The pattern and style of deglaciation of the northern Thompson Plateau, southern British Columbia

Deglaciation of the last Cordilleran Ice Sheet (CIS) remains under-researched compared to coeval ice sheets, limiting it as an analogue for modern ice sheets. The northern Thompson Plateau, a moderate relief region in south-central British Columbia (BC), is the type area for a model of downwasting of the ice sheet into stagnant tongues occupying valley floors, which dammed a series of lakes. Downwasting has been applied to the deglaciation of the CIS broadly, though this has been weakened by recent studies elsewhere in interior BC that reconstruct active recession of a contiguous margin. This thesis presents a reinvestigation of deglaciation of the northern Thompson Plateau. New remote mapping, ground-truthed using exposure sedimentology and shallow geophysical surveys, reveals abundant recessional landforms. Newly identified moraine ridges are composed of northwest-dipping beds of till and sorted glacigenic sediment recording their formation as push and de Geer moraines, deposited by active ice receding to the northwest. The evolution of glacial Lake Nicola (gLN) is refined, with at least five stages showing expansion to the north-northwest interpreted as the recession of a contiguous margin. Improved constraints on glacioisostatic tilt of reconstructed lake planes of 1.6 to 2.3 m/km to the north-northwest, place the centre of CIS loading on the Fraser Plateau. These tilts reduce from the highest to lowest lake plane, recording rapid glacioisostatic rebound. Meltwater channels record ice recession onto plateau surfaces, confirmed by the pattern of glaciofluvial sedimentation into gLN from meltwater sources on the plateau. Subaqueous outwash fans and glaciotectonised grounding line moraines also record active recession within gLN, and their locations within the basin indicate the bathymetry, geometry and evolution of gLN exerted a significant control on ice recession. The largest lake stage released a flood of between 1 and 3 x 106 m3s-1, estimated using several consilient numerical modelling techniques and clearly evidenced by a large spillway channel, coarse boulder bars and high energy sand and gravel. Tentative deglacial ages of around 13.6 ka BP are determined from 10Be dating of granodiorite erratics. This reinvestigation of the northern Thompson Plateau encourages rejection of a downwasting, lingulate ice margin in favour of an active margin receding to the north-northwest. The application of a downwasting model to the whole CIS is discouraged.