BATON ROUGE, La. (WAFB) - It has been 29 years since the National Geodetic Survey (NGS) measured Louisiana’s subsidence, but according to recent results from 2018, the state’s elevation is changing.
With the help of LSU’s Center for Geoinformatics (C4G), NGS completed four absolute gravity observations.
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“This is the second observation NGS has performed in Louisiana, with the first one having taken place at the University of New Orleans in 1989. Since then, the four additional observations through 2018 show a cumulative apparent subsidence of 147 mm in 29 years, which is 5 mm a year,” said LSU Chief of Geodesy Cliff Mugnier.
C4G says a closer look at the results show Baton Rouge, Lafayette, Oakdale, Hammond, and Shreveport have not changed in elevation, while other areas are instead sinking.
- Alexandria: -49 mm
- Old River: -34 mm
- Lake Charles: -16 mm
- Boothville: -13 mm
- Ruston: -9 mm
- Thibodaux: +7 mm
- Siciliy Island: +8 mm
- Rayville: +13 mm
- Natchitoches: +17 mm
“Changes in the absolute value of gravity at a location can be a result of uplift/subsidence, as well as variations in groundwater and tectonic motion. In a generally homogenous sedimentary basin such as Louisiana, it’s likely some combination of subsidence and groundwater,” Mugnier said.
C4G says it now has a permanent, three-person crew that travels across the state to collect data.
“These observations are expected to contribute to the knowledge of the surface motions of the state, as well as to form the basis of a new quasi-geoid model for Louisiana in collaboration among the National Geospatial-Intelligence Agency, NGS, and LSU,” Mugnier said.