Abstract
A bathymetric survey of Harrison Lake in southwest British Columbia revealed deposits of three large landslides on the lake floor. The blocky and flow-like surface morphology of the deposits suggests rapid emplacement from subaerial sources. The multibeam survey, together with a subbottom acoustic survey, allowed us to estimate deposit volumes of 2.4 Mm3, 1.3 Mm3, and 0.2 Mm3 for the Mount Douglas, Mount Breakenridge, and Silver Mountain landslides, respectively. The large volumes and inferred rapid emplacement of the Mount Douglas and Mount Breakenridge landslides suggest they were tsunamigenic. Because people live along the shoreline of Harrison Lake, our discovery and characterization of these landslide deposits and their tsunami-generating potential form an important foundation for further landslide-tsunami hazard analysis in the region.
Highlights
Fjord coastlines, notably those in Canada, Alaska, Greenland, Norway, Chile, and New Zealand, are vulnerable to landslidegenerated waves (Roberts et al 2014; Gauthier et al 2018; Higman et al 2018)
Given the apparent increase in large landslides in British Columbia (BC) in recent years, due in part to loss of glacier ice and permafrost thaw (Geertsema et al 2006; Cloutier et al 2016; Coe et al 2018; Hibert et al 2019), the potential exists for more frequent tsunamigenic landslides in the future (Roberts et al 2014; Higman et al 2018)
We document evidence of three previously unreported landslide deposits in Harrison Lake, southwestern BC (Fig. 1), that we discovered during a bathymetric survey of the lake in 2017 and 2018
Summary
Notably those in Canada, Alaska, Greenland, Norway, Chile, and New Zealand, are vulnerable to landslidegenerated waves (Roberts et al 2014; Gauthier et al 2018; Higman et al 2018). Landslide-generated waves can be much larger than earthquake-triggered tsunamis, at least near their sources (Tappin et al 2001; Graziani et al 2006; Omira et al 2019) and are common worldwide (Roberts et al 2014). In 2007, a 3 Mm3 rockslide entered Chehalis Lake, 80 km east of Vancouver, British Columbia, generating a displacement wave that reached up to 38 m above the lakeshore and ran down the 8-km length of the lake (Brideau et al 2012; Roberts et al 2013). Given the apparent increase in large landslides in British Columbia (BC) in recent years, due in part to loss of glacier ice and permafrost thaw (Geertsema et al 2006; Cloutier et al 2016; Coe et al 2018; Hibert et al 2019), the potential exists for more frequent tsunamigenic landslides in the future (Roberts et al 2014; Higman et al 2018)
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