Multiscale geomorphological analysis of primary and erosional-depositional processes in submarine volcanic environments of the Aeolian Islands

Submarine flanks of active volcanic islands undergo rapid morphological changes driven by the interaction between volcanic activity, gravitational processes and sedimentary dynamics. This PhD Thesis analyses the geomorphological evolution of the upper submarine flanks of Vulcano, Stromboli (Aeolian Archipelago) and La Palma volcanoes (Canary Archipelago) through the integrated analysis of high-resolution multibeam bathymetries and direct seafloor observations. The study has focused on and the main erosional-depositional processes acting along the steep submarine flanks and the identification of the main factors that controlled the emplacement of primary volcanic units due to the entrance into the sea of lava flows as well. As the first goal is concerned, repeated multibeam surveys allowed to quantify recent morphological variations, which can be related to a complex interplay between eruptive dynamics, meteo-marine events (storms waves and flash-floods generated hyperpycnal flows), volcano-tectonic and geomorphological settings. Seafloor imageries were essential for validating geo-acoustic interpretations and resolving small-scale features below the detection limit of multibeam data, including sedimentary structures, block accumulations, small collapses, hydrothermal activity and biological colonisation, with implications on the identification of active geomorphic processes. As the second goal is concerned, the analysis of primary volcanic morphologies reveals significant variability in the distribution and characteristics of massive lavas, pillow lavas, hyaloclastite welded and non-welded units, volcaniclastic deposits and remobilized deposits across the three islands. This variability can be related to multiple factors, among which the main ones are lava types, effusion rates, location of vents, paleo-topography (especially slope gradients). Overall, the results provide new insights for better understanding the short-term and long-term evolution of submarine volcanic slopes, having also implications on the related geohazard assessment.