scholarly journals Objective Reconstructions of the Late Wisconsinan Laurentide Ice Sheet and the Significance of Deformable Beds

2007 ◽  
Vol 39 (3) ◽  
pp. 229-238 ◽  
Author(s):  
D. A. Fisher ◽  
N. Reeh ◽  
K. Langley
Keyword(s):  
Yield Stress ◽  
Flow Direction ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Hudson Bay ◽  
Ice Streams ◽  
Ice Flow ◽  
Surface Slopes ◽  
Late Wisconsinan

ABSTRACT A three dimensional steady state plastic ice model; the present surface topography (on a 50 km grid); a recent concensus of the Late Wisconsinan maximum margin (PREST, 1984); and a simple map of ice yield stress are used to model the Laurentide Ice Sheet. A multi-domed, asymmetric reconstruction is computed without prior assumptions about flow lines. The effects of possible deforming beds are modelled by using the very low yield stress values suggested by MATHEWS (1974). Because of low yield stress (deforming beds) the model generates thin ice on the Prairies, Great Lakes area and, in one case, over Hudson Bay. Introduction of low yield stress (deformabie) regions also produces low surface slopes and abrupt ice flow direction changes. In certain circumstances large ice streams are generated along the boundaries between normal yield stress (non-deformable beds) and low yield stress ice (deformabie beds). Computer models are discussed in reference to the geologically-based reconstructions of SHILTS (1980) and DYKE ef al. (1982).

scholarly journals First recognition of a Laurentide Ice Stream : Robert Bell on Hudson Strait

2010 ◽  
Vol 61 (2-3) ◽  
pp. 211-215 ◽  
Author(s):  
Ian A. Brookes
Keyword(s):  
Ice Sheet ◽  
Late Glacial ◽  
Laurentide Ice Sheet ◽  
Hudson Bay ◽  
Baffin Island ◽  
Ice Streams ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Ice Stream ◽  
Late Wisconsinan

Abstract In papers published in 1895 and 1901, and in undated notes for a 1907 paper he did not deliver or publish, Robert Bell of the Geological Survey of Canada interpreted the pattern of glacial striae, stossing of rock knobs, and surficial sediment composition along the margins of Hudson Strait, between Labrador, Ungava Bay and Baffin Island, as evidence of what he called an ice-stream, a long river-like glacier, fed from Hudson Bay and Foxe Basin, that had moved eastward along the Strait during the Late Glacial period. This was the earliest mention of such a glaciological feature within the Laurentide Ice Sheet (LIS). It was not until ice-streams were recognized in the West Antarctic Ice Sheet in the 1970’s that Bell’s concept was revived in the next decade and subsequently, in recognition of several ice-streams within the Late Wisconsinan LIS.

scholarly journals PISM-LakeCC: Implementing an adaptive proglacial lake boundary into an ice sheet model

2020 ◽  
Author(s):  
Sebastian Hinck ◽  
Evan J. Gowan ◽  
Xu Zhang ◽  
Gerrit Lohmann
Keyword(s):  
Boundary Conditions ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Hudson Bay ◽  
Ice Streams ◽  
Ice Flow ◽  
Glacial Retreat ◽  
Proglacial Lakes ◽  
Lake Model ◽  
Ice Sheet Dynamics

Abstract. Geological records show that vast proglacial lakes existed along the land terminating margins of palaeo ice sheets in Europe and North America. Proglacial lakes impact ice sheet dynamics by imposing marine-like boundary conditions at the ice margin. These lacustrine boundary conditions include changes in the ice sheet’s geometry, stress balance and frontal ablation and therefore affect the entire ice sheet’s mass balance. This interaction, however, has not been rigorously implemented in ice sheet models. In this study, the implementation of an adaptive lake boundary into the Parallel Ice Sheet Model (PISM) is described and applied to the glacial retreat of the Laurentide Ice Sheet (LIS). The results show that the presence of proglacial lakes locally enhances the ice flow. Along the continental ice margin, ice streams and ice lobes can be observed. Lacustrine terminating ice streams cause immense thinning of the ice sheet’s interior and thus play a significant role in the demise of the LIS. Due to the presence of lakes, a process similar to the marine ice sheet instability causes the collapse of the ice saddle over Hudson Bay, which blocked drainage via the Hudson Strait. In control experiments without a lake model, Hudson Bay is still glaciated at the end of the simulation. Future studies should target the development of parametrizations that better describe the glacial-lacustrine interactions.

Ice-flow patterns and glacial transport in the eastern Hudson Bay region: implications for the late Quaternary dynamics of the Laurentide Ice Sheet

1995 ◽  
Vol 32 (12) ◽  
pp. 2057-2070 ◽  
Author(s):  
Michel Parent ◽  
Serge J. Paradis ◽  
Éric Boisvert
Keyword(s):  
Compositional Data ◽  
Late Quaternary ◽  
Regional Distribution ◽  
Ice Sheet ◽  
Glacial Maximum ◽  
Laurentide Ice Sheet ◽  
Hudson Bay ◽  
Ice Flow ◽  
Flow Phase ◽  
Late Wisconsinan

Recent field surveys in the eastern Hudson Bay region have led to the discovery of regional ice-flow sequences that require a significant reassessment of the late Quaternary dynamics of the Laurentide Ice Sheet. Two regional ice-flow phases can be recognized from till compositional data and from crosscutting relationships observed on striated bedrock surfaces: the oldest is directed toward the northwest and north-northwest, while the youngest is directed toward the west and includes a late-glacial deflection toward the southwest. The wide regional distribution of striae formed during the early northwestward glacial movement together with the recognition of palimpsest glacial dispersal trains associated with this phase suggest that it was a long-lived, time-transgressive regional event. The ensuing glacial movement is a regionally dominant westward ice-flow phase during which several large glacial dispersal trains were formed downglacier from distinctive bedrock sources. The largest of these trains extends westward over a distance of 120 km from Lac à l'Eau Claire to Hudson Bay. Regional glacial transport data as well as glacial and deglacial landforms indicate that this was a long-lived glacial phase, likely lasting throughout the Late Wisconsinan glacial maximum and until déglaciation about 8000 BP. The erosional and depositional record of the northwestward ice-flow event is quite comparable to that of the ensuing glacial phase, and it is thus thought to represent the Early Wisconsinan glacial maximum. In view of the large regional extent of the northwestward ice-flow phase, it must postdate the early buildup of the ice sheet. Along the southeastern Hudson Bay coast, the Late Wisconsinan westward glacial movement was followed by a southwestward deflection that was likely caused by glacial streaming prior to 8000 BP in James Bay, in response to calving and surging into Glacial Lake Ojibway.

scholarly journals Thermomechanical modelling of the Scandinavian ice sheet: implications for ice-stream formation

1999 ◽  
Vol 28 ◽  
pp. 83-89 ◽  
Author(s):  
A. J. Payne ◽  
D.J. Baldwin
Keyword(s):  
Three Dimensional ◽  
Ice Sheet ◽  
Ice Streams ◽  
Ice Flow ◽  
Low Viscosity ◽  
Ice Stream ◽  
Scandinavian Ice Sheet ◽  
The Baltic ◽  
Stream Formation ◽  
Initial Results

AbstractThis work attempts to explain the fan-like landform assemblages observed in satellite images of the area covered by the former Scandinavian ice sheet (SIS). These assemblages have been interpreted as evidence of large ice streams within the SIS. If this interpretation is correct, then it calls into doubt current theories on the formation of ice streams. These theories regard soft sediment and topographic troughs as being the key determinants of ice-stream location. Neither can be used to explain the existence of ice streams on the flat, hard-rock area of the Baltic Shield. Initial results from a three-dimensional, thermomechanical ice-sheet model indicate that interactions between ice flow, form and temperature can create patterns similar to those mentioned above. The model uses a realistic, 20 km resolution gridded topography and a simple parameterization of accumulation and ablation. It produces patterns of maximum ice-sheet extent, which are similar to those reconstructed from the area’s glacial geomorphology. Flow in the maximum, equilibrium ice sheet is dominated by wedges of warm, low-viscosity, fast-flowing ice. These are separated by areas of cold, slow-flowing ice. This patterning appears to develop spontaneously as the modelled ice sheet grows.

scholarly journals The Dynamics of Ice-Sheet Outlets

1985 ◽  
Vol 31 (108) ◽  
pp. 99-107 ◽  
Author(s):  
N. F. Mcintyre
Keyword(s):  
Landsat Imagery ◽  
Ice Sheet ◽  
Ice Streams ◽  
Ice Flow ◽  
Ice Shelves ◽  
Surface Slopes ◽  
Basal Sliding ◽  
Subglacial Topography ◽  
Flow Through ◽  
Pressure Melting

AbstractA comparison of data from aircraft altimetry, Landsat imagery, and radia echo-sounding has shown characteristic surface topographies associated with sheet and stream flow. The transition between the two is abrupt and occurs at a step in the subglacial topography. This marks the onset of basal sliding and high velocities caused by subglacial water; it results in crevassed amphitheatre-like basins round the head of outlet glaciers. It is also the zone of maximum driving stress beyond which values decline rapidly as velocities increase. This abrupt transition appears to be topographically controlled since basal temperatures are at the pressure-melting point well inland of the change in regime. The Marie Byrd Land ice streams exhibit qualitative differences from other ice-sheet outlets, however; the change to lower driving stresses is much more gradual and occurs several hundred kilometres inland. Such ice streams have particularly low surface slopes and appear in form and flow regime to resemble confined ice shelves rather than grounded ice. The repeated association of the transition to rapid sliding with a distinct subglacial feature implies a stabilizing effect on discharge through outlet glaciers. Acceleration of the ice is pinned to a subglacial step and propagation of high velocities inland of this feature seems improbable. Rapid ice flow through subglacial trenches may also ensure a relatively permanent trough through accentuation of the feature by erosion. This is concentrated towards the heads of outlet glaciers up-stream of the region where significant basal decoupling occurs. This may be a mechanism for the overdeepening of fjords at their inland ends and the development of very steep fjord headwalls.

scholarly journals Ice Streams of the Laurentide Ice Sheet

2006 ◽  
Vol 58 (2-3) ◽  
pp. 269-280 ◽  
Author(s):  
Monica C.M. Winsborrow ◽  
Chris D. Clark ◽  
Chris R. Stokes
Keyword(s):  
Aerial Photography ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Major Influence ◽  
Ice Streams ◽  
Spatial Organisation ◽  
Ice Flow ◽  
Strength Of Evidence ◽  
Fast Ice ◽  
The Stability

Abstract Ice streams had a major influence on the configuration and the stability of the Laurentide Ice Sheet. Their identification is crucial for an understanding of ice sheet behaviour and their importance is reflected by the recent increase in paleo-ice stream research. This paper provides a synopsis of Laurentide paleo-ice streams, compiled from published sources and our mapping from satellite imagery and aerial photography. In total, 49 hypothesised ice streams are reviewed, and categorised according to the strength of evidence for streaming and knowledge of their extent. A map of Laurentide paleo-ice streams is presented, along with tables documenting the nature of evidence on which streaming behaviour has been invoked. The distribution of ice streams demonstrates the spatial organisation of fast ice flow, and overlapping imprints document major changes in ice flow during retreat. We note that Laurentide paleo-ice streams exhibit a much greater range in size than those currently operating in Antarctica.

Coalescence of late Wisconsinan Cordilleran and Laurentide ice sheets east of the Rocky Mountain Foothills in the Dawson Creek region, northeast British Columbia, Canada

2016 ◽  
Vol 85 (3) ◽  
pp. 409-429 ◽  
Author(s):  
Adrian Scott Hickin ◽  
Olav B. Lian ◽  
Victor M. Levson
Keyword(s):  
British Columbia ◽  
Flow Direction ◽  
Ice Sheet ◽  
Rocky Mountain ◽  
Ice Flow ◽  
Oxygen Isotope Stage ◽  
Digital Elevation ◽  
Late Wisconsinan ◽  
Cordilleran Ice Sheet ◽  
River Valleys

Geomorphic, stratigraphic and geochronological evidence from northeast British Columbia (Canada) indicates that, during the late Wisconsinan (approximately equivalent to marine oxygen isotope stage [MIS] 2), a major lobe of western-sourced ice coalesced with the northeastern-sourced Laurentide Ice Sheet (LIS). High-resolution digital elevation models reveal a continuous 75 km-long field of streamlined landforms that indicate the ice flow direction of a major northeast-flowing lobe of the Cordilleran Ice Sheet (CIS) or a montane glacier (>200 km wide) was deflected to a north-northwest trajectory as it coalesced with the retreating LIS. The streamlined landforms are composed of till containing clasts of eastern provenance that imply that the LIS reached its maximum extent before the western-sourced ice flow crossed the area. Since the LIS only reached this region in the late Wisconsinan, the CIS/montane ice responsible for the streamlined landforms must have occupied the area after the LIS withdrew. Stratigraphy from the Murray and Pine river valleys supports a late Wisconsinan age for the surface landforms and records two glacial events separated by a non-glacial interval that was dated to be of middle Wisconsinan (MIS 3) age.

scholarly journals Laurentide Ice-Flow Patterns: A Historical Review, and Implications of the Dispersal of Belcher Islands Erratics

2007 ◽  
Vol 44 (2) ◽  
pp. 113-136 ◽  
Author(s):  
Victor K. Prest
Keyword(s):  
Ice Sheet ◽  
Historical Review ◽  
Flow Patterns ◽  
The Arctic ◽  
Laurentide Ice Sheet ◽  
Complex Nature ◽  
Hudson Bay ◽  
Ice Flow ◽  
Flow Models ◽  
The North

ABSTRACTThis paper deals with the evolution of ideas concerning the configuration of flow patterns of the great inland ice sheets east of the Cordillera. The interpretations of overall extent of Laurentide ice have changed little in a century (except in the Arctic) but the manner of growth, centres of outflow, and ice-flow patterns, remain somewhat controversial. Present geological data however, clearly favour the notion of multiple centres of ice flow. The first map of the extent of the North American ice cover was published in 1881. A multi-domed concept of the ice sheet was illustrated in an 1894 sketch-map of radial flow from dispersal areas east and west of Hudson Bay. The first large format glacial map of North America was published in 1913. The binary concept of the ice sheet was in vogue until 1943 when a single centre in Hudson Bay was proposed, based on the westward growth of ice from Labrador/Québec. This Hudson dome concept persisted but was not illustrated until 1977. By this time it was evident from dispersal studies that the single dome concept was not viable. Dispersal studies clearly indicate long-continued westward ice flow from Québec into and across southern Hudson Bay, as well as eastward flow from Keewatin into the northern part of the bay. Computer-type modelling of the Laurentide ice sheet(s) further indicates their complex nature. The distribution of two indicator erratics from the Proterozoicage Belcher Island Fold Belt Group help constrain ice flow models. These erratics have been dispersed widely to the west, southwest and south by the Labrador Sector of more than one Laurentide ice sheet. They are abundant across the Paleozoic terrain of the Hudson-James Bay lowland, but decrease in abundance across the adjoining Archean upland. Similar erratics are common in northern Manitoba in the zone of confluence between Labrador and Keewatin Sector ice. Scattered occurences across the Prairies occur within the realm of south-flowing Keewatin ice. As these erratics are not known, and presumably not present, in Keewatin, they indicate redirection and deposition by Keewatin ice following one or more older advances of Labrador ice. The distribution of indicator erratics thus test our concepts of ice sheet growth.

Drift carbonate on the Canadian Shield. II: Carbonate dispersal and ice-flow patterns in northern Manitoba

1988 ◽  
Vol 25 (5) ◽  
pp. 783-787 ◽  
Author(s):  
L. A. Dredge
Keyword(s):  
Acid Rain ◽  
Ice Sheet ◽  
Flow Patterns ◽  
Canadian Shield ◽  
Lake Acidification ◽  
Laurentide Ice Sheet ◽  
Ice Streams ◽  
Dispersal Pattern ◽  
Ice Flow ◽  
Natural Lake

In northern Manitoba, carbonates were glacially dispersed westwards for distances up to 260 km beyond the limit of carbonate bedrock. The dispersal pattern in the surface till reflects the interaction of Keewatin and Hudson – Labrador ice in the region during the Wisconsin glaciation and suggests the presence of ice streams within the Laurentide Ice Sheet. Pre-Wisconsinan tills show different dispersal and ice-flow patterns. In unfrozen terrain, carbonate till sheets on the Shield buffer the effects of natural lake acidification and acid rain; however, their ability to buffer appears to be severely limited in permafrost terrain.

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