How does a volcanic eruption occur?

The probability of an active volcano erupting today or tomorrow is not very high. After all, volcanologists already call a volcano “active” when it has erupted within the last ten thousand years. But if it is a volcanic eruption, the consequences can be enormous.

Perhaps the most famous example is that of Pompeii. Nearly two thousand years ago, the city disappeared under a thick layer of ash after an eruption of Vesuvius. And in 2021, a volcanic eruption on the Spanish island of La Palma caused millions of euros in damage.

Most volcanoes form at the edges of tectonic plates.

There are more than fifteen hundred active volcanoes in the world, but none of them are nearby. No wonder, because most volcanoes sit on the boundary of two tectonic plates, just like earthquakes. When one plate slides under another, so much heat is released beneath the earth’s crust that part of such a plate melts. This molten rock, also called magma, then rises from the earth’s mantle and breaks through the earth’s crust. The consequence? A Vulcano.

But not all volcanoes form on the fault line of two plates. Hotspot volcanoes are located in the middle of a tectonic plate, in places where the earth’s crust is relatively thin. This allows magma to easily rise and break through the earth’s crust. An example of this can be found on the Canary Island of La Palma, where an eruption in 2021 caused a lot of damage.

How does a volcanic eruption occur?

Most eruptions happen when the pressure under a volcano’s crust gets too high, so the magma can only go one way: up. When molten rock flows from a volcano, it is no longer called magma but lava. The temperature of these lava flows can reach over a thousand degrees Celsius. The flowing rock puts the lives of local residents at risk, as do the toxic ash clouds that are often released during a volcanic eruption. Yet some people consciously choose to live near an active volcano, for example because of the fertile soil or because of tourism, which is an important economic sector in many places.

Underground and underwater volcanic eruptions

In addition to underground volcanic eruptions like in La Palma, there are also underwater volcanic eruptions. In January 2022, a large underground volcano erupted in Tonga. The volcanic eruption also triggered a tsunami, killing three people.

Tonga is located in the Ring of Fire, a horseshoe-shaped area on the edge of the Pacific Ocean where many earthquakes and volcanic eruptions occur. Although we live far from here in Europe, there are also two underground volcanoes on Dutch territory: two dead volcanoes in the North Sea and in the Wadden Sea.

In 2020, the Geological Survey of the Netherlands discovered the Mulciber volcano, located 100 kilometers northwest of Texel. Fifty years earlier, a volcano was also discovered in the Wadden Sea: the Zuidwal volcano. In both cases, these are dead volcanoes that will no longer erupt. In the Caribbean part of the Netherlands, on Saba and Sint Eustatius, there are two active volcanoes: Mount Scenery and The Quill.

Can we predict a volcanic eruption?

Worldwide, up to eight hundred million people live near an active volcano. Some of the active volcanoes are monitored with sensors, but by no means all of them. A system based on satellite images and artificial intelligence should facilitate the prediction of volcanic eruptions in the future.

Yet a volcanic eruption often does not occur completely out of the blue. The deformations of the bedrock, the increase in temperature and the emission of gases are all warning signs of volcanic activity. But predicting exactly when a volcano will erupt – and when to evacuate? It remains difficult. For example, no one saw the volcanic eruption on White Island in New Zealand coming.

Willeke van Doorn studied journalism, traveled the world for a while and ended up working for Quest, National Geographic and Runner’s World editors via the US, Australia and New Zealand. She is curious about the world, prefers to travel every month and always takes her running shoes with her.