variations in alaska tidewater glacier frontal ablation 1985 2013 our incomplete knowledge of the proportion of mass loss due to frontal ablation the sum of ice loss through calving and submarine melt from tidewater glaciers outside of the greenland and antarctic ice sheets has been cited as a major hindrance to accurate predictions of global sea level rise we present a 28 year record 1985 2013 of frontal ablation for 27 alaska tidewater glaciers representing 96 of the total tidewater glacier area in the region calculated from satellite derived ice velocities and modeled estimates of glacier ice thickness we account for cross sectional ice thickness variation long term thickness changes mass lost between an upstream fluxgate and the terminus and mass change due to changes in terminus position the total mean rate of frontal ablation for these 27 glaciers over the period 1985 2013 is 15 11 3 63gta 1 two glaciers hubbard and columbia account for approximately 50 of these losses the regional total ablation has decreased at a rate of 0 14gta 1 over this time period likely due to the slowing and thinning of many of the glaciers in the study area frontal ablation constitutes only 4 of the total annual regional ablation but roughly 20 of net mass loss comparing several commonly used approximations in the calculation of frontal ablation we find that neglecting cross sectional thickness variations severely underestimates frontal ablation

tide modulated ice flow variations drive seismicity near the calving front of bowdoin glacier greenland glacier microseismicity is a promising tool to study glacier dynamics however physical processes connecting seismic signals and ice dynamics are not clearly understood at present particularly the relationship between tide modulated seismicity and dynamics of calving glaciers remains elusive here we analyze records from an on ice seismometer placed 250 m from the calving front of bowdoin glacier greenland using high frequency glacier flow speed measurements we show that the microseismic activity is related to strain rate variations the seismic activity correlates with longitudinal stretching measured at the glacier surface both higher melt rates and falling tides accelerate glacier motion and increase longitudinal stretching long term microseismic monitoring could therefore provide insights on how a calving glacier s force balance and flow regime react to changes at the ice ocean interface

submarine melting at the terminus of a temperate tidewater glacier leconte glacier alaska u s a heat fresh and sea water balances indicate that the late summer rate of submarine melting at the terminus of tidewater leconte glacier alaska u s a in 2000 was about 12md 1 w e averaged over the submerged face this is 57 of the estimated total ice loss at the terminus calving plus melting at this time submarine melting may thusprovidea significantcontributiontotheoverallablationofatidewaterglacier oceano graphic measurements conductivity temperature depth made 200 500m from the ter minus identified an isohaline 27ppt and isothermal 7 2 c layer extending from 130m depthto the fjord floor capping this is a 40mthick overflow plume distinguishedby high outflow rates low salinity 22 25ppt and lower temperatures 5 6 c mixing models indicate that fresh water comprised about11 of this plume it originates mostly as sub glacial discharge whose buoyancy drives convection at the terminus deep warm saline watersareincorporatedintotheplumeasitascends causingsubstantialmeltingoficealong the submarine face the calving terminus undergoes seasonal changes that coincide with changes in subglacial discharge and fjord water temperatures and we suggest that these fluctuations interminuspositionare directly relatedto changes in submarine melting

distributed subglacial discharge drives significant submarine melt at a greenland tidewater glacier this is the publisher s final pdf the article is copyrighted by american geophysical union and published by john wiley sons inc it can be found at http agupubs onlinelibrary wiley com agu journal 10 1002 28issn 291944 8007

transoceanic wave propagation links iceberg calving margins of antarctica with storms in tropics and northern hemisphere 1 we deployed seismometers on the ross ice shelf and on various icebergs adrift in the ross sea including b15a a large 100 km by 30 km fragment of b15 which calved from the ross ice shelf in march 2000 the data reveal that the dominant energy of these floating ice masses is in the 0 01 to 0 1 hz band and is associated with sea swell generated in the tropical and extra tropical pacific ocean in one example a strong storm in the gulf of alaska on 21 october 2005 approximately 13 500 km from the ross sea generated swell that arrived at b15a immediately prior to and during its break up off cape adare on 27 october 2005 if sea swell influences iceberg calving and break up a teleconnection exists between the antarctic ice sheet mass balance and weather systems worldwide

calving flux estimation from tsunami waves abstract measuring glacier calving magnitude frequency and location in high temporal resolution is necessary to understand mass loss mechanisms of ocean terminating glaciers we utilized calving generated tsunami signals recorded with a pressure sensor for estimating the calving flux of bowdoin glacier in northwestern greenland we find a relationship between calving ice volume and wave amplitude this relationship was used to compute calving flux variation the calving flux showed large spatial and temporal fluctuations in july 2015 and in july 2016 with a mean flux of 2 3 0 15 105 m3 d 1 calving flux was greater during periods of fast ice flow high air temperature and at low falling tide indicating the importance of increased longitudinal strain due to glacier acceleration and or submarine melting at the calving front long term measurements with the method introduced here are promising for understanding the complex interplay of ice dynamics melting and calving at glacier fronts

complex force history of a calving generated glacial earthquake derived from broadband seismic inversion the force applied to the earth by the calving of two icebergs at jakobshavn isbrae greenland has been quantified the source force history was recovered by inversion of regional broadband seismograms without any a priori constraint on the source time function in contrast with previous studies for periods 10 100 s the three component force can be obtained from distant stations alone and is proportional to the closest station seismograms this inversion makes it possible to quantify changes of the source force direction and amplitude as a function of time and frequency a detailed comparison with a video of the event was used to identify four forces associated with collision then bottom out and top out rotation of the first and second icebergs and ice melange motion only the two iceberg rotations were identified in previous studies all four processes are found here to contribute to the force amplitude and variability such a complete time frequency force history provides unique dynamical constraints for mechanical calving models

21st century evolution of greenland outlet glacier velocities earlier observations on several of greenland s outlet glaciers starting near the turn of the 21st century indicated rapid annual scale and large 100 increases in glacier velocity combining data from several satellites we produce a decade long 2000 to 2010 record documenting the ongoing velocity evolution of nearly all 200 of greenland s major outlet glaciers revealing complex spatial and temporal patterns changes on fast flow marine terminating glaciers contrast with steady velocities on ice shelf terminating glaciers and slow speeds on land terminating glaciers regionally glaciers in the northwest accelerated steadily with more variability in the southeast and relatively steady flow elsewhere intraregional variability shows a complex response to regional and local forcing observed acceleration indicates that sea level rise from greenland may fall well below proposed upper bounds

convection driven melting near the grounding lines of ice shelves and tidewater glaciers subglacial meltwater draining along the bed of fast flowing marine terminating glaciers emerges at the groundingline wheretheiceeithergoesafloattoformaniceshelforterminates inacalvingface theinputof freshwater to the ocean provides a source of buoyancy and drives convective motion alongside the ice ocean interface this process is modeled using the theory of buoyant plumes that has previously been applied to the study of the larger scale circulation beneath ice shelves the plume grows through entrainment of ocean waters and the heat brought into the plume as a result drives melting at the ice ocean interface the equations are nondimensionalized by using scales appropriate for the region where the subglacial drainage rather than the subsequent addition of meltwater supplies the majority of the buoyancy forcing it is found that the melt rate within this region can be approximated reasonably well by a function that is linear in ocean temperature has a cube root dependence on the flux of subglacial meltwater and has a complex dependency on the slope of the ice ocean interface the model is used to investigate variability in melting induced by changes in both ocean temperature and subglacial discharge for a number of realistic examples of ice shelves and tidewater glaciers the results show how warming ocean waters and increasing subglacial drainage both generate increases in melting near the grounding line

short lived ice speed up and plume water flow captured by a vtol uav give insights into subglacial hydrological system of bowdoin glacier abstract the subglacial hydrology of tidewater glaciers is a key but poorly understood component of the complex ice ocean system which affects sea level rise as it is extremely difficult to access the interior of a glacier our knowledge relies mostly on the observation of input variables such as air temperature and output variables such as the ice flow velocities reflecting the englacial water pressure and the dynamics of plumes reflecting the discharge of meltwater into the ocean in this study we use a cost effective vertical take off and landing vtol unmanned aerial vehicle uav to monitor the daily movements of bowdoin glacier north west greenland and the dynamics of its main plume using structure from motion photogrammetry and feature tracking techniques we obtained 22 high resolution ortho images and 19 velocity fields at the calving front for 12 days in july 2016 our results show a two day long speed up event up to 170 caused by an increase in buoyant subglacial forces with a strong spatial variability revealing that enhanced acceleration is an indication of shallow bedrock further we used the particle image velocimetry piv method to analyze water flow from successive uav images taken while flying over the main plume of the glacier we found that piv successfully captures the area of radially diverging flow of the plume and provides information on spatial and time variability as no other remote sensing technique can most interestingly the active part of the plume features pulsating water jets at the time scale of seconds and is 1 to 5 times smaller than its visual footprint defined by the iceberg free area combined with an ice flow model or a non steady plume model our approach has the potential to generate a novel set of input data to gather information about the depth of the bedrock the discharge of meltwater or the subglacial melting rate of tidewater glaciers

estimating the long term calving flux of kronebreen svalbard from geodetic elevation changes and mass balance modelling this study independently quantifies geodetic elevation change and models surface mass balance to solve the continuity equation the approach is tested on two dynamically different glaciers kongsvegen and kronebreen in northwest svalbard through two time epochs 1966 1990 95 i and 1990 95 2007 ii on kongsvegen a dynamically inactive glacier the residual term represents an error associated with determining elevation changes and surface mass balance it is apparent that centerline mass balance estimates are not representative of the entire glacier which we relate to center line accumulation being larger than the elevation bin average on kronebreen a fast flowing and actively calving glacier a significant part of the residual is identified with the long term calving flux for both glaciers the cumulative surface mass balance remained close to zero during the first epoch but became increasingly negative in the second epoch the long term calving flux of kronebreen is estimated to be 0 14 0 03 km3 w e a 1 during epoch i and 0 20 0 05 km3 w e a 1 in epoch ii

a 15 year record of frontal glacier ablation rates estimated from seismic data we present a unique time series of continuous glacier frontal ablation rates with weekly resolution over 15 years estimated from seismic calving observations at kronebreen svalbard using linear statistical models we calibrate the seismic record with seven years of satellite derived frontal ablation measurements the two basic input parameters required for our models are the cumulative duration of individual seismic calving events and the incompleteness of the seismic record to correct for the effect of seismic background noise frontal ablation follows the seasonal glacier speed up peaking 1 2 months after the melt season maximum short lived peaks are associated with melt and rain events cumulative frontal ablation of kronebreen between 2001 and 2015 is about 4 0 km3 3 7 gt with the greatest annual loss 0 45 km3 between 2013 and 2014 at the onset of the recent accelerated retreat of the glacier our approach provides a potential method for monitoring tidewater glaciers worldwide that have sufficiently close seismic instrumentation

an improved mass budget for the greenland ice sheet extensive ice thickness surveys by nasa s operation icebridge enable over a decade of ice discharge measurements at high precision for the majority of greenland s marine terminating outlet glaciers prompting a reassessment of the temporal and spatial distribution of glacier change annualmeasurements for 178 outlet glaciers reveal that despite widespread acceleration only 15 glaciers accounted for 77 of the 739 29 gt of ice lost due to acceleration since 2000 and four accounted for 50 among the top sources of loss are several glaciers that have received little scientific attention the relative contribution of ice discharge to total loss decreased from 58 before 2005 to 32 between 2009 and 2012 as such 84 of the increase in mass loss after 2009 was due to increased surface runoff these observations support recentmodel projections that surface mass balance rather than ice dynamics will dominate the ice sheet s contribution to 21st century sea level rise

does calving matter evidence for significant submarine melt abstract during the summer in the northeast pacific ocean the alaska coastal current sweeps water with temperatures in excess of 12 c past the mouths of glacierized fjords and bays the extent to which these warm waters affect the mass balance of alaskan tidewater glaciers is uncertain here we report hydrographic measurements made within icy bay alaska and calculate rates of submarine melt at yahtse glacier a tidewater glacier terminating in icy bay we find strongly stratified water properties consistent with estuarine circulation and evidence that warm gulf of alaska water reaches the head of 40 km long icy bay largely unaltered a 10 20 m layer of cold fresh glacially modified water overlies warm saline water the saline water is observed to reach up to 10 4 c within 1 5 km of the terminus of yahtse glacier by quantifying the heat and salt deficit within the glacially modified water we place bounds on the rate of submarine melt the submarine melt rate is estimated at 9 m d 1 at least half the rate at which ice flows into the terminus region and can plausibly account for all of the submarine terminus mass loss our measurements suggest that summer and fall subaerial calving is a direct response to thermal undercutting of the terminus further demonstrating the critical role of the ocean in modulating tidewater glacier dynamics

iceberg calving as a primary source of regional scale glacier generated seismicity in the st elias mountains alaska 1 since the installation of the alaska regional seismic network in the 1970s data analysts have noted nontectonic seismic events thought to be related to glacier dynamics while loose associations with the glaciers of the st elias mountains have been made no detailed study of the source locations has been undertaken we performed a two step investigation surrounding these events beginning with manual locations that guided an automated detection and event sifting routine results from the manual investigation highlight characteristics of the seismic waveforms including single peaked narrowband spectra emergent onsets lack of distinct phase arrivals and a predominant cluster of locations near the calving termini of several neighboring tidewater glaciers through these locations comparison with previous work analyses of waveform characteristics frequency magnitude statistics and temporal patterns in seismicity we suggest calving as a source for the seismicity statistical properties and time series analysis of the event catalog suggest a scale invariant process that has no single or simple forcing these results support the idea that calving is often a response to short lived or localized stress perturbations our results demonstrate the utility of passive seismic instrumentation to monitor relative changes in the rate and magnitude of iceberg calving at tidewater glaciers that may be volatile or susceptible to ensuing rapid retreat especially when existing seismic infrastructure can be used

observing calving generated ocean waves with coastal broadband seismometers jakobshavn isbrae greenland we use time lapse photography modis satellite imagery ocean wave measurements and regional broadband seismic data to demonstrate that icebergs that calve from jakobshavn isbrae greenland can generate ocean waves that are detectable over 150 km from their source the waves which are recorded seismically have distinct spectral peaks are not dispersive and persist for several hours on the basis of these observations we suggest that calving events at jakobshavn isbrae can stimulate seiches or basin eigenmodes in both ilulissat icefjord and disko bay our observations furthermore indicate that coastal land based seismometers located near calving termini e g as part of the new greenland ice sheet monitoring network glisn can aid investigations into the largely unexplored oceanographic consequences of iceberg calving

tidal and seasonal variations in calving flux observed with passive seismology the seismic signatures of calving events i e calving icequakes offer an opportunity to examine calving variability with greater precision than is available with other methods here using observations from yahtse glacier alaska we describe methods to detect locate and characterize calving icequakes we combine these icequake records with a coincident manually generated record of observed calving events to develop and validate a statistical model through which we can infer iceberg sizes from the properties of calving icequakes we find that the icequake duration is the single most significant predictor of an iceberg s size we then apply this model to 18 months of seismic recordings and find elevated iceberg calving flux during the summer and fall and a pronounced lull in calving during midwinter calving flux is sensitive to semidiurnal tidal stage large calving events are tens of percent more likely during falling and low tides than during rising and high tides consistent with a view that deeper water has a stabilizing influence on glacier termini multiple factors affect the occurrence of mechanical fractures that ultimately lead to iceberg calving at yahtse glacier seismology allows us to demonstrate that variations in the rate of submarine melt are a dominant control on iceberg calving rates at seasonal timescales on hourly to daily timescales tidal modulation of the normal stress against the glacier terminus reveals the nonlinear glacier response to changes in the near terminus stress field

glacier calving observed with time lapse imagery and tsunami waves at glaciar perito moreno patagonia calving plays a key role in the recent rapid retreat of glaciers around the world however many processes related to calving are poorly understood since direct observations are scarce and challenging to obtain when calving occurs at a glacier front surface water waves arise over the ocean or a lake in front of glaciers to study calving processes from these surface waves we performed field observations at glaciar perito moreno patagonia we synchronized time lapse photography and surface waves record to confirm that glacier calving produces distinct waves compared with local noise a total of 1074 calving events were observed over the course of 39 d during austral summer calving occurred twice more frequently than in spring the cumulative distribution of calving interevent time interval followed exponential model implying random occurrence of events in time we further investigated wave properties and found that source to sensor distance can be estimated from wave dispersion within 20 error we also found that waves produced by different calving types showed similar spectra in the same frequency range between 0 05 0 2 hz and that the amplitude of surface waves increased with the size of calving this study demonstrates the potential of surface wave monitoring for understanding calving processes

acceleration of jakobshavn isbrae triggered by warm subsurface ocean waters observations over past decades show a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning in 1997 this switch is associated with a doubling in glacier velocity hydrographic data show a concurrent sudden increase in subsurface ocean temperatures along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were triggered by the arrival of relatively warm water originating from the irminger sea observations over the past decades show a rapid acceleration of several outlet glaciers in greenland and antarctica1 one of the largest changes is a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning2 in 1997 associated with a doubling in glacier velocity3 suggested explanations for the speed up of jakobshavn isbrae include increased lubrication of the ice bedrock interface as more meltwater has drained to the glacier bed during recent warmer summers4 and weakening and break up of the floating ice tongue that buttressed the glacier5 here we present hydrographic data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were instead triggered by the arrival of relatively warm water originating from the irminger sea near iceland we trace these oceanic changes back to changes in the atmospheric circulation in the north atlantic region we conclude that the prediction of future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in regional ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets

ice front and flow speed variations of marine terminating outlet glaciers along the coast of prudhoe land northwestern greenland satellite images were analyzed to measure the frontal positions and ice speeds of 19 marine terminating outlet glaciers along the coast of prudhoe land northwestern greenland from 1987 to 2014 all the studied glaciers retreated over the study period at a rate of between 12 and 200 m a 1 with a median mean retreat rate of 30 40 m a 1 the glacier retreat began in the year 2000 which coincided with an increase in summer mean air temperature from 1 4 to 5 5 c between 1996 and 2000 in this region ice speed near the front of the studied glaciers ranged between 20 and 1740 m a 1 in 2014 and many of them accelerated in the early 2000s in general the faster retreat was observed at the glaciers that experienced greater acceleration as represented by tracy glacier which experienced a retreat of 200 m a 1 and a velocity increase of 930 m a 1 during the study period a possible interpretation of this observation is that flow acceleration induced dynamic thinning near the termini resulting in enhanced calving and rapid retreat of the studied glaciers we hypothesize that atmospheric warming conditions in the late 1990s triggered glacier retreat in northwestern greenland since 2000

seismic detection and analysis of icequakes at columbia glacier alaska 1 contributions to sea level rise from rapidly retreating marine terminating glaciers are large and increasing strong increases in iceberg calving occur during retreat which allows mass transfer to the ocean at a much higher rate than possible through surface melt alone to study this process we deployed an 11 sensor passive seismic network at columbia glacier alaska during 2004 2005 we show that calving events generate narrow band seismic signals allowing frequency domain detections detection parameters were determined using direct observations of calving and validated using three statistical methods and hypocenter locations the 1 3 hz detections provide a good measure of the temporal distribution and size of calving events possible source mechanisms for the unique waveforms are discussed and we analyze potential forcings for the observed seismicity

seismic observations of glaciogenic ocean waves micro tsunamis on icebergs and ice shelves seismometers deployed over a 3 year period on icebergs in the ross sea and on the ross ice shelf antarctica reveal that impulsive sources of ocean surface waves are frequent e g 200 events per year in the ross sea in the ice shelf and iceberg covered environment of coastal antarctica the 368 events recorded by our field deployment suggest that these impulsive events are generated by glaciological mechanisms such as 1 small scale calving and edge wasting of icebergs and ice shelf fronts 2 edge on edge closing and opening associated with iceberg collisions and 3 possibly the impulsive opening of void space associated with ice shelf rifting and basal crevasse formation the observations described here provide a background of glaciogenic ocean wave phenomena relevant to the ross sea and suggest that these phenomena may be exploited in the future using more purposefully designed observation schemes to understand iceberg calving and ice shelf disintegration processes

undercutting of marine terminating glaciers in west greenland marine terminating glaciers control most of greenland s ice discharge into the ocean but little is known about the geometry of their frontal regions here we use side looking multibeam echo sounding observations to reveal that their frontal ice cliffs are grounded deeper below sea level than previously measured and their ice faces are neither vertical nor smooth but often undercut by the ocean and rough deep glacier grounding enables contact with subsurface warm salty atlantic waters aw which melts ice at rates of meters per day we detect cavities undercutting the base of the calving faces at the sites of subglacial water sgw discharge predicted by a hydrological model the observed pattern of undercutting is consistent with numerical simulations of ice melt in which buoyant plumes of sgw transport warm aw to the ice faces glacier undercutting likely enhances iceberg calving impacting ice front stability and in turn the glacier mass balance

calving of fuerza aerea glacier greenwich island antarctica observed with terrestrial laser scanning and continuous video monitoring a short term series of quantitative observations of calving activity of fuerza aerea glacier greenwich island the south shetland islands antarctica was conducted in order to test new methods of monitoring calving the volume of single calving events was quantified by combining terrestrial laser scanning tls surveys with continuous video recording of the ice front an empirical formula for area volume scaling of the calved ice block was proposed based on the tls measured calved ice volume and the calved ice front area obtained by manual delineation on the images acquired with the video camera this combination of methods proves to be a valuable tool for glacier monitoring providing both high temporal resolution and precise quantitative measurements of the calving volume the size distribution of calving events is best approximated by a power law and within the short period of observations 14 d calving was found to be an intrinsic process not dependent on environmental forcings over the period of 21 january 04 february 2013 the ice flow velocity at the terminus of fuerza aerea glacier was 0 26 0 07 m d 1 and the calving rate was 0 41 0 07 m d 1

calving icebergs a source of low frequency seismic signals from columbia glacier alaska low frequency icequakes produced by columbia glacier alaska are caused by large icebergs which break off the glacier terminus into prince william sound occasionally many ice seracs fall in rapid succession producing complex low frequency icequake signals with durations sometimes exceeding 10 min an empirical relationship v 4000 t between the volume v of an iceberg in cubic meters and the duration t of the seismic signal in seconds can be used to estimate the calving rate of columbia glacier from seismological data alone during 1984 and 1985 a period of rapid retreat of the glacier the calculated number of icequakes per month showed seasonal fluctuations that corresponded to variations in calving rate determined by photogrammetry it is likely that most previously reported low frequency icequakes in southern alaska are produced by calving tidewater glaciers

numerical experiments on subaqueous melting of greenland tidewater glaciers in response to ocean warming and enhanced subglacial discharge the largest dischargers of ice in greenland are glaciers that terminate in the ocean and melt in contact with sea water studies of ice sheet ocean interactions have mostly focused on melting beneath near horizontal floating ice shelves for tidewater glaciers melting instead takes place along the vertical face of the calving front here we modify the massachusetts institute of technology general circulation model mitgcm to include ice melting from a calving face with the freshwater outflow at the glacier grounding line we use the model to predict melt rates and their sensitivity to ocean thermal forcing and to subglacial discharge we find that melt rates increase with approximately the one third power of the subglacial water flux and increase linearly with ocean thermal forcing our simulations indicate that consistent with limited field data melting ceases when subglacial discharge is shut off and reaches several meters per day when subglacial discharge is high in the summer these results are a first step toward a more realistic representation of subglacial discharge and of ocean thermal forcing on the subaqueous melting of tidewater glaciers in a numerical ocean model our results illustrate that the ice front melting process is both complex and strongly time dependent

seasonal variability of submarine melt rate and circulation in an east greenland fjord 1 the circulation in a glacial fjord driven by a large tidewater glacier is investigated using a nonhydrostatic ocean general circulation model with a melt rate parameterization at the vertical glacier front the model configuration and water properties are based on data collected in sermilik fjord near helheim glacier a major greenland outlet glacier the approximately two layer stratification of the fjord s ambient waters causes the meltwater plume at the glacier front to drive a double cell circulation with two distinct outflows one at the free surface and one at the layers interface in summer the discharge of surface runoff at the base of the glacier subglacial discharge causes the circulation to be much more vigorous and associated with a larger melt rate than in winter the simulated double cell circulation is consistent in both seasons with observations from sermilik fjord seasonal differences are also present in the vertical structure of the melt rate which is maximum at the base of the glacier in summer and at the layers interface in winter simulated submarine melt rates are strongly sensitive to the amount of subglacial discharge to changes in water temperature and to the height of the layers they are also consistent with those inferred from simplified one dimensional models based on the theory of buoyant plumes our results also indicate that to correctly represent the dynamics of the meltwater plume care must be taken in the choice of viscosity and diffusivity values in the model

calving seismicity from iceberg sea surface interactions 1 iceberg calving is known to release substantial seismic energy but little is known about the specific mechanisms that produce calving icequakes at yahtse glacier a tidewater glacier on the gulf of alaska we draw upon a local network of seismometers and focus on 80 hours of concurrent direct observation of the terminus to show that calving is the dominant source of seismicity to elucidate seismogenic mechanisms we synchronized video and seismograms to reveal that the majority of seismic energy is produced during iceberg interactions with the sea surface icequake peak amplitudes coincide with the emergence of high velocity jets of water and ice from the fjord after the complete submergence of falling icebergs below sea level these icequakes have dominant frequencies between 1 and 3 hz detachment of an iceberg from the terminus produces comparatively weak seismic waves at frequencies between 5 and 20 hz our observations allow us to suggest that the most powerful sources of calving icequakes at yahtse glacier include iceberg sea surface impact deceleration under the influence of drag and buoyancy and cavitation numerical simulations of seismogenesis during iceberg sea surface interactions support our observational evidence our new understanding of iceberg sea surface interactions allows us to reattribute the sources of calving seismicity identified in earlier studies and offer guidance for the future use of seismology in monitoring iceberg calving

bunbury basalt gondwana breakup products or earliest vestiges of the kerguelen mantle plume abstract in this contribution we investigate the role of a mantle plume in the genesis of the bunbury basalt using high precision 40ar 39ar geochronology and whole rock geochemistry and by using crustal basement thickness of the eastern indian ocean and the western australian continent the bunbury basalt is a series of lava flows and deep intrusive rocks in southwestern australia thought to be the earliest igneous products from the proto kerguelen mantle plume nine new plateau ages indicate that the bunbury basalt erupted in three distinct phases at 136 96 0 43 ma 132 71 0 43 ma and 130 45 0 82 ma all bunbury basalt samples are enriched tholeiitic basalts with varying contributions from the continental lithosphere that are similar to other kerguelen plume products based on plate reconstructions and the present geochronological constraints the eruption of the oldest bunbury basalt preceded the emplacement of the kerguelen large igneous province by at least 10 20 m y such age differences between a precursor and the main magmatic event are not uncommon but do require additional explanation low crustal stretching factors beneath the bunbury basalt 1 4 indicate that decompression melting could not have been generated from asthenospheric mantle with a normal chemistry and geotherm an elevated geotherm from the mantle plume coupled with the geochemical similarity between the bunbury basalt and other kerguelen plume products suggests a shared origin exists however new age constraints of the oldest bunbury basalt are synchronous with the breakup of eastern gondwana and the initial opening of the indian ocean at ca 137 136 ma which may mean an alternative explanation is possible the enriched geochemistry can equally be explained by a patch of shallow mantle beneath the southern perth basin the patch may have been enriched during gondwana suturing at ca 550 500 ma during early rifting events by magmatic underplating or by intruded melts into the subcontinental lithospheric mantle this enriched geochemical signature would then be sufficient to trigger decompression melting from passive rifting between greater india and australia with no contribution from the kerguelen hotspot we conclude that although the proto kerguelen hotspot is certainly a possible explanation for the genesis of the bunbury basalt decompression melting of an enriched patch of subcontinental lithospheric mantle is an alternative theory

the variability of tidewater glacier calving origin of event size and interval distributions calving activity at the termini of tidewater glaciers produces a wide range of iceberg sizes at irregular intervals we present calving event data obtained from continuous observations of the termini of two tidewater glaciers on svalbard and show that the distributions of event sizes and inter event intervals can be reproduced by a simple calving model focusing on the mutual interplay between calving and the destabilization of the glacier terminus the event size distributions of both the field and the model data extend over several orders of magnitude and resemble power laws the distributions of inter event intervals are broad but have a less pronounced tail in the model the width of the size distribution increases with the calving susceptibility of the glacier terminus a parameter measuring the effect of calving on the stress in the local neighborhood of the calving region inter event interval distributions in contrast are insensitive to the calving susceptibility above a critical susceptibility small perturbations of the glacier result in ongoing self sustained calving activity the model suggests that the shape of the event size distribution of a glacier is informative about its proximity to this transition point observations of rapid glacier retreats can be explained by supercritical self sustained calving

glacier fjord and seismic response to recent large calving events jakobshavn isbrae greenland 1 the recent loss of jakobshavn isbrae s extensive floating ice tongue has been accompanied by a change in near terminus behavior calving currently occurs primarily in summer from a grounded terminus involves the detachment and overturning of several icebergs within 30 60 min and produces long lasting and far reaching ocean waves and seismic signals including glacial earthquakes calving also increases near terminus glacier velocities by 3 but does not cause episodic rapid glacier slip thereby contradicting the originally proposed glacial earthquake mechanism we propose that the earthquakes are instead caused by icebergs scraping the fjord bottom during calving

glacier dynamics near the calving front of bowdoin glacier northwestern greenland to better understand recent rapid recession of marine terminating glaciers in greenland we performed satellite and field observations near the calving front of bowdoin glacier a 3 km wide outlet glacier in northwestern greenland satellite data revealed a clear transition to a rapidly retreating phase in 2008 from a relatively stable glacier condition that lasted for 20 years ice radar measurements showed that the glacier front is grounded but very close to the floating condition these results in combination with the results of ocean depth soundings suggest bed geometry in front of the glacier is the primary control on the rate and pattern of recent rapid retreat presumably glacier thinning due to atmospheric and or ocean warming triggered the initial retreat in situ measurements showed complex short term ice speed variations which were correlated with air temperature precipitation and ocean tides ice speed quickly responded to temperature rise and a heavy rain event indicating rapid drainage of surface water to the bed semi diurnal speed peaks coincided with low tides suggesting the major role of the hydrostatic pressure acting on the calving face in the force balance these observations demonstrate that the dynamics of bowdoin glacier are sensitive to small perturbations occurring near the calving front