How Do Volcanoes Form?

Guadeloupe is the proud owner of an active volcano called La Soufrière. It´s the highest point of the island and a popular hiking destination. The trail first leads through a magnificent piece of rainforest then up to a steep track where you can climb up to the top of the volcano. You have to be lucky to have a good view from the top. It´s pretty likely that your sight is covered by clouds. The hike on La Soufrière inspired me to learn more about volcanos in general. What is a volcano exactly and how do they form?

What is a volcano?

The National Geographic defines a volcano as “an opening in the Earth´s surface through which lava, volcanic ash, and gases escape“ (National Geographic, s.a.). The word derives from Vulcan, the god of fire in ancient Rome. These people believed that goods are controlling volcanos. ¹

How do volcanos form?

To better comprehend the formation of volcanoes it´s essential to understand the movement of Tectonic plates. Tectonic plates and the Earth’s outer mantle form the lithosphere. ² The majority of geologic activity is caused by the interaction of plates that meet or divide. There are three types of tectonic movement. A convergent movement means that the plates are moving into each other, they are colliding. Divergent plates are drifting apart. Transform plates are moving sideways in relation to one another. ³ Volcanos can be constructed during a divergent or a convergent movement.

Formation of volcanos through a divergent movement of the plates

When the plates move divergently, the Earth’s crust is ripped apart, allowing rising hot magma to flow to the surface. In this zone, volcanos can form, as seen in Iceland. ⁴ The upwelling magma forms a new crust within the plates moving apart from each other. Magma at the edge can rise through this new crust resulting in an explosion. ²

Formation of volcanos through a convergent movement of the plates

Volcanoes can also occur through a convergent movement of the plates. They can either form when an oceanic plate drops beneath another oceanic plate or when an oceanic plate sinks beneath a continental plate. The process that one plate descends underneath another one is called subduction. ⁴  The water of the descending plate is drawn into the mantle above, lowering its melting point. This causes the mantle to melt and form magma. The magma rises to the surface and leaks through the plate above it. This forms a volcano. The Pacific Ocean´s subduction zones form hundreds of volcanoes. This belt is known as the Ring of Fire. ¹

Conclusion

Volcanoes either form through divergent or convergent plate movements. In divergent plate movements, the upwelling magma rises between the plates which are drifting apart. In convergent movements, the magma is formed by the melting of the outer earth mantle. The magma leaks through the plate above it forming a volcano.

If you want to know what happens during a volcanic eruption and how the eruption of a super volcano could affect the climate all over the world, check out my next blog post.

References:

1. National Geographic, s.a. What is a volcano? Available at: https://www.nationalgeographic.org/forces-nature/volcanoes.html [27.11.2022].
2. ClickView, 2021. What are volcanoes and how are they formed? Youtube. Available at: https://www.youtube.com/watch?v=R_pDKyg5YKY [27.11.2022].
3. National Geographic. s.a. Plate Tectonics. Available at : https://www.nationalgeographic.com/science/article/plate-tectonics [27.11.2022].
4. British Geological Survey, s.a. How volcanoes form. Available at: https://www.bgs.ac.uk/discovering-geology/earth-hazards/volcanoes/how-volcanoes-form-2/ [27.11.2022].