A complex landslide along the Eastern Liguria rocky coast (Italy)

The paper presents the geological and geomorphological features of an ancient coastal mass movement occurred between Paraggi and Santa Margherita L., in the eastern sector of the Portofino Promontory (Liguria, Italy). It is a protected area with great landscape and environmental value within the Portofino Natural Park. The landslide, of historical significance and well known as “Frana delle Gave”, occurred along a regional tectonic lineation, at the boundary between conglomerate and marly-limestone flysch formations, and has been affected in the last century by some reactivations. The landslide’s recent evolution has been evaluated by the application of historical analysis and comparison of aerial photos, maps and rainfall data, as well as on the basis of a detailed geological and geomorphological survey of the entire landslide area and surrounding sectors, including the collection of data on drillings that were previously conducted in the area for engineering purposes. It was possible to zone the landslides in two main sectors: an upper sector of the active landslide has a complex genesis, that is affected by quick movements of rock fall and debris flow; a lower sector of the landslide, which is of older genesis, that is affected by extremely slow movements and thus does neither threaten the settlements of the area nor the communications routes to Portofino.