WASHINGTON — It’s common knowledge the Louisiana coast is quietly sinking into the Gulf of Mexico. But new research suggests we may have been underestimating how quickly it’s happening.
A paper published Wednesday in the Geological Society of America bulletin GSA Today includes an updated map of the Louisiana coastline and the rate at which it’s sinking into the sea, a process scientists call ‘‘subsidence,’’ which occurs in addition to the sea-level rise caused by climate change. The map suggests that, on average, Louisiana’s coast is sinking a little over a third of an inch per year.
‘‘I think it’s a point worth making that we are finding here that what people recently have considered worst-case scenarios are actually conditions that we already see right now,’’ said Torbjörn Törnqvist, a Tulane University geologist and coauthor of the paper.
Subsidence is believed to be a natural process that has probably been occurring in the region for thousands of years. But scientists believe it has been enhanced by human activities in the Mississippi Delta over the past century, including oil and gas extraction and the building of levees affecting the flow of the Mississippi River, which carries mud and sediment to the Gulf of Mexico and helped build up the delta in the first place.
‘‘When we started building levees along the river, we made it much harder for the sediment to disperse across the delta and beyond the delta,’’ Törnqvist said.
The new map relies on data published earlier this year in another paper Törnqvist also coauthored that was assembled using a novel approach the authors say is more accurate than other methods. It involves a combination of GPS data and special rods, driven deep into the sediment.