While waiting to see where and when the next eruption on the Reykjanes Peninsula occurs, we have updated our earthquake plots for the area between 63.746°N, 22.631°W and 63.996°N, 21.864°W from 24th October 2023 to 9th March 2024 – a total of 12,988 earthquakes. We have extended the area plotted to include Krýsuvík.
First, we start with the geodensity plot for the period 24th October 2023 to 9th March 2024. Most activity is still occurring on the magma intrusion / graben between Hagafell and Stóra-Skógafell. The earthquake density plots for the entire period also picks up some activity southwest of Grindavík, west of Fagradalsfjall and at Mount Þorbjörn. This shows best on a topographic map with a lighter background.
Next, we look at the geoscatter plot for the same area and period. This shows the activity along the magma intrusion / graben, that west of Fagradalsfjall, and, also, an upkick in activity in the Krýsuvík area. The last may be local faults accommodating the uplift at Svartsengi. Whether or not this lets magma ascend in the Krýsuvík volcanic system, itself, remains to be seen. At the time of writing, the alert level for Krýsuvík is unchanged at green.
The earthquake swarm is continuing as we write, although he magnitude of earthquakes has reduced. As the uncertainty continues, our thoughts are with those required to evacuate Grindavík, those supporting them, the Department of Civil Defence, and the scientists and others monitoring the activity.
According to IMO, ground deformation is continuing at a slower rate. It is thought that if an eruption occurs, it is most likely to be in the region of Hagafell. Yesterday, sulphur dioxide was detected in a borehole at Svartsengi located north of Mt Þorbjörn. The borehole extends eastwards towards the Sundhnúkur crater row, close to the where the magma intrusion is. This is considered evidence of magma north of Hagafell. The possibility of an eruption is still considered high.
If we ccompare the locations to our geodensity plots (ref. Fig 31 below), the areas of most seismic activity are located at the Sundhnúkur crater row, Hagafell and northwest Grindavík. The geodensity plots are often good predictors of where an eruption will occur. However, with three current seismic hot spots, the situation is not clear at the moment. If an eruption occurs, the precise location(s) will depend on where weak spots allow magma through.
Our updated earthquake plots are below. The data source is as below.
Seismic activity is occurring along the dike and also at Krýsuvík.
The earthquake swarm continues as we write. The intensity has lessened, and the size of the earthquakes decreased. The probability of an eruption is still considered high.
According to IMO, most monitoring is focussing on the dike formation and Grindavík. Ground deformation is consistent with magma flowing into the dike. Part of the magma may be solidifying at the edges of the dike. Magma inflow is thought to be near Sundhnúk. SO2 measurements show fluctuating degassing associated with the dike. Magma may have come within 500m of the surface. The sink hole which opened in Grindavík continues to widen.
We have updated our earthquake plots to 18:50 today.
The most recent earthquakes occur along the dike, and at Krýsuvík. We do not understand the relationship between Fagradalsfjall and activity further west, other we have observed than activity at Krýsuvík usually precedes activity west of it. Frustrating not to be a geologist!
Correction: Fig 20 is for the period 10th November to 13th November (Error was in the image title, not the caption. The plot, itself, is unchanged). Apologies for any inconvenience.
The earthquake swarm continues as we write. The intensity has lessened, and the size of the earthquakes decreased, most probably reflecting the fact that magma has reached less brittle rock layers nearer the surface. Scientists have said the magma inflow has lessened, seismic activity is between depths of 2km and 5km but there is no change in the assessment of the likelihood of an eruption.
The InSAR image showing the formation of the possible graben running through part of Grindavík has been published on IMO’s site today. The sudden formation of the graben on Friday night led to the evacuation of Grindavík. Local news sources have images of the damage done to roads and property.
Fig 15: InSAR image showing ground displacement caused by seismic activity between 3rd November 2023 and 11th November 2023. Source: IMO
Fig 16: Estimate of the vertical displacements caused by the dike during its initial propagation from Friday afternoon to Saturday morning. The displacements were estimated by combining ICEYE and COSMO-SkyMed pixel offset tracking results. Source: IMO.
We have updated our earthquake plots for the swarm from 10th November 2023 to 13th November 2023 14:49. We used the earthquakes published on Whole Country (vedur.is) for the Reykjanes Peninsula with a quality of over 90%., a total of 3,560 earthquakes. We may have picked up some ghosts and other errors (confirmed earthquakes have a quality of 99%) but we believe that this will give a rough idea of what is going on.
Our 3D scatter plots for the above seismic activity covered too big an area to look at the formation. We extracted earthquakes between 63.746°N, 22.211°W and 63.996°N, 22.631°W, a total of 2,974 earthquakes. For the 3D scatter plots only we removed a small earthquake with a depth of more than 40 km from the data set as it distorted the scale of the plots too much.
IMO reported this evening that there is a significant likelihood of a volcanic eruption in the coming days.
Modelling based on ground deformation and seismicity by scientists at IMO and the University of Iceland shows that there is a 15km long magma intrusion located northwest of Grindavík. The intrusion stretches from Kálffellsheiði, northeast of Grindavík, to offshore southwest of Grindavík.
Magma has ascended to 800m below the surface. Where and when an eruption will occur cannot be predicted now – other than to say that it would most likely be in the vicinity of the intrusion, if it occurs.
Fig 12 Map showing the location of the dike intrusion based on combined satellite radar imagery, GPS measurements, and geophysical modelling. Source: IMO
Since our original post below, events have moved on. The town of Grindavík was evacuated overnight when it became apparent that a dike could be forming under the town. The Svartsengi Power Plant will be operated remotely.
The swarm has continued relentlessly since yesterday.
Fig 8: Earthquakes on the Reykjanes Peninsula. Note the activity is concentrated near Mount Þorbjörn; most of the outliers are ghost in the auto system. Source: IMO.
We have plotted the activity from 10th November 2023 to 11th November 2023 05:58 using the confirmed earthquakes reported on Skjálfta-Lísa (vedur.is), a total of 134 earthquakes. Our plots show the possible dike formation.
Fig 1: Image cropped from one by Arian Zwegers of the Blue Lagoon with Mt Þorbjörn. Published under CC BY 2.0
A large earthquake swarm started north of Grindavík, Iceland, on 24th October 2023 in the vicinity of the Svartsengi Geothermal Plant and Mount Þorbjörn. This is the fifth time such a swarm has occurred during the volcano-tectonic episode which started on the Reykjanes Peninsula in December 2019, including the three eruptions of Fagradalsfjall. Earlier today (10th November 2023), the swarm intensified. The aviation code for the Reykjanes – Svartsengi system has been raised to orange.
Because this activity started near Fagradalsfjall, it was initially thought that the swarm was caused by magma movement associated with Fagradalsfjall and the earthquakes to the west were triggered earthquakes (faults moving to accommodate the magma). This was born out by initial ground deformation showing at station FEFC, southwest of Fagradalsfjall. However, this has been followed by consistent uplift at the stations near Mt Þorbjörn, raising concerns that there is magmatic activity there. It is believed that magma is accumulating in a sill at a depth of 5km. Since then, there have been seven earthquakes with a magnitude greater than 4.0M in the area (as of 9th November 2023).
Fig 3: Time series for GPS stations FEFC and Thorbjörn to 9th November 2023. Source: IMO.
Fig 4: Interferogram (InSAR) for the period 28th of October – 6th of November showing around 7cm ground deformation. The green indent SW of Mt. Þorbjörn is an offset in the deformation signal caused by fault movements by earthquakes. Source: IMO
We have plotted the earthquakes reported on Skjálfta-Lísa (vedur.is) for the Reykjanes Peninsula for the period 24th October 2023 to 10th November 2023 (16:07) to see what is going on. 3,239 earthquakes have been recorded, although many more have occurred.
The geoscatter plot shows the initial seismic activity southwest of Fagradalsfjall, followed by its migration westward.
Time will tell whether an eruption ensues. But as a precautionary measure the Blue Lagoon is now closed to visitors and the residents of Grindavík have been advised of evacuation plans.
Our plot do not include the larger recent earthquakes, including the 5M. When we get more data, we will update our plots.
The eruption site is closed to the public right now due to the danger from volcanic gasses and smoke from moss fires; some visitors have been affected. Also, some visitors have been taking insane risks (e.g., attempting to climb the crater wall). High winds yesterday also caused issues.
As we know the eruption started on 10th July 2023 at 16:40 with the opening of four fissures with a combined length of c.800m in a north easterly direction from Litli Hrútur towards Keilir. The eruption peaked at c.21:00, diminishing to form a single crater c. 400m northeast of Litli Hrútur.
Lava is flowing south with an average flow rate of 13m3/s (similar to the 2021 eruption) for the period 11 July to 13 July. As of 13 July 13:38, the lava volume is c. 3.4 million cubic metres covering an area of 0.4km2. Calculations were performed by NLSI from Pleiades satellite images.
The lava composed of vesicular glass, microphenocrysts and microlites of plagioclase, olivine, clinopyroxene and spinel, similar to the 2022 lava. Lava is estimated to have a temperature of c.1190°C. The chemical composition is similar to that of the 2021 and 2022 eruptions: MgO wt.% = 8.5, and, K2O/Ti2O = 0.26.
The gas composition is similar to that of the 2022 eruption, with a high concentration of CO2. The CO2 may have accumulated prior to the eruption. SO2 gas emissions range from 5.4-11.5 ktonnes / day and CO2 is 7.1 – 15 5 ktonnes / day.
If lava continues to flow southwards, it may reach the 2022 lavas in Meradalir.
We have updated our earthquake plots to 13th July 2023 02:06, focussing more on the area between Fagradalsfjall, Keilir and Krýsuvík.
The earthquake density plot is still showing most activity southwest of Keilir and close to the eruption site, which we determined from eyeballing the location of the crater. The area southeast of Keilir is also showing more activity. Whether the activity close to Keilir is triggered quakes, the result of faults moving to accommodate the magma intrusion, or magma-related (or, indeed, both) remains to be seen.
The Icelandic Met Office has confirmed the onset of an eruption on the eastern and northeastern flanks of Litli Hrútur, Iceland. The eruption started around 16:40 today with the opening of three small fissures on a 200m fault. Lava is collecting in a depression then flowing southwards, with gas and steam emissions going northwestwards.
IMO reported noticing a disturbance on the earthquake station at Fagradaslfjall last night and again at 14:00 today similar to those preceding the 2021 and 2022 eruptions.
Fig 3: Helicorder plot for Fagradalsfjall today. Source: IMO
The eruption site appears to be a little east of the southern end of the calculated position of the dyke intrusion.
Fig 4: Calculated position of the dyke instrusion (red line) from IMO. Red stars show the position of earlier eruptions (2021 and 2022). The blue line is the location of surface deformation from ICEYE wave interference images taken 7-8 July. Location of surface fracture and insert model determined by Michelle M. Parks and Vincent Droin, Icelandic Meteorological Office. Photo: Ásta Rut Hjartardóttir, University of Iceland
We have updated our earthquake plots from 28th June 2023 to 10th July 2023 15:04 for the Reykjanes Peninsula. We used the 764 confirmed earthquakes published by IMO on https://skjalftalisa.vedur.is/#/page/map. The total number of earthquakes in the swarm was c.12,000 as of 9th July 2023.
The earthquake swarm which started on 4th July 2023 is continuing vigorously as we write, with 7,000 earthquakes detected. InSAR has confirmed that there is a dike intrusion between Fagradalsfjall and Kelir. IMO have said that magma is likely to have reached a depth of around 1 km by 6th July, causing a fracture of a 2.8 km length between Fagradalsfjall and Keilir, centred a little north of Litli-Hrútur. The expectation is that, if an eruption occurs, it will be in hours or days. The eruption may be short but bigger in its initial stages than the 2021 and 2022 eruptions. The alert level remains at orange.
A smaller swarm is also ongoing southwest of the peninsula on the Reykjanes ridge, near the island of Eldey. This may be due to crustal accommodation of the magma intrusion between Fagradalsfjall and Kelir and/or it may be independent activity. The alert level has been raised to yellow. We will look at this in later posts.
The wrapped image (Fig 2) clearly shows a series of multicolored fringes centered bewtween Fagradalsfjall and Keilir. These fringes show ground deformation caused by the new dike intrusion which commenced on 4 July 2023. The maximum observed deformation related to the dike intrusion is up to 18 cm in the satellite‘s line-of-sight (los) in the NW direction.
Although the deformation signal extends over a large area of the western Reykjanes Peninsula, this does not mean there is magma beneath this entire region. The magma intrusion is situated bewteen Fagradalsfjall and Keilir. There is no indication of additional magma movements outside this area.
Several small lineaments are also visible in the interferogram which cut across the fringes. These represent fault movements/earthquakes that were triggered during the dike propagation.”
We have updated our earthquake plots to this morning, 7th July 2023 09:37 using the published earthquakes from https://skjalftalisa.vedur.is .
Local volcanologist have said that the likelihood of an eruption in a matter of hours or days has increased. The aviation alert level has been increased to orange.
So we have plotted the published earthquakes from https://skjalftalisa.vedur.is from 28th June 2023 to 5th July 2023 20:16 to see what is going on.
It certainly looks like a magma intrusion close to the sites of the recent Fagradalsfjall eruptions. Time will tell whether or not and where lava emerges with the current swarm.
Our thanks go again to the Icelandic Met Office, IMO, https://www.vedur.is/, for the raw earthquake data. For updates, please visit IMO.
Eruptive activity at the new fissure in Meradalir stalled on 21st August 2022 at around 6:00 am. The seismic tremor ceased following the emission of a blue grey plume. Lava was seen on webcams to be still flowing from the crater just before then. We await to see whether or not this is the end of this eruptive episode.
To quote IMO, “A new chapter is about to begin in the Fagradalsfjall fires, but whether the seismic activity will recur and it will erupt again in the near future or not, time will tell.”
What do we know of the eruption so far? The eruption started on 3rd August 2022. The initial discharge rate was c. 32 cubic metres per second, dwindling to 2 cubic metres per second by 16th August 2022. The total volume of lava emitted by 16th August 2022 was 12 million cubic metres, c. 8% of that emitted by the Geldingadalir eruption last year. At the crater the lava is 20 to 30 metres deep and 40 metres deep by the crater rims, themselves. Over the rest of the lava field the lava is between 5 and 15 metres deep. The new lava has displaced cooling older lava causing it to rise by 3 to 5 metres in places.
The lava composition is similar to the basalt emitted by Geldingadalir in September 2021. The K2O / TiO2 ratio ranges from 9.3 to 9.4 and the MgO is around 8.4 wt(%).
So, it was hours, not days! The eruption started near Fagradalsfjall / Meradalir yesterday at around 13:18 about 1.5 km north of Stóra-Hrut on a north-easterly southwest fissure. The onset was detected by a local webcam and later confirmed by scientists. The alert level is currently orange (Volcanic eruption is underway with no or minor ash emission.)
Like the previous eruption, lava is contained by the local geography so no infrastructure is currently threatened. Gas emissions are, however, a hazard. The lava flow is estimated to be 5 – 10 times that of Geldingadalir at 32 cubic meters per second in the first 24 hours; gas emissions may well be similarly larger.
Visitors are advised not to approach the site at the moment. When the site is open, bear in mind that it is not an easy walk, so for the fit only, and visitors should be properly prepared, including having gas masks and metres.
At the time of updating, we did not have confirmation of the coordinates of the eruption site, so we have guessed based on maps of the fissure. The plots will be updated when more up to date information becomes available.
Update 02/08/2022, 20:39:46, Fagradalsfjall and Grímsvötn
The earthquake swarm near Fagradalsfjall continues unabated. The aviation code for Grímsvötn has been raised to yellow following increased seismic activity there.
Fagradalsfjall
At the time of writing IMO were reporting 3,000 earthquakes in the last 48 hours detected by the SIL Seismic Network.
Rising magma has caused some large triggered earthquakes where existing faults slip to accommodate the strain, the largest so far being 5.47 on day 2 of the swarm.
The Icelandic media are reporting that new satellite images taken on 1 August 2022 show magma movements located between Fagradalsfjall and Keilir. The magma intrusion is shallow at c. 1 km below the surface. The magma influx is close to double the rate of the previous eruption. The chances of an eruption near Fagradalsfjall in the coming days or weeks have therefore increased and are considered to be significant.
We have updated our earthquake plots using confirmed earthquake data from IMO’s Skjálfta-Lísa for the area 63.75°N, 23.0°W to 64.0°N, 22°W (the western Reykjanes Peninsula). The geodensity plot shows that most of the action is centred north east of Fagradalsfjall.
The image from IMO below shows the earthquake activity at Grímsvötn.
Fig 7: Screenshot of seismic activity at Grímsvötn today. Source: Vatnajökull (vedur.is)
Hopefully, eruptions are not like buses – wait for ages, then several show up together. On a more serious note, if Grímsvötn does erupt, ash may be problematic for Europe depending on the size of the eruption and the prevailing wind direction. A jökulhlaup caused by melting of the ice-cap is another hazard. An eruption near Fagradalsfjall is less likely to produce a lot of ash unless magma encounters an aquifer or other body of water; lava and any gas emissions depending on volume and location are likely hazards. Seismic activity remains a hazard for both; the public are advised of the risk of rockfall and landslip.
A large earthquake swarm started yesterday (30/07/2022) lunchtime north east of Fagradalsfjall, Iceland. At the time of writing, IMO had reported 1,597 earthquakes in the last 48 hours for the Reykjanes Peninsula from the SIL seismic network. This network automatically detects and locates earthquakes in Iceland and the surrounding offshore region. 199 of these earthquakes had been confirmed.
At the moment the swarm is being likened to the swarm in December 2021, which did not result in an eruption. The local authorities are warning of the increased risk of rockfall as a result of increased seismic activity.
Seismic activity continues in the Svartsengi area, extending to the Sundhnúkur crater row. The earthquakes in the vicinity of Mount Þorbjörn appear to be getting shallower today as at the time of writing.
The Sundhnúkur crater row erupted c. 2,360 years ago. It is accredited with creating the Hópsnes/Þórkötlustaðanes land spit to the east of Grindavík.
Fig 8: Bird’s eye view of the Svartsengi area and Gringavík. Image from Google Earth; yellow text added by the author.
Here are our updated earthquake plots to 26th May 2022 15:06.
The following video shows both the geoscatter plots by day from 17th April 2022 to 26th May 2022 in the swarm for the western Reykjanes Peninsula, and the scatter plots for the same period for the area around Mount Þorbjörn.
While the earthquake plots are highly suggestive of more shallow magma ascent, we need to bear in mind that this area is on the plate boundary, the Mid Atlantic Ridge. Some of the seismic activity may be existing faults moving to accommodate the magma. Time will tell when and where magma emerges.
For the latest updates and alerts, please consult with IMO or the local authorities.
Armchair Volcanologist
Original Post 24th May 2022
The earthquake swarm that started on 17th April 2022 on the western Reykjanes Peninsula continues. Today we are plotting activity at the Svartsengi area near Mount Þorbjörn, which lies to the north of Grindavík, Iceland. We have used Mount Þorbjörn as the marker for Svartsengi in our plots.
Fig 1: Image cropped from one by Arian Zwegers of the Blue Lagoon looking towards Mount Þorbjörn. Published under CC-BY SA-2.0. Source: Þorbjörn (mountain) – Wikipedia
IMO reports that there has been significant uplift of 40mm to 45mm during the swarm in the area north of Grindavík indicative of magmatic activity.
From a simpler scatter plot and a geodensity plot, we can see much of the activity has occurred near Mt Þorbjörn or Svartsengi in the area enclosed in the green box below.
An Armchair Volcanologist 
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