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gstock
climber
Yosemite Valley
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Topic Author's Original Post - Jan 25, 2010 - 12:33pm PT
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2009 Rockfall Year in Review:
Several notable rockfalls occurred in Yosemite in 2009. By far the largest event was the Ahwiyah Point rockfall on March 28, which originated near the summit of Ahwiyah Point northeast of Half Dome. This rockfall had an approximate volume of 45,300 cubic meters (about 134,000 tons), making it the largest rockfall in Yosemite Valley in 22 years (considerably larger than the 1996 Happy Isles rockfall). The impact of the falling rock on the floor of Tenaya Canyon destroyed hundreds of trees and generated ground shaking similar to a magnitude 2.5 earthquake. Rocks continued to fall from this area for many weeks after the initial failure. The southern portion of the Mirror Lake loop trail, buried by rock debris, remains closed.
The other area of notable rockfall in 2009 was the Rhombus Wall immediately north of the Ahwahnee Hotel. On August 26 a series of five rockfalls fell from midway up the Rhombus Wall, with the largest occurring at approximately 1:30 pm. Large boulders reached the edge of the talus slope, and several vehicles in the Ahwahnee parking lot were damaged by smaller rock fragments. The hotel was evacuated for 48 hours to allow for geological assessment. Over the next two weeks, loud cracking and popping sounds were heard emanating from the cliff, suggesting propagation of cracks within the rockfall source area. This activity culminated in another rockfall from the source area on September 14, roughly three weeks after the initial failure. The cumulative volume of the numerous rockfalls is estimated to be about 1,200 cubic meters, or roughly 3,600 tons. Twenty-nine parking spaces in the Ahwahnee parking lot were permanently closed as a result of these rockfalls and the subsequent hazard assessment.
Other areas in Yosemite experiencing rockfalls in 2009 included El Capitan, Glacier Point, Half Dome, Royal Arches, Cathedral Rocks, and Wapama Falls at Hetch Hetchy. In all, there were 52 documented rockfalls in 2009, with an approximate cumulative volume of 48,120 cubic meters (142,000 tons); the vast majority of this volume was associated with the Ahwiyah Point rockfalls.
It is very likely that there were additional rockfalls in 2009, but these events either were not witnessed or went unreported. If you witness a rockfall of any size, or if you hear cracking or popping sounds emanating from the cliffs, please contact park geologist Greg Stock at (209) 379-1420, or at greg_stock@nps.gov, or contact Park Dispatch. Predicting rockfalls is not yet possible, but understanding the events that do happen is an important step toward this goal. (G Stock 1/25/10)
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hoipolloi
climber
A friends backyard with the neighbors wifi
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Jan 25, 2010 - 12:39pm PT
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Greg-
Would you surmise that this is on par, more, or less rockfall than a "normal" year in Yosemite? I imagine it is difficult to make comparisons as there are many factors and better records now than in the past, no? But maybe you can make a 'guess-timate'?
Keep up the good work!
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Ihateplastic
Trad climber
It ain't El Cap, Oregon
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Jan 25, 2010 - 01:53pm PT
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And the Oscar for Most Important Thread On SuperTopo So Far This Year goes to...
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gstock
climber
Yosemite Valley
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Topic Author's Reply - Jan 25, 2010 - 02:09pm PT
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It is a difficult comparison to make. The number of documented rockfalls was up this year compared to previous years (52 versus 30-40) but that probably reflects, at least in part, the fact that our ability to document rockfalls improves each year.
The Ahwiyah Point rockfall really skewed the volume numbers this year; if not for this event, the cumulative volume would have been comparatively low. Volume-frequency relations derived from historical records suggest that a rockfall of the size of the Ahwiyah Point event should occur in Yosemite Valley roughly every 20 years or so. A similar-sized rockfall (42,500 cubic meters) occurred thirteen years prior, on the opposite wall of Tenaya Canyon below Basket Dome.
All told, 2009 was a rather typical year for Yosemite rockfalls. Rockfall is without a doubt the most powerful geologic agent presently operating in Yosemite Valley. Be careful out there.
Greg
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Minerals
Social climber
The Deli
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Jan 25, 2010 - 02:21pm PT
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Good stuff!!! Thanks, Greg!
When was the last documented rockfall in Tuolumne? ;)
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karodrinker
Trad climber
San Jose, CA
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Jan 25, 2010 - 02:27pm PT
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Had a golfball size rock almost kill me on el cap last year. Doesn't have to be big to kill, wear your helmets!
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gstock
climber
Yosemite Valley
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Topic Author's Reply - Jan 25, 2010 - 02:37pm PT
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A direct answer to Bryan's question:
7 July 2009, 16:30 hrs: A single boulder, ~3 cubic meters in volume, from the cirque just east of Tenaya Peak.
Now a more general answer:
There are very few Tuolumne rockfalls in the historic database. This is due in part to low reporting rates (if you witness one, please let me know!), but it is also probably due to the fact that most of the Tuolumne landscape was overidden by glacial ice, removing much of the loose and weathered material. My guess is that rockfalls are much more common from the peaks that projected above the ice (Cathedral Peak, Matthes Crest, Conness, etc) than they are from the domes that were under the ice (Lembert, Fairview, Cottage, etc). I haven't compared their talus volumes/contributing cliff areas yet, but the answer is there.
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SteveW
Trad climber
The state of confusion
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Jan 25, 2010 - 02:38pm PT
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Thanks for the info, Greg.
Good stuff!
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Minerals
Social climber
The Deli
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Jan 25, 2010 - 04:08pm PT
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Nah, I think it’s because Cathedral Peak granodiorite is so much better behaved than those delinquent Valley rock types! :)
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aspendougy
Trad climber
Los Angeles, CA
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Jan 25, 2010 - 05:10pm PT
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Dear Greg:
Thank you for the information. Now all you need to do is go up and climb every single route that was affected by these rock falls, and then re-grade them accordingly. Please replace any bolts as needed while you're at it.
Seriously, I wonder if any particularly well-known or classic routes are being affected.
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squishy
Mountain climber
sacramento
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Jan 25, 2010 - 05:44pm PT
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There are numerous routes on Ahwiyah Point from the old green Roper guide...I do not know enough to say if they were effected or not...
Oh, and this thread rocks!! thanks for the fascinating info...
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Mighty Hiker
climber
Vancouver, B.C.
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Jan 25, 2010 - 06:04pm PT
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The rock in a Cathedral would surely be better behaved than rock elsewhere.
A photo of the Ahwiyah Point rockfall, from late April 2009:
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JesseM
Social climber
Yosemite
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Jan 26, 2010 - 03:01pm PT
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Thanks for the good info Greg. I'm back from furlough (surfing in Guerrero, Mexico!!)
After reading this thread, I think it would be interesting to have an informal survey of "close calls" or injuries from rockfall for Supertopo Forum climbers.
It seems everyone has a story, and some have had really harrowing experiences.
Jesse
Yosemite Climbing Ranger
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HighTraverse
Trad climber
Bay Area
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Jan 26, 2010 - 05:40pm PT
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On topic: When you hike up the Falls trail the clean, bright rock in the trail steps after the middle gorge are the area which was buried in the 1980 rockfall. As I recall, two or more people remain entombed there. Sobering to see the size of the devastated area and consider it's on a tourist trail. It took more than a couple of years for the trail to be rebuilt.
Jesse
welcome back, you slacker ;)
Slightly off topic as this regards a climber initiated 2010 rockfall.
Two weeks ago we climbed at Reed's Pinnacle. None of us had been there before and the approach trail was far from obvious, even trying to follow SuperTopo directions.
All 4 of us managed to get up to the base without kicking anything into the road.
Not so lucky on our way back down. One of us got off route (is there a route?) and dislodged a REALLY BIG boulder that bounded across 120 into the downhill lane. Fortunately we were able to get it out of the way before any cars/motorcycles/etc came on the scene.
I'm not in favor of modifying Yosemite for the sake of us climbers but something needs to be done there to mark and maintain a trail to reduce rockfall potential. The consequences could be fatal to passers-by.
Will be glad to discuss with you personally any time.
Fred
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Clint Cummins
Trad climber
SF Bay area, CA
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Jan 26, 2010 - 06:49pm PT
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> Two weeks ago we climbed at Reed's Pinnacle. None of us had been there before and the approach trail was far from obvious, even trying to follow SuperTopo directions.
It has been marked in the past. They have at least been cairns there.
It would be good to get a carabiner sign (back?) up there.
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Greg Barnes
climber
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Jan 26, 2010 - 06:54pm PT
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I think it would be interesting to have an informal survey of "close calls" or injuries from rockfall for Supertopo Forum climbers. Lots of small ones in the Valley for me (up to grapefruit size), but the only one that really would have squished us flat was right near the Pywiack cascade while hiking down Tenaya Canyon (2006 I think). There were 7 of us, and we hung out at the pool at the base of the cascade for a short bit, and Paul and I (the tall fast guys) started hiking, and stopped about 200 yards further on to look back. A half-refrigerator sized block came flying down from the north side (which is not that steep) at very high velocity (starting who knows where) and blasted into exactly where we had been about 10 minutes prior. Sketchy for the total randomness on a gorgeous sunny fall day, and the way it hit right where we had walked in a fairly wide canyon bottom. Nothing else came down, even small rocks - just the big one.
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Greg Barnes
climber
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Jan 26, 2010 - 06:56pm PT
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It would be good to get a carabiner sign (back?) up there. The old one was quite a ways back from the road, but I always assumed a rental RV managed to hit it anyway...
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Dr.Sprock
Boulder climber
Sprocketville
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Jan 26, 2010 - 10:43pm PT
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How do you estimate the volume?
from the missing rock, from the debris pile, or both?
thanks in advance,
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SuperTopo on the Web
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early 2000s - a flake way up around right on Stately Pleasure dome - former anchor area for Shy Tuna
Let us know!