Wednesday, July 26, 2006

Why is Louisiana Sinking?

Louisiana Coast

Louisiana Swamp

Louisiana's Sinking Coast

Louisiana Coastal Map

While there is no doubt southern Louisiana is sinking, experts disagree on the extent, speed and primary cause of its slow drop into the sea.

Two recent scientific studies point to two very different causes and rates of subsidence. Scientists fear the apparent contradiction might send a confusing message to policy makers, who are under pressure to make decisions now about the future of New Orleans and other coastal areas.

A study in the August issue the journal Geology blames the gradual compaction of river sediments, using radiocarbon-dated peat sediments deposited as far back as 8,000 years ago as evidence.

Because the peat was left behind by sea-level marshes, the sediments show past changes in sea level over time.

"Our conclusion is, of course, that the land surface is subsiding," said Törnqvist.

Törnqvist detected, on average, a loss of a tenth of a millimeter per year from the compaction of sediments.

That comes to just a tenth of a meter drop per 1,000 years. That rate of subsidence is in stark contrast to the rate — up to 170 times greater — reported in another recent study limited to the past 50 years.

"The problem with using the peat layers is that they are time-averaged," said geologist Roy Dokka of Louisiana State University. In other words, the peat can’t show changes over shorter periods, like 50 years.

Dokka led a team that recently completed a rigorous survey of data from same region and found evidence of almost 17 millimeters per year of subsidence in some places.

These are changes affecting the region now, he stressed. Dokka and his team published their results in the April issue of Geology.

Dokka has identified what looks like a gigantic landslide feature giving way in metropolitan New Orleans and slumping far out in the Gulf of Mexico. That’s something entirely beyond human control -- unlike soil compaction, which can be exacerbated by oil, gas and water extraction, and levee building.

Check out the article at Discovery News.

The last 100+ years of levee building and channel cutting have eliminated the sediment deposits and enabled saltwater to intrude upon inland marshes. Consequently, we humans have created our own sinkhole.

We need to re-engineer the coast in an attempt to counteract these man-made problems, if it's not too late.

I'm not sure if there's much we can do to fight it at this point. Nature is a powerful force, maybe we should just move to higher ground.

Check out Coalition to Restore Coastal Louisiana and Louisiana Coastal Area Ecosystem Restoration Project.

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