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 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. -from Author