Mississippi–Alabama barrier islands

The Mississippi–Alabama barrier island chain sits offshore from the Mississippi Gulf Coast and runs parallel to the coast for , roughly from the Bay of St. Louis to Mobile Bay, separating the Mississippi Sound from the Gulf of Mexico. The five main barrier islands, listed from west to east, are Cat Island, Ship Island (both in Harrison County, Mississippi), Horn Island, Petit Bois Island (both in Jackson County, Mississippi), and Dauphin Island (in Mobile County, Alabama). Another smaller island called Dog Key Island or the Isle of Caprice has intermittently formed and vanished in the inlet between Ship Island and Horn Island; it is currently submerged. The islands have sandy beaches on both their Gulf and Sound shores; the Gulf side beaches are wider and have finer sands due to the greater wave energy they face. The interiors include areas of sand flats, coastal marshes, dune fields, and brackish ponds. The islands are separated by wide inlets, several of which have been channelized through regular dredging to form deep-draft shipping channels. Ship Island Pass (between Cat Island and Ship Island) includes the shipping channel for Gulfport, Mississippi; Dog Keys Pass (between Ship Island and Horn Island) includes the channel for Biloxi, Mississippi; Horn Island Pass (between Horn Island and Petit Bois Island) includes the channel for Pascagoula, Mississippi; Petit Bois Pass (between Petit Bois Island and Dauphin Island) has not been channelized; finally, the mouth of Mobile Bay, east of Dauphin Island, includes the channel for Mobile, Alabama. ==Geomorphology==

The barrier islands are the above-water portions of a nearly continuous sand bar that runs the length of the Mississippi Sound. The bar is thought to have begun forming after about as the Gulf's mean sea level fell after the Holocene climatic optimum. Recurring major tropical cyclones have periodically altered the islands' shapes through wind, waves, and accompanying storm surges. The gradual sea level rise in the Gulf during the past century has contributed to the decrease in land area of the island chain, but the effect is not thought to have been large compared with the influence of the removal of sediment from the system through the dredging of shipping channels. ==Ecology==

The interiors of the islands are vegetated, with pine forests on the higher ridges and marsh vegetation in the lower swales. The chain's sandy beaches serve as nesting grounds for Atlantic ridley sea turtles. ==Islands==

Cat Island Cat Island runs for along the western end of the Mississippi Sound, south of Gulfport. This island has maintained a relatively stable morphology since surveys began, partly due to its relatively high interior elevation. It has a T-shape, with northward and southward spits extending out from its eastern end. Since surveys began, the southward spit has experienced more erosion than the northward one, and all parts of the island have narrowed. Dog Key Island/Isle of Caprice The shoals between Ship Island and Horn Island have intermittently formed small islands known as the Dog Keys (the namesake of Dog Keys Pass), which have been mapped at various dates between 1848 and 1940. By 1932, the island had entirely vanished beneath the surface. Horn Island Horn Island runs for along the central part of the Mississippi Sound. Since surveys began, the island's east end has receded through erosion, while its west end has grown through spit formation at the down-current end. The east end has lost more land than the west has gained, and the island has generally narrowed over the same period. Petit Bois Island Petit Bois Island runs for along the eastern part of the Mississippi Sound, south of Pascagoula. This island has undergone the most dramatic morphological changes in the island chain during the past two centuries. The wider triangular segment that now forms the island's eastern end was its extreme western end as recently as the 1840s, but, as with neighboring Horn Island, the eastern spit has receded rapidly, while a new western tail has grown more slowly. Dauphin Island Dauphin Island, which has over 1200 residents, runs for at the east end of the Mississippi Sound and marks the western edge of the mouth of Mobile Bay. The eastern quarter of the island is wider and more elevated, while the western end is narrow and more prone to disturbance by storms. The east end includes the town of Dauphin Island. Since surveys began, the long western tail has generally lengthened, due to sand deposition from the longshore drift, and shifted toward the mainland, due to erosion on the Gulf shore and overwash during major storms. Island maps File:Cat Island map.png|alt=Cat Island|Cat Island File:Ship Island map.png|alt=Ship Island|Ship Island File:Horn Island map.png|alt=Horn Island|Horn Island File:Petit Bois Island map.png|alt=Petit Bois Island|Petit Bois Island File:Dauphin Island map.png|alt=Dauphin Island|Dauphin Island ==References==