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| Messages 1 - 33 of total 33 in this topic |
Caveman
climber
Cumberland Plateau
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Interesting read, thanks!
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Ed Hartouni
Trad climber
Livermore, CA
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great read!
was that what Greg was doing up there this summer before being plucked off? collecting samples to date? that would be very cool!
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Wayno
Big Wall climber
Seattle, WA
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Interesting indeed. It evokes some intense imagery.
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Domingo
Trad climber
El Portal, CA
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Really interesting stuff. I always liked that essay by Muir.
Greg, random question: which sample isotopes did you use?
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Prod
Trad climber
A place w/o Avitars apparently
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Interesting read.
Thanks,
Prod.
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noshoesnoshirt
climber
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"If for a moment you are inclined to regard these taluses
as mere draggled, chaotic dumps, climb to the top of one
of them, and run down without any haggling, puttering
hesitation, boldly jumping from boulder to boulder with
even speed. You will then find your feet playing a tune,
and quickly discover the music and poetry of these magnificent
rock piles - a fine lesson."
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dee ee
Mountain climber
citizen of planet Earth
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I'm curious how big that earthquake was 3600+ yrs. ago!
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mongrel
Trad climber
Truckee, CA
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There is a plausible conclusion to be reached from the facts stated in the article, if one let's one's imagination run a bit. Stock states that the Taft granite, which forms most of the avalanche debris, is found in the summit area of El Cap (although he doesn't also say, not found much on the face itself). Therefore it's perfectly plausible that there was an enormous overhanging section, or even a monumental roof, at the top of the crag before the 3,600 ybp earthquake. Imagine if PO or Mescalito reared back in an awesome overhanging section or 100-ft roof right at the top. What routes there could have been on that chunk of rock!
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Captain...or Skully
Social climber
Where are YOU from?
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For a while, anyway.
I was talking to Walt one day, & he was telling me about the big chunk of Surgeon General(that he & Klaus climbed on!!)that peeled off. I think Klaus led that.
A piece , or pieces of rock that size, in flight.
Yowza!(hey, I like the word.It fits.)
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SteveW
Trad climber
The state of confusion
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Pretty darned amazing!
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ec
climber
ca
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This can make you wonder about any similar places in the Sierra that have extensive talus below huge escarpments.
"Now who you jivin' with that Cosmik Debris?"
 ec
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Ricky D
Trad climber
Sierra Westside
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I'm curious - if the debris field is composed mostly of "Taft" granite that for the most part does not appear on the face...does this imply that the flow originated as an overlying cap piece on top of of El Cap?
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gstock
climber
Yosemite Valley
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Thanks for posting the article, Chris. I was thinking that climbers might be interested to know more about that heap of rocks adorning the Nose approach. The exposure dating method utilizes beryllium-10, a rare isotope produced in quartz only by cosmic rays. Concentrations of beryllium-10 are usually very small, so measurements must be made on an accelerator mass spectrometer.
I climbed Mescalito this fall (well, a lot of it anyway) as part of an effort to determine how extensive the Taft Granite is on the SE Face, because, like mongrel, I wonder whether there might have been a big roof at the summit that collapsed. At first I didn’t think this was possible given the sheer volume of the deposit, but as the mapping has progressed it seems that scenario is back in play. No sample collecting involved, just photographing the rock at each belay with a label and a scale bar – easy! At this point I have photos from the East Buttress, Zodiac, PO Wall, Mescalito, and the Nose (many thanks to Jesse McGahey, Lincoln Else, Roger Putnam, and Holly Beck for helping with this effort). Actual petrologists (including Minerals) are now helping to identify the rock types and map them on high-resolution photos (http://www.xrez.com/yose_proj/Yose_index.html);. I’m hoping to map New Dawn in the spring, and possibly the NA Wall as well, but if anybody is planning on climbing a route on the SE Face and would be willing to shoot a few photos at the belays, let me know.
Greg Stock
Park Geologist
(209) 379-1420
greg_stock@nps.gov
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Captain...or Skully
Social climber
Where are YOU from?
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Will do, bro.
What could be easier..?
I got room on the card, after all...
RESEARCH!
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Brian Hench
Trad climber
Seattle, WA
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What attempts have been made to use cosmogenic dating techniques on rock still on the cliff face? It would seem that all you have to do is to match the date of boulders from the rockfall to in situ rock on the face.
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scuffy b
climber
On the dock in the dark
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Very interesting article. Thanks, much.
I like Brian Hench's question.
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Domingo
Trad climber
El Portal, CA
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Seems like that would be hard for a few reasons...here's a big one I can think of.
CRNs are formed on rock surfaces. If the rock fell off, that would mean a new stage of CRN formation on the wall correlated with rockfalls with different concentrations (the rockfall wouldn't necessarily match up, or only part of the rocks would if exposed to surface rays, making the appropriate dating area impossible to distinguish) - I think.
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surly B
climber
Oakland (what?), CA
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Dec 19, 2008 - 03:57am PT
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You all realize that this summary of historic documents is really a 'how to' tale, right?
"How to find awesome bouldering is Yosemite: follow the HUGE rockfalls!"
-Greg Stock, Yosemite Association, 2008
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Gene
Social climber
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Greg,
Bogus link.
g
EDIT: Works now!
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Clint Cummins
Trad climber
SF Bay area, CA
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Cool article, Greg - congrats on the publication.
Here is the abstract which gets straight to it, and a key photo/diagram:
White dashed area is computed likely source area for huge rockfall, at around 1600 BC (3.6 ka ago).
ABSTRACT: Large rock slope failures from near-vertical cliffs are an important geomorphic process driving the evolution of
mountainous landscapes, particularly glacially steepened cliffs. The morphology and age of a 2·19 × 10^6 m^3 rock avalanche
deposit beneath El Capitan in Yosemite Valley indicates a massive prehistoric failure of a large expanse of the southeast face.
Geologic mapping of the deposit and the cliff face constrains the rock avalanche source to an area near the summit of ~8·5 ×
10^4 m^2. The rock mass free fell ~650 m, reaching a maximum velocity of 100 m s^-1, impacted the talus slope and spread across the valley floor, extending 670 m from the base of the cliff. Cosmogenic beryllium-10 exposure ages from boulders in the deposit yield a mean age of 3·6 ± 0·2 ka. The ~13 kyr time lag between deglaciation and failure suggests that the rock avalanche did not occur as a direct result of glacial debuttressing. The ~3·6 ka age for the rock avalanche does coincide with estimated late Holocene rupture of the Owens Valley fault and/or White Mountain fault between 3·3 and 3·8 ka. The coincidence of ages, combined with the fact that the most recent (AD 1872) Owens Valley fault rupture triggered numerous large rock falls in Yosemite Valley, suggest that a large magnitude earthquake (≥M7.0) centered in the south-eastern Sierra Nevada may have triggered the rock avalanche.
If correct, the extreme hazard posed by rock avalanches in Yosemite Valley remains present and depends on local earthquake
recurrence intervals.
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tinker b
climber
the commonwealth
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i can't get the link to work, but thanks for everything else greg.
j-l
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Dr.Sprock
Boulder climber
Sprocketville
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are there any park rules that say you can not climb during a major earthquake?
because that would be all we need, more regulations,
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HighTraverse
Trad climber
Bay Area
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Sprock
You're specifically exempted from that regulation.
"Subpart B, Clause 9: Dr. Sprock, owing to his well documented anti-authoritarian nature is exempted from all other sections of this regulation. However, even for Dr. Sprock, the Laws of Nature will not be exempted not excluding the law that being crushed by a 5700 ton boulder will lead to instant death"
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HighTraverse
Trad climber
Bay Area
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I had wondered about that big fan of talus spreading out below ElCap. It sure seems a long way for a boulder to travel on its own.
Wonderful research Greg. Chris, thanks for posting.
It will be really interesting to follow this work through the years.
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Wade Icey
Trad climber
www.alohashirtrescue.com
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CalicoJack
climber
CA
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Big wall field work w/ big rock fall forensics - FANTASTIC!!!
Very cool work!
Cheers,
Andy
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Gunkie
Trad climber
East Coast US
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In other words, there are lots of boulder problems that need unearthing.
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FRUMY
Trad climber
SHERMAN OAKS,CA
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TFPU
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