Spatial and temporal factors of erosion by water of black marls in the badlands of the French southern Alps

Jurassic black marls constitute one of the most extensive outcrops in the Alpine massif. They include the most eroded terrains in the French Alps. Black marls are subject to strong weathering and their erosion rate can reach values close to 1 cm year" (i.e. 100 rrr ha" year"1). Many studies have focused on the processes and forms of erosion of these black marls and on the development of an original metrology to improve our understanding of the seasonal processes in these badlands areas. This study shows that alternating freeze-thaw and wet-dry cycles are the main causes of disaggregation in the marls. The exposure of hillslopes and the dip-slope angle are the main site factors explaining the variability in the action of these processes and thus, in the soil thickness lost as a result of erosion. The kinetic energy of rainfall is similar everywhere, but the volumes of regolith transported by runoff depend on the effects of previous weathering.