Category Archives: Iceland

Seismic and volcanic activity in Iceland.

Eruption at Meradalir, Iceland, Stalled 21st August 2022

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.

Fig 1:  Tremor plot for Fagradalsfjall.  Source: Tremor (vedur.is)

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.

Fig 2: Lava fields 2021 and 2022.  Source: Eldgos í Meradölum | Jarðvísindastofnun – Institute of Earth Sciences (hi.is)
Armchair Volcanologist

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(%).

Armchair Volcanologist

© Copyright remains with the author; all rights reserved, 2022.

Sources: in the text

A New Eruption Near Fagradalsfjall, Iceland, Started 3rd August 2022

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.)

Fig 1:  Image of the new fissure taken by Halldór Björnsson at the Icelandic Meteorological Office on a flight over the eruption site on 03.08.2022.  Source:  Volcanic eruption resumed on the Reykjanes Peninsula | News | The Icelandic Meteorological Office (vedur.is)

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.

Fig 2:  The red line shows the location of the new fissure on the northern edge of the lava flow from the 2021 eruption. The 2021 eruption was located near “Fagradalshraun” on the map. Source: Volcanic eruption resumed on the Reykjanes Peninsula | News | The Icelandic Meteorological Office (vedur.is)

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.

A video made by Reykjanes Grapevine shows the eruption site yesterday: RVK Newscast #203: New Volcanic Eruption In Iceland – YouTube

Seismic activity has decreased since the onset of the eruption.  We have now updated our earthquake plots to 4th August 2022 10:27- see below.

Updated earthquake plots

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.

Fig 4: Earthquake density plot of the swarm from 29th July 2022 to 4th August 2022 10:27 by the author showing how close the eruption site is to the densest parts of the current swarm. © Copyright remains with the author; all rights reserved, 2022
Fig 5: Scatter plot depth v earthquake number in the swarm from 29th July 2022 to 4th August 2022 10:27 by the author. © Copyright remains with the author; all rights reserved, 2022
Fig 6: Video by the author of geoscatter plots and 3D scatter plots of the swarm from 29th July 2022 to 4th August 2022 10:27. © Copyright remains with the author, all right reserved, 2022

Happy volcano watching and stay safe.

Armchair Volcanologist

© Copyright remains with the author; all rights reserved, 2022

Sources: within the text

A New Earthquake Swarm Near Fagradalsfjall, Iceland, Started 30th July 2022 – Updated

Updated 04/08/2022, Fagradalsfjall

A new eruption started at c13:18 yesterday, 3rd August 2022. We are following this on a new thread, A New Eruption Near Fagradalsfjall, Iceland, Started 3rd August 202.

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.

Fig 4a: Geoscatter, Latitude v Depth and Depth v Longitude and Count v Day plots by the author.  Green (grey) dots denote earthquakes less than 3.0M, yellow (old gold) stars denote earthquakes between 3.0M and 4.0M, red (wine) stars those between 4.0M and 5.0M and black (dark grey) stars those over 5.0M for the current day 2 (cumulative prior days). © Copyright remains with the author, all rights reserved, 2022.
Fig 4b: Geoscatter, Latitude v Depth and Depth v Longitude and Count v Day plots by the author.  Green (grey) dots denote earthquakes less than 3.0M, yellow (old gold) stars denote earthquakes between 3.0M and 4.0M, red (wine) stars those between 4.0M and 5.0M and black (dark grey) stars those over 5.0M for the current day 3 (cumulative prior days). © Copyright remains with the author, all rights reserved, 2022.
Fig 4c: Geoscatter, Latitude v Depth and Depth v Longitude and Count v Day plots by the author.  Green (grey) dots denote earthquakes less than 3.0M, yellow (old gold) stars denote earthquakes between 3.0M and 4.0M, red (wine) stars those between 4.0M and 5.0M and black (dark grey) stars those over 5.0M for the current day 4 (cumulative prior days). © Copyright remains with the author, all rights reserved, 2022.
Fig 5: 3-dimension scatter plot by the author.  Colour denotes earthquake number in the swarm (red the oldest and yellow the newest). © Copyright remains with the author, all rights reserved, 2022
Fig 6: Geodensity plot by the author. © Copyright remains with the author, all rights reserved, 2022.

Grímsvötn

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.

Armchair Volcanologist

© Copyright remains with the author, all rights reserved, 2022.

Source:

Raw earthquake data: Skjálfta-Lísa

News report: Kvikugangurinn liggur mjög grunnt | RÚV (ruv.is)

Original post 31/07/2022

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.

We have downloaded the earthquakes reported from the Table tab and plotted the confirmed  earthquakes (quality 99.9%).

Fig 2:  Earthquake density plot by the author of the swarm.  © Copyright remains with the author; all rights reserved, 2022.
Fig 3a:  Geoscatter, Latitude v Depth and Depth v Longitude plots for day 1 of the swarm by the author.  © Copyright remains with the author; all rights reserved, 2022.
Fig 3b:  Geoscatter, Latitude v Depth and Depth v Longitude plots for day 2 to 11:23 of the swarm by the author.  © Copyright remains with the author; all rights reserved, 2022.

For more up to date information, please consult the Icelandic Met Office, Home-page – Icelandic Meteorological Office | Icelandic Meteorological office (vedur.is)

Armchair Volcanologist

Sources:  in the article.

Updates on Seismicity in the Mount Þorbjörn Area, 17th April 2022 to date

Good Evening!

Update 26th May 2022

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.

Fig 9: Summaries of Days 39 (25th May 2022) and 40 (26th May 2022) by the author. Grey & green circles denote earthquakes < 3M, yellow stars between 3M and 4M and red stars ≥4M. Blue triangles denote volcanoes: K is Krýsuvík, Ke is Keilir, F is Fagradalsfjall, Ge is Geldingadalir, Þ is Þorbjörn, El is Eldvörp and R is Reykjanes.  © Copyright remains with the author; all rights reserved, 2022.
Fig 10: Earthquake plots depth by day by the author for the area 63.81°N, 22.5°W to 63.90°N 22.35°W from 17th April 2022 (Day 1) to 26th May 2022 (Day 40).  Size denotes magnitude.  © Copyright remains with the author; all rights reserved, 2022.
Fig 11: Geodensity plot of earthquakes by the author for the area 63.81°N, 22.5°W to 63.90°N 22.35°W from 17th April 2022 (Day 1) to 26th May 2022 (Day 40).  © Copyright remains with the author; all rights reserved, 2022.
Fig 12: Latitude v Longitude scatter plot of the area 63.81°N, 22.5°W to 63.90°N 22.35°W from 17th April 2022 to 26th May 2022. Colour indicates age: red, oldest; and, yellow, youngest.  © Copyright remains with the author; all rights reserved, 2022.

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.

Fig 13: Video by the author of the geoscatter plots and scatter plots from which the above images have been extracted. Keys are in the video.  © Copyright remains with the author; all rights reserved, 2022.

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.

Fig 2: Ground deformation (Source: IMO, Talsverð skjálftavirkni á Reykjanesskaganum)
Fig 3: Stations in the area showing uplift.  Source for each station: Icelandic Meteorological Office

Let’s look at the earthquakes.

Western Reykjanes Peninsula

Initially, we updated our plots of the area between 63.75°N,23.0°W to 64.0°N, 22°W.  Here is a summary.

Fig 4: Plots by the author of earthquake activity from 17th April 2022 (Day 1) to 24th May 2022 (Day 38) between 63.75°N,23.0°W to 64.0°N, 22°W . Grey & green circles denote earthquakes < 3M, yellow stars between 3M and 4M and red stars ≥4M. Blue triangles denote volcanoes: K is Krýsuvík, Ke is Keilir, F is Fagradalsfjall, Ge is Geldingadalir, Þ is Þorbjörn, El is Eldvörp and R is Reykjanes. Day 38 shows the earthquakes to date in the swarm.  The video below shows the progression of the swarm by day.  © Copyright remains with the author; all rights reserved, 2022.

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.

Fig 5a: Latitude v. longitude scatter plot by the author of earthquakes between 63.75N,23W to 64.0N,22W from 17th April 2022 to 24th May 2022. Colour denotes age (red being the oldest and yellow the most recent).  Blue triangles denote volcanoes: K is Krýsuvík, Ke is Keilir, F is Fagradalsfjall, Ge is Geldingadalir, Þ is Þorbjörn, El is Eldvörp and R is Reykjanes. The green square is the area selected for further analysis today (63.81°N, 22.5°W to 63.90°N, 22.35°W). © Copyright remains with the author; all rights reserved, 2022.
 Fig 5b: Geodensity plot by the author of earthquakes between 63.75N,23W to 64.0N,22W from 17th April 2022 to 24th May 2022. © Copyright remains with the author; all rights reserved, 2022.

Let’s look more closely at the area around Mt Þorbjörn.

Svartsengi Area, 63.81°N, 22.5°W to 63.90°N, 22.35°W

Fig 6: Plots by the author of earthquake activity from 17th April 2022 (Day 1) to 24th May 2022 (Day 38). Grey & green circles denote earthquakes < 3M, yellow stars between 3M and 4M and red stars ≥4M. Blue triangle is Þ, Þorbjörn. © Copyright remains with the author; all rights reserved, 2022.
 Fig 7a: Latitude v. longitude scatter plot by the author of earthquakes between 63.81°N, 22.5°W to 63.90°N, 22.35°W from 17th April 2022 to 24th May 2022. Colour denotes age (red being the oldest and yellow the most recent).  Blue triangle is Þ,  Þorbjörn. © Copyright remains with the author; all rights reserved, 2022.
 Fig 7b: Geodensity plot by the author of earthquakes between 63.81°N, 22.5°W to 63.90°N, 22.35°W from 17th April 2022 to 24th May 2022. The Svartsengi geothermal plant and Blue Lagoon are to the north of Þorbjörn and Grindavík is to the south. © Copyright remains with the author; all rights reserved, 2022.

For more up to date information on the seismic activity and the latest alerts, please refer to the local authorities or the Icelandic Met Office, IMO.

Armchair Volcanologist

© Copyright remains with the author; all rights reserved, 2022.

Sources

Raw earthquake data: IMO

Earthquake Swarm on the western Reykjanes Peninsula 17th April 2022 to date: updated earthquake plots.

An earthquake swarm started on the Reykjanes Peninsula on 17th April 2022 and is continuing at the time of writing. This swarm is part of a larger volcano-tectonic episode that started at the end of 2019 on the Reykjanes Peninsula, including the eruption at Geldingadalir.  

Local volcanologists are reporting now that recent ground deformation of 3.5cm suggests a magma intrusion in the vicinity of Svartsengi, north of the town of Grindavík. Magma is believed to be pooling at a depth of c. 4km between Mount Þorbjörn and the Eldvörp crater row. This is an area which can produce large earthquakes of 6.5M. People are advised to avoid areas where landslip is likely.

Fig 1: Image cropped from a photo by Roman Zacharij of Grindavik, Iceland (Source: Wikimedia Commons, Public Domain).

We have updated our earthquake plots to show the swarm to date.  Our plots exclude an earthquake occurring earlier today with a depth of 40.7km to keep the detail in the plots showing depth; the earthquake omitted is 19/05/2022, 00:11:14,  63.77°N , 22.75°W, 40.7km, 1 magnitude. Since we downloaded the data at 09:55 am today, there has been a 3.0 magnitude, 4.9 km NNE of Grindavík.   

Our plots show possible doming in the vicinity of Mount Þorbjörn and  the Svartsengi Volcanic System.

Fig 2:  Video by the author of earthquake activity on the western  Reykjanes Peninsula between 17th April 2022 to 19th May 2022 09:55 am.  The keys are in the video.  © Copyright remains with the author; all right reserved, 2022.

Armchair Volcanologist

© Copyright remains with the author; all rights reserved, 2022

Sources

Raw earthquake data: Icelandic Meteorological Office

From Iceland — Magma Collecting, Increased Earthquakes At Reykjanes (grapevine.is)

Earthquake Swarm between Reykjanestá and Eldey, Iceland. A look at seismicity along the Peninsula.

Good Afternoon!

An earthquake swarm started near the Reykjanes and Eldey volcanic systems on 17th April 2022.  A volcanologist was reported by the Icelandic media to have said that there is a 50% chance of another eruption on the Peninsula by the end of this year.   If the eruption occurs offshore, the resulting ash may reach Reykjavik and beyond.  Another possibility is that Fagradalsjall may erupt again.

Fig 1: Image of Eroded partially submarine volcano and boulder beaches at Reykjanestá by Diego Delso. Published under CC BY-SA 4.0.  Source: Geology of Reykjanes Peninsula – Wikipedia

So we decided to plot the earthquakes on the Reykjanes Peninsula from 1st January 1995 to 26th April 2022 for the area 63.6°N, 23.5°W to 64.2°N, 21.0°W by month.  The results are interesting.

Intense earthquake activity starts early 1995 in the east of the region to the south east of Hengill near the Hrómundartindur volcanic system, which has not erupted since the early Holocene.  Activity migrates slowly westward to Geirfuglasker via Krýsuvík, Fagradalsfjall, Reykjanes, and the intensity of activity near Hrómundartindur lessens.  The volcano-tectonic episode which resulted in the eruption at Geldingadalir started in month 300, the eruption, itself, started in month 315.

Fig 2: Video by the author of earthquake activity on the Reykjanes Peninsula between 1st January 1995 and 26th April 2022.  The keys are in the video.  The 3D rotating scatter plot is of earthquakes ≥1M. © Copyright remains with the author; all right reserved, 2022.

We have discussed the Hengill, Brennisteinfjöll, Krýsuvík and Reykjanes volcanic systems in an earlier post (Recent Seismic Activity on the Reykjanes Peninsula, 14th May 2020)  The Hrómundartindur system is about 25 km long, comprising a fissure swarm and a 500m high central volcano. The system lies at the junction of the Western Volcanic Zone and the South Iceland Seismic Zone. Its lavas range from picrite to basaltic andesite.  There is an active geothermal field in the system.  The Eldey volcanic system is a 40km long fissure system on the Mid Atlantic Ridge, here, the Reykjanes Ridge.  There is no central volcano.  It is mostly submarine; the island Eldey and the skerries, Eldeyjardrangur, Geirfugladrangur and Geirfuglasker, are the only subaerial features of the system.  Six small submarine/explosive Basaltic eruptions have occurred in the last 1,100 years, the last eruption occurring in 1926 CE.

We would not like to predict where the next eruption will be based on the above earthquake plots alone, other than to say it could be anywhere between Hrómundartindur and Geirfuglasker.  Our non-expert interpretation of the above plots is that magma is ascending between Krýsuvík and Reykjanes. The seismic activity to the east and west of that area is caused by resulting stress on the crust; whether there is enough activity to provide an additional path for magma remains to be seen. Time will tell where and when magma makes it to the surface again.

Armchair Volcanologist

© Copyright remains with the author; all rights reserved, 2022.

Sources

Reykjavik Grapevine: From Iceland — RVK Newscast 179: Underwater Volcano On The Cards (grapevine.is)

Kristján Sæmundsson (Iceland GeoSurvey) (2019 November 15). Hrómundartindur. In: Oladottir, B., Larsen, G. & Guðmundsson, M. T. Catalogue of Icelandic Volcanoes. IMO, UI and CPD-NCIP. Retrieved from http://icelandicvolcanoes.is/?volcano=HRO

Guðrún Larsen (Institute of Earth Sciences – Nordvulk, University of Iceland) (2019 November 15). Eldey. In: Oladottir, B., Larsen, G. & Guðmundsson, M. T. Catalogue of Icelandic Volcanoes. IMO, UI and CPD-NCIP. Retrieved from http://icelandicvolcanoes.is/?volcano=ELD

Raw earthquake data: Icelandic Meteorological Office

São Jorge Earthquake Swarm, Update 07.04.2022

Good morning!

The earthquake swarm is continuing on São Jorge as we write, albeit it at a much lower intensity.  The swarm is located on the Manadas Fissure system.  INVOLCAN has sent a team to assist the local scientists (CIVISA and IVAR).   CIVISA advised on 6 April 2022 that volcano-tectonic earthquakes had been detected suggesting magma movement at depth.

Fig 1: Image of Fajã dos Cubres, São Jorge, Azores, cropped from one by Jules Verne Times Two.  Published under CC BY-SA 4.0 (Source: São Jorge Island – Wikipedia).

While we wait to see what transpires, here are some statistics.

  • Number of earthquakes ≥2.0 reported on IPMA’s site: 793
  • Maximum number: 127 on 20 March 2022
  • Minimum number: 5 on 31/03/2022 and 06/04/2022 (7/04/2022 is not a complete day)
  • Maximum magnitude: 4.0 (29/03/2022, 21:56:16, 38.686°N, 28.215°W, 10km)
  • Maximum depth: 26km on 20 March 2022 and 28km on 28 March 2022.
Fig 2: Number of earthquakes by day by the author.  © remains with the author; all rights reserved, 2022.
Fig 3: Earthquake depth and magnitude by day by the author. © copyright remains with the author; all rights reserved, 2022.

We have updated our earthquake plots for 38.548°N, 27.677°W to 38.769°N, 28.350°W from 19th March 2022 to 7th April 2022.

Fig 4: Video of geoscatter and scatter plots of the earthquake swarm from 19th March 2022 to 7th April 2022.  Keys are in the video. © copyright remains with the author; all rights reserved, 2022.

Armchair Volcanologist

© copyright remains with the author; all rights reserved, 2022.

Sources

 IPMA – Seismic Map (for raw earthquake data)

Volcano-tectonic tremors recorded for first time on quake-hit Azores island | Reuters

Is it Ok? An earthquake swarm west of Ok, Iceland

Good Morning!

At the end of 2021 a large earthquake swarm started to the west of the Ok shield volcano in Iceland. At the time of writing the swarm is ongoing.  The Icelandic Meteorological Office (IMO) reported on their Icelandic site on 1st February 2022 that there is no evidence of magma intrusion. 

Fig 1: Ok volcano looking northwards, with a small tuya in the foreground.  Image from Google Earth. The remnant of the Okjökull glacier is visible with a small lake in its centre at the summit of the volcano.  The current swarm is to the west of the volcano.

The swarm is occurring west of Ok in Borgarfjörður in a low temperature region outside the main volcanic and rift area.  The earthquakes are thought to be rifting caused by horizontal tension in the crust, here of the North American Plate.  The swarm is the largest to date in the region and is continuing at the time of writing. So off we trotted to plot the earthquakes.

What’s in the Area?

We looked at the area 64.2°N, 19.2°W to 65.3°N, 21.8°W which contains the Langjökull ice cap, two Holocene volcanic systems and several Pleistocene volcanic systems.

The Langjökull ice cap is the second largest ice cap in Iceland located at the northern end of the Western Volcanic Zone (WVZ).  The WVZ is a slow spreading rift that forms the western boundary of the south Iceland microplate. Sinton et al.’s study in 2005 showed that there is no evidence for the decline in the WVZ in the Holocene; the shield eruptions are long duration with low effusion rates fed by magma from the mantle. c. 40 eruptive units have been located in the WVZ; we are focussing on those in the Langjökull area in the northern part of the zone.

Holocene Volcanoes

VolcanoLatitudeLongitudeLast Known EruptionDominant Rock Type
Prestahnúkur64.583-20.6663350 BCEBasalt / Picro-Basalt
Langjökull64.85-19.7950 CEBasalt / Picro-Basalt

Prestahnúkur is west of the Geitlandsjökull glacier in the south west part of Langjökull.  It is a 90 km ling 15 km wide  fissure system with a rhyolitic peak, on a Pleistocene basaltic plateau.  The central volcano is a hyaloclastite  massif; it has shield forming olivine tholeiite basaltic effusive eruptions, with some rhyolite.   The fissures extend southwest-north east, reaching under the Þórisjökull and Geitlandsjökull glaciers.  There is a parallel sub swarm  of tuyas 4–6 km west of the main swarm.  The last significant eruption of the central volcano was in the Pleistocene and on the fissures c.900 CE.  The Holocene eruptions occurred on rift zones to the north and south west of the volcano. 

Langjökull comprises the Hveravellir central volcano and a 100 km long and 20 km wide fissure system.  A 600m thick ice cap partly covers the system.  The central volcano is another hyaloclastic massif with a silicic component. It has had six recorded  Holocene eruptions: 2 VEI 2, Hallmundahraun 950 CE and Kjalhraun 5850 BCE; and, 4 VEI 0, Lambahraun 2050 BCE, Krákshraun 2550 BCE, Strytuhraun 3550 BCE and Leggjarbrjótur 8600 BCE. The Hallmundahraun lava flow covers 240 km2 .  Kjalhraun is a shield which erupted 11km3 lava 7,800 years ago.  The dominant magmas are olivine tholeiite basalt.

Skjaldbreiður is a shield volcano that lies in the southern part of the Langjökull system.  It erupted 13km3 of basaltic lava in the early Holocene.  The lava flows formed the basin of Þingvallavatn and Þingvellir, where Iceland’s parliament, the Alþing, was founded in 930.

Pleistocene Volcanoes

VolcanoLatitudeLongitudePrimary Volcano Type
Geysir64.32-20.3Stratovolcano
Hlöðufell64.93-20.53Tuya
Þórisjökull64.53-20.7Subglacial
Ok64.62-20.88Shield
Eiríksjökull64.77-20.4Tuya
Hrútfell64.73-19.72Tuya
Bláfell64.492-19.87Tuya
Hreppar64.42-19.5Fissure vent(s)

The Geysir geothermal area lies in the Haukadalur basin near the southern end of the Langjökull system.  Earthquake activity in June 2000 temporarily activated the normally somnolent Grand Geysir

Eiríksjökull is Iceland’s largest tuya.

Ok erupted during interglacials in the Pleistocene.  It used to have a summit glacier, the Okjökull, whose disappearance has been attributed to climate change.  Local volcanologists have reminded us that the ash from the 2010 Eyjafjalljökull eruption  would have contributed to ice loss.  “Not Ok” was a documentary about the lost glacier.  Ok overlies some of the tuyas of the sub swarm to the west of Prestahnúkur.

Hreppar is two NE-SW trending ridges which extend from the rhyolitic Kerlingarfjöll volcano located SW of the Hofsjökull ice cap.

Recent Seismic Activity

As we have extended our database of Icelandic earthquakes back to 1995, we have plotted the earthquakes for the period from 1995 to 7th February 2022 for the area 64.2°N 19.2°W to 65.3°N 21.8°W.

There is a relatively low level of background activity compared to the other volcanic regions of Iceland.  However, the following months each saw more than 200 earthquakes: 55 (July 1999) near Þórisjökull and Prestahnúkur  , 66 (June 2000) near Geysir, 67 (July 2000) near Geysir, 69 (September 2000) near Geysir, 155 (November 2007) near Hveravellir and Geysir, 240 (December 2014) near Geysir, 325 (January 2022) near Ok and 326 (February 2022) near Ok.  Note: that February 2022 is only one week.

We noted six warms to the west of Ok, including the current swarm.  They appear to be aligned along a rift / fissure.  The current swarm near Ok is one of the largest in the database to date.

Fig 2: Earthquakes by month for the Langjökjull region for the period 1995 to 7th February 2022 by the author. © Copyright remains with the author; all rights reserved, 2022.

Our geoscatter and scatter plots (including a rotating 3D scatter plot of the earthquakes to the west of Ok) are contained in the following video.

Fig 3: Video of earthquake activity in the Langjökjull region for the period 1995 to 7th February 2022 by the author. © Copyright remains with the author; all rights reserved, 2022.

It’s not clear from the plots, themselves, whether or not there is any magma movement associated with the current swarm or, indeed, any of the other activity identified.  The size of the current swarm indicates that something may be going on near Ok.  Only time will tell if volcanic activity will ensue.  In the mean time, the plots do shed some light on the activity along rifts associated with plate seperation.

Armchair Volcanologist

© Copyright remains with the author; all rights reserved, 2022.

Sources and Further Reading

Icelandic Meteorological Office: www.vedur.is for raw earthquake data

Kristján Sæmundsson (Iceland GeoSurvey) (2019). Prestahnúkur. In: Oladottir, B., Larsen, G. & Guðmundsson, M. T. Catalogue of Icelandic Volcanoes. IMO, UI and CPD-NCIP. Retrieved from http://icelandicvolcanoes.is/?volcano=PRE

Guðrún Larsen and Magnús T. Guðmundsson (Institute of Earth Sciences – Nordvulk, University of Iceland) (2016): Langjökull, Hveravellir. n: Oladottir, B., Larsen, G. & Guðmundsson, M. T. Catalogue of Icelandic Volcanoes. IMO, UI and CPD-NCIP. Retrieved from http://icelandicvolcanoes.is/?volcano=LAN

John Sinton, Karl Grönvold, Kristján Sæmundsson, “Postglacial eruptive history of the Western Volcanic Zone, Iceland”, Geochemistry, Geophysics, Geosystems, AGU, Volume 6, Issue 12, December 2005, https://doi.org/10.1029/2005GC001021

For the Pleistocene volcanoes we consulted Wikipedia and the Smithsonian Institution – Global Volcanism (www.volcano.si.edu/)

Fagradalsfjall: Aviation Code Downgraded to Yellow

Good afternoon!

Seismic activity at Fagradalsfjall, Iceland, has remained low. The recent swarm is now considered over. The aviation code has been lowered to yellow as a result.

Armchair Volcanologist

© Copyright remains with the author; all rights reserved, 2022.

Sources:

Aviation colour code map: https://en.vedur.is/earthquakes-and-volcanism/volcanic-eruptions/

Icelandic Met Office: https://en.vedur.is

Fagradalsfjall: Update 02/01/2022

Good afternoon!

Updated Earthquake Plots, 2nd January 2022 13:50

Good afternoon!

We have updated the earthquake plots for Fagradalsfjall, Iceland, for the swarm which started on 21 December 2021. 

The swarm had an intense initial period while magma moved along a lateral dike, followed by a less intense period, accompanied by magma ascent.  The Icelandic Met Office, IMO, say that the swarm is following the same pattern as that which preceded the eruption in March 2021. 

Magma is ascending under Fagradalsfjall, itself.  The outlying earthquakes, e.g., at Svartsengi and Krýsuvík, are what Iceland calls triggered earthquakes.  Triggered earthquakes are tectonic in nature, arising as local faults respond to magma movement. 

Fig 4: Geodensity plot by the author of earthquakes at Fagradalsfjall the period 21.12.2021 to 02.01.2022.  © Copyright remains with the author; all rights reserved, 2021.
Fig 5: Geoscatter plot by the author of earthquakes at Fagradalsfjall the period 21.12.2021 to 02.01.2022.  Colour denotes age: red is the oldest and yellow the youngest. © Copyright remains with the author; all rights reserved, 2021.
Fig 6: Scatter plot by the author of earthquakes at Fagradalsfjall the period 21.12.2021 to 02.01.2022.  Colour denotes age: red is the oldest and yellow the youngest. © Copyright remains with the author; all rights reserved, 2021.
Fig 7: 2D Depth v Earthquake scatter plot by the author of earthquakes at Fagradalsfjall the period 21.12.2021 to 02.01.2022.  Colour denotes age: red is the oldest and yellow the youngest. © Copyright remains with the author; all rights reserved, 2021.

Armchair Volcanologist

© Copyright remains with the author; all rights reserved, 2021

Source

Raw earthquake data: https://skjalftalisa.vedur.is/#/page/map

Update 31/12/2021

Following a drop in seismicity over the past couple of days, visitors are now advised to avoid the area.

A similar drop in seismicity was observed immediately before the March 2021 eruption.

If the volcano does erupt again, this would be considered a new eruption in the same place; the earlier eruption was declared over three months after the cessation of activity on 19 September 2021.

Update 28/12/2021

The earthquake swarm at Fagradalsfjall, Iceland, is continuing.  While the swarm has slowed down a bit, 19,000 earthquakes have been recorded by the automatic SIL system since the swarm started.  14 earthquakes over 4.0 magnitude have occurred.  An alert for the risk of rockfall and landslides in the area has been raised; visitors are advised to stay away from the area.

We have plotted the confirmed earthquakes from 20 December 2021 to 28 December 12:50.  This shows the dike propagation south west of Geldingadalur, with additional activity near Kýsuvík and Svartsengi.

Fig 1: Geoscatter plot of the earthquake swarm between 20.12.2021 and 28.12.2021 12:50 by the author.  Red denotes oldest quakes and yellow the newest.  © Copyright remains with the author; all rights reserved, 2021
Fig 2: Scatter plot of the earthquake swarm between 20.12.2021 and 28.12.2021 12:50 by the author.  Red denotes oldest quakes and yellow the newest.  © Copyright remains with the author; all rights reserved, 2021
Fig 3: Geodensity plot of the earthquake swarm between 20.12.2021 and 28.12.2021 12:50 by the author.  © Copyright remains with the author; all rights reserved, 2021.

Only time will tell where and when lava will emerge.  In the meantime, if you are lucky enough to be in the area, be aware of the risk of rock fall and landslip.

Armchair Volcanologist

© Copyright remains with the author; all rights reserved, 2021.

Sources:

Raw earthquake data: https://skjalftalisa.vedur.is/#/page/map

Icelandic Met Office: en.vedur.is