I'm at the summit of Mount Evans in Colorado, USA.
It is one of the Colorado Fourteeners,
meaning I'm more than 14,000 feet above sea level.
As Americans measure it.
For the rest of the world,
that is 4.3 kilometres above sea level,
or about half way to an airplane's cruising altitude.
And the air up here is thin:
I'm only getting about 60% of the oxygen that I normally do
each time I breathe in.
And let me tell you, this was a difficult climb.
At least, the last bit of it was.
Because this is also the most American mountain,
becacuse there is a road to the top of it.
The highest paved road in North America.
And this summit here counts as the 41st highest mountain in North America.
But how do we count that?
Just over there, the wonderfully named Meyer-Womble Observatory
is on another, slightly lower summit.
But it's surrounded by lower ground:
why doesn't that count as the 42nd highest?
And you might say, well,
the answer's obvious, it's part of the same mountain.
But where does that end?
This summit, Mount Evans, is just a smaller part of a big mountain range,
so you could try and make the case that this is just a bump
on the way to the tallest peak in the Rockies, Mount Elbert.
Or you could take it to the extreme and say
that there's only one mountain on each land mass,
that every other peak in North America is just a small bump
on the way to the enormous continent-sized mountain called Denali.
Now that's ridiculous, most people would say.
It's obvious.
That's a mountain.
And that isn't.
But in formal terms, we solve it by measuring prominence.
Prominence works like this:
imagine if you could raise sea level up to where I'm sitting now.
How many meters would it have to drop before you could connect
this mountain to another, taller one
and walk there without getting your feet wet?
For Mount Evans, that is 839m down,
or about one-fifth of its height above sea level.
That observatory summit?
It's not prominent.
Sure, you have to walk downhill from it, but after a few meters
you're going uphill again.
So where do you draw the line?
Well, there are several different lines, because of course there are.
The International Climbing and Mountaineering Federation defines a mountain
as needing 300m of prominence,
which is actually only the height of the Eiffel Tower,
which... doesn't seem like much to me?
Other folks disagree, and say it should be 500m,
or that prominence should change with altitude...
it's a mess.
I'll be honest, even after researching this, I'm not sure about it.
Even the folks I asked to check my script went,
"eh, well, I guess, basically, but technically..."
This is one of those times that the human need to categorise and catalogue everything
runs up against messy reality.
There are always edge cases, and pretty much every mountain is an edge case.
I'm going to go back down now before I get altitude sickness(!)