Yellowstone National Park, part of which is in Wyoming, is home to more geysers than any other place in the world. The most famous geyser is Old Faithful, which got its name because its eruptions can be so reliably predicted. A geyser is a spring that sprays out blasts of heated water and steam. The park has plenty of hot springs. In a geyser, steam and water build pressure beneath a narrow passageway in the ground. Steam forces the water up, and sudden changes in underground water temperature create violent explosions of water and steam on the surface. Some geysers erupt in bursts, some at angles, and some from cone-shaped rock formations, such as Castle Geyser, pictured here. Yellowstone's hot springs also form steam vents, mudpots, and vividly colored pools. The park's geysers, like Steamboat and Old Faithful, however, are far more famous.

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