Posted on by Jón Frímann

Small earthquake swarm in Katla volcano caldera

At the moment there appears to be a small earthquake swarm in Katla volcano. Currently this is just a earthquake swarm. All the tremor plots are normal and show no signs of harmonic tremors and magma on the move. The largest earthquake in this earthquake swarm in inside Katla volcano caldera was a ML1.3 with the depth of 1.7 km according to reviewed data from Icelandic Met Office.


The earthquake swarm in Katla voclano. It is deep inside Katla volcano caldera as can clearly be seen. Copyright of this picture belongs in Icelandic Met Office.


The ML1.3 earthquake as I did record it on my Heklubyggð geophone. Given the shape and how low period this earthquake is. I would say that it was created by magma pushing upwards in the crust inside Katla volcano caldera. This picture is released under Creative Commons licence, see the licence web page for more details.

At the moment (when this is written) it seems that this earthquake swarm is over. For the moment anyway. But it hard to know for sure if it resumes or something else starts in Katla volcano.

Update 1: A earthquake with the magnitude ML3.8 did happen in Katla volcano caldera at 02:02 UTC. Following this earthquake there have been many aftershocks. It is not yet clear if this means that Katla volcano is starting a eruption or not. But that should be clear in few hours if that is the case or not.


The ML3.8 earthquake that happened at 02:02 UTC. This is by the automatic SIL system, so it’s size can change. This picture is released under Creative Commons licence, see the licence web page for more details.


The location of the ML3.8 earthquake in Katla volcano caldera and the following aftershocks. Copyright of this picture belongs to Icelandic Met Office.

Blog post updated at 02:26 UTC on 18. July 2011.
Blog post updated at 02:40 UTC on 18. July 2011.

393 Replies to “Small earthquake swarm in Katla volcano caldera”

  2. Now we can see the ice cap full of holes… it was very regular some time ago!

      1. Yes, you can see some circular holes over the ice cap (as minor circular patches in the glacier), but these are difficult to see in the webcam. I see it every day I drive there and look with binoculars, or if you hike to the glacier directly (not recommended now!).

        But NO steam. I repeat, NO STEAM has been observed nor today nor in recent days. If it would happen, that would be NEWS!

        Please people, stop saying you are seeing steam, when it’s not.

        It is just clouds. Orographic clouds hang often over the glaciers, appearing like steam blowing. Now, 5 min later, the cloud does not touch the glacier, so you see, it’s not steam! Oh yes, every day I see the same “steaming” over the top of Langjokull and Hekla.

        The only real steam you can see is over the top of Eyjafjalljokull, not in every day, but in some days is very clearly visible, when it’s clear skies.

        Also other clouds appear to hang over the ice-free valleys over the slopes of Katla. Those is fog banks. The 1918 Katla eruption site is almost where the mountain appears the highest. When the eruption starts, you will see not steam, but a big and dark mushroom cloud there.

      2. I fully agree with Irpsit. If magma breaks through the crust and meets a layer of ice which is 200m in depth, it’ll be more than just a “steaming” hello. 😉
        Large explosions, a huge ash cloud and a massive release of meltwater will be the result.
        And it’ll be accompanied by earthquakes and a massive increase of tremor on all frequency bands.

        It would be exciting (and frightening as well) to actually watch this live on one of the webcams, that’s for sure.

  3. I did record the latest earthquake in Katla caldera. But it looked more like a tectonic earthquake then magma earthquake. But it did show some small signs that it might have been created by magma movement, rather then just pure tectonic movement.

    Automatic size was ML0.9 at 1.2 km depth.

    1. Jon, what if Katla is just experiencing a small rifting episode, only with minor dike intrusions, and no big eruption happening. Could that be possible?
      Apart than the everyone-expected large eruption, could that be what is happening now? I have heard that Katla has has on the past earthquakes swarms up to M 4.0, and no eruption followed.

      This makes me think of other rifting / tectonic-volcanic episodes in Iceland, as in Katla, Askja and Vatnajokull, which seem to last for a few years. Then, I could speculate that perhaps some minor fissure already broke under Myrdalsjokull and new ones might happen not in very soon but in the next couple of years.

      The other question is, why we never see earthquakes in the zone around Eldgjá, Veidivotn and Laki, why does rifting only happens there with volcanic eruptions, and these are always large ones?

      1. The fact that an earthquake has tectonic characteristics does not mean it’s not formed by magma movements. As a magma chamber inflates, the overlaying ground moves which causes ‘volcano-tectonic’ earthquakes. These have tectonic characteristics but are caused by magma.

      2. Just a thought (i’m no expert) but perhaps the eruptions are always large in the zone around Eldgjá, Veidivotn and Laki, simply because the rifting is taking place at the same time. No rifting in between eruptions so the ground just splits open because of the build up of strain from rifting either side of this area! Hmm, sounds too simple so it must be wrong!! 🙂

      3. Well I think you got it straight. However there are no records of any large rifting events, so we can’t know for sure how these eruptions occur. What we do know is that these rift eruptions are fed by the same magma source as their central volcanoes.

      4. Irpsit, I hope Katla has a minimal eruption and goes back to sleep. Prudence, however, dictates to prepare for the worst and then your no worse off.

  4. What is causing the spike at the end of most of the SIL stations?

    Is it the Magnitude 6.2 – KYRGYZSTAN ?

  5. The live webcam still is not working for me… Could any of you suggest another site where it has the same viewings?

  6. I would like to know how much inflation is estimated in Katla since 1918. Yes, I know it’s difficult. Rates of inflation were a few mm per year until the 1990s (that would make 40cm cumulative inflation), followed by an average 2cm per year in recent years (that makes about extra 20cm inflation).

    If I am not wrong, the inflation in Grimsvotn prior to the 2011 eruption was about 40cm (for 9 years), that this resulted in a 0.7 cu Km (VEI4). Hekla erupted in 2000 with 0.2 cu Km and following about 10cm inflation.

    Now, I am going to make a very rough correlation. Assuming that Katla has about 60cm cumulative inflation since 1918, and based in previous inflations of Grimsvotn and Hekla, could this mean an estimated eruption about slightly less than double size of that of Grimsvotn this year? About 1.0-1.4 cu Km (VEI5).

    But Katla has a bigger size, could this mean a difference in this estimation?

  7. I didn’t notice how long this thread became. So I’ll repeat my last comment:
    When the camera was zoomed, I could see the surface of Mýrdal glacier full of holes and cracks, pretty much the way Irpsit described.
    I wonder if all that dark ash deposited from Grimsvötn eruption doesn’t contribute to accelerate the melting process under sunny conditions, due to increased heat absorption.
    I take the chance to apologize for my insistence about the “steaming”. I am sure you people who can watch it live everyday have a totally different perspective, and if there was any geothermal activity we should know by now.
    Albeit, what we have seen yesterday did look quite different from what we are seeing now, or anything seen before, thence, my insistence.
    But not for a moment an ongoing eruption came to my mind, only a possible result of geothermal activity, which had already been confirmed in the previous joküllhlaup at Mýrdalsjökull.

    1. No problem, we are all here learning and sharing 🙂

      To answer your question, yes, the ash from Grimsvotn (and also Eyjafjallajokull) leads to much more melting, happening in a warmer than average summer. The ash is mostly from Eyjafjallajokull, because after the winter and before the eruption, the ice cap was much more white, and then become a bit more black again (but far less from how it was last summer!).

      In the news, they reported some enlargement yesterday of some of the cauldrons (holes) in the ice cap of Katla.

      To share my feeling, knowing what I know, what has been happening in Katla, and what local people and scientists have been saying, I think that yes, we are very close to a large eruption of Katla, probably a VEI5, sometime by late summer or early autumn, as Katla usually does.

      But volcanoes like to tease humans, so maybe nothing is going to happen. The other two volcanoes that we wait for, are Hekla (likely a small eruption) and Bardarbunga (this one could be large too). Finally, let me share that here in Iceland, there is no paranoia about volcanoes: it’s just the way that things are.

  8. So I’m on the earthquake table for the one that katla is locaed, and the most recent one is a -0.3 Mag….What does that mean? Would that not mean it isn’t an EQ at all?

    1. “Certain earthquakes have a negative magnitude, is this an error?

      No, it is not an error. As magnitude calculations are based on a logarithmic scale, a ten-fold drop in amplitude decreases the magnitude by 1. Let us assume that on a seismogram: an amplitude of 20 millimetres corresponds to a magnitude 2 earthquake. 10 times less (2 millimetres) corresponds to a magnitude of 1; 100 times less (0.2 millimetres) corresponds to magnitude 0; 1000 times less (0.02 millimetres) corresponds to magnitude -1. Naturally, a negative magnitude is found only for very small events, which are not felt by humans. ”

      http://earthquakescanada.nrcan.gc.ca/info-gen/faq-eng.php#negative_magnitude

  10. I wonder if the sheep on the Katla cam have signed waivers so that they can be filmed. This could be considered against the law if they were American sheep… just adding LITTLE humor to the evening. Renee

  12. Awesome blog jon. Ive been following this for over a year now. Impressive stuff. I dont know why you dont offer trips to visit some of these volcanos mate. Organised tours with yourself included as guide would make you a wealthy man and prevent the financial issues you mention. Kind Regards
    Geoff from London

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