Excelsior Geyser, a dormant fountain-type geyser in Yellowstone’s Midway Geyser Basin, is now usually seen as a vast, intensely hot pool that sends thousands of gallons of near-boiling water into the Firehole River each minute. Named in 1881 by superintendent P. W. Norris, it was first reported in 1869 as a crater showing evidence of earlier eruptions. Its observed eruptions began in 1881 and were among Yellowstone’s most violent, sometimes hurling rocks and sending water to great heights. Later active phases in 1888, 1890, 1985, and 2004–2006 were shorter and generally smaller. Its powerful, changeable behavior has made it a classic example of Yellowstone’s unstable geothermal system.

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Mammoth, Wyoming · USA