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OLD FAITHFUL GEYSER

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Old Faithful, named by members of the 1870 Washburn Expedition, was once called “Eternity’s Timepiece” because of the regularity of its eruptions. However, despite the myth, this geyser has never erupted at exact hourly intervals, nor is it the largest or most regular geyser in Yellowstone. However, it does erupt more frequently than any other of the large geysers.

An Old Faithful eruption lasts 1.5 to 5 minutes and reaches a height of 90-184 feet (27-55 m). The period of time between Old Faithful’s eruptions ranges from 35 to 120 minutes, though the average is 92 minutes. About 90 percent of eruption predictions are accurate within a window of plus or minus 10 minutes.

Old Faithful ’s interval has increased over time. Some scientists think parking lots and other development have affected the area’s groundwater and led to this increase. Others think the increase may be due to changes within the geyser’s underground channels. Following the 1959 Hebgen Lake earthquake, the period of time between Old Faithful’s eruptions became longer. This interval has increased even more following other earthquakes.

Old Faithful “plays” prior to an eruption with splashes of boiling water that may reach as high as 20 feet (6 m). A full eruption usually begins from this play. Once the eruption starts, the splashes grow larger and larger until the eruption reaches its full height. The height of the water begins waning shortly, but the eruption may continue in small splashes for as long as five minutes.

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