Morpho-acoustic characterization of the insular shelves around Stromboli Island (Aeolian archipelago)

Abstract

Stromboli is an insular volcano located in the Southern Tyrrhenian Sea, characterized by a bilateral symmetry with respect to its SW-NE axis. The volcanic flanks perpendicular to this axis are mainly dominated by large and steep-sided depressions associated with large-scale lateral collapses. In contrast, the volcanic flanks parallel to this axis are characterized by the presence of insular shelves in the first 100-200 water depth that interrupt the morphological continuity between the subaerial and submarine slopes. These shelves have been formed by wave erosion during Quaternary sea-level fluctuations. In detail, the SW shelf is relatively narrow and has the outer edge in the depth range of 100-130 m, while the NE shelf is wider and has the outer edge in the depth range of 100-200 m. In addition, narrow shelves with the edge at depths of 100-130 m are recognizable on the SE sector, being limited to the morphological highs bounding the collapse scar. The difference in shelf width around the island can be related to the different ages of the coastal sectors that, in turn, would be reflected in a longer cumulative erosive action of waves. In the SW and SE sectors of Stromboli Island, the outcropping volcanic units are less than 100 ka; the NE shelf, instead, represents the dismantling of the upper part of the older Strombolicchio edifice, which has been dated around 205 ka and whose emerged part is nowadays related to a neck emerging from the sea surface. The depth range of the shelf edge in the SW and SE sectors is compatible with the minimum sea-level reached during the last lowstand, while the deeper shelf edge in the NE shelf can be related to a tectonic tilt or subsidence that affected the Strombolicchio edifice during its evolution. The morpho-acoustic characterization of the shelf has been realized through the integration of multibeam bathymetry, side scan sonar data, seismic reflection profiles, and direct observations through scuba dives. It has enabled us to identify four main seafloor types on the shelf: sandy seafloor, volcanic outcrops, blocky accumulation, and seagrass meadows, whose spatial distribution is discussed in the paper.