A blob of errant magma gathering 6 miles beneath Yellowstone National Park—the same molten rock that makes Old Faithful spurt and heats the park's famous hot springs—has caused the caldera, or volcanic floor, to rise 3 inches since 2004. Scientists say that though the rate of increase is unprecedented, there is no imminent risk of eruption, LiveScience reports.
The dislodged magma covers an underground area as large as Los Angeles, though it is only tens to hundreds of yards thick. Yellowstone boasts North America's largest volcanic field, produced by a plume of molten rock beginning roughly 400 miles down. "There is no evidence of an imminent volcanic eruption or hydrothermal explosion," one researcher said. "That's the bottom line."