Rocky coast: geological constraints for hazard assessment

Geological hazard along rocky coasts is basically associated with processes of rapid sediment transfers. Massive transport of rock, regolith, sedimentary cover and soil occur episodically, accounting for cliff recession, sudden increase in solid load in short coastal rivers, and flank collapse of volcanic structures and rocky slopes. In geohazard terms, rocky coasts operate as transfer zones that deliver sediment directly from slopes to the coast and open sea at intermittent time intervals. Erosion and transport of material causes major physical changes and exposes coastal communities and human activity to hazard with potential damage to property and infrastructure, and loss of life. This paper focuses on geological processes that regulate rapid sediment transfers in rocky coastal areas, with examples drawn mostly from the Italian coasts. It is stressed that proper comprehension of coastal mass wasting hazard has to include marine and historical investigations. As a main delivery area, the submerged part of rocky coasts preserves reliable sedimentary records of past geological events occurring on land, which are often only partly detectable along subaerial rocky slopes and commonly reported in historical sources.