modes of operation of thermo mechanically coupled ice sheets by richard c a hindmarsh geoffrey s boulton grant institute of geology university of edinburgh west mains road edinburgh eh9 3jw scotland u k and kolumban hutter lnstitut fur mechanik technische hochschule oarmstadt hochschulstrasse i 0 6100 oarmstadt federal republic of germany dimensionless lapse rate a dimensionless model of thermo mechanically coupled ice sheets is used to analyse the operation of the system three thermal processes are identified i dissipation having a maximum time scale of thousands of years ii advection having a time scale of tens of thousands of years and iii conduction having a time scale of loo 000 years kinematical processes occur on two time scales i a marginal advective time scale of thousands of years and ii a diffusive time scale of tens of thousands of years dominant in the divide area

subglacial processes from drumlins in clew bay western ireland interpretation of subglacial processes and environments can be usefully informed by the stratigraphy and structures of sediments preserved within drumlins and the down ice variability of these sediments drumlins in clew bay western ireland were formed by westward late pleistocene ice flow onto the atlantic shelf but the depositional processes and environments of these sediments remain uncertain this study describes and interprets the drumlin stratigraphy and sediment properties and structures from two drumlins on the south side of clew bay drumlin sediments are dominated by massive to stratified diamicton deposited subglacially by deformation of flows of varying rheology folds shears and clastic dikes within the sediments suggest active subglacial water flow related to variations in ice flow and ice bed coupling the distal ends of the drumlins are dominated by stratified diamicton and gravel units with sandy interbeds these sediments reflect deposition in a leeside subglacial cavity formed coevally with bedform development a model is proposed that can account for sediment stratigraphic patterns and drumlin formation copyright 2015 john wiley sons ltd

relationship between mega scale glacial lineations and iceberg ploughmarks on the bjornoyrenna palaeo ice stream bed barents sea abstract mega scale glacial lineations msgls are ridge groove corrugations aligned in the direction of the former ice flow tens of kilometers long and up to a few hundred meters wide they are the most striking subglacial features on the beds of former ice streams and play an important role in modulating ice flow through their influence on bed roughness and subglacial hydrology despite the importance of msgls their formation remains enigmatic most studies have tended to focus on assemblages of msgls and their relationship to other landforms up ice e g drumlins or bedrock features in ice stream onset zones but fewer studies have examined their characteristics and transition to other landforms towards ice stream grounding lines in this paper we investigate the relationship between an assemblage of msgls and ploughmarks on the bed of the former bjornoyrenna ice stream in the sw barents sea which occurs in the central part of the ice stream bed a sample of msgls is used to test their potential origin based on their metrics width length and diagnostic characteristics predicted by formation theories results show a down flow depth decrease of the msgl grooves and a shallowing tendency once they transition into ploughmarks their width shows an increasing tendency which we link mostly to the strong divergence of the trough and ice flow downstream the prominent continuity from linear to curvilinear features demonstrates that the grooves associated with msgls transition into iceberg ploughmarks this observation is consistent with the hypothesis that the msgls have formed through a mechanism of groove ploughing at least in part the continuity from msgls to iceberg ploughmarks resulted from detachment of large icebergs from the grounded ice wall or grounded ice shelf and their ploughing away from the ice margin

response of sediment to ice sheet loading in northwestern germany effective stresses and glacier bed stability laboratory tests on sediment over ridden by the last ice sheet in northwestern germany reveal very low ice induced pre consolidation and high palaeo pore water pressures sediment consolidation at the base of the glacier was largely controlled by hydraulic properties of the substratum generally low permeabilities of the bed caused sustained high pore water pressure in over ridden sediments close to the flotation point this implies a serious possibility of hydraulic lifting of the ice sheet it is believed that the reduced basal coupling limited the transformation of glacier shear stress on to the bed sediments which is indicated by a lack of sedimentological evidence for widespread pervasive bed deformation ice motion was probably focused at the glacier sole by some combination of sliding and ploughing however isolated spots with deformation occur so that the subglacial system in the study area can be characterized as a stable deforming mosaic

application of a bayesian model to infer the contribution of coalbed natural gas produced water to the powder river wyoming and montana the powder river basin prb of wyoming and montana contains significant coal and coal bed natural gas cbng resources cbng extraction requires the production of large volumes of water much of which is discharged into existing drainages compared to surface waters the cbng produced water is high in sodium relative to calcium and magnesium elevating the sodium adsorption ratio sar to mitigate the possible impact this produced water may have on the quality of surface water used for irrigation the state of montana passed water anti degradation legislation which could affect cbng production in wyoming in this study we sought to determine the proportion of cbng produced water discharged to tributaries that reaches the powder river by implementing a four end member mixing model within a bayesian statistical framework the model accounts for the 87sr 86sr 13cdic sr and dic of cbng produced water and surface water interacting with the three primary lithologies exposed in the prb the model estimates the relative contribution of the end members to the river water while incorporating uncertainty associated with measurement and process error model results confirm that both of the tributaries associated with high cbng activity are mostly composed of cbng produced water 70 100 the model indicates that up to 50 of the powder river is composed of cbng produced water downstream from the cbng tributaries decreasing with distance by dilution from non cbng impacted tributaries from the point sources to 10 20 at the montana border this amount of cbng produced water does not significantly affect the sar or electrical conductivity of the powder river in montana copyright 2013 john wiley sons ltd

reconstructing the last irish ice sheet 2 a geomorphologically driven model of ice sheet growth retreat and dynamics the ice sheet that once covered ireland has a long history of investigation much prior work focussed on localised evidence based reconstructions and ice marginal dynamics and chronologies with le

thermomechanical modelling of northern hemisphere ice sheets with a two level mass balance parameterization a 3 d time dependent thermomechanical ice sheet model was used together with a two level snow accumulation runoff mass balance model to investigatethe quaternary ice sheets of the northern hemisphere the model freely generates the ice sheet geometry in response to specified changes of surfacetemperature and mass balance and includes bedrock adjustment basal sliding and a full temperature calculation within the ice the mass balanceparameterisation makes a distinction between snowfall and melting yearly snow fall rates depend on the present precipitation distribution and are variedproportional to changes of surface temperature and the moisture content of the air the ablation model is based on the positive degree day method anddistinguishes between ice and snow melting this paper discusses steady state characteristics conditions for growth and retreat and response time scales ofice sheets as a function of a prescribed lowering of summer temperature most notably the modelled extents of the eurasian ice sheet for a summertemperature lowering of 6 7 k and of the laurentide ice sheet for a cooling of 9 10 k are in reasonable agreement with most reconstructions based ongeological evidence except for the presence of a large ice sheet stretching from alaska across the bering strait to most of eastern siberia in addition wetbasal conditions turned out to be always confined to the margin whereas central areas in these reconstructions remained always cold based this is ofrelevance for processes involving reduced basal traction

sr isotope tracing of aquifer interactions in an area of accelerating coal bed methane production powder river basin wyoming sr isotope data on groundwater samples from coal and overlying sandstone aquifers in the eastern powder river basin wyoming demonstrate that the sr isotope ratio effectively identifies groundwater from different aquifers where major ion geochemistry and o and h stable isotope data fail groundwaters from sandstone aquifers have a uniform 87sr 86sr ratio of 0 7126 0 7127 waters from coal seams vary from 87sr 86sr ratio 0 7127 near the recharge area to 0 7151 farther into the basin the distinct sr isotope signatures of sandstone and coal aquifers may reflect different sources of sr in these two rock types sr in sandstones is held primarily in carbonate cement whereas coals contain more radiogenic sr in organic matter the sr isotope ratio is useful in identifying wells that contain mixed waters whether due to well construction or to incomplete aquifer isolation measurement and continued monitoring of the sr isotope ratio in groundwaters should provide a powerful tool for characterizing the impact of the burgeoning coal bed methane industry on the hydrology of the powder river basin

the meltwater hypothesis for subglacial bedforms this paper presents an historical and in places informal account of the meltwater hypothesis which invokes enormous outburst floods for the formation of subglacial bedforms it begins with a brief discussion of the difficulties of determining processes of formation for landforms which are not seen in formation analogy provides a solution to these difficulties analogy between erosional marks at the bases of turbidites and drumlins which were the starting point for this hypothesis rests on the idea that inverted erosional marks at the ice bed are subsequently infilled to form drumlins field tests on the sedimentology architecture and landform associations of drumlins in the livingstone lake drumlin field are outlined before more extensive work on bedrock erosional forms and flood routes is introduced bedrock erosional forms played a central part in establishing the hypothesis since their form and ornamentation are confidently interpreted as fluvial their form and genesis are discussed mainly with reference to sites at french river and wilton creek ontario though some remarkable bedrock erosional forms in antarctica support their regional extent initially in the meltwater hypothesis drumlins were thought to be cavity fills and erosional drumlins were recognized later this development is shown to be central to the realization that drumlin composition may be inferred from drumlin form the scale of drumlin fields measured at about 10 3 km 2 and the magnitude of the inferred floods require that the flood events were regional regional scale flood tracts in ontario quebec alberta and the northwest territories extending over 1000 km in length and several hundred kilometers in width support this suggestion floods had they occurred would have caused rapid rates of sea level rise and may have changed climate through their effects on ocean stratification and sea surface temperatures the meltwater hypothesis covers a range of bedforms besides drumlins and bedrock erosional marksffluting rogen moraine hummocky terrain and transverse ridges recent work shows how these forms are best explained by the meltwater hypothesis the roles of water storage and release which underpin the theory of the meltwater hypothesis remain poorly understood r 2002 published by elsevier science ltd

binge purge oscillations of the laurentide ice sheet as a cause of the north atlantic s heinrich events ice rafted debris in sediment cores from the north atlantic suggests that the laurentide ice sheet lis periodically disgorged icebergs in brief but violent episodes which occurred approximately every 7 000 years here i propose that heinrich events i e what these episodes are called were caused by free oscillations in the flow of the laurentide ice sheet which arose because the floor of hudson bay and hudson strait is covered with soft unconsolidated sediment that forms a slippery lubricant when thawed the proposed heinrich event cycle has two phases the growth phase occurs when the sediment is frozen and the lis is stranded immobile on a rigid bed the volume of the lis slowly grows during this phase at a rate dictated by snow accumulation the purge phase occurs when the basal sediment thaws and a basally lubricated discharge pathway i e an ice stream such as those which occur in west antarctica today developes through hudson strait the volume of the lis rapidly equilibrates to the reduced basal friction during this phase by dumping icebergs into the labrador sea the periodicity t k sl2g 2 7000 years of the proposed heinrich event cycle is a function of the thermal conductivity and diffusivity of ice k and respectively the atmospheric sea level temperature sl in degrees celsius and the excess geothermal heat flux defined by g g k where is the atmospheric lapse rate and g is the geothermal heat flux agreement between the predicted t and the apparent periodicity implied by the marine record is the main virtue of the free oscillation mechanism i propose an alternative mechanism in which heinrich events are forced by periodic variations in external climate is implausible because periodic atmospheric temperature perturbations are strongly attenuated with depth in an ice sheet

bedform signature of a west antarctic palaeo ice stream reveals a multi temporal record of flow and substrate control abstract the presence of a complex bedform arrangement on the sea floor of the continental shelf in the western amundsen sea embayment west antarctica indicates a multi temporal record of flow related to the activity of one or more ice streams in the past mapping and division of the bedforms into distinct landform assemblages reveals their time transgressive history which implies that bedforms can neither be considered part of a single downflow continuum nor a direct proxy for palaeo ice velocity as suggested previously a main control on the bedform imprint is the geology of the shelf which is divided broadly between rough bedrock on the inner shelf and smooth dipping sedimentary strata on the middle to outer shelf inner shelf bedform variability is well preserved revealing information about local complex basal ice conditions meltwater flow and ice dynamics over time these details which are not apparent at the scale of regional morphological studies indicate that past ice streams flowed across the entire shelf at times and often had onset zones that lay within the interior of the antarctic ice sheet today in contrast highly elongated subglacial bedforms on sedimentary strata of the middle to outer shelf represent a timeslice snapshot of the last activity of ice stream flow and may be a truer representation of fast palaeo ice flow in these locations a revised model for ice streams on the shelf captures complicated multi temporal bedform patterns associated with an antarctic palaeo ice stream for the first time and confirms a strong substrate control on a major ice stream system that drained the west antarctic ice sheet during the late quaternary

subglacial bedform geomorphology of the irish ice sheet reveals major configuration changes during growth and decay the belated realisation that ribbed rogen moraines form such an integral part of irish geomorphology and the piecemeal approach to previous drumlin mapping is probably responsible for the highly contrasting views of palaeoflow patterns of the irish ice sheet using a high resolution 25 m digital elevation model we present morphological maps of a large part 100 100 km of the so called drumlin belt of north central ireland the landforms comprise mostly ribbed moraine much larger than found elsewhere up to 16 km in length which in places are superimposed on each other contrary to most prior assessments we find the bedform record to contain numerous and overlapping episodes of bed formation ribbed moraine drumlins and crag and tails that provide a palimpsest record of changing flow geometries these demonstrate an ice sheet with a centre of mass and flow geometry that changed during growth and decay using distinctive flow patterns and relative age relationships between them we reconstruct ice sheet evolution into four phases during a single glacial cycle in phase 1 early in the glacial cycle scottish and local ice coalesced to form a northeast centred irish ice sheet as it grew its centre of mass migrated southwards culminating in a major n s divide positioned down the east of ireland phase 2 ca last glacial maximum during retreat the centre of mass migrated at least 120 km northwards and became established in northwest ireland and at this point a dramatic bedforming event produced one of the world s largest and most contiguous ribbed moraine fields phase 3 final deglaciation is thought to be by fragmentation into many topographically controlled minor ice caps phase 4 rather than any dramatic or unexpected behaviour the reconstructed phases indicate a relatively predictable pattern of ice sheet growth and decay with changes in centres of mass and does not require major readvances or ice stream events copyright 2001 john wiley sons ltd

the subglacial mosaic of the laurentide ice sheet a study of the interior region of southwestern hudson bay abstract reconstructions of past ice flow provide useful insights into the long term behaviour of past ice sheets and help to understand how glaciated landscapes are shaped here we present reconstruction of a 10 phase ice flow history from southwestern hudson bay in northeastern manitoba canada a dynamic region situated between two major ice dispersal centres of the laurentide ice sheet we utilize a diverse geologic dataset including 1900 field based erosional indicators 12 streamlined landform flowsets esker and meltwater corridor orientations 103 till fabrics analyses and 1344 till clast lithology counts our reconstruction suggests that both pre mis 2 and mis 2 glaciations followed similar growth patterns where ice advanced into study area from ice centered to the east probably in northern quebec followed by a switch in ice flow direction indicating flow from the keewatin ice centre to the northwest and north the cause for this switch in ice flow orientation is uncertain but the youngest switch may relate to retreat of ice during mis 3 that then left space for keewatin sourced ice to advance over the study area while modelling experiments indicate widespread cold based conditions in the study area during the last glacial cycle uniformly relict landscapes are not common instead the glaciated landscape is palimpsest and commonly fragmented forming a subglacial bed mosaic of erosional and depositional assemblages that record both shifting ice flow direction through time and shifting subglacial conditions each assemblage formed or modified during times of dynamic warm based ice and later preserved under conditions below or close to the pressure melting point slow and sluggish or cold based

large scale ice moulding a discussion of genesis and glaciological significance abstract landsat images reveal a previously unsuspected large scale pattern of streamlining within drift which comprises a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain consideration of the genesis and glaciological significance of such landforms leads to a number of conclusions it is suggested that mega scale glacial lineations were formed under conditions of fast ice flow and their presence may thus record former locations of ice streams or surge events many lineations of varying scales display a pattern that reveals that they were not formed in sub marginal positions extensive sets of lineations must have been formed approximately synchronously thus indicating that lineation generation occurs over a wide range of glaciodynamic conditions from sub marginal positions to interior portions of ice sheets subglacial deformation of tills has been widely invoked to account for rapid glacier motion criteria for identifying such tills are restricted to structures viewed in cross section and it is thus hard to assess how widespread the processes of deformation may have been lineations provide a surface marker of structure that records subsequent deformation from other ice flow events it is argued that the palaeo flow record including cross cutting patterns provides the surface or plan expression of subglacial deformation the degree of modification to pre existing lineations should permit the identification of zones favoured by deformation and thus assist in an assessment of how pervasive deforming bed processes were in influencing ice sheet dynamics

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

lacustrine interdeltaic coal in fort union formation paleocene powder river basin wyoming abstract the tongue river member of the fort union formation the major coal bearing unit in the powder river basin of wyoming and montana records a history of paludal fluvial deltaic and lacustrine sedimentation tongue river deltas filled the basin primarily from the eastern margin as they prograded into a lake lebo shale member that occupied the basin axis major streams entered the fort union coastal plain from point sources resulting in areas of broad interdeltaic coastal plain isolated from major clastic influx we mapped the clastic framework facies and the regional distribution of thick tongue river coal seams using approximately 1 400 induction electric logs a detailed study of a thick coal seam in the center of the basin shows that coal occurrence is facies dependent peat accumulation began in interdeltaic and interdistributary areas at the loci of regional ground water discharge upon delta abandonment peat swamps overspread the abandoned lobes the result is a thick strike parallel interdeltaic coal seam bounded by fluvial deltaic framework facies the depositional model and coal occurrence maps provide a guide for coal exploration and a framework for interpreting individual deposits in the powder river basin end of article last page 931

evidence for late pleistocene ice stream activity in the witch ground basin central north sea from 3d seismic reflection data abstract buried submarine landforms mapped on 3d reflection seismic data sets provide the first glacial geomorphic evidence for glacial occupation of the central north sea by two palaeo ice streams between 58 59 n and 0 1 e streamlined subglacial bedforms mega scale glacial lineations and iceberg plough marks within the top 80 m of the quaternary sequence record the presence and subsequent break up of fast flowing grounded ice sheets in the region during the late pleistocene the lengths of individual mega scale glacial lineations vary from 5 to 20 km and the distance between lineations typically ranges from 100 to 1000 m the lineations incise to a depth of 10 12 m with trough widths of 100 m the most extensive and best preserved set of lineations is attributed to the action of a late weichselian ice stream which either drained the ne sector of the british irish ice sheet or was sourced from the sw within the fennoscandian ice sheet the 30 50 km wide palaeo ice stream is imaged along its flow direction for 90 km trending nw se an older set of less well preserved lineations is interpreted as an earlier weichselian or saalian ice stream and records ice flow in an sw ne orientation cored sedimentary records tied to 3d seismic observations support grounded ice sheet coverage in the central north sea during the last glaciation and indicate that ice flowed over a muddy substrate that is interpreted as a deformation till the identification of a late weichselian ice stream in the witch ground area of the north sea basin provides independent geomorphic evidence in support of ice sheet reconstructions that favour complete ice coverage of the north sea between scotland and norway during the last glacial maximum

geomorphological criteria for identifying pleistocene ice streams ice streams are critical regulatory mechanisms in contemporary ice sheets it has been inferred that they also had a significant effect on the dynamics of former ice sheets subsequently many people have invoked their widespread occurrence from a variety of formerly glaciated areas hypothesised locations however have often outweighed meaningful evidence this paper addresses the problem using the characteristics of contemporary ice streams as a basis for their identification from former ice sheet beds a convergence of knowledge gained from contemporary ice stream research coupled with theories of glacial geomorphology allows several geomorphological criteria to be identified as suggestive signatures of ice stream activity it is envisaged that the geomorphological criteria developed here will introduce a more objective approach to the study of former ice streams the criteria are used to construct conceptual land system models of the beds of former ice streams and it is hoped such models can provide an observational template upon which hypotheses of former ice streams can be better based

a major ice drainage pathway of the last british irish ice sheet the tyne gap northern england the tyne gap is a wide pass situated between the scottish southern uplands and the english pennines that connects western and eastern england it was a major ice flow drainage pathway of the last british irish ice sheet this study presents new glacial geomorphological and sedimentological data from the tyne gap region that has allowed detailed reconstructions of palaeo ice flow dynamics during the late devensian marine isotope stage 2 mapped lineations reveal a complex palimpsest pattern which shows that ice flow was subject to multiple switches in direction these are summarised into three major ice flow phases stage i was characterised by convergent lake district and scottish ice that flowed east through the tyne gap as a topographically controlled ice stream this ice stream was identified from glacial geomorphological evidence in the form of convergent bedforms streamlined subglacial bedforms and evidence for deformable bed conditions stage ii involved northerly migration of the solway firth ice divide back into the southern uplands causing the easterly flow of ice to be weakened and resulting in southeasterly flow of ice down the north tyne valley and stage iii was characterised by strong drawdown of ice into the irish sea ice basin thus starving the tyne gap of ice and causing progressive ice sheet retreat westwards back across the watershed prior to ice stagnation copyright 2009 john wiley sons ltd

evidence for rapid ice flow and proglacial lake evolution around the central strait of magellan region southernmost patagonia this paper presents a detailed palaeoglaciological reconstruction of ice sheet dynamics in the seno skyring seno otway and strait of magellan region of the former patagonian ice sheet with a particular focus on previously hypothesised zones of rapid ice flow and the evolution of proglacial lakes geomorphological mapping from a combination of satellite imagery and oblique and vertical aerial photographs reveals a variety of glacial landforms that are grouped into several discrete flow sets and associated ice margin positions the most distinct features are represented by flow sets of highly elongate streamlined glacial lineations on both sides of the strait of magellan based on the shape and dimensions of the flow sets and their abrupt lateral margins a transverse and longitudinal variation in glacial lineation length and elongation ratio and the reported presence of a potentially deformable bed and thrust moraines the flow sets are interpreted as zones of rapid ice flow within the otway and magellan lobes we hypothesise that this provides evidence for contemporaneous surge like advances within the lobes which may explain the asymmetry in the lobate margin positions on either side of the strait the mechanisms that initiated rapid flow are unclear but are likely to have been influenced by internal factors such as a change in thermal hydrological conditions at the bed the topography of the region suggests ice dammed lakes would have formed as the ice lobes retreated the westernmost of the former lakes lake skyring is delimited by a series of palaeo shorelines surrounding the present day lake laguna blanca and we reconstruct lake evolution based on manipulation of a digital elevation model the size and orientation of meltwater channels and a large outwash plain indicate that lake skyring drained eastwards towards the strait of magellan probably quite rapidly we conclude that the potential for quasi independent surge like behaviour within adjacent lobes raises the possibility that during climate driven ice expansion some advances in this region may have been partly controlled by secondary internal feedback mechanisms

laurentide glacial landscapes the role of ice streams glacial landforms of the north american prairie can be divided into two suites that result from different styles of ice flow 1 a lowland suite of level to streamlined till consistent with formation beneath ice streams and 2 an upland and lobe margin suite of thick hummocky till and glacial thrust blocks consistent with formation at ice stream and ice lobe margins southern laurentide ice lobes hypothetically functioned as outlets of ice streams broad branching lowlands bounded by escarpments mark the stable positions of the ice streams that fed the lobes if the lobes and ice streams were similar to modern ice streams their fast flow was facilitated by high subglacial water pressure favorable geology and topography in the midcontinent encouraged nonuniform ice flow and controlled the location of ice streams and outlet lobes

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

physical environment of drumlin formation review of published descriptions of drumlin fields suggests that the following conditions are important to drumlin growth 1 compressive longitudinal and possibly extending transverse strain rates in the ice 2 thin ice such as occurs near the glacier margin and 3 high pore water pressure in the subglacial sediments most drumlin fields display all of these and no fields of well developed drumlins were found that did not on the oilier hand the lithology of drumlin forming sediment appears not to be important in promoting drumlin growth since it varied widely nor are the lithology and large scale topography of the bed

a case for cold based continental ice sheets a transient thermal model a finite difference numerical model is used to simulate the temperature profile at the center of an ice sheet throughout the course of a glaciation the ice sheet is gradually built to a thickness of 3000 m over about 10 000 years starting on permafrost a geothermal heat flux is applied at large depth for an initial surface temperature of 12 5 c our model shows that basal melting occurs 72 000 years after the onset of the glaciation the important parameters determining the basal temperatures are the initial temperature of the ice and substrate the rate of downward advection of cold ice and to a lesser extent the thickness of the ice sheet the growth history of the ice sheet does not significantly influence the time at which basal melting occurs our results show the possibility that the central parts of the continental ice sheets were cold based for a significant part of their existence heating due to the geothermal heat flux cannot account for basal melting during most or all of a glacial cycle these results may help to explain the existence of preserved land forms under the ice sheets

modification of peripheral mountain ranges by former ice sheets the brecon beacons southern uk abstract the brecon beacons in southern wales is a large upland area 900 km 2 close to the periphery of the former british irish ice sheet the geomorphology of the brecon beacons highlands and surrounding areas was mapped using satellite imagery and a digital elevation model dem a fragmentary pattern of glacial lineations is inferred to represent ice build up in the mountains a more coherent set of glacial lineations formed by southward ice flow across the area from the welsh ice cap represents recession from the last glacial maximum lgm during this phase the brecon beacons acted as an obstacle deflecting the ice around higher terrain most of the higher terrain in the brecon beacons therefore appears to have escaped significant glacial erosion during both phases of ice flow due to cold based ice or low basal ice velocities beneath a local ice cap landforms previously interpreted as cirques in fact have v shaped profiles and lack evidence of major over deepening they are interpreted to have been formed primarily by processes other than glacial erosion the overall impact of glaciation in the brecon beacons appears to be limited primarily to the time when the area was over run by the welsh ice cap and the influence of local glaciation has been minimal this study has two main implications for landscape evolution in mountain ranges that lie at the periphery of former ice sheets first due to the presence of cold based ice or low basal ice velocities beneath a local ice cap it may be possible to find fragmentary traces of pre lgm ice flow second the pattern of glacial lineations in and around the brecon beacons indicates that peripheral mountain ranges may have deflected ice flow at the lgm resulting in low basal ice flow velocities and possible frozen bed conditions over higher terrain which consequently resulted in ineffective glacial erosion within the mountains themselves

time perspectives on glacial landscape formation glacial flow chronology at lac aux goelands northeastern quebec canada we used mapping from aerial photographs and field investigations around lac aux goelands whitegull lake northeastern quebec to establish a glacial flow chronology that involves three different glacial landform systems we interpret the youngest of these systems as related to the late wisconsinan deglaciation this system has an up glacier discontinuity that marks a temporal shift from warm based subglacial conditions to non erosive cold based subglacial conditions whereby older glacial landscapes are preserved in the interior of quebec labrador furthermore our results support theories suggesting a northward migrating ice divide to a final position south of ungava bay during the final deglaciation the recognition that a glacial landscape is fragmented and consists of smaller temporally unrelated units is of considerable significance in understanding ice sheet dynamics and patterns of subglacial preservation and destruction this is because a fragmented landscape implies a fragmented formation history where formation of subglacial landforms occurred in restricted subglacial zones during restricted time periods periods of formation must have been separated by periods of preservation and inhibited subglacial reshaping based on estimates of the ice margin retreat velocity and the velocity of the warm based inward migrating zone we suggest that periods of preservation were orders of magnitude longer than periods of subglacial landform formation copyright 2003 john wiley sons ltd

ice stream flow switching during deglaciation of the southwestern barents sea ice streams dominate the discharge of continental ice sheets recent observations and reconstructions have revealed that large scale reorganizations in their flow trajectory flow switching can occur over relatively short time scales however the underlying causes of such behavior and the extent to which they are predictable are poorly known this paper documents a major episode of ice stream flow switching during the late weichselian deglaciation of the southwestern barents sea and explores various hypotheses for its causation regional bathymetric data show that two ice streams that had similar adjoining topographically constrained source areas had very different trajectories and dynamics on the outer shelf at the late weichselian maximum the hakjerringdjupet ice stream flowed westward along the cross shelf trough of hakjerringdjupet while the soroya trough ice stream flowed northward into ingoydjupet forming a tributary of the bjornoyrenna ice stream initial retreat of the hakjerringdjupet ice stream was rapid but with episodic periods of grounding as it retreated onto the higher rougher topography of the inner shelf we infer a reduction in ice velocity and a dramatic decrease in the pace of retreat as recorded by nested sequences of recessional moraines following and probably in response to this we suggest that there was a short lived surge readvance of an adjacent lobe onto fugloybanken in contrast the adjacent soroya trough ice stream remained active throughout deglaciation before retreating rapidly with no stillstands or readvances we argue that the different retreat histories of the ice streams were determined by variations in bed topography bathymetry which modulated the grounding line response to sea level variation such a mechanism is likely to be an important control on the long term behavior of marine based ice streams and outlet glaciers in antarctica and greenland and suggests that gathering data on their subglacial topography should be a priority

flow pattern evolution of the last british ice sheet we present a 10 stage reconstruction of the evolution in ice flow patterns of the last british ice sheet from build up to demise derived from geomorphological evidence 100 flowsets identified in the subglacial bedform record drumlins mega scale glacial lineations and ribbed moraine are combined with ancillary evidence erratic transport paths absolute dates and a semi independently reconstructed retreat pattern to define flow patterns ice divides and ice sheet margins during build up maximum glaciation and retreat overprinting and cross cutting of landform assemblages are used to define the relative chronology of flow patterns and a tentative absolute chronology is presented based on a collation of available dates for ice advance and retreat the ice flow configuration of the last british ice sheet was not static some ice divides were remarkably stable persisting through multiple stages of the ice sheet evolution whereas others were transient features existing for a short time and or shifting in position 10s km the 10 reconstructed stages of ice sheet geometry capture two main modes of operation first as an integrated ice sheet with a broadly n s orientated ice divide and second as a multi domed ice sheet orientated parallel with the shelf edge a thick integrated ice sheet developed as ice expanded out of source areas in scotland to envelop southerly ice caps in northern england and wales and connect with the irish ice sheet to the west and the scandinavian ice sheet across the north sea following break up of ice over the north sea ice streaming probably drove mass loss and ice sheet thinning to create a more complex divide structure where ice flow patterns were largely controlled by the form of the underlying topography ice surface lowering occurred before separation of and retreat to multiple ice centres centred over high ground we consider this 10 stage reconstruction of the evolution in ice sheet configuration to be the simplest palaeo glaciological interpretation of the flowsets identified from the geomorphological record and their relative timing this empirically based reconstruction of flow pattern geometry provides a framework for more detailed local and regional studies and numerical modelling to provide robust explanations of the observed changes in ice sheet structure in terms of climate and glacial dynamics as a minimum numerical model outputs should be able to reproduce the identified flowset patterns in space and satisfy their chronological order

evidence for a relict glacial landscape in quebec labrador abstract two major glacial landform systems occur in labrador these are the radial lineation and esker swarm reflecting late wisconsinan decay and the ungava bay lineation and esker swarm reflecting convergent northward flow in some sectors the two landform systems give conflicting evidence regarding deglaciation pattern we have interpreted the ice sheet dynamics in labrador from morphological data using a new inversion model that treats spatial patterns of deglacial meltwater landforms separately from lineation patterns in the george river area we have found that the ungava bay swarm of deglacial landforms has been overprinted at a right angle by a younger regional meltwater pattern from the last deglaciation a similar overprint also exists along the intersection line in west central labrador these relations show that the previously accepted relative ages of the two landform systems hughes 1964 boulton and clark 1990a b klassen and thompson 1993 have to be reversed we interpret the ungava bay lineation and esker swarm to represent a 0 25 106km2 pre late wisconsinan relict landscape formed during the deglaciation of an older ice sheet and later preserved in a dry based central zone of the labrador dome

theory of glacial erosion transport and deposition as a consequence of subglacial sediment deformation a theory of erosion transport and deposition of unlithified sediments by glaciers is presented it predicts the large scale areal distribution of zones and rates of erosion and deposition in time and space through a complete glacial cycle together with the resultant intensity of large scale lincations drumlins which will be incised in the landscape the theory also predicts the dispersal patterns of subglacial lithologies together with the form of dispersal trains derived from distinctive sources and the vertical and horizontal distribution of lithologies within a till it predicts major erosional discontinuities within tills and the formation of boulder pavements it suggests that the dominant proportion of the lowland tills produced by pleistocene mid latitude ice sheets was generated by subglacial deformation and explains why they are predominantly fine grained the theory is based on an analysis of glacier dynamic processes and therefore can be used to infer the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition

strontium 87 strontium 86 as a tracer of mineral weathering reactions and calcium sources in an alpine subalpine watershed loch vale colorado sr isotopic ratios of atmospheric deposition surface and subsurface water and geologic materials were measured in an alpine subalpine watershed to characterize weathering reactions and identify sources of dissolved ca in stream water previous studies have noted an excess of ca in stream water above that expected from stoichiometric weathering of the dominant bedrock minerals mixing calculations based on 87 sr 86 sr indicate that on an annual basis 26 67 of ca export in streams is atmospherically derived 23 61 is from weathering of plagioclase and the remainder is from weathering of calcite present in trace amounts in the bedrock a potential source of error when applying sr isotopes in catchment studies is determination of the 87 sr 86 sr of sr released by mineral weathering which is complicated by the wide range of mineral isotopic compositions particularly in older rocks and the variable rates at which the minerals weather in this study base flow stream chemistry was used to represent the 87 sr 86 sr of sr derived from mineral weathering because it effectively integrates the potentially variable isotopic composition of sr released by weathering in the alpine environment

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

reconstruction of palaeo ice sheets the use of geomorphological data the article discusses the nature of the glacial inversion problem which is defined as the extraction of time slice ice sheet flow patterns from the patchy and partly overprinted landform record present in former ice sheet areas a coherent inversion model for derivation of flow patterns and interior ice sheet configuration from geomorphological data is presented glacial landscapes are classified according to the three criteria of internal age gradients presence or absence of meltwater traces aligned to flow traces and basal condition frozen bed thawed bed inferred from morphology the inversion model uses landscapes classified accordingly spatially delineated into fans as input data relative chronologies at fan intersections are used to sort fans in a relative age stack that can be linked to stratigraphic dating information

ribbed moraines in sweden distribution pattern and palaeoglaciological implications abstract a detailed map of ribbed moraines in central and northern sweden is presented they are frequent features over much of the mapped area and the distribution has well defined limits the most abundant ribbed moraines are situated in close connection to areas that are inferred to have been cold based during the retreat of the late weichselian ice sheet while outer fully warm based areas lack ribbed moraine observations have also been made on a more local scale where cold based patches grade into ribbed moraines via a zone of a broken up till cover a model of origin is presented which includes contracting of a frozen core area of a retreating ice sheet at the transition from non sliding to sliding conditions there will be high stresses resulting in local extensional flow at the base of the ice sheet a rising phase change surface frozen thawed material would cause detachment and boudinage like breaking up of a pre existing till cover thawed at the bedrock contact but still frozen to the ice sole the orientation of ice flow during the formation of the ribbed moraines closely matches the ice flow directions of the deglaciating late weichselian ice sheet thus ribbed moraines are considered to be deglaciation landforms typical of shrinking cold based zones of a retreating ice sheet

contribution of glacier meltwater to streamflow in the wind river range wyoming inferred via a bayesian mixing model applied to isotopic measurements the wind river range wrr of wyoming has the largest concentration of alpine glaciers in the american rockies and contributes to several major river systems in the western united states declines in the areal extent and volume of these glaciers are well documented and eventual loss of alpine glaciers will reduce the amount of water available for agricultural and domestic use the contribution of glacial melt to streamflow remains largely unquantified in wyoming we used isotope measurements and bayesian modeling to estimate the fractional contribution of glacier meltwater to dinwoody creek dc in the wrr on bi weekly and seasonal spring summer and fall time scales over 2 years in 2007 and 2008 we made temporally intensive measurements of the stable isotope composition of water from the dc watershed samples of the primary sources of streamflow snowmelt glacier melt rain and baseflow were collected during field campaigns and automated collection of stream samples occurred over the melt season isotope data d and 18o were analyzed within a hierarchical bayesian framework that incorporated temporal and spatial correlations glacial melt contributed a significant proportion 53 59 to streamflow in a low flow year 2007 or when streamflow was low during a high flow year 2008 in 2008 a large and persistent snowpack contributed significantly 0 42 51 to streamflow in mid summer the large contribution of glacial melt to streamflow suggests that the loss of glaciers may impact riparian ecosystems and human water supplies in the late summer and in years with low snowpack copyright 2011 john wiley sons ltd

clustre semi automated lineament clustering for palaeo glacial reconstruction datasets containing large numbers 10 000 of glacial lineaments are increasingly being mapped from remotely sensed data in order to develop a palaeo glacial reconstruction or inversion the palimpsest landscape presents a complex record of past ice flow and deconstructing this information into a logical history is an involved task one stage in this process requires the identification of sets of genetically linked lineaments that can form the basis of a reconstruction this paper presents a semi automated algorithm clustre for lineament clustering that uses a locally adaptive region growing methodology after outlining the algorithm it is tested on synthetic datasets that simulate parallel and orthogonal cross cutting lineaments encompassing 1 500 separate classifications results show robust classification in most scenarios although parallel overlap of lineaments can cause false positive classification unless there are differences in lineament length case studies for dubawnt lake and victoria island canada are presented and compared to existing datasets for dubawnt lake 9 out of 14 classifications directly match incorporating 89 of lineaments for victoria island 57 out of 58 classifications directly match incorporating 95 of lineaments differences are related to small numbers of unclassified lineaments and parallel cross cutting lineaments that are of a similar length clustre enables the automated repeatable assignment of lineaments to flow sets using defined user criteria this is important as qualitative visual interpretation may introduce bias potentially weakening the testability of palaeo glacial reconstructions in addition once classified summary statistics of lineament clusters can be calculated and subsequently used during the reconstruction process

laurentide ice streaming on the canadian shield a conflict with the soft bedded ice stream paradigm elucidating the controls on the location and vigor of ice streams is crucial to understanding the processes that lead to fast disintegration of ice flows and ice sheets in the former north american laurentide ice sheet ice stream occurrence appears to have been governed by topographic troughs or areas of soft sediment geology this paper reports robust evidence of a major paleo ice stream over the northwestern canadian shield an area previously assumed to be incompatible with fast ice flow because of the low relief and relatively hard bedrock a coherent pattern of subglacial bedforms drumlins and megascale glacial lineations demarcates the ice stream flow set which exhibits a convergent onset zone a narrow main trunk with abrupt lateral margins and a lobate terminus variations in bedform elongation ratio within the flow set match theoretical expectations of ice velocity in the center of the ice stream extremely parallel megascale glacial lineations tens of kilometers long with elongation ratios in excess of 40 1 attest to a single episode of rapid ice flow we conclude that while bed properties are likely to be influential in determining the occurrence and vigor of ice streams contrary to established views widespread soft bed geology is not an essential requirement for those ice streams without topographic control we speculate that the ice stream acted as a release valve on ice sheet mass balance and was initiated by the presence of a proglacial lake that destabilized the ice sheet margin and propagated fast ice flow through a series of thermomechanical feedbacks involving ice flow and temperature

fast flowing outlet glaciers of the last glacial maximum patagonian icefield abstract glacial geomorphology around the northern patagonian icefield indicates that a number of fast flowing outlet glaciers the continuation of ice streams further upglacier drained the icefield during the last glacial maximum these topographically controlled fast flowing glaciers may have dictated the overall pattern of last glacial maximum ice discharge lowered the ice surface profile and forced the ice divide westward the influence of the fast flowing outlet glaciers on icefield behavior also helps to explain why the configuration of the patagonian icefield at the last glacial maximum is not accurately represented in existing numerical ice sheet models fast flowing outlet glaciers would have strongly influenced ice discharge patterns and therefore partially decoupled the icefield from climatically induced changes in thickness and extent

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

preservation of landforms under ice sheets and ice caps abstract this article addresses the question of whether or not distinct glacial and non glacial landforms can survive beneath ice sheets and ice caps with little or no morphological alteration a review of recent work documents the existence of pre last stadial landforms and landscapes in areas covered by the fennoscandian and laurentide ice sheets a substantial number of independent works indicate that landforms such as eskers drainage channels and boulder fields have escaped destruction despite complete ice overriding during several tens of millenia full preservation of former ground surfaces or delicate landforms probably is linked to areas where the ice sheet base was continuously frozen to its bed larger robust landforms such as large drumlins appear to have been preserved even under wet based conditions in glaciated areas patches preserved under dry cold based conditions provide important windows towards the past showing landscapes that were destroyed in surrounding areas affected by wet based and eroding ice some consequences for the research fields of non glacial geomorphology archaeology and botany include the possibility of subglacial museums and refugia a time space model describes geomorphological access to information from older events in glaciated areas

pattern and timing of retreat of the last british irish ice sheet during the last glacial the ice sheet that subsumed most of britain ireland and the north sea attained its maximum extent by 27 ka bp and with an ice volume sufficient to raise global sea level by ca 2 5 m when it melted we reconstruct the demise of this british irish ice sheet biis and present palaeo glaciological maps of retreat stages between 27 and 15 ka bp the whole land area was investigated using remote sensing data and we present maps of moraines meltwater channels eskers and drumlins and a methodology of how to interpret and bring them together for the continental shelf numerous large moraines were discovered recording an extensive pattern of retreat stretching from sw ireland to the shetland isles from an integration of this new mapping of glacial geomorphology 26 000 landforms with previously published evidence compiled in the britice database we derive a pattern of retreat for the whole biis we review and compile relevant dates 881 examples that constrain the timing of retreat all data are held within a geographic information system gis and are deciphered to produce a best estimate of the combined pattern and timing of retreat pattern information reveals an ice sheet mainly comprised of a shelf parallel configuration from sw ireland to ne scotland but it spread far enough to the south to incorporate outlying ice domes over wales the lake district and kerry final disintegration was into a number of separate ice caps rather than reduction as a single mass and paradoxically retreat was not always back to high ground by 23 ka bp ice withdrew along its northern boundaries at the same time as the southern margins were expanding including transient ice streaming down the irish sea and advances of lobes in the cheshire basin vale of york and east coast of england ice divides migrated south by 19 ka the ice sheet was in crisis with widespread marine based ice losses particularly in the northern north sea and the irish sea considerable dynamic thinning occurred during this phase final collapse of all marine sectors occurred by 17 ka bp and with most margins beginning to back step onshore disintegration of the north sea ice bridge between britain and norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted the north channel and irish sea ice streams had finally cleaved the ice sheet into separate irish and scottish ice sheets by 16 ka bp rates of ice loss were found to vary widely over space and time e g 65 260 km3 per year the role of ice streams and calving losses of marine based sectors are examined retreat rates of up to ca 150 ma 1 were found for some ice stream margins that large parts 2 3 of the biis were marine based drained by ice streams and possibly with fringing ice shelves in places makes it a useful analogue for the west antarctic ice sheet wais this is especially so because the biis deglaciated in response to rising temperatures and a rising sea level driven by melting of other ice masses which are the current forcings that might cause collapse of the wais our reconstruction when viewed from the opposite perspective documents when fresh land became exposed for exploitation by plants animals and man and records for how long such land has been available for soil and geochemical development and ecological succession

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

are drumlins a product of a thermo mechanical instability abstract of numerous theories of drumlin genesis none has been widely accepted it seems evident however that some form of positive feedback process is involved under certain circumstances perturbations are amplified herein we suggest that patchy areas of frozen bed provide the initial perturbation such frozen patches may occur in local areas underlain by material of lower thermal conductivity or on slight topographic highs drag exerted by the frozen patch deflects ice flow into its lee dragging with it mobile till eroded from the thawed area the energy balance is such that this till likely refreezes either producing a topographic perturbation or amplifying an existing one the resulting topography then deflects more of the geothermal heat away from the developing hill and into the adjacent trough resulting in a positive feedback once the thermal perturbation exceeds a critical though as yet undefined level melting may decouple the ice from the bed preventing further entrainment of till from thawed areas and thus limiting the height and length of the drumlin

large scale sst variability in the western north atlantic subtropical convergence zone during fasinex part i description of sst and wind stress fields abstract we describe properties of large scale fluctuations in the wind field represented by two analyses fnoc and noaa atoll and in the sst field represented by maps derived from 5 day composite avhrr images within an 11 longitude by 10 latitude domain during fasinex january through june 1986 fnoc and atoll wind and wind stress time series were highly correlated with each other 0 8 over the entire domain and they were also highly correlated with time series measured at the fasinex site 0 89 at periods of 2 13 days clockwise energy exceeded anticlockwise energy by an order of magnitude while the energy was nearly partitioned equally at periods of 13 40 days mean atoll winds were everywhere more eastward than mean fnoc winds probably in part because the atoll fnoc analyses are intended to represent 850 mb 19 5 m winds the 850 mb winds are expected to be more eastward due to the thermal wind balance with the mean southward air temperature gradient the sst maps represented large s

sediment deformation beneath glaciers and its coupling to the subglacial hydraulic system abstract the extent and style of shear deformation in sediments beneath modern glaciers and the geological evidence for such deformation in deposited sediments are reviewed new evidence is presented from beneath a modern glacier of the spatial and temporal patterns of water pressure fluctuation and of time dependent patterns of deformation in sediments it is concluded that in most experimental sites beneath soft bedded modern glaciers deformation is a significant or major contributor to glacier movement and the resultant discharge of till is large enough to make sediment deformation a major till forming process particular modes of deformation facilitate incorporation of underlying material into the till whilst the capacity of a deforming till to absorb strain can protect the underlying strata from deformation leading to the commonly found relationship where till overlies other strata with a sharp planar interface it is argued that the almost ubiquitous occurrence of drumlins on the beds of former ice sheets is a reflection of the widespread occurrence of sediment deformation beneath them with important implications for the coupling of ice sheet flow and bed properties it is argued that the mechanical behaviour of the subglacial system is not simply determined by till properties but largely controlled by the subglacial water pressure regime determined by the nature of subglacial drainage results of field experiments show how the nature of the basal hydraulic system can play a vital role in controlling the coupling between the glacier and till deformation processes they show that rapid glacier advances can produce undrained loading of sediments that effective pressure may increase either upwards or downwards in a till according to the direction of drainage and that interstitial water pressures in subglacial sediments can show large and rapid variations producing strong variations in the rate and distribution of strain and in the partitioning of basal movement between sliding and deformation

subglacial landforms and deposits in central and northern quebec canada with emphasis on rogen moraines abstract the development of the anatomy and the morphology of a relatively simple till sheet deposited over parts of the canadian shield is discussed this is characterized by the common occurrence of well developed streamlined landforms and rogen moraines the sedimentation of the till sheet was an alternating succession of depositional and erosional or landforming events the former leading to the sedimentation of various till lithofacies the latter leading to the development of various morainic terrains this orderly sequence of subglacial events occurred during the deglaciation of central and northern quebec with the controlling factors being bed rock topography and geology ice thickness and basal ice temperatures till lithofacies include in ascending stratigraphic order lodgement till subglacial melt out till immature lodgement till and varieties of supra glacial ablation deposits morainic terrains include drumlinized and fluted ground moraine rogen moraines as well as fluted and unfluted hummocky moraine rogen moraines are formed subglacially a few kilometers behind the glacier margin as a consequence of localized compressive stresses which result in shearing and stacking of slices of near base englacial debris later deposited as a basal melt out till the moraines are believed to be a characteristic landform associated with shield type rock surfaces namely an irregular topography of asymmetric rock basins of all sizes resulting from the areal scouring of hard rocks as well the moraines are believed to be as well a characteristic landform resulting from the flattening profile of the margin of the waning ice sheet the formation of the moraines led to enhanced flow in marginal areas generating late events of streamlining and boulder plucking

mega scale glacial lineations and cross cutting ice flow landforms landsat images reveal a previously unsuspected large scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow such a glacial grain can be regarded as a landform assemblage comprised of a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain the ice moulded landform assemblage is described and illustrated with reference to examples from canada possible modes of genesis of such landforms are discussed and their glaciological implications outlined the discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment and demands a radical re interpretation of ice sheet dynamics

palaeoglaciology of the welsh sector of the british irish ice sheet this palaeoglaciological reconstruction based on the distribution of glacial lineations interpreted from satellite imagery considers the extent thickness and dynamics of the welsh ice cap and its interaction with the british irish ice sheet two major ice flow events were identified the oldest phase of ice flow event i is characterized by ice flowing from an ice dispersal centre situated over the higher terrain in north central wales and by ice thick enough to cover the mountain summits at this time the interior of the ice cap is inferred to have been dominated by cold based ice during the growth of the welsh ice cap it became confluent with the british irish ice sheet the welsh ice cap at this time was again sufficiently thick to submerge the highest mountain summits the youngest detected phase of ice flow event ii was marked by an abrupt change in the dynamics of the welsh ice cap during event ii the welsh ice cap was drained by at least four ice streams which followed major troughs in northern and eastern wales

the tekapo glacier new zealand during the last glacial maximum an active temperate glacier influenced by intermittent surge activity abstract quaternary glaciations have created impressive landform assemblages that can be used to understand palaeo glacier extent character and behaviour and hence past global and local glacier forcings however in the southern hemisphere and especially in new zealand the quaternary glacial landform record is relatively poorly investigated with regard to glaciological properties in this study a 1 m digital elevation model dem was generated from airborne lidar data and supplemented with aerial imagery and field observations to analyse the exceptionally well preserved glacial geomorphology surrounding lake tekapo new zealand we describe a rich suite of last glacial maximum lgm and recessional ice marginal subglacial supraglacial glaciofluvial and glaciolacustrine landform assemblages these represent two landsystems comprising i fluted till surfaces with low relief push moraine ridges and ii crevasse squeeze ridges zig zag eskers and attenuated lineations the former landsystem records the behaviour of an active temperate glacier and the latter landsystem which is superimposed upon and inset within the former strongly suggests intermittent surge phases the two landsystem signatures indicate a sequential change in ice marginal dynamics during recession that was likely to have been partially non climatically driven overall we present the first evidence of surge type glacier behaviour in new zealand

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

flow mechanism of glaciers on soft beds subhourly measurements of bed deformation bed shear strength subglacial water pressure and surface speed at storglaciaren a glacier in northern sweden showed that the shear strain rates of the bed decrease during periods of high water pressure and surface speed high water pressures appear to be accompanied by a reduction in the coupling of ice with the bed that is sufficient to reduce or eliminate shearing the instability of large ice masses may result from similar decoupling rather than from pervasive bed deformation as has been commonly thought

the palaeoglaciology of the central sector of the british and irish ice sheet reconciling glacial geomorphology and preliminary ice sheet modelling digital elevation models of the area around the solway lowlands reveal complex subglacial bedform imprints relating the central sector of the lgm british and irish ice sheet drumlin and lineation mapping in four case studies show that glacier flow directions switched significantly through time these are summarised in four major flow phases in the region phase i flow was from a dominant scottish dispersal centre which transported criffel granite erratics to the eden valley and forced lake district ice eastwards over the pennines at stainmore phase ii involved easterly flow of lake district and scottish ice through the tyne gap and stainmore gap with an ice divide located over the solway firth phase iii was a dominant westerly flow from upland dispersal centres into the solway lowlands and along the solway firth due to draw down of ice into the irish sea basin phase iv was characterised by unconstrained advance of scottish ice across the solway firth forcing of a numerical model of ice sheet inception and decay by the greenland ice core record facilitates an assessment of the potential for rapid ice flow directional switching during one glacial cycle the model indicates that after fluctuations of smaller radially flowing ice caps prior to 30 ka bp the ice sheet grows to produce an elongate triangular shaped dome over nw england and sw scotland at the lgm at 19 5 ka bp recession after 18 5 ka bp displays a complex pattern of significant ice flow directional switches over relatively short timescales complementing the geomorphologically based assessments of palaeo ice dynamics the palaeoglaciological implications of this combined geomorphic and modelling approach are that a the central sector of the biis was as a major dispersal centre for only ca 2 5 ka after the lgm b the ice sheet had no real steady state and comprised constantly migrating dispersal centres and ice divides c subglacial streamlining of flow sets was completed over short phases of fast flow activity with some flow reversals taking place in less than 300 years

glacial geomorphology and geographic information systems recent developments in the field of glacial geomorphology have dramatically increased the need to acquire maintain manipulate and analyze large amounts of landform landscape and sediment data the use of geographic information systems gis has provided new platforms and tools for analysis and visualization of geomorphic data glacial geomorphologists have used gis to integrate multi source data manage multi scale studies identify previously unrecognized spatial and temporal relationships and patterns in geomorphic data and to link landform data with numerical models as part of model calibration and verification gis based analyses associated with numerical modeling are improving our understanding of glacial landscape evolution and are allowing new quantitative and systematic examinations of spatial and temporal patterns of glacial landforms and processes this has allowed for the development of insights and concepts that would be unlikely to arise using traditional methods alone key recommendations for future research and applications in glacial geomorphology include enhanced gis education and dissemination the development of standards and conventions for glacial geomorphic data community projects to collect data into readily accessible databases and enhanced use of linked gis model frameworks to address major issues in glacial geomorphology