A geyser is a rare kind of hot spring found on volcanic terrain. Under pressure, a geyser shoots boiling hot water and a lot of steam from underground into the air. A geyser’s blast is like a vent. A geyser can be thought of as the Earth releasing pressure.
For a geyser to occur, there must be a tube-like hole in the earth and hot water below. A geyser blast happens when water caught in a chamber below the Earth’s surface–as deep as the Earth’s hot crust–heats to a boil. Steam and hot water rise, faster and faster, until they reach the tube-like hole and burst out.
The tube of a geyser is lined with a milky-colored mineral found in volcanic regions called geyserite. The geyserite that flows out with the boiling hot water cools as it laps over the ridge of the hole, creating a smooth rim or terrace around the spring.
Geyser blasts persist until the water below the Earth’s surface drops below boiling and pressure returns to zero. Then the cycle begins again.
Some geysers blast multiple times a day. Others blast sporadically, sometimes with years between each blast.
The tallest geyser in the world is Steamboat Geyser at Yellowstone National Park in the United States. Steamboat Geyser has two vents that are 20 feet (6.1 m) apart. Each can shoot water more than 400 feet (122 m) into the air, but the blasts have not always been dependable. Since 2018, Steamboat Geyser has erupted an average of 30 to 45 times a year. Before that though, it would sometimes be years between eruptions.
Another geyser located in Yellowstone Park is Old Faithful. It is perhaps the most famous in the world. As its name suggests, Old Faithful is known for its frequent and dependable blasts. Old Faithful erupts on average every 60 to 90 minutes. The actual time between blasts varies from as little as 20 minutes to as much as two hours. Old Faithful blasts a few thousand gallons of boiling hot water 100-200 feet (30-60 m) into the air each time.
There are 1,000 geysers in the world. Only a handful of countries have active geysers: The United States, Russia, Chile, New Zealand, and Iceland. The word “geyser” is named after a large Icelandic geyser, Geysir.