2023-2025
Sundhnúks Eruption History
VOLCANIC UNREST ON THE REYKJANES PENINSULA
Photo taken by Landhelgisgæsla Íslands/Icelandic Coast Guard
In January 2020, rapid uplift and intense seismic activity began on the Reykjanes Peninsula around Þorbjörn. There have currently been eight eruptions on the Reykjanes Peninsula since 19 March 2021.
The first three eruptions were in and near Fagradalsfjall from March 2021 to July 2023.
The first eruption in the Fagradalsfjall area took place on 19 March 2021 at 20:45 when an eruptive fissure opened in the Geldingadalir valley. This eruption lasted for 6 months, officially being declared over in December 2021.
The second eruption opened in the Meradalir valley on 3 August 2022. This eruption's fissure opened only 1 km north of first eruption site and lasted for three weeks.
The third eruption started on 10 July 2023 at 16:40 and was active for approximately four weeks, ending on 8 August 2023. This fissure opened further inland than the previous two. When the moss fields caught fire this led to one of the biggest wildfires in Iceland's history.
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There was a short period of quiet until 25 October 2023 when a new earthquake swarm started in and around the small fishing town of Grindavík. On 10 November the town was evacuated due to strong earthquakes (most over 4 mag, centered in and around the town) that opened up the ground in town. This was the result of magma on the move underground. This intrusion event did not lead to an eruption. Magma underneath the town of Grindavík was measured at a depth of 800 meters at its shallowest point.
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Following this large intrusion event an eruption began at 22:17 on 18 December 2023, marking the first eruption in the Svartsengi system. This eruption took place along the old Sundhnúks crater row, just a few kilometers north of Grindavík. The fissure totaled 4 km in length and there was no damage to infrastructure. Following this eruption worked started on the defensive walls to protect both the town of Grindavík and its vital harbour. This eruption lasted for four days and was the first eruption of the Svartsengi system and the fourth eruption on the Reykjanes peninsula.
The eruption was declared over on 21 December 2023. The initial lava flow was 100 to 300 m³/s and the lava field is 3.7 km².
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The second eruption in the Svartsengi system began on 14 January 2024 at 07:27, this time further south at approximately 400-500 meters north of Grindavík. There were two fissures during this eruption. The northern most fissure cut through the defensive wall when it erupted. The second fissure opened just on the edge of town and took three houses under the lava flow.
The defense wall that had been built around the northern side of town directed the lava that flowed from the northernmost vent away from the town by guiding the flow along the berm. While this defense wall directed the lava away from the town itself, the consequence of saving the town was such that the flow crossed the main road, Grindavíkurvegur, at the entrance into town. The lava from the northern most vent did not travel far enough south to meet the second vent on the edge of town. Hot water needed for heating homes and for the town's electricity supply were affected during this eruption but were quickly repaired.
The eruption was declared over on 16 January 2024 just after midnight. The initial lava flow was 100 to 200 m³/s and the lava field is 0.7 km².
In the aftermath of this eruption a new graben was discovered to have formed, this one located further to the east than the one formed during the intrusion event on 10 November 2023.
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The third eruption in the Svartsengi system took place on 8 February 2024 around 06:02 in after an earthquake swarm that began at 05:30. The fissure was 3 km in length. The Blue Lagoon Spa/Resort had reopened and all visitors were evacuated safely at the start of the eruption. This eruption opened by the first fissure in the Sundhnúks craters, northeast of Sýlingarfell.
The lava flow covered parts of previous flow before channeling itself west across the main road and over the hot water pipes that supply the rest of the towns on the peninsula (approximately 30,000 residents), This cut off hot the water supply for heating homes and businesses on the peninsula during freezing temperatures.
There was a small period of explosive activity as lava mixed with groundwater. Tephra was carried by the wind and found on the ground in and around Grindavík. This eruption lasted just over 24 hours before being declared over. In the days following the eruption, workers and contractors for the heating company and road administration worked tirelessly to put in a makeshift road over the fresh lava flow and to fix the waterpipes, bringing hot water back to the peninsula.
The eruption was declared over on 10 February 2024 after signs of inactivity on 9 February 2024. The initial lava flow was 600 m³/s and the lava field is 4 km².
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On 2 March 2024, at around 16:00 , signs of activity began once again. This was determined to be a small intrusion event that did not end in an eruption.
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On 16 March 2024, the fourth eruption in the Svartsengi system and seventh eruption on the peninsula began at 20:23 between Sýlingarfell and Hagafell with a fissure 3km in length. The Blue Lagoon once again had to be evacuated.
The westward flow of lava covered the makeshift road at Grindavíkurvegur and stopped short of the hot water pipeline. Lava also flowed in a southeasterly direction along one of the defensive walls toward the south road, Suðarstrandarvegur, and stopped within a couple of hundred meters of the road. The southern flows from the eruption also filled in a quarry (Melhólsnáma) at the base of Hagafell. The material in this quarry was being used to build the defensive walls. Lava pools formed at the northern defensive wall and crews worked to strengthen and raise the berms, using fresh cooling lava that had flowed into the quarry to do so.
Moss fires broke out around the eruption site on 28 March 2024 and the Grindavík Fire Department were able to control and limit the spread of these fires as they worked to extinguish them. Gas pollution was an issue with this eruption and unhealthy levels of pollution were measured across the peninsula during the event.
On 27 April 2024 a small tongue of lava flowed over the defensive berm (L12 - northern berm protecting Grindavík). The flow was slow and and only progressed to the base of the berm it overflowed and no further.
The eruption slowly wound down and was declared over on the morning of 9 May 2024, having lasted 54 days. The initial lava flow was 1,100 to 1,200 m³/s and the lava field is 6.2 km².
***On 10 May 2024 there was approximately 14 million cubic meters of lava in the magma chamber under Svartsengi and the Icelandic MET Office (IMO) was on 24-watch to monitor the situation as the likelihood of another event was considered high.
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The fifth eruption in the Svartsengi system began on 29 May 2024 at 12:46. Grindavík and Blue Lagoon were evacuated quickly and efficiently. The eruptive fissure reached about 3.4 km in length, the initial lava fountains reaching as high as 50 meters and plumes that reached an altitude of 3.5 km. This eruption was the most powerful of the five recent eruptions. The fissure opened up along the Sundhnúks crater row at Stóra-Skógafell in the north and extended to just past Hagafell to the south. The southern end of the fissure bisected the largest crater that formed during the 16 March eruption. Within 24 hours, the activity had confined itself to between Sýlingarfell and Hagafell.
Approximately three hours into the eruption, explosive activity took place at the base of Hagafell. The lava mixed with groundwater causing explosions and tephra fall. The explosive activity seen at the beginning of this eruption was larger and contained more force than was seen during the February eruption. The initial phase of the eruption saw lava flow over Grindavíkurvegur to the south of Þorbjörn and alongside the defensive barriers on the west side of Grindavík, covering part of Nesvegur road. There was also lava flow underground that emerged just north of the defensive walls northeast of Grindavík. A lobe also flowed north of Sýlingarfell to the west toward Grindavíkurvegur on that side. On 8 June lava flowed over Grindavíkurvegur along the defensive wall after a lava pool overflowed, increasing the flow to the north of Sýlingarfell. The lava tongue reached the road at around 10:30 and stopped a mere 800 meters away from the hot water pipelines that had been damaged during the February eruption.
The beginning of this eruption saw a subsidence of 15 cm in Svartsengi followed by another 4-6 cm in the following days. This is the first time during the Svartsengi system eruptions that prolonged subsidence accompanies the onset of an eruption. On 7 June 2024, subsidence was reported, by IMO, to have stopped. On 11 June IMO stated that measurements indicated inflation had once again started in Svartsengi. There was also wildfires associated with this eruption. Volcanic smog or "vog" was particularly high during this eruptive event, causing health and safety concerns. IMO issued several warnings for gas and air pollution in populated areas.
On 18 June lava flowed from under the solidified crust and over the defensive wall that lies northeast of the Svartsengi power plant. Water pumps were used to cool the lava, along with building a smaller defensive berm inside the larger one and moving earth around to cover the lava in order to stop and control the breakout. On 22 June, lava again flowed over the same defensive wall initiating another round of water cooling.
The eruption was declared to be over on 22 June, having lasted for 24 days. Magma accumulation continued in the storage chamber underneath Svartsengi, although it was at a slower rate than in between previous eruptions. The initial lava flow was 1,500 to 2,000 m³/s and the lava field is 9.2 km² with a volume of about 41 million m³.
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The sixth eruption and seventh run (including the intrusion event in March) began in the Svartsengi system on 22 August 2024 at 21:26 local time. The emergency alert to evacuate the area was put out approximately 20 minutes prior to the start of the eruption due to pressure changes in the boreholes and increased seismic activity that had begun at 20:48.
At the beginning of the eruptive event all seismic activity was detected in the north, indicating that magma was not moving southward. The initial fissure once again opened up over Sundhnúksgígaröðinn (Sundhnúks crater row).
The initial fissure was observed to be expanding more to the north than to the south and the length was estimated at 1.4 km. These results were reported after the first Coast Guard surveillance flight.
Results from the first scientific flight over the eruption showed the fissure had expanded to almost four kilometers in length. It was reported that the fissure had extended by 1.5 km in 40 minutes. The lava was reported, at this time, to have been moving at a rate of 2 km/h.
At 22:37 a 4.1 magnitude earthquake was measured 3 km northeast of Stóra-Skógafell and was felt in settlements on the Reykjanes Peninsula and the capital area.
At 02:36 on 23 August 2024, following the 4.1 magnitude quake, it was found that a new fissure had opened north of the northernmost end of the fissure where the eruption began. The new fissure was approximately one kilometer long.
Until around 06:00 on 23 August 2024 the fissure continued to extend. The total length of the eruptive fissure was estimated to have reached approximately 7 km long, although the entire length of the fissure was not active all at once. The greatest power of the eruption remained to the northernmost end of the fissure and all activity was much further north than in previous eruptions.
For a time, lava could be observed flowing toward the main road, Grindavíkurvegur. This lobe eventually stopped some 200 – 300 meters from the road and no infrastructure was damaged.
On 24 August 2024 it was reported that lava flowed over Vogaheiði, a training ground for the US military from 1952 – 1960. This area is contaminated with unexploded munitions left over from the US military's training exercises. Several unexploded munitions were found throughout the eruption and subsequently detonated.
On 26 August 2024 it was reported that the subsidence of the land after the start of the eruption was 40 cm, almost double that of the 29 May eruption. Model calculations indicated that as of 26 August around 17 – 27 million cubic meters of lava had flowed from the magma chamber. To date, this is the largest of the six eruptions to have taken place in the Svartsengi system.
As with previous eruptions, moss fires burned around the edges of the lava flow and air pollution was observed frequently, both in Iceland as well as abroad.
Initially the land subsided by about 40 cm when magma propagated from the Svartsengi reservoir into Sundhnúksgigaröðinn. Inflation was officially reported to have begun again 6 September 2024.
The eruption was declared over on 6 September 2024, having lasted for 15 days. To date, this is now the largest eruption in the Svartsengi system. The initial lava flow was 1,500 to 2,000 m³/s and the lava field is 15.8 km².
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On 20 November 2024 at 23:14 the seventh eruption in the Sundhnúks eruption series began. The fissure opened just SE of Sýlingarfell and extended NE toward Stóra-Skógfell, reaching approximately 3 km in length.
There was a series of small earthquakes which began around 22:30 and at 22:37 pressure changes were measured in the boreholes at the Svartsengi Powerplant. These signals indicated clear signs that a magma run had begun.
Seismic activity did not increase in the weeks prior to the eruption, as had happened with the previous eruptions. The amount of magma that had accumulated in the chamber was similar to the accumulated magma prior to the August eruption (approximately 24 million m³). Grindavík, Svartsengi (including the power plant), and the Blue Lagoon were evacuated.
The initial fountain height was estimated to be 100-150 m high and the flow rate was estimated at 1,200 to 1,300 m³/s. IMO announced that the eruption had seemed to reach its peak at 01:45 and would begin to level out. Within the first seven hours, the eruption had spread to cover nearly 7 km². Around 10 million m³ of magma flowed from the chamber in the first hours of the eruption. In less than 24 hours, only three craters remained active, with the middle one producing the highest output.
On 21 November 2024 IMO put out an update stating that lava had not previously flowed as far west as was being seen, seismic activity and deformation was measured to be very low and the speed of the lava was estimated to be at over 100 m/hr.
At around 06:00 am the westward lava tongue flowed over Grindavíkurvegur and headed toward the Blue Lagoon. Once the lava flow crossed Grindavíkurvegur it then flowed over the water pipeline that had been insulated after having suffered damage in the February 2024 eruption. At 12:00 the lava flow reached the Blue Lagoon parking lot and a service building in the parking lot was taken under the lava flow. The entire parking lot was under lava by 13:30.
At 09:00 a full power outage was reported in Grindavík, other areas of the Reykjanes peninsula and Hafnarfjörður and at 09:50 electricity fully restored via backup sources. The power line’s mast was raised earlier in 2024 to protect it from lava flow however, the extreme heat from the lava caused the mast to buckle and fail. It was stated that repairs to the Svartsengi line will not begin until after the eruption ends.
During the 18:00 new, Benedikt Ófeigsson, head of deformation measurements at IMO, stated that the eruption had subsided and the reduced activity was concentrated to three craters with the middle crater having the most activity.
The lava continued to flow to the west from the Blue Lagoon parking lot and had moved from flowing along the defensive wall to flow through a natural lava field. There was concerns that the lava could affect Norðurljósavegur (road 426).
Coming into the eighth day of the eruption, the lava field had reached an area of 9.1 km² with a total volume of 47 million m³. There was only one active crater at this time. The lava flow rate had reduced and was measured at approximately 7–8 m³/s.
The volcanic activity had released an estimated 64–71 kg/s of sulfur dioxide.
During its second week, the lava primarily flowed south-eastward, advancing toward Sandhóll and Fagradalsfjall. Additionally, the eruption began to stabilize and balance was soon reached between the inflow of magma into the magma chamber and the amount of erupted lava at the surface.
On the morning of 8 December 2024, there was no more activity seen within the crater and the eruption was declared over by the IMO on 9 December 2024. Inflation was seen to be beginning again.
The eruption lasted 18 days and was the second largest eruption of the 7 that have occurred since December 2023.
As of December 30, 2024, deformation data indicates continued magma accumulation beneath Svartsengi.
The likelihood of a new magma intrusion and potential eruption is expected to rise once the volume of magma matches the amount that left the magma region during the intrusion and eruption on November 20. Geodetic modeling estimates this threshold volume to be between 12 and 15 million cubic meters.
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On 1 April 2025 at 09:44 the eighth eruption along the Sundhnúks crater row began. The eruptive fissure opened to the south near the site of the January 2024 eruption. From the start of the event through the following day after around 2,400 earthquakes had been measured.
The dike that was formed is nearly 20 km, the longest observed in the period of unrest that began in November 2023. More than 25 cm of subsidence was recorded at the Svartsengi GPS station. The vast majority of the magma that left the chamber beneath Svartsengi was about 90% of the total volume that had accumulated since December 2024, with all but a small amount being injected into the dike that was formed.
Model calculations estimated about 15 million m³ of magma had flowed from the magma chamber into the magma tunnel with only a fraction of it erupting to the surface. Approximately 22 million cubic meters of magma had accumulated in the chamber prior to the magma run beginning.
It is estimated that lava volume erupted at the surface was 0.4 million m³ and formed the smallest lava field seen to date, measuring only 1/6th the size of the lava field from the January 2024 eruption. The area of the lava field is about 0.23 km² and has an average thickness of about 1.7 meters. The height of the lava fountains has not been reported.
Deformation measurements showed that the northernmost part of the dike lies in an area about 4 km north of Keilir. Satellite images and model calculations show that the magma reached to within 1.5 km from the surface about 5 km NE of Stóra-Skógfell. Fissure movements were also confirmed to have taken across the northern most part of the magma chamber northeast of Litla-Skógfell.
At 08:20 the Icelandic Meteorological Office reported that the signals from deformation sensors had become stronger than those during recent events along the crater row, indicating that a considerable amount of magma was flowing in the subsurface. Deformation signs were seen to the south, something not seen in the eruption that took place November 2024. Earthquakes were being felt inside the town and data showing deformation within the town limits made it clear that new cracks could form within the town. The earthquake swarm that began at 06:30 had created a magma tunnel reaching approximately 11 km in length in those first couple of hours and reaching to approximately 20 km in length in total by the end of the intrusion event.
At 10:00 IMO reported that the eruptive fissure was about 500 meters long and had breached the outer defensive berm north of Grindavík and that it was not possible to rule out that it would continue to open to the south toward the town.
By 10:30 the fissure had extended to 700 meters and at 11:00 was reported to be 1,200 meters in length. A new fissure had opened a few hundred meters inside the northern and southern defensive berms north of Grindavík. Fissure extension continued and was approaching the fissure that opened during the January 2024 eruption. A hot water pipeline had broken in the northern part of Grindavík, confirming that considerable ground movement was taking place with the town.
Ground displacement was measured by GPS stations within Grindavík in connection to fault movements with more cracks forming. The largest displacements were in the eastern part of town with over 10 cm of vertical displacement and 5 - 8 cm of horizontal displacement measured on Austurvegur street. Horizontal displacement of 6cm was measured on the edge of the western part of town. The total displacement within Grindavík was at most around 50 cm, measured over several cracks within the town.
At 14:30 volcanic activity began to show clears signs of decreased activity although seismicity continued at either end of the intrusion. The seismicity was strongest on the NE end and deformation data showed northeastern movement, suggesting magma was still moving through the magma corridor. Seismic activity was located at a depth of about 4-6 km and while activity continued it was not able to rule out the possibility of magma re-emerging along the Sundhnúks crater row or near the area of greatest seismic activty on the NE end.
At 21:40 webcams showed no visible volcanic activity at the fissure that opened that morning.
On 3 April 2025
Seismicity continued and magma flow had become so small that subsidence was no longer measured. The seismic activity was seen in the northernmost part of the new dike, distributed from Stóra-Skógfell to Keilir, the depth remaining at 4 - 6 km.
The eruption was declared officially ended at 16:45 the same day, having lasted just over 6 hours and becoming the shortest-lived eruption in the series to date.