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The Mississippi River Delta region is a 3-million-acre (12,000 km2) area of land that stretches from Vermillion Bay on the west, to the Chandeleur Islands in the Gulf of Mexico on the southeastern coast of Louisiana.〔Couvillion, B.R.; Barras, J.A.; Steyer, G.D.; Sleavin, William; Fischer, Michelle; Beck, Holly; Trahan, Nadine; Griffin, Brad; and Heckman, David, 2011, Land area change in coastal Louisiana from 1932 to 2010: U.S. Geological Survey Scientific Investigations Map 3164, scale 1:265,000, 12 p. pamphlet.〕 It is part of the Louisiana coastal plain, one of the largest areas of coastal wetlands in the United States.〔Louisiana’s Coastal Area. “Ecosystem Restoration.” LCA – Louisiana Coastal Area. http://www.lca.gov/Learn.aspx〕 The Mississippi River Delta is the 7th largest delta on Earth (USGS) and is an important coastal region for the United States, containing more than 2.7 million acres of coastal wetlands (4,000 mi2 or 11,000 km2) and 37% of the estuarine marsh in the conterminous U.S.〔 The coastal area is the nation’s largest drainage basin and drains about 41% of the contiguous United States into the Gulf of Mexico at an average rate of 470,000 cubic feet per second.〔CWPPRA: Coastal Wetlands Planning, Protection, and Restoration Act. “The Mississippi River Delta Basin.” http://lacoast.gov/new/About/Basin_data/mr/〕〔Kulp, Mark; Penland, Shea; Williams, S. Jeffress; Jenkins, Chris; Flocks, Jim; and Kindinger, Jack. Spring 2005. Geologic Framework, Evolution, and Sediment Resources for Restoration of the Louisiana Coastal Zone. Journal of Coastal Research SI(44), 56-71. West Palm Beach (Florida), ISSN 0749-0208〕〔http://www.merriam-webster.com/dictionary/delta〕 The Mississippi River Delta is not to be confused with the Mississippi Delta region, an alluvial plain located some 300 miles (480 km) northward in western Mississippi along the Mississippi River. == History and growth of the Mississippi River Delta == The modern Mississippi River Delta formed over the last approximately 7,000 years as the Mississippi River deposited sand, clay and silt along its banks and in adjacent basins. The Mississippi River Delta is a river-dominated delta system, influenced by the largest river in North America. The shape of the current birdfoot delta reflects the dominance the river exudes over the other hydrologic and geologic processes at play in the northern Gulf of Mexico.〔Blum, M.D. and Roberts, H.H. 2012. The Mississippi Delta Region: Past, Present, and Future. Annual Review of Earth and Planetary Sciences, vol. 40, pp. 655-683〕 Prior to the extensive leveeing of the Mississippi River that began in the 1930s, the river avulsed its course in search of a shorter route to the Gulf of Mexico approximately every 1,000-1,500 years. The prehistoric and historic delta lobes of the Mississippi River Delta have influenced the formation of the Louisiana coastline and led to the creation of over 4 million acres of coastal wetlands.〔〔Coleman, J.M., Roberts, H.H., and Stone, G.W. 1998. Mississippi River Delta: An Overview. Journal of Coastal Research, vol. 14, pp. 698-716〕〔Kolb, C.R. and Van Lopik, J.R. (1958). Geology of the Mississippi River deltaic plain, southeastern Louisiana. Technical Report 3-483. Vicksburg, MS: U.S. Army Corps of Engineers Waterways Experiment Station〕 As the river changed course, the natural flow of freshwater and sediment changed as well, resulting in periods of land building and land loss in different areas of the delta. This process by which the river changes course is known as avulsion, or delta switching, and forms the variety of landscapes that make up the Mississippi River Delta.〔 In the natural deltaic cycle process, the delta lobe, which is the land that forms where the mouth of the river meets the sea, will grow, extending outward from the river as it overflows its banks and deposits sediments into basins. This process is known as progradation. In areas located further from the river’s mouth, the transgressive processes of subsidence, erosion and sea-level rise will dominate, leading to coastal retreat in these areas. Because of the natural progradation and degradation periods, the building of the Mississippi River Delta is an integrated and long-term process that has given the region its unique mix of ecosystems, habitats and landforms. The Atchafalaya River is the largest distributary of the Mississippi River and is also considered to be an influential part of the continual land-building processes within the Mississippi River Delta.〔Rosen, T., and Xu, Y. J. 2013. Recent decadal growth of the Atchafalaya River Delta complex: Effects of variable riverine sediment input and vegetation succession. Geomorphology, 194, 108-120. doi:http://dx.doi.org/10.1016/j.geomorph.2013.04.020〕 The river’s tributary channel was formed approximately 500 years ago and the Atchafalaya and Wax Lake deltas emerged around the middle of the twentieth century.〔 Starting with the earliest European settlement, man has struggled with the delta’s natural cycle of floods, progradation, and transgression.〔O’brien, Greg. 2002. Making the Mississippi River Over Again: The Development of River Control in Mississippi. Mississippi History Now; online publication of Mississippi Historical Society. Online. http://mshistory.k12.ms.us/index.php?id=94〕 Increased economic development and human habitation in the region created a desire to protect society from the threats posed by this mighty waterway. Beginning in the 20th century, advances in technology and engineering allowed humans to alter the river in fundamental ways. Although these changes successfully shielded many people from danger and enabled significant economic development in the region, they have proven to have profoundly negative effects on the downstream delta. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mississippi River Delta」の詳細全文を読む スポンサード リンク
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