TEMPORAL PATTERNS OF MASS MOVEMENTS IN THE FRENCH ALPS

In massmovement hazard assessment it is important to include a temporal dimension in order to give a better insight into the activity of landslides. In the French Alps the temporal pattern of active landslides in varved clays and terres noires (marls) was studied as well as the temporal occurrence of debris flows. The active landslides in varved clays and terres noires show, in detail quite different patterns of movement which is ascribed to the different hydrological conditions in the landslide bodies. The activity of debris flows is controlled by the occurrence of exceptionally high-intensity rainstorms. This means that the temporal pattern of debris-flow activity will reflect the variability of storm rainfall activity. As a first approach an average recurrence interval of some ten years was detected based on dendrochronological and lichenometrical evidence.