Old Faithful, Yellowstone National ParkMap of Old Faithful
If Yellowstone is the iconic national park, then Old Faithful is the icon's icon. Long a symbol of the park's majesty -- not to mention its powerful hydrothermal waterworks -- the great geyser has been the subject of numerous photographs, essays, cartoons, films and paintings. Less auspiciously, early visitors sometimes used it as a laundry.
Henry J. Winser wrote disparagingly of the practice in his 1883 tourist manual for Yellowstone: "Garments placed in the crater during quiescence are ejected thoroughly washed when the eruption takes place." Like other geysers, Old Faithful is a hot spring with constrictions near its surface that prevent water from flowing freely. When it erupts, Old Faithful 3,700 to 8,400 gallons of boiling water 105 to 185 feet in the air for a period of 1.5 to 5 minutes. The regularity of the geyser's eruptions, which today occur every 90 minutes on average, earned it the name "Old Faithful." Earthquakes in the Yellowstone area have affected underground water levels over the years, increasing the interval of eruptions, but making them more mathematically predictable. Research suggests that the cone geyser owes its regularity to the fact that it isn't connected to other thermals in the Upper Geyser Basin.