DEBRIS FLOWS IN AN ALPINE ENVIRONMENT

Debris flows are an important hazard in mountain environments. They ha ve characteristic features, and may extend from periglacial zones to v alley floors where they can cause disruption and devastation. Alpine d ebris flows have increasingly become the focus of geomorphological stu dy. On 20 and 21 July 1992 debris flows in the Swiss Val Ferret destro yed several bridges and blocked the main road. The events occurred aft er two weeks of prolonged precipitation and two nights of very heavy r ainfall. Contrasts in geology, and the morphology of the production, t ransport and storage zones appear to control the distribution of these debris flows. On the right bank where the slope profile is concave an d the rock type is dominantly schist there were four major debris flow s whilst on the left bank, where slopes are convex and granites domina te, only one flow was observed. In Val Ferret debris flows are expecte d annually and the community is well-adjusted to the hazard. Hazard ma nagement is event-based and relies on simple structural measures and a verbal/telephone warning system.