Bob Christiansen of the U.S. Geological Survey realizes that the entire Yellowstone National Park is the caldera (65 km in diameter!) of a volcano, which is fed by a superplume 200 km below, a magma chamber 72 km in diameter and 13 km thick; the pressure exerted by the magma still raises the park by about 500 m; the last explosion occurred 630,000 years ago and one occurs every 600,000 years on average (so the next one is already late).
