Old Faithful and the supervolcano
The Old Faithful geyser is itself part of the Upper Geyser Basin at Yellowstone, a complex geothermal area that is itself a small portion of the Yellowstone Caldera, a massive supervolcano roughly 45 miles across. Volcanic activity superheats underground water that, in turn, results in periodic geysers. 20041011 Lawrence I. Charters