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. It includes all phenomena resulting from and
causing magma within the crust or mantle of the body, to rise through
the crust and form volcanic rocks on the surface.
1 Volcanic processes
2 Driving forces of volcanism
3 Aspects of volcanism
3.5 Volcanic winter
4 Forming rocks
Volcanism on other bodies
6 See also
8 External links
Non-viscous lava during an effusive eruption of Kīlauea
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.
Driving forces of volcanism
Main article: Plate tectonics
Three types of plate boundary.
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
Aspects of volcanism
Main article: Volcano
Cross-section through a stratovolcano (vertical scale is exaggerated):
Large magma chamber
Layers of ash emitted by the volcano
Layers of lava emitted by the volcano
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.
Further information: Types of volcanic eruptions
Types of Intrusion:
Main article: Intrusion
See also: Methods of pluton emplacement
These are formed where magma pushes between existing rock, intrusions
can be in the form of batholiths, dikes, sills and layered intrusions.
Volcano tectonic earthquake
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. These
include geysers, fumaroles, hotsprings and mudpots, they are often
used as a source of geothermal energy.
Main article: Volcanic winter
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.
Igneous rock and Metamorphic rock
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
Volcanism on other bodies
Main articles: Volcanology of Io, Volcanology of Venus, Volcanology of
Mars, and Geology of Vesta
See also: Geology of solar terrestrial planets
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 2014, scientists found 70 lava
flows which formed on the Moon in the last 100 million years.
The internal structure of the inner planets.
^ "Cooling Planets: Some Background: What is volcanism?" (PDF). The
Lunar and Planetary Institute, Department of Education and Public
Outreach. 2006. p. 4. Retrieved 2012-10-14.
^ Watson, John; Watson, Kathie (January 7, 1998). "Volcanoes and
Earthquakes". United States Geological Survey. Retrieved May 9,
^ a b Nemzer, J. "Geothermal heating and cooling".
^ Robock, Alan (2000). "Volcanic eruptions and climate". Reviews of
geophysics 38 (2): 191-219. doi:10.1029/1998RG000054
Wikimedia Commons has media related to Volcanism.
"Glossary of Volcanic Terms". G. J. Hudak, University of Wisconsin
Oshkosh, 2001. Retrieved 2010-05-07.
Crumpler, L. S., and Lucas, S. G. (2001). "Volcanoes of New Mexico: An
Abbreviated Guide For Non-Specialists" (PDF). Volcanology in New
Mexico. New Mexico Museum of Natural History and Science Bulletin. 18:
5–15. Archived from the original (PDF) on 2007-03-21. Retrieved
2010-04-28. CS1 maint: Uses authors parameter (link)
Types of volcanic eruptions