geodetic observations during the 2009 eruption of redoubt volcano alaska abstract in march 2009 redoubt volcano about 160 km to the sw of anchorage alaska began its most recent explosive eruption deformation induced by this event was recorded by a gps campaign network consisting of 14 benchmarks which had been established in 1991 after the previous eruption the network was partially reoccupied in 2001 and 2008 and no volcanic deformation was detected during that period in response to precursory unrest starting in january 2009 the alaska volcano observatory temporarily deployed continuously recording gps instruments at four of the campaign benchmarks only days before the onset of explosive activity in march 2009 the only gps instrument recording continuously during the months prior to the eruption was the plate boundary observatory pbo station ac17 about 28 km northeast of the volcano s summit data from this station reveals subtle motion radially outward from the volcano beginning as early as may 2008 which reversed with the onset of explosive activity using simple analytical models we link the precursory activity to a point source intrusion of 0 0194 0 03400 0092 km3 in volume at 13 50 17 3310 17 km below sea level bsl superscripts and subscripts refer to upper and lower ends of confidence intervals at the 95 level during the explosive phase about 0 05 0 10 028 km3 of magma was evacuated from a prolate spheroid with its centroid at 9 17 15 176 92 km bsl a semimajor axis of 4 50 10 001 25 km length and a semi minor axis of 0 475 4 00 3 km the effusive activity is inferred to come from the same source decreasing in volume by 0 0167 0 02280 0106 km3 including observations from seismology and petrology we hypothesize a mid crustal two reservoir system with material sourced from 20 km flowing in at about 13 5 km depth and reheating residual material in the proposed spheroid the mixture migrated to shallower depth 2 4 5 km bsl and reheated material there as this residual magma erupted it was replaced by the material from the spheroidal reservoir at 7 11 5 km depth which renders the shallow source undetectable for geodetic instruments in addition to long term displacements we investigate sub daily kinematic positioning solutions and find that large short term positioning offsets correlate with large explosive events spikes in phase residuals plotted along the sky tracks of individual satellites can be related to individual plumes given favorable satellite station geometry which may be of use in volcano monitoring

crystal poor rhyolites and rhyodacites from volcan tepetiltic mexico evidence for melt formation crystallization and eruption over short timescales abstract a detailed petrologic study is presented for six rhyolite and rhyodacite pumices that erupted from volcan tepetiltic in western mexico to determine the pre eruptive conditions of the magma reservoir as the volcano exited a 180 kya hiatus of activity rhyolite pumices are crystal poor 6 7 and minimally saturated in seven mineral phases plagioclase titanomagnetite ilmenite apatite quartz orthopyroxene clinopyroxene hornblende zircon in all samples plagioclase is the most abundant phenocryst phase and spans a range of composition of 20 30 mol an in each sample pre eruptive temperatures determined from two fe ti oxide geo thermometry range from 703 to 857 c maximum pre eruptive h2o contents determined from plagioclase hygrometry range from 5 0 8 9 wt where the most calcic plagioclase compositions correspond to the highest water contents comparison of compositions textures and sr and ba concentrations in plagioclase are used to determine phenocrysts from xenocrysts through comparison with experiments xenocrysts are identified in one sample comp 48 comparison of plagioclase abundances textures and sizes with those grown in the run products of experiments from the literature reveals that 1 the pumices were all likely super heated prior to crystallization 2 they experienced a low degree of undercooling induced by either degassing or cooling and 3 four of the pumices those with

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

chemical element imaging for speleothem geochemistry application to a uranium bearing corallite with aragonite diagenesis to opal eastern siberia russia abstract two complementary image based microanalysis methods digital autoradiography of radioactive elements and x ray fluorescence microspectroscopy micro xrf were used to study the geochemistry of a speleothem from eastern siberia our objective was to show the interest of these micro chemical methods to investigate the distribution of u and some other elements as ca sr and si in speleothems the sample studied was a corallite concretion that formed slowly by the precipitation of minerals from moisture that had condensed underground polished sections of the sample revealed alternating laminas of gray calcite and white aragonite the concretion which is older than 400 kyr u th tims showed no signs of detrital contamination 230 th 232 th 10 000 digital autoradiography and xrf analyses indicated exceptionally high uranium contents ranging from 3 10 to more than 1300 g g 1 in different areas of the sample element maps for calcium ca uranium u strontium sr and silicon si showed inverse correlations between ca and u and between ca and si but there is a strong correlation between si and u under the optical microscope the low ca appears as corrosion voids which were found to contain uranium enriched amorphous silica replacing areas of aragonite and in some cases calcite this postgenetic amorphous and uraniferous silica is composed of two kinds of opal opal a formed by large microspheres of 30 40 m in diameter and a gray opal ct with irregular lepispheres this late opal dated around 385 412 kyr is probably due to a special volcanic event formed by uraniferous glass ashes easily soluble by meteoric waters as suggested by the presence of volcanic suite in the fine fraction of the opal opal precipitated after speleothem crystallization by evaporation or cryogenic supersaturation the study of this exceptional concretion shows the value of direct chemical imaging methods as they easily revealed the presence and distribution of u in the concretion and allowed an unusual case of opal diagenesis in a carbonate speleothem to be described given the value of speleothems as geo chronometers and recorders of environmental changes at different time scales from season to isotopic stage this methodology opens new perspectives in understanding the geochemical system and consequently the validity of radiometric datings u th and u pb especially in speleothem samples

a novel model for terrain slope estimation using icesat glas waveform data the accurate estimation of terrain slope is very important for accurately monitoring the elevation and mass changes of glacier using laser altimeter in this paper a novel physical model was proposed for accurately estimating within footprint terrain slope the new proposed model was built based on overlapping footprints of the geoscience laser altimeter system glas data namely using altitude angle footprint size shape orientation terrain aspect and ground extent ground extent estimation models were established on the basis of linear regression analyses between 1 glas derived waveform extent and airborne topographic mapper atm derived ground extent and 2 glas derived waveform width and atm derived ground extent respectively in addition the terrain slopes estimated from the overlapping footprints were validated by atm data and compared with the slopes calculated from surface elevations i e from aster global digital elevation model dem gdem and glas elevation results showed that the accuracy of waveform width predicted ground extents r 2 0 868 rmse 0 686 m n 20 and p value r mathbf 2 0 776 rmse 0 824 m n 20 and p value 0 0001 which indicated that waveform width is more suitable for estimating ground extent slopes estimated from the new proposed model have a strong consistency with those calculated from atm data corrcoef 0 786 bias 0 654 sd 1 368 and rmse 1 452 additionally results also indicated that the new proposed model performs much better than the methods based on aster gdem and the glas surface elevation in estimating within footprint terrain slope due to higher correlation lower bias standard deviation and rmse

thinning and volume loss of the arctic ocean sea ice cover 2003 2008 1 we present our best estimate of the thickness and volume of the arctic ocean ice cover from 10 ice cloud and land elevation satellite icesat campaigns that span a 5 year period between 2003 and 2008 derived ice drafts are consistently within 0 5 m of those from a submarine cruise in mid november of 2005 and 4 years of ice draft profiles from moorings in the chukchi and beaufort seas along with a more than 42 decrease in multiyear my ice coverage since 2005 there was a remarkable thinning of 0 6 m in my ice thickness over 4 years in contrast the average thickness of the seasonal ice in midwinter 2 m which covered more than two thirds of the arctic ocean in 2007 exhibited a negligible trend average winter sea ice volume over the period weighted by a loss of 3000 km3 between 2007 and 2008 was 14 000 km3 the total my ice volume in the winter has experienced a net loss of 6300 km3 40 in the 4 years since 2005 while the first year ice cover gained volume owing to increased overall area coverage the overall decline in volume and thickness are explained almost entirely by changes in the my ice cover combined with a large decline in my ice coverage over this short record there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the arctic ocean ice cover seasonal ice having surpassed that of my ice in winter area coverage and volume became the dominant ice type it seems that the near zero replenishment of the my ice cover after the summers of 2005 and 2007 an imbalance in the cycle of replenishment and ice export has played a significant role in the loss of arctic sea ice volume over the icesat record

sea ice freeboard retrieval using digital photon counting laser altimetry airborne and spaceborne altimeters provide measurements of sea ice elevation from which sea ice freeboard and thickness may be derived observations of the arctic ice pack by satellite altimeters indicate a significant decline in ice thickness and volume over the last decade nasa s ice cloud and land elevation satellite 2 icesat 2 is a next generation laser altimeter designed to continue key sea ice observations through the end of this decade an airborne simulator for icesat 2 the multiple altimeter beam experimental lidar mabel has been deployed to gather pre launch data for mission development we present an analysis of mabel data gathered over sea ice in the greenland sea and assess the capabilities of photon counting techniques for sea ice freeboard retrieval we compare freeboard estimates in the marginal ice zone derived from mabel photon counting data with coincident data collected by a conventional airborne laser altimeter we find that freeboard estimates agree to within 0 03 m in the areas where sea ice floes were interspersed with wide leads and to within 0 07 m elsewhere mabel data may also be used to infer sea ice thickness and when compared with coincident but independent ice thickness estimates mabel ice thicknesses agreed to within 0 65 m or better

validation of sea ice topographic heights derived from tandem x interferometric sar data with results from laser profiler and photogrammetry in this paper the retrieval of sea ice surface heights from the interferometric tandem x data is investigated the data were acquired over fast and drifting ice in fram strait located between greenland and svalbard additional measurements of the sea ice surface topography were carried out using a stereo camera and a laser altimeter the comparison of the surface elevation retrieved from tandem x imagery with the results of the stereo camera measurements revealed that sea ice ridges greater than 0 5 m can be estimated with a root mean square error of 0 3 m or less with the error decreasing as a function of ridge height although the helicopter borne laser data are only available as 1 d profiles with a much higher across track spatial resolution than the tandem x data they proved to be useful for the validation the need for multilook averaging to reduce the phase noise is identified as the main challenge in achieving the spatial resolution necessary for retrieving sea ice surface topography using synthetic aperture radar interferometry

normal fault growth in layered basaltic rocks the role of strain rate in fault evolution abstract conceptual models for the evolution of dilatant faults in volcanic rift settings involve a step wise growth pattern involving upward propagation of subsurface faults and surface monocline formation which are breached by subvertical open faults immature discontinuous normal faults are considered representative of the early stages of mature linked faults that accommodate extensional strains we consider the evolution of surface breaking normal faults using a comparison of the distribution and geometry of normal faults from two volcanic rift zones the koa e fault system hawai i and the krafla fissure swarm ne iceland field mapping highlights similarities to current predicted geometries but also prominent differences that are not reconciled by current models variable deformation styles record magma supply changes within the rift zones which drive local strain rate gradients building on existing studies we present a conceptual model of fault growth that accounts for spatial and temporal changes in strain rate within the deforming regions we propose that faults in separate rift systems may not advance through the same stages of evolution and that faults within individual rift systems can show differing growth patterns variations in surface strains may be indicative of subsurface magmatic system changes with important implications for our understanding of volcano tectonic coupling

geological setting and age of australopithecus sediba from southern africa we describe the geological geochronological geomorphological and faunal context of the malapa site and the fossils of australopithecus sediba the hominins occur with a macrofauna assemblage that existed in africa between 2 36 and 1 50 million years ago ma the fossils are encased in water laid clastic sediments that were deposited along the lower parts of what is now a deeply eroded cave system immediately above a flowstone layer with a u pb date of 2 026 0 021 ma the flowstone has a reversed paleomagnetic signature and the overlying hominin bearing sediments are of normal polarity indicating deposition during the 1 95 to 1 78 ma olduvai subchron the two hominin specimens were buried together in a single debris flow that lithified soon after deposition in a phreatic environment inaccessible to scavengers

a first assessment of icebridge snow and ice thickness data over arctic sea ice we present a first assessment of airborne laser and radar altimeter data over snow covered sea ice gathered during the national aeronautics and space administration operation icebridge mission we describe a new technique designed to process radar echograms from the university of kansas snow radar to estimate snow depth we combine icebridge laser altimetry with radar derived snow depths to determine sea ice thickness results are validated through comparison with direct measurements of snow and ice thickness collected in situ at the danish greenarc 2009 sea ice camp located on fast ice north of greenland the icebridge instrument suite provides accurate measurements of snow and ice thickness particularly over level ice mean icebridge snow and ice thickness agree with in situ measurements to within 0 01 and 0 05 m respectively while modal snow and ice thickness estimates agree to within 0 02 and 0 10 m respectively icebridge snow depths were correlated with in situ measurements r 0 7 for an averaging length of 55 m the uncertainty associated with the derived icebridge sea ice thickness estimates is 0 40 m the results demonstrate the retrieval of both first year and multiyear ice thickness from icebridge data the airborne data were however compromised in heavily ridged ice where snow depth and hence ice thickness could not be measured techniques developed as part of this study will be used for routine processing of icebridge retrievals over arctic sea ice the limitations of the greenarc study are discussed and recommendations for future validation of airborne measurements via field activities are provided

automatic measurement of shear wave splitting and applications to time varying anisotropy at mount ruapehu volcano new zealand 1 we present an automatic shear wave splitting measurement tool for local earthquakes with the sole manual step of choosing an s arrival time we apply the technique to three data sets recorded on mount ruapehu volcano in new zealand that have previously been determined to have fast polarizations that vary in time and with earthquake depth the technique uses an eigenvalue minimization technique applied over multiple measurement windows the dominant period of each waveform sets minimum and maximum window lengths cluster analysis determines the best solution among all the windows and quality grading criteria assess the results automatically when the same filters are used for events determined to be high quality from manual studies the automatic technique returns virtually identical results scatter increases when the automatic technique chooses the best filter but the average automatic results remain consistent with the manual results when the automatic technique is used on sets that include data previously judged as poor quality some stations yield distributions of fast polarizations that include peaks that were not present in previously published results the difference may stem from two factors automatic grading lets through some measurements that independent analysts consider poor quality but also unconscious bias in the manual selection process may downgrade measurements that do not fit expectations nonetheless the new objective analysis confirms changes in the average fast polarizations between 1994 and 2002 and between shallow and deep events therefore this new technique is valuable for objective assessment of anisotropy and its variation in time

u pb isotopic age of the stw 573 hominid from sterkfontein south africa sterkfontein cave south africa has yielded an australopith skeleton stw 573 whose completeness has excited great interest in paleoanthropology stw 573 or little foot was found 25 meters below the surface in the silberberg grotto 238u 206pb measurements on speleothems immediately above and below the fossil remains corrected for initial 234u disequilibrium yield ages of 2 17 0 17 million years ago ma and 2 24 0 07 0 09 ma respectively indicating an age for stw 573 of close to 2 2 ma this age is in contrast to an age of approximately 3 3 ma suggested by magnetochronology and ages of approximately 4 ma based on 10be and 26al but it is compatible with a faunal age range of 4 to 2 ma

age and evolution of the grand canyon revealed by u pb dating of water table type speleothems the age and evolution of the grand canyon have been subjects of great interest and debate since its discovery we found that cave mammillaries water table indicator speleothems from nine sites in the grand canyon showed uranium lead dating evidence for an old western grand canyon on the assumption that groundwater table decline rates are equivalent to incision rates samples in the western grand canyon yielded apparent water table decline rates of 55 to 123 meters per million years over the past 17 million years in contrast to eastern grand canyon samples that yielded much faster rates 166 to 411 meters per million years chronology and inferred incision data indicate that the grand canyon evolved via headward erosion from west to east together with late stage 3 7 million years ago accelerated incision in the eastern block

searching for travertines calcretes and speleothems in deep time processes appearances predictions and the impact of plants common models for modern calcite precipitation in and around caves soils springs and streams involve co 2 supplied by thick high p co 2 biogenic soils which were probably thin or non existent before vascular plants indeed plant influenced chemical weathering might have caused accelerated terrestrial carbonate production from the devonian onwards however terrestrial carbonates have also been documented from the archaean proterozoic cambrian ordovician and silurian mechanisms which could have caused non marine carbonates to precipitate without organic rich soils are described and some geological events likely to have influenced non marine carbonate precipitation up to the origin of vascular plants are highlighted as organisms have evolved so have the petrographic characteristics of non marine carbonates some examples of this are also given here

seismicity and subsidence following the 2011 nabro eruption eritrea insights into the plumbing system of an off rift volcano nabro volcano situated to the east of the afar rift zone erupted on 12 june 2011 eruptions at such off rift volcanoes are infrequent and consequently the plumbing systems are poorly understood we present posteruption synthetic aperture radar sar images from the terrasar x satellite and posteruption continuous seismic activity from a local seismic array interferometric analysis of sar data reveals a circular 12 km wide signal subsiding at 200 mm yr we inverted for the best fit mogi source finding a 4 1 107 m3 yr volume decrease at 7 1 km depth between 31 august and 7 october 2011 we located 658 and relocated 456 earthquakes with local magnitudes between 0 4 and 4 5 seismicity beneath the se edge of nabro at 11 km depth is likely associated with high strain rates from deep magma flow into the modeled reservoir this suggests that magma is supplied through a narrow conduit and then stored at 7 km depth we interpret seismicity at 4 6 km depth as brittle fracturing above the inferred magma reservoir focal mechanisms delineate a thrust fault striking ne sw and dipping 45 to the se across the caldera floor we propose that the crustal response is to slip on this fault which crosscuts the caldera rather than to deform on ring faults the ne sw fault plane is not associated with measurable surface deformation indicating that it does not contribute much to the caldera deformation we show that subsidence of the caldera is controlled by magma chamber processes rather than fault slip

stress orientations obtained from earthquake focal mechanisms what are appropriate uncertainty estimates crustal stress orientations provide important information about the mechanics of regional deformation numerous methods exist for inverting earthquake focal mechanisms for stress orientation and the more widely used methods usually obtain similar results for similar data sets however error estimates are highly variable complicating the interpretation of results the southern california stress field for example contains much statistically significant spatial and temporal variability according to the error estimates of one method michael 1984 1987b but very little according to those of another gephart and forsyth 1984 to resolve whether the southern california stress field is generally homogeneous or heterogeneous we must determine which of the error estimates best reflects the true inversion uncertainty to do this we tested both methods on a suite of synthetic focal mechanism data sets containing random errors the method of gephart and forsyth 1984 usually provides more accurate estimates of stress orientation especially for high quality data sets but its confidence regions are in most cases too large the method of michael 1984 1987b is more accurate for very noisy data sets and provides a more appropriate estimate of uncertainty implying that the stress field in southern california is probably heterogeneous

using repeating volcano tectonic earthquakes to track post eruptive activity in the conduit system at redoubt volcano alaska in the year following the end of the 2009 eruption of redoubt volcano alaska four signifi cant swarms of low frequency lowmagnitude m l 0 1 earthquakes occurred at shallow depths beneath the summit because swarms of low frequency lf earthquakes preceded eruptions in 1989 and 2009 the posteruption swarms caused considerable concern and prompted the alaska volcano observatory to raise the monitoring levels on three occasions none of these swarms led to eruptions however and most observers including us initially concluded that the swarms had been caused by minor stress adjustments in the new lava dome or in the surrounding summit glaciers new observations reveal that the shallow lf swarms were accompanied by 2 families of repeating earthquakes at depths between 3 km and 6 km below sea level where the magma storage region is thought to be these mid crustal volcano tectonic vt type earthquakes were identical to earthquakes recorded during the 2009 redoubt eruption more than 6 months earlier focal mechanisms demonstrate that these earthquakes have thrust mechanisms inconsistent with the strike slip nature of regional faulting based on these observations we conclude that they are generated through processes occurring within the magma storage region the concurrence of the repeating vt earthquakes with the shallow lf swarms indicates that the shallow lf earthquakes were also magmatically driven our results emphasize that even brief episodes of low amplitude earthquake activity such as the lf swarms observed at redoubt following the 2009 eruption can be indicative of magmatic activity perhaps more signifi cant however is the demonstration that the conduit system at redoubt remained active intact and capable of transporting heat and fl uids to the surface months after the eruption was considered over

beyond 500ka progress and prospects in the upb chronology of speleothems and their application to studies in palaeoclimate human evolution biodiversity and tectonics abstract this review summarises current research aimed at extending the chronology and thus scientific utility of speleothems beyond the 500 ka limit previously imposed by conventional u th dating methods the u pb decay scheme is familiar to all geoscientists but its application to speleothems is a relatively recent development and one set to revolutionise their use in studies of climate change human evolution and migration biodiversity tectonics and landscape evolution technological advances such as the introduction of multi collector icpms instruments have played a key role in this breakthrough and multiple inter laboratory and inter method comparisons provide evidence that the methodology is now mature and that the ages obtained are robust some impediments remain in particular with respect to corrections for initial isotopic disequilibrium younger samples and the construction of internal chronologies older samples but these are areas of intense research activity and are likely to see significant advances in the near future the coupling of speleothem u pb dating with other nascent technologies offering the prospect of precise palaeotemperature estimation is an exciting development in palaeoclimate science while u pb chronologies of archaeological sites are producing important new insights into human evolution although less well developed at this point the methodology appears equally well suited and significant for future studies of past faunal change and landscape evolution

recent changes on greenland outlet glaciers aircraft laser altimeter surveys during the 1990s showed near coastal parts of the greenland ice sheet to be thinning despite slow thickening at higher elevations the ice sheet lost mass to the ocean many outlet glaciers thinned more rapidly than could be explained by increased melting during the recent warmer summers indicating dynamic imbalance between glacier velocity and upstream snow accumulation results from more recent surveys presented here show that thinning rates have increased in most coastal regions for almost half of the surveys these increases might have resulted from increases in summer melting but rapid thinning on others is indicative of dynamic changes that increased with time in particular thinning rates on the three fastest glaciers increased to tens of m a 1 after 2000 and other observations show an approximate doubling in their velocities the deep beds of these glaciers appear to have a strong influence on rates of grounding line retreat and thickness change with periods of glacier acceleration and rapid thinning initiated by flotation and break up of lightly grounded glacier snouts or break up of floating ice tongues near simultaneous thinning of these widely separated glaciers suggests that warming of deeper ocean waters might be a common cause nearby glaciers without deep beds are thinning far more slowly suggesting that basal lubrication as a result of increased surface melting has only a marginal impact on greenland outlet glacier acceleration

speleothem palynology an undervalued tool in quaternary studies palynological analysis of cave sediments in particular the analysis of pollen from speleothems is not a widely adopted approach to palaeoenvironmental studies in the british isles this disregard of speleopalynology may be due to the lack of understanding of the cave pollen taphonomy and uncertainty and suspicion as to what cave pollen spectra actually represent however a number of studies of pollen from caves have been carried out particularly in belgium france and spain which have demonstrated speleothem pollen spectra to be representative of contemporary vegetation above the cave with pollen generally well preserved speleothems have the distinct advantage over other pollen sources that they can be dated by high precision tims u th dating up to an order of magnitude further back in time than 14c dating of organic sediments would allow this potentially allows previously unconstrained middle pleistocene palynological records to be precisely and accurately dated thus providing a geochronologically controlled terrestrial record of palaeoenvironmental change this paper presents a timely review of speleothem palynology aiming to eliminate biases and misconceptions and illustrate the enormous potential this unique source of palaeoenvironmental data holds particularly in providing accurately dated pollen records from previously understudied environments and time periods

meteorological controls on glacier mass balance in high asia the aim of this study is to investigate spatial and temporal variations of meteorological variables known to control glacier mass balance processes and to demonstrate their relevance in high asia the study uses the ncep ncar reanalysis database us national centers for environmental prediction and us national center for atmospheric research which is global and continuous since 1 january 1948 a positive degree day pdd model of annual glacier wide summer surface balance bs uses upper air temperatures at ncep ncar gridpoints near each of six glaciers between 40 and 458 n and between 71 and 878 e and two others near 508 n 878 e model error ranged between 0 19 and 0 41 m w e comparable with the observational accuracy of bs sensitivity to temperature change dbs dt ranges between 0 5 and 0 2 m w e a 1 8c 1 for these glaciers

determination of holocene cave temperatures from kr and xe concentrations in stalagmite fluid inclusions from the concentrations of dissolved atmospheric noble gases in water a so called noble gas temperature ngt can be determined that corresponds to the temperature of the water when it was last in contact with the atmosphere here we demonstrate that the ngt concept is applicable to water inclusions in cave stalagmites and yields ngts that are in good agreement with the ambient air temperatures in the caves we analysed samples from two holocene and one undated stalagmite the three stalagmites originate from three caves located in different climatic regions having modern mean annual air temperatures of 27 c 12 c and 8 c respectively in about half of the samples analysed kr and xe concentrations originated entirely from the two well defined noble gas components air saturated water and atmospheric air which allowed ngts to be determined successfully from kr and xe concentrations one stalagmite seems to be particularly suitable for ngt determination as almost all of its samples yielded the modern cave temperature notably this stalagmite contains a high proportion of primary water inclusions which seem to preserve the temperature dependent signature well in their kr and xe concentrations in future work on stalagmites detailed microscopic inspection of the fluid inclusions prior to noble gas analysis is therefore likely to be crucial in increasing the number of successful ngt determinations

validating icesat over thick sea ice in the northern canada basin only in the past eight years has the feasibility of using satellite borne altimeters to estimate sea ice freeboard and thickness been demonstrated and these estimates still have uncertainties primarily associated with limited knowledge of snow loading on sea ice because accurate estimates of arctic wide sea ice thickness and volume are fundamental inputs to global climate models validation of satellite derived thickness estimates using independent data is required a detailed assessment of freeboard retrieved by the geoscience laser altimeter system glas aboard the ice cloud and land elevation satellite has been carried out using high resolution laser altimetry from the national aeronautics and space administration s airborne topographic mapper atm the delay doppler radar altimeter and digital photography collected along a 300 km segment of sea ice in the canada basin exploiting the repeat coverage of the aircraft flight line a correction was applied to glas footprint geolocations to adjust for sea ice drift that occurred during the time between satellite and aircraft acquisitions comparisons of glas and atm measurements over sea ice show excellent agreement about a 0 00 m mean with no apparent bias between data sets freeboard estimates were examined using data from glas and atm independently employing measurements over refrozen leads to estimate local sea surface heights sshs the results demonstrate the sensitivity of freeboard and thickness calculations to an accurate estimation of local ssh snow depth derived by differencing laser and radar data was combined with the freeboard estimates to yield a mean sea ice thickness of 5 5 m over a 250 km subsection of the flight track

seismicity and stress in the vicinity of mount spurr volcano south central alaska focal mechanism solutions and hypocenters for earthquakes near mount spurr volcano in south central alaska reveal spatial perturbations in the regional stress field and in the maximum depth of seismicity at the volcano practically all the shocks during the dormant decade 1981 1991 have depths shallower than 5 km and are characterized by nearly pure normal slip in contrast earthquakes located outboard of the volcano mostly concentrate in the depth range 3 18 km and exhibit predominantly strike slip oblique reverse slip or reverse slip the regional stress field is characterized by subhorizontal maximum principal stress directed n30 w concordant with the direction of convergence between the north american and pacific plates whereas the maximum principal stress is probably more nearly vertical beneath the volcano we suggest that the shoaling of seismicity beneath the volcano reflects localized elevation of the depth to the midcrustal transition from brittle failure to plastic flow we attribute this localized elevation to relict magmatic heat associated with past volcanic eruptions the available data are not sufficient to determine the cause of the suggested rotation of the maximum principal stress axis beneath the volcano possible mechanisms include an increase in the vertical stress from the weight of the mount spurr massif and a decrease in the maximum horizontal stress associated with doming of the shallow crust from magmatic processes

temporal spatial variations of stress at redoubt volcano alaska inferred from inversion of fault plane solutions abstract we inverted fault plane solutions fps of 420 earthquakes with a largest magnitude of 3 1 mostly occupying a 4 4 10 km 3 volume beneath redoubt volcano for principal stress directions during 1989 1998 on average fpss were computed with 8 p wave readings inversions performed with 48 fps yielding misfits of 7 and the size of the 95 confidence regions of the stress directions is 30 during the 1989 1990 eruptions stresses were typically sub horizontal 1 and 2 striking ese wnw and nne ssw respectively and near vertical 3 whereas during july 1991 january 1998 we found near vertical 1 and sub horizontal 2 and 3 striking sse nnw and ene wsw respectively we found differences in plunge of 1 up to 60 between 1990 and 1991 and sub volumes with different stress at the 99 confidence level evaluated with the z test based on the changes in stress directions from the eruptive to the inactive period we infer that the magnitudes of principal stresses increased progressively during the eruptions and had subsequently decreased by the post eruption period the observations can be explained by expansion and contraction of a plexus like magma body together with changes in physical properties of the magmas involved we estimate that the absolute values of principal stresses are similar to each other and are in the range 182 187 mpa

new u th ages for pleistocene megafauna deposits of southeastern queensland australia arguments over the extinction of pleistocene megafauna have become particularly polarised in recent years causes for the extinctions are widely debated with climate change human hunting and or habitat modification or a combination of those factors being the dominant hypotheses however a lack of a spatially constrained chronology for many megafauna renders most hypotheses difficult to test here we present several new u th dates for a series of previously undated megafauna bearing localities from southeastern queensland australia the sites were previously used to argue for or against various megafauna extinction hypotheses and are the type localities for two now extinct pleistocene marsupials including the giant koala phascolarctos stirtoni the new dating allows the deposits to be placed in a spatially and temporally constrained context relevant to the understanding of australian megafaunal extinctions the results indicate that the joint texas caves megafaunal assemblage is middle pleistocene or older 292 ky the cement mills gore megafaunal assemblage is late pleistocene or older 53 ky and the russenden cave bone chamber texas caves megafaunal assemblage is late pleistocene 55 ky importantly the new results broadly show that the sites date prior to the hypothesised megafaunal extinction window i e 30 50 ky and therefore cannot be used to argue exclusively for or against human climate change extinction models without first exploring their palaeoecological significance on wider temporal and spatial scales

joint analysis of geodetic and earthquake fault plane solution data to constrain magmatic sources a case study from kīlauea volcano abstract a joint analysis of geodetic and seismic datasets from k lauea volcano during a period of magmatic unrest in 2006 demonstrates the effectiveness of this combination for testing and constraining models of magma dynamics for a complex multi source system at the end of 2003 k lauea s summit began a four year long period of inflation due to a surge in magma supply to the volcano in 2006 for the first time since 1982 k lauea s southwest rift zone swrz also experienced inflation to investigate the characteristics of active magma sources and the nature of their interactions with faults in the swrz during 2006 we integrate through coulomb stress modeling contemporary geodetic data from insar and gps with a new catalogue of double couple fault plane solutions for volcano tectonic earthquakes we define two periods of inflation during 2006 based on the rate of deformation measured in daily gps data spanning february to 15 march 2006 period 1 and 16 march to 30 september 2006 period 2 insar data for these two periods are inverted to determine the position change in size and shape of inflation sources in each period our new models are consistent with microseismic activity from each period they suggest that during period 1 deformation in the swrz can be explained by pressurization of magma in a spherical reservoir beneath the south caldera and that during period 2 magma was also aseismically intruded farther to the southwest into the swrz along a sub horizontal plane our coulomb stress analysis shows that the microseismicity recorded in the swrz is induced by overpressurization of the south caldera reservoir and not by magma intrusion into the swrz this study highlights the importance of a joint analysis of independent geophysical datasets to fully constrain the nature of magma accumulation

laser altimetry sampling strategies over sea ice with the conclusion of the science phase of the ice cloud and land elevation satellite icesat mission in late 2009 and the planned launch of icesat 2 in late 2015 nasa has recently established the icebridge program to provide continuity between missions a major goal of icebridge is to obtain a sea ice thickness time series via airborne surveys over the arctic and southern oceans typically two laser altimeters the airborne topographic mapper atm and the land vegetation and ice sensor lvis are utilized during icebridge flights using laser altimetry simulations of conventional analogue systems such as icesat lvis and atm with the multi beam system proposed for icesat 2 we investigate differences in measurements gathered at varying spatial resolutions and the impact on sea ice freeboard we assess the ability of each system to reproduce the elevation distributions of two sea ice models and discuss potential biases in lead detection and sea surface elevation arising from variable footprint size and spacing the conventio nal systems accurately reproduce mean freeboard over 25 km length scales while icesat 2 offers considerable improvements over its predecessor icesat in particular its dense along track sampling of the surface will allow flexibility in the algorithmic approaches taken to optimize the signal to noise ratio for accurate and precise freeboard retrieval

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

pleistocene water intrusions from the mediterranean and caspian seas into the black sea the hydrological balance of the black sea is governed by riverine input and by the exchange with the mediterranean sea a speleothem record from a cave in northern turkey that tracks the isotopic signature of black sea surface water suggests an open connection to the mediterranean sea in at least twelve periods in the past 670 000 years

seismological evidence for long term and rapidly accelerating magma pressurization preceding the 2009 eruption of redoubt volcano alaska abstract successful eruption forecasts are heavily dependent on the recognition of well established patterns in volcano monitoring data therefore it is critical to develop in retrospect an understanding of the physical basis for cases of abnormal precursory behavior as the basis for a a complete understanding of the range of precursory signals that may be expected at a particular volcano and b development of new monitoring approaches to detect more subtle signals of the underlying processes responsible for common patterns of seismic unrest here using a hybrid analysis of shear wave splitting sws and double couple fault plane solutions fps we document the timing and nature of local stress field changes in the months to days preceding the 2009 eruption of redoubt volcano alaska which was characterized by an abnormally long period of precursory low frequency seismicity reflected in multiple escalations of alert levels prior to the eruption we find that an approximately 90 change in the polarization of fast s wavelets accompanied the earliest signs of seismic unrest in 2008 and continued through the eruption before diminishing in 2009 a similar change in the orientation of vt fps occurred 18 48 h prior to the eruption onset on march 23 2009 but almost two months after a strong increase in the rate of shallow vt earthquakes combined our sws and fps results show the earliest and latest known changes in seismic monitoring data respectively and are suggestive of a protracted period of slow magma ascent followed by a short period of rapidly increasing magma pressurization beneath the volcano these results demonstrate the power of a combined stress field analysis for clarifying the processes driving ambiguous seismic unrest at active volcanoes

assessing the performance of 20 25 m footprint waveform lidar data collected in icesat data corridors in greenland 1 the precision and accuracy of surface elevation measurements of the greenland ice sheet provided by 20 25 m footprint waveform laser altimetry is assessed using data collected by nasa s lvis airborne lidar in september 2007 repeated data acquisitions from two 850 km long transects over the ice sheet and a 30 km long transect in the summit area are evaluated for consistency and compared to in situ data for validation comparisons to data collected by nasa s icesat system reveal good agreement in the summit area differences are better than 0 07 m 1 except for l3c where it is 0 13 m with mean offsets of 0 09 to 0 16 m depending on the campaign within the feeder zone to jakobshavn glacier ice elevation decreases of up to 12 m 2004 2008 are observed the results suggest that 25 m waveform lidar can measure ice sheet elevation precisely and accurately and that the measurement scheme could be used to complement the legacy icesat measurements

mapping sea ice surface topography in high fidelity with icesat 2 the advanced topographic laser altimeter system atlas on icesat 2 offers a new remote sensing capability to measure complex sea ice surface topography we demonstrate the retrieval of six sea ice

seismicity and stress tensor inversion in the central washington cascade mountains abstract tectonic stress in the pacific northwest washington is dominated by a n s major compressive axis 1 and a minor compressive axis 3 which varies from e w to near vertical some variations in this pattern occur in different parts of the region in this study we used 550 earthquakes in the central washington cascade mountains to study in detail the uniformity of the stress tensor in this volcanic arc earthquakes from the pacific northwest seismograph network pnsn catalog were divided into several subsets based on epicentral and depth groupings and stress tensor inversions using the gephart and forsyth technique were computed for each group as in previous similar studies the maximum compressive stress axis 1 is nearly horizontal and trending n s to nne ssw in all but one subset shallower events directly under mount rainier have a near vertical 1 for other subsets the minimum compressive stress axis 3 deviates from vertical to horizontal for different groups of events in particular events in the depth range of 10 to 14 km in the western rainier seismic zone wrsz have near vertical 3 direction whereas other depth ranges in this area show a near horizontal e w 3 orientation we hypothesize that the change in orientation of 3 in the 10 to 14 km depth range in the wrsz may be due to the influence of the nearby mount rainier magmatic system independent evidence for magma at this depth comes in the form of a few deep long period lp events

comment on age and evolution of the grand canyon revealed by u pb dating of water table type speleothems polyak et al reports 7 march 2008 p 1377 reported that development of the western grand canyon began about 17 million years ago however their conclusion is based on an inappropriate conflation of plio quaternary incision rates and longer term rates derived from sites outside the grand canyon water table declines at these sites were more likely related to local base level changes and miocene regional extensional tectonics

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

microseismicity and stress in the vicinity of the alpine fault central southern alps new zealand 1 we investigate present day microseismicity associated with the central alpine fault and the zone of active deformation and uplift in the central southern alps using 14 months of data robust hypocenter locations have been obtained for 1800 earthquakes of magnitudes between 0 3 and 4 2 we derived a magnitude scale with a frequency dependent attenuation factor f 0f where 0 1 89 0 02 10 3 s km that enables magnitudes to be calculated consistently for earthquakes of different sizes and frequency contents the maximum depth of the seismicity varies systematically with distance from the alpine fault from 10 2 km near the fault to 8 2 km within 20 km and 15 2 km further southeast this distribution correlates with lateral variations in crustal resistivity earthquake hypocenters are concentrated in areas of strong resistivity gradients and restricted to depths of resistivities 100 m rocks at greater depth are too hot too fluid saturated or too weak to produce detectable earthquakes focal mechanism solutions computed for 211 earthquakes ml 0 44 exhibit predominantly strike slip mechanisms we obtain a maximum horizontal compressive stress direction of 115 10 from focal mechanism inversion this azimuth is consistent with findings from elsewhere in the central and northern south island and indicates a uniform crustal stress field despite pronounced variations in crustal structure and topographic relief our stress estimates suggest that the alpine fault with a mean strike of 055 is poorly oriented in an andersonian sense but that individual thrust and strike slip segments of the fault s surface trace have close to optimal orientations

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

circumpolar thinning of arctic sea ice following the 2007 record ice extent minimum september 2007 marked a record minimum in sea ice extent while there have been many studies published recently describing the minimum and its causes little is known about how the ice thickness has changed in the run up to and following the summer of 2007 using satellite radar altimetry data covering the arctic ocean up to 81 5 degrees north we show that the average winter sea ice thickness anomaly after the melt season of 2007 was 0 26 m below the 2002 2003 to 2007 2008 average more strikingly the western arctic anomaly was 0 49 m below the six year mean in the winter of 2007 2008 these results show no evidence of short term preconditioning through ice thinning between 2002 and 2007 but show that after the record minimum ice extent in 2007 the average ice thickness was reduced particularly in the western arctic citation giles k a s w laxon and a l ridout 2008 circumpolar thinning of arctic sea ice following the 2007 record ice extent minimum geophys res lett 35 l22502 doi 10 1029 2008gl035710

the origin of volcano tectonic earthquake swarms volcano tectonic vt seismicity is commonly recorded prior to and during eruptions vt seismicity may reflect stresses induced by dike propagation as indicated by propagating hypocenters and fault plane solutions fps reflecting regional stresses or stresses induced by dike inflation indicated by randomly distributed hypocenters and fps with pressure axes rotated 90 to regional maximum compression although numerical models of dike induced stresses indicate that both regimes should occur during dike emplacement this has not yet been observed according to published seismic data instead 90 rotated fps are observed in some cases while propagating hypocenters mark dike formation in other cases we suggest that differences in the seismic expression of upper crustal magma migration may result from differences in the regional tectonic setting and in the nature of magma wall rock interactions ultimately it may be possible to use information contained in vt seismicity to forecast changes in a volcano s behavior by establishing the characteristic stress field response for a given volcano or through a deeper understanding of the complex relationships between vt seismicity local crustal stresses and the physical mechanisms of magma migration

speleothem climate records from deep time exploring the potential with an example from the permian speleothems are well proven archives of terrestrial climate variation recording mean temperature rainfall and surface vegetation data at subannual to millennial resolution they also form within the generally stable environment of caves and thus may remain remarkably well preserved for many millions of years and most important can be dated radiometrically to provide robust chronologies that do not rely on orbital tuning ice flow modeling or estimates of sediment deposition rates the recent adaptation of the u pb dating technique to speleothems has greatly extended their potential as paleoclimate recorders back into the more distant geological past well beyond the 500 k y limit previously imposed by u series techniques but the opportunities presented by these new methods have yet to be fully explored as an extreme example here we report on samples recovered from permian cave fills the oldest radiometrically dated speleothems so far documented using state of the art analytical techniques it is possible to determine not only their age and state of preservation but also to extract apparently nearly pristine climate proxy data armed with these methods it now seems reasonable to apply the lessons learned from more recent speleothems to ancient materials wherever they can be found and of whatever age to generate snapshots of paleoclimate that can be used to greatly refine the records preserved within the sediments and fossils of the time

a method to automatically determine sea level for referencing snow freeboards and computing sea ice thicknesses from nasa icebridge airborne lidar abstract the nasa icebridge flights have obtained critical observations for earth s polar ice since icesat stopped collecting data in 2009 this study develops an automatic method in processing icebridge airborne topographic mapper atm altimeter l1b data one elevation per 3 4 m horizontally to derive a local sea level height for referencing snow freeboards and then computing sea ice thicknesses four 30 km l1b profiles a b c and d flown on october 21 2009 over the bellingshausen sea in antarctica are selected the local sea level reference is first obtained by visual examination of atm l1b heights over leads or thin ice identified on images simultaneously acquired from the digital mapping system camera called manual selection this sea level reference is then used as ground truth to validate sea level heights derived by automatic calculations using five thresholds of 2 1 0 5 0 2 and 0 1 of the lowest l1b data the l1b 0 2 method gives a similar sea level height as from the l1b manual selection by mean absolute difference of 0 01 0 06 m the sea level heights demonstrate a near linear gradient of 0 01 m km to 0 03 m km within each 30 km l1b profile along the flight track from section a to d the resulting mean snow freeboards are 0 59 m 0 67 m 0 53 m and 0 60 m on sections a b c and d respectively three empirical equations and the buoyancy equation with zero ice freeboard assumption all give similar statistics in ice thickness estimation with mean ice thicknesses of 1 91 m for section a 2 16 m for b 1 76 m for c and 1 94 m for d the sea level over leads cannot be accurately resolved from the atm l2 data 60 m x 80 m horizontal averaging however by using a sea level reference obtained from the l1b data the atm l2 data can achieve reasonable ice thickness estimates with mean absolute difference of only 0 10 m compared to thickness derived from the l1b data

a younger thinner arctic ice cover increased potential for rapid extensive sea ice loss 1 satellite derived estimates of sea ice age and thickness are combined to produce a proxy ice thickness record for 1982 to the present these data show that in addition to the well documented loss of perennial ice cover as a whole the amount of oldest and thickest ice within the remaining multiyear ice pack has declined significantly the oldest ice types have essentially disappeared and 58 of the multiyear ice now consists of relatively young 2 and 3 year old ice compared to 35 in the mid 1980s ice coverage in summer 2007 reached a record minimum with ice extent declining by 42 compared to conditions in the 1980s the much reduced extent of the oldest and thickest ice in combination with other factors such as ice transport that assist the ice albedo feedback by exposing more open water help explain this large and abrupt ice loss

temporal changes of medium properties during explosive volcanic eruption volcanic evolutions typically accompany significant changes in medium properties monitoring the seismic properties may be useful in identifying the state of volcanic evolution temporal variation of shallow crustal vp vs ratios before and during the 2009 eruption of redoubt volcano alaska is investigated using the p and s traveltimes of local earthquakes high vp vs ratios of 1 9 are observed over a wide region in the precursory phase suggesting the presence of partial melts in the medium at least several months before explosive eruptions the high v p v s ratios decrease until the early effusive phase with rates of 0 179 year 1 in the precursory phase 65 days and 2 147 year 1 in the explosive phase 40 days which is equivalent to a decrease in the bulk modulus of fluids by 1 1 and 7 9 gpa respectively the decreasing v p v s ratios in the precursory phase may be due to increasing amounts of overpressurized gas and water vapor in the medium the rapid decrease in vp vs ratios during the explosive phase may be caused by melt eruption and gas emission the vp vs ratios were observed to be nearly stationary since the early effusive phase suggesting rare presence of melts and low levels of pore pressures with degassing these observations suggest that monitoring vp vs ratios may be useful to identify the eruption state

seismic evolution of the 1989 1990 eruption sequence of redoubt volcano alaska abstract redoubt volcano in south central alaska erupted between december 1989 and june 1990 in a sequence of events characterized by large tephra eruptions pyroclastic flows lahars and debris flows and episodes of dome growth the eruption was monitored by a network of five to nine seismic stations located 1 to 22 km from the summit crater notable features of the eruption seismicity include 1 small long period events beginning in september 1989 which increased slowly in number during november and early december 2 an intense swarm of long period events which preceded the initial eruptions on december 14 by 23 hours 3 shallow swarms 0 to 3 km of volcano tectonic events following each eruption on december 15 4 a persistent cluster of deep 6 to 10 km volcano tectonic earthquakes initiated by the eruptions on december 15 which continued throughout and beyond the eruption 5 an intense swarm of long period events which preceded the eruptions on january 2 and 6 nine additional intervals of increased long period seismicity each of which preceded a tephra eruption hypocenters of volcano tectonic earthquakes suggest the presence of a magma source region at 6 10 km depth earthquakes at these depths were initiated by the tephra eruptions on december 15 and likely represent the readjustment of stresses in the country rock associated with the removal of magma from these depths the locations and time history of these earthquakes coupled with the eruptive behavior of the volcano suggest this region was the source of most of the erupted material during the 1989 1990 eruption this source region appears to be connected to the surface by a narrow pipe like conduit as inferred from the hypocenters of volcano tectonic earthquakes concentrations of shallow volcano tectonic earthquakes followed each of the tephra eruptions on december 15 these shocks may represent stress readjustment in the wall rock related to the removal of magma and volatiles at these depths this shallow zone was the source area of the majority of long period seismicity through the remainder of the eruption the long period seismicity likely reflects the pressurization of the shallow portions of the magmatic system

effect of regional tectonic setting on local fault response to episodes of volcanic activity 1 in this study we examine the interaction of tectonic and volcanically generated stress fields and their combined effect on patterns of volcanotectonic vt seismicity by calculating coulomb stress changes on local faults induced by a constant dike inflation event in a background stress field of systematically varying magnitude and orientation we find that patterns of vt seismicity earthquake locations and fault plane solutions resulting from dike inflation depend strongly on the relative strength and orientation of background tectonic stresses patterns of vt seismicity similar to those predicted by our coulomb stress models have been observed at several recently active volcanoes and appear to correspond to the relative strength of the regional stress field thus it is critical to consider the regional tectonic setting when interpreting patterns of vt seismicity in terms of magmatic processes

numerical models of volcanotectonic earthquake triggering on non ideally oriented faults 1 calculation of inflation induced coulomb stress changes on faults of varying orientation indicates that local faults of almost any orientation are susceptible to slip in response to dike inflation additionally as dikes typically inflate in the direction of regional minimum compressive stress the sense of inflation induced strike slip faulting predicted by coulomb stress change models is opposite to that expected from regional tectonic forces observations of volcanotectonic vt earthquake fault plane solutions with pressure p axes oriented 90 to regional maximum compression confirm this prediction in detail imperfect agreement between coulomb stress change models and the ranges of fault plane orientations observed in vt fault plane solution studies and observed locations of vt seismicity indicates that the orientation and location of pre existing faults around the conduit ultimately determine the seismic response of host rock to an inflating dike

liquid vapour homogenisation of fluid inclusions in stalagmites evaluation of a new thermometer for palaeoclimate research we present a new approach to determine palaeotemperatures mean annual surface temperatures based on measurements of the liquid vapour homogenisation temperature of fluid inclusions in stalagmites the aim of this study is to explore the potential and the limitations of this new palaeothermometer and to develop a reliable methodology for routine applications in palaeoclimate research therefore we have investigated recent fluid inclusions from the top part of actively growing stalagmites that have formed at temperatures close to the present day cave air temperature a precondition for measuring homogenisation temperatures of originally monophase inclusions is the nucleation of a vapour bubble by means of single ultra short laser pulses based on the observed homogenisation temperatures th obs and measurements of the vapour bubble diameter at a known temperature we calculated stalagmite formation temperatures tf by applying a thermodynamic model that takes into account the effect of surface tension on liquid vapour homogenisation results from recent stalagmite samples demonstrate that calculated stalagmite formation temperatures match the present day cave air temperature within 0 2 c to avoid artificially induced changes of the fluid density we defined specific demands on the selection handling and preparation of the stalagmite samples application of the method is restricted to stalagmites that formed at cave temperatures greater than 9 11 c

the seismicity of the 2009 redoubt eruption article redoubt volcano erupted in march 2009 following 6 months of precursory seismic activity the 4 5 month long eruptive sequence was accompanied by phreatic and magmatic explosions periods of steady dome growth lahars seismic swarms extended episodes of volcanic tremor and changes in the background seismicity rate this study presents a seismic chronology of the eruption and places it in context with the variety of other geological and geophysical data that were recorded during the eruptive period we highlight 6 notable seismic swarms 3 of which preceded large explosions the swarms varied from an hour to several days in duration and contained tens to over 7000 earthquakes many of the swarms were dominated by low frequency type earthquakes that contained families of repeating events seismic tremor varied considerably in frequency amplitude and duration during the eruption with distinct characteristics accompanying different types of volcanic activity the explosion signals during march 23 24 were the most energetic and the explosions on march 26 29 contained proportionally more low frequency energy 0 033 0 3 hz two seismic stations were particularly well suited to recording lahars that flowed down the drift river valley data from these stations showed that lahars were generated by the majority of the explosion events as well as during the continuous eruptive activity on march 29 when no large explosions occurred we also examine the seismicity which occurred outside of the explosion and swarm episodes and find several families of repeating vt earthquakes which begin shortly before the april 4 explosion and that continue

earthquake classification location and error analysis in a volcanic environment implications for the magmatic system of the 1989 1990 eruptions at redoubt volcano alaska abstract determination of the precise locations of seismic events associated with the 1989 1990 eruptions of redoubt volcano posed a number of problems including poorly known crustal velocities a sparse station distribution and an abundance of events with emergent phase onsets in addition the high relief of the volcano could not be incorporated into the hypoellipse earthquake location algorithm this algorithm was modified to allow hypocenters to be located above the elevation of the seismic stations the velocity model was calibrated on the basis of a posteruptive seismic survey in which four chemical explosions were recorded by eight stations of the permanent network supplemented with 20 temporary seismographs deployed on and around the volcanic edifice the model consists of a stack of homogeneous horizontal layers setting the top of the model at the summit allows events to be located anywhere within the volcanic edifice detailed analysis of hypocentral errors shows that the long period lp events constituting the vigorous 23 hour swarm that preceded the initial eruption on december 14 could have originated from a point 1 4 km below the crater floor a similar analysis of lp events in the swarm preceding the major eruption on january 2 shows they also could have originated from a point the location of which is shifted 0 8 km northwest and 0 7 km deeper than the source of the initial swarm we suggest this shift in lp activity reflects a northward jump in the pathway for magmatic gases caused by the sealing of the initial pathway by magma extrusion during the last half of december volcano tectonic vt earthquakes did not occur until after the initial 23 hour long swarm they began slowly just below the lp source and their rate of occurrence increased after the eruption of 01 52 ast on december 15 when they shifted to depths of 6 to 10 km after january 2 the vt activity migrated gradually northward this migration suggests northward propagating withdrawal of magma from a plexus of dikes and or sills located in the 6 to 10 km depth range precise relocations of selected events prior to january 2 clearly resolve a narrow steeply dipping pencil shaped concentration of activity in the depth range of 1 7 km which illuminates the conduit along which magma was transported to the surface a third event type named hybrid which blends the characteristics of both vt and lp events originates just below the lp source and may reflect brittle failure along a zone intersecting a fluid filled crack the distribution of hybrid events is elongated 0 2 0 4 km in an east west direction this distribution may offer constraints on the orientation and size of the fluid filled crack inferred to be the source of the lp events

climatic and environmental controls on speleothem oxygen isotope values variations in speleothem oxygen isotope values d 18 o result from a complicated interplay of environmental controls and processes in the ocean atmosphere soil zone epikarst and cave system as such the controls on speleothem d 18 o values are extremely complex an understanding of the processes that control equilibrium and kinetic fractionation of oxygen isotopes in water and carbonate species is essential for the proper interpretation of speleothem d 18 o as paleoclimate and paleoenvironmental proxies and is best complemented by study of site specific cave processes such as infiltration flow routing drip seasonality and saturation state and cave microclimate among others this review is a process based summary of the multiple controls on d 18 o in the atmosphere soil epikarst and speleothem calcite illustrated with case studies primary controls of d 18 o in the atmosphere include temperature and relative humidity through their role in the multiple isotope effects variability and modifications of water d 18 o values in the soil and epikarst zones are dominated by evaporation mixing and infiltration of source waters the isotopically effective recharge into a cave system consists of those waters that participate in precipitation of caco3 resulting in calcite deposition rates which may be biased to time periods with optimal dripwater saturation state recent modeling experimental and observational data yield insight into the significance of kinetic fractionation between dissolved carbonate phases and solid caco3 and have implications for the hendy test to assist interpretation of speleothem d 18 o time series quantitative and semi quantitative d 18 o climate calibrations are discussed with an emphasis on some of the difficulties inherent in using modern spatial and temporal isotope gradients to interpret speleothems as paleoclimate proxy records finally several case studies of globally significant speleothem paleoclimate records are discussed that show the utility of d 18 o to reconstruct past climate

icesat observations of arctic sea ice a first look 1 analysis of near coincident icesat and radarsat imagery shows that the retrieved elevations from the laser altimeter are sensitive to new openings containing thin ice or open water in the sea ice cover as well as to surface relief of old and first year ice the precision of the elevation estimates measured over relatively flat sea ice is 2 cm using the thickness of thin ice in recent openings to estimate sea level references we obtain the sea ice freeboard along the altimeter tracks this step is necessitated by the large uncertainties in the sea surface topography compared to that required for accurate determination of freeboard unknown snow depth introduces the largest uncertainty in the conversion of freeboard to ice thickness surface roughness is also derived for the first time from the variability of successive elevation estimates along the altimeter track overall these icesat measurements provide an unprecedented view of the arctic ocean ice cover at length scales at and above the spatial dimension of the altimeter footprint of 70 m

seismic observations of redoubt volcano alaska 1989 2010 and a conceptual model of the redoubt magmatic system abstract seismic activity at redoubt volcano alaska has been closely monitored since 1989 by a network of five to ten seismometers within 22 km of the volcano s summit major eruptions occurred in 1989 1990 and 2009 and were characterized by large volcanic explosions episodes of lava dome growth and failure pyroclastic flows and lahars seismic features of the 1989 1990 eruption were 1 weak precursory tremor and a short 23 hour long intense swarm of repetitive shallow long period lp events centered 1 4 km below the crater floor 2 shallow volcano tectonic vt and hybrid earthquakes that separated early episodes of dome growth 3 13 additional swarms of lp events at shallow depths precursory to many of the 25 explosions that occurred over the more than 128 day duration of eruptive activity and 4 a persistent cluster of vt earthquakes at 6 to 9 km depth in contrast the 2009 eruption was preceded by a pronounced increase in deep lp dlp events at lower crustal depths 25 to 38 km that began in mid december 2008 two months of discontinuous shallow volcanic tremor that started on january 23 2009 a strong phreatic explosion on march 15 and a 58 hour long swarm of repetitive shallow lp events the 2009 eruption consisted of at least 23 major explosions between march 23 and april 5 again accompanied by shallow vt earthquakes several episodes of shallow repetitive lp events and dome growth continuing until mid july increased vt earthquakes at 4 to 9 km depth began slowly in early april possibly defining a mid crustal magma source zone magmatic processes associated with the 2009 eruption seismically activated the same portions of the redoubt magmatic system as the 1989 1990 eruption although the time scales and intensity vary considerably among the two eruptions the occurrence of precursory dlp events suggests that the 2009 eruption may have involved the rise of magma from lower crustal depths based on the evolution of seismicity during the 1989 1990 and 2009 eruptions the redoubt magmatic system is envisioned to consist of a shallow system of cracks extending 1 to 2 km below the crater floor a magma storage or source region at roughly 3 to 9 km depth and a diffuse magma source region at 25 to 38 km depth close tracking of seismic activity allowed the alaska volcano observatory to successfully issue warnings prior to many of the hazardous explosive events that occurred in 2009