DEGLACIATION OF THE NICOLA BASIN, SOUTHERN BC: A WINDOW INTO THE DEGLACIAL STYLE AND PATTERN OF THE LAST CORDILLERAN ICE SHEET NEAR ITS GEOGRAPHIC CENTRE

The established presence of paleo-glacial lakes in many of the valleys of southern British Columbia, and the apparent paucity of large recessional moraines has supported a paradigm of stagnation (downwasting) of the Cordilleran Ice Sheet on the interior Plateau during deglaciation from the Fraser Glacial maximum, with the lakes dammed by stagnant ice in valleys dissecting the Plateau. Previous lake reconstructions in the Nicola basin have identified four stillstands which have been used to support a stagnating ice margin: glacial lakes Quilchena, Hamilton 1 and 2, and Merritt. A reinvestigation of the basin has revealed an extensive area of ice flow-transverse ridges trending northeast to southwest. Sediment logging and electrical resistivity tomography within these ridges supports their interpretation as a series of glacitectonic moraines, here named the Chapperon Lake moraines. Ground Penetrating Radar studies on deltas and wave cut benches around the basin have reconstructed an additional paleolake (glacial Lake Spaxomin) and stillstands in the Upper Nicola Valley. These new lake reconstructions are explained by the northwestward recession of a contiguous ice margin, with the Chapperon Lake moraines implying active retreat. The deglacial history presented therefore locally disputes the accepted model of a stagnating Cordilleran Ice Sheet. Further work will seek to reconstruct potential glacial lake outburst floods from these lakes and to provide a deglacial chronology using OSL and TCN dating.