What if Katla erupted?

Myrdalsjökull glacier and the Katla Volcano. Photograph by Chris 73.

First of all, I should clearly state that there are no current signs that an eruption at Katla is about to happen in the near future.

Instead, the reason is that I was asked by one of our readers, Patricio Oliver, what would happen if the volcano erupted, especially for the inhabited areas.

This is a very good question; we rarely write about eruptions from the perspective of what the effects would be on the local population. First, we need context.


The Icelandic LIP

Conjecture – All Icelandic volcanism is a function of strain caused by the spreading of the MAR and magma intruding from the Mantleplume and the Mantle.


Katla 1918 eruption.

Iceland is a true geologic marvel, but few people realise that for the last 14 million years it has been running the tectonic show for the entire Northern Hemisphere. We know this because that before the Icelandic Mantleplume was born 16 million years ago, directly under the MAR, Northern America was moving in the opposite direction.

As the mantleplume started Northern America switched trajectory in a geologic instant. One good thing is that the oceanic crust above the mantleplume was thin, otherwise we would have seen volcanoes that was epic in size and scale of eruption.

Instead, the crust was too thin for ‘super-eruptions’, and we got numerous slightly more manageable eruptions to deal with.

On average Iceland is spreading at a rate of 2.8 centimetres per year, but at the point central of the LIP it can move apart at express speed during larger events. The largest known spreading event occurred at Eldgjá as the local rate of spread was 150 metres in a year. Don’t worry, it somehow averages out into 2.8 centimetres again over time and distance through processes that we still do not fully understand.

Now, let us look at the chain of other large volcanoes along this portion of the Mid Atlantic Rift (MAR).


The Local MAR

Overview of the Mid Atlantic Rift in Iceland. I stole this image from Alamy that stole it from a paper that I could not find online. If anyone can find a better image with more details of the various parts, I would be much oblliged to switch it out.

The Mid Atlantic Rift is more complex as it goes through Iceland than what I am describing here, I am after all concentrating on Katla now.

Katla belongs to a chain of large central volcanoes that stretches all the way from the easy to pronounce Þeistareykjarbunga down to Eldfell on Heimaey. From north to south these large volcanoes are, and yes there are more small volcanoes there, Þeistareykjarbunga, Krafla, Askja, Bárðarbunga, Grimsvötn, Þórðarhyrna (it just flows off the tongue), Torfajökull, Hekla, Vatnafjöll, Eyjafjallajökull, Katla and Eldfell.

These are all fed by plume-derived magma at various grades, and are subject to the ripping apart of the MAR. There are though a couple of features more local to Katla that is also interacting with it.


The Local Group

Katla is affected by no less than 3 different regions of the Icelandic Portion of the Mid Atlantic Rift. The first one of these is the East Volcanic Zone (EVZ) that roughly runs from Grimsvötn down to Katla.

South of Katla you have the Vestmannaeyjar Volcanic Belt (VVB), this is where the Mid Atlantic Rift is desperately trying to find a new and shorter route through Iceland. Over time this one will take over as the new MAR-route. Over time the VVB will connect the islands into a peninsula that makes landfall south of Katla.

To the west you have the South Icelandic Fracture Zone (SIFZ), this feature is mainly not volcanic, with the glaring and obvious exception named Hekla that is the Easternmost part of the SIFZ.

By now most people would feel that this was a complex enough setting for any volcano on the planet. Nope, this is where it starts to get really funky.


The Dead Zone

Eldgjá, the unzipped crack of Katla. Photograph by Andreas Tille.

In the movie Stalker by Andrej Tarkovsky, they enter a place called The Zone, a place where physical laws and causality are suspended. The Dead Zone is similar in many ways.

Obviously, the laws of physics and causality are not suspended in the Dead Zone, but we do not understand what is happening enough to yet understand what is going on in there fully.

The Dead Zone is an intensely aseismic area located roughly inside an area that is bordered by Katla, Vatnafjöll, Torfajökull, Þórðarhyrna, and back to Katla. The margins of the Dead Zone can at times be extremely seismically active, but inside the area very few earthquakes occur, and they are very small when they do happen.

It is believed that the region is made up of ductile hot crustal material that is more akin to rubber than rock, and that this causes the aseismicity.

We also know that the area is prone to suffer from the largest known effusive eruptions on Earth, and that it during those eruptions suffers from the fastest tectonic movements on Earth. What we do not know is how it happens, what is causing it, and why it is happening at this spot and at no place else.

It is the beating heart of the LIP, and I will come back to this feature in an upcoming article about Vatnafjöll.


The Katla Central Volcano

Katla is one of the Big 3 volcanoes in Iceland if you look at the combined ability of explosive and effusive eruptions. Yes, Grimsvötn have caused larger explosive eruptions, but the average explosive eruptions are smaller out of Grimsvötn, and yes Bárðarbunga has caused larger effusive eruptions. But Katla is on average as good as Bárðarbunga and Grimsvötn at producing the greatest shows on Earth.

It is the ability of causing on average large explosive eruptions that set Katla apart. Only one confirmed eruption at VEI-3 has happened in historical times. The average size is in the large VEI-4 range bordering to VEI-5, and a VEI-6 is never out of the question from this volcano.

It is also able to produce effusive eruptions in the near 20 cubic kilometre range out in the Dead Zone, this last happened in 934AD at Eldgjá.

The last confirmed eruption at Katla happened on the 12th of October 1918 and it was a borderline VEI-5. The current hiatus is unusually long, but not unheard of.

Like most other volcanoes a prolonged hiatus will often end up with a larger than average eruption, so when the eruption happens next time, it is likely to be in the VEI-5 range but that is far from a certainty.


The risks of Katla

A volcano like Katla comes with a diverse set of risks depending on the size of eruption and where it happens. I will here go through the risks in order of likelihood to cause problems.

Jökulhlaups – Katla is situated under the Myrdalsjökull Glacier. The glacier has completely filled in the caldera with Ice, and during an eruption the geothermal heat caused by the eruption will melt large amounts of the ice causing massive jökulhlaups.

The Jökulhlaup caused by the 1918 eruption was large enough to create 5 square kilometres of new land on the beaches near Katla due to the amount of tephra and ash deposited by the water.

The Jökulhlaup of 1755 had a peak discharge rate of 200 000 – 400 000 cubic metres per second. More than the combined output of the Amazon, Mississippi, Nile and Yangtze River combined. Not something you wish to be in the way of.

Ashfall – Even though this is not deadly in and of itself, it will in large amounts cause roofs to collapse and damage building and infrastructure. If the prevailing wind is southerly during an eruption the local villages will be impacted.

Southerly winds would also cause problems for airlines in the same way as happened during Eyjafjallajökull in 2010. Obviously, the problem would be even greater since the amount of airborne ash would be much larger.

Volcanic bombs – The world record of Lava Bomb killing is set by Hekla with a 12kg lava bomb being hurled 32 kilometres before decapitating a farmer, Katla is amply able to hurl lava bombs quite a distance. The safety zone here during a larger eruption would be around 30 kilometres.

Pyroclastic Base Surges – This would be counted as an uncommon risk and would only be a factor during a VEI-6 eruption. It is when an eruptive ash column collapses and hot ash and gasses fall down and come running down the sides of the volcano. If that would happen nothing within 50 kilometres would be safe.

Rifting Fissure Eruption – Having 10 to 20 cubic kilometres of lava gushing forth within a few months would be bad mojo indeed. Do not around be the safety tip here due to the ample amount of volcanic gases.

The good news is though that the volcano will give off ample warning signs prior to erupting, so evacuating the locals will not be a problem. And also, the locals are well aware of what they have to do and are well prepared to do so.


The Fallout of Katla X

The Village of Vík. Photograph by Efrainlarrea.

So, in a few years Katla will suffer from the hypothetical eruption X. It turns out to be exactly like expected, it was a medium sized VEI-5, it caused a large jökulhlaup peaking at 50 000 cubic kilometres, the beaches got extended with yet another 5km.

There was only one death that happened during the eruption, it was caused by a French volcanic tour guide who smuggled in tourists through the safety checkpoints. One of the tourists tried to steal drugs from a village pharmacy and succumbed to volcanic gases.

The Bridge across the Road 1 was washed away, and the road was closed for a week after the eruption before the Icelandic authorities had it replaced.

In Hólt and Vik several roofs caved in due to the weight of ash, but the houses was rebuilt in short order. Some houses at the outskirts of Vik were destroyed by the Jökulhlaup and was also rebuilt.

After two years all was back to normal in Iceland, and everyone was waiting for the next large eruption.

The eruption caused the SAS Airline to default due to volcanic ash and bad food. It was missed by nobody.



Why is Iceland so uniquely able to withstand large eruptions compared to other areas in the world?

The first thing to remember is that Iceland is sparsely populated, and there are not that many people living near the biggest volcanoes in Iceland.

It is also important to acknowledge that the Icelandic Met Office is among the best volcanic authorities in the world, they will be able to forecast an eruption and evacuate the locals with ample time to spare. Well, not perhaps in regards of Hekla, that one just has to be special…

Also, the knowledge and preparedness of the Icelandic people in regards of volcanic eruptions is second to none. They know what to do, they are ready to do it, and they will do it when needed.

If Katla erupted anywhere else on the planet it would be an unmitigated disaster, but in Iceland it will be a nuisance of temporary nature before the locals go back to eating the national dish, hamburgers.


754 thoughts on “What if Katla erupted?

  1. Katla has done VEI 6 in the Holocene?

    Anyway, I have been interested in Vatnafjoll since it started swarming the other week, I have made maps of the lava flow fronts exposed on the surface today, if they are anything of use to the future article that I feel I am not qualified to write. Not sure it is of the same extreme calibre as Thjorsahraun or Eldgja just based on surface area covered but definitely much more than most basalt fissure swarms that lack a caldera.


    • It’s possible. The geological record isn’t going to be perfect, and some ancient VEI 5 eruption, might have been VEI 6. Evidence of it can go surprisingly quickly away or be buried by new layers of frequently exploding volcanoes (even if the size is smaller) or lava and other geological processes. Few VEI 6 eruptions are known from early Holocene, even if we know that they certainly did happen, and perhaps even more after the end of the last ice age due to sea level changes, glacial melting and isostacy rebound.

      Katla certainly seems capable of doing so. It’s current repose period one of the longest ones that has been observed, however that’s no indication what will happen in the future.

      • Next Katla eruption will probaly be like the others large VEI 4 s alot like Grimsvötn 2011 in phenomena and style.

        Have Katlas caldera ever produced evolved tephras in the holocene? Or is magma supply and eruption frequency high enough to keep it mostly basaltic?

    • Two actually, the Vedde Ash eruption and during the opening of Eldgjá.

    • A comment from carl from the distant past “Vatnafjöll mysteriously went dormant after Heklas 1104. I hope that one never comes back to life.”

      • Not sure I agree, probably a lot safer to be around than the start of a Hekla eruption, though being downslope is not recomended.

  2. Thanks Carl, very nice article, Im too is working on my own text.

    Katla is indeed a migthy beast, and probaly haves a really huge supply, knowing how extremely large her CO2 emissions in sleep are.
    But most of that supply goes lost in passive rifting. Indeed this is probaly the Icelandic volcano with the largest eruptions on avarge, its about 5 to 10 times less active than Grimsvötn and answers that with bigger blasts. Grimsvötn erupts about 10 times per centruy, sometimes even much more, Katla about once a centruy.

    The next Katla eruption will likley look like Grimsvötn 2011 and perhaps with a terrible haulp that comes with it. Katlas magmas are more alkaline than Vatnajökull, so melting is smaller in the mantle under Katla and its deeper melting than in Vatnajökull: Eldgja is the largest semi alkaline lava flood since Ice Age ended, normaly floods are thoeltic. Katla is still Only mildly alkaline in its basalt composition.

    Grimsvötn lake have dropped 70 meters now and is finaly slowing, How many cubic meters of water was removed?

    • They are really nice, but they do not have the different sections of the MAR marked on them. And I wanted people to understand what is where. 🙂

    • Wonder why the movement of the eurasian is so strong to the north-east. Is the pcific slab-pull effect that much stronger in the Kurile/Japan area or is it mostly the African collision? Which way was it moving prior?

      • Mainly slab-pull. Africa has no effect on how Eurasia moves

  3. Looking at that map up above there is a feature called the Aegir ridge off the east coast that looks like it could have lined up with the mid-Iceland belt at some point, it’s perpendicular to the MAR. Wondered if anyone knew any more about it. I’d hazard a guess it’s extinct

    • Amusing watching the TV ads for the islands, nary a mention of the available ‘volcano tourism’. I think they’re hoping the lava-spewing will be ‘done & dusted’ by Easter 2022, ready for Summer & Autumn…

  4. Nice read. Sparsely populated is the key here esp. if you think about your own home. Education is the safety lock to it. I don’t think that all people living on Nyaragongo would have known what a devil he can be before 2021.
    And, if a region is very, very populated (like Naples) I automatically take the scenario in Henrik’s Number 1 for granted. Politicians are no magicians and know about the pitfalls of mass panic.
    Katla is interesting for hydrothemal energy and the pitfalls.

  5. Thank you Carl.
    You made an interesting statement. A bomb had flown 32 km from Hekla.
    Can we made a likely assumption about the ballistic angle?
    I would like to work out the peak height, and also the energy, ignoring air resistance and other nonlinear effects since I don’t know their math.
    I reckon in theory no law would forbid the angle be 10° or 80°, but in practice the least energy should be needed at 45°.

    So in this case the height would be such that it has just enough time to rise to a height x and fall down again (I simplify so the bomb starting point is at same height as the victim) while flying from Hekla to the victim.
    That gives
    32000 m/v0_x = 2 * v0_y/g, and it unfortunately has 2 variables. v0 denotes I am using the initial velocities.
    But if we take the 45° angle into account, as the simplest case, it must be that v_x and v_y are the same.
    32000 m/v0_y = 2 * v0_y/g
    Rearranging and filling gives
    v0 = sqrt(32000 m * 9.81 m^2/2) = 396 m/s which is slightly above Mach 1.17 (396 m/s).
    With law of energy conservation the height can be worked out:
    1/2 * m * v0_y^2 = m * g * h
    1/2 * v0_y^2 = g * h
    h = (396 m/s)^2/(2 * 9.81 m/s) = 7.99 km.
    So it flew to a considerable height, just 1 km short of the 300 hPa pressure level (about 9 km).

    The total energy would have been
    sqrt(v0_x^2 + v0_y^2)^2 * m/2 = sqrt(2 * v0_y^2)^2 * m/2
    = sqrt(2)^2 * sqrt(v0_y^2)^2 * m/2 = 2^1/2 * 2 * v0_y^(2 * 1/2 * 2) * m/2
    = 2 * v0_y^2 * m/2 = (396 m/s)^2 * 12 kg = 1.88 MJ.
    Quite some projectile!

    Taking into account the air resistance numbers would only look worse. 😮

    • Jebuz…
      I was just happy with the knowledge that it happened, I never bothered doing the math. 🙂

    • There will be significant air resistance so a very much faster initial velocity at a lower angle and likely it was dropping close to vertical when it struck ground. The energy/initial velocity would be very much more and the height probably about the same.
      Seriously impressive.

      • There we are again.
        Even faster than that M1.17, so clearly supersonic.
        What was supersonic too? Of course, a volcano’s shock waves condensing a Wilson cloud.
        Those effects all belong to the realm of detonations, here of non-chemical origin.

        Hefty, would have never expected such from a volcano, not before I got interested in volcanoes, in September 2021.

        • I have not checked your maths, I am afraid. Anything going supersonic will rapidly slow down due to air resistance. If you are right, there may be no sensible way to achieve 32km range, and the story should be put in doubt.
          Magic never happens, not even in iceland.
          Hmm, lets see what modern artillery can do.
          M109 howitzer self propelled cannon.
          Shell 43kg
          Range conventional 21km, rocket propelled 30km.
          Hmmm ……

          • PS Being ejected in a column of gas travelling supersonically for say 1000m could extend range…

          • Except that this is not a story, the guy was found decapitated in the field with a nice fresh lava bomb.
            And, there are numerous lava bombs out to this distance, and further, from Hekla. It was just that this dude was unlucky. I have seen them myself.
            Guess why the safety zone around Hekla is a whopping 50km…

          • If you wish to calculate energy needed, go with the bus sized ones that are found about 20km away from Hekla. Those ones gave me pause for thought.

            Hekla is truly not normal. It is the only volcano on the planet I am afraid of being near.

          • @Microwave:
            Welcome to the Ansari X-Prize in Volcanology…
            This is probably the greatest unsolved question in all of volcanology.

            We simply do not understand the processes that creates such a volatile magma that is so highly evolved and gas-rich so fast and in such large quantities.

            Hekla is really “special”… in all ways implied in the word. It is the psychotic cousin of volcanology.

          • Carl,
            Bus sized ones at 20km not a problem, even further in fact. Clearly air resistance will vary roughly to the second power but mass to the third power, so massive projectiles will go (much) further than small ones.
            There is another mechanism of course which is a massive body fragmenting at some height as well as being carried in a stream of bodies so air resistance locally is low because the air is going at the same speed. After all the La Palma eruption was routinely described as sounding like military jets (ie supersonic air meeting stationary air turbulence noise) and jets certainly seemed to go for ~2km at an angle.
            And la Palma is rather modest in comparison.
            There is need of a learned paper with maths and observations to back them up. Certainly if its to be used for sensible warning decisions.

          • Ah…
            The age old science vs saving lives thingy.

            You have a proven case of someone being whacked at 32 km by a lava bomb.
            Theoretical scientist goes into his chamber to prove that it either happened or not, and comes out with a paper 4 years later filled with math.

            Practical volcanologist goes out and looks if there are bombs even further afield, jots down the number of km of the furtherest one he can find, and then adds 10 percent to that number.
            Then he (it was a he), issues an instruction that the safety zone around Hekla is 50km during eruptions.

            Theoretical volcanologist argues with practical volcanologist for 50 years about it being impossible in the first place. Both of them get nice careers.

            Almannavarnaild Lögreglan becomes confused by all of the arguing and lowers the safety zone to 32km. After all, they are police, so they respect a decapitated body to be real evidence.

            Carl is a simple man, he will enjoy the theoretical debate about it, but will remain behind the 50km safety zone for once in his life. After all, real world data in this case trumps theoretical modelling. 🙂

      • Impressive is the word. I remember driving around in Iceland and all of a sudden the landscape was littered with black rocks with twisted odd shapes. I realized I had come close to Hekla and these were all lava bombs. I think this was some 20 km away from Hekla, close to the f26 road.

    • That 32KM range for a lava bomb astounded me!

      Thank you, Microwave, for digging into the math. The problem is that air resistance is a big factor, and you can’t just add a factor for it, due to it varying based on both altitude and speed during the flight profile (which is why artillery used to use mechanical computers in pre-electronic days). An example I’d like to make here is the naval 16 inch guns (from the WWII Iowa Class battleships) that fired a 16″ diameter shell from a 66ft long barrel. Those shells were both streamlined and very heavy (ranging from 1900 pounds to 2400 pounds) and had a muzzle velocity of 1900 miles per hour, or about mach 2.5 at sea level. Their max range was 22 miles, or about 35km, which is why I picked them for an example.

      A smaller projectile, especially when less aerodynamic, would require a higher muzzle velocity to attain the same range, because the surface area is higher in relation to density, so the drag factor is higher.

      Still, depending on the mass of that lava bomb, I think we can safely say that Katla ejected it at at least mach 2.5 as a minimum, and more likely (especially if the lava bomb was far lighter than the shells from a 16 inch gun) well in excess of mach 3. That simply astounds me.

      Carl, thank you for this article; I always thought that Katla was a scary one, though I had no idea that it was scary to this magnitude.

      • Ack, Carl listed the lava bomb as 12kg, I missed or forgot that! So, far smaller than I was thinking – and thus I probably understated (at mach 2.5) the launch velocity needed.

      • Thank you for your statement.
        Yes, air resistance won’t be negligible at all, I see from your thoughts, and from the fact that it is quadratic to the velocity.

        The volcano was Hekla though 🙂
        No Idea if Katla could manage the same.

        • Erk, indeed it was Hekla. I could have sworn Carl said Katla in the article, but I went and looked, and nope, it’s Hekla.

          Per Wikipedia and the 1510 Hekla eruption, it hit a village 40km away with lava bombs. Yipes! I’m starting to understand why Carl does not wish to be near it.

      • I think a molten blob at launch would swiftly deform to be an aerodynamic shape under the air pressure, so that might not be so much of an issue,

        Could you assume ‘helka summit height air pressure’ for the whole calculation – assuming the height of flight above, and below that might roughly balance out – and then iterate from there toward the correct solution – using the assumed trajectory and thus the correct air pressures,

        • From the few pictures I’ve been able to find, it indeed looks as if long-distance lava bombs do indeed assume aerodynamic shapes.

          Unfortunately, to accurately calculate this, you can’t assume any set altitude. You really have to calculate each segment, because air density is far, far less for much of the flight (an arc at 45 degrees puts apogee at around 10km). I also neglected the altitude of the launch point (which affects both range and apogee). Velocity also changes during the flight, which changes the flight profile.

          As such high velocities, one way to go is use Newtonian drag. I found an equation in one of my aerospace books that might work; Fd = – ½ cpAuV. This takes into account velocity and pressure altitude. Theoretically, we could use this to calculate each segment of the parabolic flight trajectory, so we’d know the initial velocity needed.

          I’ll give it a whirl tomorrow – after coffee. 🙂

          I can say one thing though; looks to me that including drag at these kind of ranges requires a launch velocity at least double what a simple ballistic (no drag) flight would.

          Hrmmm.. or, for a quick and dirty estimate, I’ll go with a real-world example of the 16″ naval gun, because I know the specs on it, and see what those same specs give me in a no-drag calculation. That, too, will have to wait for tomorrow, and coffee. 🙂

          • Thank you for really diving into calculus (I bet) here =D
            I couldn’t just do that, at least not right now, although I used to know calculus.

          • nice work – the gun does sound like a reasonable approximation to check you’re in the correct ball park 🙂

          • Okay, here’s what I have so far; the quick-and-dirty approach of running the specs of a 16″ naval gun (which has a max range very close to what Hekla’s 32km shot was) through a calculator where we disregard air drag.

            The result? Real-world (and thus drag); 820 meters per second at 45 degrees elevation for a range of 38km. But, if we ignore drag, that becomes 68 kilometres range with the same muzzle exit velocity.

            That’s with a very dense and massive shell (820kg for the HC class shell I’m using as a guide) so drag is less of an issue. I think that with a 12kg mass, the cross-section/mass ratio would be a lot lower, so drag more of an issue.

            So, where we’re at is we can safely say that the 820 M/S (mach 2.47 at sea level) is too low. The bad news is that even the newtonian drag equation won’t help us, because shape and density are major factors – especially as we’re dealing with supersonic flow.

            So, could we use a smaller gun as a model, such as a 5-inch bore? Nope, because so far as I know, nothing with that small a bore can fire that far. You need a very long barrel to attain those sort of velocities.

            As an upper bound though, we might want to look at the K-12 gun, which the Germans used to shell the UK coast around Dover from France in WWII. It was a railroad gun (mounted on a massive rail car) and fired a 102 KG shell up to 55 miles (88km). (though some say that to achieve that full range, they used a lighter shell). That gun had a muzzle velocity of 1500 M/S (mach 4.52). That gun had a shell almost an order of magnitude more massive than the 12kg volcanic bomb Hekla fired at that farmer, and an 8.3 inch diameter bore, so less drag. Still, I think this is a safe upper limit on velocity.

            I don’t know how to get closer without aerodynamic data for the volcanic bomb. However, I think we can safely say that the launch velocity (even after we correct for altitude – the launch point being at least a kilometre higher than the target) of 1000 M/S (Mach 3) or more. If the launch angle wasn’t optimum (such as a lobbed shot at 60 degrees) the launch velocity would be higher.

            So, here’s how this looks; if we decide to try a deterrence strategy to discourage Hekla’s bomb-throwing, we need artillery that can match it in range (and let us not forget the reports of it throwing volcanic bombs 40km!) in order to enable counter-battery fire. The only two artillery pieces that I know of that could do the job were the WWI Paris gun and the WWII K-12 (both were railway guns). This is a problem, because Iceland has no railways. 🙂

  6. Carl .. No eruption yet from Grimsvotn
    Perhaps its not pressurized enough If the magma chamber have grown? But Iceland geologists have seen very high gas emissions and its very inflated as they been up there.

    Any chance that the next eruption happens towards Thordarhyrna? .. thats one of Grimsvötns powerful satelite volcanoes

    • It is far from certain that this drainage of the lake will trigger an eruption. Grimsvotn isn’t fully ready for one, so it may or may not happen. It will not trigger an eruption anywhere else along the rift but eventually that may of course happen

    • But Grimsvötn have inflated alot since last time.. Looks like Grimsvötn is seriously inflated now with magma. Inflation of Grimsvötn have far exceeded the 2011 levels, the volcano must be absoutley stuffed with magma now.
      Probaly because its a magmatic sourge from the Iceland Hotspot
      IMO s experts also agree that Grimsvötn is ready for eruption


      • I may have mentioned this before. Grimsvotn has inflated to about to the level of 2011. The rest of its rise (another 30cm) is not due to inflation, but is glacial rebound as the Vatnajokul glacier is melting. It is seen all around Vatnajokul, not just in Grimsvotn.

      • I wrote a long answer to you Jesper over on FB explaining what is happening in regards of the GPS. Please reread that one.

  7. Thanks for the Katla update! Entertaining.

    “The eruption caused the SAS Airline to default due to volcanic ash and bad food.”
    Are you sure that it’s not the other way around?

    Folks are getting uppity about Grimsvotn. I say give it a while. Maybe Spring. This is my accurate scientific forecast based on the data so far. (People may also remember my (in)accurate forecast for Keilir earlier this year…)

    • I do think that an eruption come spring is more likely.
      But, it was close any way.

    • Yes I know .. I have saved that answer in a notes data file too. My crapbook is always troubelsome, so tested some group-posting.

      I think 4 years more should do it with waiting for Grimsvötn

  8. Katla changed after the Ejdgja eruption. Before, it erupted about four times per century. Afterwards, it was only half that with dormant periods as long as 200 years. Before it, jokulhaups went into all directions. Afterwards, they only ever came from the western glacier. At sone point, it will go back to the past. But it would probably be better if it didn’t. The jokulhaups are the biggest danger, and if they start to arise in new directions, a lot of people could be fatally surprised. The western side is unpopulated (I believe). The change may be because Eldgja left a gap in the caldera wall. In that case the water will continue to go that way.

    • Not entirely unpopulated on the western side, there are a bunch of farms scattered around, it is quite productive farmland if memory serves.

  9. Thanks for the article, Carl.
    If you’re interested in the local scenery near Katla, the Netflix series “Katla”, an Icelandic noir, has a lot of action in Vik. I liked the plot, the Nordic attitudes, and enjoyed the scenes because my family had a good time there on a pre-covid vacation.

  10. 1 Mississippi, 2 Mississippi, 3 Mississippi…
    Oh, are you counting seconds?
    No, just estimating the size of the jökulhlaup.

    Nice work, Carl!

  11. Thank you for the nice article Carl.

    Iceland is always fascinating, and with increasing activity it gets exiting.

    Right now it seems the focus of attention in Iceland is Gimsvötn. If it is ok, I have some questions I can’t find an answer for;

    Following the information here http://husbondi.rhi.hi.is/gvth/drainage.html the discharge of meltwater from Grimsvôtn has been quite high as of lately, esp. this weekend.It seems to be over the top now looking at the data.

    However when following the hydrological data from Icelandic metering-stations here https://en.vedur.is/#tab=hydro I don’t find the water… As in what would be expected surge in flow in the river(s). The only station reporting any significant rise in temperature (as a signature) is Jökulsá á Fjöllum at Grímsstaðir with fairly low flow but with apx. 17 C temperature.

    To me a bit of a mystery. Almost 3.000 M3/sec. drainage from the icecap shold in principle do something when there is an advisory for a Jôkulhlaup. Is a great portion of the meltwater still “trapped” under ice somewhere else? Or hasn’t it yet reached the mentioned station at any substantial rate?

    Since there has been no mention of steam, I would guess most is/has been fluid water. Has there been reports confirming steam from the melt?

    I also see the low frequency tremor has increased on Grimsvötn station GRF. Could this be weather-related or is the low freq. tremor associated with (possible) moving magma?

    There are few earthquakes and they are relatively small. Could this be due to a high temperature of the caldera-lid (beeing soft) or would we most certainly see an increase in number and strength in eq’s before an eruption? And if “soft” is a possibility, are any evidence of effusive eruptions from Grimsfjöll?

    Many questions, so anyone with knowledge is very velcome to answer. 🙂

    Best from Chios, Greece

    • The one you’re looking for is not in the list. Gígjukvísl is the name of the stream where the flood water goes. The discharge in the river was measured at 2600m3/s yesterday. It’s mentioned in the specialist remark on the page you linked.

    • It has ended early; I had expected the water level to go down by 100 meter or more. The jokulhaup when the glacier that blocked the lake began to float, allowing water to escape underneath. It took a long time to get going. It ended when (yesterday?) there was no longer enough water to float the ice and the glacier blocked the outflow again. What you saw is what you are going to get. The volume was not tremendous. Someone posted a link to a time lapse of the river showing the large water rise: a decent flood but not a patch on what Katla can do. And hopefully will never do.

      (The flood came down the Gígjukvísl river which I think is not one of the measurement points you linked to.)

    • I will answer the volcanic part.
      The roof of the magma reservoir is only about 2.2km, and it is fairly soft.
      This is why you rarely see any large scale seismic activity prior to an eruption from Grimsvötn.

      Technically all eruptions of Grimsvötn are effusive (not counting the 5 Saksunarvatn-tephras).
      What makes it explosive is that the lava is interacting with the lake-water, and since the volume is so high, the effect is like supercharging the volcano.

      There are currently no magmatic signals that are out of what is normal for Grimsvötn. There is just the normal slow inflow of new magma into the upper reservoir from the lower reservoir.

      Even a small eruption (if small even is possible at Grimsvötn) would be incredibly noisy and would be detected instantly.

      • Eruptions are noisy as they break the 2700 meters thick caldera lid.. But the magma
        Inflow is competely silent like at Kilaūea. Grimsvötn is generaly always inflating

        Grimsvötn must have competely open conduits, Souch volcanoes are quite rare. Grimsvötn maybe the only open conduiter thats does not have an open vent thanks the its unique geological setting.

        Eyfjallajökull will be insanely noisy If its starts to accumulate magma again as it haves a brittle interior

      • Thank you so much to all of you for taking the time to reply with the answers. 🙂

        A little wiser now. 😉

  12. Anyone knowing how Katla formed?
    How do any large central Icelandic Volcano form? Do they start as lava shields that just gets polygenetic or was the young Katla like Hekla? Is Trölladyngja that sometimes haves Earthquakes a proto – central volcano? All major Icelandic central volcanoes generaly display calderas. Hekla and Theistareykjarbunga lacks them

    That question may intrest Carl

    • Dear Lord Jesper!

      Sorry, but I am giggling where I am sitting.
      Nervously I might add.
      The reason is that this is an article, or more than an articles worth, of writing to even begin to answer.

      The question is brilliant, and it deserves an answer.

      Generally Icelandic volcanoes start as lavashields or shieldfissures that over time become polygenetic (if they are ontop of a fissure, if not they are monogenetic).

      Hekla is obviously the special one, it started out as a crack in the ground that erupted ash only for 6000 years, then it came up with the idea of building a mountain through erupting lava. Before that it was just a few low spattercones. Something is seriously wrong with that volcano… But then it is the only known example of a Stratofissure volcano on the planet.

      Problem is that we do not exactly know how the really big ones formed since any evidence is by now covered in oodles of lava and ash.
      For Katla I would say that it most likely started as a benign lava squirting volcano. At least judging from how some of it’s neighbours got started.

      Now calderas, you forgot Hengill, that one should also have a caldera.
      Hekla will go caldera as and when the edifice have grown sufficiently, currently it is to young and lightweight to go caldera.
      The same also goes for Theistareykir, that one is just about 5000 years older than Hekla. It will probably go caldera within the next couple of hundred thousand years or so. Much like its sister volcano Krafla.

      Trölladyngja is a good question. I think it is a proto-central volcano, the same goes for Urdarhals.

    • Sounds great Idea! Im working too on my own article on other stuff

      In the future too as the ERZ in Iceland gets more established and as well as the plume takes up even hotter materials its possible that Katla will become competely thoelite basalt in nature as partial melting increases.

      We will see How long Katla will live, and There is always the possibilty that there will always be one volcano or another there in one form or another as long as Icelands geological setup is in place as it is now and been since miocene. But Katla is probaly less than a million years old If I remebers correct.

      For now Grimsvötn seems to be the dominant beast in Iceland, if that magma chamber keeps growing and growing.. we will end up with some kind of caldera collapse in Grimsvötn in the future? Most other infact all other Icelandic volcanoes lacks Grimsvötns ever so even constant magma inflow

  13. Eruptions that put other volcanoes into a deep sleep are the ones that Katla chugs out on the regular! Awesome volcano

  14. Those of you with Dave channel in the UK – Steve Backshall’s Expedition: tonight’s show at 9 pm he’s looking for Saudi Arabia’s longest lava tube. A previous show was in Kamchatka and Kronotsky volcano was in the background a lot as he kayaked down the river. Well worth a watch.

  15. Not Only does I like volcanoes, I likes nuclear tests too, so much phenomena and and atmospheric features during nuclear tests. It is really the beauty of physics, condensation clouds, shockwaves, convection, ionization, humidity condensation and pressure waves!
    I can watch for a whole day really. Thermonuclear tests produce the most Beautyful pyrocumulus condensation, some of these pyrocumulus mushroom clouds like Ivy Mike test are almost supercellar in nature

    Youtube haves so many great channels that preserves archives from cold war nuclear tests
    I can watch these for hours here are channels links:




    I can watch these stuff for rest of my life really loves the condensation and stalk clouds, Its atmospheric fluid dynamics. My favorite tests are probaly the Tsar Bomba and Castle Bravo Tests .. enjoy. But I know its not volcanoes

    • Chad Thats very much like me will enjoy these links too, eyecandy really
      All atmospheric fluid dynamics and much of that we see in volcanic eruption columns. Enjoy these channels historical declassifyed

      I can just imagine how a test with 100X Tsar Bombas yeild woud look like or a Fantasy test with same yeild as Chicxlulub ( 2 million tsar bombas )
      Its possible that a nuclear test as powerful as Chicxlulub woud be worse than the asteorid itself ( But souch a Fantasy Test requires mining all of uranium in Earths surface crust )

      • “I can just imagine how a test with 100X Tsar Bombas yeild woud look like ”

        Above 240 MT, the mushroom head does not stabilise in the atmosphere and reaches space.

        I have a picture of a nuclear explosion still in the tin hut that houses the device, only 4µs after the reaction has ended. She doesn’t stay there.

        What happens in the second after the end of the nuclear reaction when the device is in the basalt of a famous South Pacific atoll is not bad either.

      • Then even larger thoretical tests with yeilds of thousands of tsar bombas woud just look like asteorid Impacts I guess then .. These are really insane forces for soure ..

        I Ask it here since comments are fast and in the VC bar it gets buried

      • vcreader

        No mushroom clouds in my Mega sized fantasy tests?
        They are too big big that I guess

        • The outside of that cavity hole will be a terryfying shockwave of like an expanding fireball perhaps

          A nuke with the same yeild of Chicxulub woud be quite a sight

          Very typical of me being addicted to this stuff, the bigger the fireballs the happier I gets
          And thats the same with volcanoes

      • There’s a very good reason that neither side built a larger bomb during the cold war.

        Even when the first bomb was exploded it was known that a large enough bomb could ignite the atmosphere by fusing nitrogen together. They even had a running bet going on if it would happen during trinity.

        Sakharov postulated that it would happen somewhere above 100MT, but at the last moment he decided to leave out the last stage of the tzar bomba. In retrospect it was a good thing since it caused a partial ignition.

        It was one of the few times that the hotline was actually used, and both sides dialed back their bombs considerably after that call.

        In other words, a 100MT would most likely be the end all of existence as we know it.

        • This fear came from WW2. Later it was shown to be impossible. You cannot start a sustaining nitrogen-hydrogen fusion reaction in the atmosphere (and nitrogen-nitrogen fusion is even harder). Even the core of the Sun does not manage it. I think it was Hans Bethe who showed that even if you could reach temperatures high enough for N-H fusion, the reaction would not be self-sustaining because the density in the atmosphere is too low. There are many good reasons not to set off nuclear devices above ground, but this is not one of them.

        • By fusing nitrogen together?
          But such a bomb is still extremely located. Wouldn’t it fuse nitrogen together only in the close vincinity?
          I presume that the nitrogen density is orders of magnitude too low to really ignite the nitrogen as in a star?
          Or where they talking about chemically burn the nitrogen?
          That shouldn’t work either since combustion of nitrogen is fairly endothermic.
          On a side note, I suspect it is exactly that energy that was put into the difficult nitrogen combustion which we then would get out from most(?) of the nitro explosives afterwards.

          • Apologies for being unclear:
            By “shouldn’t work” or “wouldn’t ignite” I’m referring to an unstoppable chain reaction.

      • Thanks for that tought Carl
        And 100MT is not even close to Chicxlulub.. not even a step towards that .. But that event got its energy from its immense speed and mass transformed Into kinetic energy .. and at really high speeds, kinetic energy is more powerful than nuclear fusion.

        Chicxlulub is equal to 2 million Tsar Bombas at once

        Enjoy the youtube channels
        Now back to Katla

      • The uranium is just the ‘fire-lighter’ for the fusion stage. And, apparently, the fusion ‘Tsar Bomba’ was ‘dialled back’ for fear of losing a lot of the island…

    • Yeeea Im silly wanting to see nuclear tests that makes Tsar Bomba look like a grain of salt .. But these atmospheric fluid dynamics and condensation are so beautyful to watch, I can watch these tests all day along really!

      And I think Carl Agree that its addictive to watch ..

      • Personally, after living through all those years of the Cold War and the militant nutters on either side, these kind of nuke pictures still make me feel very queasy. I wish the things could be gone from our world.

    • Drilling a 500 meters deep hole in Grimsvötns caldera rim and setting off Tsar Bomba in that hole woud be Intresting. The fireball is 10 km wide so that woud dig down into the shallow magma chamber If enough rock was vaporized ( crazy Idea )

      A small nuclear test on two sides of Vatnajökull coud be a useful way To map the magma chambers by seismic waves

      • Seriously, guys, I’ve lived long enough to have had the sh*t scared out of me by the threat of my family and myself suffering an appalling end by these things. I was pleased the Cold War came to an end and I don’t want it revived.

        Please talk about this in the VC Bar.

  16. Taal is now producing more earthquakes and tremor but Phivolcs is saying that the entire volcano is deflating now. I am skeptical but I have no other reports on Taal. I wonder why everything is suddenly deflating since the volcano hasn’t released any pressure and I am not aware of any other events at the volcano that could lead to deflation.

    • I am also curious about this. It is possible that part of the inflation was driven by water coming into contact with magma and it was inflated by steam expansion.
      The other option is that the magma is moving into another part.

      I would though be careful about saying that it is over. I think it is more of a hiatus.

    • If the Macolod corridor is u dergoing extension this will result in deflation at Taal. This doesnt mean it wont erupt though.
      I dont know if you ignore my other comments but Taal is not a silicic volcano, it is a basaltic volcano, just one in a very wet location. It doesnt do ignimbritic vertical caldera formation like a silicic caldera, lateral rifting instead more like Kilauea or Bardarbunga, with the depressurizing magma chamber degassing and blowing out the ring fault. Volume is unlikely to be high but the power of the eruption is enormous, basically a VEI 4 with the power of a 6. It is possible that its caldera is actually a maar structure even, not a collapse.

        • What that paper says really is that Taal was a silicic volcano once, but now it is no longer so, and hasnt been at least in the Holocene. Historical eruptions that escaped water were basaltic strombolian. So other basaltic volcanoes are presently a much better comparison. Rifting in basaltic volcanoes will cause deflation, and rifting started in 2020 and presumably is still going. In Iceland or Hawaii there probably would be eruptions along the rift, but Taal has basically 0 height advantage so there is no drive and the magma will stay underground. But there is pressure released from the magma chamber, which is going to degas. if a ring fault forms and a caldera collapse starts then the floor will sink down and force the magma foam at the top of the chamber out, or alternatively decompress any magma in the ring fault, both will be violent events. Even the fluid magma of Kilauea explodes in that setting, as happened in 1790 following the hydrothermal footprints ash, massive subplinian lava fountains. Taal would probably be entirely plinian in that situation, being that its magma has a much higher water content.

          1754 eruption was probably the last time this happened, really the only way to explain how it lasted so long. Rifting probably started a few years earlier in 1749.

          Really, if anything inflation is going to reduce the risk of a big eruption, it will show the volcano is gently refilling. Eruptions that happened without rifting became lava fountain plinian eruptions that made cones on Volcano Island, visually impressive but not that dangerous.

          • Whose to say that the volcano no longer has any felsic magma? The Holocene is only around 1/10 of the volcano’s age. I don’t think Taal is felsic volcano but I am sure it has some within it’s system.
            There are many different ways to get inflation, and without phivolcs giving anything but vague statements, we can’t say this inflation is a good sign

      • Taals caldera is enormous
        24 kilometers wide.. makes even Katlas caldera look small in comparsion. If the event that formed it was mafic, then its one of the biggest mafic calderas on the planet, the biggest. I can just imagine the event that formed it

      • It is erupting, lava is flowing from a flank fissure that is about 2 km west of the cone, almost half way to the ocean. There are 2 stages to a Cumbre Vieja eruption, cone building and then effusive flank vents. Sometimes also a last round of lava effusion. All of the last 3 months was just stage 1…

  17. In regard to the 12 kg lava bomb thrown 32 km, there are a lot of assumptions which have to be made if using air drag to calculate initial velocity (assuming maximum distance), so much so that I gave up after awhile in trying to find reasonable calculators on the internet which incorporate air friction. There is the exact nature of drag, a velocity^2 or quadratic drag seems most commonly mentioned, but then for the projectile you need surface area and the density of the lava bomb and subsequent size has to be determined. In the past Hekla threw clasts with a density of approx 5/8 of water due to gaseous vesicles in the clast, but we have no way of actually determining the size of the 12 kg fragment.

    Having said all that, the projectile calculators neglecting air drag show a 32 km flight at 45 deg launch angle for an initial velocity of approx 560 m/sec which is mach 1.63 or so. This indicates that the fragment was thrown during a supersonic volcano bang or burst. Watching Tajogaite on La Palma supersonically exploding with shock waves, I am going to guess that Hekla could accelerate rock fragments to Mach 1.6 or so.

    • Thanks for your thoughts. Air resistance of only 5/8 t/m^3 would be a different animal! 😮

      Hmmm I see you got 560 m/s without air resistance/drag.
      I only got 400 m/s. Same ballpark but would be interesting to know where I have an error in my math :/

    • The air drag on the first part of this lava bomb’s journey would be negative.

  18. I see that at 16% of alkali content rhyolite is starting out at 69% silica.
    Common window glass is suggested to have about 71% of silica, along with substantial amounts of alkali and earth alkali metals.

    Since it looks pretty much like a similar composition, at least judging from the TAS diagram, would I have the flow behavior of rhyolite if I was to heat common glass to 800 °C?
    And are we allowed to consider common glass to be some particularly glassy sort of rhyolite?

    • Common glass is lacking an organized crystalline structure I think?
      Obsidian is close, not a real mineral, because of the lacking crystallization.
      The color differs by mineral inclusions and/or air bubbles, I read.

      Very interesting study of SiO2 is presented in http://www.quartzpage.de/gen_rock.html .

      • Dumb question: Do we need a crystalline structure for a mineral?
        And must rhyolite be a mineral then? Or must it contain mineral inclusions?
        Either way, Wikipedia suggests that rhyolite can be glassy too, whatever that means in terms of “glassiness grade” and abundance of crystalline inclusions.

        Maybe the minimum 35% feldspar or something like that proves that it must contain some crystals.
        Which glass clearly wouldn’t adhere to.

        • Yes, think so.

          No, Rhyolite is a type of igneous felsic rock which fits in a classification based on relative contents of minerals as Feldspar and Quartz.
          The term glass(y) is used for rocks that have a high content of Silica (Si); but only if it is very fine grained. Bare eye visible crystal inclusions are few. So it is about texture.

          Porphyritic rhyolites do show many crystallized inclusions (Feldspar mainly). Rough grained.

          Peace of pitchstone from Zwickau, Germany. A glassy type of igneous rock, no crystallized inclusions visible.

          Cut porhyritic rhyolite from Luisenthal/Thüringer Wald, Germany, with large Feldspar crystals.
          There is Agate inside, another SiO2variety, but forget it, it has formed in watery silica rich fluids in a stage when the lava has become solid.

          • Ok, from the paper too I see that it is quite different.
            Thank you for your follow-up on the subject.

    • Fulgurites (by thunderstorm lightning, sintered quartz rich sand) is also a glassy product, sometimes nearing glass. What makes it different from rhyolite is the proces of forming I guess.

    • Admin please delete duplicate post sorry did not notice Luis has already posted this. Thanks

  19. Do Katla contain a subglacial caldera lake like Grimsvötn?

  20. A larger earthquake has occurred in the Grimsvotn caldera this morning: M3.0 at shallow depth (0.1 km).

    • So far no magmatic signals, and no tremor.
      That being said, this is at the worst (best) possible place in relation to where a vent is likely to open up prior to an eruption.
      The earthquake signal was purely tectonic.

    • I would say that it is fifty/fifty right now.
      The next 72 hours will tell what is gonna happen, if an eruption starts it will have a very short runup, probably counted in a couple of hours or less.
      Not the best time to go and oogle at the caldera.

      • Will be a lot like the warning Kilauea gave before erupting in September, very seismic but also very sudden, only an hour or so before eruption from what is basically a background signal.

    • Monday
      06.12.2021 06:16:48 64.415 -17.266 0.1 km 3.0 99.0 1.2 km NNE of Grímsfjall

    • But do the earthquakes indicate that a phreatic event is more likely? (Magma and water likely to get too close).

      • Yes and no.
        It would be phreatic in the beginning wherever the eruption would start at Grimsvötn, see Gjálp 1996 as per example. Ice would then be the driving force.
        But, if the eruption is in the lake it will continue to be phreatic throughout.

        Currently the activity is pointing to a spot 1.2km NNE of the seismometer at a known spot for eruptions to occur. If an eruption happens there the seismometer will go out within seconds (minutes at best).

        • If it blows now, it will be before the monthly earthquake count goes yellow.. That should change in a few hours, at the current rate of activity.

          • I think it will.
            If it will erupt (I am still sticking to the 50/50 ratio) within 72 hours we will probably first see about 100 earthquakes prior to onset. That is the usual number (give or take a few) for a Grimsvötn runup.

          • Interestingly enough the Cumulative Seismic Moment plot has now passed the values needed for previous eruptions. It is not yet visible since the updates are made at midnight Icelandic time.

    • The earthquake have now been upgraded:

      Monday 06.12.2021 06:16:48 64.415 -17.266 0.1 km M3.6 99.0 1.2 km NNE of Grímsfjall

  21. Yesterday I broke our main rule: “Be nice”.

    I lost my temper and answered in a way that was decidedly not nice.
    I am truly sorry about that.

    I put myself to the vote among the other Admins, and it was decided that I should clean up the mess I caused.
    For technical reasons that meant that I had to remove the entire comment thread, the reason for the removal was due to my actions, and not due to what someone else wrote. I want to make that very clear.
    If we have to remove comments and do not remove the entire thread the comment section will become a mess with comments ending up everywhere. This is why at times our moderation might seem a tad heavy handed. It is also why we often just remove the content in the comment (empty it out) if it is one comment that is deemed to be offensive.

    I was also forced to watch a truly horrible music video as punishment for obscure reasons only understood by Nick Small.

    Obviously this is a place for free discussion about science, and I should not have lost my temper.

    Any comments about moderation should be taken via email on the link up on the right.


    • Apology accepted.
      It wasn’t necessary to remove my explanation about the movement of the African Plate following the subduction of the Tethys Ocean, but it might be due to the mess.

      Hectór though is much more important than I am. You can do without my comments, but you would miss Hectór.

      If there is s.th. personal between you and the other group try to throw it over bord. I know heaving read “The Great Dinosaur Controversy” by Parsons that things can become very personal, but science should always be open to controverse facts. We are more than used to this in medicine and pharmacology.

      I myself will try to avoid pl/pl in the future and if I enroll at a university which I can only decide after I have decided whether I’ll move to France and where I will discuss it there.

      Basically I do like people who can explode like volcanoes. That was a VEI 7 😉

      If I have a request open try to contain some other guy’s phantasies about LIP’s, bombs and roasted meat a bit more, I’m not the only one who’s getting tired of that. He should read the Russell-Einstein manifesto.

      You write good pieces. I’m glad you said what you said above. It shows greatness.




      • So you are saying Carl is silicic.

        Quiet until something causes it to detonate.

  22. Not seen any comments on the Semeru eruption – looks like a good amount of ash and then rain making Lahars – so pretty nasty for the locals (and obviously very unfortunate and saddening that 14 people have died) – but Phivolcs are very good at their job, so I’m intrigued if there are any theories for why Semeru suddenly hits 15000m when “Mt Semeru is in a near permanent state of eruption and regularly spews ash up to about 4,300m, so Saturday’s eruption was a “pretty significant increase in intensity” (according to this article in the BBC https://www.bbc.co.uk/news/world-asia-59532251 )

    • Yes, it was a very bad eruption with pyroclastics and lahars. The death toll will be considerably higher than what is known so far. It erupts fairly often – I think the last time was a year ago. Such a volcano an always do a bit bigger bang than what it did last year. Too many villages were too close to the summit, apparently, and along the flood path. I don’t know the details of how that happened.

    • oh it’s indonesia – not phillipines so PVMBG not phivolcs – but still the volcano watching around the ring of fire is pretty experienced

    • I posted a GeologyHub video on the previous thread that explained that Semeru had grown a lava dome, which became unstable to the point where heavy rain washed away part of it, causing the eruption.

      Semeru is next to Bromo though and that whole complex is enormous.

  23. If Grimsvötn erupts it will look alot like the first day of the surtsey eruption, big pheratoplinian column.Lots of thick white steam and fingers and cypress like jets of black hot ash rising up into white cauliflower steam. And specialy if it erupts in the caldera lake. An eruption that last long enough will form an Island in the lake.

    If it erupts on Svianukur where Ice is very thin
    You will get lava fountains of inferno sized that quickly turns dry with massive lava falls flowing into the caldera wall.

    An eruption towards Thordarhyrna or Skaftarkatlar ( sig – katlar ) will resemble the Gjalp eruption under a thick glacier

    Carl this is Correct ?

      • For best viewing, the eruption should not happen today as the weather is bad. Tomorrow or Wednesday may be better. We will try to put it on hold for you

    • Albert its not going to erupt
      And If it erupts it will only last a week.
      What makes you think it will erupt?
      Yes I wants to see some thick cauliflower steamclouds now

      Was the earthquakes only tectonic?

  24. I predicted Grimsvotn would erupt in Spring. The volcano must have read my comment and decided to issue a stiff retort. Now it’s going that volcano thing

    If anyone else wishes to bring forward a volcanic eruption, please ask me. I’ll put a comment on this board predicting a distant future date and, Bob’s Your Uncle, bang will go your volcano.

    And I don’t charge for this service!

    • “If anyone else wishes to bring forward a volcanic eruption, please ask me. I’ll put a comment on this board predicting a distant future date and, Bob’s Your Uncle, bang will go your volcano.”

      Puy de Dome, Please. Thks


      • The cam Grimsfjal 3 you can see the column on right side

        • It might be snow on the web cam; is there a volcanic tremor yet?

          • It’s not snow! It’s water vapor column on cam Grimsfjall 3!

          • The rule for Grimsvotn is, if there is any doubt whether you are seeing a cloud or an eruption, it is not an eruption.

          • Mind you, it says it +15C on the webcam. Isn’t that a bit toastie for there?

          • 5 min i think. The present image is from 12.00 and the column is very clear on pic

          • Albert i don’t have any dout. The column is very clear. The thing is that it’s just hydrothermal activity for now. No magma/water interaction for now

      • Its snow on the side of the camera lens that looks like convective column

        Can you show me where the column is then?

        I wants to still 1 kilometers down in Grimsvötn and place Tsar Bomba there

      • Can’t see owt in the cameras. Just mist or a blank screen.
        Mila’s Jokulsarlon webcam shows a heavy blanket of cloud over the icecap so it’s more likely to be cloud.

    • No sign of large activity in the tremor/quake plots.

      Hydrothermal activity may show stronger now because there is less water?

        • jökulhlaup it’s a flood, not a water column… this is the heat of the volcano making the ice and snow to turn on water vapor and making the column. And like Rob said, for now is just hydrothermal activity and not yet magma/water interaction…

    • 2nd Grimsvotn cam on Luis’s link.
      That DOES look like a steam column on the left. Hard to be certain though. The shot shows nothing but cloud and murk.

      • I’m follow it for days and it was just snow… the column wasn’t there two hours ago!

    • Let me curb the enthusiasm a bit here.

      There is currently no tremor signal. So, there is no eruption going on. Grimsvötn is after all quite noisy when she erupts.
      There is a lot of snow on the camera, so it is hard to see clearly. But, I do think that what is sort of visible on the righthand side is the mast that is covered in snow.

      Sorry to be the official spoilsport.

  25. Three succesive images (intervall 10 min) , there is a vapor column on the right side!

  26. New cam pic update: The water vapor column is biger…

    • I think the picture didn’t change, and the column on the right side ist just ice or snow sticking to the right side of the cam.
      But i might be wrong of course

      • Yes it changed, you can see the hours and date on top of pic… will update soon because she do it with 10 min interval

      • I did the same. The column is identical in two pictures taken 10 minutes apart while the light on the rest if the image has changed (weather coming in,I think). The column is due to something on the lens.

        • Please… i’m following this for days! It wasn’t therefew hours ago… i give up!

          • Luis, I saved an image, waited for the next one, and traced the outline of the column. It was much harder to see on the second one because the light had changed. But the outline of the column had not changed at all. To make sure, I waited another ten minutes for the next image and did the same thing. No change to the outline. I don’t doubt you that it wasn’t there a few hours ago. But it not a steam column. It may be snow stuck to the camera hood.

          • It’s a pity you didn’t saw it some hours ago without anything but just snow and a clear image…

          • It is snow that has gotten stuck on the antenna-pole. If you are not used to seeing wet snow rapidly building up during a snow storm you will easily be fooled by it.

            My expertise on seeing this is Level Yoda since I come from Northern Sweden. 🙂

      • The shape of the “column” is not consistent. It looks like rising steam to me.

        • Of course it’s a steam/vapor collumn. No magma/water interaction yet but it wasn’t there this morning, just snow!

          • I image googled Grimsfjall webcam and found a thumbnail from a clear day. It clearly shows ice buildup on the mast. After visiting the page, the google thumbnail was updated to the current image, but I captured it before that. Low quality, but you can see the ice. No eruption, no steam column, just ice.


          • Swedes, destroyers of fun since 793AD…

            Good catch of the antenna pole.
            We know our snow when we see it for some reason. 🙂

          • That, plus I had a clear memory of seeing it on that exact webcam. I figured someone might have taken a screenshot for a blog or something, so did a quick search. Didn’t need to go further than the google thumbnails to find it.

          • So, this is ice acumulation? Geezzz what a terrible illusion this was!
            Sorry… what a bad day!

          • Sorry to destroy the fun…

            Do not worry, there will soon be an eruption, and then there will be no doubt, so keep the energy up Luis! 🙂

    • I am reposting this from up above…

      Let me curb the enthusiasm a bit here.

      There is currently no tremor signal. So, there is no eruption going on. Grimsvötn is after all quite noisy when she erupts.

      There is a lot of snow on the camera, so it is hard to see clearly. But, I do think that what is sort of visible on the righthand side is the antenna-mast that is covered in snow.

      Sorry to be the official spoilsport.

      • Also, if there was an eruption this close to the cam and the seismometer neither of them would be alive… 😉

        • Proven.
          I looked at it several times when the cam link was posted, and on a day of questionable light conditions it was easy to see it as a plume, but the photo from Tomas is conclusive.
          When something doesn’t stack with other evidence…

      • Aww…

        Having said that, I stupidly didn’t take a screenshot, on Esja I did see of what looked like a plume of water vapour

        • Well, Esja would be something completely else.
          That is mountain nextdoor to Reykjavik. 😉

          • My Icelandic geography needs work… I wondered why I thought I could see built-up areas… probably coming from Fagrad….

          • Mount Esja is NE of Reykjavik, it is that big honking mountain that you see wherever you are in Reykjavik. 🙂

  27. I take still images. It’s not exactly the same. To know exactly whats going on, we need an other view (plane). any other wecam?

  28. “The safety zone here during a larger eruption would be around 30 kilometres.”
    I saw the dicussion about lava “bombs” further up.
    Then I had to think of reindeer.
    “The Caribou was standing on the plains 30 kilometers away from the mountain; it had not fled the roaring mountain more than that.”

    Any comparison possible at all between Aniakchak and Katla?
    Or out of the question?
    Any comparison possible between those two volcanic zones at all?

    • As I mentioned in the article, if it would go VEI-6, and if it would suffer a columnal collapse. Well, then anything less than 50km is useless.
      That being said, there have been only 2 VEI-6 eruptions in 12000 years, and none of them are known to have produced a pyroclastic base surge or a columnal collapse, so I still feel rather sure that 30km is good enough, especially since that would cover Vík in Mýrdál.

      • The volcanoes are quite different, and it is good to remember that Aniakchak was a borderline VEI-7.
        But, theoretically Katla can do something really out there.

  29. Just for interrest sake,, a 76/62 Oto Melara will throw a 6kg projectile 16 .4 km at 45° elevation. Initial muzzle velocity is 930 m/s nominal disregarding barrel wear and internal ballistics.

    • Very interesting, thank you. Will try to think of looking for part II.

  30. La palma, 13:30 Fly by, Thermal + visible channel.

  31. Do we know what is going to be the next VEI6 aside from (unlikely) Taal?
    About when is it expected to take place?

    • Forgot to add that I know your New Decade Volcano Programme, but it doesn’t have to be VEI6 to be in there, just poorly placed.
      So that is not what I’m talking of.

    • With the exception of Taal there is no volcano that I know of that is capable of a VEI-6 that is active.

      There is though a couple of slowly inflating ones, like Mt Atitlán for instance that is slowly tilting an entire lake.
      Fourpeaked is also a candidate somewhere in the future.
      Uturunku is another one.
      There are obviously a few dozen more.
      But, my general favourite of doing something large is probably Ischia.

      • Hi Carl,

        what about all the unknown ones? Or let me rephrase – would you have come up with Pinatubo, had it decided to erupt 20 years later? Would you have thought of Reykjanes to erupt next?

        Always trying to put a percentage or likelihood on the “dark” part that no one expects. A single one of them is unlikely to pull something big unexpectedly (take Katla or Ambrym), but all of them together are significant. Not talking about black swans here at all – Reykjanes was mentioned beforehand as a candidate – but given the eruption frequency and likelihood it was dwarfed by the usual suspects.

        I think also Etna, Popo, Sakurajima, Fuji san etc etc could surprise. Percentage of a frequent small eruptor / long dormant volcano having a VEI6 could easily go as high as 50% in my eyes, but obviously very hard to put a number on it.

        Agree on the Taal bit, it could pull anything at any time really, same with Campi Flegrei!

      • Sakurajima is a vent of a volcano that can do a lot bigger than a 6, and it is currently very active. Sinabung is accessing Toba’s magma chamber (there was a paper in Nature about this a few years ago.

        If these don’t count, why? (curious as to your reasoning)

        • Think most people wouldn´t expect a frequent eruptor that has small eruptions only to go VEI6 all of a sudden, similar to how they´d be surprised to see a long dormant volcano pull the same stunt.

          Sinabung I can see going big potentially due to the nature of its eruptions.

      • There is Rabaul. A dacite magma chamber with an active ring fault. The only silicic volcano with an active ring fault that is not submarine or in a lost island in the middle of nowhere.

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