That Yellowstone has a big blob of molten rock lurking beneath it isn't news to scientists. A new analysis, however, shows that this blob is more than twice as big as they originally thought, reports Nature. Figure about 50 miles long, 20 miles wide, and shaped like a "dog's knobby chew toy," says LiveScience. The magma reservoir lies a few miles beneath the surface and is responsible for the park's geysers and hot springs. “I don’t know of any other magma body that’s been imaged that’s that big,” says a geophysicist at the University of Utah.
So does this raise fears about a giant volcanic eruption, perhaps something on the scale of those that created the park eons ago? Not so much. "The pervasive hazard in Yellowstone is earthquakes," says the Utah researcher. "They are the killer events." For the record, the probability of a quake magnitude-7 or greater is 0.125%, vs 0.00014% for a massive eruption. (Click to read about another newly discovered hot zone, this one much further afield.)