UKC

NEWS: Denali 'Shrinks'

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 UKC News 13 Sep 2013
The face says it all- about 2000m up the Cassin on a single push attempt. Winds screaming over the summit just above, 4 kbAccording to a recent survey Denali (aka Mt.McKinley) is about 25m lower than previously thought.

Read more at http://www.ukclimbing.com/news/item.php?id=68341
 Jonny2vests 14 Sep 2013
In reply to UKC News:

Interesting. As someone who does this sort of thing for a living, its worth noting that this height estimate is no more valid or official than any other surveyed estimate. What often turns out to be the case in these mountain height sagas is not the validity of one survey or another, it's our estimate of how far down mean sea level is that changes, which is tied to a guesstimate of gravitational potential. So 'Denali shrinks' might be more accurately stated as 'Mean Sea Level rises'.
 Trevers 14 Sep 2013
In reply to Jonny2vests:
> (In reply to UKC News)
>
> Interesting. As someone who does this sort of thing for a living, its worth noting that this height estimate is no more valid or official than any other surveyed estimate. What often turns out to be the case in these mountain height sagas is not the validity of one survey or another, it's our estimate of how far down mean sea level is that changes, which is tied to a guesstimate of gravitational potential. So 'Denali shrinks' might be more accurately stated as 'Mean Sea Level rises'.

Although if that were the case, it would be highly suspicious that the other mountains weren't all shrinking by the same amount too.
 Jonny2vests 14 Sep 2013
In reply to Trevers:

What makes you think their height estimates do not change? Every time we measure any big mountain (that is not close to a coast) using a different technique, you will likely see significant differences. Nothing is actually changing (significantly), I'm simply pointing out that efforts like this are fraught with difficulties and assumption, and differences of this magnitude are expected.

It wouldn't matter if I conducted a millimetric precision survey for a year, the observations may be internally consistent but that still won't tell me where MSL is underneath the mountain. Even with a gravity meter we have to make the assumption of uniform granite all the way down.
 Trevers 14 Sep 2013
In reply to Jonny2vests:
> (In reply to Trevers)
>
> What makes you think their height estimates do not change? Every time we measure any big mountain (that is not close to a coast) using a different technique, you will likely see significant differences. Nothing is actually changing (significantly), I'm simply pointing out that efforts like this are fraught with difficulties and assumption, and differences of this magnitude are expected.
>
> It wouldn't matter if I conducted a millimetric precision survey for a year, the observations may be internally consistent but that still won't tell me where MSL is underneath the mountain. Even with a gravity meter we have to make the assumption of uniform granite all the way down.

Sorry, my post was borne out of almost complete ignorance of how these things are measured. I assumed you meant that average sea levels were actually 25m higher than we had thought, which struck me as daft.

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