Deglaciation of the Cordillera of Western Canada at the end of the Pleistocene

J.J Clague

doi:10.18172/cig.3232

Abstract

Nearly all of what is now British Columbia and adjacent areas were covered by an ice sheet at the maximum of the Last Glaciation (MIS 2) about 18,000 years ago. By 11,000 years ago, the Cordilleran Ice Sheet had disappeared, a victim of warming climate, eustatic sea-level rise along its western margin, and perhaps a reduction in precipitation. Deglaciation proceeded by frontal retreat at the periphery of the ice sheet and by downwasting, complex frontal retreat, and localized stagnation in its interior areas. The chronology of deglaciation is constrained, albeit with inherent dating errors, by AMS radiocarbon and 10Be surface exposure ages. High-elevation sites at the western margin of the British Columbia Interior Plateau, east of the Coast Mountains, became ice-free between about 15,000 and 12,000 years ago. Ice cover in the southern Coast Mountains was sufficiently extensive during the Younger Dryas Chronozone (12,900-11,700 years ago) that glaciers advanced into low-lying areas north and east of Vancouver. At the same time, however, a labyrinth of dead or dying tongues of glacier ice covered some interior valleys. By 11,000 years ago, ice cover in the Canadian Cordillera was no more extensive than it is today.

Highlights

British Columbia is located within the mid-latitudes of the Northern Hemisphere adjacent to the North Pacific Ocean, which is the main moisture source for present and past glaciers in northwest North America
The Cordilleran Ice Sheet and its satellite glaciers covered almost all of British Columbia, as well as southern Yukon Territory, southern Alaska, and northern Washington, Idaho, and Montana (Fig. 1)
To the north, lobes of the Cordilleran Ice Sheet lying on the southern Yukon Plateau retreated towards mountain ranges to the east, south, and west, locally in contact with glacial lakes trapped in valleys

Summary

Introduction

British Columbia is located within the mid-latitudes of the Northern Hemisphere adjacent to the North Pacific Ocean, which is the main moisture source for present and past glaciers in northwest North America This mountainous region is dominated by northwest-trending ranges, rolling plateaus, and, on the west, by coastal lowlands. The Cordilleran Ice Sheet and its satellite glaciers covered almost all of British Columbia, as well as southern Yukon Territory, southern Alaska, and northern Washington, Idaho, and Montana (Fig. 1). Outlet glaciers of the ice sheet streamed down fjords and valleys in the coastal mountains of British Columbia and covered large areas of the Pacific continental shelf (Clague et al, 1982; Barrie and Conway, 1999), parts of which were subaerially exposed due to eustatically lowered sea levels of the Last Glaciation. An ice-free zone existed between Cordilleran glaciers and the Laurentide ice sheet to the east

Pattern of deglaciation

Chronology of deglaciation

Early retreat

The final demise of the ice sheet

Conclusion