Sleeping in our back garden, part II: The Laacher See and the secrets of dating

In the previous post Gijs described the surprising history of Europe’s most underestimated volcanic field. Much of the time the Eifel does nothing. On occasion it does a small eruption, just when you weren’t looking. And very rarely, it goes big, covering the surrounding areas in meter-thick ash.

Gijs described the area, the monogenetic volcanoes, and especially the Laacher See, the hole left by the largest eruption in Western Europe since before the ice age. The local deposits are tens of meters thick. It happened during a warm interlude in the ice age, in a newly forested area. Those forests across the region died, and took decades to recover.

Some are born great, some achieve greatness, and some have greatness erupted upon ’em.

What would a recurrence be like? (It wouldn’t be at precisely the same location because the volcanic field is monogenetic, i.e. every location erupts only once. It would be somewhere nearby.) Remember how even a small eruption in Iceland in 2010 caused transport chaos across Europe. It stopped planes from flying. A small ash cloud that would have had no impact in the stone age, became a disaster in the modern world. Nowadays, effects far away from an eruption can be more severe than those nearby, as was the case for Eyjafjallajökull. And the Laacher See was not a small eruption: this was a VEI-6 in the industrial heartland of Europe. The impact would be felt far and wide.

In a recurrence, the explosion will be heard across Europe. Imagine much of Western Europe in darkness for a day, pyroclastic flows reaching tens of kilometers from the site, and the city of Koblenz, 15 kilometers away, buried under 1.5 meters of ash. The airborne ash affects 14 separate countries. Rafts of ash block the Rhine: when the dam breaks, the Rhine delta floods and the ash rafts reach England. Transport comes to a halt for days to weeks. Six million people are significantly affected, from Bonn to Amsterdam. Health care is the biggest casualty of the eruption.

Source: Felix Riede, Past-Forwarding Ancient Calamities. Pathways for Making Archaeology Relevant in Disaster Risk Reduction Research. Humanities 6, 79 (2017)

Of course the chance of a 1-in-100,000 year event happening next year is not very high. There are more likely events, such as the 1-in-500 year rainfall the region experienced last year, and the 1-in-100 year pandemic. But then, we weren’t prepared for those either, in spite of the certainty they would happen again.

This post is not about this. It is about time.

The deposits of the Laacher See have created a marker in the soil which is used to synchronize archaeology across Europe. It acts as a time signal. You can compare it to the cannon on Signal Hill which still fires every day at noon, so that ships can set their on-board clocks. (It is one of only two cannons in the world with a twitter account. It tweets ‘Bang’ once a day.) Of course nowadays this is for the tourists, not the ships which all can use GPS for their time signals. But volcanic soil markers are like a watch with only an hour hand and no numbers: you can see time progress but still don’t know what the actual time is. Thus it is with the Laacher See. This post is about dating the eruption with water.

But that is for later. The Laacher See eruption came just before the onset of the Younger Dryas, when Europe suffered a sudden and severe set-back in its ice-age recovery program. It was portentous: a sign of a disaster to come.

The Younger Dryas also has a dating problem, written in water. So let’s start with water.

The weight of water

We could not exist without water. A drink every now and then is essential to avoid dying by dehydration. But water is a strange substance with strange properties of physics which life has come to depend on. It can crawl up the inside of a stem – hence we have plants and trees. The solid phase floats – hence we have ice on the surface rather than on the bottom of the sea, providing a home for land-dwelling life on the ocean. Water is strong: you can walk on water – if you are an insect. But water also has some properties that are more detrimental to life. It makes the ground unstable. Even a thin layer of ice can cause heavy rocks to move.

For an inert substance, water is also amazingly explosive, as Hunga Tonga proved. The Laacher See started as a powerful hydrothermal explosion. In Europe’s snow catastrophe of 1979 (this was the era before global warming took off, now hard to remember) I saw houses buried to their roofs under snow, in an area that now gets very little snow.

That snow can also record our climate. That is part of our story of the Laacher See.

Volcano’s evil manners live in brass; their virtues we write in water.


Snow provides a historical temperature record. Obviously, this record is no more permanent than the snow itself, and so the record exists only where snow can survive the summer. One such place is the glacier of Greenland, which stores snow that fell more than a hundred thousand years ago. In Greenland the ice age still lives on.

But how does snow record the ancient temperatures?

Water comes in three different phases: solid, liquid and vapour. Each of these comes in many different forms. The solid phase forms ice but also snow. The liquid phase forms oceans, but also rain or drizzle. The vapour phase forms clouds, or mist, or fog. The UK version of English has 104 expressions for rain! (but only 10 expressions for falling snow). The Inuktitut language has 93 different words for sea ice. In the end, all these different phases, phrases and expressions describe a single molecule: H2O.

But not all H2O molecules are the same. Most of the oxygen in H2O is 16O, the common isotope made from 8 protons and 8 neutrons. But a small fraction is 18O, a slightly heavier form of oxygen which carries two extra neutrons. The H in H2O can also come in two forms: normal hydrogen consisting of just a proton, or heavy hydrogen (called “deuterium” or just ‘D’) which has an extra neutron. Combining all, there are 8 possible varieties of H2O, which carry between zero (for H2O) and four (for D218O) excess neutrons. The most common form after plain H2O is H218O which accounts for 0.204% of all our water.

The excess neutrons make the water heavier and more sluggish. Think of the neutrons as a company management team: more managers make things more stable but slow everything down.

The sluggishness of the heavier forms of water shows up well in the Greenland ice cores. The ice comes from water evaporating from the oceans, forming clouds, precipitating as snow, and over time being pressurized into ice. The problem is the first step, the evaporation. The lighter water (with 16O) will evaporate but the heavier water (with 18O) is less nimble and is more likely to stay behind. The snow that precipitates from the clouds over Greenland therefore has less 18O. It is a small difference, but measurable. Snow in Greenland is down by about 3% compared to the water it came from. ( 18O accounts for 1.98% of the snow, rather than the original 2.04% before evaporation.)

When it is warmer, the higher temperature overcomes the sluggishness and more 18O joins the clouds that make the snow and ice. When it is colder, more 18O stays tucked up in the warm ocean and refuses to get up and join the action. That difference shows up in the snow. Measure the amount of 18O in the precipitation, and it tells you the temperature. In this way, by measuring the amount of heavy water in the deep ice cores, we can tell how the climate has changed. And because the ice cap is so old, we can see the temperature variations over a period spanning more than 100 millennia.

Strictly speaking, this is the temperature of the sea and air where the water evaporated. And there is a complication: if the cloud produces rain or snow before reaching Greenland (as it will), that precipitation will remove more 18O (it drops out more easily, being heavier) and this increases the deficit. But it appears that the fraction of 18O in the ice remains a very good indicator of the average annual temperature. Just don’t ask to put actual temperatures on the scale.

Vienna’s ocean

The 18O abundance is presented as the difference with respect to the 18O abundance of average ocean water. The ‘average ocean’ is (surprisingly) an official standard. It is rather better defined than for instance the ‘olympic swimming pool’ you’ll find quoted in newspapers. (An olympic swimming pool is 50 by 25 meters, and at least 2 meters deep. Let’s call this one OSP. The ‘at least’ is the tricky part, as they may be deeper. It means that if you carefully measure out 1 OSP, and use it to fill an olympic swimming pool, it may not be full.)

The ‘average ocean’ is called the ‘Vienna Standard Mean Ocean Water’ (VSMOW).

If it is not immediately obvious why land-locked Vienna has ocean water, the reference water is maintained by the International Atomic Energy Agency which is based in that city. It was created from a mix of water collected from the surface of the ocean at locations across the globe. Reference samples are for sale from IAEA. Don’t rush to buy some: it costs an eye-watering (pun intended) 10 Euro per milliliter. VSMOW is used to define a standard for the abundances of isotopes of hydrogen and oxygen – and it is used for nothing else. Why the Atomic Energy Agency? The original goal was to be able define a baseline against which to measure pollution from atomic incidents.

The samples are completely purified: everything oceanic (such as salt and calcium) has been removed, leaving only the H2O and nothing else. You might think that water supplied by the Atomic Energy Agency would be more exciting. Drink it and you will be fine, severely disappointed, and a lot poorer.

I to the world am like a drop of water
That in the ocean seeks another drop

Scientists measure the fraction of 18O in an ice core, divide it by the fraction in VSMOW (making sure they measure it in exactly the same way as the ice core water), and subtract 1. As an example. current snow in Greenland has an 18O fraction of 0.0198, while VSMOW has 0.0204. Dividing the two gives 0.97. Subtracting 1 leaves -0.03. The minus sign show that the snow has a deficit. Converted to a percentage (multiply by 100) it becomes -3%. This deficit is called δ(18O). By tradition it is presented in permille (parts per thousand, ‰) rather than percent (parts per hundred, %), so the paper that reports the number will say that δ(18O)=-30‰. It will almost always be negative, as otherwise 18O (heavy water) would need to evaporate more easily than 16O (light water) which is difficult to achieve. But if you were to evaporate an entire sea, the residual water would have a positive δ(18O).

The number for δ(18O) is now used to obtain the temperature.

This is the part of science no one talks about – it is not glamorous and is unlikely to ever make the newspapers, but it is essential for converting field measurements into meaningful numbers.

Vials of the most expensive water on Earth

Written in water: ice age’s end

The scientists take some ice from the core, at regular depths, melt it and purify it, measure the abundance of the 18O and D isotopes, and compare this to the official standard to calculate the deficit in the ice. During the depth of an ice age, that deficit becomes larger.

The figure shows the resulting plot of the 18O abundance in the Greenland ice core, from 130,000 years to 8,000 years ago. The vertical axis shows the deficit of 18O (the numbers are negative) in permille, i.e. -40 means -40‰, or -4%. I have taken the data from the recent re-analysis of Gkinis et al (2021): “A 120,000-year long climate record from a NW-Greenland deep ice core at ultra-high resolution.”, published in Science Data 8, 141 . The data is available from

A 100,000 year Greenland temperature record

Now we are ready to investigate the ice age and it’s ending around the time of the Laacher See eruption. The temperature record starts with the previous ‘interstadial’, the brief warm phase between ice ages that happened 120,000 years ago. Interstadials typically last around 10,000 years. The interstadial ended with a sharp cooling which took place over several thousand years. Between 110,000 and 80,000 years ago the climate was chilly (‘frozen’ might be a better description but I’ll let it go). Between 80,000 and 60,000 years it became a lot colder (‘deeply frozen’). After that the world re-warmed a bit, but there were many intermittent, fast changes between the ‘frozen’ and ‘deeply frozen’ state. This period culminated in another very cold but brief phase 30 thousand years ago.

Never-resting time leads summer on
to hideous winter

The intermittent, fast changes involved a large number of fast warming spikes (’warm’ is relative), lasting typically a few hundred years. They would start with a sudden upward shift in 18O (a warming ocean) followed by a slow decrease back to the previous values of the deep freeze. The sudden warming would happen within decades. At times these temperature spikes were numerous, and other times they were few and far between.

By 25,000 years ago, a slow warming began to set in, as the ice age was drawing to a close. This warming continued with ups and downs, until 14,690 years ago (b2k means ‘before the year 2000’) when there was another sharp warming spike. Because there already had been some warming, and because this spike was larger than most, it caused temperatures to rise to values approaching those of an interstadial. The ice age had ended, the glaciers were melting, and the Bølling–Allerød interstadial had arrived. Finally, there was the promise of summer.

The Younger Dryas

And through this distemperature we see
the seasons alter: hoary-headed frosts
fall in the fresh lap of the creeping oak.

Except that it wasn’t. This summer was a false dawn. Temperatures slowly dropped back over the next 1500 years, becoming chilly, but perhaps feeling mild after so much cold. The forests that had returned to much of Europe survived the slow cooling, and even two brief phases of colder weather.

The Younger Dryas

Disaster struck in 12,846 b2k. Across Europe, temperatures suddenly dropped, much faster than before. Within a century, and perhaps much faster, the continent was back in deep ice age conditions. The new-born forests died and tundra returned. This was Ice Age Resurrection. This was Frozen, that brilliant movie about a battle between cold and warm, fought by two sisters each with one foot in either camp, one with a frozen soul but a warm heart, and one a warm soul but a frozen heart.

As the trees died, a particular plant took advantage and became widespread. The small Alpine daisy is called ‘Mountain Avens’ or ‘Creeping Oak’. The official name is Dryas Octopetala (the latter meaning ‘8 petals’ – it sounds so much more impressive in sciency language). The re-emergence of this plant, where the real oak was replaced by this creeping oak, gave the cold snap its name: it became known as the Younger Dryas. (‘Younger’ because there had been two brief episodes of cooling already during the warmer weather, called the ‘Oldest Dryas’ and the ‘Older Dryas’. Room has been left for a ‘Youngest Dryas’.)

The cold snap of the Younger Dryas lasted 1200 years. It affected Europe, Asia and America. The southern hemisphere was not affected, at least not at the same time.

Why, what’s the matter,
That you have such a February face,
So full of frost, of storm and cloudiness?

After 1200 years, almost instantly, the warmth came back, and this time it remained. The holocene summer had begun.

Volcano dating

After this ice age intermezzo, it is time to return to the Laacher Sea.

The Younger Dryas dramatically changed Europe. The forests disappeared, and tundra returned. The human populations which had expanded into the newly temperate regions left again for the south – or died.

But strangely, the deterioration in the climate in Europe came more than 100 years after the cooling in Greenland. The reason for this delay is opaque. One suggestion is that the sea ice took this long to grow, after which it pushed the storm tracks further south. There are other suggestions, but none are convincing. The delay is a mystery. And the mystery is closely related to the Laacher See eruption.

that one might read the book of fate,
and see the eruptions of the times

Counting time

Counting time is a skill. In Mary Poppins, it is perfected by the chimney sweeps with their Step in Time, performed while covered in ash in a way that is strangely reminiscent of timing volcanic activity. Marie Poppins missed a trick here. But there are other ways to count distant time.

When the age is in, the time is out

The ice cores from Greenland show individual year layers which can be counted, but only for the past 2000 years or so. Further back, the layers merge into each other and we can derive approximate ages (meters of ice per century) but not individual years. The depth profiles are calibrated with known eruptions which have left deposits in the ice – which the Laacher See eruption did not do.

Tree rings also count time, and they can go a long way if we use several trees which died at different times. The trick is to match up overlapping parts of the profiles, for instance a sequence of 5 narrow rings seen in two trees may be coming from the same climate event. The uncertainty increases when we go back more than 8000 years, especially during cold periods when there weren’t many trees around.

Finally, lakes can also count, another time signal written in water. Sediment at the bottom of lakes in western Europe forms annual layers called varves. Layers with volcanic ash can be used to assign specific dates, and after that it is matter of recognizing and counting the varves. Thinner layers can be hard to distinguish, and this leaves a counting uncertainty of some 30 years.

Varves (source

Both the Laacher See eruption and the onset of the Younger Dryas in Europe are well seen in the lakes, and from this we know that the eruption pre-dated the Younger Dryas by some 180 years. The eruption caused an exceptionally thick varve in the local lakes, for obvious reasons, and this is easily recognized.

Source: Obreht et al, Quartenary Science Reviews, 231, 1 (2020)

This is a plot of tree pollen in the Meerfelder Maar, another lake in the Eifel (much older than the Laacher See). The amount of tree pollen is measured in each of the different varves and plotted against time; time runs from right to left. The grey line shows the Laacher See eruption.

Before the eruption, tree pollen was plenty (mainly birch and pine trees). Immediately after the eruption, tree pollen completely disappeared for perhaps 20 years, and then slowly recovered. Clearly, the eruption had killed all the local trees (even quite some distance from the Laacher See: the two lakes are 30 kilometers apart!), and they needed time to regrow. Some 180 years later, the pollen suddenly plunged and now it remained low. This was the start of the Younger Dryas. Many of the trees that had regrown were now killed by the abrupt climate change: they froze to death.

The date of the onset of the climate catastrophe, as measured in this dataset, is 12,730 b2k. Remember that in Greenland the cold had come in 12,846 b2k.

The next plot, taken from Brauer et al. 1999, Quartenary International, 61, 1, shows the time lines from a lake in Europe and from a Greenland ice core. The Laacher See eruption is shown as ‘LST’: it left a clearly identifiable trace in the varves in the lake. The ice core has two volcanic sulphate peaks around 13,000 years ago, listed as T1 and T2, but neither of these coincides with the Laacher See. The plot again shows a clear time difference between the onset of the Younger Dryas in Greenland and in Europe.

Comparing the varve counts in the lake to the layers in the ice core indicates that the Laacher See erupted 10-15 years after the onset of cooling in Greenland. But when the North Atlantic froze, it seems Western Europe still maintained milder weather, with even a touch of warming summers, as if subtropical air found its way to Western Europe – until suddenly, 180 years later this stopped and temperatures finally plummeted across Europe. None of the climate models could explain this time lag. It was a mystery.

It was a mystery that has now been solved.

Volcano redating

Where a volcano is dating an ice core, there is an obvious risk of an incompatibility – it is after all throwing hot at cold, like an ancient Frozen. In cases like this, a match maker is required. Frederik Reinig and collaborators stepped up to the challenge.

Their match making was published in Nature, 595, 66 (July 2021). They had looked for trees – not normally difficult in Germany (a country that loves its forests), but their trees were not in the land of the living. They looked for trees that had died in the Laacher See eruption. And with success: three remnants of trees were uncovered that had been buried in the tephra, and had succumbed to the eruption. The outermost wood on one of the trees showed that the annual growth in the final year had already started: the eruption had therefore occurred in spring or early summer.

Counting tree rings (not easy in carbonized wood) showed that the trees had been from 50 to over a 100 years old at the time of the eruption. Carbon dating was done on each annual ring (as far as possible). The time around the Laacher See eruption is a difficult one for carbon dating. The amount of C-14 declined a bit in the atmosphere at the time, in such a way that the measured carbon-14 age is almost constant over a period of about 100 real years. That has caused large uncertainties in C-14 dates for the Laacher See. By using the full range of tree rings, it was possible to make a plot of C-14 age versus tree-ring years before the Laacher See eruption. That plot was shifted in time to find the best fit to the known C-14 variations. This was repeated for each of the three trees.

This procedure gave a much more accurate age for the Laacher See eruption, and it was not the same as the age established from varve counting. The eruption had occurred in 13,056 ± 9 years b2k.

The new date made the Laacher See eruption older by about 130 years.

The varves show that the Younger Dryas started about 150 years after the eruption in the region, or around 12,857 b2k. This of course also is earlier than before, by about the same 130 years. The new age now fits the cooling in Greenland. It turns out that Europe hadn’t had an Indian summer after all. The cold weather had started here at the same time as elsewhere around the Atlantic. The mystery was solved: we had misread the clocks.


In the old dating, the Laacher See eruption happened close to the start of the Younger Dryas in Greenland. The new date puts it 150 years earlier. It leaves no doubt that the eruption could not have caused the dramatic cooling. It wasn’t there at the right time.

It is very difficult to terminate an ice age. The Younger Dryas shows how quickly it can come back. If a volcano had been to blame, that would have meant the same could happen nowadays. It seems it wasn’t. It is one less volcanic disaster to worry about.

Of course, we now have other climate clangers to concern us, with global heating and rising sea levels. But that is a problem we have made ourselves, and will have to solve ourselves. Volcanoes are neither the cause nor the solution.

The Laacher See VEI-6 eruption was the largest volcanic explosion in Western Europe for perhaps 100,000 years. A recurrence would not cause a climate catastrophe. But even without that danger, one wonders how well prepared Europe really is for such an event in its heartland. Germany (like the rest of the world) was prepared for neither the flood nor the plague in the last two years. Would we do better against fire? Remember that for global heating, we know exactly what is coming, and fairly well when. And still we aren’t prepared. We should be living in hope and planning in fear. But in reality we live in fear and plan in hope.

O, how shall summer’s honey breath hold out
Against the wreckful siege of battering days,
When rocks impregnable are not so stout,
Nor gates of steel so strong, but Time decays?

Volcanic eruptions create markers in time. What we do with those times is up to us.

So much for the Laacher See dating of an ice age event during the early days of Frozen. The story begs one question: if the Laacher See did not cause the Younger Dryas, and we have shown previously that the Hiawatha impact is also innocent, then what did cause the Return of the Ice Age? And just as mysterious but often ignored: why did it end so suddenly? That is another story.

Albert, with contributions from William (Bill) Shakespeare

150 thoughts on “Sleeping in our back garden, part II: The Laacher See and the secrets of dating

  1. You must have had a great drink, beautiful with water as a base and interesting in it, ALBERT,
    to write a charming, intersting, complex long piece about Laacher See, glaciations, the Younger Dryas, warming phases, water, different kinds of oxygen, the area around West Eifel, dating and some poetry. Gorgeous. I have to read it again tomorrow, flew into my eye while gardening those watered plants, and that eye hurts. Beautiful.

    Now one question: That incredible image of that nice looking couple in front of an ash-spitting miracle: What volcano is that?
    I love the piece.

  2. You get a nice pic from wik commons too:
    Cirque de Gavarnie, Pyrénées, France, formed during glaciations. Gorgeous, I’ve been to it three times:

  3. Was it in fact the jet stream that was disturbed causing the Younger Dryas, and if so what could have caused this?
    I’m not big on the multiple astrobleme idea, there isn’t a great deal of evidence for it.

    • There is a rule in geology not to invoke extraterrestrial causes of events on Earth unless proven beyond doubt. That rule was wrong on one occasion (ask any dinosaur), but no mass extinction, continental break-up or ice age has a known cause from outside. Obviously impact craters do occur, but once big enough to leave lasting damage are extremely rare. Don’t blame astronomers (or biologists) for the Younger Dryas ..

      • IIRC, recent re-dating of large ‘Hiawatha’ crater in NW Greenland does not correlate with any climate ‘excursion’. My reading suggests it had less ‘far-field’ effect than a ‘middling’ volcano.

        Note, this *may* be due to trapping by ‘Polar Vortex’ jet-stream. Didn’t something similar happen to plume from a ‘recent’ Antarctic Peninsula eruption ?? Like those big ‘stratospheric’ balloons flown with telescopes and such, the plume just went around and around the South Pole…

    • Yeah was liveley in that same spot a few days ago (where the lake is). If it did come up around there I guess the interaction with groundwater could lead to the creation of some Maars?

      • Would seem very likely a new rifting episode will begin at Krysuvik soon. By some accounts Fagradalsfjall is a part of Krysuvik so maybe this isnt really surprising. Maybe Reykjanes is sort of like one really big volcano with multiple magma chambers connected underground, like Kilauea is.

        Was confirmed magma is building up at 16 km depth under all of the west side of the peninsula too, not just Fagradalsfjall.

  4. Quot. Albert; “In Europe’s snow catastrophe of 1979 (this was the era before global warming took off, now hard to remember) I saw houses buried to their roofs under snow, in an area that now gets very little snow.”

    I’m sceptical, look at this:
    “Even at its peak, in the mid-17th century, the Thames in London froze less often than modern legend sometimes suggests, never exceeding about one year in ten except for four winters between 1649 and 1666. From 1400 until the removal of the medieval London Bridge in 1835, there were 24 winters in which the Thames was recorded to have frozen over at London.”

    A painting by Thomas Wyke:

    • Saying it might have been as rare as today, but there was a totally different level of information, and then when it happened – also thinking of Pieter Brueghel – it became so famous that people later thought it might have been standard.

      Imagine – the Baltic Sea was frozen in 1979 after the snow storms – exactly 40 years later we see similar snow storms in North Germany and Benelux (2009).

      • Well – that’s a personal impression. I have it too. I left my car in the city (in Munich) on New Years Eve for obvious reasons, the next day we had to shovel for two hours to get it free. After that the rest of the alcohol was gone 😉

        Then around New Year 2009 I drove to Paris. and it was a real adventure. We drove in the middle of the Belgian Highway, one lane as they didn’t manage to get rid of the snow, all nicely in a row, speed 30-60 km/h.

        Then in 2019 we had (wisely) a catastrophe alarm situation in January in Bavaria and Austria and local teams freed the roofs from the burden, got the avalanches from the streets and closed single streets.

        Same pictures from America in other years. Every few years.
        And what the wiki piece says about the frozen Thames events indicates that the freezing (a bit different) always happened in intervals of one to four decades. Nothing unusual it seems, like you were indicating about the summer storms although I’d give them around 100 years and pandemics less (1889/1890, 1918/1919, 1957/1958, 1968/1969 – haven’t checked the dates, might be wrong by one year). In between endemics of tuberculosis, Polio, Zika, Swine Flu, Bird Flu etc).

        We’d better get used to these things being rare but normal like volcanic eruptions, instead of following media hysteria. It seems to be nature at work.

        • Between 1700 and 1850, the Thames froze over during 17 winters. That is more than once a decade. Not all of those had frost fairs: that required that the tidal rang of the Thames froze to sufficient depth, and that has always been rare (and hasn’t been possible after 1830 because of alterations to this part of the river). It is hard to compare to modern days since the Thames has changed and the sea has risen. But I don’t thin k it has been cold enough over the last 25 years that the Thames could have frozen. You shouldn’t confuse climate and weather, and there will be more cold weather at some point. It will be a shock after almost 50 years since the last severe winter. England won’t be prepared, of course.

          We have had more pandemics. But the last one similar to covid was the 1918 flu. The 1898 plague did not reach Europe.

          • No, sorry. It is probably the 1889 /1890 pandemic, caused probably by a Corona-Virus, Cov-OC43, which might have jumped over from cattle, still in investigation.

            The Spanish Flu was worse and cannot be compared at all esp. as it coincided with a weakend population after nearly four years of war .

          • I meant the plague epidemic of that time, not the flu of 1889. The date isn’t particularly accurate as this was a disease that spread over more than a decade rather than a single year. Hong Kong was hit in 1894, India a few years later, and it reached the US may be around 1900. This may be when the plague was introduced to the US. There are still occasional cases there, from some animal reservoir. It is called the third bubonic plague and killed far more people than the 1889 flu.


        Possibly not the coldest (1981 was very cold) but certainly for the snow and length of the freeze. Somehow I remember all winters were like this but they were not. We burrowed into snow drifts (maybe 5m high) and had rooms and passages. Horribly dangerous now I look back.

        Still had to play rugby once they cleared the pitches, using a tractor. Freezing ground did cause a few grazes.

        I’m pretty sure there were examples of sea freezing as well as the thames,

        • Playing rugby with a tractor sounds like a winner! That winter is considered the coldest in Europe for perhaps 200 years. It is hard to be sure, of course, as for the older winters we don’t have accurate temperature records. If that winter had happened before 1830, there would have been a Thames frost fair, I expect. Same for 1947 and perhaps 1940. But nothing since 1963. Would perhaps the Younger Dryas have started with a winter like that? You can see why up to 1980 science was more concerned about the return of the ice age than about global warming.

          • Albert, would the removal of the old London bridge have an effect on the river freezing, as the flow of salt water would have been restricted on the incoming tide.

          • Yes, it did have an effect. It was part the increase of tidal salt water but mostly the increase of the flow rate. You should not directly compare the events from before and after 1831. The old bridge was like an ice dam in a bad winter. After it was replaced, the Thames never fully froze again, not even in 1963 which was equivalent to the previous frost fair winters. Note that the river was also channeled around his time with embankments which also increased the flow rate.

            I see 1963 as the end of the Little Ice Age..

      • Personally i’d be a bit wary of standing on top of a river, frozen or otherwise.
        I imagine there may have been a few deaths as it defrosted in places come spring.

  5. There is still a swarm going on at Krysuvik. Most of the quakes are around 5-8 km deep, which is well above the area magma is known to be accumulating in the area, so another conduit is probably forming. Not sure if it is rising but when it reaches the brittle zone it will probably start forming a massive dike, maybe very fast, a lot bigger than last years dike was.

    Would seem it is in the fissure swarm that Kleifarvatn sits in too, not the other two that were active before. So there could be some major ash with this one.

    • There’s activity near Grindavík on the other side of Fagradalsfjall. So the swarm could ‘just’ be a crustal response to magma rising at Fagradalsfjall. Then again, it might not, or, even if it is, magma could still find a way out near Krýsuvík.

      • Flexure response quakes would indicate there is magma building up and pushing the crust up in between then, at Fagradalsfjall. So would still be an eruption in the making and quite soon, at Fagradalsfjall again. That is better, we know how it will behave, but I think the lava will go a lot further because all the valleys are filled now. It would be interesting if it is in the immediate area of the cone from last year.

        It has been confirmed apparently that magma is accumulating at depth quite rapidly.

        • Where’s ( oso)? It has an interesting tremor plot.

          Either someone has kicked it or something is going on.

        • There is no sign of inflation. The general trend has been for a touch of deflation over the past months, stabilizing over the past month.

          • If it is at 16 km depth there probably wont be much of a surface signal. I dont recall there being significant inflation as a precursor to the eruption last year, only if there is a shallow magma chamber will there be major inflation, which none of these volcanoes have.

          • There was inflation last year, and at Thorborn the year before. It traced the dike, and later even a bit of deflation as the dike moved up and pushed the surface out. Then it erupted somewhere else.

          • There is deformation seen in the Krisuvik GPS which is probably of magmatic origin. Seen best in the east component. I would consider likely as a result of inflation to the west, from a long-lived magma storage. InSAR could best show the exact location and approximate depth of this storage.

            It can be seen magma inflation started in 2020. It was just before the first jump, the first sheet intrusion, presumably this was the sill intrusion under Thorbjorn, since then inflation has not stopped. The two additional jumps where the 2 dike intrusions of 2021 both of which started near Keillir and propagated under Fagradalsfjall, the first dike erupted the second not. The first also seems to have been bigger.

          • During the eruption movement was the opposite, westward. Presumably meaning deflation which would make perfect sense, and even necessary. Thus it is reasonable to assume eastward means inflation for this particular GPS.

          • The only InSAR I can find in IMO is from 2021 from the period just after the eruption. It shows a complicated inflation area. One location under Keillir is likely to be magma storage given that it could explain the eastward movement of KRIV. But there are also other possible sources. Maybe inflation under the southern shore of the peninsula, possibly deflation at Thorbjorn, maybe deflation of Brennisteinsfjoll? But it is not clear which signals are real and which are not. A better interferogram could help, one that covered the whole inflation period since the Dec 2021 dike. But getting interferograms is very hard.

          • The Keilir signal is interesting. It is different from the other regions and coincides with the end point of the dike. The lengthening along the southern road may be due to movement along the Reykjanes fault. If there is a bit of eastward movement, it will show up as inflation on this map because of the way the vectors go (it measures distance from the south-southwest). But not for Keilir.

          • The deflation of Thorbjorn seems real, because it is shown by the GPS that is on top of Thorbjorn. It has undone possibly as much as half of the deflation it experienced in early 2020 from the series of sill intrusions. This seems to much to be from just cooling so maybe magma has been drained away from under Throbjorn to fed activity elsewhere, it is a complicated interaction of multiple intrusions and complexes. I wish a good, thorough scientific article comes up looking at InSAR to document all the deformation.

          • I meant to say inflation in early 2020, when the sequence of sills was intruded, possibly as many as three distinct sills.

      • Significant magma intrusion is 16 km deep beneath the southern half of Krysuvik rifts, so not at Keilir and also not at Grindavik or Kleifavatn. It is sort of in the area that is in between all of these actually, perhaps a common deep source. Might also suggest that Fagradalsfjall is actually a part of Krysuvik instead of its own thing as was thought in the past but debated last year.

          • I looked at the article in question, overall a nice piece of work but it only mentions the potential caldera in a few sentences:

            The most informative section is: “Lake Kleifarvatn was envisaged as a remnant of a caldera preserved in its east at a low in volcanic production. The caldera hypothesis found support recently, when inflation amounted to 9 cm over the course of two years in 2010–2011 (Michalczewska et al., 2012b), subsequently followed by subsidence at a similar rate for the last decade (Gudjónsdóttir et al., 2018).”

            Let me know if you want me to send you the PDF.

          • Thank you. I found the same quote in another paper. Also saw a brief reference in a Google search to similarities with Krafla. Unfortunately lost the the link (it will reappear in time 🙂 ).

          • Ignore the similarities with Krafla; that would appear to relate to a geothermal area.

    • Thanks Denali…glad to see this program getting global attention.
      As you know, California in many ways is a world all in it’s own. We go our own way, inventing new roads when the going gets rough, yet pretty much we take it all in stride (floods, fires, winds, drought, etc).
      We can foul up the air, water and deplete the natural resources ad-nauseum, but wildlife is a treasured commodity (welllllll, kinda sorta).
      Up my way though in NorCal, there’s no such problem with the Mountain Lion population…they are everywhere.
      In my backyard alone, in the nearly 20 yrs. living here, I’ve noted Mountain Lion, Black and Brown Bear, an annual family of foxes, herds of deer, racoons, huge packs of feral pigs, coyotes (a lot), and everything else that goes along with a semi-rural location…yet I am less than 3 miles from the main interstate.
      And, as expected, collisions with these larger animals do cause lots of damage, sometimes involving bodily injury…but like Covid (my county has the worst vax rates in the State), we learn to live with the dangers.
      It’s our way.

      • And I forgot to mention, for the first time in over a century, two Condors raised by Native Americans (the Yurok Tribe) will once again grace the skies of northern California somewhere in the Klamath river area.
        This was a major event, gaining national news…as the project was the culmination of a 15 yr. restoration project championed by the Yurok Tribe. At present, there are two more yet to be released.
        One small step at a time. Things can change (for the better).
        Just wish it didn’t occur on geologic timescales.

        • Thank you, Craig, both answers are very enlightening. Ienvy you for the spectacle in your back garden. I’ve only seen foxes and rabbits so far, plus neighbour’s cats.

  6. GPS at Kilauea is half way recovered from the point that triggered the eruption back in September. Is also about the same height as when the intrusion down the southwest rift took place last August.

    Very early yet but it also looks like the downward trend on the ERZ has been slightly less or is even stopping in recent days, and the JOKA station east of Pu’u O’o might be gently uplifting, though it is very noisy so unclear. AHUP station south of the caldera might also be showing slight inflation from the west out on the SWRZ.

    Looks like we might get a bit of a race to see if another eruption begins on Reykjanes before something happens here 🙂
    If the signal at JOKA is real though that is not a good sign. Would be better for a surge in summit activity or eruption southwest.

  7. Insight records its largest quake on Mars so far.

    NASA’s InSight Records Monster Quake on Mars

    NASA’s InSight Mars lander has detected the largest quake ever observed on another planet: an estimated magnitude 5 temblor that occurred on May 4, 2022, the 1,222nd Martian day, or sol, of the mission. This adds to the catalog of more than 1,313 quakes InSight has detected since landing on Mars in November 2018. The largest previously recorded quake was an estimated magnitude 4.2 detected Aug. 25, 2021.

    InSight was sent to Mars with a highly sensitive seismometer, provided by France’s Centre National d’Études Spatiales (CNES), to study the deep interior of the planet. As seismic waves pass through or reflect off material in Mars’ crust, mantle, and core, they change in ways that seismologists can study to determine the depth and composition of these layers. What scientists learn about the structure of Mars can help them better understand the formation of all rocky worlds, including Earth and its Moon.

    A magnitude 5 quake is a medium-size quake compared to those felt on Earth, but it’s close to the upper limit of what scientists hoped to see on Mars during InSight’s mission. The science team will need to study this new quake further before being able to provide details such as its location, the nature of its source, and what it might tell us about the interior of Mars.

    Meanwhile Ingenuity failed to make a scheduled check-in with Perseverance a few days ago. Working on the assumption there may have been a clock fault, Percy was instructed to listen over a longer period and contact was re-established 2 days later. Telemetry indicates that during the night Ingenuity hit a battery critical low fault condition which resulted in heaters switching off and the loss of the clock. Changes have been uplinked that lower the temperature the heaters engage which it is hoped will allow normal operations to resume but risk components getting too cold and something failing permanently. The team think the issue was due to increased atmospheric dust rather than a component issue and hopefully they’ll have some more positive news soon. Fingers crossed!

    • An earthquake this size may be from valles marineris. The failing battery may mean the helicopter is getting fragile. It will get colder in the next months.

  8. Reykjanes continues to show episodic hydrothermal/tremor mixed in with both tectonic and rock fracturing signatures on the drumplots.
    Gotta think at some point soon, something near the surface is going to manifest? Just a feeling.

    • A few shallow earthquakes North of Grindavik, plus renewed uprise at Thorbjorn mountain. Keeping fingers crossed…

      Earthquake table
      Date Time Latitude Longitude Depth Magnitude Quality Location
      12.05.2022 13:52:16 63.879 -22.426 0.1 km 0.1 99.0 4.5 km N of Grindavík
      12.05.2022 13:51:02 63.879 -22.426 0.1 km 0.1 99.0 4.6 km N of Grindavík
      12.05.2022 13:47:54 63.878 -22.424 4.3 km 1.1 99.0 4.4 km NNE of Grindavík
      12.05.2022 13:47:19 63.880 -22.416 4.9 km 1.4 99.0 4.8 km NNE of Grindavík
      12.05.2022 13:41:57 63.881 -22.421 3.5 km 0.7 99.0 4.8 km NNE of Grindavík
      12.05.2022 13:40:02 63.853 -22.566 6.9 km 1.1 99.0 6.3 km WNW of Grindavík
      12.05.2022 13:07:57 63.878 -22.419 5.0 km 1.6 99.0 4.5 km NNE of Grindavík
      12.05.2022 13:01:28 63.879 -22.418 3.7 km 0.6 99.0 4.6 km NNE of Grindavík
      12.05.2022 12:58:14 63.877 -22.425 4.3 km 0.6 99.0 4.3 km NNE of Grindavík
      12.05.2022 12:57:16 63.880 -22.416 4.7 km 0.6 99.0 4.7 km NNE of Grindavík
      12.05.2022 12:56:12 63.878 -22.421 6.3 km 2.9 99.0 4.5 km NNE of Grindavík
      12.05.2022 12:53:26 63.854 -22.479 5.7 km 1.4 99.0 2.5 km NW of Grindavík
      12.05.2022 12:06:22 63.874 -22.369 0.1 km 0.3 99.0 5.3 km NE of Grindavík

        • Absolutely! Watching lava flow through an uninhabited landscape is one thing, watching it destroy a town and people’s homes and livelihoods would be another altogether.

          I agree that my earlier post wasn’t well thought out on that point.

        • Intrusion at Þorbjorn in 2020 was a sill, it looks like maybe this one is too. Uplift but there is no definite upward movement of magma yet.

          What this also means is when a dike does form that connects to this sill said dike will be much faster to fill than the one in 2021. Think something as fast as we see them form on Kilauea, hours to maybe days at most rather than months. The eruption will also be way more powerful, something like the Krafla Fires or Mauna Loa, a real lava flood, a Laki in all but volume. Just look at the Eldvorp craters nearby…

          In my unprofessional opinion Grindavik is probably the worst place you could pick to buy a new house in right now. I had sompared it to Goma, but then Goma actually had (and survived) its close call last year and has probably got some decades of safety ahead while Nyiragongo refills. Grindavik is honestly a 50/50 getting hit by a lava flood in the next decade, more like next year at this rate… 🙁

          • Yes, it also seems to me that west of Thorbjorn is the magma storage of Svartsengi volcanic system. The eruptions in the area like Arnarsetur, Eldvorp, Illahraun, or Sundhnukur, are fast fissure eruptions with high eruption rates. Svartsengi is thus similar to Hengill and Krysuvik which produce rapid eruptions and need to have substantial shallow magma storage. It is different from Reykjanes, Fagradalsfjall, and Brennisteinsfjoll systems which are instead into slow fissure eruptions and small shields and probably lack shallow storage. Thorbjorn could be the location of magma storage of Svartsengi volcanic system, which supplies those violent fissure eruptions.

        • There is a bit of a stack. As usual the largest quake is the deepest, in this case around 7km. The others are weaker and extend upwards to around 4 km. 7km is around the boundary between the upper (brittle) crust, and the deeper crust where you tend not get earthquakes. The slight inflation. suggests some magma may be involved. It could also be fluids (water) but in that case the quakes would have been a bit shallower. It seems there is a bit of activity along a deepish dike. But it is not yet focussed on one location and does not seem inclined to come to the surfqce at this time. For now.


    HVO is going to finally try and seriously investigate the Pahala earthquakes this year, and soon. It sounds like the earlier assumption of it being the hotspot location was actually never fully proven, just considered the most likely out of a number of possibilities.

    I cant help but see it as a deep sill complex that is forming and will one day rush towards Kilauea to increase its eruption output by a factor of 10 or more, something that really is a blatant early warning of a major event. Pahala swarm area and volume is massive, 20 km deep and at least as wide, a huge area that magma is accumulating within. Even if only 1% of that is liquid that is still 80 km3 of magma, and even if only 10% of that (likely far too low in Hawaii) erupts that is 8 km3 of magma that can suddenly find itself going to Kilauea.

    • I’m very glad to hear they’re going to have a close look at Pahala. I’ve long been concerned about that phenomenon, and it’s been obvious even to me that activity there is increasing over time.

      One thing I wonder about (and I may well be totally wrong) is whether Pahala, instead of being the hotspot location (which IMHO the steady increase in activity contradicts), is it a relocation of part of the hotspot plume? The Hawaiian Islands seem (to me, anyway) to not be a case of a steady drift of the source (actually a drift of the Pacific Plate) but a bit more sporadic and perhaps with “jumps”; in other words, could Pahala be a part of the source that’s trying to push up through the overburden, due to the original pathway (Mona Loa, perhaps?) having drifted a bit too far west of the plume?

      I very much hope I’m wrong, because what I just blathered above sounds rather akin to some theories of how flood basalts begin; a supply blocked by continental drift, building up a very large magma reservoir before finally breaking through. I don’t expect Pahala to manage something that bit, but it could still be very large – perhaps Laki fires scale large.

      Chad, if you’re right and Kilauea might soon have an additional source, it might not take all that long to turn the whole caldera into a lava lake.

      As for Pahala… I’ve long found it rather odd that there’s no GPS station on it. IMHO, it’d be good to see if there’s any inflation there. Also, a quick look at the last week’s quakes there seems to indicate that their average depth is a bit shallower (around a mile less) than the last time I looked (around January). *IF* that’s the case, it might be a reason why USGS is suddenly getting more interested in what’s going on.

      BTW, lest I forget, Thank You Albert for the wonderful look at Lacher See, and for ruling another suspect off the Younger Dryas suspect list.

      • The Hawai’ian islands move at a regular rate. But the volcanoes move with jumps. This is because they need to create a conduit. Once one exists, magma will take that route until the hot spot is out of range. Once that happens, a new conduit will form. This means that the spacing of volcanoes is fairly regular. In fact all volcanoes on the Big Island are a fixed distance from each other (I think there is a previous post on this. The same applies at Vatnajokul in Iceland.) This distance depends on the thickness of the crust. If you look at those spacings for bothe Mauna Loa and Kilauea, you would predict the next volcano to form at Pahala. Yes, the hot spot is currently probably around there. (Of course it is a hundred kilometers across so you can’t pinpoint it precisely.) But more importantly, the magma is collecting there because of the transport issues. Ther eis no conduit here so it doesn’t move up, but it is working on it. Give it 50,000 years.

        (What about Lo’ihi? It is a red herring. It formed too early, as on offshoot. The Big Island isn’t finished yet.)

      • The similarity of this to flood basalts is exactly what I was going for. I dont know if actual flood basalts in real LIP provinces do always behave this way, but a huge accumulation of magma in any situation is something that should be kept track of. In Iceland it is fairly obvious, the chambers are near the surface and we saw some of them historically.

        But Laki was also once in a multi-millennium event, as was Eldgja, and eruptions in Hawaii are way more frequent than that part of Iceland so if a huge event happened on the ERZ of Kilauea 3000 years ago it would be basically invisible now. If such a swarm of quakes as we see at pahala, or even a swarm that is 1/10 as powerful, was happening soemwhere in Vatnajokull, everyone would be sounding alarm bells in preparation for something huge.

        Pahala area doesnt have a GPS but it is flexing the crust enough to generate secondary quakes on the lower SWRZ of Kilauea, and that would imply it is an inflating structure, probably a sill complex. Sills like to go sideways, and the mantle fault zone it connects to goes like a paved highway right to Kilaueas deep conduit… I think it is really only a matter of time, perhaps a deep quake to open up that fault, like we saw at shallower depths in 2018 on the south flank, and then it is all set in motion.

      • Pahala is one of the biggest mysteries of Hawaii, I don’t think we fully understand what it is. However it is not the so called “hotspot”. This is because there are long period earthquakes that happen deeper than Pahala, directly under the summit of Mauna Loa. Pahala earthquakes are about 30-35 km deep, the spasmodic tremors offshore Pahala are 41 km deep, while the long period earthquakes under Mauna Loa are 45 km deep. Thus the deepest earthquakes with a magmatic signature occur directly under the summit of Mauna Loa. The deep conduit is most likely there. Mauna Loa also has the most tholeiitic magmas. Kilauea, Loihi, Hualalai and Mana Kea are more alkaline than Mauna Loa to variable degrees. When Mauna Loa is more active, Kilauea is more alkaline; and when Mauna Loa is less active, Kilauea becomes increasingly tholeiitic, although without fully reaching the composition of Mauna Loa. For example lavas erupted during the Pu’u’o’o eruption have become gradually more tholeiitic as the eruption went on, which coincides with the longest dormancy of Mauna Loa on record.

        So what is Pahala exactly? This is my current speculation, which might be wrong. It is necessary though to realize that Pahala is part of a larger whole. Pahala acts as a vertical connection between 2 areas of earthquake activity. A 40-45 km deep band of earthquakes that runs under the southern coast of the island, the spasmodic tremors offshore Pahala which in the last few years have seen large outbursts of activity are part of this band. The most seismogenic part of the Pahala Swarm is instead part of a 30 km deep band of earthquakes that runs from Pahala to the summit of Kilauea, known as the Mantle Fault Zone, it also shallows slightly. These bands of seismicity I think are horizontal faults but which likely interact with intrusions. This is further evidenced by the large earthquakes which often take place in these bands, Pahala has done M 4.6 earthquakes in 2021, and there was also a 6.2 earthquake at the western end of the 40 km deep band in 2021. So they are most likely subhorizontal reverse faults that are being pushed by intrusions. So perhaps a slow, long-lasting, deep dike intrusion along a 30 km deep dike swarm that runs towards Kilauea has been responsible for the greatly increased Pahala activity since 2019.

        • I think there is still a large possibility of a hotspot that created the Hawaiian volcanoes, however, that doesn’t mean that your theory is disproven (even though I like the theory very much with all the evidence you have brought). I think there is some sort of deeper rift under the hypothesized complexes that, like a tree bringing up nutrients from the soil to the leaf, the rift brings fresh magma to the volcanoes. I think it all starts out at the “source volcano”, where the first volcano of the complex forms. Fresh magma feeds the volcano until the hotspot (the plate itself) shifts and a new area along the rift gets fed and, combined with the magma from the original volcano (don’t know how that works when older magma from the volcano drains into the deep rift…), forms a newer volcano and so on until a new complex forms. That is how I kinda think about it.
          Also to note, there is a somewhat similar anomaly on Mauna Loa on its northwestern flank. I am quite interested as to what is going on there.
          One more thing, Lo’ihi is no longer Lo’ihi but instead Kama’ehuakanaloa (KA-mah-HUAH-KA-na-lowuh) (a bit of a tongue twister but I managed to get it right, I think).

          • I think the hotspot isnt in denial, just the method of how magma gets to the surface. Obviously the mainstream idea is that each volcano is individual, where Hector I think is proposing at least the southern half of the Big Island is all one volcano that is centered under Mauna Loa but with very complex internal plumbing, so perhaps not exactly currect to say Kilauea is a true satellite but rather that both are simply vents of a common parent.

            In saying that though, Mauna Loa is basically going to be the thickest crust too, so could be that LP quakes are deeper there than at Pahala or Kilauea summit because the crust is literally deeper down in that location and magma will interact there first.

  10. The swarm under Reykjanes continued overnight. This is a plot of the past 7 hours. It follows an inclined fault. The deepest quakes are at the southwestern end (7 km) and they become shallower towards the northeastern end (5 km). Together with the renewed inflation at Thorbjorn and Grindavik it suggests magma intrusion, although not as voluminous as last year. The earthquakes are small, maxing out at M2.8 or so. As long as it stays at that level I am not too concerned. If they get much larger, that would change, but there is no sign of that.

    • Thank you Albert. I’m finding it much easier to type, now that I’ve uncrossed my fingers (virtual wink toward Alberta).

      • Do practice – you may have to do it again if this develops further. Not now I think, but perhaps in the future. I had expected the next events to be further from Fagradalsfjal

    • Map of the lava from the last cycle of eruptions on Reykjanes had much more activity on the east end, massive eruptions from Brennisteinsfjoll at Hvammahraun and Hussfullsbruni, both probably going into as much as 2 km3 of lava. Then Krysuvik erupted, first an early eruption in the 900s AD then the Krysuvik Fires in the late 12th century as Brennisteinsfjoll fell dormant. Svartsengi/Reykjanes didnt erupt until the 13th century and while vigorous was not very voluminous.

      Previous cycle though had only a minor activity at Brennisteinsfjoll, and a big eruption at Hengill instead, about 1 km3. Instead there was massive flows at Reykjanes/Svartsengi and at the west end of Krysuvik. Now we see basically all activity at this same area again and nothing east of Krysuvik. Fagradalsfjall was not active 2000 years ago but was right in the middle of that activity.

  11. RNE drumplot has exploded with activity in the last couple of hours. There is steady-state shaking going on after an abrupt start, with signatures that suggest rock fracturing and possibly/likely some tremor.
    Biggest shock so far is a M3.5 near the very tip of the Peninsula.

  12. Bigger quake a moment ago, felt it very well in Reykjavik. Seems more and more likely that something is going to happen but of course you never know with volcanoes.

    • On the Reykjanes fault. Not related to the activity in the west, because the stress on the fault on a section between this quake and Grindavik was relieved a year ago. Let’s see whether there is any follow up.

      (All of Europe is of course glued to the telly at the moment. We can’t have an eruption now! It would be fire saga.)

  13. Also keep an eye on Grimsvotn. It is ticking over at a fairly high activity, and hasn’t calmed down after the jokulhaup

    • Which kind of answers the chicken-egg question of what is the cause of what!

      We can probably expect bigger quakes to happen there within the next weeks and months – why should it calm down now!

  14. Recent quake is on the fissure swarm that erupted in 1000 AD, and also created the shield volcano of Leitin that sent lava flows into Reykjavik. Its also very close to Hengill which I think also erupted at the same time as the Leitin shield eruption, about 5200 years ago. Maybe it is just tectonic but now we know a cycle is starting a big quake as feared would very probably set off something, really now it is literally the entire RVZ that is active, we could see an eruption just about anywhere now. I am going to bet we see more than one place go off at the same time too, no orderly progression east-west like the last cycle.

    I heard that an eruption at Hengill is considered the worst case, not because of the size of eruption or threat to inhabited area but because it would risk destroying the geothermal plants and cutting the power to Reykjavik. It would also probably cut a major section of road infrastructure.

    • Do they have contingency plans for Reykjavík? And Keflavík? Not saying that they are needed now but it might be wise to have them.

      • Reykjavik is well protected. Lava flows from the south east will tend to flow north of Reykjavik, because of the lie of the land. Flows from the south would go south of Reykjavik. Havnafjordur could be affected. The Reykjavik city area has not been affected by lava for a very long time.

        The main high way (1) would be likely cut

        Keflavik is also out of range of normal lava flows, but could have its access cut

  15. From the IMO Frettir page, published yesterday.

    “”Considerable seismic activity on the Reykjanes peninsula
    Evidence of slight overheating at Svartsengi

    Considerable seismic activity has been detected on the Reykjanes peninsula last week and the activity has been greatest at Svartsengi and in the vicinity of Grindavík. A total of 1,700 earthquakes have been detected in the automatic system in this area this week, the largest being about 2.9 in magnitude.

    A news item published at the end of last month stated that the GPS measuring network on the Reykjanes peninsula, which measures movements on the earth’s surface, shows an expansion sign that points to the magma collection at a considerable depth at Fagradalsfjall. GPS stations in the vicinity of Þorbjörn have in the last two weeks shown changes that indicate slight overheating at Svartsengi. “These displacements we see are still small, around 10-15mm where they are greatest”, says Benedikt G. Ólafsson, expert in the field of crustal movements at the Icelandic Meteorological Office, but Benedikt in collaboration with the University’s Institute of Earth Sciences closely monitors crustal movements in the area. “The post we are analyzing now is similar to the one we analyzed in the same area in the first half of 2020”, says Benedikt.

    InSAR satellite imagery, which covers the period April 29 – May 7 and April 21 – May 8, shows changes similar to those observed on GPS stations. “What we have learned from the volcanic eruption on the Reykjanes peninsula is that an increase in seismic activity and deformation can be a precondition for an eruption, but this is not always the case,” says Michelle Maree Parks, one of the scientists on the Meteorological Office’s deformation team. otherwise with a landslide. “As often before, we really need to see what the development will be. We are running models to evaluate e.g. at what depth is the magma in this particular area. We are also expecting new InSAR images later this month and they are part of the data we will process to better understand the development in the area around Svartsengi “, says Michelle.””

    • Compared to the Thorbjörn intrusions in 2020 (uplift plm 70, 60 and 50 mm), current movement is still minor plm 15 mm).

      Gps Skipastigshraun noordwest of mt. Thorbjörn.
      Credits IMO.

      • The earthquakes there are developing into a stack along the dike. Definitely an intrusion

  16. More quakes next to Grindavik right now, one big enough to get a star. It looks like there are two intrusions going on, at Reykjanes right where it enters the ocean, and just west of Grindavik. Reykjanes swarm is long in the making, several years, like at Fagradalsfjall, though it will probably be a faster eruption but not crazy, still a ‘tourist eruption’.

    Whatever is going on at Svartsengi though, it could be very fast and we might be looking at an eruption within days now, and much more intense than last year. This one will definitely not be a tourist eruption.

    May 17, 2022 The day that we see the formation of Grindavikhraun… 🙁

    • The current swarm is close to Sandfellshaed, if I read the map correct. I don’t think this is where the eruption would be though. But if it is, the land is fairly featureless around there and any lava could take a variety of directions. Grindavik is a bit far and is unlikely to be on the flow path. A more southerly or southwesterly direction is more likely, in an area with very few buildings.

    • Why would Svartsengi be more intense / bigger than Fagradalsfjall? Because of history alone?

      • This is a small intrusion compared to last year. Eruptions west of Grindavik tend to be minor. Unless off-shore in which case other effects become important

        • Yep that´s what I was thinking, there would need to be A LOT more noise before something happens – let alone something more substantial. Just compare this earthquake sequence to the runup of Fagradalsjall.. It was a lot noisier two years ago

      • Eruptions on Svartsengi are of much higher intensity. Svartsengi doesnt have a magma chamber but it seems it does have storage, lots of sills that form in advance of an eruption, so that when a dike does form there is a lot of pressure. Fagradalshraun was 0.15 km3 volume, eruptions at Svartsengi are about that big too, but erupted in a week or so instead of 6 months. Eldvorp probably was only a few days as it is only the initial sheet flow and end stage spatter cones. There are no complex shields or larger cones to indicate eruptions are slow.
        Krafla might be a good comparison, big dike with tiny eruptions at first and then later on much bigger eruptions, but never an open hole or continuous slow eruption.

        Krysuvik is the same, the eruptions of Kapelluhraun and Ogmundahraun are fast fissure eruptions. Hengill also does fast eruptions. The biggest eruptions on the peninsula are from Brennisteinsfjoll but eruptions there seem to be the same as we saw last year but a lot bigger, probably years long, they probably rise out of the mantle in big slow intrusions.

      • The reason to suspect an intense eruption would be history. Earlier Svartsengi eruptions have been very powerful, they have nothing to do with what we saw at Fagradalsfjall. The eruption rates are far superior, which becomes evident when inspecting the flows.

        In contrast Fagradalsfjall is only known to have made slow shield-like eruptions, similar to Brennisteinsfjoll, and to Langjokull but with lesser volumes.

        I did write this description of the Svartsengi activity during the Reykjanes Fires, in an old article:

        Svartsengi produced three lava flows, Arnarseturshraun, Illahraun and Eldvarpahraun, I will focus on the first two, which I think are parts of the same eruption.

        Illahraun erupted from a 200 meters long fissure, but the eruption was very intense. An area of 8 km2 was rapidly flooded by a sheet of molten pahoehoe lavas, including the present location of the Blue Lagoon. The surface flowed as a mass of crustal plates carried by the molten rock below, as it moved the slabs clashed against each other lifting into broken ridges.

        The cones that fed the eruption barely have any prominence and the flow is one simple sheet, this is all probably because the outbreak was very short lived. The total volume was 38 million cubic metres and eruption rates must have been on the order of hundreds of cubic meters per second, so that the effusion can’t have lasted much more than a few days. Illahraun however may have taken place concurrently with the opening of fissures along the same line to the northeast which fed the longer lived Arnarseturshraun flow.

        Arnarseturshraun must have opened with a line of fountains and a rapid outpouring of pahoehoe lavas, although this initial stage is largely buried under later activity. The eruption rate declined progressively. For some time a raised lava channel kept supplying lava towards the north which fed a massive slowly advancing wall of aa lava, crustal plates from the initial lava flood as large as hundreds of meters across were rafted downstream and collided with each other raising up meters high ridges of rubbly scoria, much like tectonic plates that collide to form mountain ranges. Activity kept decreasing and some more lava channels were formed to the north, however activity focused more and more around the vents.

        Because the ground is mostly flat, lava had ponded around the fountains of the Arnarseturshraun lavas, this evolved into three lava lakes raised slightly above the ground by overflows, the largest with a triangular shape and 200 meters wide. Small fountains and dome fountains probably played in the lakes and distributed lava over an intricate system of channel and lava tubes leading up to small lava flows nearby. It is clear that this must have been long lasting, more than a few weeks, but it is hard to know how long.

  17. Science,12 May 2022, :
    “Atmospheric waves and global seismoacoustic observations of the January 2022 Hunga eruption, Tonga”:

    From the Abstract:
    “The 15 January 2022 climactic eruption of Hunga volcano, Tonga, produced an explosion in the atmosphere of a size that has not been documented in the modern geophysical record.”

    And BBC’s of layman summary of the above paper:

    “The eruption of the Tonga volcano in January has been confirmed as the biggest explosion ever recorded in the atmosphere by modern instrumentation.
    It was far bigger than any 20th Century volcanic event, or indeed any atom bomb test conducted after WWII.”

    • Reminder, tonight is the total lunar eclipse for much of Europe and North America.
      Analysis of the moon’s color during totality will be interesting. Due to ejecta in the aftermath of the H.T. eruption and wildfire smoke from Asia/Siberia, (plus major fires now in the U.S. SW), the moon’s darkness is expected to increase in depth as well as some spectral changes indicating the quantity, size and location of dust/aerosols in the uppermost reaches of the atmosphere. We shall see.

      • Also South America, here in Rio my wife dragged me out of bed to go look (I had forgotten). Nice blood moon down here.

  18. 4 stars under Thorbjörn.

    Main activity between 3,5 and 6 km under surface.

    Credits IMO
    15.05.2022 12:26:25 63.861 -22.535 4.7 km 3.1 99.0 5.2 km WNW of Grindavík
    15.05.2022 12:01:09 63.863 -22.537 4.6 km 3.4 99.0 5.4 km WNW of Grindavík
    15.05.2022 12:01:00 63.864 -22.546 5.3 km 3.7 99.0 5.8 km WNW of Grindavík
    15.05.2022 11:35:13 63.857 -22.547 5.6 km 3.5 99.0 5.5 km WNW of Grindavík

  19. Sunday 15.05.2022 17:38:42 63.883 -22.558 3.9 km 4.6 56.42 7.5 km NW of Grindavík
    Sunday 15.05.2022 17:38:20 63.848 -22.552 5.3 km 5.0 99.0 5.5 km WNW of Grindavík

    • No, this is not normal. The quakes are of course of a magnitude that the Reykjanes fault can do but the cause is not pure tectonic. A dike is putting stress on the fault. The M5 broke a section of the Reykjanes fault, judging from the data perhaps 2 km or so, at a depth of only 4 km. Things are developing fast. The chances remain that this will die down but an eruption is not out of the question.

      • It´s getting more and more interesting indeed! Curious how many of the M5s are going to happen in the next couple of days/weeks, it will give an indication of how much oomp is behind this intrusion.

      • Is there an aseismic zone here? if yes, we might not see magma ascending through this.

        • There shouldn´t be an aseismic zone, it was hundreds of years since the last eruptions here, the area is not hot and flexible like the dead zone. In fact I´d say it is the opposite – before anything reaches the surface here we´ll see a lot of earthquake activity.

          This time we are closer to the city, so there should also be many more felt reports and what comes with it..

          • Not sure that is strictly true, there are abundant geothermal zones in the area so it is pretty hot underground. After looking at the way that most rift events happen too the zone between Vatnajokull and Katla probably isnt unusually hot or ductile either, just generally inactive entirely. Laki was accompanied by massive earthquakes, 6+ magnitude, it was fast because it was preceeded by perhaps millennia of sills and other intrusions beneath Grimsvotn and Thordarhyna, and when a rift opened it was like blasting a hole in a dam.

          • There was an aseismic zone underneath Geldingadalir, itself. However, there were a lot of earthquakes at most depths at the ends of the dyke intrusion.

          • Geothermal plants are also close to Fagradalsfjall, and that was very noisy for a long time before anything started spurting. They don´t need magma but residual heat is sufficient, plus they are in many different places around Iceland where there still are numerous earthquakes.

            A sudden start without prolonged runup like Hekla would be very surprising!

    • When it comes to intrusions it is important to remember that the process of magma intrusion does not make earthquakes per se. When magma cuts into rock it does not generate an VT earthquake. Volcano-tectonic earthquakes happen instead on faults next to the intruding magma, which get triggered by the stresses generated by the intrusion. These faults probably exist already and are not created in that moment.

      The following article, for example, is great, and looks at intrusions of Piton de la Fournaise. Earthquakes do not happen where the magma intrudes. The seismicity happens in the caldera ring-fault under the summit caldera of the volcano, which gets excited by the intrusion. If an intrusion happens under the west flank of the volcano then the west side of the ring fault under Dolomieu flares up with seismic activity, other than that the intrusion propagates silently.

      I have reviewed catalogs of relocated earthquakes of Kilauea, and found much the same. The dike intrusions of the Pu’u’o’o era, which there have been multiple such intrusions in the Upper East Rift, have been largely aseismic. They generally flare-up the neighboring portion of the East Rift connector conduit, which is a long-term seismogenic structure. A clear intrusion path can never be seen in seismicity.

      Sometimes dikes do have earthquakes along their base which roughly seems to match the intrusion path. However, in recollection I’m starting to think it’s not so simple, at least not always. For example the Sao Jorge unrest earlier this year, the deformation and the earthquakes where offset, so that the intrusion didn’t really coincide in location with the earthquakes. The earthquakes did happen along the base of the dike swarm, but in an area of old dikes, not where the new dike intrusion was taking place. The dike intrusion of Fagradalsfjall in December 2021, which I followed closely, did generate very clear seismicity along its base which matched deformation. However I’m not fully sure it did record directly the magma transport, previous dikes have followed that same path, the earlier 2021 dike as well as postglacial intrusions that made the tindars (subglacial fissures) that run from Keillir and across the mountain. It could very well have flared an area weakened by repeated earlier intrusions and that was ready to break.

      That is why my experience looking at intrusions shows that the seismic activity associated to an intrusion is very complex and varied, and depends a lot upon the existing faults and other seismogenic structures that surround the intrusion. It is thus extremely hard to interpret. In this case probably various faults are being affected by whatever magmatic process is occurring at Svartsengi. Could be inflation, geothermal or intrusion. The area is riddled with large faults so it is very sensitive to the changes in stress brought upon by ongoing magmatic phenomena.

      • The article I linked explains it quite well, this is a quote from it:

        “Seismicity is not always a straightforward indicator of magma propagation. Although volcano-tectonic
        earthquakes can sometimes be interpreted as a direct marker of dike pathways (e.g., Rubin et al., 1998;
        Sigmundsson et al., 2015), it can also correspond to distributed damage caused by pressure variations in the magma reservoir (Carrier et al., 2015) or alternatively as the result of pre-existing suitably oriented structures already near to failure (Rubin & Gillard, 1998). ”

        This is a quote from another article on Holuhraun. The Holuhraun dike was very seismically active but only at the base of the dike. So the intrusion path was well marked. As they note though it activated a previously weakened area, tectonic spreading combined with localized spreading caused by earlier repeated Holuhraun intrusions had likely weakened the region that then underwent fracturing in the 2014 intrusion, one can suspect that some faults that were active in 2014 could have been inherited from earlier dike intrusion events. The dike base if after all a location of intense tension al stress, and successive dikes will add more tension to the same area:

        “The ∼100 m spatial resolution achieved reveals the complexity of the dike propagation pathway and dynamics (jerky, segmented), and allows us to address the precise relationship between the dike and seismicity, with direct implications for hazard monitoring. The spatio-temporal characteristics of the induced seismicity can be directly linked in the first instance to propagation of the tip and opening of the dike, and following this – after dike opening – indicate a relationship with magma pressure changes (i.e. dike inflation/deflation), followed by a general ‘post-opening’ decay. Seismicity occurs only at the base of the dike, where dike-imposed stresses – combined with the background tectonic stress (from regional extension over >200 yr since last rifting) – are sufficient to induce failure of pre-existing weaknesses in the crust, while the greatest opening is at shallower depths. Emplacement oblique to the spreading ridge resulted in left-lateral shear motion along the distal dike section (studied here), and a prevalence of left-lateral shear failure. Fault plane strikes are predominately independent of the orientation of lineations delineated by the hypocenters, indicating that they are controlled by the underlying host rock fabric.”

        • The base of a dike will normally be at a depth where the density of the crust changes. Magma comes up but the change in density causes a horizontal weakness: it is now easier for the magma to get between the layers and move (or pond) horizontally. The lifting of the rocks above cause earthquakes. At some distance magma moves up again, often along an incline, and finally it finds a place where it can ascend vertically. The size of the earthquakes depend on the stress and the brittleness of the rock. As you say, there are no earthquakes in the dike itself. There can be a lot of crackle at the tip of the dike where small gas explosions break the rock. The larger earthquakes are always in faults in the cold rock.

          • Yes, dikes themselves may produce other types of seismicity, like tremor, or maybe long-period earthquakes, that are associated to the transport of magma or the emission of gasses. These are not easy to locate anyway so their occurrence within intrusions is not well known.

            Volcano-tectonic seismicity, brittle failure, the typical earthquakes that get located, will mostly happen outside the intrusion. In faults, like the caldera ring fault of Piton de la Fournaise, or in strongly stressed areas, like the region underlying a dike swarm.

        • Which would partly explain why it was aseismic beneath Geldingadalir, itself, but lively along the dyke (locations of previous faults?)

          • The large earthquakes have stopped this morning. Smaller ones are continuing, with a tendency for the shallower quakes (3-4 km) to be a little closer to Grindavik. If this continues, then an eruption could occur perhaps 3 or 4 km northwest of Grindavik. If the stronger quakes better show where the activity is, it will be 5-6 km from the town. The pin in the map shows where I think these larger quakes have been. There is a small old rift there, running southwest-northeast with a small lava flow which looks dark enough that it may have been from the Reykjanes fires 800 years ago. That one didn’t go far.

          • The earthquake activity is under the Eldvorp crater row, one of the largest on Reykjanes. Eldvorp was created in one of the eruptions between 1210 and 1240 though it was maybe not exactly observed as the date is not given. The fissure does go offshore, so it might have been the eruption in 1226, the R8 tephra which was a VEI 4.

            If that is the case given the length of fissure and the evident eruption rate both on land and underwater, this could be one to watch for. It probably wont reach Grindavik though.

          • The strongest earthquakes are at Eldvorp. But the shallower quakes are a few km southeast of there, and the inflation seems strongest at Skipastikshraun which is a few km east of Eldvorp. I haven’t seen the insar maps.

          • Inflation would be above a sill, or complex of layered sills. It doesnt look like there is any eruptive fissures in that particular area, they form around it but not right there. Skipstigshraun is the end of a lava flow that flowed from a crater on the other side of Eldvorp, seems that eruption must have lasted longer as it managed to form a central vent and taller fountain, like Krafla in 1984.

            In any case it looks like this is going to be quite the show when something breaks. Probably will be very fast, quakes appear and then within a few hours lava will be erupting.

  20. I’ve been looking at some recent scientific articles on Reykjanes activity. Apparently Krysuvik experienced inflation in the later half of 2020. That is interesting because we have three distinct volcanic systems that have been active already. First in the early half of 2020 Svartsengi experienced three rapid episodes of inflation, possibly sills. The later half of 2020 Krysuvik was inflating. Then in 2021 a dike intrusion started from Fagradalsfjall which culminated in a long-lasting eruption, after the eruption, Fagradalsfjall kept inflating and produced a second dike in December 2021 which did not erupt. Now we have a renewed inflation episode from Svartsengi.

    • All Thorbjorn GPS are clearly showing the inflation of Svartsengi. Maybe another sill intrusion has started. Although there is another theory shown in multiple scientific articles that the inflation is on geothermal origin, I’m not sure if I’m convinced by this idea though.

    • Interesting now that there has been a quake in Brennisteinsfjoll, to see if maybe that system has woken up too.

      I wonder if really the east-west progression of the last cycle was an actual thing. GVP says that eruptions happened from Krysuvik as late as the 1300s based on tephra studies, and Brennisteinsfjoll apparently last erupted in 1341 with reasonable reliability, which is the latest date of an eruption from the last cycle at all actually. The eruptions from Illahraun and Arnarseturhraun also happened after the eruptions at the tip of the peninsula, and formation of Eldey. Would seem maybe the systems activated from east to west but didnt not alternate, they all erupted together.

      • Most of the ages are based on radiocarbon dating which has a substantial uncertainty. Those dates were probably uncalibrated when the idea of the westward progression was made, so there would have been even more uncertainty. It would require more radiocarbon ages and abundant high quality palomagnetic dating to figure out exactly what happened, back during the Reykjanes Fires. Or to put it in another way, I do not think we know enough to be sure that there was a westward progression in activity.

        • What I can find. Eruptions happened in Brennisteinsfjoll from about the time of settlement up to 1341. Krysuvik had observed eruptions in the 1150s and 1188 and suspected eruptions as late as 1340. Svartsengi erupted in the 1220s and 1240. Reykjanes erupted many times at uncertain dates between 1200 and 1230. So it seems it did begin at Brennisteinsfjoll, but also ended there.
          The biggest eruptions were also there too, Hvammahraun erupted in around 900 AD is likely over 1 km3 in volume, as are both of the two Hussfellsbruni lava fields, erupted about 1200. Prrobably 3/4 of all of the last cycle erupted from Brennisteinsfjoll.

          The cycle 2000 years ago though Brennisteinsfjoll almost didnt erupt at all and there was much bigger eruptions further west, area of Grindavik was flooded as well as basically all of the Eldvorp area and the tip of the peninsula. Hengill also erupted in that time, a major rift probably going up to 1 km3 of lava. And then now the newest cycle has begun at a volcano that hasnt erupted in 6000 years…

      • I’m also wondering if viewing the Reykjanes Peninsula as being a few separate volcanoes isn’t a misleading idea. In reality when you start from Langjokull, and continue along the Reykjanes Peninsula you encounter volcanic vents like fissures, tindars, shields, all over the place. Where does one volcano start and where does it end? It is really impossible to distinguish this for sure, there could be many ways of seeing it. In reality the whole area is like a continuous volcanic field, a volcanic field that continues underwater through the MAR. It is as problematic to divide as the East Rift Zone of Kilauea, there are certain fissure swarms that have erupted repeatedly and thus can be distinguished as an individual structures (Pauahi, Alae …), there are also areas in which magma storage is focused, like the MERZ. But in the end an intrusion can happen anywhere along the ERZ and it is a continuum of fissure swarms and intrusions.

        Starting from the western tip of the peninsula, one encounters the Stampar fissure. 2 km to the east, one gets to Skalafell. Another two kilometres east and you arrive at a swarm of shields, Haleyjarbunga, Sandfellsdalur, and Lagafell. Another similar jump eastward and you get to the Eldvorp fissure system. Yet another jump east you encounter the Arnarsetur fissures. 3 km east and you arrive at Sundhnukur fissures. I could go on like that until I’m in Langjokull. There are fissures and vents everywhere. Separating it into 4-6 volcanoes doesn’t make that much sense really. The whole area has vents, postglacial or subglacial.

        It shows variations in eruption style. The area of Stampar and Skalafell has intense fissure eruptions. Then there is a brief break of slow eruptions and shields, they are Haleyjarbunga, Sandfellsdalur and Lagafell. Then another large area of intense fissure eruptions spanning the Eldvorp, Arnarsetur and Sundhnukur fissures. Then comes an area of shields, Þráinsskjöldur, the Fagradalsfjall tuya (subglacial shield), Geldingadalir 2021, and Vatnsheiði. After Fagradalsfjall another area of intense fissure eruptions shows up, comprising many Trolladyngja and Krysuvik tindars and younger fissures like Skollahraun, or Ogmundurhraun. East of Krysuvik shields and slow eruptions occur everywhere all the way to Krakshraun, north of Langjokull, the only exception is Hengill which has done intense fissure eruptions like Nesjahraun.

        • I wish I could make a better plot, but I’m doing it in my tablet. Yellow is the uplifted area in 2020 near Thorbjorn, magenta is the Eldvorp fissure, green is the Arnarsetur fissure and blue is the Sundhnukur fissures. All three of them had a similar eruption style consisting of long curtains of fire and an extensive sheet of lava, like Krafla eruptions. It does seem possible that there was a genetic link between the storage near Thorbjorn and these three recent fissure eruptions. Most likely the dikes tapped into the magma storage west of Thorbjorn and that could be the reason they erupted so rapidly. Dikes which form a little more to the east or to the west wouldn’t manage to tap into thus storage, presumably.

          • This is fascinating, but I am quite curious about this one thing – is there any “remnant” magma at the location of where the intrusions are? I am not saying that the intrusions are old magma pockets left over from previous eruptions but instead the intrusions interacting with the pockets, like what happened on Fissure 17 back in 2018 when Kīlauea erupted. Or is it too old to be magma anymore and that they are solidified enough to have no interaction with the newer magma coming in?

          • The dikes would easily solidify, I don’t expect a dike that is relatively isolated, like Arnarsetur, and is intruded in the upper 4-5 km of crust to survive long. That said I see the possibility that a sill complex exists under Thorbjorn and the Svartsengi geothermal plant. Sill intrusions could still remain molten at a depth of 4-5 kilometres if they have intruded repeatedly the same location and raised the temperature high enough. In fact it is probably necessary to have such a complex of sills to explain how eruptions in the area effuse lava so rapidly. They must be feeding from an existing storage that can rapidly transfer its magma upwards through the dike. If an eruption happens we will be able to test many of these ideas.

          • Yes, this is a follow-on from the 2020 intrusions, not the 2021 eruption. If it breaks through, I would have expected it to create a new fissure, not re-use an old one. But there was an M3 just now, roughly on your magenta fissure. Still relatively deep (4.5 km)

          • Think we are seeing the crustal response to inflation – old faults moving. In effect, reiterating what was said by a commenter here earlier.

            Both Reykjanes and Krysuvik are on alert level yellow (higher than background level seismicity).

          • Have had the same thought, sort of, that Reykjanes is sort of like a single volcano. Only difference to say Kilauea is that the deep rift is for sure open at the bottom into the mantle where at Hawaii its much less clean.

          • It acts like a mid oceanic ridge. In fact it almost is one.. There is no single magma feed to the surface. It comes up along the ridge, and pools at 6-7 km depth below the layers of basalt. Where it reaches the surface depends on weakness near the surface, rather than a deep feed. Vatnajokul is very different: it has much thicker crust so acts more like real volcanoes, albeit with long dikes along the rift. Reykjanes is also a bit unlike a mid-oceanic rift because it is on a large angle to the spreading direction, becoming largely (but not completely) a transform fault. It has long dikes but they go along the spreading direction, SSW-NNE. Shallow dikes (from the 7 km level) extend a few kilometers. Deep dikes (from the top of the mantle) extend for as much as 50 km – but do not reach the surface so they are in vain. But the bottom line is, this is not really a single volcano but more like a volcanic swamp, with many magma ponds along the line of the fault, ephemeral on geological time scales.

          • @Zach Trent

            The thermal residue from previous intrusions, whether they make it to the surface or not, have a cumulative effect on the surrounding ambient heat load of the rock. Over long periods, (thousands of years) the temperature will drop to some value based on the heat added or cooled over time.

            Should that not fully solidify, it will be in a mostly plastic state until it does. (<- My bet on why the "Dead Zone" is so seismically quiet.)

            If this makes no sense, don’t worry. I’m jacked up on pain meds due to a broken rib. It probably won’t make sense to me in the future either.

          • I know that magma cools down slowly over time. They get more silica-rich and less mafic as time goes, if it is left alone without any new injection, it would become andesitic-like type of magma. I had a thought that the previous eruptions might’ve had some left over (as Hector says, they would’ve solidified by then unless if they are deeper) and interacted with the fresh magma or even mixing with it. That is what happened at Fissure 17 in 2018 – essentially old magma left over that, overtime, due to heat loss, slowly becomes cooler and more siliceous until new magma came in to force it to erupt.
            I kinda had the same thought about the Reykjanes fissure system but, because they happen so slowly and deeply, the older magma pockets would already be assimilated into the magma. That could potentially explain why most of the eruptions at the Reykjanes Peninsula (other than the 2021 Fagradalsfjall eruption, which came primarily from the mantle) are, say, a little “siliceous”.
            This might be speculation, but after the last eruption(s) occurred in the, the sills slowly cooled over time to the point they are nearly solidified (due to the duration of the dormancy) until an new batch of magma intruded into it and completely assimilates the much older magma and, slowly, “gains” new magma, causing uplift until it produces an intrusion. For the most part, the dikes failed to reach the surface until, at some point, it finally reaches the surface and an eruption begins. Once it stops, it may produce another eruption, if it has the means to (pressure, volume, etc.) until the factors that produced the eruption(s) in the first place becomes unfavorable and become “dormant” and the cycle repeats. (I know, it somehow became unrelatable to my own question and got off the rails)
            I am also a little curious about another thing: could such pockets of old, stale magma possibly exist at other such volcanoes other than Kilauea?

  21. Last night’s lunar eclipse was very dark, it would seem that there are still some aerosols or ash from the Tonga in the air.

    • Thanks Jesper. Looks like Etna is building up in activity very slowly, it has now started to make some Strombolian explosions from the top.

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