A COMPARATIVE STUDY ON REGIONAL OVERWASH FROM HURRICANES FRANCES-JEANNE AND IVAN

Four strong hurricanes impacted a large portion of the Florida coast within a month during the summer of 2004. Three of the hurricanes resulted in significant sediment re-distribution along the coast in the form of overwash. Hurricane Ivan impacted nearly the entire Florida panhandle coast, causing tremendous overwash deposits. Hurricanes Frances and Jeanne, impacting nearly the same location along the south Florida Atlantic coast, also resulted in substantial overwash deposits. Overwash from Hurricane Charley is limited. This study compares the overwash deposits from Hurricanes Frances-Jeanne and Ivan. There are substantial differences in the areal extent and morphologic shape. The overwash deposits from Frances and Jeanne are relatively restricted in aerial extent, being localized north and within 30 km of the eye. In contrast, overwash deposits from Ivan are far more extensive, stretching over 120 km from the eye. Overwash from Frances-Jeanne transgressed into the back-barrier mangrove swamp and displays a tongue shape, significantly influenced by the density of the vegetation. The extensive overwash from Hurricane Ivan does not display individual fan shape. The sediment grain size and texture differ substantially between the panhandle and Atlantic Coast. The panhandle deposits are composed of homogeneous, well-sorted, medium-grained quartz sand with some heavy mineral layering. The Atlantic Coast sediments are more heterogenous in composition, poorly sorted, and contain large amounts of shell fragments. The differing overwash morphologies and sedimentological characteristics are influenced by the hurricane intensity, sediment characteristics, and especially pre-storm morphology of the coast.