Explainer: What's lurking beneath the surface in Hickory?

Explainer: What's lurking beneath the surface in Hickory?

This sinkhole opened up Thursday in Hickory.


by JEREMY MARKOVICH / NewsChannel 36


Posted on May 20, 2011 at 1:30 PM

Updated Friday, May 20 at 1:30 PM

Hickory Sinkhole

View larger map

HICKORY, N.C. -- Let’s say you are Ralph Betz, and you have just bought a yellow Corvette. You walk inside a restaurant in Hickory to grab lunch one day, and when you walk back outside your car, your only car, is now sitting 38 feet below the parking lot, at the bottom of a sinkhole.

You might be upset.

That actually happened in 2002, in the parking lot of Buffalo's Southwest Grill in Hickory. It took crews five months to pull Ralph's Corvette up from the bottom (his insurance company had bought him a new one by then). Contractors dumped more than 230 truckloads of dirt into it. In 2005, another sinkhole opened up in, wait for it, the same parking lot.

On Wednesday, another sinkhole, 12-feet wide and 18-feet deep, opened up on U.S. 70, just down the road from the old Buffalo's Southwest Grill. Smaller ones have opened up in other parts of town over the years. So what, exactly, is lurking beneath the surface in Hickory?

Red clay, mostly. Ken Taylor, the chief of the North Carolina Geological Survey, says most sinkholes in the Piedmont (including each one mentioned here) are caused simply by overflowing or busted pipes and storm drains.

Each torrential downpour might wash away bucketfuls of dirt around the rupture. Give it enough time, he says, and the weight above gets too heavy for the hole below and then, well, goodbye Corvette.

If you're lucky, you can catch the symptoms early.

"If everything coming out of the storm drain is bright red and not brown," says Taylor, "then ooh, something's up."

Geologists can also look for dips on the surface and stick a probe into the ground to see if there's anything beneath, much like hammering a nail into a drywall to look for a stud. If it goes in too easy, you might have just found your next sinkhole-to-be.

Is there something about the dirt below Hickory, then, that makes it more prone to Corvette-swallowing craters? Not really, Taylor says. The only place where the ground is a factor in forming sinkholes is out near the North Carolina coast, where acid rain can dissolve the subterranean limestone that's not found in the Piedmont.

Around Charlotte, there's a different factor at work: abandoned gold mines. Sometimes water can eat away at those old gold rush-era tunnels and the ground, occasionally, comes crashing down.

For most sinkholes, though, busted water mains, heavy rains and cracked-open drains explain the sinking terrain. Besides, Taylor says spontaneous craters are rare.

"How many times do we have a car eaten by a sinkhole in North Carolina? Maybe once a decade," he says.

Well, that's a relief.