That is very interesting. I live in Portland Oregon, recently we were driving out to a park and looked over and saw a mountain we had never seen before. It literally took us 5 minutes, looking at google maps, to realize it was Mount Hood - a mountain that we had seen hundreds of times before. But we didn't recognize it because it was snow free. In 21 years we've never seen it without it's cap of snow/ice and couldn't recognize it. It was shocking to say the least and really hit home what is going on with water in the region.
As a side tangent, Oregon is a part of the world where volcanoes do just sort of spring up practically overnight, geologically speaking. Mt Bachelor was formed between 18,000 and 8,000 years ago, according to wikipedia.
They can also disappear literally overnight. Mt Mazama erupted about 7,700 years ago and is now Crater lake. There were a lot of eruptions around Newberry caldera around that same time, and there've been eruptions as recently as about 1,300 years ago.
Good point. Also worth noting that that was comparatively mild; according to Wikipedia, St. Helens ejected a little more than a cubic mile of material, whereas Mt. Mazama is estimated to have ejected about 27 cubic miles of material. It's hard to imagine that kind of explosion.
Mt. Mazama seems to have been a bit of an outlier, though:
> The United States Geological Survey has referred to the 7,700 years ago Mazama eruption as the largest explosive eruption within the Cascades in the past million years, and one of the largest eruptions during the Holocene epoch.
Seems kind of improbable that the biggest anything happened in the most recent 0.77% of the observed time interval, which makes me wonder if there may have been others we just don't know about. Improbable events do happen though, so maybe it's just dumb luck (if we want to call it that) that we had such an event within relatively recent history.
> Seems kind of improbable that the biggest anything happened in the most recent 0.77% of the observed time interval,
The biggest has to happen sometime, and whenever it does will be an improbable time for it to have occurred if the probability is uniform and the resolution of time tracked is high relative to the total interval.
