Ice-marginal thrusting of drift and bedrock: thermal regime, subglacial aquifers, and glacial surges

Glacial thrust systems composed of blocks of drift and bedrock, associated with hummocky stagnation moraine along the margin of the Rainy lobe of the Laurentide Ice Sheet in Minnesota, are used in conjunction with paleoecological studies to constrain a numerical model of the ice-marginal thermal reg...

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Bibliographic Details
Published in:Canadian Journal of Earth Sciences
Main Author: Mooers, H. D.
Format: Article in Journal/Newspaper
Language:French
Published: Canadian Science Publishing 1990
Subjects:
Ice
Online Access:http://dx.doi.org/10.1139/e90-088
http://www.nrcresearchpress.com/doi/pdf/10.1139/e90-088
Description
Summary:Glacial thrust systems composed of blocks of drift and bedrock, associated with hummocky stagnation moraine along the margin of the Rainy lobe of the Laurentide Ice Sheet in Minnesota, are used in conjunction with paleoecological studies to constrain a numerical model of the ice-marginal thermal regime. Subglacial meltwater production in the thawed-bed zone was at least two orders of magnitude greater than the amount that could refreeze to the base of the glacier near the margin. The excess water recharged a thick subglacial aquifer, and thrust-system development was enhanced by the presence of a frozen toe and high pore-water pressures beneath the outer 2 km the glacier. The pore-water pressure required for thrusting is calculated from overburden pressures and basal shear stresses determined by numerical modeling. The heat generated by flow of water through the subglacial aquifer substantially affects the ice-marginal thermal regime, making a steady-state frozen toe 1.0–2.0 km in width unstable. Thrusting apparently occurred during multiple oscillations, or surges, when the ice was advancing over permafrost.