Gorely and the Magma Baguette

Partial view of the massive caldera of Gorely. Image from Wikimedia Commons.


Every week I go through hundreds of images of volcanoes, and almost to a fault they are bombastic images of majestic strato volcanoes in dramatic light, or images of smoke and lava pouring out of equally majestic volcanoes, only problem is that I am bone tired of them since they are really bad if I want to make a certain point about volcanoes.

There have been two articles that I have wanted to write for more than a year, but have not been able to do since I could not find any photographic material at all to show what I wanted. A few days ago Vitton Georges posted a couple of pictures on his Facebook page that where so fabulous that I almost started to play lip-banjo out of sheer joy. So here are finally the two articles in one picture rich article.

But, by all means, let us start at the beginning.


Map from Google Maps showing the size of both volcano and caldera.


All the images in this post are from the large volcano of Gorely. The volcano is a truly massive shield volcano that has gone through several phases. The bottom of the volcano is more than 25 kilometers across and it contains a massive circular caldera that is more than 12 kilometers across.

The shield volcano is in turn covered by no less than five strato volcanoes and numerous tuff cones; this makes it into a highly complex volcano. And herein lies the explanation to the oddity of the Gorely shield volcano, it is one of the few shield volcanoes on the planet that has suffered a super-eruption creating a huge ignimbrite area from its more than 100 cubic kilometer caldera forming VEI-7 eruption.

Last time Gorely had an eruption was 21st of August 2013.

Shrinking magma

Photograph by Vitton Georges, all rights reserved and used with permission. The curious baguette of magma left after the heat shrinkage of the magma.


In a volcano you have two typical reasons for earthquakes. Most of us jump when we see an earthquake in a volcano and quietly hope that it is due to magma infusion into the magmatic system of the volcano. But more often the earthquakes are caused by magma cooling, and as magma cools down it shrinks in size. This not only causes deflation of the volcano, it also causes something that is called blocking, and that is when the roof over the magma “chamber” slowly collapses. I have noticed that it is hard to encompass this function of a volcano since we can’t see the effects of the process in images, but thanks to Vitton Georges we can now do that in these spectacular images of cooled down magma in a lavatube.

Sometimes as the eruption stops magma is trapped in the tubes and stay in situ as it cools down. As that happen the magma will after a while have shrunk sufficiently to separate from the tube walls and as is shrinks it forms these beautiful “baguettes” of solidified magma.

Photograph by Vitton Georges, all rights reserved and used with permission. Here one can easily see the rusting on both the wall and the baguette, the separation between them have happened where a layer of what most likely is an iron/nickle ore.


Another process that happens to the poor trapped magma that has been trapped in the tube is that it is at shallow enough depth to degas. This causes further shrinkage, the amount is a factor of the amount of gas contained in the magma.

In the case of our magmatic baguettes a guesstimate would be that half of the shrinkage is due to cooling and half due to degassing. Only way to be certain would be to take a sample and put it under a good microscope and check for vesicles.

Geological fun in a tube

Photograph by Vitton Georges, all rights reserved and used with permission. Notice the chrystall structure on the wall.


If you take a closer look at the both the tube walls and the magma baguettes you will notice a few things. First of all the baguettes show a coating of rust, second of all you will notice that the walls look sparkly and like they are covered with a semi-crystalline layer. To get a good grip on this we will have to travel to the coldest city on the planet.

In Norilsk you find the focal point of the Siberian Trap Formation. As enormous amounts of lava came to the surface lavatubes quickly formed, and as magma travelled through them for years or decades minerals was emplaced on the tube walls as the magma crystallized. In the case of Norilsk the magma had a core/mantle boundary origin and contained large amounts of nickel. The huge Norilsk lavatubes have walls covered with several meter thick layers of nickel ore. I can’t be certain, but judging from the rusty surface of the baguettes and the look of the walls on the photographs by Vitton Georges I would not be surprised if we are looking at another nickel deposit, albeit on a much smaller scale. If so it would be fun since the magmatic origin is believed to be quite different than in Norilsk.

Photograph by Vitton Georges, all rights reserved and used with permission. Note the structure on wall and the sparkle.


Why do I call the baguettes magmatic and talk about magma instead of lava? Well, technically the material has never erupted, and as such it is still magma and not lava. You should though keep in mind that some ultra-purists would argue that it has degassed and as such can’t be magma.


183 thoughts on “Gorely and the Magma Baguette

    • Yes, those are well baked magma baguettes.

      I wanted to give people a graphic view of how much magma can actually shrink, and thanks to the spectacular photos from Vitton I finally had the chance to do so.

    • humm… I have doupts (like “almost” correct). I do not really know, but it reminds of baking plastic. You can heat and stretch plastic, and as it cools, making strands. Every modelmaker knows of this trick, how to make model antennas (even down to 1/72 scale)
      I therefore am on the opinion (*not expert*) there be some stretching involved too. That shows as a crack in the “Baguette” That stretching (pulling remaining lave along) also be reason for empty lava tubes in some locations (but incline plays heavy role).
      My two pennis 😉

      • You forget that the shrinkage is uniform, ie that a 100 meter baguette that is attached to the ends will try to shrink, and as it gets to brittle it will just break, the same goes even if it is not attached.

        • No, I am right here on this one. Not pure lava shrinkage alone.
          This lava is “extruded” from smaller lava tube (the one up ahead in photo “lavatub-2-vitton”). It likely has moved in direction towards us, but it has already been very slowly moving (very viscious) and then stopping, then cooling causing the crack we see, by Length-wise cooling. The wider cave probably formed whilst lava was more “thinner running” (hotter) but as it got cooler it simply got extruded as it was forced thrugh a smaller tunnel, that eventally plugged.

          • First I tended to agree with you, islander, but trying to picture it in my mind I think Carl is right on that. If the lava strand had become smaller by running out it would lie on the bottom of the tube with a flat top. That it has a round top is evidence that the tube was filled with it up to almost complete solidification.

            Question to me is, if it is still soft enough to shrink, why does it not flatten out like a dough with time?

            • You are absolutely correct Granyia, it would be on the bottom and have a flat top.

              It is a fairly large step to grasp these things, and imagine having to explain it without images and even with the images it is this hard to understand. This is a very well known fenomenon in the mining buisiness but few who have not been in a 1000 meter plus deep mine will run into the phenomenon “live”.

          • Well , I think I am right anyways and will not change my mind.
            This is because I have been into many old lava tubes, and seen such first hand,
            but never took pictures or imagined have to explain it

            But rash of deep quakes again today …
            05.09.2013 11:25:11 63,947 -19,023 28,7 km 0,7 99,0 5,2 km SSA Landmannalaugar
            (Torfajökull Volcano again, very deep one)

      • Tell me i have a 1-48 scale (old Aurora kit ) WW1 Gotha bomber I’m slowly finishing with that
        method of rigging… Like trying to rig a suspenion bridge..
        https://en.wikipedia.org/wiki/Gotha_G.V Wife had a not so distant couisin who was a
        Gotha pilot by the name of Brandenburg…I’m finishing that plane in his colors..
        I agree with your premise.-Looking for such formations in Oregon’s lava tube country…

      • “…but incline plays a heavy role”. The slopes for the mapped lava tubes at Gorely in the lavatube database are in the range of 1.5 to 6 degrees (average 2.9).
        If one knew the viscosity above glass transition for the Gorely lava the amount of stretching could be calculated.

  1. For me it will be a magma baguette with some Camembert and Ham please. With a glass of Red.

    Brilliant article, thanks ! I have visited a lava tube in Tenerife (Cueva del vento, worth the visit by the way). What is the difference as in that case the lava did not see the light of day before going into the tube ?

    • This is a question that I will pass over to Vitton since I do not know the exact location of the tube.
      But, in larger eruptions lavatubes form, and are then covered by fresh lava and in some cases more lava tubes, while the old lava tube remains active. Sometimes a lava tube is used as a side vent for many eruptions. This was though a general answer and not specific for the tube in question.

    • Norilsk has thousands of lavatubes, and the entire Siberia is filled with tens of thousands of tubes. That is why weird holes and tunnels pop all over Siberia.

    • Surtshellir in Ögmundarhraun (Húsafell area, Borgarfjörður). Also Raufarhólshellir just east of Reykjavík (Part of Meitill-Hengill Volcanos) – both are empty lava tubes. There are even some secret ones inside Reykjavik. I as a kid berely could crawl inside. Very tight, and dangerous. Bones were found in one of them.

    • “Inside the Volcano” was shot in Þríhnjúkagígur (part of Brennisteinsfjöll Volcano). That lies “in my back yard” so to speak, see it out my vindow, if it were not for some trees.

  2. This week in the “Volcanic Eruptions: a material science” coursera lecture is about density in silicate melts (Week 7): Expansivity and compressibility in silicate melts; Partial molar volumes; Density determinations and calculations above and below glass transition; Density models for anhydrous granitic system; thermal expansions and compressibilities of oxide components; deviation due to mixing; https://www.coursera.org/
    Highly recommended! As a warning: you got to have a hunch for plots. 🙂

    • Well to be frank, I follow the course, but am a bit disappointed. The prof is quite boring (it is the 5th course I follow on Coursera). Also they said the prerequisites were (quote) ” basic physics and chemistry”, but it must be a joke (I’m a chemical engineer by trade, with a master in chemistry) because they forgot to mention some thermodynamics and the concepts they show are far from “basic”. Also as you said you must have a hunch for plots which are far from self explanatory…..
      I will finish the course because after all it is interesting and brings very fundamental concepts and insights, but it’s not for the faint hearted. I would like to know what is the rate of defects for this course.

      • “The prof is quite boring” . Maybe that was the reason to came to Germany 😉
        I still like the course. But without two years of volcanocafé I wouldn´t know where to put all the condensed information in regard to eruptions. IIRC he didn´t even once said “decompression melting” but a couple of hundred times “glass transition temperature”.

  3. Absolutely fascinating! Thank you Carl and Vitton. There is so much new to learn about. I rather fancy some of dfm’s camembert or even a nice Brie 🙂
    Iceland has a nasty rash tonight. Not only a very shallow quake slap bang in the centre of Hekla but also Torfajokull has ayet another deepish tremor, very small but the pattern in this area is unusual. Not seen so many tremors right in the “caldera”.
    There seems to be a possible surge of magma in the hotspot to cause a rash of tremors up as far west as Öræfajökull. Please correct me if this is not a possibility .

  4. Small magmatic movement?
    04.09.2013 15:08:03 64.747 -16.483 31.1 km 0.3 99.0 13.9 km NNE of Kverkfjöll

    • Uncertain, but deep quakes may indicate magma on the move. There will be many such before anything happes, and lots o them in short sucession spells its imminent. Large deep quakes spell danger in itself. But these are tiny.

  5. Great post as always!

    Gorely is quite the interesting volcano. I’m always amazed at how I google earth volcanoes like Gorely, and while it’s quite incredible, there are often strings of volcanoes in the area that exhibit very similar styles of volcanism, with accompanying calderas of similar size. Gorely is no doubt spectacular, but it’s also one of many volcanoes in the area that exhibit explosive caldera volcanism.

    One small thing I disagree on however –


    There are actually quite a few shield volcanoes that have erupted in extremely explosive fashion. I wouldn’t say they’re more common than stratovolcanoes going caldera, but I don’t believe they’re as rare as you think. Just off the top of my head, Masaya, Colli Albani, Emi Koussi, Mazama (crater Lake), Tarawera, are among some other “shield” volcanoes with mafic lava that have had huge eruptions in the past. Even Etna has had a huge plinian eruption in the past (not sure how large however). I think if you were to go further north in Russia, you’ll find a very large nest of very large calderas, of which quite a few more mafic volcanoes currently reside (although it’s hard to tell whether they would or wouldn’t qualify as shield volcanoes, and not all calderas are necessarily related to explosive eruptions).

    The real issue is defining volcanoes by their shape, which has always seemed misleading at best. Having a steep or non-steep peak doesn’t do a lot to predict a volcano’s behavior as it can mean many different things.

      • Yes.

        But more specifically, the ease with which it can come out of solution does more to drive just how vigorous it is. Silica rich magma tends to hang on to the gas more tightly than silica poor magma. (it’s stickier).

      • Gas is the driving force for explosive eruptions. Gas-poor silica-rich magma will erupt effusively and form a dome. Gas-rich silica-rich magma will erupt explosively.

      • Pressure release = explosivity. Gas is the driving factor behind pressure release in volcanoes, and thus drives whether a volcano will “leak” out, or blow up.

        I think a good way to look at it is with a balloon analogy.

        If you take a balloon filled with air or Helium, then poke it with a needle, the entire thing explodes open as the gas “explosively” forces it’s way out. This is your explosive style of eruption.

        If you take a balloon filled with water and poke it with a needle, you get a slow leak that gradually drains. This is your more typical Hawaiian basalt eruption.

      • I guess I should have clarified. I meant Central Kamchatka, but north of Gorely. Although, looking in to it more, these volcanoes aren’t very much shield volcanoes outside the fact that they’ve erupted largely in effusive fashion in historical times, and their magma hasn’t shown to be super silica rich from current eruptions.

        Zhupanovsky, Karymsky, Polovinka, Maly Semiachik, Stena-Soboliny, Uzon, Geyserna, and Krasheninnikov are the calderas/volcanoes what I was referring to.

        These volcanoes / nested calderas all sit within a zone south of where Tolbachik is at spread out around 110km across. The crazy thing is that the average size is probably around 11-12 KM across for these. 8 massive calderas sitting in an area that likely totals only 110 km long really is quite nutty. Kamchatka = the wild west.

        • Oh. 8 11-12 km sized calderas is no small deal. Kamchatka has some other large ones, like Kurile lake. Some of them formed by explosive eruptions.

          • To be fair, there are 3 that are “only” around 4-5 km across, but those are nested calderas sitting inside a 15×20 caldera, along with quite a few others that are are in the 10-15 km range. To put this in perspective, Tambora’s caldera is 6km across. Are they from explosive eruptions? I’m not really that sure, but I have a hard time believing a 15×20 caldera would form in a quiet fashion. The area doesn’t have a ton of research on it from what I know.

            Go to southern Kamchatka, and you get Kurile Lake and the even larger (and older) Pautchetzka Caldera. Further inland and a bit south, there is another huge ancient caldera (Karymshina) that’s in the ballpark of 30km wide or so as well.

        • Some more Kamchatkan Volcanoes with Calderas:

          Akademia Nauk
          Bolshoi Semiachik
          Diky Greben
          Tao-Rusyr Caldera

          Source: GVP

    • I will have to go through your list, but most shields that have calderad have done so in a caldera subsidance, and not in a caldera explotion.

  6. Looks like our old friend Bob is picking up again, and a strange signal from La Palma at 4.40am which also shows on other islands, but nothing listed apart from a mag 6 mid altantic ridge at 4am which would be far too early.

  7. Tambora is not a proper caldera, it is an unusually large summit crater blasted out by an unusually large explosive eruption that did NOT involve the collapse of the magma chamber as the mountain is still there, even if part of the summit caved in. However, there is a very good chance that the next big explosive eruption at Tambora may be an even larger, caldera-forming event.

    Carl & co, I wish you would cease and desist with your abuse of the term caldera for anything larger than a 1-km diameter crater with scant or no regard for how it came about – a caldera-forming eruption requires the complete destruction by collapse of the magma chamber and the overlying edifice. It is only semantic titillation on your part in order to impress the reader and generate reader interest. In the name of science, cease and desist or at the very least use the full term “summit caldera” for eruptions that have caused a very large summit crater with some evidence of post-eruption collapse that has left the mountain itself is mostly intact!

    Cbus I like the way you point out that many of the smaller calderas are nested calderas, residing inside bigger ones. This reinforces a current model of volcanic development: As a (central) volcano grows, so too does it’s magma chamber with each eruption until there is an eruption big enough to clear enough of the magma chamber so that the structure above it no longer can carry the weight of the structure and the mountain collapses back into the magma chamber. Then begins a new period of building a new edifice and magma chamber but as the structure above, the rubble of the former edifice, does not have the same load-carrying capacity, subsequent caldera-forming eruption will not be as large.

    From this it’s easy to infer that the deeper the original magma chamber, the larger the initial caldera-forming eruption and resulting caldera will be. The shallower the original magma chamber, the (comparatively) smaller the eruption and caldera. Compare the 17 by 23 km-wide Aira caldera and Sakurajima in Japan with the 8.0 by 9.7 km Mount Mazama/Crater Lake caldera in Oregon and with the 1.9 by 4.2 summit caldera of Katmai, Alaska (where the emptying of the magma chamber, a sort of silicic fissure vent, resulted in the collapse of a large section of the summit into the emptied magma chamber. The caldera volume compensates for only 40% of the 13 km3 of 1912 magma erupted). In the first instance, there is nothing left of any pre-eruption (stato-)volcano. In the second instance, a circular segment of the Mount Mazama foothills remains even if most of the volcano disappeared back into the void left by the eruption. In the third case, a substantial part of the mountain collapsed even if it is mostly intact.
    From this it is clear that some VEI 7 eruptions (Tambora) do not form calderas, even if the resulting crater is so large as to dwarf other, proper calderas, while some VEI 6 eruptions do. Interesting here is that the magma chamber of Tambora is thought to be at 7.5 km (Gertisser, Self, Thomas, Handley, Calsteren and Wolff, 2011 – they mention a possible 2.5 km emplacement, but that cannot have been the main magma chamber as there would have been no such large eruption possible)) while Katmai’s lies at just 3.5 km below the current summit caldera floor (Turner, Sandiford, Reagan, Hawkesworth and Hildreth, 2010).
    Of course there are exceptions and anomalies, sub-aquatic and sub-glacially formed calderas are usually much larger than their land-bound cousins. Sub-aquatic calderas such as Thera/Santorini and Krakatau allow water to enter the still only partially emptied and mostly full magma chamber, with absolutely catastrophic results that enlarge the subsequent caldera well beyond the proportions that would have resulted on land. Sub-glacial calderas are also far larger by several magnitudes than any eruption deduced can account for such as the 12 by 18 km caldera of Torfajökull. Such a large caldera ought to have been caused by a rather large VEI 7 eruption but the largest one deduced is “only” a “small-to-medium”-sized VEI 6 – “a voluminous eruption of at least 25 km³ of rhyolite” (Saemundsson, 2009). And Katla is even more disproportionate where a 10 by 14 km caldera, again indicating a sizeable VEI 7 as its originator, cannot be explained by the maximum of smallish VEI 5 eruption proven by its eruptive history, tephrochronoloy etc.

    In the name of scientific clarity and in order to foreswear outburst of journalistic sensationalism, can we agree on the following terminology?

    a) Caldera – the result of an eruption that has left no or few remains of any progenitor (strato-) volcano.
    b) Summit Caldera – the result of an eruption that caused a very large summit crater and which was enlarged by subsequent collapse but has left most of the progenitor (strato-)volcano intact.
    c) Sub-aquatic caldera in cases where very large bodies of water has entered the still erupting volcano which resulted in its obliteration and left a caldera much larger then the original size of the eruption would indicate.
    d) Sub-glacial caldera where the caldera size differs from that of any known or deduced eruption by several magnitudes.

    Thank you and sorry for going a bit diatribic, but I am allergic to the “Improper Use of Terminology” (Tm&C Milord Pékékâr) in order to generate more interest than is merited by actual events!

    • Actually dear chap, this time I used it exactly as the word is intended, and I even went so far as to over-explain things stating that it was a large ignimbrite forming caldera explotion. I could not follow your attempt at defining calderas harder than that could I?

      I mostly agree with your definition as you know. We might argue a couple of finer points if you wish 🙂

      I do my best at over-explaining the formation style of the caldera. I would go so far that it should always be stated if the “caldera” is a “subsidance caldera” or a “explosive caldera”.
      Further on I agree with you on the difference between a caldera and a crater like in CBUSes crater of Tambora, and regarding Tarawera it is also just a crater in a Graben lake.

      So, I fail to even remotely feel hit by your criticism about “generating more interest than is merited” due to improper usage of terms.

      I would also like to state that you are the only known person on the planet that is so strict in your defining strategies of caldera-definitions. I though generally agree with you on the need for better definitions, but am a bit less rigid about if anything has the absolute size to be regarded as a 4km caldera or a 4 km crater and if every picometer of the roof have collapsed. 😉

      I restate, Gorely has suffered an explosive caldera formation that created a 100 cubic kilometer ignimbrite. But if you prefer to call it a very large crater please do so.

        • According to Henrik those would not be calderas at all if understand him correctly since they would not have destroyed the magmatic system fully. I would say that they are subsidance calderas, albeit in a serial form.

          • Though an eruption stopped when the pressure dropped far enough leaving 1/3 to 2/3 approx. of the magma in the magma reservoir.

            • Let us take Anak Krakatau as an example, as the eruption made the roof loose its support it broke and water poured down, the ensuing explosion ripped the entire roof of the magmatic system. Leaving just the deep plumbing down to the magma acreation zone. That is what I tried to say.
              I use magmatic system instead of the wildly erroneous phrase magma chamber since that makes people believe there is an actual chamber.

      • “a caldera-forming eruption requires the complete destruction by collapse of the magma chamber”

        mmmm ok…

        “and the overlying edifice.”

        mmmmm no.

        Many of the largest calderas – I’m talking about the Yellowstones and Taupos of this planet – *never had any significant edifice to collapse*.

        The largest calderas are just holes in the ground, which undergo resurgent doming on a very large scale but never build much in the way of volcanic edifices; a pre-existing volcanic edifice is not required for caldera volcanism.

      • No Carl, Gorely is a perfect example of a caldera (but you did revert to your former self in a reply on the previous topi)

        Furthermore, we’re making progress here – subsidence caldera. Take a look at the island of Vulcano (INGV Aeolian Islands, mappa stazione)! As far as I’ve been able to sleuth, it seems they are not the result of explosive eruptions but rather of subsidence as if the magma chamber was suddenly drained. We’re at the lower limit of calderas here, because there are loads of features caused by subsidence such as sink holes and up that cannot be considered as calderas. Nor can Maars even if a very large one such as Laacher See makes a strong case for inclusion whereas Ubehebe Crater doesn’t.

        Karen! I said “the complete destruction by collapse of the magma chamber and the overlying edifice”. Never did I say “fully destroy the magmatic system”

        Mike! With the Tobas, Taupos, Yellowstones, Long Valleys etc, there is no problem. Because of their sheer scale, there can never be a problem of definition.

        • Henrik, heaven forbid that I stop being confused 🙂

          I do not think I have ever been my “former self” on this one, but I can do mistakes on definitions with the best of them.

          • We all do, not least I! It’s just so, well, satisfying, when a greater mind than one’s own makes a mistake one can identify! 😉

  8. I am by no means an expert on any of this stuff, so don’t take my word for gospel. Most of what I’ve learned is from following commentary on here, asking questions, scouring through the GVP, and attempting to make sense of articles found on google scholar.

    I called Tambora’s caldera a caldera because that’s how it’s referred to in the GVP and most other sources I’ve read. I hadn’t realized it wasn’t a collapse structure, but that makes a lot more sense now.

    • Also I’m kind of curious about this – “c) Sub-aquatic caldera in cases where very large bodies of water has entered the still erupting volcano which resulted in its obliteration and left a caldera much larger then the original size of the eruption would indicate.”

      Wouldn’t this just imply that the eruption was enlarged due to the addition of water? If the caldera is larger due to the presence of water, it seems to me this just means that water acted as a catalyst, spurring the volcanic system to erupt more of it’s volatiles than it normally would have (since most volcanoes never erupt their full magma chamber).

      A caldera formed is generally similar to the size of displaced material regardless of water or not. Take two calderas, both 10×10 km for simple comparison.

      If one of these formed through the aid of water, we would assume the eruption would be around a large VEI-6 (just for example purposes).

      The non-water based eruption would on the other hand likely be a smaller sized VEI-7.

      So what’s the difference? The caldera dimensions still imply the displacement of the same volume of magma. If not, where is the extra displacement coming from with less material being ejected? It just doesn’t add up to me.

      • So to put it simply, regardless of whether water or ice plays a role, something still has to explain the displacement size of any given caldera. If anything, I would imagine water only plays the role of increasing the output of any given eruption since it more or less “washes out” magma sitting in a chamber that would otherwise not erupt.

        I would imagine the size of Torfajokull and Katla are larger than their respective largest known eruptions due to reasons that have little relation to the role water and ice play in their creation. I would presume their caldera sizes are more related to the constant string of eruptions they’ve had that gradually increase the overall size of said caldera, or potentially a miscalculation of the sizes of some of their larger eruptions.

        With that said, this is just pure speculation on my end, and i’m no scientist. With that said, the thought that adding water to an eruption creates a larger volume caldera, but doesn’t increase the output size of the eruptive material makes very little logical sense.

        • Why does Bardarbunga have so few and puny eruptions nowadays? Because it is a nested caldera. During the basaltic flare up the volcano went caldera big time, that is when that larger caldera went ka-blooy. It then spent about 10 000 years rebuilding untill it had sufficient size to erupt in a caldera forming scale (even though the caldera event was much smaller this time it still destroyed the magmatic system) in the 1477 VEI-6. After that it has had mainly miniscule eruptions and far apart. Most of the eruptions attributed to Bardarbunga has been from Loki-Fögrufjöll, another twin caldera volcano (nobody knows if it is subsidance calderas or explosive calderas).

          My point is the caldera volcanoes often have a cycle going from build-up with ever larger and more frequent eruptions, then go caldera and enter a new build up phase… Rinse repeat.

      • Good questing questions! Take a look at the descriptions of both Thera and Krakatau which are very similar. They began as regular, if large and sustained eruptions but once enough material had been ejected, the weight of the edifice could no longer be sustained and it began to collapse into a magma chamber containing about 60-70% of the original amount of eruptible magma. Becuase the Islands collapsed, water entered the magma chamber all ove the place, came in contact with magma at about 850C and – if you look up Lurkings graph, turned instantaneously into superheated steam, increasing its volume by a factor of more than five thousand times. This blasted the remains of the collapse edifice along with the a very large percentage of the remaining magma 80 km up into the stratosphere. Causing further collapses – you can see the old vent pathway on the cross-section of the old stratovolcano Rakata which was cut in half.

        When it comes to Thera, the sequence was a first intense eruption that deposited up to 7 m of tephra on surviving parts of the island (indicates a sustained VEI5?). This was followed by two further eruptions producing very large pyroclastic flows. The final and fourth phase was caldera collapse which resulted in an eruption far larger than anything that had gone before, again because huge amounts of water entered the magma chamber.

        Had these eruptions been on land, their fourth eruption would still have been the largest, exactly the same as Mount Pinatubo in 1991 but while the preceding three eruptions of all three volcanoes were of similar size, Pinatubo maxed out at a low-end VEI 6 whereas Krakatoa was upper end VEI 6 and oceanographic investigations of tephra deposits have now pushed Thera up to a VEI 7.

        Hope this makes sense?

        • It makes sense, but i already knew that water makes eruptions more explosive. That’s not really what I was disagreeing with. I guess to be more clear, let me make an example.

          Lets take two similar volcanoes that erupt VEI-7 250km^3 eruptions. The only difference is that one of these volcanoes sits as an island, and when it erupts, water accesses the magma chamber, resulting in a huge explosion.

          The water plays a role of a catalyst in the eruption, and makes it into a much larger eruption than what would have occurred without water. But if the cumulative release of magma is tied at 250km^3, then the calderas still should be similar in size, as calderas represent a volume of magma that has been displaced. Regardless of whether water played a role here or not, the caldera should still represent a volume close to 250km^3.

          So going back to Torfajokull’s 12km caldera – a VEI-6 eruption alone shouldn’t be able to produce a caldera that size simply because water was present. Regardless of water, there simply isn’t enough material ejected during a VEI-6 eruption to displace the volume that the Torfajokull caldera covers, unless the caldera was extremely shallow.

          This is why the idea that “water makes calderas larger” seems silly to me. Water doesn’t create larger calderas from small eruptions, It simply acts as a catalyst to amplify the power of any given eruption, and the increased size in an eruption subsequently creates a larger eruption.

          FWIW, I came up with a good new name for calderas. “Geologic Displacement Structures.”

          Okay, so it’s totally not necessary, but it does get the idea across better, and encompasses any of the structures regardless of how they formed.

          • Torfajökull is a nested complex caldera.
            With that I mean that it has suffered many caldera forming events, some explosive (smallish) and some as subsidance caldera events where the magma have left the volcano as basalt floods emptying the chamber untill it sags down.

            Torfajökull has several active magma chambers, so it is quite possible for one of them to go caldera while another is remaining active and potent. We can see this today where the last active magma chamber is deflating still after 1477 eruption, and another is inflating at the same time. Some quakes at Torfajökull can be due to magmatic intrusion and at the same time you have a deflation quake. Torfa is more interesting than people think.

            • Carl, I’ve come across a reference in several papers stating that the 12 by 18 km large caldera was formed by a “small-to-medium”-sized VEI 6 – “a voluminous eruption of at least 25 km³ of rhyolite” (Saemundsson, 2009). Further than that they do not go. But like you, I am convinced that the Torfajökull caldera, exactly as Askja and Katla, was formed by a large number of eruptions over a period of time measures in tens of thousands of years.

          • Hmm, cbus….

            First, with a land-bound eruption, the magma chamber never empties as fully as with a sub-aquatic, so your 250km3 identical eruption argument is flawed as the land-locked caldera would have started out with somewhere in the region of 500 – 700 km3 of eruptible magma whereas the sub-aquatic one would be no more than 300 – 400 km3 (and I’m being generous to the land-locked one here) in order for both to produce a 250 km3 eruption.

            Second, the sub-glacial ones are not, as you surmise and Carl points out, cause by a single eruption but many over a long period of time. Because of the proximity of water all the time, the volcanic mountain formed is cracked to start with and further crushed and weakened by constant hydrothermal activity plus minor basaltic eruptions. Because it is weakened, or rather shattered, down to a depth of 2½ to 3 km, just above the top of the magma reservoir, you’d not expect pressure to build up enough to allow a very large eruption but that is where a 700 – 1000 m thick ice cap comes into play. It acts like a pressure lid so that when such a volcano has an eruption powerful enough to break that glacier it gouges a very deep crater which is then rapidly widened by the collapse into the deep crater of the hydrothermally fracked rock surrounding it as happened at Askja in 1875 (Öskjuvötn Caldera). The much larger “caldera” to the north was formed about 10,000 years ago in a similar manner by a much larger eruption (of course the GVP has deleted the eruptive history and failed to present a new one citing “database problems”, so off of my head the 1875 one was VEI 5 whereas the older one was VEI 6). Together they form the Askja/Dyngjufjöll caldera.

            In a similar manner Katla’s 10 by 14 km caldera has been formed by three centers producing several large VEI 4 to small VEI 5 eruptions, two of which – the western one and the south-eastern one have been very active during the last thousand years. So as you see, the presence of water has greatly affected these eruptions – compare Askja’s 1875 Öskjuvötn Caldera, about 4 by 6 km, with Mount St Helen’s crater measuring about 1.6 km. Both are the results of similar-sized VEI 5 eruptions and even if Askja’s was larger, it does not account for the huge difference in size but water does!

            • Here I do not entirely agree with you.
              Let us take Gorely as an example with its 100 cubic kilometer plus Ignimbrite. That caldera formed in one go.
              I think we have to discern that there can be alternate functions for a complete caldera event with the same amount of magma that can happen to a non-aquatic volcano and that there is no necessity for that to have a higher magmatic load than an aquatic or semi-aquatic volcano.
              Some types of magma either due to enrichment, or by gas content can have very large eruptions without water in large quantities nearby. Though it should be noted that often the magma itself is water rich and thusly is enhanced in explosive capabillity.

              My rather wordy point is, there is always exceptions to any good rule…

            • Very well put! Furthermore, I applaud disagreement as part of the scientific process. Otherwise we’d all have agreed thousand of years ago that it was Hefaistos/Vukcanus smithies that were the root cause of all volcanism and still cling to that silly belief.

              (Scientific method is to observe, then make a generalisation called hypothesis or theory that explains as much of the observed data as possible – only for new data and sharper minds to inflict chaos and confusion on the well-ordered generalisation rendering it immediately useless and obsolete, much to the annoyance of the originator who will then most likely use any means at his disposal to discredit his critics before he leaves the field and becomes a linguist like Noam Chomsky or TV-personality lik Michio Cuckoo, sorry, Kaku. 😀 )

            • What actually made me cross with Michio is that he did not use the tools at his disposal… As a former collegue of his (in a sense since we are both physicists, albeit I am trying to turn into physician) I am dismayed that he did not use those tools to think out something that was profound about volcanoes, instead he opted for the cheap and lazy version of going “Oh my God, she is going to BLOW!” Gwarkh!

  9. Another one near Hamarinn or Loki.
    05.09.2013 13:08:45 64.505 -17.664 9.7 km 2.0 99.0 7.2 km ENE of Hamarinn

    • It does not really work that way.
      The plume is cyclical with a roughly 260 year cycle. About 3 years ago the IMO issued a warning that we have started to enter the high in the cycle, but back then it was said that the actual peak is 20 years away.
      Many other things also interfere, we also have the icelandic rift cycle that tends to be about 125ish years apart. That is when the SIFZ is ripped apart and we get a rifting fissure eruption, ie. Laki, Vatnaöldur, Eldgja or Veidivötn.
      Then we have a rapid melt of the glacier ontop of Vatnajökull due to increase in global heat. This is inducing decompression melt at a rate not seen since the great post-glacial basalt flare-up.
      Uhm, did I say that all 3 of these are going to happen at about the same time?

  10. FYI 😉 I see quakes in other places than are the usual, and many deep ones. No particular volcano is suspect (save Hekla, Katla & Grimsvötn – the usual suspects) but – ME DO EXPECT MORE – exact timeframe can be soon. The period already has begun, so to speak.

    • Yes and No, it was a “wet” one (of unspecuified size) coming from Godabunga at 18:32, (not Hekla related) not yet shown in any EQ list. You notice Green line (medium frequency) has highest peak. If these are close top is blue, medium distance is Green and far away is Red spking. Problem with these quakes are they probably have no clean break, so auto system does not pick them up.

    • Yes, it basically is Blue is highest frequency, Green is medium, and Red lowest (and far away EQ always register at lower frequency due wave physics).

    • A ha, somebody be building a SIL of his/her own powers, to have unrestricted data for him to see how far the authorities have “sunk” in scaling it down 🙂
      Seems the “Pirates of The Carabeean” have struck them Spaniards a blow

      • I’m afraid it is more prosaic than that, the thieves are stealing the solar panels and batteries to get some free electricity I suppose, they do not seem interested in the scientific equipment per se. By doing this they make IGN loose data from their equipment arrays. Maybe this can explain some of the outages on the seismometers.

  11. Far out dude…!

    While we are comparing earthquakes. This earthquake is due east of Vestmannaeyar. The crust there is about 8 km thick…

    05.09.2013 15:08:04 63.340 -19.790 16.0 km 1.1 99.0 25.8 km SW of Skógar

    • Not that far out “Master Dude”. This is very remote location for quake, BUT in recent months many ones have appeared in that general location (on auto lists) that do not make it into the main lists. I think we possibly might get a submarine event there abouts, and I belive the crust be slightly thicker, because of “subsidence” from nearby Katla?
      Possibly Katla once was 3,000 meters high, then went caldera… *not expert*

      • Might be up to ten, but not more than that.
        Yes, I have noticed that there have been quite a few quakes out there, and also some around the islands themselves.

        • signal be “skewed” by magma chamber (that the signal has to travel thrught) between that spot and the SIL in the Vestmann Islands, or there be huge wad of magma down there, just waiting to erupt, he?

            • Might actually be Godabunga, there has been Godabungingly deep quakes there lately.
              (Katka denialist at your service)

            • Oh my, denna bliver en vulkanudbrud, ja, denn bliver kaboooooooo .. mm…. (end if story for much of the country in the area around Godabunga).

              (Seriously I think there is “singular” wad of some lighter material inching its way up. Not a Volcano in its own right, it has to erupt first, right?. Only a sidenote for K or E)

            • Speaking of Godabunga Carl, have you forgotten that during my Katla article writing, you specifically asked me to avoid presenting a possible conclusion about Godabunga as you wanted to do it yourself?

              Now where is that d-d article! 🙂

            • Ohh myyy!!! Did that one get lost in translation?

              Then I have to get around to it… But I think I did write it…?

  12. http://www.vedur.is/skjalftar-og-eldgos/jardskjalftar/reykjanesskagi/

    Quake at “core” of Brennisteinsfjöll Volcano. Almost an 3 R event, possibly felt in my chair today, And area is potent for up to 7 R and an effusive event of rather small proportions.
    But it does represent danger mountain roads or far away houses (+20 km away). More danger can resault from the systems largest earthquakes (mostly possible broken windows and cracked walls in Reykjavik area, possible walls with design flaws can fall or collapse). This area is the number one that can produce the most dangerous quakes for Reykjavik City general area.

    • Hope you have an eruption, then you can field test the drive over a lava flow performed by Piers Brosnan. Just make certain that it is a statistically significant number of drivers and vehicles employed. Also, you cannot limit it Icelanders, so you will have to bring in equal numbers of ethnic groups living near volcanoes that can produce lava flows that may have to be traversed by car.


        • That was a statistically insignificant number of traverses made by a specially prepared vehicle which the one we see on the screen certainly wasn’t meant to be protrayed as. Doesn’t count, has to be repeated if it is to be anything but a curiosity.

          • It is just a proof of concept for your big experiment.
            And you should not be so androcentric in your experiment. We should invite loads of Aliens to, who know if not the Alpha Centaurians will prove to be the best lava-drivers. My personal favourite contender would be the ever cool Vorlons.

            • Surely you mean homocentric as androcentric means male-oriented? But perhaps we should specify that for any species to take part, from Homo Sapiens Sapiens to Dalek Drwhoiensis, there must be an equal sample of all applicable genders? 😀

            • Of course regarldess of the amount of sexes present in the particular species.

              I blame Carl Sagan on this one, he and my favourite befuddled professor, Freeman Dyson, coined the expression “the androcentric principle” for our human lust to set ourselves as the yardstick to compare anything to. The strong androcentric principle goes further and states that the Universe looks like it does due to us (humans) existing.

              Freeman Dyson is a lovely person and a great thinker, he is in my personal trinity of great thinkers among Feynman and Ed Fredkin. The rest are just copycats.

    • We do not have field test this, vehicle on tracks (like Tanks and Bulldozers) can make an track or road across an running lava (“Apalhraun” or the thick variety) and then APC like vehicles on tracks can use that for traversing. Water cooled or not, it does not matter. I think better leave out them on Rubber wheels. Less fire risk. Such “roads” were in fact used in the Vestmann Islands 1973.

    • “Livet är skönt
      Himmelen är grön
      Följ mig en bit på livets stig

      (Svensktoppen c1968-73)

      • “Minne,
        jag har tappat mitt minne.
        Är jag schwensk eller finne!”
        Min bror spontanskaldande på karaoken mellan Umeå och Wasa. Close encounters with sudden violent death. 😉

        At another time I was out on a road trip with a few friends. At a gas station a large ancient american car drives up filled with neo-nazis. A sudden brain melt occurs and I walk over and lean into the car and sing this for them…

        “Jag är snäll,
        Jag är säll,
        Jag är homosexuell”…

        Good time to have a two meter friend as a back up carrying a claymore while wearing a kilt. And yes… we where going to the Wisby medieval week.

        • Well, they were American, neo-nazis. In all likelihood they would have taken it as an offer… provided they understood the meaning. In the right context, you could have gotten them to walk around verbally proclaiming that to each other with great enthusiasm and pride.

          At one time, I loved to prank people on the ship. Generally the best ones are when you convince them the accuracy of a statement that they themselves have made or come up with. Later, when they realize what an utter idiot that they have made themselves out to be… you quietly chuckle to yourself and bask in the glow of your accomplishment.

          This worked quite well on haughty Junior Officers.

          If someone passing by here is or was a Junior Officer… then know that there are thousands upon thousands of mid to senior enlisted like me who were or are playing you for the fool that you are. Not all of us are looking out for you or your precious career path.

          You had best hope that the senior enlisted in your division is on your side. He can set you straight so that you don’t look like an idiot.

          Enjoy 😀

          • Actually these where swedish neo-nazis of the football hooligan type. About as deadly as a pit of vipers (actually the vipers are more intelligent and better behaved, your general viper is a splendid conversationalist in comparison).
            I do not know whom they had stolen the car from, probably some veteran car show.

            • For some reason my then wife found it particularly hilarious to see me singing that I was “nice and gay” dressed in florentinian recreated garb from 1542 together with a barechested giant with a huge sword. There is something to italian renaissance clothing that says you are “a mans man” 😉
              My ex wife had her points, among them luring me to medieval weeks where I could eat huge pieces of meat and drink to my hearts content while wearing utterly silly clothes. Only place I’ve been to where you fought before you drank.

            • Hm, in a very broad sense, err… mmyes… But to be brave requires that one recognises danger and experiences fear and rise above them by an effort of will to perform an act that greatly benefits others. At least if “brave” is properly used. A person who is fearless is not brave, he or she is stupid as nature has not endowed them with a sufficient sense of preservation to make them recognise and avoid danger. But “de mortui nil nisi bonum” – “of the dead nothing but good” – has ensured that many stupid men have given the epitaph incorrectly in order to comfort bereaved relatives. There are many examples of alpinists who know that at 8km altitude, judgement is impaired, yet make calls that kills them in a vainglorious attempt to reach the summit. While their decision to attempt a Himalayan climb generously could be said to be brave, even if it is of no benefit to anyone but themselves, the decisions that kill them are downright insanely stupid.

        • One of the better ones that I saw, was self inflicted. We were set to offload all of the ordinance from an AO (ammo stores ship) that was part of the outchopping CV battle group. At the wardroom briefing our Ops Boss (admittedly, our new Ops Boss) stood up in front of the wardroom and clearly stated that it was going to take four days of alongside time to move that much ammunition to our ship.

          He had evidently never talked to Deck department or our Weapons department. We were done in about 9 to 11 hours. The biggest bottle neck was that the offloading ship had only one weapons elevator. We had six…. and copious amounts of space for the palletized ordinance, internal, along the forklift runway and also along each side on the main deck. While the helo was shuttling pallets, Weapons department personnel were moving among the pallets doing inventory, while the forklift crews were dropping the pallets down to the magazines via the elevators.

          See, that class of ship had been designed specifically to move ordinance… and fast.

          The humor was in that he had made his incorrect statement to a senior Skipper who knew full well what his ship could do.

        • Lurk, I have two Marine Gunnys one a CSM, and a retired Senior Chief (old Nuke propulsion guy) in my family-they are scattered on both sides. -You speak truth . From what I have heard…
          “Do not get on the bad side of your noncoms-you will regret it forever.” My cousin the senior
          Chief told that to an Ensign-as a bit of friendly advise.

  13. Drove 200 km just so I could call up the server operations center and have them make a change on a server configuration. Then I drove 200 km back. I am what is known as “bored shitless.” Wife wants to order a pizza rather than cook, I’m good with that. Get home, tells me how much it is, I write out a check. She wants my license number so she can put it on the check. I prattle on about having a “V” and a gold star on my license. She asks what they are for. The “V” denotes that I am a veteran, so I can be shot on sight in a traffic stop. The Gold star means that my address has been verified so that they know where to send the body.

    Meanwhile in China, they have a traffic jam that has been going on for three days due to construction. Reportedly, they are averaging 1/3 mile per day in travel speed. People living near the highway have been selling noodles to those stuck in traffic.

    I also hear that the UK has jumped into the traffic snarl with a California or Mobile Bay bridge style traffic accident. You know, the one where everybody stacks up due to low visibility from the fog… at interstate speed. Usually those are a horking mess.

    • The Californian ones are actually fairly simple.


      Enter the Germans with their Autobahns and free speed (at least almost). Imagine thousands of BMWs and Mercedes’s going 250 kilometers an hour doing a pile-up during commuter hours? Not a nice sight…

    • I’m actually sort of lucky in that regard. Of all my moaning and groaning about having to drive… I don’t have to do it at night… usually.

      Some of our fog down here can be too thick to see the front of your own vehicle. Typically this level of fog is over water… like Mobile Bay. Complete with guard rails so that your vehicle is kept in play. (think pin-ball)

      The greatest hazard that I encounter are the gully buster rain events with the standard idiot poking a long with his four way flashers on since he can’t see shit. Every now and then you find them in the “hammer” lane doing 65 kph.

      • I have to drive La Grande to Baker City Oregon once or twice a week. I have this solder GM van. I cruise the speed limit (65 mph) Saturday (Labor Day weekend) I noted the Oregon
        State Police were out in force. There is this steep freeway pitch-Ladd Canyon. At the bottom of the steep grade there is this freeway exit-invariably there is a Policeman with Radar there.
        Especially on the holiday weekend. I was passed by a 700 series BMW as I was entering
        the canyon like I was sitting on jacks. I am a fair judge of speed, I’d say oh 100+mph.
        Washington plates. I hit the flat as I break out into the Grande Ronde valley-there is a 7mile straight. The BMW driver was pulled over and the red headed State Trooper (who is a friend of mine) was probably writing a very expensive ticket-at about six miles from the overpass.

    • And there lies the value of the little “rat dogs.”

      Though they are small, they are still genetically quite close to wolves in their sensory capability. Far better than a human. And if you have enough of them, they can be more worrisome to an intruder than a larger dog.

      At one time I did have a larger dog, (quite larger) that would only give you one low “woof” for a warning. After that, you would likely loose a body part if you got any closer. She would just sit there and watch you to see if you were a threat. Jet black and unobtrusive she was quite shy unless she felt that she needed to take your gonads off.

    • {snicker}

      Pizza Crust shards can be fun. Faked a toss of one for the dog and he leaps to the edge of the couch to see where it lands, eyes locked on the ceiling so that he can detect the flying morsel of goodness. The other dog sees him and starts scouring the floor, yet nothing had been tossed.

      Double fake out… “woot!”

    • That was very interesting, thank you! But if you compare Tamu Massif directly with Olympus Mons. Firstly, you cannot count the outliers a) just below the legend “Tamu Massif,” and b) to the NE on the lines carrying the M16 and M17 legends as part of Tamu Massif proper as not even lava that runny can run uphill. That makes Tamu Massif half the basal area and and only one-fourth the prominence of Olympus Mons (which is inlaid for reference). Roughly, 1/2 by 1/2 by 1/4 should make Tamu Massif only 1/16th as voluminous as Olympus Mons, but it is still mighty impressive!

      By my estimation, Olympus Mons thus still comfortably rules as the Solar system’s grandest volcano but the quintuple-vented Mauna Kea/Mauna Loa/Kilauea/Hulalai/Kohala volcano with it’s 10100 m prominence and one-eighth the basal area (guesstimated) should be outranked by Tamu Massif as the latter is at least twice as voluminous.

      It is not everyday that news of this magnitude comes your wat, again thank you!

  14. Oh, I see I am the night shift again.
    Once again, I have learned a lot from an excellent and interesting post. I’m in the midst of a move from my city condo to a country-ish apartment. These posts are keeping me sane. Almost. I had a dream about exploding water last night. Well, maybe not so sane.

  15. The quakes at Hamarinn have moved up.

    06.09.2013 09:16:33 64.522 -17.713 0.0 km 0.6 99.0 6.0 km NE of Hamarinn
    06.09.2013 09:08:52 64.521 -17.743 2.1 km 0.5 99.0 5.0 km NE of Hamarinn
    06.09.2013 08:55:59 64.484 -17.864 0.0 km 0.2 99.0 2.6 km W of Hamarinn
    06.09.2013 08:54:48 64.491 -17.678 4.3 km 0.7 99.0 6.3 km E of Hamarinn
    06.09.2013 08:51:48 64.493 -17.762 0.1 km 1.9 99.0 2.4 km ENE of Hamarinn

    • Yes, and there is forecast (any day or week) a Glacial Flood from Eystri-Skaftárkatlar (Skaftá Kettles), its now three years, it usually empties every two-or-three years. The pressure relief can cause decompression melt or water flashing to steam. To me “the area” might become interesting.

      This SIL (Jökulheimar) has raise in Green Band (medium distance) so it could have effect on this, if it starts. http://hraun.vedur.is/ja/oroi/jok.gif

  16. And now Vatnafjöll has entered the Deep Quake Squad… Those are list as south of hekla quakes.
    06.09.2013 10:07:03 63.842 -19.822 12.7 km 1.1 99.0 18.3 km SSW of Hekla

    And Torfajökull had a deep quake:
    06.09.2013 11:23:02 63.951 -19.087 11.0 km 0.6 99.0 4.6 km SSW of Landmannalaugar

    • I dawns on me, if them deep quakes (10 km or more) might be because of “overall rifting effect”, indicative of beginning of next “Rubber Band Dead Zone Snapping”. It would be nice to see if these “statisticall exceed the known background level” (say perhaps if this last 6 months exceed the average of previous dataset available.. Food of thought for the data munchers … hint hint ..)
      What part, or how long part is something not known, but might be from 8 km to 20 km in depth, perhaps 10 to 40 km long overall. In my view the middle or northern part possibly be next (likely in next two give/take forty years). Yes, I am thinking of Laki, Veiðivötn, Langisjór or Eldgjá.
      *end of Friday rumination*

      • I would spontaneously say that the last 3 months exceed anything I have ever seen. But… Datamuncher to the forefront! 🙂

        I would not rule out Askja or Veidivötns smaller sibling Vatnaöldur.
        And a really long shot. A rifting fissure opening in the EW direction. That way has not rifted for 10 000 years, and it would explain the activity we are seeing.
        Loki-Fögrufjölls swarm starts east of Grimsvötn and goes through that bad boy, straight trough the double calderas of Loki-Fögrufjöll (Skaftár Cauldrons) onwards straight through Hamarinn and onwards through another volcano (last eruption at deglaciation) all the way into Hofsjökull. The pent up potential there should by now be rather plentifull. And it also covers more than half of the deep and anomulous earthquakes that we have seen, and also would explain the odd uplift pattern. Pure speculation on my side, kind of the true nightmare scenario. Remember, this has happened once.

  17. Sometimes things get clearer if you fill it with absolutely clear water. This picture is taken close to Potosi. I found it as I looked at the latest quake there. The nested caldera is very clear.

    Image and video hosting by TinyPic

      • I month ago I saw a documentary about the miners in Potosi, since then I have kept track of earthquakes from Potosi. And when I looked up the last 4M I saw that it was close to this beautiful nested caldera lake. Also the name is nice, Laguna de Pozueli, Lake of Ignimbrites.

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