Half Dome Post-Rock Fall Conditions: One Year Later

Avatar:
Author:
Publish date:
Social count:
487

The following report was provided by Yosemite Climbing Rangers and Park Geologist Greg Stock. Find more news and info at Yosemite Climbing Information.

Photo: Courtesy Yosemite Climbing Rangers

Photo: Courtesy Yosemite Climbing Rangers

The Regular Northwest Face of Half Dome was the United States’ first Grade VI rock climb. Jerry Gallwas, Royal Robbins, and Mike Sherrick spent five days on the wall during the first ascent in 1957. Their ascent required they manufacture innovative equipment and execute wild new techniques like the pendulums at the top of the Robbins Bolt Ladder. They encountered features still famous with climbers such as “Thank God Ledge” and “The Zig-Zags”. Half Dome’s iconicism and the quality of the Regular Northwest Face route have made this one of Yosemite’s most popular big wall rock climbs.

58 years after the first ascent, in early July, 2015, a rock sheet some 200 feet tall and 100 feet wide fell off the Northwest Face of Half Dome, removing more than two pitches of the Regular route.

Steve Roper chronicles the changing route in his book, Camp 4: “Higher was what became known as the Psyche Flake, a forty foot-high shard of granite the men had to chimney behind. Although this pitch was easy, stones rattled in the black depths of the slot, indicating that the flake was slightly loose (and fragile it was, parting company with the cliff during the winter of 1966-67).”

In September 2016, Yosemite National Park Climbing Rangers and Park Geologist Greg Stock climbed the route to assess its present condition.

Analysis of Rockfall Source Area

Photo: Courtesy Yosemite Climbing Rangers

Photo: Courtesy Yosemite Climbing Rangers

Several geological observations are worth conveying. First, the interior portion of the rockfall scar is remarkably clean, consisting of an almost flawless slab. Water staining on this slab suggests that large portions of the rock sheet that fell were completely separated from the adjacent (and now exposed) rock for decades prior to failure. Second, the margins of the rockfall scar display various degrees of instability, ranging from moderately unstable along the upper and western (climber’s right) margins to highly unstable along the lower margin. A 20 by 30-foot flake along the lower margin of the scar appears to have been partially dislodged by the rockfall, with the flake pushed outward by as much as three feet; rock debris associated with the rockfall has wedged into the gap behind the flake, further adding to its instability.

It doesn’t appear that there have been any substantial secondary rockfalls following the rockfall in July last year.

Associated Risk

The majority of the Regular Northwest Face route climbs out of the fall-line for these unstable areas, staying left of the fall-line in the first 11 pitches, and traversing across the top of the scar for pitch 12. Only where the new route pendulums right into the chimneys at the top of the scar does it briefly cross the new roofs formed by the rockfall; fortunately that section can be climbed relatively quickly, or avoided altogether by climbing higher before penduluming right.

Photo: Courtesy Yosemite Climbing Rangers

Photo: Courtesy Yosemite Climbing Rangers

The upper Death Slabs approach, and to a lesser extent the bivy platforms near the base of the route, are directly beneath the remaining unstable areas and are therefore subject to equal—or perhaps even greater—rockfall risk than the route itself is.

Taking a wider view, there are many examples of partially detached exfoliation sheets throughout the Regular Northwest Face Route, not just around the recent rockfall scar. This puts the recent rockfall in context. Although the 2015 rockfall was certainly large and impressive, it was also completely in character for the Northwest Face of Half Dome, which has been shaped by ongoing exfoliation for thousands of years. Future rockfalls from the route are guaranteed; unfortunately their timing cannot be known.

“Several hundred feet above the base, the narrow crack in which we were inserting pitons widened. It became a chimney, large enough to crawl inside. At either side of the back wall of the chimney there was a three-inch crack, continuing out of sight for hundreds of feet overhead. The back wall was eight feet behind the present surface, parallel to the main cliff. The cracks completely separated it from the outer rock, on which I was climbing. Here was the northwest face of the future, fully cleaved and waiting patiently, be it one or one hundred thousand years until it gleams for a geological moment in the noonday sun.” —Galen Rowell

An Alpine Climb

Commonly referred to as an excellent introductory wall, the September patrol reminds us that the RNWF of Half Dome is an adventurous and committing climb 2000’ above the Valley floor. The first half of the climb is lower angle with difficult route finding and large ledge systems. At roughly halfway the route commits to the steep northwest face. From there, a combination of chimneys and direct aid continue to the summit. There are multiple methods for accessing the chimneys beyond the rock scar, all generally require more time than the original route.

Climbers interested in the Regular route are reminded that loose rock exists not only on the periphery of the rock scar but along the entire route. Bivying in the traditional sites at the base of the route is allowed with an NPS wilderness permit but not recommended. If the route returns to its popular status in future years, climbing the route with multiple parties on the wall warrants extra rockfall caution.

Special thanks to the Yosemite Climbing Rangers and Park Geologist Greg Stock for assessing the route and sharing this report.