A geyser is the result of underground water under the combined conditions of high temperatures and increased pressure beneath the surface of the earth. Since temperature rises approximately 1 F for every sixty feet under the earth's surface, and pressure increases with depth, the water that seeps down in crack and fissures until it reaches very hot rock in the earth interior becomes heated to temperature in excess of 290 F. Because of the greater pressure, the water shoots out 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, 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 some regions of the world including New Zealand, Iceland, and the Yellowstone National Park area of the United States. The most famous geyser in the world is Old Faithfull in Yellow Park. Old Faithfull erupts almost every hour, rising to a height of 125 to 170 feet and expelling more than ten thousand gallons during each eruption. Reservoir The place where the water can be stored until the temperature rises to an unstable point is called a. opening b. geyser c. channels d. eruption e. reservoir