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Tork
climber
Yosemite
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Topic Author's Original Post - May 17, 2010 - 01:39pm PT
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Tell me about this, in granite?
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Dapper Dan
Trad climber
Menlo Park
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May 17, 2010 - 01:40pm PT
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where
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Minerals
Social climber
The Deli
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May 17, 2010 - 01:52pm PT
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Weren’t these previously posted in a Wawona Dome thread? Hmmmm… You must have just read my post on Power Dome… :)
Before I comment, do you have any close-up photos of the rock on the walls of those “tubes” that show the individual minerals and their color?
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Tork
climber
Yosemite
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Topic Author's Reply - May 17, 2010 - 02:27pm PT
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Yep, read your Power Dome blah, blah , blah.
Was hoping for some blah, blah, blah about Wawona Dome. I kinda like reading that sh#t even if I don't understand it.
Greg Stock said he had never seen anything like it in Granite.
I don't have any close up photos. If you check out Nanook's Wawona Dome site he has a mega high res shot that zooms in close.
The pics are of a tunnel through found on the third pitch of Fatty Can't Fit on Wawona Dome (Aka Flanders fits). One of the coolest routes I have ever climbed. To bad an hour approach is to much for most folks. Although, on the other hand, there will never be a line for any of the great routes there.
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msiddens
Trad climber
Mountain View
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May 17, 2010 - 05:21pm PT
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I'd hike that in a second.....so damn cool looking.
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Mungeclimber
Trad climber
sorry, just posting out loud.
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May 17, 2010 - 10:29pm PT
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caused by worms
take some flagyl, be right as rain in a couple weeks, er years.
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ß Î Ø T Ç H
Boulder climber
from the Leastside
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May 17, 2010 - 10:31pm PT
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Ultimately , anything molten could have bubbles / venting I'm guessing .
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Minerals
Social climber
The Deli
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May 18, 2010 - 02:40pm PT
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OK, sorry this took so long…
Hmmmmm, without seeing the outcrop up close, I’m simply making an educated “blaw” guess here, so if anyone would like to chime in to correct me, or to help out, feel free, please.
Wawona Dome is composed of 103-million-year-old (103 Ma) El Capitan granite. This rather large pluton is exposed from roughly the northern boundary to the southern boundary of Yosemite National Park (see link to Park map below). The erosion feature pictured above appears to be much different than the typical “solution pockets” (or series of solution pockets) that form on gently to moderately inclined granitic surfaces due to water runoff, pooling of water, and the resulting physical/chemical weathering. In this regard, I don’t see how surface weathering could create a “tube” in a mass of (relatively) homogenous and quite solid granite.
As far as the Valley goes, I don’t recall ever seeing any features like this in El Cap granite, however such features are somewhat common in both Half Dome granodiorite and Cathedral Peak granodiorite of the ~93–85 Ma Tuolumne Intrusive Suite. There are several of these holes on the South Face of Half Dome. Take a look at the Reid big wall guide and the topos for the routes on the South Face (I don’t have a copy in front of me now…). There are at least a few holes on the Harding route, some of which are named. The notation “Bivy Hole” appears on the Lost Again topo; Klaus said that you could crawl inside the hole and it was so deep that he couldn’t see the far end. On Cataclysmic Megasheer, Klaus made some wicked free and aid moves to climb out of the “Courtney Love Hole.”
Although it lacks tube-like geometry, “The Pod” (as I call it) is a similar example of such weathering features and can be seen while climbing Cathedral Peak, in Tuolumne. “The Pod” is located down and (climber’s) left of “The Chimney” and is labeled as “alcove” in the SuperTopo guide. There is a hole on the upper section of Dumpster Evangelist on Dozier Dome; I wedged myself in the hole in order to drill and place the next bolt.
So, what’s the deal with these holes and how do they form? If you look closely at the mineralogy in the rock surrounding the hole in the examples that I listed above, you will notice that the black minerals (biotite and hornblende) are absent and have been replaced, usually by two green minerals – epidote and chlorite. You may also notice that the rock overall appears more white or lighter in color than normal; this is because calcium has been chemically removed from the plagioclase feldspar, shifting the plagioclase composition towards albite (see plagioclase link below).
This difference in mineralogy is the result of hydrothermal alteration of the granitic rock which occurs at depth, after the rock has formed and is fully crystallized, but long before the rock is uplifted and exposed at the surface.
Hydrothermal = hot fluids.
Alteration = chemical changes in rock whereby new minerals are formed at the expense of old minerals (no kids for me, thank you…).
Hydrothermal fluids may percolate through certain areas of granitic bedrock, as a finger-like network, altering the existing granitic rock along fluid pathways. When the rock is eventually exposed at the surface (or lies near the surface), it is exposed to surface weathering, which begins to break down the rock. The secondary minerals that form during the alteration of granitic rock are less resistant to chemical and physical weathering and thus, altered zones weather at a faster rate, leaving depressions or holes in the rock.
We discussed epidote and hydrothermal alteration in the Geology Quiz thread a little while back:
http://www.supertopo.com/climbing/thread.php?topic_id=1048215&msg=1058381#msg1058381
Epidote:
http://en.wikipedia.org/wiki/Epidote
Chlorite:
http://en.wikipedia.org/wiki/Chlorite_group
Plagioclase feldspar:
http://en.wikipedia.org/wiki/Plagioclase
I can’t be sure that the crazy feature/hole that you have pictured above has formed by the weathering of altered granite, but considering that it is not in a major drainage, I don’t know what else would cause this to form. If this feature is halfway up a route, in the middle of a cliff, then it seems doubtful that it could be a pothole of sorts, formed by the erosive action of sediment-laden flowing water (i.e. creek/river or sub-glacial creek/river). Does the hole have a name?
What is interesting is how the section in your first photo appears to be so cylindrical – this may reflect an initial, roughly cylinder-shaped hydrothermal fluid flow pathway and/or the continued rounding of the walls and widening of the hole by subsequent weathering/erosion at the Earth’s surface. The multiple openings at the bottom of the feature may be caused by the branching of hydrothermal fluid pathways or simply by additional weathering. If the mineralogy of the rock on the walls of the hole is the same as that of the surrounding rock, then it is possible that all of the altered granite has weathered away, leaving “normal” looking granite.
So, why don’t we see holes on the front side of Half Dome if we see them on the South Face? The answer is they never really have a chance to develop.
The hydrothermal alteration that contributed to the formation of the holes on the South Face most likely propagates through the entire rock mass of Half Dome as well as the Upper Tenaya Canyon/Tuolumne Meadows areas, although it has influenced only a very, very minor percentage of the total rock mass of the area (almost insignificant). The Northwest Face of Half Dome is quite steep and is often characterized by climbers as having the feel of a series of expanding sheets or shells of rock that are barely stuck to the wall.
Half Dome lost its dome on its Valley side because of the major joint system that cuts right through the monolith. Glaciers alone cannot turn the side of a dome into a sheer, vertical plane of rock – joint systems provide huge weaknesses in solid rock for freeze/thaw cycles and “bulldozers of ice” to take advantage of. Loose rock is carried away by the conveyor belt, which later disappears, leaving all of us to look up (and down) in awe.
As opposed to its counterpart face that continually sheds its skin to renew, the South Face of Half Dome has an armored skin that has been exposed to the tests of time and has endured the weathering of thousands of years of Sierra climate, winter and summer alike. With the exception of the joints that form the two major left-arching features, the South Face is nothing less than the epitome of an impenetrable fortress of monstrous proportions – Sierra granodiorite (or any rock, for that matter) at its very finest.
But not every square foot of this dreamy face is as golden as can be, and altered zones of Half Dome granodiorite have been exposed to the elements on this lower-angle face for much longer periods of time than the more-temporary sheets of rock on the Northwest Face. Because it is lower in angle, the South Face is subjected to much more runoff and pooling of water over its surface than does the steep Northwest Face. This greater amount of water runoff accelerates surface weathering, which is accentuated where the granodiorite has been altered, forming the wild bivy holes.
Those who have traveled the Bushido Gully route to the top of the Diving Board/Porcelain Wall may have noticed that the rock in the bottom of the gully is not only full of joints (parallel cracks), but is much more pink in color; the pink color is due to the alteration of potassium feldspar (orthoclase). The major joint system that cuts through Half Dome served as a pathway for hydrothermal fluid flow that altered the rock that surrounds the joints.
Here are a few examples of hydrothermal alteration in granodiorite in the Tuolumne area:
A weathered-out pod in a section of hydrothermally altered Half Dome granodiorite provides a small haven for vegetation. This slab exposes a cross section of a cylindrical hydrothermal fluid pathway; the accelerated weathering observed here is due to the presence of secondary alteration minerals that are less resistant to surface weathering. This outcrop is located a little ways downstream of Tenaya Lake. Note juice bottle for scale.
Hydrothermal alteration in Cathedral Peak granodiorite (red arrows). This outcrop is located a little ways up the hill, to the NW of Micro Dome. Note pocketknife at base of outcrop on far right for scale.
Closer view of alteration on right side of above photo. Unaltered rock consists of orthoclase feldspar megacrysts in a coarse-grained matrix of plagioclase, orthoclase, quartz, and biotite (plus what we can’t see…). Altered rock contains epidote, chlorite, and albite-rich plagioclase and lacks biotite.
Closer view of the above photo – the light-green is epidote and the large dark-green patches are chlorite (pardon the poor 4 megapixel photo quality).
Hydrothermal alteration concentrated along an aplite/pegmatite dike in Cathedral Peak granodiorite at the base of Dozier Dome, on its far right side. Notice darker patches of epidote and chlorite within altered zone and acceleration of weathering as shown by the concave shape of the altered zone. Note pocketknife for scale.
Multiple weathered alteration pods, centered along an aplite/pegmatite dike in Cathedral Peak granodiorite. This slab is located just north of the drainage of Lower Cathedral Lake and can be seen while descending Dozier Dome to the south. As seen in the above photo, these alteration pods will often form along the plane of felsic dikes; this is most likely due to the structural planar weakness that exists at the boundary between the dike and the host rock, which provides a path of least resistance for hydrothermal fluids to flow. Alteration affects both dike rock and host rock. As opposed to a series of solution pockets in a granitic surface that form a chain of pods that is oriented parallel to the slope of a slab, these pods follow the dike, which is oriented at an oblique angle to the slope of the slab (notice the faint blacks steaks that are oriented parallel to the slope that form from water runoff).
A pothole in Cathedral Peak granodiorite, a couple hundred feet above the Tuolumne River and upstream of Glen Aulin. This pothole formed during sub-glacial water flow, rather than within an ancestral Tuolumne River drainage. Potholes should not be confused with weathered alteration holes and pods and are not the result of hydrothermal alteration; potholes result from the physical scouring of bedrock by solid rock fragments (of varying size) that are entrained in flowing water.
If one stops to pay attention, evidence of hydrothermal alteration can be seen here and there in the granitic rock of Yosemite and elsewhere. I remember explaining some of this stuff to fellow climbers at the base of East Cottage Dome, down and left, by the route Flintstone. There is at least one good example of hydrothermal alteration of Cathedral Peak granodiorite there on the slab at the base. Take a look around next time you are there. The slabs above the road at Olmsted Point are also hiding another good example that is not difficult to access, if you don’t mind walking for a few minutes.
Well… You said “talk to me”… so I got’a “blaw” ramblin’… Hope this helps and isn’t too much.
My comments and explanation above aren’t terribly scientific, considering that I haven’t referenced much in the way of sources… (Wiki and geologic maps linked below don’t really count). Although I did do a quick Google search that turned up stuff that would not be understandable if posted (links) and is full of jargon, what I have written above has been pretty much based on my understanding of what I have seen in the field, and discussions with professional geologists and professors in the past. Any other interpretations of Tork’s photos are gladly welcomed!!! What do you think, Greg Stock? Others?
For more info on El Capitan granite and the rocks of the Wawona area, see the following:
Yosemite National Park Geologic Map:
http://geomaps.geosci.unc.edu/parks/crops/YNP.jpg (cropped version)
http://geomaps.geosci.unc.edu/parks/fulls/Yosemite%20National%20Park.jpg (full version)
Yosemite Geologic Quad Map:
http://geomaps.geosci.unc.edu/quads/crops/Yosemite%20c.jpg (cropped version)
http://geomaps.geosci.unc.edu/quads/fulls/Yosemite.jpg (full version)
Ratajeski, K., Glazner, A.F., and Miller, B.V., 2001, Geology and geochemistry of mafic to felsic plutonic rocks in the Cretaceous intrusive suite of Yosemite Valley, California: Geological Society of America Bulletin, v. 113, p. 1486-1502.
http://bulletin.geoscienceworld.org/cgi/content/abstract/113/11/1486
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Minerals
Social climber
The Deli
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May 18, 2010 - 02:40pm PT
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“Ultimately , anything molten could have bubbles / venting I'm guessing .”
For the most part, yes, that is correct. The most common form of “bubbly” rock is referred to as vesicular basalt – the “bubbles” are called vesicles. Vesicles form when confining pressure is released, as magma ascends from depth in the Earth’s crust and volatiles (gas) within the magma expand. “Bubbles” or gas pockets may form in felsic granitic rock and are referred to as miarolitic cavities. I have not seen any miarolitic cavities in El Cap granite, however they are quite common in Johnson granite (the youngest plutonic unit in the Tuolumne Intrusive Suite). Miarolitic cavities are usually lined with well-developed crystals that are larger in size than that of the host rock. The tube in Tork’s photo does not appear to be a miarolitic cavity. It also does not appear to be related to a pegmatite pod within El Cap granite.
We discussed miarolitic cavities a bit in this thread:
http://www.supertopo.com/climbing/thread.php?topic_id=731799&msg=745947#msg745947
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mike m
Trad climber
black hills
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May 18, 2010 - 02:52pm PT
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Bubbles?
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Nate D
climber
San Francisco
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May 18, 2010 - 03:01pm PT
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Cool stuff. Thanks for taking the time to share, Minerals. The explanation for the differences in the rock on the S. vs. N. Face of HD, seems to apply to many other Sierra domes. Shuteye domes and crags illustrate much of this - a prime example being High Eagle Dome.
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Minerals
Social climber
The Deli
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May 18, 2010 - 03:14pm PT
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Mike, the pools atop Aquarium Rock appear to be simple solution pockets, which are quite common, especially in coarse-grained granitic rock in areas like JT and the Buttermilks.
Solution pockets in coarse-grained desert granite, Nevada. These solution pockets are formed by chemical and physical weathering of the surface of the granite, in areas of additional water runoff/pooling.
Nate, I’d love to check out Shuteye and the Southern Yosemite areas! Looks like wonderful stone.
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Dickbob
climber
Colorado
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May 18, 2010 - 03:38pm PT
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Once again, one of the reasons I do the Taco. learned a lot. My break is over. Thanks for that minerals.
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Mighty Hiker
climber
Vancouver, B.C.
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May 18, 2010 - 04:03pm PT
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Groovy stuff on the Apron at Squamish. This is nearly chimney-sized - you can get inside it in places and do armbars and heel-toes, or gastons if you're modern. Most just do high-steps, which is why some call it the elephant steps. Overall the feature runs for over 100 m, deeper at bulges, shallower on open flat slabs. There are some similar features elsewhere on the Apron, but nothing so long or deep.
Edit: It's graded "beyond category" - there's nothing else like it. Essentially water falling on the slabs above is funneled into this area, collecting stuff en route, and then shoots down. 10,000 years later, and voila.
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Minerals
Social climber
The Deli
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May 18, 2010 - 04:32pm PT
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That’s cool, Anders!
Anyone have a good photo or two of a climber on the Water Cracks on Lembert Dome, Tuolumne?
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MisterE
Social climber
Across Town From Easy Street
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May 18, 2010 - 09:44pm PT
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From Mountain Project:
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Tork
climber
Yosemite
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Topic Author's Reply - May 18, 2010 - 10:20pm PT
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Minerals, thanks for all the time you put into that, nice read!
Come up and climb on Wawona dome this summer.
Jeff
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hooblie
climber
from where the anecdotes roam
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May 18, 2010 - 10:32pm PT
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great contribution minerals, a lot of work and much appreciated
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Technogeekery
Trad climber
Tokyo, Japan
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May 18, 2010 - 10:32pm PT
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Minerals, thanks for posting, interesting stuff
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Fritz
Trad climber
Hagerman, ID
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May 18, 2010 - 10:46pm PT
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Minerals: Thank you for taking the considerable time to do a decently researched and very informative post!
You the man!
So-------thinking of hydrothermal alteration in granitic rocks: makes me think of a strange arch at City of Rocks Idaho.
As I recall: most arches are caused by erosion from wind or water, and/or exfoliation of the surface layers. However, an area of weakness from hydrothermal alteration seems like it could start bizarre formations such as this one.
Of course when you compare it to a limestone arch in Idaho: that was almost certainly caused by wind and water erosion------they are not that different.
Geology: The more I learn, the less I know.
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kpinwalla2
Social climber
WA
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May 18, 2010 - 11:04pm PT
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In case you're interested, I wrote a book about the evolution of granite landforms in the City of Rocks. It's called "Etched in Stone" - available from the Idaho Geological Survey. What you guys are calling "solution pockets" are actually called panholes, armchair hollows, and tafoni. In Germany they're called "opferkessel" and "gnammas" in Australia. They don't necessarily need a zone of hydrothermal alteration to initiate. Solution is only one of many processes that contribute to their formation. Rowl Twidale of Australia is "the man" when it comes to granite weathering - he literally wrote the book - "Granite Landforms".
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adam d
climber
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May 18, 2010 - 11:28pm PT
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Minerals... thanks for the lesson!
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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May 18, 2010 - 11:54pm PT
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That's a strange feature. Doesn't look natural. Hard to imagine a natural process that would bore a tunnel through granite like that. I agree with Minerals that it might possibly be a hydrothermally-altered, xenolith that was more vulnerable to normal weathering processes and was eroded out of the granite.
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Fritz
Trad climber
Hagerman, ID
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May 19, 2010 - 12:00am PT
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Kpinwalla2: Thank you for info on your City of Rocks publication: "Etched in Stone"
I will buy it, so I can learn more, and understand less about: Idaho geology.
However: a truly open and enlightened mind, might well ask if those holes in Yosemite Granite may relate to current ST posts on the artifact on the far side of the moon.
Minerals??? Are you covering up other theories?
Think of the headlines: "Alien Wormholes in Yosemite!!"
Then again: those holes may have grown giant------ and now eroded crystals.
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Mighty Hiker
climber
Vancouver, B.C.
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May 19, 2010 - 12:06am PT
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Maybe it was made by wonky space aliens, who thought they were making crop circles. :-)
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pyro
Big Wall climber
Calabasas
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May 19, 2010 - 12:09am PT
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Hey minerals geology about Yosemite is way cool.
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Shack
Big Wall climber
Reno NV
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May 19, 2010 - 01:24am PT
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Bryan is a great source of information that I'll never understand.
Excerpt from last weekend:
Me:"Hey Bryan, what's this?" (me holding up a some interesting looking rock I found)
Bryan:"A rock"
Me:"Oh yeah, right, hehe..."
a couple minutes later:
Me:"Hey Bryan, I think I found a quartz crystal!"
Bryan:"Nope, that's calcite."
Me:"Damn,....It looks cool though"
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nutjob
Trad climber
Berkeley, CA
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May 19, 2010 - 03:03am PT
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OK, what about these things on top of Lower Brother?
Off-thread question, but the pics were nearby. Where is Phantom Pinnacle in this photo?
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kpinwalla2
Social climber
WA
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May 19, 2010 - 09:47am PT
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First photo is a pod of pegmatite with what looks like big crystals of k-feldspar
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pc
climber
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May 19, 2010 - 10:31am PT
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Thanks very much for the posts and info Minerals!
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cragnshag
Social climber
san joser
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May 19, 2010 - 10:44am PT
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good stuff, maynard!
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Minerals
Social climber
The Deli
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May 20, 2010 - 08:39pm PT
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Jeff and others, glad to be of help and thanks for all of your replies! I always like talking about rocks, even if it is about this surface stuff that I don’t know so well... ;)
Yeah, that north wall on Wawona looks like it needs some more bolts, Jeff! :) Maybe have to pay you a visit some time.
Thanks, Fritz! But I didn’t do any research really, and am just a wannabe igneous petrologist – I’ve never studied weathering in any detail and am certainly no geomorphologist. Just gave it my best shot off the top of my head. Those are some cool photos that you posted, especially the second one! Don’t tell the sport climbers about that place… I tend to doubt that the weathering in your first photo is due to hydrothermal alteration but that is something that would be best explained by a local geologist, like Kpinwalla2, who understands that stuff better than I do. I’ve only been to the City once, and that was a looong time ago, before I studied rocks. Neat place.
“Geology: The more I learn, the less I know.”
Yes, most certainly! I remember saying to a professor about 10 years ago… “The more I know, the more I don’t know.” Isn’t that the truth! But it’s good in that it makes us continue to question and to ask why… otherwise things would get kinda boring.
Kpinwalla2, thanks for posting up! Yeah, my use of the term “solution pocket” is pretty much climber slang and shouldn’t be regarded as proper geologic terminology. Thanks for catching that. My geomorph terminology could use some help, big time. So, those are “panholes” on the top of the boulder in Nutjob’s second and third photos? Aquarium Rock too?
http://en.wikipedia.org/wiki/Panhole
So, this is your book?
http://www.idahogeology.org/Products/reverselook.asp?switch=title&value=Etched_in_Stone:_The_Geology_of_City_of_Rocks_National_Reserve_and_Castle_Rocks_State_Park,_Idaho
And this is the book that you speak of, by Twidale?
http://www.amazon.com/Granite-Landforms-C-R-Twidale/dp/0444421165/ref=sr_1_1?ie=UTF8&s=books&qid=1274385955&sr=1-1
Whew…! 300 bones, if you can find one…
How about this one?
http://www.amazon.com/Landforms-Geology-Granite-Terrains-Charles/dp/0415364353/ref=sr_1_2?ie=UTF8&s=books&qid=1274385955&sr=1-2#noop
Or this one?
http://www.amazon.com/Granite-Landscapes-World-Geomorphological/dp/0199273685/ref=sr_1_4?ie=UTF8&s=books&qid=1274385955&sr=1-4#noop
Tradster, with regard to the tube on Wawona Dome, I wasn’t thinking of an altered xenolith, just altered granite. Of the holes that I have seen in Yosemite, none of them appeared to be related to xenoliths or any other inclusions in the rock, but all have evidence of alteration of the granodiorite. Cool sculpted staircase! J-Tree?
Pyro, is that malachite?
http://en.wikipedia.org/wiki/Malachite
Image: http://en.wikipedia.org/wiki/File:Azurite_with_malachite_and_others.jpg
Shack, don’t forget gypsum!
Nutjob, as Kpinwalla2 said, that’s pegmatite, a very coarse-grained, granitic rock type. Aplite is roughly the fine-grained equivalent of pegmatite, although pegmatite may contain additional accessory minerals, as well as some “weird” minerals. In your photo, it looks like the pegmatite is part of a dike, as you can see more pegmatite in the bottom of the photo. The large crystals of pink potassium feldspar (K-feldspar or K-spar) look like they make up the center of the dike. The white feldspar is plagioclase and the rust-colored stains are due to the weathering of iron-bearing minerals, such as hematite or magnetite. Pegmatite can be really cool looking, especially when tourmaline and other neat minerals are present. Pegmatite can also be mafic/gabbroic in composition and contain large crystals of mafic minerals (dark in color).
http://en.wikipedia.org/wiki/Pegmatite
http://www.pegmatology.com/basic_info.htm
http://geology.about.com/od/rocks/ig/igrockindex/rocpicpegmatite.htm
http://www.gemandmineral.com/peg.html
Here are a few more photos of weathered granite in Nevada…
Evening light. I sent this photo to a professor who looked at the photo and described the rock as “weathered rat shit”… I guess I have to agree, but it’s still nice to look at and fun to explore. We are spoiled by the clean, glaciated exposures in the Sierra.
Neat patterns
A series of panholes (correct, Kpinwalla2? Or are these armchair hollows?)
Potholes in drainage
Panholes, fine-grained mafic enclave with negative weathering relief, and xenolith of schist with positive weathering relief – schist wins
Kpinwalla2, what do you think about the features in these photos? Anything to add?
Here’s a video of a trip down a really cool drainage in the same area as the above photos. The quality is pretty crappy – my 4-megapixel free-bee camera isn’t so great for video and it doesn’t adjust exposure for changes in brightness/darkness (video is too dark at times…). It also won’t film for very long. It stopped and I had to start it up again, but the exposure is much different (brighter). Anyways, it’s not so great, but gives you an idea of how cool this maze of slots is. Gotta go get a new point-n-shoot…
Desert granite slots:
http://www.youtube.com/watch?v=wEFIpKQaAok
Any of you J-Tree locals seen stuff like this down there? How ‘bout in the City of Rocks?
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pyro
Big Wall climber
Calabasas
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May 21, 2010 - 01:26am PT
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minerals it's just a small sample of Uranium from Africa. I wonder if you guys have ever run accross that stuff in the sierras? (just curious)
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R.B.
Trad climber
Cascadia
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May 21, 2010 - 01:40am PT
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I think a lot of the "weird" formations we find in climbing are mostly related to the processes of wind and water weathering ... together with the inherit mineralogical variability of intrusive granitic batholiths.
I think those holes were probably formed from water action.
Just an opinion.
RB
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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May 21, 2010 - 01:47am PT
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Yes the photo I posted is JTree, Split Rock area. Here's another photo showing an ice-filled pocket at the top of the Blob taken on Jan 1, 2008.
Pyro: your mineral looks like Sklodowskite. Mg(UO2)2Si2O7 - 6H2O
Is the sample from the Shinkolobwe mine in the Congo?
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Robb
Social climber
The other "Magic City on the Plains"
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May 21, 2010 - 11:50am PT
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Any of you guys/gals found the galium deposits in the valley?
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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May 21, 2010 - 01:05pm PT
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No please tell us where the Gallium deposits are.
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Minerals
Social climber
The Deli
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Jan 10, 2012 - 02:33am PT
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Back to weathering of hydrothermally altered granitic rock…
On Saturday, I noticed this small “cave” on the upper far right side of West Farthing Wall (in Tuolumne) when I walked by… Somehow I missed this before on previous descents. It’s pretty cool looking, although warm would probably be more appropriate if one were in desperate need of a sheltered bivy in bad weather, either rain or snow. The cavity would comfortably sleep two, if necessary. Here are a couple of photos, looking in and looking out. I should have taken a photo of the outside from farther away, with something for scale. Ah, good enough for now…
Looking into the small “cave”
Looking out, towards Olmsted Point and the Tioga road, etc.
This “cave” is another example of accelerated weathering of hydrothermally altered granitic rock (Cathedral Peak Granodiorite in this case), and is similar in geologic origin to the Wawona Dome feature posted by Tork.
We have been continuing our research on hydrothermal alteration within the Tuolumne Intrusive Suite and Allen gave a talk on the subject last month. From field observations, it appears that alteration is commonly associated with aplite/pegmatite dikes, which form during the last magmatic stages of pluton formation and final crystallization of residual felsic melt.
Abstract:
http://static.coreapps.net/agu2011/html/V14B-05.html
…found here:
http://m.core-apps.com/agu2011/abstract/575bd9e9b6f37808cc38b4ce53d4b39a
Here are a few more photos of examples of hydrothermal alteration in Half Dome Granodiorite in the Tuolumne area that are exposed on slabs; the material contained in the depressions is loose, coarse-grained sand that has accumulated from the weathering of the rock.
Weathered depression in hydrothermal pipe
Weathered depression in hydrothermal pipe centered along aplite/pegmatite dike
Weathered depression in hydrothermal pipe within aplite/pegmatite dike
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cleo
Social climber
the canyon below the Ditch!!!!
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Jan 10, 2012 - 10:19am PT
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That's weird stuff, Brian, thanks for sharing!
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Tony Bird
climber
Northridge, CA
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Jan 10, 2012 - 10:36am PT
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doesn't look like bubbles to me, looks like scoured-down-by-current, as you see at fossil falls. remember, lots of glaciation history, all kindsa water flow in the past. they didn't want to believe it with the channeled scablands.
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scuffy b
climber
heading slowly NNW
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Jan 10, 2012 - 03:07pm PT
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Awesome, Minerals!!
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Tony Bird
climber
Northridge, CA
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Jan 10, 2012 - 08:05pm PT
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why dingus, all it takes is one uintathere to fall down a tube like that. messes it up somethin' terrible.
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tom Carter
Social climber
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Jan 11, 2012 - 12:31am PT
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Thanks BL
Reminds me of the cave on Sorcerers
Have you been there?
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Minerals
Social climber
The Deli
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Jan 12, 2012 - 12:11am PT
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One thing that I should have been more clear on above… The coarse-grained sand within the depressions is not just from the weathering of the altered rock itself, but more of a collection of material that has weathered from the bulk of the rock and has washed or blown across the slab and was caught in the depressions.
“… much of that chlorite is likely altered hornblende.”
In Half Dome Granodiorite, yes, but Cathedral Peak Granodiorite contains very little hornblende; most of the mafic minerals are biotite. So in the cave photos above, it’s pretty much altered biotite. On a few occasions, I have seen biotite pseudomorphs after hornblende where a clot of fine-grained biotite occurs in the shape of a rectangular hornblende crystal, 1 to 2 cm in length. But these pseudomorphs are most likely due to a magmatic process, if not a metasomatic process, rather than hydrothermal alteration. I don’t understand the exact mechanisms and chemistry behind it and have heard it described as very complicated, chemistry-wise.
It’s interesting how some mafic enclaves and xenoliths weather more quickly than the surrounding rock and thus form a depression or hole whereas others are more resistant and have positive relief. Sometimes, it appears that grain size of the inclusion versus grain size of the host rock plays a more significant role than the difference in composition – finer-grained rocks can be more resistant to weathering. The giant “chickenheads” on routes in the western part of Yosemite Valley (Pat and Jack area, Elephant Rock, etc.) protrude significantly from the surrounding rock, making great climbing holds, even though these mafic enclaves are composed of mafic minerals which are less resistant to weathering than the host El Capitan Granite, which is quite felsic in composition, but coarse-grained.
I’ve got a few plutonic-related geo maps by D. A. John… pretty cool stuff!
Thanks for the paper, Wes. Saved it and will check it out further.
“Reminds me of the cave on Sorcerers
Have you been there?”
Nope. But I’m not badass like you, Tom!
It is shown at the beginning of the last pitch of the route in the Reid/Falkenstein guide. Got any photos of it to share? Do tell! :)
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Jan 12, 2012 - 01:04am PT
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Looking at this thread reminded me of this photo taken of the Trummelbach Falls near Lauterbrunen, Switzerland.
The Trummelbach Falls are a series of subterranean glacier-waterfalls made accessible by tunnel-lift. It drains the Eiger, Mönch, and Jungfrau glaciers (24 km²)and carries 20,200 tons of boulder detritus per year and discharge at 20,000 liters per second.
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cleo
Social climber
the canyon below the Ditch!!!!
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Jan 21, 2012 - 10:56pm PT
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On a little recording excursion to Lower Cathedral Lake, we stopped by to look for the cave.
Turns out to have a great sunset view:
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Minerals
Social climber
The Deli
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Jan 21, 2012 - 11:50pm PT
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That looks wild, Tradster! Limestone?
Nice photos, Cleo! Glad that you found it! :)
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Phil_B
Social climber
CHC, en zed
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Aug 23, 2016 - 03:40pm PT
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Cleo and I were up at West Farthing Wall this weekend. Thanks Minerals for the great routes for us less than bold climbers. We had a kid making the transition from gym to outdoors and he now loves slab.
Dang, but that wall gets a lot of sun. I was cooked!
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