English: Abyss Pool, northern Lower Group, West Thumb Geyser Basin, Yellowstone Hotspot, northwestern Wyoming, USA.

Abyss Pool is a hot, moderately deep, intensely-colored pool. It has been blue-colored in the past. A combination of bubble-brained vandals throwing objects into the pool and almost basin-wide cooling has lowered the temperature of this feature, resulting in yellowish extremophile bacterial mats lining most of the pool’s walls. The “blue” water plus the yellowish-colored bacterial mats results in a deep green color. Abyss Pool has had rare geyser eruptions, including in 1904 and 1905, when water columns reached up to 100 feet high. Surrounding geyserite was sometimes ripped from the upper walls of Abyss Pool during these powerful eruptions, resulting angular, up-to-boulder sized geyserite clast deposition. 1987 had a single geyser eruption from Abyss Pool. In 1991 and 1992, it was quite active, with forceful eruptions reaching up to 100 feet high.

July 2012, looking ~NW.