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Cleveland Volcano in the Aleutian Islands of Alaska photographed from the International Space Station, May 2006
convert}} during the climactic explosive eruption at Mount Pinatubo, Philippines in 1991.
A 2007 eruptive column at Mount Etna producing volcanic ash, pumice and lava bombs
Aerial view of the Barren Island, Andaman Islands, India, during an eruption in 1995. It is the only active volcano in South Asia.
Santa Ana Volcano, El Salvador. A close-up aerial view of the nested summit calderas and craters, along with the crater lake.

A volcano is a rupture on the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.

Earth's volcanoes occur because its crust is broken into 17 major, rigid tectonic plates that float on a hotter, softer layer in its mantle.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging. For example, a mid-oceanic ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates pulling apart; the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates coming together. Volcanoes can also form where there is stretching and thinning of the crust's interior plates, e.g., in the East African Rift and the Wells Gray-Clearwater volcanic field and Rio Grande Rift in North America. This type of volcanism falls under the umbrella of "plate hypothesis" volcanism.<ref name=Foulger>{{#invoke:citation/CS1|citation |CitationClass=book }}</ref> Volcanism away from plate boundaries has also been explained as mantle plumes. These so-called "hotspots", for example Hawaii, are postulated to arise from upwelling diapirs with magma from the core–mantle 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 with jet engines where ash particles can be melted by the high operating temperature; the melted particles then adhere to the turbine blades and alter their shape, disrupting the operation of the turbine. Large eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the Earth's lower atmosphere (or troposphere); however, they also absorb heat radiated up from the Earth, thereby warming the upper atmosphere (or stratosphere). Historically, so-called volcanic winters have caused catastrophic famines.


Volcano sections
Intro  Etymology  Plate tectonics  Volcanic features  Erupted material  Decade volcanoes  Effects of volcanoes  Volcanoes on other planetary bodies  Traditional beliefs about volcanoes  See also  References  Further reading  External links  

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