A giant deep-seated slope deformation in the Italian Alps studied by paleoseismological and morphometric techniques

This work proves the existence of a large deep-seated gravitational slope deformation (DGSD) in a hilly region of the southwestern Alps, whereas DGSD are usually linked with high relief energy in mountain environments. Moreover, we describe the usefulness of applying paleoseismological techniques by means of trench excavation to date and understand the deformation history and genesis of recent morphostructures, and we found evidence of causative relationships between DGSD and surface landslides. The studied DGSD of Mt. Croce della Tola–Mt. Scincina, Italy, is the largest of the western Alps: it is 7-km long and involves a minimum area of 16 km² with a volume ≥3.5 km³ probably extending further NE beneath Lake Maggiore surface. Several parallel scarps, representing the surface expression of slip-planes, affect the upper part of the slope, whereas the lower part presents a convex profile. DGSD at Mt. Croce della Tola started in the last interglacial period (120–40 ka BP) and the following glacial phase was not able to significantly modify the general slope geometry. Post-glacial deformation also occurred, especially at Mt. Scincina, after 25 ka BP. Post-glacial and active surface landslides developed on the convex lower part of the slope, suggesting that they resulted from instability due to the new profile assumed by the slopes during the deep-seated deformation. The occurrence of Mt. Scincina DGSD with a very low topographic gradient is interpreted as an effect induced by on other large DGSD.