Solitary Geyser, Fountain geyser in Upper Geyser Basin, Yellowstone National Park, United States

Solitary Geyser is a fountain-type geyser above the Upper Geyser Basin in Yellowstone National Park. Its eruptions last about a minute and are spaced four to eight minutes apart, most rising less than 6 feet (1.8 m). The pool shows clear blue water over a base tinted orange.

Solitary Geyser began as Solitary Spring, a hot spring that did not erupt. In 1914 water was diverted from it to heat a swimming pool, lowering the water level so that boiling occurred at depth and the spring began erupting regularly. The pool was removed and the diversion stopped in 1951, and the water returned to its earlier level, yet eruptions continue.

The name Solitary comes from its position apart from the main Upper Geyser Basin clusters, reached by the Observation Point loop trail behind Old Faithful. Its eruptions, about a minute long and four to eight minutes apart, usually rise less than 6 feet (1.8 m), so visitors often watch several cycles from the trailside.

You can reach this geyser via the Observation Point Loop Trail behind Old Faithful, a walk with clear markings and gentle terrain. Eruptions happen every four to eight minutes, so you will likely see one if you wait a few minutes at the site.

Solitary Geyser was a non-erupting hot spring called Solitary Spring until 1914, when water was diverted to heat a swimming pool; the lowered water level let boiling begin at depth and eruptions started. The pool was removed and the diversion stopped in 1951, yet the geyser kept erupting.