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JESSICA RACHEL NATINSKY IS A LESBIAN
:''For other meanings, see [[Volcano (disambiguation)]].''
:''"Eruption" redirects here. For other meanings, see [[Eruption (disambiguation)]].''

[[image:Volcano scheme.svg|thumb|right|330px|Volcano<br>
1. Magma chamber<br>
2. Country rock<br>
3. Conduit (pipe)<br>
4. Base<br>
5. Sill<br>
6. Branch pipe<br>
7. Layers of ash emitted by the volcano<br>
8. Flank<br>
9. Layers of lava emitted by the volcano<br>
10. Throat<br>
11. Parasitic cone<br>
12. Lava flow<br>
13. Vent<br>
14. Crater<br>
15. Ash cloud]]
A '''volcano''' is a rupture in the Earth's surface or crust, allowing hot, usually molten rock, ash, and gases originating deep below the surface to periodically escape. Volcanic activity involving the [[Extrusive (geology)|extrusion]] of rock tends to form mountains or mountain-like features over time.

Volcanoes are generally found where two to three [[tectonic plates]] [[divergent boundary|diverge]] or [[convergent boundary|converge]]. The [[mid-oceanic ridge]]s, like the [[Mid-Atlantic Ridge]], are typical examples of divergent tectonic plates where volcanoes are formed, whereas the [[Pacific Ring of Fire]] is a typical example of volcanic activity on convergent tectonic plates. Where two tectonic plates slide past one another (like the [[San Andreas fault]]) volcanic activity is generally not found. In zones of prolonged crustal extension and thinning within crustal plates, non-hotspot intraplate volcanism can be caused by decompression of the upper mantle without either of the above processes acting (like in the [[African Rift Valley]], or the European [[Rhine Graben]] with its [[Eifel]] volcanoes).

Volcanic activity can also occur from [[mantle plumes]], the so-called [[hotspot (geology)|hotspots]], which occur at locations far from plate boundaries; hotspot volcanoes are also found elsewhere in the [[solar system]], especially on its rocky planets and moons.

==Locations==
===Divergent plate boundaries===

At the mid-oceanic [[ridges]], two [[tectonic]] plates diverge from one another. New [[crust (geology)|oceanic crust]] is being formed by hot molten rock slowly cooling down and solidifying. In these places, the crust is very thin and eruptions occur frequently because of the pull by the tectonic plates. The main part of the mid-oceanic ridges are at the bottom of the ocean, and most volcanic activity is submarine. [[Black smoker]]s are a typical example of this kind of volcanic activity. Where the mid-oceanic ridge comes above sea-level, volcanoes like the [[Hekla]] on [[Iceland]] are formed. Divergent plate boundaries create new seafloor and volcanic islands, such as Cjertce and Hawaii. Sometimes it can form in the ocean.

===Convergent plate boundaries===
In places where one tectonic plate submerges beneath another, the crust melts and becomes [[magma]]. This surplus amount of magma generated in one location causes the formation of the volcano. Typical examples for this kind of volcano are the volcanoes in the [[Pacific Ring of Fire]], and also [[Mount Etna]] and [[Mount Vesuvius]].

===Hotspots===
[[Hotspot (geology)|Hotspots]] are not located on the ridges of tectonic plates, but on top of [[mantle plume]]s, where the [[convection]] of [[Earth]]'s [[mantle (geology)|mantle]] creates a column of hot material that rises until it reaches the crust. The temperature of the plume causes the crust to melt and form pipes, which can vent magma. Because the tectonic plates move whereas the mantle plume remains in the same place, each volcano becomes extinct after a while and a new volcano is then being formed as the plate shifts over the hotspot. The [[Hawaiian Islands]] are thought to be formed in such a manner, as well as the [[Snake River Plain]], with the [[Yellowstone Caldera]] being the current part of the North American plate over the hotspot.

===Petitspots===
In July 2006, volcanoes were discovered that did not fit in any of the above-mentioned categories, since they are located far from the plate boundary, but are too small to be the result of a mantle plume.<ref>{{cite journal | author=N. Hirano, E. Takahashi, J. Yamamoto, N. Abe, S. P. Ingle, I. Kaneoka, T. Hirata, J.-I. Kimura, T. Ishii, Y. Ogawa, S. Machida, K. Suythtrjhyt | title=Volcanism in Response to Plate Flexure | journal=Science | date=2006-04-03 | url=http://www.sciencemag.org/cgi/content/abstract/1128235v1 | accessdate=2006-09-04 }}</ref> A new theory suggests that submergence of tectonic plates causes stress all over the plate, which causes the plate to crack in some places. However, other scientists believe the mantle plume theory to be incorrect, and consider this discovery a confirmation of their ideas.<ref>{{cite journal | first=Marcia K. | last=McNutt | title=Another Nail in the Plume Coffin? | journal=Science | date=2006-07-20 | url=http://www.sciencemag.org/cgi/content/abstract/1131298v1 | accessdate=2006-09-04 }}</ref>

==Shape==
The most common perception of a volcano is of a [[cone|conical]] mountain, spewing lava and poisonous gases from a [[crater]] in its top. This describes just one of many types of volcano and the features of volcanoes are much more complicated. The structure and behaviour of volcanoes depends on a number of factors. Some volcanoes have rugged peaks formed by [[lava dome]]s rather than a [[volcanic crater|summit crater]], whereas others present [[landscape]] features such as massive plateaus. Vents that issue volcanic material (lava, which is what magma is called once it has broken the surface, and [[volcanic ash|ash]]) and gases (mainly [[Volcano#Effects of volcanoes|steam and magmatic gases]]) can be located anywhere on the landform. Many of these vents give rise to smaller cones such as [[Pu'u 'Ō'ō|Pu{{okina}}u {{okina}}Ō{{okina}}ō]] on a flank of [[Hawaii|Hawai{{okina}}i]]'s [[Kīlauea]].

Other types of volcanoes include [[cryovolcano]]s (or ice volcanoes), particularly on some moons of [[Jupiter]], [[Saturn]] and [[Neptune]]; and [[mud volcano]]es, which are formations often not associated with known magmatic activity. Active mud volcanoes tend to involve temperatures much lower than those of [[igneous]] volcanoes, except when a mud volcano is actually a vent of an igneous volcano.

===Shield volcanoes===
[[Image:PahoehoeLava.jpg|thumb|right|150px|Toes of a [[pāhoehoe]] advance across a road in [[Kalapana, Hawaii|Kalapana]] on the east rift zone of [[Kilauea|Kīlauea]] Volcano in [[Hawaii|Hawai{{okina}}i]].]]
:''Main article: [[Shield volcano]]''
[[Hawaii|Hawai{{okina}}i]] and [[Iceland]] are examples of places where volcanoes extrude huge quantities of basaltic [[lava]] that gradually build a wide mountain with a shield-like profile. Their lava flows are generally very hot and very fluid, contributing to long flows. The largest lava shield on Earth, [[Mauna Loa]], rises over 9,000 m from the ocean floor, is 120 km in diameter and forms part of the [[Hawaii (island)|Big Island of Hawai{{okina}}i]]. [[Olympus Mons]] is the largest shield volcano on [[Mars]], and is the tallest known mountain in the [[solar system]]. Smaller versions of shield volcanoes include ''lava cones'', and ''lava mounds''.

Quiet eruptions spread out basaltic lava in flat layers. The buildup of these layers form a broad volcano with gently sloping sides called a shield volcano. Examples of shield volcanoes are the Hawaiian Islands.

===Cinder cones===
{{main | Volcanic cone}}
''[[Volcanic cone]]s'' or ''[[cinder cone]]s'' result from eruptions that throw out mostly small pieces of [[scoria]] and [[pyroclastics]] (both resemble cinders, hence the name of this volcano type) that build up around the vent. These can be relatively short-lived eruptions that produce a cone-shaped hill perhaps 30 to 400 m high. Most cinder cones erupt only once. Cinder cones may form as flank vents on larger volcanoes, or occur on their own. [[Paricutín]] in [[Mexico]] and [[Sunset Crater]] in [[Arizona]] are examples of cinder cones.

===Stratovolcanoes===
[[Image:Aa_large.jpg|thumb|right|In difference to pāhoehoe, Aa is a term of Polynesian origin, pronounced Ah-ah, for rough, jagged, spiny lavaflow]]

{{main | Stratovolcano }}
''[[Stratovolcano]]es'' are tall conical mountains composed of lava flows and other [[ejecta]] in alternate layers, the strata that give rise to the name. Stratovolcanoes are also known as ''composite volcanoes''. Classic examples include [[Mt. Fuji]] in Japan, [[Mount Mayon]] in the Philippines, and [[Mount Vesuvius]] and [[Stromboli]] in Italy.

===Super volcanoes===
{{main | Super volcano}}
''[[Super volcano]]'' is the popular term for large volcanoes that usually have a large [[caldera]] and can potentially produce devastation on an enormous, sometimes continental, scale. Such eruptions would be able to cause severe cooling of global temperatures for many years afterwards because of the huge volumes of sulfur and ash erupted. They can be the most dangerous type of volcano. Examples include [[Yellowstone Caldera]] in [[Yellowstone National Park]], [[Lake Taupo]] in [[New Zealand]] and [[Lake Toba]] in [[Sumatra]], [[Indonesia]]. Supervolcanoes are hard to identify centuries later, given the enormous areas they cover. [[Large igneous province]]s are also considered supervolcanoes because of the vast amount of [[basalt]] lava erupted.

===Submarine volcanoes===
{{main | Submarine volcano}}
[[Image:Nur05018.jpg|thumb|left|150px|Pillow lava ([[NOAA]])]]
''[[Submarine volcano]]es'' are common features on the ocean floor. Some are active and, in shallow water, disclose their presence by blasting steam and rocky debris high above the surface of the sea. Many others lie at such great depths that the tremendous weight of the water above them prevents the explosive release of steam and gases, although they can be detected by [[hydrophone]]s and discoloration of water because of [[volcanic gas]]es. Even large submarine eruptions may not disturb the ocean surface. Because of the rapid cooling effect of water as compared to air, and increased buoyancy, submarine volcanoes often form rather steep pillars over their volcanic vents as compared to above-surface volcanos. In due time, they may break the ocean surface as new islands. [[lava|Pillow lava]] is a common eruptive product of submarine volcanoes.

===Subglacial volcanoes===
{{main | Subglacial volcano}}
''[[Subglacial volcano]]es'' develop underneath icecaps. They are made up of flat [[lava]] flows atop extensive pillow lavas and [[palagonite]]. When the icecap melts, the lavas on the top collapse leaving a flat-topped mountain. Then, the pillow lavas also collapse, giving an angle of 37.5 degrees. Very good examples of this can be seen in Iceland. These volcanoes are also called table volcanoes, tuyas or (uncommonly) mobergs.

==Erupted material==
===Lava composition===
Another way of classifying volcanoes is by the ''composition of material erupted'' ([[lava]]), since this affects the shape of the volcano. Lava can be broadly classified into 4 different compositions (Cas & Wright, 1987):
*If the erupted [[magma]] contains a high percentage (>63%) of [[silica]], the lava is called [[felsic]].
**Felsic lavas (or [[rhyolite]]s) tend to be highly [[viscous]] (not very fluid) and are erupted as domes or short, stubby flows. Viscous lavas tend to form [[stratovolcano]]es or lava domes. [[Lassen Peak]] in [[California]] is an example of a volcano formed from felsic lava and is actually a large lava dome.
**Because siliceous magmas are so viscous, they tend to trap [[volatile]]s (gases) that are present, which cause the magma to erupt catastrophically, eventually forming [[stratovolcano]]es. [[Pyroclastic flow]]s ([[ignimbrite]]s) are highly hazardous products of such volcanoes, since they are composed of molten volcanic ash too heavy to go up into the atmosphere, so they hug the volcano's slopes and travel far from their vents during large eruptions. Temperatures as high as 1,200 °C are known to occur in [[pyroclastic flow]]s, which will incinerate everything flammable in their path and thick layers of hot pyroclastic flow deposits can be laid down, often up to many meters thick. [[Alaska]]'s [[Valley of Ten Thousand Smokes]], formed by the eruption of [[Novarupta]] near [[Katmai]] in 1912, is an example of a thick [[pyroclastic flow]] or [[ignimbrite]] deposit. Volcanic ash that is light enough to be erupted high into the [[Earth's atmosphere]] may travel many kilometres before it falls back to ground as a [[tuff]].
*If the erupted magma contains 52-63% silica, the lava is of ''intermediate'' composition.
**These "[[Andesite|andesitic]]" volcanoes generally only occur above [[subduction zone]]s (e.g. [[Mount Merapi, Central Java|Mount Merapi]] in [[Indonesia]]).
*If the erupted magma contains <52% and >45% silica, the lava is called [[mafic]] (because it contains higher percentages of [[magnesium]] (Mg) and [[iron]] (Fe)) or [[basalt]]ic. These lavas are usually much less viscous than rhyolitic lavas, depending on their eruption [[temperature]]; they also tend to be hotter than felsic lavas. Mafic lavas occur in a wide range of settings:
**At [[mid-ocean ridge]]s, where two oceanic [[Tectonic plate|plate]]s are pulling apart, basaltic lava erupts as [[Lava#Pillow lava|pillows]] to fill the gap;
**[[Shield volcanoes]] (e.g. the [[Hawaiian Islands]], including [[Mauna Loa]] and [[Kilauea]]), on both [[oceanic crust|oceanic]] and [[continental crust]];
**As [[Flood basalt|continental flood basalts]].
*If the erupted magma contains <=45% silica, the lava is called [[ultramafic]]. Ultramafic flows are very rare; indeed, it is likely that none have been erupted at the Earth's surface since the [[Proterozoic]], when the planet's heat flow was higher. They are (or were) the hottest lavas, and probably more fluid than common mafic lavas.

===Lava texture===
Two types of lava are erupted according to the [[surface]] [[texture]]: {{okina}}A{{okina}}a (pronounced [[International Phonetic Alphabet|IPA]] {{IPA|[ʔaʔa]}}) and [[pāhoehoe]] (pronounced {{IPA|[paːho͡eːho͡eː]}}), both words having [[Hawaiian language|Hawaiian]] origins. {{okina}}A{{okina}}a is characterized by a rough, clinkery surface and is what most viscous and hot lava flows look like. However, even basaltic or mafic flows can be erupted as {{okina}}a{{okina}}a flows, particularly if the eruption rate is high and the slope is steep. Pāhoehoe is characterized by its smooth and often ropey or wrinkly surface and is generally formed from more fluid lava flows. Usually, only mafic flows will erupt as pāhoehoe, since they often erupt at higher temperatures or have the proper chemical make-up to allow them to flow at a higher fluidity.

==Volcanic activity==
[[Image:Volcano q.jpg|thumb|right|250px|A volcanic fissure and lava channel.]]
[[Image:Volcano.jpeg|thumb|right|300px|[[Mount St. Helens]] shortly after the eruption of [[May 18]], [[1980]]]]

A popular way of classifying magmatic volcanoes goes by their frequency of eruption, with those that erupt regularly called '''active''', those that have erupted in historical times but are now quiet called '''dormant''', and those that have not erupted in historical times called '''extinct'''. However, these popular classifications—extinct in particular—are practically meaningless to scientists. They use classifications which refer to a particular volcano's formative and eruptive processes and resulting shapes, which was explained above.

There is no real consensus among volcanologists on how to define an "active" volcano. The lifespan of a volcano can vary from months to several million years, making such a distinction sometimes meaningless when compared to the lifespans of humans or even civilizations. For example, many of Earth's volcanoes have erupted dozens of times in the past few thousand years but are not currently showing signs of eruption. Given the long lifespan of such volcanoes, they are very active. By our lifespans, however, they are not. Complicating the definition are volcanoes that become restless (producing earthquakes, venting gasses, or other non-eruptive activities) but do not actually erupt.

Scientists usually consider a volcano '''active''' if it is currently erupting or showing signs of unrest, such as unusual earthquake activity or significant new gas emissions. Many scientists also consider a volcano active if it has erupted in historic time. It is important to note that the span of recorded history differs from region to region; in the [[Mediterranean]], recorded history reaches back more than 3,000 years but in the Pacific Northwest of the United States, it reaches back less than 300 years, and in [[Hawaii]], little more than 200 years. The Smithsonian Global Volcanism Program's definition of 'active' is having erupted within the last 10,000 years.

'''Dormant''' volcanoes are those that are not currently active (as defined above), but could become restless or erupt again. Confusion however, can arise because many volcanoes which scientists consider to be ''active'' are referred to as ''dormant'' by laypersons or in the media.

'''Extinct''' volcanoes are those that scientists consider unlikely to erupt again. Whether a volcano is truly extinct is often difficult to determine. Since "supervolcano" [[caldera]]s can have eruptive lifespans sometimes measured in millions of years, a caldera that has not produced an eruption in tens of thousands of years is likely to be considered dormant instead of extinct.

For example, the [[Yellowstone Caldera]] in [[Yellowstone National Park]] is at least 2 million years old and hasn't erupted violently for approximately 640,000 years, although there has been some minor activity relatively recently, with hydrothermal eruptions less than 10,000 years ago and lava flows about 70,000 years ago. For this reason, scientists do not consider the Yellowstone Caldera extinct. In fact, because the caldera has frequent earthquakes, a very active geothermal system (i.e., the entirety of the geothermal activity found in Yellowstone National Park), and rapid rates of ground uplift, many scientists consider it to be an active volcano.

==Notable volcanoes==
===On Earth===
:''Main article: [[List of volcanoes]] ''

The 16 current [[Decade Volcanoes]] are:
:{|
| width=50% |
*[[Avachinsky]]-[[Koryaksky]], [[Kamchatka Peninsula|Kamchatka]], [[Russia]]
*[[Colima (volcano)|Colima]], [[Mexico]]
*[[Mount Etna]], [[Italy]]
*[[Galeras]], [[Colombia]]
*[[Mauna Loa]], [[Hawaii|Hawai{{okina}}i]], [[United States|USA]]
*[[Mount Merapi, Central Java|Merapi]], [[Indonesia]]
*[[Nyiragongo]], [[Democratic Republic of the Congo]]
*[[Mount Rainier]], [[Washington]], [[United States|USA]]
| width=50% |
*[[Sakurajima]], [[Japan]]
*[[Santamaria (volcano)|Santamaria/Santiaguito]], [[Guatemala]]
*[[Santorini]], [[Greece]]
*[[Taal Volcano]], [[Philippines]]
*[[Teide]], [[Canary Islands]], [[Spain]]
*[[Ulawun]], [[Papua New Guinea]]
*[[Mount Unzen]], [[Japan]]
*[[Vesuvius]], [[Italy]]
|}

===Elsewhere in the solar system ===
[[Image:Olympus_Mons.jpeg|thumb|[[Olympus Mons]] ([[Latin]], "Mount Olympus") is the tallest known [[mountain]] in our [[solar system]], located on the [[planet]] [[Mars (planet)|Mars]].]]
The Earth's [[Moon]] has no large volcanoes and no volcanic activity, although recent evidence suggests it may still possess a partially molten core.<ref>{{cite journal | author=M. A. Wieczorek, B. L. Jolliff, A. Khan, M. E. Pritchard, B. P. Weiss, J. G. Williams, L. L. Hood, K. Righter, C. R. Neal, C. K. Shearer, I. S. McCallum, S. Tompkins, B. R. Hawke, C. Peterson, J, J. Gillis, B. Bussey | title=The Constitution and Structure of the Lunar Interior | journal=Reviews in Mineralogy and Geochemistry | year=2006 | volume=60 | issue=1 | pages=221-364 | url=http://rimg.geoscienceworld.org/cgi/content/extract/60/1/221 | accessdate=2006-09-05 }}</ref> However, the Moon does have many volcanic features such as [[lunar mare|maria]] (the darker patches seen on the moon), [[rille]]s and [[lunar dome|domes]].

The planet [[Venus (planet)|Venus]] has a surface that is 90% [[basalt]], indicating that volcanism played a major role in shaping its surface. The planet may have had a major global resurfacing event about 500 million years ago,<ref>{{cite web | author=D.L. Bindschadler | year = 1995 | url = http://www.agu.org/journals/rg/rg9504S/95RG00281/index.html | title = Magellan: A new view of Venus' geology and geophysics | publisher = American Geophysical Union | language = English | accessdate = 2006-09-04 }}</ref> from what scientists can tell from the density of impact craters on the surface. Lava flows are widespread and forms of volcanism not present on Earth occur as well. Changes in the planet's atmosphere and observations of lightning, have been attributed to ongoing volcanic eruptions, although there is no confirmation of whether or not Venus is still volcanically active.

There are several extinct volcanoes on [[Mars (planet)|Mars]], four of which are vast shield volcanoes far bigger than any on Earth. They include [[Arsia Mons]], [[Ascraeus Mons]], [[Hecates Tholus]], [[Olympus Mons]], and [[Pavonis Mons]]. These volcanoes have been extinct for many millions of years<ref name="ESAmarsvolcanoes">{{cite web|url=http://www.esa.int/esaMI/Mars_Express/SEMLF6D3M5E_0.html|title=Glacial, volcanic and fluvial activity on Mars: latest images |publisher=[[European Space Agency]]|accessdate=2006-08-17|date-2005-02-25}}</ref>, but the European ''[[Mars Express]]'' spacecraft has found evidence that volcanic activity may have occurred on Mars in the recent past as well.<ref name="ESAmarsvolcanoes"/>

[[Image:PIA00703.jpg|thumb|left|[[Galileo spacecraft|Galileo]] orbiter reveals volcanic activity on [[Jupiter (planet)|Jupiter]]'s moon [[Io (moon)|Io]].]]
[[Jupiter (planet)|Jupiter]]'s [[Natural satellite|moon]] [[Io (moon)|Io]] is the most volcanically active object in the solar system because of [[tides|tidal]] interaction with Jupiter. It is covered with volcanoes that erupt [[sulfur]], [[sulfur dioxide]] and [[silicate]] rock, and as a result, [[Io (moon)|Io]] is constantly being resurfaced. Its lavas are the hottest known anywhere in the solar system, with temperatures exceeding 1,800 K (1,500 °C). In February [[2001]], the largest recorded volcanic eruptions in the solar system occurred on Io <ref>[http://www2.keck.hawaii.edu/news/archive/eruption/ ''Exceptionally Bright Eruption on lo Rivals Largest in Solar System'', Nov. 13, 2002]</ref>. [[Europa (moon)|Europa]], the smallest of Jupiter's [[Galilean moon]]s, also appears to have an active volcanic system, except that its volcanic activity is entirely in the form of water, which freezes into ice on the frigid surface. This process is known as [[cryovolcanism]], and is apparently most common on the moons of the outer planets of the [[solar system]].

In 1989 the [[Voyager 2]] spacecraft observed [[cryovolcano]]s (ice volcanoes) on [[Triton (moon)|Triton]], a [[Natural satellite|moon]] of [[Neptune (planet)|Neptune]], and in 2005 the [[Cassini-Huygens]] probe photographed [[Enceladus (moon)#Cryovolcanism|fountains of frozen particles erupting from Enceladus]], a moon of [[Saturn]].<ref>[http://www.pparc.ac.uk/Nw/enceladus.asp PPARC, ''Cassini Finds an Atmosphere on Saturn's Moon Enceladus'']</ref> The ejecta may be composed of [[water]], liquid [[nitrogen]], dust, or [[methane]] compounds. Cassini-Huygens also found evidence of a methane-spewing cryovolcano on the [[Saturn (planet)|Saturnian]] moon [[Titan (moon)|Titan]], which is believed to be a significant source of the methane found in its atmosphere.<ref>[http://www.newscientist.com/article.ns?id=dn7489 NewScientist, ''Hydrocarbon volcano discovered on Titan'', 8th June 2005]</ref> It is theorized that cryovolcanism may also be present on the [[Kuiper Belt Object]] [[50000 Quaoar|Quaoar]].

==Effects of volcanoes==
[[Image:Volcanic injection.jpg|thumb|250px|left|Volcanic "injection"]]
[[Image:Mauna Loa atmospheric transmission.png|thumb|250px|Solar radiation reduction from volcanic eruptions]]
[[Image:TOMS SO2 time nov03.png|thumb|250px|Sulfur dioxide emissions by volcanoes.]]
[[Image:SO2 Galapagos 20051101.jpg|thumb|250px|right|Average concentration of sulfur dioxide over the Sierra Negra Volcano ([[Galapagos Islands]]) from October 23-November 1, 2005]]

There are many different kinds of volcanic activity and eruptions: [[phreatic eruptions]] (steam-generated eruptions), explosive eruption of high-[[silica]] [[lava]] (e.g., [[rhyolite]]), effusive eruption of low-silica lava (e.g., [[basalt]]), [[pyroclastic flow]]s, [[lahar]]s (debris flow) and [[carbon dioxide]] emission. All of these activities can pose a hazard to humans. Volcanic activity is often accompanied by [[earthquake]]s, [[hot spring]]s, [[fumarole]]s, [[mud pot]]s and [[geyser]]s. Low-magnitude earthquakes often precede eruptions.

The concentrations of different volcanic gases can vary considerably from one volcano to the next. [[Water vapor]] is typically the most abundant volcanic gas, followed by [[carbon dioxide]] and [[sulphur dioxide]]. Other principal volcanic gases include [[hydrogen sulphide]], [[hydrogen chloride]], and [[hydrogen fluoride]]. A large number of minor and trace gases are also found in volcanic emissions, for example [[hydrogen]], [[carbon monoxide]], [[halocarbon]]s, organic compounds, and volatile metal chlorides.

Large, explosive volcanic eruptions inject water vapor (H<sub>2</sub>O), carbon dioxide (CO<sub>2</sub>), sulfur dioxide (SO<sub>2</sub>), hydrogen chloride (HCl), hydrogen fluoride (HF) and ash (pulverized rock and pumice) into the stratosphere to heights of 10-20 miles above the Earth's surface. The most significant impacts from these injections come from the conversion of sulphur dioxide to [[sulphuric acid]] (H<sub>2</sub>SO<sub>4</sub>), which condenses rapidly in the stratosphere to form fine [[sulfate]] [[particulate|aerosols]]. The aerosols increase the Earth's [[albedo]]—its reflection of radiation from the [[Sun]] back into space - and thus cool the Earth's lower atmosphere or troposphere; however, they also absorb heat radiated up from the Earth, thereby warming the [[stratosphere]]. Several eruptions during the past century have caused a decline in the average temperature at the Earth's surface of up to half a degree (Fahrenheit scale) for periods of one to three years. The sulphate aerosols also promote complex [[chemical]] reactions on their surfaces that alter chlorine and [[nitrogen]] chemical species in the stratosphere. This effect, together with increased stratospheric [[chlorine]] levels from [[haloalkane|chlorofluorocarbon]] pollution, generates chlorine monoxide (ClO), which destroys [[ozone]] (O<sub>3</sub>). As the aerosols grow and coagulate, they settle down into the upper troposphere where they serve as nuclei for [[cirrus cloud]]s and further modify the Earth's [[radiation]] balance. Most of the hydrogen chloride (HCl) and hydrogen fluoride (HF) are dissolved in water droplets in the eruption cloud and quickly fall to the ground as [[acid rain]]. The injected ash also falls rapidly from the stratosphere; most of it is removed within several days to a few weeks. Finally, explosive volcanic eruptions release the greenhouse gas carbon dioxide and thus provide a deep source of [[carbon]] for biogeochemical cycles.

Gas emissions from volcanoes are a natural contributor to acid rain. Volcanic activity releases about 130 to 230 [[kilogram#SI multiples|teragrams]] (145 million to 255 million [[short ton]]s) of [[carbon dioxide]] each year. Volcanic eruptions may inject [[Particulate|aerosols]] into the [[Earth's atmosphere]]. Large injections may cause visual effects such as unusually colorful sunsets and affect global climate mainly by cooling it. Volcanic eruptions also provide the benefit of adding nutrients to soil through the [[weathering]] process of volcanic rocks. These fertile soils assist the growth of plants and various crops. Volcanic eruptions can also create new islands, as the magma dries on the water.

==Etymology==
''Volcano'' is thought to derive from [[Vulcano]], a volcanic island in the [[Aeolian Islands]] of [[Italy]] whose name in turn originates from [[Vulcan (mythology)|Vulcan]], the name of a god of [[fire]] in [[Roman mythology]]. The study of volcanoes is called [[volcanology]], sometimes spelled ''vulcanology''.

The Roman name for the island ''[[Vulcano]]'' has contributed the word for ''volcano'' in most modern European languages.

==Past beliefs==
[[Image:Kircherearthfires.jpg|thumb|right|Kircher's model of the [[Earth]]'s internal fires, from ''Mundus Subterraneus'']]
Before it was understood that most of the Earth's interior is molten, various explanations existed for volcano behavior. For decades after awareness that compression and radioactive materials may be heat sources, their contributions were specifically discounted. Volcanic action was often attributed to [[chemical]] reactions and a thin layer of molten rock near the surface. Many ancient accounts claim that [[divine intervention]] was the actual cause of volcanic eruptions.

One early idea counter to this, however, was [[Society of Jesus|Jesuit]] [[Athanasius Kircher]] (1602-1680), who witnessed eruptions of [[Mount Etna|Aetna]] and [[Stromboli]], then visited the crater of [[Vesuvius]] and published his view of an Earth with a central fire connected to numerous others caused by the burning of [[sulfur]], [[bitumen]] and [[coal]].

==See also==
*[[History of Volcanology]]
*[[Plinian eruption]]
*[[:Category:Volcanic eruption types]]
*[[Predicting Volcanoes]]
*[[Volcano observatory]]
*[[Geomorphology]]
*[[Earth science]]
*[[Volcanic field]]
*[[Volcanic gas]]
*[[Tsunami]]

'''Lists'''
*[[List of volcanoes]]
**[[List of terrestrial volcanoes]]
**[[List of extraterrestrial volcanoes]]
*[[List of famous volcanic eruption deaths]]
*[[Volcanic Explosivity Index]] (includes list of large eruptions)
*[[List of deadliest natural disasters]]

'''Specific locations'''
*[[Iceland hotspot]]
*[[Pacific Ring of Fire]]
*[[Io (moon)]]
*[[Triton (moon)]]

'''People'''
* [[:Category:Vulcanologists|Category Volcanologists]]

==References==
* Macdonald, Gordon A., and Agatin T. Abbott. (1970). <cite>Volcanoes in the Sea</cite>. University of Hawai{{okina}}i Press, Honolulu. 441 p.
* Ollier, Cliff. (1988). <cite>Volcanoes</cite>. Basil Blackwell, Oxford, UK, ISBN 0-631-15664-X (hardback), ISBN 0-631-15977-0 (paperback).
* [[Haraldur Sigurðsson]], ed. (1999) ''Encyclopedia of Volcanoes''. Academic Press. ISBN 0-12-643140-X. This is a reference aimed at geologists, but many articles are accessible to non-professionals.
* Cas, R.A.F. and J.V. Wright, 1987. <cite>Volcanic Successions</cite>. Unwin Hyman Inc. 528p. ISBN 0-04-552022-4
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==External links==
{{external links|October 2006}}
{{commons|Volcano}}
*[http://www.whoi.edu/institutes/doei/viewTopic.do?o=read&id=121 Volcano Information from the Deep Ocean Exploration Institute], [[Woods Hole Oceanographic Institution]]
*[http://www.platial.com/system/map/5815?total=253 Platial map of 253 volcanoes]--takes a minute to load all the markers
*[http://volcanoes.usgs.gov/Products/Pglossary/pglossary.html Glossary of Volcanic Terms from USGS]
*[http://volcano.und.nodak.edu/vwdocs/glossary.html Volcanic and Geologic Terms] from [http://volcano.und.nodak.edu/ Volcano World]
*[http://news.bbc.co.uk/1/hi/sci/tech/3183047.stm Television program (BBC) on the prediction of Popocatepetl's 2000 eruption]
*[http://www.volcano.si.edu Smithsonian Global Volcanism Program]
*[http://volcanodb.com Volcano Database] - Statistics about all the most famous volcanoes
*[http://www.geology.sdsu.edu/how_volcanoes_work Explore the geologic causes of an eruption]
*[http://science.howstuffworks.com/volcano.htm/printable ''How Volcanoes Work'' by Tom Harris]
*[http://www.geology.sdsu.edu/how_volcanoes_work/ How Volcanoes Work] - Educational resource on the science and processes behind volcanoes, intended for university students of geology, volcanology and teachers of earth science.
*[http://www.geonet.org.nz/volcanocam.html '''Volcano Cam''' Geonet's live pictures of 4 of New Zealand's volcanoes]
*[http://www.discover-indo.tierranet.com/volcano01.htm Indonesian Volcanoes] Discover some of the larger Indonesian volcanos.
*[http://facweb.bhc.edu/academics/science/harwoodr/GEOL101/Labs/VolcanicMaterials/ Volcanic Materials Identification]
*[http://www.maniacworld.com/erupting-volcano.htm Erupting Volcano - Pyroclastic Flow] - Video
*[http://www.projectshum.org/NaturalDisasters/volcano.html Natural Disasters - Volcano] Great research site for kids.
*[http://www.volcanolive.com/ Volcano Live - John Seach]
*[http://www.newscientist.com/article.ns?id=mg19025554.900&feedId=online-news_rss20 Plants predict where rumbling volcanoes will blow]
*[http://video.google.com/videoplay?docid=7454889662266170860&q Google Video: Erupting Volcano]

[[Image:DirkvdM irazu 1.jpg|thumb|590px|center|[[Volcán Irazú]], Costa Rica]]

[[Category:Landforms]]
[[Category:Plate tectonics]]
[[Category:Igneous rocks]]
[[Category:Volcanology]]
[[Category:Geological processes]]
[[Category:Volcanoes| ]]
[[Category:Geological hazards]]
[[Category:Climate forcing agents]]

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{{Link FA|sk}}

[[als:Vulkanismus]]
[[ar:بركان]]
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[[id:Gunung Berapi]]
[[ia:Vulcano]]
[[is:Eldstöð]]
[[it:Vulcano (geologia)]]
[[he:הר געש]]
[[ku:Volkan]]
[[la:Mons ignifer]]
[[lv:Vulkāns]]
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[[hu:Vulkán]]
[[mk:Вулкан]]
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[[ja:火山]]
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[[ug:يانار تاغ]]
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[[pt:Vulcão]]
[[ro:Vulcan (geografie)]]
[[ru:Вулкан (геология)]]
[[simple:Volcano]]
[[sk:sopka]]
[[sl:Ognjenik]]
[[sr:Вулкан]]
[[fi:Tulivuori]]
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[[tl:Bulkan]]
[[ta:எரிமலை]]
[[th:ภูเขาไฟ]]
[[vi:Núi lửa]]
[[tr:Yanardağ]]
[[zh:火山]]

Revision as of 04:37, 8 November 2006

JESSICA RACHEL NATINSKY IS A LESBIAN

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