Researcher: La. Subsurface Mostly Stable

Parts of coastal Louisiana have remained stable 30 to 50 feet underground for the past 8,000 years with little or no subsidence, a Tulane University researcher writes in a study that contradicts some other recent findings.

That means Louisiana, though disappearing quickly in many spots, might be firmer than previously thought.

“At this point, the most-important implication is that we have heard a lot of doomsday scenarios – everything is subsiding at these incredible rates, and there is nothing you can do,” Tulane geology professor Torbjorn Tornqvist said. “But below the surface, the ‘basement’ is holding up well.”

His research was published recently in Geology, the scholarly journal for the Geological Society of America. He worked with researchers from the University of Illinois and Utrecht University in the Netherlands.

Subsidence – the sinking of the land – is occurring near the surface in the more recently deposited sediments rather than deeper underground, Tornqvist said.

Tornqvist said people need to worry more about rising sea levels than about sinking land.

Understanding subsidence is critical for scientists as Louisiana attempts to fight land loss and protect the southern portions of the state from hurricanes.

Tornqvist and his team based their findings on reconstructing the rate of sea-level rise over the past 8,000 years by taking peat samples. Peat forms as soon as water levels rise above the land surface.

The team compared results from Louisiana with sea level data from the same period in areas in the Caribbean that are tectonically stable, such as Florida and the Bahamas. The researchers found no difference.

Tornqvist’s findings contradict other studies that suggest deep geologic faults are causing much of south Louisiana to sink.

The Tornqvist team chose to sample the Bayou Sale area because of the presence of a fault there, but the fault did not affect rates of subsidence, Tornqvist said.

Information from: The Advocate, www.theadvocate.com.