We haven't seen a real volcanic event at least in 74,000 years - [Mount Toba] in Indonesia, in Sumatra, where the crater itself is 100 kilometers across. It was so monumental, what happened, that for a very long time the entire atmosphere of our planet was darkened. It's not the lava and the heat per se; it's the obscuring of the entire atmosphere, and it made it very difficult for the human race to survive.