Geologists said a 260-foot-deep sinkhole that grew to the length of three football fields over just two days seemed to be slowing down Thursday, but that it could take months before it's clear whether surrounding areas are stable.
The 900-foot-long sinkhole, with crumbling dirt around its edges resembling sharp teeth, has swallowed up oil tanks and barrels, tires, telephone poles and several vehicles in Daisetta, a once-booming oil town of about 1,000 residents about 60 miles northeast of Houston.
Residents feared the appetite of the sinkhole, which began as a 20-foot hole in the ground on Wednesday, would continue unabated Thursday and threaten nearby homes. But by Thursday afternoon officials and geologists allayed those concerns.
"We're not sure it has completely stopped. We're confident it has slowed down," said Tom Branch, coordinator of the Liberty County Office of Emergency Management. "We feel a whole lot better today."
Looking like a tar pit
A day earlier, Branch, other officials and residents had watched as large chunks of earth, as well as the oil field equipment, trees and vehicles that sat on them tumbled into the crater. The mixture of oil and mud at the bottom of the sinkhole made it look like a tar pit.
Carl Norman, a geologist working with officials, said he planned to measure the change of ground elevation around the sinkhole over the next few days to try to determine whether it is still growing or is now stabilized. But he added, "It will be at least three months before we can say if it's stable or not."
Jayme Downs, whose home is about 300 yards from the sinkhole, said she wasn't sure if her nerves can hold out that long.
"I'm very worried," Downs said as she and her 5-year-old daughter stood in front of the local high school, about a quarter of a mile from the sinkhole. Classes were in session on Thursday.
"You don't know what is going to happen. There's no way to tell. The whole town could cave in. You never know," she said.
Officials said any further growth of the sinkhole probably would be very slow, and if nearby homes were in danger, there would be advance warning. There are about 100 homes in the immediate area.
Cpl. Hugh Bishop with the Liberty County Sheriff's Office said no homes had been evacuated and there had been no reports of injuries.
Cause still uncertain
Officials are still trying to figure out what caused the sinkhole.
Daisetta sits on a salt dome, a natural formation created below the ground over millions of years where oil brine and natural gas accumulate. Oil drilling in the area, still dotted with working oil derricks, might have weakened the dome and caused it to collapse, Norman said.
But the sinkhole might also be a natural occurrence caused by ground water leaking into the salt dome and dissolving parts of it.
Don Van Nieuwenhuise, a geosciences professor at the University of Houston, said oil production usually doesn't affect the integrity of a salt dome. He said he thinks the sinkhole is probably related to saltwater waste that is being stored underground in the area. The saltwater is a byproduct of oil production and has to be stored underground so it won't contaminate water supplies and the environment.
"It probably fractured part of the salt dome and it's leaking out," he said.
Investigators with the Texas Railroad Commission were checking pipelines and trying to determine if any regulations have been violated. Officials with Texas Natural Resources and Conservation were monitoring air and water quality. So far, no pollutants have been detected.
Petroleum refiner Sunoco Inc. secured two 6-inch crude oil pipelines near the sinkhole that had started to leak Wednesday.