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SoloBolo
Trad climber
groveland, ca
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Topic Author's Original Post - Jun 14, 2005 - 10:01pm PT
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hey, i was meandering the base of el cap today and to the right of the 4th class leading to the nose (i am guessing) there are a series of drilled (most only partially) 1.5" in diameter holes. what are they for/why were they put there?
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WBraun
climber
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Jun 14, 2005 - 10:10pm PT
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Core samples ..... some curious scientist.
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Ahwahnee Bartender
Big Wall climber
Fog Town
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Jun 14, 2005 - 10:29pm PT
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Here's another holes question. Now how about the El Cap holes along the base that start just east of the nose and are comprised of 3 triangular hole sets. Each hole is approximately 4" wide and 1" deep. There are a number of these every 50-100 feet or so. Some of the drilled holes have been plugged and others not. Almost looks like some time of anchor/crane was mounted to the rock years ago.
Theo
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WBraun
climber
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Jun 14, 2005 - 10:32pm PT
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Those were made by those little guys Yabo saw one night while he was flying his mental kite at the base.
He told me the story when he came down.
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Minerals
Social climber
The Deli
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Jun 14, 2005 - 11:23pm PT
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From Russ’ link:
Bob Harrington wrote:
Potassium/argon dating or possibly paleomagnetism come to mind.
Bingo! Dolt cart anchors worked for me for a long time… until I studied geology. Not sure if it was the USGS or others that drilled those holes but… they sure are ugly and need to be filled. Somebody recently wedged a rock in one of them… InstaCrete would probably work better. The two smaller diameter holes are filled with threaded inserts (kinda like the crapola Petzl Caving bolts). These two bolts were used to mount a larger drill, which drilled the top hole (~1.5 inches in diameter x 1 inch deep). Paleomagnetism seems most likely to me – they remove a solid ‘disk’ of rock and are careful to record the exact orientations of the sample before/as it is removed from the rock. The sample is then taken to a lab where iron-bearing minerals are analyzed for any record of what the Earth’s magnetic field was like at the time of crystallization of the granite (El Capitan Granite in this case; crystallized ~104 million years ago). Potassium/argon dating was probably the main method of dating granites at the time that these holes were drilled, however, newer techniques have allowed geologists to date granitic rocks more precisely. K/Ar dates on minerals such as hornblende and biotite record cooling ages, which are younger than initial crystallization ages. Newer techniques involve the analysis of uranium’s radioactive decay to lead, as it passes thorium. Uranium is found in trace amounts in the mineral zircon, as its atomic radii is similar to zirconium, providing a nice home for trace uranium. Blah, blah, blah… Sorry.
If everyone agrees that these holes are ugly (and not part of history) then one of us can go patch them with the appropriate materials.
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WBraun
climber
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Jun 14, 2005 - 11:36pm PT
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I like those holes. They are a nice curiosity and mysterious.
Please do not disturb, Minerals. Not everything has to be fixed, .... please .........
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Minerals
Social climber
The Deli
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Jun 14, 2005 - 11:42pm PT
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Ok Werner, sounds good to me. I'll leave 'em alone. They are kinda neat, even though they are ugly. Gotta preserve history, right? Cheers Werner.
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WBraun
climber
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Jun 14, 2005 - 11:53pm PT
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Thanks Minerals. Gotta preserve history, right?
Mystery definately is always nice too.
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Minerals
Social climber
The Deli
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Jun 15, 2005 - 12:05am PT
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Yeah, you’re right. But… after rereading the thread… I couldn’t help myself from this one…
Not everything has to be fixed
And that’s why we went up on Zodiac… ;) Details in the near future (and we hope I'm not talking geologic time...).
Werner, I’d buy you a beer next time I’m around if you’d drink it. We should sit down and chat sometime. Was it the LeMans? I think so... And yes, YOU are the one who needs to WRITE A BOOK!!!
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WBraun
climber
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Jun 15, 2005 - 12:33am PT
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Yea, it was the Le Mans. Those were pretty fun days with Russ and the Duce and the rest of the crew.
But, you can fix everything else on El Cap. I understand your heart.
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Weenis
Trad climber
Shastafaria
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Jun 15, 2005 - 11:08am PT
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Donny Reid was under the impression that those holes were for a dam survey.
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bobh
climber
Bishop, California
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Jun 15, 2005 - 11:55am PT
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I'd think the Pulpit Rock/Mojo Tooth area would be a better dam site.
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deuce4
Big Wall climber
the Southwest
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Jun 15, 2005 - 12:05pm PT
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Here's a good article about what they found using Paleomagnetism therories in the Grand Canyon, where along the river you can see many of the core sample holes (as found at the base of El Cap), usually a series of samples from a single area.
http://www.geol.ucsb.edu/faculty/porter/Papers/Karlstrom-et-al2000.pdf
Quote from the research:
"Magnetization is west and shallow down (interpreted to be normal
polarity based on a comparison with Cambrian-Ordovician magnetizations
from North America), or east and shallow up (reversed polarity). The inclination
data yield an inferred paleolatitude of ~5°N for the lower Chuar
Group and ~10°N for the upper Chuar Group. These data are in broad
agreement with results reported by Elston et al. (1993) and
are important for helping define the orientation and position of Laurentia during fragmentation of the near-equatorial Rodinia supercontinent."
It's all about mapping the Paleozoic planet.
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WBraun
climber
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Jun 15, 2005 - 12:12pm PT
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So Ducey babe, ... all those big ass heavy words in that article make my head swim. What does all this mean in terms that a simpleton such as me can understand?
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TradIsGood
Trad climber
Gunks end of country
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Jun 15, 2005 - 02:09pm PT
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Compass doesn't work so well down there. But heck, there's only up, up river, or down river down there anyway, right?
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deuce4
Big Wall climber
the Southwest
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Jun 15, 2005 - 02:33pm PT
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Werner, it's all based on the assumption that at the time the rock was created (crystalized, or sedimentized with trace magnetic elements like hematite), its magnetism lined up with the poles.
Now two things have happened since then:
*the magnetic poles may have changed their axis, and
*the land masses have moved.
There are several theories of what the planet looked like during earlier times (Werner, I remember those pictures in Bhaagavata as one of them too), but general theories of the Grand Canyon,
which has most of the Paleozoic eras represented--250 to 540 or so million years ago--on top of mostly eroded and interesting billion or so year old precambrian rock layers called the Chuar and Unkar groups, and that on top of older base layers of granites and shists,
involve the mythical supercontinent of Rodinia, when the bulk of North America was one of many clumped land masses (sorry, California came later).
By comparing the magnetism direction today with the magnetism direction many layers of rock with assumed ages, you can piece together some clues of how the land masses and poles have moved in the past billion years.
Here's a movie of how Gondwanaland, a more recent supercontinent, may have moved around:
http://www.gps.caltech.edu/%7Edevans/iitpw/movie3.html
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Minerals
Social climber
The Deli
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Jun 15, 2005 - 02:56pm PT
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Nice, Deuce. Looks like you are becoming a geologist!
And how about these magnetic reversals that are recorded in oceanic crust - if one looks at a spreading ridge (as is found in the center of the Atlantic Ocean) on a magnetic data map, one will see that there is a mirror image pattern of magnetic reversals on either side of the ridge. But the question is: why do the magnetic reversals happen in the first place?
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deuce4
Big Wall climber
the Southwest
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Jun 15, 2005 - 08:56pm PT
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That's right, I think, the record of the spreading ridges provides information on how the poles have moved over time; combine that information with the magnetism direction of rock in any particular area (based on its assumed age) pinpoints the original direction, so you can tell how much it has rotated.
Not sure how geologists have worked out how far a particular land mass has moved since it was formed--I think some clues are given by the type of sedimentary rock, which tells something about the climate.
Lots and lots of pieces of information that can be interpreted many ways.
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Minerals
Social climber
The Deli
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Jun 16, 2005 - 07:19pm PT
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This is what happens when you spend too much time looking at rocks – they start looking back at you!
Dr. Core Sample lives on top of a blasted outcrop along the Tioga road, somewhere near the trailhead for Porcupine Flat, or one of those turn outs... The rock is tonalite of Glacier Point/Glen Aulin – it is darker in color than granite or granodiorite. These holes were probably drilled at least 20 or 30 years ago and the samples were probably used for geochemistry and geochronology work. What’s really in them there rocks…?
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