The Reykjanes Peninsula has made the headlines a lot in the past few weeks due to its volcanic activity. There were points were we believed an eruption was imminent. This got the team at Hidden Iceland wanting to understand what’s going on at a deeper level. So, we’ve invited Dr Holly Spice, who has a PhD in the Geochemistry of Icelandic Basaltic Lavas, to give us a brief overview of what is happening under the ground. She has done an excellent job of explaining the geology in an easy to understand format. Read on to learn all about the Volcanic Activity in the Reykjanes Peninsula. 

GUEST WRITER: Dr Holly Spice

There has been a lot of excitement about earthquakes and a potential volcanic eruption on the Reykjanes Peninsula, just a short distance from Reykjavík. On Wednesday 3rd of March 2021 Icelandic authorities held a press conference and it was reported that an eruption was “imminent”. Thankfully (or ‘disappointingly’ if you’re as obsessed with volcanoes as I am) things have settled down for the moment but that doesn’t mean a volcanic eruption is not going to happen in the future. So I thought it would be a good idea to lay down what’s going on under the ground in this often overlooked part of the country.

Hidden Iceland, who I often guide for, actually run day tours around the Reykjanes Peninsula with a trip into the Raufarhólshellir lava tunnel. If you haven’t been I highly recommend it. Who knows, you might even get me as a guide, if you’re lucky. 

Geology of Reykjanes: An Overview

The Reykjanes Peninsula is a paradise for anyone with an interest in geology and volcanoes. It is located in the south-west of Iceland and hosts Iceland’s main International Airport and the Blue Lagoon which most tourists are familiar with. However, there is so much more to the Reykjanes Peninsula than tourist attractions.

It has been 781 years since the last eruption on Reykjanes

It contains 3 of Iceland’s 30 active volcanic systems and is perhaps the best place in Iceland to see the diversion of the North Atlantic and Eurasian tectonic plates. A feature known as The Mid-Atlantic Ridge. Reykjanes is often overlooked by tourists, however visitors to this area are rewarded with relative solitude and an otherworldly volcanic landscape to explore, with many interesting sites that demonstrate the active volcanism and motion of the tectonic plates.

The Mid-Atlantic Ridge rises out of the ocean on the southwestern tip of the Reykjanes Peninsula.

The arrangement of the plates in the region produces two types of faulting in Reykjanes. The first is extensional faulting as a result of the diverging tectonic plates. This produces northeast-southwest aligned volcanic systems with features typical of extensional tectonics such as fissure faults. There are 3 such active volcanic systems on the Peninsula, which together comprise the Reykjanes Volcanic Belt.

These are from west to east, Reykjanes, Krýsuvík and Brennisteinsfjöll. To the east of the Peninsula lies a 4th volcanic system called Hengill. The second component of faulting on Reykjanes is strike-slip caused by lateral motion of the plates against each other (the most famous example of this is the San Andreas fault in California). This produces a belt of high seismic activity. Earthquakes up to a magnitude of 6.5 are possible in this belt, however quakes above 3.5 have been quite rare historically in the Reykjanes Peninsula until recently. 

Reykjanes Peninsula Volcanic Zones Map.

The arrangement of the active volcanic systems (shown in yellow) and the seismic belt (shown in red) on the Reykjanes Peninsula. Mountains within the Reykjanes Volcanic System where activity has been high recently are marked.

Types of Eruptions

There are two main types of eruptions that produce different volcanic rocks and landscape forms. Effusive volcanic eruptions and sub-glacial volcanic eruptions.

The first, effusive eruptions, are where fluid basaltic lava is erupted by fissures or gentle low-angle volcanoes known as shield volcanoes, resulting in fluid flowing lava that spreads out to form low-lying lava fields. Most of the journey between Keflavík Airport and Rekjavík travels through such lava fields. 

The second eruption type are subglacial eruptions that occurred under ice during periods when the area was covered by glaciers. The introduction of very hot (often over 1000°C) lava melts the ice above the eruption site and results in explosive volcanism that fragments and alters the lava and produces ash. Due to the presence of overlying ice, the volcanic material cannot escape and a structure known as a moberg ridge or cone builds up over the lava vent. These moberg structures stand higher than the surrounding lava plains.

Keilir Mountain. Reykjanes Peninsula. Wikimedia Commons.

The Keilir moberg cone (above) is clearly seen from the road between Keflavík and Reykjavík on the north side of the Reykjanes Peninsula. Keilir was erupted under glacial ice and rises steeply from the surrounding lava fields that were produced by effusive style eruptions. 

Recent volcanism in the Reykjanes Peninsula

Recent volcanism on Reykjanes has been cyclical with 200-300 year periods where eruptions occur frequently, interspersed with years to decades of quiescence, separated by 700-800 year periods during which only seismic activity occurs.

The most recent volcanic period began in the 10th century and ended in 1240 with the Reykjanes Fires, a major event in the Reykjanes Volcanic System between 1210-1240. During that period, several effusive eruptions occurred along fissures 1-10km in length, producing several lava fields that covered about 50km² of land. 

It has been 781 years since the last eruption on Reykjanes and scientists have been warning for some years that the onset of a new phase of volcanic activity could happen in the near future. 

Recent seismic and volcanic activity

Increased activity on Reykjanes began at the end of 2019 with an earthquake swarm and uplift around a volcano called Þorbjörn close to the Blue Lagoon and the town of Grindavík. Measurements indicated an intrusion of magma at a depth of 3-4km and resulted in considerable surface uplift which was measured by GPS instruments.

Uplift at Mount Thorbjorn. ISOR.

The Surface uplift in mm of the area around Þorbjörn, between January and March 2020, as a result of magma intrusion. Location of earthquakes are also shown. 

Frequent earthquake activity continued regularly on Reykjanes throughout 2020.

I witnessed the ground moving as the earthquake waves arrived.

A large earthquake swarm with earthquakes up to 5.1 in magnitude occurred in the Fagradalsfjall area in July. Increased activity continued in the region until a 5.6 magnitude earthquake struck the area near the boundary of the Reykjanes and Krýsuvík Volcanic Systems in October, which was strongly felt in Reykjavík and South Iceland. Many thousands of aftershocks followed the main earthquake and regular earthquake activity has continued on the Reykjanes and Krýsuvík Volcanic Systems.

On the 24th of February 2021, a 5.7 magnitude earthquake shook the region close to Keilir and Fagradalsfjall. This was widely felt across South Iceland. The earthquake triggered small landslides and avalanches on steep slopes close to the epicentre. No buildings were seriously damaged. At the time of writing, over 22,000 earthquakes have been recorded in this ongoing seismic episode.

On the ground observation

A few hours after the 5.7 magnitude earthquake epicenter, I took a walk in the area to see the changes myself. I observed avalanche debris triggered by the earthquake. A 4.8 aftershock struck a few hundred meters from me while I was walking in the hills and I witnessed the ground moving as the earthquake waves arrived. An awesome experience!

Avalanche in the Reykjanes Peninsula. Photo by Dr Holly Spice. Hidden Iceland.

Location of earthquake activity on Reykjanes when the tremor was detected on Wednesday afternoon.

On the afternoon of the 3rd of March, authorities warned that an eruption may be imminent in the Keilir/Fagradalsfjall area in the Reyjanes Peninsula. This was due to the detection of tremor, a type of seismic signal that has previously been detected immediately ahead of other volcanic eruptions in Iceland and is thought to be caused by moving magma close to the surface. The tremor was accompanied by an increase in earthquake activity. However, detailed analysis of the data revealed that the tremor was instead caused by injection of magma, which has a different frequency to the tremor that usually precedes eruptions.

What’s happening now?

Since Wednesday the tremor has died out and an eruption has not yet occurred. However, the earthquake swarm is still ongoing at the time of writing. Scientists say that magma is moving laterally in a vertical intrusion along a corridor that is around 5km in length and 1 meter wide (known to geologists as a dyke).

The top of the magma is around 1km deep in the crust and is present down to at least 6km. For an eruption to happen the magma must find a way to the surface. There is currently no evidence to suggest that the magma is moving quickly upwards, so an eruption is presently unlikely, however the situation could change rapidly and new magma continues to flow into the intrusion every day. The area is being closely monitored for the possibility of tremor that precedes eruptions and the authorities are making contingency plans for a potential eruption.

What will happen next in the Reykjanes Peninsula?

It is impossible to know for sure how the situation will evolve. However, there are several possible scenarios that scientists consider likely to occur:

  1. Seismic activity dies out over the next few days/weeks.

  2. Seismic activity increases with larger earthquakes which may reach up to magnitude 6 in the Fagradalsfjall area.

  3. An earthquake up to magnitude 6.5 will occur further east in the Brennisteinsfjöll Volcanic System.

  4. The magma intrusion continues but starts to cool before it reaches the surface.

  5. The magma intrusion continues and leads to an effusive eruption along a fissure most likely in the Fagradalsfjall area.

If an eruption does occur, it is thought to be unlikely to threaten settlements. Although likely small, the eruption could be spectacular with fire fountaining lava in the beginning, similar to the last eruption in Iceland in 2014-2015, but on a smaller scale. Depending on wind direction, there may be air pollution from volcanic gases in Reykjavík and other nearby towns.

Regardless of how the present situation plays out, it seems that we are entering a new period of volcanic and seismic unrest on the Reykjanes Peninsula. It is likely that we will see this evolve over the coming months and years.

It is definitely an exciting time to be a geologist living in Reykjavík!

Other exciting locations in the Reykjanes Peninsula

I hope I’ve inspired some of you to explore this volcanically active part of the country. It really is a unique place. So if you were to come on a tour with me, some of the places we would visit are great examples of how this peninsula has been shaped by volcanic eruptions and activity.

We would follow Hidden Iceland’s Between Continents: Reykjanes & Lava Tunnel tour. On this trip we travel across the Reykjanes, Krýsuvík and Hengill Volcanic Systems.

Depending on which direction we start the tour, the first stop is a lava tunnel from an eruption 5200 years ago that occurred in the Hengill Volcanic System. Inside the tunnel you will learn how lava fields form and have a real life insight into how the potential eruption at Fagradalsfjall will happen.

We also visit the Seltún Hot Springs inside the Krýsuvík Volcanic System with its steam vents, bubbling mud-pots and Lunar-like landscape.

We then make a stop at Reykjanesviti Lighthouse with its spectacular sea cliffs, ocean waves and birdlife. This is the location that the Mid-Atlantic Ridge rises out of the Atlantic Ocean and onto land. A must for geology enthusiasts. We then visit the closeby Gunnuhver Hot Springs inside the Reykjanes Volcanic System. This highly active geothermal area contains Iceland’s largest hot mud spring.

At lunch, we visit the fishing village Grindavík for tasty local lobster soup and other Icelandic delicacies. Being closest to the earthquake epicenters, this town has been most affected by the activity since 2019. In addition, the volcano Þorbjörn is directly above the town and caused concern in early 2020 when magma was inflating inside the volcano. Dealing with the risk of natural hazards has become a necessary part of life in Grindavík.

Finally we visit the Bridge Between Continents, a bridge which links a fissure within the Mid-Atlantic Ridge between the tectonic plates of North America and Europe.


If you are suitably inspired to come and see this wonder of nature then you can book Hidden Iceland’s small group tour of the Reykjanes Peninsula. Or if you prefer a private tour you can simply get in touch and we’ll plan something special together. Oh, and make sure to ask for Holly as your guide. 

See you there!

Dr. Holly Spice. Our Hidden Iceland glacier guide. About Us.

Hi, I’m Holly, geologist and glacier guide at Hidden Iceland. I have a PhD during which I studied the geochemistry of Icelandic basaltic lavas. When on tour, I love to teach people about volcanoes and geology! I am also a passionate climber and outdoor enthusiast. 

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