DEGLACIAL STYLE, PATTERN AND TIMING OF THE CORDILLERAN ICE SHEET, SOUTH-CENTRAL INTERIOR BRITISH COLUMBIA (Invited Presentation)

The prevailing view of lateglacial Cordilleran Ice Sheet (CIS) decay over the interior plateaus of British Columbia is one of regional stagnation attributed to a rapid rise in equilibrium line altitude (ELA). However, a new conceptual model of lateglacial CIS decay has emerged from recent landform mapping and morphosedimentary classification across the northern Thompson and southern Fraser plateaus, facilitated by the availability of higher resolution topographic data, geophysical surveys and sedimentology at available exposures. Patterns of paleoglacial lake evolution and moraines suggest an active ice margin systematically retreating northwestward toward the Coast Mountains, consistent with the pattern of eskers, ice-marginal channels and reconstructed glacioisostatic tilt from paleolake shorelines. Lake-ice interactions likely enhanced ice margin dynamics and retreat, at least partially decoupling it from broader climate patterns. Ice margin retreat was accompanied by thinning recorded by the presence of nested ice-marginal channels and supraglacial eskers. A high ELA and lake-ice interactions enhanced melt rates allowing supraglacial lakes to form on the ice surface and drain through crevasses or moulins forming subglacial meltwater corridors and glacial lake outburst flood (GLOF) eskers. Pockets of localized stagnation, supported by the presence of hummocky terrain, crevasse-fill ridges and ice-walled canyon eskers, existed during regional retreat across the northern Thompson and southern Fraser plateaus. ¹⁰Be ages on granitic erratics deposited atop moraines suggest the region was deglaciated by ~14ka. This interpretation of the decay of the last CIS in the region is similar in style and pattern to that proposed for the last Fennoscandian Ice Sheet and is analogous to the decay of the Greenland Ice Sheet today.