Some places saw the ground rise by ten inches, experts report. Yellowstone National Park's supervolcano just took a deep "breath," causing miles of ground to rise dramatically, scientists report. The simmering volcano has produced major eruptions—each a thousand times more powerful than Mount St. Helens's 1980 eruption—three times in the past 2.1 million years. Yellowstone's caldera, which covers a 25- by 37-mile (40- by 60-kilometer) swath of Wyoming, is an ancient crater formed after the last big blast, some 640,000 years ago. (See "When Yellowstone Explodes" in National Geographic magazine.) Since then, about 30 smaller eruptions—including one as recent as...