Yellowstone magma chamber 2.5 times larger than previously believed

San Francisco Chronicle : Yellowstone National Park is frequently referred to as a supervolcano because of the large magma chamber that sits below it. A new study by Jamie Farrell of the University of Utah and his colleagues has revealed that the magma chamber is significantly larger than previously estimated. They used seismic waves from earthquakes to map the shape of the chamber. The seismic waves, which bend as they pass into and out of the molten rock, create a picture of the chamber, much like a sonogram. Farrell’s team measured the chamber as 55 miles (88.5 km) long, 18 miles (29 km) wide, and between 3 and 9 miles (4.8 to 14.5 km) deep. It contains more than 2000 times as much material as was ejected by the 1980 Mount St. Helens eruption. If it were to erupt, it could rival the largest of the three known eruptions of the Yellowstone volcano that have occurred over the past 2 million years. The most recent of the eruptions was 640 000 years ago, and some researchers believe that the volcano is due to erupt again soon. However, Farrell thinks that there is not enough information available to make that claim.