Small-scale crescent-shaped bedforms in submarine volcanic settings: examples from Stromboli and Salina islands (Italy).

Newly collected high-resolution multibeam bathymetry around Stromboli and Salina islands (Aeolian Archipelago, Southern Tyrrhenian Sea) shows a large number of small-scale crescent-shaped bedforms within flat-bottomed channelized features carving the submarine volcanic flanks. The bedforms have wavelength of tens of meters and wave height of some meters; their crest-lines are roughly perpendicular to the maximum slope and generally have concave-downslope shapes. The origin of these bedforms has been mainly related to repeated mechanisms of erosion and deposition due to sediment-laden gravity flows on the basis of their geometry and the morphological setting. Time-lapse bathymetric surveys show an upslope migration of the bedforms within Piscità Channel at Stromboli, highlighting active sedimentary dynamics. This is consistent with the shallow depths (< 10 m) of the headwall of Piscità Channel, interacting with local costal dynamics and fed by the products of the persistent strombolian activity. Differently, no significant morphological variations are observed at the 10-years scale for the bedforms within the North Salina Channel. This is consistent with the deeper headwall of this channel (depth > 90 m), which was likely inactive during the present high-stand conditions (i.e., the last 6 ka). At Salina, the generation of the bedforms has been tentatively related to sediment-gravity flows fed by the products of the most recent explosive eruptions occurred on the island at ~27 and 17 ka, in different paleo-environmental conditions relative to the present-day level.