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Denali Shrinks 83 Feet

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Denali Shrinks 83 Feet

Postby cab » Thu Sep 12, 2013 6:19 pm

(CNN) -- North America's tallest mountain has lost some of its stature -- 83 feet of it to be precise.
Alaska's lieutenant governor announced Wednesday that new mapping technology puts Mount McKinley at 20,237 feet rather than the 20,320 it was pegged at.
"That's 83 feet shorter than we thought," Lt. Gov. Mead Treadwell said in a statement. She made the announcement Wednesday at a symposium of the International Map Collectors' Society in Anchorage.
The 20,320 height had stood since 1952, when the mountain was measured using a technology called photogrammetry, Treadwell's announcement said.
The new height was measured last year with a radar mapping system deployed by the Statewide Digital Mapping Initiative in cooperation with the U.S. Geological Survey. The project will produce 11,000 new maps of the 49th state by 2016, according to the statement.
Alaskans, including two who've climbed Denali, as it is called in Alaska, were unfazed by the news.
"It's hard to climb, and the air is just as thin," mountaineer Stan Justice told the Fairbanks News Miner.
"It's still high, it's still hard, it's still cold," climber Nick Parker told the Anchorage Daily News. "As long as it's higher than Texas, I don't care."
And still hundreds of feet ahead of Canada. That's where North America's second-tallest peak, Mount Logan at 19,551 feet, sits.
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Re: Denali Shrinks 83 Feet

Postby surgent » Fri Sep 13, 2013 10:10 pm

It will be interesting to see if all the main peaks in the Alaska Range shrink by a similar amount, thus suggesting that the older measurement was not in error, but based on an inaccurate datum (for that area). It would be more suspect if only Denali shrunk, and the others did not, perhaps suggesting the new elevation was taken on a point nearby the summit (the USGS is famous for doing this) or some other error, either back from 1952 or from now, took place.

The word "highest" should be used in place of "tallest". This is my little pet peeve. I saw this same article on CNN and cringed just a little bit. Oh well.
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Re: Denali Shrinks 83 Feet

Postby MoapaPk » Fri Sep 13, 2013 10:52 pm

Not only has the datum changed (now earth-centered) but the geoid as well.
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Re: Denali Shrinks 83 Feet

Postby Scott » Sat Sep 14, 2013 4:46 am

Denali has been long suspected to be slightly lower than the official 1952 surveyed figure of 20,320 feet.

In 1989, for example, the much published satellite calculations gave a figure on 20,306 feet and were considered to be more accurate than Washburn's figure. (The old figure before Washburn's was 20,300 feet; though I don't know what year that was surveyed. Sometime before 1910 for sure since the books on the first ascent use this figure).

It wasn't that Washburn and team were bad surveyors; quite the contrary. It's that Denali has such a huge bulk and stands so much higher than its neighbors that it distorts gravity (as do other mountains). Surveyors know this and have for a long time, but with such a big and solitary mountain, it is possible that it could have skewed the results more than expected or more than was usual for a mountain of its elevation.

Satellites can provide more accurate calculations, but just because someone comes up with a new figure that doesn't quite match the old one, it may or not become the official elevation.

The 1989 measurement was 24 years ago and still hasn't taken precedence over the 1952 figure. I wouldn't expect the 2013 figure to start showing up on all the maps soon and I would also suspect that down the road a few years someone else is going to come up with another figure they claim to be more accurate. This kind of thing actually happens every few years (or perhaps a decade or two in some cases) with mountains such as Denali and Everest.
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Re: Denali Shrinks 83 Feet

Postby MoapaPk » Sat Sep 14, 2013 8:01 pm

The OP quoted a source that implied the elevation was obtained by photogrammetry, not by direct optical surveying. I have my own issues with photogrammetry: http://www.summitpost.org/picacho-usgs- ... 7/c-837597

Beside errors near cliffs, photogrammetry often has troubles with relatively rounded summits that don't have significant changes in reflectivity-- e.g., troubles with big snowy lumps.

The new mapping was by strm? Or are they screwing up and calling lidar radar?

EDIT: this article gives more info. The unpublished 1989 measurement was ny GPS, which technically is a satellite method (the newer satellite methods don't depend on a ground receiver).
http://www.huffingtonpost.com/2013/09/1 ... _ref=green

Current measurement by IFSAR: http://ned.usgs.gov/downloads/documents ... _Aug13.pdf
Latter source also says the 1952 elevation was from photogrammetry, not direct optical surveying.
Last edited by MoapaPk on Mon Sep 16, 2013 4:39 pm, edited 3 times in total.
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Re: Denali Shrinks 83 Feet

Postby ScottyP » Mon Sep 16, 2013 4:59 am

Glad it did not grow or I would have to go back!,
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Re: Denali Shrinks 83 Feet

Postby MoapaPk » Mon Sep 16, 2013 3:37 pm

Much of the US digital elevation model (now intergrown with NED, used in the following comparison) was obtained by photogrammetry. The following comparison is a bit sobering:
http://geology.er.usgs.gov/eespteam/ter ... _gis04.pdf
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