volcanoes

Julie D. per.4



media type="custom" key="5997587" width="206" height="152" align="center"

A **volcano** is an opening, or [|rupture], in a planet's surface or [|crust], which allows hot [|magma], [|ash] and gases to escape from below the surface. The word //volcano// is derived from the name of [|Vulcano] island off [|Sicily] which in turn, was named after [|Vulcan], the [|Roman] god of fire.[|[1]] 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] (called "non-hotspot intraplate volcanism"), such as in the [|African Rift Valley], the [|Wells Gray-Clearwater volcanic field] and the [|Rio Grande Rift] in North America and the European [|Rhine Graben] with its [|Eifel] volcanoes. Volcanoes can be caused by [|mantle plumes]. These so-called [|hotspots], for example at [|Hawaii], can occur far from plate boundaries. Hotspot volcanoes are also found elsewhere in the [|solar system], especially on rocky planets and moons.

[|Subduction zones] are 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. Water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, creating [|magma]. This magma tends to be very [|viscous] due to its high [|silica] content, so often does not reach the surface and cools at depth. When it does reach the surface, a volcano is formed. Typical examples for this kind of volcano are [|Mount Etna] and the volcanoes in the [|Pacific Ring of Fire]. []