VOLCANO

Nature Description:

A

Volcano

is an opening, 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. 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.

The most common perception of a volcano is of a conical mountain, spewing lava and poisonous gases from a crater at its summit. This describes just one of many types of volcano, and the features of volcanoes are much more complicated. The structure and behavior of volcanoes depends on a number of factors. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater, whereas others present landscape features such as massive plateaus. Other types of volcano include cryovolcanoes, particularly on some moons of Jupiter, Saturn and Neptune; and mud volcanoes which are formations often not associated with known magmatic activity. Active mud volcanoes tend to involve temperatures much lower than those of igneous volcanoes, except when a mud volcano is actually a vent of an igneous volcano.

Lava

domes are built by slow eruptions of highly viscous lavas. They are sometimes formed within the crater of a previous volcanic eruption, but can also form independently, as in the case of Lassen Peak. Cryptodomes are formed when viscous lava forces its way up and causes a bulge.