April 4, 2012
Crust Below Mississippi Delta Still Subsiding, Just Much Slower
New data suggests that the Mississippi Delta is still sinking, but at a much slower rate than previously estimated.
A new paper published in the journal Earth and Planetary Science Letters reports these new findings.Geoscientists arrived at this new conclusion after comparing detailed sea-level reconstructions from different areas of coastal Louisiana.
The new findings not only reveal new information about the subsidence of the Mississippi Delta, but also admonishes the continuous measurements of Earth´s environments.
Speaking with reporters from NSF.gov, Thomas Baerwald, geography and spatial sciences program director at the National Science Foundation (NSF) said, “The findings demonstrate the value of research on different facets of Earth system dynamics over long time periods.”
This research was funded by NSF´s Directorates for Geosciences and for Social, Behavioral & Economic Sciences
“The results provide valuable new insights about the factors that affect shorelines and other locations in the Gulf Coast area now and into the future,” says Baerwald. “Our study shows that the basement underneath key portions of the Mississippi Delta, including the New Orleans area, has subsided less than one inch per century faster over the past 7,000 years than the more stable area of southwest Louisiana,” says paper co-author TorbjÃ¶rn TÃ¶rnqvist of Tulane University.
This difference is much less than scientists had previously estimated.
“Other studies have assumed that a large portion of the Earth´s crust underneath the Mississippi Delta subsided at least 30 times faster due to the weight of rapidly accumulating sediments in the delta,” says TÃ¶rnqvist.
This research brings a bit of good news to the people of New Orleans. Widely understood to be sinking at a slow yet steady rate, this research shows New Orleans may not be sinking as quickly as previously thought.
The research team used a number of methods to gauge the subsidence of the Delta region. By taking core samples of dark, gray wetland soil and measuring GPS data, the researchers were able to accurately log their findings. While large structures like coastal defense systems could remain relatively stable, shallower, water rich deposits are more likely to subside more quickly.
This new research has also, however, revealed another troubling issue. Sea levels along the Gulf Coast are rising up to five times faster than industrial era estimates.
TÃ¶rnqvist said, “These subsidence rates are small compared to the rate of present-day sea-level rise from the Florida panhandle to east Texas.”
“The rate of sea-level rise in the 20th century in this region has been five times higher compared to the pre-industrial millennium as a result of human-induced climate change.”
In fact, in the past century alone, sea levels have risen more than eight inches.
This rise in sea-levels is especially noticeable when hurricanes and tropical weather events strike the area. Storm surges from the gulf coast have been destroying Delta land, and in recent years these surges have been winding up further and further on mainland than years before.
“Looking forward 100 years, our main concern is the continued acceleration of sea-level rise due to global warming, which may amount to as much as three to five feet,” says TÃ¶rnqvist. “We can now show that sea-level rise has already been a larger factor in the loss of coastal wetlands than was previously believed.”
Image 1: Geoscientists report new findings on sea level rise and coastal subsidence in Louisiana. Credit: NOAA
Image 2: Aerial view of Delacroix, Louisiana, mostly abandoned due to sea-level rise and wetland loss. Credit: Tor TÃ¶rnqvist