Nugget C: Cool Facts about Hot Springs and Geysers

Hot springs, geysers, 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 (left). In the picture, the spring itself is the turquoise wedge with colored steam rising from it, and there are small terraces in the very wide channel where the water runs off. 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).

A: Nobody knows. Actually, a thorough inventory is under way. Until that is completed, the best guess seems to be that the park has about 10,000 thermal features. Most geyser experts put the number of geysers in Yellowstone at 400 to 500. According to T. Scott Bryan's The Geysers of Yellowstone, "There are more geysers [in Upper Geyser Basin alone] than in any other area of either Yellowstone or the world."

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 82 to 84 in Yellowstone Treasures.

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 (shown here) 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.

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: in 2003, Steamboat erupted three times, on March 26, April 27, and October 22. 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 photos of Grand Prismatic Spring and Silex Spring are by Bruno Giletti; Surprise Pool photo by Leslie Kilduff.

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 Grand Prismatic Spring is the largest and one of the most beautiful pools in Yellowstone. To learn what makes its phenomenal colors, see pages 59–60.

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