Yellowstone is a thermal "hot
spot" in the earth. In fact, most of the western part of the
Park sits in an ancient caldera of a volcano. About 600,000 years
ago, the volcano erupted
creating the landscape that is Yellowstone today. Yellowstone is
filled with geysers,
relief valves, as it were, from the earth's inner heat. Old Faithful
goes off more or less predictably
every 90 minutes. It is one of the most popular sights of the Park.
Indeed, Yellowstone was
America's first National Park and was intended to preserve these
amazing - and fragile -
natural features. See
in the area around Old Faithful.