Louisiana Coast Sinking 50 Percent Faster than Thought, New Study Says

Land along Louisiana's coastline is sinking 50 percent faster than was estimated just two years ago, according to a new map published Wednesday (June 14) as part of a study by Tulane University geologists.  It says the average subsidence is 9 millimeters a year, more than one third of an inch.

In the worst spots, the subsidence rate is closer to 12 millimeters, or almost a half inch.  Among them:

• Along the Mississippi River below New Orleans, including near Caernarvon
• Onshore just north of the Isles Dernieres, at the Atchafalaya and Wax Lake deltas west of Morgan City
• In an inverted triangle of land between Kaplan and Lake Arthur along the eastern part of the Chenier Plain.

The new study measures only the sinking of ground and not the sea level rise of an additional 3 millimeters, or one 10th of an inch, says Torbjorn Tornqvist, a geology professor at Tulane and one of the authors of the study.  The combination of subsidence and sea level rise is called "relative sea level," which in this case would average 12 millimeters across the coast and 15 millimeters, approaching two thirds of an inch, in areas with the fastest subsidence.

The study was published in the online journal GSA Today by the Geological Society of America.  The lead author of the study was Jaap Nienhuis, a post-doctoral fellow at Tulane.

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