[Photo] Greg Stock/NPS
Over 4th of July weekend more than 200 feet of rock fell off of Half Dome in Yosemite National Park, erasing part of the famous Yosemite big wall route, the Regular Northwest Face (RNWF, 5.9 C1, 2,000′, Robbins-Sherrick-Gallwas, 1957; FFA: 5.12a, Coyne-Jackson-Lorrimer, 1979).
The rockfall, probably occurring at night and after heavy rainfall, removed half of Pitch 10 and all of Pitch 11. The belay bolts on top of Pitch 11 remain in place, but are currently unreachable because the ledge below them is now a pile of rubble at the base of the wall. In its current state, the route is likely unclimbable and the National Park Service recommends that climbers don’t attempt it until more information about the rockfall and current dangers is available. Since the initial incident, there has not been subsequent rockfall but the Park Service is observing the wall for further damage.
Fortunately there were no reported injuries and no reports of missing climbers on the usually busy route. “It happened after a strong rainstorm that drove everyone off. I think that’s really lucky,” Yosemite Park Geologist Greg Stock told Alpinist. “Unfortunately we can’t say with certainty what happened up there.”
The rockfall occurred directly above the famed Robbins Traverse, a key section on the route that links the lower section with the exposed upper pitches. This is not the first reported rockfall on Half Dome’s Northwest Face. The guidebook SuperTopo: Yosemite Big Walls notes that after the Robbins Traverse during the 1957 first ascent of the route, the team “found heads-up climbing through loose chockstone-choked chimneys. Two committing features, the Undercling Flake and Psych Flake, were especially unnerving and with good reason-years later they would both depart from the wall.”
On Monday, July 6, geologist Greg Stock and Yosemite Climbing Ranger Brandon Latham hiked to the base of the wall to find out more about the rockfall. “I’m thinking how big is it, what triggered it [and the] implications for people. Since this happened on one of the most famous routes in the world, we want to be mindful of the climbers,” Stock said.
Stock reports that a three- to nine-foot-thick slab fell off. He described it as a “triangular-shaped rock sheet at least 60+ meters (200+ feet) on the longest side…suggesting an approximate volume of roughly 800 cubic meters.” Dry weather followed by rain on July 2 and 3 likely contributed to the loosening of the granite triangle.
We asked Stock if he expects additional rockfall in the area. “We can’t really say. There are examples like this where rockfall left an overhanging roof and did lead to additional rock falls above. [After] the Rhombus rockfall in 2009 and 2010…rockfalls were progressive for about a year. But then there are plenty of other examples where nothing additional happened.”
Though this is a huge rockfall by climbing standards, Stock points out that as a geologist he believes it’s not that significant in geologic time. In 2009 a rockfall occurred northeast of the Regular route on nearby Ahwiyah Point, generating a force 40 times the size of the past weekend’s rockfall. The Ahwiyah Point rockfall was the largest in Yosemite Valley since the Middle Brother slide in 1987.
“In terms of what’s possible in Yosemite, it’s not really that large,” Stock said.