ROCK FALLS AND CLIFF RETREAT RATES IN PYROCLASTIC SLOPES: THE CASE STUDY OF THE PHLEGREAN COAST (SOUTHERN ITALY)

The coastal area between the towns of Naples and Pozzuoli represents a unique environment in the Italian peninsula, because of the diffuse presence of Greek and Roman archaeological sites in a dynamic landscape. The geomorphological evolution of this area has been strongly influenced by the young (<40 ka) eruptive history of the Phlegrean Fields, the largest active volcanic fields in Italy. The alternation of explosive volcanism, caldera collapse and bradyseism events have shaped the coastline, that is characterized by steep sea cliffs, embayment, sand beaches and coastal lagoon. Regarding sea cliffs, their shape is strongly controlled by rock-type, with the highest cliffs cut in consolidated tuff deposits and the smallest one cut in ash falls and volcanic scoriae units. Geomorphological and structural analysis suggest the occurrence of a dense net of mainly NE-SW trending faults, that causes the diffuse presence of fractures in tuff deposits often acting as critical points from which rock falls originated. In the area, ~100 rock falls were recognized, the largest one being represented by the Capo Miseno fall, with a volume of ~40,000 m3. Here, we carried out a comprehensive analysis consisting in drone surveys, geomorphological analysis and geo-structural measurements that allowed to derive the 3D model of the rockfall and to decipher the mechanism of failure. In addition, the combination of geomorphological and archaeological data along the Phlegrean coastline allowed to estimate cliff retreat rates at different time scales, thus highlighting sea-cliffs more susceptible to rock falls. The presence of human structures and infrastructures and of archaeological sites has been also taken into account allowing to define possible rock-fall risk scenarios.