Cyclic Steps at the Head of Channelized Features Along the Calabrian Margin (Southern Tyrrhenian Sea, Italy)

High-resolution multibeam bathymetry have revealed coaxial trains of crescent-shaped bedforms within the heads of channelized features lying in shallow-water sectors along the tectonically-controlled Calabrian Margin. These bedforms have wavelengths of tens or a few hundreds of metres and wave heights of a few metres, and their crest-lines trend perpendicular to the maximum slope gradients. Repeated multibeam surveys carried out in 2007, 2008, 2012 and 2013 showed a rapid and significant morphological evolution of the channel's floors, with the generation or upslope migration of the bedforms. Based on their size, upslope migration and similarities to crescent-shaped bedforms recognized in other active canyon heads, these features can be interpreted as cyclic steps. The bedforms are, in fact, formed or modified by frequent slope failures and related sedimentary flows, whose occurrence is favoured by the concurrent presence of several predisposing and triggering mechanisms, such as a high sedimentation rate due to a steep coastal creek, severe storms and seismic events.