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30. Texas and Louisiana Gulf Coast, Barrier Islands
This synoptic oblique view along the Gulf coast of Texas and Louisiana was taken with the Linhof camera using a 90-mm lens. Notice the smoothly curving line, molded by successive hurricanes, of barrier islands along the Gulf coast. The Mississippi Delta, seen in close-up detail in slide #29, can be seen on the horizon at top right. Notice how much more sediment is disgorging from the Atchafalaya River into the Gulf through Atchafalaya Bay than from the Mississippi Delta. Dams built upstream for hydroelectric power and water supplies have reduced the amount of rich silt reaching the mouth of the river, and the delta is being eroded.
Though a large flood barrier has been constructed to separate the trunk channel from the Atchafalaya distributary, the continen’s longest river is finding an easier route to the sea. In a short period of geological time, the existing delta will subside and a new delta will extend into Atchafalaya Bay, where the majority of sediment is now being deposited. Notice the current-born sediment movement along the coast. Toward the bottom left of the frame, the Galveston Bay/Trinity Bay inlet can be seen discharging a balloon-shaped stream of sediment — the outpourings of the Trinity River in the vicinity of the Houston metroplex.
Galveston Island, at the northern end of the chain of barrier islands that line the Texas coast, can be seen at the bottom of the frame. Over the course of geological history since the peak of the last ice age 18,000 years ago, the barrier islands have migrated toward the present coast. The Gulf-facing coasts of the barrier islands have been eroded by the steady rise in sea level. Historically the landward side of the islands has extended, built up by sand deposits from overwash during storms, as the Gulf coast retreated. Today that process has ceased in the case of many of the Texan barrier islands. The beaches of the islands are also being eroded by wave attack promoted by sea walls, jetties, and vegetated dunes. The islands are getting narrower through both natural processes and the influence of mankind, whose disturbance of the fragile natural environment has hastened the erosion of these natural storm barriers.
STS-41C, April 1984. Picture #13-51-2422