Investigating the potential hazard, mechanisms of failure, and evolution of the Cascade Bay landslide

The Cascade Bay landslide is a large postglacial bedrock failure on the east side of Harrison Lake in southwestern British Columbia. It occurs in meta-sedimentary and meta-volcanic bedrock near the Harrison Lake Shear Zone (HLSZ), a large right-lateral strike-slip fault. Data derived from airborne LiDAR, terrestrial laser scanning, differential GPS, field observations, and laboratory techniques were analyzed for spatial relationships using GIS databases. The landslide boundaries appear to strike parallel to zones of damaged bedrock and secondary Riedel faults related to the HLSZ. A wedge-shaped failure forms the upper half of the landslide, while the lower failure zone probably daylights through a combination of low angle shear surfaces and intact rock fracture. Geomorphic mapping shows secondary debris failures extensively remobilized the primary landslide deposit. Differential GPS measurements and field observations show ongoing deformation in portions of the landslide deposit. Recent failures occur in fine-grained black colluvium with moderate plasticity.