Cool Facts about Hot Springs and Geysers

Hot springs, geysers, mudpots, and fumaroles (or steam vents) can together be called thermal features.

The largest hot spring in the park, and one of the largest in the world, is Grand Prismatic Spring. In this picture, the spring itself is the turquoise wedge with colored steam rising from it. (See page 61 of Yellowstone Treasures for an even more colorful photo.) Precipitation from the run-off water creates many small terraces and multi-colored microbial mats. The water temperature as it leaves the spring has got to be quite near the boiling point. The orange microbial mats on the terraces thrive at about 70°C (158°F).

Q: What exactly is a geyser?
A: A geyser is a hot spring that throws forth jets of water and steam intermittently. See the Upper Geyser Basin excerpt for some telltale signs of active geysers. For a full explanation of how a geyser works, see pages 88 to 90 in Yellowstone Treasures.

Q: How hot are Yellowstone’s hot springs?
A: Too hot for anybody to touch! Seriously, Yellowstone’s hot springs cover a large range, from lukewarm up to superheated. Two examples of cool or lukewarm hot springs are Liberty Pool in Upper Geyser Basin, where the water is sometimes cool enough for frogs to live in, and the vandalized pool along the boardwalk in West Thumb Geyser Basin. An example of a superheated pool is Surprise Pool on Firehole Lake Drive, where the temperature is above the boiling point.

Geysers are among the hottest of the hot springs; in fact, some springs will be calm pools for years or decades and then their temperature will rise and they become geysers, at least for a while. Typical examples of this are Silex Pool (left) in the Fountain Paint Pot area and Black Pool at West Thumb Geyser Basin.

Q: How many thermal features are there in Yellowstone?
A: A complete inventory by the Research Coordination Network of Montana State University found at least 10,000 features of all types and sizes in the park’s many hydrothermal areas, a great many of which are far from the roads. Most experts believe that 400 to 500 of these are geysers.

Q: Where’s the biggest geyser in the world?
A: Steamboat Geyser. Located in Yellowstone’s Norris Geyser Basin, its eruptions can go as high as 380 feet (116 meters). Though Steamboat is now the world’s highest geyser, it doesn’t show off very often. The latest eruption was September 3, 2014, in the middle of the night. What a wonderful surprise when it erupted on July 31, 2013 after eight years! Before that, Steamboat erupted twice in 2002 (April 26 and September 13); in 2003, three times (March 26, April 27, and October 22); and once in 2005, on May 23. [Editor’s note: After almost five dormant years, Steamboat came back to life on March 15, 2018, and lucky visitors occasionally witness it. There have been five eruptions so far in 2023, as one can see on GOSA’s Geyser Times app.] But Waimangu Geyser in New Zealand, before it was destroyed by landslides in 1904, erupted to the unprecedented height of over 1000 feet (300 meters). Another big geyser that is justifiably famous is Geysir in Iceland, the namesake of all the geysers in the world.

CREDITS: The photo of Silex Spring is by Bruno Giletti; Surprise Pool photo by Leslie Kilduff.

IN THE GUIDEBOOK: Grand Prismatic Spring is the largest and one of the most beautiful pools in Yellowstone. To learn what makes its phenomenal colors, see pages 61–62 of Yellowstone Treasures.

Many bicyclists you may see in the geyser basins are members of the Geyser Observation and Study Association (see page 361 of Yellowstone Treasures, sixth edition).

Revised September 8, 2023. Copyright Janet Chapple. All Rights Reserved.