Sinkhole work stops as tremors increase

Another round of increased tremors has halted work at the sinkhole near the Bayou Corne community, Assumption Parish officials said Monday.

Work stopped Sunday and again Monday on the sinkhole itself and inside a 1.5-mile containment berm, which surrounds 71 acres that encompass the sinkhole near Bayou Corne and Grand Bayou, parish officials said.

John Boudreaux, director of the parish Office of Homeland Security and Emergency Preparedness, said Monday the halt in work is done in an abundance of caution based on past experience with the tremors.

Upticks in tremor frequency have sometimes been followed by burps of gas, oil and debris and edge collapses in the sinkhole.

“We just get everybody out of the area and wait for what is going to occur, to occur,” Boudreaux said, adding tremor activity typically slows down afterward.

The 13-acre, 160-foot-deep sinkhole has forced the evacuation of about 350 people for more than eight months from the Bayou Corne and Grand Bayou communities lying on either side of the swampland hole.

The increased numbers of tremors Monday are around the sinkhole and near a failed subterranean Texas Brine Co. cavern, the collapse of which is suspected of causing the sinkhole last year. The cavern was carved inside the Napoleonville Dome near its western face.

This collapse has allowed millions of cubic yards of earth and rock to enter the cavern and rise up inside it. That sidewall is still collapsing, scientists have said.

State and local officials have scheduled a community briefing on the sinkhole at 6 p.m. May 1 in the Assumption Parish Community Center, 4910 La. 308, in Napoleonville.

Texas Brine spokesman Sonny Cranch said Monday that construction on the berm also was halted Sunday and Monday but due to wet weather.

He said work would have been suspended due to the tremors, however, had the weather been better.

Boudreaux said scientists reported that in this instance, the number of micro-earthquakes has increased from about 10 tremors per day to 50 per day.

Sometimes known as sharp tremors, the micro-earthquakes have been attributed to breaking rock underground, scientists have said. The breaking rock is filling the failed cavern, which at last measurement was 97 percent full.

Increases in different kinds of tremors several times last month halted work and preceded edge collapses that added more than 1.25 acres to the sinkhole’s surface area, taking down trees and part of a well pad used for access to the lake-like hole and for seismic monitoring.

The stretched out tremors increased in number several times last month are known as “very long period” events. They indicate fluid or gas movement through a zone of fractured rock 800 feet across and 6,000 feet deep that rises up along side the salt dome and under the sinkhole, according to an April 5 scientific presentation made to the state’s expert sinkhole panel.

The fracture zone was created deep underground in conjunction with the Texas Brine cavern failure and rose over a period of at least months to the surface, the presentation says.

The fracture zone also may have tapped into oil and gas bearing formations along the salt dome’s face and is acting as a pathway for the hydrocarbons, as well as salty groundwater, to the reach far shallower strata and the sinkhole.

Boudreaux said Monday the long period events are occurring but not at an increased level.