Deep beneath Yellowstone National Park is an enormous volcanic crater hundreds of thousands of years old. Researchers have found a new way to track changes in the crater by studying electromagnetic fields instead of seismic activity.

A team of geologists at the US Geological Survey, working with a trio of colleagues from Oregon State University, and another from the University of Wisconsin-Madison, has found evidence of rhyolitic volcanism in Yellowstone caldera shifting northeast.

Large explosive eruptions occur in Yellowstone around once every 700,000 years, according to the U.S. Geological Survey.