Volcanic alert at Þorbjörn Volcano

Þorbjörn Volcano seen from across The Blue Lagoon. Photograph taken from unknown photographer (Please tell us who we should credit for this lovely photograph, and please excuse our theft in the name of science).

The Icelandic Met Office has released an Official Bulletin about the possibility for an upcoming eruption at Þorbjörn on the Reykjanes Peninsula in Iceland.

Þorbjörn belongs to a class of volcanoes that I normally like to call Unknownabunga, one of all of those volcanic features in Iceland that pretty much nobody knows anything about, until they all of a sudden erupt out of the blue.

Currently it is not certain if Þorbjörn is a standalone volcanic fissure (central volcano), or is part of a wider known central volcano called Svartsengi. This will probably become clearer in a few hours as we get around to plotting things and checking against more well-known culprits on the Reykjanes Peninsula like Svartsengi.

So far both we and IMO are happy to call the volcano Þorbjörn and are treating it as a standalone unit. Suffice it to say that we are in for a possible treat.

For anyone who wishes to go to see the possible future eruption I recommend A) that you go quickly since this will close down Keflavik International Airport as soon as it starts, and B) that you head all instructions from the helpful and very competent local authorities.

Currently this has been an ongoing seismic episode with tectonic and volcano-tectonic signals, and marked inflation as evidenced on INSar.

We will update this article as news comes along, and there will be a new article as soon as we are done with the usual juicy plots so that we have something solid to interpret.



Iceland Met Office Bulletin in full

Sentinel-1 data for Þorbjörn Volcano. Image from the Icelandic Met Office.


(2) Issued: 20200126/1715Z

(3) Volcano: Reykjanes (371020)

(4) Current aviation colour code: YELLOW

(5) Previous aviation colour code: green

(6) Source: Icelandic Meteorological Office

(7) Notice number: 2020-164

(8) Volcano location: N6349 W02243

(9) Area: Reykjanes Volcanic Zone

(10) Summit elevation: 140 M

(11) Volcanic activity summary: Change to yellow code for Reykjanes – ICAO 371020,
because of signals above normal background. GPS-system and InSAR images indicate rapid rise of the surface around

Reykjanes volcano system has ICAO location N6349 W0226 but Mt. Thorbjorn, is located seven nautical miles to the east at N6352 W02226.

(12) Volcanic cloud height: N/A

(13) Other volcanic cloud information: N/A

(14) Remarks:
Possible magma accumulation beneath Mt. Thorbjorn on Reykjanes peninsula.
• Inflation has been measured the last few days.
• An earthquake swarm has been ungoing during the same period.

An inflation has been measured since January 21st and it‘s centered just west of Mt. Thorbjorn on Reykjanes peninsula. The inflation is unusually rapid, around 3-4 mm per day and has accumulated to 2 cm to date. It has been detected both on continuous GPS stations and in InSAR images. The inflation is most likely a sign of magma accumulation at just a few km depth. If the signal is indeed a magma accumulation it is very small, first volume estimate is around 1 million cubic meters (0,001 km3).

This is the conclusion of a meeting held with the Scientific council of the Civil Protection at the IMO this morning.

Accurate measurements of crustal deformation on Reykjanes peninsula span appoximately three decades. During this period no comparable signal has been measured. This is unusual for this period. An earthquake swarm has been ongoing, since January 21st, alongside the deformation signal just east of the inflation center (northeast of Grindavík). The largest earthquakes occurred on January 22nd and were of M3,7 and 3,6. They were felt widely on the Reykjanes peninsula and all the way up to Borgarnes region. The earthquake swarm is currently in decline. Swarms like this are common and not unusual by itself in the area.

The fact that an inflation is occurring alongside the earthquake swarm is a cause for concern and closer monitoring.

Background information:
The inflation is occurring on plate boundaries and within the volcanic system of Svartsengi which is either considered a separate system or part of the Reykjanes volcanic system. The last known eruption was during Reykjanes fires, which occurred between 1210-1240 AD. Within that period a several eruptions occurred within that system, thereof there were three eruptions in Svartsengi system. The eruptions were effusive (non-explosive) fissure eruptions erupting on 1-10 km long fissures. No explosive eruptions are known from this system. The largest eruption in the swarm, from 13th century, formed Arnarseturshraun lava (estimated 0,3 km3 and 20 km2). The duration of these eruptions are usually from a few days up to several weeks. Seismic activity is very common in this area and is linked to the plate boundaries, geothermal activity and possible magma intrusions. The largest earthquakes measured in this area are about M5.5.

For more information Catalogue of Icelandic volcanoes.

Possible scenarios:
The activity has only been ongoing for a few days and it is uncertain if it will escalate to more serious activity. Based on current information, the following scenarios are considered possible, without stating which is most likely or within what timeframe.
1. If the inflation is due to magma accumulation:
• Magma accumulation will cease soon without further activity.
• Magma accumulation continues for some time without further activity.
• Magma accumulation will lead to a magma intrusion.
• Magma accumulation will lead to magma intrusion and eruption (effusive fissure eruption).
• Magma accumulation triggers seismic activity with larger earthquakes (up to M6.0).

  1. If the inflation is not caused by magma accumulation:
    • The inflation might be linked to tectonic activity and lead to larger earthquakes (up to M6.0).
    The Civil Protection has declared Uncertainty phase.

Quick plot of the seismic stack under Þorbjörn. Image by Gaz Dale.

228 thoughts on “Volcanic alert at Þorbjörn Volcano

    • I’d guess rock fracturing with gases/fluids chuntering through afterwards.
      Stuff on the move.
      I invite experts to stamp on my comment, naturally!

      • But still not much tremor signal, if this is happening under that old fissure the path up can’t be too difficult.

        Lots of cracking but still no rumbles yet

      • Will an IMO sspecialist suffice ?
        Specialist remark
        Ongoing earthquake activity has been recorded around Grindavík. This evening at 22:22 a M4.0 earthquake occurred approximately 5km NE of Grindavik and another one M4.3 at 22:24. A number of aftershocks have been detected. No signs of volcanic tremor. Reports have been received, that the earthquakes have been felt in Reykjanes, the capital area and north to Akranes. These are the largest earthquakes in the swarm. There is still ongoing uplift west of Mt. Thorbjorn.

        With increased monitoring efforts, IMO now receives more data which gives a clearer picture of the ongoing events close to Mt. Þorbjörn. The latest GPS processing shows that the uplift west of Þorbjörn is still ongoing. In total the uplift is over 4 cm since the 20th of January. The most likely explanation of the uplift and earthquake activity is that we have a magmatic intrusion at 3 to 9 km depth just west of Þorbjörn. It is most likely that this activity will stop without any volcanism.
        Written by a specialist at 31 Jan 23:26 GMT

  1. Size Time Quality Location
    4.3 31 Jan 22:24:55 Checked 4.3 km NNE of Grindavík
    4.0 31 Jan 22:22:21 Checked 5.0 km NNE of Grindavík
    3.4 31 Jan 21:45:46 Checked 5.0 km NNE of Grindavík

  2. I’m sure the last time we seen activity like this was in 2014. Scattered all over the island. But looking at the drums puzzles me.

    • Keep in mind that the location of many earthquakes is not very precise. When they have been checked and verified by the specialist on duty, the map will clear up a bit.

  3. In the entire mess of red dots, there’s also a verified 3.0, which has snuck in, just south of Eyjafjallajökull. Don’t expect anything from it, just struck me as funny/interesting for some reason

      • The listed time of that one corresponds to exactly the time when the P-waves from the M4.3 arrived at Eyjafjallajökull. I don’t see any trace of it in any of the drums. Either it didn’t happen or the waveform is completely hidden by the 4.3.

  4. It seems to be cranking up over the last few hours, but a bit of a ‘scattergun’.

    • As Dirk S said above, the map will clear up once IMO staff have manually checked the quake locations. The automatic detection by the SIL system gets messed up when something like this happens. It looked like this also during the time when the dyke propagated from Bárðarbunga to Holuhraun. After manual correction of quake locations, the hypocenters became very much focused on the dyke.

  5. Did anybody knows something about the Michoacán-Guanajuato Field in Mexico? Especially about Paracutin? In the last 3 weeks is an EQ-swarm active ongoing , M3 – 4, 25 till 11 Km deep. This volcano started existing on 20. Feb 1943 when he surprisingly breaks out at a corn field. The eruption lasted till 1952 and the cone rose to 424 Meters height. I found it at http://www.vulkane.net from Marc Szeglat. Greetings

  6. At https://translate.google.com/translate?sl=nl&tl=en&u=https%3A%2F%2Fwww.rd.nl%2Fmeer-rd%2Fwetenschap-techniek%2Feifelvulkaan-een-slapend-monster-in-de-achtertuin-1.1622144 ” Eifel volcano, a sleeping monster in the back yard ” about the dormant Laacher See volcano in the VulkanEifel in Germany:

    “For several decades, micro vibrations have been detected here at depths of 40 to 10 kilometers. These tremors are becoming shallower. They have now reached a depth of 8 kilometers below the earth’s surface. “That is the bottom of the old magma room of the Laacher See,” De Reijke knows. Volcanologists therefore anticipate a new eruption. “Magma is taking off anyway.””

    This means that fresh basaltic magma from the mantleplume below the Eifel region can remobilize the magmachamber of the Laacher See Volcano, triggering a new and a violent eruption.

  7. If this should develop into an eruption. How important are those antennas to the west of Grindavik?

  8. I just glanced at the Iceland quake map. It looks like Thor sneezed over the South West of Iceland!
    The MAR must be restless.

  9. Does anybody have an explanation, or maybe just a good guess… most of the inflation seems to be taking place west of Mt. Þorbjörn, while most of the quake activity seems to be happening around a fault line east of the mountain? Doesn’t this seem a bit strange in the overall picture?

    • When the eruption happens: I will visit it
      If Svartsengi volcanic system erupts … There will be the most gentle and friendly hawaiian style volcanism.

      Wants to photobomb myself infront of the lava fountains
      Cannot wait Cannot wait until the magma is lets loose.

      Coud be because the inflation is pushing against the faults?
      The inflating boulge have likley not began to stress the upper cold rocks really yet

    • It looks like an old fissure line which could be the weakness and first to come apart.

        • Seems to parallel most of the sprungar along the SISZ. (Reidel sheer associated with the underlying transform fault.)

          In my line of thought, this means that not as much pressure is required to get magma to the surface. Like Hekla, a tectonic event can simply open up a path and if any pressurized magma is there, it will use it.

  10. Most of the earthquakes come from 5-7 km down. They are not on the surface although they are felt on the surface. Magma moving around is supposed to be the source of both the inflation and the quakes. Still somehow those two do not seem to be in the same location.

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