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Details in the Devil’s

Digital imaging offers a new perspective on a 350-foot-deep geologic wonder.

By Rob McCorkle

It was back in 1955 that Fritz Holt first cast his eyes upon the cavernous hole, known as Devil’s Sinkhole, on the surface of the Edwards Plateau. Twenty years old at the time, Holt and a buddy descended on a crude, steel cable ladder into the 350-foot-deep geologic wonder outside Rocksprings to explore what most people will never see.

“Climbing up and down was a real highlight,” Holt recalls. “But what I enjoyed more were the two lake rooms on the sinkhole floor, which bells out at the bottom. The water, which was probably 20 feet deep, was so clear you could see the bottom and couldn’t tell where the limestone shelf met the water.”

The 72-year-old Houstonian recently went back to dance with the Devil’s Sinkhole one more time. Holt is a member of the Texas Cave Management Association, which is working with the Texas Parks and Wildlife Department and the University of Texas to digitally map the entire cavern. He was on hand to observe and to perhaps get a chance to descend again into the state’s largest single-chambered cavern.

Over three weekends, members of the Light Detection and Ranging project team set up a makeshift camp and spent days rappelling into and out of the collapsed limestone pit that sits at the heart of the Devil’s Sinkhole State Natural Area. Team members used state-of-the-art laser mapping equipment to record the interior’s details so a three-dimensional map can be produced later to serve as an educational and management tool. But unlike most conventional maps, the team’s rendition of the sinkhole will be linked to digital photographs to create an unprecedented three-dimensional virtual view of the cave.

In addition to producing eye-popping images, the effort has many practical implications, according to project leader Geary Schindel, the aquifer science manager for the Edwards Aquifer Authority.

Already, a water-level monitoring device placed inside the sinkhole more than a year ago has been taking measurements every four hours and registering the data in a log. Schindel says TPWD wants to know how rainfall affects the sinkhole’s lakes so it can better understand how water levels fluctuate in the Edwards Aquifer at this westernmost edge of the Edwards Plateau as compared to water levels in the Edwards Aquifer around San Antonio. The initial project was undertaken for a Witte Museum World of Water exhibit to demonstrate how water flows through the surface karst, or fractures in the limestone surface, and into the underground reservoir.

Park superintendent Randy Rosales asked the crew to return last November to map the entire cave. He hopes to use digital imaging to give Devil’s Sinkhole visitors, who can only peer into the abyss from a platform on its edge, another perspective of the geologic wonder.

“We may be able to create a 3-D movie where they could ‘fly down’ the cable into the cave and fly around the interior,” Rosales said.

And, yes, Fritz got to see the sinkhole from down below once again. This time, though, it was much easier. The self-described “young man in an old body” was lowered in and out of the gaping hole in a harness, letting the young whippersnappers above provide the muscle.

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