LANDSLIDES IN FLYSCH TERRANES OF SWITZERLAND - CAUSAL FACTORS AND CLIMATE-CHANGE

Landslide-prone areas in flysch sequences are widespread in Switzerlan d, covering approximately 1000 km(2). Mass movements can be caused by ground conditions inherited from geological or glacial history, by pre paring causal factors linked to climate or human activities and by tri ggering causal factors related to weather, public works or earthquakes . We identified three periods of major crisis in unstable zones of fly sch terranes during the past ten thousand years (Holocene): using dend rochronological analysis and C-14 dating on fossil wood collected in l andslides. We correlated these periods to other data (glacier fluctuat ion and timberline) and we underscore a strong relationship between cl imate change and landslide activity. Taking into account the latest pr edictions of the Intergovernmental Panel on Climate Change (IPCC 1996) , the spatial distribution of landslides in flysch terranes will not c hange in the future but the unstable zones located between 1000 m and 1500 m will probably suffer from a marked increase in the rate of move ments in landslides already active.