Volcano ecology

Space is a precious resource. We hoard it and guard it. Together with air, water, warmth and tomato ketchup, it is one of the essential ingredients for life. We are happy to share empathy, food, and money, but letting someone else invade our personal space is a big step well beyond that. Social distancing is a fundamental part of our lives. The walls around us are invisible, but strongly defended. It is why the internet has become such a big part of our lives: distance makes the heart grow fonder.

It is not just us. The crows feeding in the field keep their equal distance to each other. This is abandoned only in danger. When birds flock and animals herd, it is a sign of predation. There is safety in numbers, but there is happiness in separation. And the plants do it too. Immovable trees keep their distance from each other. In a semi-desert, you’ll find small bushes which occupy their own personal space. Other bushes stay well away. This is not government-imposed, but is because of water constraints. Each bush needs a certain amount of water and it takes a certain area to collect that. Any other bush encroaching on the water space will not get enough and will quickly shrivel and fail. Each bush needs space to grow. This is the basis of ecology.

It is not just the living world. Volcanoes too need space to grow, and they too have ecology. Each needs a certain amount of magma, and if another volcano gets too close, a battle for this precious resource will ensue. The real battle happens out of sight, underground where magma chambers collect their precious resource. The competition is not so much between volcanoes but between their magma chambers. But we judge what we see. So to us, it is a competition between volcanoes. It is a geological ecology.

Can we see this? Just like the crows, the bushes and the people, do volcanoes have their ideal separation? There is not much published on what constitutes adequate personal space for a volcano. How can we find out? The volca-biologist would plant a series of volcanoes and see which ones grow. The volca-physicist would measure the growth rate of volcanoes, and plot this against the number of volcanoes per area. The volca-psychologist would talk to volcanoes and find out how stressed they feel: are they about to blow their top? The volca-geologist would apply for a big grant and travel the world. We can’t do any of these. So let’s look at Iceland instead. All volcanic roads go to Iceland, after all.

Between Icelandic volcanoes

To find out whether volcanoes have their ideal distance, I compiled a list of active or at least non-extinct volcanoes in Iceland (to be precise, I just copied it from wikipedia and removed a few entries). It is a bit of a funny list which mixes central volcanoes and rifts, but I kept them as long as there was a single centre for the eruption (Laki mountain was kept, but the Laki and Eldgja rift eruptions were removed). The list is complete for now, but every time an old system re-awakens, it may need adding to the list. The way things are going, the next one to join may be Thorbjörn. But it is important not to include extinct volcanoes. In the competition for resources, the dead don’t count. They have no ecological needs apart from respect. And the dead outnumber the living: all of Iceland is an volcanic graveyard. Let’s stick to the living.

With this list, I calculated the distance between every conceivable pair of volcanoes. This was done using the coordinates given by wikipedia (accurate to 1 km or so) and applying the haversine equation to get the proper distance on the curved surface of the earth.

It gave me an old-fashioned looking distance table, but that is fine by me. Each distance is listed twice on the table, depending where you start from, and the empty diagonal are distances whether the starting point and end points are the same location. The only aspects that differ from those kind of tables that used to be attached to road atlasses (remember those?) is that (1) these are distances between very unsafe places, and (2) the distances are as the (socially distant) crow flies, if a crow could be convinced to fly from one volcano to the next. A sample of the table is shown below. The full table is available at the VC shop. The distances are given in kilometers, by the way, as volcanoes have long gone metric. (Only Yellowstone still erupts virtual cubic miles.) The accuracy is limited to around 1 km: don’t try to land your plane using this table because you will miss. My apologies to the crow.

Extract of the distance table of Icelandic volcanoes. Distances in kilometers. The full table is available in the VC shop.

For information on each of the volcanoes, the best source is Carl’s mammoth guide.

If you look through the list used here, you’ll find some volcanoes that are not on the main land, and one is even stuck below sea. But wikipedia included them, so I did too.

Nearest neighbour

Sometimes it is obvious which volcano is the nearest neighbour to another volcano. Sometimes it isn’t, and by eye there seems to be two volcanoes at about the same distance, just in a different direction. The real one can be found by looking for the smallest number in each row or column of the table (the full table, not the extract above). The result is shown in the table below. Each row in this table shows the name of the volcano, its height in meters, the year of its last eruption, the distance to the nearest neighbour in km, the name of that nearest neighbour and its height and last time of eruption.

Volcano height last eruption distance (km) neighbour height last eruption
Askja 1516 1961 23 Holuhraun 778 2015
Bárðarbunga 2005 1864 21 Tungnafellsjökull 1535 dormant
Brennisteinsfjöll 626 1341 11 Thrihnukagigur 550 2 BC
Eldfell 279 1973 1 Helgafell 227 3950 BC
Esjufjöll 1760 1927 25 Thordarhyrna 1650 1910
Eyjafjallajökull 1666 2010 11 Þórólfsfell 574 unknown
Fremrinámur 939 800 BC 10 Hverfjall 420 ~500BC
Grensdalur 497 dormant 6 Hrómundartindur 540 10,000 BC
Grímsnes 214 ~3500 BC 15 Grensdalur 497 dormant
Grímsvötn 1725 2011 25 Loki-Fögrufjöll 1570 1910
Hekla 1491 2000 7 Vatnafjöll 1235 750AD
Helgafell 227 3950 BCE 1 Eldfell 279 1973
Hengill 803 90 AD 15 Hrómundartindur 540 10,000 BC
Herðubreið 1682 dormant 11 Kollóttadyngja 1177 unknown
Hofsjökull 1782 dormant 26 Kerlingarfjöll 1488 dormant
Holuhraun 778 2015 22 Trölladyngja 1468 ~2980
Hrómundartindur 540 10,000 BC 6 Grensdalur 497 dormant
Hverfjall 420 500 BC 10 Fremrinámur 939 800 BC
Hveravellir 1360 950 AD 34 Hofsjökull 1782 dormant
Katla 1512 1918 16 Krakatindur 300 unknown
Kerlingarfjöll 1488 dormant 26 Hofsjökull 1782 dormant
Kolbeinsey Ridge 5 1755 122 Theistareykjarbunga 564 750 BC
Kollóttadyngja 1177 unknown 11 Herðubreið 1682 dormant
Krafla 650 1984 18 Theistareykjarbunga 564 750 BC
Krýsuvík 379 ~1340 14 Brennisteinsfjöll 626 1341
Krakatindur 300 unknown 16 Katla 1512 1918
Kverkfjöll 1920 1968 23 Holuhraun 778 2015
Laki 1725 1783 52 Torfajökull 1259 1477
Loki-Fögrufjöll 1570 1910 22 Bárðarbunga 2005 2015
Ljósufjöll 988 960 AD 51 Lýsuhóll 540 dormant
Lýsuhóll 540 dormant 28 Snæfellsjökull 1448 200 AD
Öræfajökull 2119 1727 23 Thordarhyrna 1650 1910
Prestahnúkur 1386 7550 BC 36 Hveravellir 1360 950 AD
Reykjanes 230 1879 21 Krýsuvík 379 ~1340
Reykjaneshryggur -80 1970 50 Reykjanes 230 1879
Snæfellsjökull 1448 200AD 28 Lýsuhóll 540 dormant
Surtsey 174 1963 24 Helgafell 227 3950 BC
Theistareykjarbunga 564 750 BC 18 Krafla 650 1984
Thordarhyrna 1650 1910 23 Öræfajökull 2119 1727
Þórólfsfell 574 unknown 9 Tindfjallajökull 1463 dormant
Thrihnukagigur 550 2BC 11 Brennisteinsfjöll 626 1341
Tindfjallajökull 1463 dormant 9 Þórólfsfell 574 unknown
Torfajökull 1259 1477 26 Vatnafjöll 1235 750AD
Trölladyngja 1468 ~2980 BC 22 Holuhraun 778 2015
Tungnafellsjökull 1535 dormant 21 Bárðarbunga 2005 1864
Vatnafjöll 1235 750 AD 7 Hekla 1491 2000



(If you like, the table can be downloaded from the VC check-out as a word document.

Interestingly, a nearest neighbour can be a one-sided affair. Sometimes it is a monogamous relation involving pair-bonding, much like albatrosses. For instance, the relation between Katla and Krakatindur is mutual. But sometimes it is not: the nearest volcano to Askja is Holuhraun, but the nearest volcano to Holuhraun is not Askja. This is more of an open relation. A particular dominant volcano may have to keep several partners happy.

A quick glance through this table suggests that a typical distance is some 20 km, but with many variations. A calculation shows that the average separation is 21 km, and the median is 20 km. Does that make sense? Could we have predicted this?

Let’s assume that volcanoes are distributed randomly over all of Iceland. Our slightly edited list has 46 volcanoes. For a surface area of Iceland of 103,000 km2, that gives us on average 1 volcano per 2200 km2. A quick calculation finds that typically, the nearest volcano to you (assuming you are in Iceland) should be about 27 km away. That also applies to each volcano: if you are an average Icelandic volcano (we’d love to hear from you), the nearest volcanic neighbour should be that far away. In reality, only 8 of the 46 volcanoes have a nearest neighbour 26 km or more away (and one of those is on the Kolbeinsey Ridge and perhaps should not be in this study). They are a bit too close together, and therefore Iceland’s volcanoes are not randomly placed across the country.

Of course you already knew this. They are located in several volcanic zones which together cover some 30% of the country. If all volcanoes are in these zones, the typical distance to the nearest neighbour would be less than 20 km. That is more like what we see.

But is the distribution random within these zones? Did Thor drop volcanoes at random within the predesignated areas, or did he try to space them out?

The histogram shows the set of distances to the nearest other Icelandic volcano. The dashed line shows the expectation if the volcanoes are randomly distributed.

The plot shows the answer. It takes the distance between each pair of nearest volcanoes, and plots them as a histogram. There is a broad peak between 10 and 25 km, with a sharp drop-off for larger separations. The dashed line shows the expected curve if the volcanoes are distributed randomly within the area of volcanic activity in Iceland. It also shows a broad peak, at similar separations, but the random distribution doesn’t have the steep fall-off.

So it looks like close to other volcanoes, Iceland’s boom-boxes are quite independent, but the volcanoes don’t like being too far apart. It is less like the endless field of well-separated crows, and more like animals on the African plains staying within walking distance of the water holes. In science terms, the volcanoes ‘cluster’. Or to a volca-ecologist, they ‘flock’, ‘herd’, or ‘school’.

Volcano migration

The volcanic zones in Iceland are about 50 kilometers wide. Are we perhaps seeing the effect of this limited width, beyond which the volcanic fields lie fallow? If you draw a circle which is larger than 50 km diameter around a volcano, part of the circle falls in the area where there are no active (or potentially active) volcanoes, and which lacks suitable partners.

In fact, the typical distance to a nearest neighbour is something like half the width of the volcanic zone. This suggests there typically are two volcanoes across the zone, and these act as nearest neighbours. We can explain why this might be the case. An Icelandic volcanic zone is centred on a spreading rift. A spreading rift spreads – that is how it makes it living. Now assume that a volcano develops on or near the rift. The spreading will slowly take this volcano off to one side. While this happens, another volcano may form and start to move away in the other direction. The volcano dies when it gets to some 20-30 km from the rift, but by that time other volcanoes are already taking its place.

What the plot may tell you is that you indeed tend to have two volcanoes at any one time, on either side of the rift. These volcanoes will not have the same age but they will have the same fate.

The reality is a bit more complex, as it always is. Each of the volcanoes itself develops a rift, which can take up some of the spreading. A series of parallel rifts develops, rather than just one main one. But the basics of the model works well.

Snuggly volcanoes?

But is there a minimum distance? This is not obvious from the plot, but there are indications in the table that there are few pairs closer than about 10 km. And of the 8 such pairs in the table, only two involve pairs where both have recently been active. If I look at the 26 volcanoes that have erupted in the last 2020 years, only two (8%) have a nearest neighbour less than 10 km away. In contrast, of the 19 volcanoes for which the most recent activity is older, five (26%) have a closer neighbour than this.

So it seems that older, sedate volcanoes can snuggle together, but more dynamic ones need their space. To test this, I removed all volcanoes listed as ‘dormant’ from the list, and reran the nearest-neighbour algorithm. I could have been harsher and also excluded the ones listed as ‘unknown’ or have an eruption date more than a few thousand years in the past, but it becomes a bit arbitrary. I went for the minimum exclusion. A few volcanoes now had to find new partners, as their previous nearest neighbour was no longer. The new partnerships are listed below, with the separation in km and in brackets the separation to the previous partner. The dormant volcanoes are themselves also removed from the above table: they had nearest neighbours at 6, 8, 11, 20, 25, 25, and 26 km.

Bárðarbunga 21.16 (20) Loki-Fögrufjöll
Grímsnes 16.66 (15) Hrómundartindur
Hrómundartindur 13.76 (6) Hengill
Hveravellir 33.88 (32) Prestahnúkur
Kollóttadyngja 15.60 (11) Hverfjall
Ljósufjöll 73.70 (48) Snæfellsjökull
Snæfellsjökull 73.70 (26) Ljósufjöll
Þórólfsfell 10.31 (8) Eyjafjallajökull

Now I have remade the distance plot for nearest neighbours, with rather large bins (10 km) because we are looking at small differences.

Black: nearest neighbours for all volcanoes in the list; red: with all volcanoes listed as ‘dormant’ removed.

With these rather large bins, the difference is notable for the first bin only: the number of pairs with separation less than 10 km has almost halved. So indeed, close pairs are more likely to involve one (or two) dormant volcanoes. It is hard to prosper in the shadow of an active neighbour.

So in conclusion, there is a minimum distance of 10 km below which Icelandic volcanoes become uncomfortable. But this separation applies mainly to more frequently active volcanoes. Close neighbours are tolerated if they are dormant.

It takes a village

The well-known expression is that it takes a village to raise a child. (This may explain a lot about New York City.) It is not just the nearest neighbour: we should look at the full set of distances between volcanoes. This is done below.

Distances between all pairs of Icelandic volcanoes

The plot shows a rapid increase, up to about 20 km: this is the typical separation between closest volcanoes. It is followed by a gradual increase up to 100 km, with a fairly flat peak at larger distances, after which it declines again. The gradual increase shows the effect of clumping together of volcanoes: the increase stops when it reached the typical size of a clump. Thus, a clump of volcanoes is typically some 100 km across. If the volcanoes had been distributed randomly over all of Iceland, the plot would show an increasing trend until it ran out of Iceland. Once the distance becomes more than half the diameter of Iceland, there will be fewer pairs: volcanoes near the centre of Iceland run out of volcanoes to pair up with. This is seen in the plot from about 250 km onward. But between 100 and 250 km, the plot is fairly constant. This means that the distribution is not uniform but condensed: most volcanoes are close together but others are sparsely distributed well outside the clump.

I have mentioned that the nearest neighbour plot shows the behaviour of the spreading rift. In contrast, the pairing plot (also called the two-point correlation) shows the effect of the hot spot. The size of a volcanic area is something like 100 km. This is the area over which the hot spot can melt through the crust. Beyond this, the hot spot runs out of heat.

Anything else?

The closest pairing is that of Eldfell and Helgafell, on the island of Heimaey. The two are less than 1 kilometer apart! One is a recent eruption, and the other one erupted 6000 years ago. It appears that the underlying magma found the same weakness in the crust at both times, but during the recent eruption the old (cold) conduit had become unusable. A new one was therefore formed. In a larger volcano, this might have counted as two eruptions from the same volcano, but here they are listed as separate events.

We have already mentioned that the closest pairs tend to consist of less frequently active volcanoes. If a volcano has not erupted in a very long time, and perhaps is listed as dormant or unknown, there is a good chance that its nearest neighbour is also quite inactive. There are exceptions, but typically, quiet volcanoes have quiet neighbours. And the opposite is trued as well: if a volcano erupts frequently (i.e. has a fairly recent date of last eruption), the neighbour has a good chance of doing the same.

It is obvious from the table that nearest neighbours tend to have similar heights, perhaps not surprisingly. Adjacent volcanoes often have access to similar amounts of magma to build up their edifices.

And one final comment: do you know which is the best connected volcano in Iceland? There are various ways to define this. I used as definition the number of volcanoes between 20 and 40 km distance. This excludes most of the closest neighbours, and instead gives an indication of how dense the volcanic field is far enough away to not be affected by the particular volcano, but close enough to be inside the ‘clump’ (if one exists at this location). Curious? Have a guess. I’ll reveal the answer in a few days.

Feeding frenzy

What does this tell us? It is all about the magma. This is the precious resource for which there is strong competition. Just like African animals congregate around the water holes, so Iceland’s volcanoes cluster around the magma hole. And these are greedy creatures. An Icelandic volcano is the elephant in the pool, quite capable of finishing the whole supply itself, leaving little for the other animals. Dormant volcanoes don’t drink much, and they are happy to be denied access while lurking nearby. But a typically active Icelandic volcano needs a monopoly on a drinking area of some 10 km diameter. No other dynamic volcano can be tolerated within this area.

Not every area in Iceland is equally productive. The eastern volcanic zone from Katla to Askja is best at producing magma. Most of Iceland’s lava erupts here. So you might expect that volcanoes elsewhere in Iceland, who have to live on drier ground (as far as magma is concerned) would be further apart, just like those semi-desert bushes grow further apart as conditions become more desert-like. But the table does not show this. The typical distance between volcanoes is the same across Iceland. It seems that if the magma production is less, volcanoes grow less active but not more distant.

Volcanoes are warts growing on magma chambers. The real activity is in those chambers. Sometimes the chambers fill up and leak out a bit: the volcano erupts. At other times the chamber is less full and the wart on top is sitting idle. When we talk about the ecology of volcanoes, it is really those magma chambers that do the competing. In our African analogy, we are counting the oxpeckers rather than the buffaloes they feed on. The magma chambers are locked in a struggle for life. Their food is magma and only the fittest will get it. Where do magma chambers get their magma from?

The melt production happens deep down, near the bottom of the crust. This is the underground aquifer, sitting around and below the spreading rift. The magma chambers have their roots into this aquifer and draw up the magma, each to their own chamber. This is why adjacent volcanoes often have similarities: their magma chambers feed on the same aquifer. And a magma chamber will not allow a nearby chamber to grow. Only some 10 kilometers away is magma independence achieved. The real personal space of volcanoes is underground.

As an aside, you may guess that the depth of the magma chambers is comparable to half the distance between adjacent volcanoes since otherwise a volcano could too easily access the wrong chamber, in an act of volcanic piracy or parasitism.

I mentioned the migrating volcanoes. Now we can understand why a new volcano does not start growing as soon as the previous one has left the rift. It can’t do anything until that volcano is some 10 km away. It also explains why the new volcano will probably start on the other side of the rift, as this is further from the old one. But why do we not get a long line of volcanoes? Wy do they die? This is because the aquifer is mainly located around the rift. The magma chamber has its roots into this area. As the volcano migrates, like wildebeest on the savannah, the roots (ok – not quite like wildebeest and perhaps more like ents) become angled towards the rift. But the magma needs a steep enough angle to move up. As the volcano becomes more distant, the angle shallows; the magma flow is slowly impeded and the volcano dries up and dies. It will survive only if it is lucky enough to find another aquifer, and begins to fight another volcano for this resource.

Schooling in isolation

People need both company and space. So do animals. And so do volcanoes. For they too interact, compete, and predate each other. It is a volcanic ecology, perhaps missing only the packs of roaming wild volcanoes attacking the herds and stealing their magma. In Iceland, volcanoes need some 10 km of social distancing for maximum comfort. Perhaps in this, Iceland’s volcanoes resemble its people. They need their space to grow.

Albert, June 2020

Alone, and too close for comfort

And remember the challenge question: which do you think is the best connected volcano in Iceland?

Answer Defining the connection as the number of other volcanoes between 20 and 40 km distance, there are two winners. The top prize (shared) goes to Torfajökull and Eyjafjallajökull, with 6. Third prize (shared) goes with Þórólfsfell, Trölladyngja and the angry one, Grímsvötn, each with 5.

97 thoughts on “Volcano ecology

    • Will Grimsvötn have a VEI 6 eruption? That would cool the planet and temporally halt the global warming.

      • Among basaltic holocene volcanism thats rare.

        But Grimsvötn did a 150 km3 basalt plinian phade split into numerous 30 km3 episodes a few 1000 years ago.
        In its caldera.
        Postglacial decompression melting was likley the culprit.

        Grimsvotn haves a large magma supply
        But most of it goes into passive rifting.
        Skaftareldahraun was an Ice free flood basalt from Grimsvötn line.

        If any above 10 km3 event happens in Iceland, it will likley be a Laki like eruption.

        A subglacial Laki is not Impossible
        in Thordarhyrna
        Starts as a long line of 2011 ash columns and after a while .. 1000 meters lava fountains shoots up the icesheet.

        Grimsvotn can do a VEI 6, but thats very unlikley now
        Extremely unlikley

      • Next eruption will likley be a smaller or medium sized VE4

        If we haves luck We may get a 1996 again

        But I see it unlikley for Grimsvotn to react the 2011 show next time

      • VEI 6
        Is either a basaltic pheratoplinian

        Or an Ice free flood basalt in Grimsvötn rift

        The slow and very long lived compound shield flows like Trölladyngja and
        Puu Oo, cannot be ranked in VEI system

      • Albert question
        Next time Grimsvötn:
        Is it possible for a surtsey phase in the caldera? Pheratoplinian first and then surtseyan in the lake and then a small ”lava bunga Island” grows out the meltwater lake.
        Im soure it have happened before.
        But I knows Grim likes to do short fast eruptions.

        But both 2004 and 2011 formed small tuff cone Islands in the meltwater lakes blown in the icesheet

        • The lake does not last long if the eruption is in it. The ice melt has more effect. It can get quite ashy

      • It an eruption last long enough in Grimsvötn

        Will it go effusive?
        Building up a tephra cone in the meltwater lake

        2004 and 2011 had tephra Islands in the final phases

  1. If you discard Eldgja and Skaftar rift eruptions should you also not discard Holuhraun and other rift eruptions?

    My logic is that you’re looking at the influences one volcano has on neighboring volcanoes – I think you’re much more likely to see a consistent neighbor effect on volcanoes with a magmatic system instead of a transitory magma supply intruded along a rift. Mixing the two situations may end up confusing your results.

    Also, my guess for densest clump (without looking at a map, this is more fun as a closed book test) is the surroundings of vatnafjoll?

    • Yes, there is a case to discard Holuhraun. But I decided to keep every eruption where there was a single point of eruption, and this was the case in Holuhraun. I only removed ones where the eruption could not be pinpointed but happened over an extended rift. I am not sure why Laki and Eldgja were in the original list and older similar eruptions were not. This way the list became more uniform. And Holuhraun has created a nice shield.

      • Holuhraun is a crater row vent and Aá lava flow field
        Not a shield volcano

        Trölladyngja is an Icelandic shield volcano, its like a
        Puu Oo on steroids

        • Yes, there were but they left no surface expression. But once you start deselecting data you have to be consistent. Otherwise you are biased by what you know (or expect). Removing Laki or Eldgja was allowed as they erupted at many different location and you can’t define a distance. A holuhraun 1500 years ago would have been listed as a single, normal eruption. Removing those puts in knowledgfe ‘you can’t have a volcano there’. And that makes the result biassed. So I didn’t do that.

  2. What is the most connected volcano in Iceland?
    To my mind comes either one of these:
    1) Tindfjallajokull (near it, lies Hekla, Eyjfjallajokull, Torfajokull and Katla)
    2) Eyjafjallajokull (near it, lies Hekla, Westman Islands, Torfajokull and Katla)
    3) Bardarbunga (near it, lies Tungnafellsjokull, Grimsvotn, Hamarinn, Kverkfjoll) I think Hofsjokull is more than 40-50km away…
    4) Grimsvotn (near it, lies Bardarbunga, Hamarinn, Kverkfjoll, Oraefajokull and Esjufjoll perhaps) And also Thordarhyrna

    I am only considering major and well-defined volcanic systems (central volcanoes), not the small types like Trolladynja, Holuhraun and other even smaller mountains.

    Grimsvotn might be the best connected one.

    • Looks like a normal swarm so far. Happens in the region every few weeks/month.

  3. Probably another sheet rifting event. The quake intensity is fairly high.

  4. Recent observations by scientists from the Icelandic Met Office (IMO) monitoring the sub-glacial volcano lead to this conclusion, IMO reported in a recent press release.
    In the last weeks, several measurements were done at Grimsvötn volcano. They discovered a currently very high output of SO2 gas in the southwest corner of the caldera in Grimsvötn, very close to the eruption sites of 2004 and 2011, a clearly alarming finding: “This is the first time that we measure so much SO2 at a volcano in Iceland that is not in an eruptive phase and its presence is indicative of magma at shallow level”, said volcanologist Melissa Anne Pfeffer from the IMO who was among the specialist during the recent measurements. In the area where geothermal activity of the volcano can be detected at the surface, this has also notably increased.
    Sulfur dioxide (SO2) is one of the principal volcanic gasses contained in solution in the magma at depth, but released early when magma reaches shallower depths and pressure drops. It can be regarded as one of the most common precursors when volcanoes erupt.
    Earthquake activity under the volcano has been slightly elevated at the volcano for a while, along with an inflation of the ground surface. All these data likely reflect the gradual rise and refilling of magma into the volcano’s shallow reservoirs.

    Rising sub-glacial lake water levels
    In addition, the level of the volcano’s sub-glacial crater lake has been found to have risen, due to elevated heat release and consequent accumulation of melt-water.
    The latter is of particular concern as it increased the likelihood of the occurrence of a glacial flood (jökulhlaup), if the lake suddenly drains from underneath the glacier in a massive flood: once a critical point is reached, the water can lift the ice and create an outlet channel that is quickly widened by a combination of erosion and further melting, resulting in a catastrophic water release that typically devastates the flood planes in its path, destroying almost everything in its path and almost certainly cutting the ring road.

    Increased chance of eruption starting at the end of a glacial flood
    The next glacial flood of Grimsvötn cold very well also trigger an eruption, as sudden pressure drop above the magma chamber would induce rapid degassing in the magma, similar to the effect of opening a champagne bottle. A glacial flood would also almost certainly occur if an eruption starts without being triggered by a flood in the first place.
    According to IMO, “The current conditions of Grimsvötn volcano are such that the water level is rather high and the pressure in the magma chamber below the caldera has reached values comparable to those prior to the last eruption. Therefore, the possibility of an eruption triggered by a glacial flood, which could occur in the coming weeks or months, has to be considered. However, this may not be the case, and the next glacial flood may not lead to an eruption.”

    When will the volcano erupt?
    Grimsvötn is one of Iceland’s most active volcanoes, with eruptions occurring every 5-10 years on average, the last having occurred in 1996, 2004, and 2011. Statistically, the next one would be expected to happen any time now or in the few next years.

  5. What’s going on in the Tjornes fracture zone?(I suppose the clue is in the name)

  6. Nicely collated stats !!
    Looks like the Iceland ‘zones’ don’t get much of the ‘monogenetic’ volcanic field effects, as spreading too rapidly for one eruption’s chilled ‘pipe’ to totally inhibit neighbours. In effect, flank eruptions ensue…

    I’m reminded of a so-scary pic taken along the Cascade range, with that line of vast cones. The odd-one-out, of course, of course, is Mt St Helens. IIRC, offset by ~25 km due to subducting plate’s break diverting rising magma. A situation akin to Naples area ??

    • Is it me, or is the IMO geologist going to have some overtime work tonight? A serious swarm! (with initial locations scattered all over the place)

  7. Tjörnes fracture zone is gong bananas, that’s what happends. 22 quakes in range from 3 to 3.9 an one above 5.
    And when it comes to Grimsvötn is my bet: eruption starts wednesday at 16.53 gmt.

      • The quakes of the last five hours still need their IMO review. The location and magnitude is final only after that.

  8. Albert,
    Thanks to you for all the effort you put in for the data crunch. Very informative.

  9. Can someone tell me how IT is thst when a big swarm like this in tjornes, IT is quiet elswhere in iceland. IT happends every time its a big swarm

    • Humbly, I must note that Iceland has been anything but quiet in the last few days. The Reykjanes Peninsula just spit out over 1500 quakes in a single day this last week, and these latest shocks in the Tjörnes fracture zone swarm triggered activity south to Bárðarbunga (and maybe Greip?)…all together meaning that heightened seismicity is spanning the entire country (with a few gaps here and there) at this time.

    • Not likely. No “wet” signals in the drumplot to indicate magmatic tremor/movement. Most likely purely tectonic from the looks of “aftershock zone” that lit up like a Christmas tree minutes/seconds after the first main shock. Most likely the aftershocks away from the hypocenter are induced (i.e. not direct stress triggered).

  10. From what I can see (so far) it looks like a tectonic adjustment.

    This period is supposed to be the height of the general Icelandic cycle of decreased / increased volcanic activity. If I remember the peak of the activity is @ every 120 years or so. And we are approaching the next peak.

    With the seismic activity in the Reykjanes Peninsula, across Iceland and now here in the Tjornes Fracture Zone, I should expect this to be a symptom of the peak activity.

    That volcanic activity may follow this peak is something yet to be witnessed. But it stands to reason it will, because heightened volcanic activity occurred in the previous maxima of icelandic seismic activity.

    • Hmm that should really have been posed as a question… I’m spouting off like an expert (and I am not, though I am good at making a cup of tea). Feel free to knock the wheels off my cycle theory!

  11. Wonder how much stronger quake is needed to cause a tsunami wave in the narrowing bay towards Akureyri🙄😬

    • Main risk for that is not from earthquakes but from submarine landslides. Rare but not impossible

  12. Biggest so far if it hold on review

    Sunday
    21.06.2020 19:07:52 66.440 -18.770 1.1 km 5.9 50.5 33.8 km NNE of Siglufjörður

    • Google translated

      https://www.vedur.is/um-vi/frettir/jardskjalftahrina-20-km-nordaustur-af-siglufirdi

      At 19:07, an earthquake of over 30 km NNA Siglufjordur, of the size 5.7 according to Art. initial results. The quake was found in many parts of the North. Kl. 18:20 an earthquake of magnitude 4.4 occurred about 35km north of Siglufjörður. There have been reports that all the earthquakes were found from Siglufjörður to Akureyri. The quake that raged over at. 19:07 is the biggest quake ever recorded in the hryvnia. The quake, on the other hand, recorded far more land than the previous quakes, so the effects of these quakes were not so great inland.

      • USGS has it a M6.0. IMO is probably more accurate. It is lucky that it was a fair distance off-shore.

        97 stars now. Solstice fireworks.

    • A feast of stars! 92 at the moment. That is impressive.
      Many of them have not been checked yet, so strength and location aren’t accurate.


      Credits data and graph IMO.

  13. Does anyone have a link for Cumulative Seismic Moment for the current mega-swarm?
    I’m guessing maybe in the lo-7’s by now?

    • More like low 6’s. It takes around 30 M6 to get to one M7 and M5.8 is quite far from an M6.

      To get a graph, you can go to the new (?) tool Skjálfta-Lísa at skjalftalisa.vedur.is, select Svæði -> Tjörnesbrotabeltið and then click on the third icon on the menu bar. That will take you to some plots. Only verified quakes are included and there is a delay in the updates, so the M5.8 is not included yet.

      • I make it as a cumulative M5.9 at the moment. The energy increases very rapidly up the scale, so in most cases only the largest few earthquakes count in the cumulative energy.

        • Tricky thing, that logarithmic scale. BTW, I wonder what formula IMO uses to convert between moment magnitude and Nm. Their graphs don’t seem to match the formula 2/3*log10(M0)-6.06. Do they go by radiated energy or something else? I never got my own CSM plots to match the ones from IMO. The general shape looks similar, but the scale is always way off.

        • Thanks to you and Tomas for the correction(s). Not sure how I ended up with lo-7’s per my envelope. Lo 6’s seem much more realistic.

  14. Wonder if this ongoing swarm is the result of a suddenly increased tension in the crust by forces from below or if it is the result of a long build up ending in this release swarm.

    • Yes, Albert, You and VC spoil “The News” for me….. i keep thinking: “That’s old news.” when i hear stuff on tv. i keep thinking, they must read the stuff i read. Hubby keeps saying,”Don’t You want to know what’s going on??” and i say…. i already know… 😉

    • Even my dad mentioned this in casual conversation. He does some work relating to climate change though.

  15. Nice Popo timelapse from yesterday, with lighting. Very tall stratovolcano that Popo.

    • “The capital of Reykjavik recorded the largest warning.” Sounds like one of the quakes popped around to Reykjavik to deliver a personal message.
      Bless them. Well, it has entertainment value I suppose.

      • Bless them

        Err… BUAHAHAHAHA!

        (Don’t ask, it’s a southern thing… and not the nicest thing to say to or about someone.
        It’s not purely derisive, and I’m sure you had all good intentions for stating it.
        )

        • In the UK we may choose to use it in a “very very dim, but well meaning” sense.
          Which is what I used.
          I’ll look up your version…!

          • Which I did. Now it makes me wonder about the game, Skyrim, where on paying a beggar you get the response: “Bless your kind heart.”
            A world of new meaning! Thanks GL!

      • Probably a mistake in the translation from Icelandic. “Jarðskjálftinn fannst í Reykjavík” was probably translated as “the earthquake was found in Reykjavik”, instead of “the earthquake was felt in Reykjavik.”

  16. Remember the quiz question? The answer has been appended to the post. Birgitcarow gets the point

    • 🙂

      It´s actually me. But I posted my guess while accidentally logged with my wife´s wordpress account.

      The largest clusters of Icelandic volcanoes lie in two locations:

      – One is around Eyjafjallajokull, with the famous neighbours of Katla to the east, Tindfjallajokull and Vatnsfjoll and Hekla to the north, the Westman Islands to the southwest, and further to the northeast (but still within walking distance), Torfajokull. Counting 6 neighbors to Eyjafjallajokull. I forgot Vatnsfjoll in my original comment (although it is not an established central volcano per se, it is considered an independent volcanic system)

      – The other region is centered around Grimsvotn, where the hotspot center is located. Neighbours are Bardarbunga to the north, Hamarinn to the northwest, Kverfjoll to the northeast, Esjufjoll to the southeast, Thordarhyma to the southwest, and Oraefajokull further to the south. Counting 6 neighbors to Grimsvotn, but not sure if all are within 40km.

      • For Grimsvotn, most neighbours are close to my (artificial) 40-km limit. Your list is pretty good, with Kverkfjoll at 39 km. (For some reason Hamarinn is not in the wikipedia list, so an appeal could be made against the outcome.) Same for Eyjafjallajokull: it has close neighbours, but wins because of both Hekla and Helgafell are 39 km. That was not a deliberate choice but based on the sharp decline in the graph for that distance.

        • Hamarinn is Loki-Fögrufjöll, the other central volcano southwest of Bardarbunga, within its volcanic system.

          It erupted last in 1910 (with ash) but it had many unconfirmed eruptions since then, one of which in 2011, in the same week that Katla also had a potencial subglacial eruption. Hamarinn is a significant volcano and it has active cauldrons which release water in glacial floods, periodically.

          https://en.wikipedia.org/wiki/Loki-F%C3%B6grufj%C3%B6ll

          • Thanks for the information. 1910 is also the data for the last eruption of Bardarbunga itself but I could find no details on it. When did Bardarbunga last have a summit eruption?

          • I think it´s very difficult to know that.
            While Grimsvotn erupts regularly and its ash plume can be seen erupting from two nearby settlements at the edge of the ice cap (from about 50km afar), Bardarbunga is some 30km behind it and therefore out of view from any settlement. If it erupts, it will be hard to spot it, and an ash plume could have occurred anywhere else in Vatnajokull (Gjalp, Hamarinn, the Loki-Fögrufjöll cauldrons southeast of Hamarinn, or northwest of Bardarbunga towards Holuhraun).

            Just to complicate, the weather is often cloudy at the ice cap, which makes visual observation difficult, even in modern age.
            In 1996, after the glacial flood and Grimsvotn eruption, Bardarbunga erupted for about an hour or two (ash plume) but the visual observation was difficult from an airplane. It wasn´t confirmed where exactly happened.

            Between 1902 and 1910, there seems to have occurred two significant events in Vatnajokull, and in both cases possibly somewhere in Bardarbunga outside of the caldera.

            It is unclear when was the last time that the caldera erupted.

            Katla on another hand is much clearer, erupting almost always from its caldera and easily seen from the populated areas nearby.

    • Is it possible for a Surtsey Island to form in the Grimsvötn caldera, after erupting for a while?

      All Grimsvötn eruptions is like Surtseys first phase
      But they rarely go beyond tuff cone Islands in the meltwater lakes before stopping.

      • The lake would have disappeared long before. You need a lot of water for this. The Atlantic Ocean has the advantage.

        • 1996, 1998, 2004 and 2011 all formed small Islands in the end in the meltwater lake

  17. Here Albert .. good video.
    You can see Nyiragongos lavas viscosity in extremely high closeupZ
    It does not appear as fluid as the legends say.

    Infact it looks No more fluid than
    typical runny basaltic lava.
    Despite extremely low sillica it
    looks No more fluid than Hawaii.

    Maybe Nyiragongos steep slopes is a huge part of the media legend about Nyiragongos low viscosity.

    Temperature is important too

    https://m.youtube.com/watch?v=toETgVljr9o

    • Eruption rates are also very important, and they are quite high during flank eruptions of Nyiragongo.

      • Yes thats true
        But seeing it as slow flows

        Really gives away Nyiragongos viscosity

    • That’s cool! Nishinoshima keeps puffing away and is slowly growing both on its cone and through the lava flows.

      Yes, it is a bit lonely, far from any other island (at least above the ocean surface).

  18. This is not really a reply but more of a shared experience, I bought a lava bomb for landscaping purposes. I carve a hole in it fill it with soil and plant hens and chicks succulents in it. Well I got one at a landscapers and carved it this week. I should mention I have done about 7 of these befor and so have experiance but this one was different! It was pure glass! I have 2 kilns and do glass fusing so recognized complete vitrification, it was so foamy! It was like whipped eggs. It cut through you befor you even felt it.I was wondering what temperature that would have been when it was thrown out and it seems to me to be so foamy it must have been a he’ll of a big eruption. I have heard this Feather Rock comes from out west in the USA anyone know anything about the eruptions that produced such a lava bomb?

    • It requires very rapid cooling. It doesn’t have to be particularly hot to begin with. It is hard to cool fast if you are a big rock. The foamy structure comes from gas bubbles in the rock. Perhaps it was ejected from quite deep? Perhaps it fell in water? I am guessing here.

    • We have such all over E.Oregon, particularly The lava country around Bend, Redmond and SE Oregon. Got a quanity of that rock in the garden in my years flying out of Redmond. NE Oregon is Columbia River Basalt Mother lode country so there is less of that.
      and what isn’t Basalt is some sort of Granitic type. Lava Butte area ,McKenzie lava beds Newberry caldera, etc. Crater lake are are too. Lots of energetic gas filled lava..
      I have a succulent in one of those lava bombs right now..

        • Fun basaltic area to look at is the Boring Lava – a little bit older, but it runs from SW Washington State down almost to Salem. All monogenetic, but the activity comes in pulses separated by several thousand years. Weak area in the crust, some extensional faulting is my guess. Some of the cones are right in Portland city limits, so I see them every day while I’m at work. Part of Portland’s water supply comes from a lake inside the crater of one of the cones.

          • Yeah my cousin lived on side of Mt. Tabor. Lots of cones for sure..

  19. Just a amateur observation. Since the Tjornes swarm has been on going I have noticed the rest of the country has gone fairly quiet seismically speaking. Are there teleconnections through out Iceland that allow pressure release even though there is pretty good distance between normally active seismic zones or is this just coincidence?

    • Also amateur bit have noticed the same at many occasions. I think a part of this is that an intensive swarm like this makes so much noise so it drowns all weaker quakes around to the detectors.

  20. Thanks all, everyone I showed this bomb was amazed at how glass like it was,truely like glass shards not like pumice at all. I have visited the Big Iland and thought I knew lava but this is not like Hawiian lava at all. I would love to get out to the West coast to see where this type comes from.

    • Ellen…you mentioned before how much the rock foamed up when melted, was the foam white in color ? Also, does the rock fracture in curved or conchoidal manor ?

      • Hi Glen it is light grey and has several thin rings of white around the circumference it doesn’t fracture conchoidal as it is pure foam not obsidian, picture egg whites whipped to a stage before they turn to meringue, they are cells about 1/16th inch to 1/8th inch not at all like the pumice I have had before they are glass. They are so sharp they are like ground glass to handle. I have kept them to see what they will do in the kiln added to a glass project down the road.

        • Thanks for the reply Ellen. I am not sure what you have…..pictures might help, but I am not an expert. Does the foam consist of lots of large bubbles only, or does it have lots of microscopic bubbles ? (If you can see)

  21. Iceland is Teaseland right now. );
    Thorbjorn is stuck in neutral, Katla is doing nothing, Grimsvotn is slowly inching forward and, Tjornes not even close! Everything is so slow!!! Any volunteers for sacrifice? It would speed things up!

      • They now appear to be working. There appears to be a slight amount of tremor associated with some 40km deep quakes at around midnight UTC.

        2020-06-30 00:12:34 2.4 40
        2020-06-30 00:03:00 1.9 43

    • Holidays are upcoming. Can’t have too much rubble in the skies by then 😎

  22. Grimsvötn gas emissions and heat is increasing on the South Caldera wall
    Very similar to the run up of Halemaumau 2007
    Gas emissions and heat is increasing.

    But it will be a pheratoplinian – surtsyean eruption like 2004

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