Sleeping in our back garden, part III: the Laacher See and the Younger Dryas

Rough winds do shake the darling buds of May

In the previous posts we looked at the Eifel volcanics, the Laacher See (the largest eruption in western Europe for the past 1000 centuries), and volcanic dating of the Younger Dryas. The eruption occurred a bit over a century before the sudden cooling. But what caused that cooling?

Let’s go back further, to the depth of the ice age long before the Younger Dryas. In the middle of the ice age there were multiple rapid warmings followed by slow cooling. They called Dansgaard-Oeschger cycles (no, this is not the name of a plant); at least 25 of these spikes are recognized in the ice core record. In each spike, local temperatures would rise by as much as 10C. They were most common during the period between 60,000 and 30,000 years ago, but were rare during the coldest phases of the ice age.

The fact that they are seen so well in 18O shows that they started with warming of the ocean. The events also coincided with strongly increased iceberg activity, perhaps caused by the warming water destabilizing the ice pack. The precise cause remains disputed. A popular option is that melt water from the glaciers disrupted the ocean circulation. Another is a change in wind patterns, induced by the height of the glaciers (a 3-km tall ice cap adds a substantial barrier to the air circulation!). Either way, the suddenness of the changes indicates that there was a significant instability in the ice age climate.

The fall of winter

Now is the winter of our discontent

The Younger Dryas resembles a Dansgaard–Oeschger event – but in reverse. Instead of rapid warming, it started with fast cooling. It also lasted longer, and while during a Dansgaard–Oeschger event there is a slow temperature drop during the (typically) few hundred years of (relative) mildness, the Younger Dryas showed a slow re-warming. Both events show a very sudden end, in the case of Dansgaard–Oeschger a temperature collapse back into deep ice age, and in the case of the Younger Dryas an almost instant warming. Really, it was nothing like a Dansgaard–Oeschger event.

The plot shows the comparison between the events. The Younger Dryas as seen in the Greenland ice core record is shown by the bottom curve, as the black dots. The axis is labeled in thousand years. The sharp cooling just after 13,000 b2k is visible, followed by a bit of recovery, and finally a very sharp rewarming.

The lines above it, using plus signs, show three ice age events. Obviously they happened much earlier than the Younger Dryas: they are shown shifted in time. They also were colder: the δ(18O) of these events has been shifted upward. Otherwise they fall on top of the Younger Dryas or below it.

The top two show two long-lasting, one starting around 43,400 and the other one at 38,200 (all in b2k). While most Dansgaard-Oeschger events lasted some 500 years, the longest such events were of similar duration to the Younger Dryas.

The lower of the three lines shows two faster Dansgaard-Oeschger events. The first one begins immediately at the leftmost of the line (which was 34,700 b2k) and ends 700 years later. The second one begins 1200 years later and lasted 400 years. By coincidence, the time between the events looks just like the Younger Dryas: fast cooling followed by rewarming 1200 years later! Perhaps the sudden warming at the end of the Younger Dryas was itself a Dansgaard Oeschger event, where the warming just didn’t end.

The quick repeat of Dansgaard Oescher events was not uncommon during the ice age. I found 10 such ‘pairs’ in the record which were separated by typically 1000-1400 years. This seems to be a common time scale.

Causes of climate change in extremis

Weary of solid firmness, melt itself
Into the sea

The Younger Dryas was an ecological disaster in Europe. Interestingly, the southern hemisphere survived much better. There was no cooling there, and in fact temperatures increased. The Younger Dryas was only in the north. It certainly wasn’t the Sun. It is a bit of a diversion for this post, but it is an irresistable question. What did cause the Younger Dryas and why did it end so sudden?

The favourite explanation for the Younger Dryas relates to a huge lake (‘sea’ is more appropriate) of melt water that had collected at the edge of the North American ice cap during the years of warmer weather. It was contained by a combination of a depressed surface (which was only just beginning to recover from the weight of the glacier) and an ice barrier. Ice barriers are a bad idea in an era of warming. It melted and collapsed, and the lake suddenly emptied into the North Atlantic. Think jokulhaup on a continental scale. Cold fresh water now flooded the ocean. ‘Flooded’ sounds a bit strange (how do you flood something that is already water?) but it is actually the right word. The fresh water was less dense than the salty sea, refused to mix, and remained as a layer of fresh water on top of the ocean of salt – a reverse margarita. It caused chaos.

The North Atlantic is a source of heat for Europe. The salty Gulf Stream brings in the warm water. Here it gives up its warmth to the air and cools. As it cools, the water becomes more dense, and it sinks. This sinking pulls in the next batch from the Gulf Stream. But now there was an insulating fresh water lid on the sea, less dense, which refused to sink. This stopped the Gulf Stream from coming north, and the North Atlantic plunged into deep freeze. 1200 years later, the Gulf stream restarted and the north suddenly rewarmed.

This explains the onset of the Younger Dryas well. But the sudden end has received much less attention. What made the temperature rise so fast, by 10C in a few decades? And why did it last for 1200 years? How could a fresh water lid last so long?

And how about the Dansgaard-Oeschger events which look like an inverse of the Younger Dryas? Were they caused by whatever ended the Younger Dryas, and did they end by with renewed failure of the Gulf stream, in just the opposite sequence of the Younger Dryas?

The answer is most likely in the ocean. But where?

The main suspect is the Labrador current, around Newfoundland. It comes down the west coast of Greenland and floods the ocean with ice-cold water. Fish love it. The Gulf stream has to find its way around it. The idea is that the failure of the Gulf stream after the fresh water flood allowed the Labrador current to expand southward, taking the polar front with it. The Gulf stream found its territory occupied and decided to go to Spain rather than Scandinavia. It took 1200 years before the battle lines shifted again.

There is some evidence that around Newfoundland, there was a slow rewarming of the ocean starting a few hundred years before the end of the Younger Dryas. The Gulf stream was slowly re-invading the occupied territory. At some point it pushed the Labrador current back far enough, re-established dominance, and started flowing north again. The Younger Dryas now suddenly ended.

This puts the cause in the ocean circulation, with a slow strengthening of the Gulf stream. There are other indications for this, which show changes in the tropics around the end of the Younger Dryas.

The main model is that the weakening of the Gulf stream warms the southern Atlantic (south of 20o north), because less tropical warmth is now transported to the far north. This restrengthens the Gulf stream and normal service resumes. But that would predict a relatively fast response, where the cold phase is short-lived. Instead it lasted for 1200 years. And this same time scale shows up in the times between Dangsgaard Oescher events.

There is a possible cause in the deep ocean. The water that sinks in the far north forms a new, icy cold current on the bottom of the sea. It follows the bottom of the Atlantic, skirts Antarctica (where it collects even more cold water), moves east and finally turns back north into the Pacific. In the north Pacific, close to Alaska, it resurfaces, now as a warm current, having picked up heat from the tropics. Another branch does the same in the Indian ocean. The surface current retraces the path and ends up in the Atlantic where it closes the cycle.

This is called the ‘conveyor belt’: it is a major contributor to cycling heat across the globe. The full path takes around a millennium. Close down the cold water input in the North Atlantic, as happened at the start of the Younger Dryas, and the southern and Pacific ocean get less cold water coming to the surface. They become warmer, and send this excess heat back to the Atlantic. After a millennium, like an exceptionally late echo, this heat pulse begins to arrive. It strengthens the Gulf stream, which now begins to push back the invader. It takes a few hundred years before it becomes strong enough to re-occupy the north Atlantic. Sinking resumes, and the Gulf stream again become self-sustaining. Like an ice age Baron von Munchausen, it pulls itself up (or rather, down) by its bootstraps. (In the original story, it was actually by his own pigtail. That never caught on.)

In this model, the cause of the rapid cooling is above water, but the rapid warming comes from the deep, and an ocean away.

GLENDOWER: I can call spirits from the vasty deep.
HOTSPUR: Why, so can I, or so can any man;
But will they come when you do call for them?

The missing eruptions

Let’s go back to the Laacher See. One of the mysteries of this eruption is that it is missing from the Greenland ice record. Other eruptions left their trace of sulphur and sometimes tephra. But no such spike coincides with the Laacher See. How is this possible, seeing how much tephra was distributed over Europe? A VEI 6 in Germany should have shown up there. Was this an accident, with the winds blowing in the most unfavourable location, not even reaching Greenland the long way around? Was the eruption perhaps smaller or less dusty than we thought? (Hunga Tonga, the largest explosion for almost 140 years may leave no trace in the ice because it put its energy mainly into putting water into the atmosphere.) Or did we just look in the wrong place? After all, we had our times wrong for the eruption by more than a century.

The main volcanic marker of the time is the Vedde ash. It dates from midway through the Younger Dryas, is seen across Europe and parts of Russia (deposits in Norway are up to 50cm thick), and came from Katla. The origin was determined from the basaltic and rhyolitic composition. (Yes, that is correct. It produced both, probably within days of each other.) The ash is not present at Katla itself, which was probably thickly glaciated at the time, but it is found in north Iceland, as the so-called Skógar Tephra. There is another rhyolitic ash layer from the Younger Dryas which was found (of all places) in Abernethy forest in Scotland, is a few hundred years younger but has similar composition and is also attributed to Katla.

There are four other ash layers in Greenland which are slightly older than Vedde but date from the Younger Dryas and just before it. One occurred less than a century before the Vedde eruption, was rhyolitic and has the same composition as the rhyolitic component of Vedde. It is also attributed to Katla, as a precursor hickup to the big event.

The next older one is extremely rhyolitic and low potassium. There is no known Icelandic source, but it may have been North American.

An eruption from the early part of the Younger Dryas left a basaltic ash layer. It is called ‘Tv-1’ (no idea why) and is attributed to Grimsvotn.

The last one was shortly before the Younger Dryas and has been seen as the Laacher See deposits. It was at about the right time. However, the chemistry rules it out. It has similarities to Hekla, but this volcano may not have existed at the time.

But most volcanic eruptions in the ice have no tephra in them. Instead we see the sulphate from the emission, which can travel much further than the ash. Below is a plot of sulphate spikes seen in the ice in the time just before the Younger Dryas. This is from Abbott et al, 2021, Quaternary Science Reviews, 274, 107260. The dark orange is the date range for the Laacher See, and the light orange the time before the drastic cooling.

There are several sulphate spikes, including two large ones. There are in fact 8 detectable spikes in the light orange zone. The very strong spike in the dark orange band is dated to 12,980 BP and would seem a very good candidate. However, it is also seen in Antarctica and therefore appears to be a tropical eruption. The same is true for the strongest spike, at 12,871 BP, which is also too late for the Laacher See. Five eruptions are in principle possible counterparts of the Laacher See, including the one we just ruled out. The other four have a very weak sulphate signal. Three of the four have a weak signal in Antarctica. The final one is dated to 12,985 BP (note: add 50 years for B2k dates), and is the most likely counterpart of the Laacher See. It is not impressive, but it is there.

Now all we need to do find some tephra in this ice core layer.

But this was too easy. Models for the eruption predict a larger sulphate deposit than found for this eruption. That is true even for low estimates for the total sulphate emissions. The large spike at 12980 BP would fit, and in fact the models suggest some of the sulphate will reach Antarctica, 5 times weaker than the signal in Greenland. This is about what is seen. So this suggests that the large spike in the dark orange band may be it, after all. Who said science was decisive? Any of the five could still qualify!

The large spike does in fact have some tephra in it. I have already mention it: it is the one with Hekla-like ash. This seems to rule out the Laacher See. However, there is an indication that the sulphate signal was a double peak. In that case it could be a combination of the Laacher See and another (Icelandic?) volcano. We may never know.


It is notable that there are four significant eruptions in a 110-year period, two of which were rather large (Tambora size). Both the large ones were probably in the northern hemisphere although not as far north as Iceland. The largest one was 25 years before the onset of the Younger Dryas. It was an impressive cluster of eruptions!

Abbott et al discuss whether this cluster could be the cause of the Younger Dryas. They decide against this, because of the 25 year delay. But could it have provided a push? Remember the Greenland Viking colonies? Their demise coincided with significant eruptions. It turns out that sea strait west of Greenland can cool dramatically after an eruption. Whether this pushed the settlements over the edge is something we may never know. Did the cluster make the warm climate of the time unstable, and thereby sowed the seed for the catastrophe of the Younger Dryas? The authors says that it is unlikely to be the sole cause, but that it may have acted as a trigger.

We have not found a single culprit. The consistency in time scales between the Dansgaard-Oeschger events and the Younger Dryas suggest ocean circulation is a major part of the puzzle. It may explain especially how it ended. A series of volcanoes, including the Laacher See may have provided conditions in which the Younger Dryas could erupt on an unsuspecting world. The 25 years delay makes this far from certain. But if it did, the Laacher See is co-responsible for one of the largest environmental crimes of the ages.

And it may tell us something about the fate of the Viking settlements. But in the end, catastrophes do not have single causes. Triggers only work if conditions are set.

The fault, dear Brutus, is not in our stars, but in ourselves

Albert, May 2022

Remember this? Will we get an encore?

100 thoughts on “Sleeping in our back garden, part III: the Laacher See and the Younger Dryas

  1. I can’t find Skógar in Tephra Base. Does it possibly have another name?

    For All: If you poke around there, you can find geochemistry for several tephra deposits…. even down to which eruption it was a part of. Tephra base is a storehouse of tephra information. Any specific use of that data should refer to the original author(s). They can be found in the Tephrabase references.

    • I just noticed the dates range from April 21 to May 8, so there’s one week of deformation missing here. There will probably be updated maps in the coming days.

      • Will probably keep going until a crack opens that connects to it. Then we get an eruption in very short order I expect.

    • Yes, looks like another sill is growing in the same location as the 2020 Thorbjorn sill. It doesn’t look likely to me that there will be an eruption here. Most likely the sill won’t attempt going towards the surface, just like the one in 2020, or the sill at Kilauea in 2021, or the sill at Askja also in 2021. In the future there may be a dike intrusion which will feed from the sills, and erupt onto the surface. At least that’s what I think.

      • I mean I don’t think an eruption would happen as an immediate consequence of this intrusion. Because it’s a horizontal sheet of magma, a sill. Of course in the future, months or years from now, it may eventually happen.

  2. Map of Reykjanes, showing the elevation of the various landforms on the peninsula as well as the vents of the last cycle. Generally speaking it is quite obvious that the biggest overall volume is found south of Reykjavik, at Brennisteinsfjoll and Blafjoll volcanoes, which might be one system or separate systems. Hengill is taller and more prominent but the volume of lava erupted seems less. Krysuvik looks like it was once a more substantial mountain that got torn apart by rifting. Fagradalsfjall is sort of like a mini-Brennisteinsfjoll, a prominent if low mountain. West of there it is basically dead flat at near sea level.

    Still some of the lack of prominence might be because Hengill, Krysuvik and Svartsengi erupt fast so the lava flows a long way in a flat sheet, instead of building a shield or a large cone. I imagine given the large flow fields made of distinct a’a flows that the big eruptions at Brennisteinsfjoll would have been a lot like the early growth of Pu’u O’o, episodic fountains with high effusion rate but not continuous so overall rate of eruption is low.

    • The shape of Krysuvik, two large elongated ridges is because of fissure eruptions. When a fissure eruption happens underwater, or under a glacier, the ejecta piles up near the vents, making a ridge which is known as a tindar. Tindars in Krysuvik make two parallel complexes Trolladyngja and Krysuvik, and in between runs the valley of Mohalsadalur. It can be seen that the area has been producing powerful fissure eruptions for quite some time, extending well into glacial times. Tuyas are absent in the Krysuvik area, they form when a shield erupts under a glacier. Tuyas are however common in the areas of Fagradalsfjall, Brennisteinsfjoll, and Blafjoll.

    • Also here is a map that shows all of the vents that were active around 2000 years ago, in the previous Reykjanes cycle before the middle ages.

      This one also seems to have been almost entirely fast eruptions, Brennisteinsfjoll was weakly active and there was a major fissure from Hengill which is a relative rarity. Not sure of the total volume of this episode compared to the Reykjanes Fires but Nesjahraun north of Hengill is about 0.5 km3, and was only half of that total eruption which also created Hellishieldarhraun on the south side of Hengill, so possibly a 1 km3 eruption, maybe near the upper limit for the area today.
      Krysuvik was similar to its historical eruptions, being that it also did a large lava flood of similar sclae and extent to what happened in the 1150s, but the activity further west at Svartsengi and Reykjanes that dates to around 2000 YBP seems to have been larger than it was during the middle ages.

  3. That millennium delay would accord with the thermo-haline circulation time…
    Correlation does not prove causation but, IMHO, the time-line and circumstantial evidence fit like a tailored suit…

    FWIW, Australian plate is trundling N-NE at a couple of inches per year. What happens to the Indian Ocean branch of thermo-haline when the inter-island pass is pinched off ? I’ve read that is just deep enough to stay open during glacial low-stands, but a continental plate’s inexorable advance is a different matter…

    Like Panama closing or Drake Passage opening, there will be far-flung consequences…

  4. Fascinating article, Albert. Than you very much for it. I’m looking forward to re-reading it to pick up pieces that I missed in the first pass. Some of the literay allusions zipped over my head while running through it the first time.

    • PS: Whether it’s Calvin & Hobbes or Shakespeare, the outside-the-box comments are both entertaining and illuminating. I’m a fan.


    Video about the very recent activity. There have been a lot of earthquakes under the Sundhnukur craters, which are shown well here. The larger quakes were under Eldvörp but that is not really where the majority of quakes are. Just this past hour there have been quakes at this location actually.

    The inflation from 2020 to now is not huge but then the eruptions on Reykjanes are caused by direct mantle intrusions. We saw from Fagradalshraun and also on La Palma that the intrusion need not be particular large to end up with a substantial volume when the eruption comes from the mantle. Only difference now at Svartsengi is that magma seems to get stuck and form sills first before erupting, so can build some pressure. I recall reading that Svartsengi has inflated a number of times in the last 20 years so there might be a lot of magma down there and the mantle will be decompressing now a cycle has begun.

  6. The Krisuvik Highpass is looking rather noisy this morning. And the tremor chart is…interesting.

    • The earthquakes are picking up again but have moved to the other side of Grindavik, close to a hill called Hagafell. That does not mean that the magma intrusion has moved: it may just be a fault that is feeling the stress from the nearby inflation. But if it erupt there, Grindavik would be directly in the firing line. It is only 2-3 km away and the lava might well follow route 43 into town. Time to build the barricades? They worked well at Fagradalsfjall

    • Would you expect any signal/change at the HS Orka plant prior to the eruption if it happens near there? It seemed like the Puna Geothermal Plant did not have any change in output that I heard of before the 2018 eruption, but this magma intrusion is coming up more generally from below rather than draining from an uphill source through channels.

  7. That large spike at 12,985 bp has been my volcanoholic obsession for years. I posted this graphic to the old volcanocafe blog 10 years ago (!).

    Carl mentioned multiple times that he was fairly certain it was the theistareykjarbunga eruptions combined with being close to Greenland, yet the idea that this was a multipolar eruption seems to refute that. Question is whether this eruption was concurrent with a independent southern hemisphere eruption or if this was sourced from the same eruption.

    I added a few labels for comparison. Note the So2 size difference between this eruption compared to Toba / Taupo in the past. Keep in mind, that while this shows the magnitude of whatever happened at this time, it likely is underplaying the true So2 emissions from these eruptions since the intervals for taking the records in the Gisp2 series has larger gaps the further back you go. IE: after a certain amount of time, records are only taken every 5 years, or every 10 years, instead of every 2 years. This means that the records for the largest eruptions in the distant past only capture the So2 after it had been significantly sequestered from the atmosphere.

    All that said, there is an absolute whopper of an eruption that we have absolutely no clue about. That I think warrants more attention and research than it has received (to my knowledge).

      • Could it be one of the Japanese calderas? Kussharo for instance.
        Just thinking would have to be northern hemisphere and there are more caldera eruptions there than anywhere bar TVZ.

        • Personally, I doubt its one of the Japanese calderas. Those are all pretty well researched and I don’t think it would be quite so unknown. But I wouldn’t totally write off the possibility.

    • Theystareykjarbunga was a lava shield, an event that probably lasted many decades if not centuries. No way it was the cause of that spike. Probably is not even going to register in Greenland at all. There are some very big calderas in the Aleutian chain, as well as Kamchatka and Japan, and some of those especially those extremely remote are probably not dated accurately. Being on an island in a time when the sea level is changing rapidly is a good start.

      If I wanted to be annoying and talk about Hawaii, the Pahala ash sequence has got some huge eruptions, and stops around that time. It is also relatively subtropical, so might be far south enough. Obviously we know Hawaii basalt is basically the same as Icelandic basalt, both high in sulfur by weight… 😉

      Being serious though I think in a lot of cases Iceland is maybe getting a bit too much credit on these signals, you need fast powerful eruptions. Iceland maxes out at about 30 km3 for both lava floods and tephra. There are many calderas of probably Holocene or late Pleustocene ages that are way bigger than that, all it takes is one of those.

  8. Has there been any update on the activity at Askja, or do we have to wait for the snow to melt? There are constantly a few earthquakes on the map. Some years ago any earthquake there was noteworthy. Since summer last year there is much more activity now, I guess the intrusion is still alive and kickin! An update on the uplift would be especially interesting.

    • Olafsgigar is online again! The inflation is still ongoing. Not that fast as in september though.
      Stands out that the uplift is quite local, measured in the caldera only.

      In research the 75 cm (cm!) subsidence at Askja in the period 1983 – 1998 has been interpreted as mostly a result of magma solidification at depth and part of the subsidence may be attributed to the location of Askja on the divergent plate boundary and drainage of magma into the Askja fissure swarm as well. Changes in the shallow magma chamber at 3 km depth could cause such subsidence.

      Likely that shallow chamber takes in fresh magma.

      Credits graph IMO

      Interesting gps pages to follow

  9. Calm before the storm.

    Although the last 2 years to be fair have been volcanically busy.
    Expect Grimsvotn to erupt soon as the weather warms.

    • New swarm just starting northeast of Grindavik, 1-2 km due east of the Blue Lagoon.

      • Curious that it’s either quakes or tremor. The same pattern is evident on several SIL locations.
        Here is BJA as an example.

  10. While the tourist volcano rumbles, an actually dangerous volcano in Indonesia is having an earthquakes swarm on May 10, the volcano Awu has had 200 deep earthquakes and the swarm has shown no signs of slowing down. This volcano has had a history of producing bad PDCs and lahars so it should be taken very seriously.

  11. While we all are waiting, “just icelandic” have published a good video for those who want to familiarise with the area around Grindavik and the old eruptions in the area.

    • Thanks Ulwur for posting that link. It was a very informative video about Grindavík and it’s surroundings. Putting things into perspective, quite literally through those gorgeous drone videos.

      Also a good source of “before” videos in case an eruption should occur in one of those locations.

  12. Something I noticed, along the south side of Reykjanes going from right east of Hveragedi to south of Kleifarvatn is a very obvious steep cliff, in part buried by an early Holocene shield about at its middle length. Is this an old shoreline or a fault scarp?

    Some of th eruptions from Brennisteinsfjoll sent a lot of lava cascading down this cliff into the ocean, one that was erupted in the late 900s has even got a channel still. It must have looked like that lavafall down into Natthagi back in late August last year but a lot bigger.

    • I think this is an old shore line, now uplifted due to isostatic rebound and sedimentation

    • Does it look east or west? Most of the quake activity right now is under the Sundarhnukur craters which is east of Thorbjorn, and goes into Grindavik. The quakes the other day were at Eldvorp which is west of Thorbjorn and should be a bit of a safer location all other things equal.

      After looking at the maps of the lava flows though, it is a very high likelihood that the blue lagoon and power plants are going to be taken out. Both of the respective locations flooded that area in their eruptions. The lava of Illhraun that the plant is built on is from 1240 🙁

      • The intrusion is not over, but is migrating back and forth along the Reykjanes fault. Looking for a way up. This morning’s swarm was back to the northwest of Grindavik

        • Or that’s how the fault responds to the pressure from magma.

      • The JPL programmers can do miracles with remote fixing of the spacecraft. A somewhat similar problem 12 years ago in Voyager 2 was traced to a flipped bit which they managed to reset. Hopefully this will be something similar, and fixable.

    • How long did it take to erupt from this depth at the intrusion at Fagra, can anyone remember?
      I remember it moved at about 0.5km a day when it geared towards reaching the surface.

      • The earthquake swarm associated with the magma intrusion which preceded the eruption at Geldingadalir started on 22nd Feb 2021 with the eruption, itself, starting on 19th Mar 2021.

        However, there have been magma intrusions near Svartsengi before this one in the current volcano-tectonic eruption which have not resulted in eruption.

        There’s no knowing what the magma will do until it does it.

        • I seem to recall that Fagradalsfjall first came to our attention in 2017, because of an earthquake swarm there

          • Hasnt there been intrusions at Svartsengi and Krysuvik for a long time? Fagradalsfjall has no magma chamber so nothing to stop the eruption but the actual volume of magma. Krysuvik and Svartsengi have actual magma storage, as does Hengill, that us why they have got significant heat flow. Hengill has got some rhyolite even, so these volcanoes stay hot underground a long time.

            Given the severity of activity now though it definitely looks beyond an inflationary episode and that at least one intrusion is ongoing. I wouldnt expect a swarm as extreme as last year because the ground is hotter and more ductile, and magma is shallower and there is probably a lot more of it.

          • Wow, I completely forgot about those two, back-to-back 2017 articles about Fagradalsfjall and the seismic unrest at that time. Definitely worthwhile to read them again, including the lively debate in the comments.

            Gives us some perspective on the current unrest under Grindavík. If the same time scale would come to play (and there is no guarantee for that), we would see an eruption close to Grindavík in 2026 only…

          • Perhaps 2024.. After all, the Grindavik activity started in early 2020.

          • There were a few >5 magnitude earthquake preceding Geldingadalir.

            A handful of >5 magnitudes may be an indication that an eruption is imminent.

  13. As of a couple of hours ago, I really thought this swarm as shown on VOS drumplot was leading to something.
    But as fast as it started, it’s shut down again.
    But that could change in a hurry…and certainly something to watch for.
    Lot’s of volatility in the “status quo” at the moment fer sure.

      • I’m more and more convinced that the whole riddle is solved once we translate the drumplots into sound files and just listen to it. It will tell us what it is all about.

        • So what does it tell you Quinauberon? I would love to know as I am not to knowledgable to guess.

          • Rejkyanes looks really interesting to me and I really wish for an underwater eruption there rather than severe disruption around Grindavik. My heart goes out to the poor residents suffering such uncertainty currently!

  14. If Awu was a European or North American volcano, absolutely no one would be ignoring it right now. A quick bit of research has pointed to this volcano having a plug from it’s last eruption and with what appears to be a renewed and strong magma intrusion, this has some nasty potential.
    But reykjanes is having a swarm! We might have another small harmless eruption! Now that takes precedent over actually dangerous volcanoes and dangerous situations.

    • I think people here would rather talk about a harmless eruption than how deadly another one probably will be. The problem with explosive eruptions is that they are over before anyone even has time to react. Hunga Tonga was a couple of hours and probably the biggest eruption in a century. If Awu blows up it will be a VEI 3-4 with an extreme intensity, it will probably last only a couple of minutes and anything set up to watch it happen will be destroyed immediately. Effusive eruptions can be of similar intensity but as a liquid lava at least will not rush up the side of a mountain. Lava is also bright incandescent abd visible, where ash is usually not, unless in perfect light there isnt much of anything to see at all.

      USGS put up an archived post about St Helens on the anniversary day after, talking about how sudden and unexpected everything was. That eruption lasted 9 hours at high intensity, and in strong wind so it was relatively safe to get close up to the plinian stage.

      • For me, the spectacle doesn’t matter as much as the impact. To each their own but I find the sight of a large explosive eruption is infinitely more mesmerizing than whatever eruption reykjanes could produce

        • At the rate things are going as we speak, the next eruption from reykjanes will be in the place that is actually called Reykjanes, and in the ocean slightly. If it is anything like the historical record it will probably be at least somewhere up your alley, a fast fissure underwater. Therevwas a VEI 4 in 1226,and an actual proper VEI 4 erupted in a couple of days.

          There is also a possibility Krysuvik could erupt under Kleifarvatn, or Hengill could erupt towards and under Þingvallavatn, both of which could be a borderline VEI 5 and very high intensity, and both have probably actually happened. So its not always tiny lava flows 🙂

        • An eruption near Reykjanes / Svartsengi could be very damaging, explosive or not, if there is enough lava.

          • Awu will always have the edge over any reykjanes eruption when it comes to impact

          • Not sure that is a fair point. Awu doesnt always explode, it erupts lava domes about half the time and then can explode. Most eruptions on Reykjanes are going to be harmless but if something happens at the north end of Krysuvik it will flood the southern part of Reykjavik, an eruption from Svartsengi could rapidly destroy Grindavik. An eruption from Hengill will initially do not much, but could cut off the power to Reykjavik entirely, which is a serious natural disaster and will affect Iceland long term.

            I think you might also be forgetting that the volcano that tops the USGS danger list is one that was considered harmless for over a century. And the biggest explosive eruption in 2 centuries killed no-one. It is not black and white. Awu is also known, it reminds me of Kelud but dry. That one historically was a repeat disaster but its last eruption in 2014 was one of its most powerful yet few lives were lost.

          • Awu has more frequent explosive eruptions over a more populated area, the worst case scenario for Reykjanes and Hengill is bad but not as bad as Awu’s. With more than 20,000 living 10 km away from the volcano. An intense VEI 4 could kill all of those people,

          • There was an article not long ago about Awu. It is a very dangerous volcano that has produced many deadly eruptions before. It has a similar eruption style to Kelut and La Soufriere. It produces extremely powerful explosions in which pyroclastic density currents and lahars spread around the crater killing everybody. I have read about the 1902 eruption of La Soufriere, and some things about the last two eruptions of Kelut, resemblances are very obvious. It alternates with peaceful dome eruptions, like the two others do as well.

            These three volcanoes erupt basaltic andesite magmas but with a high content of crystals, so it has a high viscosity. The melt in between the crystals is more evolved, probably dacite in the three. The eruption style is not due to the composition however, because Anak Krakatau erupts the exact same magma and doesn’t explode at all like Awu and the others do. I suspect it has to do more with the plumbing, or the crater lakes, or both.

            Here is the article:


          • It has to do with the speed of magma ascent. Fast (continuous) rising magma gives non-explosive (fountaining) eruptions. This is because gas bubbles don’t have time to grow. Slow magma (or stationary) cause explosions. At Fagradalsfjall, the explosive phase started when the magma pressure had declined a bit.

          • Think you’ll find that a lot of people live within striking distance to each of Hengill, Krysuvik and Reykjanes too. Reykjanes’s 1226 eruption was a VEI4 – enough to do serious damage to the airport and geothermal plant, if it were to recur. Lahars may be less likely but all the other hazards are relevant.

          • I don’t think it would be too bad. It was off shore, with ash but no lava flows. The airport would be covered under a couple of centimeters of ash, unusable for some days or a week but it would be closed anyway. The plant also should be able to recover. Of course anything with air intake would be at risk of damage – that ranges from engines to humans, but at leats the former are replaceable and the latter can be kept under cover indoors. Of course such an eruption just off the coast of Grindavik would be problematic. But also note that the dominant wind here is from the east, i.e. towards Greenland.

    • I expect that an eruption close to Grindavik remains the more likely outcome. The activity there is shallower and longer-lasting compared to the Reykjanes swarm. Of course no volcano will do as it’s told.

      • There have been swarms at that exact spot near the tip for a few years now

  15. I haven’t heard or read much about Sao Jorge in the Azores lately. Is anything newsworthy going on there?

  16. Seems to have been a M5.8 near the Geographic North Pole and quite a few aftershocks, some of which are M4-5.3.

    Quite an unusual place but I guess it’s no different from anywhere else with plate boundries.

    • In a way, this is still the separation of Europe and America. This is the region where they remain closest together

    • It might actually be volcanic-tectonic. It’s clearly on a Mid-Oceanic Spreading Ridge. It’s around 150-200 km’s north/northeast of Sukan Seamount which was discovered in 2001 by the German Polarstern.

      Glacier melting might decrease pressure on this Mid-Oceanic Ridge for magmatic intrusions i believe too.

      “The ridge is the slowest known spreading ridge on earth, with a rate of less than one centimeter per year. Until 1999, it was believed to be non-volcanic; that year, scientists operating from a nuclear submarine discovered active volcanoes along it. The largest, the Gakkel Ridge Caldera, is a supervolcano that erupted approximately 1.1 million years ago during the Pleistocene.[3] In 2001 two research icebreakers, the German Polarstern and the American Healy, with several groups of scientists, cruised to the Gakkel Ridge to explore it and collect petrological samples. Among other discoveries, this expedition found evidence of hydrothermal vents.”

  17. Such a great article (and ultimately series), thank you for this one Albert.

    I greatly enjoy when you guys delve into the climatology of the past. Endlessly fascinating.

    • Apparently part of the cone has been gradually collapsing and lava has been pouring out from this location. At the same time the summit of the SE Crater is active with strombolian activity, probably because it is degassing the flow that comes up from the side of the cone.

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