A wandering eruption

Since the eruption in Iceland started, some of us have been wondering about other past volcanic events that we could compare it to, in such a search I came up with an Icelandic eruption that I believe might by a good analogue, and no, it’s not the Krafla Fires.

Currently some of the characteristics of the ongoing eruption in Fagradalsfjall are that it is slow, both in intrusion and eruption, and that new vents keep popping up a considerable time after it started.

The Krafla Fires may seem like an adequate comparison to the Reykjanes Fires, and the current eruption of Fragradallsfjall, given that they all are episodic fissure eruptions, although even Laki was episodic, two-year-long and punctuated by short intense surges, there are thus many ways an eruption may be episodic. Rekyjanes and Krafla also have in common that their lavas are very fluid, some of the most fluid basalts in Iceland, they easily take on the smooth pahoehoe texture, even at high rates, and with very low explosivity, fountains not exceeding a height of 200 meters. But otherwise their similarities end there. Although it is not how the situation in Fragradallsfjall will turn out the Krafla Fires is one of the most fascinating volcanic events that I know of, so I will delve into them.


The Krafla Fires

Krafla is a basaltic caldera system, with just a bit of rhyolite. Although somewhat unappreciable in the landscape, its vast caldera collapse is 10 kilometres wide, up there with Grimsvotn, Bardarbunga, or Katla. The top of its magma storage lies only 2 kilometres from the surface, the magma was accidentally drilled into during a geothermal exploration in 2009, really shallow compared to Reykjanes where the magma comes from near the mantle-crust boundary 15-20 kilometres down!

Inside Krafla Caldera. Source Wikimedia.


The Krafla Fires opened in 1975 with a massive magma intrusion underground, a megadyke, that rifted a length of 70 kilometres. This triggered a rapid influx of magma into the shallow magma chamber under the caldera to restore the enormous amount it lost during the first intrusion. The caldera inflated rapidly until the rift snapped again, a dyke propagated into the fissure swarm, and then the caldera deflated sharply as magma drained into the growing fractures. This inflation followed by sharp deflation pattern repeated over and over again. A total of 18 dyke intrusions happened from 1975 to 1984, initially they stayed underground or had small eruptions that were almost accidental, where the dykes grazed the surface here and there. They filled the rift progressively so that the intrusions became shorter, closer to the caldera, a few of the last ones did have significant eruptions when the filling was mostly done,

This whole landscape is the Krafla volcanic system, normal faults and fractures visible in the image form when dykes intrude below the surface and open up the ground. Source USGS, by Michael Ryan.

Laki wasn’t so different, a series of dyke intrusions that breached the surface producing magma surges over a period of 2 years, 1783-85 , what sets them apart is that Grimsvötn had enough magma available to fill the rift multiple times over, so every dyke vastly overflowed, and the repressurization must have been much faster because the fissure swarm snapped again while the previous dykes were still erupting.

Eruptions of Krafla followed the typical sequence of fissure eruptions, they open with a curtain of fire, a flood of pahoehoe, then effusion rates drop exponentially, later it can focus into one vent and go on at a lower intensity for some time. One of its largest eruptions was in November 1981, the dyke travelled in one hour from the magma chamber to the surface, within another two hours a curtain of fire 8 kilometres long was already shooting from rows fountains and sending forth floods of fluid lavas. During the initial peak hours of the strongest eruptions in 1984 and 1981 effusion rates of 800 m3/s were probably reached, if not surpassed, and this was similar to the rate at which the previous intrusive dykes expanded.

Krafla erupting on September 5, 1984, the day after the onset, the eruption intensity had already waned considerably by this time. Source USGS, by Michael Ryan.

Krafla vs Reykjanes

I have been inspecting some of the old lava flows of the Reyjanes Peninsula in Google Earth, which I was talking about in my last article, it turns out there is some variety.

Hengill, Krýsuvík-Trölladyngja and Svartsengi erupt with great intensity, a curtain of fire feeds a flood of pahoehoe lavas of similar proportions to Krafla’s strongest, the eruption rate decays exponentially and may last for a total of a few weeks or so.

Brennisteinsfjöll is the exception, its eruptions are slow, long, complex, they don’t follow any general trend of decrease or increase in intensity. Fagradalsfjall, although shoulder to shoulder with volcanoes that are into lava floods, seems to have actually turned out the Brennisteinsfjöll way. In hindsight the rate at which the dyke grew, a mere 15-20 m3/s, a snail’s pace in the world of racing dykes, already pointed towards the eruption being a slow one. There is evidently a lot of magma in the mantle below Fagradalsfjall that is buoyant or pressurized and could readily erupt, 800 years of melting building up below the region, and if it could come out faster it would. If the dyke grew out so slowly it is probably because that is all that the conduit system that brings magma from the mantle into the dyke is capable of transporting. Presumably the space in the conduit somewhere down there is very little, so that the small opening and friction against the sides does not allow ascent to be any greater than that. As such, it is unlikely the eruption rates will exceed much more than 20 m3/s at any moment in the future.

The idea of a lava flood may sound attractive, however one should realize that this is something that happens very quickly, the peak eruption in a matter of a few hours, should it happen in the middle of a blizzard then perhaps the best part might go unseen entirely by everyone. Instead Fagradalsfjall seems to be putting a slow, long lasting, show that keeps changing.

I’ve got the impression from inspecting the lava flows of Brennisteinsfjöll that these probably formed in multistage eruptions where the active vent shifted location multiple times, that may have went on for multiple years and erupted more than 1 km3. Fagradallsfjall seems to be intent on shifting the eruption location, it has already opened three different fissures, this has surprised some scientists who, following the model where the dyke solidifies and output focusses into stable pipes, didn’t thought it should be possible for it to happen so far into an eruption. If we look into the recent past there are however a number of examples of eruptions that simply kept moving their vents around.


I think that the eruption of Surtsey might be a good analogue to the current eruption of Fagradalsfjall, as long as we ignore the difference that one was partly submarine whilst the other is subaerial. Fagradalsfjall is like a Surtsey out of the water. The eruption rates of Surtsey were low, around 5 m3/s when converted to lava, it lasted a total of 3.5 years, 1963-67.

Surtsey was a wandering eruption, from multiple vents along a 3 kilometre-long line. The eruption started from the vent Surtur I, which was joined 1.5 months later by Surtla that erupted for several days, Surtur I went on for about ~2.5 months. The activity moved to the vent Surtur II when Surtur I had waned, Surtur II erupted for about ~16 months. After Surtur II, a new vent, Syrtlingur, opened and erupted for ~5 months. After a brief break in activity, yet another vent, Jólnir, became active for ~10 months. Later effusion shifted to the first vent, Surtur I, for the 10 final months of the eruption.

Surtsey erupting in 1966 from the Surtur I vent. From USGS.

The way Surtsey kept shifting the action around defies the typical assumption that after initial fissure opening, the first hours or days, then the eruption settles into a single or a few nearby vents and stays there, this is because the rest of the dyke solidifies so output concentrates into small pipes, which is how it happens almost every time. However, there are several examples of eruptions that do not obey this law, during the eruption of 1730-36 eruption of Timanfaya, in Lanzarote Island, the focus of activity kept shifting, the last outbreaks were as strong as the first ones, the activity being overall rather slow. During the 1991-93 eruption near Nyamuragira Volcano, a new vent would open every 2 weeks on average, a few or one of them being active at any given time, they did not open through a single line but sporadically over an oval area.

Timanfaya, a spectacular volcanic landscape reshaped by the great eruption of 1730-36. By Dario Garavini, from Wikimedia.

Why do new fissures keep opening up?

Fagradalsfjall has opened 6 fissures already, it does seem to be walking down the path of Surtsey, or Timanfaya, or Brennisteinsfjöll. I do think it is likely that new vents may keep opening until the eruption stops because it is how this kind of volcanic event seems to typically progress, a fissure eruption that does not have a proper curtain of fire, that does not have a exponential reduction in effusion rate.

How is it possible that new vents would open up even when the dyke should have solidified already? It doesn’t seem likely the magma would come for the initial intrusion which should be solid by now, and not able to flow any more. However there are pipes filled with hot new magma rising from depth into the vents. Geldingadalir, or Smeagol, or Bob, or was it the Twins? however it was called, this vent was fed with hot magma from depth, its magma pipe could have broken at some location down below and fed a lateral magma-filled fracture that opened fissures 2 and 3, a small dyke branch. This does seem like a plausible reason.

Fissure 2 of the current eruption. From Wikimedia, by Almannavarnadeild ríkislögreglustjóra.

Some ground cracks did form between fissure 1 and the site of the incipient fissure 2. Ground cracks are possibly the best way of tracking the way magma moves underground, because at this point intrusions are small they may not generate detectable earthquakes or ground deformation, but they will probably open cracks. It is difficult however to monitor the opening of tiny cracks on the ground.

Often we may underestimate the complexity of a situation, for example we know that the dyke feeding the current eruption extends down to a depth of 5 kilometres, and yet we also know that the magma comes directly from a depth greater than 15 kilometres, with no intermediate magma chambers, so what happens in the 5-15 km depth range? Certainly the magma must have found a way through, not a very effective connection given that the intrusion and the eruption receive magma att such slow rates, however the exact way it happened remains unclear. When did magma start to rise upward? In January 2020 there was an intrusion, a sill, below Mount Thorbjörn, this is quite close to Fagradalsfjall, was magma already rising from the mantle then? Perhaps the intrusion was already growing long before it is assumed and it continues to grow now, as shown by the new fissures that opened up recently, and will probably keep doing so. How does the intrusion look like? a system of interconnected sills, dykes, with molten pipes transporting magma towards the vents and growing dyke branches? I guess this is up to our imagination.



The eruption in Fagradalsfjall is the subaerial equivalent of a Surtsey-like eruption, it seems also similar to the historical eruptions of the Brennisteinsfjöll Fissure Swarm, which happened around the 11th century, they were of significant volume and long-lasting.

New fissures will probably open along the dyke axis that runs from the eruption site to Keilir, at some point, days, weeks, or months from now. A decrease in surface volcanic activity may indicate that magma is moving into fractures towards a new eruption location, same is true for the formation of ground cracks. Old vents can be abandoned if the flow is redirected towards a new fissure. The eruption will probably end up lasting multiple months or years because the transport of magma from source to surface is slow.

This eruption is turning out to be really interesting, can’t wait to see what volcanic surprises await us!






349 thoughts on “A wandering eruption

  1. well relogging in was scary…. this is just a test to see if i did it right?

  2. Oh – I tried to register but I’m registered already. Ummm err…….

  3. The RUV.is Geldingadalir cam zoomed out, and now we get a glimpse of the ‘Southie’ vent (at the very right hand side of the image). Strong glow and occasional lava bombs visible, clearly not extinct yet – yeah!

    • I think the scoria cone ‘wings’ are wrapped around the vent, so the cameras can’t peek inside; or it has turned into pizza oven version 3. Still lots of gas being produced, so I wasn’t too worried.

  4. I’ll be doing a test, I’ve been selected by the Imperial College covid background monitoring programme. They’ll tell me what I already know; I’ve not had the virus, and one dose of vaccine.

    • I have had the virus, worst I have been ill ever. I was vaccinated first dose 6 weeks ago and I felt like I had caught COVID again, but it cleared up after a couple of days and was nowhere near as bad as the actual virus.
      My taste for chocolate was lost for 1 year, now it is back with vengeance LOL

      • Odd, absolutely no effect from vaccination whatsoever, second dose end of week. Its just possible I caught it in april last year, 12 hrs slight shakiness and food noticeably boring in flavour for a week, but who knows?

      • I had the AZ jab. Sore arm immediately (but that might have been the jabbar)
        Twelve hours later in the wee sma’s I awoke to pounding heart nearly 2-3 times my resting heartbeat of 58ish; sweat breaking out, general aches, pains and malaise.
        Dose of paracetamol and ibuprofen to boost the effects. I felt awful for another 12 hours with the pounding heart beat happening intermittently. There is a history of heart disease in the family.
        Monitoring the heart rate and O2 saturation levels were ok. It took me about three days to really get back to my normal.

        Your immune system recognised the intruder and called in the cavalry, the 100 pounders and the SWAT team. Once they had rounded up the advanced guard, there was no more for the IS to do as there was no repicating viable virus. Congratulations on having a strong, responsive immune system. 🙂

        I would die if I lost my taste for chocolate… just call me the chocolate Lemmy, and pass the infusion…

  5. Since my first test was so successful, I’m doing a second test to make sure my first test was the success it appeared to be. Statistically, it has a 50% chance of failing. However, I decided to adopt the Schrodinger Quantum Cat theorem. This means my test will be both successful and unsuccessful, until an outside dragon looks at what I am doing and freezes me into one state or another.

    That said, my personal theory remains that an observation only freezes a quantum spin state because the instrument of observation is so crude. If humans refined the instrument of observation to such a fine state, the spin would not be interrupted. Cue Albert to slap me down…

    • Which universe am I in, the one where this worked or the one where it did not? Perhaps both.

    • The cat is objecting to such intrusive monitoring, and requests more discrete behaviour from its human slave

  6. Grazing in the grass is a gas ..
    Can you dig it ??

    Tets .. test ..
    Is this thing on ??

  7. Repeated deep activity southeast of Bardabunga. Looks wet, as newmagma is arriving (to my amateur eyes), Our embryovolcano Greip snatching food from Grims?

    • More likely Greip is going towards Bardarbunga, it had a big drain of magma from Holuhraun, at least 2 km3 and Grimsvotn is fully recovered from its last eruption now, so would not be an easy destination. Bardarbunga in active periods does seem to be able to do multiple relatively large rifting events within a span of a few decades so must get a faster resupply rate than it has had in recent decades, its just been rather inactive in the 20th century and took a while to build up to Holuhraun, but there were at least 3 rifting events of large scale between 1860 and 1910. Probably we will see more from it in the coming years.

      Grimsvotn isnt as productive as Bardarbunga generally, but it is more intense, with fast eruptions that dont last long enough to become effusive except in the 1780s. It has probably has already got enough magma to do something impressive so dont worry 🙂

  8. Speaking of testing, is Mauna Loa testing the boundaries? Things got busy.

  9. Testing testing, I think a post with an image link I posted got eaten

    • I know that Newsround is aimed at children (I used to watch it at 5pm before tea every schoolday), but really BBC!? Come on, you can do better than this!

      “The eruption that took place in St Vincent is the result of tectonic plates moving together and in cases like this, the magma is stronger and flows in much more powerful way, this generally leads to bigger explosions.” stronger and more powerful? What the actual…?

      How about “the magma contains more water, and is therefore more solid and allows less gas bubbles to escape, this generally leads to bigger explosions.”

      • I once had to explain the leap second live on newsround. They do do harder topics – at least it was hard for me!

  10. Here are the recent non-verified quakes near the eruption site, gruped by depth (and latitude):

    • I’ve seen many eq plots over the years. Do we have some accommodation going on, a little bit of elbows out jostling along the dyke to the northeast?

      The blue 2 and it’s green companion interest me.

      And I’d love to know what it is about the integrity of the geology, that the dyke stopped and the fissures have not opened to the south-west past F1 Nordri-Sudri. Except for that steaming crack, which steamed and steamed enigmatically until – is it still steaming, or has it been buried yet? It was at the top of the first kipuka…

      • I think the crack isn’t there anymore (overrun by lava). But vent 1 is smoking like hell, literally. Although it has to be pointed out that smoking is dangerous and not good for your health, kids!

        Wonder when we get a first insightful and detailed overview from scientists regarding the whole event. At least as a preprint. With maps, more info on the dike, chronology of events, extrapolation of the future development and stuff. Especially stuff.

  11. This is a post to test if I’ve successfully made it from Lurker to Lurker with posting priviliges.

  12. This is not a test. This is me screaming silently into the void as my beloved username or password, freshly minted not yet a week old (give or take, cut me some slack), is not recognised.

    And why have I got to type my name and email addy to post this reply?

    I really really hate itech sometimes.
    *bangs head repeatedly on desk*

    I neeed more tea *wanders off to kitchen*

    Nice flat topped cumulus on mbl camera

    • One check you may want to make: do you have a VC account? You may have used an external account and those will currently not work because of the WP login bug.

    • I have taken a look through the logs, and it looks like the password was the issue.

      No further info beyond that I am afraid :/

      • Interesting. It was a Lastpass generated password, 20 characters long. Is there any restriction on pw size or characters?

      • I seem to have achieved login, and changed emails. Everything looks ok except for the wordpress app password thingy. I put in a password, then that got changed into gobbledejook.
        Please can some one kind explain to this bear of very little techy brain?

  13. https://imgur.com/a/bbYshEd

    Been working on this a while, the current eruption compared to the Krysuvik Fires in the 1100s (orange) as well as the eruptions about 2000 years ago during the cycle before that (pink). Current eruption is the leftmost orange spot.

    We have not seen anything yet… 🙂

    • That’s interesting, someone used the same mould again.

      I can understand the general ne-sw trend, and the spreading out as the lava hit the coastal plain, but the right angle turns to the north are a bit puzzling.

      Is this topography controlled? Or by faults? Or a bit of both?

      • Its all very flat but the north side of the peninsula is in large part from lava flows, and particularly from two shields from the early Holocene. The central and southern parts of the Reykjanes area are faulted old terrain, the mountain inbetween the two flows on here in fact has a surface that is very old probably hundreds of thousands if not a million years old, or even more, similar age to Esja mountain north of Reykjavik. It would seem Krysuvik is an ancient system, likely all the Reykjanes volcanoes are, but they are kept young and active by being on the ridge.

        Both these eruptions were mostly lava floods though, not visibly similar to the activity we see now. That doesnt mean the current eruption cant become like this though, an increase in rifting would do it, and so would the hell machine effect, though that would be gradual so not quite as intense. Still I expect we will see bigger flows than we see now at some point in the near future coming from Fagradalsfjall.

    • Thanks CHAD, very exciting. But, the erupted lava this time is much more primitive, directly from the mantle top. The older hrauns were much more evolved lava, or did I get it wrong? If I got it right, this could mean a very different scenario to expect. And, back to your exciting Hell Machine. How is the stop button acting? Not all Hell Machines end up with siberian or Deccan traps!

    • Great map. Maybe you should make the current eruption another color.

    • That’s interesting and if the currnt cycle starts erupting closer to Keilir, thenyou start to get the same sort of shape, if it lasts long enough or is intense enough to produce the same levels of lava.

  14. “The lava that breached the eastern pass out of Geldingadalir at 10 am today. Looks like something needs to change for it to reach Meradalir.”

    • I’m still convinced that the narrow pinch point at Fissure 1 Smeagol-Gollum Northy-Southy etc controls the lava flowing to the east.
      Since the lava from the newest fissures is the first to flow this way, it will take time to fill in all the spaces and cracks and gas pockets created by the slabby pahoehoe of the very first flow from way back in March.

      I need to go back and find all my posts to get it all together. It might make an interesting starting place for a written piece.
      Looking at that land surface, there is a very slight doming to it, as if this is not the first time that lava has spilled out into a shallow fan at this site.
      The micro topography will be crucial here, just a small dip at the edge of the lava might be enough for gravity to send the whole shebang that way, unable to get the oomph to push for the opposite break of slope.

      So the jury is still out as to which way the lava will fall.

      Which way is the wind blowing? North. Hmm. Interesting again. Now looking at how much shelter from the wind that ridge provides.

      Can any one tell I’m enjoying this? 😉

      • If we’re looking at a prolonged eruptive event ..
        Is there an eventual path SW to the ocean or will this
        flow be content to spill over into adjacent valleys ??

        • Given the production rate, I think any lava flow would stagnate before coming anywhere close to the coast, tubed-over or not.

  15. Test. All coal power plant drag there chimney outlet to 1 vent..

    • I don’t have a link but you can see it in Geldingadalir’s zoom at 11:12:30

      • That’s a different camera, that I didn’t know about. The timelapse in the twitter link above is just across from the Geldingadalir cam, around here

      • Thanks for the link! Just what we needed.

        If you scan the 10-minute interval pictures quickly you get your very own time-lapse ‘movie’. Clearly, the lava field is moving forward at a slow but steady clip. We’ll see how long it can keep it up…

        • There is a button at the bottom – ‘Keyra’. Press that and you get the slideshow.
          If you go up a level:
          You get thumbnails of various available cams. I used to like checking the water levels of ‘JokulsaS’ for some reason (it is in the holahraun area, and runs up past Vaðalda where the webcam used to be.

          • Keyra comes from ProtoGermanic *kausjan, which is a causative verb from the preterite-singular *kaus. *kaus is the O-grade ablaut of the strong verb *keusan which means to choose. The Dutch strong verb kiezen is almost the same as the ProtoGermanic one.

          • @Dawmast

            We have to word “kjósa” which means to choose. “Keyra” on the other hand I’m not so sure about.

  16. Hello – am I here? Do I exist?
    Completelt confused about logging in an no activation e-mail but have managed to “like” a post so something working

    • I’m on my desk pc in its new permanent position, in the left hand alcove, next to the orchids. And I can like and comment. Yay!

      I don’t have a screen to throw the laptop images, yet; but that should be sorted tomorrow when the TV gets rehung above the fireplace.

      One more 6ft bookcase to move, and then Dear Son’s table for his WFH laptop and computer can get put in its place, in the opposite alcove. Then I’ve got to refill the books, rearrange modular furniture into a craft storage/work station behind me, then the downstairs re-jig is almost there. When I have the luxury of choosing pictures from the attic, it will be done. My back aches, but from good exercise, not overstraining.

      • while moving furniture, you may also want to move the discussion to the current post.. not sure how many readers still check past posts for new comments

  17. Some one has come up with an explanation/idea about the thick smoke coming from vent 1?

    • I was wondering if there’s a sort of pizza oven thing going on again, but because the wings of the spatter ramparts wrap around the vents like sand dunes/barchans, we cannot see inside. The angles are wrong for both cameras.

  18. Test:
    I wonder if these flows will develop hexagonal cooling cracks after the fact.

    • Testing.
      If memory serves the conditions for columnar jointing to form are pretty specific.
      The lava needs to cool in a rather extreme fashion to do so.I forgot which extreme if it was fast or slow but I think it was fast, at least that is what makes sense in my mind. I’m sure somebody more knowledgeable will correct me or elaborate further.

  19. Are we seeing a possible undersea eruption off the ridge?

    I’ve noticed uptick on tremor unrelated to the eruption in last few days on charts in that region.

    There is also a concentration of recent quakes in the one spot off the coast of the end of the ridge.

    • Artwork inspired by the ELP album “Tarkus”

      Somewhat appropriate for the landscape now, perhaps?

  20. Great views of the “east exit lava river”. Gives a great overview of both the exit and the scale of the lava-flow. And of course some actual much needed lava-outbreaks up close. Almost perfect, except for the panning towards the people, but he is forgiven! 🙂

    • And some up-close shots of the cones, just as the doctor ordered!

    • It’s astonishing just how high the levees built themselves.

      It took 8 more fissure cones to push the levee to breaking point for the eastern exit.

      Shaking my head in amazement.

      Now I really want to see the other two potential breakout valley points. WE could end up with two or three lava flows in different directions.

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