Comparing debris flow relationships in the Alps and in the Pyrenees

Abstract

Debris flows are a well known geomorphic process all over the World, as can be seen in the map presented by Innes (1983). In fact, many authors consider that debris flows are the most active geomorphic hazard in mountain areas, affecting human settlements, infrastructures and touristic resorts (Takahashi et al., 1981). Many papers even report the loss of lives, both in developed and in developing countries. This is the reason why many studies have been devoted to identify the factors that trigger debris flows and to understand the relationships between these factors. There is a general agreement in the definition of two essential parameters in order to establish debris flow hazards: first of all, the volume of material carried out by debris flows, and, secondly, the distance travelled by debris flows (especially the runout distance). As it was pointed out in other report within the DAMOCLES Project (Lorente et al., 2001), this information is especially relevant for debris flow modelling and to predict which areas will most probably be affected in the future. Blijenberg (1998) also stresses the crucial importance of displacement, runout and volume.