A large clear blue pool, Sapphire Pool has 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.

Hot Springs

Hot springs are the most common hydrothermal features in Yellowstone. Their plumbing has no constrictions.

Superheated water cools as it reaches the surface, sinks, and is replaced by hotter water from below.

This circulation prevents water from reaching the temperature needed to set off an eruption.

Use Caution in Hydrothermal Areas

• Stay on boardwalks and designated trails.
• Hydrothermal water can severely burn you.
• Never run, push, or shove.
• Supervise children at all times.
• Do not scratch hydrothermal mats.

You are responsible for your safety.

Think safety, act safely. Yellowstone is a dangerous place.