Downstream Geomorphic Response of the 2014 Mount Polley Tailings Dam Failure, British Columbia

On August 4, 2014, the failure of the Tailings Storage Facility dam at the Mount Polley copper and gold mine in British Columbia (Canada) produced a dynamic and complex geomorphic response downstream. The dam breach was caused by rotational sliding of the embankment due to foundation failure, resulting in sudden loss of containment of water and tailings. The released volume was estimated to be 25 Mm³. The resulting flow traveled approximately 9 km down the Hazeltine Creek valley over a vertical elevation of 205 m. The August 2014 event is the largest tailings dam failure recorded in Canada and the second largest recorded globally in the last decade. This investigation documents and analyzes the general downstream geomorphic response of the event in the Hazeltine Creek channel and floodplain. It utilizes an integrated approach of geomorphological mapping, topographic analysis, historical aerial photograph analysis, and field surveys to identify and quantify the geomorphic impacts of the event. Overall results indicate that these impacts are significant and comparable to those resulting from extreme debris flow and outburst flood events in mountainous environments in Canada and worldwide.