rise in frequency of surface melting at siple dome through the holocene evidence for increasing marine influence on the climate of west antarctica 1 a new melt layer history from siple dome west antarctica indicates notable late holocene summertime warming visual stratigraphic analyses of the 1004 m ice core identified 62 years with melt layers melting events began around 11 7 ka followed by a period of no melting from 8 8 6 6 ka melt layer frequency increased from 6 6 ka to the present with the 1000 year average melt layer frequency reaching a maximum of 2 at 0 8 ka we use our millennial scale archive of melt events as a unique seasonal paleothermometer to elucidate changes in west antarctic holocene summer climate our calibration suggests the change in melt frequency from 0 to 2 may represent a summer temperature increase of 2 c from the middle to late holocene this temperature change cannot be explained entirely by local change in ice elevation or summer insolation and is in contrast to east antarctic climate records which show peak warmth in the early holocene followed by stable or decreasing temperature we interpret the rise in melt frequency as evidence of an increasing marine influence on the ross sea sector of west antarctica although the surface elevation of siple dome has not changed greatly the continued lateral retreat of the west antarctic ice sheet from its last glacial maximum configuration across the outer continental shelf and the delayed drawdown in ice thickness from the adjacent coastal marie byrd land region in conjunction with periods of increased cyclogenesis perhaps related to variations in enso would allow a moderated maritime climate to more easily reach west antarctica

impactoclastic density current emplacement of terrestrial meteorite impact ejecta and the formation of dust pellets and accretionary lapilli evidence from stac fada scotland abstractwe present an impactoclastic density current model for terrestrial meteorite impact ejecta emplacement that is based on a hitherto unreported threefold sequence of lithofacies in the recently identified stac fada impact ejecta outflow blanket in scotland massive suevite division a grades seamlessly up into massive suevite containing whole and broken accretionary lapilli division b and this is overlain by a thin layer of clast supported dust pellets division c the sequence closely resembles sequences in accretionary lapilli bearing ignimbrites emplaced by pyroclastic density currents at volcanoes and we deduce similar emplacement mechanisms we propose that 99 of the thickness of the stac fada ejecta blanket as seen at outcrop was deposited from a single depletive spatially decelerating granular fluid based density current that rapidly waxed and then waned a previously unreported thin layer of pellets division c records direct fallout from a residual atmospheric dust plume we pro

persistent surface snowmelt over antarctica 1987 2006 from 19 35 ghz brightness temperatures 1 persistent melting e g continuing for more than three days or for one consecutive day and night is mapped in antarctica 1987 2006 using night and day time special sensor microwave imager brightness temperatures tb at 19 35 ghz horizontal polarization snowmelt is indicated when tb and relative daily difference exceed threshold values respectively tc and t computed for each pixel and year or when both daytime and nighttime tb exceed tc results from an electromagnetic model suggest that the minimum detectable liquid water content ranges between 0 2 and 0 5 in volume we find that melting areas have been moving inland since 1987 a first time extensive melting 1987 2006 is detected over the transantarctic mountains on january 2005 875 km inland and 2000 m above sea level melting extent and index have been decreasing over antarctica since 1987 although either positive and negative trends are observed from a sub continental scale analysis

detection of snowmelt regions on the greenland ice sheet using diurnal backscatter change snowmelt regions on greenland ice are mapped daily with the seawinds wideswath ku band 13 4 ghz scatterometer on the quikscat satellite the approach exploits the high temporal resolution of seawinds quikscat data for the melt mapping using diurnal backscatter change independent of the absolute calibration the results reveal several pronounced melting and refreezing events and effects of topography are evident in the melt patterns the spatial resolution is sufficient to identify melt features on the sukker toppen iskappe west of the main ice sheet an anomalous warming event caused by downward mixing of warm air is detected in late september 1999 over the west flank of the southern greenland ice sheet time series images of melt regions are presented over the period from summer to the fall freeze up the satellite observations are verified with in situ measurements from the greenland climate network stations

undrained anisotropy and rotational shear in granular soil the impact of fabric anisotropy on the behaviour of granular soil remains a subject of great interest in particular the effects of principal stress rotation on the undrained response of saturated sand are not fully understood this paper describes an experimental investigation conducted in an automated hollow cylinder apparatus into the undrained anisotropic behaviour of saturated sand in rotational shear which is defined as a class of non proportional loading with a continuous rotation of the principal stress directions but a constant deviatoric stress special attention in this investigation was placed on the influence of the relative magnitude of the intermediate principal stress characterised by the parameter b 2 3 1 3 on the pore pressure response and deformation characteristics the experimental observations indicate that soil specimens even in very dense state were weakened by the build up of pore water pressure in rotational shear the intermediate principal stress parameter b

a multiscale subpixel mixture analysis applied for melt detection using passive microwave and radar scatterometer image time series of the antarctic peninsula 1999 2009

climate and surface mass balance of coastal west antarctica resolved by regional climate modelling west antarctic climate and surface mass balance smb records are sparse to fill this gap regional atmospheric climate modelling is useful providing that such models are employed at sufficiently high horizontal resolution and coupled with a snow model here we present the results of a high resolution 5 5 km regional atmospheric climate model racmo2 simulation of coastal west antarctica for the period 1979 2015 we evaluate the results with available in situ weather observations remote sensing estimates of surface melt and smb estimates derived from radar and firn cores moreover results are compared with those from a lower resolution version to assess the added value of the resolution the high resolution model resolves small scale climate variability invoked by topography such as the relatively warm conditions over ice shelf grounding zones and local wind speed accelerations surface melt and smb are well reproduced by racmo2 this dataset will prove useful for picking ice core locations converting elevation changes to mass changes for driving ocean ice sheet and coupled models and for attributing changes in the west antarctic ice sheet and shelves to changes in atmospheric forcing

spatiotemporal variations of snowmelt in antarctica derived from satellite scanning multichannel microwave radiometer and special sensor microwave imager data 1978 2004 1 we derived the extent onset date end date and duration of snowmelt in antarctica from 1978 to 2004 using satellite passive microwave scanning multichannel microwave radiometer smmr and special sensor microwave imager ssm i data a wavelet transform based method was developed to determine and characterize melt occurrences about 9 12 of the antarctic surface experiences melt annually this is more than twice the surface melt extent measured in greenland seasonally surface melt primarily takes place in december january and february and peaks in early january regression analysis over the 25 year period of study reveals a negative interannual trend in surface melt nevertheless the trend inference is not statistically significant large year to year fluctuations characterize the interannual variability extremely high melt occurred in the 1982 1983 and 1991 1992 summers while extremely weak melt occurred in the 1999 2000 summer a strong correlation with air temperature suggests that the melt index can serve as a diagnostic indicator for regional temperature variations periodic melting has been observed over ross ice shelf ronne filchner ice shelf the west antarctic ice streams and outlet glaciers in the transantarctic mountains the antarctic peninsula west ice shelf shackleton ice shelf amery ice shelf and the ice shelf along the princess ragnhild coast experienced the most persistent and intensive melt and should be closely monitored for their stability in the future given the recent disintegration of the larsen ice shelf a and b

flow of variably fluidized granular masses across three dimensional terrain 2 numerical predictions and experimental tests numerical solutions of the equations describing flow of variably fluidized coulomb mixtures predict key features of dry granular avalanches and water saturated debris flows measured in physical experiments these features include time dependent speeds depths and widths of flows as well as the geometry of resulting deposits three dimensional 3 d boundary surfaces strongly influence flow dynamics because transverse shearing and cross stream momentum transport occur where topography obstructs or redirects motion consequent energy dissipation can cause local deceleration and deposition even on steep slopes velocities of surge fronts and other discontinuities that develop as flows cross 3 d terrain are predicted accurately by using a riemann solution algorithm the algorithm employs a gravity wave speed that accounts for different intensities of lateral stress transfer in regions of extending and compressing flow and in regions with different degrees of fluidization field observations and experiments indicate that flows in which fluid plays a significant role typically have high friction margins with weaker interiors partly fluidized by pore pressure interaction of the strong perimeter and weak interior produces relatively steep sided flat topped deposits to simulate these effects we compute pore pressure distributions using an advection diffusion model with enhanced diffusivity near flow margins although challenges remain in evaluating pore pressure distributions in diverse geophysical flows riemann solutions of the depth averaged 3 d coulomb mixture equations provide a powerful tool for interpreting and predicting flow behavior they provide a means of modeling debris flows rock avalanches pyroclastic flows and related phenomena without invoking and calibrating rheological parameters that have questionable physical significance

characterization and formation of melt layers in polar snow observations and experiments from west antarctica author posting international glaciological society 2005 this article is posted here by permission of international glaciological society for personal use not for redistribution the definitive version was published in journal of glaciology 51 2005 307 312 doi 10 3189 172756505781829395

surface melting derived from microwave radiometers a climatic indicator in antarctica this paper aims at presenting a new dataset including the melt events derived from microwave remote sensing occurring in antarctica from summer 1979 80 to 2005 06 the method for detecting melt events and sources of error is presented and then trends in melt duration for every pixel are extracted from the dataset mapped and analyzed the analysis focuses on two particular cases and the main results show that 1 the trends over the period 1980 2006 in the antarctic peninsula match with lengthening of the melt season on the ice shelves and surprisingly shortening of the melt season in the mountainous area of the peninsula and 2 the trends over the period 1996 2006 on the entire continent show a dipolar pattern with the western regions experiencing decreasing melt duration whereas east antarctica and the ross ice shelf experience increasing melt duration this pattern closely mirrors the temperature pattern expected when the southern annular mode is in a decreasing trend as it is over the period 1996 2006 for further analysis and validation the dataset has been made available at http www lgge obs ujf grenoble fr picard melting

a comparison of pyroclastic flow and debris avalanche mobility many pyroclastic flows have runout distances longer than expected from basic frictional arguments in these cases the ratio of the height descended h and the runout l are as small as 0 2 a feature which has been attributed to fluidization however significant fluidization by gases is now considered unlikely during emplacement of debris avalanches where h l and volume are inversely related we determine whether pyroclastic flows are more mobile than debris avalanches of the same volume and if different emplacement mechanisms are needed to describe their runout h l and volume data were compiled for 34 nonvolcanic and 40 volcanic debris avalanche deposits as well as 15 pyroclastic flow deposits systematic differences in the volume versus h l plots were explored by statistical analysis results show an inverse relationship between h l and volume for both nonvolcanic and volcanic debris avalanche deposits as expected and also for pyroclastic flow deposits regression lines for plots of pyroclastic flow and volcanic debris avalanche data are statistically indistinguishable and the non volcanic debris avalanche line is parallel to the other two we argue that the nonvolcanic and volcanic debris avalanche differences are due to material properties rather than emplacement mechanisms therefore since pyroclastic flows and volcanic debris avalanches have indistinguishable h l versus volume it is unlikely that pyroclastic flows have a significantly different primary emplacement mechanism based on the data in hand we conclude that it is unnecessary to invoke gas fluidization to explain the mobility of the types of pyroclastic flows examined or the excess runout of large volume debris avalanches

evaluation of passive microwave melt detection methods on antarctic peninsula ice shelves using time series of sentinel 1 sar abstract passive microwave datasets have been used to quantify the extent and duration of surface melt in greenland and antarctica from 1978 on with daily and near daily intervals these results have important implications for climate analysis and may help evaluate ice shelf stability however the accuracy of passive microwave methods used to detect melt is difficult to quantify especially on the antarctic peninsula here four different melt detection methods are employed including a new formulation of a statistical analysis of brightness temperature time series using a k means clustering algorithm strikingly two of the most widely used passive microwave melt detection methods are found to vary by 48 mean days of melt per year across six different locations on the larsen c wilkins and george vi ice shelves in the absence of ground truth observations time series of sentinel 1 sar observations from 2016 on provide a comparison dataset in topographically flat regions where surface melt is spatially uniform the passive microwave melt detection method based on a k means analysis and the cross polarization gradient ratio method demonstrate the highest agreement and correlation with active radar melt detection methods one issue which has plagued passive microwave analysis is its coarse spatial resolution high resolution sar images are able to demonstrate and quantify the spatial variability of melt within individual passive microwave pixels melt is shown to be suitably uniform in space for passive microwave applications at the study sites on antarctic peninsula ice shelves but not so in other regions of the antarctic peninsula spatial heterogeneity of surface melt on the sub pixel scale is often related to varying surface topography

seasonal evolution of supraglacial lakes on an east antarctic outlet glacier supraglacial lakes are known to influence ice melt and ice flow on the greenland ice sheet and potentially cause ice shelf disintegration on the antarctic peninsula in east antarctica however our understanding of their behavior and impact is more limited using 150 optical satellite images and meteorological records from 2000 to 2013 we provide the first multiyear analysis of lake evolution on langhovde glacier dronning maud land 69 11 s 39 32 e we mapped 7990 lakes and 855 surface channels up to 18 1 km inland 670 m above sea level from the grounding line and document three pathways of lake demise i refreezing ii drainage to the englacial subglacial environment on the floating ice and iii overflow into surface channels on both the floating and grounded ice the parallels between these mechanisms and those observed on greenland and the antarctic peninsula suggest that lakes may similarly affect rates and patterns of ice melt ice flow and ice shelf disintegration in east antarctica

pyroclastic flow deposits of the 1991 eruption of volcan de colima mexico the april 16 1991 eruption of volcan de colima represents a classical example of partial dome collapse with the generation of progressively longer runout merapi type pyroclastic flows that traveled up to 4 km along the el cordoban gullies east central and west the flows filled the gullies with block and ash flow deposits up to 10 m thick of which after 7 years of erosion only remnants remained in the el cordoban west and east gullies the el cordoban central gully however provided a well preserved and incised longitudinal section of the 1991 deposits the deposits were emplaced as proximal and distal facies separated by a change in slope angle from 30 to 20 the proximal facies consists of massive clast supported flow units up to 1 m thick with andesite blocks locally supported by a matrix of coarse ash and devoid of segregation structures or grading the distal facies consists of a massive matrix supported deposit up to 8 m thick which contains dispersed andesite blocks in a fine ash matrix in the distal facies a train of blocks marks flow unit upper boundaries and although sorting is poor some grading is present thin finely stratified or dune bedded layers of fine ash material are locally present above or below units of both facies sedimentologic parameters show that the size or fraction of large pyroclasts larger than 1 decreases from proximal to distal facies as the percentage of matrix 0 to 4 increases especially immediately beyond the break in slope we propose that the propagation of the colima pyroclastic flows is critically dependent on local slope angle the presence of erodible slope debris and the decrease in grain size with distance from the vent the progressive fining is probably caused by some combination of erosion clast breakup and deposition of larger pyroclasts and is itself influenced by the slope angle in the proximal region the flows moved as granular avalanches in which interacting grains ground each other and erosion occurred to produce an overriding dilute ash cloud the maximum runout distance of the avalanches was controlled by the angle of repose of the material and the volume and grain size of source and eroded material because the slope angle is close to the repose angle for this debris granular avalanches were not able to propagate far beyond the change in slope if however an avalanche had enough mass in finer grain size fractions at least part of the flow continued beyond the break in slope and across the volcano apron propagating in a turbulent state and depositing surge layers or in an otherwise settling modified state and depositing block and ash flow layers

granular mass flows and coulomb s friction in shear cell experiments implications for geophysical flows 1 granular mass flows of rock fragments are studied in the lab by means of a high speed video camera at 2000 frames per second these granular flows are generated using beds of pumice fragments positioned on a rough rotating disk whose angular velocity is controlled by a motor the experimental apparatus allows an understanding of the arrangement of the particles in granular mass flows with relatively small and relatively large values of the savage number the savage number represents the ratio between grain collision stresses and gravitational grain contact stresses in particular these flows develop a basal layer of agitated and colliding particles underneath a relatively rigid upper layer our experimental results suggest the validity on average of the coulomb s relationship between shear and normal forces at the base of granular mass flows irrespective of their savage number value in coulomb s equation the shear stresses do not depend on the shear rate we expect the coulomb friction law to be valid also in moving pyroclastic flows our experiments suggest that the collisions and subsequent comminution of pumice fragments in moving pyroclastic flows could provide ash for the overriding ash clouds in our experiments the amount of ash generated by particle particle and particle boundary interactions increases as the value of the savage number increases in nature part of this ash may also simply move toward the base of the flows because of kinetic sieving

numerical modeling of self channeling granular flows and of their levee channel deposits when not laterally confined in valleys pyroclastic flows create their own channel along the slope by selecting a given flowing width furthermore the lobe shaped deposits display a very specific morphology with high parallel lateral levees a numerical model based on saint venant equations and the empirical variable friction coefficient proposed by pouliquen and forterre 2002 is used to simulate unconfined granular flow over an inclined plane with a constant supply numerical simulations successfully reproduce the self channeling of the granular lobe and the levee channel morphology in the deposits without having to take into account mixture concepts or polydispersity numerical simulations suggest that the quasi static shoulders bordering the flow are created behind the front of the granular material by the rotation of the velocity field due to the balance between gravity the two dimensional pressure gradient and friction for a simplified hydrostatic model competition between the decreasing friction coefficient and increasing surface gradient as the thickness decreases seems to play a key role in the dynamics of unconfined flows the description of the other disregarded components of the stress tensor would be expected to change the balance of forces the front s shape appears to be constant during propagation the width of the flowing channel and the velocity of the material within it are almost steady and uniform numerical results suggest that measurement of the width and thickness of the central channel morphology in deposits in the field provides an estimate of the velocity and thickness during emplacement citation mangeney a f bouchut n thomas j p vilotte and m o bristeau 2007 numerical modeling of self channeling granular flows and of their levee channel deposits

divergent trajectories of antarctic surface melt under two twenty first century climate scenarios ice shelves modulate antarctica s contributions to sea level rise regional climate model simulations and observations suggest historical ice melt intensification before collapse of antarctic peninsula shelves and project future melt evolution

mobility of dry granular flows of varying collisional activity quantified by smart rock sensors highly instrumented particles i e smart rocks were included in monodisperse dry granular landslide experiments to quantify the collisional nature of such flows and to investigate the influenc

extent and duration of antarctic surface melting the extent and duration of surface melting on the antarctic ice shelves and margins of the antarctic ice sheet are derived from satellite passive microwave data for 1978 87 the occurrence of surface melting in daily maps of t b is indicated by a marked increase in microwave brightness temperature t b which is caused by moisture in the near surface firn t b increases of more than 30 deg above the annual mean t b are chosen to indicate melting most antarctic surface melting occurs during december and january the observed melting is correlated with regional air temperatures but some melt patterns also appear to be related to katabatic wind effects the correlations suggest that the surface melting in antarctica increases about 3 5 10 6 d km 2 per degree of summer temperature increase the surface melt index duration times area of melting calculated for antarctica is 24 10 6 d km 2 averaged over nine summers the observed inter annual and regional variability is large surface melting was most extensive during the 1982 83 summer 36 10 6 d km 2 and least extensive during the 1985 86 summer 15 10 6 d km 2 the data indicate a decline in surface melting over the 9 years but meaningful inferences regarding trends in surface melting are precluded by the large inter annual variability

stratigraphy sedimentology and inferred flow dynamics from the july 2015 block and ash flow deposits at volcan de colima mexico abstract the july 2015 block and ash flow baf events represent the first documented series of large volume and long runout bafs generated from sustained dome collapses at volcan de colima this eruption is particularly exceptional at this volcano due to 1 the large volume of baf material emplaced 0 0077 0 001 km3 2 the long runout reached by the associated bafs max 10 km and 3 the short period 18 h over which two main long sustained dome collapse events occurred on 10 and 11 july respectively stratigraphy and sedimentology of the 2015 baf deposits exposed in the southern flank of the volcano based on lithofacies description grain size measurements and clast componentry allowed the recognition of three main deposit facies i e valley confined overbank and ash cloud surge deposits correlations and lithofacies variations inside three main flow units from both the valley confined and overbank deposits left from the emplacement of the second series of bafs on 11 july provide detailed information about 1 the distribution volumes and sedimentological characteristics of the different units 2 flow parameters i e velocity and dynamic pressure and mobility metrics as inferred from associated deposits and 3 changes in the dynamics of the different flows and their material during emplacement these data were coupled with geomorphic analyses to assess the role of the topography in controlling the behaviour and impacts of the successive baf pulses on the volcano flanks finally these findings are used to propose a conceptual model for transport and deposition mechanisms of the july 2015 bafs at volcan de colima in this model deposition occurs by rapid stepwise aggradation of successive baf pulses flow confinement in a narrow and sinuous channel enhance the mobility and runout of individual channelized baf pulses when these conditions occur the progressive valley infilling from successive sustained dome collapse events promote the overspill and lateral spreading of the upper and marginal regions of the main flow body generating highly mobile overbank flows that travel outside of the main valley volume and distance dependent critical channel capacities for the generation of overbank flows are used to better estimate the inundation area of these hazardous unconfined pyroclastic flows these results highlight the importance of including and correctly assessing the hazards posed by large volume and long runout bafs associated with frequent small vei sustained dome collapse eruptions

drivers of ascat c band backscatter variability in the dry snow zone of antarctica c band backscatter parameters contain information about the upper snowpack firn in the dry snow zone the wide incidence angle diversity of the advanced scatterometer ascat gives unprecedented characterisation of backscatter anisotropy revealing the backscatter response to climatic forcing the a isotropic component and m2 bi sinusoidal azimuth anisotropy parameters are investigated here in conjunction with data from atmospheric and snowpack models to identify the backscatter response to surface forcing parameters wind speed and persistence precipitation surface temperature density and grain size the long term mean a parameter is successfully recreated with a regression using these drivers indicating strong links between the a parameter and precipitation on long timescales while the ascat time series is too short to determine which factors drive observed trends factors influencing the seasonal and short timescale variability are revealed on these timescales a strongly responds to the propagation of surface temperature cycles anomalies downward through the firn via direct modulation of the dielectric constant the influence of precipitation on a is small at shorter timescales the m2 parameter is controlled by wind speed and persistence through modification of monodirectionally aligned surface roughness this variability indicates that throughout much of coastal antarctica a microwave snapshot is generally not representative of longer term conditions

depressurization of fine powders in a shock tube and dynamics of fragmented magma in volcanic conduits abstract samples of fine glass beads mean grain size equal to 38 and 95 m have been depressurized within a vertical shock tube these short lived rapid decompressions resemble discrete cannon like vulcanian explosions and produce two phase flows that are inhomogeneous in density in both vertical and horizontal directions because of the presence of bubble like heterogeneities we suggest that also volcanic flows may present similar inhomogeneities in density in the experimental apparatus the flow velocities increase from approximately 1 to 13 m s when the pressure drop increases from approximately 200 to 900 mbar a physical model of the initial velocities of expansions in the shock tube has been applied to a range of volcanic overpressures between 0 1 and 20 mpa suggesting initial velocities of volcanic flows caused by the removal of a rock plug in volcanic conduits between 25 and 400 m s during the experiments at large pressure drops as the mixture expands and moves up the tube the flow front becomes highly irregular and bubble like heterogeneities form the shape of these bubbles becomes distorted and stretched in the turbulent flow during the experiments at relatively small pressure drops the sample oscillates when the particles after the expansion flow back and bounce upward again jets with diameter smaller than that of the tube are ejected from the oscillating samples generating independent pulses large bubble like heterogeneities whose diameter is a significant fraction of the tube diameter can also discretize the flows similar mechanisms in real volcanoes may produce pulse like ejections of gas particle mixtures out of the vent

antarctic surface and subsurface snow and ice melt fluxes abstract this paper presents modeled surface and subsurface melt fluxes across near coastal antarctica simulations were performed using a physical based energy balance model developed in conjunction with detailed field measurements in a mixed snow and blue ice area of dronning maud land antarctica the model was combined with a satellite derived map of antarctic snow and blue ice areas 10 yr 1991 2000 of antarctic meteorological station data and a high resolution meteorological distribution model to provide daily simulated melt values on a 1 km grid covering antarctica model simulations showed that 11 8 and 21 6 of the antarctic continent experienced surface and subsurface melt respectively in addition the simulations produced 10 yr averaged subsurface meltwater production fluxes of 316 5 and 57 4 km3 yr 1 for snow covered and blue ice areas respectively the corresponding figures for surface melt were 46 0 and 2 0 km3 yr 1 respectively thus demonstrating the dominant role of subsurface ov

pressures at the base of dry flows of angular rock fragments as a function of grain size and flow volume experimental results geophysical granular flows such as pyroclastic flows and rock avalanches kill people and damage properties worldwide the pressures exerted at their base affect the retarding forces that act on them and for this reason affect also their mobility that is important to foresee when assessing natural hazards in mountain regions here we present the results of experiments obtained by measuring with a load cell the basal pressures exerted by dry and cohesionless granular flows that descend a curved chute in the laboratory the interaction between these flows and the chute surface on which they travel is dominated by collisions of particles and or clusters of particles a dimensional analysis suggests that the energy dissipation of these flows increases as grain size increases and as flow volume decreases all the other features equal therefore the smaller the grain size and the larger the volume the larger is expected to be flow mobility although the longer travel distances of the centre of mass of finer grain size flows are easily discernible in our experiments the effect of volume is probably hidden by additional phenomena such as the deposition first of the frontal portion of longer flows on the less steep more distal part of the slope that prevents the rear portion and the centre of mass of the flows to travel further downhill

mapping of ice layer extent and snow accumulation in the percolation zone of the greenland ice sheet 1 the greenland ice sheet underwent record extensive melt in 2002 and prolonged melt in 2003 the severe melting created a significant and extensive ice layer over the greenland ice sheet an innovative approach is developed to detect the ice layer formation using data acquired by the seawinds scatterometer on the quikscat satellite quikscat backscatter together with in situ data from automatic weather stations of the greenland climate network are used to map the extent of ice layer formation the results reveal areas of extensive ice layer formed by the 2002 melt which is consistent with the maximum melt extent in 2002 moreover during freezing seasons quikscat data show a linear decrease in backscatter in decibels or db that is related to the amount of snow accumulation in the ice layer formation region this snow accumulation signature is caused by the attenuation of radar waves in the snow layer accumulating since the last major melt event whose thickness appears as an exponential function in relation to the backscatter signature we use the greenland climate network data to calibrate the quikscat accumulation rate in order to estimate and map snow accumulation quikscat results capture the extreme snowfall in mid april 2003 which deposited more than 0 5 m of snow in a day as measured by the automated weather station at the nasa south east site large scale quikscat results show an anomalous increase of snow accumulation over the southeast region of greenland during the 2002 2003 freezing season

strong surface melting preceded collapse of antarctic peninsula ice shelf 1 during the austral summer of 2001 02 melting at the surface of larsen ice shelf in the antarctic peninsula was three times greater than the average of five previous summers this exceptional melt event lasted for three months and was followed by the collapse of larsen b ice shelf during which 3 200 km2 of ice shelf surface was lost the strong melting was caused by a persistent atmospheric circulation anomaly which depleted sea ice concentrations in front of larsen ice shelf and transported warm air to the ice shelf throughout the 2001 02 summer this supports the theory that large meltwater fluxes accelerate the retreat of antarctic peninsula ice shelves

undrained anisotropy and principal stress rotation in saturated sand this paper describes an investigation carried out in a new hollow cylinder apparatus into anisotropy and the effects of principal stress rotation in a medium loose sand tested under undrained conditions principal stresses have been rotated at a constant shear stress during both monotonie and cyclic loading the experimental observations are described and then explained within a framework based on the concept of state boundary surfaces the over riding importance of initial anisotropy in determining the response of the sand to rotations in principal stress directions is demonstrated pore pressures are shown to be generated by rotation of principal stress directions at constant shear stress and their accumulation during cyclic principal stress rotation can lead to failure l article presente une etude de l anisotropie effectuee dans un nouvel appareil creux cylindrique et decrit les effets de la rotation de la contrainte principale dans un sable moyennement l che teste dans des conditions non drainees l

remote sensing of glacier and ice sheet grounding lines a review abstract the precise positioning and long term monitoring of the grounding line forming the boundary between grounded and floating ice of marine ice sheets and tidewater glaciers is critical for assessing ice sheet glacier stability ice sheet glacier mass balance calculations and numerical ice modelling however mapping of the grounding line is a challenging task since it is a subglacial and transient feature remote sensing techniques do not map the grounding line directly but locate surface features in the grounding zone that serve as proxies for the true grounding line position the large variety of methods products and publications as well as an inconsistent use of terminology additionally complicate the topic we present the first detailed review of existing remote sensing techniques and data for grounding line mapping benefits and limitations of the different techniques and data sources are discussed and illustrated with examples we identify a present tradeoff between accuracy and both spatial coverage and temporal resolution of the derived grounding line products rather new methods like sentinel 1 sar synthetic aperture radar differential range offset tracking drot and pseudo crossover radar altimetry pcra offer the potential for recent measurements and to fill gaps in some areas nevertheless there is a high demand of new spaceborne radar sensors that provide time series of very short repeat pass data to enable regular grounding line monitoring with most accurate differential sar interferometry dinsar on a continental scale

a new bathymetry for the southeastern filchner ronne ice shelf implications for modern oceanographic processes and glacial history the filchner ronne ice shelf the ocean cavity beneath it and the weddell sea that bounds it form an important part of the global climate system by modulating ice discharge from the antarctic ice sheet and producing cold dense water masses that feed the global thermohaline circulation a prerequisite for modeling the ice sheet and oceanographic processes within the cavity is an accurate knowledge of the sub ice sheet bedrock elevation but beneath the ice shelf where airborne radar cannot penetrate bathymetric data are sparse this paper presents new seismic point measurements of cavity geometry from a particularly poorly sampled region south of berkner island that connects the filchner and ronne ice shelves an updated bathymetric grid formed by combining the new data with existing data sets reveals several new features in particular a sill running between berkner island and the mainland could alter ocean circulation within the cavity and change our understanding of paleo ice stream flow in the region also revealed are deep troughs near the grounding lines of foundation and support force ice streams which provide access for seawater with melting potential running an ocean tidal model with the new bathymetry reveals large differences in tidal current velocities both within the new gridded region and further afield potentially affecting sub ice shelf melt rates

glacier acceleration and thinning after ice shelf collapse in the larsen b embayment antarctica 1 ice velocities derived from five landsat 7 images acquired between january 2000 and february 2003 show a two to six fold increase in centerline speed of four glaciers flowing into the now collapsed section of the larsen b ice shelf satellite laser altimetry from icesat indicates the surface of hektoria glacier lowered by up to 38 6 m in a six month period beginning one year after the break up in march 2002 smaller elevation losses are observed for crane and jorum glaciers over a later 5 month period two glaciers south of the collapse area flask and leppard show little change in speed or elevation seasonal variations in speed preceding the large post collapse velocity increases suggest that both summer melt percolation and changes in the stress field due to shelf removal play a major role in glacier dynamics

snow and ice facies variability and ice layer formation on canadian arctic ice caps 1999 2005 1 time series of enhanced resolution data from the seawinds scatterometer aboard quikscat were used to map the distribution of snow and ice surface facies and ice layer formation in the percolation zone on ice caps in the queen elizabeth islands during the period 1999 2005 iterative self organizing data analysis classification of the mean postfreeze up biweekly average 0 signal for the 7 year period resulted in the delineation of four snow and ice surface facies interpreted as the percolation saturation superimposed ice and glacier ice zones analysis with national centers for environmental prediction national center for atmospheric research reanalysis reveals that changes in geopotential height in the troposphere 700 500 and 300 hpa and air temperature 700 hpa level are positively negatively correlated with area changes in the glacier ice percolation and saturation zones and changes in facies boundary elevation the change in biweekly averaged backscatter following the freeze up periods between successive autumns was used to map changes in the distribution of ice layers formed by meltwater percolation and refreezing in the snowpack within the percolation zone strongly positive air temperature anomalies at the 700 hpa level in 2001 and 2005 are consistent with extensive ice layer formation in the percolation zones of all ice caps such large interannual changes in ice layer formation are likely associated with large changes to the density profile of the snowpack and may be associated with surface elevation changes that are unrelated to changes in surface mass balance

quantifying vulnerability of antarctic ice shelves to hydrofracture using microwave scattering properties abstract recent ice shelf disintegrations on the antarctic peninsula and subsequent increases in ice sheet mass loss have highlighted the importance of tracking ice shelf stability with respect to surface melt ponding and hydrofracture in this study we use active microwave scatterometry in time series to estimate melt season duration and winter backscatter levels as a proxy for relative concentration of refrozen ice lenses in antarctic ice shelf firn we demonstrate a physical relationship between melt days and firn ice backscatter using scatterometry and field data from greenland and apply the observed relationship to derive and map a vulnerability index for antarctica s ice shelves the index reveals that some remaining antarctic peninsula ice shelves have already reached a firn state that is vulnerable to hydrofracture we also show that the progression of an ice shelf towards vulnerability is affected by many factors such as surface mass balance internal stresses and ice shelf geometry

the contribution of experimental volcanology to the study of the physics of eruptive processes and related scaling issues a review abstract the experimental approach has become a major tool increasingly used by volcanologists in recent decades to investigate the physics of eruptive processes in complement to field and theoretical works researchers have developed various methodologies to study volcanic phenomena at reduced length scale the works involve natural or analogue materials and their types range from first order tests to identify fundamental processes and make qualitative comparison with field observations to more sophisticated experiments in which precise data obtained in a controlled environment can be used to validate outputs of theoretical models scaling is a central issue to ensure dynamic similarity between the small scale experiments and the large scale volcanic phenomena when natural conditions cannot be simulated due to inherent length scale difference and or technical limitations in this respect dimensionless numbers are used to map physical regimes and to define scaling laws which allow experimental results to be extrapolated to natural scale this review presents the variety of experimental studies conducted to investigate subterraneous and aerial volcanic phenomena involving in particular fluid particle mixtures we focus on the major scaling issues and the physical regimes investigated and we also highlight in a historical perspective some of the major advances achieved through experimental studies finally we conclude on some perspectives for future works

grain size and flow volume effects on granular flow mobility in numerical simulations 3 d discrete element modeling of flows of angular rock fragments the results of three dimensional discrete element modeling presented in this paper confirm the grain size and flow volume effects on granular flow mobility that were observed in laboratory experiments where batches of granular material traveled down a curved chute our numerical simulations are able to predict the correct relative mobility of the granular flows because they take into account particle interactions and thus the energy dissipated by the flows the results illustrated here are obtained without prior fine tuning of the parameter values to get the desired output the grain size and flow volume effects can be expressed by a linear relationship between scaling parameters where the finer the grain size or the smaller the flow volume the more mobile the center of mass of the granular flows the numerical simulations reveal also the effect of the initial compaction of the granular masses before release the larger the initial compaction the more mobile the center of mass of the granular flows both grain size effect and compaction effect are explained by different particle agitations per unit of flow mass that cause different energy dissipations per unit of travel distance the volume effect is explained by the backward accretion of the deposits that occurs wherever there is a change of slope either gradual or abrupt our results are relevant for the understanding of the travel and deposition mechanisms of geophysical flows such as rock avalanches and pyroclastic flows

the impact of a changing southern hemisphere annular mode on antarctic peninsula summer temperatures since the mid 1960s rapid regional summer warming has occurred on the east coast of the northern antarctic peninsula with near surface temperatures increasing by more than 2 degrees c this warming has contributed significantly to the collapse of the northern sections of the larsen ice shelf coincident with this warming the summer southern hemisphere annular mode sam has exhibited a marked trend suggested by modeling studies to be predominantly a response to anthropogenic forcing resulting in increased westerlies across the northern peninsula observations and reanalysis data are utilized to demonstrate that the changing sam has played a key role in driving this local summer warming it is proposed that the stronger summer westerly winds reduce the blocking effect of the antarctic peninsula and lead to a higher frequency of air masses being advected eastward over the orographic barrier of the northern antarctic peninsula when this occurs a combination of a climatological temperature gradient across the barrier and the formation of a fohn wind on the lee side typically results in a summer near surface temperature sensitivity to the sam that is 3 times greater on the eastern side of the peninsula than on the west sam variability is also shown to play a less important role in determining summer temperatures at stations west of the barrier in the northern peninsula similar to 62 degrees s both at the surface and throughout the troposphere this is in contrast to a station farther south similar to 65 degrees s where the sam exerts little influence

melt detection in antarctic ice shelves using scatterometers and microwave radiometers ku band dual polarization radar backscatter measurements from the seawinds on quikscat scatterometer are used to determine periods of surface freeze and melt in the antarctic ice shelves the normalized horizontal polarization radar backscatter sigmao and backscatter polarization ratio are used in maximum likelihood estimation of the ice state this method is used to infer the daily ice surface conditions for 25 study locations located on the ronne ross larsen amery shackleton and other ice shelves the temporal and spatial variations of the radar response are observed for various neighborhood sizes surrounding each given location during the study period criteria for determining the dates of melt onset and freeze up for each austral summer are presented validation of the ice state and melt onset date estimates is performed by analyzing the corresponding brightness temperature tb measurements from special sensor microwave imager ssm i radiometers quikscat sigmao measurements from 1999 to 2003 are analyzed and found to be effective in determining periods of melt in antarctic ice sheets at high temporal and spatial resolutions these estimates can be used in studies of the climatic effects of the seasonal and interannual melting of the antarctic ice sheets

acceleration of snow melt in an antarctic peninsula ice core during the twentieth century over the past 50 years warming of the antarctic peninsula has been accompanied by accelerating glacier mass loss and the retreat and collapse of ice shelves a key driver of ice loss is summer melting however it is not usually possible to specifically reconstruct the summer conditions that are critical for determining ice melt in antarctic here we reconstruct changes in ice melt intensity and mean temperature on the northern antarctic peninsula since ad 1000 based on the identification of visible melt layers in the james ross island ice core and local mean annual temperature estimates from the deuterium content of the ice during the past millennium the coolest conditions and lowest melt occurred from about ad 1410 to 1460 when mean temperature was 1 6 c lower than that of 1981 2000 since the late 1400s there has been a nearly tenfold increase in melt intensity from 0 5 to 4 9 the warming has occurred in progressive phases since about ad 1460 but intensification of melt is nonlinear and has largely occurred since the mid twentieth century summer melting is now at a level that is unprecedented over the past 1 000 years we conclude that ice on the antarctic peninsula is now particularly susceptible to rapid increases in melting and loss in response to relatively small increases in mean temperature

accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf acceleration exceeds 27 km 3 per year and ice is thinning at rates of tens of meters per year we attribute this abrupt evolution of the glaciers to the removal of the buttressing ice shelf the magnitude of the glacier changes illustrates the importance of ice shelves on ice sheet mass balance and contribution to sea level change index terms 1827 hydrology glaciology 1863 1863 hydrology snow and ice 1827 3349 meteorology and atmospheric dynamics polar meteorology 6924 radio science interferometry 9310 information related to geographic region antarctica citation rignot e g casassa p gogineni w krabill a rivera and r thomas 2004 accelerated ice discharge from the antarctic peninsula following the collapse of larsen b ice shelf geophys res lett 31 l18401 doi 10 1029 2004gl020697

dynamic characteristics of a sandy seabed under storm wave loading considering the effect of principal stress rotation abstract this paper aims to investigate the cyclic characteristics of soil under storm waves with the typical irregular character in which a generalized plasticity model considering the effect of principal stress rotation psr was adopted to model soil behavior in the present model the plastic strain generated by principal stress rotation was considered to be an additional item in the constitutive relationship of soil and the normalized loading and plastic flow directions were determined based on the stress tensor invariants comparisons between the present model previous hollow cylinder apparatus hca tests and geotechnical centrifugal wave tests all show good agreement numerical results indicate that the moveable and random characteristics of the storm wave result in similar and irregular dynamic responses in sandy deposits along the extension direction of the seabed moreover the severest wave loading in a real storm will significantly magnify both the speed and extent of liquefaction of the sandy seabed numerical results also demonstrate that ignoring the psr involved in the storm wave seabed interaction will significantly underestimate the build up of pore water pressure additionally when considering the impact of psr the sandy seabed exhibits higher liquefaction resistance when subjected to the random wave compared to the representative regular wave however since the sharply weakening liquefaction resistance of soil under the severest wave condition cannot be captured with the regular wave it is suggested that the random wave be adopted to further investigate the storm wave seabed interaction parametric studies show that soil properties e g permeability and saturation significantly affect the liquefaction characteristics of soil under storm waves

the 17 july 1999 block and ash flow baf at colima volcano new insights on volcanic granular flows from textural analysis abstract on july 17 1999 a strong explosion occurred at colima volcano mexico that produced a 10 km high eruptive column the partial column collapse originated a block and ash flow baf that flowed to the south along the san antonio and montegrande ravines travelling 3 3 km from the volcano summit the flow filled the ravines with a volume estimated at 7 9 105 m3 the erosion of these deposits occurred between 1999 and 2002 time of sampling providing excellent longitudinal outcrops that allowed their detailed textural study the study was carried out by means of quantitative textural analysis 1 rosiwal intersections for carrying out vertical granulometric profiles 2 total grain size analysis from 11 to 9 and 3 fourier and fractal analysis of the particle morphology grain size and morphometric parameters obtained with these methods were used to identify vertical and longitudinal variation patterns in the baf deposit the grain size variations allowed to infer the main particle segregation mechanisms that acted during transport and deposition of the studied bafs the two methods used for studying the particle shape morphologies yielded results with different accuracy and reliability in particular fractal analyses have been found to be the most effective in describing the particle support mechanisms that acted during transport and deposition of the studied bafs the results highlight the importance of the information obtained by means of these techniques and provide new insights in transportation and deposition mechanisms of bafs

rapid drawdown of antarctica s wordie ice shelf glaciers in response to enso southern annular mode driven warming in the southern ocean abstract here we investigate the largest acceleration in ice flow across all of antarctica between 2008 insar and 2014 landsat velocity mappings this occurred in glaciers that used to feed into the wordie ice shelf on the west antarctic peninsula which rapidly disintegrated in 1989 between 2008 and 2014 these glaciers experienced at least a threefold increase in surface elevation drawdown relative to the 2002 2008 time period after 20 yrs of relative stability it is unlikely that the ice shelf collapse played a role in the large response instead we find that the rapid acceleration and surface drawdown is linked to enhanced melting at the ice ocean boundary attributable to changes in winds driven by global atmospheric circulation patterns namely the el nino southern oscillation enso and southern annular mode sam linking changes in grounded ice to atmospheric driven ocean warming

retrieval of wet snow by means of multitemporal sar data an algorithm has been developed for mapping wet snow in mountainous terrain using repeat pass synthetic aperture radar sar images as a basis for algorithm development backscattering properties of snow free and snow covered alpine surfaces were investigated using ers sar data and field measurements at test sites in the austrian alps the incidence angle dependence of backscattering derived from sar data is compared with simulations for snow free surfaces and for surfaces covered by dry snow and wet snow significant seasonal changes of backscattering are observed which are mainly caused by variations of the snow liquid water content and of the surface roughness the importance of surface roughness for backscattering of wet snow is demonstrated by a surface roughness experiment the algorithm for mapping wet snow applies change detection using ratios of wet snow versus snow free or dry snow surfaces the main steps include coregistration speckle reduction thresholding of ratio images geocoding and optionally combination of crossing passes to reduce the loss of information due to layover a threshold of 3 db was found to be appropriate for both radarsat and ers sar to separate wet snow from other surfaces postprocessing steps based on historic snow maps or topographic information are used to correct for dry snow areas at high elevations effects of imaging geometry are investigated by comparing ers sar images with a look angle of 19 spl deg and radarsat sar beam mode s7 images with a look angle of 40 spl deg the comparison of snow maps from sar and landsat 5 thematic mapper images shows good agreement in areas of closed snow cover whereas near the snow line sar tends to slightly underestimate the snow extent

effect of grain size on mobility of dry granular flows of angular rock fragments an experimental determination abstract rapid mass movements of rock fragments are among the most hazardous natural phenomena they are too dangerous to be approached and studied directly and for this reason experiments are necessary to understand their flow mechanisms here we present the results of experiments on granular flow mobility obtained releasing batches of angular rock fragments down a curved chute our experiments demonstrate that the finer the grain size of the flow the larger its mobility this is accompanied by a decrease of fragments agitation when grain size decreases as shown by particle image velocimetry measurements of high speed video camera images the smaller the agitation the smaller is also the energy dissipated by flows per unit of travel distance this explains the effect of finer grain size on flow mobility these results are an important step towards the prediction of runout distances as a function of the features that characterize the different geophysical flows

experiments on the flow behaviour of granular materials at high velocity in an open channel a series of laboratory flume experiments has been conducted to investigate the flow behaviour of dry sand at high velocities the first incentive for this experimental programme was an attempt to explain the high mobility of apparently dry masses of rapidly moving broken rock during rock avalanches sturzstroms test velocities of over 5 m s and most other parameters of the tests were found to be dimensionally similar to those for a typical rock avalanche yet the conclusion was negative even the most rapid of the experiments indicated flow behaviour which is in conformity with the constant volume uniform coulomb friction relationship as applicable to slow shearing this conclusion was confirmed independently both by direct measurements of base friction and mean density of the flows and by detailed observations of flow uniformity acceleration and velocity profiles the surprising mobility of st umlrzstroms therefore requires a different explanation une serie de tests a canaux a ete entreprise dans le

stress strain response of soft clay to traffic loading approximately 25 of china s 120 000 km of expressway as well as many new metro lines and airports rest on soft clay deposits however service settlements are proving larger than expected especially in southeast china this note describes laboratory experiments on k0 consolidated intact samples of soft clay taken near wenzhou south east china that explore whether cyclic traffic wheel loading contributes significantly to the observed settlement trends cyclic triaxial ct tests are reported together with cyclic hollow cylinder chca experiments that imposed cardioid shaped 2 z z stress paths cyclic principal stress axis rotation is shown to have an important influence on vertical straining once a certain threshold has been exceeded the resilient and permanent strains developed in the chca tests become progressively larger than their counterparts in ct tests conducted at the same vertical cyclic stress ratio with trends that diverge progressively as vertical cyclic stress ratio incr

antarctic surface melting dynamics enhanced perspectives from radar scatterometer data 1 antarctic ice sheet surface melting can regionally influence ice shelf stability mass balance and glacier dynamics in addition to modulating near surface physical and chemical properties over wide areas here we investigate variability in surface melting from 1999 to 2009 using radar backscatter time series from the seawinds scatterometer aboard the quikscat satellite these daily continent wide observations are explored in concert with in situ meteorological records to validate a threshold based melt detection method radar backscatter decreases during melting are significantly correlated with in situ positive degree days as well as meltwater production determined from energy balance modeling at neumayer station east antarctica these results support the use of scatterometer data as a diagnostic indicator of melt intensity i e the relative liquid water production during melting greater spatial and temporal melting detected relative to previous passive microwave based studies is attributed to a higher sensitivity of the scatterometer instrument continental melt intensity variability can be explained in part by the dynamics of the southern annular mode and the southern oscillation index and extreme melting events across the ross ice shelf region may be associated with el nino conditions furthermore we find that the antarctic peninsula accounts for only 20 of antarctic melt extent but greater than 50 of the total antarctic melt intensity over most areas annual melt duration and intensity are proportional however regional and localized distinctions exist where the melt intensity metric provides greater insight into melting dynamics than previously obtainable with other remote sensing techniques

static and cyclic liquefaction potential of fraser delta sand in simple shear and triaxial tests the potential for static and cyclic liquefaction of the sand that underlies the highly seismic fraser delta is assessed under simple shear test conditions typical of an earthquake shaking a comparison of liquefaction potential is also made between simple shear and conventional triaxial stress conditions it is shown that the liquefaction potential of sand is profoundly influenced by the stress path the reduction factors currently applied to the cyclic triaxial resistance for representing simple shear response may involve a large degree of conservatism in design a direct measurement of soil behaviour under stress conditions typical of earthquake loading may thus have large economic benefits key words sand liquefaction static cyclic triaxial simple shear

mountain glaciers and ice caps around antarctica make a large sea level rise contribution the intergovernmental panel on climate change ipcc estimates that the sum of all contributions to sea level rise for the period 1961 2004 was 1 1 0 5 mm a 1 leaving 0 7

undrained anisotropy and cyclic resistance of saturated silt subjected to various patterns of principal stress rotation although the undrained anisotropic behaviour of sand has been extensively studied little is known about undrained anisotropy and liquefaction susceptibility of silt soil this paper presents a sys

surface microscopic examination of quartz grains from rock avalanche basal facies the wenchuan earthquake which occurred on 12 may 2008 triggered many rock avalanches that presented abundant fractured surface textures the surface textures of the rock avalanche clasts bear abundant characteristic signatures that are significant for understanding the mechanical behavior of rock avalanche dynamic fragmentation to study this mechanism of rock avalanche basal facies further two large rock avalanches were investigated using microscopic surface texture examination of quartz grains sampled from their basal facies with a scanning electron microscope after the morphological and statistical analyses of the surface textures on the quartz grains the following features are noted i surface textures on the quartz grains are all fresh with obvious irregular shapes and very sharp edges ii the display of brittle fractures including conchoidal fractures step fractures concavities and v depressions or marks is very common iii cracks or fissures are also visible on the quartz grains t

the melt anomaly of 2002 on the greenland ice sheet from active and passive microwave satellite observations 1 active and passive microwave satellite data are used to map snowmelt extent and duration on the greenland ice sheet the passive microwave pm data reveal the extreme melt extent of 690 000 km2 in 2002 as compared with an average extent of 455 000 km2 from 1979 2003 a statistical analysis of the melt time series affirms an increased melt extent earlier in the melt season the quikscat qscat or am analysis for 1999 to 2004 confirms the extreme melt situation in 2002 qscat data show a significant increase in melt season length over several areas in 2003 ssm i and qscat melt data reveal that the later detects melt earlier and is more sensitive to surface melt qscat detects an earlier stage of melt and ssm i detects a later stage of melt the ssm i xgpr melt extent is approximately confined to the qscat melt areas experiencing 2 weeks or more of melting time

modelling channelized surface drainage of supraglacial lakes supraglacial lakes can drain to the bed of ice sheets affecting ice dynamics or over their surface relocating surface water focusing on surface drainage we first discuss observations of lake drainage in particular for the first time lakes are observed to drain 70 km across the nivlisen ice shelf east antarctica inspired by these observations we develop a model of lake drainage through a channel that incises into an ice sheet surface by frictional heat dissipated in the flow modelled lake drainage can be stable or unstable during stable drainage the rate of lake level drawdown exceeds the rate of channel incision so discharge from the lake decreases with time this can prevent the lake from emptying completely during unstable drainage discharge grows unstably with time and always empties the lake model lakes are more prone to drain unstably when the initial lake area the lake input and the channel slope are larger these parameters will vary during atmospheric warming induced ablation area expansion hence the mechanisms revealed by our analysis can influence the dynamic response of ice sheets to warming through their impact on surface water routing and storage

widespread acceleration of tidewater glaciers on the antarctic peninsula over the last half century the antarctic peninsula ap has been among the most rapidly warming regions on earth this has led to increased summer snowmelt loss of ice shelves and retreat of 87 of marine and tidewater glacier fronts tidewater glacier flow is sensitive to changes in basal water supply and to thinning of the terminus and faster flow leads directly to sea level rise the flow rates of most ap tidewater glaciers have never been measured however and hence their dynamic response to the recent changes is unknown we present repeated flow rate measurements from over 300 glaciers on the ap west coast through nine summers from 1992 to 2005 we show that the flow rate increased by similar to 12 on average and that this trend is greater than the seasonal variability in flow rate we attribute this widespread acceleration trend not to meltwater enhanced lubrication or increased snowfall but to a dynamic response to frontal thinning we estimate that as a result the annual sea level contribution from this region has increased by 0 047 0 011 mm between 1993 and 2003 this contribution together with previous studies that assessed increased runoff from the area and acceleration of glaciers resulting from the removal of ice shelves implies a combined ap contribution of 0 16 0 06 mm yr 1 this is comparable to the contribution from alaskan glaciers and combined with estimated mass loss from west antarctica is probably large enough to outweigh mass gains in east antarctica and to make the total antarctic sea level contribution positive

assessment and development of snowmelt retrieval algorithms over antarctica from k band spaceborne brightness temperature 1979 2008 abstract results from several previously published algorithms for wet snow detection in antarctica from k band spaceborne brightness temperature are compared and evaluated vs estimates of wet snow conditions from ground measurements in addition a new physically driven algorithm in which the detectable liquid water content is assumed constant is proposed and assessed all algorithms are also evaluated by analyzing their results during collapses of ice shelves two algorithms are selected for deriving updated trends of melting index mi the number of melting days times the area subject to melting between 1979 and 2008 over the whole antarctica and at sub continental scales in the first algorithm wet snow is identified when brightness temperature exceeds the mean of winter brightness temperature plus 30 k and the second is the new model based approach described here both negative and positive mi trends are obtained depending on the algorithm used a high number of melting days up to 100 days are detected over the wilkins ice shelf the peninsula and the george vi ice shelf over east antarctica the west and amery ice shelves are subject to melting for a maximum of approximately 50 days positive trends of number of melting days are detected over most of the west antarctica with peak values up to 1 2 days year over the larsen c ice shelf 1 8 days year over the george vi ice shelf and 0 55 days year over the wilkins ice shelf area the correlation between mi values and december january dj averaged air surface temperature over selected locations show values ranging between 0 8 and 0 4 results suggest that a 1 c increase in the monthly averaged dj air surface temperature corresponds to an average mi increase of approximately 2 106 km2 day

radar measurements of snow experiment and analysis this paper considers two specific types of experiments conducted to improve the authors understanding of radar backscatter from snow covered ground surfaces the first experiment involves radar backscatter measurements at cand x band of artificial snow of varying depths the relatively simple target characteristics combined with an exhaustive ground truth effort make the results of this experiment especially amenable to comparison with predictions based on theoretical methods for modeling volume scattering media it is shown that both conventional and dense medium radiative transfer models fail to adequately explain the observed results a direct polarimetric inversion approach is described by which the characteristics of the snow medium are extracted from the measured data the second type of experiment examined in this study involves diurnal backscatter measurements that were made contemporaneously with detailed measurements of the snow wetness depth profiles of the observed scene these data are used to evaluate the capability of a recently proposed algorithm for snow wetness retrieval from polarimetric synthetic aperture radar sar measurements which has hithertofore been applied only to data from very complex and extended mountainous terrains

recent loss of floating ice and the consequent sea level contribution we combine new and published satellite observations and the results of a coupled ice ocean model to provide the first estimate of changes in the quantity of ice floating in the global oceans and the consequent sea level contribution rapid losses of arctic sea ice and small antarctic ice shelves are partially offset by thickening of antarctic sea ice and large antarctic ice shelves altogether 746 127 km 3 yr 1 of floating ice was lost between 1994 and 2004 a value that exceeds considerably the reduction in grounded ice over the same period although the losses are equivalent to a small 49 8 m yr 1 rise in mean sea level there may be large regional variations in the degree of ocean freshening and mixing ice shelves at the antarctic peninsula and in the amundsen sea for example have lost 481 38 km 3 yr 1

influence of particle density on flow behavior and deposit architecture of concentrated pyroclastic density currents over a break in slope insights from laboratory experiments abstract geological granular flows are highly complex gravity driven phenomena whose different behaviors depend on the mechanical properties density and granulometric distributions of the constituent materials years of research have produced significant advances in understanding transport and deposition processes in granular flows however the role and effects of clast densities and density contrast in a granular flow are still not fully understood in this paper we show the effect that pumice has on dry granular flows specifically on flow velocity and longitudinal segregation of the deposits our work confirms by experimental results field observations on pumice lithic segregation and longer pumice runout we report results of velocity decay and deposit architecture for a granular flow passing over a break in slope from 38 to 4 inclination the 30 experimental runs were carried out in a five meter long laboratory flume equipped with a series of sensors that include laser gates and high speed cameras 400 fps we used two polydisperse mixtures of dacitic lithics and rhyolitic pumice in varying amounts with weibull and gaussian particle size distributions the pumice lithic ratio changes the flow response passing over a break in slope this effect is particularly evident starting from 10 of pumice volume into the flow mixture independently of its granulometric distribution runout relates to mass following a power law with an exponent close 0 2 the experiments confirm that pumice segregation affects polydispersed mixtures similarly to what has been observed in real field deposits where density decoupling produces lithic enriched proximal areas and pumice enriched distal areas the results obtained prove that the presence of low density materials in a dense granular flow has a strong influence on its behavior

melt season duration on canadian arctic ice caps 2000 2004 1 the extent and duration of summer melt on ice caps in the queen elizabeth islands qei nunavut canada in 2000 2004 were mapped using enhanced resolution quikscat qscat scatterometer images the mean melt duration depends mainly on surface elevation and distance from baffin bay over most ice caps inter annual variations in melt duration and the variation in melt duration with elevation are closely related to variations in the july 500 hpa height over the qei pressure related variability in the vertical gradient of near surface air temperature appears to be a major control on the inter annual variations in average melt duration

granular pressure at the base of dry flows of angular rock fragments as a function of grain size and flow volume a relationship from laboratory experiments 1 experiments are carried out by releasing angular rock fragments down a curved chute and by measuring the basal pressures that are exerted by the granular flows on the basal containing surface the substrate the purpose of these experiments is to understand the mechanisms of energy dissipation and interaction with the ground of rock avalanches and dense pyroclastic flows our data show that collisions due to particle agitation affect significantly the basal interaction of granular flows in particular our experiments reveal that particle agitation per unit of flow mass increases as grain size increases or as flow volume decreases with all the other features the same this is so because as grain size increases or as flow volume decreases with all the other features the same there are fewer particles in the flows and the agitation due to the interaction with the rough containing boundary surfaces penetrates relatively more inside the flows the analysis of the experimental data generates a linear relationship between particle agitation expressed as a dimensionless basal pressure deviation and a parameter which is directly proportional to the square of grain size and inversely proportional to the cube root of flow volume this relationship shows the intrinsic ability of the granular flows to dissipate more energy larger particle agitation per unit of flow mass or less energy smaller particle agitation per unit of flow mass as a function of flow volume and grain size

vertical segregation in granular mass flows a shear cell study 1 non fluidised dry granular mass flows are obtained with rock fragments located on a rough rotating disk in these flows that develop a quasi rigid upper layer and a basal layer of colliding particles dense clasts sink whereas light ones rise when surrounded by particles with intermediate density our experiments demonstrate that the presence of a quasi rigid upper layer in granular mass flows does not prevent vertical segregation and that the formation of coarse tail grading in pyroclastic flows does not require fluidising gases high speed videos reveal that vertical segregation in granular mass flow of rock fragments is generated by inertia differences between segregating clasts and matrix when they are both pushed upward by collisions with the basal layer coarse tail grading occurs because the average segregation velocity of smaller clasts is smaller than that of larger clasts

pumice pumice collisions and the effect of the impact angle 3 in nature particles have irregular shapes and their collisions are not necessarily normal to surfaces thus we present here the studies of oblique collisions of pumice cylinders on flat pumice surfaces cylinders were used to increase the complexity of the particle shape compared to that of a sphere the purpose of these experiments is to understand the effect of the impact angle on the rebound features and provide an example of their variability that can be useful in modelling pumice pumice collisions in geophysical flows the rebound features are the rebound angles the ratios of the components of velocities and the energy losses our results reveal a complexity which suggests that the description of pumice pumice impacts using a constant coefficient of restitution is an oversimplification 4 here we do not refer to the coefficient of restitution also because it applies to collisions where the energy losses are only due to plastic deformations and vibrations in geophysical flows the collisions are more complex because of for example erosion shattering and comminution of the rock fragments the coefficient of restitution e purports to describe the degree of plasticity in collisions of two bodies and is generally defined as the ratio of the final to initial components of the relative velocities normal to the contact surface goldsmith 2001 this coefficient can be measured by dropping a non rotating particle onto the horizontal surface of a large rigid body if the particle has been dropped from the height h1 and rebounds to the height h2 then e is equal to ffiffiffiffiffiffiffiffiffiffiffiffi

dynamics of the 2008 earthquake triggered wenjiagou creek rock avalanche qingping sichuan china abstract the wenjiagou creek rock avalanche was triggered by the 2008 wenchuan earthquake it traveled 4 6 km and left a granular deposit of 1 5 108 m3 in wenjiagou creek valley the dynamics of the rock avalanche were studied through field and laboratory investigations and remote sensing the dynamic course was divided into three segments 1 failing the original slope failed due to the huge earthquake ground accelerations acting on a rock mass weakened by severe karstification 2 falling the rock mass experienced several drops due to abrupt changes in slope and broke into granular debris during collisions with the ground and mountain flanks and 3 flow the broken granular mass flowed approximately 3 km down the valley of wenjiagou creek the transport mechanism of the granular mass of debris was studied by analyzing the structure of the deposit and through ring shear tests a gully incised into the deposit by rainfall runoff and debris flows enabled the internal structure of the deposit to be examined and sampled in cross section the exposed deposit was finest near the base and gradually became coarser towards the surface inverse grading in longitudinal section deposits near the base and on the surface both became finer with increasing travel distance near the base the granular debris experienced the maximum normal and shear stresses and fragmented into the finest grains both normal and shear stresses between the grains gradually decreased from near the base to the surface samples were sheared in a ring shear apparatus to simulate the shearing within the granular debris shear resistance between grains was found to decrease as grains became finer due to pervasive fragmentation which is one of the possible mechanisms by which the granular debris was able to travel a long distance at a high speed

melt season duration and ice layer formation on the greenland ice sheet 2000 2004 1 time series of enhanced resolution quikscat images were used to map the extent and duration of surface melt and the distribution of ice layer formation on the greenland ice sheet in the period 2000 2004 apart from the bare ice and the mixed pixels 10 along the ice sheet margin where melt cannot be determined reliably annual melt duration and melt anomaly maps were produced across the ice sheet 90 for each summer over the 5 year period the mean melt duration for the ice sheet ranged from 14 3 to 20 5 d the proportion of the ice sheet that experienced melting in a given year ranged from 44 2 to 79 2 extensive melt in 2002 was caused by a single melt event of a few days duration this event was associated with the intrusion of a ridge of high pressure from the north atlantic ocean that brought warm air onto the ice sheet the change in biweekly averaged backscatter between the freeze up periods in the current and previous falls was used to identify changes in the distribution of ice layers in snow between successive melt seasons the year 2002 had the maximum melt extent and duration and ice layer formation extended to higher elevations than in other years interannual changes in the distribution of ice layer formation may be associated with changes in surface height that are not necessarily indicative of mass balance changes mapping of ice layer formation is thus potentially useful for interpreting both real and apparent height changes measured by altimetry

evaluating titan2d mass flow model using the 1963 little tahoma peak avalanches mount rainier washington the titan2d geophysical mass flow model is evaluated by comparing its simulation results and those obtained from another flow model flow3d with published data on the 1963 little tahoma peak avalanches on mount rainier washington the avalanches totaling approximately 10 10 6 m 3 of broken lava blocks and other debris traveled 6 8 km horizontally and fell 1 8 km vertically h l 0 246 velocities calculated from runup range from 24 to 42 m s and may have been as high as 130 m s while the avalanches passed over emmons glacier titan2d is a code for an incompressible coulomb continuum it is a depth averaged dshallow watert granular flow model the conservation equations for mass and momentum are solved with a coulomb type friction term at the basal interface the governing equations are solved on multiple processors using a parallel adaptive mesh godunov scheme adaptive gridding dynamically concentrates computing power in regions of special interest mesh refinement and coarsening key on the perimeter of the moving avalanche the model flow initiates as a pile defined as an ellipsoid by a height z and an elliptical base defined by radii in the x and y planes flow parameters are the internal friction angle and bed friction angle results from the model are similar in terms of velocity history lateral spreading location of runup areas and final distribution of the little tahoma peak deposit the avalanches passed over the emmons glacier along their upper flow paths but lower in the valley they traversed stream gravels and glacial outwash deposits this presents difficulty in assigning an appropriate bed friction angle for the entire deposit incorporation of variable bed friction angles into the model using gis will help to resolve this issue d 2004 elsevier b v all rights reserved

semi empirical model for radar backscatter from snow at 35 and 95 ghz radar backscatter experiments were conducted at 35 and 95 ghz to measure the response of snow covered ground to snow depth liquid water content and ice crystal size the measurements included observations over a wide angular range extending between normal incidence and 60 spl deg for all linear polarization combinations a numerical radiative transfer model was developed and adapted to fit the experimental observations next the radiative transfer model was exercised over a wide range of conditions and the generated data were used to develop relatively simple semi empirical expressions that relate the backscattering coefficient for each linear polarization to incidence angle snow depth crystal size and liquid water content

melting of small arctic ice caps observed from ers scatterometer time series 1 time series of active microwave backscatter data from the ers wind scatterometers are used to demonstrate 1 the timing of melt onset can be observed over small ice caps as well as the major ice sheets and multi year sea ice and 2 temporally integrated backscatter reduction r is strongly correlated with total annual positive degree days pdd as measured at four automated weather stations on the surface of the greenland ice sheet the latter is particularly interesting because unlike melt onset r is a measure of melt processes integrated over an entire ablation season both methods work owing to the well known sharp decrease in radar backscatter triggered by the appearance of liquid water in a glacier snowpack melt onset and r are determined for 14 small arctic ice caps from 1992 2000 interannual and regional variability in the timing of melt onset are comparable averaging 33 9 and 38 13 days respectively regional variability in r exceeds interannual variability averaging 906 164 and 309 130 db d respectively the brevity of the derived nine year records limits their statistical testing for trend however their qualitative interpretation suggests that the timing of melt onset is more variable for arctic ice caps than for sea ice and the intensity of summer surface melting increased by about 20 in the 1990s

liquefaction and flow failure during earthquakes two aspects of seismically induced liquefaction are discussed which are of vital engineering significance the triggering condition and the consequences of liquefaction the triggering condition is examined with respect to liquefaction analysis note being taken of the onset condition which is governed by cyclic strength consequences of liquefaction are discussed with respect to post seismic stability analysis in which the residual strength plays a major role procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced and the applicability of this method for estimating associated ground settlements is discussed the evaluation of residual strength requires a better understanding of undrained sand behaviour results of extensive laboratory rests on japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better the results of laboratory tests on silty sands are examined in the same way ah the results are

a benchmark dataset of in situ antarctic surface melt rates and energy balance abstract surface melt on the coastal antarctic ice sheet ais determines the viability of its ice shelves and the stability of the grounded ice sheet but very few in situ melt rate estimates exist to date here we present a benchmark dataset of in situ surface melt rates and energy balance from nine sites in the eastern antarctic peninsula ap and coastal dronning maud land dml east antarctica seven of which are located on ais ice shelves meteorological time series from eight automatic and one staffed weather station neumayer ranging in length from 15 months to almost 24 years serve as input for an energy balance model to obtain consistent surface melt rates and energy balance results we find that surface melt rates exhibit large temporal spatial and process variability intermittent summer melt in coastal dml is primarily driven by absorption of shortwave radiation while non summer melt events in the eastern ap occur during fohn events that force a large downward directed turbulent flux of sensible heat we use the in situ surface melt rate dataset to evaluate melt rates from the regional atmospheric climate model racmo2 and validate a melt product from the quikscat satellite

the link between climate warming and break up of ice shelves in the antarctic peninsula a review of in situ and remote sensing data covering the ice shelves of the antarctic peninsula provides a series of characteristics closely associated with rapid shelf retreat deeply embayed ice fronts calving of myriad small elongate bergs in punctuated events increasing flow speed and the presence of melt ponds on the ice shelf surface in the vicinity of the break ups as climate has warmed in the antarctic peninsula region melt season duration and the extent of ponding have increased most break up events have occurred during longer melt seasons suggesting that meltwater itself not just warming is responsible regions that show melting without pond formation are relatively unchanged melt ponds thus appear to be a robust harbinger of ice shelf retreat we use these observations to guide a model of ice shelf flow and the effects of meltwater crevasses present in a region of surface ponding will likely fill to the brim with water we hypothesize building on weertman 1973 hughes 1983 and van der veen 1998 that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat a thermodynamic finite element model is used to evaluate ice flow and the strain field and simple extensions of this model are used to investigate crack propagation by meltwater the model results support the hypothesis