Landslides: Extent and economic significance in Canada

Regions of Canada prone to slope movements include the offshore, the Canadian Cordillera, the Interior Plains, permafrost areas, the St. Lawrence Lowlands and the shores of the Great Lakes. The historic record of landsliding is short and localized as average population density is low, at 2.6 persons per km, and over 75% of the population live in cities. Landsliding is a hazard specifically excluded from comprehensive residential insurance policies in Canada. Local and provincial governments may protect the public by zoning areas at risk as hazard land. Judicial decisions have protected these governments from liability for losses in land value arising from land zoning decisions. Recovery of losses of property in slope movements has depended on ex gratia payments by the governments. Knowledge of the extent of landsliding in Canada is not complete. The problems with debris flows on the Pacific Coast, obvious in retrospect, were not predicted 20 years ago. Further mapping of offshore landslides is needed to determine their effects on structures and to assess seismic hazard. Other surprises may be waiting in the less well known parts of the country. It is also clear from the history of slope movements on the Interior Plains that development itself may reduce slope stability. Independent estimates of annual loss need to be made in Canada. They may show losses of hundreds of millions of dollars per year. As a first step, a catalogue of damaging historic landslides in Canada has been set up and agencies collecting information on landslides are encouraged to contribute information both on historic and current landslide problems.