Seafloor waveforms in submarine volcanic setting as proxy of active sedimentary dynamics

High-resolution morpho-bathymetric and side scan sonar data collected in the central and eastern part of the Aeolian volcanic arc (Southern Tyrrhenian Sea) depict widespread waveforms on their volcaniclastic aprons from shallow-water sectors up to 3.200 m water depth (Casalbore et al., 2014). These features are characterized by an high variability in wave parameters (wavelength of 30-1600 m and wave height of 1-200 m), plan-view morphology (from sinuous to crescentic) and cross-section (from undulating to stepped), indicating that different sedimentary processes, at variable spatial and temporal scale, are responsible for their formation. By relating the morphological characters of the different waveforms with the local boundary conditions (morphological setting, regional slope gradients, sediment source and dynamics), we try to better constrain the factors controlling their formation. For instance, some of these features occur at the seabed just below a marked decrease of slope gradients, and could be interpreted as cyclic steps, i.e. a class of class of slow upslope migrating turbiditic sediment waves, where each downward step is bounded by a hydraulic jump. By comparing the morphometric characteristics of the recognized waveforms with the results of experimental evidence and numerical modeling proposed in literature, we attempt to test if they can be generated as cyclic steps and, more in general, discuss what the waveforms characteristics may tell us about the sediment dispersal and the nature of the flows that generated them. Some small-scale waveforms showed significant morphologic variations (i.e. upslope migration) on repeated multibeam surveys at the 10-year scale, indicating that they are due to active morphodynamic processes.