Ricostruzione dell’evoluzione di una complessa deformazione di versante presso Ventimiglia (Liguria di Ponente).

The coastal tract to the immediate west of Ventimiglia, to the orographic right of the Roia River and to the south of its tributary the Bevera, shows strong evidence of slope deformations. Relict remains of delta-fan deposits, referable to the Lower Pliocene, crop out; these lie discordantly above a substratum of Ventimiglia Flysch (Eocene). The Pliocene deposits, which have a thickness up to 300 m in this sector, are situated along a ridge that extends from Mt. Magliocca (515 m) to the sea. The study is of major interest for the morphological and stratigraphic features of the slope deformation and for the events that most probably caused it. The first are represented by various trenches, scarps and terraces at different altitudes along the slope and by superficial landslides. In at least two cases the trenches affected the ridge near the summit of Mt. Magliocca, causing evident splitting phenomena. The causes can be found in the Plio- Quaternary uplifting of the area, which caused notable valley deepening and a height variation of a good 500 m between Mt. Magliocca and the bed of the Roia; in the geomorphological configuration that developed during the Quaternary and that is now characterised by a real relief inversion; in the disjunctive Plio-Quaternary tectonics, which caused the development of the fault system that is clearly visible in the drainage pattern; in the seismicity caused by tectonic activity in the sector, which is the most notable in Liguria, having its origin in hypocentres on the continental shelf and in the Maritime Alps; in the peculiar stratigraphic-structural features, characterised by the superimposition of rock masses with different mechanical characteristics and inclinations. The Pliocene succession prevalently consists of marly clays often up to 180 m thick and overlain by conglomeratic bodies up to 150 m thick. The basal erosive surface, which dips 7° towards SE, cuts the Flysch of Ventimiglia whose strata dip towards the E (Roia River valley) with an inclination of 30-50°. It is possible to hypothesise the chronological collocation of the landslides bearing in mind the probable sedimentation depth of the Pliocene clays, their age and their actual altitude. The velocity of the uplifting so calculable allows us to determine when the reliefs of an altitude able to initiate the observed gravitative phenomena were formed. Given the notable anthropisation of the area involved in the deep-seated gravitational deformation, which includes the slope and valley floor, and the regional seismicity, a risk assessment of the area is highly recommended.