ABSTRACT: The Geological Framework of Coastal Land Loss in Louisiana
Shea Penland, Harry H. Roberts, S. Jeffress Williams
The Mississippi River delta and chenier plains in Louisiana are experiencing catastrophic coastal land loss rates exceeding 100 km2/yr. Louisiana's coastal zone contains 40% of the U.S. wetlands and 80% of the nation's loss occurs here. The origin and stability of these coastal environments are tied to the sediments discharged by the Mississippi River through the delta cycle process. Sediments accumulate in well-defined delta complexes at approximately 800-1000 year intervals followed by abandonment and barrier island formation. The delta-cycle process, which builds new deltas and barrier islands, has been stopped by flood control structures. These harness the flow of the Mississippi River within a massive levee system, channeling most of the sediments off of t e continental shelf. Deprived of sediments and subsiding rapidly, Louisiana's wetlands are disintegrating and the shoreline is eroding. Subsidence is a key critical process driving the submergence of Louisiana's sediment-starved coastal zone. The thickness of the Holocene sequence controls the subsidence rate. Where the Holocene delta plain sequence is greater than 50 m, the submergence rates are 1 - 1.25 cm/yr and the land loss rates are 80 km2/yr. In contrast, where the Holocene chenier plain thickness is less than 15 m, the submergence rates are 0.4-0.6 cm/yr, and the land loss rate is 10 km2/yr.
AAPG Search and Discovery Article #90999©1990 GCAGS and Gulf Coast Section SEPM Meeting, Lafayette, Louisiana, October 17-19, 1990