Volcanism
Volcanism (or vulcan activity) is the eruption of magma onto the surface of the Earth.
Magma under the crust is under very great pressure. When folding and faulting occur, cracks or fractures appear. These are lines of weakness.
When these lines of weakness develop downward in the crust and reach the magma, they will release the pressure in the magma. This allows magma to rise up along the lines of weakness and intrude into the crust. Some magma may even reach the Earth's surface as lava.
Volcanoes
Volcanoes are the 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
Intrusive volcanism is when magma is forced into the rocks that make up the Earth's crust. When it cools and become solid while still underground, different features called plutons are formed. The rock formed is intrusive igneous rock.
These plutons will be exposed at the surface of land when the overlying rocks are removed after a long time of denudation (laid bare by erosion).
Major features formed by intrusive volcanicity include: batholith, laccolith, dyke, pipe and sill.
- Batholiths: Have large scale magma that has been solidified at the base of the mountain.
- Dyke: Is a small scale magma cooled within the earths crust that stands vertically to the existing rocks.
- Sill: Is a small scale magma cooled near the earths surface that lies horizontally to the existing rocks.
- Laccolith: A small scale magma that pushes the overlying layers of rocks to form a dome shaped structure.
Extrusions
The molten magma under great pressure forces its way through the fissure of underground rocks and reaches the Earth's surface to form "igneous extrusion". Major extruded materials include gas, liquid and solid.
- Gas - sulphur, hydrogen, carbon dioxide and hot steam (geysers). When uprising magma decreases in pressure suddenly, gases within magma explode to the Earth's surface and cause destruction.
- Solid - pyroclast. Mainly composed of: country rock,[1] fragments of solidified lava and fine materials (volcanic ash and dust). It can be classified by size into volcanic bombs, volcanic blocks, lapilli, volcanic ash and volcanic dust.
- Liquid - lava, hot springs.
Features formed are:
- Caldera: a large depression in a former volcanic site. When it is filled with water it is called a 'caldera lake'.
- Composite cones: a large volcanic mountain formed by solidified lava on the surface.
- Geysers: eruption of hot water and steam shooting into the air at regular intervals.
- Hot springs: springs of hot water that flow out continuously without shooting up into the air.
Volcanism Media
Cross section diagram of Earth showing some settings for volcanism on the planet
Some features of volcanism found in Earth's crust
The high initial temperatures of silicate lavas mean that they emit visible light before cooling.
Eruption of mud at Dashgil mud volcano in Gobustan, Azerbaijan
A gentle, or effusive, volcanic eruption, in which liquid material (lava) gently flows from a vent, in this case in south-eastern Hawai’i island
Satellite animation of the initial ash plume and shockwave of the 2022 Hunga Tonga–Hunga Ha’apai eruption and tsunami. The massive explosive eruption was hundreds of times more powerful than the atomic bomb dropped on Hiroshima.
Diagrammatic representation of a plume on Enceladus
Olympus Mons (Latin, "Mount Olympus"), located on the planet Mars, is the tallest known mountain in the Solar System.
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Notes
- ↑ meaning the rock native to an area
Other websites
- "Glossary of Volcanic Terms". G. J. Hudak, University of Wisconsin Oshkosh, 2001. Retrieved 2010-05-07.