Plate tectonics map

Volcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface.

Volcanic processes[link]

Magma from the planet's mantle rises through the planet's crust, if the magma from the mantle reaches the planet's surface it behaves differently depending on the viscosity of the molten constituent rock. Viscous (thick) magma produces volcanoes characterised by explosive eruptions, while non-viscous (runny) magma produce volcanoes characterised by an effusive eruptions pouring large amounts of lava onto the surface.

In some cases, rising magma can cool and solidify without reaching the surface of a planet. Instead, the cooled and solidified igneous mass freezes within the crust of a planet to form an igneous intrusion.

Driving forces of volcanism[link]

Three types of plate boundary.

Movement of molten rock in the planet's mantle, caused by thermal convection currents, coupled with gravitational effects of changes on the earth's surface (erosion, deposition, even asteroid impact and patterns of snow fall and melt) drive plate tectonic motion and ultimately volcanism.

Aspects of volcanism[link]

Volcanoes[link]

Volcanoes are places where magma reaches the earth's surface. The type of volcano depends on the location of the eruption and the consistency of the magma.

Intrusions[link]

These are formed where magma pushes between existing rock, intrusions can be in the form of batholiths, dikes, sills and layered intrusions.

Earthquakes[link]

Earthquakes are generally associated with plate tectonic activity, but some earthquakes are generated as a result of volcanic activity (though that itself is ultimately driven by the same forces).

Hydrothermal vents[link]

These are formed where water interacts with volcanism. These include Geysers, Fumaroles, Hotsprings and Mudpots, they are often used as a source of geothermal energy.

Volcanic winter[link]

The amount of gas and ash emitted by volcanic eruptions has a significant effect on the planet's climate. Large eruptions correlate well with some significant climate change events.

Forming rocks[link]

When the magma cools it crystallises and forms rocks, the type of rock formed depends on the chemical composition of the magma and how rapidly the magma cools. Magma that reaches the surface to become lava cools rapidly resulting in rocks with small crystals such as basalt. Magma that remains trapped below ground in thin intrusions cools slower than magma exposed to the surface and produces rocks with medium sized crystals. Magma that remains trapped in large quantities below ground cools most slowly resulting in rocks with larger crystals - such as granite and gabbro

Existing rocks that come into contact with Magma are often melted by the heat, those that do not come into direct contact with the magma do not melt fully but retain some of their original structure - this process results in changes to the structure of the original rocks changing them so much they become a new type of rock - metamorphic rocks.

Volcanism on other planets[link]

Volcanism is not confined only to Earth, but is thought to be found on any planet which has a solid crust and molten (liquid) mantle. And so its effects should still be found on any planet that has had volcanism at some point in its history. Volcanoes have indeed been clearly observed on other bodies in the solar system; on some, such as Mars, in the shape of mountains that are unmistakably old volcanoes (most notably Olympus Mons), but on Io actual ongoing eruptions have been observed. It can be surmised that volcanism exists on planets and moons of this type in other solar systems as well.

The internal structure of the inner planets.

See also[link]

• Bimodal volcanism
• Continental drift
• Hotspot
• Volcanic arc

References[link]

This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (September 2011)

External links[link]

• "Glossary of Volcanic Terms". G. J. Hudak, University of Wisconsin Oshkosh, 2001. http://www.d.umn.edu/~rmorton/ronshome/Volcanology/VolcanicGlossary.htm. Retrieved 2010-05-07. 
• Crumpler, L. S., and Lucas, S. G. (2001). "Volcanoes of New Mexico: An Abbreviated Guide For Non-Specialists". Volcanology in New Mexico. New Mexico Museum of Natural History and Science Bulletin 18: 5–15. http://www.nmnaturalhistory.org/pdf_files/NMvolcanoes.pdf. Retrieved 2010-04-28. ^{[dead link]}

Walter David Pyle (12 December 1936–8 February 2002) was a professional footballer who played as a centre half in The Football League for Bristol Rovers and Bristol City between 1955 and 1963.

Born in Trowbridge, Pyle started his career playing in his home town for Trowbridge Colts, before graduating to senior side Trowbridge Town in 1954. After a year playing non-League football for them he signed his first professional contract in 1955 when he joined Bristol Rovers. He played 139 League games for Rovers in seven years, but when they were relegated to the Football League Third Division in 1962 he crossed the city to join Bristol City. During his single season with City he played eight games in the Football League, but returned to non-League football at the end of the campaign when he joined Westbury United.

After a year playing for Westbury United he was appointed as their manager, and he remained in the position for two years. Away from football Pyle was landlord of a series of public houses. While playing in Bristol he ran the Pelican in Old Market, before returning to his home county of Wiltshire and running the Horse and Groom in Westbury and then the Kings Arms in Hilperton.

Sources[link]

• Jay, Mike; Byrne, Stephen (1994). Pirates in Profile: A Who's Who of Bristol Rovers Players. Bristol: Potten, Baber & Murray. pp. 214–215. ISBN 0-9524835-0-5. 
• Byrne, Stephen; Jay, Mike (2003). Bristol Rovers Football Club - The Definitive History 1883-2003. Stroud: Tempus. p. 504. ISBN 0-7524-2717-2.