Fagradalsfjall in Iceland erupted in 2021 - revealing its deep roots

The restrained Icelandic volcano Fagradalsfjall on the Reykjanes peninsula stepped into the spotlight on the evening of March 19, 2021, when an eruptive fissure opened in the Geldingadalir valleys.

It had been quiet for over six thousand years and is the first active volcano in the Reykjanes UNESCO Global Geopark area for 800 years.

Some frequently asked questions are: Did it come as a surprise, or did scientists see any precursors? When did the eruption start and how long did it last? Why was it called a tourist eruption? Is it possible to come and see the eruption site? What are the latest developments of the Fagradalsfjall volcano?

Here we try to answer those questions and discuss the geological history and characteristics of the Faradalsfjall eruption and the likelihood of continuation of events in the near future.

Three weeks of shaking

The Icelandic musician Eliza Newman who lives close to the Fagradalsfjall volcano wrote a song about the eruption.

Three weeks prior to the volcanic outbreak, an intense earthquake episode began on the Reykjanes peninsula near Fagradalsfjall mountain. It started with an M5,7 earthquake that stirred people in large parts of Iceland. 

In the following three weeks, we had more than 40.000 earthquakes. However, most of them were small and unnoticed, but several were large enough to leave people in the neighboring town Grindavík and the Reykjavík capital area sleepless. One of them was the musician Eliza Newman, and as expected, she wrote a song about it Fagradalsfjall (you're so pretty), just as she did when the notorious volcano Eyjafjallajökull erupted in 2010.

Waiting with anticipation

Our most experienced geoscientists from the University of Iceland and the Icelandic Met Office interpreted geophysical data from seismometers, GPS stations, and satellites. They concluded that a rapid crustal uplift produced the earthquakes. 

Furthermore, it was clear to them that a magma dike intrusion was the cause. During the three weeks of shaking, the dike was steadily propagating at both ends, and the magma intruded further up in the crust. 

The question everyone was asking was: Will it erupt? 

As the dike grew, anticipation increased, but it was impossible to predict whether the 8 km long dike would manage to touch the surface and end in an outbreak or by freezing in the crust as most basalt magma intrusions do.  

It’s Oh So Quiet - And so peaceful until

Helicopter hovering over the flowing lava from Fagradalsfjall eruption in 2021

The earthquakes finally stopped, and everything was quiet for three days. But on a Friday evening, at 20:45 on March 19, 2021, people in Grindavík town and elsewhere on the Reykjanes peninsula reported a glowing light in the sky. No eruption tremor was detected, so the only way to confirm if an eruption had started was to have a look. 

Later in the evening, scientists onboard a Coast guard helicopter confirmed that an eruptive fissure had opened in Geldingadalir valleys. However, they described it as a tiny eruption, far from populated areas, and not expected to threaten people or properties. 

A typical "tourist" eruption

The eruption has been described as a "tourist eruption," a term commonly used by Icelanders for minor eruptions that can easily be accessed. Of course, the usual thing to do when a volcano erupts is to get as far away as possible. But in Iceland, the "usual" response is the opposite.  So Icelanders started flocking to the eruption site to look at the spectacular show nature was offering. 

The eruption site turned out to be pretty safe with the proper precautions of avoiding the hot lava and gas. The Icelandic voluntary search and rescue teams also immediately showed up to ensure safety at the site, and their valuable work continues while the eruption is ongoing. 

So how big is the "tiny" eruption?

The fissure that first opened was estimated to be 180 m (600 ft) long. The lava flow was soon concentrated in two craters that erupted continuously. There was no explosive activity producing ash plumes, as happened in the Eyjafjallajökull 2010 eruption, causing a shutdown in air traffic over Europe. In this case, the eruption turned out to be an effusive fissure eruption, producing a steady outflow of basaltic lava of about 6 m3 and releasing volcanic gases. 

After a few weeks, new fissures formed and new vents started to open while others became inactive. At one point, six craters were erupting simultaneously. 

The three faces of Fagradalsfjall

A geologist sampling magma for geochemical analysis

The eruption changed phases regularly for most of the time it has was ongoing. The activity was characterized by periods of (1) pulsating activity with fire fountains, (2) steady outflow of lava, and (3)  quiet periods where no activity was seen on the surface or the tremor graphs.

The timespan of each phase varied from hours to days. It is unclear what was happening in the quiet periods; if the eruption was paused or continued below the surface in lava tunnels, but the former is thought to be more likely. Now there has been a pause since September 18, 2021 and the eruption has been officially declared finished by authorities.

Updated figures and maps

The Institute of Earth Sciences at the University of Iceland regularly updated data from the monitoring of the Fagradalsfjall eruption. On September 18, after six months of eruptive activity, the volcanic activity was concentrated in one large crater with a periodic outflow of lava of about 10-12 m3/s. But the day after it paused and has been in a quiet phase since but continues some emission of volcanic gasses.

The eruption built up a small lava shield that covers 4,85 km2 and the volume is estimated to be about 0,15 km3. *

The Icelandic Institute of Natural History has created a 3D map of the Fagradalsfjall area. 

* Numbers from October 1, 2021

Latest developments - Will an eruption break out again?

The eruption paused on its six-month anniversary on September 18, 2021, but 9 days later, on September 27, a new earthquake episode began at the northern end of the magma dike that formed in February-March, about 5 km north of Fagradalsfjall. 

Most scientists believed that the magma was trying to find a new way out since the former feeding vent collapsed. Geophysical data indicated that a new magma dyke formed beside the old one, but this time didn't manage to reach the surface and the episode ended after three weeks.

The area is still thought to be active and magma may be accumulating at depths without being detected, so it will be exciting to see if and when the next dyke starts to form and if we will witness another outbreak in the area in the near future.

Visiting the volcano

Icelanders started flocking to the eruption site to witness the spectacular show nature was offering. 

If you are interested in coming to Iceland to visit the volcano, you might want to stay for a few days to improve your chances of good weather and visibility. 

Even though the volcano is quiet, the magnificent crater and the freshly made lava formations are a spectacular sight on their own and a popular destination. Below you can find links to articles on preparation and how to get there.

And even though you miss this one, one of Iceland's other active volcanoes and volcanic systems that show signs of unrest, is likely to erupt within the following couple of years.