Abstract

Evidence of late Wisconsin subglacial megafloods includes fields of giant flutings, drumlins, tunnel channels, and scoured bedrock tracts. Scoured tracts are marked by channeled scabland, water-eroded depressions (s forms), and postglacial development of solonetzic (saline clay pan) soils on Cretaceous bedrock. Belts of hummocky terrain and small zones of moraine plateaus are remnants left by incomplete sheet-flood erosion of initial subglacial sediment later modified by ice pressing. Among multiple subglacial discharges, the largest was the Livingstone Lake event, which transmitted Laurentide water from the Northwest Territories and northern Saskatchewan through Alberta to Montana and the Mississippi drainage. This flood was augmented by Cordilleran water relayed under valley glacier piedmonts coalescent with south-western Laurentide ice. The short-duration megaflood probably occurred within the longer time interval of ∼18-15 ka.

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