In Short About Geysers

Geyser: definition. A geyser is a hot spring that periodically erupts, throwing water into the air accompanied by steam. The word geyser comes from Geysir, the name of an erupting spring at Haukadalur, Iceland; that name, in turn, comes from the Icelandic verb geysa, "to gush" or “to spout”, the verb itself from Old Norse.
How it works. Generally all geyser field sites are located near active volcanic areas, and the geyser effect is due to the proximity of magma. Surface water works its way down to an average depth of around 2,000 metres where it contacts hot rocks. The resultant boiling of the pressurized water results in the geyser effect of hot water and steam spraying out of the geyser's surface vent or cone geyser. The formation of geysers specifically requires the combination of three geologic conditions that are usually found in volcanic areas.
Intense heat. The heat needed for geyser formation comes from magma that needs to be near the surface of the earth, in the outermost layer. The fact that geysers need heat much higher than normally found near the earth's surface is the reason they are associated with volcanoes or volcanic areas. The pressures encountered at the areas where the water is heated makes the boiling point of the water much higher than at normal atmospheric pressures.
Water. The water that is ejected from a geyser must travel underground through deep, pressurized furrows in the earth's crust.
A plumbing system. This includes a reservoir to hold the water while it is being heated. The plumbing system is made up of a system of fractures, furrows, rifts, porous spaces and sometimes trenches. Constrictions in the system are essential to the building up of pressure before an eruption.
The stages of spout of eruption.
1. Steam rises from heated water
2. Pulses of water swell upward
3. Surface is broken
4. Ejected water spouts upward and falls back
The eruption will continue until either the water is used up or the temperature drops