Abstract

Late Wisconsinan Fraser Glaciation retreat-phase deposits and landforms in the east-central Taseko Lakes area, British Columbia, are used to demonstrate a four-phase model of deglaciation. During phase I, at the onset of ice retreat, the Cordilleran Ice Sheet occupied much of the study area, blocking southward drainage of Fraser River. Phase II was marked by the deglaciation of uplands and plateaux. Meltwater drainage patterns were controlled by stagnating glaciers confined to valleys. Phase III commenced as remnant ice in the Fraser Valley downwasted to between 850 and 760 m elevation. At this time, interlobate glacial lakes formed in hanging valleys east of Fraser River. Drainage of glacial lakes occurred subglacially, and was accompanied by disintegration of remnant ice and an increase in mass movements in valleys. These events were followed by decreased sedimentation rates, reflecting lower meltwater volumes and exhaustion of unstable glacial debris during phase IV. Postglaciation valley fill was subject to fluvial degradation and terracing as modern drainage patterns became established.

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