Great Fountain Geyser

The Great Fountain Geyser is a fountain-type geyser located in the Firehole Lake area of Lower Geyser Basin of Yellowstone National Park, Wyoming. It is the only Lower Geyser Basin feature that the park makes predictions for.
The geyser erupts every 9 to 15 hours. Great Fountain's maximum height ranges from about 75 feet to over 220 feet . Its duration is usually about one hour but durations of over two hours have been seen. The duration of an eruption affects the interval that will elapse before the next eruption, so that if the duration of an eruption is recorded, the time of the following eruption can be predicted to a precision of about two hours. The prediction can be refined, to plus or minus 15 minutes or so, through observation of overflow from the crater during the period between eruptions. While this pattern of behavior is observed most of the time, there are occasional episodes of so-called "wild-phase" activity during which the eruptions are of greatly extended duration and intervals between eruptions may be as long as three days. The geyser is then unpredictable until wild-phase activity ceases and more normal eruptions resume.

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