Geyser

A geyser is an intermittent or semi-regularly periodic spout of geothermally heated groundwater and steam.

Any subsurface encounter between water and heat produces a hydrothermal process. The heat is usually supplied by upwellings of magma from the mantle, the water by precipitation that percolates downward through surface rocks . Some oceanic water enters the mantle at subduction zones and becomes an important ingredient in upper-mantle magmas.

Most hydrothermal processes are driven by convection . Convection occurs because water, like most substances, expands when heated. The result is that hot water rises and cool water sinks. Convection occurs when any water-permeated part of the earth's crust is heated from below: heated water fountains upward over the hot spot and cool water descends around its edges. These movements occur through cracks and channels in the rock, forcing the water to move slowly and remain in constant contact with various minerals . Water convecting through rock is thus an effective means of dissolving, transporting, and depositing minerals. Most deposits of concentrated minerals, including large, shapely crystals, are created by hydrothermal processes.

Manifestations of hydrothermal processes can be dramatic, including the geysers and hot springs that sometimes occur where shallow magma is present. However,
most hydrothermal circulation occurs inconspicuously in the vicinity of large magmatic intrusions. These can cause water to convect through the rocks for miles around.

Some geysers erupt as perdictable intervals, others irregularly; a few send jets of water and steam hundreds of feet into the air, others only a few feet. There are fewer than 700 geysers in the world, all concentrated in a few dozen fields. More than 60% of the world's geysers are in Yellowstone National Park in the northwestern United States, including the famous geyser, "Old Faithful."

The word geyser comes from the name of a single Icelandic geyser, Geysir, written mention of which dates back to a.d. 1294.

Geysers form only under special conditions. First, a system of underground channels must exist in the form of a vertical neck or series of chambers. The exact arrangement cannot be observed directly, and probably varies from geyser to geyser. This system of channels must vent at the surface. Second, water deep in the system—tens or hundreds of meters underground—must be in contact with or close proximity to magma. Third, this water must come in contact with some rock rich in silica (silicon dioxide, SiO2), usually rhyolite.

Silica dissolves in the hot water and is chemically altered in solution . As this water moves toward the surface, it deposits some of this chemically altered silica on the inner surfaces of the channels through which it flows, coating and sealing them with a form of opal termed sinter. Sinter sealing allows water and steam to be forced through the channels at high pressure ; otherwise, the pressure would be dissipated through various cracks and side-channels.

The episodic nature of geyser flow also depends on the fact that the boiling point of water is a function of pressure. In a vacuum (zero pressure), liquid water boils at 0°C; under high pressure, water can remain liquid at many hundreds of degrees. Water heated above 100°C but kept liquid by high pressure is said to be superheated.

The sequence of events in an erupting geyser follows a repeating sequence. First, groundwater seeps into the geyser's reservoirs (largely emptied by the previous eruption), where it is heated—eventually, superheated—by nearby magma. Steam bubbles then form in the upper part of the system, where the boiling point is lower because the pressure is lower. The steam bubbles eject some water onto the surface and this takes weight off water deeper in the system, rapidly lowering its pressure and therefore its boiling point. Ultimately, the deeper water flashes to steam, forcing a mixed jet of water and steam through the geyser's surface vent.

Many of the world's geysers are endangered by drilling for geothermal energy in their vicinity. Drilling draws off water and heat, disrupting the unusual balance of underground conditions that makes a geyser possible.

See also Bedrock.

Geyser

A geyser is an intermittent spout of geothermally heated groundwater . The word geyser comes from the name of a single Icelandic geyser, Geysir, written mention of which dates back to a.d. 1294.

Some geysers erupt periodically, others irregularly; a few send jets of water and steam hundreds of feet into the air, others only a few feet. There are fewer than 700 geysers in the world, all concentrated in a few dozen fields. More than 60% of the world's geysers are in Yellowstone National Park in the northwestern United States, including the famous geyser, "Old Faithful."

Geysers form only under special conditions. First, a system of underground channels must exist in the form of a vertical neck or series of chambers. The exact arrangement cannot be observed directly, and probably varies from geyser to geyser. This system of channels must vent at the surface. Second, water deep in the system—tens or hundreds of meters underground—must be in contact with or close proximity to magma . Third, this water must come in contact with some rock rich in silica (silicon dioxide, SiO₂), usually rhyolite .

Silica dissolves in the hot water and is chemically altered in solution. As this water moves toward the surface, it deposits some of this chemically altered silica on the inner surfaces of the channels through which it flows, coating and sealing them with a form of opal termed sinter. Sinter sealing allows water and steam to be forced through the channels at high pressure; otherwise, the pressure would be dissipated through various cracks and side-channels.

The episodic nature of geyser flow also depends on the fact that the boiling point of water is a function of pressure. In a vacuum (zero pressure), liquid water boils at 0°C; under high pressure, water can remain liquid at many hundreds of degrees. Water heated above 100°C but kept liquid by high pressure is said to be superheated.

The sequence of events in an erupting geyser follows a repeating sequence. First, groundwater seeps into the geyser's reservoirs (largely emptied by the previous eruption), where it is heated—eventually, superheated—by nearby magma. Steam bubbles then form in the upper part of the system, where the boiling point is lower because the pressure is lower. The steam bubbles eject some water onto the surface and this takes weight off water deeper in the system, rapidly lowering its pressure and therefore its boiling point. Ultimately, the deeper water flashes to steam, forcing a mixed jet of water and steam through the geyser's surface vent.

Many of the world's geysers are endangered by drilling for geothermal energy in their vicinity. Drilling draws off water and heat, disrupting the unusual balance of underground conditions that makes a geyser possible.

See also Bedrock; Country rock; Crater, volcanic; Geothermal deep ocean vents; Geothermal gradient; Hotspots; Magma chamber; Pluton and plutonic bodies; Volcanic eruptions; Volcanic vent; Water table

geyser (gī´zər) [Icel.], hot spring from which water and steam are ejected periodically to heights ranging from a few to several hundred feet. Notable geysers are found in Iceland, New Zealand, and W United States, which are areas of recent volcanic activity. Geyser action in Iceland was studied by the German chemist R. W. Bunsen, whose explanation of it (1847) is generally accepted. Water, mainly from rainfall, is heated by absorbing hot gases or by contact with hot rocks. If it flows into a crooked tube or fissure in the ground, the heat fails to circulate by convection and is concentrated in one section of the tube, located well below the surface. Here the water may be superheated without boiling because of the pressure of the colder water above. When at last it does turn to steam it raises the upper part of the column of water, causing it to overflow. This reduces the pressure on the water below, a great deal is abruptly converted into steam, and the whole column—steam and water—is forced to erupt. Geyser activity is influenced by earth tides, which are caused by the moon's gravitational pull on the earth. Geysers often build cones of opaline silica called geyserite around their vents. "Old Faithful" in Yellowstone Park usually erupts at intervals of about 66 min, but it has become less regular in recent years. Mud geysers or mud volcanoes are eruptive mud springs. Geothermal generating plants, notably in California and New Zealand, use geysers to produce electricity. Geyserlike eruptions have been observed by the space probe Cassini on Enceladus, one of the moons of Saturn.

See G. A. Waring, Thermal Springs of the United States and Other Countries of the World (rev. ed. 1965); T. S. Bryan, Geysers (2005).

geyser A small opening on the Earth's surface which periodically spouts a fountain of boiling water into the air. The largest fountain height recorded was 500 m, from a now extinct geyser in New Zealand. Water beneath the mouth of a geyser is heated by conduction from surrounding hot rocks, water at the base of the column boiling before that higher in the column. Expanding vapour bubbles rise in the column of water, expelling water at the top and lowering the pressure at the base. This allows the onset of further boiling, the system being self-sustaining, until the entire column of water is blown out of the system as a water spout. The water involved carries a large load of dissolved minerals which precipitate around the mouth of the geyser as siliceous sinter. The name is from Geysir, about 45 km from the active volcano Hekla, Iceland, and was first used as a technical term in 1847 by the German chemist R. W. von Bunsen, who spelled it ‘geysir’. This spelling is still sometimes used.

gey·ser / ˈgīzər/ • n. 1. a hot spring in which water intermittently boils, sending a tall column of water and steam into the air. ∎  a jet or stream of liquid: the pipe sent up a geyser of sewer water into the street. 2. Brit. a gas-fired water heater through which water flows as it is rapidly heated. • v. [intr.] (esp. of water or steam) gush or burst out with great force: yellow smoke geysered upward.

geyser •Balthazar, Belshazzar, jazzer •bonanza, Braganza, Constanza, extravaganza, kwanza, organza, Panzer, stanza •parser, plaza, tabula rasa •Shevardnadze • dopiaza •Nebuchadnezzar • Demelza •cadenza, cleanser, credenza, influenza, Penza •appraiser, blazer, eraser, Fraser, gazer, glazer, grazer, laser, mazer, praiser, razor, salmanazar, Weser •stargazer • trailblazer • hellraiser •appeaser, Caesar, easer, Ebenezer, El Giza, freezer, geezer, geyser, Louisa, Pisa, seizer, squeezer, teaser, Teresa, Theresa, visa, wheezer •crowd-pleaser • stripteaser •fizzer, quizzer, scissor •Windsor

geyser Hot spring that erupts intermittently, throwing up jets of superheated water and steam to a height of c.60m (200ft), followed by a shaft of steam with a thunderous roar. Geysers occur in Iceland, New Zealand and the USA.

geyser gushing hot spring XVIII; water-heating apparatus XIX. — Icel. Geysir proper name of a certain hot spring in Iceland, rel. to geysa gush.