Plate tectonics and formation: That is why there are always volcanic eruptions in Iceland

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A volcano erupted on Iceland’s Reykjanes Peninsula for the fourth time in less than three years on Monday evening. The eruption was preceded by a series of earthquakes that lasted for weeks. But why is Iceland so volcanic?

Iceland was shaped over millions of years by four major geological forces: plate tectonics, volcanism, ice ages and erosion. The island lies directly on the Mid-Atlantic Ridge, the boundary between the Eurasian and North American plates. This 20,000 kilometer long trench runs from southwest to northeast through Iceland.

Plates drift 1 inch apart every year

About 20 million years ago, Iceland’s landmass was formed by volcanism that continues to this day. 80 percent of the island consists of volcanic basalt, small parts of tuff, rhyolite, liparit and lava. With around thirty active volcanoes today, the number is greater than anywhere else in the world, explains Geo magazine.

The most important of the fire-breathing mountains are located along the boundary between the two continental plates. These tectonic plates are diverging, meaning they are drifting about an inch apart every year. Magma rises from the Earth’s mantle and fills the hole left by a volcanic eruption.

Hotspot and glacier

But there is a second force at work beneath the island: a so-called hotspot. Magma rises from a depth of up to 2,900 kilometers. A mushroom-shaped diapir (also called a plume) forms above the hotspot: hot magma continuously flows up through the stem and collects in the cap. While the diapir is stationary, the crustal plate moves over it. Occasionally, the hot, liquid molten rock burns through the solid crust: a volcano erupts, adding new lava to the land.

In a magma chamber beneath an active volcano, rising material accumulates continuously over many years. If this volcano is located under a glacier, the eruption is held back for a long time by the enormous ice cap. In Iceland this is often the case. As a result, the pressure continues to build – until it finally explodes.

Eruptions are unpredictable

The volcanic rock and glass particles break down into fine particles with a maximum diameter of two millimeters, called volcanic ash. The enormous force throws it up to 25 kilometers high into the atmosphere. The island’s glacier cover is therefore the main reason why Icelandic volcanoes erupt more than elsewhere – and often produce huge amounts of ash.

Volcanic eruptions are anything but rare in Iceland. However, they cannot be predicted: the next eruption could happen tomorrow – or many years from now.

Source: Blick