A geyser is a rare kind of hot spring that is under pressure and erupts, sending jets of water and steam into the air.

Geysers are made from a tube-like hole in the Earth's surface that runs deep into the crust. The tube is filled with water. Near the bottom of the tube is molten rock called magma, which heats the water in the tube.

Water in the lower part of the tube, close to the magma, becomes superhot. Gradually, it begins to boil. Some of the water is forced upward. The boiling water begins to steam, or turn to gas. The steam jets toward the surface. Its powerful jet of steam ejects the column of water above it. The water rushes through the tube and into the air.

The eruption will continue until all the water is forced out of the tube, or until the temperature inside the geyser drops below boiling (100 degrees Celsius, or 212 degrees Fahrenheit, at sea level).

After the eruption, water slowly seeps back into the tube. The process begins again. In some small geysers, the eruption process can take just a few minutes. In larger geysers, it can take days. The most famous geyser in the United States, Yellowstone National Park's Old Faithful, erupts about every 50-100 minutes.

In the 19th century, Old Faithful was used to wash clothes.

Geyser Central
Yellowstone National Park in Wyoming has more than 300 geysersabout two-thirds of the number of geysers in the entire world. Other geyser hot spots are Siberia, Chile, Iceland and New Zealand.


rocky outermost layer of Earth or other planet.


to get rid of or throw out.


to explode or suddenly eject material.


release of material from an opening in the Earth's crust.


natural hot spring that sometimes erupts with water or steam.

hot spring

small flow of water flowing naturally from an underground water source heated by hot or molten rock.


molten, or partially melted, rock beneath the Earth's surface.


solid material turned to liquid by heat.

Old Faithful

geyser in Yellowstone National Park in the U.S. state of Wyoming.


to slowly flow through a border.


water vapor.


degree of hotness or coldness measured by a thermometer with a numerical scale.