APPLYING INDIRECT APPROACHES TO EVALUATE THE CONTRIBUTION OF THE ROCKFALL PHENOMENA TO THE EVOLUTION OF A ROCKY COAST IN NORTHERN SICILY (ITALY)

Abstract

Rocky coasts evolve on a wide range of temporal and spatial scales also in light of the fact that the resistance of the bedrock of the cliffs and shore platforms persists for a long time. Their morphology can be inherited from past climatic conditions, which affect the geohazard conditions of the rocky shores today. The study area (Monte Gallo; Northern Sicily) shows a landscape marked by a series of topographic highs and lows of coastal plains bounded inland by wide abandoned coastal cliffs, hundreds of meters high as resulting from the interaction between differential uplift, river incision, and eustatic changes (Parrino et al., 2023). In this peculiar morphodynamic system, the evolution of the coastline is also influenced by the rockfall phenomena that affect the back of nearby cliffs and whose propagation areas extend to the sea. These geomorphological processes involve high hazard and risk conditions and are likely to impact rock coast morphology also due to the presence of the scattered boulders constituting the landslide deposits along the coastline (Cafiso et al., 2021). In the framework of the rockfall hazard assessment, the indirect study focusing on the evaluation of the magnitude of potentially unstable blocks could be an important tool to define the contribution of the rockfall phenomena to the evolution of these peculiar geomorphological environments. Over the past decade, scientific literature has placed particular emphasis on indirect approaches to identifying key discontinuity sets, developing advanced point cloud analysis techniques, and implementing Graphical User Interfaces (GUIs) for rock mass characterization. These tools have significantly improved the efficiency of the rock mass characterization process. However, the topic of magnitude, understood as the volume of unstable blocks and their associated potential energy, remains less explored, representing a promising frontier for the development of indirect approaches. In the selected area, characterized by high hazard levels and restricted accessibility, a fully indirect approach was employed for cliff characterization, particularly where the morphological evidence and propagation studies have found the arrival of blocks to the sea. A terrestrial laser scanning survey generated a detailed point cloud representation. To evaluate detachment propensity, the main discontinuity sets were identified using the Discontinuity Set Extractor (DSE; Riquelme et al., 2014) software, followed by kinematic analysis. Moreover, factors influencing detachment magnitude were assessed by identifying potentially unstable blocks within the point cloud and calculating their volumes (Mineo et al., 2025), which ranged from a few cubic meters to several hundred. Finally, the acquired volume data was used to conduct propagation analysis on the developed digital model. This approach could be a useful tool for the geomorphological characterization of the coastline, and also for future scenarios in terms of the contribution of collapses as geomorphological processes which modify the rocky slopes and coasts in the framework of climate change risks, including relative or eustatic change in sea level