Geological heritage in the Western rocky coast of Portofino Promontory (Italy): degradation risk assessment of an active geosite

In recent times, studies concerning geoheritage and geodiversity have given more focus on the issues of active geosites and their evolution. The more or less rapid evolution of a geosite could pose a risk towards exposed elements, such as the human population, buildings or infrastructures. This research presents a case study on the rocky coast evolution of the western side of Portofino Promontory, on which lies the village of San Rocco di Camogli (Liguria, Italy). The seacliffs of San Rocco represent a typical example of active geosite shaped mainly by gravitational, running waters and marine processes, although the anthropogenic factor plays also a significant role. The cliffs are more than 1 km long and 80-to-200 m high. They are made by a marly-limestone flysch and affected by well-known landslides phenomena with different kinematics and state of activity, which have been represented in a detailed geomorphological map. In order to assess the evolution rate of this geosite a multitemporal analysis of the seacliff has been performed, taking into account: i) a DTM derived from a LIDAR survey carried out in 2008; ii) a DTM derived from a LIDAR survey carried out in 2021; iii) a photogrammetric survey carried out in 2023. By comparing the DTMs, a reconstruction of the net variation in height on the cliffs in the last 15 years has been possible. Variations are scattered all along the cliff, as they correspond with the zones on which gravitational processes occurred. The northern sector of the cliff shows variations up to 10 meters. The results provide useful knowledge to the understanding the state of activity of the geosite and its evolution rate, and thus to its effective management in order to mitigate its degradation as well as the possible related geomorphological risk.