OBSRVATIONS AND IMPLICATIONS OF THE 2007 AMALGAMATION OF SAND-PELICAN ISLAND TO DAUPHIN ISLAND, ALABAMA

Dauphin Island is an typical east-west oriented Gulf Coast barrier island with Sand-Pelican Island a smaller northwest-southeast oriented island located immediately offshore of Dauphin Island. Sand-Pelican Island is fed by sediment moving out of Mobile Bay and across Mobile Bay Pass from the east, where it is temporarily stockpiled before longshore current redistribution to the west. This unusual barrier island configuration changed in December 2007 when Sand-Pelican Island amalgamated to Dauphin Island, disrupting longshore drift currents and changing beach characteristics. Mineral composition of the “plug” is not unique; however, sediment texture and sedimentary structures reveal characteristics about substrate maturation of the newly formed island connection. One year later, sedimentary and biogenic structures reflecting lack of complete sediment consolidation include: tide pool filling from below, liquefaction and collapse features, burrow volcanoes and collapsed burrows, increased burrow density relative to stable island areas, collapsing auger holes, and ease of hand augering. Microbial activity is playing an important role in near surface sediment binding producing a slightly firm “crusty” upper sand surface which reduces erosion and encourages sedimentation. Continued amalgamation is indicated by sediment infilling the remaining tidal pools, numerous en echelon sand spits resulting in significant westward longshore sand transport, wide shallow offshore sand bars west of the amalgamation, and beach widening. The sand source for the westward beach growth is now Sand-Pelican Island rather than Dauphin Island beach. Infilling of Pelican Bay is expected.