Rock slope movements in the Canadian Cordillera

Abstract

Some recent work on natural rock slope movements in the Cordillera is reviewed. Climate, geology, and seismicity combine to produce rockslides in the Mackenzies and Rockies; slower, more complex bedrock flows in the Omineca Belt; spreads and flows within the volcanics of the Intermontane Belt; and rockslides, falls, debris flows and earthflows in the Coastal and Insular Belts.Major rockslides occur on overdip slopes in sedimentary, metamorphic, and volcanic successions. Natural causes of the slides include erosion of the toes and lateral margins of the rock slopes, destruction of cohesion along discontinuities by physical weathering and solution, high pore-water pressures, and seismicity. Some of the rockslides from the Mackenzies and from the young volcanoes in the Coast Plutonic Complex have shown travel distances that are extremely high for their volumes.While no regional mapping of landslide risk has been carried out in the Cordillera, some regional mapping of landslides has been undertaken, usually as part of a surficial geology mapping program. Detailed studies of hazards have sometimes followed settlement rather than preceded it, though some useful maps of particular hazards have been produced. In two cases, landslide hazard has caused the relocation of communities. Key words: landslides, rockslides, spreads, flows, rockfalls, natural hazards, Cordillera, Rockies.