The Lafourche Delta And The Grand Isle Barrier Island

The evolution of barrier islands along the northern Gulf of Mexico coast is directly related to source of sediments and littoral processes. Johnson formulated his hypothesis on barrier island formation in 1919, and his theory prevailed for several decades. Johnson's theory resulted from consideration of only two dimensions normal to the coastline; a third, longshore drift, was not regarded as critical for the initiation of barrier island development. In this study, which is confined to the northern Gulf coast, major sources of sediment supply and transportation patterns of barrier forming sand were examined, along with results of recent oceanographic investigations in the Gulf of Mexico. This study is based on a comprehensive survey of the literature, maps, and marine charts, which were correlated with field observations. To obtain a perspective, only gross forms and processes of barrier development were considered. Evidence indicates that Santa Rosa Island, Mississippi Sound, and Bolivar Peninsula barriers developed downdrift of sediment-supplying coasts of Quaternary age. These barriers evolved with the Recent rise of sea level to its present stand. Apalachicola barriers formed on the flanks of the Pleistocene deltaic plain. Coasts such as the stretch between Destin and Panama City, Florida, and the zero-energy coast of Florida do not have barrier islands. In these cases the modern shoreline is abutted against Pleistocene deposits which are the local source of sediments. (Author).