Geyser: Definition & Explanation

Instructor: Maria Howard

Maria is a teacher and a learning specialist and has master's degrees in literature and education.

Learn about how geysers like Old Faithful create spectacular explosions of water and steam. Explore geysers from Yellowstone National Park to Iceland to the ocean floor deep under the Pacific Ocean.

What Is a Geyser?

Movie directors really love using the shrill of a boiling tea kettle to create tension in a scene. Just imagine it: the heroine puts the water on the stove and then hears a noise in the backyard. She thinks she sees someone, but it's just the neighbors' cat. Then the tea kettle shrieks in the background, and we all jump in our seats.

A whistling tea kettle is a perfect metaphor for tension because the pressure from the building steam is what makes it whistle. The water reaches such a high temperature that the steam has nowhere to go but out.

A tea kettle is often used to create tension in a movie, but it is also a good model for a geyser.
Photo of a tea kettle

A whistling tea kettle is also a perfect model to explain a geyser, a hot spring of water that erupts steam and water into the air. Water from rain and snow is absorbed into the ground, and when enough of this groundwater collects, it bubbles up to the surface through vents in the Earth's crust. These pools of water are called springs.

Only a few springs are located near hot spots, areas where breaks in the Earth's crust allow hot magma to rise close to the surface. Some of the 40-50 hot spots in the world produce volcanoes, like those in Hawaii and Iceland. Other hot spots heat nearby groundwater and create hot springs, reaching temperatures hot enough to boil the groundwater (100 degrees Celsius or 212 degrees Fahrenheit) and send it up through narrow vents.

A geyser is a rare type of hot spring that, like a tea kettle, erupts from the pressure of building heat and steam. Think of the rising magma as the heat from the stove, the spring as the water put in the kettle, and the resulting geyser as the escaping steam and water from the kettle's spout. One thing to note, though, is that unlike small household kettles, geysers blast hot water along with their steam, making them spectacular sights to behold.

Old Faithful and Yellowstone National Park

Yellowstone National Park in the U.S. state of Wyoming is home to two-thirds of the world's geysers. The most famous of Yellowstone's over 300 geysers is Old Faithful, named because of the reliability of its eruptions. Each eruption spews between 14,000 and 32,000 liters (3,700 and 8,400 gallons) of water. If you figure that an average American family of four uses about 8,000 gallons of water a month, that is a lot of a water expelled in a single blast.

Old Faithful in Yellowstone National Park, Wyoming, erupts every 50-100 minutes.
Photo of Old Faithful

Yellowstone's impressive concentration of hydrothermal activity includes the Great Fountain Geyser, which spews water up to 67 meters (220 feet) into the air. Another geyser, the Castle Geyser, is named for how silicone dioxide and other minerals have mixed with groundwater and have, over time, built a great mound of sediment around the geyser.

Castle Geyser, Yellowstone National Park by Ansel Adams, 1942.
Photo of Castle Geyser

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