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Mighty Hiker
Social climber
Vancouver, B.C.
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Oct 11, 2008 - 10:44pm PT
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Thanks, Bryan. Have you seen anything from NPS geotechnical engineers or geologists on the stability of the rockfall zone, and what should be done?
A helmet might not do much good in a major rockfall, except for carrying away whatever's within it.
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Karl Baba
Trad climber
Yosemite, Ca
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Oct 11, 2008 - 11:39pm PT
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In a litigious society, it really does seem that this rockfall will be the last straw and at least some buildings may close.
The question, and probably only minerals knows this well enough to answer, is the extent of various levels of risk in Curry? Are some areas safe enough to keep?
Poor DNC, first they lost tons of housing and hotel rooms in the flood. We lost campgrounds. They couldn't rebuild in the 100 year flood plane so they just finished a ton of brand new fancy employee housing in curry! Give me the water every 100 years anyday.l
I guess we'll see how this all shakes out.
Peace
Karl
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gstock
climber
Yosemite Valley
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Oct 12, 2008 - 12:46am PT
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I wish it were that simple, Minerals. It does appear that this rockfall consisted of Glacier Point tonalite, but as you know there have been plenty of recent rockfalls from the NW face of Half Dome, squarely in the Half Dome granodiorite. Plotting all of the historic rockfalls in Yosemite Valley shows that they are widely distributed, with little regard to rock type. The height of the Tioga glacier actually appears to play a more important role, with larger rockfalls occurring from the cliffs above the limit of glaciation where the rock is more weathered.
As far as the detachment area goes, we are still in the process of determining the stability of the remaining rock mass. It is a tricky business as you might imagine, particularly because this is a difficult area to access. The larger issue, as has been pointed out, regards the wisdom of having cabins on the talus slope - I can assure you that I am working hard on this issue.
If interested, a recent paper detailing our investigation and hazard assessment of a different area of Glacier Point can be found here:
http://www.nat-hazards-earth-syst-sci.net/8/421/2008/nhess-8-421-2008.html
Greg Stock
Park Geologist
(209) 379-1420
greg_stock@nps.gov
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mongrel
Trad climber
Truckee, CA
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Oct 12, 2008 - 01:19am PT
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Gstock, that is one beautifully executed and documented piece of science. Love it, thanks for posting that link. Somewhere, I once surfed to rockfall maps for the Valley (basically, talus fields by BIG age classes), they are wonderful and aesthetic and do emphasize the point that nearly everywhere that we climb and hike there has had a big rock avalanche sometime in the last umpty thousand years. I bet people who are following this thread would love to see those maps, can you post the link?
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gstock
climber
Yosemite Valley
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Oct 12, 2008 - 01:38am PT
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Check out Plate 1 in this document:
http://pubs.usgs.gov/of/1999/ofr-99-0578/
There have been several notable rockfalls since this map was produced, but even so it reveals the wide distribution of slope movement events (rockfalls, rockslides, debris flows) in Yosemite Valley.
Greg
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Anastasia
climber
Not there
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Oct 12, 2008 - 01:50am PT
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gstock!
I am going to use you to replace my previous hero! The reason is that when you give scientific data to a few outspoken tenacious citizens, it becomes a catalyst for change.
Thanks for the spark,
AF
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Minerals
Social climber
The Deli
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Oct 12, 2008 - 03:24am PT
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There you have it, Anders.
Yes, Greg. If it were only that simple. I hope that you didn’t think that my Park Service comments were directed at you in any way; I wouldn’t think so, considering the conversations that we’ve had in the past. Among the many different factors contributing to these rockfalls, rock type must be considered. I honestly doubt that the right side of El Cap would be concave if it weren’t for the presence of the North America Diorite. Joint systems are not blind; they certainly are controlled by rock type, as well as other factors. The NW face of HD lies right in the middle of a major joint system - exfoliation shapes the face. Other than the isolated bodies of diorite, which rock type in the Valley is most susceptible to weathering, regardless of surface rock quality and jointing?
Which other housing/populated areas in Yosemite Valley are in a more active rockfall area?
Thanks for posting the link to the USGS article; that rockfall map is neat – way cool. I think I posted a link to the article in the past, in other discussions.
You are probably quite busy with all of this but it would be fun to meet up in Tuolumne again sometime. There are a lot of cool things that I still want to show you. Any more thoughts on the tilted mini-seds? Is that an ash layer?
Bryan
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Minerals
Social climber
The Deli
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Oct 12, 2008 - 03:40am PT
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Hey, while we’re at it…
There is a wide (~ fist to offwidth) crack on top of the summit slabs on the climber’s left side of the Diving Board. The crack runs roughly NE/SW and when you walk along it, you can often feel cool air rising from below. A Valley view of the face, to the left of the Porcelain Wall proper reveals a large, arching roof crack with black streaks running down beneath it. This crack separates a huge amount of rock from the rest of the wall. When this sucker goes, it’s going all the way to Mirror Lake. Have a look if any of you haven’t already. It’s pretty wild.
Tick, tock…
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gstock
climber
Yosemite Valley
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Oct 12, 2008 - 11:15am PT
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Hey Bryan, of course you are right that rock type affects joint density, which in turn controls rockfall initiation. The difference in slope between the Rockslides (diorite) and the western side of El Cap (granite) illustrates this beautifully. But oddly this seems to be more true for the smaller rockfalls than the larger ones; for example, the two largest rock avalanche deposits shown on that USGS map (Mirror Lake and El Capitan Meadow) came from what you and I would probably consider to be the strongest granites in the Valley. So there is a connection between rock type and rockfalls, but not one that makes it any easier to predict future activity.
When all the "dust" settles from this event, it would be great to talk more with you about the various geologic things we've discussed, especially your earlier mapping of the SE face of El Cap. I wasn't able to finish my mapping of Mescalito, but we are making progress on that effort, and I'd really like your input.
Greg
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gstock
climber
Yosemite Valley
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Oct 12, 2008 - 11:17am PT
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And yeah, I've seen that crack behind the Diving Board. Wow.
Greg
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Mighty Hiker
Social climber
Vancouver, B.C.
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Oct 12, 2008 - 01:09pm PT
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The emperor has no clothes! The emperor has no clothes!
I just thought someone should say it. Now back to an adult conversation about geology and risk management. Someday I hope to learn more about these subjects, vis-a-vis the Valley.
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Minerals
Social climber
The Deli
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Oct 12, 2008 - 01:13pm PT
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Thanks for the reply, Greg. Ahh, what do I know about rockfalls… You are the geomorphologist with the PhD! Yeah, the El Cap project sounds like fun. I’d love to help out.
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Dr. Rock
Ice climber
http://tinyurl.com/4oa5br
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Oct 12, 2008 - 01:49pm PT
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Camping in Curry is just as dangerous as climbing these days.
Maybe we should move Camp 4 to Curry, and put the Normal people in Camp 4.
I don't mean to be cold, but when someone croaks, it just means more food, gas, and toilet paper for us.
If you don't know someone personally, they are just vermin, right?
Just another car in your way, right?
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Mighty Hiker
Social climber
Vancouver, B.C.
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Oct 12, 2008 - 01:51pm PT
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"but why is there not call to evacuate the coastal fault region of California, for many many more will surely perish in the next big one"
Could be the current government doesn't care too much for looking out for Democrats. Even if they're American.
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Minerals
Social climber
The Deli
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Oct 12, 2008 - 01:53pm PT
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Hear ye, hear ye!!!
California is now deemed an extremely dangerous place… Especially Yosemite!
You are all advised to leave the state immediately, until further notice. Quck, quick… time is ticking!
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Slabmonger
climber
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Oct 14, 2008 - 07:39pm PT
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I was up on the Prow during both of the rockfalls, and fortunately had a camera handy for both. It was quite a show to see from a distance, I'll see if I can get some video up later:
I believe this is from the second rock fall.
-Dan
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bluering
Trad climber
Santa Clara, Ca.
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Oct 14, 2008 - 07:47pm PT
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spectacular, Dan!!! Thanks for sharing that.
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Mighty Hiker
Social climber
Vancouver, B.C.
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Oct 14, 2008 - 07:50pm PT
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Fascinating! Which rockfall is that picture from?
The NPS (Greg S) may be interested in seeing your photos and video, as they may tell them more about the falls. He's posted up-thread.
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Slabmonger
climber
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Oct 16, 2008 - 03:51pm PT
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I've added some short video and stills to you tube--the quality is rather amatuerish but I can't expect much with a point and shoot camera.
Out of the video of the first rockfall, I edited out my opening comments, something to the effect of "Holy f#!& ..."
http://www.youtube.com/watch?v=uYvCirdgoeo
-Dan
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JuanDeFuca
Big Wall climber
Stoney Point
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Oct 16, 2008 - 03:58pm PT
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I sure hope the seismic signal I am recording is not from Yosemite?
Juan
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