Snow in Yosemite National Park
Sierra Sun Times file photo
January 30, 2023 - Yosemite National Park officials report 2022 proved to be an active year for rockfalls and other slope movements in Yosemite, particularly along lower elevation roadways. Although there weren’t any especially large-volume rockfalls in 2022, the year was a reminder that even relatively small rockfalls can be highly consequential.
The first significant rockfall occurred at 2:37 pm on May 15, originating from just below Union Point. A rock outcrop at the top of the slope there slid over a cliff, breaking into boulders that tumbled down a gully, crossing nine switchbacks of the Four Mile Trail before falling to the valley floor. Two visitors hiking the trail were hit by rocks, sustaining minor injuries.
Rockfall activity increased in the fall as storms swept across Yosemite. The Big Oak Flat Road was damaged by a rockfall on the evening of November 8, and again by a larger rockfall on the early morning of December 12; in both cases the road was closed for a few days while rocks were removed and the road repaired.
The largest rockfall of 2022 originated from midway up Middle Brother on the evening of November 12. A slab of rock of about 1,344 cubic meters in volume (about 4,000 tons) detached from the face, hitting a ledge; that impact then dislodged another 158 cubic meters (446 tons) from two other points lower on the cliff. Most of the resulting rock debris was deposited on the talus slope below the cliff, but some boulders bounced over Northside Drive, causing minor road damage.
The most consequential rockfall of 2022 occurred at 9 am on December 27. About 60 cubic meters (about 180 tons) of rock fell from the north rim of the canyon east of the Arch Rock Entrance Station, fragmenting into dozens of boulders that tumbled down to the El Portal Road. A vehicle traveling toward Yosemite Valley was struck by a boulder, tragically killing the two occupants.
The final days of 2022 corresponded with another period of heavy rain, resulting in at least 15 rockfalls and debris slides within a 24-hour period that again affected park roads.
Other substantial rockfalls in 2022 occurred from El Capitan, Half Dome, near Pulpit Rock, and in the Grand Canyon of the Tuolumne. In all, there were 52 rockfalls documented in 2022, with a cumulative volume of about 2,100 cubic meters (23,150 tons).
If you witness a rockfall of any size or encounter fresh rock debris, please contact park geologist Greg Stock at 209/768-1028 or by email at greg_stock@nps.gov, or contact Park Dispatch by dialing 911 within the park. Documented rockfalls are added to the park database (in new interactive map form here https://experience.arcgis.com/experience/03e5fb490eaf4bef92494923a99c4fa0/., enabling long-term evaluation of rockfall activity to improve public safety.
Source: NPS
