Katla and the art of reading data

Hand coloured picture from the 1918 eruption of Katla.

Hand coloured picture from the 1918 eruption of Katla.

There are several factors that are monitored in an active volcano. For most Icelandic volcanoes the things that are monitored and are publicly available are tremor, earthquakes and GPS. In the case of Hekla there is also available mountain strain data from borehole strainmeters.

For some volcanoes there are also periodic gas measurements taken and measurements of the conductivity in the water. These are though normally not made publicly available. But, the available data is enough to give us a lot of information on any given volcano.

A brief background on Katla

Katla is one of Iceland’s larger central volcanoes and is capable of having eruptions that are VEI-5. It is not one of the more prolific volcanoes in Iceland, at least compared to Bárdarbunga, Hekla and Grimsvötn. Including the 934 Éldgja eruption Katla has only erupted 15 times since settlement of Iceland. That would make an average of one eruption about every 72 years. The last real eruption at Katla was a large VEI-4 in 1918. After that there has been at least one episode of what could have been a hydrothermal event or a phreatic detonation in 2011.

Katla has a large and shallow magmatic chamber situated between what is believed to be 2 to 6 km depth. The eruptions have a tendency to happen in different parts of the caldera. In 2002 a period of increased seismic unrest began under the volcano. It is though important to differentiate the seismic activity going on in the Gódabunga cryptodome and the earthquakes inside the caldera since they originate from different magmatic emplacements that most likely are not related.

At the current moment there is not much pointing towards an eruption in Katla, let us be very clear on this.

Reading Katla

Image from Icelandic Met Office. Legend of earthquake activity and data from 1999 to present.

Image from Icelandic Met Office. Legend of earthquake activity and data from 1999 to present.

The first one has to remember is that one has to read all the data put together and not obsess with just one data set, and then one has to compare it with known historical data that is available. If one does not do this one will be lead astray time and again and start jabbering about Katla being close to erupting.

Let us start with the earthquakes at Katla. These can be divided into 3 categories, shallow earthquakes between 0 to 2 kilometers depth, medium depth earthquakes at 2 to 12 kilometers depth, and the deep earthquakes that take place between 12 to 30 kilometers depth.

If we look at the shallow earthquakes they are cyclical in pattern and happen far more often in the summer. This is most likely due to them being caused by an increase of water due to glacial melt affecting the hydrothermal system in the caldera. There is also blocking and fracturing occurring at the caldera floor. These earthquakes are mainly uninteresting unless they are large and accompanied by a sharp rise in tremor. If that occurs there is most likely a hydrothermal event or a phreatic event taking place. A real eruption would give more data that would show well in advance, mostly as large and fast uplift of the GPS stations.

The medium depth earthquakes take place due to motion of magma from different parts in the system or by cooling and contraction of a part of the magmatic system. These earthquakes are normal for a volcano that is active and are not normally a sign of an impending eruption. During a magmatic emplacement there will be an increase in these earthquakes, but then you will also see uplift at the GPS stations. There is currently no uplift being recorded at the GPS stations of Katla.

3D-plot of the current earthquake activity at Katla made by Cryphia

The most interesting earthquakes are the deep earthquakes. They are often taking place as new magma is forming, or as new magma moves up into the system. One can see these earthquakes as a potential for a new magmatic emplacement, or as an early warning for increased activity further up in the system. Since 1999 the amount of deep earthquakes have slowly increased, they normally consist of small earthquakes, but there has been a few that have been about 2M. From 1999 up until now the trend have been towards ever deeper earthquakes, as well as an increase in numbers. This is so far the only real evidence that Katla might be nearing an eruption.

If we then read the GPS data we can see that Katla has had at least two minor episodes of magmatic infusion into the system. These have not been large and are normal for an active volcano. If we compare with the uplift of other volcanoes in Iceland we believe that we will see a much grander amount of uplift before a real eruption.

If we put it all together we see an increasing amount of deep earthquakes that might be a sign of future unrest, but when we take into account that pretty much every other sign is lacking we get a picture that is rather different than what people think. In reality Katla is at least 1 to 10 years away from being able to have an eruption. This could of course change at any time, and rest assured that you will read about it here if that happens.

So, now that we know that the world press is wrong about her being ready to blow, how about the idea that she is a doomsday volcano? That is not true either. If we look at historical eruption data for Katla we see that a likely eruption would be between 10 times smaller to about ten times larger than the 2010 Eyjafjallajökull eruption. If we compare with the Grimsvötn 2011 eruption a Katla eruption would most likely be 50 times smaller to twice the size. And that is far from a doomsday volcano. One should though note that the ash from Katla could cause problems for aviation. So, if an eruption occurred there would most likely be widespread problems during the first week or two of the eruption, but that is about it.



89 thoughts on “Katla and the art of reading data

  1. Nice post, but a question regarding the rotating plot:
    What is the surface expression of the pale blue stack of quakes that seems separate from the rest of the clump?
    I can’t get the thing to go full screen for some reason – so I can’t read the lat/long.
    The stack looks to be beneath the blue blob at the very top edge of the plot on the 4 second mark.

    • If you right click on the video you can copy the URL and open in another tab.

      I guess you mean the swarm going to Eyjafjallajökull in the west.

      • Area there is Snaefell. Its a volcano (not confuse with Snaefelljokull) that is just in the edge between what it dormant and what is extinct.

        No one knows its last eruption but it was late Pleistocene. No geothermal activity, so by definition it is an extinct volcano, but with potential to erupt one day again.

        It is a stratosvolcano taller than Hekla. And it placed along a volcanic belt that includes the mighty Oraefajokull, Esjufjoll and Snaefell itself. Little is known about these 3 volcanoes, except that Oraefajokull had two large and violent eruptions in 1362 and 1727. And Esjufjoll something in the late twenties, some unconfirmed VEI0-2 eruption.

        • Thank you Irpsit. I think to label any Volcano in Iceland as extinct would be tempting fate! It just needs a change of direction from the “Plume” beneath or a bit of a tweak from the micro Plate to keep volcanologists on their toes 😀

  2. />Hi

    Very interesting on 2 main points. First one is that personnally I’m not very well informed on Iceland volcanoes (there are really too many of them !).
    Second one is your explanations, Carl, which shed a very clear light on the present situation and on monitoring in general and in understandable terms. For this Thanks !

    There will be a plot zooming on Katla tonight. It’s presently running. I think it will come as a complement of Chryphia’s. I’ll explain also why it took me so much time.

    • Silicic magma is formed by either partial melting of the lower crust beneath Iceland, or by stagnant basaltic magma which differentiates inside the magma chamber and becomes dacite or rhyolite. I think that both Katla and Grimsvötn are able to produce VEI6-eruptions like the Pinatubo did in 1991.

      Did the Eyafjallajökull during its explosive eruption in 2010 also produce pyroclastic flows by collapsing of the eruption column?

      If you’d like to erupt your own volcano on your PC, use the program Erupt developed by Wohletz. You can simulate all kinds of eruptions, from basaltic Hawaiian eruptions to cataclysmic VEI8-eruptions with massive pyroclastic flows and caldera collapses. Program is described at http://www.ees1.lanl.gov/Wohletz/Erupt.htm and can be downloaded at http://geodynamics.lanl.gov/Wohletz/KWare/Erupt3_Install.exe.

      • Katla has done a few VEI5 in the past 10.000 years but most of its eruptions were VEI4. just like Eyjafjallajokull or Grimsvotn 2011. I am not particularlty worried with Katla. Neverthesless, Katla has also probably done a VEI6 (the Vedde Ash, it could have been anythng between a VE5 and a small VEI6). Read the reports on it, including Iceland, and you stay with the impression that this was a massive ash eruption.

        VEI6 in Iceland occurred more often that most people think, t.ough they are still rare. Examples were Bardarbunga (1477), Grimsvotn (early Holocene), Hekla and Oraefajokull (these two were either a large VEI5 or a small VEI6, Hekla3 and 1362 Oraefajokull eruption)

        So we had 2 VEI6 eruptions in the last 1000 years in Iceland. I reckon they happen once every thousand years in Iceland, while VEI5 happen every other century in Iceland (last one was Katla 1918 and Askja 1875). VEI4 happen a few times per century in Iceland.

        Did Eyja produced pyroclastic flows? No. But Hekla 2000 did, albeit extremely tiny ones.

        In Iceland, pyroclastic flows are mostly unknown. But most volcanoes are located in inhabited areas or within glaciers.

  3. Dead zone quake?
    24.07.2013 18:43:37 64.230 -19.305 1.1 km 1.0 44.38 11.4 km WNW of Sigöldustöð

    • Yeah, its dead zone. Eruptions have happened there but apparently all way smaller than any Laki like thing. They have happened even in recent centuries, but smaller fissure fires. Some of these are attributed (wrongly) to Hekla, in GVP.

  4. There seems to be many misunderstands out there on Katla. The public have improperly been informed. Well that is usual nowadays.

    Looking at eya’s eruption wouldn’t that eruption be considered big for a volcano of that size?

    Katla should not be as big of a concern as has been described. I would imagine that those tidal waves it creates are big though.

    • Tidal waves? I assume that you are implying tsunami.

      Katla making a tsunami… interesting thought experiment. The only two mechanisms that I can envision it being able to do that, would be via a large eruption’s column collapse hitting the ocean, or a full on beyond science fiction lateral flank collapse/blast that takes a chunk of the island with it.

      In the first scenario, that’s still not gonna be much of a tsunami, in the second, I don’t thing the effects are going to be of much concern considering the other effects that would have to be dealt with.

      Scenario #1, Sort of plausible, but highly unlikely. Scenario #2, “GTFOOH, You’re kidding, right?”

      (Note, both of these scenarios are of my own construct and do not reflect any scientific study that I know of… in other words, pure fiction. There was a study that I saw a while back that looked at base surge induced tsunami like effects, but that was on a completely different system… and involved a closed body of water)

      As for Jökulhlaups, though destructive in their wash plain, I don’t think they are going to have much of a tsunami like effect on the open ocean basin.

      From WickerPeeAtYa:

      Mýrdalsjökull is subject to large jökulhlaups when the subglacial volcano Katla erupts, roughly every 40 to 80 years. The eruption in 1755 is estimated to have had a peak discharge of 200,000 to 400,000 m3/s.

      • The glacial flooding is what I was thinking about probably. Another misconception in definition to what the public or for people like me just entering this subject of volcanism, thanks.

        • If the lore interests you… ask about Katla, Bardi, and the Whey…

          Interesting story… except Bardi didn’t make out so well.

          Irpsit, the floor is yours if you like 😀

      • I have heard but not confirmed that a tsunami-like wave was reported in several coastal towns in Iceland (Eyrarbakki, Þorlákshöfn, Westman islands) but it was a flooding wave, with very minor destructive power.

        I also heard the 1918 jokulhlaup enlarged the coastline by 5km further into the sea. And that they had to redefine what was the southernmost point of Iceland, due to that.

        Anyways, if you compare old maps of Iceland with the new ones, I think I can remember it being slightly different in that area, due to increase in sediment deposition in the region southeast of Myrdalsjokull. But very old maps were even crazier due to bad scaling of the maps. They are funny to look to.

        Still Katla does not generally have a bad fame as Hekla has, or as horrible as the story of Laki. Hekla was known to ash cover Iceland several times. Katla never. Dead zone eruption did that too; at least Vatnaoldur and Laki.

        • I must say these are local reports and I do not know whether they are true. The 1918 eruption goes back so long before any living person that memories and stories fade away.

          Must be a way of finding it out. Probably Jon (jonfr.com) knows about this.

  5. Many years ago, I was tasked with a rather tedious but illuminating job. “Data fusion”.

    This involved accumulating target position data and melding it with detected target data from radar and esm. The purpose was for the outbreifing of the exercise, and for use by the team evaluating how the event went. Another data monkey would take my info and meld it with what the team running the event gathered, and then some engineering level group would then analize it and come up with some “thing” based on the research.

    • As volcano fans, we have to do our own data fusion. Occasionally, a more knowlegable person will come along to set us straight, but lacking that, we have to rely on critical thinking in order to come up with a plausible explanation for what we see. In order for it to be plausible, it has to fit all of the observed data, or at least a really good fit. athe better the fit, the more likely that it is correct. Most important is to realize that no matter how well it fits, there is always the chance of being wrong… and accepting that.

  6. PuterMan also, some new info (to me) on your comments about the quakes being seasonal: The earthquakes under Goðabunga show a clear seasonal correlation with a distinct activity during the autumn. This pattern changed in 2002 to more continuous activity. The earthquakes in the caldera have a swarm character, and the largest earthquakes occur there. Again this is from another scientific document here . Page 13. So did this change to more continual activity change again back to seasonal only in recent years? Or does this still apply? Note part of the conclusion in that document: In recent years Katla and Grı´msvo¨ tn have shown the highest inflation rates with ca. 3 cm/a. and tilt data from Hekla suggest that magma accumulation is taking place. At Katla, continued uplift coincides with elevated seismicity. If uplift and internal pressure build-up continues at these volcanoes, eruptive activity is a likely consequence within several years. Considering that paper was put out in 2006, within several years means right about now, or last year really. Sounds to me like we’re already overdue for Katla to erupt.

    Released from the dungeon by Kilgharrah

    • One thing to remember is that the seasonal quakes are the shallower ones, and that the medium ones are following a more standard earthquake swarm pattern. The deep ones do not follow any recognisable pattern except that they are becoming more frequent and tend to be deeper over time.
      This makes the picture confusing unless one divides them up.

  7. I’m still skeptical that the large caldera systems of Iceland were created by long periods of recurring vei-4 and vei-5 eruptions. Carl confirmed my thoughts in that Grimsvotn cycles through caldera collapse, often collapsing after VEI-6 eruptions. I think this is likely quite true for the other volcanoes that have large calderas as well, although they probably go about the process via more evolved magma due to a lower rate of magmatic input.

    Most caldera structures produced from gradual subsistence over a period of years or centuries are small, and don’t feature steep walls. I believe quite a few of the Icelandic calderas feature somewhat steep, and deep walls. If sudden caldera collapse were possible from gradual subsistence, it would mean that the caldera ceiling would have to stay put for years, or even centuries despite no support structure beneath it to hold it up, which simply doesn’t happen.

    What we do see in Iceland is two things – Relatively large calderas, and quite a few volcanoes that have a history of producing lots of rhyolite. Usually those two signify either a past history, or a potentiality to produce large eruptions in the VEI-6 to VEI-7 range. I don’t know if there has ever been a VEI-7 in Iceland, but I don’t think that it would be entirely crazy to believe that some time in Iceland’s geological history there has been, or could be a VEI-7 eruption. The catch here is it could be buried under miles of sediment, glacial till, lava beds, or simply eroded into oblivion and entirely extinct.

    • Katla, Hofskokull, Bardarbunga have all deep and steep calderas. But at same time they are burried under thick ice. My guess was that either the ice dug the caldera, or it was caused by past explosive eruptions. Bardarbunga for example is something like 600m deep and steep, on its 15km wide caldera. Many other similar sized and shaped calderas around the world are described as explosive calderas.

      I think most Icelandic volcanoes are not only little studied but their evidence is mostly burried and eroded under huge glaciers and thick ice caps.

    • i don’t think that you can infer collapse speed from the sheerness of the wall angle.

      Even with a slow evacuation of an underlying chamber, the roof will not collapse until enough stress accumulates to overcome the tensile strength of the roof rock. Later erosive action will/can act to lessen the slope angle of the resulting scarp.

    • I would say that you are correct.
      Regarding VEI-7 eruptions. Well, I think that there might have been one or two over the entire Icelandic geological existance, but there has been none during the last 12 000 years.

      Regarding the possibility of a large steep walled caldera. You are forgetting that Icelandic volcanoes on occation can produce eruptions where tens of cubic kilometers erupt within a few months. That would leave a rather large unsupported magma chamber roof.
      There is actually a neat trick to see if a caldera has formed this way or not. Just look at the angle of the ring faultline. If the are angled outward there was an explosive formation and if they are inwards it is subsidance.
      Katla, Bardarbunga and Grimsvötn 1 to 3 caldera are explosive calderas. Askja is probably a subsidance caldera (Askja 1 that is), Krafla one is explosive and Krafla two is subsidance. And so on…

  8. Hi

    This is Iceland earthquakes’ animation from July 1st to 24th. With a final zooming on the recent Katla zone quakes.

    The first part of the video is an event by event display with rotation. Current earthquake is shown in bright red. Its size is proportional to 16 times the event’s magnitude.

    The other earthquakes are shown as colored dots according to left side of the colorbar (date). The size of the dot is proportional to 2 times the magnitude. The right side of the colorbar shows terrain elevation scale.

    On the last part there is a progressive zoom on the Katla zone.

    From what was written recently in the post, the shallow depth of the majority of earthquakes could come from the interaction of thawing ice water with hot rocks.

    Data from IMO, NOAA, made on Gnu Octave using avconv for the video.

    I’ve modified a few things with this bit of code, mainly the date on the colorbar and the zooming factor in the end.

    Enjoy !

      • The zooming effect is quite empirical, I’ve played a bit with the settings. In short you have to take into account the rotation (1 degree at a time) and the zooming (here in 480 steps for a zooming effect of 500 times). There is also some tilt (the rocking chair), but I reduced the effect to avoid confusion – getting people seasick -:)) . I was lucky to get this orientation on the second try only. FY information, a run like this takes about 6 hours of puter time. Of course I’m a lazy boy and have not tried to optimise the code.

  9. Nice Article Carl

    Did’nt the UK fund the installment of more monitoring around Katla after the “Eyja watcha call the” eruption? Is it possible that increased monitoring has captured the more events that appear evident in 2011 onwards?

    Also I think the Katla fear originated from Locals as a threat of Glacier Floods, more so than ash. That has been mis-interpreted by the world media that since katla is a bigger mountain then they assume much bigger eruption/ash landing on Europe, when really (as you pointed out) it only has the potential of slighty more than the last Grimsvötn eruption at best.

    • You are correct. there are more minute quakes now. But anything above 0,3M was detected before the upgrades. Locationing has though become much better.

      You are absolutely correct, it is the Jöökulhlaup risk that worries the Icelanders, not the ash per se.

    • If detection bias would be the only reason one would expect an increase of smallish eqs but not of the 3+ earthquakes, which can also be sensed from remote.

    • Jon has a lot of experience looking at those webicorders. I wouldn’t discount his opinion of them so quickly. That doesn’t mean he is 100% correct, but it is very very likely that he is.

  10. OT. We have had snow in more than 150 cities in three states of southern Brazil.
    That’s rare! I’ll put the link for some pictures taken by locals. Noteworthy is the snow covered slopes of surrounding hills in Florianopolis, a well known summer resort.
    Rio is now gray and rainy and temps haven’t gone beyond 16º C. Since there’s no heating systems whatsoever, I’m wearing clothes I keep for traveling to Europe and USA. 🙂

    • Hi Renato

      I’m wearing my summer clothes (T shirt and the like), which I nearly never do in summer in the north of France -:)) ! (only joking, hope it will not last for you as you’re not used to it). Thanks for the link, this is a noteworthy event.

    • Wow! Never think Brazil and snow. Argentina and Chile, But my concept is Amazonia and
      We are 36C forecast and Dry lighting humidity about 10%..In Ne Oregon..

      • You lucky you, I just have to reacclimatize from the 14 degrees at Svalbard back to the 30C here… *Phew… 🙂
        Well, they invented beer for days like this. 🙂

    • Erroneous quakes that have been removed. No fracking going on there. All earthquakes taking place there would be either tectonic or magmatic.

      • Them are real quakes, made by dynamiting – new dam is still under construction!
        (Dam construction vas verified by own Mk.I eyeballs two days ago, augmented by correction leses… – Pics can be posted for 100% validatey).

        • Well… one could call ’em quakes… of sorts. But, I would call them detonations.
          We have a lot of them here when they blast in the mines. Largest sofar was a 4.3M earthquake blast. And rumour has it that the new mine at Björkdal will try to surpass that in it’s inaugural blast, rumour is that they will go for a 5M blast.

        • True, detonations they are (see depth 0,0 km), not arguing any. All I wanted come across they are not tetonic or magmatic. This is rockfill dam, so needs lots of sorted rock, both on surface and in layers to improve “non-leakage”, and to avoid erosion by wind and rain over next hundered years or so.
          BTW, I observed (from air) yesterday the crater rows from the Veiðivötn fissure, from year 1500hundreds I guess, truly awesome to look at, both in black desert sands and beyond they spring Gray-Moss, quite in-contrast to other areas. I could not take many pics of that as that was on other side of plane (me did some “light steering” whilst captain was taking pictures)
          Attached is similar direction (not same angle) as Katla 1918 photo in header of this blog post. Godabunga is the rather steep mountain behind Thorsmork (Langidalur, Þórsmörk), Katla Caldera and Mr. Bardi behind 😉 http://i41.tinypic.com/rur30j.jpg

    • Done it. Thanks for the hint, cbus. I’m having problems logging into Erik’s blog lately, so I seldom visit his page, which is a pity.
      I’m sure everyone here will enjoy the post very much – sort of food for thought that is fit to our tastes.

      • Most definitely. Re the logging in, I finally succumbed and got a disqus account much against my will. so far it has worked ok but I feel kind of, well, dirty.

  11. I would like to highlight all the work going on to keep this site growing and amount of excellent, hard work that is required to get every post online. If I could I would buy a round of beers for you all.

    As you all cannot be here to do so, I will buy beers and drink them all in your honor. 😀
    I see that our heat wave has now left Ireland and what is left is affecting Iceland. I think some extra melting will happen these next few days.



    Sea ice is low again this year, not as low as 2012 season.

    • Thanks! Yes, hot as hell here, but sea fog is cooling the beaches. Two days ago I saw 25°C on thermometer in dashboard, and I was moving at 90 km/h, today there was 21° at Thingvellir…. That was quite hot enough … and there is lots of red areas on my skin. Don know what this is,,,, not seen such since last year … 😉

      • Been out helping a friend irrigate her sapling trees. various conifers, oaks,maples etc.
        She runs a nursery, I help when she needs extra people and I get paid for it. Don’t need
        to pay a gym or a tanning salon. Due to my mongrel heritage I never burn,just get tan…
        37°C today.No rain…

    • 36°C as I was walking into the last call for the day.

      Spotted at a Bank Sign over grass. The parking lot seemed a bit hotter. (several acres of asphalt)

      Last week, over in Alabama, a child playing outside managed to get himself locked in a car. The grandparent found the child when he didn’t come inside when called. He didn’t make it.

      • It whould not be turned around if you channel-ed some of this warmth up here, or you actually are, via the Gulf Current conveyor belt .. 🙂

        • Unfortunately, we did have winds out of the East for a few days, then it spun 245° and is now flowing towards the SE. That is indicative of a low forming up towards the NE from here. If it gathers itself up propper, it will head off towards Icelands area… eventually.

          Weather dude was yammering about the weak arsed cold front stalling out and heading back to the north… which is not something that bona fide Lows are fond of. That would mean it was a high instead. My guess is it’s confused about what it wants to be.

          • Might be that a low is making love to a high out over the Atlantic… and we know what the offspring of that would be…

            Here it is a balmy 34 C today. The idea of traipsing down into the basement office felt like a good idea.

  12. Well, I guess no one is gonna tell it. Here is a snippet:

    Once it happened that the Abbot of the Monastery of Thykkvabœ had a housekeeper whose name was Katla, and who was an evil-minded and hot-tempered woman. She possessed a pair of shoes whose peculiarity was, that whoever put them on was never tired of running. Everybody was afraid of Katla’s bad disposition and fierce temper, even the Abbot himself. The herdsman of the monastery farm, whose name was Bardi, was often dreadfully ill-treated by her, particularly if he had chanced to lose any of the ewes.


    Most tellings I have read, they were trousers and not shoes… but I’m just some guy wandering around on the Internet and not a historian.

    I can postulate that Katla was still a Pagan and had not converted. If so, this may have been a warning tale about the evils of paganism. I don’t know if Bardi is connected to Bardabunga (the bard’s bulge or something to that effect.)

    Bard → “minstrel poets who composed and recited verses celebrating the legendary exploits of chieftains and heroes.” Bardi was probably related in some fashion to a Bard… or was a Bard when not looking after the sheep. Hell, he may have even sang to the sheep on occasion.

    • Brenda la Fay is quite correct in questioning CNNs misconception. 😀

      It implies that there is a lake of magma. At best, you have a chamber of melt and mush. But most likely, its a colllection of interconnected tendrils… much like the threads in a ball of cotton… but larger.

      If I remember correctly, that “threads in a cotton ball” analogy was from quite a while back.

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s