BAYOU CORNE, Louisiana — There's been a drop in the rock and sediment pushed into the failed salt dome cavern suspected of creating a 15-acre sinkhole in Assumption Parish.
That may indicate increased stability around the site, regulators and Texas Brine Co. told The Advocate (http://bit.ly/12oMcDL ).
Since autumn, rock in the cavern has risen about 27 feet a week but a measurement Friday showed a 29-foot drop from the previous week's level — the first drop since the sinkhole emerged, parish emergency director John Boudreaux said.
Over nearly three decades, Texas Brine used pressurized fresh water to mine brine from the Napoleonville dome, a vast solid salt deposit stretching miles below the surface, creating a roughly cylindrical cavern in the salt.
Scientists think the 2,258-foot-tall cavern broke a bit more than a mile below the surface, near its bottom. The pressure of 5,600 feet of rocks, dirt and muck forced rocks and sediment into the cavity.
"It had reached a point where 98 percent of the cavern had been filled with sediment," Texas Brine spokesman Sonny Cranch said Sunday. "Now that sediment, under the weight and pressure of that depth, is starting to compact. That's our speculation."
When earth moved into the cavern, that undermined shallower layers of rock and sediment, creating a sinkhole that is now 174 feet deep, scientists have said. The flow of rock has continued, fueling growth of the sinkhole and certain types of earth tremors.
Scientists have said that the sinkhole would begin to stabilize after the cavern gets filled to its roof with rock.
If Texas Brine experts are right, dirt inside and outside the sinkhole could reach equilibrium before that.
State regulators said it was too soon to make claims about equilibrium but stability may be improving.