The Assumption Parish sinkhole near the Bayou Corne community produced one of its periodic burps early Tuesday after several days of increased seismic activity suggested another might be coming, parish officials said.
Scientists working on the sinkhole recorded a certain kind of seismic signal known as a “very long period” event at 3:24 a.m. Tuesday, officials said in a brief blog post. “And it is likely that this is when the burp happened,” officials said.
Seismic activity has waxed and waned for more than nine months around the swampland sinkhole between the Bayou Corne and Grand Bayou communities as the hole has continued to grow and find its final shape, at times expelling gas, crude oil and vegetation. Residents of both communities were ordered to evacuate for their own safety when the sinkhole was discovered Aug. 3.
Scientists think the sinkhole is connected to deeper strata where oil and gas have been unleashed by the failure of an underground Texas Brine Co. salt dome cavern that is in the process of being filled with rock.
Known as VLPs, the very long period events are a type of seismic activity that can last as long as 15 minutes and indicate gas or fluid movement in the rock under the sinkhole.
John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness, said Tuesday scientists are checking video recorders at the sinkhole to see if gas escaped during the burp or if water in the sinkhole moved.
The burps, which normally involve a release of gas and debris, sometimes also create tidal-like motions in the water at the surface of the normally tranquil 15.1-acre sinkhole.
Boudreaux said no edge collapses, or slough-ins, have been noted around the sides of the sinkhole and little new debris has surfaced.
On Sunday, parish and state Office of Conservation officials raised the response level to the sinkhole to the highest stage after micro-earthquakes reached a frequency that in the past indicated an imminent edge collapse or burp — more than 50 micro-quakes per day.
Micro-earthquakes are an indication of breaking rock underground and consist of brief events sometimes known as sharp tremors.
By Monday, Boudreaux said, both the micro-earthquakes and very long period events had reached daily frequencies that pointed to an imminent event.
Neither kind of seismic event is normally felt at the surface by people and haven’t been reported in this latest occurrence, Boudreaux said.
He said Tuesday morning that work inside the 71-acre area contained by the berm surrounding the sinkhole remains stopped, as it has since Sunday.
Increased seismic activity had begun limiting some work on the sinkhole starting on May 1, Boudreaux has said.
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