Wave Generation of Gravity‐Driven Sediment Flows on a Predominantly Sandy Seabed

Wave‐supported gravity flows (WSGFs) generate rates of sediment flux far exceeding other cross‐shelf transport processes, contributing disproportionately to shelf morphology and net cross‐shelf fluxes of sediment in many regions worldwide. However, the conditions deemed necessary for the formation of WSGF limit them to a narrow set of shelf conditions; they have been observed exclusively in regions where the seabed consists of very fine‐grained sediment and typically co‐occur with nearby river flood events. Here we document the occurrence of a WSGF event on a predominantly sandy seabed and in the absence of a preceding river flood. Our measurements confirm that the dynamics are governed by the friction‐buoyancy balance observed in other WSGF and that WSGF can form in mixed grain‐size environments and transport high concentrations of sand. The occurrence of WSGF on a predominantly sandy seabed suggests that they may occur under a much wider range of conditions and, given the global prevalence of sandy shelves, they may be a more frequent and more ubiquitous feature of shelf dynamics than previously thought. Plain Language Summary The processes that exchange sediments in gently sloping ocean regions are still not well understood. Previous studies have identified wave‐supported gravity flows (WSGFs) as a leading process for the exchange of muds in many regions worldwide. These sediment flows occur when wave action resuspends seabed sediment and generates a thin near‐bed layer with very high concentrations that is able to move downslope due to gravity. The measurements we present here suggest that these type of flows can also move large amounts of sediments in predominantly sandy environments and therefore may occur more frequently than previously thought. Key Points Wave‐supported gravity flows can contribute to cross‐shelf transport and morphological evolution on sandy inner shelves Particle size plays a key role in determining the dynamics of the wave‐supported gravity flow Wave‐supported gravity flows may occur more frequently and in a much wider range of shelf locations than previously thought