THE GEOLOGY AND EVOLUTION OF THE BRENOT CREEK LANDSLIDE

The Brenot Creek landslide in northeastern British Columbia, Canada, reactivated in September 2014, impacting water quality downstream. The landslide is located within the Peace River lowland, a broad undulating plain with deeply incised stream-cut valleys. Landslides are ubiquitous on valley walls, as valley downcutting has de-buttressed and undercut valley slopes, promoting bedrock and surficial instability, particularly in areas of buried valleys where Quaternary deposits are the thickest. The Quaternary deposits reflect a glacial history of multiple Cordilleran sourced glaciers from the west and the Laurentide Ice Sheet from the east. Regionally, deep-seated landslides in glaciolacustrine sediments tend to undergo episodic movements, with only a few examples of rapid long runout flows. The Brenot Creek landslide is one such unusual example. After a relatively long dormancy, it reactivated with successive, extremely rapid, mobile flows. Groundwater fluctuations seem to be driving retrogression through saturation, piping and main scarp collapse, which leads to occasional rapid mobilization of saturated materials. Since 2014 the landslide has retrogressed approximately 120 m contributing over 500,000 m³ of sediment into Brenot Creek causing elevated heavy metal concentrations. The main scarp is nearly 60 m tall, with fresh, vertically and laterally extensive exposure of Late Pleistocene glacial sediments, much of which is a silty sand glaciolacustrine deposit. Stratigraphic evidence supports refinements to the understanding of the regional glacial history and provides a basis for understanding the unusual landslide. This presentation will summarize the geology and the evolution the Brenot Creek landslide.