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Topic

Last-Glacial Proglacial Lake Systems in the Canadian Cordillera with Hydraulic Modelling of the Largest Known Outburst Flood in British Columbia

Department of Geography

Date & location

• Thursday, August 7, 2025
• 10:00 A.M.
• David Turpin Building, Room B215

Examining Committee

Supervisory Committee

• Dr. Sophie Norris, Department of Geography, ßÉßɱ¬ÁÏ (Supervisor)
• Dr. John Clague, Department of Geography, UVic (Member)

External Examiner

• Dr. Brent Ward, Department of Earth Sciences, Simon Fraser University

Chair of Oral Examination

• Dr. Jon Willis, Department of Physics and Astronomy, UVic

Abstract

Climate change at the end of the Pleistocene caused the retreat of the Cordilleran Ice Sheet, generating vast quantities of meltwater in what is now British Columbia. This resulted in dozens of glacial lakes forming in valleys and topographic depressions across the region's newly exposed land. The largest of these lakes is thought to have been Glacial Lake Fraser, which at its maximum stage occupied ~7700 km² and stored ~520 km³ of water in the central area of the province. This lake drained catastrophically during an outburst flood into the Salish Sea between ~11.5-12.5 ka yrs BP. This thesis provides an overview of glacial lake formation in British Columbia during the last deglaciation, identifying outburst flood events and drainage pathways by synthesizing existing literature. It then focuses on the largest Glacial Lake Fraser outburst flood, which affected the Fraser valley. Flood deposits and erosional features, including ice-marginal meltwater channels, boulder fields, and giant gravel bars, were studied in the field and using bare-earth DEMs. The features were then used to calibrate multiple numerical models which quantified catastrophic drainage and contributed to a discussion of dam breach dynamics and spillway formation. The Glacial Lake Fraser outburst flood had a peak discharge of at least 500,000-800,000 m³s^-1 and incision of the ice dam was likely initiated by overtopping or the expansion of an englacial piping network; modelling results do not support a breach via subglacial tunnelling or a sudden collapse. Formation of the Fraser River spillway followed a gradual incision pattern, with outer channel scouring during the rising stage of the flood hydrograph followed by erosional concentration creating a deepened inner channel where giant gravel bars were deposited during peak discharge. During the waning stage of the flood, continued flow from the lake streamlined the gravel bars. This thesis shows the spatial extent of glacial lakes in British Columbia during the last deglaciation, and uses a case study to demonstrate the influence that glacial lakes and their associated outburst floods on regional landscapes.