This goo, he said, surges and pulsates, then slides until it is stopped by friction. The last big round of movement was in 1970.
Dixon, of the University of Miami, said that south Louisiana's movement is a slow and natural process, but one that has been increased by human activities such as building levees and exploring for oil.
Authur Berman, a petroleum geologist from Houston, Texas, who has studied subsidence in the Gulf Coast, agreed, adding that the sliding phenomenon is commonly seen around the Gulf of Mexico.
Berman said that over thousands of years the area that extends 150 miles (240 kilometers) inland around much of the Gulf Coast has been continually subsiding.
Quakes and Floods
Large earthquakes that have been occurring south of New Orleans over the past 20 or 30 years are likely tied to the region's sliding movement, Dokka said.
The quakes usually happen far south of New Orleans, he said (related news: "Rare Earthquake Shakes Gulf of Mexico" [September 11, 2006]).
"But they're all connected to this stuff that is right below south Louisiana about five miles [eight kilometers] deep. It's the bottom of this thing that is sliding out."
According to Dokka, there is a slight potential for a seriously damaging earthquake, but nothing that could cause south Louisiana to suddenly break away from the rest of the state.
What's more, study co-author Dixon added, the region that is sliding sits over a layer of salt that may prevent earthquake-type stresses from building up enough to trigger a large quake.
The report authors all agree that flooding remains Louisiana's main concern and that the state can help protect itself by monitoring coastal subsidence through a global positioning system network that is already in place.
With proper monitoring, levees can be raised and flood protection can be altered as the land sinks and shifts.
"What's important," Dokka said, "is that we've been able to recognize one of the important processes that makes south Louisiana vulnerable."
Free Email News Updates
Best Online Newsletter, 2006 Codie Awards
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
|
SOURCES AND RELATED WEB SITES
|
