On the inner shelf, the RSDs have a similar but more subdued profile that is below the resolution of the bathymetric surveys. Their morphology here has been mapped exclusively by diver surveys. The formation and maintenance of RSDs is probably related to processes at several spatial and temporal scales. At a scale of tens to hundreds of meters, subtle variations in topography may enhance downwelling currents within the RSDs, resulting in scour and winnowing of fine sediments. Their composition, location and orientation suggests they have formed in response to localized sediment surpluses on an otherwise sediment-starved shelf sector.
Local areas consist primarily of adjacent marine hardbottoms.
Additional sources include outcropping Quaternary sediments or possibly beach nourishment material from the shoreface. The dunes are oriented obliquely offshore, which is transverse to the probable mean direction of storm-induced inner shelf flows. The mapping results and interpretations presented here suggest that both the surficial morphology and underlying geologic framework play a critical role in modern sedimentation patterns that couple the beach and the inner shelf.