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Volcanism

An image of a volcano erupting - a form of volcanism.

Volcanism is anything having to do with the eruption of a volcano, geyser or fumaroles.

 

What is Volcanism?

Volcanism is anything having to do with the eruption of a volcano. This doesn’t only include lava (molten rock) overflowing from the opening of the volcano. It also includes pyroclastic fragments (parts of rock), as well as hot water or steam. Volcanism takes place both above the surface of Earth, as well as beneath its surface. However, volcanism does not just occur in volcanoes, or even just on Earth! It can occur in geysers and fumaroles and on the planets Mercury, Venus, and  Mars! 
 
What are the Different Types of Volcanism?
 
There are three different types of volcanism: extrusive, intrusive and plutonic.
 

Extrusive

This is when molten lava escapes the Earth and reaches the surface.
 

Intrusive

This is when molten magma cools and hardens beneath the surface of the Earth.
 

Plutonic

This is when molten magma cools and hardens deep beneath the surface of the Earth, far below the crust. This creates igneous rock.
 

Where does Volcanism Occur?

Convergent Boundaries:

 
Volcanism occurs in very specific geographic areas. Most of these are distinguishable by the plates in the Earth’s lithosphere. Most active volcanoes are above two lithospheric plates, one overlapping the other. These plates are very heavy. The weight of the top plate drags the bottom plate down to the Earth’s mantle, where it is then reabsorbed.
 

Many explosive volcanoes form in areas like this in a chain, called island arcs. They can be one long chain (a single arc), or two chains with one in front of the other (a double arc). 

An aerial view of the island Bora-Bora, created by volcanism.

Many islands in the Pacific Ocean, such as Bora-Bora, are island arcs.

Mid-Ocean Ridges

Another type of plate structure where volcanism is found in an oceanic ridge system. This is a mountain range that is underwater, and it’s found in every ocean of the entire world!
 
These plates move away from each other to both sides of the ridge. Magma then comes up from the Earth’s mantle and fills the space in between the two plates. This creates a new ocean floor! This all happens underwater, but occasionally the ridges do rise above the water. This is subaerial volcanism. 
 

Hotspots, and Island Chains

The last type of plate structure is rare but can happen. This is volcanoes forming in the middle of a tectonic plate. Scientists think it is from the plates passing over a hot spot“, where magma has risen close to the surface.
 
These also form in chains. However, you can tell these from others because they move from young volcanoes to older. This is because the older volcanoes are where the plate was. The young volcanoes are the plate moving over the hot spot. 
 
For more information on volcanism, watch this video:

Other Useful Resources:

KidzSearch on Volcanism: https://wiki.kidzsearch.com/wiki/Volcanism

‘Volcanism Facts’ by Kiddle: https://kids.kiddle.co/Volcanism

Smithsonian Volcanism Program: https://volcano.si.edu/

(Video) What is a Volcano: https://www.youtube.com/watch?v=WgktM2luLok

Written by: Lindley Lund