Sinkholes: The hole truth

(CBS News) We can't claim to have the "whole truth and nothing but" . . . but there is a growing body of research into those headline-making sinkholes that can turn an abode into an abyss in the twinkling of an eye. Our Cover Story is reported now by Mark Strassmann:

If you're a fan of science fiction B-movies from the 1950s, sinkholes make perfect sense. They seem almost as improbable as alien body snatchers. The Earth suddenly opens up, with no warning and no escape, and swallows whatever's on the surface -- cars, homes, entire neighborhoods.

But sinkholes, of course, are all too real worldwide, in places like China, Brazil and Guatemala. Florida has so many of them, it has been called "Swiss cheese covered by soil."

In 1981, a sinkhole in Winter Park, Fla., grew longer than a football field. One resident described a sound like "giant beavers chewing." And just last month, a sinkhole in Chicago ate up three cars.

Of course, the sinkhole horror story most of us know best is that one back in February in Seffner, Florida, near Tampa, where a sinkhole 20 feet wide and 60 feet deep opened in the middle of the night.

His body was never found -- the fourth known sinkhole fatality in Florida.

"About anywhere you live in Florida, there is potential for a sinkhole to occur," said state geologist John Arthur, an expert on sinkholes.

Florida's surface has close to 70,000 likely sinkholes; at least 3,400 of them reported since the 1950s.

A sinkhole is a naturally-occurring feature that forms when a cavity in the subsurface collapses. That cavity forms from the natural dissolving of rock.

What was a hole in the ground becomes a hole at land surface.

Florida's bedrock, mostly limestone, lies below layers of soil sand and clay. That bedrock is porous and over time can erode and become unstable, forming what geologists call "karst." From time to time, natural or man-made changes in the water table collapse this karst and create sinkholes.

Those collapses can happen in minutes, and take months to settle.

All states but Hawaii have at least some karst. "That's true," said Arthur. "If you look at a map of karst for the nation, there are little corners of even South Dakota that have the potential for some type of karst activity."

Though some states have a greater risk of sinkholes than others -- and not all sinkholes are the work of nature.

Louisiana is one of those states. Ask Nick and Brenda Romero about a sinkhole's impact. In 1997, they moved full-time to Bayou Corne, a mix of working families and retirees 45 miles south of Baton Rouge.

"It first started out as a fishing community," said Nick Romero. "People were friendly, they stopped, they talked-- shared their stories.

People liked each other so much, every year the community held its own Mardi Gras parade -- part of its Cajun charm.

But last May, people started noticing something odd: gas bubbles in the water nearby.

Then on August 3, a sinkhole opened one-third of a mile from the Bayou Corne neighborhood. Over the last nine months, that hole has stretched fifteen acres wide, and plunged 170 feet deep. It filled up with water, rock, oil and natural gas.

No one enforced the mandatory evacuation order, but roughly 80 percent of Bayou Corne's 350 residents -- including both of Romero's next-door neighbors -- packed up and left.

Romero wants to stay put.

"I'm just not ready to just move out and depend on the sheriff or somebody to protect my property and everything I've worked so hard for," said Nick. "This is home."

And, again, while most sinkholes are natural disasters, this one was not. It was, Romero said, a preventable mistake.

An oil and gas service company called Texas Brine was drilling into a massive underground salt deposit near Bayou Corne. The excavation caused the sidewall of a salt dome to collapse. Three months later, the sinkhole opened.

"We don't have a complete understanding of why that failure occurred," said Bruce Martin, vice-president for operations at Texas Brine. He says his company has drilled 30 relief wells trying to contain and burn off natural gas leaking from the sinkhole into the aquifer.

Martin believes the sinkhole will never threaten the homes in Bayou Corne. But the company, pressured by the state of Louisiana, is preparing buyout offers for all the residents.

"I understand why the homeowners are upset; I would be upset if that was my home over there, too," said Martin. "The response has been very challenging. It's been an all-encompassing, full-frontal assault for the past eight months, and I think we're starting to see a light at the end of the tunnel that it's coming to an end."

But Martin also admits the sinkhole could continue to grow for another year or two.

"When is this going to end? Is it going to end correctly? My concern is about, will it happen again?" said Marylee Orr, the executive director of LEAN, the Louisiana Environmental Action Network.

The group says Bayou Corne's disaster should be a warning to other communities about developing in sinkhole-prone areas.

"Sadly, we do have sinkhole potential here, and we really want to make sure that there are buffer zones -- that there are no homes, or nursing homes or schools or hospitals anywhere near these salt domes," said Orr. "So there won't be another community like Bayou Corne, I hope, here in Louisiana to suffer the kind of heartache they have."

John Arthur, Florida's state geologist, says states could map land surfaces for their sinkhole risks and, where needed, toughen construction codes.

If a home is built in a sinkhole-prone area, Strassmann asked, is there anything that can be done to prevent a collapse?

"There's always a way to mitigate that risk," said Arthur. "You can grout inject and fill that hole and make the land more stable. It's a combination of geology and engineering that can hold the key to that answer."

Texas Brine has been paying residents in Bayou Corne $875 a week to cover temporary housing costs. Buyout offers are expected in the next couple weeks.

But Nick Romero says trust between residents like him and the company has collapsed, like the sinkhole.

He wants to stay, but he's torn between two loves: "My wife has had cancer twice, and she doesn't want to be here, and I don't blame her. And I'm not going to force her to stay here. So we've looked for other places to go, but until that time, I'm staying here. I'm not going anywhere."

"You love your house, you love your wife more," said Strassmann.

"Yeah, yeah."

The last thing the Romeros ever thought would be their major worry in retirement . . . was a sinkhole.

For more info:

• Florida Geological Survey
• Louisiana Environmental Action Network (LEAN)
• Texas Brine
• Sinkholes, Florida Dept. of Environmental Protection
• Edward Ball Wakulla Springs State Park , Florida
• Contact your state's geological survey about sinkholes at stategeologists.org