glacial lake camelsfoot a late wisconsinan advance stage proglacial lake in the fraser river valley gang ranch area british columbia in the gang ranch area british columbia interaction between the regional physiography and ice flow during the late wisconsinan fraser glaciation resulted in the formation of a proglacial lake confined to valleys of the fraser river and its tributaries lithostratigraphic and geomorphic evidence suggests that ponding was initiated in the big bar creek area where the fraser river is confined to a deep canyon in the camelsfoot range during ice advance a proglacial lake system developed that progressively deepened and reached a minimum upper elevation of approximately 710 m asl prior to being overridden by ice we propose that this system be formally named glacial lake camelsfoot a composite stratotype comprising lithostratigraphic units associated with glacial lake camelsfoot is described from eight reference sections along fraser river churn and lone cabin creeks in the gang ranch area additional geomorphic evidence indicates that at the fraser glaciation maximum the cordilleran ice sheet in th

history and isostatic effects of the last ice sheet in southern british columbia abstract the late wisconsinan cordilleran ice sheet covered british columbia southern yukon territory and parts of alaska washington idaho and montana its major source areas were the high mountain ranges of the canadian cordillera and flow was strongly controlled by topography the last ice sheet began to develop about 30 000 25 000 14c yr ago but it did not achieve its maximum extent until 15 000 14 000 14c yr bp ice sheet growth was interrupted locally by stillstands and retreat ice sheet decay was rapid and was characterized by complex frontal retreat at the periphery accompanied locally by brief readvances and by downwasting and stagnation by 10 000 14c yr bp

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

jokulhlaups a reassessment of floodwater flow through glaciers 1 in glaciated catchments glacier generated floods jokulhlaups put human activity at risk with large sporadic jokulhlaups accounting for most flood related fatalities and damage to infrastructure in studies of jokulhlaup hydrodynamics the view predominates that floodwater travels within a distinct conduit eroded into the underside of a glacier however some jokulhlaups produce subglacial responses wholly inconsistent with the conventional theory of drainage by focusing on icelandic jokulhlaups this article reassesses how floodwater flows through glaciers it is argued that two physically separable classes of jokulhlaup exist and that not all jokulhlaups are an upward extrapolation of processes inherent in events of lesser magnitude and smaller scale the hydraulic coupling of multiple nonlinear components to the flood circuit of a glacier can induce extreme responses including pressure impulses in subglacial drainage representing such complexity in mathematical form should be the basis for upcoming research as future modeling results may help to determine the glaciological processes behind heinrich events moreover such an approach would lead to more accurate predictive models of jokulhlaup timing and intensity

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

the pleistocene of schoningen germany a complex tunnel valley fill revealed from 3d subsurface modelling and shear wave seismics abstract the pleistocene deposits of schoningen represent an outstanding geological and archaeological archive where an up to 45 m thick middle to late pleistocene succession has been preserved and unique artefacts from the lower palaeolithic have been discovered the preservation of such a thick and complete glacial interglacial succession is very rare in the geological record and requires a specific depositional setting we will present a new depositional model for the pleistocene succession of schoningen integrating outcrop data borehole data and high resolution shear wave seismics a total of four outcrop sections and 744 borehole logs were examined to document the complex facies architecture all collected sedimentological and geophysical data sets were integrated into a high resolution 3d geological model gocad for reconstructing the spatial distribution of facies associations and the large scale depositional architecture the spatial distribution of the artefacts will be discussed with respect to the depositional environment the elsterian and holsteinian deposits are restricted to a nnw sse trending elongated trough which is deeply incised into unconsolidated lignite bearing palaeogene deposits the geometry of this erosional structure points to a tunnel valley origin that was incised below the elsterian ice sheet the basal tunnel valley fill consists of cross stratified pebbly sand and gravel overlain by till after deglaciation the tunnel valley remained underfilled and acted as a depocentre for interglacial deposition during the subsequent holsteinian interglacial mis 9 a lake formed within this depocentre and lacustrine sediments accumulated this interglacial succession consists of peat organic rich silt and fine grained sand interpreted as lake bottom and deltaic sediments fed by surface run off shed from the elm ridge the lacustrine deposition was controlled by repeated lake level fluctuations in the range of 1 6 m leading to the formation of laterally stacked delta systems these lake level changes were probably triggered by climate causing variations of precipitation and surface run off during the late saalian glaciation the remnant tunnel valley was completely filled with meltwater deposits the sedimentary facies and depositional architecture point to a shallow water delta subsequently the meltwater deposits were overlain by till the deposition of the middle pleistocene sediments within an elsterian tunnel valley explains the unique preservation of the sedimentary succession of schoningen the long lived interglacial lake provided an attractive site for animals and early humans ambushing them artefacts mainly became embedded on the delta plain which rapidly was transgressed during lake level rise and artefacts were thus preserved

sediment petrography mineralogy and geochemistry of the miocene islam dag section eastern azerbaijan implications for the evolution of sediment provenance palaeo environment and post depositional alteration patterns

seasonal speedup of the greenland ice sheet linked to routing of surface water we use interferometric synthetic aperture radar observations recorded in a land terminating sector of western greenland to characterise the ice sheet surface hydrology and to quantify spatial variations in the seasonality of ice sheet flow our data reveal a non uniform pattern of late summer ice speedup that in places extends over 100 km inland we show that the degree of late summer speedup is positively correlated with modelled runoff within the 10 glacier catchments of our survey and that the pattern of late summer speedup follows that of water routed at the ice sheet surface in late summer ice within the largest catchment flows on average 48 faster than during winter whereas changes in smaller catchments are less pronounced our observations show that the routing of seasonal runoff at the ice sheet surface plays an important role in shaping the magnitude and extent of seasonal ice sheet speedup

the role of subglacial water in ice sheet mass balance subglacial water can significantly affect the velocity of ice streams and outlet glaciers of ice sheets depending on the geometry and capacity of the subglacial hydrologic system increased surface melting in greenland over the coming decades may influence the ice sheet s mass balance furthermore subglacial lakes in antarctica can modulate ice velocities and act as nucleation points for new fast flowing ice streams in the coming decades significant changes in the polar regions will increase the contribution of ice sheets to global sea level rise under the ice streams and outlet glaciers that deliver ice to the oceans water and deformable wet sediments lubricate the base facilitating fast ice flow the influence of subglacial water on fast ice flow depends on the geometry and capacity of the subglacial hydrologic system water moving rapidly through a well connected system of conduits or channels will have little impact on ice sheet velocities but water injected into a spatially dispersed subglacial system may reduce the effective pressure at the base of the ice sheet and thereby trigger increased ice sheet velocities in greenland the form of the subglacial hydrologic system encountered by increasing surface melt water will determine the influence of changing atmospheric conditions on ice sheet mass balance in antarctica subglacial lakes have the capacity to both modulate velocities in ice streams and outlet glaciers and provide nucleation points for new fast ice flow tributaries climate models of ice sheet responses to global change remain incomplete without a parameterization of subglacial hydrodynamics and ice dynamics

the sedimentary architecture of outburst flood eskers a comparison of ground penetrating radar data from bering glacier alaska and skeiðararjokull iceland we present ground penetrating radar gpr profiles that reveal the sedimentary architecture of an esker deposited during a surge associated outburst flood at the bering glacier alaska the wide up flow end of the esker contains a transition from large backset beds to large foreset beds interpreted to reflect composite macroform development in an enlarged part of the conduit by contrast the narrow down flow portion of the esker is dominated by plane beds interpreted to have been deposited where the conduit was constricted and the flow was faster a previously studied outburst esker at skeidararjokull iceland has a similar morphology and stratigraphic architecture this suggests that outburst floods generate distinct depositional signatures in eskers both in terms of morphology and sedimentary architecture identification of these distinct signatures in ancient eskers will help assess the paleohydraulic conditions under which ancient eskers formed and by extension the nature of meltwater drainage systems beneath the laurentide and eurasian ice sheets

seasonal evolution of supra glacial lakes on the greenland ice sheet abstract a survey of supra glacial lakes on the western margin of the greenland ice sheet reveals a seasonally driven hydrological system culminating in widespread lake drainage in late summer we used satellite imagery to study the evolution of 292 lakes across two sites totalling 22 000 km 2 in area during 2001 the lakes combined area increased to 75 5 km 2 by the beginning of july over the following 25 days an area totalling 36 3 5 km 2 drained from 216 lakes at one study site we used meteorological data and a positive degree day model to calculate the volume of water generated by melting in the lake catchments based on this estimate the mean depth of filling lakes surveyed rose from 1 5 0 7 m on 7th july to 3 9 1 1 m on 1st august in agreement with a value for one lake of 4 4 0 9 m we have derived from airborne altimetry during this 25 day period we estimate that 38 18 10 7 m 3 of water drained from the surface at this site and that there was an average water flux of 1 3 0 3 m 3 s 1 passing through each lake that drained completely

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

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

evolution of the subglacial hydrologic system beneath the rapidly decaying cordilleran ice sheet caused by ice dammed lake drainage implications for meltwater induced ice acceleration abstract a positive correlation between ice dammed lake drainage and ice acceleration at antarctic ice sheets ais and land terminating sections of the greenland ice sheet gris has been implicated in enhanced ice sheet decay however the paucity of direct measurements at the ice sheet bed restricts our understanding of subglacial drainage system evolution in response to transient water inputs we present evidence that two meltwater corridors on the former bed of the thin 600 m at last glacial maximum over the interior plateaus of british columbia and rapidly decaying cordilleran ice sheet cis were generated subglacially in response to the drainage of an ice dammed lake and operated as canals tunnel channels geomorphological ground penetrating radar gpr and electrical resistivity tomography ert data reveal a simple event sequence that includes initial propagation of a broad at least 2 5 km wide floodwave inefficient drainage from an ice dammed lake over relatively short 3 24 km zones at the corridor heads that collapsed into efficient canals large up to 0 25 2 5 km wide channels incised down into the sediment bed and up into the ice downglacier canal formation on the southern fraser plateau involved synchronous along the full canal length system development including elements of headward erosion and plunge pool formation our data suggest that ice dammed lake drainage beneath a rapidly decaying thin ice mass that has an efficient antecedent drainage network is not conducive to large scale ice acceleration these data may aid better assessment of the role of ice dammed lake drainage on the dynamics of former as well as contemporary ice sheets

regional reconstruction of subglacial hydrology and glaciodynamic behaviour along the southern margin of the cordilleran ice sheet in british columbia canada and northern washington state usa abstract subglacial landsystems in and around okanagan valley british columbia canada are investigated in order to evaluate landscape development subglacial hydrology and cordilleran ice sheet dynamics along its southern margin major landscape elements include drumlin swarms and tunnel valleys drumlins are composed of bedrock diamicton and glaciofluvial sediments their form truncates the substrate tunnel valleys of various scales km to 100s km length incised into bedrock and sediment exhibit convex longitudinal profiles and truncate drumlin swarms okanagan valley is the largest tunnel valley in the area and is eroded 300 m below sea level over 600 m of late wisconsin age sediments consisting of a fining up sequence of cobble gravel sand and silt fill okanagan valley landform substrate relationships landform associations and sedimentary sequences are incompatible with prevailing explanations of landsystem development centred mainly on deforming beds they are best explained by meltwater erosion and deposition during ice sheet underbursts during the late wisconsin glaciation okanagan valley functioned as part of a subglacial lake spanning multiple connected valleys few 100s km of southern british columbia subglacial lake development started either as glaciers advanced over a pre existing sub aerial lake catch lake or by incremental production and storage of basal meltwater high geothermal heat flux geothermal springs and or subglacial volcanic eruptions contributed to ice melt and may have triggered along with priming from supraglacial lakes subglacial lake drainage during the underburst s sheetflows eroded drumlins in corridors and channelized flows eroded tunnel valleys progressive flow channelization focused flows toward major bedrock valleys in okanagan valley most of the pre glacial and early glacial sediment fill was removed a fining up sequence of boulder gravel and sand was deposited during waning stages of the underburst s and bedrock drumlins in okanagan valley were enhanced or wholly formed by this underburst s subglacial lake development and drainage had an impact on ice sheet geometry and ice volumes the prevailing conceptual model for growth and decay of the cis suggests significantly thicker ice in valleys compared to plateaus subglacial lake development created a reversal of this ice sheet geometry where grounded ice on plateaus thickened while floating valley ice remained thinner due to melting and enhanced sliding with significant transfer of ice toward the ice sheet margin subglacial lake drainage may have hastened deglaciation by melting ice lowering ice surface elevations and causing lid fracture this paper highlights the importance of ice sheet hydrology its control on ice flow dynamics distribution and volume in continental ice masses

the harricana glaciofluvial complex abitibi region quebec its genesis and implications for meltwater regime and ice sheet dynamics abstract interlobate moraines have been defined by their relationshio to adjacent landforms and sediments with minimal reference to any genesis suggested from their own geomorphology and sedimentology a case in point is the harricana interlobate moraine the harricana complex a relatively continuous linear accumulation of glaciofluvial sediments is investigated in terms of its geomorphology sedimentology stratigraphic context and landform associations for the portion between latitudes 48 n and 50 n the complex is narrower to the north than to the south in the narrower northern part better rounding and poorer preservation of less resistant clasts suggest more vigorous transport in a narrower conduit the inverse in the wider southern part favours less vigorous flows and higher deposition rates these inferences together with unidirectional paleoflows towards the ice margin and the relatively continuous upslope path of the southward widening complex favour synchronous formation of the harricana complex in a continuous closed conduit beneath an ice sheet which thinned southward subaqueous fans and grounding line deposits with fine gravel and sandy in phase wave structures in the south may have been deposited in subglacial cavities adjacent to the complex or later deposited in reentrants in calving ice fronts the basic building blocks of the harricana complex are gravel facies which indicate generally high energy but unsteady transport these facies are arranged into macroforms composite and oblique accretion avalanche bed oaab macroforms are attributed to deposition by unsteady and non uniform flows in conduit enlargements pseudoanticlinal macroforms were deposited in relatively narrow conduit segments of uniform width gravel sand couplets register flow unsteadiness perhaps related to variations in supraglacial metlwater supply the origin of the harricana complex as a mainly synchronous subglacial landform is linked to formation of adjacent streamlined bedforms and bedrock erosional marks by meltwater outburst floods the complex is located where the orientation of these subglacial bedforms indicate strong flow convergence post flood ice sheet collapse along this convergence zone initiated redirection of ice flow resulting in cross cutting striae later subglacial meltwater systems followed new hydraulic gradients toward this trough of thinner ice forming a major conduit and depositing the harricana glaciofluvial complex

evidence for rapid sedimentation in a tunnel channel oak ridges moraine southern ontario canada abstract in south central ontario a late wisconsinan regional unconformity consisting of tunnel channels and drumlinized till crops out north of lake ontario the tunnel channels are locally infilled and the unconformity buried by sediment of the oak ridges moraine based on seismic reflection profiling and drillcore the tunnel channels are known to continue beneath the moraine detailed sedimentological analysis of 300 m of continuous core from two drillholes located 7 km apart in subparallel tunnel channels identified three facies the gravel facies is 17 m thick and occurs in only one of the cores it directly overlies the unconformity and may include a number of upward fining units seismic reflection data suggests the gravel forms stacked gravel mesoforms or quasi horizontal gravel layers bed load sheets deposited from fluidal flows along the deep channel axis the graded massive sand facies up to 37 m thick is the most common facies and consists of silty medium sand with minor coarse sand strata are reverse graded normal graded or massive with isolated silt intraclasts and evidence locally for dewatering this facies is interpreted to have been deposited from hyperconcentrated dispersions downflow of a hydraulic jump or major channel confluence the third facies consists of medium scale and small scale cross stratified sand medium scale cross stratification occurs predominantly in the lower 37 m of the core and is interbedded with the graded massive sand facies small scale cross stratified sand is progressively more common upward in core medium and small scale cross stratified sands was deposited respectively by subaqueous dunes and ripples formed in dilute fluid flows the complete succession is interpreted to have been deposited very rapidly within a subglacial tunnel channel before discharge ceased along the channel deposition followed closely and in part coincided with rapid expansion of the channel by erosion in a hydraulic jump or at a major channel confluence along the grounding line of a subglacial lake scour into unconsolidated sediment contributed to the sediment flux and quickly overloaded the flow with suspended sediment which in turn resulted in extremely high rates of sedimentation immediately downflow such depositional conditions support the notion that tunnel channels in the study area formed and or served as conduits for subglacial jokulhlaup discharges and that the laurentide ice sheet most probably did not generally drain by steady state processes but instead by short lived catastrophic events

tunnel valley formation in northwest germany geology mechanisms of formation and subglacial bed conditions for the bornhoved tunnel valley the bornhoved tunnel valley consists of a relatively broad elongated depression filled primarily with tills and a narrow channel in the axial part filled with outwash glaciolacustrine sediments and tills the tunnel valley is at least 13 km long 222 m deep bottom at 191 m b s l and extends parallel to the axis of a peripheral sink between two permian salt diapirs in the substratum it is suggested that the initiation of the tunnel valley was controlled by a differential response of the bed materials to ice overriding on top of and between the salt structures the bornhoved tunnel valley is a polygenetic feature that resulted from different erosional processes throughout all three main glaciations in northern germany during the elsterian glaciation glaciotectonic squeezing occurred to be later replaced by subglacial meltwater erosion during the ice retreat and the holsteinian interglacial the valley was filled with fine grained glaciolacustrine and marine sediments which were subsequently removed and redeposited further down ice as a 200 m thick glaciotectonic melange by the first saalian advance the second saalian advance caused only minor changes and the tunnel valley was reactivated as a subglacial channel during the weichselian glaciation it is suggested that at the time of the first weichselian ice advance a large subglacial water reservoir developed in the area of the baltic sea basin and caused a rapid surge like ice movement as the ice sheet advanced out of the baltic sea basin drainage of the water reservoir was prevented by the ice toe overriding the permafrost on the saalian highlands during the ice retreat frozen ground was left beyond the ice margin and subglacial meltwater catastrophically drained through the tunnel valley with a discharge roughly estimated at about 3 75 103 m3 s it seems possible that drainage of the subglacial water collector through the bornhoved tunnel valley and other similar channels south of the baltic sea led to increased ice sheet basal friction and was one reason for successively smaller extents of the subsequent weichselian advances evidence against pervasively deforming bed materials in the vicinity of the bornhoved tunnel valley in the weichselian glaciation indicates that the valley served as an efficient drainage path for porewater from the subglacial sediments

evidence for subglacial water transport in the west antarctic ice sheet through three dimensional satellite radar interferometry 1 radarsat data from the 1997 antarctic mapping mission are used interferometrically to solve for the 3 dimensional surface ice motion in the interior of the west antarctic ice sheet wais an area of 125 km2 in a tributary of the kamb ice stream slumped vertically downwards by up to 50 cm between september 26 and october 18 1997 areas in the bindschadler ice stream also exhibited comparable upward and downward surface displacements as the uplift and subsidence features correspond to sites at which the basal water apparently experiences a hydraulic potential well we suggest transient movement of pockets of subglacial water as the most likely cause for the vertical surface displacements these results and related lidar observations imply that imaging the change in ice surface elevation can help reveal the key role of water in the difficult to observe subglacial environment and its important influence on ice dynamics

seismic facies and regional architecture of the oak ridges moraine area southern ontario analysis of over 50 line kilometres of land based shallow seismic reflection profiles has provided a means of investigating the subsurface architecture and stratigraphic relationships of the glac

rapid discharge connects antarctic subglacial lakes a hidden subglacial world consisting of more than 140 lakes lies beneath the antarctic ice sheet it is widely assumed that these lakes are a static ecosystem cut off from each other and the rest of the world far from it according to a 16 month study of surface elevation changes in the region changes indicating a rapid discharge of water from one lake to another were detected and it is possible that the entire subglacial drainage basin is flushed through periodically by massive water transfers observation of surface elevation changes over 16 months in an area of the east antarctic ice sheet overlying subglacial lakes suggests a rapid discharge of one lake to at least two other lakes involving a water volume of 1 8 km3 in conflict with previous expectations that subglacial lakes have long residence times and slow circulations the existence of many subglacial lakes1 provides clear evidence for the widespread presence of water beneath the east antarctic ice sheet but the hydrology beneath this ice mass is poorly understood2 such knowledge is critical to understanding ice flow basal water transfer to the ice margin glacial landform development and subglacial lake habitats here we present ice sheet surface elevation changes in central east antarctica that we interpret to represent rapid discharge from a subglacial lake our observations indicate that during a period of 16 months 1 8 km3 of water was transferred over 290 km to at least two other subglacial lakes while viscous deformation of the ice roof above may moderate discharge the intrinsic instability of such a system3 suggests that discharge events are a common mode of basal drainage4 if large lakes such as lake vostok or lake concordia1 are pressurizing it is possible that substantial discharges could reach the coast5 6 our observations conflict with expectations that subglacial lakes have long residence times and slow circulations2 7 8 and we suggest that entire subglacial drainage basins may be flushed periodically the rapid transfer of water between lakes would result in large scale solute and microbe relocation and drainage system contamination from in situ exploration is therefore a distinct risk

on the formation of the tunnel valleys of the superior lobe central minnesota abstract when considering the formation of tunnel valleys most researchers have appealed to basal melting as the primary source of water erosion of the tunnel valleys can then be accomplished by steady state drainage over a long period or by storage and subsequent catastrophic release however field relationships in a large system of tunnel valleys formed by the superior lobe in central minnesota indicate that another source of water must be considered the minnesota tunnel valleys are composed of individual segments 10 20 km long and the segments commonly terminate in subaerial outwash fans at recessional ice margin positions eskers associated with the tunnel valleys are also composed of short segments frequently beginning at moulin kames and terminating at the head of outwash fans the dominant source of the water responsible for tunnel valley formation was seasonal meltwater from the glacier surface that reached the bed through moulins and crevasses the apparent continuity of the valleys resulted from the headward development of the englacial drainage system during ice retreat

landform characterization using geophysics recent advances applications and emerging tools abstract this paper presents an overview of the strengths and limitations of existing and emerging geophysical tools for landform studies the objectives are to discuss recent technical developments and to provide a review of relevant recent literature with a focus on propagating field methods with terrestrial applications for various methods in this category including ground penetrating radar gpr electrical resistivity er seismics and electromagnetic em induction the technical backgrounds are introduced followed by section on novel developments relevant to landform characterization for several decades gpr has been popular for characterization of the shallow subsurface and in particular sedimentary systems novel developments in gpr include the use of multi offset systems to improve signal to noise ratios and data collection efficiency amongst others and the increased use of 3d data multi electrode er systems have become popular in recent years as they allow for relatively fast and detailed mapping novel developments include time lapse monitoring of dynamic processes as well as the use of capacitively coupled systems for fast non invasive surveys em induction methods are especially popular for fast mapping of spatial variation but can also be used to obtain information on the vertical variation in subsurface electrical conductivity in recent years several examples of the use of plane wave em for characterization of landforms have been published seismic methods for landform characterization include seismic reflection and refraction techniques and the use of surface waves a recent development is the use of passive sensing approaches the use of multiple geophysical methods which can benefit from the sensitivity to different subsurface parameters is becoming more common strategies for coupled and joint inversion of complementary datasets will once more widely available benefit the geophysical study of landforms three cases studies are presented on the use of electrical and gpr methods for characterization of landforms in the range of meters to 100 s of meters in dimension in a study of polygonal patterned ground in the saginaw lowlands michigan usa electrical resistivity tomography was used to characterize differences in subsurface texture and water content associated with polygon swale topography also a sand filled thermokarst feature was identified using electrical resistivity data the second example is on the use of constant spread traversing cst for characterization of large scale glaciotectonic deformation in the ludington ridge michigan multiple cst surveys parallel to an 60 m high cliff where broad 100 m synclines and narrow clay rich anticlines are visible illustrated that at least one of the narrow structures extended inland a third case study discusses internal structures of an eolian dune on a coastal spit in new zealand both 35 and 200 mhz gpr data which clearly identified a paleosol and internal sedimentary structures of the dune were used to improve understanding of the development of the dune which may shed light on paleo wind directions

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

constraints on the lake volume required for hydro fracture through ice sheets 1 water filled cracks are an effective mechanism to drive hydro fractures through thick ice sheets crack geometry is therefore critical in assessing whether a supraglacial lake contains a sufficient volume of water to keep a crack water filled until it reaches the bed in this study we investigate fracture propagation using a linear elastic fracture mechanics model to calculate the dimensions of water filled cracks beneath supraglacial lakes we find that the cross sectional area of water filled cracks increases non linearly with ice sheet thickness using these results we place volumetric constraints on the amount of water necessary to drive cracks through 1 km of sub freezing ice for ice sheet regions under little tension lakes larger than 0 25 0 80 km in diameter contain sufficient water to rapidly drive hydro fractures through 1 1 5 km of subfreezing ice this represents 98 of the meltwater volume held in supraglacial lakes in the central western margin of the greenland ice sheet

drumlin formation related to inverted melt water erosional marks drumlin forms are described from maps and air photographs of a part of the athabasca plains northern saskatchewan three major forms spindle parabolic and transverse asymmetrical are recognized these forms which may show superimposed minor elements depart from classical descriptions of drumlins but are similar to moulds of erosional marks created by separated fluid flows assemblages of drumlins also show characteristics similar to those of erosional marks the form analogy between drumlins and moulds of erosional marks is carried to a conclusion that drumlins may be formed by the infilling of erosional marks created on the under side of glaciers by separated subglacial melt water flows estimates of specific discharge are obtained by means of an expected range of reynolds number geomorphological evidence is given for large scale erosion by subglacial melt water a discussion of the sedimentology stratigraphy and deformational structure of the interiors of drumlins shows that they may be explained by the erosional mark hypothesis this paper emphasizes the importance of melt water as a geomorphic agent and may have broad implications for ice sheet dynamics and profiles rates of deglaciation and the occurrence of bedrock thrusting by ice

seasonal speedup of a greenland marine terminating outlet glacier forced by surface melt induced changes in subglacial hydrology we present subdaily ice flow measurements at four gps sites between 36 and 72 km from the margin of a marine terminating greenland outlet glacier spanning the 2009 melt season our data show that 35 km from the margin seasonal and shorter time scale ice flow variations are controlled by surface melt induced changes in subglacial hydrology following the onset of melting at each site ice motion increased above background for up to 2 months with resultant up glacier migration of both the onset and peak of acceleration later in our survey ice flow at all sites decreased to below background multiple 1 to 15 day speedups increased ice motion by up to 40 above background these events were typically accompanied by uplift and coincided with enhanced surface melt or lake drainage our results indicate that the subglacial drainage system evolved through the season with efficient drainage extending to at least 48 km inland during the melt season while we can explain our observations with reference to evolution of the glacier drainage system the net effect of the summer speed variations on annual motion is small 1 this in part is because the speedups are compensated for by slowdowns beneath background associated with the establishment of an efficient subglacial drainage system in addition the speedups are less pronounced in comparison to land terminating systems our results reveal similarities between the inland ice flow response of greenland marine and land terminating outlet glaciers

superimposition of ribbed moraines on a palaeo ice stream bed implications for ice stream dynamics and shutdown the sediments and landforms preserved on palaeo ice stream beds can provide important information about their subglacial conditions and flow mechanisms and the processes accompanying their shutdown in this paper detailed observations of an intriguing subglacial landform assemblage of ribbed moraines superimposed on glacial lineations on the dubawnt lake ice stream bed north west canadian shield are presented including their morphometry internal structure from ground penetrating radar gpr surveys and from glaciogeological analysis and sedimentological characteristics from sediment architecture and lithofacies analysis the observations suggest an abrupt change in ice dynamics that correlates with two phases of glacial landform development this hypothesis is based on evidence from a deformed lodgement till which subsequently underwent brittle deformation and developed prominent thrust shear structures and tension fractures tension fractures are observed in a sediment exposure and thrust structures are observed in gpr surveys where they occur most prominently in the ribbed moraine ridge crests the presence of the fractures and their association with a population of clasts in the till that are orientated with their a axes transverse to the inferred ice flow direction suggests a compressional flow regime it is therefore inferred that the glacial lineations were formed under an extensional flow regime during ice stream activity but that at some point patches of till under the ice stream stiffened through dewatering the subsequent increase in basal shear stress resulted in compressional flow and the development of subglacial thrusting and the building of ribbed moraines we therefore suggest that ribbed moraines may form in areas of compressional flow under ice streams i e sticky spots and or at the transition between slow and fast ice flow along parts of an ice stream the general absence of ribbed moraines on most other palaeo ice stream beds suggests that either these ice streams continued operating during deglaciation or processes other than the development of localized compressional flow sticky spots led to their shutdown e g ice depletion

connected subglacial lake activity on lower mercer and whillans ice streams west antarctica 2003 2008 we examine patterns of localized surface elevation change in lower mercer and whillans ice streams west antarctica which we interpret as subglacial water movement through a system of lakes and channels we detect and measure the lake activity using repeat track laser altimetry from icesat and image differencing from modis image pairs a hydrostatic potential map for the region shows that the lakes are distributed across three distinct hydrologic regimes our analysis shows that within these regimes some of the subglacial lakes appear to be linked with drainage events in one reservoir causing filling and follow on drainage in adjacent lakes we also observe changes near ice raft a in lower whillans ice stream and interpret them as evidence of subglacial water and other changes at the bed the study provides quantitative information about the properties of this complex subglacial hydrologic system and a relatively unstudied component of ice sheet mass balance subglacial drainage across the grounding line

surface melt induced acceleration of greenland ice sheet flow ice flow at a location in the equilibrium zone of the west central greenland ice sheet accelerates above the midwinter average rate during periods of summer melting the near coincidence of the ice acceleration with the duration of surface melting followed by deceleration after the melting ceases indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice bedrock interface interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting with larger increases accompanying higher amounts of summer melting the indicated coupling between surface melting and ice sheet flow provides a mechanism for rapid large scale dynamic responses of ice sheets to climate warming

glacial curvilineations new glacial landforms produced by longitudinal vortices in subglacial meltwater flows abstract the glacial landscape of the dobrzyn plateau in central poland contains a complex suite of enigmatic bedforms consisting of elongate and sinuous sediment ridges occurring within an anabranched network of tunnel channels terminating at a former ice margin marked by extensive glaciofluvial fans the term glacial curvilineations is proposed to describe these enigmatic bedforms that occur as fields of parallel sinuous ridges separated by troughs the regional pattern of glacial curvilineations replicates the morphology and pattern of tunnel channel margins and suggests a common genesis tunnel channels and glacial curvilineations are eroded in the interbedded diamictons and glaciofluvial sediments of the plateau we propose that tunnel channels and glacial curvilineations are the products of subglacial meltwater erosion curvilineations are erosional remnants produced by longitudinal vortices within the tunnel channel forming flows parallelism of curvilineations reflects spacing of turbulent structures within the subglacial flow tunnel channel margins also control the sinuosity of curvilineations by dictating both the path and curvature of longitudinal vortices arguments for meltwater erosion are strengthened by the presence of extensive glaciofluvial fans at tunnel channel termini they are the depositional counterparts to the extensive subglacial fluvial dissection of the plateau understanding curvilineation genesis may shed light on glacier hydrologic processes tunnel channels develop abruptly in the plateau surface suggesting localized point sources of meltwater such as drainage of subglacial and or supraglacial lakes the extent of tunnel channels and lateral continuity of glacial curvilineations suggests broad sheet like flows as wide as a few kilometres

ice stream sticky spots a review of their identification and influence beneath contemporary and palaeo ice streams rapidly flowing ice streams are the arterial drainage routes in continental ice sheets and exert a major influence on ice sheet mass balance recent observations have revealed that ice stream flow exhibits considerable variability with relatively rapid changes taking place in speed and direction this spatial and temporal variability is intimately linked to the conditions at the base of the ice streams and the distribution of localised patches of basal friction known as sticky spots in this paper we provide a detailed review of sticky spot observations from both contemporary and palaeo ice stream beds in order to better understand their nature and influence observations and theoretical considerations reveal four primary causes of stickiness i bedrock bumps ii till free areas iii areas of strong well drained till and iv freeze on of subglacial meltwater these may act together in one location or in isolation and a progressive increase in their distribution could lead to ice stream shut down bedrock bumps are influential under active ice streams where they provide form drag and can create thinner ice which increases the likelihood of basal freeze on increased bed roughness may prevent the lateral migration of some ice streams but bedrock bumps are unlikely to cause ice stream shut down because over long time scales ice stream erosion might be expected to reduce their amplitude the influence of till free areas beneath an ice stream will depend critically on the amount of water that might be drawn out of the surrounding till to lubricate such areas they are likely to be most important in ice stream onset zones but their identification has proved difficult beneath active ice streams if an ice stream operates solely by till deformation it is conceivable that a progressive increase in the exposure of till free areas could lead to shut down through a process of sediment exhaustion areas of strong well drained till have been identified beneath both active and ancient ice streams and are most likely to result from the reorganisation of subglacial meltwater the collapse of an inefficient cannalised system to a more efficient channelised system can occur rapidly and this mechanism has been hypothesised as a candidate for ice stream shut down in both contemporary and palaeo settings basal freeze on has also been observed and inferred from beneath modern and palaeo ice streams and a reduction in basal meltwater supply coupled with ice stream drawdown and the advection of cold ice increases the likelihood of switching off an ice stream a paucity of data from ice stream sticky spots limits a better understanding of their nature distribution and evolution beneath ice streams future technological advances are likely to improve the resolution of the data collected from the beds of modern ice streams but well preserved palaeo ice stream beds also hold potential for investigating their influence on ice stream flow and we present simple landsystems models to aid their identification such data will considerably enhance the basal boundary condition in ice stream models which will ultimately refine our predictions of the response of contemporary ice sheets to future changes in climate

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

glaciofluvial infilling and scour of the puget lowland washington during ice sheet glaciation the puget lobe the southwesternmost extension of the cordilleran ice sheet last advanced into the puget lowland of western washington at about 15 ka the advancing ice sheet deposited voluminous sediment on a prograding proglacial outwash plain that extended from the olympic mountains to the cascade range herein recognized as the great lowland fill subsequent overrunning by the ice sheet excavated deep linear troughs now occupied by the large lakes and marine waters of puget sound excavation of these troughs and valleys of the puget lowland required the net transport of about 1000 km3 of sediment almost entirely during ice occupation and primarily by subglacial water these landforms of glaciofluvial deposition and erosion define the modern landscape here emphasizing the importance of these processes in the region s geomorphology

macroforms large bedforms and rhythmic sedimentary sequences in subglacial eskers south central ontario implications for esker genesis and meltwater regime abstract eskers of south central ontario were deposited in closed subglacial conduits which were continuous main conduits this interpretation is supported by the intimate association of eskers with an anastomosing network of tunnel channels relatively continuous esker ridges minimal post formational disturbance of esker sediments intercalation of till and stratified sand and gravel diapiric folding at an esker core low variability in palaeocurrent direction and upslope flow paths down esker trends in clast lithology roundness and sphericity indicate continuous conduits with sediment supply by subglacial deformation of adjacent material into the conduits melt out of sediment from the conduit walls and fluvial resedimentation esker ridge morphology is attributed to synchronous erosion transportation and deposition along the main conduits such that ridge discontinuities are primarily explained as zones of non deposition during esker formation composite pseudoanticlinal and oblique accretion avalanche bed macroforms are identified gravel facies within these macroforms were deposited from fluidal flows or hyperconcentrated dispersions progradation of macroforms or migration of constituent large bedforms through the main conduits may have temporarily blocked constricted portions of those conduits and acted as possible internal autogenic controls on sediment availability and flow resistance the location of macroforms within conduits was primarily controlled by conduit geometry and sediment availability and later by feedback between macroform and conduit geometries sand and gravel units alternate rhythmically in vertical section rhythmicity is interpreted as a response to episodic flood flows controlled by seasonal changes in water supply but not necessarily representing annual events fans beads anabranched reaches and extended hummocky deposits are intimately associated with the main esker ridges they are interpreted in terms of subglacial cavities and localized flotation zones connected to the main conduits during flood events in phase wave structures are the products of hydraulic jumps in hyperconcentrated flood flows at flow expansions into swells within the main conduits into cavities connected to the main conduits or at a grounding line esker ridges record only the most powerful flood events whereas fans and beads record flow events in finer detail being primarily depositional reservoirs laterally fining deposits record the waning stages of conduit operation

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

morphology and evolution of bars in a wandering gravel bed river lower fraser river british columbia canada a hierarchical typology for the channels and bars within aggradational wandering gravel bed rivers is developed from an examination of a 50 km reach of lower fraser river british columbia canada unit bars built by stacking of gravelly bedload sheets are the key dynamic element of the sediment transfer system linking sediment transport during individual freshets to the creation development and remoulding of compound bar platforms that have either a lateral or medial style primary and secondary unit bars are identified respectively as those that deliver sediment to compound bars from the principal channel and those that redistribute sediment across the compound bar via seasonal anabranches and smaller channels the record of bar accretion evident in ground penetrating radar sequences is consistent with the long term development of bar complexes derived from historical aerial photographs for two compound bars inter annual changes associated with individual sediment transport episodes are measured using detailed topographic surveys and longer term changes are quantified using sediment budgets derived for individual bars from periodic channel surveys annual sediment turnover on the bars is comparable with the bed material transfer rate along the channel indicating that relatively little bed material bypasses the bars bar construction and change are mainly accomplished by lateral accretion since the river has limited capacity to raise bed load onto higher surfaces styles of accretion and erosion and therefore the major bar form morphologies on fraser river are familiar and consistent with those in gravelly braided channels but the wandering style does exhibit some distinctive features for example 65 year histories reveal the potential for long sequences of uninterrupted accretion in relatively stable wandering rivers that are unlikely in braided rivers

the late wisconsinan deglacial history of the east central taseko lakes area british columbia late wisconsinan fraser glaciation retreat phase deposits and landforms in the east central taseko lakes area british columbia are used to demonstrate a four phase model of deglaciation during phase i at the onset of ice retreat the cordilleran ice sheet occupied much of the study area blocking southward drainage of fraser river phase ii was marked by the deglaciation of uplands and plateaux meltwater drainage patterns were controlled by stagnating glaciers confined to valleys phase iii commenced as remnant ice in the fraser valley downwasted to between 850 and 760 m elevation at this time interlobate glacial lakes formed in hanging valleys east of fraser river drainage of glacial lakes occurred subglacially and was accompanied by disintegration of remnant ice and an increase in mass movements in valleys these events were followed by decreased sedimentation rates reflecting lower meltwater volumes and exhaustion of unstable glacial debris during phase iv postglaciation valley fill was subj

controls on the sedimentary architecture of a single event englacial esker skeiðararjokull iceland eskers have been used to infer the dynamics and palaeo hydrology of large ice sheets yet there are few suitable contemporary analogues for esker sedimentation during quaternary glaciations consequently models of esker sedimentation have been derived from morpho sedimentary analyses of quaternary eskers but these lack rigorous constraints on their depositional timescales we identify the controls on the large scale sedimentary architecture of a large 700 m long 10 inclined reflections interpreted as backset accretion associated with large scale bedform development 4 down flow dipping high angle 15 inclined reflections interpreted as foreset accretion associated with macroform progradation 5 quasi hyperbolic reflections interpreted as zones of boulder clustering and 6 zones of enhanced noise and em signal attenuation bounded on the upper surface by a continuous reflection sub parallel to the ground surface interpreted as buried ice associated with the conduit channel base these data suggest that deposition took place within a non uniform englacial conduit which has resulted in major up flow to down flow variations in sedimentary architecture the complexities observed are a direct consequence of variations in sediment supply and the within event evolution of conduit geometry this study provides the first detailed insight into the large scale sedimentary architecture of a single event jokulhlaup proto esker

saginaw lobe tunnel channels laurentide ice sheet and their significance in south central michigan usa abstract a network of tunnel channels in southern michigan records substantial subglacial meltwater activity beneath the saginaw lobe of the laurentide ice sheet the channels are incompletely filled with outwash contain eskers and in many places crosscut and continue beyond upland ridges previously mapped as recessional moraines the presence of the tunnel channels and drumlins on these upland ridges indicate that the ridges are not recessional moraines instead outwash fans and minor ridges record deglaciation in the area a palimpsest relationship between buried bedrock valleys and tunnel channels records the presence of multiple generations of tunnel channels evidence for a subglacial meltwater sheetflow consists of sheets of boulder gravel in upland 15 km wide with a hummocky upper surface the hummocks transform down flow into erosional remnant drumlins possibly the result of flow acceleration on a negative slope tunnel channels at the distal end of the drumlin swarm suggest collapse of the sheetflow into a channelized flow the tunnel channels then end at the sturgis moraine at the heads of large outwash fans the observed geomorphic relationships between tunnel channels moraines and drumlins in south central michigan are applicable to glacial landform studies elsewhere and indicate the important role of meltwater in landscape evolution

a new species of sorbinichthys teleostei clupeomorpha ellimmichthyiformes from the late cretaceous of morocco a new species of ellimmichthyiform fish represented by three specimens has been recovered from deposits of the akrabou formation of morocco the new species is described in the existing genus sorbinichthys family sorbinichthyidae as sorbinichthys africanus sp nov closely related to the type species sorbinichthys elusivo the ellimmichthyiformes is an extinct order of clupeomorph fishes that includes both freshwater and marine species ranging from the early cretaceous through the eocene sorbinichthys elusivo is known from cenomanian deposits of the eastern mediterranean tethys lebanon whereas the new species is possibly early turonian but more probably late cenomanian in age from the western tethys eastern morocco at lower taxonomic levels the assemblage from the akrabou formation has a primarily tethyan composition exemplified by the genus sorbinichthys whereas supra generic taxa found there include groups with trans atlantic e g sorbinichthyidae macrosemiidae or near cosmopolitan

deposition in an esker bead and fan complex lanark ontario canada abstract a glaciofluvial landform complex comprising a single esker ridge proximally multiple ridges and beads in the middle section and a complex of ridges and fans distally is mapped and described we present detailed successions in the associated sediment showing sedimentary structure grain size and palaeocurrent estimates sediment in the esker is mainly coarse grained and varies from boulders with a fine sand matrix deposited at maximum discharges to diamicton interpreted as a product of ice pressing under low discharges early stage deposition in the esker at high flow was from suspension and bed load intermediate stage deposition was mainly from bed load and late stage deposition was from hyperconcentrated suspension the esker rests in a bedrock channel which functioned as a nye channel prior to esker formation the channel surface carries a variety of fluvial erosional marks short distributary ridges of the ridges and beads complex contain mainly cobbles and boulders but beads are mainly in sand with rapid down flow fining and change in sedimentary structure faulting and overfolding of bead sediment suggest a subglacial origin deposition of the esker fan complex was highly variable in space and time down fan sedimentary changes with transitions from gravel to cross laminated fine sand in a few tens of metres indicate rapid loss in competence fan location lateral to the esker indicates a broadening of the zone of subglacial meltwater with time deposition from suspension and steep sided scours are interpreted to result from deposition and erosion by hyperconcentrated flows a model of underflows with submerged hydraulic jumps spilling laterally from the esker tunnel into subglacial cavities explains the morphological and sedimentary characteristics of the fans detailed analysis of small scale fining upwards sequences in the fans and beads indicates deposition by a large number of flow events these events are explained by glacier hydraulics whereby periodic separation of the glacier from its bed caused water with a high suspended sediment concentration to spill out from the esker tunnel into adjacent subglacial cavities evolution of the subglacial drainage system indicates a complexity of subglacial sedimentation near to a grounding line which is not readily apparent from observations at modern glaciers terminating in relatively deep water

lithostratigraphy and limiting optical ages of the pleistocene fill in fraser river valley near clinton south central british columbia the fraser river valley near clinton contains a thick sediment fill that is presently incised down to bedrock the sequence approximately 500 m thick is generally upward fining and consists of up to 100 m of glacigenic debris flow diamicton and glaciofluvial deltaic gravel and sand at the base overlain by about 350 m of glaciolacustrine sedi ments and minor diamicton which is in turn capped by several metres of till the sequence is interpreted to represent i valley aggradation in response to glaciation followed by ii the impoundment of the valley by sediment and or ice and the formation of a large proglacial lake s and finally iii overriding of the valley fill by glaciers this glacial advance sequence can be readily correlated with previously studied units situated immediately to the north most of which have been associated with the last glaciation however the age of these units has been based only on strati graphic relations we introduce limiting optical ages from a widespread glaciolacustrine unit that show that the glacial advance sequence was formed at the earliest during the penultimate okanagan centre glaciation oxygen isotope stage 4 ca 74 59 ka but almost certainly during the last fraser glaciation oxygen isotope stage 2 ca 24 12 ka it could not have been deposited during oxygen isotope stage 6 or during an older glaciation

late wisconsinan glacial history in the bonaparte lake map area south central british columbia implications for glacial transport and mineral exploration1this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia 2earth sciences sector contribution number 20100093 this study is centred on the bonaparte lake map area located in the southern interior plateau of south central british columbia the reconstruction of the late wisconsinan glacial history of this part of the southern sector of the cordilleran ice sheet incorporates i the analysis and interpretation of landforms of various scales ii the sedimentology and stratigraphy of glacial sediments and iii the geochemical and mineralogical composition of till and analysis of regional glacial dispersal of these components the onset of the last glacial event was initiated by ice advancing westerly and southwesterly into the study area from an alpine source region located in the cariboo mountains as glaciation intensified ice from the coast mountains coalesced with the cariboo mountain ice over the interior plateau and developed into an ice divide around 52 north latitude which resulted in ice flow to be diverted to a southerly direction over the study area the two dominant ice flow directions produced pal

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

channel networks carved by subglacial water observations and reconstruction in the eastern puget lowland of washington channels of inferred subglacial fluvial origin channelways are conspicuous across the recently deglaciated eastern puget lowland of washington state exploiting the unusually well defined geometry of the former puget lobe ice sheet we have reconstructed the subglacial hydraulic head in this region to better understand the location and orientation of these channels we used established principles of channelized water flow under static ice because a three dimensional linear viscous ice model shows that sliding induced pressure variations can be ignored at all but the smallest scales of individual landforms two types of predicted subglacial flow paths emerge one drained continuously from the interior toward the ice sheet margin the other diverted water into a series of valleys in the flanking cascade range forming ice marginal lakes that discharged episodically and probably catastrophically these reconstructed flow paths correlate very well with the independently mapped distribution of channelways and also of ice marginal lakes throughout this area our study suggests that the formation and preservation of these landforms require both the concentration of subglacial water notably near ablation zone ice margins and favorable preglacial bed rock topography where these elements occur together landforms of subglacial fluvial origin should be recognizable across the now exposed beds of other former ice sheets as well

melt induced speed up of greenland ice sheet offset by efficient subglacial drainage fluctuations in surface melting are known to affect the speed of glaciers and ice sheets but their impact on the greenland ice sheet in a warming climate remains uncertain although some studies suggest that greater melting produces greater ice sheet acceleration others have identified a long term decrease in greenland s flow despite increased melting here we use satellite observations of ice motion recorded in a land terminating sector of southwest greenland to investigate the manner in which ice flow develops during years of markedly different melting although peak rates of ice speed up are positively correlated with the degree of melting mean summer flow rates are not because glacier slowdown occurs on average when a critical run off threshold of about 1 4 centimetres a day is exceeded in contrast to the first half of summer when flow is similar in all years speed up during the latter half is 62 16 per cent less in warmer years consequently in warmer years the period of fast ice flow is three times shorter and overall summer ice flow is slower this behaviour is at odds with that expected from basal lubrication alone instead it mirrors that of mountain glaciers where melt induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient a model of ice sheet flow that captures switching between cavity and channel drainage modes is consistent with the run off threshold fast flow periods and later summer speeds we have observed simulations of the greenland ice sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage a simple model of basal lubrication alone misses key aspects of the ice sheet s response to climate warming

structural controls on englacial esker sedimentation skeiðararjokull iceland we have used ground penetrating radar gpr to observe englacial structural control upon the development of an esker formed during a high magnitude outburst flood jokulhlaup the surge type skei ararjokull an outlet glacier of the vatnajokull ice cap iceland is a frequent source of jokulhlaups the rising stage waters of the november 1996 jokulhlaup travelled through a dense network of interconnected fractures that perforated the margin of the glacier subsequent discharge focused upon a small number of conduit outlets recent ice marginal retreat has exposed a large englacial esker associated with one of these outlets we investigated structural controls on esker genesis in april 2006 by collecting 2 5 km of gpr profiles on the glacier surface up glacier of where the esker ridge has been exposed by meltout in lines closest to the exposed esker ridge we interpret areas of englacial horizons up to 30 m wide and 10 15 m high as an up glacier continuation of the esker sediments high amplitude dipping horizons define the base of esker materials across many lines similar dipping surfaces deeper in the profiles suggest that 1 the dipping surfaces beneath the esker are englacial tephera bands 2 floodwaters were initially discharged along structurally controlled englacial surfaces tephra bands 3 the rapid increase in discharge resulted in hydrofracturing 4 establishment of preferential flow paths resulted in conduit development along the tephra bands due to localized excavation of surrounding glacier ice and 5 sedimentation took place within the new accommodation space to form the englacial structure melting out to produce the esker

neogene chilcotin basalts in south central british columbia geology ages and geomorphic history an extensive but generally thin mantle of basalt flows the chilcotin group covers much of the interior plateau of south central british columbia it provides material for dating and for reconstructing the original form of the paleosurface on which it was deposited k ar whole rock dates demonstrate that several ages of basalt are represented from early miocene or even late oligocene to early pleistocene with particularly abundant eruptions about 14 16 9 6 and 1 3 ma ago basalts of middle miocene and later ages if not the early miocene relics as well clearly rest on land surfaces of low local relief in places the low relief surfaces had been incised to depths of 100 200 m and the valleys backfilled with mid or late cenozoic sediments prior to burial by the basalts the low relief surfaces throughout the area are believed to have been developed close to a common base level and regional differences in their present elevation are thus largely a product of post basalt deformation this is recorded

large scale effects of subglacial meltwater flow in the southern slave province northwest territories canada broad corridors in the southern slave province of the northwest territories are marked by meltwater scoured bedrock irregular and transverse gravel ridges gravel bars crag and tail features tails formed of gravel drumlins boulder lags potholes plunge pools meltwater sculpted slopes in some cases defining till plateaus and eskers most of the above features can either be attributed to the subglacial erosion of till by high velocity turbulent meltwater under high pressures and or meltwater transport and deposition of the eroded material potholes plunge pools and meltwater sculpted slopes developed in unconsolidated deposits have received little attention in the literature although they are the equivalent of similar features in bedrock that have had their origin attributed to subglacial meltwater erosion in the case of inverted plunge pools eroded materials including boulders have been transported upwards by meltwater some tens of metres during their formation features and deposits o

late quaternary mass movement events in lake el gygytgyn north eastern siberia lake el gygytgyn is situated in a 3ae6 myr old impact crater in north eastern siberia its sedimentary record probably represents the most complete archive of pliocene and quaternary climate change in the terrestrial arctic in order to investigate the influence of gravitational sediment transport on the pelagic sediment record in the lake centre two sediment cores were recovered from the lower western lake slope the cores penetrate a sub recent mass movement deposit that was identified by 3ae5 khz echo sounding in the proximal part of this deposit deformed sediments reflect an initial debris flow characterized by limited sediment mixture above and in front of the debrite a wide massive densite indicates a second stage with a liquefied dense flow the mass movement event led to basal erosion of ca 1 m thick unconsolidated sediments along parts of its flow path the event produced a suspension cloud whose deposition led to the formation of a turbidite the occurrence of the turbidite throughout the lake and the limited erosion at its base mainly suggest deposition by pelagic rain following stokes law very similar radiocarbon dates obtained in the sediments directly beneath and above the turbidite in the central lake confirm this interpretation when applying the depositional model for the late quaternary sediment record of lake el gygytgyn the recovered turbidites allow reconstruction of the frequency and temporal distribution of large mass movement events at the lake slopes in total 28 turbidites and related deposits were identified in two 12ae9 and 16ae6 m long sediment cores from the central lake area covering approximately 300 kyr

hypothesis for mega outburst flooding from a palaeo subglacial lake beneath the east antarctic ice sheet subglacial outburst floods at the margins of the antarctic and laurentide ice sheets have been linked to changes in global ocean circulation and climate the impact of palaeo hydrological systems beneath the east antarctic ice sheet eais has however remained elusive by analysing bed morphology in the wilkes subglacial basin we hypothesise the occurrence of a major palaeo subglacial lake and associated outburst floods in the interior of east antarctica at similar to 70 km wide and over 100 km long the inferred area of outburst flooding is the most extensive in antarctica and the palaeo subglacial lake from which the floods originated is the second largest after lake vostok the scale of inferred outburst flooding is similar to mega floods beneath the laurentide ice sheet we suggest that this major hydrological system developed during expansion of the eais in the middle miocene and probably affected ice sheet stability ocean circulation and climate evolution

deglacial meltwater drainage and glaciodynamics inferences from laurentide eskers canada abstract this paper evaluates current knowledge of laurentide eskers in canada in the light of developments in glacier hydrology and glacial sedimentology questions regarding the morpho sedimentary relations of eskers the synchroneity and operation of r channel systems the role of supraglacial meltwater input and proglacial water bodies the controls on esker pattern and the glaciodynamic condition of the ice sheet at the time of esker formation are discussed a morphologic classification of eskers is proposed five types of eskers are identified and investigated type i eskers likely formed in extensive synchronous dendritic r channel networks under regionally stagnant ice that terminated in standing water type ii eskers likely formed in short subaqueously terminating r channels or reentrants close to an ice front or grounding line that may have actively retreated during esker sedimentation type iii eskers plausibly formed in short r channels that drained either to interior lakes in or tunnel channels under regionally stagnant ice type iv eskers may have formed as time transgressive segments in short subaerially terminating r channels or reentrants that developed close to the ice margin as the ice front underwent stagnation zone retreat or downwasted and backwasted regionally stagnant ice however formation in synchronous r channels cannot be discounted on the basis of reported observations type v eskers may have formed in h channels that terminated subaerially the spatial distribution of these esker types is discussed the factors that determined laurentide r channel pattern and operation were likely a complex combination of i supraglacial meltwater discharge ii the number and location of sink holes iii the ice surface slope thickness and velocity and iv the permeability topography and rigidity of the bed these factors cause and respond to changes in ice dynamics and thermal regime over the glacial cycle

tunnel channels and associated landforms south central ontario their implications for ice sheet hydrology the peterborough trenton drumlin field and associated meltwater erosion marks s forms were interpreted as the products of erosion by turbulent separated flows within a catastrophically released subglacial meltwater sheet the algonquin event recent theoretical modelling of ice sheet hydrology suggests progressive channelization of meltwater during the collapse of such a sheet inductive testing of this hypothesis using observations in south central ontario forms the crux of this paper a geometric model of the interaction of rough ice base and bed surfaces gives inferred meltwater flow patterns such a rough interactive geometry is suggested as the bed is drumlinized and flows responsible for drumlins may be expected to have eroded similar forms into the ice base three landforms in south central ontario namely tunnel channels megachannels and late stage sheet flow scours are described and interpreted as evidence of progressive channelization and flow diversion processes governed by the geometri

short pulse radar wavelet recovery and resolution of dielectric contrasts within englacial and basal ice of matanuska glacier alaska u s a wavelets transmitted by short pulse radar are recovered from continuous profiles and used to determine interfacial dielectric contrasts within the englacial and basal ice at the terminus area of matanuska glacier alaska u s a the field studies were in the ablation region where radar horizons could at some point be identified with interfaces between clear ice and air water or basal ice and were performed in early spring before drainage fully developed the profiles usedclosely spaced antennas with bandwidths centered near 50 and 400 mhz transmitted wavelets reflected from interfaces of known dielectric contrasts are used to establish a phase reference for other events from interfaces between unknown contrasts migration and fourier transform filtering are then applied to the profiles and shown to recover these wavelets from diffractions and reflections interfacial dielectric contrasts are determined from the relative phase of the wavelets near the terminus lake some basal ice events above 8 m depth are interpreted as voids further up glacier most englacial events are interpreted as voids but deeper localized reflectors and horizons to 90 m depth and within the basal zone are interpreted as voids water or debris phase cannot be determined for the basal substrate transition reflections recommendations are made for improving the wavelet recovery process and the quality of gpr migration

remote sounding of greenland supraglacial melt lakes implications for subglacial hydraulics a supraglacial lake depth retrieval function is developed based on the correspondence between moderate resolution imaging spectroradiometer modis reflectance and water depth measured during raft surveys individual lake depth area and volume statistics including short term temporal changes for greenland s southwestern ablation region were compiled for 2000 05 the maximum area of an individual lake was found to be 8 9 km 2 the maximum volume 53 0 10 6 m 3 and the maximum depth 12 2 m sampling over 0 0625 km 2 pixel areas the total lake volume reaches 1 km 3 in this region by july each year the importance of melt lake reservoirs to greenland ice sheet flow may be a feedback between abrupt lake drainage events and ice dynamics lake outburst volumes up to 31 5 10 6 m 3 d 1 are capable of providing sufficient water via moulins to hydraulically pressurize the subglacial environment since the overburden pressure at the base of a flooded moulin is greater than that provided by ice lake outburst events seem capable of exerting sufficient upward force to lift the ice sheet locally if water flow in the subglacial environment is constrained laterally considering a moulin with a 10 m 2 cross sectional area basal pressurization can be maintained over lake outburst

thermal conditions beneath parts of the last cordilleran ice sheet near its centre as inferred from subglacial till associated sediments and bedrock subglacial sediments and bedrock associated with the last fraser glaciation were studied in a mountain valley and on a mountain plateau ca 1200 m elevation near the south central spreading centre of the last cordilleran ice sheet in order to gain information on subglacial thermal conditions our study indicates that as ice advanced it was probably initially coupled to or dragged along a largely frozen and immobile substrate that fractured as glaciation proceeded subglacial till was deposited mainly by lodgement in most places however eld evidence suggests that as till thickened and pore water content increased the till experienced ductile deformation at some sites there is evidence that pore water increased to a point where till owed as a viscous slurry while eroding entraining and transporting pieces of soft bedrock in places brittle deformation was superimposed on ductily deformed till a transition that we associate with subsequent till dewatering and sti ening a deformable substrate would have contributed to extending ice ow thus increasing ow velocity while decreasing ice surface pro les if this situation was wide spread then the interior of the cordilleran ice sheet would have consisted of local accumulation areas that were drained by rapidly owing glaciers ice streams this is supported by previously recorded ice ow patterns inferred from large scale ice ow indicators and by other evidence of rapid ice movement along the southern fringe of the ice sheet 2000 elsevier science ltd and inqua all rights reserved

the origin of major incisions within the pleistocene deposits of the north sea a seismic survey to resolve the geometry of major incisions within the upper pleistocene has been run over an area of 1600 km2 in the mid north sea twelve separate incisions have been identified ranging up to 5 km wide and 25 km long with incised depths from 100 to 350 m deposits categorised into four recurring types infill the incisions to form a flat sea bed the surveyed features are comparable to others widely found beneath the northern continental shelves and lowlands of europe asia and america such incisions have a similar range of sizes and shapes were cut during at least three separate periods in the pleistocene and are down cut into substrates of various lithologies ranging from precambrian to pleistocene in age the major incisions are believed to be the product of a singular mechanism the outburst of intra ice sheet lakes forming jokulhlaup plunge pools except for late stage hollow infills which have interglacial temperate deposits the incision infills are periglacial the former deposits are similar to the sediments accumulating in the present day bathymetric enclosed deeps such as the lambay deep and devil s hole found on continental shelves it is suggested that the enclosed deeps are large kettle holes which resulted from the thawing of ice formerly buried in the incision infills