Perhaps the most famous geyser in the World, Old Faithful Geyser has become one of the most recognizable features of Yellowstone National Park. It was named for its consistent performance by members of the Washburn Expedition in 1870. Although its average interval has lengthened through the years (due to earthquakes and vandalism), Old Faithful is still as spectacular and predictable as it was a century ago.

Old Faithful erupts more frequently than any of the other big geysers, although it is not the largest or most regular geyser in the park. It is an example of a Cone Geyser, which erupts in a concentrated jet of water usually from a cone or nozzle-like formation.

The average interval between eruptions is about 90 minutes, plus or minus 10 minutes. Intervals vary from 65 - 92 minutes. An eruption lasts 1.5 to 5 minutes, expels 3,700 - 8,400 gallons (14,000 - 32,000 liters) of boiling water, and reaches heights of 106 - 184 feet (30 - 55m). At the vent, water is 204 degrees fahrenheit (95.6 degrees Celsius. However, Water underneath the geyser is well above boiling temperature because of the pressure from overlaying rock and water.

Mathematicians, statisticians, and dedicated observers have analzyed Old Faithful Geyser for years. A relationship exists between the duration of Old Faithful's eruption and the lenght of the folling interval.

During a short eruption, less water and heat are discharged; thus, they rebuild again in a short time. Longer eruptions mean more water and heat are discharged and they require more time to rebuild.

Check at the Old Faithful Visitor Education Center for predictions of Old Faithful and five other geysers in the area.

Information Provided by the National Park Service.