Storm-Generated Sediment Distribution Along the Northwest Florida Inner Continental Shelf

Hurricane Ivan made landfall along the Alabama-Florida coastline on September 16, 2004 as a category 3 storm. Ivan provided a rare opportunity to quantify surficial sediment changes following a significant storm event. Sidescan sonar imagery was collected immediately offshore Santa Rosa Island, FL, five days before and after Ivan´s landfall 100 km west of the study area. Particle-size, multisensor core logger, X-radiography, photography, scanning electron microscopy (SEM) grain shape, direct shear, radiocarbon isotope, and lignin-phenol analyses were performed on grab or vibracore samples collected after the storm. Sonar observations before Ivan´s landfall revealed a mostly sand bottom with uniform, small-scale wind-wave ripple morphology, and a distinct area of low backscatter trending NW-SE that was interpreted to be a mud swale. Ivan introduced new material to the relict sediments and resulted in the deposition of fine-grained material across the shelf that settled in the bathymetric lows and formed mud flaser deposits. Hardbottoms were draped by sand in some locations, but exposed in others. Ripple morphology changes occurred along sand ridges. Hurricane Ivan created major sediment distribution changes along the near-shore shelf, yet served to reinforce and to maintain the ridge-and-swale topography of the northeastern Gulf of Mexico near-shore continental shelf.