Destructive mass movements in high mountains: hazard and management

Abstract
The remote valleys and high mountain areas of western Canada have experienced accelerated economic develop­ment only in recent years. Although there have been occa­sional mass movements of destructive impact in this region in the past, the short history of human settlement makes it difficult to properly evaluate the potential hazard and appropriate countermeasures during future development of steep mountainsides and narrow valleys. A large body of documented experience from long-inhabited mountain re­gions, notably the Alps of Europe, suggests that major mis­takes can be avoided if this experience is used properly. Most destructive mass movements are complex and re­lated to mountain torrent systems and instabilities of steep bedrock slopes. They can be conveniently grouped into (1) de bris flows from surficial deposits, (2) de bris flows from bedrock failures, (3) mass movements on volcanoes, (4) glacier-related mass movements, and (5) rockfalls and rock avalanches. Each of these requires a different type of hazard appraisal and particular set of remedial or preventive measures. The range of possible destructive impacts and appropriate countermeasures are illustrated with 137 case histories from the Alps which are presented in a coherent geological-climatic framework transcending the traditional political boundaries. Analysis of these case histories, com­bined with insights gained elsewhere, is used to outline the application of active measures (forestry, control works, pro­tective works), passive measures (zoning, planning), mon­itoring, and acceptance of risk. The decisions regarding which active or passive measures should be applied and what Level of risk is acceptable are based on (1) information on recurrence and magnitude of mass movements and (2) a broad social-economic consensus.

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