Geyser (noun, “GUY-sir”)
Geysers are underground springs. On Earth, they are found near active volcanoes. The springs have narrow vents that open at the surface. Heat from below warms the underground water. At the surface, the water isn’t so hot. But it presses down on the hotter water below. That means the lower water can’t boil. It eventually becomes superheated — hotter than 100° Celsius (212° Fahrenheit). That ultrahot water rises up through the cooler water on top of it. As it rises, the pressure on the water lessens, so it starts to boil. That releases steam and hot water that spews through the vents at the surface. The result is a geyser that spurts up into the sky — sometimes for more than 42 meters (140 feet). That’s the maximum height of Old Faithful in Yellowstone National Park in the United States.
Geysers are rare. There are less than a thousand across the whole planet. And because geysers are only associated with active volcanoes, they are not distributed evenly. New Zealand, Russia and Chile have geysers, though. And Iceland is also known for its geysers. Iceland even has a geyser named the Great Geysir— which lends its name to all the other geysers around the world.
About half the world’s geysers can be found in Yellowstone National Park. There’s no flowing magma there, of course. But Yellowstone is the site of an active volcano. It just hasn’t erupted in hundreds of thousands of years.
In a sentence
The icy moon Enceladus also boasts warm geysers — warmth that might help support life.