Iceland’s Tremors: Unraveling the Earth’s Secrets on the Reykjanes Peninsula

Lava field from the 2021 Fagradalsfjall eruption. Tamsin Mather, Author provided (no reuse)

The Reykjanes peninsula in southwest Iceland experienced a significant earthquake swarm on November 10, raising concerns of a potential eruption, the fourth since 2021. Iceland’s geological activity is due to its location on the Mid-Atlantic Ridge, where the North American and Eurasian plates diverge. The brittle surface rocks break as the plates pull apart, releasing strain in bursts.

The Reykjanes peninsula, formed by tectonic forces, undergoes rifting every few hundred years. The current phase involves hundreds of earthquakes, signaling the arrival of magma near the surface. Similar events have occurred globally, such as in northern Iceland (1975-1984) and Afar, Ethiopia (2005-2010).

Magma lubricates the rifting process, rising through fractures in the brittle crust. Monitoring by the Icelandic Meteorological Office, using seismometers and satellite data, tracks ground movements and detects signs of potential eruptions.

The recent earthquake swarm, part of events since early 2020, focuses around the Thorbjörn volcanic system. Surface deformation indicates magma entering the crust, creating a fracture that extends to about 15km depth. While an eruption seems likely, confirmation depends on detecting specific signs like volcanic tremors or shallow earthquakes.

If an eruption occurs beneath the town of Grindavik, similar to the 2021-2023 Fagradalsfjall eruptions, it could pose threats. Gas emissions, combined with burning peat and vegetation, may create toxic air. Pre-emptive evacuations have been considered, particularly if the eruption occurs in Grindavik, similar to the 1973 Eldfell eruption in Heimaey.

If the eruption is at the southern end of the dike, offshore, it could lead to submarine eruptions with small-scale explosions and local ash clouds. While not as widespread as the 2010 Eyjafjallajökull eruption, even a small submarine eruption presents challenges for authorities to manage.