Volcano

A volcano is commonly defined as a vent or fissure in the <a href="/facts/Crust_(geology)/FYG1kP4F">crust</a> of a <a href="/facts/Planetary-mass_object/rbPjE6Bx">planetary-mass object</a>, such as <a href="/facts/Earth/HLLmDfj0">Earth</a>, that allows hot <a href="/facts/Lava/q2an5SVN">lava</a>, <a href="/facts/Volcanic_ash/c3cqgBfV">volcanic ash</a>, and <a href="/facts/Volcanic_gas/uu7qYRHS">gases</a> to escape from a <a href="/facts/Magma_chamber/1Rr0cPSa">magma chamber</a> below the surface.
On Earth, volcanoes are most often found where <a href="/facts/List_of_tectonic_plates/CvbfSfeC">tectonic plates</a> are <a href="/facts/Divergent_boundary/wVC8x3Ft">diverging</a> or <a href="/facts/Convergent_boundary/rhgWhQx3">converging</a>, and because most of Earth's plate boundaries are underwater, most volcanoes are found underwater. For example, a <a href="/facts/Mid-ocean_ridge/wYdgdSW3">mid-ocean ridge</a>, such as the <a href="/facts/Mid-Atlantic_Ridge/q1Fgk4P1">Mid-Atlantic Ridge</a>, has volcanoes caused by divergent tectonic plates whereas the Pacific <a href="/facts/Ring_of_Fire/UpRWnP2P">Ring of Fire</a> has volcanoes caused by convergent tectonic plates. Volcanoes resulting from divergent tectonic activity are usually non-explosive whereas those resulting from convergent tectonic activity cause violent eruptions. Volcanoes can also form where there is stretching and thinning of the crust's plates, such as in the <a href="/facts/East_African_Rift/o82Q47Uc">East African Rift</a>, the <a href="/facts/Wells_Gray-Clearwater_volcanic_field/nVEKsKD4">Wells Gray-Clearwater volcanic field</a>, and the <a href="/facts/Rio_Grande_rift/fxNCItmb">Rio Grande rift</a> in North America. Volcanism away from plate boundaries most likely arises from upwelling <a href="/facts/Diapir/3IgntJKj">diapirs</a> from the <a href="/facts/Core%25E2%2580%2593mantle_boundary/EWHuuEdT">core–mantle boundary</a> called <a href="/facts/Mantle_plume/wLXJ0Q4a">mantle plumes</a>, 3,000 kilometres (1,900 mi) deep within Earth. This results in <a href="/facts/Hotspot_(geology)/drIyXSLs">hotspot volcanism</a> or <a href="/facts/Intraplate_volcanism/juIu61FA">intraplate volcanism</a>, in which the plume may cause thinning of the crust and result in a <a href="/facts/Volcanic_island/uD8BN9K7">volcanic island</a> chain due to the continuous movement of the tectonic plate, of which the <a href="/facts/Hawaiian_hotspot/msoGwLPg">Hawaiian hotspot</a> is an example. Volcanoes are usually not created at <a href="/facts/Transform_fault/3VyTyvrE">transform tectonic boundaries</a> where two tectonic plates slide past one another.
Volcanoes, based on their frequency of eruption or volcanism, are referred to as either <a href="/facts/Active_volcano/c2M5upml">active</a> or extinct. Active volcanoes have a history of volcanism and are likely to erupt again while extinct ones are not capable of eruption at all as they have no magma source. "Dormant" volcanoes have not erupted in a long time- generally accepted as since the start of the Holocene, about 12000 years ago- but may erupt again. These categories aren't entirely uniform; they may overlap for certain examples.
Large eruptions can affect atmospheric temperature as ash and droplets of <a href="/facts/Sulfuric_acid/Wom6fymJ">sulfuric acid</a> obscure the Sun and cool Earth's <a href="/facts/Troposphere/JPDQq8cL">troposphere</a>. Historically, large volcanic eruptions have been followed by <a href="/facts/Volcanic_winter/SAnA3nsU">volcanic winters</a> which have caused catastrophic famines.
Other planets besides Earth have volcanoes. For example, volcanoes are very numerous on Venus. Mars has significant volcanoes. In 2009, a paper was published suggesting a new definition for the word 'volcano' that includes processes such as <a href="/facts/Cryovolcanism/YyWhVCJ3">cryovolcanism</a>. It suggested that a volcano be defined as 'an opening on a planet or moon's surface from which <a href="/facts/Magma/hRotHju9">magma</a>, as defined for that body, and/or magmatic gas is erupted.'
This article mainly covers volcanoes on Earth. See § Volcanoes on other celestial bodies and <a href="/facts/Cryovolcano/YyWhVCJ3">cryovolcano</a> for more information.

Volcano open-in-new

Volcano