Prominence of rock towers

Discuss geopolitical area highpoints, prominence, and similar lists.

Prominence of rock towers

Postby Scott Patterson » Sun May 10, 2015 11:21 am

It is difficult to tell what the prominence of a rock tower is by looking at a topo map. I believe that many rock towers actually have more prominence than is indicated on LoJ using the topo maps.

Perhaps two famous examples would be Devils Thumb Colorado or Ancient Art Utah.

I believe Devils Thumb actually has quite a bit more prominence than 40' and likewise, Ancient Art surely has more than 80', though I don't know what that prominence is. I believe many of the Fisher Towers and towers in places such as Monument Basin actually have more prominence that is indicated on LoJ. Unfortunately, it isn't possible to figure the prominence by looking at the topo maps. It would be interesting if someone took some GPS readings on some of these or used other survey methods when they climbed them.
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Re: Prominence of rock towers

Postby John Kirk » Mon May 11, 2015 11:28 am

Measuring by rap length tends to be most accurate. Most of the Fishers and towers found in the Desert Rock series have prominence derived this way (or from photos).

I added one assumed contour for Devils Thumb but no more, because a single 60m gets you back to the saddle (60/2*3.28=98.4'; that's also at an angle, not vertical, so make it 80'). It's actually debatable whether there is a missing contour or not, because a single closed contour essentially already covers the optimistic end of the spectrum (12040 low to 12120 high = 80')

This demonstrates why Ancient Art doesn't have much prominence:
a_.png
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Re: Prominence of rock towers

Postby John Prater » Mon May 11, 2015 1:38 pm

Regarding Ancient Art, I'm guessing most (that have checked it off) are referring to the corkscrew summit? It seems that Ancient Art is a formation with multiple summits, though, and it appears that the corkscrew isn't the highest (Desert Rock probably clarifies this, but I don't have it in front of me).

http://mountainproject.com/v/ancient-art/105716859
http://mountainproject.com/v/105917931
https://books.google.com/books?id=YJuqsqDTPbEC&lpg=PP1&dq=Desert%20Rock%20III&pg=PA188#v=onepage&q=Desert%20Rock%20III&f=false

Dunno if multiple summits (maybe main and corkscrew?) should be listed or not. And that doesn't help with the prominence question.
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Re: Prominence of rock towers

Postby John Kirk » Mon May 11, 2015 2:20 pm

John Prater wrote:Regarding Ancient Art, I'm guessing most (that have checked it off) are referring to the corkscrew summit? It seems that Ancient Art is a formation with multiple summits, though, and it appears that the corkscrew isn't the highest (Desert Rock probably clarifies this, but I don't have it in front of me).


This image indicates that the corkscrew is not highest on the formation, so maybe it's even less than 80':
http://mountainproject.com/images/86/93/107418693_large_888b5a.jpg
The formation HP looks to be in the neighborhood of 200'
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Re: Prominence of rock towers

Postby Furthermore » Mon May 11, 2015 9:11 pm

If I remember correctly, Corkscrew is taller than Middle Summit but North Summit is the highest. Based on my poor memory on rappel lengths, I would estimate 160-180 feet of prominence for the North Summit. I think 60-80 feet is correct for the Corkscrew.

Looks like we just need to climb them all to figure out the correct prominences. I know the Bridger Jacks were skewed initially and I imagine several other sets of towers are skewed as well.
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Re: Prominence of rock towers

Postby Scott Patterson » Thu May 28, 2015 8:12 pm

I added one assumed contour for Devils Thumb but no more, because a single 60m gets you back to the saddle (60/2*3.28=98.4'; that's also at an angle, not vertical, so make it 80'). It's actually debatable whether there is a missing contour or not, because a single closed contour essentially already covers the optimistic end of the spectrum (12040 low to 12120 high = 80')


When we climbed it, we did it in two raps because the 60m didn't quite reach. Maybe we took a different line down though and as you said, it's at an angle.

Ormes list Devils Thumb as 12,150 feet, which would if accurate, would be 90' (which is not far from 80), but I don't know where Ormes got the altitude.

It seems that Ancient Art is a formation with multiple summits, though, and it appears that the corkscrew isn't the highest (Desert Rock probably clarifies this, but I don't have it in front of me).


The highest summit of Ancient Art is the northern middle summit; the one with the sand pipe sticking up as can be seen in the link:

https://books.google.com/books?id=YJuqs ... II&f=false

Desert Rock III:

https://books.google.com/books?id=YJuqs ... mb&f=false

I guess either way it would be unranked, but I assume it would have over 80' prominence. :?:

Some rock towers may be ranked though that are missing on the list. Standing Rock, in Monument Basin, for example, is said to be "almost" 350' high.

http://www.summitpost.org/standing-rock/716910

Image

There are actually many free standing towers in the basin that may have 300' prominence, but it's not something that can be determined by looking at the topo maps.

Towers such as the Pixie Stick wouldn't make the 300' prominence criteria, but they do demonstrate why a topo map is useless in trying to determine the prominence!

Image

LOJ (understandably!) list only two summits in Monument Basin that have over 300' prominence, but I'm guessing that there are actually more that would qualify. Other than with a survey, laser, shadow measurement with a trigonometric calculation, or a climber using a GPS, it would be hard to determine the prominence.
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