Is the Yellowstone Caldera active right now?
— Eileen Meyering, Oak Lawn
The Yellowstone Caldera (located primarily in northwest Wyoming) is a massive depression in the Earth’s surface, 34 by 45 miles across, formed when the huge magma chamber beneath the Yellowstone volcano emptied during its last major eruption about 640,000 years ago and the surface collapsed into the evacuated chamber.
Geysers and other thermal features of Yellowstone National Park offer proof that the volcano (actually, it’s a supervolcano because of the amount of material ejected) is indeed still active. It is impossible to know when Yellowstone’s next major eruption will occur, but the volcano is closely monitored. Minor earthquakes occur in the Yellowstone area 50 or more times per week, but a major eruption is not expected in the foreseeable future.