GLACIATION OF THE CONTINENTAL SHELF OF THE PACIFIC NORTHWEST

Glaciation affected the Pacific margin of Canada many times, although evidence has only been found offshore for the Fraser Glaciation. As ice moved offshore from the Coast Mountains of the Canadian Cordillera it only covered portions of the continental shelf with different timings, depending on region. Within the Salish Sea ice reached its maximum extent at 17 ka BP and covered all marine areas out to the continental shelfbreak on southern Vancouver Island shelf. However, most of the continental shelf of western Vancouver Island north of Barkley Sound was ice free. On the Pacific North Coast ice extended westward across northern Hecate Strait and through Dixon Entrance and coalesced with ice from Haida Gwaii. An ice stream moved south down the central trough in Hecate Strait and coalesced with ice from moving out to the continental shelf from the British Columbia mainland and northern Vancouver Island, reaching its maximum extent by sometime after 21 ka BP. There is no evidence of glacial refugia within any of these inshore waters. The narrow shelf off western Haida Gwaii was ice free, as well as large shelf areas of southeastern Alaska. Deglaciation of the Pacific North Coast was rapid with an eastward retreating ice shelf leaving the marine areas ice free by 13.5 ka BP, while the Salish Sea was ice free by 11.3 ka BP with rapid downwasting and widespread stagnation. Resulting sea level change is complex and heterogeneous. On the continental shelf changing sediment supply resulted in the formation of large deltas, outwash plains, wave-cut terraces with 30 to 50 m of relief, and spit platforms that were all subsequently drowned with rising sea level. The un-glaciated regions of the continental shelf and the extensive coastal plains that emerged during deglaciation may have provided suitable habitat for early human migration.