volume loss from antarctic ice shelves is accelerating the floating ice shelves surrounding the antarctic ice sheet restrain the grounded ice sheet flow thinning of an ice shelf reduces this effect leading to an increase in ice discharge to the ocean using 18 years of continuous satellite radar altimeter observations we have computed decadal scale changes in ice shelf thickness around the antarctic continent overall average ice shelf volume change accelerated from negligible loss at 25 64 cubic kilometers per year for 1994 2003 to rapid loss of 310 74 cubic kilometers per year for 2003 2012 west antarctic losses increased by 70 in the past decade and earlier volume gain by east antarctic ice shelves ceased in the amundsen and bellingshausen regions some ice shelves have lost up to 18 of their thickness in less than two decades

rock fall hazard assessment in asar hill ancient mabolla city mugla sw turkey this paper discusses the potential rock fall hazard of asar hill this flat topped hill containing upper miocene conglomerate and finer grained sedimentary rocks hosts to the ancient mabolla city the seasonal temperature differences are high in this rainy region block sizes bed and joints attitudes were measured along three profiles during field study schmidt hammer was applied to grains and matrix of conglomerates for determining strength in situ one joint set in profile a 3 in profile b and 4 in profile c were determined via dips analysis an intersection of joints and bedding directed 25 35 nw caused the block formation control slope angle and mass movement type at least 10 blocks 0 6 1241 085 tons were fixed on top of profiles two blocks on top of the eastern profile a contain archaeological ruins after back analysis for determining restitution coefficients rocfall version 4 9 software program was used to determine possible end points of those blocks most of the blocks can reach the valley and pass the other side which includes settlements and gardens consequently the possible rock fall hazard in asar hill is threatening visitors and settlers the cleaning of detached blocks on top of slope is one of the easiest ways however in situ preservation of blocks with archaeological ruins via tensioned rock anchors and or patterned rock bolts has vital importance relocation of settlers and gardens opening trench around hill and establishing green belt forest would be considered as other measures

ice shelf melt response to changing winds and glacier dynamics in the amundsen sea sector antarctica it has been suggested that the coastal southern ocean subsurface may warm over the 21st century in response to strengthening and poleward shifting winds with potential adverse effects on west antarctic glaciers however using a 1 128 ocean regional model that includes ice shelf cavities we find a more complex response to changing winds in the amundsen sea simulated offshore subsurface waters get colder under strengthened and poleward shifted winds representative of the sam projected trend the buoyancy driven circulation induced by ice shelf melt transports this cold offshore anomaly onto the continental shelf leading to cooling and decreased melt below 450 m in the vicinity of ice shelf fronts ekman pumping contributes to raise the isotherms in response to changing winds this effect overwhelms the horizontal transport of colder offshore waters at intermediate depths between 200 and 450 m and therefore increases melt rates in the upper part of the ice shelf cavities which reinforces the buoyancydriven circulation and further contributes to raise the isotherms then prescribing an extreme grounding line retreat projected for 2100 the total melt rates simulated underneath thwaites and pine island are multiplied by 2 5 such increase is explained by a larger ocean ice interface exposed to cdw which is then amplified by a stronger melt induced circulation along the ice draft our main conclusions are that 1 outputs from ocean models that do not represent ice shelf cavities e g cmip5 models should not be directly used to predict the thermal forcing of future ice shelf cavities 2 coupled ocean ice sheet models with a velocity dependent melt formulation are needed for future projections of glaciers experiencing a significant grounding line retreat

eddy transport as a key component of the antarctic overturning circulation the exchange of water masses across the antarctic continental shelf break regulates the export of dense shelf waters to depth as well as the transport of warm mid depth waters towards ice shelves and glacial grounding lines the penetration of the warmer mid depth waters past the shelf break has been implicated in the pronounced loss of ice shelf mass over much of west antarctica in high resolution regional circulation models the antarctic shelf break hosts an energetic mesoscale eddy field but observations that capture this mesoscale variability have been limited here we show using hydrographic data collected from ocean gliders that eddy induced transport is a primary contributor to mass and property fluxes across the slope measurements along ten cross shelf hydrographic sections show a complex velocity structure and a stratification consistent with an onshore eddy mass flux we show that the eddy transport and the surface wind driven transport make comparable contributions to the total overturning circulation eddy induced transport is concentrated in the warm intermediate layers away from frictional boundaries we conclude that understanding mesoscale dynamics will be critical for constraining circumpolar heat fluxes and future rates of retreat of antarctic ice shelves

an analytical solution for analysis of toppling slumping failure in rock slopes abstract when a slope consists of a horizontal weak rock or soil overlaid by some vertical strong slender rock columns the slope is prone to a secondary toppling failure which is known as toppling slumping failure in the slope rock columns impose pressure on the lower continuous weak rock or soil mass which leads to a differential settlement at the base of each rock column or a circular shear failure in the continuous mass if the differential settlements reach a special threshold rock column overturn and toppling slumping will happen however the circular shear failure of the soil or weak rock mass which is a well recognized failure mechanism will occur when shear stress in the slope exceeds its shear strength in this paper an attempt has been made to better understanding of the toppling slumping failure mechanism through developing an analytical solution for this purpose first an airy stress function is acquired for the lower continuous soil mass and its stress distribution and displacement are accordingly determined analytically due to the overlaid rock columns loads then differential settlements at the base of all rock columns and shear stresses in the soil or weak rock mass are computed and compared with the toppling and shear failure criteria to assess slope failure finally several design charts are developed that determine the stability of a slope against toppling slumping failure mechanism based on geometric characteristics of the slope and shear strength of its constituent material also a mathematica package code was developed to evaluate the stress distribution within the slope and the safety factor the results show that the vertical stress distribution plays a significant role in the settlement of the rock columns results also manifested that at a certain distance from the slope crest the set of rock columns will act like a single column on a half plane the shear or toppling failure of the slope not only depends on the material s strength but also on the geometry and the normalized column distance

variability of the antarctic slope current system in the northwestern weddell sea the dense water outflow from the antarctic continental shelf is closely associated with the strength and position of the antarctic slope front this study explores the short term and spatial variability of the antarctic slope front system and the mechanisms that regulate cross slope exchange using highly temporally and spatially resolved measurements from three ocean gliders deployed in 2012 the 22 sections along the eastern antarctic peninsula and west of the south orkney islands are grouped regionally and composited by isobaths there is consistency in the front position around the powell basin varying mostly between the 500 and 800 m isobaths in most of the study area the flow is bottom intensified the along slope transport of the antarctic slope current upper 1000 m varies between 0 2 and 5 9 sv 1 sv 10 6 m 3 s 1 and does not exhibit a regional pattern the magnitude of the velocity field shows substantial variability up to twice its mean value higher eddy kinetic energy 0 003 m 2 s 2 is observed in sections with dense water possibly because of baroclinic instabilities in the bottom layer distributions of potential vorticity show an increase toward the shelf along isopycnals and also in the dense water layer glider sections located west of the south orkney islands indicate a northward direction of the flow associated with the weddell front which differs from previous estimates of the mean circulation this study provides some of the first observational confirmation of the high frequency variability associated with an active eddy field that has been suggested by recent numerical simulations in this region

a first description of the antarctic peninsula coastal current abstract we present hydrographic and shipboard adcp data collected during the fall april june and winter july august and moored velocity observations collected from 2001 to early 2002 on the west antarctic peninsula wap shelf during the southern ocean global ecosystems dynamics so globec program in fall a geostrophically balanced buoyant current flows southward along the coast this antarctic peninsula coastal current apcc forms during the ice free season and extends from adelaide island to alexander island although its path inside marguerite bay is uncertain during the fall of 2001 the apcc had a volume transport of 0 32 0 13 sv and a freshwater transport relative to a reference salinity of 34 4 of 126 50 km 3 yr 1 from early july to late october the apcc disappears from the coast as the freshwater input from the coast diminishes and sea ice forms on the shelf an examination of the relative sizes of the freshwater sources suggests runoff from land and precipitation over the ocean are the primary sources for the apcc

strength of jointed rock masses jointed rock masses comprise interlocking angular par ticles or blocks of hard brittle material separated by discontinuity surfaces which may or may not be coated with weaker materials the strength of such rock masses depends on the strength of the intact pieces and on their freedom of movement which in turn depends on the number orientation spacing and shear strength of the discontinuities a complete understanding of this problem presents formidable theoretical and experi mental problems and hence simplifying assumptions are required in order to provide a reasonable basis for estimating the strength of jointed rock masses for engineering design purposes this paper summarizes some of the basic information upon which such simplifying assumptions can be made a simple empirical failure criterion is presented and its application in engineering design is illustrated by means of a number of practical examples des masses jointives de rochers comprennent des particules angulaires enchevetrees ou des

impact of local winter cooling on the melt of pine island glacier antarctica the rapid thinning of the ice shelves in the amundsen sea is generally attributed to basal melt driven by warm water originating from the continental slope we examine the hypothesis that processes taking place on the continental shelf contribute significantly to the interannual variability of the ocean heat content and ice shelf melt rates a numerical model is used to simulate the circulation of ocean heat and the melt of the ice shelves over the period 2006 2013 the fine model grid grid spacing 1 5 km explicitly resolves the coastal polynyas and mesoscale processes the ocean heat content of the eastern continental shelf exhibits recurrent decreases around september with a magnitude that varies from year to year the heat loss is primarily caused by surface heat fluxes along the eastern shore in areas of low ice concentration polynyas the cold winter water intrudes underneath the ice shelves and reduces the basal melt rates ocean temperatures upstream i e at the shelf break are largely constant over the year and cannot account for the cold events the cooling is particularly marked in 2012 and its effect on the ocean heat content remains visible over the following years the study suggests that ocean atmosphere interactions in coastal polynyas contribute to the interannual variability of the melt of pine island glacier

ocean forcing of glacier retreat in the western antarctic peninsula in recent decades hundreds of glaciers draining the antarctic peninsula 63 to 70 s have undergone systematic and progressive change these changes are widely attributed to rapid increases in regional surface air temperature but it is now clear that this cannot be the sole driver here we identify a strong correspondence between mid depth ocean temperatures and glacier front changes along the 1000 kilometer western coastline in the south glaciers that terminate in warm circumpolar deep water have undergone considerable retreat whereas those in the far northwest which terminate in cooler waters have not furthermore a mid ocean warming since the 1990s in the south is coincident with widespread acceleration of glacier retreat we conclude that changes in ocean induced melting are the primary cause of retreat for glaciers in this region

ice and ocean processes in the bellingshausen sea antarctica 1 in the vicinity of the antarctic peninsula observations show diminishing sea ice and a rapid warming of atmosphere and ocean these changes have led to the collapse of ice shelves and retreat acceleration and thinning of inland ice however ocean observations in the center of the nearby bellingshausen sea are spatially and temporally coarse in this study ocean and sea ice models forced by atmospheric reanalyses are used to investigate this data gap by simulating processes in the bellingshausen sea for the years 1979 2007 the model suggests flow features in the region and predicts the basal melting of local ice shelves modeled ocean conditions are found to be less variable than in the nearby amundsen sea which is situated closer to foci of annual and interannual atmospheric variability melt rates beneath george vi ice shelf are investigated in detail concluding that the ice shelf may have been melting out of balance and therefore thinning for decades the melt rate contains significant interannual variability that the model links to variation in sea ice conditions offshore of the southern end of the ice shelf this stands in contrast to the amundsen sea where models suggest that ice shelf melting is controlled by variable transport of circumpolar deep water onto the continental shelf

on the characteristics of circumpolar deep water intrusions to the west antarctic peninsula continental shelf 1 hydrographic and current velocity observations collected from march 2001 to february 2003 on the west antarctic peninsula shelf as part of the southern ocean global ecosystems dynamics program are used to characterize intrusions of upper circumpolar deep water ucdw and lower circumpolar deep water lcdw onto the shelf and marguerite bay ucdw is found on the middle and outer shelf along marguerite trough which connects the shelf break to marguerite bay and at another location farther south ucdw intrudes in the form of frequent four per month and small horizontal scales 4 km warm eddy like structures with maximum vertical scales of a few hundred meters however no evidence of ucdw intrusions was found in marguerite bay lcdw was found in several deep depressions connected to the shelf break including marguerite trough forming a tongue of relatively dense water 95 m thick on average that reaches into marguerite bay through marguerite trough a steady advective diffusive balance for the lcdw intrusion is used to make an estimation of the average upwelling rate and diffusivity in the deep layer within marguerite trough which suggest the lcdw layer is renewed approximately every six weeks

oceanic heat transport onto the amundsen sea shelf through a submarine glacial trough glaciers which drain the west antarctic ice sheet wais into the amundsen sea are accelerating and thinning rapidly these observations have been attributed to the regional oceanography whereby heat contained within circumpolar deep water cdw drives the basal melting of floating glaciers on the basis of new data we calculate that 2 8 terra watts 1012 of oceanic heat flow onto the continental shelf and toward the glaciers via a submarine glacial trough this is enough to account for most of the basal melting in the entire region suggesting the ocean is supplying an excess of heat toward the antarctic continent

circulation and meltwater distribution in the bellingshausen sea from shelf break to coast west antarctic ice shelves have thinned dramatically over recent decades oceanographic measurements that explore connections between offshore warming and transport across a continental shelf with variable bathymetry toward ice shelves are needed to constrain future changes in melt rates six years of seal acquired observations provide extensive hydrographic coverage in the bellingshausen sea where ship based measurements are scarce warm but modified circumpolar deep water floods the shelf and establishes a cyclonic circulation within the belgica trough with flow extending toward the coast along the eastern boundaries and returning to the shelf break along western boundaries these boundary currents are the primary water mass pathways that carry heat toward the coast and advect ice shelf meltwater offshore the modified circumpolar deep water and meltwater mixtures shoal and thin as they approach the continental slope before flowing westward at the shelf break suggesting the presence of the antarctic slope current constraining meltwater pathways is a key step in monitoring the stability of the west antarctic ice sheet

fault displacement accumulation and slip rate variability within the taupo rift new zealand based on trench and 3 d ground penetrating radar data 1 in offshore regions studies based on densely spaced reflection seismic data tied to stratigraphic logs demonstrate that active faults can have variable displacement rates over relatively short distances and short time intervals here we demonstrate how high resolution 3 d ground penetrating gpr data tied to trench derived stratigraphic logs provide similar information for active faults in onshore regions to investigate recent 24 4 ka fault activity within the taupo rift of new zealand we analyze 3 d gpr data acquired over 10 fault strands within the maleme fault zone after correlating three prominent gpr reflection horizons with three faulted chronostratigraphic units observed within a trench we extrapolate the geometries of the horizons over a 150 250 m area of the fault zone and determine slip accumulation patterns and rates profiles of cumulative fault displacement measured for horizons older than 12 5 ka exhibit characteristic displacement distributions by calculating average cumulative displacements with time for five practically complete fault strands we obtain robust slip rate estimates slip rates are variable for time intervals 12 5 ka long suggesting that at least four earthquakes are required for these faults to exhibit uniform slip rates characteristic of their long term behavior

circulation and melting beneath george vi ice shelf antarctica introduction george vi ice shelf sandwiched between the western coast of palmer land and the eastern coast of alexander island is the largest and most studied of the west antarctic peninsula ice shelves it covers an area of approximately 25 000 km2 and is underlain by circumpolar deep water cdw with temperatures in excess of 1oc giving rise to rapid basal melting bishop and walton 1981 lennon et al 1982 the maximum ice thickness of about 500 m occurs about 70 km from the southern ice front where a ridge of thick ice extends across george vi sound near 70ow see figure 1 effectively dividing the upper water column into northern and southern regions the northern ice front which faces marguerite bay appears to be near the geographical limit of ice shelf viability and has undergone a gradual retreat in recent decades lucchitta and rosanova 1998 a timeframe over which much of the nearby wordie ice shelf disintegrated doake and vaughan 1991 there is extensive surface melting over the northern parts of the ice shelf and much of the ice column near the northern ice front appears to be temperate paren and cooper 1986 conditions in the south where the ice front faces into ronne entrance are colder and the ice front position appears to be steady the vast majority of the flow into the ice shelf comes from palmer land but basal melting is sufficient to remove most of this so that the ice is derived almost exclusively from local accumulation by the time it reaches the ice fronts potter et al 1984 there is some evidence at the margins of the ice shelf to suggest that it may have disappeared completely during the early holocene before reforming sugden and clapperton 1981 bentley et al 2005

role of tides on the formation of the antarctic slope front at the weddell scotia confluence the structure of the antarctic slope front asf and the associated antarctic slope current asc on the scotia sea side of the weddell scotia confluence wsc is described using data from a hydrographic survey and three 1 year long moorings across the continental slope the asc in this region flows westward along isobaths with an annual mean speed of 0 2 m s 1 with time variability dominated by the k1 and o1 tidal diurnal constituents a narrowband oscillation with 2 week period attributable to the spring neap tidal cycle and seasonal variability realistic and idealized high resolution numerical simulations are used to determine the contribution of tides to the structure of the asf and the speed of the asc two simulations forced by realistic atmospheric forcing and boundary conditions integrated with and without tidal forcing show that tidal forcing is essential to reproduce the measured asf asc cross slope structure the time variability at our moorings and the reduced stratification within the wsc two idealized simulations run with tide only forcing one with a homogeneous ocean and the other with initial vertical stratification that is laterally homogeneous show that tides can generate the asc and asf through volume flux convergence along the slope initiated by effects including the lagrangian component of tidal rectification and mixing at the seabed and in the stratified ocean interior climate models that exclude the effects of tides will not correctly represent the asf and asc or their influence on the injection of intermediate and dense waters from the wsc to the deep ocean

a method for the study of crack propagation in rock structures a method is presented for analysing the stability of rock structures based on the propagation of geological discontinuities discontinuities are modelled as flat cracks and their propagation is analysed using fracture mechanics methods as rock structures are brittle these phenomena can be studied using linear elastic fracture mechanics lefm problems in the application of lefm methods are analysed with regard to the states of compressive stress present in rock a numerical procedure is described which simulates the propagation of natural discontinuities in rock the crack propagation trajectories determined from this analysis are compared with experimental results obtained on mortar specimens the applicability of the method to the study of rock mass stability is shown with reference to the behaviour of rock slopes l article presente une methode permettant d analyser la stabilite de structures rocheuses cette methode est fondeve sur petude de la propagation de discontinuites geologiques ces discon

amundsen and bellingshausen seas simulation with optimized ocean sea ice and thermodynamic ice shelf model parameters recent studies suggest that the thickness of winter water ww that is water with potential temperature below 1 c located below antarctic surface water and above circumpolar deep water cdw is critical in determining the ice shelf melt rate especially for the pine island glacier pig existing model studies however misrepresent ww thickness and properties in the amundsen sea as here we adjust a small number of model parameters in a regional amundsen and bellingshausen seas configuration of the massachusetts institute of technology general circulation model in order to reproduce properties and thickness of ww and cdw close to observations with significant improvement for ww compared to previous studies the cost which is defined as weighted model data difference squared is reduced by 23 although a previous modeling study points out that the local surface heat loss upstream from pine island polynya could be the reason for the observed 2012 pig melt decline and ww thickening they did not show ww freshening which was observed at the same time model sensitivity experiments for surface heat loss pig melt rate and precipitation fail to replicate ww freshening concurrent with pig melt decline implying that these processes can not fully explain the observed pig melt decrease

modeling the spreading of glacial meltwater from the amundsen and bellingshausen seas it has been suggested that an increased melting of continental ice in the amundsen sea as and bellingshausen sea bs is a likely source of the observed freshening of ross sea rs water to test this hypothesis we simulate the spreading of glacial meltwater using the finite element sea ice ice shelf ocean model based on the spatial distribution of simulated passive tracers most of the basal meltwater from as ice shelves flows toward the rs with more than half of the melt originating from the getz ice shelf further the model results show that a slight increase of the basal mass loss can substantially intensify the transport of meltwater into the rs due to a strengthening of the melt driven shelf circulation and the westward flowing coastal current this supports the idea that the basal melting of as and bs ice shelves is one of the main sources for the rs freshening

a new tide model for the antarctic ice shelves and seas we describe a new tide model for the seas surrounding antarctica including the ocean cavities under the floating ice shelves the model uses data assimilation to improve its fit to available data typical peak to peak tide ranges on ice shelves are 1 2 m but can exceed 3 m for the filchner ronne and larsen ice shelves in the weddell sea spring tidal ranges are about twice these values model performance is judged relative to the 5 10 cm accuracy that is needed to fully utilize ice shelf height data that will be collected with the geoscience laser altimeter system scheduled to be launched on the ice cloud and land elevation satellite in late 2002 the model does not yet achieve this level of accuracy except very near the few high quality tidal records that have been assimilated into the model some improvement in predictive skill is expected from increased sophistication of model physics but we also require better definition of ice shelf grounding lines and more accurate water column thickness data in shelf seas and under the ice shelves long duration tide measurements bottom pressure gauge or gps in critical data sparse areas particularly near and on the filchner ronne and ross ice shelves and pine island bay are required to improve the performance of the data assimilation model

shelf ocean exchange and hydrography west of the antarctic peninsula a review the west antarctic peninsula wap is a highly productive marine ecosystem where extended periods of change have been observed in the form of glacier retreat reduction of sea ice cover and shifts

dynamic response of the chamousset rock column western alps france 1 this paper investigates the variation of the first resonance frequency of the chamousset limestone column 21 000 m3 vercors french alps before its collapse in november 2007 the site was instrumented with seismometers and extensometers during a 4 month period with some gaps in the measurements experimental results and numerical modeling showed that the resonance frequency of a prone to fall column can be derived from the spectra of continuous seismic noise records at the chamousset site the evolution of the resonance frequency appeared to be strongly controlled by the temperature when temperatures were positive slight resonance frequency variations correlated well with thermal fluctuations irreversible damage can occur during freeze thaw cycles and to a lesser extent during strong wind it coincided with a significant drop in resonance frequency which was interpreted as the result of rock bridge breakage this hypothesis is supported by fresh rupture observations after the collapse seismic event records and numerical modeling this study suggests that seismic noise recording could be used for assessing the potential failure of unstable columns in rigid rocks

circum antarctic shoreward heat transport derived from an eddy and tide resolving simulation almost all heat reaching the bases of antarctica s ice shelves originates from warm circumpolar deep water in the open southern ocean this study quantifies the roles of mean and transient flows in transporting heat across almost the entire antarctic continental slope and shelf using an ocean sea ice model run at eddy and tide resolving 1 48 horizontal resolution heat transfer by transient flows is approximately attributed to eddies and tides via a decomposition into time scales shorter than and longer than 1 day respectively it is shown that eddies transfer heat across the continental slope ocean depths greater than 1 500 m but tides produce a stronger shoreward heat flux across the shelf break ocean depths between 500 m and 1 000 m however the tidal heat fluxes are approximately compensated by mean flows leaving the eddy heat flux to balance the net shoreward heat transport the eddy driven cross slope overturning circulation is too weak to account for the eddy heat flux this suggests that isopycnal eddy stirring is the principal mechanism of shoreward heat transport around antarctica though likely modulated by tides and surface forcing

multiconfiguration gpr measurements for geometric fracture characterization in limestone cliffs alps rock mass fracturing is a key parameter in rock fall hazard assessment however traditional geologic observations can provide information only about discontinuities at the surface in this case study detailed ground penetrating radar gpr measurements with antennas of 50 mhz 100 mhz 200 mhz and 400 mhz were conducted on a test site using different acquisition configurations deployed on vertical cliff faces conventional 2d profile data common midpoint cmp survey data and transmission data were acquired to evaluate the potential use of radar waves to characterize the geometry and properties of the major discontinuities fractures within a mesozoic limestone massif results showed that the continuity and geometry orientation and dip of the major observed fractures which are crucial parameters for assessing rock stability can be obtained by combining vertical and horizontal profiles measured along the cliff we used 100 mhz antennae and reached a maximum penetration of 20 m which limi

oceanographic observations at the shelf break of the amundsen sea antarctica the part of the west antarctic ice sheet that drains into the amundsen sea is currently thinning at such a rate that it contributes nearly 10 of the observed rise in global mean sea level acceleration of the outlet glaciers appears to be caused by thinning at their downstream ends where the ice goes afloat indicating that the changes are probably being forced from the ocean observations made since the mid 1990s on the amundsen sea continental shelf have revealed that the deep troughs carved by previous glacial advances are flooded by almost unmodified circumpolar deep water cdw with temperatures around 3 4 c above the freezing point and that this water mass drives rapid melting of the floating ice here we report observations of water properties and currents made in the region where one of those troughs reaches the continental shelf edge we estimate the absolute circulation within the trough from a combination of detided acoustic doppler current profiler data and geostrophic shear derived from conductivity temperature depth sections the shelf edge region is characterised by a landward deepening of the pycnocline separating cdw from the overlying colder and fresher surface waters this feature the so called antarctic slope front asf is almost circumpolar in extent and is typically a full depth feature the pycnocline intersecting the seabed over the upper continental slope however the asf is weaker in the amundsen sea where it is rarely a full depth feature geostrophic shear associated with the asf leads to a weakening of the associated westward current with depth and an eastward undercurrent of varying strength has been reported at other locations at the time of our amundsen sea observations the westward surface flow was weak giving rise to a strong eastward undercurrent flowing along the continental shelf edge and upper slope at the upstream western side of the trough the undercurrent turns south driving a net on shelf flow of cdw in the western part of the trough and leaving a weakened shelf edge flow that re establishes itself on the downstream eastern side of the trough an analogous feature was captured albeit crudely in an earlier coarse resolution model of the circulation on the amundsen sea shelf and variability in its strength associated with variability in the surface wind stress was the main cause of variations in the heat content of the waters on the inner continental shelf our observations thus lend support to the earlier hypothesis that changes in atmospheric forcing over the continental shelf edge could be the ultimate driver of changes in the west antarctic ice sheet outlet glaciers that drain into the amundsen sea

genesis of the antarctic slope current in west antarctica the stability of the west antarctic ice sheet wais depends on ocean heat transport toward its base and remains a source of uncertainty in sea level rise prediction the antarctic slope current asc a major boundary current of the ocean s global circulation serves as a dynamic gateway for heat transport toward antarctica here we use observations collected from the bellingshausen sea to propose a mechanistic explanation for the initiation of the westward flowing asc waters modified throughout the bellingshausen sea by ocean sea ice and ocean ice shelf interactions are exported to the continental slope in a narrow topographically steered western boundary current this focused outflow produces a localized front at the shelf break that supports the emerging asc this mechanism emphasizes the importance of buoyancy forcing integrated over the continental shelf as opposed to local wind forcing in the generation mechanism and suggests the potential for remote control of melt rates of wais largest ice shelves

mapping of sea ice production for antarctic coastal polynyas 1 active sea ice production in antarctic coastal polynyas causes dense water formation finally leading to antarctic bottom water aabw formation this study gives the first mapping of sea ice production in the antarctic ocean based on heat flux calculation with ice thickness data derived from satellite data the highest ice production occurs in the ross ice shelf polynya region the ice production there decreased by 30 from the 1990s to the 2000s which can be one candidate for causing the recent freshening of aabw the cape darnley polynya in east antarctica is found to be the second highest production area suggesting a possible aabw formation area according to our estimation around 10 of southern ocean sea ice is produced in the major antarctic coastal polynyas the mapping provides surface heat and salt flux conditions in the ice covered region which have not been well understood

multidecadal warming of antarctic waters decadal trends in the properties of seawater adjacent to antarctica are poorly known and the mechanisms responsible for such changes are uncertain antarctic ice sheet mass loss is largely driven by ice shelf basal melt which is influenced by ocean ice interactions and has been correlated with antarctic continental shelf bottom water asbw temperature we document the spatial distribution of long term large scale trends in temperature salinity and core depth over the antarctic continental shelf and slope warming at the seabed in the bellingshausen and amundsen seas is linked to increased heat content and to a shoaling of the mid depth temperature maximum over the continental slope allowing warmer saltier water greater access to the shelf in recent years regions of asbw warming are those exhibiting increased ice shelf melt

eddy mediated transport of warm circumpolar deep water across the antarctic shelf break the antarctic slope front asf modulates ventilation of the abyssal ocean via the export of dense antarctic bottom water aabw and constrains shoreward transport of warm circumpolar deep water cdw toward marine terminating glaciers along certain stretches of the continental shelf particularly where aabw is exported density surfaces connect the shelf waters to the middepth circumpolar deep water offshore offering a pathway for mesoscale eddies to transport cdw directly onto the continental shelf using an eddy resolving process model of the asf the authors show that mesoscale eddies can supply a dynamically significant transport of heat and mass across the continental shelf break the shoreward transport of surface waters is purely wind driven while the shoreward cdw transport is entirely due to mesoscale eddy transfer the cdw flux is sensitive to all aspects of the model s surface forcing and geometry suggesting that shoreward eddy heat transport may be localized to favorable sections of the continental slope

rapid subsurface warming and circulation changes of antarctic coastal waters by poleward shifting winds the southern hemisphere westerly winds have been strengthening and shifting poleward since the 1950s this wind trend is projected to persist under continued anthropogenic forcing but the impact of the changing winds on antarctic coastal heat distribution remains poorly understood here we show that a poleward wind shift at the latitudes of the antarctic peninsula can produce an intense warming of subsurface coastal waters that exceeds 2 c at 200 700 m depth the model simulated warming results from a rapid advective heat flux induced by weakened near shore ekman pumping and is associated with weakened coastal currents this analysis shows that anthropogenically induced wind changes can dramatically increase the temperature of ocean water at ice sheet grounding lines and at the base of floating ice shelves around antarctica with potentially significant ramifications for global sea level rise

antarctic ice sheet loss driven by basal melting of ice shelves accurate prediction of global sea level rise requires that we understand the cause of recent widespread and intensifying glacier acceleration along antarctic ice sheet coastal margins atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves potentially limiting their ability to buttress the flow of grounded tributary glaciers indeed recent ice shelf collapse led to retreat and acceleration of several glaciers on the antarctic peninsula but the extent and magnitude of ice shelf thickness change the underlying causes of such change and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum antarctic pattern of ice shelf thinning through increased basal melt we deduce that this increased melt is the primary control of antarctic ice sheet loss through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow the highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of antarctic ice shelves through ocean upwelling in the amundsen and bellingshausen seas and atmospheric warming on the antarctic peninsula this implies that climate forcing through changing winds influences antarctic ice sheet mass balance and hence global sea level on annual to decadal timescales

failure mechanisms and triggering factors in calcareous cliffs of the subalpine ranges french alps in order to enhance the detection of prospective rock falls in calcareous cliffs 25 rock falls have been described in a more detailed way than for an inventory they are representative of middle size rock falls 10 to 100 000 m3 occurring in the french subalpine ranges at an elevation between 200 m and 2 000 m structural conditions of the rock masses morphology of the initial cliff surface and the scar possible failure mechanisms and processes have been studied typical failure configurations have been identified based on the attitude of the failure surface in relation to the bedding planes and the cliff surface irregular cliff morphology appears to be another important susceptibility factor in most cases the classical comparison of the average planes of the main joint sets with the average plane of the slope could not define the potentially unstable masses rather those ones are due to joint planes that deviate from their mean set plane or to irregularities of the cliff surface the proposed investigation method to detect prospective rock falls mainly consists in observing stereoscopic aerial photographs in order to look for critical configurations once a critical mass has been detected its failure probability for a period of the order of one century must be evaluated or its life expectancy the main factor to consider for this purpose appears to be the proportion of rock bridges in the potential failure surface the triggering factors of rock falls in our study area have been investigated by analysing an inventory of 46 rock falls statistical tests have been carried out to study the relation between rock falls and daily rainfall freeze thaw cycles or earthquakes a good correlation has been obtained with freeze thaw cycles a slight correlation with rainfall and no correlation with earthquakes this suggests that ice jacking could the main physical process leading to failure by causing microcrack propagation

direct observations of the antarctic slope current transport at 113 e the antarctic slope current asc defined here as the region of westward flow along the continental slope off antarctica forms the southern limb of the subpolar gyres it regulates the exchange of water across the shelf break and provides a path for interbasin westward transport despite its significance the asc remains largely unobserved around most of the antarctic continent here we present direct velocity observations from a 17 month current meter moored array deployed across the continental slope between the 1000 and the 4200 m isobaths in the southeastern indian ocean near 113 e the observed time mean flow consists of a surface intensified jet associated with the antarctic slope front asf and a broader bottom intensified westward flow that extends out to approximately the 4000 m isobath and is strongest along the upper slope the time mean transport of the asc is 29 2 sv fluctuations in the transport are large typically exceeding the mean by a factor of 2 they are mainly due to changes in the northward extent of the current over the lower slope however seasonal changes in the wind also drive variations in the transport of the asf and the flow in the upper slope both mean and variability are largely barotropic thus invisible to traditional geostrophic methods this article is protected by copyright all rights reserved

stability analysis of slopes with a potential of slide head toppling failure abstract toppling is a mode of slope instability that may occur in a wide range of layered or blocky rock masses if this instability is caused by some natural or man made external factors it is termed a secondary toppling failure one of the important modes of toppling instability is the slide head toppling failure when a layer of soil or weak rock is overlaid by a blocky or layered rock mass the combination of a toppling failure in the rock at the top and a circular sliding in the soil or weak rock in the bottom leads to this hybrid failure the mechanism of this hybrid failure is extremely complicated and it may occur in some special geological conditions in civil engineering and mining projects in this paper the mechanisms of toppling failures in general and the mechanism of slide head toppling failure in particular are presented and described then the outcomes of seven physical models which were constructed with base friction materials and conducted under static loading conditions by a tilting table apparatus are summarized to investigate this hybrid failure mechanism subsequently a new step by step theoretical approach is proposed for assessment of this failure mode and a typical example is analyzed to better demonstrate the results finally the results of the physical modeling are compared with the outcomes of the proposed theoretical method and an existing analytical approach this comparison shows that there are acceptable agreements between the physical and analytical results hence both proposed and existing analytical approaches can be used for the analysis of the slide head toppling slope failure

modelling and back analysing failures in steep limestone cliffs abstract the observation of 12 rock fall scars in steep limestone cliffs has shown that the fallen masses were stable as a result of relatively small rock bridges these results demonstrate that consideration of rock bridges is necessary for a realistic evaluation of stability limit equilibrium methods of analysis are presented for sliding and toppling for both isostatic and hyperstatic conditions these methods are illustrated with four case histories the results of nine back analyses of rock falls with volumes between 24 and 3500 m 3 are presented the rock cohesion obtained from back analysis appears to be significantly lower than the cohesion obtained from classical laboratory tests this discrepancy can be attributed to several factors including a spatial and temporal scale effect the oversimplified modelling two dimensional limit equilibrium and some uncertainties affecting the geometrical data when analysing the stability of a cliff with a limit equilibrium method the authors suggest dividing the cohesion by a scale and method factor of 3

on the potential of ground penetrating radar to help rock fall hazard assessment a case study of a limestone slab gorges de la bourne french alps the stability of a potentially unstable rock mass is highly sensitive to the continuity of the joints cutting it the rock fall hazard assessment generally based on surface geological observations and on a simple geomechanical model suffers from the lack of information on the 3d geometry and the properties of the joints this case study investigates the potential of ground penetrating radar gpr measurements regarding hazard assessment in hard rock gpr was used to detect and characterize joints that could cause the failure of an overhanging rock mass located above a road in the gorges de la bourne france gpr data were acquired using high frequency shielded antennae 500 and 800 mhz to assess the extension of these joints and to detect other possible fractures combined with a velocity profile deduced from a common mid point cmp analysis these measurements provided detailed images of the fracture network which were locally consistent with turn rate velocity measurements performed within two horizontal boreholes the rock bridge percentage in the critical joints was estimated from gpr data to be too low to ensure the stability of the overhanging rock mass consequently mining of the rock mass was decided on afterwards a comparison between gpr images and the real joints observed after mining also confirmed the gpr interpretation for the location and the extension of the joints

forensic analysis of rockfall scars abstract we characterise and analyse the detachment scar surfaces of rockfalls to understand the mechanisms that underpin their failure rockfall scars are variously weathered and comprised of both discontinuity release surfaces and surfaces indicative of fracturing through zones of previously intact rock known as rock bridges the presence of rock bridges and pre existing discontinuities is challenging to quantify due to the difficulty in determining discontinuity persistence below the surface of a rock slope rock bridges form an important control in holding blocks onto rockslopes with their frequency extent and location commonly modelled from the surface exposure of daylighting discontinuities we explore an alternative approach to assessing their role by characterising failure scars we analyse a database of multiple rockfall scar surfaces detailing the areal extent shape and location of broken rock bridges and weathered surfaces terrestrial laser scanning and gigapixel imagery were combined to record the detailed texture and surface morphology from this scar surfaces were mapped via automated classification based on rgb pixel values our analysis of the resulting data from scars on the north yorkshire coast uk indicates a wide variation in both weathering and rock bridge properties controlled by lithology and associated rock mass structure importantly the proportion of rock bridges in a rockfall failure surface does not increase with failure size rather larger failures display fracturing through multiple rock bridges and in contrast smaller failures fracture occurs only through a single critical rock bridge this holds implications for how failure mechanisms change with rockfall size and shape additionally the location of rock bridges with respect to the geometry of an incipient rockfall is shown to determine failure mode weathering can occur both along discontinuity surfaces and previously broken rock bridges indicating the sequential stages of progressively detaching rockfall our findings have wider implications for hazard assessment where rock slope stability is dependent on the nature of rock bridges how this is accounted for in slope stability modelling and the implications of rock bridges on long term rock slope evolution