Submarine instability processes on the continental slopes off the Campania region (Southern Tyrrhenian sea, Italy): the case history of the Ischia island (Naples Bay)

The continental slope off the Campania region (southern Tyrrhenian sea, Italy) represents a natural laboratory for the study of geological events and processes related to submarine gravity instabilities in deep waters, as a base to evaluate geological and environmental hazards triggered by earthquakes, volcanic eruptions and tectonic activity in correspondence to regional faults. The identification of submarine instabilities on continental slopes shows important implications in terms of applied research for the coastal zone knowledge and management, also in terms of geological and environmental hazard. This study is carried out by using marine geophysical data collected by the CNR-IAMC Institute, in particular Multibeam bathymetry and reflection seismics (Sparker Multitip seismic source). The submerged sectors of the Ischia island are the site of submarine gravity instability processes, having both catastrophic (instantaneous) and continuous characteristics (accelerated erosion along submarine canyons or channels, debris fluxes along channels and creeping). The geological interpretation of the marine DEM (Digital Elevation Model) of Ischia island has put in evidence an articulated topography of the sea bottom. A complex stratigraphic architecture, with intercalations between volcanic and sedimentary units is revealed by the interpretation of high resolution seismic reflection profiles. The Ischia Debris Avalanche (IDA) has a southern dispersal axis with a transport of blocks of up to 40-50 kilometres from the island. The interpretation of Multibeam bathymetry has shown that IDA is bounded northwards by a large scar, coincident with the Mount Epomeo block; its emplacement is probably younger than the eruption of the Green Tuffs of the Mount Epomeo volcano (55 ky BP). Piston cores, sampled on the southern, submerged flank of Ischia Island along the IDA, recovered blocks of Mount Epomeo Green Tuff Ignimbrites enclosed in a sandy-to muddy matrix, constututing the main bulk of the avalanche deposit. These products are covered by tephra layers, correlatable to Ischia eruptions younger than 10 ky based on major and trace element chemistry. Other important debris avalanche occur in the northern and western sectors of the island, as put in evidence by Sidescan Sonar profiles recorded on the same navigation lines as the Multibeam bathymetry.