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UTAH COUNTY -- A rock slide tumbled down a mountainside Tuesday afternoon in American Fork Canyon -- but this was no accident. It was triggered on purpose with high explosives, for safety reasons.
It was quite a blast. The National Park Service set it off to protect 80,000 visitors a year who go up the canyon to visit Timpanogos Cave. No one knows how long a big hazard has been there, hanging over their heads.
The hazard? A huge rock on the face of a limestone cliff.
"It's about 30 feet long, 2 feet thick, 4 feet wide. It's a pretty big piece of rock," said Karissa DeCarlo with the National Park Service.
A team of climbers went up the cliff with ropes and high explosives. Their mission was to alter nature, just a little bit.
"I got to tell you, this is a last resort thing in the National Park Service," DeCarlo said.
The rock potentially threatened a shelter that hundreds of visitors file through daily as they exit from the popular Timpanogos Cave. Further below there's also a power line. And far below, a sometimes busy highway.
Late last year, a rock-fall expert discovered that the rock is separating from the cliff by a 4-inch crack. No one knows if the crack is new or has been there for millennia.
"Once we know about an issue like this, it is in our best interest to mitigate that, basically take care of the problem for the safety of visitors," DeCarlo said.
The fiery blast surrounded the rock and tore it apart, converting the big rock into a shower of little rocks. An avalanche of debris thundered down the mountain, but the visitor shelter remained intact and the debris never reached the highway.
"The power lines wiggled quite a bit but didn't fall, and a great boom," DeCarlo said. "So I'm thinking we're going to call this good at this point."
Now that the rock is out of the way, the Park Service plans to build a new exit shelter and to re-route the trailhead.
Also, there's still a lot of snow up there, so the cave is still closed for winter. It opens for visitors on May 8.