Catastrophic landslides off Ischia volcanic island (Italy) during prehistory

Generally the evaluation of the geological hazards from active volcanoes chiefly concerns the prediction of eruptions whereas less attention is generally paid to other volcanic-related phenomena, such as avalanching-landsliding. This is the case for Ischia (Italy), an active volcanic complex, whose collapse behaviour is only now being evaluated and recognized following extensive marine geophysical and geological investigations. The island of Ischia represents the emerged section of a larger east-west-trending volcanic ridge. The central sector of the island, Mt. Epomeo, has risen to at least 800 m above sea level (a.s.l.) in the past c. 30 ka, at an average rate of 20 mm a-1. The major consequence of such volcano-tectonic uplift includes either sudden collapses, with attendant debris avalanches, or other mass movements in the form of mud-debris flows, debris slides and rock-falls, all radiating out from Mt. Epomeo and most of them entering the sea. During prehistoric times the island of Ischia underwent major catastrophic collapses resulting in debris avalanche deposits of >1 km3 to <0.5 km3 that have been recognized offshore both NW and south of the island. This study provides possible scenarios for the emplacement of these deposits, with particular reference to the resulting landslide-related tsunami hazard.