ScienceDaily (Nov. 15, 2011) — The geological record holds clues that throughout Earth's 4.5-billion-year lifetime massive supervolcanoes, far larger than Mount St. Helens or Mount Pinatubo, have erupted. However, despite the claims of those who fear 2012, there's no evidence that such a supereruption is imminent.
http://www.sciencedaily.com/releases/2011/11/111115180313.htm