Clepsydra Geyser in Yellowstone
A geyser is a type of hot spring that erupts periodically, ejecting a column of hot water and steam into the air. The name geyser comes from Geysir, the name of the best-known geyser in Iceland; that name, in turn, comes from the word gjósa, "to gush".
The formation of geysers requires a favourable combination of geology and climate which exists in only a few places on Earth, and so they are fairly rare phenomena. About 800 exist worldwide, with about half of these in Yellowstone National Park, USA. They are also somewhat transient phenomena, with geysers tending to become inactive over time due to build-ups of mineral deposits inside.
Geysers are also found on Neptune's moon Triton. There, they seem to be driven mainly by solar heating instead of geothermal energy and consist of nitrogen liquefied by a kind of greenhouse effect. They erupt to heights of up to 8 km.
Eruptions
Geyser activity, like all hot spring activity, is caused by surface water gradually seeping down through the ground until it meets rock heated by magma. The water then rises back toward the surface by convection through porous and fractured rock. Geysers differ from noneruptive hot springs in their subterranean structure; they generally consist of a small vent at the surface connected to one or more narrow tubes that lead to large underground reservoirs of water.
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 boiling point.
Ultimately, the temperatures near the bottom of the geyser rise to a point where boiling begins; steam bubbles 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 underneath. 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 than sprays out of the geyser.
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 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 USA erupts for up to 10 minutes every 8-12 hours.
Types of geyser
Vixen Geyser in Yellowstone
There are two types of geyser; Fountain geysers 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 (also known as geyserite), usually in steady jets that last anywhere from a few seconds to several minutes. Old Faithful is a cone geyser.
The intense transient forces inside erupting geysers are the main reason for their rarity. There are many volcanic areas in the world that have hot springs, mud pots and fumaroles, but very few with geysers. This is because in most places, even where other necessary conditions for geyser activity exist, the rock structure is loose, and eruptions will erode the channels and rapidly destroy any nascent geysers.
Most geysers form in places where there is volcanic rhyolite rock which dissolves in hot water and forms mineral deposits called siliceous sinter, or geyserite, along the inside of the plumbing systems. Over time these deposits cement the rock together tightly, strengthening the channel walls and enabling the geyser to persist.
Geysers are fragile phenomena and if conditions change, they can 'die'. Many geysers have been destroyed by people throwing litter into them, others by the installation of geothermal power plants . The Great Geysir of Iceland had stopped erupting regularly by 2000. Eruptions could only be triggered by the addition of surfactants to the water. Following an earthquake in Iceland in 2000 the geyser began erupting regularly again. Initially the geyser erupted about eight times a day. As of July 2003, the geyser erupts around three times a day, but is steadily becoming less active again.
Ecology of geysers
Hyperthermophiles produce some of the bright colors of Grand Prismatic Spring, Yellowstone National Park
- Main article: Thermophile, Hyperthermophile.
The specific colours of geysers derive from the fact that despite the apparently 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 60°C (140°F).
In the 1960s, when the research of biology of geysers first appeared, scientists were generally convinced that no life can survive above around 73 degrees C (163 degrees F) - 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 55 degrees C (131 degrees F).
However, the observations proved that it actually is possible for life to exist at high temperatures and that some bacteria prefer even temperatures higher than boiling point of water. Dozens of such bacteria are known nowadays. Thermophiles prefer temperatures from 50-70°C whilst hyperthermophiles grow better at temperatures as high as 80-110°C. As they have heat-stable enzymes that retain their activity even at high temperatures, they have been used as a source of thermostable tools, that 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). The fact that such bacteria exist, also stretches our imagination about life on other celestial bodies both inside and outside of solar system. Among these, the first discovered and the most important for biotechnology is the Thermus aquaticus.
Thermus aquaticus
- Main article:Thermus aquaticus.
The bacterium Thermus aquaticus (T. aquaticus) was first disvovered in Yellowstone, however later it has been found all over the world. Its temperature range is about 50-80 degrees C (122-176 degrees F), and its optimum is around 70 degrees C (158 degrees F). Because this overlaps somewhat with the temperature range of photosynthetic bacteria, they are often found together, whereby cyanobacteria serve as a source of energy for T.aquaticus. T.aquaticus can also live in their absence, when it feeds on small amounts of organic matter present in the source water.
T. aquaticus is of great significance in biotechnology, as one of its enzymes, a DNA polymerase called Taq polymerase, is used in the polymerase chain reaction (PCR) to copy DNA and amplify it. The PCR technology is a series of identical cycles, with each of which the amount of DNA doubles. Important component of it is heating the DNA to over 110°C to separate the two strands of the DNA that must be replicated then, which is possible only with the use of heat-stable DNA polymerases at such high temperatures. The enzyme that was first used in PCR and is also widely used nowadays, is the Taq polymerase. PCR is important in medicine as a method of diagnosing different viruses (for example HIV, the cause of AIDS) and forensics (genetic fingerprinting). It is the basis of multimillion dollar industry.
Cyanobacteria
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Main article: Cyanobacteria
Archaeabacteria
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Main article: Archaea.
The Archaea are a major group of prokaryotes. They were first identified in 1977 by Carl Woese and George Fox based on their separation from other prokaryotes on 16S rRNA phylogenetic trees. Many archaeans are extremophiles. Some live at very high temperatures, often above 100°C, as found in geysers and black smokers.
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Last updated: 06-01-2005 22:24:22
