Wednesday, June 17, 2020

An objective measure of how majestic a mountain is

Ever since our days in Seattle, I have been endlessly fascinated with mountains like Rainier and Denali - mountains that stand much taller than their neighbouring mountains thereby offering dramatic and spectacular views, often from long distances. It turns out there is an objective measure that measures this quality: topographical prominence (thanks to a Windows screen saver photo of Mt. Kilimanjaro which led me to this Wikipedia page). Some really high peaks (like K2) don't have as much topological prominence as they are surrounded by mountain masses that are also very high.
The definition of topographic prominence is a bit tricky but makes intuitive sense if you think about it. Wikipedia defines it as " the height of a mountain or hill's summit relative to the lowest contour line encircling it but containing no higher summit within it". Basically:

1. Find the maximal land area surrounding the peak which contains no higher peak
2. Find the lowest point in that area. 
3. Topographic prominence is the height of the peak from that point. 

Now, which mountain do you think is #1 in terms of topological prominence? As per another helpful Wikipedia page on the Ranking of Mountains by Topological prominence, it is indeed Mt. Everest. Well, no surprise there, you might say. But I was actually surprised. I knew that you need to get to a very high altitude before you even see Everest. The base camp for a mountaineer making an attempt at Mt. Everest is at a whopping 17000 ft. So I would have thought Mt. Everest's topological prominence would be around 12000 ft, not that high. I thought even Mt. Rainier might beat it, Denali for sure. You can see Denali from 100 miles. 

But then if you go back and read the definition again, Mt. Everest gets the top nod based on a technicality. You see, as per step 1, you need to find the maximal area surrounding the peak which contains no higher peak. Since there is no higher peak than Everest, the maximal area is the Earth's entire landmass (or at least Eurasia if you want to be very precise). And the lowest point in that area (step 2) is sea level. Hence the topological prominence of Everest is its entire height from sea level, all 29000ft of it. So the measure actually doesn't really work that well for the tallest mountain in the world because it is no. 1 by definition, but it works well for others. So none of the high peaks in the Himalayas other than Mt. Everest  come up in the top 10, because they are surrounded by really high contiguous landmasses that includes higher peaks  and they don't stand out as much. 

Not surprisingly, Mt. Aconcagua and Mt. Denali the tallest mountains in South and North America respectively are 2nd and 3rd in the list. And Mt. Kilimanjaro, the highest mountain in Africa is fourth.  And my favourite neighbourhood Mt. Rainier comes in at a respectable 21st  in the list. 

- Balaji

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