Black Pool
Black Pool is a hot spring in the West Thumb Geyser Basin of Yellowstone National Park in the United States.When combined with the blue of the water, the pool appeared to be an exceptionally dark green to almost black, hence the name.[3] An exchange of function took place in 1991, shifting thermal energy to Black Pool and nearby Abyss Pool, causing them to heat up.The pool also had frequent boiling eruptions on August 15, 1991, doming the water to 3 feet and causing heavy runoff.Black Pool remains extremely hot, and is now one of Yellowstone's most beautiful and intensely blue pools.