[Opal Pool] can eject water up to 70 feet in the air!
This lesser-known hot spring in the Midway Geyser Basin is called Opal Pool. This hot spring sits at roughly 132 degrees Fahrenheit. It is classified as a fountain geyser. Although its eruptions are rare and random Opal Pool is still considered active. Typically, the eruptions are one big blast. There is often little warning, but perhaps some swirling water activating in advance of the eruption. Sometimes there are smaller eruptions that will follow, but typically not for very long.
The first recorded eruption of Opal Pool was in 1947. The most recent eruption was in October of 2024. Opal Pool is considered the largest active geyser in the Midway Geyser Basin because it can eject water up to 70 feet in the air! Opal Pool acts mostly like a hot spring, quiet and still most of the time, as you see it in this photograph. However, be aware this is actually a power geyser.
Adjacent to Opal Pool are other geysers and the Firehole River. In this area, Grand Prismatic hot spring steals the show. Grand Prismatic is the largest hot spring in the United States and the third largest hot spring in the world! Frying Pan Lake in New Zealand and Boiling Lake in Dominica are the only larger hot springs in the world. To give you an idea of its size, Grand Prismatic is ~160 feet deep and ~370 feet across. It discharges ~560 gallons of water per minute!
Why is it so colorful? The bright diverse color spectrum is due to microbial mats of thermophilic bacteria. The center of the spring ejects mineral rich water. Towards the edges of the hot spring mats of bacteria form. The colors of these microbial mats depends on the ratio of chlorophyll to carotenoids and on the water temperature of the runoff area. If you visit Grand Prismatic in the winter months, the mats are typically dark green. If you visit during the summer months, the mats are usually orangish-red. Because of this fluctuation, this is a place I would love to return to at different times of the year. I took this photograph in late April. Shortly before taking this photograph, we saw a bear off in the distance. The bear was near the edge of the geyser activity, where the water meets the tree line. This was a good reminder of how this part of the country is the wild wild west.
Grand Prismatic is the largest hot spring in the United States
Did you know?
- In 2005, Opal Pool completely drained its water. A few years later in 2008, Opal Pool filled up again. This time the water was vivid green in color. This was due to different minerals and algae that grow in and around the spring.
- Yellowstone National Park is ~2,219,791 acres!
- Yellowstone National Park had 3,744,353 visitors in 2024!
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