Sapphire Pool, Yellowstone National Park Postcard

"Sapphire Pool, Biscuit Basin, Upper Geyser Basin, Yellowstone National Park, Wyoming" by Catherine Sherman. Sapphire Pool is a beautiful blue jewel in Biscuit Basin in the Upper Geyser Basin of Yellowstone National Park. Biscuit Basin is named for the unusual biscuit-like deposits that used to surround Sapphire Pool. Following the 1959 Hebgen Lake earthquake, Sapphire Pool erupted, and the “biscuits” were blown away. Sapphire Pool last erupted in 1991. Sapphire remains one of the most beautiful blue pools in the park. According to the National Park Service, Sapphire Pool is a "large clear blue pool with a solid sinter rim level with the ground surface. The edges of the pool have shallow sinter shelves that contain yellow and orange thermophiles. Sapphire Pool use to be an active geysering pool prior to the 1959 earthquake. After the earthquake, the gorgeous pool was filled with muddied water and began to have larger eruptions. It wasn't until 1971 that the pool's color cleared and activity stopped. The minor geysering prior to 1959 has not returned, and the pool has not had an eruption since 1991, indicating a change to the plumbing system as a result of the 1959 earthquake. Sapphire Pool has an average temperate of 159.8°F (71°C), an average pH of 7.9, and an average conductivity of 2239 uS/cm." The majority of world’s active geysers are in the Upper Geyser Basin, including Old Faithful. Only four other places in the world have large concentrations of hydrothermal features: Russia (Kamchatka), Chile, New Zealand, and Iceland.