Posted on by Jón Frímann

Earthquake swarm and minor harmonic tremor in Katla volcano

There has been a minor earthquake swarm in Katla volcano today. This earthquake swarm started around 09:00 UTC and lasted with breaks until 14:39 UTC. The largest earthquake in this swarm was ML1.7 with the depth of 3.5 km. Following this earthquake swarm there was a small harmonic tremor spike seen on few SIL stations around Katla volcano. It is unknown at this time if there has been a small glacier flood taking place. But if that is the case, it should be known in the next few hours if that is the case or not.


The earthquake swarm in Katla volcano caldera. Copyright of this picture belongs to Icelandic Met Office.


The harmonic tremor spike can be seen on this SIL station. It is located close to the end of tremor plot. Copyright of this picture belongs to Icelandic Met Office.


The harmonic tremor spike can be seen on this SIL station. It is located close to the end of tremor plot. Copyright of this picture belongs to Icelandic Met Office.

This harmonic tremor is small, but larger then last harmonic tremor that took place in this are about one week ago (far as I can remember). Currently there is nothing that suggests that eruption is imminent. This is just earthquake activity in the same place as it has been for the past five or so weeks.

Sorry for the short blog post. I have gone sick with some cold. No advice needed on how to get rid of it. That is going to take few days on it’s own.

96 Replies to “Earthquake swarm and minor harmonic tremor in Katla volcano”

  2. Get well soon Jon. Thanks for clearing up that little debate and you will get a small donation from me tomorrow sometime in the afternoon hope it helps.

    1. I would recommend zinc and vitamin C – either from diet (zinc = red meat, plus penty of fruit or juice for Vitamin C) or supplements @ Zn = 100% RDA + 1000mg Vitamin C in a soluble form. It wont cure it but may help to shorten your illness duration and reduce your risks of developing a secondary infection. Get well soon.

  3. The best for you Jon!

    After all, this was a minor harmonic tremor.
    The weather is stormy in South Iceland, and even so it was possible to take notice of this tremor event.

    I think this type of activity (tremor and swarms) is going to continue for a few more months until the sudden build-up to the large eruption. Could be this late summer, could be next year.

  6. One thing I take for granted: these colds spread faster than volcanic ash. Just getting rid of mine here too. 🙂
    We could compare those small spikes and harmonics in Katla with small “colds” .
    After three days they leave us.
    Nothing like “the final moment is approaching”. 🙂

    1. Caveat: respiratory disorders work fine as metaphors for volcanic events, although not as much as digestive ones. However, I prefer to stick to the first not to be… well… unpleasant.

      1. Oh, I don’t know. Here in the UK, the Doctors’ Surgeries are full of posters warning that if you have been coughing for more than a couple of weeks, then you need to see a Doctor to check that there is nothing more serious than a few earthquakes and harmonic tremors going on… 😉

      2. lol @ Cathy. I’ve been applying volcano/earthquake terminology to all sorts of illnesses and giggling away to myself. The kids believe that I have finally lost it. 🙂

        Hope you’re feeling better today, Jon.

    1. This just appears to be a rain water. As the conductivity is low when the water did rise.

      So I am guessing that this just a rain water.

  8. If you change it to 14 days it shows a similar spike – is that spike coinciding with the recent glacial flood?

  9. “No advice needed on how to get rid of it.”

    Too bad. Whiskey works wonders. It won’t fix your cold, but you won’t care.

    (grin)

  10. That graph has just dropped down to zero. I’d love to know what it means.

  12. This might just be the weather fooling me. Sudden wind change or something like that. It sometimes happens that I get fooled by the weather also.

    Next few hours are going to reveal if that is the case or not.

    1. Wednesday
      27.07.2011 00:54:16 63.613 -19.192 1.7 km 2.8 90.07 4.1 km SE of Goðabunga

      1. I don’t know. There is a storm in this area at the moment. We have to wait until it passes to know for sure.

        Until then I am going to get some sleep. Being sick + tired is not a good mix I think.

  15. Wednesday
    27.07.2011 01:18:33 63.614 -19.148 1.1 km 1.5 90.01 4.5 km NNW of Hábunga

  16. What is strange is that 28 seconds after the 2.8 M earthquake in Katla’s caldera, a 3.0 M earthquake occurred 192 km north in the middle of nowhere, not near any volcano nor the plate boundry.

    1. 33.31 % quality, I expect that is a phantom quake from the Katla quake and it will be deleted later.

    2. Does any focal mechanism describe these earthquakes available? or they are just volcanic earthquakes?

      If any agency can supply strike, dip and slip number of these earthquakes?

  18. Get some well-deserved sleep. (No, that’s not cold advice, just general life advice. 😉

  19. Wednesday
    27.07.2011 05:34:22 63.658 -19.092 1.8 km 2.0 84.36 8.0 km ENE of Goðabunga

  20. Get well soon Jon.
    Can someone explain the tremors graph at Askja please?
    http://hraun.vedur.is/ja/oroi/ask.gif
    Why are the low frequency tremor levels more “spikey” than those near Myrdalsjokull?
    What is causing the ” wavey” pattern to the higher frequencies?
    Is it due to being more exposed to wind or is there more running water nearby?
    Thanks for any help with interpreting this.

    1. I’ve been looking at askja for a while, she is very spiky but it seems normal for her.

      1. Thank you Helena. I have been watching too. I was told it is quite normal but nobody has explained yet what is making it so “spikey” also the rhythmic waves of tremors in the higher frequencies. Is there a local weather anomaly near the SIL station? Some of our hills here have a definite local “climate”. More strange wind currents and cloud than a mile or two up the road!

      2. Askja seemed to adopt this ‘wavy’ and dense tremor pattern at around the time of the Grimsfjall eruption; occasionally it settles down to the more familiar pattern seen at other stations. As to why, I have no idea but have been curious about this for the last months.

  21. I was looking at the graphs from http://vmkerfi.vedur.is/vatn/vdv_gmap.php then klik “innskraning”. I see rising water at station 413 with no apparent change in conductivity. At station 431 there’s also high water but with deacreasing conductivity.
    This means, I think, that the two fenomana are not related.

    I know there’s a storm. The rising of water at station 413 could be due to the rain’s. Leave’s us with the rising of water at station 431 with low conductivity. I think that’s melting water from the glacier due to geothermal activity. This doesn’t mean that I think that there’s an eruption is going on.

    1. Wouldn’t a rise in discharge due to geothermal activity show high conductivity due to the high concentration of solutes involved? As is the case with groundwater leaching as well. I would interpret a rise in discharge with low conductivity as rainwater in a efficient drainage network, as the water normally is more ‘pure’. I haven’t looked at any charts or anything, just my thoughts on the subject.

  22. I think that the initial warm water has a high conductivity. But this water melts the glacier ice. The melting water would then have a low conductivity. Similar to the flo0d water of the last flash flood.

  23. Hullo all! I’ve lost the link for the geophones, can anyone help me out please?

    1. Jon is the only one with “geophones” as far as I know …
      http://www.simnet.is/jonfr500/earthquake/tremoren.htm

      But if you are referring to tremor detectors, they can be found buy passing mouse over dots on the map and hoping onewill work (30% chance) …

      http://hraun.vedur.is/ja/oroi/tremor.html

      Or if you wana see all at once, from all over iceland …
      http://hraun.vedur.is/ja/oroi/allarsort.html

      If you can figure out anything definitive from any of those “tremor” plots, you may have great mystical powers which mere mortals lack. 😀

  25. I am now pretty certain if there is a VEI 4 – VEI 6 eruption at katla in the next few months, it will occur at the south end of the caldera, where this recent earthquakes swarm has occured, as I have been mapping the quakes recently and this is the spot with the highest concentration of quakes.

    Of course, I’m sure the experts will correct me if I’m wrong! 🙂

    1. Lets see if it will be in the next few months or even a year form now. Impossible to know.

      Given that the quakes are still quite deep (many within the theoretical magmachamber) the way to the surface can still take a few detours. I read somewhere that there is a cryptodome beneath Godabunga which could be the place for a new eruption. Lets see where the dragon will rear its face. 😉

      Also this is the beginning of the active season for myrdalsjökull. seismicity often increases during the late summer/autumn.

    2. I basically agree.

      I estimate 4+ to 5+ magnitude eruption, and will last 2 to 3 weeks.

      But there is minimal or no inflation/deformation shown on the GPS detectors, so yes I think it must be a month or more away, since I expect inflation/deformation must preceed eruption, as was the case with Eyja, and probably at least 2 or 3 weeks of inflation/deformation …

      http://strokkur.raunvis.hi.is/~sigrun/KATLA11.html

      Any opinions on whether or not clear signs of inflation and deformation are virtually certain to occur before any eruption?

      Any opinions on whether or not is it probable that at least 7 to 14 days of clear inflation and deformation (as seen on GPS plots) are likely before eruption?

      If an animation is made of weekly quake maps of myrdalsjokull over 1 years time, it shows a three-part progression …
      1.) weeks of building of quakes at Eyjafjallayokull cauldera, eruption, and decline
      then
      2.) weeks of building of quakes of Gola, peak, then a decline
      and now
      3.) just beginning of weeks of building of quakes at Katla Cauldera, with relative absence of quakes at Eyja and Gola

      If I had that as an animation, I’d post a link … but I just have the individual weekly map files (about 100) in a folder, with time-sequential filenames, and I sequence through them manually with a graphic viewer, so they appear as an animation.

  27. Well we dont know the cause of the tremor but it is rising again. Maybe Katla wont wait a few months, or maybe its just ice melting, but there are a lot of earthquakes at magma chamber depth..

    1. Weather has been getting worse there again over the past couple of hours.

  28. Does anybody know the avarage thickness of the ice that is covering Katla and how this thickness vary’s over the seasons. I would like to calculate the seasonal difference in pressure that is on top of the caldera.

  32. I think the un-named “observers” and “geophysicists” might be Jon and posters here?

    “as observers today reported an increase in the strength of tell-tale earth tremors.”

    “a week after geophysicists warned of an ‘imminent danger’ of an eruption on the island”

    http://www.clickgreen.org.uk/news/international-news/122385-iceland\s-feared-katla-volcano-shows-further-signs-of-eruption.html

    “Observers believe ‘unusual’ magma movement deep beneath Katla could signal the early stages of activity that could lead to a huge explosion”

  34. Thank you Jules.
    I shall continue to watch and see how she settles. I wonder why I think of Volcanoes as feminine!

    1. Could be the fickle way they tease……….

      never mind
      🙂

    2. So difficult to find time these days, but You nearly have me starting an essay on why some of us so utterly seem to need classifying things in feminine and masculine… 🙂
      To be shorter I prefer to go in Your direction and put it that way – because like women, volcanoes make life better and worse at the same time. So dangerous, but they add immense quality to our existence. And they are simply beautiful.
      And I say that after 17 years of relation… 🙂

      1. Awwwww! GeoLoco . How eloquent.
        @ Dan. You know you loves us like that!
        A little spot of revision in Jon’s ost back in May this year about the Askja area . Interesting happenings and very useful information too.
        http://icelandgeology.net/?p=901

      2. The truth is always easy to tell…
        Ok, get’s terribly slimy. But who would put me wrong?
        🙂
        Besides, I don’t know if RonF still takes the bets (?). I say significant increase in Katla activity in the night of the 15 to the 16th of September. VEI5 at may 18th of 2012, followed by 10 days of “production”. explosive the first 3 days, then turning in effusive. Hekla rumbles august the 15th, but no real eruption yet. I’m talking of 2011.

      3. This all based on precise calculation knowing the position of the main quake-zones in the last 14 month, of course… And the chemistry of our underground soup in Iceland is so simple that it makes it all very easy to predict… 🙂
        It’s nearly like women between 13 and 53 in front of a big Zara-boutique in Paris that announces huge sales. How many may go inside? Hm, 89.7%, the rest are at H&M…
        Uhm, yeah, aah, it’s ok to hate me after having read these lines… Wasn’t meant bad… 🙂

    3. Perhaps it is because they have trouble making up their minds about what they are going to do.

    4. The name Katla is a female name in Iceland… haven’t found male names among the volcanos in Iceland 😉

  36. Wednesday
    27.07.2011 18:38:55 64,094 -19,433 2.1 90.01 0.9 km 16.1 km NE of Hekla
    A bit far

    1. Jep but on the “good” side of Hekla, not in the SISZ… and the location and depth might change since its 90%

  37. at what point does normal earthquake activity in katla become not so normal? my understanding is that most quakes that occur there are nothing special, unless if they occur in swarms and if harmonic tremor is detected? is that correct?

    1. Even some swarms and harmonic tremor are nothing else than “normal” phenomena in a build-up phase of such a volcano. It’s indeed this kind of previewing sings that are worth looking at, but still all can happen by some kind of surprise. If something really starts happening, You will not need to be any specialist to see it on the different quake, tremor, gps and and and plots and charts.
      But if anyone may “sense” things before they happen, then it will be great “freaks” as the ones around Jon. Oooooooh yesss! 🙂

  38. Hi everyone —

    Perhaps this has been covered before on the blog, but I have some geographical confusion in regard to the exact location of Katla. When you look at the IMO map of Mýrdalsjökull, it shows what seems to be one giant caldera with two smaller ones within. Is Katla the one to the southeast, and Goðabunga the other to the west, or does “Katla” imply most of the area covered by Mýrdalsjökull?

    Also, is Goðabunga a volcano in its own right, or does it just designate a part of the Mýrdalsjökull area?

    I would love to see a map showing the exact location of the Katla volcano along with the previous eruption sites, if such a thing exists.

  39. Goðabunga and Hábunga seem to be summits, Goðabunga being the highest.

    Katla is the big caldeira.

      1. Thanks to TBVH and Marie for the info and maps! I am a map junkie so they are very much appreciated, and the area makes a lot more sense to me now. It is hard to imagine that the Katla caldera is so vast (100 sq. km!) and could erupt in so many different locations. In case anyone else is interested I also found a map on Wikipedia that shows some of the former eruption sites: http://en.wikipedia.org/wiki/File:Location_of_Katlas_caldera.png

  40. This is the most interesting quake in a long time:

    Tuesday 26.07.2011 06:04:39 64.007 -19.576 20.8 km 1.2 99.0 4.8 km ENE of Hekla

    Take note of the depth, 20.8 km, and the location, on the SW-NE trending “fissure line”right under Hekla. This quake could signal that magma is on the move and as Hekla is “almost aseismic”, the next thing might be a few very large quakes (ML 5 – 6)followed within an hour or two by an eruption.

    Then again, this quake might signify absolutely nothing! 😉

    1. The owner of the garage did go too close the geophone, or his mobile phone did get a call at that time.

      This is just noise, it happens on my geophones all the time.

      1. Thanks!

        Is that the same kind of mobile phone interference that makes my computer makes strange clicking noises when my phone is about to ring?

      3. Well, in that case, I have learnt something today! As I was posting my question, I was just thinking that my computer hasn’t clicked for ages, and now I know why. Strange old world! 🙂

  42. I’ve noticed in that over the past 48hrs there have been some deep quakes around the habunga area of Katla. I seem to remember this happing a few weeks back in the days before the big flood.

    Starting with most recent:
    19.4km
    9.8km
    14.1km
    16.3km

    Could this be a fresh load of Magma pumping up into Katla’s magma chamber??

    1. It might be new magma, but most likely it is the magma that is already there that is moving inside the magma chamber.

      I do not think that the deep earthquakes are good news. But so far the magma is quiet where it currently is.

  44. Sorry, but has the IMO page frozen? Or is it all just a bit quiet around Katla?

    Thanks in Advance 🙂

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