When the Yellowstone supervolcano last erupted cataclysmically 640,000 years ago, it formed the Yellowstone Caldera, a 30 by 50 mile crater. Smaller, non-explosive eruptions have happened since, the most recent about 70,000 years ago.
Previous estimates of the plume have used seismic images, which measure the reflection of seismic waves from earthquakes off of different types of materials below the surface. They reached even deeper than the new images -- to more than 400 miles down.
The new method detects differences in electrical conductivity generated by the different types of rocks and minerals below Yellowstone National Park, which provides clues to what they are made of.
Using supercomputers, the research team, led by Michael Zhdanov of the University of Utah in Salt Lake City, created images of the plume based on the electromagnetic measurements from 115 stations in Idaho, Montana and Wyoming.
"We see that there is a partially melted, conductive plume at great depths starting in the mantle, and going up," Zhdanov said.