A geyser is a special 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."
|Table of contents|
2 Misnamed geysers
3 Geysers on Triton
4 Exploding geyser
5 Further reading
6 External links
Geysers are quite rare, requiring a combination of geology and climate that exists in only a few places on Earth. There are only six geyser fields of any size in the world: Yellowstone National Park, Wyoming; Iceland; North Island, New Zealand; Kamchatka, Russia; El Tatio, Chile; and Unmak Island, Alaska. (There used to be two more fairly large geyser fields in Nevada, called Beowawe and Steamboat Springs, but they were destroyed in the 1980s by the installation of nearby geothermal power plants, which reduced the available heat and lowered the local water table to the point that geyser activity could no longer be sustained.) There are a few more individual geysers scattered around the world, in Peru, Bolivia, Mexico, Dominica, Azores, Kenya and Japan, but no other places where geysers are clustered in large numbers.
Yellowstone is by far the largest and most active geyser field, containing as many geysers in its nine geyser basins as the rest of the world combined--nearly 400 in all--including both the world's tallest geyser (Steamboat Geyser in Norris Geyser Basin) and the most famous (Old Faithful Geyser in Upper Geyser Basin).
There are two types of geyser: Fountain geysers erupt from pools of water, typically in a series of intense, even violent, bursts; cone geysers 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.
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, then rising 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--that is, 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 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 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 '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 by 2000 stopped erupting regularly. 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 and is steadily becoming less active again.
In a number of places where there is geothermal activity wells have been drilled and fitted with impermeable casements that allow them to erupt like geysers. Though these so-called artificial geysers--technically known as erupting geothermal wells--are not true geysers, they can be quite spectacular. Old Faithful of California, in Calistoga, California, is an erupting geothermal well.
Sometimes drilled cold-water wells erupt in a geyserlike manner due to the build-up of pressure from dissolved carbon dioxide in the water. These are not true geysers either, but are often called cold-water geysers. The best known of these is probably Crystal Geyser, near Green River, Utah.
A perpetual spouter is a natural hot spring or geothermal well that spouts water constantly. Some of these are incorrectly called geysers, but because they are not periodic in nature they are not considered true geysers either.