A huge slab of Landscape Arch the longest arch in Arches National Park and one of the longest in the world - fell this week, and park officials expect more to slough off soon from its 306-foot span.
Sunday afternoon several tourists witnessed a 60-foot-long, 8-foot-wide and 4 1/2-foot-thick piece fall from the underside of the arch near the center of the span, and a ranger arrived minutes after the fall, the Park Service said.Popping, cracking and snapping before the fall alerted tourists to capture the unique moment on film. The video was recorded by a European whose tape isn't compatible with American equipment. But park officials said the tourists promised to mail copies of videos and photos to park offices in Moab once they arrive home.
"Amazingly enough, no one was injured," a Park Service statement says. "The arch was only 16 feet at its thickest point. With 41/2 feet less for support, it must have seemed that barely anything was holding it up."
Rangers closed off the trail crossing under the arch. And it's a good thing. Two more small slabs apparently fell sometime Wednesday evening.
Park Superintendent Noel Poe said there were no witnesses Wednesday, but in making comparisons early Thursday rangers could see that more had fallen since Sunday.
Two more pieces - one of them estimated to be 12 feet long - are expected to fall soon, he said. "The arch is still making popping noises as it adjusts to the loss of weight. Thursday morning we were there and heard a loud pop. Nothing fell, but there is still some settling going on."
Although the short loop crossing under the arch is closed, tourists can see the arch from the Double Garden trail, which leads to the loop. Poe said that with binoculars you can see the stress fractures and cracks in the arch. The surface is a fresh pink where the slabs have broken off, contrasting with the darker sandstone.
Poe said it's unusual for rock formations to spall during summer. Pieces slough off usually because of freezing and thawing during winter or early spring.
The last recorded rockfall at Landscape Arch happened sometime in winter 1941, when a large boulder slipped from the north end of the arch. That fall increased the arch's length from 291 feet to its current length.
"This is quite unusual, and to be honest we're at a loss as to how to explain it outside of the normal erosion process," Poe said of this week's rockfall from Landscape Arch.
Poe wouldn't guess how much longer the arch will stand. But he said he won't make any attempt to salvage the landmark.
"The whole idea of a park is to let natural processes continue," he said. "We couldn't do anything of value anyway, and we may just hasten its falling."