Discussion Topic |
|
This thread has been locked |
Ed Hartouni
Trad climber
Livermore, CA
|
|
|
Jun 15, 2012 - 10:50am PT
|
thanks for the links Greg, loved seeing this reference to "Zimmer et al., 2012"
is the 1-meter DEM available from the USGS? (or whoever?)
Zimmer, V.L., Collins, B.D., Stock, G.M., and Sitar, N., 2012, Rock fall dynamics and
deposition: An integrated analysis of the 2009 Ahwiyah Point rock fall, Yosemite National
Park, USA: Earth Surface Processes and Landforms, v. 37, p. 680-691, doi:
10.1002/esp.3206.
|
|
Tony Bird
climber
Northridge, CA
|
|
|
Jun 15, 2012 - 11:04am PT
|
so the beryllium exposure indicates the time it broke from the cliff? 4-5,000 years ago, roughly. the ice age "ended" 10-12,000 years ago, but when did the glacier disappear entirely from the bottom of the valley? not an erratic? evidence of alteration of the boulder's shape by glaciation?
4-5,000 years ago would place it close to a climatic thermal high, as i recall from some reading on the subject--warmer times than the present, in which we're undergoing a rapid swing of warming nevertheless, and we argue whether it's natural or due to human activities. effects of this warming on overall rockfall?
|
|
Tony Bird
climber
Northridge, CA
|
|
|
Jun 15, 2012 - 11:29am PT
|
i thought they were pretty simple questions. maybe you don't know what an erratic is. i sure as hell don't know what a DEM LIDAR is.
|
|
gstock
climber
Yosemite Valley
|
|
|
Jun 15, 2012 - 11:34am PT
|
Sometimes, Tony, people post at the same time. I was answering Ed's question first.
To your questions: Yosemite Valley was deglaciated about 15,000 years ago. Although there are a few moraines in the Valley, there are very few erratics. This is probably because the valley experienced a few meters of aggradation just after the glacier retreated, burying those boulders. The boulders on the valley floor, with only a few exceptions, are from rock falls. We know this because the rock types of the boulders match those of the cliffs right above them (and there are about 12 different types of granite in the Valley), there are no "exotic" rock types like Cathedral Peak Granite, and the boulders we have dated all are younger than 15,000 years. The cosmogenic exposure age dates how long a rock-fall boulder has been sitting on the floor of the valley, exposed to cosmic ray bombardment and thus production of cosmogenic isotopes.
|
|
bergbryce
Mountain climber
South Lake Tahoe, CA
|
|
|
Jun 15, 2012 - 11:51am PT
|
DEM = Digital Elevation Model
LIDAR is a sensor used to map variances in elevation. It's akin to radar in that a beam (actually a laser) is shot out of the bottom of an aircraft and uses metrics like time to calculate the distance from the aircraft to the ground. After millions of these signals "bounce" back to the aircraft, a very clear picture of the surface of the earth can be made. It's by far the most accurate tool for mapping elevation and at 1 meter, it's a very accurate dataset.
Basically ever square meter of ground within that dataset has an elevation value applied to it, as opposed to a 100 meter dataset, where only every 100 square meters has an elevation value applied to it.
Man, if I got to work on projects like these I probably wouldn't be leaving the GIS industry.
|
|
Tony Bird
climber
Northridge, CA
|
|
|
Jun 15, 2012 - 11:59am PT
|
ah, appreciate that, and sorry for being impatient. if ed would only talk in the same language he plays scrabble in ...
i guess we'd all like to know where you think this is going, although it may be too soon to ask.
thanks to you too, bergbryce.
don't know if it's been noted, but i recall the deaths from one of the glacier point rockfalls were due to trees being knocked down at some distance from the cliff by the wind created at impact. seems pretty hard to anticipate such stuff. there was also some kind of lawsuit over outhouses up on glacier point, alleging they loosened rock over time. what came of that?
|
|
bergbryce
Mountain climber
South Lake Tahoe, CA
|
|
|
Jun 15, 2012 - 12:05pm PT
|
Where it's going appears to be done. A handful of places have been determined to be exposed to a higher level of rockfall danger than others and some structures are being moved or demolished. Not sure if there is going to be any other outcome other than this.
I think the goal of the study was to determine the areas most likely to see dangerous levels of rockfall, identify any structures/activities that took place there and either move or remove them to safer locations.
|
|
Drewid
Boulder climber
New Helvetia, CA
|
|
|
Jun 15, 2012 - 01:20pm PT
|
So according to the Bee article they're going to close some of those new employee dorms they just built in 2005 near the Curry boulders (Huff area) I presume. What a joke, spend a few million on brand new buildings and then just shutter them, what nonsense. And closing only 6 sites at Camp 4, how ridiculous is that? I presume those are the along the back row (northern) sites which are a whole 20 feet away from the "safe" sites. Give me a break. When you're dealing with rock fall, I'm going to go out on a limb and assume that you can't predict the danger zone down to the nearest 20 feet. If one site in Camp 4 is truly at risk, the whole place is at risk which just highlights Greg's comment that no place in the Valley is free of danger. If you get too far from the cliffs, you're too close to the floodplain and sensitive river corridor blah blah so you're damned if you do damned if you don't.
|
|
mouse from merced
Trad climber
merced, california
|
|
|
Jun 15, 2012 - 01:36pm PT
|
Greg, especially, and the rest of you, it's an elevating discussion this morning. I am stoked to hear the NPS is employing the likes of Greg, who is walking in the footsteps and standing on the shoulders of men like Muir and Matthes and Francis Farquhar, even though none of them worked for the Park Service (that I ever heard). It counters the perception of John Law, et al.
Thanks for the enlightenment, Greg. You should be a McClatchy stringer, maybe? We might get less Bee S. out of their hive.
IMO, trundling is a stupid thing if done in the Park. Don't, please.
"It's not what you do, it's what you get caught doing," in which case John Law should do his thing.
Parting shot: It is a real sad thing to think that some unlucky soul may have tried to duck behind Big C., only to get blind-sided by the little guy! :(
|
|
JEleazarian
Trad climber
Fresno CA
|
|
|
Jun 15, 2012 - 01:43pm PT
|
I never did understand why they closed the river campgrounds. So what if every 50 years they flood in wintertime, when they're closed? Pretty much everything else in the Valley is also on a floodplain.
Hear, hear! I've had cynical thoughts about that since 1996, Anders.
John
|
|
|
SuperTopo on the Web
|
Let us know!