A little bit about geysers

A little bit about geysers:

A geyser is a hot spring that erupts intermittently in a column of steam and hot water. Some geysers erupt at regular intervals, but the majority erupt irregularly, the intervals ranging from a matter of minutes to years. The length of time of the eruption varies with the geyser, from seconds to hours. The height of the column ranges from about 1 m to about 100 m, and the amount of water ejected in a single eruption varies from a few liters to hundreds of thousands of liters.

A geyser erupts when the base of a column of water resting in the earth is vaporized by hot volcanic rock

The force with which the water column is expelled depends on its depth. The weight of the water column increases with its depth. The weight, in turn, increases the pressure exerted on the base of the column, thereby increasing the boiling point of the water there. When the water finally boils, it expands, driving some water out into the air. With the weight of the column reduced, the pressure correspondingly drops, and the boiling point of the water remaining in the column falls below its actual temperature. Thereupon, the entire column instantly vaporizes, causing the geyser to erupt. Eruption intervals depend on such variables as the supply of heat, the amount and rate of inflow of subsurface water, and the nature of the geyser tube and its underground connections.

Almost all known geysers are located in three countries of the world—New Zealand, Iceland, and the United States.

The vast majority of water in a geyser system is meteoric. Often geyser fields are found on the banks of rivers, which is usually a significant component of a geyser's water source. Rainfall and circulating groundwater also play a significant role. Analysis of the tridium content of geyser water indicates that groundwater expelled from a geyser system is on the order of 500 years old; this is obviously the amount of time it takes for groundwater to circulate to depth, become heated, and move back up to shallower levels.

Heat source:

The eruption of water or gas from a geyser is due in significant part to an interaction between hot and cool fluid sources. This necessitates a constant, steady supply of heat. Every geyser field in the world is located near some sort of volcanic, shallowly-lying heat source. Frequently, geyser fields are located near lithospheric plate boundaries, which are typically characterized by active volcanism. Other geyser fields, such as Yellowstone, are assumed to lie above hot spots or plumes. The overwhelming majority of all geyser fields lie above large bodies of rhyolite, although some fields are associated with more mafic volcanic rocks such as andesite or basalt.

Pohutu Geyser in Rotorua:
The Pohutu Geyser is the most spectacular geyser at Rotorua’s Whakarewarewa Thermal Village. The geyser usually erupts every hour and shoots hot water around 20 metres high. Pohutu is Maori for ‘big splash’ or ‘explosion’.	All of the geysers are mostly in the Roturua region, on the north est of new zealand.