Magmatic or Tectonic Earthquake?

Picture taken over the Blue Lagoon towards the Svartsengi Powerplant. On the other side is the Svartsengi volcano.

Picture taken over the Blue Lagoon towards the Svartsengi Powerplant. On the other side is the Svartsengi volcano.

I get this question often about Iceland, especially when there is an earthquake swarm. The problem is that it is rarely clear cut if it is magmatic or tectonic when it happens in Iceland. First of all you have all of the rift zones being tectonic, but they are also subject to rift and hotspot volcanism, so if they are at the right depth, or adjacent to a magma reservoir, there can quite often be a magmatic component to them.

First of all, there are few completely magmatic earthquakes except when you have a run up for an eruption in one of the central volcanoes. And even then there is quite often tectonic components to them since the moving magma releases pent up tectonic tension. One of the few magma only earthquakes I know of is the odd double-couple earthquake that struck Bárdarbunga and that seemed to have triggered the Gjálp eruption close to Grimsvötn.

Reykjanestá, the spot where tectonic forces pull Iceland apart.

Reykjanestá, the spot where tectonic forces pull Iceland apart.

A couple of weeks ago we had a persistant earthquake swarm up in northern Iceland at Eyjafjarðar at Gjögurtá. That earthquake swarm was interesting since it started as a tectonic swarm, but quickly changed into having more and more magmatic components. As the swarm went on it caused lowered pressure at the MOHO boundary and decompression melt occurred and magma started to move upwards. In the end a classic wedge shaped magmatic intrusion formed. Here the swarm went from purely tectonic to almost purely magmatic.

Image by Icelandic Met Office. Earthquake swarm, Green stars are larger than M3, one of them is the M4.8 earthquake.

Image by Icelandic Met Office. Earthquake swarm, Green stars are larger than M3, one of them is the M4.8 earthquake.

A few days ago we had medium sized earthquake swarm that topped off with a M4.8 earthquake. One of my pet peeves is that it is hard to interpret what is going on before you can compare different sets of data.

Before it started we had anomalous tremor readings at the two closest SIL-stations. The tremor was in 2 – 4 Hz range. After about two days of low level tremor the earthquake swarm started. This lead me to suspect that the swarm was caused by a magmatic intrusion that in turned caused a tectonic stress release. But, without better data it was impossible to prove anything. IMO declared that the largest earthquakes was of tectonic nature after they had looked closer at the earthquake signatures.

You need GPS data collected over several days or preferably weeks to be able to analyze what has happened, and it is not until now we have that data. So let us analyze what happened from the combined data of the tremor, the earthquakes and the GPS-data. It is quite interesting.

Image from University of Iceland - Institute of Earth Sciences, Sigrún Hreinsdóttir. Red line, onset of up component, green line, M4.8 earthquake. Click on image to view full size.

Image from University of Iceland – Institute of Earth Sciences, Sigrún Hreinsdóttir. Red line, onset of up component, green line, M4.8 earthquake. Click on image to view full size. Lines added by author.

From the GPS data from Syrfell (almost straight ontop of the action) we get a pattern that is fairly different from what one could expect from a purely tectonic event. The green line is when the M4.8 earthquake happened. The earthquake within an instant pushed the GPS 1 full centimeter westwards and a couple of millimeters to the north. This is what we would expect from a pure tectonic event, a sudden jolt. Problem is that it is not all that we are seeing.

Roughly two weeks (red line) before the M4.8 we start to see uplift at Syrfell and just a few days before a local bradyseism starts and the GPS accelerates to the north. So, we have up component with associated north motion. This is happening at the same time as we have the anomalous 2 – 4 Hz tremor. This means that we have magma moving into the system causing inflation prior to the earthquake swarm, this in turn shifted the faultline enough to cause a release of pent up tectonic energy.

The svartsengi lava field.

The svartsengi lava field.

What is really interesting is what is happening after the earthquake swarm ended. Most often the trajectories will return to the same type of pattern observed before the tectonic earthquake. But that does not seem to be the case here. Instead we get a slight down-component while the north and west movement continues unabated. What now is going on?

My interpretation is that a magmatic intrusion occurred into a known and active volcanic field (Svartsengi) with a known magmatic reservoir and an associated hydrothermal field (with a power-plant). The system seems to be open into depth so no earthquake activity associated with the magma motion occurred, or was drowned out by the tectonic activity. As the tectonic swarm happened it opened up a void which was filled with magma, this relieved the pressure built up in the magma reservoir and deflation occurred, but this did not decrease the pressure in the NW direction since the rifting and magma reservoir is south-east of the Syrfell GPS.

So, we have magmatic intrusion that releases a tectonic event that in turn enables the magma to move further on. Since the motion in the NW direction continues my guess is that we will soon see inflation resume.

The ground rule for Iceland is that it very rarely is purely tectonic or purely magmatic earthquakes that happen, it is a combination of both and the question is more how the magmatic and tectonic components interact.

CARL

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133 thoughts on “Magmatic or Tectonic Earthquake?

    • It does not really work like that, it is if there is very rapid (straight down) motion that is a worry, and it will be a very large motion.
      As the saying goes, when Hekla goes you will not be asking, you will be running… Expect motions so violent that you think the equipment has gone bonkers. And, it will show on every equipment possible.

  1. Agreed – solid article on a topic that I would guess many people don’t know a ton about (myself included)!

    I know it’s impossible to predict eruptions, but is there a decent chance that there could be an eruption here, or does that seem rather unlikely?

    • Are there any VC articles on how to interpret seismic signals? I know seismicity can get a bit complex, but I know I personally have never really learned how to properly read & interpret what is going on when I see an earthquake, especially with Iceland’s quake graphs and such.

      For instance, how would one spot a “wet” quake when looking at seismic data? How does one differentiate tectonic quakes from volcanic tremor when looking at a webicorder / seismogram? How do you read and interpret beach balls? I think it would be really useful if there were an article that could show a picture of what said signal looks like, then give an explanation of it, and how to spot it when searching.

      If there already is an article like this, I apologize, but if not, this would be something that would help the amateur volcanologist quite a bit when looking at stuff that’s little bit more on the technical side of things.

    • DING!

      I had hidden that option well had I not?
      Yes, there is quite the possibility here that it might be the start of a run up for an eruption. We know that the area is highly volcanic, and we also know that there is tremendous tectonic build up, and to top it off, it is also rated as a 3 (from 1 to 3, where 3 is highest risk) on the risk for rifting volcanism scale.
      If the magma keeps on coming and we see resuming of the uplift we might very well see an eruption there.

      Actually, predicting volcanic eruptions is not entirely impossible, just very very hard. But it is done almost all the time, quite often successfully too. But this is an article that one of the pros should write like Boris, Kjartan or Páll should write. I am just a happy amateur with a pretty good track record so far. (3 predictions, two blew… Bloody Hekla of letting me down).

      • Oh, predicting volcanic eruptions is dead easy, anyone can do it. F’rinstance there’s a 100% chance that Hekla will erupt again, the hard part is to say exactly when. Because we have modern science, super-modern equipment and highly trained specialists, the “man in the street” expects volcanologists to predict an eruption to within an hour weeks, if not years in advance as well as the size and “fall-out pattern”.

        People are funny that way…

        • No, people are flat out stupid.

          Nearby, UPS is having the concrete slab in front of it’s door replaced since the large number of trucks that drive across it have caused it to crack.

          The new slab is about 4″ thick… and has no rebar or other reinforcing structure. How much you want to bet that it also manages to crack and deteriorate?

      • So what would the implications be if this were to erupt? Krafla style eruption? It’s pretty close to populated areas, which I would believe would cause some challenges, right?

        • If it would erupt it would cause a bit of trouble, mainly due to cut off roads and a bit due to the power plant nearby. But, it would be more Krafla than anything else, unless it erupts out at sea, which is equally possible. There is even the remote possibility that the GPS drop was caused by a small eruption out at sea, though, that is almost impossible to have been missed.

        • Still, we need verification. We can ruminate all day long about what the sensor data seems to indicate, and the possible ramifications on it, but in the end, we still do not know.

          Face it, someone (probably from IMO) is gonna have to ski out there and take a look in order to get hard fast evidence of it.

        • Most likely Reykjanes-Svartsengi region would erupt Krafla-style. But, and this is important, sometimes, that region has large ashy eruptions, in the range VEI4 (similar to Eyjafjallajokull), like in the year 1226, That historical event was well known at the time.

          I am not sure if it is due to interaction with water, since plenty of ocasions, Reykjanes has erupted in submarine locations with weak VEI0-2 eruptions. But in that year, it did erupted a stronger and ashy VEI4 eruption. Just like Surtsey.

          I would say that this has to do, with how much void the precursor tectonic-rift event opens a space. Often, swarms in Reykjanes create voids which are filled with magma (like last week) but then magma rarely erupts. When it does, it is usually small size eruptions. But in rare ocasions, magma can erupt in big fashion.

  2. Did I just write a comment or did I not just write a comment? Oh cripes…. nomen est omen. I could have sworn I wrote a comment just now. Anyway, great reasoning Carl! Sounds good to me.

    • Definitely an interesting phenomena. It wouldn’t be the first time an animal is aware of stuff that humans aren’t. It’s interesting to see articles about this from 2010 before the fukushima quake hit.

      http://www.telegraph.co.uk/news/worldnews/asia/japan/7365076/Oarfish-omen-spells-earthquake-disaster-for-Japan.html

      With that said, I could see this if it were a few months out, but predicting something like this an entire year in advance is another story.

    • ““We think that they come inshore to die actually because they’re in distress for some reason, but we don’t know what the reason is,” said Feeney, adding that the fish could have been starving or disoriented.” What precursors to big earthquakes could possibly make deep sea fish so sick? And evolutionary speaking it is quite disadvanterous to swim close to shore before a megathrust eq so this behaviour should have been erased long time ago. I could imagine dead fish surfacing before or during underwater volcanic eruptions though.

      • I totally agree.
        Yes, I can buy that there are piezo electric phenomenii popping up a year before a megathrust, but something that would whack the fish? No, I would look for something else that happened, changed currents would be my favourite.
        Loved how you wrote the comment Cryphia!

        • Maybe an “aroma” that the fish conciders foul. Say some sort of gas or chemical squeezed out of the sediment.

          Or… Pizo events all chained together that keep sending annoying jolts of electricity through the water.

          DragonEdit: Addy fix

        • Those electric currents would need to be pretty substancial.
          To get any potential difference over the length of a fish you need a strong current in such a good conductor as salt water. Probably in theorder of a few amps for a couple of Volt. The crosssection of this conductor is also very large wich makes the current density low.

  3. How would it be if a new volcanic vent would open up in the crawlspace under your house or in a concrete floor slab in a factory hall? At first you would have an indoor volcano with lava and scoria filling the house or factory. The volcano will eventually break through the roof and the walls.

    I think that a risk of a new indoor volcano erupting in a house or factory is rather big in Iceland.

    • I am thinking about Paricutin which was born in 1943, or Eldfell on Heimaey in 1973. Both volcanoes developed on a pasture. But what would happen if such a volcano would erupt in a large factory hall. The concrete floor in the factory would crack. Steam and hot gases would escape from the crack. Employees would flee for their lives. A few minutes later lava and scoria would be spewed out of the crack in the concrete floor in the factory. Lava would flow through the factory and break through the walls and doors. Ejected scoria would break through the roof and the volcano would be filling the factory. A few weeks later the industrial estate would be completely covered by the new volcano with remains of industrial buildings protruding from the scoria and lava.

    • Mast, if a normal Icelandic eruption started under a house you would not have people running. You would have people emediately dead.
      Even an effusive eruption like Eldfell or Krafla is so explosive in the start that the house would be vaporized in under one second. Remember, even a very large building is miniscule compared to a kilometer long rip in the ground where 300 to 1800 meter high fire fountains gush forth. Instaboil™

      • That is true Carl, but what about a monogenetic eruption starting far more modestly like Paricuitin is reported to have? Just a pit, then gas whistling, then emission of a few glowing stones. I think it is feasible for that to break through a human structure without immediate mass destruction.

        • A monogenetic eruption (like Paricutin) starting modestly with a pit in the floor of a building is a real threat in volcanic fields with monogenetic cinder cones. For example Auckland Volcanic Field, Vulkaneifel in South-West Germany, etc.

        • I would say that you would be gassed to death. It is one thing with a gassy vent out on a field, and something completely different in an enclosed space.
          So, first gassed, then stones would blast you and the house to pieces, and then a fire flood and a bit of pyroclastic activity to completely end whatever was left.
          Let me state it like this, even if it was the worlds smallest volcano that erupted in your house you would die just from heat radiation. That would be Thor Zawar, it only erupted 7.2 cubic meters of lava. But it would still have whacked you if you where indoors.

          • The factories at Reykjanes Volcano are of many sorts, there is one or more fish-head drying factory (some staff obviously), possibly salt-facotry(?) and there are Steam-Electric-Generating plant(s), but these have very few staff “on duty”, largely controlled by far away-grid system. I have been to this area as tourist, two times or three.
            Carl, u got “lash-ing-mail”, cos of not let me be in the loop …
            But thanks for brilliant mail. 😉

          • I was listening to a representative from the Montserrat Volcano Observatory yesterday. He was asked if people climb the Soufriere Hills volcano. He said that not even scientists climb up there. The only way to get readings is from a helicopter because the fumaroles, besides being toxic, are 600 degrees C and the land around the crater is 200 degrees C. Not a nice place to visit.

            • Also, they are in the process of drilling into hydrothermal vents for their energy. Guess where the company doing this is from?

            • I listened to that on Nautililus, very interesting…
              The test boreholes are looking good and they may not have to rely on diesel generators for too much longer.
              I wonder which country would have the expertise for such an operation? 😀

            • Hi Bobbi

              plus the fact that the dome can collapse again at any given time. And it is the rainy season so Lahars are a possibility.
              As for Geothermal energy, the nearby island of Guadeloupe has a 30 mW plant just the other side of the Montserrat fault in Bouillante. Been running since the 80’s I think. Dominica also is making some research but the project seem to be at a stand still. Considering the size of their population (around 6 k I think now) thay could seel some electricity to the nearby islands.

    • I live in the South Iceland Seismic Zone, which is between Hengill, Hekla and Geysir, you get the point.

      Here, eruptions do happen, once every few thousand years, in monogenic cones, from the called Grimsnes volcanic system, the smallest in Iceland.

      So, yes, there is even a change that a volcano could erupt in my bedroom and went through the roof! How cool would that be?!

  4. Thank you Carl. I know you may get a complaint that in VC we tend to talk “Iceland” but before anyone has chance to complain that we are biased towards “the Land of Fire and ice” I wish to add my thoughts.
    This Post of Carl’s demonstrates and answers several recurring comments.
    1. Because of the excellent availability data to the public we are able to see and discuss events in real time. A big thank you to IMO.
    2. This data is only available because of the intensive monitoring and recording systems which networks the whole of Iceland. Thanks to the Icelandic scientific and government bodies decisions to allow scientists from a wide range of countries and scientific fields to help in research. This openness and sharing is not always forthcoming so limiting what we amateurs here on line can actually see as fact.
    3. Iceland’s position on the MAR , a hotspot, a remnant of an ancient plate and the Eurasian Plate provides us with an assortment of types of Volcanic and seismic events . It also makes explanation of events more difficult as we (both professional and amateurs) are still learning.
    4. Taking factors 1, 2, and 3 together Iceland is a good place to start learning about even the most basic facts of Volcanicity as well as highly complex volcanic systems. Once that knowledge is gained and a good understanding of the mechanics of how magma and tectonics work, this knowledge can be applied to volcanic activity in other parts of the world where data is less accessible for the layman .
    5. The question of how magmatics and tectonics interplay is still on going and Iceland is really the only place I have found where, as a mere amateur, I can observe, record, and evaluate events, and VC is one of the few places on line that I feel I can ask questions and discuss these events without fearing a backlash towards my ignorance.
    Quite the opposite. VC is, for me , despite the intrusions of magmatically OT subjects, a real place of learning.
    ( No! Carl has not bribed me with free drinks to write this 😀 and honestly , I have learned some amazing things during OT discussions too 😯 )

    • Foul!

      Where do I get the free drinks?

      I’d like to note that “arjanemm” responded to the electric fish subtopic with some insightful points of fact. (and very important items that directly affect what a fish would or could feel, things that have to be seriously considered in order for that cause and effect relationship to be valid.)

      This is the sort of thing that VC gives us. Knowledgeable people from disparate fields sharing info and opinion.

      And for you Diana… something interesting from biology. Oncogenes are present in many organisms. They have been implicated in the occurrence of cancer. In essence, they are deactivated segments of “old code” that don’t take part in the normal operation of a cell. While poking around in that subject, I ran across a whole slew of inter-operable pieces that control whether segments of dna are turned on or off. I was astounded at the complexity of it.

      Sayer Ji, Founder has written an article that puts forth the idea that Cancer is not actually some random mutation that causes a cell to go nuts and start reproducing… but that entire packages of traits are turned on that revert a cell to a previously mode of operation… traits that have been shut down for millions of years.

      Has Cancer Been Completely Misunderstood?

        • Snakes… for some unfathomable reason cancer is not an issue for a snake. Nor is the self replication degradation issue. The flowerpot snake became parthogenetic (self reproducing where the female fertilizes her own egg with her own genetic code) many millions of years ago, and seems to have suffered no ill effect of its cloning. This makes it into an insanely robust snake that in short time have travelled the globe and spreading like wildfire since it only need one snake to start a large colony.
          Most likely the snakes are so old that the genetic code have stabilized, both the active and deactivated parts of the DNA. To me a snake is one of the most function perfect natural designs.
          http://en.wikipedia.org/wiki/Ramphotyphlops_braminus

          • I’ve heard tell that the Seven Banded Armadillo has offspring where the entire litter are essentially clones of each other.

            That’s anecdotal, so I have no proof. I do know that a freind of mine from years ago used to love shooting them. He carried a grudge from when he shot at one with a bow and managed to mess up an arrow. (The arrow went skipping down the road. Fast way to ruin a broad point, so don’t shoot at stuff meandering across the road with an arrow that you don’t want to mess up.)

            I think of Armadillos as armored Possoms. They are probably just as ill tempered when cornered.

            • Actually I have found Armadillos to be pretty friendly buggers. I had one visiting every breakfast I made for a few weeks when I was working outside of Austin.

            • I have a friend who lives near Austin. His only complaint prior to moving to where he is now was when the scorpions would fall through from the attic onto the ceiling fan and get slung around the room all pissed off when they landed.

              BTW, this is the same person that charbroiled the hamster in a failed cremation attempt.

        • Quite an interesting website there – thanks Lurking – for researching evidence which seems likely to support the macrobiotic system developed by Michio Kushi after the bombings of Nagasaki and Hiroshima. Brown rice and seaweed – yay

      • Thanks GeoLurking. I could see some bottom dwelling fish feeling something but definately not in the middle of the ocean. (the source of the current comes from the seafloor)
        This is exactly why i like this place so much, everyone is contributing. Some are just clever, some just know alot. Some actually studied geology, some are a pro, some plot, some ruminated and some just vent some morning observations with a cup of coffee. And all this happens basicly without exception, very nice and friendly! 🙂
        That’s why i read this place everyday. It’s nice and you learn.
        I should contribute a bit more, cause i feel like i know all of you but i’m not much of a writer and geology is not something i know very much about. It’s a subject i like to learn and read about.
        But when i’m confident about something you will hear it 🙂

        Great work everyone! And a special thanks to the dragons and the writers of these great articles!

        DragonEdit: Changes according to commenters wishes.

        • “But when i’m confident about something you will hear it”

          It’s always good to be confident in ohms law. One instructor I used to teach with loved using it to freak out the students (by using the related power law) After getting them up to speed on the relationships, he would then propose a hypothetical problem with a 9 VDC battery driving a resistive load that slowly dropped to near zero ohms. With a constant voltage, the students would eventually be coming up with power levels that approached that of nuclear bombs as they worked through each part of the problem. In reality, the 9 VDC battery would give up the ghost if this were done live. Heating would destroy the battery or the electrolyte would evaporate rapidly. But it was handy in getting the students involved/interested in the math.

          P = I2 x R
          I = E / R

          • Good story. Add the batteries internal resistance to the equation and the numbers get a lot more realistic 🙂

          • Got to walk before you run. At the level of these students, internal resistance would have been a mind “f”. Sometime after covering voltage dividers, when they have gotten a bit more confident in the formulas, internal resistance would be an approachable topic. This was the sort of thing that kept getting me in trouble when I was initially going through the course 30 years ago. I kept asking about stuff that was a bit beyond what the course wanted to teach. The instructor would stare back in befuddlement and the rest of the class would groan. This mainly happened in the transistor part of the course when I was questioning the “tunneling” aspect of a junction. Later, when I was teaching and managing the course, had one instructor who got in trouble for drawing a circle on the VAP board and putting the phrase “I believe” in it. When a particularly vexing topic came up, he would push the “I believe” button, signifying to the class that they had to take what was said on faith (for the time being) so that they class could continue with the requisite material. From a professional point of view, it’s a bad way of dealing with it, but I had known this guy for 20 years and knew what he was getting at by doing it that way. If the question was too deep for what the class was being taught, defer it until you can give the student the low down on the phenomena without throwing the whole class off track and confusing them.

            In part, it was not his fault… they had thrown him into teaching a course on a piece of equipment that he had never seen before in his life. Kevin was a pure analog guy. The system was digital with a LOT of “general purpose processors” arranged in some really novel configurations. Since it was an operations course, the aspect of what you did with the resultant data was what was being taught rather than how it operated.

    • Dear Diana, you are being unfair here. Nobody has ever complained about mainly Iceland being discussed (as far as I know). It was at a time when Carl had asked for our opinion and suggestions to make VC still more interesting that 2 or 3 (two or three) of us made so bold as to confess preferring less Icelandic and more worldwide articles. That was the one and only time if I remember right. Since then you and one other are harping on and on about us complaining. That is simply NOT true.

      True is that I have taken to skipping all endeless Icelandic comments that go on and on about what could happen if and when and why not if not. That does NOT mean I complain.

      And, true is that I read and loved Carl’s article, as well as some further explanatory comments, glad to get a handle on discerning between magmatic and tectonic events. Thank you, Carl, dfm an GL!

      As Gb below sais: Nothing wrong with discussing Iceland. I agree and may add: Nothing wrong with discussing different volcanoes of the world also; and even: Nothing wrong with people having differing interests and opinions.

      • Actually, I got a bit of “done that, bene there” comments about Iceland a few months ago, and that is what Diana is talking about. But, Iceland is handy when discussing things as Diana said. Why now? Because everyone has “done that, been there” it gives us a wonderful common ground to discuss things from.
        And I have found that knowing Iceland (a bit) gave me a freebee on El Hierro, and whenever something in the Azores erupt we will know almost exactly what is happening since for most points and purposes the Azores is Iceland shaped differently.
        I even find that it helps me to understand the African Superplume and what is happening around the Tanzanian Craton in a much grander scale. Understanding Iceland gives you two thirds of all volcanism for free, namely hotspot volcanism and rift volcanism. Without Iceland I would never have been able to write an article debunking Yellowstone as the “worlds most dangerous volcano” in the way I was able.
        It even helps a bit with understanding subduction volcanism, but not nearly as much as I would wish for.

        In the end it is though where it all started for me. With the Krafla Fires (as a child on TV), Hekla 2000, Gjálp, visiting Hengill, Svartsengi and Krafla power-plants, Eyjafjallajökull and Grimsvötn 2011. For me Iceland defines what volcanism is. Whenever I see a lava tube I think about my day walking around in the labyrinthian complex that Laki created (not recommended really, dangerous as hell). Whenever I see a lava field I think about the Icelandic ones… And when I need to put an eruption in perspective, it is from having seen the large volcanoes of Iceland. Boris may forgive me, but walking down the entire length of the Laki fissures is, and will always be my yardstick for an eruption and at the same time the most beautiful thing I have ever seen.
        Yes, walking on Anak Krakatau or climbing Etna is very nice and Yellowstone is majestic. And Ischia, Campi Flegreii and Vesuvius are wonderful, but they for some reason do not speak to me in the same way. I have never heard them sing in the night for me in the same way as some of the Icelandic ones have done.

          • I did not have the time to walk there, but I have over-looked the Éldgja fissure, it is impressive. Also the Veidivötn fissure landscape is impressive. But, Odhadhahraun… That one is stumping.

          • “Cannot imagine what the eruption must have looked like.”

            Imagination… thats the ticket!

            Image by GeoLurking, done to support the “Dead Zone” post. The black buildings are some well known skyscrapers as compared to a commonly discussed fissure eruption. The fountain heights are as reported in some of the historical literature.

          • OT {snicker}

            Found in the Urban Dictionary for “Paratrooper”

            “Anyhow, a paratrooper is someone who jumps out of airplanes (with a parachute) for the purpose of performing a military action on the ground.”

            I’m guessing that parachute bit is sort of important.

            • Yepp, we tend to think that the parachute part is quite important… So paras tend to have jump patches, and a pin with a dagger over a parachute.

    • I must go to a lecture now. And will read the rest of comments and join the talk, tonight.

      But Carl, I want to say, this post is excellently written and it makes very clear about the whole aspect of earthquakes in Iceland. They are nearly always tectonic and magmatic, at same time.

      The most often are;: tectonic episodes that do create voids that magma rushes to fill in. Occasionally, the process can be more intensive, hence larger swarms, larger quakes, and some tremor associated.

      This month we got two already: Tjornes and Reykjanes. Excellent to know that Reykjanes swarm also had magma involved. I always expect that system to erupt one of these days, as it is the one that erupts most often in the region, more often than Krisuvik or Hengill.

  5. Hi all. Photo texts with this article are not correct, of what the images are said of. I have sent him mail on this some hours ago (13:49 my time), but no replay. For example, third image shows “Gunnuhver” area, but that one is nowhere near Svartsengi, and Reykjanes Lighthouse (nearby), a major landmark, is in the background.
    Also the photo of Reykjanes-tá, shows an old volcanic cone, partly eroded by the sea. Good picture, but Reykjanes-tá is actually flat spit of land, only nearby to the south.
    Regards “Islander”

  6. Shiveluch

    From the appearance when the clouds finally lifted, it seems the large explosion on the 18th did blow out huge crater on the side of the lava dome.

    Shiveluch 131023 1930 GMT

    • Same crater, but on the photo from January it was largely infilled. Does not look that way now – If you look closely there’s a tiny, smoking dome at the bottom of the pit now and much of the infill is gone by the looks of it.

      I guess we will have to wait for some really clear weather in order to see exactly what has happened. 🙂

  7. Oh Hekla….

    So far no changes in strain (but Hekla was going in decreasing strain, as expected, but data stop transmitting today). Also no changes in GPS but I am not sure we could get something from it.

    Ideally one hiking at Hekla should be able to detect sulphur smells a few hours before an eruption, but sadly we have no sensor for it, something that should really have. And Co2 too.

    • They do have a set of gas sensors on the top of Hekla, it is called the Hekla Café.
      Nothing except the earthquake, no strain, no tremor.
      Just Hekla being a terrible tease again…

      • curious, I think Hekla is internet connected, Carl fall-a-sleep then BANG, I fail checking for two hours in-a-row tonight, then BANG ( I really wonder what she is up to )

  8. Looking at clear shots from 15th and 22nd October I must admit I can’t see any real difference. Maybe a tiny bit of fall from the very steep slope that faces the camera on the left-hand side of the dome, and maybe a tiny bit of growth on the right-hand side of the dome.

    Although relatively clear, the photos are taken at either end of the day, so the shadow patterns are different, and can be quite deceptive.

    @mdatc – I assume you mean either 1964 or 1854! (actually, it is thought that the crater is probably from the collapse event of around 1430 AD)

    • If you have both images… and if they are from the same camera/vantage point, you can run them through an image program and subtract one image from the other to see the differences. PaintShop Pro has a “difference” function that allows you to do this pretty easily. Don’t use the Corel versions of PaintShop Pro, they gunked up the program with useless crap (signature move by Corel). Adobe’s product may have a similar function. (I use PSP 8.0, one of the last versions that is not hopelessly screwed up. I think 10 and higher are the horked up versions)

      In the past I’ve done this trying to discern changes in Hekla, Other than some snow that had gotten up and walked to the other side of the mountain, I didn’t see anything interesting.

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