Volcano

A volcano is an opening, or rupture, in the surface or crust of the Earth or a planetary mass object, which allows hot lava, volcanic ash and gases to escape from the magma chamber below the surface.

On Earth, 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 not usually 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 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.[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 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 stratosphere. Historically, so-called volcanic winters have caused catastrophic famines.

Contents [hide]

1 Etymology

2 Plate tectonics

2.1 Divergent plate boundaries

2.2 Convergent plate boundaries

2.3 "Hotspots"

3 Volcanic features

3.1 Fissure vents

3.2 Shield volcanoes

3.3 Lava domes

3.4 Cryptodomes

3.5 Volcanic cones (cinder cones)

3.6 Stratovolcanoes (composite volcanoes)

3.7 Supervolcanoes

3.8 Submarine volcanoes

3.9 Subglacial volcanoes

3.10 Mud volcanoes

4 Erupted material

4.1 Lava composition

4.2 Lava texture

5 Volcanic activity

5.1 Popular classification of volcanoes

5.1.1 Active

5.1.2 Extinct

5.1.3 Dormant

5.2 Technical classification of volcanoes

5.2.1 Volcanic-alert level

5.2.2 Volcano warning schemes of the United States

6 Decade volcanoes

7 Effects of volcanoes

8 Volcanoes on other planetary bodies

9 Traditional beliefs about volcanoes

10 See also

11 References

12 Further reading

13 External links

Etymology

The word volcano is derived from the name of Vulcano, a volcanic island in the Aeolian Islands of Italy whose name in turn originates from Vulcan, the name of a god of fire in Roman mythology.[2] The study of volcanoes is called volcanology, sometimes spelled vulcanology.

Plate tectonics

Map showing the divergent plate boundaries (OSR – Oceanic Spreading Ridges) and recent sub aerial volcanoes.

Main article: Plate tectonics

Divergent plate boundaries

Main article: Divergent boundary

At the mid-oceanic ridges, two tectonic plates diverge from one another. New oceanic crust is being

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