Authors: STOKES, CHRIS R.¹; CLARK, CHRIS D.²

Source: Boreas, Volume 32, Number 1, 1 March 2003 , pp. 263-279(17)

Publisher: Wiley-Blackwell

Abstract:

We report evidence for a major ice stream that operated over the northwestern Canadian Shield in the Keewatin Sector of the Laurentide Ice Sheet during the last deglaciation 9000-8200 (uncalibrated) yr BP. It is reconstructed at 450 km in length, 140 km in width, and had an estimated catchment area of 190000 km². Mapping from satellite imagery reveals a suite of bedforms (`flow-set') characterized by a highly convergent onset zone, abrupt lateral margins, and where flow was presumed to have been fastest, a remarkably coherent pattern of mega-scale glacial lineations with lengths approaching 13 km and elongation ratios in excess of 40:1. Spatial variations in bedform elongation within the flow-set match the expected velocity field of a terrestrial ice stream. The flow pattern does not appear to be steered by topography and its location on the hard bedrock of the Canadian Shield is surprising. A soft sedimentary basin may have influenced ice-stream activity by lubricating the bed over the downstream crystalline bedrock, but it is unlikely that it operated over a pervasively deforming till layer. The location of the ice stream challenges the view that they only arise in deep bedrock troughs or over thick deposits of `soft' fine-grained sediments. We speculate that fast ice flow may have been triggered when a steep ice sheet surface gradient with high driving stresses contacted a proglacial lake. An increase in velocity through calving could have propagated fast ice flow upstream (in the vicinity of the Keewatin Ice Divide) through a series of thermomechanical feedback mechanisms. It exerted a considerable impact on the Laurentide Ice Sheet, forcing the demise of one of the last major ice centres.

Document Type: Original article

DOI: http://dx.doi.org/10.1111/j.1502-3885.2003.tb01442.x

Affiliations: 1: ), Landscape and Landform Research Group, Department of Geography, University of Reading, Reading, RG6 6AB, UK 2: ), Department of Geography, and Sheffield Centre for Earth Observation Science, University of Sheffield, Sheffield, S10 2TN, UK

Publication date: 2003-03-01

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