As I am found of saying, "humanity is allowed to exist because of two things - geology and climatology - change either of them and you change the human race.
Here is an excellent story on the supervolcano that exists under Yellowstone National Park. This was a centerpiece of the disaster flick '2012'.
Yellowstone IS going to blow again - in fact it is overdue. WHen it does, humanity and civilization as we know it is going to change as a result.
Reda More ABout It: http://www.cnn.com/2012/08/30/us/wus-supervolcanoes-yellowstone/index.html?hpt=hp_c3
Sky Guy in VA
Tomorrow: Blue Moon Friday