The slope movements within the Mondores graben (Drome, France); the interaction between geology, hydrology and typology

The Mondores graben in the south-eastern French Alps is an uncommon structu ral feature, which originates in a complex polyphasic tectonic evolution. I n contrast with its immediate surroundings, with hardly any huge landslides , the Mondores graben is characterised by various types of landslides. A hu ge sagging caused part of the limestone cliff to subside some 50 m within 5 0 years. Two recent mud flows that occurred were considered a potential thr eat to some inhabited places downstream. The hydrologic aspects of the Boul c-Mondores landslide resemble the geology: infiltration (and karst input?) in the rock-sliding zone and exfiltration in the marls resulting in slumps and mud flows. The mass movement interactions could be explained by a struc tural geology analysis with geodetic monitoring using different techniques. It is also shown that hydrochemistry as well as geophysical surveys are of importance in unravelling the hydrologic systems and the geological subsur face structures. The present paper aims at explaining the geological contro l of the different slides in view of estimating their potential danger. Und erstanding the geological structure and its evolution therefore is a necess ary prerequisite. (C) 2000 Elsevier Science B.V. All rights reserved.