Morphological evolution of small submarine canyons in active volcanic settings and their interaction with coastal infrastructures (Vulcano Island, Italy)

Flanks of active volcanic islands are dynamic environments that may create geohazards for the surrounding communities. This is the case of the submarine Gelso Canyon along the southern flank of the active Vulcano volcano in the Southern Tyrrhenian Sea. This canyon is characterized by two main branches, cutting back to some meters of water depths, close the coast. A small pier, representing an important infrastructure for the evacuation of the island (a UNESCO site) in case of volcanic eruption, is located in correspondence of one of these branches. In this study, we show the rapid morphological evolution of the upper section of the Gelso Canyon over the last 20 years through the integrated analysis of repeated bathymetric surveys and seafloor videos. This evolution has been dominated by seafloor erosion due to the occurrence of sedimentary gravity flows over steep slopes (> 15 degrees). Multiple factors have promoted the development of such flows, such as: (a) the morphological link between canyon branches and the subaerial drainage network, made up of short and steep creeks with torrential regime, (b) the interception and downslope funnelling of the littoral drift, due to the pier construction, (c) the frequent storm-waves that hit the coastline, as recently occurred on 8-10 January 2024. Localized seafloor erosion has generated a progressive deepening around the submarine base of the pier, so mining its stability. These results support the use of a multiscale geomorphological approach for monitoring active volcanic areas, providing insights for a geohazard assessment of coastal environments.