Sediment spatial patterns in a Hurricane Katrina overwash fan on Dauphin Island, Alabama, USA

Hurricane Katrina scoured the seaward side of Dauphin Island, Alabama, and then deposited the sediment on the back side of the island into a repeating pattern of are-shaped overwash fans. We set out to determine if sediment sorting operated at the scale of the individual overwash fan during the storm. Variograms and kriging were used to create maps of the topography and sediment patterning in terms of the mean grain size, standard deviation, skewness, and mineral composition. Mantel tests were used to correlate hypothesized directional processes with the patterns. We found that sands near the surface were spatially sorted in a direction consistent with the north-northwesterly forces of Katrina. The spatial distribution was not correlated with the topography. Our results support the concept that horizontal spatial pattern formation primarily begins as the extreme forces of a hurricane subside.