearing that creates a sharp wedge shaped root progressively sinking deep into the mantle the main thickening takes place inside the lower crust where it can reach a factor 2 this indentation and crustal imbrication process is controlled by a buckling instability occuring inside the uppermost part of the mantle the evolution of the topography can be related to these phenomena lateral conductive heat transfer overtakes the advective transfer in the vicinity of the inflow of colder crustal material inside a warmer mantle the deformation pattern can be explained by a three layer mechanical lithosphere with a soft ductile internal layer of potential decoupling between two more competent layers characterized by a significant elastic stored energy the overall response of this composite plate is not much influenced by smaller scale variations of crustal rheology but is very much dependent on the contrast in rates of viscous dissipation between the lower crust and the upper mantle and on the possibility of singling out a layer of significant elastic stored energy by the balance between rate of loading and rate of dissipation inside the uppermost mantle predicted deformation pattern is found to agree with the seismic reflection and gravity data even though extrapolation to other rates of shortening must be verified by appropriate numerical modelling these physical mechanisms may be regarded as a paradigm for other crustal imbrication phenomena found in the himalayas tibet or the alps

axi symmetric deformation of a thermo poro elastic half space inflation of a magma chamber summary the deformation observed at phlegraean fields italy during the recent 1982 1984 crisis is interpreted in terms of overpressure in a shallow magma chamber and migration of hot pressurized fluids elastic effects are studied first and previous results obtained from maruyama s strain nuclei are corrected poro elastic and thermo elastic effects are found to be as important as the elastic ones in a semi pervious medium the three terms are typically of the same magnitude results are applied to interpreting the bradyseismic crisis of 1982 84 at phlegraean fields pf near naples italy the concave shape of the first phase of the deformation history at pf can be reproduced by linearly increasing fluid pressure and or temperature at the boundary of a spherical cavity the convex shape of the second phase is interpreted in terms of a gradual return to normal conditions the late phase of slow subsidence is interpreted as the effect of diffusional dissipation of temperature and pressure excess the deconvolution of the real source time history at pf is largely non unique but in any case the importance of fluids in the deformation history is assessed furthermore the inclusion of fluid migration in the deformation model allows simple explanations of several geochemical and geophysical observations made during the bradyseismic crisis

multiscale modeling of ice deformation behavior understanding the flow of ice in glaciers and polar ice sheets is of increasing relevance in a time of potentially significant climate change the flow of ice has hitherto received relatively little attention from the structural geological community this paper aims to provide an overview of methods and results of ice deformation modeling from the single crystal to the polycrystal scale and beyond to the scale of polar ice sheets all through these scales various models have been developed to understand describe and predict the processes that operate during deformation of ice with the aim to correctly represent ice rheology and self induced anisotropy most of the modeling tools presented in this paper originate from the material science community and are currently used and further developed for other materials and environments we will show that this community has deeply integrated ice as a very useful model material to develop and validate approaches in conditions of a highly anisotropic behavior this review by no means exhaustive aims at providing an overview of methods at different scales and levels of complexity

interannual variations in the southern hemisphere winter circumpolar vortex relationships with the semiannual oscillation abstract several studies of southern hemisphere circulation report changes in the late 1970s and 1980s through the mid and high latitudes that are associated with a weakening in the semiannual oscillation sao of sea level pressure and geopotential height this weakening is thought to reflect changes in the amplitude of zonal wavenumber 3 a deepening of the subantarctic trough intensification of subtropical ridging and an increase in the strength of the westerlies these conclusions suggest an equatorial expansion of the circumpolar vortex in high latitudes and a poleward contraction of the vortex in the midlatitudes the goal of this study is to examine the size and spatial variation of the southern hemisphere circumpolar vortex in winter for evidence of such change the size of the 500 hpa vortex was calculated for the mid and high latitudes in 5 longitude sectors from both the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis dataset 1

deformation around the creede caldera a consequence of isostatic adjustment following caldera formation the pattern of deformation around the creede caldera 26 5 ma southwest colorado may provide clues to the physical mechanisms of caldera evolution particularly resurgent doming this paper considers the hypothesis that the deformation is due to isostatic relaxation of surface load topography following caldera formation involving uplift of the caldera floor and subsidence of a surrounding tumescent dome this hypothesis is tested by constructing finite difference models of relaxing topography which have as parameters the mechanical properties of rocks surrounding the caldera the goal is to find models that predict spatial and temporal patterns of deformation matching those observed around the caldera as inferred from 1 the present structural form of the region as indicated by the surface distribution of stratigraphic units and 2 past structural forms as indicated by the locations orientations and ages of faults which are presumed to be due to a combination of regional tension and stresses caused by bending at the surface successful models of the deformation have been found using a variable viscosity half space overlain by a thin elastic plate in general the nature of deformation at the surface is strongly dependent on the radial variation of viscosity at shallow depths beneath the elastic plate and is much less sensitive to variation of viscosity with depth models with relatively low viscosities beneath the caldera and relatively high viscosities in the surrounding region accurately predict uplift of the caldera floor which is rapid compared to the rate of marginal subsidence the results indicate that the rate of deformation is governed by the flow of material with viscosities characteristic of wallrock roughly 1019 1024 pa s rather than magma a gap in faulting around the caldera at about one caldera radius outside the wall suggests the existence of a relatively low radial viscosity gradient in that position higher viscosity gradients inside and outside of this low may reflect the margins of two nested magma bodies at depth a central stock within a larger batholith in order to match the observed pattern of faults around the caldera the orientation of the regional tension that is superimposed on the bending stresses must rotate clockwise with time this change in stress direction is consistent in sense but earlier than that proposed by others for the western united states

genetic links between ash flow calderas and associated ore deposits as revealed by large scale thermo mechanical modeling abstract in addition to a number of epithermal ore deposits some porphyry type ore deposits are also hosted by ash flow calderas spatial correlation between ash flow calderas and these deposits is observed in several parts of the world but temporal correlation between the mineralization and the episode of caldera formation remains unclear especially because geochronological data indicate that the mineralization may date to several million years before or after caldera formation because caldera collapse represents only a very short event in a long time scale evolution between a silicic magma chamber and its host rocks we have developed a thermo mechanical model of upper crustal and magmatic system behavior during the pre and post caldera formation stages major petrophysical properties of ash flow caldera related rocks are incorporated into the model which accounts for brittle elasto ductile rheology and heat transfer and reproduces fault initiation and various caldera collapse scenarios large scale mechanisms of initiation of thermal and structural traps for epithermal ore deposits are described in particular we found that the outer sides of caldera border faults are associated with both anomalous heat transfer and a high fracture density the finite size of the insulating intracaldera units forces the accumulated heat excess to be laterally transferred across the border faults in most cases the model predicts y shaped fault geometry which is surprisingly similar to that of mineralized faults in the field variations in lithostatic pressure on the magma chamber roof and in the vicinity of the border faults can reach 10 to 20 mpa with deep overpressured zones close to the inner edge of the chamber corners despite the fact that hydrothermal convection and fluid geochemistry are not included in the model these thermal and mechanical results are believed to constrain the conditions for mineralization processes our results show that in the presence of regional extension the development of caldera border faults may be suppressed to the advantage of deep seated fractures clustered above the central part of the magma chamber thus favoring conditions for the formation of porphyry type ore deposits finally we demonstrate that well before the eruption the gradual emplacement of a hot and large silicic magma chamber may create significant extensional stress in the brittle upper crust resulting in breakup and pre eruptive normal faulting and thus allowing for conditions of pre caldera mineralization

thermomechanical behavior of large ash flow calderas the fundamental thermal and mechanical processes that occur within the ash flow caldera magma chamber systems remain largely enigmatic to date the only models of caldera collapse are simple mostly elastic or viscoelastic mechanical models that can predict some of the conditions preceding the collapse they cannot however predict the collapse itself because they are incapable either of reproducing the formation of faults or of accounting for the brittle ductile transitions and fault related thermal anomalies we have constructed analytical and numerical therrnomechanical that account for both elastic plastic ductile rheology and physical properties of the caldera rocks the overpressured magma is evacuated through a central vent and transforms into ash flow units deposited within the forming caldera brittle deformation faulting and subsequent collapse of the structure are reproduced the results show that in the absence of a regional stress field the collapse on both sides will occur only for aspect ratios i e caldera diameter to the depth of the magma chamber exceeding 5 and that internal embedded faults may also appear when the aspect ratio exceeds 10 thermal conductivity contrasts in ash flow calderas give rise to strong heat refraction that localizes deep seated thermal anomalies to the outer sides of the faults in the presence of regional extension the border faulting can be attenuated or disappear and the faults tend to localize around the central part of the chamber roof coupled therrnomechanical modeling suggests that the outer sides of the border faults have high trapping capabilities for hydrothermal fluids the geometry of the brittle ductile transition largely controls that of the fractured zones within and around the chamber roof thus justifying a new mechanical definition of magma chamber geometry

influence of bubbles on grain growth in ice abstract numerical static grain growth simulations of ice with air bubbles as a second phase show a significant drop in grain growth rate compared to bubble free ice the magnitude of this drop in growth rate is dependent on the bubble boundary mobility the volume fraction of air the average bubble size and the bubble size distribution the rate of grain growth decreases at first as the microstructure evolves towards a steady state only then does grain growth follow the expected linear increase of mean grain area with time in experiments this decrease in growth rate could erroneously be interpreted as growth with a deviating growth exponent

nonlinear teleseismic tomography at long valley caldera using three dimensional minimum travel time ray tracing the authors explore the impact of three dimensional minimum travel time ray tracing on nonlinear teleseismic inversion this problem has particular significance when trying to image strongly contrasting low velocity bodies such as magma chambers because strongly refracted and or diffracted rays may precede the direct p wave arrival traditionally used in straight ray seismic tomography they use a simplex based ray tracer to compute the three dimensional minimum travel time ray paths and employ an interative technique to cope with nonlinearity results from synthetic data show that their algorithm results in better model reconstructions compared with traditional straight ray inversions the authors reexamine the teleseismic data collected at long valley caldera by the u s geological survey the most prominent feature of their result is a 25 30 low velocity zone centered at 11 5 km depth beneath the northwestern quandrant of the caldera beneath this at a depth of 24 5 km is a more diffuse 15 low velocity zone in general the low velocities tend to deepen to the south and east the authors interpret the shallow feature to be the residual long valley caldera magma chamber while the deeper feature may represent basaltic magmas ponded in the midcrust the deeper position of the prominent low velocity region in comparison to earliermore tomographic images is a result of using three dimensional rays rather than straight rays in the ray tracing the magnitude of the low velocity anomaly is a factor of approximately 3 times larger than earlier models from linear arrival time inversions and is consistent with models based on observations of ray bending at sites within the caldera these results imply the presence of anywhere from 7 to 100 partial melt beneath the caldera 40 refs 1 fig 1 tab less

on the mechanics of caldera resurgence the mechanisms suggested to cause caldera resurgence can be categorized as 1 viscous rebound of magma 2 regional detumescence and 3 pressure against the base of the caldera block due to magmatic vesiculation and convection or addition of new magma the critical observation that resurgence takes of the order of 103 105 years insists that the causative mechanism be regulated by a highly viscous e g 1022 pa s structural member of the crust the relatively low viscosity magma and a purely elastic crust cannot be important in achieving this time scale the most likely mechanism is the coupled effect of regional detumescence and magmatic vesiculation detumescence compresses the magma chamber squeezing magma upward against and through the caldera block vesiculation also compresses the chamber and tends to dome the caldera block the times of both detumescence and doming of the caldera block by magmatic pressure are probably inversely proportional to the size of the magma chamber but the rate of cooling of the chamber is proportional to its size because solidification spreads viscous relaxation over a wide region of the crust and curtails resurgence there is likely to be a minimum volume of magma that can undergo resurgent doming it is difficult to be exact about this critical size until more precise models have been developed

baroclinicity meridional temperature gradients and the southern semiannual oscillation abstract it has long been known that a strong half yearly oscillation exists in surface pressure at high southern latitudes there are two minima during the year the one occurring in october being more intense than that in march the semiannual oscillation sao has been related to the different surface types and inertia at 50 and 65 s these conspire to produce a semiannual wave in the meridional temperature gradient between those two latitudes the timing of the maxima for these is as above but the stronger is in march however if the arguments of van loon are applied literally then the seasonal evolution of temperature gradient should follow a comparable seasonal evolution of baroclinicity and surface pressure a full calculation of baroclinicity shows that the seasonal evolution of static stability combined with the twice annual maxima of meridional temperature gradient produces a larger peak of baroclinicity in october consistent with the sao in surface pressure

constraints on the upper crustal structure of the long valley mono craters volcanic complex eastern california from seismic refraction measurements during the summers of 1982 and 1983 field work was completed on 10 new seismic refraction profiles in the long valley mono craters region located within the technically active zone between the eastern sierra nevada and the basin and range province the four profiles presented here sample the upper 7 10 km of the crust within the western half of long valley cladera the mono craters ring fracture system and the normal crust north and northeast of long valley the entire area shares a common crystalline basement consisting primarily of mesozoic granitic rocks at a depth of 2 km beneath the topographic surface the p wave velocity is uniformly 5 6 km s beneath which the velocity increases with a gradient of about 0 1 s 1 clear secondary arrivals observed on a profile crossing the west part of the caldera support evidence from 1972 seismic refraction profiles for a reflecting boundary at a depth of 7 8 km beneath the west margin of the resurgent dome which may represent the top of a magma chamber structural details resolved in the upper 2 km of the crust lead to the following conclusions 1 p wave velocities in the crystalline basement at depths shallower than 2 km vary from 3 6 to 5 0 km s this variation reflects differences in the degree of fracturing of the upper portion of the basement 2 an apparently homogeneous basement in the upper 7 10 km beneath the mono craters ring fracture system indicates that any extensive magma chamber must be at least 10 km deep there 3 the downdropped crystalline basement beneath the western half of long valley caldera dips genty 5 10 to the northeast apparent offsets along steeply dipping caldera bounding faults are 1 0 1 7 km along the northern western and southern sides of the caldera with largest offsets in the north 4 rocks forming the caldera fill fall into essentially three p wave velocity groups from the surface downward these velocity groups are 100 400 of 1 2 1 8 km s material corresponding to unconsolidated fluvial or lacustrine deposits or highly fractured rhyolite flows 200 400 m of 2 8 3 1 km s material corresponding to sparsely jointed postcaldera rhyolite rhyodacite and basalt flows and approximately 1000 m of 3 9 4 4 km s material corresponding to deposits of bishop tuff

the subsurface structure of long valley caldera mono county california a preliminary synthesis of gravity seismic and drilling information long valley caldera is a 0 7 m y old volcanic eruptive center associated with an elliptical collapse structure on the eastern margin of the sierra nevada two dimensional models of caldera fill are presented in this study resulting in structures compatible with existing seismic refraction and gravity data modifications to previous seismic models include shifting the north caldera rim to the south and decreasing the dip of the west and south boundaries densities in the model are not varied independently but are based on empirical velocity density relationships and measured densities from surface outcrops and drill cores these density values are adequate to account for observed gravity anomalies indicating that the assumed subsurface lithologies are approximately correct the large gravity anomaly in the shallow eastern caldera is modeled by assuming that the area is underlain by a layer of exceptionally low density

crater relaxation on ganymede implications for ice rheology controversy has existed over whether or not viscous relaxation is an important process on the icy satellites previous models involved large extrapolations of newtonian flow laws for ice whereas ice is known to exhibit non newtonian behavior recently the flow law parameters for ice at the appropriate temperatures and stresses have been measured numerical modelling of the viscous relaxation of basins on ganymede using these parameters has given implausibly short relaxation times however this model treated ice as a purely viscous substance so that no elastic lithosphere could develop near the surface here we treat ice as a maxwell visco elastic material and numerically model the relaxation of basins on ganymede we find that realistic young s moduli lead to little relaxation occurring in basins even 4 0 ga after their formation further we demonstrate that within broad limits the near surface temperature gradient has little effect on this result finally through examination of the distribution of maxwell times in the vicinity of the crater we show that most viscous relaxation occurs early in the basin s history when stresses are high and thus maxwell time is short as stresses are relieved the maxwell time becomes long and relaxation essentially ceases

the interpretation of gravity changes and crustal deformation in active volcanic areas simple models like the well known point source of dilation mogi s source in an elastic homogeneous and isotropic half space are widely used to interpret geodetic and gravity data in active volcanic areas this approach appears at odds with the real geology of volcanic regions since the crust is not a homogeneous medium and magma chambers are not spheres in this paper we evaluate several more realistic source models that take into account the influence of self gravitation effects vertical discontinuities in the earth s density and elastic parameters and non spherical source geometries our results indicate that self gravitation effects are second order over the distance and time scales normally associated with volcano monitoring for an elastic model appropriate to long valley caldera we find only minor differences between modeling the 1982 1999 caldera unrest using a point source in elastic homogeneous half spaces or in elasto gravitational layered half spaces a simple experiment of matching deformation and gravity data from an ellipsoidal source using a spherical source shows that the standard approach of fitting a center of dilation to gravity and uplift data only excluding the horizontal displacements may yield estimates of the source parameters that are not reliable the spherical source successfully fits the uplift and gravity changes overestimating the depth and density of the intrusion but is not able to fit the radial displacements

three dimensional gravity modeling of the geologic structure of long valley caldera a 48 mgal gravity low coincides with long valley caldera and is mainly attributed to low density caldera fill gravity measurements by unocal geothermal have been integrated with u s geological survey data vastly improving gravity station coverage throughout the caldera a strong regional gravity trend is mainly attributed to isostasy a best fitting based on regional control of basement densities airy heiskanen isostatic model was used for the regional correction a three dimensional multiple unit gravity modeling program with iterative capabilities was developed to model the residual gravity the density structure of long valley caldera and vicinity was modeled with 22 discrete density units most of which were based on geologic units information from drill hole lithologies surface geology and structural geology interpretations constrain the model some important points revealed by the three dimensional gravity modeling are that 1 the volume of ejected magma associated with the bishop tuff eruption is greater than previously thought 2 the caldera structure is strongly influenced by precaldera topography and the extensions of major active faults 3 the main west ring fracture is coincident with the inyo domes mono craters fracture system 4 a relatively low density region probably underlies the caldera and 5 a silicic magma chamber may underlie devils postpile

modelling of viscoelastic plume lithosphere interaction using the adaptive multilevel wavelet collocation method summary modelling of mantle flows with sharp viscosity contrasts in a viscoelastic medium is a challenging computational problem in geodynamics because of its multiple scale nature in space and time we have employed a recently developed adaptive multilevel wavelet collocation algorithm to study the dynamics of a small rising diapir interacting with a stiff lithosphere in a maxwell viscoelastic mantle in this kinematic model we have prescribed the upward velocity of the diapir and then we need to integrate in time only the momentum equation governing the temporal evolution of the pressure stress and velocity components which together constitute a sixth order system in time the total number of collocation points did not exceed 10 4 compared to more than 10 6 gridpoints using conventional evenly spaced grid methods the viscosity of the diapir is 10 x4 times lower than that of the surrounding mantle while the viscosity of the thin lithosphere about 5 10 per cent of the entire layer depth is 10 4 10 8 times stiffer than the ambient mantle our results demonstrate the efficacy of wavelets to capture the sharp gradients of the stress and pressure fields developed in the diapiric impingement process the interaction of the viscoelastic lithosphere with the rising viscoelastic diapir results in the localization of stress within the lithosphere the magnitude of the stress fields can reach around 100 300 mpa our simple kinematic model shows clearly that viscoelasticity can potentially play an important role in the dynamics of the lithosphere especially concerning the potential severage of the lithosphere by mantle upwellings

contemporary vertical surface displacements in yellowstone national park relative vertical displacements and average relative vertical velocities have been determined for bench marks located throughout yellowstone national park ynp by comparing geodetic leveling measurements made in 1923 second order 1936 third order 1941 third order 1955 third order 1960 first order and 1975 1977 first order the 1923 1975 data indicate uplift greater than 400 mm 7 7 mm yr of an area approximately 15 20 km wide and at least 40 km long which is centered along the northeast trending axis of the 600 000 year old yellowstone caldera the maximum 1923 1975 vertical displacement in this area is 726 mm 14 0 mm yr the existence of a well defined and untilted yellowstone lake terrace implies that the 1923 1975 average vertical velocities cannot have been maintained for more than a few hundred years the 1955 1977 data from central ynp indicate that the northeastern caldera half has risen relative to the southwestern half at an average velocity of about 8 mm yr a similar bias is present in the 1923 1975 data but it is less pronounced the 1923 1960 and 1960 1975 data from northwestern ynp and a 200 mm depression in the 1923 1975 data near norris junction may be interpreted in terms of deformation associated with the 1959 hebgen lake earthquake and the 1975 yellowstone park earthquake a composite profile of the 1936 1977 and 1941 1977 average vertical velocity data which skirts the edge of the yellowstone caldera in northeastern ynp is most easily explained as the result of random leveling error and or bench mark instabilities the apparent youth of the 1923 1975 yellowstone uplift and its close association with the yellowstone caldera suggest that the most likely cause of the uplift is a recent not more than 500 years ago influx of molten material into the upper crust beneath the caldera

the microstructure of polar ice part ii state of the art an important feature of natural ice in addition to the obvious relevance of glaciers and ice sheets for climate related issues is its ability to creep on geological time scales and low deviatoric stresses at temperatures very close to its melting point without losing its polycrystalline character this fact together with its strong mechanical anisotropy and other notable properties makes natural ice an interesting model material for studying the high temperature creep and recrystallization of rocks in earth s interior after having reviewed the major contributions of deep ice coring to the research on natural ice microstructures in part i of this work faria et al 2014 here in part ii we present an up todate view of the modern understanding of natural ice microstructures and the deformation processes that may produce them in particular we analyze a large body of evidence that reveals fundamental flaws in the widely accepted tripartite paradigm of polar ice microstructure also known as the three stage model cf part i these results prove that grain growth in ice sheets is dynamic in the sense that it occurs during deformation and is markedly affected by the stored strain energy as well as by air inclusions and other impurities the strong plastic anisotropy of the ice lattice gives rise to high internal stresses and concentrated strain heterogeneities in the polycrystal which demand large amounts of strain accommodation from the microstructural analyses of ice cores we conclude that the formation of many and diverse subgrain boundaries and the splitting of grains by rotation recrystallization are the most fundamental mechanisms of dynamic recovery and strain accommodation in polar ice additionally in fine grained high impurity ice layers e g cloudy bands strain may sometimes be accommodated by diffusional flow at low temperatures and stresses or microscopic grain boundary sliding via microshear in anisotropic ice sheared at high temperatures grain boundaries bulged by migration recrystallization and subgrain boundaries are endemic and very frequent at almost all depths in ice sheets evidence of nucleation of new grains is also observed at various depths provided that the local concentration of strain energy is high enough which is not seldom the case as a substitute for the tripartite paradigm we propose a novel dynamic recrystallization diagram in the three dimensional state space of strain rate temperature and mean grain size which summarizes the various competing recrystallization processes that contribute to the evolution of the polar ice microstructure dedicated to sepp kipfstuhl on occasion of his 60th birthday

geometrical and mechanical constraints on the formation of ring fault calderas ash flow plate subsidence piston like calderas are bounded by a set of arcuated sub vertical collapse faults named ring faults experimental studies on caldera formation performed mostly using spherical or cylindrical magma chamber geometries find that the resulting ring faults correspond to steeply outward dipping reverse faults and show that pre existing fractures developed during pre eruptive phases of pressure increase may play a major role in controlling the final collapse mechanism a situation that should be expected in small to medium sized ring fault calderas developed on top of composite volcanoes or volcanic clusters on the other hand some numerical experiments indicate that large sill like elongated magma chambers may induce collapse due to roof bending without fault reactivation as seems to occur in large plate subsidence calderas formed independently of pre existing volcanoes also numerical experiments allow the formation of nearly vertical or steeply inward dipping normal ring faults in contrast with most of the analogue models using a thermoelastic model we investigate the geometrical and mechanical conditions to form ring fault calderas in particular the largest ones without needing a previous crust fracturing results are given in terms of two dimensionless geometrical parameters namely and e the former is the chamber extension to chamber depth ratio whereas the latter stands for the chamber eccentricity we propose that the e pair determinates two different types of ring fault calderas with different associated collapse regimes ring fault region a is related to large plate subsidence calderas i e andean calderas or western us calderas for which few depressurisation is needed to set up a collapse initially governed by flexural bending of the chamber roof in contrast ring fault region b is related to small to moderate sized calderas i e composite volcano calderas for which much depressurisation is needed our opinion is that collapse requires in the latter case reactivation of pre existing fractures and it is therefore more complex and history dependent

crustal structure beneath long valley caldera from modeling of teleseismic p wave polarizations and ps converted waves in this study the authors present new constraints on the nature of the low velocity zone beneath long valley caldera based on the measured propagation directions of teleseismic p waves and on modeling of p to s converted waves the low velocity body is a large asymmetrical volume which deepens to the east extending from depths of 7 to 30 km it contains lower velocities than originally proposed by earlier teleseismic studies in particular there is a tabular feature between 7 and 11 km depth that has a reduction in velocity of about 30 these low velocities imply a much greater percentage of melt in the crust beneath long valley caldera than previously estimated array analysis of large delayed arrivals identifies them to be ps converted waves from the shoulders and roof of this tabular zone these conversions bound the depth to the magma chamber roof to be within about 10 km of the surface these results are consistent with elements from several other studies and the authors present an integrated and improved model of crustal structure at long valley the concordance of the deeper low velocity zones with regional structural trends implies that the shallow low velocity feature is a cupola on topmore of an asymmetric diapiric ridge rising up from the migmatized lower crust of the basin and range the authors present two contrasting interpretations of the geometry of low velocity zones in the crust one implies a time invariant magma chamber and conduit system for long valley caldera the other implies an evolution of that system from a simple vertical regime to its current asymmetrical geometry 37 refs 19 figs 1 tab less

a structural outline of the yenkahe volcanic resurgent dome tanna island vanuatu arc south pacific abstract a structural study has been conducted on the resurgent yenkahe dome 5 km long by 3 km wide located in the heart of the siwi caldera of tanna island vanuatu arc south pacific this spectacular resurgent dome hosts a small caldera and a very active strombolian cinder cone the yasur volcano in the west and exhibits an intriguing graben in its central part detailed mapping and structural observations make it possible to unravel the volcano tectonic history of the dome it is shown that following the early formation of a resurgent dome in the west a complex collapse caldera plus graben occurred and this was associated with the recent uplift of the eastern part of the present dome eastward migration of the underlying magma related to regional tectonics is proposed to explain this evolution

deformation of long valley caldera between august 1982 and august 1983 geodetic and seismic data collected between july 1982 and august 1983 document an important event in the recent evolution of long valley caldera in january 1983 a substantial change in the pattern of deformation was associated with the most intense seismic swarm since may 1980 the earthquake hypocenters of the january 1983 swarm formed a vertical roughly tabular zone beneath the south moat of the caldera analysis of extensive intracaldera horizontal control data indicates that the shear strain distributed throughout this zone could not all be attributed to slip along any single fault plane the surface deformation of the resurgent dome and caldera floor is temporally associated with the swarm and was caused by an expansion of the upper levels of the residual magma chamber analysis of the 1983 data indicates a pressure distribution 2 5 km shallower than could be fit by analysis of the 1979 1982 caldera deformation the volume of this shallow expansion is 10 15 of the whole chamber expansion that occurred between 1979 and 1982 most of the 1983 deformation occurred between december 14 1982 and january 20 1983 and thus was associated with the january 6 7 1983 swarm though right lateral shear strain continued to accumulate in the south moat through 1983 we conclude that a shallow pressure increase probably occurred within the upper levels of the residual magma chamber of long valley caldera during the 5 week period following december 14 1982 it is not clear however whether this pressure increase preceded or accompanied the january 1983 earthquake swarm

almost a sharp cut a case study of the cross point between a continental transform and a rift based on 3d gravity modeling abstract transform faults displace older structures crossing their paths marking a visible shift between the two sliding plates the fate of these pre transform structures within the damage zone is less understood and so is the dynamics of plate boundaries and their changes through time to what extent are they preserved and what structural heritage do they dictate the current study focuses on a crossing region between the oligo miocene nw trending irbid rift and the n trending miocene to recent dead sea transform dst the structural heritage aspect is examined through 3d forward modeling of gravity data across the kinneret kinarot beit she an kkb basin complex of the dst the model includes pre senonian to recent formations highlighting key volcanic and evaporitic units by modeling the depth thickness and 3d density distribution of each lithological unit the study constructs the volumetric geometry of the sub basins and suggests central stages in its geological development the southern beit she an basin began as part of the irbid rift and was later hijacked by the younger dst at the transform rift cross region the transform displacement initiated en echelon mini basins from the beit she an basin northwards to form the proto kinarot and kinneret sea of galilee basins volcanic phases record the deformation leaving a reliable time frame for the subsidence mode faulting and the role of salt tectonics during the late miocene the lateral displacement formed a trishear structure that evolved by the plio pleistocene into the kinneret kinarot beit she an complex bounded by longitudinal faults stemming from a single deep rooted fault

airborne laser altimeter survey of long valley california summary airborne laser altimetry has proved useful in recent years in examining volcanic landforms and glacial ice sheets with the advent of accurate differential gps aircraft tracking we believe that airborne lasers will also prove useful in monitoring timevarying topographic uplift with rates as low as several centimetres of vertical motion per year the long valley california caldera provides an excellent testing ground for this new technology the region has a history of extensive volcanism and its central dome has recently been undergoing resurgent uplift of up to 4 cm per year in september 1993 we conducted three aircraft topographic surveys over the caldera and resurgent dome utilizing a nasa t39 jet aircraft outfitted with a nadir profiling altimetric laser atlas two p code gps receivers a litton ltn92 inertial unit for attitude and aerial cameras in addition we operated two base station gps receivers for post flight differential navigation and conducted a kinematic automobile survey of roads crossing the dome the aircraft flew at a mean altitude of 500m above ground and at speeds of 80 100 m s the laser had a divergence of 1 7 mrad and output 50 pulses per second yielding footprints of 0 9 m diameter separated by about 2 m along track precision flying yielded multiple profiles along nearly identical paths including crossing profiles over the resurgent dome off the dome and along a nearby highway the surveys included daily flights over mono lake for roll and pitch bias calibrations and over the well surveyed lake crowley to provide an independent check of estimated elevations much progress has been made in developing analysis procedures for the laser timing and attitude corrections crossover points from repeated profiles over the dome and the lake indicate that although some profiles contain relative bias errors of up to 10 cm most are substantially more accurate the accuracy of the measurements will increase as the various sources of error are better defined and dealt with even with the present analysis level the distribution of crossovers near the centre of the dome is roughly gaussian with a mean of 2 6 cm and a standard deviation of 11 cm the standard error of the mean is low 1 cm due to the high number of crossover points which holds promise for measuring systematic changes in the dome height from year to year also comparison of laser heights of lake crowley to tidal gauge heights yields only a 1 4 cm difference in absolute height these encouraging results serve to confirm further the concept of using aircraft laser surveys for geodetic tectonic monitoring

vertical surface displacements at yellowstone caldera wyoming 1976 1986 between first order leveling surveys in 1976 and 1986 the east central floor of yellowstone caldera rose 15 4 1 4 mm yr and the west central floor rose 17 0 2 0 mm yr with respect to points on the south caldera rim the same pattern has prevailed since an initial survey in 1923 except that the western caldera rose 30 faster during 1976 1986 than during 1923 1976 the 1976 1986 uplift extends beyond the northwest caldera rim near the adjacent hebgen lake fault zone site of a magnitude 7 3 earthquake in august 1959 marginally significant displacements in the eastern caldera suggest that uplift continued during 1983 1984 stopped during 1984 1985 and reversed to subsidence during 1985 1986 thus long term uplift may accumulate episodically historical uplift is especially noteworthy because regional crustal extension and thermal contraction during cooling would cause the caldera floor to subside if other processes were not acting to warp it upward the pattern and dimensions of the uplift indicate a source in the upper crust beneath yellowstone caldera probably a reservoir of rhyolite magma within a cooling granitic pluton a simple point source model would suggest a source 10 15 km deep but the reservoir is probably lens shaped and closer to the surface uplift may be caused by basaltic intrusions near the base of the reservoir or accumulation of magmatic fluids during cooling and crystallization within the reservoir subsidence might be a response to regional tectonic extension or release of trapped magmatic fluids magmatic inflation volatile accumulation and crustal extension may culminate eventually in renewed eruptive activity but there is no evidence of an imminent volcanic hazard

the phlegraean fields structural evolution volcanic history and eruptive mechanisms abstract the main event within the volcanic history of the phlegraean fields was the eruption about 35 000 years ago of a huge alkali trachytic ignimbrite 80 km 3 dre followed by caldera collapse the pre caldera activity evidence from geothermal wells and surface outcrops changed from submarine to subaerial shortly before the ignimbrite eruption the caldera was subsequently invaded by the sea and became progressively filled with tuffites and subordinate submarine flows in its northern half the last submarine explosive activity dates back to 12000 10500 yr with the eruption of mostly hydroplinian yellow tuffs recent mostly subaerial activity consists of a series of explosive eruptions whose volume decreases with time until the last eruption of mt nuovo in 1538 a d two peaks in recent activity occur at 10000 8000 and 4700 3000 years ago during post caldera activity eruptive vents migrated from the caldera rim toward the center where there are two distinct zones of recent vents minor collapses occurred within the caldera after the main eruptions often they are eccentric to the vent and displaced toward the caldera center phlegraean explosive activity is characterized by water magma interaction eruptive events without a hydromagmatic component are extremely rare in most cases the evolved trachytic magmas interacted with surface water either the sea or intracaldera lakes however there is evidence of interaction of magma with deep seated aquifers for some plinian events explosivity i e the efficiency of the transformation of thermal into kinetic energy during magma water interaction is largely controlled by the primary fragmentation of the magmatic melt

a new isostatic residual gravity map of the conterminous united states with a discussion on the significance of isostatic residual anomalies to display more clearly the gravity anomalies caused by geologic bodies in the upper parts of the crust a new colored isostatic residual gravity map of the conterminous united states has been prepared using the gravity data set compiled for the gravity anomaly map of the united states society of exploration geophysicists 1982 the new isostatic residual gravity map is based on an airy heiskanen model of local compensation in which the surface load requiring compensation is defined by 5 min topographic and bathymetric data sets a colored first vertical derivative map of isostatic residual gravity further enhances the short wavelength anomalies produced by bodies at or near the surface and emphasizes the regional fabrics and trends in the gravity field for the purpose of displaying gravity anomalies caused by shallow bodies of geologic significance the nature of the isostatic model and the values of its parameters are of lesser importance than the application of an isostatic correction of some sort most isostatic models result in residual gravity maps that appear nearly identical in their main patterns and features anomalies on isostatic residual gravity maps should not be casually interpreted in terms of undercompensation or overcompensation because large amplitude anomalies can be produced by crustal bodies in complete local isostatic equilibrium many isostatic residual gravity anomalies less than several hundred kilometers wide can be related to known geologic bodies we present here a classification scheme that attempts to categorize such anomalies on the basis of tectonic environment in general highs correlate with intruded or accreted mafic material or with upthrusted crustal sections whereas lows occur over low density sedimentary or volcanic sections felsic intrusive bodies or down warped crustal sections although some longer wavelength anomalies such as the broad gravity high centered over montana could be manifestations of density contrasts deep in the mantle many such anomalies can also be modeled by geologically reasonable density contrasts that are isostatically compensated and confined to depths of less than several hundred kilometers so that their source bodies need not be deep the fact that certain of these broader anomalies have well defined boundaries which correlate with near surface geologic features increases the likelihood that their sources lie entirely within the lithosphere if so then the density contrasts required to explain the gravity data imply fundamental anomalies in chemical composition or thermal state for the crustal and upper mantle columns under these regions we have investigated spectral analysis as a method to quantitatively characterize regional anomaly patterns contoured plots of normalized amplitude spectra were prepared for various areas of the isostatic residual gravity field of the united states these fourier domain representations show characteristic patterns that can be interpreted in terms of the trends and wavelengths of anomalies and may help to more objectively distinguish geologic basements with different origins or tectonic histories

interaction between intraseasonal oscillations of the midlatitude flow and tropical convection during 1979 northern summer the pacific ocean abstract it has been inferred and illustrated by many studies in terms of outgoing longwave radiation olr and velocity potential that energy is input into the intraseasonal oscillation through tropical cumulus convection especially over the monsoon region the existence of this low frequency oscillation of regional extratropical oscillation has been observed by other studies previous findings lead us to speculate upon a hemispheric interaction between tropical cumulus convection and extratropical circulation in terms of an intraseasonal time scale this study demonstrates that during the 1979 summer a coherent intraseasonal oscillation existed between cumulus convection and divergent circulation over the equatorial western pacific and mid pacific troughs moreover the intraseasonal oscillations of streamfunction associated with these troughs the tropical olr and the tropical field exhibit coherent eastward propagations based upon these two coherent relations it is hypothesized that a tro

the structure and maintenance of stationary waves in the winter northern hemisphere abstract previous studies of extratropical stationary waves in the winter northern hemisphere nh often focused on effects of orography and land ocean thermal contrast on the formation structure and maintenance of these waves in contrast research attention to tropical stationary waves was attracted by the summer monsoon circulations and the enso related climate variability consequently the structure and basic dynamics of tropical stationary waves and the relationship of these waves with those in mid high latitudes have long been neglected thus the following several distinct features of observed winter nh stationary waves have not been explained 1 an abrupt change in the longitudinal phase across 30 n 2 a transition from the vertical phase reversal of tropical stationary waves to the vertically westward tilt of extratropical stationary waves and 3 a longitudinally quarter phase relationship between stationary waves and east west circulations and a reversal of this relationship across 30 n

ascent and emplacement of buoyant magma bodies in brittle ductile upper crust 1 the emplacement of silicic magma bodies in the upper crust may be controlled by density such that there is no buoyancy to drive further ascent or temperature such that surrounding rocks are too cold to deform significantly over geological timescales evidence for the latter control is provided by negative gravity anomalies over many granitic plutons conditions of diapir ascent and emplacement in this case are studied with a numerical model for deformation and heat transport allowing for ductile elastic and brittle behavior a large strain formulation is used to solve for temperature stress strain and strain rate fields as a function of time for a range of diapir sizes density contrasts and background geotherms the method allows for large viscosity contrasts of more than 6 orders of magnitude and determines the dominant deformation mechanism depending on the local values of temperature strain and strain rate emplacement depth and final deformation characteristics depend on diapir size and buoyancy small diapirs less than about 5 km in diameter cannot reach shallow crustal levels and do not involve brittle deformation in the ductile regime the diapir flattens significantly upon emplacement due to stiff roof rocks and to the free surface above late stage deformation proceeds by horizontal spreading with little upward displacement of roof rocks and is likely to be interpreted as ballooning large diapirs more than about 5 km in diameter rapidly rise to shallow depths 1 5 km and induce brittle faulting in the overlying rocks in this regime buoyancy forces may lead to faulting in roof rocks in this case late stage ascent proceeds by vertical intrusion of a plug of smaller horizontal dimensions than the main body buoyant diapirs keep on rising after solidification long after the relatively short lived high temperature magmatic stage this may account for some phases of late caldera resurgence in extinct volcanic systems

from structure to erosion controlled subsiding calderas evidence thresholds and mechanics collapse calderas evolve by increasing their depth diameter ratio to properly characterize caldera evolution a structural s d ratio between structural subsidence and ring fault diameter ss ds and a topographic s d ratio between topographic caldera depth and topographic caldera width st dt are considered we review the evolution of the a d 2000 miyakejima caldera with two concentric ring faults at earlier collapsing stages and erosion of its wall accumulating debris on the floor at later collapsing stages while st dt and ss ds show a similar increase at initial stages when ss ds 0 33 the ss ds becomes significantly different from st dt while continuous caldera subsidence monotonically increases ss ds the erosion of the wall and the filling of the floor decrease st dt this evolution finds close similarities with recent caldera collapses of krakatau 1883 katmai 1912 fernandina 1968 tolbachik 1975 1976 pinatubo 1991 and dolomieu 2007 analog experiments mimic the observed variation evolving from a depression controlled by the activity of the double ring faults to that controlled by the erosion of the wall and sedimentation at the floor these natural and modeling results show that the control on the shape of mature calderas ss ds 0 07 and approaching ss ds 0 3 0 4 passes from a mainly structural to a mainly erosional control both st dt and ss ds are needed to describe the evolution of a collapse and the processes accompanying it evaluating st dt and ss ds allows proper description of the precise evolutionary stage of a caldera and of the relative importance of the structural and erosional processes and allows making semiquantitative comparisons between evolutionary stages

numerical modelling of caldera dynamical behaviour summary the study of the mechanics of caldera formation can yield valuable insight into the behaviour of near surface magma chambers and their mechanical interaction with the crust we have addressed the problem of physical processes responsible of long term ground deformation from the emplacement of magma in the crust to a final resurgent stage a mechanical model based on a thermally coupled elastovisco plastic rheology and a finite deformation formulation has been used and solved via a finite element approximation the history of an ideal caldera is modelled in the following two stages 1 a doming phase corresponding to the growth of the magma chamber this stage is constrained by values of amplitude half width and time constant of regional doming and by a range of realistic over pressures this uplift is linked to the plastic strain field within the crust which strongly depends upon the pressure and temperature fields 1 a resurgence phase which results from a collapse stage with an instantaneous change in shape of the topography the magma chamber is passive and this stage is basically similar to a crater relaxation process the rebound amplitude and half width are controlled by the length scale of the collapse a gravitational rebound is a very likely mechanism explaining large caldera uplift without over pressure mechanisms for most intracrustal loading processes the crustal deformation is critically influenced by the relative importance of the upper crustal rheology pressure dependent plasticity versus the lower crustal rheology temperature dependent viscosity because the upper part of the crust can deform without time dependent dissipation it may be responsible for large uplift variations that can occur for moderate loading variations by contrast the creep of the middle crust acts as a regulating medium

the microstructure of polar ice part i highlights from ice core research polar ice sheets play a fundamental role in earth s climate system by interacting actively and passively with the environment active interactions include the creeping flow of ice and its effects on polar geomorphology global sea level ocean and atmospheric circulation and so on passive interactions are mainly established by the formation of climate records within the ice in form of air bubbles dust particles salt microinclusions and other derivatives of airborne impurities buried by recurrent snowfalls for a half century scientists have been drilling deep ice cores in antarctica and greenland for studying such records which can go back to around a million years experience shows however that the ice sheet flow generally disrupts the stratigraphy of the bottom part of deep ice cores destroying the integrity of the oldest records for all these reasons glaciologists have been studying the microstructure of polar ice cores for decades in order to understand the genesis and fate of ice core climate records as well as to learn more about the physical properties of polar ice aiming at better climate record interpretations and ever more precise models of ice sheet dynamics in this part i we review the main difficulties and advances in deep ice core drilling in antarctica and greenland together with the major contributions of deep ice coring to the research on natural ice microstructures in particular we discuss in detail the microstructural findings from camp century byrd dye 3 grip gisp2 northgrip vostok dome c edml and dome fuji besides commenting also on the earlier results of some pioneering ventures like the jungfraujoch expedition and the norwegian british swedish antarctic expedition among others in the companion part ii of this work faria et al 2014 the review proceeds with a survey of the state of the art understanding of natural ice microstructures and some exciting prospects in this field of research

diabatic and orographic forcing of northern winter stationary waves and storm tracks abstract in this study a dry global circulation model is used to examine the contributions made by orographic and diabatic forcings in shaping the zonal asymmetries in the earth s northern hemisphere nh winter climate by design the model mean flow is forced to bear a close resemblance to the observed zonal mean and stationary waves the model also provides a decent simulation of the storm tracks in particular the maxima over the pacific and atlantic and minima over asia and north america are fairly well simulated the model also successfully simulates the observation that the atlantic storm track is stronger than the pacific storm track despite stronger baroclinicity over the pacific sensitivity experiments are performed by imposing and removing various parts of the total forcings in terms of the nh winter stationary waves in the upper troposphere results of this study are largely consistent with previous studies diabatic forcings explain most of the modeled stationary waves with orographic

a numerical model for simulating deformation of mount st helens volcano previous work on surface deformation associated with volcanic activity has revealed significant departures from ideal elastic and homogeneous behavior to account for the highly heterogeneous and discontinuous mechanical behavior of volcanic edifices a numerical model named bloc was used to model surface deformation data the basic assumption of this model is that the volcanic edifice behaves mechanically as an assemblage of rock blocks that can move in relation to one another the well documented eruption of mount st helens in 1980 was used to test this model and to compare the fit between the observed and computed surface deformation from the north south cross section of the volcano several two dimensional models were developed to study the effect of various parameters geometry boundary conditions coefficient of friction etc the models were loaded with a step by step increasing internal pressure simulating the intrusion of magma within the volcano and with a horizontal acceleration simulating an earthquake the deformation and failure patterns are highly dependent on the coefficient of friction on block boundaries for the lower value of this coefficient 0 5 a good fit is found between the observed and computed surface displacements the failure mode by gravitational sliding of the north flank is obtained with internal pressure loading alone as well as with internal pressure and an earthquake trigger however the second kind of loading gives a better fit with the particular deformation pattern observed

associations between twice yearly oscillations of the north pacific cyclone track and upper tropospheric circulations over the eastern hemisphere abstract a reexamination is made of the seasonal course of extratropical cyclone activity over the north pacific based mainly on monthly cyclone statistics by whittaker and horn and upper tropospheric wind analyses by sadler with support by other investigations in the asiatic coastal region the prevailing cyclone track is south of japan from midwinter through spring shifting abruptly northward following a collapse of kuroshio cyclogenesis from june to july farther east over the central pacific this sequence gives way to a twice yearly oscillation tracks are farthest north in april and august and farthest south in january february and secondarily in june eastward from japan the oscillations of cyclone activity take place in unison with fluctuations in latitude of the monthly mean jet stream it is related to the intensifying and weakening phases of the subtropical jet during the winter monsoon regime and migrations of the mean jet between positions south and north of the tibetan plateau during mos

two dimensional numerical modeling of fracturing and shear band development in glacier fronts in this contribution we present a two dimensional numerical model of a deforming glacier front the model is based on a hybrid lattice spring network approach where particles in the model can deform in a volume conservative visco elastic manner but at the same time they can be compressed elastically and fracture by discrete failure we restrict ourselves to a simple setting where the glacier sits on a frictionless slope that dips with 5 10 the ice block is fixed on one side and has a free surface on the other the glacier varies in viscosity and can flow at the base whereas it is brittle at the top results show that the head of the glacier is unstable failure happens as a combination of extension fractures crevasses at the top surface of the glacier and shear fractures that are dipping toward the glacier head once the shear fractures intersect with the free side wall of the glacier a triangular ice block is carving from the glacier head during successive flow of the glacier the failure is stepping backwards into the glacier and large shear planes develop that connect the sliding ice at the base with crevasses at the top variations of overall viscosity of the glacier indicate that higher viscosities and thus a more brittle glacier lead to larger spacing of shear surfaces and thus to larger ice blocks that are carving from the head of the glacier in addition the geometry of the deformation structures within the glacier does not vary significantly with the height of the ice indicating that larger glaciers carve larger blocks a higher tilt of the ground surface however leads to tighter spacing of shear surfaces and a more pronounced crevasse development this indicates that glacier heads that lie on steeper slopes will carve smaller blocks than glacier heads that lie on shallower slopes failure and carving of ice from the model glaciers is a combination of early developing closely spaced extension fractures crevasses and later developing wider spaced and more localized shear fractures or shear zones

evidence for 600 year old basalt and magma mixing at inyo craters volcanic chain long valley caldera california andesite inclusions are found within the vent areas of two 600 year old rhyolite domes in the inyo craters volcanic chain eastern california both domes lie within the present northwestern sector of 0 73 ma long valley caldera inclusion morphology indicates that they were partially molten and ductile during incorporation within coarsely porphyritic rhyolite the xenocryst assemblage within the inclusions plagioclase hornblende biotite quartz sanidine is identical to the phenocryst assemblage within the host rhyolite microprobe analyses of xenocrysts within the andesite inclusions show that they have compositions similar to phenocrysts in the host rhyolite these data suggest that the andesite inclusions are the result of mixing of the coarsely porphyritic rhyolite with a more mafic end member whole rock geochemistry of the inclusions generally supports a simple mixing model between the coarsely porphyritic rhyolite of the inyo domes and typical postcaldera mafic lavas found throughout the western caldera moat the inclusions provide the first evidence for involvement of basaltic magma in the 600 year old rhyolite eruptions of the inyo craters volcanic chain and suggest the possibility that the rhyolitic eruptions were initiated by injection of basalt into the lower part of the silicic magma system periodic thermal replenishment of the magmatic system through basaltic injection may explain the relatively high temperatures encountered in drill holes within the western caldera moat the inclusions further suggest that although rhyolite eruptions are statistically more likely from the inyo craters volcanic chain future basaltic eruptions cannot be ruled out

modes and times of caldera resurgence the 10 ka evolution of ischia caldera italy from high precision archaeomagnetic dating abstract ischia is a well exposed and densely populated late quaternary caldera in the campanian magmatic province of italy ischia caldera experienced an average uplift rate of 3 3 cm year in the last ca 30 ka and is still actively resurging during the last 10 ka coeval with the resurgence a volcanic field of alkali trachytic to trachyandesitic lava domes lava flows tuff and scoria rings and pumice cones developed mainly on the eastern sector of the caldera along both resurgence related faults and regional nnw and ne striking faults in order to improve both our understanding of the recent volcanic history and the evaluation of future risks on ischia island a high precision archaeomagnetic dating method was applied to the products of 12 volcanic centres with probable age 14 c ages archaeomagnetic and other geochronological data as well as stratigraphic constraints show that during the studied time interval ischia volcanism occurred in five periods separated by phases of quiescence and coeval with earthquake and landslide events this fact suggests a pulsating mode of uplifting and deformations of the ischia resurgence during the two oldest periods of activity 7200 6800 bc and 4100 2300 bc resurgence probably produced a dome shaped structure location and geometry of vents suggest the occurrence of magma uprise along the fractures produced by bending of the overburden crustal block most of magma was emplaced as intrusions at the interior of the resurgent block whereas volcanism was represented by very viscous differentiated and crystallized lavas that emplaced as domes and high aspect ratio flows the resurgent dome caused recurrent lateral collapses that removed about 2 5 km 3 of rocks during the three youngest periods of activity 1800 1000 bc 650 bc 355 ad and 1302 ad resurgence affected a fault bounded asymmetric block this resulted from both a hydrostatic rebound of the crustal block after removal of material involved into huge slope instability triggering an increase in uplift rate and b new influxes of less evolved magma batches into the shallow reservoir that in turn favoured the intense volcanism of the last 4000 years

location and configuration of magma bodies beneath long valley california determined from anomalous earthquake signals recordings of 281 small earthquakes which occurred recently near the southern edge of long valley caldera at depths from 1 to 15 km are used to map the subsurface geometry of shear wave attenuating bodies in the caldera signatures of these events recorded northwest north northeast and east of long valley with ray paths through the caldera are often anomalous in that s wave arrivals have very low amplitudes and high frequency p and s wave energy is missing for the same station event combinations the volcanic and geothermal history of the region suggests that ray paths for these anomalous signals have passed through magma which absorbed much of the s wave energy and also attenuated the higher frequencies with over 1200 normal and anomalous ray paths through the caldera we have located two apparently massive magma bodies in the central and northwest caldera as well as two more dispersed magma areas in the southern caldera and beneath crowley lake the central magma body extends from 4 5 to at least 13 km beneath the surface and the northwest body is as shallow as 5 5 km these two magma bodies are probably connected below about 8 km secondary arrivals seen on select seismograms are tentatively interpreted as reverberations inside the central magma chamber and are consistent with the interpreted lateral extent of the magma the northwest and central magma bodies lie beneath the northwest and southeast corners of the caldera s resurgent dome and probably connect beneath the dome s center also the shallower parts of these magma bodies and the southern anomalous area lie beneath the surface expression of the medial graben faults suggesting that structural features seen at the surface of the valley may be related to magma location at depth

basement structure and implications for hydrothermal circulation patterns in the western moat of long valley caldera california detailed surface mapping subsurface drill hole data and geophysical modeling are the basis of a structural and hydrothermal model for the western part of long valley caldera six fault zones are recognized in the western caldera with dominant orientations of north northwest and northeast sub parallel to regional fault trends in the surrounding sierran basement the internal structural geometry of the cores of 12 exogenous domes inside and outside the caldera suggests that the domes erupted at the intersections of these principal fault trends rather than along the axis of a single dike gravity modeling and subsurface data from deep geothermal wells indicate that the floor of the caldera is segmented into a number of discrete fault blocks with varying offsets one of the northeast trending fault zones designated discovery fault in this paper appears to be part of the original sierran embayment that existed before caldera collapse recent hydrothermal alteration occurs along discovery fault strands and composite vertical offset of intracaldera volcanic units across the entire fault zone may be as much as 400 m field relationships geophysical interpretations and interpretaions of drill hole data suggest that this fault is a fundamental flaw in the western caldera the preexisting tectonic framework of the basement rocks controlled the configuration of the western caldera floor and through it the location of postcollapse eruptive centers these deep basement structures may also provide the high fracture density which controls circulation in the present geothermal system of long valley

organization of storm track anomalies by recurring low frequency circulation anomalies abstract from previous studies it is known that anomalous momentum fluxes by bandpass eddies are important in maintaining long lasting tropospheric flow anomalies evidence is presented that suggests that these anomalous fluxes do not occur at random but happen because the structure of storm track activity is modified by the presence of prominent low frequency large scale circulation anomalies this behavior is noted in an extended integration of a perpetual january simulation with a general circulation model gcm because nonlinear feedbacks between low and high frequency variability make it difficult to establish causal relationships between these two ranges of variability a model is constructed that approximates the storm track activity that would be expected to accompany a given low frequency without including the feedback of the high frequencies onto the low frequency state this model is based on the linearized primitive equations and uses a series of short integrations from random initial condi