Glaciation of the northern British Columbia continental shelf: the geomorphic evidence derived from multibeam bathymetric data

We describe a revised understanding of the extent and dynamics of the Cordilleran Ice Sheet on the continental shelf of northern British Columbia, Canada. During the Local Last Glacial Maximum ice streams occupied two of the three shelf-crossing troughs in Queen Charlotte Sound (Goose Island Trough and Mitchell's Trough). A 25-km-wide outlet glacier - the Hecate Glacier - flowed south in Hecate Strait, parallel to the modern coast. It reached a grounding line at the head of Moresby Trough, beyond which an ice shelf may have extended to the edge of the continental shelf. The southern part of the independent Haida Gwaii Ice Cap formed piedmont lobes dissected by tunnel valleys. An emergent area east of the ice cap corresponds with the 'Hecate Refugium'. Subsequently grounded ice retreated from the shelf troughs. The Hecate Glacier retreated incrementally towards the north. Mainland ice then stabilized along a north-south margin near modern coasts, marked by submarine moraines in the Chatham Sound region and elsewhere. This margin was probably contemporaneous with the margin at Mt. Buxton in the south of the study area, dated at c. 17.6 to 16.6 ka (Darvill et al. 2018). Off southern Haida Gwaii, following a retreat, a glacier margin was established east of Juan Perez Sound, proximal to a sandur plain graded to a water level of -150 m. Proglacial lakes to the north of here were the likely source for an outburst flood that created gravel bedforms and an area of sea-floor scour. In a final phase, diminished mainland ice was confined to fjords, and retreat inland is marked by a succession of submarine moraines, beginning with a moraine at the Douglas Channel sill. The study has implications for the migration pathways for human migration into the Americas following deglaciation.