diurnal variations in vertical strain observed in a temperate valley glacier 1 during a period of diurnal fluctuations in glacial flow speed vertical strain was measured with sub daily temporal resolution on unteraargletscher switzerland mean vertical strain in boreholes up to 300 m deep in 400 m thick ice was found to fluctuate diurnally vertical strain rates were tensile in the daytime and compressive at night with a magnitude of up to 10 3 day 1 horizontal surface strain was observed to fluctuate in a manner consistent with the vertical deformation diurnal surface flow speed variations correlated well with basal water pressure suggesting a basal control on temporal flow variations nevertheless the strain rate measurements indicated that changes in surface flow speed are affected by internal ice deformation and not a direct measure of local basal motion basal conditions in the surrounding neighborhood and their temporal variations take an important role in short term glacial flow fluctuations

seasonal evolution of water contributions to discharge from a greenland outlet glacier insight from a new isotope mixing model the greenland ice sheet gris subglacial hydrological system may undergo a seasonal evolution with significant geophysical and biogeochemical implications we present results from a new isotope mixing model to quantify the relative contributions of surface snow glacial ice and delayed flow to the bulk meltwater discharge from a small 5k m 2 land terminating gris outlet glacier during melt onset may and at peak melt july we use radioactive 222 rn and stable isotopes 18 o deuterium to differentiate the water source contributions atmospherically derived 7 be further constrains meltwater transit time from the glacier surface to the ice margin we show that 1 222 rn is a promising tracer for glacial waters stored at the bed and 2 a quantitative chemical mixing model can be constructed by combining 222 rn and the stable water isotopes applying this model to the bulk subglacial outflow from our study area we find a constant delayed flow stored component from melt onset through peak melt this component is diluted first by snowmelt and then by increasing glacial ice melt as the season progresses results from this pilot study are consistent with the hypothesis that subglacial drainage beneath land terminating sections of the gris undergoes a seasonal evolution from a distributed to a channelized system

hydro biogeochemical coupling beneath a large polythermal arctic glacier implications for subice sheet biogeochemistry 1 we analyze the interannual chemical and isotopic composition of runoff from a large high arctic valley glacier over a 5 year period during which drainage evolved from a long residence time drainage system feeding an artesian subglacial upwelling sgu at the glacier terminus to a shorter residence time drainage system feeding an ice marginal channel imc increased icemelt inputs to the sgu are thought to have triggered this evolution this sequence of events provides a unique opportunity to identify coupling between subglacial hydrology and biogeochemical processes within drainage systems of differing residence time the biogeochemistry of the sgu is consistent with prolonged contact between meltwaters and subglacial sediments in which silicate dissolution is enhanced anoxic processes e g sulphate reduction prevail and microbially generated co2 and sulphide oxidation drive mineral dissolution solute in the imc was mainly derived from moraine pore waters which are added to the channel via extraglacial streams these pore waters acquire solute predominantly via sulphide oxidation coupled to carbonate silicate dissolution we present the first evidence that microbially mediated processes may contribute a substantial proportion 80 in this case of the total glacial solute flux which includes coupling between microbial co2 generation and silicate carbonate dissolution the latter suggests the presence of biofilms in subglacial ice marginal sediments where local perturbation of the geochemical environment by release of protons organic acids and ligands stimulates mineral dissolution these data enable inferences to be made regarding biogeochemical processes in longer residence time glacial systems with implications for the future exploration of antarctic subglacial lakes and other wet based ice sheet environments

impact of an extreme melt event on the runoff and hydrology of a high arctic glacier on 28 30 july 2000 an extreme melt event was observed at john evans glacier jeg ellesmere island 79 40 0 n 74 00 0 w hourly melt rates during this event fell in the upper 4 of the distribution of melt rates observed at the site during the period 1996 2000 synoptic conditions during the event resulted in strong east to west flow over the northern sector of the greenland ice sheet with descending flow on the northwest side reaching ellesmere island on jeg wind speeds during the event averaged 8 1ms 1 at 1183 m a s l with hourly mean wind speeds peaking at 11 6ms 1 air temperatures reached 8 c and rates of surface lowering measured by an ultrasonic depth gauge averaged 56 mm day 1 calculations with an energy balance model suggest that increased turbulent fluxes contributed to melt enhancement at all elevations on the glacier while snow albedo feedback resulted in increased melting due to net radiation at higher elevations the event was responsible for 30 of total summer melt at 1183 m a s l and 15 at 850 m a s l conditions similar to those during the event occurred on only 0 1 of days in the period 1948 2000 but 61 of events occurred in the summer months and there was an apparent clustering of events in the 1950s and 1980s such events have the potential to impact significantly on runoff mass balance and drainage system development at high arctic glaciers and changes in their incidence could play a role in determining how high arctic glaciers respond to climate change and variability copyright 2003 john wiley sons ltd

theoretical contemporary observational and palaeo perspectives on ice sheet hydrology processes and products publisher elsevier articletitle theoretical contemporary observational and palaeo perspectives on ice sheet hydrology processes and products journaltitle earth science reviews articlelink http dx doi org 10 1016 j earscirev 2016 01 010 content type article copyright copyright 2016 elsevier b v all rights reserved

geometry bed topography and drainage system structure of the haut glacier d arolla switzerland as part of an integrated study of the hydrology meltwater quality and dynamics of the haut glacier d arolla switzerland the glacier s drainage network structure was determined from patterns of dye recovery in 342 injection experiments conducted from 47 moulins distributed widely across the glacier this structure was compared with theoretical predictions based upon reconstructed patterns of water flow governed by a the subglacial hydraulic potential surface and b the subglacial bedrock surface these reconstructions were based on measurements of ice surface and bedrock topography obtained by a combination of ground survey and radio echo sounding techniques the two reconstructions simulate the drainage system structures expected for a closed channels in which water is pressurized by the overlying ice and b gravity driven open channel flow the closed channel model provides the best fit to the observed structure even though theoretical calculations suggest that under summer discharge conditions open channel flow may be widespread beneath the glacier possible reasons for this apparent discrepancy are discussed

debris transport in a temperate valley glacier haut glacier d arolla valais switzerland hambrey m j goodsell becky glasser n f 2005 debris transport in a temperate valley glacier haut glacier d arolla valais switzerland journal of glaciology 51 172 pp 139 146

modeling the diurnal variation of tracer transit velocity through a subglacial channel 1 tracer injections into a moulin connecting to a subglacial channel at unteraargletscher were repeated at intervals of about two hours over two diurnal discharge cycles in august and september 2000 the pronounced hysteresis in the relationships between tracer transit velocity and proglacial discharge may be explained by adjustments of the channel cross section in response to discharge variations or alternatively by modulation of inflow from the tributary moulin into a main subglacial channel to test these hypotheses we employ a physically based time dependent model of channelized subglacial drainage in a series of numerical experiments we explore the general characteristics of each mechanism before the model is applied to diurnal discharge variations measured during the tracer tests at unteraargletscher we found that the ability of a rothlisberger channel to adjust its size to the prevailing hydraulic conditions can contribute to the hysteresis in the velocity discharge relationships however using plausible parameter values r channel hydraulics alone is not satisfactory in reproducing the magnitude of observed transit velocities the model further confirms that retardation of the tracer in the tributary moulin due to inflow modulation has major effects on transit velocities both in magnitude and timing with appropriate assumptions on channel sinuosity and moulin size a combination of both mechanisms can be found that is capable of reproducing the observed transit velocities

the effect of the subglacial water pressure on the sliding velocity of a glacier in an idealized numerical model in order to interpret observed short term variations of the sliding velocity of a glacier the effect of a variable subglacial water pressure on the sliding velocity has been studied using an idealized numerical model in particular the transient stages of growing or shrinking water filled cavities at the ice bedrock interface were analysed it was found that the sliding velocity was larger when cavities were growing than when they had reached the steady state size for a given water pressure the smallest sliding velocities occurred while cavities were shrinking when cavitation is substantial a small drop of water pressure below the steady state value e g by 0 5 bar can temporarily cause backward sliding a limiting water pressure at which sliding becomes unstable is derived the consequences of more realistic assumptions than those of the model are discussed

a m gurnell and m j clark eds 1987 glacio fluvial sediment transfer an alpine perspective chichester etc john wiley and sons ltd

nitrate production beneath a high arctic glacier svalbard natural environmental isotopes of nitrate and ammonium are used in conjunction with major ion chemistry and hydrological data to establish controls upon the biogeochemical cycling of nitrogen beneath a high arctic polythermal glacier midtre lovenbreen here high nitrate concentrations in subglacial meltwaters suggest that the subglacial environment may be furnishing nitrate in excess of that released from the snowpack and glacier ice isotopic values of 18ono3 suggest the provenance of such excess nitrate to be microbial in origin and 15nno3 indicates the source nitrogen compounds to have high 15n values relative to supraglacial runoff we address the nitrification of supraglacial ammonium the mineralization of organic nitrogen and the oxidation of geologic ammonium as potential sources of this additional nitrate mass fluxes of n compounds in a subglacial river and their 15n ratios indicate that the nitrification of supraglacial ammonium delivered to the glacier bed can account for much but not all of the excess nitrate the additional source most likely involves the mineralization of organic nitrogen although 15n values in rock samples suggest that the dissolution of rock derived ammonium cannot be discounted if large fractionation effects occur during dissolution our results therefore agree with previous catchment scale mass balance studies at the site which report a major internal loss of nh4 from the snowpack following melt however at the catchment scale the nh4 loss is greater than the excess of no3 observed in runoff indicating that microbial assimilation of ammonia into organic matter in a range of other habitats is also likely the identification of nh4 assimilation and nitrification further highlights the non conservative behaviour of nitrogen in glacial environments and testifies to the importance of microbially mediated reactions in the biogeochemical cycling of nitrogen in an environment that has until recently been regarded as biologically inert

links between acceleration melting and supraglacial lake drainage of the western greenland ice sheet 1 the impact of increasing summer melt on the dynamics and stability of the greenland ice sheet is not fully understood mounting evidence suggests seasonal evolution of subglacial drainage mitigates or counteracts the ability of surface runoff to increase basal sliding here we compare subdaily ice velocity and uplift derived from nine global positioning system stations in the upper ablation zone in west greenland to surface melt and supraglacial lake drainage during summer 2007 starting around day 173 we observe speedups of 6 41 above spring velocity lasting 40 days accompanied by sustained surface uplift at most stations followed by a late summer slowdown after initial speedup we see a spatially uniform velocity response across the ablation zone and strong diurnal velocity variations during periods of melting most lake drainages were undetectable in the velocity record and those that were detected only perturbed velocities for 1 day suggesting preexisting drainage systems could efficiently drain large volumes of water the dynamic response to melt forcing appears to 1 be driven by changes in subglacial storage of water that is delivered in diurnal and episodic pulses and 2 decrease over the course of the summer presumably as the subglacial drainage system evolves to greater efficiency the relationship between hydrology and ice dynamics observed is similar to that observed on mountain glaciers suggesting that seasonally large water pressures under the ice sheet largely compensate for the greater ice thickness considered here thus increases in summer melting may not guarantee faster seasonal ice flow

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

do debris covered glaciers demonstrate distinctive hydrological behaviour compared to clean glaciers abstract supraglacial debris is known to strongly influence the distribution of glacier surface melt since melt inputs drive the formation and evolution of glacial drainage systems it should follow that the drainage systems of debris covered glaciers will differ from those of debris free glaciers this would have implications for the proglacial runoff regime subglacial erosion and glacier dynamics this paper presents analysis of return curves from 33 successful dye injections into the extensively debris covered miage glacier italian alps it demonstrates that the spatial distribution of supraglacial debris influences the structure and seasonal evolution of the glacial drainage system where the debris cover is continuous melt is lower and the surface topography is chaotic with many small supraglacial catchments these factors result in an inefficient englacial subglacial drainage network beneath continuous debris which drains to the conduit system emanating from the upper ablation zone melt rates are high in areas of clean and dirty ice above the continuous debris runoff from these areas is concentrated by inter moraine troughs into large supraglacial streams which encourages the early season development of an efficient englacial subglacial conduit system downstream of this area drainage efficiency from the debris covered area increases over the melt season but dye trace transit velocity remains lower than from moulins on the upper glacier future runoff models should account for the influence of supraglacial debris on the hydrological system

modelling ice bed coupling during a glacier speed up event haut glacier d arolla switzerland fischer u h mair d kavanaugh j l willis i nienow p hubbard b 2011 modelling ice bed coupling during a glacier speed up event haut glacier d arolla switzerland hydrological processes 2599 1361 1372

numerical modeling of glacial erosion and headwall processes in alpine valleys abstract how rock relief is developed by glacial erosion in alpine landscapes is a key question in understanding the controls on mountain range topography any generation of relief by glaciers at the highest elevations in mountain ranges can affect the distribution of precipitation in alpine landscapes creating feedbacks between glacier mass balance and glacial erosion relief production at high elevation mountain crests is addressed using a numerical model that incorporates glacier dynamics and subglacial erosion as well as relevant hillslope processes blowing snow from a valley bounding plateau and avalanching onto the accumulation zone of the glacier is included in the model furthermore temperature dependent frost cracking is used as a proxy for headwall backwearing the parameterization of subglacial erosion produces about 500 m of erosion over the 400 ka of each numerical simulation in steady and varying climate scenarios valley floors flatten as headwalls increase in height and retreat headward over time headwall slopes increase in simulations in which quarrying is explicitly incorporated rates of quarrying are high near the base of the headwall increasing headwall length and slope as a result of valley floor lowering high rates of subglacial erosion and production of headwall relief also result when elastic flexural uplift occurs in response to mass unloading small overdeepenings form at the base of the headwall in steady climate simulations when the glacier is small at the end of the model run while the final profiles are relatively insensitive to the erosion rule used quarrying is most effective near the head of the glacier whereas rates of abrasion reflect the instantaneous pattern of integrated ice discharge or ice flux in simulations in which cirques are formed the equilibrium line altitude is hundreds of meters above the cirque floor however the time averaged horizontal position of the equilibrium line corresponds well with the downvalley position of the cirques

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

velocity discharge relationships derived from dye tracer experiments in glacial meltwaters implications for subglacial flow conditions repeated dye tracer tests were undertaken from individual moulins at haut glacier d arolla switzerland over a number of diurnal discharge cycles during the summers of 1989 1991 it was hoped to use the concepts of at a station hydraulic geometry to infer flow conditions in subglacial channels from the form of the velocity discharge relationships derived from these tests the results however displayed both clockwise and anticlockwise velocity discharge hysteresis in addition to the simple power function relationship assumed in the hydraulic geometry approach clockwise hysteresis seems to indicate that a moulin drains into a small tributary channel rather than directly into an arterial channel and that discharges in the two channels vary out of phase with each other anticlockwise hysteresis is accompanied by strong diurnal variations in the value of dispersivity derived from the dye breakthrough curve and is best explained by hydraulic damming of moulins or sub englacial passageways despite the complex velocity discharge relationships observed some indication of subglacial flow conditions may be obtained if tributary channels comprise only a small fraction of the drainage path and power function velocity discharge relationships are derived from dye injections conducted during periods when the supraglacial discharge entering the moulin and the bulk discharge vary in phase analyses based on this premise suggest that both open and closed channel flow occur beneath haut glacier d arolla and that flow conditions are highly variable at and between sites

sedimentological and deformational criteria for discriminating subglaciofluvial deposits from subaqueous ice contact fan deposits a pleistocene example ireland a pit located near ballyhorsey 28 km south of dublin eastern ireland displays subglacially deposited glaciofluvial sediments passing upwards into proglacial subaqueous ice contact fan deposits the coexistence of these two different depositional environments at the same location will help with differentiation between two very similar and easily confused glacial lithofacies the lowermost sediments show aggrading subglacial deposits indicating a constrained accommodation space mainly controlled by the position of an overlying ice roof during ice bed decoupling these sediments are characterized by vertically stacked tills with large lenses of tabular to channelized sorted sediments the sorted sediments consist of fine grained laminated facies cross laminated sand and channelized gravels and are interpreted as subglaciofluvial sediments deposited within a subglacial de coupled space the subglaciofluvial sequence is characterized by glaciotectonic deformation structures within discrete beds triggered by fluid overpressure and shear stress during episodes of ice bed recoupling clastic dykes and folds the upper deposits correspond to the deposition of successive hyperpycnal flows in a proximal proglacial lake forming a thick sedimentary wedge erosively overlying the subglacial deposits gravel facies and large scale trough bedding sand are observed within this proximal wedge while normally graded sand beds with developed bedforms are observed further downflow the building of the prograding ice contact subaqueous fan implies an unrestricted accommodation space and is associated with deformation structures related to gravity destabilization during fan spreading normal faults this study facilitates the recognition of subglacial submarginal depositional environments formed in part during localized ice bed coupling episodes in the sedimentary record the sedimentary sequence exposed in ballyhorsey permits characterization of the temporal framework of meltwater production during deglaciation the impact on the subglacial drainage system and the consequences on the irish sea ice stream flow mechanisms

first surface velocity maps for glaciers of monte tronador north patagonian andes derived from sequential pleiades satellite images we apply cross correlation to pleiades satellite images to generate accurate high resolution monthly surface velocity maps of monte tronador glaciers between march and june 2012 measured surface displacements cover periods as short as 19 days with a precision of 0 58 m 11 m a 1 these glaciers follow a radial flow pattern with maximum surface speeds of 390 m a 1 associated with steep icefalls the lower reaches of the debris covered tongues of verde and casa pangue glaciers are almost stagnant whereas ventisquero negro another debris covered glacier shows acceleration at the front due to calving into a proglacial lake low elevation debris covered glacier tongues show increasing velocities at the beginning of the accumulation season whereas higher elevation clean ice tongues reduce their speed during this period this contrasting behavior is probably in response to an increase in water input to the subglacial system from winter rainfall events at low elevations and a decrease in meltwater production at higher elevations these sequential velocity maps can help to identify the controls on glacier surface velocity aid in the delimitation of ice divides and could also contribute to more realistic calibration of ice flux mass balance models in this glacierized area

incremental subglacial meltwater sediment deposition and deformation associated with repeated ice bed decoupling a case study from the island of funen denmark abstract on the island of funen denmark sediments that are 4 7 m below the land surface consist of a 2 4 m thick sequence of stacked and folded glaciofluvial sediments overlain by a 2 3 m thick basal till the glaciofluvial sediments consist of tabular beds of planar stratified massive and cross stratified sand and gravel with localized channel fills of open framework gravel sand and gravel beds exhibit curvilinear sheath folding often leading to eye folds this folding is attributed to repeated glacier bed decoupling and recoupling with subglacial deposition of sand and gravel by meltwater occurring during the decoupling phase and deformation occurring during recoupling sand and gravel beds are typically separated by silty clay beds and laminations recording slackwater deposition within subglacial cavities folds frequently display attenuated upper limbs reflecting shearing associated with overlying ice movement on lower fold limbs only localized thrusting is observed suggesting water saturation of sands and gravels during deformation and relatively low strain rates folds are frequently truncated by overlying sand and gravel beds no evidence of shearing is found along these contacts which are interpreted as erosional surfaces thus we propose that the glaciofluvial sediment sequence records incremental step wise subglacial deposition and deformation rather than wholesale deformation following emplacement of the entire glaciofluvial sequence specifically we envisage that individual beds were deposited and folded subglacially with ice bed decoupling occurring during sediment deposition followed by recoupling and shearing of the upper bed surface by the ice base to produce folds with attenuated upper limbs incremental deformation and folding were facilitated by elevated porewater pressure within the sediments silty clay beds helped to maintain elevated porewater pressure by acting as local aquitards a general absence of till from the glaciofluvial sequence save for localized cm scale blocks suggests either non deposition or reworking into the glaciofluvial sediments deposition of tabular sand and gravel beds and open framework gravel filling scours within single beds suggest broad sheet like subglacial flows 10 100 m wide that become increasingly channelized we propose that the sedimentary sequence records a highly dynamic glaciohydraulic system characterized by repeated localized subglacial cavity development and storage and release of meltwater leading to glacier decoupling that may have facilitated fast flow of the baltic ice stream

changes in geometry and subglacial drainage derived from digital elevation models unteraargletscher switzerland 1927 97 digital elevation models of the bed and surface of unteraargletscher switzerland are used to reconstruct the theoretical pattern of basal water drainage for the years 1927 1947 1961 and 1997 during which period the glacier was thinning and receding the theoretical drainage pattern for 1997 compares well in a broad sense with the locations of active moulins and the hydraulic connection status of boreholes drilled to the glacier bed changes in the basal water flow pattern over the period 1927 97 that are revealed by the theoretical reconstructions of the subglacial drainage system structure are likely to have resulted from changes in glacier geometry concurrent with the retreat and thinning of the glacier the height of medial moraines increased probably due to the insulating effect of the debris cover reducing the melt of the underlying ice this increase of moraine heights has led to the formation of hydraulic barriers at the glacier bed such that water flow has become channelized beneath the ice along drainage axes that parallel the course of the medial moraines on the glacier surface

molecular characterization of dissolved organic matter associated with the greenland ice sheet abstract subsurface microbial oxidation of overridden soils and vegetation beneath glaciers and ice sheets may affect global carbon budgets on glacial interglacial timescales the likelihood and magnitude of this process depends on the chemical nature and reactivity of the subglacial organic carbon stores we examined the composition of carbon pools associated with different regions of the greenland ice sheet subglacial supraglacial proglacial in order to elucidate the type of dissolved organic matter dom present in the subglacial discharge over a melt season electrospray ionization esi fourier transform ion cyclotron resonance ft icr mass spectrometry coupled to multivariate statistics permitted unprecedented molecular level characterization of this material and revealed that carbon pools associated with discrete glacial regions are comprised of different compound classes specifically a larger proportion of protein like compounds were observed in the supraglacial samples and in the early melt season spring subglacial discharge in contrast the late melt season summer subglacial discharge contained a greater fraction of lignin like and other material presumably derived from underlying vegetation and soil these results suggest 1 that the majority of supraglacial dom originates from autochthonous microbial processes on the ice sheet surface 2 that the subglacial dom contains allochthonous carbon derived from overridden soils and vegetation as well as autochthonous carbon derived from in situ microbial metabolism and 3 that the relative contribution of allochthonous and autochthonous material in subglacial discharge varies during the melt season these conclusions are consistent with the hypothesis that given sufficient time e g overwinter storage resident subglacial microbial communities may oxidize terrestrial material beneath the greenland ice sheet

evidence for basal cavity opening from analysis of surface uplift during a high velocity event haut glacier d arolla switzerland high rates of surface uplift and horizontal velocities were measured during a hydrologically induced spring speed up event spatial patterns of surface uplift are analyzed to estimate components of vertical motion due to flow along an inclined bed and vertical strain areas are identified where surface uplift was most likely due in part to the opening or enlargement of subglacial cavities by bed separation results suggest a widespread enlargement of subglacial cavities during the event and survival of residual cavities after the event the spatial pattern of cavity enlargement closely matches previously identified axes of preferential subglacial drainage it is suggested that localized cavity opening along axes of preferential drainage may constitute the initial stage in the seasonal development of channelized subglacial drainage it is concluded that spatial and temporal variations in glacier motion may play an active role in determining the structure and rate of development of subglacial drainage during the summer melt season

variability in ice motion at a land terminating greenlandic outlet glacier the role of channelized and distributed drainage systems we use a combination of field observations and hydrological modelling to examine the mechanisms through which variability in meltwater input affects ice motion at a land terminating greenlandic outlet glacier we find a close agreement between horizontal ice velocity vertical ice velocity and modelled subglacial water pressure over the course of a melt season on this basis we argue that variation in horizontal and vertical ice velocity primarily reflects the displacement of basal ice during periods of cavity expansion and contraction a process itself driven by fluctuations in basal water pressure originating in subglacial channels this process is not captured by traditional sliding laws linking water pressure and basal velocity which may hinder the simulation of realistic diurnal to seasonal variability in ice velocity in coupled models of glacial hydrology and dynamics

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

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

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 glacier ice deformation haut glacier d arolla switzerland mair d hubbard b nienow p willis i fischer u h 2008 diurnal fluctuations in glacier ice deformation haut glacier d arolla switzerland earth surface processes and landforms 33 8 1272 1284 sponsorship carnegie trust for the universities of scotland

structure morphology and water flux of a subglacial drainage system midtdalsbreen norway digital elevation models of the surface and bed of midtdalsbreen norway are used to calculate subglacial hydraulic potential and infer drainage system structure for a series of subglacial water pressure assumptions ranging from atmospheric to ice overburden a distributed degree day model is used to calculate the spatial distribution of melt on the glacier surface throughout a typical summer which is accumulated along the various drainage system structures to calculate water fluxes beneath the glacier and exiting the portals for the different water pressure assumptions in addition 78 dye tracing tests were performed from 33 injection sites and numerous measurements of water discharge were made on the main proglacial streams over several summer melt seasons comparison of the calculated drainage system structures and water fluxes with dye tracing results and measured proglacial stream discharges suggests that the temporally and spatially averaged steady state water pressures beneath the glacier are 70 of ice overburden analysis of the dye return curves together with the calculated subglacial water fluxes shows that the main drainage network on the eastern half of the glacier consists of a hydraulically efficient system of broad low channels average width height ratio 75 the smaller drainage network on the west consists of a hydraulically inefficient distributed system dominated by channels that are exceptionally broad and very low average width height ratio 350 the even smaller central drainage network also consists of a hydraulically inefficient distributed system dominated by channels that are very broad and exceptionally low average width height ratio 450 the channels beneath the western and central glacier must be so broad and low that they can essentially be thought of as a linked cavity system

evolution of glacial flow and drainage during the ablation season proglacial discharge is controlled by the geometry of the glacial drainage network and by meltwater processes the glacial drainage systems of some alpine glaciers have been characterised using a model based on a proglacial discharge analysis in this paper we apply high frequency systemic analysis to data collected from the baounet glacier french alps during two successive ablation seasons our approach is based on an analysis of the evolution of daily recession curves during the ablation period the observed data are fitted by a single coefficient dependant recession law changes in are compared to variations in the daily discharge amplitude and the time lag between air temperature and proglacial discharge the changes in the values do not appear to be related to changes in the time lag and the amplitude of the daily discharge there were significant variations in the coefficient during the two ablation periods studied here even if there was no time lag or the daily discharge amplitude change high values of correspond to high drainage velocities therefore increases in values can be used as an indicator of the evolution of the glacier s internal drainage network

subglacial hydrology at rink isbrae west greenland inferred from sediment plume appearance marine terminating outlet glaciers discharge most of the greenland ice sheet s mass through frontal ablation and meltwater runoff while calving can be estimated by in situ and remote sensing observations submarine melting and subglacial meltwater transport are more challenging to quantify here we investigate the subglacial hydrology of rink isbrae a fast flowing west greenland tidewater glacier using time lapse photography modeled runoff estimates and daily satellite imagery from 2007 to 2011 we find that sediment plumes appear episodically at four distinct locations across the terminus and last between 2 h and 17 d this suggests short term variability in discharge and the existence of persistent pathways the seasonal onset of sediment plumes occurs before supraglacial lake drainages shortly after the onset of runoff and only after the wintertime ice melange has begun disintegrating plumes were also visible after the cessation of runoff 23 5 d which is indicative of subglacial storage the lack of either a seasonal velocity change or a correspondence between meltwater availability and plume occurrence suggests that the subglacial system persists in a state of inefficient drainage subglacial hydrology at tidewater glaciers is of critical importance in understanding dynamics at the ice front

controls on the location morphology and evolution of complex esker systems at decadal timescales breiðamerkurjokull southeast iceland this paper uses detailed mapping of eskers to address three questions which are important for reconstructing meltwater behaviour beneath contemporary and ancient ice masses what controls the morphology of simple and complex esker systems how do esker systems evolve through time and are esker patterns compatible with the groundwater controlled hydraulic spacing of esker tunnels esker crestlines and widths are mapped on the brei amerkurjokull foreland for eight time slices between 1945 and 2007 from high resolution 50 cm aerial photography permitting their long term morphological evolution to be analysed in a high level of detail we find that complex eskers develop where meltwater and sediment is abundant such that sediment clogs channels forming distributary eskers isolated eskers are simpler and smaller and reflect less abundant meltwater and sediment which is unable to clog channels eskers may take several decades to emerge from outwash deposits containing buried ice and can increase or decrease in size when ice surrounding and underlying them melts out it has been suggested that groundwater channel coupling dictates the spacing between eskers at brei amerkurjokull our results do not dispute this but suggest that the routing of sediment and meltwater through medial moraines is an additional important control on esker location and spacing these results may be used to better understand the processes surrounding esker formation in a variety of geographical settings enabling a more detailed understanding of the operation of meltwater drainage systems in sub marginal zones beneath glaciers and ice sheets this article is protected by copyright all rights reserved

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

growth and collapse of the distributed subglacial hydrologic system of kennicott glacier alaska usa and its effects on basal motion nearly 100 days of hourly glacier motion hydrology and hydrochemistry measurements on kennicott glacier alaska usa demonstrate the complicated relationship between water and motion at the glacier bed our observations capture the transient glacier response to seasonal and daily melt cycles and to a jokulhlaup that prompts a sixfold increase in glacier speed sliding is promoted whenever the water inputs to the glacier exceed the capacity of the subglacial hydrologic system to transmit the water sensitivity of sliding to daily meltwater inputs varies strongly through the season implying that the state of the hydrologic system governs the sensitivity of basal sliding a numerical model constructed to explore these relationships reveals the roles of the effective pressure the exponent to which this is taken in the sliding law 0 1 0 6 glacier macroporosity 2 and the cavity generating capacity of the glacier bed which encapsulates the sizes and spacing of bed roughness elements temporal changes in the effective pressure associated with evolution of both water inputs and subglacial water transmission capacity can explain the varying strength of diurnal velocity fluctuations of kennicott glacier spatial patterns of glacier macroporosity and of basal roughness govern variation in sensitivity of sliding to water inputs

short term velocity variations and sliding sensitivity of a slowly surging glacier we use daily surface velocities measured over several weeks in 2007 and 2008 on a slowly surging glacier in yukon canada to examine the ordinary melt season dynamics in the context of the ongoing surge horizontal velocities within and just below the 1 5 km long zone of fastest flow where the surge is occurring are often correlated during intervals of low melt this correlation breaks down during melt events with the lower reaches of the fast flow zone responding first velocity variability in this lower reach is most highly correlated with melt velocities above and below appear to respond at least as strongly to the velocity variations of this reach as to local melt gps height records are suggestive of ice bed separation occurring in the fast flow zone but not below it pointing to a hydrological cause for the short term flow variability in the surging region independent velocity measurements over 6 years show a maximum july flow anomaly coincident with the location most responsive to melt results from a simple model of dashpots and frictional elements lend support to the hypothesis that this zone partly drives the dynamics of the ice above and below it we speculate that the slow surge may enhance glacier sensitivity to melt season processes including short term summer sliding events

in situ measurements of basal water quality and pressure as an indicator of the character of subglacial drainage systems continuous subglacial measurements of turbidity and electrical conductivity two indicators of basal water quality can be used to help characterize subglacial drainage systems these indicators of water quality yield information that complements that provided by water pressure measurements quantitative attributes of subglacial drainage systems such as water velocity and subglacial residence time as well as qualitative behaviour for example spatial and temporal variations in system morphology can be deduced using water quality measurements interpretation is complicated by the many potential influences on turbidity and electrical conductivity but when these complications are appreciated a richer interpretation results to demonstrate the utility of basal water quality measurements observations from trapridge glacier yukon territory canada were examined the data reveal complex behaviour of the drainage system but constraints imposed by basal water quality measurements help to clarify the nature of the subglacial flow system the measurement and interpretation methods described and demonstrated are applicable to other glaciers as such they should prove useful for characterizing different subglacial drainage configurations and behaviours thereby improving our general understanding of the hydrology and dynamics of wet based glaciers

supraglacial forcing of subglacial drainage in the ablation zone of the greenland ice sheet 1 we measure hydrological parameters in meltwater draining from an outlet glacier in west greenland to investigate seasonal changes in the structure and behaviour of the hydrological system of a large catchment in the greenland ice sheet gris our data reveal seasonal upglacier expansion and increase in hydraulic efficiency of the subglacial drainage system across a catchment 600 km2 to distances 50 km from the ice sheet margin this expansion occurs episodically in response to the drainage of surface meltwaters into a hitherto inefficient subglacial drainage system as new input locations become active progressively further upglacier this system is similar to alpine glaciers these observations provide the first synopsis of seasonal hydrological behaviour in the ablation zone of the gris

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

feedbacks between coupled subglacial hydrology and glacier dynamics on most glaciers and ice sheet outlets the majority of motion is due to basal slip a combination of basal sliding and bed deformation the importance of basal water in controlling sliding is well established with increased sliding generally related to high basal water pressure but the details of the interactions between the ice and water systems has not received much study when there is coupling between the systems here we use coupled subglacial hydrology and ice dynamics models within the community ice sheet model to investigate feedbacks between the ice and water systems the dominant feedback we find is negative sliding over bedrock bumps opens additional cavity space which lowers water pressure and in turn sliding we also find two small positive feedbacks basal melt increases through frictional heat during sliding which raises water pressure and strain softening of basal ice during localized speedup causes cavities to close more quickly and maintain higher water pressures our coupled modeling demonstrates that a sustained input of surface water to a distributed drainage system can lead to a speedup event that decays even in the absence of channelization due to increased capacity of the system through opening of cavities which is enhanced through the sliding opening feedback we find that the negative feedback resulting from sliding opening is robust across a wide range of parameter values however our modeling also argues that subglacial channelization is required to terminate speedup events over timescales that are commensurate with observations of late summer slowdown on mountain glaciers

seasonal variations in greenland ice sheet motion inland extent and behaviour at higher elevations abstract we present global positioning system observations that capture the full inland extent of ice motion variations in 2009 along a transect in the west greenland ice sheet margin in situ measurements of air temperature and surface ablation and satellite monitoring of ice surface albedo and supraglacial lake drainage are used to investigate hydrological controls on ice velocity changes we find a strong positive correlation between rates of annual ablation and changes in annual ice motion along the transect with sites nearest the ice sheet margin experiencing greater annual variations in ice motion 15 18 than those above 1000 m elevation 3 8 patterns in the timing and rate of meltwater delivery to the ice bed interface provide key controls on the magnitude of hydrologically forced velocity variations at each site in the lower ablation zone the overall contribution of variations in ice motion to annual flow rates is limited by evolution in the structure of the subglacial drainage system at sites in the upper ablation zone a shorter period of summer melting and delayed establishment of a hydraulic connection between the ice sheet surface and its bed limit the timeframe for velocity variations to occur our data suggest that land terminating sections of the greenland ice sheet will experience increased dynamic mass loss in a warmer climate as the behaviour that we observe in the lower ablation zone propagates further inland findings from this study provide a conceptual framework to understand the impact of hydrologically forced velocity variations on the future mass balance of land terminating sections of the greenland ice sheet

moulin density controls drainage development beneath the greenland ice sheet this work was funded through a uk natural environment research council doctoral training grant lcag 133 a bowring junior research fellowship st catharine s college cambridge and a leverhulme newton trust early career fellowship all awarded to a f b i j h was supported by a marie curie fp7 career integration grant within the 7th european union framework programme

sediment export transient landscape response and catchment scale connectivity following rapid climate warming and alpine glacier recession abstract in the face of rapid climate warming rapid glacier recession should lead to a marked increase in the spatial extent of the paraglacial zone in glaciated drainage basins the extent of the paraglacial zone has been well established to be transient but there are very few studies of this transient response and what it means for sediment export there is good reason to expect that glacier recession could increase basin scale sediment connectivity as sediment becomes less dependent on glacier surface transport proglacial streams are more able to migrate laterally than subglacial streams and so access sediment for transport and glacier debuttressing may aid the development of gullies that can dissect moraines and so aid hillslope to proglacial zone connectivity by using records of the flushing of hydroelectric power installations we were able to develop a record of coarse sediment sand and gravel export from a basin with a rapidly retreating valley glacier the haut glacier d arolla from 1977 to 2014 modelling suggested that these data could only be partially controlled by transport capacity implying an important role for sediment supply and potentially for the influence of changing sediment connectivity indeed there was evidence of the effects of glacial debuttressing upon gullying processes and hence a possible increase in the ease of connection of upstream basins to the proglacial area more recently we were able to show possible temperature control on sediment export which may only have become apparent because of the progressive development of better sediment connectivity however whilst rapid glacier recession should result in theory in a progressive increase in connectivity of sediment sources to the basin outlet the supply to capacity ratio does not increase continually with glacier recession until maximum capacity is reached we identified two possible examples of why first gullying was also accompanied by the sediment accumulation at the base of moraines that was too coarse to be transported by the proglacial stream maintaining disconnection of the upper basins second the sediment capacity ratio appeared to be elevated during periods of more rapid retreat and we attribute this to the importance of a continued supply of unworked glacial till before fluvial reworking and sorting of freshly exposed sediment increased the resistance of sediment to entrainment and hence export rates thus the transient geomorphic response of glaciated basins to glacier recession may involve negative feedbacks that can reduce the extent to which increases in connectivity elsewhere in the basin lead to increased sediment export

geoscience the plumbing of greenland s ice observations of the water pressure in drilled boreholes and natural moulins on the greenland ice sheet show how its underlying plumbing system controls ice motion during the course of the summer melt season see letter p 80 increased meltwater delivery to the base of the greenland ice sheet will increase the ice sheet velocity accelerating its inevitable rush towards the ocean and subsequent sea level rise or will it debate on this topic is at the forefront of cryospheric research but has been hampered by the lack of simultaneous observations of hydraulic head in moulins vertical shafts that deliver water to the base of the ice sheet and boreholes which monitor basal water pressure lauren andrews and colleagues now provide these observations from a small region in western greenland and reveal that water delivery by moulins into channelized basal flow is indeed linked to short term fluctuations in ice velocity late season decelerations in ice velocity however seem to be controlled by changes in unchannelized flow rather than any shifts in the moulin system

using concurrent dna tracer injections to infer glacial flow pathways author s dahlke he williamson ag georgakakos c leung s sharma an lyon sw walter mt abstract 2015 john wiley a sons ltd catchment hydrology has become replete with flow pathway characterizations obtained via combinations of physical hydrologic measurements e g streamflow hydrographs and natural tracer signals e g stable water isotopes and geochemistry in this study we explored how our understanding of hydrologic flow pathways can be improved and expanded in both space and time by the simultaneous application of engineered synthetic dna tracers in this study we compared the advective dispersive transport properties and mass recovery rates of two types of synthetic dna tracers one consisting of synthetic dna strands encapsulated into biodegradable microspheres and another consisting of free dna i e not encapsulated the dna tracers were also compared with a conservative fluorescent dye all tracers were injected into a small 3 2 km2 valley glacier storglaciaren in northern sweden seven of the nine dna tracers showed clear recovery during the sampling period and similar peak arrival times and dispersion coefficients as the conservative fluorescent dye however recovered dna tracer mass ranged only from 1 to 66 while recovered fluorescent dye mass was 99 resulting from the cold and opaque subglacial environment provided by the glacier mass loss associated with microbial activity and photochemical degradation of the dna is likely negligible leaving sorption of dna tracers onto suspended particles and loss of microtracer particles to sediment storage as probable explanations despite the difference in mass recovery the advection and dispersion information derived from the dna tracer breakthrough curves provided spatially explicit information that allowed inferring a theoretical model of the flow pathways that water takes through the glacier

mechanisms of subglacial cavity filling in glacier de tete rousse french alps the deadliest outburst flood from an englacial cavity occurred on glacier de tete rousse in the mont blanc area french alps in 1892 a subglacial reservoir was discovered in the same glacier in 2010 and drained artificially in 2010 2011 and 2012 to protect the 3000 inhabitants downstream the mechanism leading to the spontaneous refilling of the cavity following these pumping operations has been analyzed for this purpose the subglacial water volume changes between 2010 and 2013 were reconstructed the size of the cavity following the pumping was found to have decreased from 53 500 m 3 in 2010 to 12 750 m 3 in 2013 creep and the partial collapse of the cavity roof explain a large part of the volume loss analysis of cavity filling showed a strong relationship between measured surface melting and the filling rate with a time delay of 4 6 hours a permanent input of 15 m 3 d 1 not depending on surface melt was also found the meltwater and rain from the surface is conveyed to bedrock through crevasses and probably through a permeable layer of rock debris at the glacier bed the drainage pathway permeability was estimated at 0 054 m s 1 from water discharge measurements and dye tracing experiments

evolution of the internal drainage system in the lower part of the ablation area of storglaci aren sweden during the 1989 melt season ten tracer experiments were conducted to investigate seasonal diurnal and spatial variations in the internal drainage system in the ablation area of storglaciaren sweden dye was injected into moulins and dye concentration and discharge were monitored in two streams at the glacier terminus sydjakk and nordjakk dye emerged only in sydjakk transit velocities ranged from 0 07 to 0 29 m s implying that drainage was through a well defined conduit system velocity and discharge relations suggest that these conduits are part of a multi branched arborescent network of individually braided wide low passages a progressive decline in dispersivity during the early part of the melt season reflects structural changes in these conduits presumably including a decrease in the degree of braiding and an increase in size the system reached its late season configuration in early august by which time the energy dissipated by the flowing water would have sufficed to melt between 0 7 and 21 m 3 of ice per meter of conduit length depending on conduit size potential closure rates exceed melt rates on conduit walls throughout most of the drainage system and so conduits are probably full of water during periods of higher daily discharge with water pressures exceeding atmospheric pressure variations in tracer return curves and dispersivity on a diurnal time scale also appear to reflect changes in the degree of braiding in this case resulting from drowning of low divides between channels as discharge increases

transient subglacial hydrology of a thin ice sheet insights from the chasm esker british columbia canada abstract glacier drainage systems are never steady state instead they fluctuate over time and space in response to variation in water input in order to improve numerical models of glacier hydrology it is important to fully understand the processes controlling subglacial drainage system evolution but contemporary ice sheet beds are typically inaccessible thus esker distribution morphology and sedimentology have been used to infer the dynamics and hydrology of former ice sheets however debate remains as to the processes responsible for esker formation and most theoretical investigations have assumed that they formed due to processes that operated beneath thick ice despite many field investigations to the contrary we investigate esker formation during the final stages of the thin inactive and rapidly decaying cordilleran ice sheet cis in interior british columbia canada a combination of geomorphological ground penetrating radar gpr and electrical resistivity tomography ert data suggest esker ridge sedimentary architecture is consistent with synchronous formation during a glacial lake outburst flood glof these data reveal esker ridge deposition most likely took place within an ice tunnel that evacuated late waning stage flow following erosion and partial fill of a broader meltwater corridor esker ridge sedimentary architecture reveals this depositional environment was dynamic reflecting complex interaction between ice thickness ice structure ice tunnel geometry flow conditions and sediment supply under these thin inactive ice conditions ice tunnel location was initially governed by structural weaknesses in the ice and or equipotential gradient because creep closure rates were low the ice tunnel evolved through feedbacks between conduit growth via frictional melting mechanical ice excavation and conduit closure due to sediment infilling rather than ice creep this resulted in a non uniform ice tunnel that enlarged in an upglacier direction and locally unroofed to form open channels during its final stages these data suggest that eskers may record unsteady rather than steady flows in a drainage network and so the assumptions often made when using eskers to inform hydrological components of ice sheet models may not be applicable to all ice sheet settings

englacial and subglacial water flow at skalafellsjokull iceland derived from ground penetrating radar in situ glacsweb probe and borehole water level measurements we reconstruct englacial and subglacial drainage at skalafellsjokull iceland using ground penetrating radar gpr common offset surveys borehole studies and glacsweb probe data we find that englacial water is not stored within the glacier water content 0 0 3 instead the glacier is mostly impermeable and meltwater is able to pass quickly through the main body of the glacier via crevasses and moulins once at the glacier bed water is stored within a thin 1 m layer of debris rich basal ice 2 water content and the till the hydraulic potential mapped across the survey area indicates that when water pressures are high most of the year water flows parallel to the margin and emerges 3 km down glacier at an outlet tongue gpr data indicates that these flow pathways may have formed a series of braided channels we show that this glacier has a very low water storage capacity but an efficient englacial drainage network for transferring water to the glacier bed and therefore it has the potential to respond rapidly to changes in melt water inputs

seasonal variations in ice deformation and basal motion across the tongue of haut glacier d arolla switzerland records of surface motion englacial tilt and repeat inclinometry are used to determine patterns of surface internal and basal motion across the tongue of haut glacier d arolla switzerland over temporal scales ranging from days to months findings are interpreted with reference to contemporaneous measurements of subglacial water pressures and prior knowledge of the glacier s subglacial drainage system structure long term inclinometry results show pronounced extrusion flow over a subglacial drainage axis with basal velocities up to twice those measured at the glacier surface deformation profiles are more conventional away from the drainage axis with basal velocities 60 70 of surface velocities comparison of long term tilt rates from repeat inclinometry and englacial tilt meters shows close correspondence englacial tiltmeter data are used to reconstruct internal velocity profiles and to split surface velocities into internal deformation and basal motion contributions over spring summer and autumn winter periods although spatial patterns of surface movement are similar between periods patterns of internal and basal motion are not results are interpreted in terms of the location of sticky and slippery spots with temporally changing patterns of basal drag reflecting changing distributions of water pressure

geochemical weathering at the bed of haut glacier d arolla switzerland a new model waters were sampled from 17 boreholes at haut glacier d arolla during the 1993 and 1994 ablation seasons three types of concentrated subglacial water were identified based on the relative proportions of ca 2c h co 3 and so4 2 to si type a waters are the most solute rich and have the lowest relative proportion of si they are believed to form in hydrologically inefficient areas of a distributed drainage system most solute is obtained from coupled sulphide oxidation and carbonate dissolution so cd it is possible that there is a subglacial source of o2 perhaps from gas bubbles released during regelation because the high so4 2 levels found up to 1200 eq l are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 c c 414 eq l a more likely alternative is that sulphide is oxidized by fe 3c in anoxic environments if this is the case exchange reactions involving fe iii and fe ii from silicates are possible these have the potential to generate relatively high concentrations of hco3 with respect to so4 2 formation of secondary weathering products such as clays may explain the low si concentrations of type a waters type b waters were the most frequently sampled subglacial water they are believed to be representative of waters flowing in more efficient parts of a distributed drainage system residence time and reaction kinetics help determine the solute composition of these waters the initial water rock reactions are carbonate and silicate hydrolysis and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites hydrolysis is followed by so cd the so4 2 concentrations usually are 414 eq l although some range up to 580 eq l which suggests that elements of the distributed drainage system may become anoxic type c waters were the most dilute yet they were very turbid their chemical composition is characterized by low so4 2 h co3 ratios and high ph type c waters were usually artefacts of the borehole chemical weathering environment true type c waters are believed to flow through sulphide poor basal debris particularly in the channel marginal zone the composition of bulk runoff was most similar to diluted type b waters at high discharge and was similar to a mixture of type b and c waters at lower discharge these observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric co2 t he progression of reactions is from carbonate and silicate hydrolysis through sulphide oxidation by first oxygen and then fe iii which drives further carbonate and silicate weathering a crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 1 we speculate that microbial oxidation of organic carbon also may occur both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions hence we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric co2 and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity which catalyses the reduction of fe iii and the oxidation of fes2 copyright 2002 john wiley sons ltd

interannual variability of glacier basal pressure from a 20 year record basal pressure has been recorded at the svartisen subglacial laboratory northern norway for 20 years and is measured by load cells installed at the ice rock interface under 200 m of glacier ice synchronous pressure variations between load cells are investigated as evidence of stress redistribution and hydrological bed connectivity a running pearson correlation is used to study the temporal variation in the response of several sensors by studying the nature of this correlation as well as the correlation between sensor pairs it is possible to investigate the evolution of the degree of synchronous response and to some extent basal connectivity at the glacier bed persistent seasonal variations associated with the melt season are observed throughout the measurement period indicating dependence on surface hydrological forcing overlying this pattern specific years with longer periods of positive and negative correlation of pressure between sensors are presented to show contrasting interannual variability in basal pressure an anticorrelated connectivity is associated with a local increase in the rate of daily subglacial discharge and is caused by load transfer or passive cavity opening stable weather appears to enhance connectivity of the sensors which is attributed to the development of a persistent drainage system and stress redistribution

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

a classification scheme for epigenetic archaean lode gold deposits recent research has shown that archaean lode gold deposits occur in environments that range in their metamorphic grade from prehnite pumpellyite to lower granulite facies based on this data a new classification is proposed for these deposits in this classification shallow level gold deposits are classed as epizonal the so called mesothermal deposits are mesozonal and the deeper deposits commonly in mid amphibolite or lower granulite terrains are hypozonal

geomorphic implications of subglacial drainage configuration rates of basal sediment evacuation controlled by seasonal drainage system evolution abstract although basal sediment evacuation by subglacial meltwater is widely assumed to dominate the sediment budget of most temperate glaciers and ice caps its potential influence for glacial geomorphic processes and landforms has largely been overlooked in the glacial literature data collected at haut glacier d arolla switzerland during the 1998 ablation season are used to test theoretical predictions that subglacial drainage configuration should exert a primary control on rates of basal sediment evacuation by subglacial meltwater seasonal evolution of the subglacial drainage system enables observation of sediment evacuation from both distributed and channelised drainage systems daily suspended sediment load exhibits an extreme nonlinear increase with respect to discharge between winter and summer periods which correspond to periods of predominantly distributed and channelised subglacial drainage respectively these results suggest that subglacial drainage configuration should significantly impact upon a rates of subglacial erosion and debris production b the nature of debris transport and the proportion of sediment in glacial versus fluvioglacial transport pathways and c rates and styles of ice marginal sedimentation in contrast to their distributed counterparts channelised drainage configurations are predicted to encourage subglacial erosion through the removal of basal sediment from the ice bedrock interface and with the exception of supraglacial transport will discourage sediment transport by alternative glacial mechanisms direct sedimentation at the glacier margin may therefore be reduced resulting in smaller moraines despite an overall increase in sediment production an appreciation of the coupling between glacier hydrology and geomorphic processes suggests new frameworks for the understanding of rates and styles of glacial erosion sediment transfer and deposition and the complex geomorphology of ice marginal environments

a hydrological approach to estimating daily glacier ablation reduced meltwater discharge owing to glacier retreat can have severe impacts on downstream water users to assess these impacts it is essential to differentiate between water from glacier melt and other sources we propose a method for doing this on a daily time scale by applying a mixing law to electrical conductivity and proglacial discharge measurements daily ablation is then estimated by applying a recession law to the glacier melt component testing this method on summer hydrology and meteorology measurements from the baounet glacier france taken over six consecutive years 2008 2013 allowed us to reconstruct daily ablation during the ablation period mean ablation rates ranged from 20 to 30 mm day 1 air temperature measurements showed that periods of low ablation during the summer were linked to cooler days and snowfall periods comparisons for three consecutive summers showed that the ablation rates obtained by summing calculated daily ablation were statistically similar to the rates recorded

surface ice motion deviating toward the margins during speed up events at gornergletscher switzerland 1 high frequency ice flow measurements during speed up events in gornergletscher switzerland revealed intriguing ice motion which has never been reported in detail before during the summer 2005 more than a 100 flow speed increase was observed three times at four gps stations installed across gornergletscher the speed ups were accompanied by a decimeter scale surface uplift two of the events were triggered by intensive surface melt and rainfall while the third one was due to the outburst of gornersee a glacier dammed lake located 2 km upglacier an interesting observation was ice motion deviating toward the side margins during the events as the glacier accelerated a transverse cross glacier velocity component was generated turning the flow direction away from the central flow line toward the margins when the glacier decelerated the transverse velocity component reversed so that the ice flowed back to the azimuth of the initial flow direction in the most significant case the trajectory of the survey stake deviated from the original track by 0 2 m in the transverse direction we hypothesize that the observed lateral ice motion was caused by locally elevated subglacial water pressure when the ice sole decoupled from the bed at a part of the glacier a point source of vertical displacement was transmitted to the surface through viscous ice this caused the transverse as well as vertical surface motion as observed in ground motion during magma intrusion the hypothesis was tested with a two dimensional ice flow model applied to the transverse glacier cross section the model confirmed that the surface ice would move toward the margins as observed in gornergletscher if subglacial water pressure exceeded the ice overburden pressure over a limited part of the bed

subglacial drainage system structure and morphology of brewster glacier new zealand a global positioning system and ground penetrating radar surveys is used to produce digital elevation models of the surface and bed of brewster glacier these are used to derive maps of subglacial hydraulic potential and drainage system structure using three different assumptions about the subglacial water pressure pw i pw ice overburden ii pw half ice overburden iii pw atmospheric additionally 16 dye tracing experiments at 12 locations were performed through a summer melt season dye return curve shape together with calculations of transit velocity dispersivity and storage are used to infer the likely morphology of the subglacial drainage system taken together the data indicate that the glacier is underlain by a channelised but hydraulically inefficient drainage system in the early summer in which water pressures are close to ice overburden by mid summer water pressures are closer to half ice overburden and the channelised drainage system is more hydraulically efficient surface streams that enter the glacier close to the location of major subglacial drainage pathways are routed quickly to the channels and then to the glacier snout streams that enter the glacier further away from the drainage pathways are routed slowly to the channels and then to the snout because they first flow through a distributed drainage system copyright 2008 john wiley sons ltd

hydrological controls on patterns of surface internal and basal motion during three spring events haut glacier d arolla switzerland three early melt season high velocity events or spring events occurred on haut glacier d arolla switzerland during the melt seasons of 1998 and 1999 the events involve enhanced glacier velocity during periods of rapidly increasing bulk discharge in the proglacial stream and high subglacial water pressures however differences in spatial patterns of surface velocity internal ice deformation rates the spatial extent of high subglacial water pressures and in rates of subglacial sediment deformation suggest different hydrological and mechanical controls the data from two of the events suggest widespread ice bed decoupling particularly along a subglacial drainage axis creating the highest rates of basal motion and plug flow in the overlying ice the other event showed evidence of less extensive ice bed decoupling and sliding along the drainage axis with more mechanical support for ice overburden transferred to areas adjacent to decoupled areas we suggest that 1 plug flow may be a common feature on glaciers experiencing locally induced reductions in basal drag 2 under certain circumstances enhanced surface motion may be due in part to non locally forced enhanced bed deformation and 3 subglacial sediment deformation is confined to a depth of the order of centimetres to decimetres

cross coupled flow modeling of coincident streaming and electrochemical potentials and application to subglacial self potential data 1 this study aims to demonstrate that self potential measurements can yield unique information about subglacial drainage conditions which has so far been doubtful at the bed of warm based glaciers arborescent and distributed drainage systems interact and streaming and electrochemical potentials coincide a key secondary aim of this study is therefore the development of a mathematical framework for the analysis of self potentials generated by such interacting flow systems we consider cross coupling between hydraulic electrical and chemical driving forces and apply the resulting model solution to self potential data recorded beneath haut glacier d arolla switzerland we find that 1 the streaming and electrochemical contributions to the total self potential signal can be separated mathematically 2 streaming potentials directly reflect the direction of water flow at the glacier bed 3 combination of streaming potentials with hydraulic conductivity estimates from slug tests allows estimation of in situ subglacial water flow velocities 4 the subglacial zeta potential calculated from estimated values of the streaming coupling coefficient is small 0 022 v due to systematic flushing of clay minerals from the channel area during the melt season and 5 uncertainties in exact electrode location in the borehole are unlikely to produce self potential noise self potential measurements may therefore yield unique information about subglacial drainage conditions and especially the direction and velocity of in situ subglacial water flow are difficult to obtain by other methods we further anticipate that our mathematical framework will be applicable to other areas of subsurface hydrology especially where spatially distributed seepage feeds preferential flow pathways

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

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

passive microwave ssm i satellite predictions of valley glacier hydrology matanuska glacier alaska 1 we advance an approach to use satellite passive microwave observations to track valley glacier snowmelt and predict timing of spring snowmelt induced floods at the terminus using 37 v ghz brightness temperatures tb from the special sensor microwave imager ssm i we monitor snowmelt onset when both tb and the difference between the ascending and descending overpasses exceed fixed thresholds established for matanuska glacier melt is confirmed by ground measured air temperature and snow wetness while glacier hydrologic responses are monitored by a stream gauge suspended sediment sensors and terminus ice velocity measurements accumulation area snowmelt timing is correlated r2 0 61 to timing of the annual snowmelt flood peak and can be predicted within 5 days

novel wireless sensors for in situ measurement of sub ice hydrologic systems wireless sensors have the potential to provide significant insight into in situ physical and biogeochemical processes in sub ice hydrologic systems however the nature of the glacial environment means that sensor deployment and data return is challenging we describe two bespoke sensor platforms electronic tracers or etracers and cryoegg for untethered wireless data collection from glacial hydrologic systems including subglacial channels both employ radio frequencies for data transmission are designed to endure harsh environmental conditions and can withstand low temperatures high pressure turbulence and abrasion we discuss the design optimization and field testing of the etracers and cryoegg culminating in test deployments beneath the greenland ice sheet the small low cost etracers were able to travel through subglacial drainage channels from where they returned water pressure measurements through 100m of ice and could measure water depth in crevasses the larger cryoegg was able to return multi parameter data from moulins through 500m of wet ice to receivers up to 2km away and from 12m depth in a proglacial lake to a receiver on the shore the tests demonstrate that the cryoegg and etracers are low power versatile robust wireless sensor platforms suitable for glacial environments which may be used with portable low cost receiving equipment

evolution of drainage system morphology at a land terminating greenlandic outlet glacier 1 the influence of meltwater on the dynamics and geomorphic impact of the greenland ice sheet is strongly controlled by the morphology of the ice sheet s drainage system however this system and its evolution through the melt season remain poorly understood here we present the results of an intensive programme of dye tracing experiments undertaken along the lower 14 km of a land terminating greenlandic outlet glacier over a period of four months during the 2010 melt season these data are interpreted in conjunction with observations of proglacial discharge englacial water storage surface melt rates and ice velocity to produce a detailed picture of the changing hydrology of the glacier following the onset of melt in the spring inputs to the drainage system regularly exceed outputs causing the englacial water level to rise to the ice sheet surface during this time there is a rapid transition from distributed to channelized drainage in those parts of the drainage system closed by ice deformation over winter as the melt season progresses channel efficiency increases and englacial storage and ice velocity decrease high velocity events continue to be observed following the channelization of the drainage system however indicating that hydrological forcing of ice velocity occurs despite the existence of channels during periods when meltwater inputs exceed the capacity of the subglacial drainage system

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

the 2002 june 22 changureh avaj earthquake in qazvin province northwest iran epicentral relocation source parameters surface deformation and geomorphology summary the m w 6 4 changureh avaj earthquake occurred on 2002 june 22 in qazvin province northwest iran we use observations from seismology field investigation and analysis of satellite imagery and digital topography to suggest that slip on a previously unrecognized thrust fault herein named the abdarreh fault was responsible for the earthquake inversion of longperiod p and sh body wave seismograms shows rupture on a thrust fault dipping 49 to the southwest and with a centroid depth of 10 km multiple event relocation of the main shock and aftershock epicentres and discontinuous surface ruptures observed after the earthquake are compatible with a northwest propagating rupture on a southwest dipping thrust but maximum recorded displacements are much less than expected from seismology suggesting that much of the slip failed to reach the surface and was accommodated as folding at the surface instead long term folding is difficult to see in the topography of the epicentral region as the abdarreh fold is growing through a relict neogene topography anticlinal uplift can however be inferred from drainage disruption and stream incision the 2002 june 22 changureh earthquake shows the importance of being able to interpret diagnostic features of active faulting in the landscape

seasonal evolution of subglacial drainage and acceleration in a greenland outlet glacier an acceleration of ice mass loss has been observed near the margin of the greenland ice sheet partly as a result of faster ice motion observations by gps receivers reveal high seasonal variability in ice motion with summer motion up to 220 higher than winter background levels the greenland ice sheet contains enough water to raise sea levels by 7 m however its present mass balance and future contribution to sea level rise is poorly understood1 accelerated mass loss has been observed near the ice sheet margin partly as a result of faster ice motion2 3 4 surface melt waters can reach the base of the ice sheet and enhance basal ice motion5 6 however the response of ice motion to seasonal variations in meltwater supply is poorly constrained both in space and time here we present ice motion data obtained with global positioning system receivers located along a 35 km transect at the western margin of the greenland ice sheet throughout a summer melt season our measurements reveal substantial increases in ice velocity during summer up to 220 above winter background values these speed up events migrate up the glacier over the course of the summer the relationship between melt and ice motion varies both at each site throughout the melt season and between sites we suggest that these patterns can be explained by the seasonal evolution of the subglacial drainage system similar to hydraulic forcing mechanisms for ice dynamics that have been observed at smaller glaciers

the dynamic response of kennicott glacier alaska usa to the hidden creek lake outburst flood glacier sliding is commonly linked with elevated water pressure at the glacier bed ice surface motion during a 3week period encompassing an outburst of ice dammed hidden creek lake hcl at kennicott glacier alaska usa showed enhanced sliding during the flood two stakes 1 2 km from hcl revealed increased speed in two episodes both associated with uplift of the ice surface relative to the trajectory of bed parallel motion uplift of the surface began 12 days before the flood initially stabilizing at a value of 0 25m two days after lake drainage began further uplift reaching 0 4m occurred while surface speed peaked at 1 2md maximum surface uplift coincided with peak discharge from hcl high water level in a down glacier ice marginal basin and low solute concentrations in the kennicott river each of these records is consistent with high subglacial water pressure we interpret the ice surface motion as arising from sliding up backs of bumps on the bed which enlarges cavities and produces bed separation the outburst increased water pressure over a broad region promoting sliding inhibiting cavity closure and blocking drainage of solute rich water from the distributed system pressure drop upon termination of the outburst drained water from and depressurized the distributed system reducing sliding speeds expanded cavities then collapsed with a 1 day time scale set by the local ice thickness

comments on 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