Fagradalsfjall in Iceland erupting 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 thearea 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 will it last? Why is it called a tourist eruption? Is it possible to come and see the eruption? What are the latest developments of the eruption?
Here we try to answer those questions and discuss the geological history and characteristics of the Faradalsfjall eruption.
Three weeks of shaking
Three weeks before 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 , 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 intruding 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
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 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
The eruption has been changing phases regularly for most of the time it has been ongoing. The activity has been characterized by periods of (1) pulsating activity with fire fountains, (2) steady outflow of lava, and (3) quiet periods where no activity is seen on the surface or the tremor graphs.
The timespan of each phase varies from hours to days. It is unknown what is happening in the quiet periods; if the eruption is paused or continues below the surface in lava tunnels.
Updated figures and maps
The Institute of Earth Sciences at the University of Iceland regularly updates 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 with a steady emission of volcanic gasses.
The eruption has already built up a small lava shield that covers about 5 km2 and the volume is estimated to be about 150 million km3. *
The Icelandic Institute of Natural History has created a 3D map of the Fagradalsfjall area.
* Numbers from October 1, 2021
How long will the eruption last?
That is the million-dollar question that scientists can’t answer. Predicting the duration of eruptions is always tricky and the best indicator is the past eruption history or course of outbreaks of a similar type. Most eruptions last from days to months and the Fagradalsfjall eruption has already become the longest-lasting eruption in the 21st Century in Iceland.
To find the answer we may need to "dig deeper" into the roots of Fagradalsfjall and see what the geochemistry of the magma reveals about its history: The magma comes from a very deep source at the crust/mantle boundary, so there is no way to measure or estimate how large the magma reservoir might be.
The eruption might as well continue for years or decades, our leading volcanologists have said. It has all the characteristics of a shield volcano eruption, and that type of eruption can continue for a very long time. And even though it pauses, we know from similar kinds of eruptions in Surtstey island and Hawaii that they can be in a quiet phase for a while and then pick up the activity.
Latest developments - Will the magma break out in a new area?
The eruption paused on its six-month anniversary, 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. Just under 10.000 earthquakes have been detected, 16 of them between M3-M4.2 at 5-7 km depth, but they are slowly moving upwards in the crust. Most scientists believe that the magma is trying to find a new way out since the former feeding vent collapsed. Therefore, the area around Keilir mountain has now been declared a danger zone due to a possible outbreak.
Visiting the volcano
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 and the possibility to see the volcano in an active phase.
However, if the volcano is quiet, the magnificent crater and the freshly made lava formations are a spectacular sight on their own. Below are some useful links with tips for preparation and how to get there.
Last updated October 6, 2021