Eruption has little in common with Eyjafjallajökull

After weeks of anxiety and waiting due to sometimes violent earthquake activity on the Reykjanes Peninsula in Iceland, huge fountains of lava have been shooting out of a fissure up to four kilometers long since last night. Nevertheless, a volcanic disaster like the one in 2010 is not to be expected.

There were already signs of the volcanic spectacle that has now begun in Iceland at the beginning of November, when first the ground uplift and shortly afterwards the earthquake activity in southwest Iceland suddenly shot up. In some cases, there were thousands of earthquakes per day. The main cause for concern was that the activity was very close to the fishing village of Grindavík and deep cracks, fissures and sinkholes opened up in the middle of the village. Even in Iceland, this was anything but a normal occurrence. Some feared that a volcanic eruption could take place in the middle of the village or flood it with lava from outside. Something similar happened in 1973 on the island of Heimaey in the south of Iceland.

By the end of November, however, the situation seemed to have calmed down again. Earthquake activity and ground movement decreased significantly and there was speculation that an eruption might not occur. However, the ground at the famous Blue Lagoon a few kilometers north of Grindavík continued to rise by about one centimeter per day and now reached a critical point again. The ground finally gave way to the steadily increasing pressure from the magma chamber, which is around five kilometers deep, and a fissure around four kilometers long opened up. Since last night, lava fountains have been shooting out of it, some of them over 100 meters high into the air.

The volcanism on Iceland's Reykjanes Peninsula differs from most other known volcanoes in one important respect. This is an active plate boundary where the North American and Eurasian continental plates are drifting apart. In the process, new earth crust is formed by volcanism. The lava that comes to the surface here is very thin and the gases dissolved in it can easily escape like from a bubble bottle. This creates the impressive lava fountains - but no explosive phases with large clouds of ash. This is also known as an effusive eruption.

Danger not yet averted

Because the lava is so fluid, it flows quickly to the sides and does not form a large volcanic cone. As a result, large lava plateaus have already been formed there in the past, as well as the impressive images of glowing lava flows flowing like a river at the neighboring Fagradalsfjall. However, the current eruption is much larger and much closer to the village of Grindavík. It could therefore affect parts of the village and the nearby geothermal power plant. Icelandic volcanologists therefore speak of a "worst-case scenario".

In recent weeks, a large dyke has been built around the famous Blue Lagoon and the geothermal power plant to protect them from lava flows from a possible eruption. However, the exact position of an eruption was only partially foreseeable and could now be so unfavorable that considerable damage could still occur. The eruption is also significantly larger than the eruptions of the last three years at Fagradalsfjall and, according to the news website ruv.is, has already covered several square kilometers of land with lava. Most of the lava is expected to flow northwest into uninhabited areas, but could destroy an important road to Grindavík.

Although the intensity of the eruption has already decreased, it could continue for a long time and therefore affect a large area and even reach the town of Grindavík. The authorities are currently asking people not to drive or travel to the site of the eruption: "We are not dealing with a tourist attraction here."

Air traffic at nearby Keflavík Airport has so far hardly been affected by the eruption, although there are currently some major delays, although the cause is unclear. In any case, some flights are expected to be handled on time. According to the authorities, the European mainland is not expected to be affected in any way, as was the case with the eruption of Eyjafjallajökull in 2010.

The reason for this is that there are several factors in Iceland that influence the type and intensity of eruptions. One is the aforementioned plate tectonics, which mainly leads to effusive fissure eruptions. Only when the lava flows into the ocean or erupts in shallow water can smaller explosions occur, but these are hardly capable of causing problems in a wider area.

Explosive volcanic eruptions have other causes

Explosive eruptions such as that of Eyjafjallajökull, on the other hand, are linked to the hotspot on which Iceland is located and the Icelandic glaciers. Iceland lies above a so-called mantle plume, in which hot material flows thousands of kilometers from the Earth's interior to the surface. More magma, a thicker earth crust and also more viscous lava is formed there, from which the gases can escape less easily. This alone can increase the explosiveness of the eruptions.

Due to the formation of higher volcanic mountains, large glaciers still lie on their peaks in the center of Iceland. If the lava, which is more than a thousand degrees hot, hits the glacier ice, eruptions can turn into an explosive phase in which the lava is torn into tiny pieces by contact with the glacier water and thrown high into the air.

Huge ash clouds can then be formed from fine particles of volcanic rock, which can reach great heights and bring air traffic to a standstill. This is because if the fine rock particles get into the engines of airplanes, they can become lodged there and cause major damage. Aircraft must therefore not fly into such ash clouds under any circumstances.