GNGTS 2013 - Atti del 32° Convegno Nazionale

formation (Orsi et al. , 1991; Acocella et al. , 1997; Acocella and Funiciello, 1999). Consequently, the volcanic activity of the island has been conditioned by a complex phenomenon of calderic resurgence, started from 30 ky B.P., allowing for the gradual uplift and emersion of the rocks deposited in the caldera, initially submerged under the sea level. The rate of uplift, indicating the caldera resurgence, has been evaluated in about 800-1100 m (Barra et al. , 1992). The tectonic activity is characterized by systems of extensional faults, NW-SE and NE- SW trending, Plio-Quaternary in age (Acocella and Funiciello, 1999; Acocella et al. , 2004). NW-SE and NE-SW systems of extensional fractures predominate in all the island and around the resurgent caldera block, suggesting a close relationship with the regional extensional structures. N-S and E-W trending normal faults have been found along the rims of the Epomeo block and interpreted as controlled by the caldera resurgence. The process of resurgence has locally substituted the volcanic activity during the last 33 ky, since the most of the pyroclastic products coeval with the resurgence has been erupted out of the uplifted area. Marine geological studies already showed that the Ischia island lies on a E-W trending volcanic ridge (Bruno et al. , 2002; Passaro, 2005; de Alteriis et al. , 2006; Aiello et al. , 2009a, 2009b, 2012a, 2012b). The continental slope off the south-western Ischia island is incised by a dense network of canyons and tributary channels, starting from a retreating shelf break, parallel to the coastline and located at varying depths. Large scars characterize the platform margin off south-western Ischia island, in particular the scar of the southern flank of the island, corresponding onshore to the Mount Epomeo block and probably at the origin of the Ischia Debris Avalanche (Chiocci and de Alteriis, 2006). Volcanic banks, having irregular morphologies, have been identified on the south-western flank of the island, as the “Banco di Capo Grosso” and the banks “G. Buchner” and “P. Buchner” (Passaro, 2005; de Alteriis et al. , 2006). A large field of hummocky deposits, named the Ischia Debris Avalanche has put in evidence by swath bathymetric surveys coupled with Sidescan Sonar imagery and Fig. 1 – Sketch diagram showing the elevation intervals versus average slopes offshore the Ischia island (modified after Aiello et al. , 2012b). 226 GNGTS 2013 S essione 1.3