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Iceland and Indonesia, very different volcanic eruptions. Why?

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The volcanic eruption of January 14, 2024 took place just 400 meters from the village of Grindavik.

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Unlike recent volcano eruptions in Indonesia, those observed southwest of Reykjavik in Iceland are much less intense. For what? Volcanologist Fiona D'Arcy from McGill University explains.

There are two main types of volcanic eruptions, effusive and explosive , first indicates the scientist.

The first present eruptions without explosions, but characterized by lava flows. The latter are rather composed of projections of magma, rocks, ash and fiery clouds of gas.

A quote from Fiona D'Arcy, McGill University

The researcher notes that Iceland, with its 33 volcanic systems considered active, is a unique place in the world because the island is home to volcanoes with eruptions of both types.

This is because the island is located at the boundary of the North American and Eurasian tectonic plates which are quietly separating, moving North America away from Eurasia along the mid-Atlantic ridge.

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A volcano spews lava and smoke during an eruption in Grindavik, Iceland, December 18, 2023.

For the past eight centuries, the Reykjanes Peninsula, south of the capital Reykjavik, had been spared from volcanic activities. But, since March 2021, five eruptions have been observed in the territory, including the fissures of December 2023 and January 2024, which appeared north of the small Icelandic port town of Grindavik.

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Effusive volcanoes do not have a crater, and the lava flows through cracks that form on the ground or on the side of the cone, explains Fiona D'Arcy.

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The volcanic eruption near Grindavik

The tranquil character of these lava flows contrast with the explosive flow of other Icelandic volcanoes, notably Eyjafjöll, which erupted in 2010. The cloud of ash projected into the atmosphere for more than a week had forced the cancellation of 100 000 aircraft flights, mainly in Europe.

In the current case in Grindavik, it is a volcanic fissure in relatively flat terrain, notes Fiona D'Arcy, who recalls that this “ It is not necessarily the size or height of volcanoes that pose a danger, but rather the type of eruption.”

In this type eruption, lava does not usually erupt explosively, adds Ms. D'Arcy.

In fact, the thinness of the earth's crust in this region facilitates the release of pressure and opens faults that allow magma to quietly escape to the surface, which usually gives authorities more time to react by carrying out, for example, earthworks.

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Workers carry out earthworks to divert lava flow following a volcanic eruption on the outskirts of the town of Grindavik , in Iceland.

Indonesia has nearly 130 active volcanoes that lie in the Pacific Ring of Fire, where the meeting of continental plates causes great pressure and significant seismic and volcanic activity.

The Marapi volcanoes in Sumatra and Merapi in Java, which recently erupted, are quite different from the volcanic activity observed in Grindavik since these behemoths are of the explosive type. Last May, Merapi projected lava more than two kilometers from its crater.

Its magma has a thick and viscous composition, a bit like honey. It tends to trap gases and, much like a soft drink under pressure, opening the magma chamber (or opening a can after shaking it) tends to trigger an explosion .

A quote from Fiona D'Arcy, McGill University

This type of volcano is more dangerous, particularly in inhabited areas, than the current fissures in Iceland from which lava flows appear, continues the volcanologist.

For example, the eruption of the Marapi volcano left at least 22 dead last December.

Additionally, these volcanoes consist of numerous layers of hardened lava and are generally characterized by a conical shape and steep profile. They often have a central crater and have secondary cones on the flanks.

However, cracks like those observed in Iceland are not without danger and can lead to evacuations and wash away buildings, as has been the case in recent days. A man even lost his life falling into one of these cracks.

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