Via MSNBC from geology.com:
It's no mere doomsday pseudoscience: The Yellowstone supervolcano really could be the end of us all. When the Yellowstone Caldera — the name of the national park's geographic structure, which roughly translates as "caldron" — blows its lid, much of the continental United States will get covered in a blanket of ash. That ash will clog the atmosphere enough to block out the sun, disrupting the global climate enough to cause mass extinctions.
The last full-scale eruption of that kind occurred 640,000 years ago, and the ones prior to that occurred 1.3 million years and 2.1 million years ago. Interspersed with the big ones have been smaller-scale but still major eruptions, most recently 70,000 years ago...
Graphic: National Park Service
