Small-scale bedforms generated by gravity flows in the Aeolian Islands

Small-scale crescent-shaped bedforms were identified within flat-bottomed channelized features carving the submarine volcanic flanks of the Stromboli and Salina edifices. The bedforms are downslope-asymmetric, with a sub-horizontal stoss side and a steep lee side. They have a wavelength of tens of metres and a wave height of metres, and their crest-lines are roughly perpendicular to the maximum slope. Based on their size, texture and similarities to other bedforms, they can be interpreted as cyclic steps, i.e. a class of upslope-migrating turbidite sediment waves. Although their genesis must be similar, some differences are observed between the two cases. At Stromboli, repeated multibeam surveys at an 11-year scale showed a significant upslope migration of the bedforms because they lie on the bottom of a channel connected to active coastal dynamics, whose headwall is located at a few metres depth. By contrast, the surveys showed no significant morphological variations at Salina, where the bedforms are larger than at Stromboli and the channel headwall is located at about −100 m, suggesting that these feature are mostly inactive at present.