What’s going on at Katla? Part III

Image from Wikimedia. Aerial picture of Katla.

Trying to make sense of complex phenomenae

In the first two instalments, we had a look at Katla as she appears through media and what she has done historically. It is now time to have a look at what’s going on and try to paint a coherent picture of what she actually is, is up to and able to do, but first let us recapitulate what we found previously:

  • There is a general interest in Katla because she is and has been regarded as a very dangerous volcano by generations of Icelanders.
  • The presentation of Katla in media is skewered by vested interests ranging from scientists who hope to increase their professional and/or public standing, people trying to cash in on the interest generated such as journalists and bloggers, and finally, there are people trying to increase their standing within the subculture of doomsaying and alarmism.
  • Katla is a massive but relatively young volcano, located on the MAR, and formed when Iceland was covered by glaciers.
  • The records include two large fissure eruptions on the NE flank of Katla; the prehistoric 5 km3 Hólmsá Fires of 5550 BC and ~22 km3 Eldgjá eruption in 934 AD. In historic times, the 1100 years or so that Iceland has been settled, there have been 27 listed eruptions (28 if the inferred minor subglacial 2011 eruption is included), 23 of which have been explosive.
  • Of the 23 explosive eruptions, three have been assigned VEI 3, thirteen VEI 4 and four VEI 5.
  • The four VEI 5 eruptions are remarkably alike in size at 1.2 – 1.5 km3, which is at the upper end of what Katla probably is able to do but at the very lower end of VEI 5 eruptions.
  • Tephrochronology (in some cases complemented by radiocarbon dating) has identified a further 103 eruptions going back ~8,500 years, and in the few cases where a VEI has been assigned, none have been greater than a VEI 4.
  • Katla does not possess a caldera-sized magma chamber.
  • In order to account for the great number of explosive eruptions which involve more evolved magmas, Katla could have more than a single magma chamber.
  • The available evidence suggests that in order to break through the up to 700 meters thick Mýrdalsjökull glacier, an eruption must be at least a substantial VEI 3.
  • Direct and (primarily) indirect evidence suggests that smaller eruptions, mainly basaltic VEI 0 – 2 eruptions are severely underrepresented in her eruptive record and ought to exceed the number of observed eruptions.

Fig 1. Mýrdalsjökull showing the main glacier outlets, directions of jökulhlaups and areas affected. E –
Entajökull, S – Sólheimajökull, K – Kötlujökull, M – Markarfljot, Ss – Sólheimasandur, MS – Mýrdalssandur.
Eyjafjallajökull is to the left and the smaller glacier above is Tindfjallajökull (adapted from Google Maps).

The greatest danger from Katla comes from the very quick and extensive melting of the glacier caused by large eruptions which results in destructive jökulhlaups. There are three major outlets from the glacier: Entujökull to the NW that empties into the Markarfljot river and valley north of Eyjafjallajökull, Sólheimajökull to the SSW that empties onto the Sólheimasandur and finally, Kötlujökull to the SE that empties in a great arc east through south onto the Mýrdalssandur. What ought to be prime farmland and in fact once was settled, is nowadays an unsettled wasteland because of the devastating jökulhlaups unleashed by Katla. This is the true reason why Katla is considered to be such a dangerous volcano.

The fact that one often comes across the reference that in the days before the Hringvegur (ring road), “people were afraid to traverse the Sólheima- and Mýrdalssandur because of the frequent jökulhlaups” is another indication that smaller and unrecorded eruptions that cause only minor hlaups are far more frequent than the 40 – 80 years often given as the interval between main, and thus visible, eruptions.

Fig. 2. The foundations of the old bridge across the Múlakvísl river destroyed by the July 9th 2011 jökulhlaup
are visible to the left. The new bridge was laid down a week later. (photo John A Stevenson, GVP website)

Apart from the postulated connection between the Eyjafjallajökull and Katla volcanoes, one question that always crops up is the Goðabunga cryptodome. Many volcanologists maintain that it is a part of the volcanic system of the Katla central volcano. Others, notably Sturkell and his co-workers, claim it is part of the Eyjafjallajökull volcanic system. In order to shed some light on this issue, I asked our own GeoLurking if he could make a plot of all the earthquakes from 1994 up to and including the 2010 Eyjafjallajökull eruption. The results are quite clear and do throw up a surprise:

Fig 3. E-W cross section, view from south, through Eyjafjallajökull, Goðabunga and Katla. Plot by and
courtesy of GeoLurking. The “lines” formed at approximately 5, 3 and 1.1 km at Goðabunga and Katla are most
likely artefacts caused by quakes being assigned a poorly defined depth. The latter, 1.1 km, is the default depth
assigned by the automatic system in case it cannot compute a depth within the predetermined level of certainty and unless they are manually checked, which is not the case of every quake, automatic depth remains uncorrected, hence these artefacts.

From this cross section, it is quite clear that there is no connection between the Eyjafjallajökull volcanic system and Katla. Eyjafjallajökull has its own, well-defined feeder system from the Moho (first molten layer beneath the Earth’s solid crust) as does Katla, thus they are wholly independent of one another. As can also be seen, albeit not as clearly, Goðabunga too seems to be independent of either Eyjafjallajökull and Katla, the ramifications of which will be the subject of a later post by Carl. Sufficient to say that when we contemplate what Katla herself may be up to, we must differentiate between activity at Goðabunga and activity at Katla. Once we do, we see that while Goðabunga is more or less continuously active, Katla operates in bursts and seems to be most active during summer and autumn when the ice cap is at its, relatively speaking of an up to 700 m thick glacier, thinnest.

Fig 4. Activity post-Eyjafjallajökull. Activity at Eyjafjallajökull is minor and has to do with the system settling down after the end of the eruptive phase. Note that at a depth of 0 to 5 km or so, there seem to be three separate areas of activity at Katla. (Plot by and courtesy of GeoLurking.)

After the Eyjafjallajökull eruption, Katla seems to have entered an active phase with a suspected subglacial eruption on July 9th 2011 and several pits or craters forming on top of the glacier. This activity seems to be localised to three main areas within the caldera:

Fig. 5. Earthquake activity at Katla July 9th 2011, the day of the jökulhlaup and suspected subglacial eruption. Both the 1823 and 1918 eruptions occurred close to but just east of this area. The 1823 eruption occurred close to the easternmost red spot while the 1918 eruption was roughly at the rightmost dark blue spot below it. (IMO)

Fig 6. Earthquake activity at Katla July 17th 2011. (IMO)

Fig. 7. Earthquake activity at Katla July 21st 2011. The 1755 eruption was situated in the same area as the three overlapping orange spots. (IMO)

As can be seen, there are at least three distinct areas of activity inside the caldera with the one associated with the inferred July 9th eruption well to the south. The pits formed in the glacier also align with these three areas, albeit the pits to the northeast seem more drawn out along the caldera wall and not over the center of activity. These three areas seem to tie in with the three areas of activity noted in fig 4 as do the locations of three of Katla’s major eruptions. Thus there is not a single vent, but at least three at surface distances of approximately 5 to 8 km from each other. It is equally likely to judge from Fig 3. and Fig 4. in conjunction, that at great depth, they do have a common source.

I will now present you with my personal view of Katla, but do not be afraid to disagree or draw your own conclusions (within reason please, no Katlatubos here):

Katla is a young volcano and far more active than has previously been thought. Unlike the similarly aged but much less active Eyjafjallajökull, Katla has had more time to develop her system of sills to the point where they are fewer in number than they originally were but have a substantially larger magma-carrying capacity and approach or may have reached the point where they can be considered magma chambers proper. Since cooking evolved magmas takes a long time, usually millennia in the case of cubic kilometre-sized silica-rich magmas and at the very least many centuries for intermediate magmas, it is highly likely that Katla possesses several pockets of magma capable of eruptions ranging from high VEI 3s to small VEI 5s. Not only do the times between such eruptions argue this, their wide spread of location within the caldera does so too.

The most common type of eruption at Katla is the small, subglacial eruption of a few tens of millions of cubic meters of basaltic magmas. These eruptions are not energetic enough to break through the very thick Mýrdalsjökull glacier and the only proofs of their existence are intense earthquake swarms followed by minor jökulhlaups and later observations of deep pits or craters, sometimes water-filled, in the glacier ice. My guesstimate is that there may be many such small eruptions over any given ten-year period, and possibly in the case of a period of high activity, there may even be more than one in a single year. By back-tracking and investigating old accounts over the past few centuries of jökulhlaups in the area not associated with visible eruptions, it ought to be possible to identify many of these minor eruptions.

While a larger “proper” eruption of Katla in the VEI 3 – 5 range cannot be ruled out, I find one unlikely at present as the current activity mostly is in areas already depleted of evolved magmas by geologically speaking very recent major eruptions. Also there is little sign of the uplift required on GPS. If one were to occur, the odds for one towards the upper end of what Katla is able of ought to be better in the Eastern to Northern parts of the caldera.

Finally, what we do see when we look at SIL-stations such as Austmannsbunga, located on the NE caldera rim (not a coincidence, see above), is hydrothermal activity following a period of possibly still ongoing magmatic intrusion and not signs of an imminent, large eruption.

Fig 8. Hydrothermal activity at Katla as shown on the Austmannsbunga SIL (IMO)

I’m sorry to be such a boring old fart, but if this is unsatisfactory, start looking for intense earthquake activity at some 25 – 10 km depth, showing on the IMO map for Mýrdalsjökull as being in the Eastern to Northern part of the caldera, activity that shows a clear upwards trend and spreads when it reaches depths approaching 5 km!


114 thoughts on “What’s going on at Katla? Part III

  1. Nice post.

    Continuing from last thread since my Internet went out and said screw it and got on the road.

    The Sparks/Magamp connection is the curve, not the name, though it is an odd synchronicity.

    A lot of chem reactions are pressure/temperature modulated. Example: Black Powder burns at a fixed rate. Smokeless Powder (modern firearms) burns at a dynamic rate… the higher the pressure the faster the burn. The higher chamber pressure could easily blow apart a black powder.

  2. .. weapon.

    This lead to many injuries/deaths when it was first introduced.

    Silica/Zircon formation and dynamics… diffusion rates etc are probaly directly affected by temperature and pressure. A lot of syttems are, and it would not be out of the question.

    Any chemists out there want to chime in on this?

  3. Katla tephra layers show that there have been 100+ basaltic and at least 12 felsic explosive subglacial eruptions in the past 10,000 years. There have also been 5 -10 small effusive eruptions on the northern periphery of Mýrdalsjökull. (source: “Iceland” Thordarson & Hoskuldsson, Terra Publishing, 2002).

    Also read somewhere recently (but Icelanders will know this better than me) that the Eyjafjallajokull eruption occurred in two stages – a smaller one in March 2010 (Fimmvörðuháls), which then opened a route for magma direct from the mantle resulting in the larger eruption in April 2010.

    • & Henrik, a great post. Thank you.

      The more we find out about volcanoes, the more complex the processes involved in their evolution seem to be.

      • I agree, very nice posts all together. I very much enjoy reading posts like this from various readers. Thanks Henrik and Carl!

    • *Right. Firmly engraved in long-term memory: Fimmvörðuháls running from 20 March to 7 April 2010, Eyjafjallajökull from 14 April to 20 May. 2010 (with some singular steam/ash explotions into June 2010). Status: Inactive.

    • Thank you everyone for your kind words! Since you can be a bit more free with what you say in a reply than in a main post, I consider it entirely likely that many of the visible eruptions on record have been large, basaltic fissure eruptions (VEI 3 – 4) and that the “mildly alkalic rhyolitic ones” are among the larger VEI 4 and 5 on record. But without a complete record linking the year of the eruption with a specific erupted type of magma no such speculation should, in my opinion, be presented in a main post even if the description of the 1755 VEI 5 eruption as having many eruption columns suggest it may have been a large fissure eruption, albeit much smaller than either Eldgjá or Holmsa fires.

      Continuing speculation; the way earthquake activity lines up through the caldera from W to E with a sligth northerly trend to the E, suggests there may be a pre-existing fissure which coincides with the pattern of the 1755 eruption. If this is the case, it’s not wholly out of the question that far in the future, a possible worst-case scenario would be a fissure eruption on an order of magnitude between Holmsa fires and Eldgjá. 10-15 cu km of magma subglacially over a period of three to four weeks would result in the granddaddy of Surtseyan (magmatophreatic; water + magma) eruption and glacial flood.

      But since the interval suggested by the Holmsa fires and Eldgjá eruptions is some 6,000 years and that we may have had a minor rift eruption as late as 1755, such a scenario must be many thousands of years in the future.

  4. Great post, Henrik. Also thank you to GeoLurking for the plots.These plots and the earthquake activity maps were very informative for me since I am a visual person. For example: if I am to assemble something, I might as well throw the directions away and hope the drawings/pictures are detailed and accurate. So when I am reading any detailed journal/report on volcanoes or earthquakes, my understanding level is dependent on the visual figures contained within. Good job 🙂

  5. Wow, those were three very interesting posts thank you!!
    But I have just one question about Katla and other icelandic volcanoes, too.
    Why if many volcanoes do erupt evolved magmas, and there associated fissure swarms many kilometers away from them produce basaltic eruptions, are they considered to be part of the same volcano? For example here in the Canary islands the Teide central volcanic complex(cvc) is considered apart from the rift zones extending from it, because they erupt completely different magmas (different magma chambers). The same thing goes for the Roque Nublo edifice and the NW-SE rift zone in Gran Canaria, the former erupted evolved phonolites and the other ultra basic to basic magmas, therefore they are considered two different volcanoes with different magmatic systems.

    • Thank you Charly, glad you liked it. I see you have already received some good replies from KarenZ and LAKAT. I’d like to add that it all depends on what you think a volcano looks like. I think we both have seen the classical oversimplification: a cone-shaped mountain with an orange-red balloon beneath which is the magma chamber with a thin red line from below attached to it. When this simplified model erupts, magma moves first from below into the ballon which expands (red directional arrows) and then makes a crack to the crater & boom.

      Iceland’s volcanoes teach us that it is much more complex than that. The primitive, basaltic magma may make its way to the surface on its own such as the baslatic lava fountains at Fimvörduhals in late March to early April 2010. But it could also enter the pre-existing channels and magma chamber-s/sills and bring about an eruption of more evolved magmas such as the andesites that began erupting through Eyjafjallajökull’s main crater on April 14th 2010. This is what may be called a bimodal eruption; a volcano erupting two distinct and separate types of magma.

      In Iceland, both the Holmsá fires and Eldgjá fissure eruptions are considered as being associated with Katla even if the fissure type of eruption is considered separately. If Katla had been in the Canaries, apparently they would not. It all depends on how you define what is a “volcano”.

      • Thank you all for your good answers!!, and for the links!, I haven’t had time to read them, but I will get to it right now XD

  6. @ Henri le Revenant

    Great post, Henrik and particularly liked the summary. Very helpful as there is a lot to take in, there.

    Regarding the Eyjafjalljokull/Katla connection.

    There are several examples of stress transfer causing twin eruptions in other volcanoes around the world(Kamchatka – Karysky and Akademia Nauk etc) and I still wonder whether that is the mechanism.involved somehow. In that example it is as a result of tectonic stress leading to simultaneous eruptions so not a near correlation but I still wonder. Geographically Lady E and Lady K are close enough for me to think it could be some sort of stress transfer that is at work. ( Henri don’t hit me! Stop!)

    Have a read of this:http://www.sciencedirect.com/science/article/pii/S0012821X07005626

    • Why should I hit you? While there is no direct magmatic link between the two, they are close enough that the uplift or sudden deflation of the one could affect the other.

      • @ Henri le Revenant


        Sometimes you can be quite fearsome when you disagree with someone’s hypothesis and this is not much more than a hunch on my part rather than a well thought out argument with masses of supporting documentation.

        Gut feel as often served me well in the past but I could say something ridiculous through lack of in-depth knowledge!!

        However, unlike some. I don’t mind people telling me I’m wrong so as long as it is done gently and politely. Infact, it is great to be taught something new by someone in the know.

  7. An comment. First picture in post is not an aerial one (not taken from aeroplane), it is clear the photographer stands on firm ground (at Morinsheiði or near Fimmvörðuháls ?) and at first sight shows an gacier tounge falling to the west from Godabunga.

    • You are correct. Since I didn’t have a nice, introductory picture I asked Carl to add one and a lovely one it is too even if, as you say, it’s not aerial.

      • Ok. No prob. Only point I found lacking is age, that Katla and Eyjo are said 700.000 years (young, well). The last 10,200 years be since last Glacial Age (therefore traciable in Iceland sediments), but looking loosely at MAR spread across Iceland, then once upon a time Katla was (perhaps) formed beside Hengill but drifted away.

        • That is indeed an issue. With the rate at which the MAR spreads, how long does a volcano stay in position? Can a volcano sit indefinitely astride the MAR or will it eventually be ripped apart and a new volcano form later on in the same-ish position? If it moves off the MAR, for how long will it be active? Why is it that while there are many volcanoes west of the EVZ on the American plate, there seemingly are none east of it on the Eurasian plate (except at Vatnajökull)?

          • Iceland Volcanos, on both sides, drift, along with their roots, new ones seem not to form outside of the MAR it seems. South-East of MAR (likely drifted there) we have side crack Vestmann Islands, then Eyjo, Katla, Öræfajökull, Esjufjöll, likely ending at Kverkfjöll in east. Looking at what Volcanoes are active, It seems to me the alledged hotspot be like fountain and most active at edges (the exception beeing Hekla). So does the Hotspot spin, anti-clockwise, and them active Volcanoes be like fan blades, scooping or sucking up magma as they drift? *ranting, mentally preparing for beeng inactive period of Sheepy Dalek cometition duration, ah…*

          • Iceland has had a few “rift jumps.” In all cases the rift moved further to the east.

            Hotspot–ridge interaction produces a wide range of phenomena including excess crustal thickness, geochemical anomalies, offaxis volcanic ridges and ridge relocations or jumps. Ridges are recorded to have jumped toward many hotspots including, Iceland, Discovery, Galápagos, Kerguelen and Tristan de Cuhna. The causes of ridge jumps likely involve a number of interacting processes related to hotspots. One such process is reheating of the lithosphere as magma penetrates it to feed near-axis volcanism.

            Mid-ocean ridge jumps associated with hotspot magmatism Mittelstaedt, Ito, Behn
            Earth and Planetary Science Letters 266 (2008) 256–270

            Click to access Mittelstaedt_etal_EPLS08.pdf

          • Jepp. Thanks so much for link, Just heard one more rift sound *similar to beer can (default brand) beeing torn open, hummm, soon time for party*

      • Oh, I don’t think so.

        Daily Quake Count, 40km radius around 19.313°N 155.339°W

        2000 to present. (all of the 31st may not be in here)

      • If you want interesting, these quakes seem to be around the periphery of the landward region next to the Papau Seamount. Futher to he North is Hilina Pali (land slump scarp… still ongoing, could take a few thousand years to finish)

  8. HenriK and Lurking. What a team!. As others have said before me, the combination of visual and written information is superb. “Seeing” beneath Myrdalsjokull accounts for the activity currently showing on the Sils. I am sure that other’s like myself ,who get greatly bogged down with the more technical writings about the Eyaf, God. and Katla systems, will find these three posts invaluable to help, not only the understanding of these three volcanoes but also will help with a clearer picture of how other systems may work..Congratulations on a job well done!

    • Thank you Diana & al, glad you liked it and hopefully the “lurkers” will feel the same way about it.

  9. Great posts on Katla, Henrik, ‘tack så muckett!’.
    This quote could serve as an antidote yo Katlamongering:
    “The most common type of eruption at Katla is the small, subglacial eruption of a few tens of millions of cubic meters of basaltic magmas. These eruptions are not energetic enough to break through the very thick Mýrdalsjökull glacier…”

  10. Henri, I liked most of the post but there are some assumptions you make as truth, while they are uncertain and therefore can be wrong.

    ” four VEI 5 eruptions are remarkably alike in size at 1.2 – 1.5 km3, which is at the upper end of what Katla probably is able to do “; you cannot say just because of 1000 years of history, also tephrology dated eruptions are very much estimated and cannot be accurate in their VEI. You can say that Katla almost always delivers only up to a weak VEI5, but more is not out of question while being rare.

    “Katla does not possess a caldera-sized magma chamber.”
    this is uncertain, some researchers have said posited a caldera-sized chamber while others not. Henri, best to play in safe side that come with a fact that is not even settled, and is controversial. Again, it seems to have a bias downplaying Katla size or its eruption history. I am not in the alarmist side, you know it, and while I understand you are trying to downplay alarmism and excess in Katla but I prefer to paint a correct view rather than a biased one. Katla is generally Eyjafjallajokull sized in eruptions, but its not out of question much larger eruptions, and also its uncertain chamber.

    “From this cross section, it is quite clear that there is no connection between the Eyjafjallajökull volcanic system and Katla.”
    Now I am going to place a great tease on you 😉 Well, applying this reasoning, then there is no connection also between Laki and Grimsvotn because I never saw earthquakes linking them. We must be careful with this, this is how scientists are, while Geolurking data seems to point at a link between Eyja and Godabunga and no link with Katla, because of what I said before for Laki, one must be careful with drawing conclusions. On Geolurking data we cannot see any chamber clearly at 3-5km as if often mentioned, why possibly because that’s precisely where magma is and where earthquakes happen less. While I don’t think there is a direct link to Eyja, I also don’t go around saying I am sure of that. I am cautious and open to both possibilities, while believing more in the no link.

    “Since cooking evolved magmas takes a long time, usually millennia in the case of cubic kilometre-sized silica-rich magmas and at the very least many centuries for intermediate magmas, it is highly likely that Katla possesses several pockets of magma capable of eruptions ranging from high VEI 3s to small VEI 5s. Not only do the times between such eruptions argue this, their wide spread of location within the caldera does so too.” A great insight, this totally makes sense and explains a lot. Maybe the guys of a large caldera-sized chamber are wrong, but still we must be cautious, nevertheless I think you are on spot here.

    “subglacial eruptions” yes, they probably occur something like every few decades or even more often. The events of 1955, 2000 and 2011 come to my mind. There are plenty of historical reports as well, with floods and no visible eruptions. Whether this depletes magma? Hmm, not sure, magma pushing from deep would be tthe main factor to trigger the (large) eruptions I think.

    “Also there is little sign of the uplift required on GPS.”
    It has been GPS going on for years but quite stalled now. I think no new magma has came into Katla. Why? At present there are no deep earthquakes, or rarely. This is a sign that a large eruption of Katla cannot happen in soon. Unless deep quakes up to M3 occur, like before Eyja. So, I think any pressure at 3km would only result on this tiny VEI1 eruptions that only result in small floods.

    I think Katla will erupt only and very likely with the first big new fresh influx of new deep magma. Which hasn’t happened yet. It can be years until then…

    ps: finally some researchers have also pointed whether the westman islands activity in 60s 70s might have helped relieved pressure in Katla. I have no idea… the distance to there is similar to Eyja… perhaps a bit more

    • Interesting comments Irpsit. I am not clear on some points . If a magma chamber is revealed usually on a plot like Lurking’s by an area with few quakes. Since Katla’s “Chambers” are many complex dykes would these not fill and still be prone to severe cracking causing smaller quakes as the magma constantly adds pressure and so not show the earthquake – less space on the plot?.Would the dyke filling also not keep spreading sideways and away from the center until an eruption is triggered say by a huge push from magma which makes a break upward through to the surface? Could a dyke from, say , Eyaf not be also used from another direction from Katla and then they are broken through to join the two systems up?

    • Irpsit.

      First, I said “probably” which is an uncertainty marker (“which is at the upper end of what Katla probably is able to do”). As I speculated in a reply above, I can imagine scenarios that could result in greater eruptions, even if I think them highly unlikely.

      Second, researchers (who??? please name them and put up a link) that claim that Katla may have a caldera-wide magma chamber do not take account of the facts. If there had been one, the 1755 VEI 5 eruption, which most likely was a large fissure eruption through the middle of such a hypothetical caldera-wide magma chamber and probably involved juvenile magmas, would have set it off. And there have been well over 100 eruptions over the past 10,000 years of which NONE have set off such a magma chamber even if all must have passed through it. Therefore, in my opinion, it cannot be there.

      Third, the Lurking graph shows the Eyjafjallajökull feeder system during the build up to, through and after the eruption. You cannot get better data. It is absolutely and unmistakably clear that there is no magmatic link between Eyjafjallajökull and Katla.

      Finally, I said “do not be afraid to disagree or draw your own conclusions (within reason please, no Katlatubos here)”. I do not dictate what you should believe, you are indeed free to form your own opinion and believe what you will, even should it go against all scientific principles and ignore fact, as we all are.

      It is entirely possible that events will prove me wrong…

      • A small caveat: earthquakes only occur where rock fractures in or near a magma reservoir so while they are a very good indication of where magma is, or where pressure is, they aren’t the whole story.

        A magma reservoir can be a single chamber or a complex structure of many chambers. Probably depends on the age of the volcano (the latter may take time to evolve) and / or the local geology.

        Also read somewhere (sorry I did not keep the reference) that a volcano does not completely empty its magma chamber – it either loses a third or keeps a third in the eruption. If anyone knows the link, they may be able to shed more light. But one way for a caldera to form is that the volcano only has to lose enough gas or magma from the reservoir so that it can no longer support the weight of the rock above it;

      • So Henri why do think we have seen this increase in Katla activity (even if without a large eruption) just after Eyjafjallajokull?

        Could very deep there, just above the mantle, the plume divide into both Eyja and Katka? And when new magma rises, it causes activity in both places. Even if one has a major eruption and the other a minor eruption.

        I think earthquakes are not everything. If you recall after Krafla erupted, Askja just started to deflate. But there was no earthquake connection between them. I still think there are more links between icelandic volcanoes that we generally suspect.

        Well, there is no proof at all of all these suspected links, and even though some data shows no link I am not fully convinced of a total no link between Eyja and Katla, or any other two volcanoes nearby.

        For instance, at each hotspot pulse, we see eruptions more often at Vatnajokull, in several volcanoes within a few years. So, it might be that the magma coming from the deep, goes to several volcanoes during that pulse. However, this only goes for Vatnajokull volcanoes and dead zone, I never seen any link between hotspot pulse and Katla activity (or Hekla), as far I know.

        • Irpsit, forgive me but you really are clutching at straws here when you invoke the MOHO & below as evidence of an Eyjafjallajökull – Katla connection. In that sense, every single Icelandic volcano is interconnected because they all depend on the Iceland hot spot / mantle plume.

          Your question why we have seen this increase in Katla activity has already been answered by Iceland’s volcanologists – they see the Iceland hotspot as entering a more active period and have said so publicly. Not only Eyjafjallajökull has erupted but also Grímsfjall – do you claim that because G erupted a year after E, there must be a connection between them? There are signs of increased activity elsewhere such as the suspected minor subglacial eruption at Hammarin, an interpretation I know you share, the unseasonal ice-free state of Lake Öskjúvatn, anomalous earthquakes in the Dead Zone and what appears to be episodes of magma injection in volcanoes such as Theistareykjarbunga and elsewhere where it is hard to assign the intrusions to a specific volcano. Furthermore, you have the inflation-deflation episode at Krísuvík, off-shore swarms at known or suspected underwater volcanoes etc, etc, etc.

          Even without the postulated increase in hotspot activity, I’m not surprised by the increase in activity at Katla as I believe her to be a far more active volcano than the 40 – 80 years between major eruptions suggests and also quite capable to do things on her own without asking Lady E’s permission or being influenced by what she does.

    • A perhaps rather naive question on whether Eyjafjallajökull and Katla are connected magmatically or not…..
      Can we not model the two volcanoes as a system filled with an incompressible fluid? Then if connected to any degree, an injection of magma would show simultaneous initiation of inflation at both volcanos even if the degree of inflation varies widely?
      I can understand a lag in eruptions due to latency of heat transfer, chemical evolution of magma, differing rock overburden etc but if they are connected there should be concurrency of mass flow initiation due to a pulse of magma.
      Why is an examination of timing of inflation/deflation of the two not enough to determine their connectedness? Too close to each other to differentiate inflation measurements?

  11. Pheww relief, i am done.
    Ok ALL, even if Carl might not be around today there will be a Sheepy Dalek #13 at the same time as always 6pm CET(summertime) or 4pm blogtime, so be prepared ( or prepare food early Diana! ) I just finished editing the draft and all it takes now is one mouse-klick so it can go in. I do not know the answers, and also i do not know when the riddles correct answers will be awarded .
    Personally i think i have a clue what it could be and if i am right, it is an easy one, but i might be totally wrong also.
    Good luck and make sure to be around.

  12. Oh and thanks Ursula for editing the broken RSS feeds for me and placing links instead. If one from vulcanodiscovery or earthquake report reads this, your RSS feeds are not working.

    Your devoted dragon is overworked and sleep deprived and was set on a strict diet, so no sheep meals anymore just veggies and fruit…. sigh.

    • I have just had a shower and weighed…..I will be joining you with he veggies and fruit..and of course drinks with no calories..Sigh!
      Food will not take long to prepare….3 lettuce leaves,, weightless bread and a small slice of ham. and some carrots or pears for dessert.. then a weekend digging..That should loose a few inches…..Huge sigh. 🙄

      • I’m going on holiday to Normandy on Monday and have been trying to diet – not so that I’ll look good, but so I’ll still fit into my clothes when I get back. I always put on a huge amount of weight when in holiday mode! 😀

  13. Morning Everyone
    I am back from holiday but my disastrous year goes on. I fell on holidayand hurt my knee and leg two days after I arrived due to two tiles missing on the ramp I was walking on and my foot got caught in the hole and ended up in a wheelchair for the rest of the holiday. Hotel paid for all my medical expenses and have offered us another two weeks and the weather was not that good .We enjoyed being away and our time together but did not have the holiday we wanted as we could not go anywhere we had planned to go.
    My test is booked for next Tuesday under GA so hopefully will know whats happening next week.
    Lots to catch up on here will keep me occupied for a while.

    • Sorry to hear about the accident. Wish you a speedy recovery and good luck with the tests.

      P.S. not sure if this will come through twice or not as WordPress said I was posting too quickly (Huh? Only had one coffee so far 😕 )

    • @ Judith: So sorry things didn’t go well on your holiday, I hope you have a speedy recovery. At least Pop was quiet while you were over there!
      @KarenZ: I’ve had that message a couple of times. At first I thought it was a comment on my speedy typing skills! 😀

    • So sorry this happened to you. Hopefully the second half of the year will be so much better for you. 🙂

    • Oh what a bummer Judith,so sorry your holiday wasn’t all you wished for. It’s good to have you back .Speedy recovery and good luck with your tests.

  14. Dear Judith
    What a lot of sadness i hope your test next week is coming good i will pray for you! I wish you a good recovery Here things are also very bad. My nice 46 and her husband 51 had a motorcycle accident my nice is badly heart and it is critical and is laying at the intensive care and her husband broke his neck and is dead. They have 2 children of 16 and the other is today 21 birthday My father is not very good and i have a bloodpressure mmmmm. So im almost not here on vulcanocafe.

    • Sorry Dean to hear of the accident in your family and that your father is not that good and wish you strength to get through the next weeks . The saying is true enjoy today as we really dont know whats around the corner.

      • Yes Judith the struggle for life but we are fighting but i was yesterday at de ic hospital we are hoping at a miracle but when their is hope …… their was a file i dont no the word in english a man was turning at the street and didn’t see them.

    • Oh Dean! That is so desperately sad. I’m so sorry. Please keep coming to here to take your mind off things. I’ll be thinking of you. (Hugs)

      • Thanks Talla its good to feel lov! from other people now I life in a dream but standing with both feets on the ground i am a social worker but even for me is this is a little to much now and than

      • A short message from me to all of you. Also our neice (46) is died friday afternoon in hospital she and her husband (51) were burried next wednesday its very sad such a tragic accident . friendly greetings to all of you thanks for thinking at us. Deanne

    • Dean, what can I say. That is truly horrendous, awful news. Wish there was something one could say but there isn’t.

      • yes their are no words for thank you henri i t is really very sad one boy is studiing at the university and 1 boy is in the army but they are living at home where their is now no father anymore and mother in hospital very badly hurt . They are now constantly in the hospital i was yesterday their another surgery 4 hours but her kidneys dont work and a lot more of the organen are badly hurt her stomage is the greatest problem

    • Dean, so sorry to hear about your neice and her husband. Hope your neice recovers fully. Thoughts with you and your family.

      • A short message from me to all of you. Also our neice (46) is died friday afternoon in hospital she and her husband (51) were burried next wednesday its very sad such a tragic accident . friendly greetings to all of you thanks for thinking at us. Deanne

        • My thoughts are with you and your family, Deanne. Words are so inadequate at times like these, but you can show your love for their children who must be devastated. Take care. Love and hugs to you.

        • Very sad to hear this. I hope they rest in peace and my thoughts are with you and their children.

    • So sorry to hear such bad news. You are having a very bad year. I hope and pray that the coming months will get better for you and your family. Hoping for the best outcome for your niece. Hugs.

    • Oh Dean this is so very sad, I am so sorry for you and your family. What a terrible tragedy. Words are so inadequate at times, but please know I am thinking of you all. Big hugs.

    • Thank you, Dean! I’m not leaving till Monday night – we have the Jubilee Celebrations here in UK this weekend, so a big public holiday. Then from Tuesday I’ll be camping near Bayeux with the small dog – but no volcanoes to visit!

      • Mexico: The monitoring system of the volcano Popocatepetl has recorded movement of magma. Increased tremor “in harmony” (very constant in amplitude and frequency), and “jerky” (more irregular signal with pulse frequency or higher amplitude, low to medium range). Occurrence of various exhalations of low to medium intensity, with moderate amounts of ash and gas. – Google translate –

    • Weird – I’ve looked at various news sites and this BBC article is the only thing that comes up. A bit Daily Fail in it’s headline and a non-story. Another sign of BBC standards slipping?

      • Don’t know as Popo has resumed “steaming” again.

        @ WordPress: how can I be posting too quickly when it is almost 90 minutes since my lsat comment 😕 😡

    • Don’t have my glasses on and the coffee hasn’t finished. Stuff is still blurry. So… I’m trying to figure out why or who the Vatican is threatening. Turns out that’s an “o,” not an “e” on the end.

      Yes, it is possible to read too fast.

      • Popo appears to have a light over it here:

        It is something to do with the steam / gas he is emitting and the sunlight. Seen similar “ice” clouds over London – but ice clouds seem a bit unlikely over a volcano in a hot country.

    • Which begs the question… what is the southern extent of the Adriatic Plate?

      “The Gargano–Dubrovnik zone (GDZ) is taken as the southern boundary of the Adriatic microplate.”

      So.. what is that deep area to the south, under the Ionian Sea? It’s not part of African Plate proper, and not part of the Adriatic plate (which was part of the African Plate at one time) is a fragment unto itself. The GDZ is seismically active and serves as the demarcation point between the two.

  15. Very suspicious article, I mean scientifically speaking.

    I totally agree with Irpsit on many items. I did also immediately pay attention to the bias clearly evident in the article. It was clearly written with a certain predefined outcome in mind. It seems it was written for the scaremongerers, and motivated by fear of being linked by them. Thus it does not even fulfill the basic conditions for a scientific article even though it “plays like a one”. However, it should have had done that, as it still makes scientific claims on the issue (Katla) itself! In reality, many claims provided in the article are just personal opinions without any real merit or justification. I find this shameless bashing of the work of many volcanologists who have followed the scientific rigor in their quest to try to understand these volcanoes.

    Further, IMHO, Lurking’s figure can not say anything meaningful on the Eyjafjöll – Godabunga – Katla connection. First, Eyjafjöll and Katla are different beasts. Eyjafjöll erupts seldom (when compared to Katla), hence magma has some time to fractionate. And, when a new eruption cycle starts, new magma pushing up will thus surely create quakes in the cooled = solidified magma from the previous cycle. Hence we see clearly the extent of Eyjafjöll’s magmatic conduits, “chamber”, etc. in Lurking’s figure, but just because it covers the time of the last eruption.

    Katla erupts frequently, when compared to Eyjafjöll. Hence, Katla’s magmatic system MAY not be that cool or closed (depends on many other factors). Additionally, we most probably have not yet seen the start of new eruptible magma pushing up inside Katla. So in reality we do not yet even KNOW what is the ACTUAL extent of quakes when Katla prepares for the next REAL show.

    Hence, speaking with scientific scrutiny and skepticism in mind, Lurking’s figure does provide nice illustration of the magmatic system of Eyjafjöll only (so far). Speaking of the possible connection at this stage is thus like comparing the driving comfort of empty tires and inflated tires. The same can not be said on Katla until we see the real thing, i.e. new magma entering in AND the real eruption starting.

    IMHO, it does not even matter how many “chambers” Katla does have, or what kind of they are. Until Katla’s next REAL eruption (breaking the ice cover) any discussion on the Eyjafjöll – Godabunga – Katla connection is pure speculation, nothing more! And still after the eruption, it is NOT certain that we can provide any meaningfull new statements on this connection.

    I’m sorry but science is like this. Quite often we’re very incapable of being right. Either we do not have the right question, the question is not clearly enough formulated, or we do not have enough good-quality, relevant empirical data to evaluate the answer. Yet, most of the time it’s fun to speculate (if it is acknowledged accordingly). This article or it’s writer did not recognize it.

    • One fact – Jack is one of the regulars of Jón’s place and has been since Jón set his place up. Thus his comments come as no surprise. While it’s nice to see that you stick up for your friend, the underhanded manner in which you do so is very disappointing.

      • I did not comment on who wrote it. Actually, it does not really matter at all who wrote it! Though I see, you’re a quite capable writer, and I’m glad about it.

        I commented on the information content of your article. The one-liner stating it’s your opinion does not hide the fact, that you do not make a difference between known facts and your own opinions. You state everything as they were known facts (including your own speculation and opinions). This is misleading the readers of this blog!

        Hence, I’m a bit disappointed, as I used to know a different kind of Henri on the many other volcano blogs, where you’ve been writing during the last few years. You used to me much more objective…

        • “You state everything as they were known facts (including your own speculation and opinions). This is misleading the readers”

          Bullshit! Go back to your beloved Jón then wjich is where you find exactly that which you are accusing me of. You, “sir”, are so utterly biassed and dishonestly so that this is my last comment to you. Ever.

          • Since you asked for it, just two examples (there are others):

            “Katla is a massive but relatively young volcano, located on the MAR, and formed when Iceland was covered by glaciers.”
            Actually Katla is at least 800 000 years old, maybe even a few millions of years old (e.g. Sturkell 2003). Geologically speaking relatively young, yes. But, AFAIK, no-one KNOWS the exact conditions (during an ice age or not) which prevailed during its birth.

            “Katla does not possess a caldera-sized magma chamber.”
            Again, stated as a fact, but there is no empirical data nor scientific consensus on these hypotheses. The next eruption combined with modern instrumentation can prove us all wrong. The types of eruptions occurred can be explained otherwise, too.

            I’m not at you, but your article. You said “… do not be afraid to disagree or draw your own conclusions …”. It is the very virtue of science not to mix feelings or opinions or nature of human thinking with facts.

          • I have to correct myself: There is clear empirical evidence, that Katla does have a single well-developed magma chamber.

    • I’ll answer myself: I’d expect to see a connection – if there is any – after all three (Eyjafjöll, Godabunga and Katla) have had a proper eruption at least once. Only after that we can see, if the filling process for the next eruption uses any common routes.

  16. @ Jack @ Finland ( re: your comment above at 17.26)

    @ Henri le Revenant (I’m quoting you so thought you should be duly advised!)

    James, you missed something which is quite important –
    HenriK clearly stated this in his post:

    ” I will now present you with my personal view of Katla, but do not be afraid to disagree or draw your own conclusions (within reason please, no Katlatubos here):”

    I wishes to open the debate!

    • I have found that Jack is quite pragmatic and doesn’t mince words. I value his opinion since it did force me to question a line of thinking I had a while back. His insight forced me to question whether a nuance of data really meant something probable or if it was just “humans seeing patterns.”

      We tend to do that, even with noise. I ought to know, I spent a significant part of my career staring at the video trace of the noise floor up in the Ghz range looking for radars. You get to learn a lot about the nature of noise when you stare at it long enough.

      One odd thing that I found, is that if you had what seemed to be a signal there, you could drive the pan trace with an audio signal to force the “thing” to form a fin that would slowly race across the background noise. It only did this if you got within a the band that is was modulated at. In other words, you had to use signal processing to dig it out. If it’s there, it will show itself… eventually.

      Jack’s observations about Katla are quite accurate. Henri’s opinions are Henri’s opinion based on his observations and a few plots as requested of me. These ideas are stated as such. It doesn’t mean he is fully correct, and it doesn’t mean that he is wrong. Generally, you will find that the “truth” (in this case, what ever the situation actually is) is somewhere in between.

      This is one of the reasons that I try to never state specifically what something means, unless it is a lock and there is certainty. With regards to Hekla, Katla and the other entities there, far more people know a lot more about it than I do, and I defer to that knowledge. I can try to find oddities and point them out, but what they mean… I’m not really the person to ask.

      One thing about Katla, that I haven’t the foggiest notion about.. is a cluster of quakes outside of Katla’s south rim. Jon first mentioned them, but they have been popping up in the plots quite regularly… I even focused on them to try and see if they pointed anywhere, but they don’t . They are just a rogue cluster that seem to lie on a lineament with the north caldera cluster and the endpoint of Eldja.

      Yeah, I know. Weird.

      • There has been one smaller Katla eruption outside the caldera rim, on the southern side. I read a paper on it a while ago. I don’t remember the details (e.g. exact location) but IIRC the eruption was in the 14th century.

      • maybe another cone in the making, I say that because in NZ there are bunches of EQ in lines further to some active volcanoes and vents, sorry can’t think clearly at the moment

  17. Edit in last line of my post above:” I “should read “He”, although I welcome the debate, as always, too!


  18. @ Dean

    @ Judith

    So sorry to hear about all this.

    Life has a way of going in cycles whether it be good or bad. Hopefully a better one is about to start for both of you.

  19. Pingback: What’s going on at Katla? Part III | LucifersHammer.net

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