How do volcanoes form?

                           *_How do volcanoes

    Deep inside Earth, between the molten iron core and the thin crust
at the surface, there is a solid body of rock called the *mantle*. When
rock from the mantle melts, moves to the surface through the crust, and
releases pent-up gases, volcanoes erupt.
    Extremely high temperature and pressure cause the rock to melt and
become liquid rock or *magma*. When a large body of magma has formed, it
rises thorugh the denser rock layers toward Earth's surface.  Magma that
has reached the surface is called *lava*.}}



Volcano - Wikipedia, the free encyclopedia


** Volcano **

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This article is about the geological feature. For other uses, see Volcano
"Volcanic" redirects here. For other uses of "volcanic", see Volcanic
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Cleveland Volcano in the Aleutian Islands of Alaska photographed from the
International Space Station, May 2006.
Ash plumes reached a height of 19 km during the climactic eruption at
Mount Pinatubo, Philippines in 1991.

A *volcano* is an opening, or rupture, in a planet's surface or crust,
which allows hot magma, volcanic ash and gases to escape from the magma
chamber below the surface.

Volcanoes are generally found where tectonic plates are diverging or
converging. A mid-oceanic ridge, for example the Mid-Atlantic Ridge, has
examples of volcanoes caused by divergent tectonic plates pulling apart;
the Pacific Ring of Fire has examples of volcanoes caused by convergent
tectonic plates coming together. By contrast, volcanoes are usually not
created where two tectonic plates slide past one another. Volcanoes can
also form where there is stretching and thinning of the Earth's crust in
the interiors of plates, e.g., in the East African Rift, the Wells
Gray-Clearwater volcanic field and the Rio Grande Rift in North America.
This type of volcanism falls under the umbrella of "Plate hypothesis"
volcanism.^[1] 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.

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


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