Yosemite Rockfall Year in Review: 2017

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gstock

climber
Yosemite Valley
Topic Author's Original Post - Jan 29, 2018 - 08:50am PT
There many large and consequential rockfalls in Yosemite in 2017, with a record 85 events (including rockfalls, rockslides, and debris flows) documented. The cumulative volume of these events was about 36,800 cubic meters. Although this is not the largest annual volume recorded, greater volumes in previous years were typically dominated by one very large event (for example, the 46,700 cubic meter rockfall from Ahwiyah Point in 2009), whereas the cumulative volume for 2017 resulted from several large and medium-sized rockfalls.

The largest event in 2017 almost escaped notice. On the stormy morning of January 12, road crews encountered downed trees and a damaged manhole on the road between Pohono Bridge and the Big Oak Flat Road junction. They also noticed a suspiciously fresh-looking boulder in the Merced River. Subsequent investigation revealed that the boulder was part of a very large rockslide that originated far above the road in an area known (appropriately) as “The Rockslides”. The total volume of this slide was about 20,000 cubic meters (almost 60,000 tons), most of which was scattered throughout the forested slopes above the road. If not for the single boulder that hit the road, this rockslide might have escaped notice for some time.

Much greater road damage occurred on June 12, when about 650 cubic meters (nearly 2,000 tons) of rock fell from “Parkline Slab”, a sloping cliff just east of the park boundary near El Portal. About one-third of the rock debris landed on the El Portal Road, burying a 60 meter (200 foot)-long section of road under tons of rock; fortunately, there were no cars directly under this area, despite the rockfall occurring around noon during the busy summer season. The road was closed for five days as crews cleared debris and repaired the roadbed. Much loose debris remains on the slope above the road, and could continue to slide during intense rainstorms.

The year’s most consequential rockfalls occurred from the southeast face of El Capitan in September. The first of these occurred at 1:52 pm on September 27, when 290 cubic meters (860 tons) of rock fell from the cliff near the path of Horsetail Fall. Two rock climbers were walking along the base of the cliff directly under the area, and, sadly, one of them was killed and the other seriously injured. YOSAR quickly extracted both climbers, as several more rockfalls totaling 163 cubic meters (440 tons) pummeled the base of the cliff over the next few hours. At 3:21 pm the following day (September 28), a much larger rockfall occurred from the same location. This rockfall, totaling 10,324 cubic meters (27,875 tons), buried trees at the base of the cliff and generated a huge dust cloud that fanned out across the valley. A small rock fragment hit a vehicle traveling on Northside Drive, puncturing the sunroof and injuring the driver. Northside Drive was closed for 24 hours as geologists assessed the potential for additional activity. Several smaller rockfalls occurred from this same area in October and November.

Other substantial rockfalls in 2017 occurred at Little Windy Point on the El Portal Road, Ahwiyah Point, Glacier Point, El Capitan, Middle Cathedral Rock, and Hetch Hetchy.

It is very likely that there were additional rockfalls and rockslides in 2017, but these events either were not witnessed or went unreported. If you witness a rockfall of any size, encounter fresh rock debris, or hear cracking or popping sounds emanating from the cliffs, please contact park geologist Greg Stock at 209-379-1420 or greg_stock@nps.gov, or contact Park Dispatch by dialing 911 within the park. Documented rockfalls are added to the park database (http://pubs.usgs.gov/ds/746/ ), enabling long-term evaluation of rockfall activity to improve public safety.
Ed Hartouni

Trad climber
Livermore, CA
Jan 29, 2018 - 08:57am PT
thanks for the update Greg!

always good to hear about the dynamic landscape, and be reminded that things naturally fall down.

Be careful out there y'all!
skywalker1

Trad climber
co
Jan 29, 2018 - 08:58am PT
Thanks Greg. Always interesting to read.

S...
Pete_N

Trad climber
Santa Cruz, CA
Jan 29, 2018 - 09:21am PT
Thanks indeed Greg! Clicking on the database link, by the way, includes an extraneous ')'--removing this from the url in your browser will get you to the data.
mcreel

climber
Barcelona
Jan 29, 2018 - 10:44am PT
Thanks! I suppose that seismographs don't help to detect falls like the big one that almost escaped notice? I would have thought so.
gstock

climber
Yosemite Valley
Topic Author's Reply - Jan 29, 2018 - 11:43am PT
Seismometers can certainly detect rockfalls, but in my experience here it works best if the rockfalls are particularly large and energetic (usually by free-falling onto bedrock at the base of the cliff) or if there is a dense array of seismometers on the cliff to record smaller rockfalls. We have had such an array temporarily installed in Yosemite Valley in the past (see this paper), but we don't have one at present.
Toker Villain

Big Wall climber
Toquerville, Utah
Jan 29, 2018 - 12:31pm PT
If you call it "mass wasting" in California too many people misinterpret.
gstock

climber
Yosemite Valley
Topic Author's Reply - Jan 29, 2018 - 01:25pm PT
"You mean you can't just sense a disturbance in the force, young Geo-Jedi?"

One of the biggest rockfalls in Yosemite's history occurred in March of 2009, when 46,700 cubic meters of rock fell from Ahwiyah Point at about 5:30 am. Hundreds, maybe even thousands, of people in the campgrounds and lodges felt the ground shake and heard the rumble. I slept right through it.

That morning happened to be the start of the Yosemite Association's spring gathering, and the Superintendent gave an opening address. As I wandered over I heard him say "So I'm not sure what happened this morning, but here's our Park Geologist and I'm sure he can tell us!" Everyone turned to look at me expectantly, and he beckoned me up to the podium.

I had no idea what he was talking about, so I walked slowly, stalling for time. Just as I reached the podium a friend pushed to the front of the crowd and thrust a piece of paper into my hand. It was a printout from the USGS showing a magnitude 2.4 earthquake centered a mere 500 meters underneath Half Dome. Guessing that it was actually a rockfall masquerading as an earthquake, I stammered out something about a big rockfall up by Half Dome, excused myself, and hurried up to Mirror Lake, where the dust from the rockfall was still hanging in the air.
SC seagoat

Trad climber
Santa Cruz, Moab, A sailboat, or some time zone
Jan 29, 2018 - 01:29pm PT
I love your work Greg.
Whenever I’ve heard you speak I learn so much.
You have a gift for making the very complex understandable.

Thanks!

Susan
Honu

Big Wall climber
Boulder
Jan 29, 2018 - 01:45pm PT
I was on t trip when part of pitch two fell off and on zodiac when pitch five of ZM fell off. I thought I'd share this photo I got of the ZM fall
Mighty Hiker

climber
Outside the Asylum
Jan 29, 2018 - 01:51pm PT
The spring 2009 Ahwiyah Point stealth rockfall, to which Greg refers. Taken a few weeks later.
looks easy from here

climber
Ben Lomond, CA
Jan 29, 2018 - 02:10pm PT
I always appreciate these posts when I'm nice and comfy at home. But I always seem to remember them much less happily when belaying right against a sheer 900' face.
Clint Cummins

Trad climber
SF Bay area, CA
Jan 29, 2018 - 04:15pm PT
Great stuff, Greg - thanks for sharing.
Especially the Ahwiyah Point story!

Got any photos to share of what fell off in "The Rockslides" in 2017?
gstock

climber
Yosemite Valley
Topic Author's Reply - Jan 30, 2018 - 08:17am PT
Here are a couple of photos showing the "The Rockslides" rockslide of 12 January 2017, as well as the new boulder in the Merced River.



Grippa

Trad climber
Salt Lake City, UT
Jan 30, 2018 - 11:07am PT
Excellent write up Dr. Stock! Thanks for the year in review.
Contractor

Boulder climber
CA
Jan 30, 2018 - 11:30am PT
I loaded this video late, after a long involved retreat, dive home and much needed chill period. I shot this footage several seconds into the second fall, viewed from Lay Lady Ledge.

I felt compelled to erase video of the first fall due to the tragic circumstances and distressful audio content. I will always remember the heroics of Andrew.

https://youtu.be/-c-1eikMjh8
BrassNuts

Trad climber
Save your a_s, reach for the brass...
Jan 30, 2018 - 06:58pm PT
Thanks for the data Greg!
SteveW

Trad climber
The state of confusion
Jan 30, 2018 - 07:35pm PT

Thanks for the update, Greg. Always veddy, veddy interesting!
Clint Cummins

Trad climber
SF Bay area, CA
Jan 30, 2018 - 09:54pm PT
Thanks, Greg - I had fun finding this on Xrez.

The "before" shot does not look all that scary to an outsider,
but I can see how a couple of big round boulders could hit the road from there.
ryankelly

climber
Bhumi
Jan 30, 2018 - 09:57pm PT
haha great story Greg
donini

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.
gstock

climber
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
Pete_N

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
healyje

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)

doi:10.1038/s41467-017-02728-1

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

Abstract:

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

climber
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?
Zay

climber
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..
Pete_N

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.
gstock

climber
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:

https://www.nps.gov/yose/learn/nature/upload/Zimmer-et-al-2012-ESPL-Ahwiyah-Point.pdf

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?
eeyonkee

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).
Zay

climber
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
Zay

climber
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
ne'er–do–well
Sep 28, 2018 - 11:34pm PT
[Click to View YouTube Video]
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