File:Great Fountain Geyser (12 July 2014) 2.jpg

English: Great Fountain Geyser is a major geyser in Yellowstone's Lower Geyser Basin. Eruptions occur about twice a day and are 1 to 2 hours in duration. The geyser consists of a large, subcircular, concentrically-terraced geyserite platform that is 55 to 60 meters in diameter. The slightly off-center, irregularly-shaped vent is 5.5 to 6.5 meters across. Runoff channels radiate outward to the west, northwest, north, and northeast. Much of the eruption runoff ends up percolating downward in the surrounding fields. Some runoff ends up draining into White Creek and the Tangled Creek valley.

About 70 to 100 minutes before an eruption, overflow commences from the vent. As the eruption nears, moderately energetic, marginal boiling occurs in the vent. Eruption initiations are called "meter boils", involving a decent-sized upward-doming of water. Tall eruptive bursting can occur immediately or will be delayed by many minutes (this is called a "pause").

Great Fountain Geyser erupts in "series", during which there is a succession of small to very tall bursts for about ten minutes. The first series is typically the tallest and showiest. Pauses between series are about five minutes long. Eruption heights are generally lower in successive series. The first few bursts of any individual series are often the tallest and most energetic.