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A volcanois aruptureon thecrustof aplanetary mass object,such as the Earth, which allows

hotlava,volcanic ash,and gases to escape from amagma chamberbelow the surface.

Earth's volcanoes occur because the planet's crust is broken into 17 major, rigid tectonic plates that

float on a hotter, softer layer in the Earth's mantle.[1]

Therefore, on Earth, volcanoes are generally

found wheretectonic platesaredivergingorconverging.For example, amid-oceanic ridge,such as

theMid-Atlantic Ridge,has volcanoes caused bydivergent tectonic platespulling apart; thePacific

Ring of Firehas volcanoes caused byconvergent tectonic platescoming together. Volcanoes can

also form where there is stretching and thinning of thecrust'sinterior plates, e.g., in theEast African

Riftand theWells Gray-Clearwater volcanic fieldandRio Grande Riftin North America. This type of

volcanism falls under the umbrella of "plate hypothesis" volcanism.[2]Volcanism away from plate

boundaries has also been explained asmantle plumes.These so-called "hotspots", for example

Hawaii, are postulated to arise from upwellingdiapirswith magma from thecoremantle boundary,

3,000 km deep in the Earth. Volcanoes are usually not created where two tectonic plates slide past

one another.

Erupting volcanoes can pose many hazards, not only in the immediate vicinity of the eruption. One

such hazard is that volcanic ash can be a threat to aircraft, in particular those withjet engineswhere

ash particles can be melted by the highoperating temperature;the melted particles then adhere to

theturbineblades and alter their shape, disrupting the operation of the turbine. Large eruptions can

affect temperature as ash and droplets ofsulfuric acidobscure thesunand cool the Earth's lower

atmosphere (ortroposphere); however, they also absorb heat radiated up from the Earth, thereby

warming the upper atmosphere (orstratosphere). Historically, so-calledvolcanic wintershave

caused catastrophicfamines.

Contents

1 Etymology

2 Plate tectonics

o 2.1 Divergent plate boundaries

o 2.2 Convergent plate boundaries

o 2.3 "Hotspots"

3 Volcanic features

o 3.1 Fissure vents

o 3.2 Shield volcanoes

o 3.3 Lava domeso 3.4 Cryptodomes

o 3.5 Volcanic cones (cinder cones)

o 3.6 Stratovolcanoes (composite volcanoes)

o 3.7 Supervolcanoes

o 3.8 Submarine volcanoes

o 3.9 Subglacial volcanoes

o 3.10 Mud volcanoes

4 Erupted material

http://en.wikipedia.org/wiki/Rupture_(engineering)http://en.wikipedia.org/wiki/Rupture_(engineering)http://en.wikipedia.org/wiki/Rupture_(engineering)http://en.wikipedia.org/wiki/Crust_(geology)http://en.wikipedia.org/wiki/Crust_(geology)http://en.wikipedia.org/wiki/Crust_(geology)http://en.wikipedia.org/wiki/Planetary_mass_objecthttp://en.wikipedia.org/wiki/Planetary_mass_objecthttp://en.wikipedia.org/wiki/Planetary_mass_objecthttp://en.wikipedia.org/wiki/Lavahttp://en.wikipedia.org/wiki/Lavahttp://en.wikipedia.org/wiki/Lavahttp://en.wikipedia.org/wiki/Volcanic_ashhttp://en.wikipedia.org/wiki/Volcanic_ashhttp://en.wikipedia.org/wiki/Volcanic_ashhttp://en.wikipedia.org/wiki/Magma_chamberhttp://en.wikipedia.org/wiki/Magma_chamberhttp://en.wikipedia.org/wiki/Magma_chamberhttp://en.wikipedia.org/wiki/Volcano#cite_note-1http://en.wikipedia.org/wiki/Volcano#cite_note-1http://en.wikipedia.org/wiki/Volcano#cite_note-1http://en.wikipedia.org/wiki/Tectonic_plateshttp://en.wikipedia.org/wiki/Tectonic_plateshttp://en.wikipedia.org/wiki/Tectonic_plateshttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Mid-oceanic_ridgehttp://en.wikipedia.org/wiki/Mid-oceanic_ridgehttp://en.wikipedia.org/wiki/Mid-oceanic_ridgehttp://en.wikipedia.org/wiki/Mid-Atlantic_Ridgehttp://en.wikipedia.org/wiki/Mid-Atlantic_Ridgehttp://en.wikipedia.org/wiki/Mid-Atlantic_Ridgehttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Pacific_Ring_of_Firehttp://en.wikipedia.org/wiki/Pacific_Ring_of_Firehttp://en.wikipedia.org/wiki/Pacific_Ring_of_Firehttp://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Crust_(geology)http://en.wikipedia.org/wiki/Crust_(geology)http://en.wikipedia.org/wiki/Crust_(geology)http://en.wikipedia.org/wiki/East_African_Rifthttp://en.wikipedia.org/wiki/East_African_Rifthttp://en.wikipedia.org/wiki/East_African_Rifthttp://en.wikipedia.org/wiki/East_African_Rifthttp://en.wikipedia.org/wiki/Wells_Gray-Clearwater_volcanic_fieldhttp://en.wikipedia.org/wiki/Wells_Gray-Clearwater_volcanic_fieldhttp://en.wikipedia.org/wiki/Wells_Gray-Clearwater_volcanic_fieldhttp://en.wikipedia.org/wiki/Rio_Grande_Rifthttp://en.wikipedia.org/wiki/Rio_Grande_Rifthttp://en.wikipedia.org/wiki/Rio_Grande_Rifthttp://en.wikipedia.org/wiki/Volcano#cite_note-Foulger-2http://en.wikipedia.org/wiki/Volcano#cite_note-Foulger-2http://en.wikipedia.org/wiki/Volcano#cite_note-Foulger-2http://en.wikipedia.org/wiki/Mantle_plumehttp://en.wikipedia.org/wiki/Mantle_plumehttp://en.wikipedia.org/wiki/Mantle_plumehttp://en.wikipedia.org/wiki/Hotspot_(geology)http://en.wikipedia.org/wiki/Hotspot_(geology)http://en.wikipedia.org/wiki/Hotspot_(geology)http://en.wikipedia.org/wiki/Diapirhttp://en.wikipedia.org/wiki/Diapirhttp://en.wikipedia.org/wiki/Diapirhttp://en.wikipedia.org/wiki/Core%E2%80%93mantle_boundaryhttp://en.wikipedia.org/wiki/Core%E2%80%93mantle_boundaryhttp://en.wikipedia.org/wiki/Core%E2%80%93mantle_boundaryhttp://en.wikipedia.org/wiki/Core%E2%80%93mantle_boundaryhttp://en.wikipedia.org/wiki/Core%E2%80%93mantle_boundaryhttp://en.wikipedia.org/wiki/Jet_enginehttp://en.wikipedia.org/wiki/Jet_enginehttp://en.wikipedia.org/wiki/Jet_enginehttp://en.wikipedia.org/wiki/Operating_temperaturehttp://en.wikipedia.org/wiki/Operating_temperaturehttp://en.wikipedia.org/wiki/Operating_temperaturehttp://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Sulfuric_acidhttp://en.wikipedia.org/wiki/Sulfuric_acidhttp://en.wikipedia.org/wiki/Sulfuric_acidhttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Tropospherehttp://en.wikipedia.org/wiki/Tropospherehttp://en.wikipedia.org/wiki/Tropospherehttp://en.wikipedia.org/wiki/Stratospherehttp://en.wikipedia.org/wiki/Stratospherehttp://en.wikipedia.org/wiki/Stratospherehttp://en.wikipedia.org/wiki/Volcanic_winterhttp://en.wikipedia.org/wiki/Volcanic_winterhttp://en.wikipedia.org/wiki/Volcanic_winterhttp://en.wikipedia.org/wiki/Faminehttp://en.wikipedia.org/wiki/Faminehttp://en.wikipedia.org/wiki/Faminehttp://en.wikipedia.org/wiki/Volcano#Etymologyhttp://en.wikipedia.org/wiki/Volcano#Etymologyhttp://en.wikipedia.org/wiki/Volcano#Plate_tectonicshttp://en.wikipedia.org/wiki/Volcano#Plate_tectonicshttp://en.wikipedia.org/wiki/Volcano#Divergent_plate_boundarieshttp://en.wikipedia.org/wiki/Volcano#Divergent_plate_boundarieshttp://en.wikipedia.org/wiki/Volcano#Convergent_plate_boundarieshttp://en.wikipedia.org/wiki/Volcano#Convergent_plate_boundarieshttp://en.wikipedia.org/wiki/Volcano#.22Hotspots.22http://en.wikipedia.org/wiki/Volcano#.22Hotspots.22http://en.wikipedia.org/wiki/Volcano#Volcanic_featureshttp://en.wikipedia.org/wiki/Volcano#Volcanic_featureshttp://en.wikipedia.org/wiki/Volcano#Fissure_ventshttp://en.wikipedia.org/wiki/Volcano#Fissure_ventshttp://en.wikipedia.org/wiki/Volcano#Shield_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Shield_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Lava_domeshttp://en.wikipedia.org/wiki/Volcano#Lava_domeshttp://en.wikipedia.org/wiki/Volcano#Cryptodomeshttp://en.wikipedia.org/wiki/Volcano#Cryptodomeshttp://en.wikipedia.org/wiki/Volcano#Volcanic_cones_.28cinder_cones.29http://en.wikipedia.org/wiki/Volcano#Volcanic_cones_.28cinder_cones.29http://en.wikipedia.org/wiki/Volcano#Stratovolcanoes_.28composite_volcanoes.29http://en.wikipedia.org/wiki/Volcano#Stratovolcanoes_.28composite_volcanoes.29http://en.wikipedia.org/wiki/Volcano#Supervolcanoeshttp://en.wikipedia.org/wiki/Volcano#Supervolcanoeshttp://en.wikipedia.org/wiki/Volcano#Submarine_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Submarine_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Subglacial_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Subglacial_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Mud_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Mud_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Erupted_materialhttp://en.wikipedia.org/wiki/Volcano#Erupted_materialhttp://en.wikipedia.org/wiki/Volcano#Erupted_materialhttp://en.wikipedia.org/wiki/Volcano#Mud_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Subglacial_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Submarine_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Supervolcanoeshttp://en.wikipedia.org/wiki/Volcano#Stratovolcanoes_.28composite_volcanoes.29http://en.wikipedia.org/wiki/Volcano#Volcanic_cones_.28cinder_cones.29http://en.wikipedia.org/wiki/Volcano#Cryptodomeshttp://en.wikipedia.org/wiki/Volcano#Lava_domeshttp://en.wikipedia.org/wiki/Volcano#Shield_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Fissure_ventshttp://en.wikipedia.org/wiki/Volcano#Volcanic_featureshttp://en.wikipedia.org/wiki/Volcano#.22Hotspots.22http://en.wikipedia.org/wiki/Volcano#Convergent_plate_boundarieshttp://en.wikipedia.org/wiki/Volcano#Divergent_plate_boundarieshttp://en.wikipedia.org/wiki/Volcano#Plate_tectonicshttp://en.wikipedia.org/wiki/Volcano#Etymologyhttp://en.wikipedia.org/wiki/Faminehttp://en.wikipedia.org/wiki/Volcanic_winterhttp://en.wikipedia.org/wiki/Stratospherehttp://en.wikipedia.org/wiki/Tropospherehttp://en.wikipedia.org/wiki/Sunhttp://en.wikipedia.org/wiki/Sulfuric_acidhttp://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Operating_temperaturehttp://en.wikipedia.org/wiki/Jet_enginehttp://en.wikipedia.org/wiki/Core%E2%80%93mantle_boundaryhttp://en.wikipedia.org/wiki/Diapirhttp://en.wikipedia.org/wiki/Hotspot_(geology)http://en.wikipedia.org/wiki/Mantle_plumehttp://en.wikipedia.org/wiki/Volcano#cite_note-Foulger-2http://en.wikipedia.org/wiki/Rio_Grande_Rifthttp://en.wikipedia.org/wiki/Wells_Gray-Clearwater_volcanic_fieldhttp://en.wikipedia.org/wiki/East_African_Rifthttp://en.wikipedia.org/wiki/East_African_Rifthttp://en.wikipedia.org/wiki/Crust_(geology)http://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Pacific_Ring_of_Firehttp://en.wikipedia.org/wiki/Pacific_Ring_of_Firehttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Mid-Atlantic_Ridgehttp://en.wikipedia.org/wiki/Mid-oceanic_ridgehttp://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Tectonic_plateshttp://en.wikipedia.org/wiki/Volcano#cite_note-1http://en.wikipedia.org/wiki/Magma_chamberhttp://en.wikipedia.org/wiki/Volcanic_ashhttp://en.wikipedia.org/wiki/Lavahttp://en.wikipedia.org/wiki/Planetary_mass_objecthttp://en.wikipedia.org/wiki/Crust_(geology)http://en.wikipedia.org/wiki/Rupture_(engineering)

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o 4.1 Lava composition

o 4.2 Lava texture

5 Volcanic activity

o 5.1 Popular classification of volcanoes

5.1.1 Active

5.1.2 Extinct

5.1.3 Dormanto 5.2 Technical classification of volcanoes

5.2.1 Volcanic-alert level

5.2.2 Volcano warning schemes of the United States

6 Decade volcanoes

7 Effects of volcanoes

8 Volcanoes on other planetary bodies

9 Traditional beliefs about volcanoes

10 See also

11 References

12 Further reading

13 External links

Etymology

The word volcanois derived from the name ofVulcano,a volcanic island in theAeolian Islandsof

Italy whose name in turn originates fromVulcan,the name of a god of fire inRoman

mythology.[3]

The study of volcanoes is calledvolcanology,sometimes spelled vulcanology.

Plate tectonics

Map showing the divergent plate boundaries (OSR Oceanic Spreading Ridges) and recent sub aerial volcanoes.

Main article:Plate tectonics

Divergent plate boundaries

Main article:Divergent boundary

At themid-oceanic ridges,twotectonic platesdiverge from one another as newoceanic crustis

formed by the cooling and solidifying of hot molten rock. Because the crust is very thin at these

http://en.wikipedia.org/wiki/Volcano#Lava_compositionhttp://en.wikipedia.org/wiki/Volcano#Lava_compositionhttp://en.wikipedia.org/wiki/Volcano#Lava_texturehttp://en.wikipedia.org/wiki/Volcano#Lava_texturehttp://en.wikipedia.org/wiki/Volcano#Volcanic_activityhttp://en.wikipedia.org/wiki/Volcano#Volcanic_activityhttp://en.wikipedia.org/wiki/Volcano#Popular_classification_of_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Popular_classification_of_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Activehttp://en.wikipedia.org/wiki/Volcano#Activehttp://en.wikipedia.org/wiki/Volcano#Extincthttp://en.wikipedia.org/wiki/Volcano#Extincthttp://en.wikipedia.org/wiki/Volcano#Dormanthttp://en.wikipedia.org/wiki/Volcano#Dormanthttp://en.wikipedia.org/wiki/Volcano#Technical_classification_of_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Technical_classification_of_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Volcanic-alert_levelhttp://en.wikipedia.org/wiki/Volcano#Volcanic-alert_levelhttp://en.wikipedia.org/wiki/Volcano#Volcano_warning_schemes_of_the_United_Stateshttp://en.wikipedia.org/wiki/Volcano#Volcano_warning_schemes_of_the_United_Stateshttp://en.wikipedia.org/wiki/Volcano#Decade_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Decade_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Effects_of_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Effects_of_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Volcanoes_on_other_planetary_bodieshttp://en.wikipedia.org/wiki/Volcano#Volcanoes_on_other_planetary_bodieshttp://en.wikipedia.org/wiki/Volcano#Traditional_beliefs_about_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Traditional_beliefs_about_volcanoeshttp://en.wikipedia.org/wiki/Volcano#See_alsohttp://en.wikipedia.org/wiki/Volcano#See_alsohttp://en.wikipedia.org/wiki/Volcano#Referenceshttp://en.wikipedia.org/wiki/Volcano#Referenceshttp://en.wikipedia.org/wiki/Volcano#Further_readinghttp://en.wikipedia.org/wiki/Volcano#Further_readinghttp://en.wikipedia.org/wiki/Volcano#External_linkshttp://en.wikipedia.org/wiki/Volcano#External_linkshttp://en.wikipedia.org/wiki/Vulcanohttp://en.wikipedia.org/wiki/Vulcanohttp://en.wikipedia.org/wiki/Vulcanohttp://en.wikipedia.org/wiki/Aeolian_Islandshttp://en.wikipedia.org/wiki/Aeolian_Islandshttp://en.wikipedia.org/wiki/Aeolian_Islandshttp://en.wikipedia.org/wiki/Vulcan_(mythology)http://en.wikipedia.org/wiki/Vulcan_(mythology)http://en.wikipedia.org/wiki/Roman_mythologyhttp://en.wikipedia.org/wiki/Roman_mythologyhttp://en.wikipedia.org/wiki/Roman_mythologyhttp://en.wikipedia.org/wiki/Volcano#cite_note-3http://en.wikipedia.org/wiki/Volcano#cite_note-3http://en.wikipedia.org/wiki/Volcano#cite_note-3http://en.wikipedia.org/wiki/Volcanologyhttp://en.wikipedia.org/wiki/Volcanologyhttp://en.wikipedia.org/wiki/Volcanologyhttp://en.wikipedia.org/wiki/Plate_tectonicshttp://en.wikipedia.org/wiki/Plate_tectonicshttp://en.wikipedia.org/wiki/Plate_tectonicshttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Mid-oceanic_ridgeshttp://en.wikipedia.org/wiki/Mid-oceanic_ridgeshttp://en.wikipedia.org/wiki/Mid-oceanic_ridgeshttp://en.wikipedia.org/wiki/Tectonic_platehttp://en.wikipedia.org/wiki/Tectonic_platehttp://en.wikipedia.org/wiki/Tectonic_platehttp://en.wikipedia.org/wiki/Oceanic_crusthttp://en.wikipedia.org/wiki/Oceanic_crusthttp://en.wikipedia.org/wiki/Oceanic_crusthttp://en.wikipedia.org/wiki/File:Spreading_ridges_volcanoes_map-en.svghttp://en.wikipedia.org/wiki/File:Spreading_ridges_volcanoes_map-en.svghttp://en.wikipedia.org/wiki/File:Spreading_ridges_volcanoes_map-en.svghttp://en.wikipedia.org/wiki/File:Spreading_ridges_volcanoes_map-en.svghttp://en.wikipedia.org/wiki/Oceanic_crusthttp://en.wikipedia.org/wiki/Tectonic_platehttp://en.wikipedia.org/wiki/Mid-oceanic_ridgeshttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Plate_tectonicshttp://en.wikipedia.org/wiki/Volcanologyhttp://en.wikipedia.org/wiki/Volcano#cite_note-3http://en.wikipedia.org/wiki/Roman_mythologyhttp://en.wikipedia.org/wiki/Roman_mythologyhttp://en.wikipedia.org/wiki/Vulcan_(mythology)http://en.wikipedia.org/wiki/Aeolian_Islandshttp://en.wikipedia.org/wiki/Vulcanohttp://en.wikipedia.org/wiki/Volcano#External_linkshttp://en.wikipedia.org/wiki/Volcano#Further_readinghttp://en.wikipedia.org/wiki/Volcano#Referenceshttp://en.wikipedia.org/wiki/Volcano#See_alsohttp://en.wikipedia.org/wiki/Volcano#Traditional_beliefs_about_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Volcanoes_on_other_planetary_bodieshttp://en.wikipedia.org/wiki/Volcano#Effects_of_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Decade_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Volcano_warning_schemes_of_the_United_Stateshttp://en.wikipedia.org/wiki/Volcano#Volcanic-alert_levelhttp://en.wikipedia.org/wiki/Volcano#Technical_classification_of_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Dormanthttp://en.wikipedia.org/wiki/Volcano#Extincthttp://en.wikipedia.org/wiki/Volcano#Activehttp://en.wikipedia.org/wiki/Volcano#Popular_classification_of_volcanoeshttp://en.wikipedia.org/wiki/Volcano#Volcanic_activityhttp://en.wikipedia.org/wiki/Volcano#Lava_texturehttp://en.wikipedia.org/wiki/Volcano#Lava_composition

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ridges due to the pull of the tectonic plates, the release of pressure leads toadiabaticexpansion and

the partial melting of themantle,causing volcanism and creating new oceanic crust. Mostdivergent

plate boundariesare at the bottom of the oceans; therefore, most volcanic activity is submarine,

forming new seafloor.Black smokers(also known as deep sea vents) are an example of this kind of

volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed, forexample,Iceland.

Convergent plate boundaries

Main article:Convergent boundary

Subduction zonesare places where two plates, usually an oceanic plate and a continental plate,

collide. In this case, the oceanic plate subducts, or submerges under the continental plate forming a

deep ocean trench just offshore. In a process calledflux melting,water released from the subducting

plate lowers the melting temperature of the overlying mantle wedge, creatingmagma.This magma

tends to be veryviscousdue to its highsilicacontent, so often does not reach the surface and cools

at depth. When it does reach the surface, a volcano is formed. Typical examples of this kind of

volcano areMount Etnaand the volcanoes in thePacific Ring of Fire.

"Hotspots"

Main article:Hotspot (geology)

"Hotspots"is the name given to volcanic areas believed to be formed bymantle plumes,which are

hypothesized to be columns of hot material rising from the core-mantle boundary in a fixed space

that causes large-volume melting. Because tectonic plates move across them, each volcano

becomes dormant and is eventually reformed as the plate advances over the postulated plume.

TheHawaiian Islandshave been suggested to have been formed in such a manner, as well as

theSnake River Plain,with theYellowstone Calderabeing the part of the North American plate

currently above the hot spot. This theory is currently under criticism, however.[2]

Volcanic features

Lakagigarfissure vent inIceland,source of the major world climate alteration of 178384.

http://en.wikipedia.org/wiki/Adiabatic_processhttp://en.wikipedia.org/wiki/Adiabatic_processhttp://en.wikipedia.org/wiki/Mantle_(geology)http://en.wikipedia.org/wiki/Mantle_(geology)http://en.wikipedia.org/wiki/Mantle_(geology)http://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Black_smokerhttp://en.wikipedia.org/wiki/Black_smokerhttp://en.wikipedia.org/wiki/Black_smokerhttp://en.wikipedia.org/wiki/Icelandhttp://en.wikipedia.org/wiki/Icelandhttp://en.wikipedia.org/wiki/Icelandhttp://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Subduction_zoneshttp://en.wikipedia.org/wiki/Subduction_zoneshttp://en.wikipedia.org/wiki/Flux_meltinghttp://en.wikipedia.org/wiki/Flux_meltinghttp://en.wikipedia.org/wiki/Flux_meltinghttp://en.wikipedia.org/wiki/Magmahttp://en.wikipedia.org/wiki/Magmahttp://en.wikipedia.org/wiki/Magmahttp://en.wikipedia.org/wiki/Viscoushttp://en.wikipedia.org/wiki/Viscoushttp://en.wikipedia.org/wiki/Viscoushttp://en.wikipedia.org/wiki/Silicahttp://en.wikipedia.org/wiki/Silicahttp://en.wikipedia.org/wiki/Mount_Etnahttp://en.wikipedia.org/wiki/Mount_Etnahttp://en.wikipedia.org/wiki/Mount_Etnahttp://en.wikipedia.org/wiki/Pacific_Ring_of_Firehttp://en.wikipedia.org/wiki/Pacific_Ring_of_Firehttp://en.wikipedia.org/wiki/Pacific_Ring_of_Firehttp://en.wikipedia.org/wiki/Hotspot_(geology)http://en.wikipedia.org/wiki/Hotspot_(geology)http://en.wikipedia.org/wiki/Hotspot_(geology)http://en.wikipedia.org/wiki/Hotspot_(geology)http://en.wikipedia.org/wiki/Hotspot_(geology)http://en.wikipedia.org/wiki/Hotspot_(geology)http://en.wikipedia.org/wiki/Mantle_plumehttp://en.wikipedia.org/wiki/Mantle_plumehttp://en.wikipedia.org/wiki/Mantle_plumehttp://en.wikipedia.org/wiki/Hawaiian_Islandshttp://en.wikipedia.org/wiki/Hawaiian_Islandshttp://en.wikipedia.org/wiki/Hawaiian_Islandshttp://en.wikipedia.org/wiki/Snake_River_Plainhttp://en.wikipedia.org/wiki/Snake_River_Plainhttp://en.wikipedia.org/wiki/Snake_River_Plainhttp://en.wikipedia.org/wiki/Yellowstone_Calderahttp://en.wikipedia.org/wiki/Yellowstone_Calderahttp://en.wikipedia.org/wiki/Volcano#cite_note-Foulger-2http://en.wikipedia.org/wiki/Volcano#cite_note-Foulger-2http://en.wikipedia.org/wiki/Volcano#cite_note-Foulger-2http://en.wikipedia.org/wiki/Lakihttp://en.wikipedia.org/wiki/Lakihttp://en.wikipedia.org/wiki/Icelandhttp://en.wikipedia.org/wiki/Icelandhttp://en.wikipedia.org/wiki/Icelandhttp://en.wikipedia.org/wiki/File:Lakagigar_Iceland_2004-07-01.jpghttp://en.wikipedia.org/wiki/File:Lakagigar_Iceland_2004-07-01.jpghttp://en.wikipedia.org/wiki/File:Lakagigar_Iceland_2004-07-01.jpghttp://en.wikipedia.org/wiki/File:Lakagigar_Iceland_2004-07-01.jpghttp://en.wikipedia.org/wiki/Icelandhttp://en.wikipedia.org/wiki/Lakihttp://en.wikipedia.org/wiki/Volcano#cite_note-Foulger-2http://en.wikipedia.org/wiki/Yellowstone_Calderahttp://en.wikipedia.org/wiki/Snake_River_Plainhttp://en.wikipedia.org/wiki/Hawaiian_Islandshttp://en.wikipedia.org/wiki/Mantle_plumehttp://en.wikipedia.org/wiki/Hotspot_(geology)http://en.wikipedia.org/wiki/Hotspot_(geology)http://en.wikipedia.org/wiki/Pacific_Ring_of_Firehttp://en.wikipedia.org/wiki/Mount_Etnahttp://en.wikipedia.org/wiki/Silicahttp://en.wikipedia.org/wiki/Viscoushttp://en.wikipedia.org/wiki/Magmahttp://en.wikipedia.org/wiki/Flux_meltinghttp://en.wikipedia.org/wiki/Subduction_zoneshttp://en.wikipedia.org/wiki/Convergent_boundaryhttp://en.wikipedia.org/wiki/Icelandhttp://en.wikipedia.org/wiki/Black_smokerhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Divergent_boundaryhttp://en.wikipedia.org/wiki/Mantle_(geology)http://en.wikipedia.org/wiki/Adiabatic_process

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Skjaldbreiur,a shield volcano whose name means "broad shield"

The most common perception of a volcano is of aconicalmountain, spewinglavaand

poisonousgasesfrom acraterat its summit; however, this describes just one of the many types of

volcano. The features of volcanoes are much more complicated and their structure and behavior

depends on a number of factors. Some volcanoes have rugged peaks formed bylava domesrather

than a summit crater while others havelandscapefeatures such as massiveplateaus.Vents that

issue volcanic material (includinglavaandash)and gases (mainlysteam and magmatic gases)can

develop anywhere on thelandformand may give rise to smaller cones such asPuu on a flank

of Hawaii'sKlauea.Other types of volcano includecryovolcanoes(or ice volcanoes), particularly on

some moons ofJupiter,Saturn,andNeptune;andmud volcanoes,which are formations often not

associated with known magmatic activity. Active mud volcanoes tend to involve temperatures much

lower than those ofigneousvolcanoes except when the mud volcano is actually a vent of an igneous

volcano.

Fissure vents

Main article:Fissure vent

Volcanic fissure ventsare flat, linear cracks through whichlavaemerges.

Shield volcanoes

Main article:Shield volcano

Shield volcanoes, so named for their broad, shield-like profiles, are formed by the eruption of low-

viscosity lava that can flow a great distance from a vent. They generally do not explode

catastrophically. Since low-viscosity magma is typically low in silica, shield volcanoes are more

common in oceanic than continental settings. The Hawaiian volcanic chain is a series of shield

cones, and they are common inIceland,as well.

Lava domes

Main article:Lava dome

Lava domesare built by slow eruptions of highly viscous lava. They are sometimes formed within

the crater of a previous volcanic eruption, as in the case ofMount Saint Helens,but can also form

independently, as in the case ofLassen Peak.Like stratovolcanoes, they can produce violent,

explosive eruptions, but their lava generally does not flow far from the originating vent.

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Cryptodomes

Cryptodomesare formed when viscous lava is forced upward causing the surface to bulge.

The1980 eruption of Mount St. Helenswas an example; lava beneath the surface of the mountain

created an upward bulge which slid down the north side of the mountain.

Volcanic cones (cinder cones)

Main articles:volcanic coneandCinder cone

Izalco (volcano)located in theCordillera de Apanecavolcanic range complex in El Salvador, only a few generations

old, is the youngest and most well known cone volcano. Izalco erupted almost continuously from 1770 (when it

formed) to 1958 earning it the nickname of "Lighthouse of the Pacific".

Volcanic conesor cinder conesresult from eruptions of mostly small pieces

ofscoriaandpyroclastics(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 meters high. Most cinder cones erupt onlyonce.Cinder cones may form asflank

ventson larger volcanoes, or occur on their own.Parcutinin Mexico andSunsetCraterinArizonaare examples of cinder cones. InNew Mexico,Caja del Riois avolcanic fieldof

over 60 cinder cones.

Based on satellite images it was suggested that cinder cones might occur on other terrestrial bodies

in the Solar system too; on the surface of Mars and the Moon.[4][5][6][7]

Stratovolcanoes (composite volcanoes)

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Cross-section through astratovolcano(vertical scale is exaggerated):

1. Large magma chamber2. Bedrock

3. Conduit (pipe)4. Base5. Sill6. Dike

7. Layers of ash emitted by the volcano8. Flank

9. Layers of lava emitted by the volcano10. Throat

11. Parasitic cone12. Lava flow13. Vent14. Crater

15. Ash cloud

Main article:Stratovolcano

Stratovolcanoesor composite volcanoesare tall conical mountains composed of lava flows and

other ejecta in alternate layers, thestratathat gives rise to the name. Stratovolcanoes are also

known as composite volcanoes because they are created from multiple structures during different

kinds of eruptions. Strato/composite volcanoes are made of cinders, ash, and lava. Cinders and ash

pile on top of each other, lava flows on top of the ash, where it cools and hardens, and then the

process repeats. Classic examples includeMt. Fujiin Japan,Mayon Volcanoin the Philippines,

andMount VesuviusandStromboliin Italy.

Throughout recorded history,ashproduced by theexplosive eruptionof stratovolcanoes has posed

the greatest volcanic hazard to civilizations. Not only do stratovolcanoes have greater pressure buildup from the underlying lava flow than shield volcanoes, but their fissure vents andmonogenetic

volcanic fields(volcanic cones) have more powerful eruptions, as they are many times

underextension.They are also steeper than shield volcanoes, with slopes of 3035 compared to

slopes of generally 510, and their loosetephraare material for dangerouslahars.[8]

Supervolcanoes

Main article:Supervolcano

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See also:List of largest volcanic eruptions

A supervolcanousually has a largecalderaand can produce devastation on an enormous,

sometimes continental, scale. Such volcanoes are able to severely cool global temperatures for

many years after the eruption due to the huge volumes ofsulfurand ash released into the

atmosphere. They are the most dangerous type of volcano. Examples include:Yellowstone

CalderainYellowstone National ParkandValles CalderainNew Mexico(both western United

States);Lake Taupoin New Zealand;Lake TobainSumatra,Indonesia;Ngorongoro Craterin

Tanzania; andKrakatoanearJavaand Sumatra, Indonesia. Because of the enormous area they

may cover, supervolcanoes are hard to identify centuries after an eruption. Similarly,large igneous

provincesare also considered supervolcanoes because of the vast amount ofbasaltlava erupted

(even though the lava flow isnon-explosive).

Submarine volcanoes

Main article:Submarine volcano

Submarine volcanoesare common features of the ocean floor. In shallow water, active volcanoes

disclose their presence by blasting steam and rocky debris high above the ocean's surface. In the

ocean's deep, the tremendous weight of the water above prevents the explosive release of steam

and gases; however, they can be detected byhydrophonesand discoloration of water because

ofvolcanic gases.Pillow lavais a common eruptive product of submarine volcanoes and is

characterized by thick sequences of discontinuous pillow-shaped masses which form under water.

Even large submarine eruptions may not disturb the ocean surface due to the rapid cooling effect

and increased buoyancy of water (as compared to air) which often causes volcanic vents to form

steep pillars on the ocean floor.Hydrothermal ventsare common near these volcanoes, andsomesupport peculiar ecosystemsbased on dissolved minerals. Over time, the formations created by

submarine volcanoes may become so large that they break the ocean surface as new islands or

floatingpumice rafts.

Subglacial volcanoes

Main article:Subglacial volcano

Subglacial volcanoesdevelop underneathicecaps.They are made up of flat lava which flows at

the top of extensive pillow lavas andpalagonite.When the icecap melts, the lava on top collapses,

leaving a flat-topped mountain. These volcanoes are also calledtable mountains, tuyas,or

(uncommonly) mobergs. Very good examples of this type of volcano can be seen in Iceland,

however, there are also tuyas inBritish Columbia.The origin of the term comes fromTuya Butte,

which is one of the several tuyas in the area of the Tuya RiverandTuya Rangein northern British

Columbia. Tuya Butte was the first suchlandformanalyzed and so its name has entered the

geological literature for this kind of volcanic formation. TheTuya Mountains Provincial Parkwas

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recently established to protect this unusual landscape, which lies north ofTuya Lakeand south of

theJennings Rivernear the boundary with theYukon Territory.

Mud volcanoes

Main article:Mud volcano

Mud volcanoesor mud domesare formations created by geo-excreted liquids and gases, although

there are several processes which may cause such activity. The largest structures are 10 kilometers

in diameter and reach 700 meters high.

http://en.wikipedia.org/wiki/Tuya_Lakehttp://en.wikipedia.org/wiki/Tuya_Lakehttp://en.wikipedia.org/wiki/Tuya_Lakehttp://en.wikipedia.org/wiki/Jennings_Riverhttp://en.wikipedia.org/wiki/Jennings_Riverhttp://en.wikipedia.org/wiki/Jennings_Riverhttp://en.wikipedia.org/wiki/Yukon_Territoryhttp://en.wikipedia.org/wiki/Yukon_Territoryhttp://en.wikipedia.org/wiki/Yukon_Territoryhttp://en.wikipedia.org/wiki/Mud_volcanohttp://en.wikipedia.org/wiki/Mud_volcanohttp://en.wikipedia.org/wiki/Mud_volcanohttp://en.wikipedia.org/wiki/Mud_volcanohttp://en.wikipedia.org/wiki/Yukon_Territoryhttp://en.wikipedia.org/wiki/Jennings_Riverhttp://en.wikipedia.org/wiki/Tuya_Lake