Few right and wrong things about geology in Iceland, part 1

I have seen many speculations on how geology works in Iceland. Some of it is good and based on observation and factual basic. Other however is nothing but speculation and far from anything based on factual evidence on how geology works in Iceland.

Few right and wrong things about volcanism in Iceland

Volcano interaction Status: Limited truth to this

Volcano interaction is something of a debated among scientists. But what is not debated is the interaction between volcanoes that lies far apart. That interaction is none by it’s nature. So while I have been seeing discussion in the comments here that there is some connection between activity between Hengill volcano and Hekla volcano. This is untrue. There is no connection between those volcanoes and never has been. The reason is simple. The volcanoes are far apart. They don’t even share the same magma source. But that is evident by the lava that comes from this two volcanoes. But Hekla volcano has mixed types of eruption sometimes. But Hengill volcano only has Hawaii styles eruptions (if not hit by water) when it erupts, in style with other volcanoes on the Reykjanes ridge rift zone.

The only real life examples of volcano interaction are from Bárðarbunga volcano and Torfajökull volcano. The reason for this interaction is quite simple and logical one. Bárðarbunga fissure swarm cuts right trough Torfajökull volcano. When magma travels south-east in the fissure swarm (it last happened in the 15th century) it can hit the magma inside Torfajökull volcano. When this happens there is a big bang in Torfajökull volcano. As the magma in Torfajökull volcano seems to be colder and more Intermediate (andesitic) [link, Wikipedia] in nature. But in Bárðarbunga volcano the magma is Mafic (basaltic) in nature. When the two magmas mix, it ends with a bang and eruption in both volcanoes. But normally the process that starts this is because there is a ongoing eruption in Bárðarbunga volcano. So when Bárðarbunga volcano. I would worry about that rather then anything else.

See, no connection at all between Hekla and Hengill volcano. Copyright belongs too this picture owner. Owner unknown to me.

Iceland is going to have VEI-8 eruption. Status: Not likely.

All volcanoes can do a VEI-8. But the thing is that they are just not likely to do so. As the size of the eruption is directly connected to the inflow of magma it is getting. In the case of Icelandic volcanoes the inflow just seems to be few magnitude too small to make a VEI-8 eruption. The largest VEI eruption known in Iceland was a VEI-6 eruption that took place in Bárðarbunga volcano in the year 1477 (?).

As for VEI-8 eruption. I am not expecting that type of eruption any time soon in Iceland.

Iceland is one volcano. Status: False.

The simple answer is no. The long answer is. Iceland has many volcanoes, not just one. So the answer is no to this.

Geology in Iceland is well understood. Status: False

Geology in Iceland is understood. But far from being fully understood. As it happens geology science is just starting to now understand what complex progress are taking place in Iceland. A lot have been learned. But a lot more needs to be learned about how geology works in Iceland.

Volcano eruptions comes in active cycles. Status: True

This has been observed by actual data. But volcano activity happens in periods of 80 to 160 years. With a quiet period of 50 to 90 years. But numbers are approximation. During the quiet time there are fewer eruptions and they are smaller (hint: Large eruption can still happen however during the quiet period). Last quiet period started in around the year 1870 and did not end until the year 1983. But that year there was a eruption in Grímsfjall volcano. But then Grímsfjall volcano had not erupted since the year 1954, but that break was 29 years long for Grímsfjall volcano.

This graph here also shows this clearly. But this is volcanism in Iceland during the years 1875 and to the year 1993.

Copyright holder unknown. Copyright of this picture belongs to this owner.

It is impossible to know for sure when the high peak in the current cycle is going to be be. But most geologist are estimating that to be sometimes from the year 2020 and to 2080 or about that. So the years ahead is going to be quite busy in Iceland in the terms of volcano activity.

I am going to write more right and wrongs about Icelandic volcanoes soon. But for now this is good enough.

Sources and other things.

Volcano-tectonic Interaction in the Hengill Region, Iceland during 1993-1998 (pdf)
Volcano geodesy and magma dynamics in Iceland (ScienceDirect)
Interaction between Continental Lithosphere and the Iceland Plume—Sr-Nd-Pb Isotope Geochemistry of Tertiary Basalts, NE Greenland
Tomographic evidence for a narrow whole mantle plume below Iceland (ScienceDirect)
Pdf document on Hengill volcano crustal deformation.
Magma (Wikipedia)
Volcano geodesy and magma dynamics in Iceland (pdf)

59 Replies to “Few right and wrong things about geology in Iceland, part 1”

  1. Jón, let me point out one thing once and for all.

    I have never ever talked about magmatic interaction between Hengill and Hekla, it does not exist such a connection.
    What I have been talking about is energy in the form of pressure within the area between the Sprungur area and Hekla. Something completely different.
    It is a fact that energy is being released there, the Sprungur themselves are the evidence of that. That energy is represented as the quake-release in the area in question.
    That energy (not magma) is going somewhere. Energy can only be “stored” in a certain quantity in any media (with the possible exeption of a Hawking materia-zink), so it needs be always to go somewhere and it is governed by an entire set of physical laws, called the Laws of entropy.
    So far so good. The thing I wished to know is where it is going since I had observed a bit of cause and effect. So I asked Lurking to make the plots, and when I saw them it was obvious in what form and where it was going.
    I know that what I have written is pretty spread out over 3 (now 4) blog post commentary threads. So it has started to be hard to follow. I will one of these days write it down in a single paper, but that will take a little while (and needs that Lurking and BVH let me use their plots). Then it should be clearer. Or perhaps not, because then I will write in the form of equations. Be it that.
    Sofar it is just a loose reasoning about a future theory without the mathematical formalism, but… I have been carefull to follow every rule in the book concerning scientific reasoning (even if masked behind mushy bananas and the art of squeezing zits).
    First observation of reality, then came a simple cause-effect that I formulated into a question, then massive observation of reality (Lurkings astounding plots which I never would have been able to do), out of this I formed a theory. And as any real theory it is testable and predictive. Ie, there are clearly defined ways of experimentations to prove or disprove them, and it makes a clear prediction. The cumulative seismic value in the 3 last wave-bands will be ruffly the same for every eruption (quite straightforward as a prediction).

    So, by stating that there is no connection between these volcanos whatsoever and giving evidence about no magmatic connection misses the point. The only way to say that the theory is wrong is to prove it wrong by practical experiments. I will openly say that I might be glaringly wrong, I have been that often before in my own field.
    But, untill the theory is proven wrong, or replaced with a simpler theory that explains something that is added to it, the theory stands.
    I have given 1 way of experimentation to prove me wrong, and one example of prediction that over time will prove if I am wrong. Only one of the two needs to fall to make the theory fall.

    But if you want to prove that there is no connection between any volcanos on Iceland, you are welcome to have a beef with Professor Haizel Rymer about the mechanical/magmatic connection between Askja and Krafla, and Askja and Herdubreid. She is the one who let the cat out of the box for real. That is all in her book published in 2010. Because to prove your point above, you must disprove that connection too, and that is very well documented, so it will be hard to prove for you.
    Of course there are connections between many volcanos, it is not so odd, they are after all often sharing their respective faultlines/volcanic zones.

    My few cents about science theory and what I actually wrote about.

    1. After re-reading the blogpost I feel I should be even clearer and shorter to the point.

      1. I have never ever said that Hengill and Hekla is the same volcano.
      2. They are not connected in any way.
      3. The Sprungur area south of Hengill are though through third order harmonic energy transfer connected in this, and only this way, to Hekla.
      4. The energy transfered is of earthquake origin, and thusly tectonic and not magmatic.
      5. Magma has nothing with the theory to do.
      6. My theory never had anything with the cause of an eruption in Hekla, it is about a possible triggering factor being accumulated over time.

      1. The energy does not come from Hekla og Hengill volcano. But the energy comes from SISZ.

        But the energy build up on SISZ is quite a lot over short period of time. As it is released in large earthquakes on 10 to 80 years intervals. Any energy build up from volcanoes close to SISZ would simple be “eaten” by SISZ soon as it would somehow transfer too it. Ground also does not transfer energy all that easy, when it does. We normally have a earthquake.

        This is most evident when Hekla volcano erupts. But that is normally followed (has been recorded) by small earthquakes swarms in SISZ. As there are stress changes in Hekla volcano during and after eruption. Those changes do transfer to SISZ for unknown reason at the moment, resulting in small earthquake swarm along it.

        Science article on SISZ: http://www.sciencedirect.com/science/article/pii/S0264370799000460

      2. Jón, you know that I was not talking about the Hengill volcano per se, I was talking about the Sprungur are south of Hengill. And as far as I know that is a part of the SISZ system, if I am wrong about this please feel free to tell me.
        The reason I chose that specific point is that there seemed to be a cause-effect relationship that was traceable from that area to Hekla.
        The reason for the limitation was mainly to limit the data into something manageable. And that was a lucky guess, because it contained an area where the pattern is very clear.
        Actually, ground transfers energy quite easilly. That is why we can feel and detect quake energy from far away. I think you are thinking about mechanical pressure here, and that is much harder to transfer over longer distances.
        But as you noted in your reply, energy has a tendency to come out as an earthquake. And so it does, aparantly in one of these beautifull bands in Lurkings plots. And that quake releases new energy that goes to the next and so on. Please note that I am not talking about rapidly cascading earthquakes, they do occur, but I am talking about slower transferal and build-up than that (with exceptions of course). And that in the end that energy ends up in Hekla. Not much, per instance of energy transferal, but over time we are talking about a lot of energy. Problem here is just that Hekla is aseismic, probably due to ductility of the surrounding bedrock. (Fun fact, the deepest part of the Kiruna mine requires more explosives to break the rock than at the topp, due to higher temperature of the rock 1300 meters depth.) So, because of the aseismicity the energy cannot be released as an earthquake at Hekla, instead it is dumped in and stored as strain. And as the strain build up it will become as any battery, sooner or later something gives.
        So, yes, I am talking about the energry transfer from SISZ to Hekla. The only difference is that I made a modell of how, and started at the Sprungur area to the south of Hengill (more people know where Hengill is, than the Sprungur area).
        The swarm afterwards are probably travelling the same way, but backwards as a form of inverted energy strain release (But this is just a guess sofar).

      3. Jon,

        If Hekla transfers mechanical stresses to SISZ, the in principle it can also happen the other way around: From SISZ to Hekla. No natural laws prevent this from happening!

      4. Well, no. The reason is that SISZ moves from East to West when large earthquakes happen. This pattern is no something that happens in smaller earthquakes it seems.

        See here, http://www.sciencedirect.com/science/article/pii/S0191814106002653


        It is also worth notice that Hekla volcano is on the edge or even inside the SISZ. But it is hard to know for sure (at least for me) what is the actual fact on that.

  2. Empirically, your theory Carl should be easy to confirm or disprove.

    We should plot all eruptions in Hekla, and correlate that with earthquake swarms in Hengill and at the SISZ. If you see the connection for most of the times, then your link is probably occuring, if not, it’s not true. And since we have plenty of Hekla eruptions you should be have to confirm or disprove that. And what I found more difficult in your theory, is that once in a while, Hekla decides to sleep for longer periods (as before 1104 or 1947); what happens then?

    Jón, interactions are not only confirmed for Bardarbunga to Torfajokull, but also Grimsvotn and Bardarbunga (as in 1996). Possible connections can also exist between: Askja and Krafla (deflates/inflation links at the same time in both volcanos); and the link of simultaneous activity in Katla and Eyjafjallajokull (this is happening now for the 4th time, after 1625, 1821 and 1999). Some authors even went further to suggest a link to the Westman Islands, but that might be only speculation and not occurring at all.

    The point is that at least several connections can exist within the same volcanic belt. But of course it is a very controversial topic.

    1. I have been thinking about the Hekla slow-periods.

      And here I am opening up for a big attack since this is unabridged speculation on my part… I think that Hengill (and this time I am actually talking about the actual volcano) might be diminishing the energy transferal towards Hekla. But here I am probably wrong. A simpler explanation would probably be something happening with the feeding mechanism. I am not so sure that my theory has anything to do with it, most likely not at all. Remember that I might have uncovered one small thing about why Heklas eruptions are triggered, not how they are caused. And I think “the causation” is causing the lulls in eruptions, not the triggering mechanism I theorized about. The more I have thought about and studied Hekla, the more I appreciate how complicated she is and how insanely much more there is to learn about her.
      I could probably spend the rest of my grown life studying her, without uncovering even half, and if I really want to I can cover it in equipment to get a wide variety of data to study.
      But, I would rather go for Hengill. It is a volcano that very little is known about. Hekla is much better understood.

      This is just my personal view of things, but if any volcano on Iceland deserves to be studied more it is Hengill. If Katla is the hype-queen of Volcanos and get undue attention, Hengill is the over-looked and forgotten orphan. An orphan that is a gently sleeping giant. And since Reykjavik and other cities are close by, it warrants more attention than it is getting.

      1. Or, a simpler alternative. Small eruptions tend to clog the conduits. And with little or no space in conduits, you’ll end up sleeping longer. After the pressure exceeds the limit, you’ll have the throat-clearing event, a major erupion.

        Remember, Hekla’s magma chamber is deeper, very deep. So there’s plenty of conduits until anything reaches ground level.

      2. An example in short time could be Etna. The lates eruption was a day late from the 6 day cycle and the eruption was shorter and more violent than previously. Can’t say for sure that extra day to build pressure was the reason, stupid causation arguement.lol

    2. Not so easy to prove.

      Correlation does not prove causation, as we hear all the time on The Eruption Blog.

      For example, something more fundamental could be causing two events which are seen repeatedly to occur one after the other, without either of the two events otherwise connected and without any causation between the two events.

      1. As these two corresponding events continue to happen, the probability of correlation of causation goes up significantly right? I don’t know the math but after four instances like at Katla and Eyjafjallajokull odds are slim that they are not related.

      2. Actually, the odds are extremely slim.

        With an average repose time of 45.1 years, it is difficult for Eyjafjallajokull not not erupt sometime near a Katla eruption. In fact, numbers state that it will be within 9 years 40% of the time. Within 18 years 60% of the time.

      3. I thought I heard it was within 2 years? Sorry if I don’t remember it right. I knew you would respond when I said math…hehe

      4. Well, it’s mainly from the point of view that there are so few samples do obtain a meaningful relationship or to hint at a correlation.

        We have four samples. Two within the same year, one within two years, and the fourth within ten years (lagging Katla). By that same criteria, the last eruption would be classed as lagging Katla by eleven years. (If that was eruption, it’s still classed as uncertain)

        The more samples you get the better your chance of seeing a connection. It’s not that it proves there is none, it proves that we don’t have enough to reliably make that statement.

        I’ve read that generally you need about 31 samples to get a good feel for the total population. The more the better (increases the confidence factor). Four (or five if you count the last) just won’t cut it.

  3. irpsit
    “The point is that at least several connections can exist within the same volcanic belt. But of course it is a very controversial topic.”

    It is also a fascinating discussion the listen in on being a ex flt eng in P3’s and having spent a lot of time in iceland it is doubly intresting

  4. Another small quake at Öræfajökull. Does this volcano usually have earthquakes or is it normally quiet?

  5. One limitation with Lurking’s plot is that it is limited in area to – that’s right – Hengil to Hekla. Do a plot, or rather, ask Lurking very nicely if he’d do a plot over a much larger area than just the Selfoss graben such as the entire area covered by the IMO map. Then see if the pattern remains, if there are similar patterns elsewhere (Tjörnes?) etc.

    The strong point about Carl’s hypothesis is that strain is invoked by Norvulk volcanologists as an explanatory mechanism for the eruptive activity in Hekla and Carl has supplied the mechanism by which that is generated. As long as it is understood that Carl’s hypothesis is a “work in progress” and not established fact, what Carl is doing is sound science.

    Unlike Professor Pall-Einarsson’s continued insistence upon a physical connection between E & K.

    1. The issue is going to be isolating linear fault runs and making corners. The Reykjanes and MAR are probably easy to do. Those are fairly straight. The binning operation gets sort of nasty if I cover an area much larger than the one I did at that resolution. Even on a quad core AMD machine with 4 Gigs of ram, it took about 2 minutes to run. Wrangling the data into digestible form took a couple of days of spare time as I found it. I finally had to tell everyone to bugger off and leave me alone. (data munching provides a moment of Zen)

      I’m just happy someone found it useful.

      BTW, a less useful but much scarier plot was the US Dow Jones industrial average priced in gold. According to that, the world is ending shortly. At least from our perspective.

  6. Like to add though that what Jón is doing is sound science too! You have to draw a line between fact and fiction, science and speculation and clearly state which is which. Unless you do, there is danger that people who understand nothing about science but everything about spinning yarns will use a statement of opinion as a statement of fact in order to lend and air of versimilitude to the crap they’re selling the public.

  7. Öræfajökull still has little quakes, she will quieten soon. She is one volcano that is better seen and not heard. We have enough fun from Iceland without OJ.

  8. Henrick I am with you on this. Here we have two viewpoints, not airy, fairy, doomsday opinions, but genuine scientific argument with related evidence.
    These discussions and debates allow the less scientific viewers of this blog to see science in action. Hopefully it will discourage scaremongering and sensationalism.
    It should encourage THEM to think about each argument and realise that there may not a a single or simple answer. That is, until the theories have been tested by observations, recordings and mathematics.
    Eish! Maths! How that word scares me!

    This discussion has taken me back to my Physics classroom back in 195……., a long time ago. Where Miss Gudderidge of the purple jumper and grey pleated skirt tried to enthuse us about energy transfer….. and failed miserably. Until now!
    I am now remembering and revising my lessons. I can almost visualise the rocks beneath the SISZ. Huge blocks separated only by narrow fracture lines. I imagine something like a Gigantic Newton’s cradle, but made up of tons rock blocks floating on a hot plastic, like a spring. Something in the West, a sudden powerful up -thrust of magma from the MAR maybe, starts an energy tsunami wave…….Slowly this transfers to the next block.. and the next…..until the energy can escape, like the last ball of Newton’s Cradle into visual or felt evidence of that energy.
    This is just my way of visualising forces so slow and powerful it is hard to gain a true concept . I may have got the actual mechanics wrong but at least I can appreciate the hugeness and complexity of what is going on under Iceland.
    Jon, I think you are doing a great job of keeping your Blog “Open”. You are right to dissuade scaremongers and to encourage genuine scientific reasoning .
    As I have said before this Blog is highly educational, more so than I think you realise.

    1. Well said, Diana! It also proves how important constructs are to our understanding (Piagét; constructivism) – we try to visualise and relate to what we already know in order to gain new insights. This is why it’s a good idea to tell young children that babies come with the stork, patently untrue and easy to unlearn once they have grasped the true concepts.

      1. I am still intrigued by the tremor patterns that were clearly visible post the grimsfjall eruption where there was a clear synergy at SIL stations 100s of km apart where there is clearly no volcanic or magma linkage, and wonder if this was simply a visible manifestation of energy transfer from either the trigger for the grimsfjall eruption or the eruption itself; I am particularly intrigued that the pattern at Askja held for so long, but appears to be dissapating now – and wonder if these two phenomena could, in some way, be linked or perhaps be a visual manifestation of said energy transfer? Food for thought anyway, as I am no physicist or mathmatician!

  9. GAH!!!!

    This is a preliminary version. It goes from about 35 km SW of the Reykjanes to the junction/turn at Hengill.

    I haven’t done coordinate rotation since 1979. My brain hurts.


    I’ll clean it up… eventually.

    NOTE, the x axis is just an indication of how far along the track you are from the start until the end…. expressed in 0.001° increments. (not longitude, not latitude)

    1. Even at this stage it’s easy to see (?) that Hengil is not an end point but the feature continues west. Will be very interesting to see the cleaned up version and read Carl’s interpretation.

      Thank you Lurking, Lord of the Graphs!

    2. Lurking….What a misnomer! Probably the most productive graphics contributer to all Blogs about volcanism!
      I sympathise. My head hurts from information overload at the moment!I am trying to understand……
      In my quest for understanding, somehow I got into quantum physics and the non linear Schrödinger equation. I know! this is for liquids and optics…. but why not for viscous materials or moving solids?
      Could a volcano collect energy from the surrounding rocks?
      This equation proves impossibles are possible.

      I need coffee!!!!

    3. Okay… a few problems with that graph that I will eventually correct.

      1) At the ends of the trace some of the quakes fall out of the batch due to the end points not being in alignment with my selection box when rotated. This skews the curve downward on the ends. I can fix that by setting and tracking two reference points, over extending my selection area and paring it down afterwards (using the two tracked reference points) This should yield end limits that are at 90° to the trace and be more accurate.

      2) Decreasing the size of the bins to 0.0005° will probably help with the sparseness of the plotable points. Since I’m using a log scale and I throw out bins that are calculated as negative this should help a bit. (the bins are effectively the difference in a running sum window. This means that some will have bogus negative values, that’s why I throw them out)

      And last but not least, the further you get from Iceland the poorer the data becomes. Small events just don’t show up. I can’t fix that. Well, I could try to compensate, but that would introduce another ambiguity. Best to leave it as raw data.

  10. So what you guys are saying, is that it is no known connections between the volcanoes in iceland? But like, if you think like this; two different volcanoes with each their own caledra lies beside each other. And one of them two erupt, wouldn’t that make the pressure in the ground go away? Like it would make more space, and the the other volcano’s caledra would expand, or just that the volcano would sink back and relax? Just speculating..

    1. Depends on how you define “connection.”

      They are connected in the sense that they share a common mechanism that caused them to form? Yes. They are all the product of the interaction of the Mid Atlantic Ridge and the Icelandic Hotspot. Some will be more affected by one than the other.

      Are they connected as in a direct magmatic conduit from one to the other? Probably not, except in some circumstances. A lot of conjecture has been made about a possible Eyj-Katla connection.

      Can one influence another due to the release of strain/stress on the surrounding area? Possibly. But it would take a lot more statistical evidence than we have available to prove that. It would also require the services of a good stats person who understands the nuances of stress / strain and geology. (no, I don’t count, I am an amateur and what I do know for certain, is that there is a lot that I don’t know.)

      Effectively, what Carl has been ruminating upon is not if there is a direct connection, but why the features appear where they do. This falls back into my first paragraph. What he has noticed is that the orientation and spacing of areas of activity seem to follow patterns that are usually seen in wave mechanics. (harmonics, wavelengths etc). For these patterns to appear in something as far from that field as geology, is pretty bizarre.

      The central questions are “Is it real?” and if so, “What causes it?” And, if proven false, then “Why does it look like that?”

  11. 22.08.2011 12:39:25 64.006 -16.750 3.7 km 0.9 34.96 3.5 km WSW of Hvannadalshnjúkur

    Öræfajökull is really shaking these days, I know Fagurholsmyri is the nearest SIL, but what is the nearest GPS, is that Høfn? Is there any GPS close enough to detect inflation?

    1. Höfn is way too far to be able to pick up any possible ground movements at Öræfajökull.

  12. Not sure Christina. There is light wind below the mountain at Heklubyggð but that’s not to say there are local gusts due to height of mountains.
    Heklubyggð is where Jon’s webicorder equipment is situated.
    To find out local wind information.
    Go up to top of this page, click on “My web pages”
    Click on webicorders from drop down menu.
    Click on “Here” on first page
    Click on English
    Next page croll down and you will see “information about wind noise” Click
    This brings you to a page that shows roughly the strength of the wind in southern Iceland. Of course it can be stronger nearer the coast or up a mountain. It just gives a general idea. It also will show on the Webicorder.

  13. Could the recent earthquakes in Öræfajökull mean that it is waking up? It’s something to think about since it’s last eruption was in 1728.

  14. These quakes there do seem interesting. Whats the estimated depth of Öræfajökull’s magma chamber?

  15. Well done Jon! I know it’s many a year since I studied igneous petrology – borehole log interpretation took over – but surely a comparison of lava species would be a clue as to the connection or otherwise of the various volcanic systems. I can’t think of a mechanism for petrographically different magmas in the same local system – rhyolites/andesites/basalts other than separate centres or fractionation in a chamber and I can’t think of a fractionated magma chamber.
    OT, I must admire you guys, when do you sleep!!! Or is it the coffee?
    @ Henrik
    Is Herdubreid deeply eroded, ‘cos it looks ‘odd’.

    1. There are a few papers about this. I recommend Gunnarsson et al. (1998) (Generation of Icelandic rhyolites: silicic lavas from the Torfajokull central volcano) and Jonasson (2007) (Silicic volcanism in Iceland: Composition and distribution within the active volcanic zones) as a starting point.

      For my mind Jonasson’s near-solidus differentiation theory is the most convincing but your opinion may vary!

  16. I recall a couple of years ago many people in the public and many media types were talking about earthquake activity being greater and more frequent in recent years, but the volcanologists and scientists were very quick to dismiss that and say it was not true.

    However, I think the volcanologists were wrong, and will, as time goes bye, continue to be proved wrong about that.

    Here’s a look at the total strength of all mag 6+ earthquakes per year over the past 38 years …


    … “and it looks like up to me”, as Jim Morrison might say ( http://www.youtube.com/watch?v=DwMc0TjW_6Y ).

    I did that for mag 6+ so as to rule out possible anomolies from more quakes being counted in recent years due to better world coverage and more sensitive detectors.

    But what about just a couple of big quakes skewing the results? Well, here’s a plot of numbers of 5+ quakes per year over the past 39 years …


    And here is the same data smoothed out by averaging over time …


    Yah, Jim, whether by strength or number, it looks like up to meeeeeeee.

  17. What of the proposed link between Eyjafjallajokull and Katla? Magmas are from different sources but there is some evidence for a physical link (perhaps pressure-based).

    Also the graph of ‘cycles’ is almost meaningless. There is nowhere near enough data over too short a time period (not to mention with ropey coverage in past decades) to draw any kind of meaningful conclusion there. Activity cycles are a theory with some supporting evidence but the theory has not been categorically proven as true.

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