A geyser (, ) is a spring with an intermittent water discharge ejected turbulently and accompanied by steam. The formation of geysers is fairly rare and is caused by particular hydrogeological conditions that exist only in a few places on Earth.
Generally, 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 where it contacts hot rocks. The pressurized water boils, and this causes the geyser effect of hot water and steam spraying out of the geyser's surface vent.
A geyser's eruptive activity may change or cease due to ongoing deposition of minerals within their plumbing, exchange of functions with nearby hot springs, earthquake influences, and human intervention. Like many other natural phenomena, geysers are not unique to Earth. Jet-like eruptions, often called cryogeysers, have been observed on several of the moons of the outer Solar System. Due to the low ambient pressures, these eruptions consist of vapour without liquid; they are made more easily visible by particles of dust and ice carried aloft by the gas. Water vapour jets have been observed near the south pole of Saturn's moon Enceladus, while nitrogen eruptions have been observed on Neptune's moon Triton. There are also signs of carbon dioxide eruptions from the southern polar ice cap of Mars.
In the case of Enceladus, the plumes are believed to be driven by internal energy. In the cases of the venting on Mars and Triton, the activity may result from solar heating via a solid-state greenhouse effect. In all three cases, there is no evidence of the subsurface hydrological system which differentiates terrestrial geysers from other sorts of venting, such as fumaroles.
Etymology
The term 'geyser' in English dates back to the late 18th century and comes from Geysir (), the name of a specific geyser in Iceland, meaning "Gusher" in Icelandic.
Geology Form and function
Geysers are nonpermanent geological features. Geysers are generally associated with areas of recent magmatism. As the water boils, the resulting pressure forces a superheated column of steam and water to the surface through the geyser's internal plumbing. The formation of geysers specifically requires the combination of three geologic conditions that are usually found in volcanic terrain: heat, water, and a subsurface hydraulic system with the right geometry.
The heat needed for geyser formation comes from magma that needs to be close to the surface of the Earth. For the heated water to form a geyser, a plumbing system (made of fractures, fissures, porous spaces, and sometimes cavities) is required. This includes a reservoir to hold the water while it is being heated.
Geysers tend to be coated with geyserite, or siliceous sinter. The water in geysers comes in contact with hot silica-containing rocks, such as rhyolite. The heated water dissolves the silica. As it gets closer to the surface, the water cools and the silica drops out of solution, leaving a deposit of amorphous opal. Gradually the opal anneals into quartz, forming geyserite. Geyserite often covers the microbial mats that grow in geysers. As the mats grow and the silica is deposited, the mats can form up to 50% of the volume of the geyserite.
Eruptions
Geyser activity, like all hot spring activity, is caused by surface water gradually seeping down through the ground until it meets geothermally heated rock. In non-eruptive hot springs, the heated water then rises back toward the surface by convection through porous and fractured rocks, while in geysers, the water instead is explosively forced upwards by the high steam pressure created when water boils below. Geysers also differ from non-eruptive hot springs in their subterranean structure: geysers have constrictions in their plumbing that create pressure build-up.
As the geyser fills, the water at the top of the column cools off, but because of the narrowness of the channel, convective cooling of the water in the reservoir is impossible. The cooler water above presses down on the hotter water beneath, not unlike the lid of a pressure cooker, allowing the water in the reservoir to become superheated, i.e. to remain liquid at temperatures well above the standard-pressure boiling point.
Ultimately, the temperatures near the bottom of the geyser rise to a point where boiling begins, forcing steam bubbles to rise to the top of the column. As they burst through the geyser's vent, some water overflows or splashes out, reducing the weight of the column and thus the pressure on the water below. With this release of pressure, the superheated water flashes into steam, boiling violently throughout the column. The resulting froth of expanding steam and hot water then sprays out of the geyser vent.
Eventually the water remaining in the geyser cools back to below the boiling point and the eruption ends; heated groundwater begins seeping back into the reservoir, and the whole cycle begins again. The duration of eruptions and the time between successive eruptions vary greatly from geyser to geyser; Strokkur in Iceland erupts for a few seconds every few minutes, while Grand Geyser in the United States erupts for up to 10 minutes every 8–12 hours.
General categorization
There are two types of geysers: fountain geysers which erupt from pools of water, typically in a series of intense, even violent, bursts; and cone geysers which erupt from cones or mounds of siliceous sinter (including geyserite), usually in steady jets that last anywhere from a few seconds to several minutes. Old Faithful, perhaps the best-known geyser at Yellowstone National Park, is an example of a cone geyser. Grand Geyser, the tallest predictable geyser on Earth (although Geysir in Iceland is taller, it is not predictable), also at Yellowstone National Park, is an example of a fountain geyser.
There are many volcanic areas in the world that have hot springs, mud pots and fumaroles, but very few have erupting geysers. The main reason for their rarity is that multiple intense transient forces must occur simultaneously for a geyser to exist. For example, even when other necessary conditions exist, if the rock structure is loose, eruptions will erode the channels and rapidly destroy any nascent geysers.
Geysers are fragile, and if conditions change, they may go dormant or extinct. Many have been destroyed simply by people throwing debris into them, while others have ceased to erupt due to dewatering by geothermal power plants. However, the Geysir in Iceland has had periods of activity and dormancy. During its long dormant periods, eruptions were sometimes artificially induced—often on special occasions—by the addition of surfactant soaps to the water.
Biology
Some geysers have specific colours because, despite the harsh conditions, life is often found in them (and also in other hot habitats) in the form of thermophilic prokaryotes. No known eukaryote can survive over .
In the 1960s, when the research of the biology of geysers first appeared, scientists were generally convinced that no life can survive above around —the upper limit for the survival of cyanobacteria, as the structure of key cellular proteins and deoxyribonucleic acid (DNA) would be destroyed. The optimal temperature for thermophilic bacteria was placed even lower, around .
However, the observations proved that they can exist at high temperatures and that some bacteria even prefer temperatures higher than the boiling point of water. Dozens of such bacteria are known. Thermophiles prefer temperatures from , while hyperthermophiles grow better at temperatures as high as . As they have heat-stable enzymes that retain their activity even at high temperatures, they have been used as a source of thermostable tools, which are important in medicine and biotechnology, for example in manufacturing antibiotics, plastics, detergents (by the use of heat-stable enzymes lipases, pullulanases and proteases), and fermentation products (for example ethanol is produced). Among these, the first discovered and the most important for biotechnology is Thermus aquaticus.
Major geyser fields and their distribution
Geysers are quite rare, requiring a combination of water, heat, and fortuitous plumbing. The combination exists in few places on Earth.
Yellowstone National Park
Yellowstone is the largest geyser locale, containing thousands of hot springs, and approximately 300 to 500 geysers. It is home to half of the world's total number of geysers in its nine geyser basins. It is located mostly in Wyoming, USA, with small portions in Montana and Idaho. Yellowstone includes the world's tallest active geyser (Steamboat Geyser in Norris Geyser Basin).
Valley of Geysers, Russia
The Valley of Geysers (), located in the Kamchatka Peninsula of Russia, is the second-largest concentration of geysers in the world. The area was discovered and explored by Tatyana Ustinova in 1941. There are about 200 geysers in the area, along with many hot-water springs and perpetual spouters. The area was formed by vigorous volcanic activity. The peculiar way of eruptions is an important feature of these geysers. Most of the geysers erupt at angles, and only very few have the geyser cones that exist at many other of the world's geyser fields. On 3 June 2007, a massive mudflow influenced two-thirds of the valley. It was then reported that a thermal lake was forming above the valley. Four of the eight thermal areas in the valley were covered by the landslide or by the lake. Velikan Geyser, one of the field's largest, was not buried in the slide: the slide shortened its period of eruption from 379 minutes before the slide to 339 minutes after (through 2010).
El Tatio, Chile
The name "El Tatio" comes from the Quechua word for oven. El Tatio is located in the high valleys of the Andes in Chile, surrounded by many active volcanoes, at around above mean sea level. The valley is home to approximately 80 geysers at present. It became the largest geyser field in the Southern Hemisphere after the destruction of many of the New Zealand geysers, and is the third largest geyser field in the world. The salient feature of these geysers is that the height of their eruptions is very low, the tallest being only high, but with steam columns that can be over high. The average geyser eruption height at El Tatio is about .
Taupō Volcanic Zone, New Zealand
The Taupō Volcanic Zone is located on New Zealand's North Island. It is long by and lies over a subduction zone in the Earth's crust. Mount Ruapehu marks its southwestern end, while the submarine Whakatāne seamount ( beyond Whakaari / White Island) is considered its northeastern limit. Many geysers in this zone were destroyed due to geothermal developments and a hydroelectric reservoir: only one geyser basin at Whakarewarewa remains.
In the beginning of the 20th century, the largest geyser ever known, the Waimangu Geyser, existed in this zone. It began erupting in 1900 and erupted periodically for four years until a landslide changed the local water table. Eruptions of Waimangu would typically reach and some superbursts are known to have reached . Recent scientific work indicates that the Earth's crust below the zone may be as little as thick. Beneath this lies a film of magma wide and long.
Iceland