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West Thumb
Geyser Basin

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Black Pool

The dark water of Black Pool when it really was black..

Black Pool as it appears in 2004Not long ago, Black Pool really was black. Lower water temperature allowed thick mats of dark green and brown thermophiles (heat-loving microorganisms) to grow in the pool, causing it to appear black. The water temperature rose during the summer of 1991, killing these organisms. Black Pool also erupted that summer and several times the following winter. Like Abyss, Black Pool is now one of Yellowstone's most beautiful pools.

West Thumb Geyser Basin Tour

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Last Updated: Wednesday, 22-Dec-2004 10:11:42 Eastern Standard Time
http://www.nps.gov /archive/yell/tours/westthumb/blackpool.htm