A new study shows the chamber of hot molten rock below Yellowstone National Park is more than 2 and a-half times larger than previously estimated.
Lead author Jamie Farrell of the University of Utah said Monday the magma chamber is about 55 miles long, 18 miles wide and runs at depths from 3 to 9 miles below the earth.
That means the supervolcano below Yellowstone has the potential to erupt with the force of its largest-ever eruption 2.1 million years ago.
Farrell says that eruption was about 2,000 times the size of Mount St. Helens in 1980, and a similar explosion would be a "global event."
Farrell says there have been three eruptions of the supervolcano, and scientists don't know when the next will happen.
The BBC first reported Farrell's study.