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Spider Savage
Mountain climber
The shaggy fringe of Los Angeles
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Jan 25, 2012 - 04:33pm PT
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Greg - Thanks for the photo and all the great technical stuff you give us.
I'd like to volunteer for the Yosemite Trundle and Roll Department (YOSTARD).
Looks like a few loose ones up there need to be sent down just to be sure.
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Clint Cummins
Trad climber
SF Bay area, CA
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Jan 25, 2012 - 05:21pm PT
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Greg,
Do you have any thoughts about how the "roundness" of the boulder might contribute to a longer path of destruction as it rolls downhill unchecked?
I wonder if the same mass was a flake that just dropped down in the same plane as the surface of the cliff,
if it would be expected to travel less distance,
because it might not gain the angular momentum of rolling?
This may be an insignificant factor, since it just concerns a single object impacting forest/talus.
While most big rockfalls would appear to impact rock and might yield a more elastic collision?
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bearbnz
Trad climber
East Side, California
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Jan 25, 2012 - 05:24pm PT
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Thanks Greg, interesting stuff.
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HighTraverse
Trad climber
Bay Area
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Jan 25, 2012 - 05:41pm PT
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Can anyone identify the climbing area in the immediate slide zone?
(I can't)
Going to be a one lane road for quite a while after they get it open.
That whole slope to the west of this tunnel (Reed's) is equally squishy. Someone in my party (who will remain nameless) knocked down a kitchen table sized boulder right into 120 a few years ago. Very fortunately, there were no cars/motorcycles/bicycles/walkers on the road at that precise minute. Four of us managed to get traffic stopped and then push the boulder off to the side. If a car/motorcycle/bicycle had run into it at even moderate speed it would have been nasty. Not even considering if it had fallen ONTO someone.
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gstock
climber
Yosemite Valley
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Jan 25, 2012 - 05:54pm PT
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Hi Clint,
Those are great questions, and we are investigating them as I write - a colleague from the Austrian Geological Survey (on "sabbatical" right now in Yosemite) is working on 3D computer simulations of this event that we can use to tease out the relative importance of boulder shape and volume, as well as the properties of the substrate the boulder moves over. I'm especially interested in how much energy was dissipated by trees in this event - people often think that trees offer little resistance, and yet this boulder did stop on the slope. So I'll let you know what we learn from the simulations.
Generally speaking, though, boulder shape matters a lot. Thin flakes will tend not to travel as far both because of their angular shapes, which get caught up more easily in the roughness of the talus, and also because they tend to break up more easily on impact. Big rounded boulders tend to roll right over talus roughness and don't break up very much.
There is good reason why the boulders that are farthest out from the talus slopes in Yosemite Valley - think Columbia Boulder, LeConte Boulder, Chapel, etc. - are really big and rounded.
Greg
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throwpie
Trad climber
Berkeley
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Jan 25, 2012 - 08:51pm PT
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Could some of the big boulders you mentioned have been deposited by ice instead of rockfall? It just seems that something the size of Columbia would have broken up on impact.
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throwpie
Trad climber
Berkeley
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Jan 25, 2012 - 08:56pm PT
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Now that I think of it, some of the boulders from the cookie cliff slide were pretty huge...but they didn't come from very far up.
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gstock
climber
Yosemite Valley
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Jan 25, 2012 - 09:23pm PT
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As it happens, there is very good evidence that most of the big boulders like Columbia were not deposited by glaciers. First, they are almost without exception composed of the same type of granitic rock as the cliff just above, whereas many glacial erratics are composed of rock found far upvalley.
Second, and more compelling, is the fact that we have dated about 40 of these boulders in Yosemite Valley using cosmogenic beryllium-10 exposure dating (we did this primarily for purposes of hazard assessment). Most of the notable boulders on the floor of the Valley have ages of a few thousand years (Columbia Boulder for example has an exposure age of 4,400 years), much younger than the timing of deglaciation about 15,000 years ago. So I am pretty certain that almost all of the big boulders are of rock fall, not glacial, origin. The few exceptions may be in the western Valley near Bridalveil Falls and Valley View, which do seem to be glacial (though we have not yet dated those).
The interesting thing to consider is that boulders like Columbia may have actually come off the walls much bigger and their present size is all that is left left after multiple impacts.
Greg
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throwpie
Trad climber
Berkeley
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Jan 25, 2012 - 10:35pm PT
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Pleasant dreams, Camp Four
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YosemiteSteve
Trad climber
CA
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Jan 27, 2012 - 04:15pm PT
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Road to Reopen Tomorrow, January 28 at 8:00 a.m.
Yosemite National Park announces that the Big Oak Flat Road (the continuation of Highway 120) within the park will reopen tomorrow morning, January 28, 2012, at 8:00 a.m.The park's Roads and Trails Crew worked throughout the week to clear the road of debris and rocks after a large rockfall occurred late last Sunday evening, January 22, 2012.Two lanes have been re-established on the road and it will be open to unrestricted traffic tomorrow morning.
"All of the work on the road this week has been accomplished by the efforts of our Roads and Trails Crew in the Division of Facilities Management," stated park Superintendent Don Neubacher."I'd like to personally praise them for their tireless work, dedication, and skill in getting the road back open.This opening is a testament to the efficiency and fortitude of our Roads and Trails Crew."
Temporary road closures will be in place next week to allow the park unrestricted access to pave the road.Exact days and times have not been established.Visitors are asked to call 209-372-0200 for 24-hour updated road and weather information.
The road will reopen tomorrow morning with a gravel surface.Park visitors are urged to use extreme caution and drive slowly through the rockfall area.
http://www.nps.gov/yose/parknews/bofreopen.htm
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labrat
Trad climber
Nevada City, CA
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Jan 27, 2012 - 04:17pm PT
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Nice work road crew!
Thank you.
Erik
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JEleazarian
Trad climber
Fresno CA
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Jan 27, 2012 - 04:20pm PT
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Superb work, NPS! When I saw the pictures of the damage, I figured it would require weeks for temporary opening, and months long-term.
John
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HighTraverse
Trad climber
Bay Area
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Feb 14, 2012 - 12:21pm PT
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Any update on the road status?
The Yosemite park site lists it as "open".
Did they get it repaired in both directions?
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cleo
Social climber
the canyon below the Ditch!!!!
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Feb 14, 2012 - 12:44pm PT
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I'm pretty sure it is open in both directions (gravel) but still will need work in the future.
YOSEMITE FORUM talk today about rock falls including this one - noon in the auditorium, if you're local and free. Not by me - by Sandra Melzner - but I will be there.
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k-man
Gym climber
SCruz
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Topic Author's Reply - Feb 14, 2012 - 02:31pm PT
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Yep, open in both directions. And like cleo said, it's gravel for now (about a 25' section).
The Iota is still there, this thing came down a few hundred yards from the 140/BOFR Tee. I hear there was a fear it'd roll down and damage 140 too boot.
Man, that is one heck of a lane that thing carved coming down! Certainly worthy of a picture...
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briham89
Trad climber
los gatos. ca
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Feb 14, 2012 - 03:18pm PT
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they said it will be closed in the future for more permanent fixing, so check the status before you go up each time
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