Volcanism , also spelled vulcanism , any of various processes and phenomena associated with the surficial discharge of molten rock , pyroclastic fragments , or hot water and steam , including volcanoes , geysers , and fumaroles. On Earth , volcanism occurs in several distinct geologic settings. Most of these are associated with the boundaries of the enormous rigid plates that make up the lithosphere —the crust and upper mantle. The majority of active terrestrial volcanoes roughly 80 percent and related phenomena occur where two tectonic plates converge and one overrides the other, forcing it down into the mantle to be reabsorbed.
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Volcanism is the phenomenon of eruption of molten rock magma onto the surface of the Earth or a solid-surface planet or moon, where lava , pyroclastics and volcanic gases erupt through a break in the surface called a vent. Magma from the mantle or lower crust rises through its crust towards the surface. If magma reaches the surface, its behavior depends 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 effusive eruptions pouring large amounts of lava onto the surface. In some cases, rising magma can cool and solidify without reaching the surface. Instead, the cooled and solidified igneous mass crystallises within the crust to form an igneous intrusion.
As magma cools the chemicals in the crystals formed are effectively removed from the main mix of the magma by a process known as fractional crystallization , so the chemical content of the remaining magma evolves as it solidifies slowly. Fresh unevolved magma injections can remobilise more evolved magmas, allowing eruptions from more viscous magmas.
Movement of molten rock in the 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 post-glacial rebound drive plate tectonic motion and ultimately volcanism.
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. These are formed where magma pushes between existing rock, intrusions can be in the form of batholiths , dikes , sills and layered intrusions.
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. These are formed where water interacts with volcanism. The amount of gas and ash emitted by volcanic eruptions has a significant effect on the Earth's climate.
Large eruptions correlate well with some significant climate change events. When magma cools it solidifies and forms rocks. The type of rock formed depends on the chemical composition of the magma and how rapidly it cools. Magma that reaches the surface to become lava cools rapidly, resulting in rocks with small crystals such as basalt.
Some of this magma may cool extremely rapidly and will form volcanic glass rocks without crystals such as obsidian. Magma trapped below ground in thin intrusions cools more slowly than exposed magma 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 may be melted and assimilated into the magma. Other rocks adjacent to the magma may be altered by contact metamorphism or metasomatism as they are affected by the heat and escaping or externally-circulating hydrothermal fluids.
Volcanism is not confined only to Earth, but is thought to be found on any body having a solid crust and fluid mantle. Evidence of volcanism should still be found on any body 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 planetary systems as well. In , scientists found 70 lava flows which formed on the Moon in the last million years. From Wikipedia, the free encyclopedia. This article is about the process that forms volcanoes and other igneous formations. For the 18th century geological theory, see Plutonism. Main article: Plate tectonics. Main article: Volcano. Further information: Types of volcanic eruptions. Main article: Intrusion.
See also: Methods of pluton emplacement. Main article: Volcano tectonic earthquake. Main article: Hydrothermal vents. Main article: Volcanic winter. Main articles: Igneous rock and Metamorphic rock. See also: Geology of solar terrestrial planets. Archived PDF from the original on Retrieved United States Geological Survey.
Archived from the original on March 26, Retrieved May 9, Archived from the original on Reviews of geophysics 38 2 : Retrieved 6 May Types of volcanic eruptions. Subglacial Submarine Surtseyan. Magmatic processes. Liquid phase Igneous minerals Dissolved and exolved gases. Igneous rock Geothermal systems Geothermal gradient anomalies Volcanism. Authority control GND : Categories : Volcanism.
Volcano Facts and Types of Volcanoes
Volcanic Landforms and Surface Features pp Cite as. Two major types of volcanic activity are recognized : fissure eruptions and central eruptions. The broader classification of volcanoes according to characteristics of their eruptions, proposed by Lacroix in and formalized by Sapper in 2 , is summarized in Table I. The general world wide distribution of volcanic belts, with specific location of well-known individual volcanoes, is depicted in Figure 1. Unable to display preview.
I guess the main good effect that volcanoes have on the environment is to provide nutrients to the surrounding soil. Volcanic ash often contains minerals that are beneficial to plants, and if it is very fine ash it is able to break down quickly and get mixed into the soil. Perhaps the best place to look for more information about this would be to look up references about some of the countries where lots of people live in close proximity to volcanoes and make use of the rich soils on volcanic flanks. I suppose another benefit might be the fact that volcanic slopes are often rather inaccessible, especially if they are steep. Thus they can provide refuges for rare plants and animals from the ravages of humans and livestock. Finally, on a very fundamental scale, volcanic gases are the source of all the water and most of the atmosphere that we have today.