Katla: My First Love

/ 12/07/2025

It seemed like yesterday, the day I first discovered volcanic winter while conducting research on the infamous 1993 “storm of the century,” and some passing weather enthusiast had brought up Pinatubo and volcanic winter, and from that moment, I would delve into volcanology headfirst. The first Vixen volcano that caught my eye was the Illustrious Katla volcano. She’s an enigmatic volcano that needs no introduction, the most intense volcano of Iceland, she gave birth to the largest effusive eruption in history, all while producing the most VEI 4+ explosion on the island by a mile. She’s nothing short of a beast, but unfortunately for me the beast seems to be sleepy as of late. Only meager uplift and glacial swarms has been noted at this volcano. For 13 years, I’ve silently watched her, my mind ablaze with desire, my overwhelming lust for her magma and power. Her history has entrapped me, and her potential is beyond alluring. It’s like I was born to see her erupt, made to track her movements, but alas! She’s been quiet (not recently). Do I dare to hope, though? Do I dare to wonder if she’s been silently preparing her return? It’d be a stretch even for me to think so; a mind overwhelmed with a desire is a mind that is not rational. You be the judge…

Over the past 2 months, Katla has been a little noisier with some regular quakes and some decent uplift. The seismic activity isn’t impressive for the volcano, but the uplift is pretty interesting. It’s a bit too soon to draw any definite conclusions, but there is an uplift signal that is seen throughout most of the stations at the volcano with peak rates of around 2-3 cm in June. It remains to be seen if this will last or fizzle. If this leads to anything, it’d probably be another Jokuhallap. For the past 15 years, however, Katla has been relatively restless, experiencing frequent glacier floods, glacier and deep volcanic swarms, and perhaps even small sub-glacial eruptions. Geothermal activity is high but that doesn’t mean that the volcano is building to an eruption; with anthropogenic climate change and strong hydrothermal activity could cause the unrest we see, independent of magmatic activity. The deep quakes could just be part of the normal process with Katla. However, that’s boring! The fun answer is that a series of complicated factors have hidden Katla’s great return to the stage, and the volcano has been preparing one of its largest eruptions ever! Could I prove this statement? no. Could I entertain the possibility and explain why it isn’t an insane statement to say? Yes!

The first thing we have to deal with is the lack of strong deformation with Katla, the fastest average uplift rate for the past 14 years is about 1.1 cm/yr…not very fast. Over the past 4 years, it went up to 1.8 cm/year. Compare this to Grimsvotn, whose uplift rates are 5.2 cm/year; this should prove that Katla is feeling a bit lazy. How could Katla be charging a big eruption with such pitiful uplift rates? Comparing to volcanoes is fun and can be informative, but it’s never absolute, even these 2 siblings are very different. First issue is that Grimsvotn has it easy, the glacier that covers it is only 200 m thick and it has a subglacial lake that is sustained by strong geothermal heat. Contrasted with Katla, whose 750-meter deep caldera is completely full of ice and then some. This fact shouldn’t be understated, despite the intrusion at Grimsvotn being maintained nonstop for 14 years, it always pauses and reverses in winter, and even then, it doesn’t grow as thick as the ice over Katla, thanks to the strong geothermal activity.

With this fact, it’s not unreasonable to suggest that Katla has a heavy hill to climb to produce strong, persistent uplift.

The types of magmatic recharge seem to be completely different as well. Grimsvotn’s shallow chamber is under intrusion, but the deeper system seems to be normal with little seismic activity. Katla, on the other hand, seems to be the opposite. Activity in the shallow chamber seems to be relatively norma,l barring strong glacial quakes; the real magmatic activity seems to be concentrated at 10-25 km at depth. Over the past 14 years, persistent seismic activity at this depth related to magma ascent has been noted. It’s been speculated that this is related to either a deeper chamber or a permanent feeder dike reactivating. Deep volcanic activity doesn’t produce the same strong surface warning signs that shallow unrest does in most cases. For reference, Ljósufjöll may be currently going through a deep magmatic intrusion and there is no deformation at all despite this. If Katla’s deeper system has been receiving significant amounts of magma and its thick glacier, it’s completely possible that we wouldn’t see particularly strong uplift or seismic activity. This deep recharge likely would’ve started after the 1918 eruption, perhaps with some breaks in between.

The fact is, that despite the pathetic deformation, we know that the volcano is awakening thanks to the seismic activity relating to magma ascent. The intensity of this awakening is unknown; it could be a slow and methodical resurgence, and my first vixen won’t do anything for another 20 years. There’s a non-zero chance that this was never the case, and the volcano has been chugging along full steam ahead in its restlessness. It’s no fun, there’s nothing that proves the latter, but nothing disproves it either. In my opinion, it would depend on the nature of the deeper system. If a permanent feeder dike, then I would consider the “fun” option extraordinarily unlikely. Feeder dikes are not magma chambers, and the longer they take to become active, the less of a chance there is for a fun eruption. The fact that it’s taking so long for it to produce an eruption would imply that Katla truly has been sleeping since its last eruption, and its next one shall not be special, as the gears of the volcano would still need some grease.

If the deeper system is more akin to a proper reservoir, then the “fun” option becomes more likely. Magma chambers can undergo massive amounts of magma influx and not erupt. Iwo-jima has been undergoing the most impressive caldera resurgence of the past 800 years and only just started producing magma eruptions in 2022. For Katla, this could mean that the supply to the deep chamber over the last 100 years hasn’t decreased at all; instead, the shallow system temporarily got a pause while the deeper chamber system got all the magma. Resulting in an overpressurized and primed loaded gun just waiting to be unleashed. Either Katla has spent its 100-year pause taking a break from being Iceland’s biggest firework and intends to wait even longer or it’s been spending 100 years preparing for one of its larger shows.

Unfortunately for my first Vixen, I shall lean to the former. There is simply not enough evidence for the “fun” option. It’s possible, but still firmly hypothetical. The only 2 things that could super-maybe, kind of, slightly hint at the “fun” option are the facts  that the geothermal activity has always been high at this volcano, and it’s still steadily increasing. Katla is a prolific CO2 producer, being responsible for an incredible 4% of the global volcanic CO2 emissions.  But that’s not concrete enough for me to come out and say Katla is about to go crazy. We’ve got no good measurement of how strong Katla’s geothermal activity or CO2 emissions were before the 1918 eruption, and for all we know, what we’re seeing now could be weak in the grand context of Katla. Unfortunately for my first vixen, I’ve got all the other volcanoes. After spending 12 years waiting and hoping, I’ve moved on in a way. My time with Katla is a hobby, and she no longer occupies my thoughts like the past. Chiles-Cerro Negro, Grimsvotn, and Ioto have stolen my gaze and they never disappoint with their constant and incredible unrest. Another swarm building, Strain accumulating, and an extremely complicated situation at each of these volcanoes, respectively, will continue to steal my attention away from my first vixen. Still, I can’t help but hope a little for my dearest Katla, to remind the world why her name is special. Maybe, just maybe…

Tallis, July 2025

The ice-free caldera map of Katla. This view is from the southwest. Image from Helgi Björnsson et al, 2000, Jokull 49, 29 (https://www.researchgate.net/publication/285499559_Surface_and_bedrock_topography_of_the_Myrdalsjokull_ice_cap_Iceland_The_Katla_caldera_eruption_sites_and_routes_of_jokulhlaups).

For further reading, we refer to Henrik’s post from 2012 which was reposted and updated in 2023 when Katla last showed unrest:

katla: a retrospective

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218 thoughts on “Katla: My First Love”

  2. Heatwave in Scandinavia localy 25 – 32 c in some local spots with very high humidity, really Im litteraly DYING in only +26 c. Seeing Kuala Lumpurs 37 C makes it impossible for me to live in a equatorial place or even in Big Islands lowlands

      • The lowlands can get to 34 C in the shadow at the drier spots add in that with high sea humidity that feels like being inside an oven sauna combined with a blowtorch over your head when you walk in the sun. I only finds Kona side attractive due to the lovely warm clear ocean and peaceful small town life and Hawaii Volcanoes National Park on the other side acessible by road .. otherwise the tropical sickening humidity in both Hilo and Kona and the hot sun is repulsive.

        Upslope its much cooler and more pleasant for soure but almost none live upslope on the Big Island excluding a few small farm towns on Kilauea and volcano village

    • It was a bit torture of waiting for Kilauea, but now it’s begun … without an explosive beginning. Until now the lava fountain is relatively low, but more can follow.
      I’m not sure whether the eruption only happens on the old crater or also on a second opening.

      Prior to the onset of the episode were some quakes on the greater caldera rim. Maybe they indicated a flow of magma.

    • A beautiful cumulus plume above Kilauea:

      The volcanic heat source causes a uplift of air in which steam condensates like in a weather cloud.

  5. Even at the very early stage where there isnt even a real fountain yet, the lava is really flowing fast down the side of the cone. Its been seen a million times by now but the crazy low viscosity of lava in Hawaii is always a delight to watch. When it was measured on pahoehoe from Pu’u O’o in 2016, it was about twice as viscous as maple syrup, and that was degassed lava probably about 40c colder than the stuff now. Todays lava is probably half that viscosity, it moves like a true liquid.

    https://www.sciencedirect.com/science/article/abs/pii/S0012821X18302310

    • Summit magmas are likey as fluid or more fluid than Nyiragongo even simply because Kilauea is a very hot basalt lava, at halemaumau over 1200 c so almost all polymerization is broken down of course at high temperatures the Sio2 does not matter that much at all. These lavas when they drain away from a vent also forms these paper – thin sheets seen at Nyira as well

    • How well matches the tremor with the time of onset of the episode?

      ?fileTS=1753025238

    • I dont think there is much diffrence between Halemaumau and Nyiragongo in their erupting surface lavas they are both VERY fluid mantle melts. Kilauea is hotter, having higher supply and potentialy much more fluid at depth where the lavas are even much hotter but its not the eruption temperatures

      • The speed of Nyiragongo’s lavas is very high, faster than humans can run. 1950 Mauna Loa did 24km/h, that’s also faster than most humans can run in a 100m sprint.
        1977 Nyiragongo’s lavas had 100km/h. They probably had the advantage of steep slopes during flank eruptions. And alkali magmas can sometimes be very fast. Vesuvius did sometimes Nyiragongo’s style.

        • I dont know if that 100km/hr number is absolutely verified. 2021 drainout was in the same place and had similar flow but the lava was never reported to move that fast.

          Very fast lava flows have also been seen on recent video at Kilauea, La Palma, Reunion, Etna, Reykjanes and multiple in the Galapagos. The very first hours of the filling of Halemaumau in late 2020 saw lava cascading into the lava lake from the vent, and it was clearly flowing almost as fast as the lava was freefalling out of the fountain, which is probably at least the fastest lava flow that a video actually clearly shows. But in general all of the fluid volcanoes like these have comparable viscosity, so its hard to pick a clear winner. It would be easy to just pick the steepest, but they all actually have steep slopes to some degree…

  6. If you zoom in on V3, lava is flowing out of many cracks in the cone besides the fountaining vent. Its flowing directly out of the top of the previously very stable structure in front. The fountain is also very inclined in two directions.

    It looks like this lava is still relatively degassed, or the vent is blocked and that is obstructing a tall fountain. At some point soon it might just all blow sky high.

    Seems the other flowing spot is silent, maybe not a real vent after all.

  7. Was about to say this but there are new vents appearing near the cone. One near the north crater edge and now another that is visible. I think the pressure is too much for one to hold…

      • The tephra slide has clearly affected the cone. The only fountain is now pointing sideways, spraying lava uphill. The lava flow is quite spectacular. It will be interesting to see whether the change is permanent or not.

        • I dont see it permanently altering much, but it could take some time for the vent to reorganise. I guess, at Pu’u O’o it took 2 episodes to sort out a similar collapse in late 1983, although it took months in real life as Pu’u O’o had much wider spacing between episodes.

          It is pretty likely that whatever overhang is diverting the fountain will fall in after it is done. Or eventually one of the many vents in the north crater will just melt out the obstruction.

          Maybe there will be a phase of moderate fountaining building up the spatter cone again until it is completely clear and then it goes sky high again, alternating spatter cone building near the vent and getting taller with huge fountains building the surroundings up around it, repeat until the caldera rim doesnt exist… If the cone builds up I put it a likely chance tge south vent also erupts again, its alive and degassing just not open enough to erupt from. But its too early to say it is gone yet.

        • I guess, its also a perfect demonstration of why this kind of pyroclastic cone is called a cinder-spatter cone, it is exactly a combination of both if those features. It was building a cinder cone recently, but it was too low still and got buried when the cone collapsed on it. Now it is building a spatter cone.

  9. Erta Ale did collapse and have a new flank eruption the other day.

    https://www.volcanodiscovery.com/erta_ale/news/275845/Erta-Ale-volcano-Ethiopia-dramatic-changes-to-caldera-and-new-lava-flow.html

    Not particularly big though, but the flank vent is far away down to the south and possibly on the same fissure as 2017 but beyond it. If it becomes another long lived flank vent again will be interesting. The 5000 MW thermal signal must have been either an overflow right before collapse (same as 2017) or the collapsing north crater exposing a lot of incandescent material.


  10. (B1, live)

    Seems the lava has gotten very close to the other side. Maybe the low fountain helps with the lava volume.

    • Yes low fountains or fountains falling into a lava pond keep the lava fluidand it flkws a long way. Fountain fallout cools down a lot and the lava flows are basically as viscous as a much more evolved magma. It was really obvious at Pu’u O’o there it sent lava as far as 14 km away but also as few as 3, roughly same volume and magma.

      Thing is this episode probably keeps up the trend of the last 7, large volume high intensity, but fountains kept low. The tiltmeter hasnt even fallen half of what it might be expected to.

      • Maybe this might be a norm for a bit until either the slump stabilizes, the blockage is clear or the vent becomes elevated. In that time, it’ll expand the field by filling the east end with lava. Once the tall fountains start again, the lava flows would shorten again but the cone will construct again…

  11. E29 completed, and 19 microradians of tilt change, probably the biggest since E3. If the other episodes are a guide, then the volume is probably close to 10 million m3, and most likely at least 7.

    E30 might not be for a while, probably not until late next week. But this could be a trend that sees wider intervals and much larger episodes, both in volume and intensity. The pressure to erupt is getting higher, so when it does go there is more force. Its 80 meters higher than at tbe start of the year.

    • HVO counted 14 hours and estimated 7 mio cubic m.
      The lava fountain was lower than previous episodes. Was the rate lower, but total volume appr. the same?

      During the eruption the cone looked like a real shield volcano. The soft slopes of the shield volcano grow faster & higher than other parts of Halema’uma’u. Lava flows ran towards the east, where they allow the volcanic shield to grow and increase stability of the structure. That’s different to the fallout of previous fountains that took a SW direction outside the caldera with a bad stability of the volcanic cone.


      https://bigislandnow.com/2025/07/20/precursory-low-level-activity-is-ongoing-for-episode-29-of-the-halema%ca%bbuma%ca%bbu-eruption/

      • The low fountain is the cause of all the other stuff, the lava doesnt cool falling out so stays fluid. The eruption rate is only slightly lower with those numbers.

        The huge area of flowing lava also meant there was an enormous heat emission, twice showing a reading of 11.5 GW during E29.

        • During the lava episode, the lava fountain was rather a lava falls event. It resembled the Rhine Falls of Schaffhausen https://rheinfall.ch/en but with lava 😉
          The Rhine Falls do on average 373 cubic meters per second of water. It is above the eruption rate of episode 29 measured for all 14 hours, but during peak activity the eruption rate of Kilauea was probably close to the Rhine Falls.

          The episode was predominantly a Pelean-Hawaiian eruption. Lava left the vent horizontally and fell down into the caldera. It was the effusive version of explosive versions (f.e. St. Helens).

      • What woud Kilaueas landscapes look like If Big Island where at the antartica ocean close to the continent? Puu Oo woud be a giant tuya formation in a glacier? Halemaumau maybe icecapped nearly completely during the less active hot periods ( 1982 – 2007 ) ?

        • Before Holocene Iceland probably looked a lot like this. A great glacier island with all the volcanoes below the ice. That’s the way all the peaks and hills of Fagradalfjall, Svartsengis, … were created. Below the glacier lava behaved different to normal lava eruptions.
          Maybe during glaciation also Mauna Loa had some temporary glaciers that were lost quickly afterwards. Mauna Kea has evidence for glaciation, but is not much higher than Mauna Loa. So it seems credible that Mauna Loa did subglacial eruptions like Grimsvötn.

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