Geomorphological hazard and monitoring activity in the western rocky coast of the Portofino Promontory (Italy)

Abstract The results of geomorphological studies and monitoring activity conducted in the western sector of the Portofino Promontory are presented here. This sector is characterized by numerous, extensive landslide masses and there is evidence of their reactivation during the last century. The instability phenomena can be attributed to landslides with complex kinematics classifiable as rock slump and rock topple, rock slide and rock fall, and rock fall and rock flow. They have involved hamlets and communication routes, with observable damage to man-made structures and terraced agricultural terrain, including collapses and deformations of the dry-stone walls. The geomorphological surveys, the boreholes and the monitoring activity have shown that several landslides are active, with movement rates of some cm/year. With the presence of predisposing factors relating to the structural lithology and geomorphology of the rocky slopes, the triggering causes of the gravitational movements are attributable to extreme heavy rainfall and to wave cutting, often with concomitant action on the part of both. The study offers a contribution to encourage concrete efforts to continue the monitoring of this area; the overall objective would entail the planning of general stabilization measures, or at least measures to reduce evident geomorphological risks, also taking into account the remarkable environmental value and qualities of this coastal sector.