Icelandic Geology 101

Every Icelandic child knows that Iceland is a volcanic island and perhaps not surprising when we have an eruption going on almost in the backyard of the capital area. Remarkably, a third of the nation has already made its way to the eruption site at Fagradalsfjall. Yet, there is good reason to go over the basics behind Iceland’s volcanic activity.

▪️Iceland the Volcano Island
A volcano is considered active if it has erupted in the last 12 thousand years. There are 30 active volcano systems in Iceland and 41 if you include the underwater volcano systems that extend beyond the island itself, for example on the Reykjanes ridge (see map in article showing all volcanic systems in Iceland marked with colors and numbers). Nowhere else on earth are so many volcano systems concentrated in such a small area as in Iceland.
Some volcano systems are “young” and relatively immature. They are characterized by fissure swarms (like the Fagradalsfjall volcano system, no. 11 in the article map). However, the majority of Icelandic volcano systems are so-called central volcanoes (marked with triangles in the picture), which erupt again and again at regular intervals. Central volcanoes have magma chambers where magma gathers until the pressure causes the magma to seek a way out, sometimes with magma intrusions as happened in Holuhraun in 2014 (volcano system no. 21), but sometimes in the caldera itself, as happened in the eruption of Eyjafjallajökull in 2010 (volcano system no. 34) that stopped air traffic for days all over the northern hemisphere.
In Iceland, eruptions occur on average every 4-5 years. The most active volcano system in Iceland is the Grímsvötn volcano system (no. 22 in the picture), which has erupted every ten years for the past 1000 years. The largest volcano system in the country is Bárðarbunga (no. 21 in the picture) from where the Holuhraun eruption in 2014 originated.

▪️ Why Are Eruptions So Common in Iceland?
There are basically two reasons why Iceland is one of the most volcanic areas on earth. On one hand, the land lies on diverging plate boundaries. In Iceland, the plate boundary is marked by the Mid-Atlantic-Ridge that crosses the Atlantic Ocean from north to south and cuts through Iceland. The northwestern part of the country is called the Norð-American plate and moves steadily to the west while the southeastern part of the country is called the Eurasian plate and moves eastwards (see image in article). This constant separation causes magma to have easier access to the earth’s surface through cracks and fissures that form in the crust. When the magma reaches all the way to the surface, a volcano eruption occurs.
On the other hand, Iceland is located directly above a mantle plume which further enhances volcanic activity. Mantle plumes are so-called “hot spots”, where hotter magma rises deep from within the earth towards the surface and puts increased pressure on the earth’s crust. Magma plumes are 200-300°C hotter than the surrounding mantle material and therefore rises towards the surface. As a result, the earth’s crust becomes thinner above mantle plumes, which in turn makes it easier for the magma to break its way to the surface in a volcano eruption.
These two phenomena, the diverging plate boundaries and the mantle plume, are the reason behind Iceland’s intense volcanic activity. The consequences vary in severity. Volcanic eruptions can be extremely violent and destructive, but sometimes we are lucky and get relatively small eruptions (like the one at Fagradalsfjall) that literally allow us to see new land being created (see video in article). But volcanic eruptions are always magnificent to witness and show us, without a doubt, how small and insignificant we are against the forces of nature.

▪️The Lava Nerds

It is worth noting that we [the authors of this article – see image in article] are neither geologists nor volcanologists. However, we are embarrassingly enthusiastic about Icelandic volcanic activity, self-appointed volcanic and lava nerds, so to speak.
We took full advantage of this great interest when we launched the first and only live lava show in the world in Vík, South Iceland. The objective of Icelandic Lava Show was to create an educating yet fun and exciting experience on Icelandic volcanism and lava. We seek information and advice from geologists and volanologist but our main goal is to explain Icelandic geology in a memorable way that everyone can understand.