A new report by scientists studying Louisiana's sinking coast says the land here is not just sinking, it's sliding ever so slowly into the Gulf of Mexico.
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Researchers have known for years that the swampy land under south Louisiana is sinking (potholed streets and wobbly porches and floors are visible evidence of that) but a lateral movement of the land into the Gulf enters largely unstudied terrain.
The report, which appeared in December's Geophysical Research Letters, a peer-reviewed journal published by the American Geophysical Union, says the bedrock under heavily populated southeast Louisiana is breaking away at a glacial speed — at the pace fingernails grow.
The southward movement, the study says, is triggered by deep underground faults slipping under the enormous weight of sediment dumped by the Mississippi River.
The slippage, though, is confined to a large egg-shaped area approximately 250 miles long and 180 miles wide that encompasses the delta of the Mississippi, which was built up by river deposits over the past 8,000 years, the report says
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"People should not be afraid that we're going to fall into the Gulf. That's not going to happen," said Roy Dokka, lead researcher and executive director of the Center for GeoInformatics at Louisiana State University.
He described the slide into the Gulf as "a kind of avalanche of material, except that it is happening very slowly. It moved about the width of two credit cards this year."
To put this in perspective, that is 5 inches a year, compared to sea level rise which has historically been 7 inches a century. Even if some of the most dire predictions on sea level rise come true (which I tend to doubt) the next 100 years are supposed to see the sea rise 0.17 inches a year on average. That would make the sliding factor 30 times that of the sea level factor.
Please don't misunderstand me, what this means for the Louisiana coast isn't entirely clear (to me at least.) Much would depend on the unique topology of the Gulf. All I would like folks to remember is that there are other factors at play. So maybe, just maybe, you should take the next doom and gloom article about sea levels on the Louisiana coast with a grain of salt.
The article underscores the point in the following discussion:
Flood protection planners have their work cut out for them as they choose between often competing theories about what is causing Louisiana to lose land at alarming rates. Since the 1930s, more than 2,000 square miles of coast sank or eroded.
Some scientists believe oil and natural gas extraction in the middle and late 20th century caused much of the sinking; others say the land is caving in because the Mississippi River and other waterways were straightjacketed by levees, which stopped floodwaters from replenishing the soil.
And some scientists have suggested the debate over subsidence is overstated.
Torbjorn Tornqvist, an associate professor of earth and environmental sciences at Tulane University, found much of the region surprisingly stable and the rate of sinking to be at least 10 times less than previously reported.
Problems like this can be overstated?? Who would have thought such a thing was even possible....
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