Keeping An Eye Beneath The Sea: Knowledge Of Volcanic Islands Through Case Studies From Italian Seas

The exposed portions of volcanic islands represent the emergent tip of the overall volcano structure, which largely lies below sea level. Over the last decade, marine investigations through swath bathymetry, long-rangeside scan sonar, seismic, and seafloor sampling were carried out on several Italian volcanic islands (i.e. Stromboli, Ischia, Pantelleria, and Pontine Archipelago). They revealed several previously unknown constructive and destructive features, which constitute key insights for volcano-tectonic studies and geo-hazard assessment. For instance, offshore Pantelleria edifice, the morphological differences between the well-preserved eruptive cones identified on the NW sector (including the latest 1891 eruption) compared to the more degraded morphologies of the SE sector corroborate the northwestward migration of the activity over time. At Western Pontine Archipelago, marine data allowed for significant renewal of the general volcanological setting in terms of areal distribution, ages, and compositional relationships among the different magmatic events which occurred during Pleistocene and Pliocene time. Regarding destructive features, a large spectrum of mass-wasting, across different scales and frequencies, has been recognized all along the volcanic edifices. Medium scale landslide and gravity flows are more common (in time and space) than sector collapses that produced debris avalanche deposits recognized only at Stromboli and Ischia edifices. Despite their relatively smaller size with respect to their oceanic counterparts, the debris avalanches can be very hazardous for coastal communities and facilities, also because of their tsunamigenic potential. Small to medium-scale submarine slides (e.g., Stromboli 2002 landslide) can be more hazardous, as they are widespread, occur at much higher frequency than sector collapses, and often evolve upslope affecting coastal infrastructures and can generate tsunamis as well. The achieved results represent an important step towards the complete understanding of volcano-tectonic history of insular volcanoes as well as the refinement of interpretative models for submarine volcanic activity