The sinkhole that swallowed a swamp

The sinkhole doesn’t look like an ongoing environmental disaster. If you didn’t read the newspapers, watch the YouTube video, or look closely enough to see the miniature bubbles of methane breaking at the surface like a simmering pot, you’d think it was just a lake with a few oil slicks. It even has alligators.

In reality, the sinkhole is a human achievement. It opened up overnight in August of 2012, when the wall of an empty salt mine around 5,000 feet underground suddenly broke. Dirt and rock poured into the cavern, creating a hole at the surface that filled in with water.

Source: Texas Brine and Louisiana Department of Natural Resources

The sinkhole is now 25 acres at the surface, more than 350 feet deep at its lowest point, and expected to double in size. It’s mostly dormant, except for occasional earthquakes and "burping," in which large bubbles of air, oil, and gas erupt at the surface. Every now and then it sucks down a few trees from the surrounding swamp.

While it hasn’t actually swallowed any property — as far as massive sinkholes go, it’s pretty tame — it has caused methane to leak into a nearby aquifer. The fear is that the highly combustible gas will collect in a crevice or enclosed space and then ignite.

The case has become a curiosity for geologists around the world. Salt mines have collapsed before, and not far from Bayou Corne: the collapse of a salt mine at Lake Peigneur, 45 miles away, led to a sinkhole that swallowed 11 barges. But other mines always collapsed from the top. The salt mine in Bayou Corne breached from the side, so the sediment displacement is harder to predict.

Even after recruiting a team of international researchers to study the sinkhole, local officials still don’t know exactly what caused it or what it will do next. Scientists are using 3D seismic imaging, a mapping technique similar to sonar, to produce mangled-looking images of the subterranean topography. Just these maps take six weeks to set up and several months to process.

"I use the BP oil spill and the difficulty of working in 5,000 feet of water for comparison," says Patrick Courreges, policy analyst at Louisiana Department of Natural Resources. "It took five months to get that thing under control. We’re dealing with 5,000 feet of rock."

Louisiana, Mississippi, and parts of Texas sit atop large salt deposits shaped like domes. The easiest way to mine the salt is to dig out a cavern, pump water through, and suck it back out as brine. The salt is then extracted and sold for use in household petrochemical products such as PVC pipe, CDs, and bleach.

In 2010, this particular mine, one of many underneath Bayou Corne, failed a routine pressure test. The owner, Texas Brine Company, "plugged and abandoned" the hole it had created in the salt, which included filling it with brine to equalize the pressure. No one from Texas Brine or the state regulatory agency, the Department of Natural Resources, thought there was any danger of a breach.

But two years later, something happened. "Our employees came to work and looked out, and the swamp had disappeared," says Sonny Cranch, the crisis public relations specialist hired by Texas Brine.

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