subglacial drainage for an ice sheet resting upon a layered deformable bed the subglacial hydrology is considered for a temperate ice sheet resting upon a deformable aquitard till with a hydraulic conductivity several orders of magnitude lower than that of an underlying aquifer the evacuation of basal meltwater by the aquifer channel bed hydraulic system is studied particularly as it affects aquifer pressurization till deformation and channel failure sensitive parameters are aquifer hydraulic conductivity ice sheet length and elevation and basal meltwater rate a criterion is developed to determine channel length channels need not extend all the way to the divide the model predicts that in general there is a region adjoining the terminus where the bed pore water pressure is equal to the overburden pressure and drainage along the bed is possible outside this region the bed pore water pressure is below the overburden pressure and ice penetrates the soil to prevent drainage along the bed an important result is that deformable substrates beneath temperate based ice sheets may be unstable particularly under conditions of a diminishing profile

dynamics of the laurentide ice sheet in hudson bay canada abstract interpretation of sidescan sonar and high resolution sub bottom seismic data from hudson bay has led to the development of a model for final disintegration of the laurentide ice sheet the well preserved geomorphic features observed from the bay floor are similar to subaerially exposed glaciogenic features observed around the perimeter of hudson bay and can be related to the following three paleoenvironments subglacial erosion deposition ice margin deposition and reworking and post glacial reworking and burial subglacial features observed include fluted terrains with superimposed rogen moraines relief attributed to ice surging eskers subglacial channels and dead ice topography de geer moraines and recessional moraine complexes indicate the mechanism and orientation of ice breakup retreat the orientations of these features are locally consistent with regional trends indicating the overall direction of ice sheet flow and retreat during the last phase of the laurentide ice sheet subglacial channel complexes incised into the till and bedrock and high energy bedforms deposited on the till surface occur in present day water depths down to 160 m due to isostatic depression these could have been as much as 315 m deeper at the time of formation they indicate a wet based glacier with high energy subglacial drainage during the late phases of ice retreat the sidescan sonar data also reveal numerous zones of distinctive morphology attributed to ice breakup and post glacial processes cross cutting relationships allow the determination of the relative ages of these zones from oldest to youngest these zones are interpreted to represent scouring of the bedrock and overburden by the remnants of the ice sheet seafloor scouring by tabular icebergs which moved in a tidally induced arcuate pattern or under the influence of massive glacial lake outflows development of dead ice topography under residual ice masses and random iceberg scouring by smaller icebergs restricted to present day water depths of less than 180 m recently published reconstructions of the collapse of the laurentide ice sheet based on dated quaternary sections on land suggest that the bay was rapidly deglaciated in approximately 400 years the well preserved and distinctive glaciogenic and stratigraphic indicators observed from the bay floor suggest that they were formed by a succession of mechanisms which were too short lived to obliterate the underlying evidence of deglaciation this supports the interpretation of extremely rapid deglaciation of hudson bay and points out that subsequent marine processes have not been sufficient to obliterate the glacial features

erosion of bedrock by subglacial meltwater cantley quebec several erosional forms on bedrock at cantley quebec differ from well known glacial abrasion forms the forms consist of obstacle marks hollows depressions and channels which are defined by sharp rims smooth inner surfaces divergent flow features and remnant ridges these forms are found on lee lateral and overhung rock surfaces this assemblage of features is best explained by differential erosion produced by separation eddies along lines of reattachment rapid sediment laden turbulent subglacial melt water flows likely produced the forms by corrasion and cavitation erosion sculpted fluvial forms in terrain subject to flooding in australia are identical to some of the cantley forms which confirms their formation by water erosion although glacial abrasion may not be eliminated as an explanation for sculpted forms it is not necessary ice abrasion forms such as striations and such plucked forms as gouges and crescentic fractures are also present at the cantley site pitted forms polishing and carbonate precipitate are also found the occurrence of abrasion pitting polishing and carbonate precipitate with meltwater forms suggests that the meltwater flows were subglacial decoupling of abrading ice from its bed temporarily suspended glacial abrasion whereas reattachment of ice to the bed may have led to the rounding of sharp edges and the production of striations superposed on the glacifluvial forms the association of forms produced both by glacifluvial erosion and ice abrasion suggests that the glacier was alternately lifted from and reattached to the bed during periodic subglacial floods these floods may have affected the dynamics of the ice sheet and depositional sequences related to catastrophic meltwater outbursts probably were laid down in adjacent basins

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

moraine formation in northwestern ontario product of subglacial fluvial and glaciolacustrine sedimentation long arcuate stratified end moraines in northwestern ontario may represent major and rapid sedimentation events in glacial lake agassiz rapid lowering of the lake or lift of a marginal ice dam m

the nature and origin of a jokulhlaup near casey station antarctica description de la nature de l episode d eruption d eau et resultats des etudes menees pour determiner l origine et la source de cette eau

sakami moraine quebec a 500 km long moraine without climatic control the laurentide ice sheet in eastern canada disintegrated step by step as evidenced by several morainic complexes although commonly interpreted as reflecting climatic events it seems probable that the disintegration simply related to changes in the dynamics of the ice margin without climatic control from the example of the late glacial sakami moraine in quebec formed during the drainage of lake ojibway into the tyrrell sea the concept of a re equilibration moraine already briefly proposed is developed the construction of such a moraine implies a stabilization of the ice front when the glacier margin previously floating or calving in a lacustrine or marine basin is suddenly grounded because of topographic blocking or abrupt drop of water level due to drainage the glacial retreat then pauses until the equilibrium profile of the ice is restored and a morainic accumulation can form during the halt

a box model test of the freshwater forcing hypothesis of abrupt climate change and the physics governing ocean stability 1 observations and an ocean box model are combined in order to test the adequacy of the freshwater forcing hypothesis to explain abrupt climate change given the uncertainties in the parameterization of vertical buoyancy transport in the ocean the combination is carried out using bayesian stochastic inversion which allows us to infer changes in the mass balance of northern hemisphere nh ice sheets and in the meridional transports of mass and heat in the atlantic ocean that would be required to explain dansgaard oeschger interstadials dois from 30 to 39 kyr b p the mean sea level changes implied by changes in nh ice sheet mass balance agree in amplitude and timing with reconstructions from the geologic record which gives some support to the freshwater forcing hypothesis the inversion suggests that the duration of the dois should be directly related to the growth of land ice our results are unaffected by uncertainties in the representation of vertical buoyancy transport in the ocean however the solutions are sensitive to assumptions about physical processes at polar latitudes

a glacier flow model incorporating longitudinal deviatoric stresses le modele d ecoulement de glacier developpe introduit les effets de la composante longitudinale du deviateur des contraintes dans les equations les hypotheses sous jacentes peuvent etre appliquees au developpement de modeles pour des cas de figures variees ici elles sont envisagees pour des glaciers glissant en ecoulement plan a l etat stationnaire et non stationnaire le modele se ramene a une generalisation adequate de la theorie pseudo hydrostatique en ecoulement plan si la contrainte longitudinale deviatrice est negligee devant la contrainte de cisaillement basale

sedimentology and paleohydrology of glacial lake outburst deposits in southeastern saskatchewan and northwestern north dakota glacial lake outbursts occurred in the northern great plains as ice marginal lakes suddenly drained forming an interconnected system of glacial lake spillways the outbursts were highly erosive and consequently deposits from such discharges are rare in the spillways glacial lake outburst deposits in the souris des lacs and moose mountain spillways saskatchewan and north dakota have distinct bar shapes and internally are more massive and homogeneous than those of outwash systems in this paper the outburst deposits are described and the sedimentologic and hydrodynamic characteristics of the outburst discharges are interpreted coarse grained sediment eroded from till formed large scale bars in the spillways as much as 2 km long and 30 m thick both as pendant bars and bars in alcoves next to contemporaneous landslides internally the bars consist of homogeneous masses of massive matrix supported very poorly sorted pebbly cobble gravel containing boulders as much as 3 m in diameter the maximum particle sizes in individual bars decrease downstream and toward spillway sides the lithology of the bars resembles the local glacial drift material from the tertiary bedrock in which the spillways are partially incised is not concentrated in the bars paleohydraulic calculations based on data of maximum particle size and on the shields9 entrainment function yield unreasonably large values supplementary calculations based on depth limits established from field observations yield realistic values this method indicates that velocities of 2 9 to 11 7 ms 1 and discharges of 5 8 10 4 to 8 2 10 5 m 3 s 1 were achieved by the outburst sediment water concentrations during the outburst estimated by dividing the volume of sediment eroded by the source lake volume averaged 20 by weight because of this estimate the abundant amount of fine grained material that was eroded and structure of the outburst deposits we infer that outburst flows were hyperconcentrated with sediment water concentrations being as much as 40 by weight in some areas we further infer that sediment transport was extremely efficient and that most particles including coarse gravel were transported in suspension this interpretation is consistent with the sedimentology of the deposits and other conjectural evidence expanding sections caused coarser sediment to be deposited indiscriminate of clast size as poorly sorted massive gravel bars finer grained sediment sand to clay size was transported through the spillway system into downstream glacial lakes

drumlins and catastrophic subglacial floods shaw j kvill d and rains b 1989 drumlins and catastrophic subglacial floods in j menzies and j rose editors subglacial bedforms drumlins rogen moraine and associated subglacial bedforms sediment geol 62 177 202 a number of lines of evidence are shown to be consistent with drumlin formation by catastrophic meltwater floods drumlins are associated with landforms related to such floods and landscapes produced by outburst floods in extragiacial areas contain drumlin like landforms some drumlins which contain mainly residual materials are compared to similar forms covering a wide range of scales and are interpreted to be scour remnant ridges produced by the action of horseshoe vortices on subgiacial materials these vortices are a product of flow separation in turbulent fluids and this interpretation implies drumlin formation by meltwater other drumlin calied cavity fill drumlins have distinctive shapes that are analogous with infilled erosional marks produced by turbulent separated flows these drumlins are interpreted as the infills of cavities eroded upwards into glacier beds by broad subgiacial meltwater sheetflows the sedimentology and internal structure of the cavity fill drumlins indicate rapid deposition from hyperconcentrated flow clast shape surface texture and lithology are consistent with the short distance of giaciofhivial transport predicted by the cavity fill hypothesis estimates of flow discharge 0 6 6 x 107 m3 s total volume of flow 84 1 103 km3 and flow duration 16 162 days are given for the catastrophic flood proposed to have produced the livingstone like saskatchewan drumlin field subgiacially derived floods are used to explain the sudden drainage of extraglacial lakes and major depositional events in proglacial lakes and it is suggested that they might have contributed to the lid of cold freshwater over the north atlantic held to have caused a late glacial cooling event the flood hypothesis requires extensive subgiacial lakes to have occurred beneath the laurentide and fennoscandian ice sheets which if they existed must have influenced the form and behaviour of these major bodies of ice

a glaciofluvial origin for drumlins of the livingstone lake area saskatchewan the livingstone lake drumlin field of northern saskatchewan is on the athabasca plains it is draped over high ground underlain by the precambrian athabasca sandstone the drumlins occur in spindle parabolic and transverse asymmetrical forms a map of individual drumlins shows that features of similar form occur together the drumlins are related on a regional scale to even larger landforms there is also an arrangement of drumlins in streams parallel to the assumed flow direction these patterns illustrate spatial organisation of the drumlin forming flows the livingstone lake drumlins are closely related to tunnel valleys large crescentic scours and eskers exposed bedrock reveals widespread scalloping and sichelwannen an argument is made that drumlins are related to these glaciofluvial forms but were created at different times and by different flows than those forming small scale flutings and other lodgment features sediments within the drumlins are mainly primary water sorted deposits some of wh

erosion of bedrock by subglacial meltwater georgian bay ontario a regional view a spectacular series of sculpted erosional forms s forms is mapped and described from a 70 km wide area along the shore of georgian bay ontario which except for a scattered boulder lag has been swept clean of sediment a great variety of sculpted forms is described and illustrated and grouped into three classes transverse longitudinal and nondirectional forms transverse forms comprise transverse troughs muschelbruche sichelwannen and comma forms longitudinal forms comprise spindle flutes cavettos and furrows and nondirectional forms consist of undulating surfaces and potholes transverse forms are preferentially located on stoss slopes and longitudinal forms on lee slopes of rock rises undulating nondirectional forms are found on distal slopes and potholes at major breaks in slope this correlation of form and bed topography suggests that relief exerts considerable control on both form and location form geometry is also inferred to be related to coherent flow structures and their int

icelandic jokulhlaup impacts implications for ice sheet hydrology sediment transfer and geomorphology abstract glaciers and ice sheets erode entrain and deposit massive quantities of debris fluxes of subglacial meltwater exert a fundamental control on ice dynamics and sediment transport budgets within many glacial systems outburst floods jokulhlaups constitute high magnitude high frequency fluxes of meltwater relative to normal ablation controlled discharge this paper presents a synthesis of research on recent icelandic jokulhlaups and their geomorphological and sedimentary impact we identify jokulhlaup impacts within subglacial englacial and proglacial settings and discuss their wider significance for ice sheet hydrology sediment transfer and geomorphology because jokulhlaups erode deposit and re work sediment simultaneously they usually cause significant glaciological and sedimentological impacts jokulhlaups that propagate as subglacial flood waves often produce widespread hydromechanical disruption at the glacier base recent icelandic jokulhlaups have been recognised as highly efficient agents of reworking subglacial sediment and glacial sediment entrainment models of jokulhlaup impact therefore need to encompass the sub and englacial environment in addition to the proglacial zone where research has traditionally been focussed most jokulhlaups transport sediment to proglacial sandar and often directly to oceans where preservation potential of the impact is greater proglacial jokulhlaup deposits form distinctive sedimentary assemblages coupled with suites of high energy erosional landforms this study of modern jokulhlaup processes and sedimentary products may be useful for the interpretation of meltwater processes associated with quaternary ice sheets

glacial tunnel valleys and quaternary history of the outer scotian shelf high resolution seismic reflection data indicate the presence of huge sub surface channel networks on the outer nova scotian continental shelf channel axes extend to over 450 m below present sea level b s l channel walls average 2 3 km in width mechanisms capable of producing such channels include fluvial submarine canyon or glacial erosion considerable debate has focused on the positions of the tertiary quaternary t q and pleistocene holocene p h boundaries1 4 in this region and the relationship of the t q boundary to the unconformity at the base of the channel networks uncertainty also surrounds the extent of pleistocene ice sheets on the south east canadian continental margin4 7 here we present a new stratigraphy for the sable island region fig 1 based on seismic profiles with lithologic and biostratigraphic control provided by two strategically placed boreholes this strati graphic analysis establishes the positions of the t q and p h boundaries outside the valleys at 51 m and 220 m b s l respectively our analysis also implies that the large channel systems are tunnel valleys cut by a sub ice meltwater process under a pre to early wisconsinan ice sheet which extended close to the shelf edge

late quaternary fluvial landscape evolution in desert grasslands of northern chihuahua mexico presented here is the first comprehensive late quaternary alluvial stratigraphic record from desert grasslands in northern mexico the stratigraphic history was temporally constrained by radiocarbon dating whereas the ecology of c4 plants was inferred by stable carbon isotopes from buried soils environmental relationships within the casas grandes and san pedro river basins of the juanaquena study area provide a picture of evolving landscapes where fluvial behavior is driven by climate change and ecosystem instability seven periods of flood plain construction and six episodes of paleosol formation and channel erosion occurred during the last 14 000 1 4 c yr b p in the latest pleistocene channel erosion ensued in response to a general warming trend and landscape instability although c3 plants still dominated in the alluvial valleys in the holocene when c4 plants began to dominate channel erosion was typically initiated by a shift from relatively warmer and drier to cooler and wetter climates the timing of erosion events exhibits a remarkable correlation to arroyo formation and paleosol formation of ephemeral streams in the north american southwest in contrast to arroyos the casas grandes and san pedro rivers created flood plains having mixed to bedload mean derbelts that persisted throughout the late quaternary however bedrock valley constrictions accelerated flood plain building leading to periodic channel avulsion although intervals of landscape instability occurred numerous times in the late quaternary fluvial style was largely governed by the dominance of c4 grasslands which appears to have maintained sufficient upland vegetative cover to mitigate flash flooding typical of arid environments

evidence of cordilleran late wisconsinan glaciers in the ice free corridor abstract glaciers flowing down the athabasca river valley during the last glacial period were fed both by local montane glaciers and by cordilleran ice moving easterly across the continental divide from british columbia resulting in a major eastward surge into the ice free corridor the timing of this event has been disputed for many years and has important implications for the study of paleoenvironmental conditions and the north south migration of biota in the corridor chronologic and lithostratigraphic data from the jasper region suggest that this event took place in the late wisconsinan subtill radiocarbon dates on wood in the athabasca river valley indicate that non glacial alluvial sediments began accumulating there sometime before 48 ka a finite date of 29 100 560 bp gsc 3792 on wood under till near jasper provides a maximum age for the onset of the last glaciation in the region although ice from west of the rocky mountain trench probably did not cross the continental divide until after 21 5 ka the occurrence of supraglacial metamorphic erratics as well as the distribution and nature of mapped glacial deposits and the trend of subglacial paleoflow indicators in the region east of the rockies suggests that late wisconsinan glaciers flowing from the mountains coalesced with laurentide glaciers and were deflected southeasterly along the mountain front an even more extensive glacial event may have effected the region in pre late wisconsinan times the model of late wisconsinan glaciation presented here is in agreement with all known radiocarbon data from the area and is especially attractive when supratill dates on non woody lacustrine organics are viewed in light of possible contamination by old carbon

relict ice scour marks and late phases of lake agassiz in northernmost manitoba in northern manitoba intersecting grooves 300 1800 m long are ice scour marks created by the dragging of iceberg keels along rises in the bed of a glacial lake whose water plane was at about 305 m asl the lake was bounded by glacial ice on its northern and eastern margins the occurrence of scours on topographic divides indicates that a single extensive lake thought to be a northern extremity of lake agassiz occupied the area as far north as seal river at the time the ice scours were formed the lake extended as far west as sprott lake and eastwards into the hudson bay lowlands into an area later occupied by tyrrell sea the preservation of the scour marks suggests that the lake drained suddenly ice scour marks are easily recognized on air photographs and provide a means of identifying areas that have been inundated by glacial lakes scours in emerged marine sediment are generally obliterated by littoral processes

glaciofluvial erosional morphology and sediments of the coronation spondin scabland east central alberta spatially discontinuous meltwater channel networks on the canadian prairies are usually interpreted as having formed subaerially in front of the retreating laurentide ice sheet evidence in the coronation spondin scabland east central alberta supports an alternative formation by progressive channelization of a subglacial sheetflow of water the scabland is an integrated channel network with varying degrees of anabranching the channels having highly variable sizes shapes and orientations enhanced scour at some channel confluences reflects contemporaneous channel utilization channels also display convex up concave up and undulatory along channel profiles with some junctions at the same elevations longitudinal grooves in large scale channels are associated with numerous boulder deposits residual hills demarcated by channels display composite and streamlined forms superimposed on residuals are erosional transverse bedforms longitudinal grooves and undulating surfaces that indicate submergence

buried and open tunnel valleys in denmark erosion beneath multiple ice sheets abstract tunnel valleys are large elongate and irregular depressions cut beneath the margin of former ice sheets they are generally believed to play a substantial role for the entire hydraulic system beneath ice sheets and thus also for ice sheet behaviour their origin however remains poorly understood examination of newly collected danish hydrogeophysical and lithological data has revealed numerous systems of buried valleys 50 350 m deep and 0 5 4 km wide these valleys are similar to the open tunnel valleys found in the present day landscape infills comprise a variety of sediments often with subglacial clay till and meltwater deposits the incised substratum consists of limestone heavy paleogene clay sand and silt the tunnel valleys have preferred orientations and can be divided into several generations each ascribed individual ice advances or ice sheets occurring during multiple glaciations the processes forming the valleys appear to prefer pre existing open and buried valleys for the renewed erosion thus old subglacial erosion pathways have been re used several times and some of the present tunnel valleys may have been established in the middle or early quaternary or even earlier this valley re use effect causes apparently anastomosed valley systems to emerge in the data images the valleys were mainly eroded by meltwater supposed to have drained from subglacially stored reservoirs probably behind a frozen margin the water was most likely released in repeated jokulhlaups and flowed in relatively small channels on the floors of the tunnel valleys which gradually became ice filled with the lowering of the bed selective linear glacial erosion is also believed to have contributed to the erosion this however was most pronounced for the widest valleys and is supposed to have played a secondary role

water sheet outburst floods from the laurentide ice sheet field evidence and a theoretical model support the concept that during wisconsinan glaciation subglacial water sheet outburst floods issued from a large subglacial lake located in the hudson bay ba

on the formation of large subglacial lakes the role of subglacial water storage beneath continental ice sheets is investigated primarily for a deformable bed subglacial ponding is shown to occur under most regions of warm based ice sheets and large subglacial lakes can become established for example in the hudson bay basin the formation of large lakes depends upon the fact that the ice surface gradient is reduced once subglacial ponding occurs and upon the feedback between the reduced ice surface gradient and increased subglacial ponding subglacial ponding likely played a large role in determining the ice sheet topography during late deglaciation and in speeding up the deglaciation process

abrupt changes heinrich events in late quaternary north atlantic marine environments a history and review of data and concepts in the last several years evidence has mounted that a series of abrupt changes in sediment delivery and palaeoceanography effected the north atlantic they are recorded in a variety of proxy records but most dramatically in changes of grain size and mineralogy associated with postulated iceberg rafting events specifically heinrich h events this review paper examines the evidence for such evidence prior to the development of the heinrich event concept 1988 1992 and then examines the explosion of data and correlations that stemmed from the acceptance and use of this paradigm specific attention is focused on ideas pertaining to the cause s of glaciological mechanisms sediment delivery and sediment source and major gaps in our understanding of the underlying glaciological glacial geological and glacial marine processes are stressed abrupt changes across boundaries associated with h 2 in the labrador sea are illustrated from core hu87033 009lcf the case is made that correlations between records need to be more rigorous especially within the range of radiocarbon dating but it appears that abrupt changes in the delivery of iceberg rafted debris which characterize these intervals are multisourced it is unclear how global climate can simultaneously influence the abrupt behaviour of ice margins in different parts of the world for marine based margins changes in relative sea level are one possibility a qualitative model is presented for triggering h events which includes global changes in mass balance changes in relative sea level at ice margins due to glacial isostasy and changes in the basal thermal regime of tidewater ice streams 1998 john wiley sons ltd

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

internal geometry and evolution of moulins storglaciaren sweden depart ment of physical geog raphy university of stoc kholm s 106 91 stockholm sweden abstract the initial conditions needed for formation of moulins are crevasses and a supply of melt water water pouring into a crevasse may fill it until it ove rflows at the lowest point which is normally near the margin however as the crev asse deepens it intersects englacial chann els through which the water can drain these chann els may be finger tip tributaries in a dendritic system such as that described by shreve 1972 and observ ed by raymond and harrison 1975 when the cre vasse closes heat in the melt water keeps the conne ction open and a moulin is formed the englacial channel enlarges rapidly by melt ing utilizing mechanical energy released by the descending water descents into moulins and mapping of stru ctures exposed at the surface after many years of melting demonstrate that the drainage channels leading down from the bottoms of the moulins have incli nations of 0 450 from the vertical these channels trend in the dire ction of the original crevasse but appear to be deeper than the expected depth of the crevasse they have not

drumlin formation by subglacial meltwater erosion some drumlins are shown to belong to a family of remnant erosional ridges associated with subglacial meltwater the lengths of these ridges vary in scale from a few tens of millimetres to over 5 km similar form elements are illustrated for three scales of forms it is concluded that some drumlins are composed of preexisting sediment or bedrock left upstanding in ridges as a result of the removal of surrounding materials this erosional theory is related to an earlier theory in which drumlins are held to result from the infilling of subglacial cavities the unifying factor for both theories is the role of sheets of subglacial meltwater

evidence for large scale subglacial meltwater flood events in southern ontario and northern new york state flow line patterns constructed from the orientation of drumlin long axes are used to infer two major subglacial meltwater floods in southern ontario and northern new york state in this interpretation the flood waters of the first event the algonquin surged southward in the later ontarian event powerful floods streamed southwestward along the basins of lakes ontario and erie bedrock fluting upstream pointing noses on escarpments and tunnel channels give supporting evidence for the regional flood hypothesis regional distributions of drift thickness may be explained by this hypothesis