How did the Geldingadalir volcano eruption at Mt. Fagradalsfjall Reykjanes Peninsula start and when will it end?

  • On the second day of the eruption at Geldingadalir Mt. Fagradalsfjall
Apr 17 2021

The period from the initial indication that an eruption was likely at Reykjanes Peninsula up to the time the magma broke through to the surface, tells a fascinating story about volcanic eruptions in Iceland—how a possible eruption is spotted and how the information is communicated to the public. One can also find out how an eruption typically begins in this small volcanic island and observe the deep fascination Icelanders have for eruptions like this one in Geldingadalir.

The long period of earthquakes

When increased seismic activity began north of the town of Grindavík at the beginning of 2020, the immediate and common conclusion was an eruption. This possibility was then repeatedly communicated to geologists, who were well prepared in a country where inhabitants live through 20–25 eruptions in a lifetime, on average.
At that time, the scientific community held the unified opinion that the increased activity did not necessarily point to an eruption, at least not in the short run. There were limited signs of magma accumulation in the crust around the center of the earthquakes. Conversely, most scientists also agreed that the situation was unusual and an eruption within a few months, possibly a few years or decades, was not out of the question. Some earth science jargon has been accepted among Icelanders for a long time as regular communication between the public and the scientists where two contradictory options are possible—one being soon, and the other an unclear event in the near or far future.
In the months that followed the seismic activity, the Reykjanes Peninsula— including Grindavík, the geothermal powerplant of Svartsengi, and the Blue Lagoon—was hit by severe seismic activity, repeatedly shaken by stronger-than-usual earthquakes. With more seismographs and increased monitoring, a large part of the Reykjanes Peninsula, particularly the Mt. Fagradalsfjall volcanic system and its neighboring valleys, was monitored more thoroughly by the University of Iceland, The Icelandic Meteorological Office (IMO), and various other institutions and companies in the field of geology. For months, everything was unstable and living in the region proved to be stressful for the inhabitants, particularly the town of Grindavík.  

The lava field looked small on the second day of the Geldingadalir eruption

The lava field looked small on the second day of the Geldingadalir eruption

The big 5.7 earthquake that changed the mood

On February 24th, 2021, at 10:06 AM, a big earthquake of magnitude 5.7 hit. It was felt by everyone in the Reykjavik capital area as well the Reykjanes Peninsula. In a country where powerful natural forces are integrated into our way of life, it didn’t take a lot of imagination to understand that this was a game-changer. When an unusually high number of big quakes and thousands of smaller ones ensued in the following days, it was evident that the situation was serious. Kristín Jónsdóttir, a scientist and seismologist at the IMO and the leader of the group delegated to deal with natural disasters, was assigned the responsibility of liaising with the media. Although experienced in communicating information, her role was now much more challenging—she and her colleagues had to analyze the rapidly accumulating scientific data and respond to questions that were difficult or almost impossible to answer. Furthermore, it was unusual to have such activity so close to the Reykjavik capital area. From Jónsdóttir’s initial answers, it was clear that the possibility of eruption was climbing higher on the list of possible outcomes of this enormous increase in seismic activity.
The possibility of an eruption was also supported by satellite photos showing magma approaching the surface through the crust in a narrow fissure at the Nátthagi valley, in the eastern part of Mt. Fagradalsfjall. It was evident that the magma was drawing closer to splitting the earth apart, making it possible for a glowing stream to surge up to the surface.

The splash of the magma fire is mesmerizing

The splash of the magma fire is mesmerizing 

The whole nation on alert

Around noon on March 3rd, a period of continuous quakes began, labeled by geologists as a relentless pulse of earthquakes. It pushed all scientists, the entire natural disaster group, and the Department of Civil Protection and Emergency Management to one conclusion: An eruption was imminent, possibly mere hours away. The whole nation was put on high alert. It was a very serious event as it was impossible to predict the fissure's size or the nature or force of the lava flow. Overwhelming facts from prior volcanic activity throughout four centuries, at the time of settlement at the Reykjanes Peninsula, new data from monitoring the area, and satellite photos of the area indicated a relatively small eruption and a fissure that would open at Nátthagi valley. As it was impossible to predict the fissure's length, everyone was asked to stay out of the area.
The nation held its breath as a truckload of earth scientists expressed opinions on social media and various broadcasting services about a possible eruption, staying true to their scientific jargon. Again, the scientific community was reasonably relaxed, and most of our scientists believed that if an eruption occurred, it would be a small lava flow with a limited amount of ash or tephra; no danger to buildings or infrastructure was indicated. However, nothing happened on that day as the magma, despite continuing upwards, kept its place below the surface.

In a matter of hours, the Geldingadalur valley started to disappear under the lava

In a matter of hours, the Geldingadalur valley started to disappear under the lava

The perfect tourist eruption

In the evening of March 3rd and the days that followed, the nationwide alarm appeared to be a “false one”. However, about two weeks later, on the evening of March 19th, a small eruption quietly began. It was small in every sense of the word, at least in the beginning. The fissure that opened was less than 500 meters long and looked like a shallow scratch on the surface; a much longer fissure of 5 or even up to 25 kilometers is not unusual in Iceland's geological history. The flow of magma was moderate, about 5 m/sec, just like a small river. The valley where it opened, Geldingadalir, was remote and also unusually small compared to most other valleys in Iceland, which provided only a small hill for the fissure to form. The mountains surrounding the eruption were also all small. In a matter of hours, the opening had delivered lava to both sides of the fissure and quickly formed a crater that became the flowing magma's main vent. The crater and the glowing lava river instantly became a stunning sight as the eruption quietly began laying a carpet of lava at the bottom of the small valley. It was a relief for the geologists handling national disasters that their reasons for a full national alarm a few days earlier had materialized. They were able to predict an eruption reasonably accurately. However, instead of a national disaster, mother nature had delivered only a small eruption. Immediately the outbreak was labeled “tourist eruption,” meaning that it would be a great attraction and easy to visit. 

The eruption is truly a magnificent sight

The eruption is truly a magnificent sight 

What kind of eruption was it?

It only took a day or two for the main question directed to the earth science community to switch from “will there be an eruption?” to “how long will the eruption last?” One of the leading geologists at the University of Iceland, Professor Magnús Tumi Guðmundsson, flew over the new eruption in a helicopter and confirmed it to be a tiny one, making the statement that it was just a “little punk” (ræfill, in Icelandic). In the days before the event, Kristín Jónsdóttir had often made a statement that the awaited eruption would probably be short and small. True to their jargon, most earth scientists stated that the event was, on the other hand, most likely the beginning of a long eruption period at the Reykjanes Peninsula, an area that had been dormant for more than 800 years but was highly active for centuries before it calmed down. Although most Iceland regions are well documented in the Sagas, the Reykjanes Peninsula is hardly mentioned, most likely because continuing eruptions at the time of settlement around 950 AD made it almost uninhabitable.
In the first two to three days of the small eruption, there was an analytical void among earth scientists as most of their answers were based on research gathered before the eruption. Most scientists assumed that the magma was a typical basalt magma of 1000°C that had slowly accumulated for centuries in the crust and was now pushing its way to the surface, very much in accordance with the many lava flows that had occurred around the time of settlement, from the 9th up until the 13th century. Just like many recent Iceland eruptions originating in magma chambers fed by the mantel plumb, the giant fireball was placed below our little island. However, then came a surprising fact from the geophysicists who had spooned the new glowing magma at Geldingadalir into a small container with water for analysis on the first day of the eruption: The chemical composition was extremely interesting and another game-changer in the short life of this fascinating event. This magma resembled lava that had surfaced at Reykjanes Peninsula around the end of the Ice Age, around 10 to 14 thousand years ago. It was probably the beginning of a lava shield, just like its neighbor (hold your breath) Þráinsskjöldur, a vast lava shield that emerged in a long and slow eruption around 13 thousand years ago. It did not resemble the chemical composition of the lava that surfaced around the settlement, and the temperature was much higher, about 1200°C. This meant that the lava came from a deeper source, about 20 kilometers deep—from the mantle. It also meant that the small eruption could last for (and now the geological jargon came in handy) weeks, months, years, decades, or even centuries, as the supply in the mantle was almost infinite compared to most magma chambers within the crust at a depth of 2 to 5 kilometers. Some geophysicists could hardly conceal their excitement as they presented this discovery to the media. It was much appreciated news everywhere in Iceland. We all know how much the Eyjafjallajökull eruption did for the economy, and that was a volcano you couldn’t even visit!

Two weeks into the volcanic activity, it was clear that this was a spectacular event

Two weeks into the volcanic activity, it was clear that this was a spectacular event

A new permanent natural wonder?

Iceland has many fascinating natural wonders and a variety of colorful landforms and places to experience and visit: waterfalls, basalt columns, icebergs, deep and long canyons, basalt column canyons, erupting hot spring, glaciers, lakes, rivers, ice caves, mountains, fjords, black beaches, black deserts, sea stacks, craters, a magical, colorful rhyolite caldera, and, now, possibly an active volcano you can easily visit and photograph. After the scientific discovery of the massive supply of magma, and the fact that the flow was pushed through a long, possibly 20 km long, “pipe” in the crust at a moderate speed of flow compared to many other eruptions, the question of the length of the eruption became more pressing. Obviously, an easily accessible ongoing eruption would most likely draw a lot of tourists to Iceland. An eruption that was only about 40 minutes’ drive from the Reykjavík capital area and the international airport at Keflavik would obviously become a popular destination. Although we have, on average, about 45 eruptions active on our planet every year, few are as accessible as the volcanic activity in Geldingadalir. It is a rare opportunity for anyone who can make a moderate hike of 9 kilometers, 5 to 6 miles, to experience an eruption and see glowing magma emerging from the ground at only a short distance from where they stand. For many, it is the opportunity of a lifetime. For Iceland, an economic factor was thus added to the volcanic and geological factors.

Even when the weather isnt that good the eruption is spectacular

Even when the weather isn't that good, the eruption is dramatic 

Two weeks into the eruption, over 40 thousand had hiked to the new volcano

Icelanders, as a people, have an interesting behavioral pattern when it comes to eruptions that could be labeled “eruption culture”. This is no wonder since eruptions have been a dominating factor from the time of settlement. Undoubtedly, this trend looks a bit peculiar to people in many other countries, especially where any natural disasters are scarce, as natural forces have limited effects on daily life. People in other parts of the world might feel intimidated and scared when they hear about an eruption as close to their home as the eruption is to Reykjavík, the most populated area on the island. However, in a country where an eruption is part of our daily life, so to speak, we feel the urge to visit it. This is, of course, not always the case, as some eruptions throughout the centuries have been extremely powerful and even devastating. Overall, however, Icelanders have a lot of respect and admiration for volcanos rather than fear. One of our most catastrophic volcanos, Hekla, which has been expected to erupt since 2013, is probably loved more than hated. For centuries Hekla was called the gate to Hell in Europe. If an eruption is accessible, it becomes an invisible magnet that draws inhabitants toward it, and people flock with their families to the fire like a herd of sheep, myself being no exception. This has been the case for decades, although it depends on the nature of the eruption. In the first two weeks of this small eruption, almost 40 thousand people visited the site to view the new crater. Keep in mind that the population in this tiny country is only about 360 thousand. And in times of the COVID-19 pandemic, only a few were people from other countries. The admiration also depends on the nature of the eruption, like this one at Geldingadalir—a simple lava flow with reasonable viscosity and limited amount of ash and tephra—which is our favorite. Sometimes though, we have an eruption where there is only one option: to run away, as the landslide of mud, icebergs, ash, and water flowing from the crater is highly dangerous. This was the case in the glacier/volcano Katla in 1918 or the Skaftáreldar in 1783 that caused extensive difficulties and are defined as major natural disasters. A lot of people who hiked up to Geldingadalir had never seen an eruption before, and without exception, they were amazed by the experience. It is such an unusual and powerful sight.

In three weeks more and more vents had opened

In three weeks more and more vents had opened 

How does an eruption stop?

On the second day of the eruption, most geologists expected the outbreak to fade out in a few days or weeks. At that point, the magma's low flow was thought to come from a magma chamber that would lack the force to continue to push a flow of 5 m/sec through the vent for a long time. A well-known reason why a crater stops delivering is that the lava starts to solidify at the vent and finally closes the crater. If the lava flow drops down to 2 m/sec, the eruption probably stops. In their assessment, geologists referred to other similar eruptions and sizes of lava fields at Reykjanes Peninsula from the time of settlement. Many of those lava fields have been researched quite thoroughly by earth scientists in recent decades.  
After the analysis of the chemical composition of the magma mentioned above, everything changed. For days, the magma's flow was consistent and supported the assumption that this could be a long eruption based on the deep origin, chemical composition, and temperature. There are, of course, other factors that can stop an eruption, like the composition of gases, seismic activity, the temperature of the magma, etc. Given this discovery of the magma's origin, however, the expectation is high that the eruption is a new natural wonder that can be added to all the others to see, experience, and discover in the years to come.
Around April 7th and 9th, both scientists and people visiting Geldingadalir felt that the twin craters' stream was diminishing. Despite the expectation that the flow would be consistent, small changes were noticeable. There was a slight possibility that the eruption would be short-lived, and the craters could close. But then another new sequence of events started, a new game-changer. On April 9th, a new fissure opened north of the main activity in Geldingadalir. In a matter of hours, a new vent opened and formed quite an active crater, delivering a similar magma flow as the original twin craters. Between the two sets of craters, the flow almost doubled, reaching about 9 m/sec. Since then, we have seen a similar course of events where new fissures open up or the magma forces its way through part of the old fissure when active craters fail to deliver the pressure from beneath. On the morning of April 13th, five new craters opened, adding to the flow by up to about 15 m/sec, according to Þorvaldur Þórðarson, Professor of Volcanology.
This development has surprised scientists, who are now experiencing the eruption as a live laboratory set up by nature. 
So, we can expect the eruption to sustain for a long time. The fissure will likely continue to develop and open to the north, stretching to a few kilometers long, in the months to come. Most of the scientific data points to a rather long eruption. However, in accordance with the geological jargon of our highly respected earth scientists, it is also possible that the outbreak will end in a matter of weeks.

More and more lava is poured into the small valley Geldingadalur

More and more lava is poured into the small valley Geldingadalir 

Reasons why you should visit Iceland and the volcanic activity

Currently, there are more reasons to assume that the eruption will continue for months, even years, than to expect it to stop soon. As with nature, the eruption is not relying on forces that can be controlled or governed by men; It depends solely on the forces of nature. So, there is no way we can ever predict the development accurately. Based on our most prominent earth scientists' views and assumptions, there is a good possibility that the eruption and accompanying fascinating volcanic activity will continue for a long time. If you are interested in seeing this unbelievable sight with your own eyes—and experiencing something that is not possible anywhere else on the planet—you should visit us in Iceland and take the hike to the Geldingadalir volcano.

Text and photos: Einar Páll Svavarsson