Yellowstone, 640K years ago (VEI 8)
Believe it or not, the whole Yellowstone National Park is volcano that can explode anytime. It is what is called a super volcano. It has already exploded in the past. It shows signs of 3 level 8 VEI scale eruptions. The last of the three was 640,000 years back. Experts say that the amount of ash from all three could fill the entire Grand Canyon. Recent studies show a gargantuan collection of magma beneath Yellowstone.
