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Mantle Plume

Most volcanoes occur at plate boundaries, where two tectonic plates meet. But some volcanoes appear in the middle of a tectonic plate! Scientists had to scramble to find an explanation for this. In 1963, J. Tuzo Wilson proposed a potential solution: the mantle plume hypothesis

An image of the Yellowstone Caldera. This is the product of a mantle plume.

The Yellowstone Caldera is a volcano that lies in the middle of the North American plate!

Mantle Plumes and Hotspots 

A mantle plume is a column of hot rock that rises through the Earth’s mantle. Think about convection currents, or how heat moves through liquids. Hot water rises to the surface, cools down, then sinks back down again. The same thing can happen deep underground. The core of the Earth heats up the rock in the mantle. This rock then rises through the Earth’s mantle to the surface as magma in mantle plumes. 

An illustration of the different types of plate boundaries.

Normally volcanoes appear between 2 divergent plates. Mantle plumes make volcanoes in the middle of convergent plates!

Mantle plumes are shaped a little bit like mushrooms. They have thin stalk-like bodies, and a large, circular end – kind of like a bobblehead figurine! When the end of a mantle plume reaches the lithosphere, it heats up and melts the rock there. Where it touches the lithosphere, two things can form: a flood basalt or a hotspot. 

An image showing the surface of a lava pool.

Normally volcanoes appear between 2 divergent plates. Mantle plumes make volcanoes in the middle of convergent plates!

Flood basalts are basically plateaus of hardened, basaltic lava. A flood basalt appears when a mantle plume melts an area of basalt magma. As huge amounts of basalt lava erupt, they start to pile up. Enough of these eruptions create flood basalts. 
Hotspots develop on top of mantle plumes. The difference is that hotspots are continuously fed by the magma in the mantle plume. They melt the lithosphere to make chambers full of hot magma. These magma reservoirs feed volcanoes that pop up overground. Hotspots exist in Hawaii and Iceland.

An illustration of a volcano cross-section.

Mantle plumes feed magma into the volcanoes.

What can mantle plumes explain?

The mantle plume hypothesis is useful for explaining a lot of things. For one, it can explain why some volcanoes are active in the middle of a tectonic plate. It can also explain how volcanic chains form.
 
Because mantle plumes form so far underground, hotspots have a fixed location. As the upper levels of crust move, new volcanoes form in different locations. These combine into a row of volcanoes, some of which are extinct. An example of this would be the Hawaiian-Emperor seamount – a string of volcanoes on the Pacific plate. 
 

Do They Even Exist?

There’s a lot of evidence for the existence of mantle plumes. However, we still have to remember that mantle plumes are just a hypothesis. This means that they haven’t been proven to be 100% real. After all, it’s very hard to prove something that we can’t see because it happens within the Earth’s crust! So use the mantle plume hypothesis with caution! 

Other Great Resources:

Websites

Study Lesson on the Subject: https://study.com/academy/lesson/mantle-plume-definition-lesson-quiz.html

What is a Hotspot?: http://volcano.oregonstate.edu/what-is-a-hot-spot

Universe Today on Mantle Plumes: https://www.universetoday.com/39700/mantle-plume/

Videos

What are Mantle Plumes?: https://www.youtube.com/watch?v=UcpPA6JkELg

What is a Volcanic Hotspot?: https://www.youtube.com/watch?v=AhSaE0omw9o

Convection Beneath the Earth: https://www.youtube.com/watch?v=nhrbtnIt-Hk

 

Written by: Minh Nguyen