character of the englacial and subglacial drainage system in the upper part of the ablation area of storglaciaren sweden on 4 july 1986 dye was injected at a point slightly above the equil ibrium line on storglac iliren a small valley glacier in northern sweden just below the equilibrium line the glacier bed is over deep ened the dye re appeared in a stream at the glacier terminus over the next 35 d this stream normally carries relatively little sediment in constrast to the situ ation in another nearby stream that also emerges from the glacier this sugge sts that the dye traveled in englacial rather than subglacial conduits tracer tests utilizing salt in bore holes in the overde epening support this interp retation as the bore holes were draining well above the bed the dye appeared during three distinct events suggesting that it became divided into at least three separate parcels shortly after iojection this probably occurred in the crevassed area in the vicinity of the inje ction point the englacial location of the drainage may be explained by the fact that in order to remain at the pressure melting p oint water in subg lacial conduits coming out of the overde epening may have had to warm up faster than would be possible by visc ous heating alone such

a direct method for assimilating sea surface height data into ocean models with adjustments to the deep circulation abstract there is as yet no consensus an the best method for inserting surface data into ocean models so that appropriate information is transmitted to the deeper layers in a rapid and efficient manner first we consider the correlation of sea surface pressure which is related to sea surface height as measured by altimeters and the surface and subsurface currents within the framework or a four layer quasi geostrophic model we begin by suggesting that the homogenization of potential vorticity q in the unforced layers discussed by rhines and young ensures that the potential vorticity anomalies in the deep ocean are weak it follows that instantaneous q information from thew deep layers may not need to be accurately known in order to reconstruct the deep eddy currents i e climatological q information may be sufficient taking the fields from the model we use the instantaneous surface streamfunction 1 data along with various approximate subsurface q climatologies and attempt to reconstruct the low

a coupled sheet conduit mechanism for jokulhlaup propagation 1 the largest glacier outburst flood jokulhlaup ever recorded in iceland occurred in 1996 and came from subglacial lake grimsvotn in vatnajokull ice cap among other noteworthy features this flood was characterized by an unprecedentedly high lake level prior to flood initiation extremely rapid linear rise in lake discharge delay between the onset of lake drainage and floodwater arrival at the glacier terminus formation of short lived supraglacial fountains and initially unchannelized outbursts of floodwater at the terminus observations suggest that the 1996 flood propagation mechanism was fundamentally different than that of previously observed floods from grimsvotn we advance a new model whereby floodwater initially propagates in a turbulent subglacial sheet which feeds a nascent system of conduits this model is able to explain key observations made of the 1996 jokulhlaup and may shed light on other outburst floods that do not conform to the standard model

hydraulics of subglacial outburst floods new insights from the spring hutter formulation using a slightly modified form of the spring hutter equations glacial outburst floods are simulated from three classic sites hazard lake yukon canada summit lake british columbia canada and grimsvotn iceland in order to calibrate the hydraulic roughness associated with subglacial conduits previous work has suggested that the manning roughness of the conduits is remarkably high but the new calibration yields substantially lower values that are representative of those for natural streams and rivers the discrepancy can be traced to a poor assumption about the effectiveness of heat transfer at the conduit walls the simulations reveal behaviour that cannot be interred from simplified theories 1 during flood onset water pressure over much of the conduit can exceed the confining pressure of surrounding ice 2 local values of fluid potential gradient can differ substantially from the value averaged over the length of the conduit contradicting an assumption of simple theories 3 as the flood progresses the location of flow constrictions that effectively control the flood magnitude can jump rapidly over large distances 4 predicted water temperature at the conduit outlet exceeds that suggested by measurements of exit water temperature

glaciohydraulic supercooling a freeze on mechanism to create stratified debris rich basal ice ii theory simple theory supports field observations lawson and others 1998 that subglacial water flow out of overdeepenings can cause accretion of layered debris bearing ice to the bases of glaciers the large meltwater flux into a temperate glacier at the onset of summer melting can cause rapid water flow through expanded basal cavities or other flow paths if that flow ascends a sufficiently steep slope out of an overdeepening the water will supercool as the pressure melting point rises and basal ice accretion will occur diurnal occasional or annual fluctuations in water discharge will cause variations in accretion rate debris content of accreted ice or subsequent diagenesis producing layers under appropriate conditions net accretion of debris bearing basal ice will allow debris fluxes that are significant in the glacier sediment budget

investigating the stability of subglacial lakes with a full stokes ice sheet model despite the large amount of subglacial lakes present underneath the east antarctic ice sheet and the melt processes involved the hydrology beneath the ice sheet is poorly understood changes in subglacial potential gradients may lead to subglacial lake outbursts discharging excess water through a subglacial drainage system underneath the ice sheet such processes can eventually lead to an increase in ice flow in this paper a full stokes numerical ice sheet model was employed which takes into account the ice flow over subglacial water bodies in hydrostatic equilibrium with the overlying ice sensitivity experiments were carried out for small perturbations in ice flow and basal melt rate as a function of ice thickness general surface slope ice viscosity and lake size in order to investigate their influence on the subglacial potential gradient and the impact on subglacial lake drainage experiments clearly demonstrate that small changes in surface slope are sufficient to start and sustain episodic subglacial drainage events lake drainage can therefore be regarded as a common feature of the subglacial hydrological system and may influence to a large extent the present and future behavior of large ice sheets

evolution of subglacial water pressure along a glacier s length observations from along the length of bench glacier alaska usa show that the subglacial water pressure field undergoes a multiphase transition from a winter mode to a summer mode data were collected at the glacier surface the outlet stream and in a network of 47 boreholes spanning the length of the 7 km long glacier the winter pressure field was near overburden with low magnitude centimeter to meter scale and long period days to weeks variations during a spring speed up event boreholes showed synchronous variations and a slight pressure drop from prior winter values diurnal pressure variations followed the speed up with their onset associated with a glacier wide pressure drop and flood at the terminus stream diurnal variations with swings of up to 80 of overburden pressure were typical of mid summer several characteristics of our observations contradict common conceptions about the seasonal development of the subglacial drainage system and the linkages between subglacial hydrology and basal sliding 1 increased water pressure did not accompany high sliding rates 2 the drainage system showed activity characteristic of the spring season long before abundant water was available on the glacier surface 3 the onset of both spring activity and diurnal variations of the drainage system did not show a spatial progression along the length of the glacier

modelling the evolution of subglacial tunnels due to varying water input the time evolution ofa subglacial tunnel cross section is examined using a two dimensional finite element ice flow model coupled to an idealized drainage system simulations are driven by physically based calculations of surface water input variations at storglaciaren sweden highlights of the model are its ability to handle unsteady conditions and irregular tunnel shapes agreement between modelled water pressure and borehole water levels is good the following conclusions are reached i tunnels adapt to fluctuating inflow on time scales of days storms during which effective pressure ranges from 0 to 0 9 mpa cause significant adjustments but daily fluctuations due solely to meltwater inflow are minor ii open channel flow may become commonplace late in the ablation season iii initial tunnel shape influences subsequent tunnel evolution and seasonal water pressure variation over the course of a summer tunnels retain some of their initial shape though in all experiments the width to height ratio increased with time iv tunnel contraction forms broad low tunnels however v given two tunnels of equal initial area the higher narrower one expands more rapidly thus more semi circular tunnels may capture flow from broader neighbours early in the summer

subglacial drainage eskers and deforming beds beneath the laurentide and eurasian ice sheets glaciological theory predicts that the subglacial drainage network at the base of gently sloping ice sheets resting on deforming sediment should consist of many wide shallow probably braided canals distributed along the ice sediment interface rather than an arborescent network of relatively few large tunnels as would develop over a rigid substrate a corollary prediction examined here is that eskers which form in large subglacial tunnels should be rare where subglacial bed deformation occurred but they may be relatively common where the bed was rigid bed deformation would be most likely where subglacial till was relatively continuous fine grained and of low permeability that is in regions where till is derived primarily from underlying sedimentary bedrock but unlikely where discontinuous coarse grained high permeability till was derived from underlying crystalline bedrock the observed distribution of eskers in areas covered by the laurentide and eurasian british scandinavian and barents sea ice sheets during the last glaciation shows that most eskers occur over crystalline bedrock overlain by discontinuous high permeability till but are rare or absent over sedimentary bedrock overlain by fine grained low permeability till thus matching reasonably well our prediction glaciological theory and geologic evidence indicate that esker systems on a subcontinental scale are time transgressive sedimentological evidence for a canal drainage system appears to be present in fine grained tills where eskers are largely absent

a multicomponent coupled model of glacier hydrology 1 theory and synthetic examples 1 basal hydrology is acknowledged as a fundamental control on glacier dynamics especially in cases where surface meltwater reaches the bed for many glaciers at midlatitudes basal drainage is influenced by subaerial englacial and subsurface water flow one of the major shortcomings of existing basal hydrology models is the treatment of the glacier bed as an isolated system we present theoretical and computational models that couple glacier surface runoff englacial water storage and transport subglacial drainage and subsurface groundwater flow each of the four model components is represented as a two dimensional vertically integrated layer that communicates with its neighbors through water exchange governing equations are derived from the law of mass conservation and are expressed as a balance between the internal distribution of water and external sources the numerical exposition of this theory is a time dependent finite difference model that can be used to simulate glacier drainage in this paper we outline the theory and conduct simple tests using an idealized glacier geometry in the companion paper the model is tailored to trapridge glacier yukon territory canada where results are compared with measurements of subglacial water pressure

flow switching and water piracy between rutford ice stream and carlson inlet west antarctica rutford ice stream and carlson inlet are neighbouring glaciers in west antarctica rutford ice stream flows at speeds greater than 350m a 1 whereas carlson inlet which has some similar dimensions and supports a similar driving stress flows 10 50 times slower we discuss a range of observations concerning carlson inlet and conclude that there is good indirect evidence that it is a relict ice stream which ceased streaming more than 240 years bp but sufficiently recently that its surface morphology basal water content and basal morphology still retain characteristics produced by streaming an analysis of expected subglacial drainage pathways indicates that carlson inlet is not streaming because it is currently starved of subglacial water which is currently directed beneath rutford ice stream this current state of water piracy by rutford ice stream is however sensitive to minor thickness changes on the ice streams a similar to 120 m 4 thickening of rutford ice stream would divert almost all the subglacial water in the system towards carlson inlet and could reactivate its flow the result highlights the importance of subglacial drainage in controlling ice stream evolution and the requirement for ice sheet models to couple ice flow with subglacial drainage

modifications to the theory of intraglacial waterways for the case of subglacial ones on defend l idee que dans les glaciers de montagne temperes les voies d eau sont sous glaciaires pour un conduit noye sous glaciaire il faut introduire deux processus importants l accroissement de la deformation plastique sur les cotes amont des bosses et la chaleur apportee par l eau des sources qui en hiver rend compte de la plus grande partie du debit la theorie explique pourquoi rothlisberger 1972 dut adopter une valeur non realiste pour le parametre rheologique de la glace elle conduit a la conclusion que dans les zones non surcreusees la plus grande partie de l annee les conduits sous glaciaires doivent rester non noyes et a la pression atmospherique cas des surcreusements l incidence de ce nouveau modele sur la theorie du glissement des glaciers

mechanisms of englacial conduit formation and their implications for subglacial recharge abstract ideas about the character and evolution of englacial drainage systems have been deeply influenced by the theoretical model developed by shreve 1972 movement of water in glaciers journal of glaciology 11 62 205 214 the shreve model is based on three main assumptions 1 englacial drainage is in steady state 2 englacial water will flow along the steepest hydraulic gradient within the glacier and 3 pressure head equals the pressure of the surrounding ice minus a small component due to melting of the walls the shreve model has been widely adopted as a fundamental component of englacial drainage theory there is no evidence however that the model provides a realistic picture of actual glacial drainage systems to evaluate shreve s theory we used speleological techniques to directly survey englacial conduits we mapped a total of 8 25 km of passage in 27 distinct englacial conduits in temperate polythermal cold based and debris covered glaciers between 2005 and 2008 new information reported here is supplemented by published data on 40 other englacial conduits located worldwide and surveyed to ice depths of 176 m using speleological techniques in all cases englacial drainage systems consisted of a single unbranching conduit englacial conduit morphologies were found to be intimately linked to the orientation of a glacier s principal stresses or the presence of pre existing lines of high hydraulic conductivity if a sufficient supply of water is available hydrofracturing forms vertical conduits in zones of longitudinal extension and subhorizontal conduits where longitudinal stresses are compressive on unfractured glacier surfaces relatively shallow subhorizontal conduits with migrating nickpoints form by cut and closure provided channel incision is significantly faster than surface lowering conduits can also form along permeable debris filled crevasse traces that connect supraglacial lake basins of different potential our results suggest that shreve type englacial drainage systems do not exist and implies that englacial conduits can only penetrate through thick ice to recharge the bed where supraglacial water bodies either intersect or are advected through zones of acceleration

geometry and flow conditions of subglacial water at south cascade glacier washington state u s a an analysis of tracer injections tracers were injected into south cascade glacier to determine the flow condition and geometry of the subglacial water system results indicate that two distincts drainage basins on the glacier feed the two main streams flowing from the glacier in the largest basin two parallel drainage networks exist one englacial and the other subglacial

seasonal waves on glaciers seasonal waves accompanying annual changes in the sliding velocity of ice travel down glacier at speeds much faster than the ice itself a simple explanation for these waves in terms of the passage of a pressure wave through the subglacial drainage system is given drainage by both distributed and localized systems is explored with the sliding velocity governed by a dependence on the effective pressure waves are caused by drainage through a slow distributed system but may be damped if this is well connected to an efficient channelized system a possible connection between these waves and high velocity spring events is discussed

hydraulics of subglacial cavities modele theorique du comportement a l etat stationnaire des cavites remplies d eau et interconnectees sur le lit du glacier

structure and stability of the former subglacial drainage system of the glacier de tsanfleuron switzerland a well developed subglacial drainage system consisting of large cavities developed in the lee of bedrock steps connected together by a network of nye channels is exposed on an area of recently deglaciated limestone bedrock in front of glacier de tsanfleuron switzerland this system covers some 51 per cent of the bedrock surface area and is believed to have transported the bulk of supraglacially derived meltwaters through the glacier using the cavity hydraulics model of kamb 1987 it is shown that the geometry of the system rendered it stable against collapse by meltback of channel roofs into a tunnel dominated system for likely combinations of glacier geometry and meltwater discharge the steady state water pressure in this system would have been only a small fraction of that required for flotation and for discharges of less than about 0 5 5 m3 s 1 water would have flowed at atmospheric pressure the system appears to have adjusted to varying discharges by a combination of varying water pressure and changing the total cross sectional area of flow by altering the number of active channels connecting cavities glacier sliding velocity would have been independent of meltwater discharge for discharges at which water flowed at atmospheric pressure but would have risen with increasing discharge for higher flows velocities on the order of 0 1 m d 1 are predicted for a realistic range of discharges and effective pressures and these are believed to be plausible episodes of enhanced sliding in glaciers with similar drainage systems could be triggered by a rise in meltwater discharge across the threshold between flows at atmospheric pressure and flow under pressure from the glacier

on the role of mechanical energy in maintaining subglacial water conduits at atmospheric pressure recent theo retical studies of glacier hydrology have assumed that subglacial conduits are completely filled with water under steady state conditions this however is not necessarily the case where discharges are larger than a few tens of liters per second and the down glacier slope of the bed is more than a few degrees the potential energy released by water descending this slope may be capable of melting the walls of a subglacial conduit many times faster than the conduit can close by plastic flow of the ice as a result the pressure in such tunnels may normally be atmospheric or possibly even at the triple point pressure if there is no open connection to the glacier surface simple calcu lations suggest that such pressures in subglacial conduits may be more common than herclofore anticipated the positions of such open conduits may be unstable to small per turbations in discharge or ice veloci ty this is because the mechanical energy available in excess of that needed to balance closure can instead offset the gene ral flow of the ice cond ui ts can thus trend diago nally across the direction of ice aow if an increase in the angle which such a conduit makes with the ice flow direction also results in an increase in slope of he conduit more mechanical energy will become available resulting in a positive feedback process subglacial channels at atmospheric pressure may inauence the origin and morphology of certain glacial landforms such as eskers and plastically molded features resume sur le role de l inergie newtonnienne dam le maintien du riseau aquiflrl sous glaciaire cl la pression almosph irique de recentes etudes theoriques d hydrologie glaciaire ont suppose que le reseau sous glaci aire clait corn pletement rempli d eau en condition d cquil ibre stable ceci neanmoins n est pas necess airement le cas lorsque les debits sonl superieurs a quelques dizaines de litres par seconde et que la pente du lit du glacier est superieure a quelques degres i energie potentielle mise en oeuvre par i eau descendant celle pente peut ire capable de fondre les parois d un chenal sous glaciaire beaucoup plus vite que le chenal ne peut se refermer par le auage plastique de la glace il en resuhe que la pression dans de tels chenaux peut nor rnalement etre atrnospherique

diurnal fluctuations in borehole water levels configuration of the drainage system beneath bench glacier alaska usa water levels were measured in boreholes spaced along the entire length of bench glacier alaska usa for a period in excess of 2 years instrumented boreholes were arranged as nine pairs along the center line of the glacier and an orthogonal grid of 16 boreholes in a 3600 m 2 region at the center of the ablation area diurnal fluctuations of the water levels were found to be restricted to the late melt season pairs of boreholes spaced along the length of the ablation area often exhibited similar fluctuations and diurnal changes in water levels three distinct and independent types of diurnal fluctuations in water level were observed in clusters of boreholes within the grid of boreholes head gradients suggest water did not flow between clusters and a single tunnel connecting the boreholes could not explain the observed pattern of diurnal water level fluctuations inter borehole and borehole cluster connectivity suggests the cross glacier width of influence of a segment of the drainage system connected to a borehole was limited to tens of meters a drainage configuration whereby boreholes are connected to a somewhat distant tunnel by drainage pipes of differing lengths often hundreds of meters is shown with a numerical test to be a plausible explanation for the observed borehole behavior

an active subglacial water system in west antarctica mapped from space satellite laser altimeter elevation profiles from 2003 to 2006 collected over the lower parts of whillans and mercer ice streams west antarctica reveal 14 regions of temporally varying elevation which we interpret as the surface expression of subglacial water movement vertical motion and spatial extent of two of the largest regions are confirmed by satellite image differencing a major previously unknown subglacial lake near the grounding line of whillans ice stream is observed to drain 2 0 cubic kilometers of water into the ocean over 3 years while elsewhere a similar volume of water is being stored subglacially these observations reveal a wide spread dynamic subglacial water system that may exert an important control on ice flow and mass balance

seasonal changes in the morphology of the subglacial drainage system haut glacier d arolla switzerland dye tracing techniques were used to investigate the glacier wide pattern of change in the englacial subglacial drainage system of haut glacier d arolla during the ablation seasons of 1990 and 1991 analysis of breakthrough curve characteristics indicate that over the course of a melt season a system of major channels developed by headward growth at the expense of a hydraulically inefficient distributed system by the end of the melt season this channel system extended at least 3 3 km from the snout of the 4 km long glacier and drained the bulk of supraglacially derived meltwater passing through the glacier the upper limit of the channel system closely followed the retreating snowline up glacier rates of headward channel growth reached c 65 m d 1 although these rates decreased in the upper 1 km of the glacier where snowline retreat exposed a patchy firn aquifer it appears that the removal of snow with its high albedo and significant water storage capacity from the glacier surface resulted in a dramatic increase in the volume of runoff into moulins and in the peakedness of daily runoff cycles this induced transient high water pressures within the distributed drainage system which caused it to evolve rapidly into a channelised system it is therefore likely that at a local scale channel growth occurred down glacier from moulins and that the overall up glacier directed pattern of channel formation was caused by the retreating snowline exposing new moulins and crevasses to inputs of ice derived meltwater damping of diurnal melt inputs by storage in the firm aquifer accounts for the slowing of channel growth in the upper glacier 1998 john wiley sons ltd

testing a numerical glacial hydrological model using spring speed up events and outburst floods 1 we describe a numerical model of a glacial hydrologic system that reproduces the salient features of two hydrological and ice motion events commonly observed on temperate alpine glaciers these include the pattern of ice sliding and water discharge characteristic of spring speed up events and the triggering and structure of outburst floods from ice marginal lakes these behaviors result from strong internal feedbacks between water storage in englacial macro pores or an ice marginal lake ice motion by sliding and deformation and a subglacial hydrologic system consisting of a slow flow linked cavity network and a fast flow centerline conduit

rothlisberger channel theory its origins and consequences the theory of channelized water flow through glaciers most commonly associated with the names of hans rothlisberger and ron shreve and their 1972 papers in the journal of glaciology was developed at a time when interest in glacier bed processes was expanding and the possible relationship between glacier sliding and water at the bed was becoming of keen interest the r channel theory provided for the first time a physically based conceptual model of water flow through glaciers the theory also marks the emergence of glacier hydrology as a glaciological discipline with goals and methods distinct from those of surface water hydrology

character of the englacial and subglacial drainage system in the lower part of the ablation area of storglaciaren sweden as revealed by dye trace studies

dynamic distributed drainage implied by the flow evolution of the 1996 1998 adventure trench subglacial lake discharge abstract the transport of subglacial water beneath the east antarctic ice sheet is an enigmatic and difficult to observe process which may affect the flow of the overlying ice and mixing of the oceans in the sub ice shelf cavities and ultimately global climate periodic outbursts are a critical mechanism in this process recent analysis of satellite data has inferred a subglacial hydraulic discharge totaling 2 km 3 traveling some 260 km along the ice bed interface of the adventure subglacial trench between 1996 and 1998 wingham et al 2006 rapid discharge connects antarctic subglacial lakes nature 440 1033 1036 using radar echo sounding data from the adventure subglacial trench region in conjunction with the previously reported satellite observations along with some basic modeling we calculate a mass budget and infer a flow mechanism for the 1996 1998 event the volume released from the source lake exceeded the volume received by the destination lakes by 1 1 km 3 this discrepancy indicates that some water must have escaped downstream from the lowest destination lake from 1997 onward the downstream release of water from the destination lakes continued until at least 2003 several years after the 1998 cessation of surface subsidence at the source lake by 2003 a total of 1 5 km 3 or nearly 75 of the water released by the source lake had traveled downstream from the destination lakes the temporal evolution of discharge from the outlet can be simulated with the classic ice walled semicircular channel model if and only if the retreat of the source lake shoreline is taken into account further downstream the ice bedrock geometry along the inferred flow path downstream includes many sections where thermal erosion of the overlying ice would not be sustainable along these reaches mechanical lifting of the ice roof and or erosion of a sedimentary substrate by a broad shallow water system would be most effective means of sustaining the discharge a distributed system is also consistent with the 3 month delay between water release at the source lake and water arrival at the destination lake observations of intermittent flat bright bed reflections in radar data acquired along the flow path are consistent with the presence of a broad shallow water system ultimately the presence of large subglacial lakes along the flow path of the 1996 1998 adventure subglacial trench flow path delayed the arrival of water to points downstream by approximately 12 months

late wisconsin ice surface profile calculated from esker paths and types katahdin esker system maine abstract values of the gradient of the former ice surface can be inferred at points along a flow line from deviations of esker paths or transitions in esker type and numerically integrated to give the profile a profile calculated in this way shows that during formation of the katahdin esker system about 12 700 yr ago the ice thickness at distances of 10 20 50 100 and 140 km from the terminus which is about two thirds of the distance to the ice divide was approximately 200 300 600 750 and 900 m the terminal reach was computed by assuming an unknown uniform basal drag and matching the profile to its known elevation at the terminus and known gradient 10 km upglacier correction for isostatic rebound based on the elevations of contemporaneous deltas and of the marine limit proved unnecessary because the tilt due to the difference in uplift at the two ends of the profile is only 0 1 m km 1 with other plausible assumptions as to sea levels in the past elevations of the marine limit or exact location of the terminus the profile could be as much as roughly 100 m higher it hits mount katahdin about 500 m below its summit which is at 1600 m in agreement with the geological evidence farther west the steepening of the upper part of the profile suggests that the mountain dammed and diverted the ice basal drag computed from the profile varies from about 20 kpa 0 2 bar near the terminus to 30 kpa 0 3 bar at 100 km to 70 kpa 0 7 bar at 140 km the relatively low values away from the influence of mount katahdin agree with independent evidence from deep sea cores of substantial late wisconsin ice sheet thinning without comparable areal reduction the method has potential for application over wide areas that were occupied by the laurentide and scandinavian ice sheets

glaciohydraulic supercooling a freeze on mechanism to create stratified debris rich basal ice i field evidence debris laden ice accretes to the base of matanuska glacier alaska u s a from water that supercools while flowing in a distributed drainage system up the adverse slope of an overdeepening frazil ice grows in the water column and forms aggregates while other ice grows on the glacier sole or on substrate materials sediment is trapped by this growing ice forming stratified debris laden basal ice growth rates of 0 1 m a 1 of debris rich basal ice are possible the large sediment fluxes that this mechanism allows may have implications for interpretation of the widespread deposits from ice that flowed through other overdeepenings including heinrich events and the till sheets south of the laurentian great lakes

a multicomponent coupled model of glacier hydrology 2 application to trapridge glacier yukon canada 1 a new glaciohydraulic model is tailored to trapridge glacier yukon canada where long term measurements of subglacial water pressure provide parameter constraints and a platform for model evaluation using digital elevation models and meteorological data as input we investigate hydrology on diurnal and seasonal timescales quantitative comparisons of simulated and observed pressure records allow us to select a reference model objectively from which we gain first insights into the gross spatial characteristics of the drainage system equilibrium simulations highlight target areas for water storage and potential sticky spots both of which have established relevance to glacier dynamics seasonal simulations capture the key signatures of spring and autumn transitions and corroborate our understanding of the processes involved successfully modeled features of the spring transition include increased hydraulic coupling between the surface and bed with time temporary augmentation of subglacial storage and rapid subglacial transitions from a hydraulically unconnected to connected state autumn transitions are characterized by deterioration of the basal drainage network drawdown of subglacial storage reservoirs and heightened sensitivity to precipitation and surface refreezing finally we draw attention to the important role of groundwater transport in cold glacial environments where permafrost can impede drainage from the ice margin

osl dating of offset streams across the altyn tagh fault channel deflection loess deposition and implication for the slip rate abstract two deflected streams flowing across the altyn tagh fault atf were investigated at the aksay segment nw china due to strike of the atf stream channels are deflected and elongated by adding new sections along the fault line after subsequent water erosion and fluvial refreshment banks of these deflected streams are overlain by aeolian loess geomorphological features suggest that stream deflections along the fault were developed as a result of faulting activities and displacements were progressively accumulated from multiple faulting cycles each faulting cycle is composed of faulting event triggered elongation of channels creation of stream banks or risers and subsequent aeolian loess deposition on the banks a model is proposed to illustrate the relationship between fault movement and loess deposition which is supported by osl dating of the loess on the offset stream channels our results demonstrated that 1 loess deposits along deflected streams can be used to trace fault slip history given specific geomorphic assumptions discussed in the text and 2 based on stream channel offsets and loess ages the holocene slip rate of the atf is estimated to be 11 2 mm year along the aksay segment

vertical extension of the subglacial drainage system into basal crevasses water plays a first order role in basal sliding of glaciers and ice sheets and is often a key constituent of accelerated glacier motion subglacial water is known to occupy systems of cavities and conduits at the interface between ice and the underlying bed surface depending upon the history of water input and the characteristics of the substrate full understanding of the extent and configuration of basal water is lacking however because direct observation is difficult this limits our ability to simulate ice dynamics and the subsequent impacts on sea level rise realistically here we show that the subglacial hydrological system can have a large volume of water occupying basal crevasses that extend upward from the bed into the overlying ice radar and seismic imaging combined with in situ borehole measurements collected on bench glacier alaska reveal numerous water filled basal crevasses with highly transmissive connections to the bed some crevasses extend many tens of metres above the bed and together they hold a volume of water equivalent to at least a decimetre layer covering the bed our results demonstrate that the basal hydrologic system can extend high into the overlying ice mass where basal crevasses increase water storage capacity and could potentially modulate basal water pressure because basal crevasses can form under commonly observed glaciological conditions our findings have implications for interpreting and modelling subglacial hydrologic processes and related sliding accelerations of glaciers and ice sheets

subglacial modulation of the hydrograph from glacierized basins the extent of basin glacierization has important implications for the hydrograph in part because snow firn and ice impart different delays in water transport through the system here the significance of subglacial drainage morphology in modulating the hydrograph is examined with a one dimensional physically based model the conceptual model of subglacial drainage comprises both fast and slow elements respectively associated with summer and winter drainage regimes the additional possibility of a permeable glacier substrate is taken into account by allowing water transport in a subglacial aquifer forced by prescribed rates of melt water delivery to the glacier bed the model predicts glacier discharge by drainage system provenance the effects of 1 hard versus soft glacier beds 2 subsurface permeability and groundwater flow and 3 glacier geometry are then investigated hydrograph character in the form of peak timing and amplitude symmetry with respect to the forcing and the amplitude of diurnal fluctuations is affected by the partitioning of water through the various flow elements hard beds and impermeable substrates maximize the discharge routed through the fast drainage system in the simulations generally resulting in higher seasonal discharge maxima and stronger diurnal variations in discharge high hydraulic transmissivities either at the glacier bed or in underlying strata hinder the development of the fast drainage system in the simulations producing hydrographs of lower amplitude glacier geometry has a modest effect with adverse bed slopes very thick or very thin ice and short glacier lengths favouring prolonged drainage through the slow system these results suggest that the morphology and evolution of the subglacial drainage system may play a significant role in determining the character of the hydrograph from glacierized basins

borehole water level variations and the structure of the subglacial hydrological system of haut glacier d arolla valais switzerland late summer subglacial water pressures have been measured in a dense array of boreholes in the ablation area of haut glacier d arolla switzerland interpolated surfaces of minimum diurnal water pressure and diurnal water pressure variation suggest the presence of a subglacial channel within a more widespread distributed drainage system the channel flows along the centre of a variable pressure axis vpa some tens of metres wide that is characterized by low minimum diurnal water pressures frequently atmospheric and high diurnal water pressure variations these characteristics are transitional over a lateral distance of c 70 m to higher and more stable subglacial water pressures in the adjacent distributed system water pressure variations recorded in boreholes located close to the centre of the vpa reflect the delivery of surface derived meltwater to the glacier bed and result in a diurnally reversing transverse hydraulic gradient that drives water out from the channel into the distributed system during the afternoon and back to the channel overnight subglacial observations suggest that such flow occurs through a vertically confined sediment layer borehole turbidity records indicate that the resulting diurnal water flows are responsible for the mobilization and transport of fine debris in suspension analysis of the propagation velocity and amplitude attenuation of the diurnal pressure waves suggests that the hydraulic conductivity of the sediment layer decreases exponentially with distance from the channel falling from c 10 4 m s 1 at the channel boundary to c 10 7 ms 1 70m away these apparent hydraulic conductivities are consistent with darcian flow through clean sand and typical glacial till respectively we suggest that fine material is systematically flushed from basal sediments located adjacent to large melt season drainage channels beneath warm based glaciers this process may have important implications for patterns of glacier erosion hydrochemistry and dynamics

investigations of glacier hydrological systems using dye tracer techniques observations at pasterzengletscher austria a l aide de traceurs colores on a mis en evidence une division laterale du drainage dans le bas de la langue qui n est pas determinee par la direction des crevasses obliques la reapparition de l eau dans les differents moulins est complexe bien qu elle reste constante dans le temps

persistent englacial drainage features in the greenland ice sheet 1 surface melting on the greenland ice sheet is common up to 1400 m elevation and in extreme melt years even higher water produced on the ice sheet surface collects in lakes and drains over the ice sheet surface via supraglacial streams and through the ice sheet via moulins water delivered to the base of the ice sheet can cause uplift and enhanced sliding locally here we use ice penetrating radar data to observe the effects of significant basal melting coincident with moulins and calculate how much basal melt occurred we find that more melting has occurred than can be explained by the release of potential energy from the drainage of surface meltwater during one melt season suggesting that these moulins are persistent for multiple years we find only a few persistent moulins in our study area that drain the equivalent of multiple lakes per year and likely remain active over several years our observations indicate that once established these persistent moulins might be capable of establishing well connected meltwater drainage pathways

tv video observations of englacial voids in storglaciaren sweden tv video observations of four boreholes in storglaciaren sweden revealed that 1 3 of the observed ice column was composed of englacial voids the form of the voids is presented by photographs from the video it is suggested that they are openings into englacial channels and cavities which were intersected during drilling the observations further showed that about 11 of the ice column consisted of air bubble poor blue ice inclusions the observations show a relation between the blue ice inclusions and the voids which indicates that the origin and development of these features are coupled to each other it is suggested that crevasses in the accumulation area are an important factor in this process

subglacial till a physical framework for its properties and processes the continuum theory of mixtures provides a framework around which present knowledge of subglacial till can be organized the proposed framework is provisional in two senses the constitutive description of till will require improvement and not all potentially significant processes have been included till is treated as a three component mixture of water clasts coarse grained solids and fine grained matrix solids these components obey mass balance equations and their behavior is subject to constitutive relations that describe such processes as darcian water transport fine grained sediment transport consolidation shear deformation dilatancy and comminution five state variables uniquely determine the compressibility permeability shear strength and other physical properties numerical solutions of the state evolutions equations illustrate that the properties of till are highly responsive to changes in the subglacial environment