fracture propagation to the base of the greenland ice sheet during supraglacial lake drainage surface meltwater that reaches the base of an ice sheet creates a mechanism for the rapid response of ice flow to climate change the process whereby such a pathway is created through thick cold ice has not however been previously observed we describe the rapid 2 hours drainage of a large supraglacial lake down 980 meters through to the bed of the greenland ice sheet initiated by water driven fracture propagation evolving into moulin flow drainage coincided with increased seismicity transient acceleration ice sheet uplift and horizontal displacement subsidence and deceleration occurred over the subsequent 24 hours the short lived dynamic response suggests that an efficient drainage system dispersed the meltwater subglacially the integrated effect of multiple lake drainages could explain the observed net regional summer ice speedup

vibrational modes of hydraulic fractures inference of fracture geometry from resonant frequencies and attenuation oscillatory seismic signals arising from resonant vibrations of hydraulic fractures are observed in many geologic systems including volcanoes glaciers and ice sheets and hydrocarbon and geothermal reservoirs to better quantify the physical dimensions of fluid filled cracks and properties of the fluids within them we study wave motion along a thin hydraulic fracture waveguide we present a linearized analysis valid at wavelengths greater than the fracture aperture that accounts for quasi static elastic deformation of the fracture walls as well as fluid viscosity inertia and compressibility in the long wavelength limit anomalously dispersed guided waves known as crack or krauklis waves propagate with restoring force from fracture wall elasticity at shorter wavelengths the waves become sound waves within the fluid channel wave attenuation in our model is due to fluid viscosity rather than seismic radiation from crack tips or fracture wall roughness we characterize viscous damping at both low frequencies where the flow is always fully developed and at high frequencies where the flow has a nearly constant velocity profile away from viscous boundary layers near the fracture walls most observable seismic signals from resonating fractures likely arise in the boundary layer crack wave limit where fluid solid coupling is pronounced and attenuation is minimal we present a method to estimate the aperture and length of a resonating hydraulic fracture using both the seismically observed quality factor and characteristic frequency finally we develop scaling relations between seismic moment and characteristic frequency that might be useful when interpreting the statistics of hydraulic fracture events

slow spreading of a sheet of bingham fluid on an inclined plane to study the dynamics of fluid mud with a high concentration of cohesive clay particles we present a theory for a thin sheet of bingham plastic fluid flowing slowly on an inclined plane the physics is discussed on the approximate basis of the lubrication theory because of the yield stress the free surface need not be horizontal when the bingham fluid is in static equilibrium nor parallel to the plane bed when in steady flow we then show that there is a variety of gravity currents that can advance at a constant speed and with the same profile experimental confirmation of one type is presented by solving a nonlinear partial differential equation transient flows due either to a steady upstream discharge or to the sudden release of a finite fluid mass on another fluid layer are studied in the first case there is a mud front which ultimately propagates as a constant speed as a steady gravity current in the second case when the ambient layer is sufficiently shallow that there is no initial motion the flow induced by the new fluid can terminate after the disturbance has travelled a finite distance the extent of the final spread is examined disturbances due to an external pressure travelling parallel to the free surface are also examined it is found in particular that a travelling localized pulse of pressure gradient not only generates a localized mud disturbance which travels along with the forcing pressure but further leaves behind a permanent footprint

a physically based calving model applied to marine outlet glaciers and implications for the glacier dynamics we present results from numerical ice flow models that include calving criteria based on penetration of surface and basal crevasses which in turn is a function of longitudinal strain rates near the glacier front the position of the calving front is defined as the point where either 1 surface crevasses reach the waterline model cdw or 2 surface and basal crevasses penetrate the full thickness of the glacier model cd for comparison with previous studies results are also presented for a height above buoyancy calving model qualitatively both models cdw and cd produce similar behaviour unlike previous models for calving the new calving criteria are applicable to both grounded termini and floating ice shelves and tongues the numerical ice flow model is applied to an idealized geometry characteristic of marine outlet glaciers results indicate that grounding line dynamics are less sensitive to basal topography than previously suggested stable grounding line positions can be obtained even on a reverse bed slope with or without floating termini the proposed calving criteria also allow calving losses to be linked to surface melt and therefore climate in contrast to previous studies in which calving rate or position of the terminus is linked to local water depth the new calving criterion is able to produce seasonal cycles of retreat and advance as observed for greenland marine outlet glaciers the contrasting dynamical behaviour and stability found for different calving models suggests that a realistic parameterization for the process of calving is crucial for any predictions of marine outlet glacier change

tailings subaerial and subaqueous deposition and beach slope modeling abstractthe tailings beach slope is a fundamental parameter for the design and operation of tailings storage facilities because it affects the tailings storage capacity pond levels and phreatic surfaces within the containment structures understanding tailings beach development is particularly important for thickened and paste tailings facilities where the tailings can form a self stacking structure this paper presents a theoretical tailings deposition model that can describe the formation of tailings beach slopes in both subaerial and subaqueous deposition environments the depositional behavior and deposition mechanisms are investigated from both geotechnical and hydraulic engineering perspectives the model is developed to capture deposition mechanisms based on the principles of soil mechanics and fluid mechanics the governing differential equations can be solved using a numerical technique and the solution scheme can readily be implemented in computer languages case studies for subaerial deposi

depth determination for shallow teleseismic earthquakes methods and results the depths of moderate sized shallow earthquakes can be routinely determined to an accuracy of several kilometers using teleseismic data alone making it possible to determine the vertical positions of earthquakes within the lithosphere this capability provides a valuable tool for plate tectonic studies since earthquake depths can be used to constrain lithospheric thermal and mechanical structure at plate boundaries and in intraplate regions two basic techniques are used for depth analyses surface wave spectra can be used to determine focal depths as mode excitation reflects the behavior of the eigenfunctions with depth the primary limitation on such studies stems from lateral heterogeneity of velocity structure the waveforms of body waves are also diagnostic of focal depth which controls the time separation between the direct arrival and near source surface reflections these studies can be limited by a partial trade off between depth and source time function duration the reliability of the body wave modeling approach now in general use is shown by excellent agreement between depths determined by different investigators using different algorithms the depth determination is robust to typical uncertainties in focal mechanism and near source structure the trade off with source time function duration generally does not produce major difficulties for small events ms 6 5 for larger events the trade off can be resolved using a approach in which for a given depth the time function yielding the best fit to a suite of seismograms is found by deconvolution deconvolution at a series of depths yields a misfit function whose minimum indicates the focal depth tests with synthetic data show that the deconvolution process yields reliable depth estimates even given uncertainties in focal mechanism and near source structure it successfully handles multiple sources moderate sized finite sources and horizontally propagating ruptures good results are obtained for vertically propagating ruptures until the fault area becomes so large that waveforms differ significantly from the point source approximation a number of important tectonic results have emerged from studies using these depth determination methods the maximum depth of oceanic intraplate seismicity increases with lithospheric age and is approximately bounded by the 750 c isotherm this depth roughly equals the flexural thickness of the lithosphere but is much less than the depth to the low velocity zone indicated by surface wave dispersion the maximum depth of continental intraplate seismicity is also temperature limited but by a lower temperature these observations are consistent with the rapid weakening of the appropriate rocks with depth predicted by standard temperature dependent rheologies the maximum depth of oceanic transform seismicity corresponds to an isotherm of about 400 c this temperature is lower than would be predicted from the intraplate results and may indicate that transforms are either hotter or weaker than expected the depths of ridge crest earthquakes large enough for teleseismic analysis are extremely shallow 0 8 km the depth distribution of seismicity in continental normal faulting regions provides constraints on the nature of the extension process at subduction zones precise depth determinations can resolve the upper and lower flexural regions in the bending downgoing plate precisely locate the plate interface and map the vertical extent and position of faulting in large earthquakes

vulnerability of antarctica s ice shelves to meltwater driven fracture atmospheric warming threatens to accelerate the retreat of the antarctic ice sheet by increasing surface melting and facilitating hydrofracturing 1 7 where meltwater flows into and enlarges fractures potentially triggering ice shelf collapse3 5 8 10 the collapse of ice shelves that buttress11 13 the ice sheet accelerates ice flow and sea level rise14 16 however we do not know if and how much of the buttressing regions of antarctica s ice shelves are vulnerable to hydrofracture if inundated with water here we provide two lines of evidence suggesting that many buttressing regions are vulnerable first we trained a deep convolutional neural network dcnn to map the surface expressions of fractures in satellite imagery across all antarctic ice shelves second we developed a stability diagram of fractures based on linear elastic fracture mechanics to predict where basal and dry surface fractures form under current stress conditions we find close agreement between the theoretical prediction and the dcnn mapped fractures despite limitations associated with detecting fractures in satellite imagery finally we used linear elastic fracture mechanics theory to predict where surface fractures would become unstable if filled with water many regions regularly inundated with meltwater today are resilient to hydrofracture stresses are low enough that all water filled fractures are stable conversely 60 10 per cent of ice shelves by area both buttress upstream ice and are vulnerable to hydrofracture if inundated with water the dcnn map confirms the presence of fractures in these buttressing regions increased surface melting17 could trigger hydrofracturing if it leads to water inundating the widespread vulnerable regions we identify these regions are where atmospheric warming may have the largest impact on ice sheet mass balance using a neural network trained on continent wide data and a fracture model the ice shelves in antarctica that may be prone to hydrofracturing under further atmospheric warming are identified

distributed acoustic sensing of seismic properties in a borehole drilled on a fast flowing greenlandic outlet glacier distributed acoustic sensing das is a new technology in which seismic energy is recorded at high spatial and temporal resolution along a fibre optic cable we show analyses from the first glaciol

basal crevasses and associated surface crevassing on the larsen c ice shelf antarctica and their role in ice shelf instability we identify a series of basal crevasses along a 31 km transect across the northern sector of the larsen c ice shelf antarctica using in situ ground penetrating radar the basal crevasses propagate from a region of multiple shallow basal fractures to form widely spaced 0 5 2 0 km but deeply incised 70 134 m features surface troughs observed in visible imagery exist above the basal crevasses as the ice vertically shears to reach hydrostatic equilibrium while widespread surface crevassing occurs along the crests and on the flanks of the undulations primarily aligned with the topography we suggest based on the location of the surface crevasses and the along flow evolution of the basal crevasses that the former are induced by a bending stress created by gradients in hydrostatic forces using a linear elastic fracture mechanics model we investigate the sensitivity of basal crevasse propagation to observed trends of ice shelf thinning and acceleration basal crevasses are large scale structural weaknesses that can both control meltwater ponding and induce surface crevassing together these features may represent an important mechanism in both past and future ice shelf disintegration events on the antarctic peninsula

glacier crevasses observations models and mass balance implications we review the findings of approximately 60 years of in situ and remote sensing studies of glacier crevasses as well as the three broad classes of numerical models now employed to simulate crevasse fracture the relatively new insight that mixed mode fracture in local stress equilibrium rather than downstream advection alone can introduce nontrivial curvature to crevasse geometry may merit the reinterpretation of some key historical observation studies in the past three decades there have been tremendous advances in the spatial resolution of satellite imagery as well as fully automated algorithms capable of tracking crevasse displacements between repeat images despite considerable advances in developing fully transient three dimensional ice flow models over the past two decades both the zero stress and linear elastic fracture mechanics crevasse models have remained fundamentally unchanged over this time in the past decade however multidimensional and transient formulations of the continuum damage mechanics approach to simulating ice fracture have emerged the combination of employing damage mechanics to represent slow upstream deterioration of ice strength and fracture mechanics to represent rapid failure at downstream termini holds promise for implementation in large scale ice sheet models finally given the broad interest in the sea level rise implications of recent and future cryospheric change we provide a synthesis of 10 mechanisms by which crevasses can influence glacier mass balance

potential antarctic ice sheet retreat driven by hydrofracturing and ice cliff failure abstract geological data indicate that global mean sea level has fluctuated on 103 to 106 yr time scales during the last 25 million years at times reaching 20 m or more above modern if correct this implies substantial variations in the size of the east antarctic ice sheet eais however most climate and ice sheet models have not been able to simulate significant eais retreat from continental size given that atmospheric co2 levels were relatively low throughout this period here we use a continental ice sheet model to show that mechanisms based on recent observations and analysis have the potential to resolve this model data conflict in response to atmospheric and ocean temperatures typical of past warm periods floating ice shelves may be drastically reduced or removed completely by increased oceanic melting and by hydrofracturing due to surface melt draining into crevasses ice at deep grounding lines may be weakened by hydrofracturing and reduced buttressing and may fail structurally if stresses exceed the ice yield strength producing rapid retreat incorporating these mechanisms in our ice sheet model accelerates the expected collapse of the west antarctic ice sheet to decadal time scales and also causes retreat into major east antarctic subglacial basins producing 17 m global sea level rise within a few thousand years the mechanisms are highly parameterized and should be tested by further process studies but if accurate they offer one explanation for past sea level high stands and suggest that antarctica may be more vulnerable to warm climates than in most previous studies

automated detection of basal icequakes and discrimination from surface crevassing thomas s hudson jonathan smith alex m brisbourne robert s white journal annals of glaciology

basal icequakes recorded beneath an alpine glacier glacier d argentiere mont blanc france evidence for stick slip motion while basal icequakes associated with glacier motion have been detected under antarctica for several decades there remains very little evidence of stick slip motion for alpine glaciers here we analyzed 2357 basal icequakes that were recorded at glacier d argenti ere mont blanc massif between february and november of 2012 and that are likely to be associated with basal sliding these events have been classified into 18 multiplets based on their waveforms the strong similarity of the waveforms within each multiplet suggests an isolated repeating source despite this similarity the peak amplitude within each multiplet varies gradually in time by up to a factor of 18 the distribution of these events in time is relatively complex for long time scales we observe progressive variations in the amplitudes of events within each multiplet for intermediate time scales hours the events occur regularly in time with typical return times of several minutes up to several hours for short time scales from 0 01 to 100 s the largest multiplet shows clus tering in time with a power law distribution of the interevent times the location of these events and their focal mechanisms are not well constrained because most of these events were detected by a single seismometer nevertheless the locations can be estimated with an accuracy of a few tens of meters using a polarization analysis the estimated average depth of the basal events is 179 m which is in good agreement with the estimated glacier thickness the relative changes in distance between the source and the sensor can be measured accurately by correlating separately the p wave and s wave parts of the seismograms of each event with the template waveforms which are obtained by averaging the signals within each multiplet we observed small variations in the times between the p wave and the s wave of up to 0 6 ms over 50 days these variations cannot be explained by displacement of the sensor with respect to the glacier but might be due to small changes in the seismic wave velocities with time finally we found using numerical simulations that the observed signals are better explained by a horizontal shear fault with slip parallel to the glacier flow than by a tensile fault these results suggest that the basal events are associated with stick slip motion of the glacier over rough bedrock the rupture length and the slip are difficult to estimate nonetheless the rupture length is likely to be of the order of meters and the total seismic slip accumulated over one day might be as large as the glacier motion during the most active bursts

changes in the velocity structure of the greenland ice sheet using satellite radar interferometry observations of greenland we detected widespread glacier acceleration below 66 north between 1996 and 2000 which rapidly expanded to 70 north in 2005 accelerated ice discharge in the west and particularly in the east doubled the ice sheet mass deficit in the last decade from 90 to 220 cubic kilometers per year as more glaciers accelerate farther north the contribution of greenland to sea level rise will continue to increase

minimum froude number and the equilibrium of alluvial sand rivers rivers adjust towards an equilibrium condition the stability of which depends upon a set of controlling factors expressed by the froude number as alluvial river channels approach stable conditions the froude number of the channel flow will tend to attain a minimum value which reflects minimum bed material motion and maximum channel stability under the constraints imposed by water discharge sediment load and particle size computer simulations for sand bed rivers show that the froude number of the flow tends to a minimum value when the equilibrium river tends to a certain hydraulic geometry evidence from 57 alluvial sand material rivers and stable canals shows that this simulated hydraulic geometry with minimum froude number corresponds to the natural equilibrium state

total electron content behavior over japan during geomagnetic storms 1 the total electron content tec obtained from gps signals is used to study ionospheric dynamics over japan during geomagnetically disturbed conditions the numerous tec measurements are averaged in cells with a size 1 5 1 5 geographic scale and formatted as time series within the years 2000 2002 to extract the storm time changes of tec the diurnal and 27 day periodicities are subsequently removed diurnal variations are removed by replacing absolute tec values in each cell with their relative deviations rtec from medians the hourly rtec values from all cells within the central 4 wide band over japan area are then approximated by a plane surface this surface is represented by two parameters its value at the center rt and the slope b along the main axis taken as constants of the linear regression the 27 day periodicity was approximated by fourier waves with main period of 640 hours and two harmonics separately for rt and b and subtracted from them the analysis of rt and b behavior during a number of geomagnetic storms allowed us to reveal several repeatable features of average tec behavior it was found that tec behavior during the storms is similar to that of fof2 at the f region and was local time dependent a marked poleward expansion of the equatorial ionosphere crest region at the end of recovery phase is persistently observed feature produced probably by intensified eastward zonal winds such an expansion of equatorial ionosphere is observed also during isolated substorms outside main geomagnetic storms an oscillation like change of positive and negative disturbances with period of 24 hours is observed during a 4 day period following a moderate storm in the absence of geomagnetic activity driver that effect is probably caused by the alternative expansion and contraction of equatorial ionosphere

the robustness of seismic moment and magnitudes estimated using spectral analysis we present an assessment of how microseismic moment magnitude mw e stimates vary with the method and parameters used to calculate seismic moment this is an important topic for operators and regulators who require good magnitude estimates when monitoring induced seismicity it is therefore imperative that these parties know and understand what errors exist in given magnitude values something that is poorly reported this study concentrates on spectral analysis techniques and compares mw computed in the time and frequency domains using recordings of mw 1 5e vents at cotton valley east texas the maximum discrepancy between mw estimated using the different methods is 0 6 units a significant variation by adjusting parameters in the mw calculation we find that the radiation pattern correction term can have the most significant effect on m w generally up to 0 8 units following this investigation we make a series of recommendations for estimating microseismic m w using spectral methods noise should be estimated and removed from recordings and an attenuation correction should be applied the spectral level can be measured by spectral fitting or taken from the low frequency level significant factors in obtaining reliable microseismic mw estimates include using at least four receivers recording at 1000 hz and making radiation pattern corrections based on focal mechanism solutions not average values

joint inversion for earthquake depths using local waveforms and amplitude spectra of rayleigh waves reliable earthquake depth is fundamental to many seismological problems in this paper we present a method to jointly invert for centroid depths with local distance 5 seismic waveforms and regional distance of 5 15 rayleigh wave amplitude spectra on sparse networks we use earthquake focal mechanisms and magnitudes retrieved with the cut and paste cap method to compute synthetic amplitude spectra of fundamental mode rayleigh wave for a range of depths then we grid search to find the optimal depth that minimizes the joint misfit of amplitude spectra and local waveforms as case studies we apply this method to the 2008 wells nevada mw6 0 earthquake and a mw5 6 outer rise earthquake to the east of japan trench in 2013 uncertainties estimated with a bootstrap re sampling approach show that this joint inversion approach constrains centroid depths well which are also verified by independent teleseismic depth phase data

seismicity on the western greenland ice sheet surface fracture in the vicinity of active moulins we analyzed geophone and gps measurements collected within the ablation zone of the western greenland ice sheet during a 35 day period of the 2011 melt season to study changes in ice deformation before during and after a supraglacial lake drainage event during rapid lake drainage ice flow speeds increased to 400 of winter values and icequake activity peaked at times 7 days after drainage this seismicity developed variability over both diurnal and longer periods 10 days while coincident ice speeds fell to 150 of winter values and showed nightly peaks in spatial variability approximately 95 of all detected seismicity in the lake basin and its immediate vicinity was triggered by fracture propagation within near surface ice 330m deep that generated rayleigh waves icequakes occurring before and during drainage frequently were collocated with the down flow west end of the primary hydrofracture through which the lake drained but shifted farther west and outside the lake basin after the drainage we interpret these results to reveal vertical hydrofracture opening and local uplift during the drainage followed by enhanced seismicity and ice flow on the downstream side of the lake basin this region collocates with interferometric synthetic aperture radar measured speedup in previous years and could reflect the migration path of themeltwater supplied to the bed by the lake the diurnal seismic signal can be associated with nightly reductions in surface melt input that increase effective basal pressure and traction thereby promoting elevated strain in the surficial ice

joint geodetic and seismic analysis of surface crevassing near a seasonal glacier dammed lake at gornergletscher switzerland seasonal lake gornersee forms at the confluence of gornergletscher and grenzgletscher switzerland and experiences outburst floods annually in midsummer to study the interplay between lake drainage glacier movement and crevasse activity high frequency seismometers and gps receivers were deployed in networks near gornersee during the summer ablation seasons of 2004 2006 and 2007 we use a rayleigh wave coherence method to locate 3289 7939 and 4087 icequakes respectively primarily along well defined surface crevasses we calculate two dimensional strains from triads of gps stations and find mean differential strain rates of 300 10 6 d 1 with diurnal variations up to 800 10 6 d 1 crevasse icequake activity and glacial velocity are highest during early season then decrease as meltwater channels erode and subglacial water pressure decreases glacial response to gornersee drainage varied year to year with icequake activity promoted at some crevasses and inhibited at others suggesting syn drainage icequakes may be indicative of local drainage patterns and small scale features of the stress field diurnal pulses in icequake activity exhibit peak activity at different times of day in different locations coincident with a southeast to northwest trending concentrated shear zone near the gornergletscher grenzgletscher confluence likely due to differences in the timing of peak strain rate in these regions

observation of surface seismic activity changes of an alpine glacier during a glacier dammed lake outburst during the 2004 outburst flood of gornersee switzerland we observed surface microseismic activity so called icequakes near the glacier dammed lake on gornergletscher using surface waves we located near surface tensile fracturing events by inverting time delays using a quasi newton scheme we located 8520 near surface events with uncertainties of less than 10 m seismic activity increased during the lake drainage and the icequake epicenters migrated downglacier furthermore we identified events whose fault plane orientations are nearly perpendicular to the local pattern of surface crevassing these observations can be explained by the rotation of principal strains at the glacier surface deduced from local ice flow measurement which occurred during the flotation of the ice dam at the onset of the lake drainage in general we suggest that our technique is a useful tool to locate large data sets of microseismic events and can be used to monitor the temporal evolution of fracture processes and their dependence on glacier flow and glacier hydrology

crevasse patterns and the strain rate tensor a high resolution comparison values of the strain rate tensor represented at a 20 m length scale are found to explain the pattern and orientation of crevasses in a 0 13 km 2 reach of worthington glacier alaska u s a the flow field of the reach is constructed from surveyed displacements of 110 markers spaced 20 30 m apart a velocity gradient method is then used to calculate values of the principal strain rate axes at the nodes of a 20 m 20 m orthogonal grid crevasses in the study reach are of two types splaying and transverse and are everywhere normal to the trajectories of greatest most tensile principal strain rate splaying crevasses exist where the longitudinal strain rate x is 0 and transverse crevasses are present under longitudinally extending flow i e x 0 the orientation of crevasses changes in the down glacier direction but the calculated rotation by the flow field does not account for this change in orientation observations suggest that individual crevasses represent local values of the regional flow field and are transient on the time scale of 1 2 years they are not persistent features that are translated and rotated by flow crevasse patterns are thus found to be a useful tool for mapping the strain rate tensor in this reach of a temperate valley glacier

is an unusual large enhancement of ionospheric electron density linked with the 2008 great wenchuan earthquake 1 on 12 may 2008 at 0628 ut a major earthquake ms 8 0 struck wenchuan county 31 0 n 103 4 e in southwest china the maximum ionospheric electron density at f2 peak nmf2 recorded an unusual large enhancement during the afternoon sunset sector by the chinese ionosondes over wuhan 30 5 n 114 4 e and xiamen 24 4 n 123 9 e which are close to the earthquake epicenter an averaged increase at these two stations is about 2 times on a geomagnetic quiet day 9 may kp 2 3 days prior to the earthquake relative to the median value of 1 12 may whereas the increase was much less significant over yamagawa 31 2 n 130 6 e and okinawa 26 7 n 128 2 e in japan combining the data from the network of 58 global positioning system receivers around china and the global ionospheric map the variations of the total electron content reveal the region where enhancement persisted for a long period to be within longitudes 90 130 e our results suggest that this abnormal enhancement is most possibly a seismo ionospheric signature

probabilistic earthquake locations of induced seismicity in the groningen region the netherlands the groningen gas reservoir situated in the northeast of the netherlands is western europe s largest producing gas field and has been in production since 1963 the gas production has induced both subsidence and seismicity seismicity is detected and located using the koninklijk nederlands meteorologisch instituut shallow borehole array for the period 2015 2017 incorporating the back projection techniques of quakemigrate and the nonlinear location procedure to constrain earthquake locations and depths the uncertainties on the estimated depths are estimated taking into account velocity model changes in station array geometry and uncertainties in the measurement of arrival times of the p and s waves we show that the depth distribution of seismicity is consistent with nucleation within the reservoir 28 per cent or in the overburden 60 per cent within 500 m from the top of the reservoir earthquakes with hypocentres in the overburden likely originate from overlying zechstein anhydrite caprock based on their depth distribution it seems like the earthquakes are primarily driven by the elastic strain in the reservoir and overburden induced by the reservoir compaction we estimate the probability of earthquakes nucleating beneath the reservoir in the underlying carboniferous limestone and basement to be no more than 12 per cent

channel dynamics sediment transport and the slope of alluvial fans experimental study a b s t ra c t we present the results of an experimental study of alluvial fan sedimentation under conditions of constant inflow water discharge qw sediment supply qso and median grain size d the study was designed to complement and test a recently formulated model of alluvial fan sedimentation and to emphasize the interactions between and controls on flow channelization and equilibrium fan slope flow channelization and fan sedimentation were studied under conditions of nearly steady uniform aggradation steady conditions were achieved by imposing a steadily rising base level just in balance with the average sediment aggradation rate experimental inflows covered a wide range of conditions allowing examination of the effects of variations in qw q so and d in both bedload and suspension dominated environments experimental results were most consistent with an expanding flow channel model key experimental findings successfully and quantitatively predicted by the expanding flow theory include 1 straight to slightly concave radial profiles of bedload dominated fans 2 distinctly convexo concave profiles of suspension dominated fans 3 a strong inverse relationship between qw and fan slope 4 a strong but secondary relationship between q so and fan slope and 5 near independence of d and fan slope so long as transport stage is high and bedload transport dominant however potential scale effects in the experiments arose from reduced flow reynolds numbers and incorrect geometric scaling of channel widths no confident conclusions regarding the debate over the relative importance of sheetfloods and braided channel flows can be drawn from the experimental data extrapolation to field scale is best accomplished through appropriate application of the theoretical model herein confirmed against experimental data

on the disintegration of ice shelves the role of fracture dans une plateforme glaciaire contrairement au cas des glaciers les crevasses de surface peuvent atteindre le niveau de mer et les crevasses de fond remonter jusqu a ce niveau les crevasses jouent alors un role important dans la desintegration de la plateforme la fracturation est examinee en fonction des contraintes generales et locales on applique l etude a la stabilite de plateformes de l antarctique ouest

alluvial fans formed by channelized fluvial and sheet flow i theory alluvial fans and fan deltas are of three basic types those built up primarily by the action of constantly avulsing river and stream channels those constructed by sheet flows and those resulting from the successive deposition of debris flows the present analysis is directed toward the first two types a mechanistic formulation of flow and sediment transport through river channels is combined with a simple quantification of the overall effect of frequent avulsion to derive relations describing the temporal and spatial evolution of mean i e averaged over many avulsions bed slope and elevation in an axially symmetric fan an example of a fan formed predominantly by the deposition of sand is compared to a similar one formed predominantly by the deposition of gravel in each example the case of channelized flow is compared to the case of sheet flow the model is applied to the tailings basin of a mine in the companion paper

breaking the ice identifying hydraulically forced crevassing hydraulically forced crevassing is thought to reduce the stability of ice shelves and ice sheets affecting structural integrity and providing pathways for surface meltwater to the bed it can caus

seismic multiplet response triggered by melt at blood falls taylor glacier antarctica 1 meltwater input often triggers a seismic response from glaciers and ice sheets it is difficult however to measure melt production on glaciers directly while subglacial water storage is not directly observable therefore we document temporal changes in seismicity from a dry based polar glacier taylor glacier antarctica during a melt season using a synthesis of seismic observation and melt modeling we record icequakes using a dense six receiver network of three component geophones and compare this with melt input generated from a calibrated surface energy balance model in the absence of modeled surface melt we find that seismicity is well described by a diurnal signal composed of microseismic events in lake and glacial ice during melt events the diurnal signal is suppressed and seismicity is instead characterized by large glacial icequakes we perform network based correlation and clustering analyses of seismic record sections and determine that 18 of melt season icequakes are repetitive multiplets the epicentral locations for these multiplets suggest that they are triggered by meltwater produced near a brine seep known as blood falls our observations of the correspondingp wave first motions are consistent with volumetric source mechanisms we suggest that surface melt enables a persistent pathway through this cold ice to an englacial fracture system that is responsible for brine release episodes from the blood falls seep the scalar moments for these events suggest that the volumetric increase at the source region can be explained by melt input

the role of hydrologically driven ice fracture in drainage system evolution on an arctic glacier 1 observations from ellesmere island suggest that the connection between surface and subglacial drainage on a predominantly cold glacier is made abruptly by hydrologically driven propagation of fractures from the surface to the bed where ice is 150 m thick water ponded to a depth of 6 9 m within a supraglacial stream system before establishing a permanent bed connection multiple premonitory drainage events preceded the final drainage of ponded water implying that fracturing is necessary but insufficient to establish a permanent link between surface and subglacial drainage refreezing of water that penetrates the first fractures to form may reseal the connection while flow resistance within the subglacial system may delay the onset of continuous through flow a large volume of ponded water is required to enlarge fractures sufficiently by melting to maintain continuous drainage while feedbacks between subglacial hydrology and ice dynamics may assist in maintaining the connection and initiating subglacial outflow

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