Unrest at Fagradalsfjall

The pleistocene volcano of Fagradalsfjall has started a phase of uncertainty due to a medium sized tectonic swarm associated with the volcano. At the time of writing there have been around 400 earthquakes ranging up to M4.0 in size. Fagradalsfjall last erupted during the last glacial period in Iceland.

Image by IMO.

The earthquake swarm is fairly intense for the location, but not unheard of in the region. All earthquakes so far have been tectonic, but in Iceland that can change if a swarm is prolonged.

As of now there are no signs that an eruption is near, but we need to wait a couple of days for GPS-stations to catch up. It also depends on how prolonged the swarm will be.

There has been no intrusion as indicated by the plots since 1997 in this location. Judging from the plots by Andrej Flis this is a magmatic intrusion from depth. This is supported by later earthquake signatures. So far 5 earthquakes are M3+ and 1 is M4.

More news, if any, will follow on this site. We also hope to be able to present plots of the earthquake swarm later on.

Earthquakes filtered at M2. No previous swarms visible in the data indicating that no intrusions has occured since 1997 in the area. Image by Andrej Flis.

Intrusion from East/West. Image by Andrej Flis.

Intrusion viewed from North/South. Image by Andrej Flis.

 

And a video also made by Andrej Flis, which shows the swarm in 3D. More graphics will be produced in the coming days, as IMO updates their earthquake catalogue with new data.

CARL REHNBERG

30 thoughts on “Unrest at Fagradalsfjall

    • In what may be a new record for Iceland the earthquakes have started to be mixed pure tectonic earthquakes with small VT earthquakes. This is normal for Iceland with a bit of magma moving up after large tectonic swarms, but it usually takes a bit of time before it happens.
      The earthquakes that are well located (M2+ and 99 percent) ranges from the MOHO at 10 km and have moved to a depth of 3km in only 4 hours. Also very fast.

    • The earthquake are migrating slightly towards Mt Keilir as they become more shallow. Keilir is also a pleistocene volcanic cone from the latter half of the last glacial period in Iceland.
      Neither Fagradalsfjall, nor Keilir, are central volcanoes, instead they are located on the same fissure swarm volcanic area.
      This means that if an eruption would happen it would be a Reykjanes Peninsula rifting fissure style eruption. Do note that there is a big big IF in that sentence.

    • It is a mystery. A ding for the right answer

      I should point out that swarms have happened at this location before.

      • Actually, this is a new thing at this location. Andrej could not find a swarm at this spot since 1997, and even the swarms nearby are about 100 times less energetic.

  1. Been sat quietly watching blogs and stuff since Bard…. this one looks like a rapid turn of events so far. IF there was to be an eruption, would you expect it to be a slow build like Bard was or more of a HIYA I WOKE UP sudden shouty type of thing.

    • I would expect intense seismic activity like this for a minimum of 48 hours and up to as much as weeks or months.

  2. Iceland Monitor says “Earthquakes like this are common to the area and occur annually.” Do they really? I don’t think I have seen a swarm like this for years in that location … or is my memory deceiving me?

    Held for admin approval by the system – sorry!

  3. One more: Wednesday
    26.07.2017 20:25:02 63.901 -22.312 6.7 km 3.8 99.0 1.9 km W of Fagradalsfjall

  4. Picking up in deed at Fdf. 43 M2+ already right now at IMO website. At the office they will have to check many of them still though.
    I am hoping to see a sequence of them tomorrow or so. Great effort, Carl and Andrej, thanks a lot! 🙂

  5. One more star:
    Wednesday
    26.07.2017 21:40:55 63.877 -22.302 7.9 km 3.6 90.01 3.1 km SSW of Fagradalsfjall

  6. The very rapid magma rise reminds me of the start of the Chaitan eruption in Chile. I don’t suppose the sheep are hiding any rhyolite domes in their pastures? 🙂

    Released from the Dungeons /Admin

  7. Pingback: Iceland seismicity – monthly review (July 2017 edition) | VolcanoCafe

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