Living dangerously: a Grimsvotn prediction

Grimsvotn 2011.

Grimsvotn (‘Grim’s lakes’) is Iceland’s secret. Of all its volcanoes, this is the most frequent erupter, exploding as often as every 5-10 year. It also causes jokulhaups with decadal frequency. And worst of all, it is a mass murderer, which has killed as many as a quarter of Iceland’s population. And all of this is done from its hiding place, like a troll living underneath the immense ice sheet of Vatnajokull.

The Grimsvotn calderas. The location of the recent eruptions is indicated. Source: Benedikt Gunnar Ófeigsson, 2013

There are three, overlapping calderas. This fact alone already shows its potential: Grimsvotn does not do one-off eruptions. The central caldera is the youngest, and is the location of the most recent eruptions. But the hole of the caldera doesn’t show on the surface, at least when not erupting. Everything is deeply buried under its blanket of ice.

Grimsvotn is the source of the Laki eruption, 1783-1785, which devastated Iceland, caused major casualties in Europe from breathing sulphurous gases, and caused a famine that lead to the French revolution. In Iceland this international diplomatic incident is known as the Skaftar Fires, after the river valley through which the lava flowed. Laki erupted a staggering 15 km3 of lava along a fissure, far from the glacier: Grimsvotn acted its vengeance from a distance. But it wasn’t completely hidden. During Skaftar, there were reports of fires seen from the area of the glacier. Looking at where those reports were made, and which direction they gave, allows the source of those fires to be triangulated. This leaves no doubt: during the Skaftar fires, Grimsvotn also erupted. And if that wasn’t enough evidence, the Laki fissure points directly at Grimsvotn. It did not hide its tracks well enough.

Fires seen from the direction of Grimsvotn during the Laki eruption. From Thordarson & Self, 1993, Bulletin of Volcanology, 55, 233

The fissure system associated with Grimsvotn extends for over 100 kilometer. Since the end of the ice age, Grimsvotn has produced some 50 km3of lava, a third of which erupted during Laki. About 20 km3 was erupted outside of the glacier (dominated by Laki), and the rest closer to the volcano. How much came from the caldera(s) itself is not known.

I have argued elsewhere, regarding Elgja, that fissure eruptions are driven by gravity: the weight of the volcano pushes the magma out of the chamber. This means that the eruption must occur at a (much) lower elevation than the peak of the mountain, that the caldera which forms from the emptying magma chamber should have a volume comparable to the magma moved out of the chamber, and that the caldera cannot collapse any lower than the exit point. The bottom of Katla is indeed around the same elevation as its main fissure eruption (Eldgja) and it has roughly to right volume. The youngest (currently active) of the three calderas of Grimsvotn is about 20 km2 in area, and 300 meter deep. That means its volume is too small compared to Laki by a factor of 3. However, the caldera may have been much deeper after that eruption. The caldera is at an elevation of 1700 meter, and Laki is at 800 meter. So the caldera could have been as deep as 900 meter, which gives a volume of 18 km3, very close to the volume erupted by Laki. So I think this caldera may have formed during Laki. It is very young indeed.

The magma chamber would have been thoroughly emptied during the Skaftar fires. Grimsvotn has two magma chambers, one 10 kilometer deep and the other one shallow, between 1 and 5 kilometer according to different studies. Over time, the caldera became shallower again (speculation alert), a combination of rebound and refilling of the upper magma chamber.

Grimsvotn has had over 30 eruptions since 1589, on average 10-15 years apart. Tephra deposits show an average rate of 7 eruptions per century during the past 5000 years, with no obvious quiet periods. But after the Skaftar fires, it remained silent for 38 years.

More recently, Grimsvotn has gone through times of (relative) quiet and times of frequent eruptions. There were eruptions in 1867, 1873, 1883, 1897, 1903, 1922, 1934, 1983, 1998, 2004, and 2011, showing a cluster in late 1800’s, and from 1983. The 1873 and 2011 eruptions were large. Eruptions last around 1 week, and they are explosive events from within the caldera, very different from the Laki fissure eruption. The rising magma interacts with the water underneath the ice, which has collected in a subglacial lake within the caldera. (After an eruption punches through the glacier, the lake becomes briefly visible.) The recent eruptions have all come from the southern edge of the central caldera. Eruptive volumes (tephra) range from 0.1km3 in 1998 to 0.7 km3 in 2011.

Grimsvotn lake during the 2011 eruption. Source: (The link gives a vivid description of a mad trip to Grimsvotn during its eruption.) On the photo, the edges of the lake are not the caldera walls but are the walls of ice of the glacier, around the hole burned by the eruption. All the black surrounds is ice covered in ash.

An eruption in September 1996 is not in this list. This was a fissure event from Gjalp. There is some uncertainty where the lava came from. The composition of the lava is closer to that of Grimsvotn, but the earthquakes that preceded the eruption were at Bardarbunga. Given what we now know about the reach of Bardarbunga, it is quite possible the eruption came from there, and not from Grimsvotn.

The regular eruptions should make Grimsvotn one of the most predictable volcanoes. Indeed, during the last two cycles, leading to the 2004 and 2011 eruptions, the behaviour developed very similar, with increasing earthquake activity, and horizontal and vertical motion of the nearest GPS (GFUM, on the caldera rim), until a breaking point was reached. The horizontal motion needs to be corrected for the normal continental plate motion: once this is done, it shows additional motion in the years before an eruption, a definite sign of an inflating magma chamber. Vertical motion shows a pattern of a sharp deflation during the eruption, with a brief exponential recovery afterwards. Once this is done, there is linear inflation, with changes to a faster increase. The linear increase is the steady-state influx of magma into the lower magma chamber, and the faster increase is when the shallow magma chamber begins to refill. Earthquake activity also follows this pattern.

At the moment, earthquake activity at Grimsvotn is on the rise but not as fast as during the previous cycles at this point in time, and GFUM is moving up by 3 cm per year (note that only GPS data from July-September is usable. At other times you get huge deviations from winter weather, including snow on the site.)

The seismic moment (earthquake activity added up over time) is also increasing. But compared to the previous cycles, it is well behind schedule. The current cycle included one unusually large earthquake (unusual for Grimsvotn, not for Iceland in general) and perhaps this one should be discounted as not part of the pattern: it may have released unrelated tectonic stress.

Now let’s see whether we can use the earthquakes to predict something about when the next eruption may occur. I use the standard equation for cumulative damage:

where tc is the time when things break. A similar equation is used by Got et al, 2014: An analysis of the nonlinear magma-edifice coupling at Grimsvötn volcano . (They use it for the number of earthquakes rather than for the earthquake moment).

The Grimsvotn eruptions. Plotted is the cumulative seismic moment (total energy released by earthquakes) since the previous eruption. Sorry for the poorly visible green colour! Click on image for better detail.

The plot shows the results obtained with this equation. Green is for data leading up to the 2004 eruption, blue the 2011 eruption, and red for the current cycle. The data has been read off from the IMO plots and there may be some inaccuracies. I first fitted the equation to the data leading up to the 2004 eruption. The curve fits the data well if I take the numbers tc=2200 days and k=1.2. When I fit the data leading up to the 2011 eruption in the same way, it yields tc=2550 days, and the same value for k. Interesting, the curve suggests that the 2011 eruption happened slightly ahead of schedule, by some 100 days.

We can also now fit the current cycle in the same way. There are two problems with this: the cycle isn’t far enough yet to give a unique solution, and the fit is quite dependent on the single earthquake around day 1850. Regarding the first problem, the range of dates for which the fit is made to work is quite small. That makes is susceptible to noise, random fluctuations in the earthquakes. I went for a fit which works best towards the later dates, where the random noise becomes (hopefully) less important. For the second problem, I have plotted the cycle both with this jump, and without it (the lower red line at the end). Using the same value of k as found in the previous two cycles, that gives me two possible values for tc (noting that both are still quite uncertain!), tc=3200 days including the jump, and tc=4000 days excluding it. Say 8.5 to 11 years. But be aware that the current cycle is still in an early phase and the fit could easily change – it is not yet well determined.

I can take the outcome as the possible range of dates for the time of the next eruption. Starting from June 2011, the early date corresponds to January 2020, and the later date is June 2022. There is a good chance the eruption may occur between these dates.

As a reality check, how does this compare to the past? In the eruption sequence starting in 1867, you can see that the times between eruptions get longer, and that the time after the 1873 eruption, similar in size to the 2011 one, was 10 years. I find the same lengthening of eruption intervals for the current cycle, and a similar time for the next eruption after a large bang. So there is some kind of agreement with the (very limited) historical data.

I should warn first that making predictions is dangerous, very uncertain, and should strictly be limited to the past. I am failing here on all counts. Grimsvotn is by no means bound by my numbers and will do whatever it wants. Second, it is too early in the sequence to make strong predictions. A small fluctuation in earthquake activity can still change the fit by quite a lot. It would be better to wait until the earthquake activity begins to accelerate, which hasn’t happened yet. If the fit was repeated in 6 months time, the numbers could easily come out quite different.

A final point to make is that after the 2011 eruption, there was a two-year period of very little activity, much more so than after the two preceding eruptions. In fact, the activity over this period is well below what is predicted by the equation. If I leave the first 600 days of the current cycle out, i.e. shift the red curve to left by 600 days, it fits rather better with the blue and green curves. That would still give an eruption around the year 2020.

Grimsvotn past and present. The vertical lines show the eruptions. The two extrapolations into the future, give eruptions in 2020 or 2022. Be aware this is an uncertain prediction – it is not a schedule.

So this is it! Grimsvotn is a prodigious erupter, varying in style between effusive long-distance fissures, and explosive events within the caldera. The frequency of eruptions is high enough that it is worth trying out predictions – the predictions can be tested against reality within a reasonable amount of time. And although the amount of ash and tephra is not huge, it is significant, and problematic for people and for aircraft. Thus, predicting its future is of economic (and human) value.

Will this prediction work? Wait and see! It assumes that Grimsvotn will continue to behave as it has done in the recent past, and that is far from certain. It ignores the silent two years after 2011. And if the next event is a fissure eruption, all bets are off.
Otherwise, Grimsvotn 2021? You heard it here first.

Albert, August 2017

The contrarian view

A week ago, I suggested to Albert that we should write this article together. Both of us looking at the same data, and both of us trying to predict when the next Grimsvötn eruption is likely to occur. It was meant that I should give the contrarian view to Alberts part.

There are two things in Alberts part that I wish to contraire upon before I get back to contraire the likely date of the next Grimsvötn eruption.

The first part is about the calderas of Grimsvötn. They are not as young as Albert suggests in the article, instead they are likely to have formed during 3 out of the 5 Saksunarvatn tephra’s, something I wrote about in a previous article about Grimsvötn.

The other part is about the source of the Lakí lavas. In a six-part article series I wrote about the chemical composition of the lavas where I found that the lavas are not matching the known samples from the South-Central magma chamber, nor the North-West magma chamber (responsible for the Gjálp 1996 magma).

Grimsvötn is a bad bet for being the culprit for the Skaftár Fires since there are two large central volcanoes SSW along the fissure swarms. The northerly of those are the Háabunga volcano that may, or may not, be a fourth magma chamber of Grimsvötn. The southerly of them is the powerful Þórðarhyrna volcano.

The Þórðarhyrna lavas are closer in composition to the Skaftár Fires lava, but it is not matching well enough. In the previous articles I surmised that the lava originated directly from a deep common magma reservoir that feeds all of the above mentioned central volcanoes.

The reason for that is that I found commonalities pointing towards the magma originating from a deep common source, and that the magmas evolved due to melt inclusions and varying times in situ at the magma chambers of the various volcanoes. And the Skaftár Fires lava was less evolved than the other by a fair degree.

There are also similarities with MORB-magmas (Mid Ocean Ridge Basalt), and the MORB similarities was higher at the SSW end of the Lakí Fissure compared to the NNE beginning.

I do agree with Albert that most fissure eruptions are gravity driven, but not all. Some are driven by other functions, even though we do not fully understand those functions currently. It may also be that we do not understand all functions of the gravity theory of volcanoes yet, and that Albert will turn out to be more correct than he believed.

But, I will give an example of a volcano that throughout its history has had major fissure eruptions with no possibility of them being gravity driven according to the current theory, and that is Vatnafjöll.

For some reason, it has produced at least 3 eruptions as large as Veiðivötn 1477. Those eruptions occurred at the fissure that is the top of the mountain, and to even confound us more, it has not gone caldera even though it is among the top 5 volcanoes in Iceland if we rate it after volume of lava produced. The same also goes for another of the top 5 lava producers in Iceland, Þeistareykir.

And now that I have contraired on that I will return to the point at hand and see if I will reach to a different conclusion than Albert.

Grimsvötn 2019

The Cumulative Seismic Moment-plot has over the years proven to be a highly useful plot for estimating when a Grimsvötn eruption is likely to occur. We have data for the CSM for 2011, 2004 and 1998 eruptions. The 1998 data is not shown any longer on the public CSM-plot, but it was pretty much exactly in the middle between 2011 and 2004.

The dataset is not long enough to determine if the CSM-values are true for what the lowest and highest values will be for an eruption at Grimsvötn. One way to think about it is that the high rate of eruptions that we are seeing now are weakening the magma reservoirs, so that the CSM-value will decrease over time for an eruption to be possible to occur.

This line of thinking kind of makes sense compared to the not so small fact that the 2011 eruption had the lowest CSM-value at the start of the eruption, and that it still produced the largest of the 3 eruptions.

1998 had a value of 3.5, 2004 had a value of 4 and 2011 a value of 3. Let us therefore toy with the idea that it is possible that an eruption can occur at as low a CSM-value as 2.5, that would set the next possible eruption closer in time.

Now let us ponder the opposite, we know that the Grimsvötn eruption of 2011 was the most voluminous since the Skaftár Fires in Iceland. It is also the single largest eruption since the large VEI-5 eruption of Cerro Hudson in 1992.

It is probable that the size of the eruption lowered the pressure of the magma reservoir sufficiently that it will take a longer time to refill, and that it therefore may be able to withstand more cumulative seismic release than before. If this line of thinking holds true it could be that Grimsvötn may reach a higher CSM-value at perhaps as much as 4.5.

Here I should point out that the CSM-value of Grimsvötn is very low, the same current known number for Katla is in excess of 140 (if my memory serves), and then we only have a partial record for Katla. This has nothing to do with a potential future eruption size, I just mention it to give a background of how little it would take to set of Grimsvötn in regards of an earthquake swarm.

Now we return to that pesky M3 earthquake that occurred between Grimsvötn and Hamarinn. It offsets the CSM-value with roughly 0.5, so it is pretty significant. On one hand, it is not directly related to the pressure of the magma reservoirs of Grimsvötn. On the other hand, it is pointing towards the possibility of a future Gjálp style eruption in, or around, that location.

With that earthquake counted in we have a CSM-value of 1.5 currently, without it we are currently at 1.

This gives at hand that the earliest possible eruption according to the curves of Albert is somewhere between December 2018 to February 2019 if we assume that the pesky earthquake is related and that the true CSM-value is 1.5 and that an eruption can occur at as low a CSM-value as 2.5.

If we instead go for the latest possible scenario of a eruptive CSM-value of 4.5 and discount that pesky earthquake we end up all the way into the summer of 2022.

Is the CSM lying?

Image by the University of Iceland, Sigrun Hreinsdottir.

I am here going to postulate that the CSM-value is a false presumption for the upcoming eruption, even though I myself have often used it. So, I am here going to contraire myself for the sake of scientific debate.

As evidenced by the Gjálp eruption, Bárdarbunga has for quite some time exerted a significant amount of pressure on Grimsvötn compressing its deep magma reservoir and upper magma chambers. During the 2014-2015 eruption at Holuhraun this pressure dropped quite a bit as evidenced on the GPS-stations. During the eruption, the inflation of Grimsvötn stood still, and even for a period reversed.

This lowered systemic pressure resulted in a period of less earthquakes in Grimsvötn and hid quite a bit of pressure build-up and inflation since the magma system increased slightly in volume.

The second reason that the CSM-value might be off is that the GPS-system is pointing towards enough influx of magma to reset the volcano back to a value higher than prior to the 2011 eruption. And it is when we merge the GPS-data with the CSM-value that we get interesting tools to forecast the next Grimsvötn eruption.

The GPS-data negates the idea of higher CSM-value and increases the likelihood of a lower CSM-value. I will therefore state that likely CSM-span is between 2.5 and 3.5 with the peak at 3. I will also postulate that there is a risk that a future Gjálp-style eruption can occur between Grimsvötn and Hamarinn. I will therefore leave the pesky earthquake in the plot and count our current true CSM-value as 1.5.

If we know superimpose this on the Albert-curve we reach a probable time span for the next eruption ranging between December 2018 and December 2019. The if here is if the upwards motion of the Albert-curve will go as he has formulated it above, it is though likely that it will do so.

I will though here like to point out once more that the CSM-values at Grimsvötn are very low. In fact, there could at any time come a rogue earthquake swarm, or a single M4 earthquake, that punches the value fast into the eruptive ranges. It is though not as likely judging from previous behaviour of Grimsvötn.

In the end nature is a messy beast, and even the best models can be side-tracked by rogue events.



This week there are the usual five riddles with one picture riddle. As usual only I and Gaz has the answers to the riddles. We may award bonus-points for advanced Volcanocafeishness. Good luck with these brainbusters!


Name Last week’s points Total
Bjarki 0 3
Daisaster 0 3
Albert 0 2
Spike Page 0 2
Thomas A 0 2
Bobbi 0 1
Chris Cookie Cooke 0 1
Inannamoon 1 1
KarenZ 0 1
Virtual 1 1
zfid 1 1
  1. Warm (Spanish speaking) salty waters from the bull
  2. The one living saint (in Moulin Rouge!)
  3. (Roccella Tinctoria covered) Basalt of Anthony and Matthew – Urzelina, answered by Irpsit
  4. Flowing badly read viral kiwi – Nyamuragira, answered by mjf
  5. French saint + Boomerang Seamount, Answered by Thomas A
    answered by Tomas A

157 thoughts on “Living dangerously: a Grimsvotn prediction

    • Albert is the one who pulled the heavy lifting on this one. I just had the privilige of being my own grumpy self.

  1. Very nice post! Interesting discussion comparing two differrent views! Good piece of science!

  2. Grims also wanted to comment on your post with a 1.9 quake! Can you interpret what he wanted to tell us??:-?

  3. Great article, and nice to see that IMO has got the CSM graph to work again(or perhaps they manually adjust it again from time to time)after it broke when a M2.5 quake happened on 3/5-2017.

  4. To contraire the contrary view, regarding the origin of the Laki magma: the composition of Laki was affected by partial melt. It was (in part) a mush. Passmore et al ( calculate the composition of the liquid from which the mush formed, and find it was very similar to that of 18th century Grimsvotn eruptions. Of course you can not tell from just the composition whether it came from the same magma chamber, or had a common source. The mush to me suggest the rift that fed Laki had formed well before the eruption, but again that doesn’t say where it got its magma from. But the productivity of Grimsvotn, the extreme volume of Laki, and the composition, to me suggest it can only have come from the direct feed of Grimsvotn – probablty the deeper (10 km) magma chamber, but of course if you empty a magma chamber to this degree, it may not reform quite the same as it was before, so you have to be careful with extrapolating from the current structure to that prior to Laki.

    The second argument is that the Laki rift lines up with Grimsvotn, and Grimsvotn was active during Laki. If Laki had a separate source. Grimsvotn would not have been active at the same time.

    The third argument is that 15km3 magma extraction must leave a hole. The only obvious hole along the entire line is underneath Grimsvotn. And the obvious reason why Grimsvotn erupted would be the collapse of its caldera.

    Regarding the age of the caldera, earlier eruptions would also have formed calderas. But in a system as active as Grimsvotn, calderas may not last long. The refilling of the chambers wipes them out. The calderas reform time and again. St Helens shows how quickly an active volcano can rebuild itself.

  5. I saw on the facebook a question why the ‘living dangerously’ title? It was mine (don’t blame Carl..), and chosen for its duplicitous meaning. The obvious meaning is the danger of Grimsvotn (and any volcano that at one time caused the population of Iceland to decrease by 25% should be considered dangerous!), but to me it meant the danger of trying to predict an eruption. Volcanoes are like fatigue failure: eruptions can be predicted statistically but not specifically. Volcano prediction can be career-ending.

  6. Great article, and I will suggest you are both correct, that Laki was both fed by Grimsvotn and that melting decompression also happened locally at the fissure. And that this is what makes the difference between a Holuhraun and a Laki or a Trolladyngja (which is near Holuhraun).

    In fact evidence, magma composition and sight of fires towards Grimsvotn location, support both sources if magma.

  7. and then Holuhraun changed everything. Hreppar moved and we can’t play with same rules as before 2014. There has been also a hotspot pulse of fresh new deep magma beneath Vatnajokull and this has changed things.

    Other than the central volcanoes, perhaps the key to predict the future site of other eruptions has to do with tectonics and with rifting. Where is rifting stress?

    Prior to 2014, I knew something was due north if Bardarbunga. Why? Because over the past 150 years, Askja, Krafla, the area between these two, and a section of Veidivotn, all rifted. Where was rifting missing?

    And where is rifting missing now?

    • Two areas have since long not rifted. One is Theistareykarbunga and Tjornes (though tectonics there are a transform fault so plate movement takes form as a massive seismic crisis following a M7). The other area is Reykjanes peninsula. At least I expect something major to take place north of Krafla in the next decade or two. I also expect an eruption somewhere near Reykjanes volcano.

      Other than these, I can think of Askja and Kayla as two other sites under greater tectonic strain. I expect eruptions in both of them.

  8. Very interesting to see two different interpretations. I’ll throw in a couple of observations:

    1. One of the most interesting papers on this stuff is Sigmarsson et. al. – getting into the isotope ratios of Grimsvotn magmas and how they can be interpreted. Definitely worth a read for those who haven’t:

    2. I seem to remember discussion of a conjectured mechanism of eruption for at least some voluminous Icelandic fissures which involved decompression melting and magma transfer direct from the fertile mantle to the fissure without intermediate residence in, or passage through, a magma reservoir associated with a central volcano. Thus the eruption would become self-sustaining until the fertile mantle in the immediate vicinity was depleted. No trace of gravity-driven magma supply in this model. Where does this model stand? Is it deprecated today? It appears (with few possible caveats) that Holuhraun was a perfect model for such a gravity-fed eruption – but that may not apply to some of the more voluminous fissures?

    • Thank you for the link. Quite detailed and very informative!

  9. Interesting read! A few points: Did the part of the build-up towards the Holuhraun eruption at Bardarbunga that occurred before the 2011 eruption (from 2007) influence the size or timing of the 2011 eruption? Do we know why the 2011 eruption was so much larger than usual? Why did Grimsvotn erupt in 1998 just two years after the previous one (I presume the cumulative seismic moment jumped up significantly faster than before 2004, 2011 and now) considering the pattern seen since then? Are there any indications of how large the next eruption might be at this stage? And do we have any more of a breakdown of the individual eruptions of the Saksunarvatn series, or still only of the overall collective?

    • I think ‘no’ to most of your questions. Predicting the _size_ of an eruption is even more difficult than the timing. And if it depends on water-magma interaction, there are too many unknowns. Does the continuing melting of the glacier contribute? Who knows. The last eruption was large but not out of historical range (the 1873 eruption was similar). Whether Bardabunga affected Grimsvotn: probably, as it changed the stress field in the area. But how that actually affects Grimsvotn is a much harder question.

      My guess for the next eruption would be VEI3, just because that is most common. But that is not a prediction.

      • I was thinking along the same lines roughly, though the 1873 eruption barely reached VEI-4, and was 8 times smaller than 2011.

  10. On a separate note, can “regular” readers contribute to future riddles? I think I have a good one which would require two answers!

    • All readers are welcome to contribute material of all kinds 🙂
      Send it via email to us and we will use it.

    • I think this work (from 1991) has been superseded. The Passmore paper (2013), including the same author as the 1991 paper, finds less uniformity. But the bottom line is that Grimsvotn itself is not fully uniform, and the source liquid of Laki agrees in composition with Grimsvotn tephra from the 18th century.

      And if you remove 15km3 of magma, you are going to leave a hole somewhere. If someone proposes a different origin, they need to come up with a hole that fits their source. The deeper the chamber, the wider (and shallower) the hole. But you can’t make it too deep because the large volume came out rather quickly. The deeper, or more dispersed, you make the chamber, the more difficult it becomes to make it all come out in a short period of time. If you propose a 10-km deep chamber (seems reasonable), there should be a hole of perhaps twice that width. Grimsvotn fits the bill. I can’t see anything else that is obvious.

      • How deep do you want to go?

        See my comment citing another paper a little further up the thread. There’s some evidence – on isotope ratio grounds – that the Laki eruption *recharged* the Grimsvotn system rather than depleting it, and that every Grimsvotn eruptions up to 2011 was in a sense erupting the progressively slightly more isotonically evolved ‘dregs of Laki’.

        Can you point to any work that’s been done on the rate of magma generation possible with decompression melting of fertile mantle with the magma ascending directly from the bottom of the crust to the eruptive fissure? I’ve heard that suggested as a self-sustaining eruption model for Laki-type fissures but never seen the numbers worked out to support or rule out the magma generation rates required.

        (OK we’re not writing formal papers here. But I would suggest BTW, that where papers inform what is written here, citations with links to the papers should be provided in the conventional way as a matter of course. Now I have to google Passmore et. al. 🙂 )

        • Sorry: Passmore et al was linked in a comment above. It is at

          The direct-feed model was proposed for Holuhraun, but the simultaneous collapse of Bardarbunga left little doubt where the magma came from (if the earthquake sequence left any doubt, that is). At the very least there was pressure equilibrium between the two systems.

          Magma chambers push up the ground (because they have lower density than the rock they displace, so in equilibrium there has to be more rock above them). You can get a good idea where the major magma chambers are by looking at the topography. The Laki rift is low, and therefore has no major magma chamber underneath it. I think that already makes the continuous magma generation difficult to

          Yes, I have seen the paper arguing for the increasing evolution of Grimsvotn, which suggests it is still emptying an older magma chamber, which also sourced Laki. But that doesn’t say where that magma chamber is.

          • Note I said ‘Grimsvotn eruptions up to 2011’. It’s no longer erupting something evolved from the Laki magma pulse; with the 2011 eruption the thorium isotope ratio changed radically back to something more similar to that seen in Laki lavas. Ergo, a new magma pulse has arrived.

      • Couldn’t you argue that the “hole” produced when Laki erupted is accounted for by the rifting and spreading of the dead zone region?

          • Bonus point! Although, rifting and spreading would make the hole worse. You still need to take out 15km3 from somewhere, and rifting needs filling too. So it still leaves the question, where did the magma reside before it came as lava flowing down the Skaftar valley?

          • All will be answered Albert as soon as I have finished doing my 3-year old spastic doodle’s and poor Gaz has transformed it into beautiful art. 🙂

          • The difference in our predictions (post-2020 versus pre-2019) is due to the earthquake moment that indicates an eruption (I used a higher value) and whether the large earthquake should be included. Note that the cumulative moment is in itself not a measure for accumulated strain, but is the strain that has been released by the earthquakes. We are really assuming that the amount that is released is a fixed fraction of the total accumulated strain. It is unlikely that it works the same way for rift eruptions, and so either way the M3 quake should be discounted, in my opinion.

            I think Katla will go first.

  11. Splendid discussion up above.
    The comments and questions are so good and requires highly deliberate explanations that I think would make for a fantastic article. I will therefore cut and paste and answer them in a new article. I think the title will be “Grimsvötn: The Contrarian contraires on contrarianisms” 🙂

  12. Shouldn’t the title be the epoch of living dangerously,,,,,,NO? intellectual property issues ??

    • You may mean the year of living dangerously. But the phrase has been used in a variety of ways, although not for trying to predict a volcano, as far as I am aware.

    • I guess Barrow Hill volcano. Saint is another word for ‘holy’. David Bowiehad a record ‘holy holy’ with subtitle ‘black country rock’. Barrow hill is in Black Country in the UK, and it is an ancient volcano which is named as if it is burial mount – which it isn’t.

  13. 3: St. Catherine volcanic system in Grenada (Mount Sinai being a sub-feature from the GVP page)? My searches brought me to biblical references of basalt, Saint Anthony (of the desert) and the biblical Mount Sinai being a volcano, of course Matthew being one of the books of the bible.

  14. #4 – Pukekiwiriki of Auckland Field? ViralRead dotcom was not terribly helpful..but I can think of few worse ways to flow.

  15. 2 The one living saint

    Mt. St. Helens, it’s the only “saint” volcano which is hmm really living atm, has had an eruption within living memory, well monitored. “The one” hints at importance, and could be a Carl’ish tongue in cheek remark at US thinking themselves more important than others.

    • It is a continuation of the Fagradalsfjall swarm last week. It is magma slowly migrating. Question is where it will end up, or if it will stay below the surface. I have a “feeling”, that this may turn into a Herdubreid-wanderer magma blob.

  16. Pretty far fetched, salty mineral water is found in the Borjormi gorge in Georgia. I think this place is in the old kingdom of Colchis (the Colchis bulls). This area is supposed to be based on lava flows from the Mukheri volcano, not that I could find any record of this volcano outside of the one text.

    However, I did find reference to lava flows (Borjomi- Bakuriani formation) said to come from Mount Samsari. So I’m going with the latter.

  17. Warm salty waters from the bull, Mount Hasan or another nearby near lake Tuz and Taurus mountains in Turkey
    Basalt of Anthony and Matthew, Vanuatu Matthew island
    Flowing badly read viral kiwi, The Pukapuka volcanic chain?
    French saint + Saint-Ours, Puy-de-Dôme, France, or Soufriere Volcanic Centre, Saint Lucia, I have a few ideas other French saint ideas but these are my quickest guesses

    • Derinkuyu caldera-Gollu dome, Mount Erciyes, and caldera Acıgöl–Nevşehir are also possibilities for #1

      In Pukapuka, one possibility is that it might be also another of the Cook islands….

  18. Responding to Albert from before: So I mentioned that the “hole” produced during a laki-like eruption is accounted for by the rifting process. But Albert made a good point in that there is still 15km of excess magma outside of the actual rift, so there still needs to be something to account for this loss of space / volume. Here are my thoughts and theories on that:

    First off, as we all know, there is a LOT of magma leaking out, so if we were to only account for rifting, the magma produced by the rifting itself should simply “fill the hole” left by the rift, and not erupt outward, but that obviously did not occur. To that thought, I think there are a few things worth keeping in mind. First off, the magma produced that formed the actual Laki lava flows was likely comparatively small when taking into consideration the potential size of the entire volcanic system. And by system, I’m referring to the entire rift, which likely is enormous, very deep, and much more structurally sound than a typical magma chamber due to the fact that a rift would be rather narrow. If we are assuming that the magma production here was largely rift-driven, then you don’t need to account for a central magma chamber experiencing a caldera drop since a rift can simply fill in the space driven by the excess magma erupted by pulling up more melt from the mantle.

    • Second, aside from the basic fact that the displaced magma is accounted for from below (not above), there are some other factors at play that come up when considering the fact that the magma was likely turned into a molten state extremely quick.

      Remember that magma compresses when it’s not molten, and when crystallized, it also traps volatiles inside. So if we were to assume a model where the Laki fissure formed it’s magma due to a combination of being inherently hot, and extremely rapid rifting lowering the melt point of the rock in this region, we also need to realize that turning crystallized rock into fresh melt will result in a significant expansion and release of some volatiles. This basically causes the excess magma to “leak out”, resulting in the actual excess lava flows seen at Laki.

      • You are raising good points. But I still don’t buy it.. The magma should have been in place before the eruption. Decompression melt during a rifting event is negligible. Even if you pull the plates apart by 1 meter, to a depth of 5 kilometer (a typical locking depth: at this depth you can’t get holes in rock any more), for a 10 kilometer deep magma reservoir the pressure only decreases by the equivalent of 1 to a few meter of rock. That is nothing. So the question still is, where are these huge magma chambers? On Iceland, the main ones are underneath Katla and environment, and Vatnjokull. There is no evidence for large magma chambers underneath the Laki zone.

        Laki started at the soutwestern end of the rift, and later eruptions came progressively towards the northeast. ( This fits with a model where the overpressure of the magma, or the flow rate, slowly decrease over time. A lower flow rate means the magma can’t travel as far before solidifying underground (it is the pressure of the flowing magma that keeps the dyke open. Low flow rate means a narrower dyke, and faster cooling. You could see this in Holuhraun which ended when the magma could no longer reach the eruption site.) As the eruption moved northeast as the flow rates diminished, this indicates that is the direction of the magma feed. If it had been directly underneath the rift, and along its length, you wouldn’t see this: eruptions would occur everywhere until the end.

        The Thodarson paper (2003) argues that Laki was fed from the deep magma chamber underneath Grimsvotn, not the shallow one. That makes sense. But the argument that the eruptions at Grimsvotn itself shows that the shallow magma chamber again started to receive magma from the deep chamber is open to discussion. If that were true, the long period of quiet at Grisvotn after Laki is unexplained. More likely, Grimsvotn erupted from magma that was already in the shallow chamber. Caldera collapse would seem a more likely cause, in my (unrefereed) opinion. Carl will disagree.

        • So if this is the case, where does the magma come from in sub-ocean mid-atlantic ridge eruptions? Does the magma get pulled from central magma chambers? If not, decompression would have to be the culprit here, would it not?

          • Basically, my premise here is that the “dead zone” and to a larger extent, the overall fissure systems in Iceland are just an extension of the MAR, except that they’re on land and a bit more active than traditional MAR systems due to the hotspot also providing input.

            Based on what we know of MAR volcanism, we know that the spreading is actually induced by the sinking of slabs far off on the other side of the tectonic plate (or other linked plates). So from this, we know that MAR volcanism is a top-down induced system, which implies that the magma production comes as a result of decompression.

          • That is why your point is a good one. But I would point out that the MAR is a 2 kilometer (or more) high range, pushed up by the hot magma below. (Or at least the hot rock, with increasing melt fraction as it ascends). Very little of that ever reaches the sea bottom. The vast majority ends up forming the 8-kilometer thick crust. The subsea volcanoes tend to be a bit outside of the rift. Iceland is not quite like the MAR. It doesn’t have the linear elevated range, nor the deep depression in the centre of the rift, for instance.

            Where we see eruptions in a continental rift (for instance Ethiopia), it seems the magma is carried by long-distance dykes from a known volcanic area. Iceland works that way too. But the deep MAR may be different – I don’t know.

          • More interesting question, why are eruptions southwest of Vatnajokull in form of fissures, and those north are shield volcanoes?

            One clue: different orientation to both plates and also presence of Hreppar nearby.

            Conclusion, tectonics play a big role

            The dead zone is about tectonics.

            Second clue: volumes of Eldgja and Laki were similar, I suspect that melting decompression occurred locally and explain the insane large volumes of lava

            But at same time, magma leaves the central volcano, leaving its Calder’s sinking

            Third clue: Grimsvotn Post ice age eruptions were extremely large, but where did they occur? Central volcano or fissure?

          • Perhaps it is related to topography. Magma dykes follow the route of least resistance, and that is a combination of the stress field in the rift, and the weight of the ground (and ice) above. When the topography is flat, it takes or releases little energy for magma to flow further, and so it can decide to come up at any point. When there is a distinct valley point along the dyke, a lowest point, that is where the dyke will stop and erupt because it is expensive (in terms of energy) to go any further. That is what Holuhraun did: it came out just before the ground along the rift started rising, towards Askja.

        • Carl is partially disagreeing.
          But, Carl is a good Carl and is preparing an entire post on the subject. 🙂

  19. 2. Mt. Rainer – now that Roger Moore is dead, the living saint is Adam Rayner

    • 5 – Perhaps – Elbrus? A ‘montagne Russe’ first summited by mountaineers from St. Nicolas?

    • 1 – Karapinar? Near the warm salt lake that forms from waters flowing down from the Taurus mountains.

    • 3 – Euganean Hills, near the town of Padua, home of St. Anthony and St. Matthew… ?

      I really need to get back to work….

      • That was actually a good one, but not even close to being the right volcano.

    • I will return to these answers later to see if I should award a bonus point or not. It depends upon if you come back and get the right answers yourself.
      But, basically you have at least one point.

  20. 2: – The one living saint – Mother Teresa was known as this.

    Therasia in the Santorini archipelago.

    • Since I am one of those pesky atheists I recognise saints of all religions, so nope.

      Also a nope on Suc de Bauzon.

  21. 5: French saint….

    Suc de Bauzon
    This is near Saint-Cirgues-en-Montagne.
    Montagne russa is french for roller coaster and Saint Cirgues may or may not have been an actual saint but is the name of a commune in the Ardeche region.

  22. 3: Karacadag?
    2: Augustine, Alaska (also known as Mt. St. Augustine)?

  23. Celestine was known as the living saint. The mineral Celestine, which looks like quartz comes from the Tromen Volcano in Argentina

  24. #5 Maar de Beauloup of Chaine des Puys? The name sounds kind of like the town Saint-Martin-le-Beau in France..and the rollercoaster is a loop.

  25. #5 Kerguelen islands, it’s a little bit Joan of arcy 😉

  26. Woke up at 5am this morning with an answer to a riddle popping out of nowhere. I would have thanked my subconscious for doing the work for me if it weren’t for the fact the answer my imagination came up with overnight was Nibiru Tenzin. Sigh

  27. 5: Boomerang Seamount

    Marks the location of the Amsterdam-Saint Paul hotspot in the French Southern and Antarctic Lands. Boomerang Coast to Coaster is the name of the roller coaster in the picture.

  28. #1 – Thera.

    Warm salty waters make me think of the Mediterranean. The bull makes me think of the Minoan culture that was devastated by the eruption of Thera/Santorini. Could it be that simple?

  29. #2 – Monte Simone (pyroclastic cone of Etna)

    The Saint – Simon Templar. Here is a saint that is very much alive, although only in fiction. Simone is the italian spelling of the name Simon.

    • Largest blobs of magma that deep is under the region of Vanuatu and New Zealand, and another in Africa, possibly feeding several nearby hotspots

      • Thanks!! Would be interested if you could recomend some more reading:-)

Comments are closed.