Fatal landslides and landslide risk in Canada 1

An analysis of a data-base on fatal landslides in Canada, that occurred between 1840 and 1996, indicates that approximately 600 people have died in 84 events. Included in the data base are landslides on natural slopes as well as geotechnical failures involving constructed and excavated slopes. The geographic distribution of the fatal events is heavily concentrated in the provinces of British Columbia and Quebec even though Canada’s largest landslide disaster occurred at Frank, Alberta in 1903. Rock avalanches (> 100,000 m³ in volume) are the most destructive landslide type, followed jointly by Leda Clay landslides and small rockslides and rockfalls (< 100,000 m³ in volume). Geotechnical failures and rain-triggered debris flows complete the destructive ranking. Based on the historical record of landslide disasters the landslide mortality rate for Canada in 1994 was 0.013 per 100,000. This compares to, for example, mortality rates for malignant neoplasm of 188.3, for accidents and adverse effects of 29.1, and for HIV infection of 5.5. The snow avalanche mortality rate based on published accident statistics between 1970 and 1996 is 0.028. In 1994, the annual probability of an individual meeting death in a landslide in Canada was 1.31 × 10⁻⁷. For British Columbia and Quebec the probability is 6.48 × 10⁻⁷ and 1.85 × 10⁻⁷, respectively. Frequency-consequence (F/N) plots for Quebec and British Columbia, indicate an annual regional frequency of deadly landslides that provide a lower bound for acceptable landslide risks at individual sites. The slope of the F/N plots approximates -1 indicating that landslide risk is constant over a range of magnitudes of consequences. Acceptable landslide risk is examined with reference to British Columbia. The suggested acceptable landslide risk criteria corresponds to some of those proposed for dams and industrial sites elsewhere in the world. The criteria contrasts with other studies that set a higher level of acceptable risk, particularly with respect to landslides involving a heavy loss of life.