Double Arch, rock formation as old as the dinosaurs, collapses in Utah

The Double Arch formation at Glen Canyon National Recreation Area in Utah collapsed last week. National Park Service officials theorize erosion was the culprit.

No one was injured in the tumble Thursday, GCNRA officials said in a release Friday. Witnesses said people cleared out from the water under the formation just before its implosion.

There were “20 or 30 people that had kind of just jumped off and were hanging out inside the bowl,” witness Merril Campbell told Salt Lake City NBC affiliate KSL-TV, when they heard a splash that seemed louder than one made by a person.

“I looked over, and a couple of the guys I was with had seen a big piece of rock fall off the bottom of the arch into the lake,” Mr. Campbell said, adding that the fallen boulder was about the size of a Volkswagen.

The Double Arch, also called the Crescent Pool and the Hole in the Roof, formed from sandstone dating back 190 million years to the late Triassic and early Jurassic periods.

Officials suspect erosion was the feature’s downfall, specifically rising water levels in Rock Creek Bay on Lake Powell inside the recreation area. Lake Powell is an artificial reservoir created by the Glen Canyon Dam starting in 1963.

GCNRA Superintendent Michelle Kerns said the ultimate cause of the collapse isn't 100% certain.

“These features have a life span that can be influenced or damaged by manmade interventions. While we don’t know what caused this collapse, we will continue to maintain our resource protection efforts on Lake Powell,” she said.

Other NPS officials noted that collapses are the natural conclusion to the span of a geological arch’s existence.

“The great thing about geology is that it happens extremely slowly — except for when it doesn’t. Arches National Park doesn’t protect arches. It preserves the natural processes that both make arches and eventually unmake arches,” Karen Garthwait, a spokeswoman for the Arches and Canyonlands national parks that are also in Utah, told The Salt Lake Tribune.

Previous collapses at Arches National Park included those of the Wall Arch in 2008 and the Rainbow Arch in 2018.