According to some GPS data compiled by geological scientists, New Orleans is sliding into the Gulf of Mexico. It seems that the city is situated on a big, moving mass of bedrock that is detached from the North American Continent. Over the next few thousand years, this rock will slowly move south toward the Gulf, but it is simultaneously sinking at more than twice the rate at which it is moving.
I wonder who New Orleans Mayor Nagin, Louisiana Governor Blanco and the Democrats will blame for this other natural phenomenon?
GPS data collected between 1995 and 2006 suggest that southeast Louisiana, including New Orleans and the larger Mississippi Delta, are both subsiding vertically and moving southward with respect to stable North America. Both motions are likely related due to their common tectonic setting. Subsidence in the New Orleans area occurs in part because it is located in the hanging wall of a large listric normal fault system that forms the northern boundary of a 7-10 km thick allochthon (a large, moving block of rock) that is detached from stable North America. Southward motion of this allochthon relative to stable North America occurs at 2.2 ± 0.6 mm/yr.
The average subsidence rate for GPS sites located on the allochthon is 5.2 ± 0.9 mm/yr relative to Earth’s center of mass, or ∼7 mm/yr relative to mean sea level. Motion of the allochthon is likely due to the gravity instability created by rapid Holocene sediment deposition in the delta following continental glacial retreat and is facilitated at depth by weak salt horizons. Because New Orleans and other communities of southeastern Louisiana lie atop this active allochthon, future motion of this body should be considered during rebuilding of the region following Hurricanes Katrina and Rita.
Abstract in Geophysical Research Letters December 2006: Tectonic control of subsidence and southward displacement of southeast Louisiana with respect to stable North America
by
Roy K. Dokka – Center for GeoInformatics and Department of Civil and Environmental Engineering, Louisiana State University, Baton Rouge, Louisiana, USA
Giovanni F. Sella – National Geodetic Survey, National Oceanic and Atmospheric Administration, Silver Spring, Maryland, USA
Timothy H. Dixon – Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, USA