Surges of gas-charged fluid may have explosively generated the earthquakes preceding a giant sinkhole in Louisiana, researchers say.
On Aug. 3, 2012, a giant sinkhole formed overnight near Bayou Corne in southeast Louisiana, prompting a declaration of emergency from state officials and evacuation of nearby residents. The sinkhole — filled with a slurry of water, debris and crude oil — swallowed cypress trees, and recent estimates suggest it is now more than 215,000 square feet (20,000 square meters) and about 330 feet (100 meters) deep.
Frequent tremors were reported in the two months before the sinkhole opened. Researchers had suspected the collapse of a plugged-up, abandoned salt cavern underneath the nearby Napoleonville salt dome may have caused these small earthquakes and the sinkhole.
To find out what might have caused these tremors, scientists analyzed data gathered by a temporary network of seismic stations that the U.S. Geological Survey had set up in the area. The scientists detected 62 tremors — which ranged in magnitude from 1.3 to 1.6 — in the day before the sinkhole was discovered.
Unexpectedly, the scientists found that the tremors originated about 1,540 feet (470 meters) beneath the western edge of the Napoleonville salt dome.
The seismic data suggested that the sinkhole-linked quakes were caused by explosive events similar to volcanic eruptions. While hot magma causes volcanic eruptions, these sinkhole-linked quakes were apparently triggered by high-pressure gushes of either natural gas or water charged with natural gas.
The surges of natural gas that caused the tremors may have weakened the salt cavern and caused its collapse. Alternatively, a collapse of part of the salt cavern may have caused a nearby gas pocket to give off surges of gas, later followed by the complete collapse of the salt cavern.
—Charles Q. Choi, LiveScience