What is geyser and how is it formed?(odd no.)

What is Geyser ?
A geyser is a hot spring characterized by intermittent discharge of water ejected turbulently and accompanied by a vapour phase(steam). The name geyser comes from Geysir, the name of an erupting spring at Haukadalur,Iceland; that name, in turn, comes from the Icelandic verb gjosa,"to gush".

The formation of geyser is due to particular hydrogeological conditions, which exist in only a few places in the Earth, and so they are a fairly rare phenomenon. Generally all geyser field sites are located near active volcanic areas, and the geyser effect is due to the proximity of magma.Generally, surface water works its way down to an average depth of around 2,000 meters (6,600 ft) where it meets up with 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.
About a thousand known geysers exist worldwide, roughtly half of which are in Yellowstone National Park, United States. A geyser's eruptive activity may change or cease due to ongoing mineral depostion within the geyser plumbing, exchange of functions with nearby hot springs, earthquake influences, and human intervention.

Erupting fountains of liquefied nitrogen have been observed on Neptune's moon Triton, as have possible signs of carbon dioxide eruptions from Mar's south polar ice cap. These phenomena are also often referred to as geysers. Instead of being driven by geothermal energy, they seem to rely on solar heating aided by a kind of solidstate greenhouse effect. On Triton, the nitrogen may erupt to heights of 8 kilometres (5 mil)

How is it formed ?
Natural geysers are hot springs that intermittently throw up a jet of hot water, stream, etc. The earth's crust has cracks and vents. Waters occupies these and gets heated due to geothermal energy.

Due to heating, water turns into steam and pressure increases. In this case, if the opening of the vent/crack is narrow, it erupts like a volcano, otherwise it flows like a stream. The 'Old Faithful' geyser at Yellowstone National Park in the US is one of the most famous geyser.

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Tricia