Yellowstone Supervolcano is a Much Bigger Time Bomb Than We Thought

 The supervolcano that lies beneath Yellowstone National Park is 2.5 times larger than previously thought, it was revealed at an American Geophysical Union meeting. 

Scientists knew the supervolcano was big, and set out to find out just how big, in order to assess the threat level. What they discovered, they said, was "astounding."
Between 125 and 185 billion cubic miles of magma is pooled under the surface, representing an existential threat to America, as well as the rest of the world. One scientist estimates an eruption would be 2,000 times the size of Mount St. Helens.