Yosemite Rockfall Year in Review: 2017


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Trad climber
Ouray, Colorado
Jan 31, 2018 - 02:34am PT
Nice report...thanks! What’s keeping Boot Flake up there? Looks like it’s attached with chewing gum...gives me the creeps.

Yosemite Valley
Topic Author's Reply - Jan 31, 2018 - 08:15am PT
Hopefully my Swiss colleagues will have something new to say about the attachment of Boot Flake later this year - new results based on thermal imaging and modeling.
Spider Savage

Mountain climber
The shaggy fringe of Los Angeles
Jan 31, 2018 - 08:50am PT
Thanks for this report Greg. This is like the best use of my tax dollars and park admission fees that I am experiencing this year.

Must be so cool to have a job where you get to use calculus!
The Real Mad Dog

Gym climber
Napa, CA
Feb 21, 2018 - 01:34pm PT
Rockfall capital of the Sierra Nevada, about 3 million years and counting. Be careful out there. Will lead-climb something safe for our 75th birthday (April Fools Day for Twins).

Keep up the good work, Greg

Trad climber
Santa Cruz, CA
May 23, 2018 - 02:01pm PT
Hi Greg: I was skimming your 2012 paper on the potential for Glacier Pt water systems to have caused or contributed to rockfall events in the late 90s. I was struck by the sentence, "Observed cracking and audible popping sounds preceded many of these rock falls by days or weeks" (p 1171). Would it be possible to use passive acoustic monitoring to predict the location and timing of large rockfall events? Practical? Thanks, Pete

Trad climber
Portland, Oregon
May 23, 2018 - 03:04pm PT
With the right filtering and machine learning that would probably be a good idea. Figuring out the filtering might be tough though. But on just now checking, it would appear Greg is already well onto it...

Thermal influences on spontaneous rock dome exfoliation

Nature Communications volume 9, Article number: 762 (2018)


GeomorphologyNatural hazards

Received: 20 July 2017 | Accepted: 20 December 2017 | Published: 22 February 2018

Brian D. Collins, Greg M. Stock, Martha-Cary Eppes, Scott W. Lewis, Skye C. Corbett & Joel B. Smith


Rock domes, with their onion-skin layers of exfoliation sheets, are among the most captivating landforms on Earth. Long recognized as integral in shaping domes, the exact mechanism(s) by which exfoliation occurs remains enigmatic, mainly due to the lack of direct observations of natural events. In August 2014, during the hottest days of summer, a granitic dome in California, USA, spontaneously exfoliated; witnesses observed extensive cracking, including a ~8000 kg sheet popping into the air. Subsequent exfoliation episodes during the following two summers were recorded by instrumentation that captured—for the first time—exfoliation deformation and stress conditions. Here we show that thermal cycling and cumulative dome surface heating can induce subcritical cracking that culminates in seemingly spontaneous exfoliation. Our results indicate that thermal stresses—largely discounted in dome formation literature—can play a key role in triggering exfoliation and therefore may be an important control for shaping domes worldwide.
Mighty Hiker

Outside the Asylum
May 23, 2018 - 05:02pm PT
Camp 4, about 3:30 PM on September 28, 2017. It was a bright, sunny day until then. Surprisingly, we didn't hear or feel the rockfall from the right side of El Capitan, although it was 10,000 cubic metres+.

If a rock falls in the Valley, does anyone hear?

Monterey, Ca
May 23, 2018 - 05:39pm PT
when me and a friend climbed a route on el cap a few weeks ago, that friend pointed out a huge amount of damaged trees and vegitation that he said indicated significant rockfall of likely smaller debris, judging by the damage to branches and the color of the leaves (many still had significant chlorophyl display). he is a very experienced arborist. does this type of observation get taken into account for rockfall study?

edit: that friend is a local arborist who does lots of work in yosemite west. he said that despite the size of the aparent rockfall event, no one has talked about it, suggesting it happened unwitnessed during darkness or storm... i find the the inferrence of damaged vegitation to br a fascinating incite into unwitnessed rockfall events..

Trad climber
Santa Cruz, CA
May 28, 2018 - 05:10pm PT
Thanks for the GStock paper, healyje! Did you watch the video with it? Super cool! That said, it'd take the judicious placement of a great many acoustic emission sensors like those used in that study to "monitor" the Valley.

Mighty Hiker: Fair question! In some ways, I'm not surprised that you didn't hear the rockfall, given how noisy things are that time of year.

We use remote hydrophones to listen for marine mammal activity and comparable devices for learning about bats. These instruments are tuned to the expected frequencies of the taxa in question. Maybe something similar could be devised for this purpose.

Yosemite Valley
Topic Author's Reply - May 29, 2018 - 04:07pm PT
Pete, we have experimented with infrasonic acoustic sensors in Yosemite Valley in the past, primarily to augment seismic monitoring. The details of that experiment are in this paper:


I think there is a lot of potential for using acoustic sensors to detect cracking and pinpoint where it is happening; however, given that cracking sometimes - but not always - indicates imminent rockfall, the challenge is in deciding what to do with that information.

As far as using the state of damaged vegetation to figure out when rockfalls happened, I am on this. A couple of years ago we collected branches from the major vegetation types in Yosemite Valley, then photographed them against a white background every week as they dried out. Some dried up rather quickly, whereas others (especially incense cedar) stayed green for a long time. Local microclimates will undoubtedly have some effect, but this photographic "key" can help pin down when rockfalls happened to within a couple of weeks.

Zay, where on El Cap is this new debris from?

Trad climber
Golden, CO
May 29, 2018 - 04:33pm PT
Well done! Great presentation of the data. My guess is that we are going to be able to predict the likely future big rock falls by analysis of photos by drones -- like, tomorrow. I already was looking for, and finding obvious patterns in the El Capitan rock falls (hint: overhangs are a good place to start).

Monterey, Ca
May 29, 2018 - 07:02pm PT
gstock, the damaged vegitation was present around the fixed lines to the heart ledges. if you were to stand against the wall with your back to the ropes, and start wandering into the trees towards your "2-o-clock" direction, there are numerous bushes and trees with branches having been severed entirely and-or ripped partialy from their trunks. the area over which this type of damage was present was at least 60 yards, as that was about as far as we went to stash gear.

my friend, the arborist, said that judging by the color of the leaves on the severed branches (on the ground), and by the color of the leaves on the partially attached branches, he judges the incident to be roughly 2 or 3 months old (if i am to correctly recall what timeframe he gave)

i took some pictures ill try to upload them in a minute

Monterey, Ca
May 29, 2018 - 07:10pm PT
here are some pictures, please note that i only took a few, and those few were of some of the more obvious damages that i thought would be noticeable in a cell phone picture. hence, "mostly intact" branches were not photographed.

ß Î Ř T Ç H

Boulder climber
Sep 28, 2018 - 11:34pm PT
[Click to View YouTube Video]
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