Glacial Sediments Add to Louisiana Coastal Subsidence
The sediments pose a particular challenge for New Orleans, causing it to sink irreversibly at a rate of about 0.4 centimeters (0.17 inches) a year, according to data from a network of global positioning system stations and a model of sediment data collected from the northern Gulf of Mexico and the Mississippi Delta.Hurricanes Katrina and Rita in 2005 focused national attention on the Gulf coast's vulnerability to hurricanes due to loss of wetlands and sea level rise. These new findings add another factor for scientists, government agencies and the public to consider when assessing the vulnerability of the region to hurricanes and large storms.A science team led by Erik Ivins of NASA's Jet Propulsion Laboratory, Pasadena, Calif., hypothesized that Earth's very slow gravitational flow response to the weight of the sediments, combined with a 130-meter (427-foot) rise in sea level that took place thousands of years ago, are contributing to the sinking of a 199,000-square kilometer (77,000-square-mile) section of coastal Louisiana.To test their theory, the team developed a physical model of sinking caused by both the weight of the sea level rise and the flow of glacial sediments into the Gulf of Mexico following the retreat of the great ice sheet that covered much of North America some 22,000 years ago. The model spanned the past 750,000 years. Results were compared with actual global positioning system measurements and other geophysical data for southern Louisiana and the Gulf, collected from multiple sources over the past 60 years.The scientists found the model results were in good agreement with the actual geophysical data, predicting sinking of between 0.1 centimeters (0.04 inches) and 0.8 centimeters (0.3 inches) a year. The highest sinking rates were observed where coastal land loss is greatest, near the center of the Mississippi and Atchafalaya River Delta complexes.
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