A massive crack has opened up on a Yosemite National Park cliff face, raising the risk of a dangerous rockfall and forcing the indefinite closure of part of a popular trail, park officials said.

Rock climbers recently reported the crack on the western side of the Royal Arches, near a climbing route known as Super Slide above the Yosemite Valley Loop Trail, according to the National Park Service.

Upon further investigation, officials found that the crack had partially detached a large pillar of rock, and the split was growing.

A climbing guide who scaled the rock face Aug. 6 did not see the crack; by the time of his Aug. 20 climb, the crack had appeared, up to an inch wide and 200 feet long, the recreational magazine Outside reported.

“A climbing ranger and a geologist observed it firsthand and they could hear it cracking like a frozen lake that wasn’t consolidated,” supervisory park ranger Jesse McGahey told Outside. “And there were pieces of rock rattling down the crack without touching it. The park geologist said they’d never seen anything like this. He’s never been able to observe that in his 15 years in Yosemite.”

As a precaution to reduce the risk from potential rockfalls, the National Park Service closed a quarter-mile of the Yosemite Valley Loop Trail at the Ahwahnee hotel. There is no timeline for a complete reopening of the trail, but in the meantime hikers can take a detour.

All climbing routes from Peruvian Flake West to the Rhombus Wall are also closed, including the popular routes Serenity Crack/Sons of Yesterday and Super Slide.

Rockfalls are relatively common in Yosemite, increasing last year as strong fall storms hit the area. In 2022, Yosemite had a documented total of 52 rockfalls within the park, recent data show.

The largest rockfall of 2022 occurred in November from halfway up Middle Brother, part of the Three Brothers granite formation. A roughly 4,000-ton slab of rock detached from the face of Middle Brother and hit a ledge, dislodging over 440 tons more of rock from two other points on the lower end of the cliff. Some boulders caused damage to Northside Drive.

On Dec. 27, another rockfall east of the park’s Arch Rock Entrance fragmented into dozens of boulders, striking a vehicle on El Portal Road and killing two people inside.