A geyser is result of underground water under the combined condition of high temperature and increased pressure beneath the surface of the earth. Since temperature rises approximately one degree Fahrenheit for every sixty feet under the earth’s surface, and pressure increases with depth, water that seeps down in cracks and fissures until it reaches very hot rocks in the earth’s interior becomes heated to a temperature in excess of 290 degrees Fahrenheit. Because of the greater pressure, it shoots of the surface in the form of steam and hot water. The result is a geyser.
In order to function, then, a geyser must have a source of heat, a reservoir where water can be stored until the temperature rises to an unstable point, an opening through which the hot water and steam can escape, and underground channels for resupplying water after an eruption.
Favorable conditions for geyser exist in region of geologically recent volcanic activity, especially in areas of more than average precipitation.
For the most part, geyser are located in three regions of the world : New Zealand, Iceland, and the Yellowstone National Park area of the United states. The most famous geyser in the world is Old Faithful in Yellowstone Park. Old Faithful erupts almost every hour, rising to a height of 125 to 170 feet and expelling more than ten thousand gallons during each eruption.