Crews discover large cave underneath RM 620


by SHANNON MURRAY / KVUE News and Photojournalist Dennis Thomas

Bio | Email | Follow: @ShannonM_KVUE

Posted on July 9, 2013 at 6:29 PM

Updated Tuesday, Jul 9 at 6:41 PM

ROUND ROCK, Texas -- Construction crews working on the RM 620 expansion project have unearthed a large cave system. Geologists say, although it's an exciting discovery, it's not surprising.

Improvements to the road continue, except for the two-mile stretch from Wyoming Springs Drive to Cornerwood Drive. That's where a small hole turned out to be much more.

As crews were installing a storm sewer line, they found a cave sprawling 100 feet long, 60 feet wide and at some points reaching as high as 20 feet.

"It's the continuous learning process," said geologist Jim Sansom. "I know there are some caves very close to it and caves across the road from it and down the road because it's along the Edwards."

In 1963 a similar situation happened in Georgetown when crews drilling for a railroad overpass on I-35 found what we now know as Inner Space Cavern.

"We just found it by accident," Sansom explained.

At 26 years old, he became one of the first to venture inside

"I had no idea it'd be this big," he said of the discovery.

He says these cave systems, common along the Edwards Aquifer, are made up of calcium carbonate limestone.

"It's very dissolvable by rain and our natural rainfall is acidic," Sansom said. "Then you put a fault zone in the middle of it that faulted this and gives avenues for the water to come down."

"In Central Texas it's kind of common when you're doing a construction project that you might find a carsed feature," said Williamson County Spokesperson Connie Watson.

Watson says right now the area is blocked off for safety.

"It's dangerous for people to go near it. And we want to keep the cave in tact while we are deciding what to do in this circumstance," she explained.

They have three options: put a bridge over it, fill it and seal it up, or re-route the road.

"We know there's some more caves out there. Whether it's worth developing, the developers have to answer," Sansom said.

Even 50 years after his Inner Space discovery, Sansom says he's still curious about what's going on underground.

"Every time I come in I see something different and I keep looking," he said. "There's probably a lot to be discovered. Just like this one. You have to dig into them and find them."

Watson says there's a possibility of more caves along RM 620. Crews are submitting a report to the Texas Commission on Environmental Quality. In the meantime, they will continue working on the rest of the project. Right now Watson says everything is still on schedule.

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