The massive volcano that lurks under Yellowstone National Park took a “breath” recently, causing miles of earth to rise dramatically, scientists tell National Geographic. From 2004 to 2010, parts of the 925-square-mile caldera have swelled as much as 10 inches, most likely pushed up by a magma pocket four to six miles underground. “At the beginning, we were concerned it could be leading up to an eruption,” says one volcanist.
But once scientists saw that the magma was deep enough, they calmed down. “If it had been at depths of two or three kilometers (instead of 10), we’d have been a lot more concerned,” the volcanist says. Yellowstone has taken such breaths regularly over the past 15,000 years, but one of them could eventually lead to an eruption. The park's supervolcano has produced eruptions a thousand times stronger than Mount St. Helens’ 1980 blast three times in the last 2.1 million years.