Late-glacial lakes in the Thompson Basin, British Columbia: paleogeography and evolution

Abstract

During the decay of the Cordilleran Ice Sheet 10 000 – 13 000 BP, glacial lakes developed within valleys that dissect the Interior Plateau of British Columbia. In this paper, we (1) illustrate a procedure for assessing paleo water planes that has general application, (2) document lake paleogeography and evolution in the Thompson Valley, (3) provide new data on the glacio-isostatic response of the central Cordillera, and (4) present new evidence of its late-glacial environment. We employ geomorphology and sedimentology, digital elevation models, and new technologies (differential global positioning systems, ground penetrating radar, and geographic information systems) to refine paleogeographic reconstructions of glacial lakes. Glacial Lake Thompson and Glacial Lake Deadman were ribbon-shaped (width to length ratio ≈ 3:100), deep (>>140 to ~50 m) lakes that contained significant water volumes (84–24 km3). They lengthened to the west and their water level lowered as ice decayed. Final ice dam failure resulted in an ~20 km3jökulhlaup that eroded bedforms and deposited flood eddy bars within the lake basin, travelled ~250 km along the Fraser River system, and may have deposited exotic mud offshore between 10 190 and 11 940 BP. Glacio-isostatic tilts of water planes are among the highest in the world (1.7–1.8 m km–1). Their orientations suggest that ice sheet loads were greater or longer- lived to the north-northwest of the study area, lending support to the notion of an ice divide centred on the Fraser Plateau.