the origins of s forms form similarity process analogy and links to high energy subglacial meltwater flows abstract this paper first presents the history of ideas on s form formation with an emphasis on meltwater models the main approach is based on form similarity between modern erosional marks and subglacial s forms form similarity is then extended to process similarity which promotes understanding of s forms three classes of erosional marks are identified obstacle scours basin shaped erosional marks and landforms related to escarpment flow identification is based on form with recognition of elements though it mainly depends on recognition of the whole form in much the same way as we recognize family members or familiar flowers flow conditions related to the various flow features are determined by flow visualization and computational fluid dynamics some s forms are produced in flume models though most are natural features observed in the field examples from beneath past ice sheets are seen in the field and illustrated by air and ground photographs satellite images and dem digital elevation model the results of this work show remarkable similarity between modern erosional marks and ancient subglacial s forms consequently established processes are attributed to ancient forms in turn s forms may be used abductively to interpret subglacial hydrological conditions the lack of waning stage bedforms scoured into primary forms suggests that erosional marks form under abruptly terminating catastrophic flow

the subglacial thermal organisation sto of ice sheets abstract this paper examines ice sheet wide variations in subglacial thermal regime and ice dynamics using the landform record exposed on the beds of former mid latitude ice sheets the laurentide cordilleran fennoscandian and british irish ice sheets we compare the landform patterns beneath these former ice sheets to the flow organisation beneath parts of the contemporary antarctic ice sheet inferred from radarsat 1 antarctic mapping project ramp data the evidence preserved in the landform record and observed on contemporary ice masses can be grouped into four major ice dynamical components that collectively define the subglacial thermal organisation sto of ice sheets these ice dynamical components are frozen bed patches ice streams ice stream tributaries and lateral shear zones frozen bed patches appear at a wide range of spatial scales spanning four orders of magnitude in some areas frozen bed zones comprise large proportions of the bed e g near the ice divide in continental areas whilst in other areas they constitute isolated islands in areas dominated by thawed bed conditions ice streams narrow zones of fast flow in ice sheets that are otherwise dominated by slow sheet flow are also common features of quaternary ice sheets tributaries to ice streams flow at velocities intermediate between full ice stream and sheet flow and may divert ice drainage from one primary ice stream corridor to an adjacent one sharp lateral boundaries between landforms indicate sliding and non sliding conditions respectively these lateral boundaries represent important discontinuities in the glacial landscape and mark the location of shear zones between thawed bed ice streams and intervening frozen bed areas we use the landform evidence in the area around great bear lake canada to trace the evolution of an ice stream web through time demonstrating that frozen bed patches are integral components of this complex system we conclude that frozen bed patches are important for the stability of ice sheets because they laterally constrain and isolate peripheral drainage basins and their ice streams

the succession of ice flow patterns in north central quebec labrador canada abstract quebec labrador canada is one of the postulated dispersal centres of the late wisconsinan laurentide ice sheet and also contains an unusually complex and rich glacial geological record a reliable reconstruction of glaciation history represented by this record would improve our comprehension of the dynamics of the eastern sector of the laurentide ice sheet such as the evolution of the basal thermal regime and the timing of enhanced ice flow into ungava bay we mapped glacial landforms over a 200 000 km2 area using aerial photographs and conducted a detailed field based survey of the central part of the area to establish the relative age of crosscutting glacial geological features the position of the last ice remnant was south of ungava bay well north of what has commonly been perceived as the location for this dispersal centre southward radial flow from a northward migrating and predominantly cold based dispersal centre was the last glacial event in north central quebec labrador a widespread occurrence of older ice flow traces towards the southwest was detected in some areas large drumlins formed during this ice flow event occur in alignment with landforms formed during the last deglaciation this older southwestward flow is however overprinted by and therefore predates traces of northward convergent flow into ungava bay ungava bay flow traces of a northeastward flow event and in some areas traces of the deglacial flow event flutes and glacial striae indicating ice flow towards northeast are superimposed on the ungava bay flow the northeastward ice flow system has been recognised across the mapped area and because of its direction and regional significance we infer formation approximately during the last glacial maximum

palaeo ice stream onsets examples from the north eastern laurentide ice sheet in this paper we report on observations of glacial landscapes at the head of geomorphologically interpreted palaeo ice streams i e palaeo ice stream onsets our work is based on the results of sy

a general cooling trend on the central tibetan plateau throughout the holocene recorded by the lake zigetang pollen spectra abstract a 741 cm long laminated sediment core covering the last 10 800 years was collected from lake zigetang central tibetan plateau 90 9 e 32 0 n 4560 m a s l and analysed palynologically at 69 horizons biome reconstruction suggests a dominance of temperate steppe vegetation mainly artemisia and poaceae on the central tibetan plateau during the first half of the holocene 10 8 4 4 cal ka bp while alpine steppes with desert elements mainly cyperaceae poaceae chenopodiaceae and characteristic high alpine herb families tend to dominate the second half 4 4 0 cal ka bp the artemisia cyperaceae ratio a semi quantitative measure for summer temperature indicates a general cooling trend throughout the holocene dense temperate steppe vegetation and maximum desert plant withdrawal however indicate that a suitable balance of wet and warm conditions for optimum vegetation growth likely occurred during the middle holocene 7 3 4 4 cal ka bp severe early holocene cold events have been reconstructed for 8 7 8 3 and 7 4 cal ka bp

palaeo ice streams abstract the location and behaviour of ice streams is one of the most important controls on ice sheet configuration and stability in order to reconstruct former ice sheets we need to know ice stream location and timing once identified the beds of palaeo ice streams provide an unprecedented opportunity to glean information about their basal environment something that remains very difficult under contemporary ice streams this paper represents the first synthesis and discussion of palaeo ice stream research from a variety of former ice sheets and includes new insights relating their configuration and activity to the evidence they leave behind the ambiguous use of the term ice stream is addressed and four possible configurations for ice streams are presented diagnostic landforms and landform assemblages that we would expect an ice stream to produce are discussed and the temporal context of bedform generation is described as either a rubber stamped or smudged bedform imprint resulting from isochronous or time transgressive landform generation in particular we focus on the configuration of terrestrially terminating ice streams for which there are no modern analogues technological advances in marine geophysics are helping to generate a convergence of interest between antarctic glaciology and palaeo glaciology it is suggested that investigations around the fringes of contemporary ice sheets i e west antarctica can provide evidence that directly links the geomorphological record of palaeo ice streams with their contemporary counterparts in addition computational advances and modelling adaptations have permitted the incorporation of ice streams within ice sheet models we argue that data from palaeo ice stream beds are invaluable to ice sheet stream modelling experiments and will help us understand ice stream operation and the linkages between climate perturbations and both palaeo and contemporary ice sheets

regional unconformities and the sedimentary architecture of the oak ridges moraine area southern ontario seismic stratigraphy geometry and sediment facies within the oak ridges moraine orm area of ontario record major structural elements and surfaces of the quaternary sedimentary sequence the derived stratigraphic architecture can be used to identify the key elements of a regional erosional surface represented by an unconformity in the subsurface and associated overlying channel sediments the erosional surface unconformity forms a distinct time datum in the quaternary sequence which provides an important aid to lithostratigraphic correlation the architecture also gives improved understanding of the effects of erosion on the late glacial landscape the surfaces of erosional drumlins and intervening troughs and the beds and banks of meltwater channels in the orm area define the regional unconformity highlighted by seismic profiles linked to continuously cored boreholes these features are attributed to regional scale subglacial meltwater flow events the sculpted surfaces which are analogous to water eroded forms the presence of boulder lags and coarse grained deposits on the regional erosional surface and the channels with undulating profiles provide the vital supporting evidence for a meltwater interpretation the inter regional extent of the unconformity is inferred from the coherence of regional paleoflows and the extent of drumlinized uplands tunnel channels and scoured bedrock terrain across 75 of the landscape from the orm area east and south to the finger lakes new york the implied magnitude of erosion suggests a pressing need for directed sedimentological study in those ocean basins that were probable depositional sites for flood deposits

formation of mega scale glacial lineations observed beneath a west antarctic ice stream most discharge from large ice sheets takes place through fast flowing ice streams and their speed is strongly modulated by interactions between the ice and the underlying sediments seismic surveys and investigations through boreholes have revealed a spatial association between fast ice flow and saturated deformable sediments nevertheless our knowledge of the morphology of the interface between ice and sediments is still limited resulting in only rudimentary understanding of the basal boundary conditions beneath ice streams and the generation of subglacial bedforms here we present radar data from the bed of a west antarctic ice stream that reveal the presence of mega scale glacial lineations we combine these data with previously published seismic data and show that these lineations develop in areas of dilatant deforming till and are part of a dynamic sedimentary system that undergoes significant change by erosion and deposition on decadal timescales we find that the mega scale glacial lineations are indistinguishable from those found on beds of palaeo ice streams providing conclusive evidence for the hypothesis that highly elongate bedforms are a characteristic of fast flow regions in ice sheets

genesis of the glacial curvilineation landscape by meltwater processes under the former scandinavian ice sheet poland abstract dobrzyn plateau in central poland contains a suite of enigmatic glacial bedforms termed glacial curvilineations gcl these landforms occur within tunnel valleys forming a complex anabranched network gcl consist of a series of parallel ridges extending for as much as 5 km over their length gcl ridges are parallel to neighboring ridges and to tunnel valley margins internal gcl composition consists of sand gravel and till distributed randomly within ridges and in intervening troughs electric resistivity tomography surveys confirm the sediment distribution seen in field exposures truncated beds near the ridge forms and the heterogeneous nature and distribution of sediments suggest an erosional rather than accretionary origin for gcl in this case internal gcl composition is not related to gcl genesis it records proglacial and subglacial conditions prior to gcl shaping by erosion the terminal zone of the anabranched tunnel valley network is characterized by a broad apron like ice marginal sedimentary complex sand and gravel dominate sedimentary facies within this zone sediments record evidence of meltwater sedimentation associated with supraglacial melting near the ice margin and high energy subglacial outbursts emanating from tunnel valleys this interpretation suggests that the gcl surface is a regional unconformity representing an erosional landscape where sediments within landforms offer limited insights into landform genesis cf sharpe et al 2004 subglacial meltwater erosion is proposed as unifying model of landscape development as it accounts for both erosion of tunnel valleys and gcl and meltwater dominated sedimentation in the ice marginal sedimentary 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

late wisconsin subglacial megaflood paths in alberta evidence of late wisconsin subglacial megafloods includes fields of giant flutings drumlins tunnel channels and scoured bedrock tracts scoured tracts are marked by channeled scabland water eroded depressions s forms and postglacial development of solonetzic saline clay pan soils on cretaceous bedrock belts of hummocky terrain and small zones of moraine plateaus are remnants left by incomplete sheet flood erosion of initial subglacial sediment later modified by ice pressing among multiple subglacial discharges the largest was the livingstone lake event which transmitted laurentide water from the northwest territories and northern saskatchewan through alberta to montana and the mississippi drainage this flood was augmented by cordilleran water relayed under valley glacier piedmonts coalescent with south western laurentide ice the short duration megaflood probably occurred within the longer time interval of 18 15 ka

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

hairpin erosional marks horseshoe vortices and subglacial erosion abstract crescentic erosional marks wrapped around obstacles and extending into straight grooves are termed hairpin erosional marks they are u shaped to semi circular in cross section are deepest around the upstream shoulders of the obstacles and range over seven orders of magnitude in scale some are asymmetrical with one groove better developed than the other the straight grooves may broaden and shallow rapidly in the downflow direction upstream grooves merge with rather than cross downstream crescentic marks grooves are distinct from glacial abrasion forms and many are not striated hairpin erosional marks are interpreted as being products of scour by horseshoe vortices in turbulent fluids this interpretation is supported by the close similarity of these marks to scours produced experimentally and in nature by horseshoe vortices estimated reynolds numbers show that such vortices are probable around obstacles in wind and flowing water but are extremely unlikely in ice aeolian hairpin erosional marks related to yardangs are illustrated to support this conclusion the surface texture cross sectional shapes and spatial patterns of hairpin erosional marks also discount formation by ice a model for the evolution of isolated erosional drumlins from an initial field of hairpin erosional marks extends earlier research on a meltwater hypothesis for drumlins

glacial terrain zone analysis of a fragmented paleoglaciologic record southeast keewatin sector of the laurentide ice sheet abstract a highly fragmented subglacial landscape is recognized at the regional to sub regional scales in northeastern manitoba canada in the southeast keewatin sector a core region of the laurentide ice sheet new field based ice flow indicator measurements mapping of subglacial landforms remote sensing and aerial photograph and a re examination of previously published data from an 8100 km2 area in northeastern manitoba show that the preserved subglacial record reflects a complex and potentially long glacial history five streamlined landform flowsets are mapped a much higher degree of inheritance in the field based ice flow indicator data than previously reported allows for recognition of multiple ice flow phases analysis of the characteristics of the subglacial landscape combined with a relative age chronology established with field based indicators led to the recognition of disjoint zones with internally consistent glacial histories termed glacial terrain zones gtz these gtz were then classified as 1 relict glacial 2 palimpsest or 3 deglacial in nature our data suggest that while the southern keewatin sector was affected by regional ice divide translocation this alone cannot explain the fragmented high inheritance landscape we suggest that the subglacial landscape was continually evolving and subject to spatio temporal variations in intensity of erosion transportation and or deposition throughout multiple glacial events subglacial bed mosaic preservation of relict and palimpsest terrain likely occurred under large sticky low erosion regions these regions could have formed by at least two different mechanisms heterogeneous switch from warm based to cold based ice or within a warm based subglacial environment from wet to stiff dewatered till establishment of the regionally extensive 700 km wide by at least 500 km long dendritic esker channel system may have caused rapid spatially variable dewatering of the substrate far back under the ice sheet the gtz approach integrates all available data e g flowsets and other landform data striations to advance our interpretation of the spatio temporal evolution of subglacial dynamics in areas where the degree of landscape inheritance and overprinting is spatially highly variable this mosaic may be a characteristic net effect of landscape evolution beneath the core regions of ice sheets

ice streams in the laurentide ice sheet identification characteristics and comparison to modern ice sheets this paper presents a comprehensive review and synthesis of ice streams in the laurentide ice sheet lis based on a new mapping inventory that includes previously hypothesised ice streams and includes a concerted effort to search for others from across the entire ice sheet bed the inventory includes 117 ice streams which have been identified based on a variety of evidence including their bedform imprint large scale geomorphology topography till properties and ice rafted debris in ocean sediment records despite uncertainty in identifying ice streams in hard bedrock areas it is unlikely that any major ice streams have been missed during the last glacial maximum laurentide ice streams formed a drainage pattern that bears close resemblance to the present day velocity patterns in modern ice sheets large ice streams had extensive onset zones and were fed by multiple tributaries and where ice drained through regions of high relief the spacing of ice streams shows a degree of spatial self organisation which has hitherto not been recognised topography exerted a primary control on the location of ice streams but there were large areas along the western and southern margin of the ice sheet where the bed was composed of weaker sedimentary bedrock and where networks of ice streams switched direction repeatedly and probably over short time scales as the ice sheet retreated onto its low relief interior several ice streams show no correspondence with topography or underlying geology perhaps facilitated by localised build up of pressurised subglacial meltwater they differed from most other ice stream tracks in having much lower length to width ratios and have no modern analogues there have been very few attempts to date the initiation and cessation of ice streams but it is clear that ice streams switched on and off during deglaciation rather than maintaining the same trajectory as the ice margin retreated we provide a first order estimate of changes in ice stream activity during deglaciation and show that around 30 of the margin was drained by ice streams at the lgm similar to that for present day antarctic ice sheets but this decreases to 15 and 12 at 12 cal ka bp and 10 cal ka bp respectively the extent to which these changes in the ice stream drainage network represent a simple and predictable readjustment to a changing mass balance driven by climate or internal ice dynamical feedbacks unrelated to climate or both is largely unknown and represents a key area for future work to address

extent and basal characteristics of the m clintock channel ice stream abstract the m clintock channel palaeo ice stream drained the northwestern margin victoria island arctic canada of the laurentide ice sheet functioning for 200 years prior to 10 ka bp from its bed imprint it is reconstructed as 720 140 km with a cross sectional area of 100 km2 comparable in size to the hudson strait ice stream it drained an estimated 80 000 km3 of ice enough to significantly affect the shrinking ice sheet and drive the keewatin ice divide south eastwards such discharges likely produced heinrich events and influenced the temperature and salinity of the western arctic ocean ice stream location was controlled by a topographic trough but glaciological regulation rather than properties of the bed controlled margin locations and hence ice stream width the ice stream eroded into pre existing unconsolidated sediments and left a pattern of subglacially produced landforms recording a snapshot view of the bed prior to shutdown frictional shutdown occurred once downcutting through sediments reached bedrock in places high sediment availability appears critical for ice stream functioning with a drift thickness of 50 m required to sustain its 200 year lifespan debris discharge was exceptionally high 73 000 m3 a 1 m 1 this ice stream demonstrates non steady response of ice sheets to climate change and their large impact on mass balance and stability of ice sheets

a flowline map of glaciated canada based on remote sensing datathis paper is accompanied by a large foldout map entitled a flowline map of glaciated canada based on remote sensing data see pocket on back cover the map a flowline map of glaciated canada based on remote sensing data presents flowlines for the former laurentide and cordilleran ice sheets based on flow indicators derived from aggregated flo

sandy submarine braid plains potential deep water reservoirs sandy submarine braid plains like their fluvial counterparts on land are sand rich depositional environments that may display excellent reservoir characteristics in terms of sediment volume porosity and permeability the submarine examples may be laterally associated with potential source rocks such as the fine grained levee deposits of deep sea channels a side scan sonar study of the central labrador sea revealed the existence of a more than 700 km long and up to 120 km wide submarine sand and gravel plain that has been supplied with sediment by high density turbidity currents possibly resulting from subglacial lake outburst flooding in the hudson strait the side scan imagery of parts of the plain displays a conspicuous streaky pattern of alternating high and low backscatter intensity high resolution 3 5 khz seismic profiles and 12 khz bathymetric profiles show that the pattern represents a furrow and ridge erosional or channel and bar depositional topography similar to a braided alluvial plain the furrows or channels have low acoustic backscatter are less than 10 m deep and are separated by ridges or bars having high backscatter some channels terminate in depositional lobes individual channels and bars or furrows and ridges are less than 100 m wide and can be followed up to 40 km downcurrent on sleeve gun seismic profiles the total sand thickness appears to be between 200 m proximal and 100 m distal piston cores from the plain recovered massive sand layers up to 4 m thick buried under 1 m of holocene hemipelagic ooze texturally the sands and gravelly sands display a trend of improving sorting with increasing mean grain size some very coarse grained samples are moderately well sorted and almost matrix free the flooding events that deposited the sands might be the submarine counterpart of heinrich events but need not be restricted to such events radiocarbon ages of about 10 k y from the base of the ooze overlying the youngest sand gave a minimum age for the sand that is similar to the age of heinrich event 0 estimates for the discharge volume of individual events are poorly constrained and range from 103 to 105 km3 braided channel patterns in deep water begin page 1500 sandy depositional environments are not restricted to high latitudes but also have been identified in various submarine fan settings in the lower latitudes for example the orinoco var and monterey deep sea fans and in the santa monica basin the largest examples however are known from high latitudes suggesting that melt water discharge from continental ice sheets may favor the formation of this habitat of giant sands in the deep sea the occurrence of sandy braided deep water environments having favorable reservoir characteristics in a variety of tectonic settings makes this type of environment a potentially interesting deep water target

laurentide subgiacial outburst floods landform evidence from digital elevation models various lines of landform evidence in many parts of canada are comprehensively explicable as products of subglacial sheetfloods outburst floods in the northwest territories northern saskatchewan and alberta landform associations such as scoured bedrock tracts cavity fill drumlins erosional drumlins erosional giant flutes remnant ridges tunnel channels channeled scabland and hummocky terrain with upstanding moraine plateaus reflect primary glaciofluvial erosional processes and secondary depositional activities the livingstone lake event major sheetfloods path arcs obliquely upslope from the keewatin district northwest territories through northern saskatchewan and much of alberta into montana u s a hill shaded maps generated from digital elevation models at widely varying scales are used to illustrate regional to local examples of megaflood landform suites complementary maps and diagrams are derived from more conventional data sources speculations regarding extraglacial implications of th

subglacial bedform evidence for a major palaeo ice stream and its retreat phases in amundsen gulf canadian arctic archipelago ascertaining the location of palaeo ice streams is crucial in order to produce accurate reconstructions of palaeo ice sheets and examine interactions with the ocean climate system this paper reports evidence for a major ice stream in amundsen gulf canadian arctic archipelago mapping from satellite imagery landsat etm and digital elevation models including bathymetric data is used to reconstruct flow patterns on southwestern victoria island and the adjacent mainland nunavut and northwest territories several flow sets indicative of ice streaming are found feeding into the marine trough and cross cutting relationships between these flow sets and utilising previously published radiocarbon dates reveal several phases of ice stream activity centred in amundsen gulf and dolphin and union strait a large erosional footprint on the continental shelf indicates that the ice stream ca 1000 km long and ca 150 km wide filled amundsen gulf probably at the last glacial maximum subsequent to this the ice stream reorganised as the margin retreated back along the marine trough eventually splitting into two separate low gradient lobes in prince albert sound and dolphin and union strait the location of this major ice stream holds important implications for ice sheet ocean interactions and specifically the development of arctic ocean ice shelves and the delivery of icebergs into the western arctic ocean during the late pleistocene copyright c 2006 john wiley sons ltd

drumlins subglacial meltwater floods and ocean responses drumlins and erosional marks in bedrock give evidence for broad subglacial meltwater floods that have discharge rate estimates of about 10 6 m 3 s similar discharge rates are obtained for other late glacial catastrophic floods the total volume of meltwater that is thought to have formed the livingstone lake saskatchewan drumlin field is estimated at 8 4 x 10 4 km 3 this volume is equivalent to a eustatic rise of 0 23 m in global sea level meltwater release and roughly contemporaneous formation of drumlin fields in north america and europe could have involved several metres of sea level rise in a few years the implications of such floods for the generation of myths and the interpretation of the oxygen isotopic record of the oceans are discussed high meltwater discharges are of potential importance to the generation of a lid of cold fresh water over the north atlantic and its effects on late glacial climate

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 highly mobile laurentide ice sheet revealed by satellite images of glacial lineations satellite images of the north american continent reveal previously unrecognized patterns of crossing drift lineations reflecting unexpected shifts of centres of mass of the laurentide ice sheet throughout the last glacial cycle such shifts must must have been associated with major global atmospheric circulation changes

fennoscandian palaeoglaciology reconstructed using a glacial geological inversion model the evolution of ice sheet configuration and flow pattern in fennoscandia through the last glacial cycle was reconstructed using a glacial geological inversion model i e a theoretical model that formalises the procedure of using the landform record to reconstruct ice sheets the model uses mapped flow traces and deglacial melt water landforms as well as relative chronologies derived from cross cutting striae and till lineations as input data flow trace systems were classified into four types i time transgressive wet bed deglacial fans ii time transgressive frozen bed deglacial fans iii surge fans and iv synchronous non deglacial event fans using relative chronologies and aggregation of fans into glaciologically plausible patterns a series of ice sheet configurations at different time slices was erected a chronology was constructed through correlation with dated stratigraphical records and proxy data reflecting global ice volume geological evidence exists for several discrete ice sheet configurations centred over the scandinavian mountain range during the early weichselian the build up of the main weichselian fennoscandian ice sheet started at approximately 70 ka and our results indicate that it was characterised by an ice sheet with a centre of mass located over southern norway this configuration had a flow pattern which is poorly reproduced by current numerical models of the fennoscandian ice sheet at the last glacial maximum the main ice divide was located overthe gulf of bothnia a major bend in the ice divide was caused by outflow of ice to the northwest over the lowest part of the scandinavian mountain chain widespread areas of preserved pre late weichselian landscapes indicate that the ice sheet had a frozen bed core area which was only partly diminished in size by inward transgressive wet bed zones during the decay phase

the pattern and style of deglaciation at the late wisconsinan laurentide and cordilleran ice sheet limits in northeastern british columbia this paper reports on the landform assemblages at the northern confluence of the late wisconsinan laurentide and cordilleran ice sheets with montane and piedmont glaciers in the northern rockies and southern mackenzie mountains recent observations in northeastern british columbia refine our knowledge of the pattern and style of ice sheet retreat glacial lake formation and meltwater drainage at the onset of deglaciation confluent laurentide and cordilleran terminal ice margins lay between 59 n 124 30 w and 60 n 125 15 w from this terminal limit ice sheets retreated into north central british columbia and yukon territory with remnant cordilleran ice and montane glaciers confined to mountain valleys and the liard plateau distinctive end moraines are not associated with the retreat of cordilleran ice in these areas laurentide ice retreated northeastward from uplands and the plateaus then separated into lobes occupying the fort nelson and petitot river valleys ice retreat landforms include recessional end moraines sometimes overridden and drumlinized hill hole pairs crevasse fill deposits de geer like ribbed till ridges hummocky moraines kames meltwater features and glacial lake deposits that fall within the elevation range of glacial lake liard and glacial lake fort nelson ca 840 380 m meltwater and sediment transport into glacial lakes fort nelson liard nahanni and mackenzie was sustained by remnant ice in the liard river and fort nelson river drainage basins until the end of glaciation optical dating of sand from stabilized parabolic dunes on the liard plateau indicates that proglacial conditions lake formation and drainage began before 13 0 0 5 ka calendar years the petitot fort nelson and liard rivers all occupy spillways incised into glacial deposits and bedrock by meltwater overflow from glacial lakes peace and hay

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

landform signature of the laurentide and cordilleran ice sheets across alberta during the last glaciation government geological survey maps and research publications have portrayed the distribution of glacial landforms associated with the advance and retreat of the laurentide and cordilleran ice sheets across alberta at a local regional and continental scale to date this information has not been systematically synthesized into a single compilation at a consistent scale although this original work provided valuable information to constrain reconstructions of former ice sheet extent configuration and flow geometry its derivation primarily from the interpretation of aerial photographs and the shuttle radar topography mission 90 m digital elevation model dem may result in methodological inconsistencies and spatial biases these biases together with challenges associated with geomorphic mapping in densely forested areas of western and northern alberta limit the usefulness of previous mapping when applied to inversion based ice sheet reconstructions which have specific input data demands recently ligh

major changes in ice stream dynamics during deglaciation of the north western margin of the laurentide ice sheet abstract victoria island lies at the north western limit of the former north american laurentide ice sheet in the canadian arctic archipelago and displays numerous cross cutting glacial lineations previous work suggests that several ice streams operated in this region during the last wisconsinan glaciation and played a major role in ice sheet dynamics and the delivery of icebergs into the arctic ocean this paper produces the first detailed synthesis of their behaviour from the last glacial maximum through to deglaciation 21 9 5 cal ka bp based on new mapping and a previously published radiocarbon constrained ice sheet margin chronology over 70 discrete ice flow events flow sets are fitted to the ice margin configuration to allow identification of several ice streams ranging in size from large and long lived thousands of years to much smaller and short lived hundreds of years the reconstruction depicts major ice streams in m clure strait and amundsen gulf which underwent relatively rapid retreat from the continental shelf edge at some time between 15 2 and 14 1 cal ka bp a period which encompasses climatic warming and rapid sea level rise meltwater pulse 1a following this overall retreat was slower and the ice streams exhibited asynchronous behaviour the amundsen gulf ice stream continued to operate during ice margin retreat whereas the m clure strait ice stream ceased operating and was replaced by an ice divide within 1000 years this ice divide was subsequently obliterated by another short lived phase of ice streaming in m clintock channel 13 cal ka bp the timing of this large ice discharge event coincides with the onset of the younger dryas subsequently a minor ice divide developed once again in m clintock channel before final deglaciation of the island shortly after 9 5 cal ka bp it is concluded that large ice streams at the nw margin of the laurentide ice sheet equivalent in size to the hudson strait ice stream underwent major changes during deglaciation resulting in punctuated delivery of icebergs into the arctic ocean published radiocarbon dates constrain this punctuated delivery as far as is possible within the limits imposed by their precision and we note their coincidence with pulses of meltwater delivery inferred from numerical modelling and ocean sediment cores

geomorphological reconstruction of the labrador sector of the laurentide ice sheet abstract the labrador sector formed one of three major domes of the laurentide ice sheet during the last wisconsinan glaciation reconstruction of its evolution is important because it modulated atmospheric and oceanic circulation over 1 100 ka time scales this paper reports new geomorphological evidence of ice flow which is used to reconstruct glimpses of the behaviour of the labrador sector during its evolution flow evidence indicates a southern position 51 n of the labrador ice divide presumed to be the usual location when the ice sheet was close to its maximum extent a previously inferred dramatic surge of labrador ice across hudson strait and onto baffin island at 9 9 9 4 ka is verified seemingly contradictory evidence regarding deglaciation in northern quebec has been analysed and a reconstruction developed that solves this problem deglacial retreat of the labrador ice sheet was highly asymmetric with rapid retreat of the southern margin northwards migration of the centre of mass by 500 km and slow retreat along the northern margin as it shrank its thermal regime changed from cold centred to entirely cold based and it finally fragmented into many residual ice caps and glaciers this dynamic and asymmetric behaviour may be due to destabilisation of the labrador ice sheet triggered by heinrich event ice streaming through hudson strait

glacial flow systems in the zone of confluence between the scandinavian and novaja zemlya ice sheets abstract the glacial geomorphology of the eastern kola peninsula northwestern russian plain pechora lowland northern ural mountains and southern novaya zemlya 1 000 000 km 2 was mapped using landsat satellite imagery glacial flow parallel lineations and marginal and interlobate features were identified the directions of glacial flow and the patterns of deglaciation were reconstructed the scandinavian ice sheet expanded northeastwards into the southern barents sea while the novaya zemlya ice sheet spread southwestwards into the same area the two coalesced in the kanin region and subsequently flowed from the barents sea towards the land during the deglaciation of the scandinavian ice sheet flow was initially oriented from the white sea region towards the barents sea subsequently several ice streams controlled by the regional topography were formed the growth of the novaya zemlya ice sheet occurred east of the islands whereas during the decay there was more ice on the western side a compilation of dated sequences up to 300 km inland from the coast indicate a late weichselian age of deglaciation separation of the two ice sheets occurred along the saddle between the kanin and kola peninsulas at about 13 000 bp 15 500 cal years bp which became the locus for discharge of the proglacial dvina pechora lake into the sea beyond the presumed late weichselian limits older flow patterns are recognised these patterns along with dispersal of erratics suggest that the growth of a more extensive glaciation started in the novaya zemlya region later the scandinavian ice sheet occupied areas previously covered by the novaya zemlya ice sheet