Submarine Slope Failures along the Northern Sicilian Continental Margin (Southern Tyrrhenian Sea) and Possible Implications for Geo-hazard

Mass wasting and downslope movements are common processes that have contributed to shape the northernSicilian continental margin (southern Tyrrhenian Sea) since the Late Quaternary. Nevertheless, processescontrolling their evolution are still partially unknown and a variety of geologic factors can be responsible fortheir formation. In this work we present an overview of the main mass wasting features (submarine canyons,landslides, debris flows) observed and mapped in different sectors of the northern Sicilian margin. The margin ischaracterized by a narrow, steep continental shelf (1-2°) and a very irregular and steep (6-8°) upper slope. Themain aims of this work are: (1) to outline the morphology of the submarine canyons and of the related massfailure features, (2) to describe the main geological processes that control mass failure and (3) highlight theirpotential implications for the geo-hazard. The study is based on Multi Beam echosounder, Side Scan Sonar dataand seismic reflection profiles, for a depth range of 20-1500 m, and on sediment samples and scattered gravitycores, collected to define the textural and compositional properties of the seafloor. Our study focused on theCastellammare Gulf-San Vito Trough system, the Gulf of Palermo, the Termini-Cefalù offshore and the Usticaoffshore. In the Castellammare Gulf two main channel systems converge at the San Vito Canyon. This latterdevelops northwards with a very sinuous pattern, crossing the San Vito through. In the western margin of theGulf, where the upper slope is very steep (12-13°) and the continental shelf is very narrow or absent, there are alot of short, straight, sub-parallel gullies that are only few metres deep. In this sector the gully heads are locatedvery close to the coastline and are associated to retrogressive slides. According to the aforesaid, downwarderosive flows appear to be the most common mechanism generating widespread slope failure inside theCastellammare Gulf. In the Palermo Gulf a difference in slope configuration can be observed between westernand central-eastern sector. Submarine canyons are confined to the upper slope or indent the shelf-edge and enterthe Palermo intraslope basin at a depth of around 1,300 m. The canyons evolved through concurrent top-downturbiditic processes and bottom-up retrogressive mass failures. Most of the mass failure features of the area arerelated to canyon shaping processes. The western sector of the Palermo Gulf slope displays a highly dissectedsubstrate, showing steep to very steep gradients, that appear to favour a retrogressive evolution of the canyons.Headward erosion processes are the main controlling factor in shaping this sector. NNE trending canyonsoccurring in the central-eastern sector develop in connection with the Oreto and Eleuterio rivers, breaching theshelf break, and show a linear to sinuous thalweg path. A similar pattern can be recognized in the eastern sectorof the Termini-Cefalù offshore. The occurrence of pockmarks and carbonate mounds also suggests the probablerole that fluid seeps play in the mass wasting processes of the area. Furthermore, the occurrence of pockmarksand highs that probably consist of authigenic carbonates above faulted and folded strata suggests a localrelationship between structural control, fluid escape processes and mass failure. In the Ustica offshore volcanismrelated features (debris avalanche, gravitational collapse of volcanic edifices) are mainly linked to neotectonicactivity and volcanism that tends to build, load and steepen the submarine slopes with time. This paper prese