Living dangerously: another Grimsvotn prediction

The Grimsfjall cliff overlooking the Grimsvötn caldera. Photo taken in 1972


Grimsvötn is heading for an eruption. There can be no doubt about that. Of course, it is always heading for an eruption. This volcano has ADHD. For Grimsvötn, more than a decade of brooding is unusual: normally it just throws it out. A misplaced snow flake can set it off. And it produces not only volcanic ejecta. In hindsight, it was unwise to grow a glacier on such a hot head. The ice melts and collects in a subglacial lake. Once enough water has collected, it lifts the constraining glacier and escapes. The jökulhaup that follows heads straight for the south coast, carrying big blocks of ice with it. The volume of water Grimsvötn generates exceeds the volume of its volcanic ejecta. This is the ultimate mountain of ice and fire, with a temper to match.

Grimnsvötn is heading for an eruption: no doubt about it. But science wants to know more. It wants to understand how the mountain works and why (and when) it erupts. That means making a model, and to validate a model requires making a prediction. If the prediction come true, the model is deemed to work – for now. If it fails, science goes back to the drawing board. And it is essential that the prediction is about the future. Predicting the past does not count: that is inside knowledge which already went into making the model and so can’t be used to validate it.

Grimsvötn will erupt. A year ago, Carl and I had a challenge, to predict when the next eruption would be. I used math and came up with January 2020 to June 2022. Carl used magic  sorry insider knowledge insight and knowledge and came up with December 2018 to December 2019. So far, nothing has happened, so we were both right. But when the activity increased during the past month, we decided to revisit our predictions. After all, a prediction is only a validation if you check whether it worked! We are not politicians: we cannot quietly ‘forget’ what we said last year. Science is brutally honest, and a wrong prediction is not a failure but an opportunity. It improves the models. Carl wrote his update last week and failed to change his prediction. It remains December 2018 to December 2019. So what about my prediction? Is it time to throw in the towel?

The closer to the eruption, the better the forecast is likely to be. I had a bit more time than Carl so decided to wait, and see whether Grimsvötn would do anything that helped my models. If that gave me an advantage over Carl, who am I to complain? Against magic knowledge, I need all the help I can get! And indeed, things did happen.

Volcanoes are like metal fatigue. A minute crack forms, and over time it grows into a full scale failure. The final failure is certain. The speed at which the cracks grow it accelerates as the crack grows: it is self-reinforcing. But the ‘when’ of fatigue failure is not predictable because it depends on the chance stress events which first cause or enlarge the cracks. So it is with volcanoes. The crack can suddenly and unexpectedly grow. A year ago, Carl wrote: In fact, there could at any time come a rogue earthquake swarm, or a single M4 earthquake, that punches the value [of cumulative stress] fast into the eruptive ranges. It is though not as likely judging from previous behaviour of Grimsvötn. But this week, Grimsvötn did do just that. A single quake pushed up the plots to the danger area.

But before going into how this affects the predictions, first a bit of background. There is a lot of background.


Grimsvötn is Iceland’s most active volcano. It is also the best hidden one. Hiding an active volcano is not easy: an extended icecap helps, but eruptions leave signs even if the area is inaccessible. The fires above the glacier were a dead give-away that there was a volcano somewhere amidst the ice. The frequent jokölhaups were another.

And ‘frequent’ is the word. For the past 800 years, Grimsvötn has erupted on average every decade. Before that, it is was even more frequent. Most eruptions are small, around 0.1 km3, such as the 2004 eruption. But when the occasion is right, it can also go bigger, as it did in 2011 when it had its biggest burp for 140 years. And 2011 was by no means the worst it can do. The so-called Saksunarvatn ash is a 10,000 year old layer of tephra found across the Faroe islands, northern Europe and Greenland. The composition of the ash shows that it came from the Grimsvötn magma reservoir. In the Faroe islands, the ash is in places a staggering 45 centimeter deep. In addition to this large explosion, there are several smaller tephra layers close to the thick ash, showing that several smaller eruptions occured within about 500 years of the main event. Grimsvötn really threw a tantrum! The total tephra volume of the Saksunarvatn ash may be over 30 km3 although the precise value is very poorly known – so much ended up in the ocean. In comparison, even 2011 was just a hick-up.

Grimsvötn also mixes up eruption styles. Most often it does explosions from the summit or along small fissures near the summit, but on occasion it also feeds effusive eruptions from a much more extended rift system, 90 kilometers in length. Mount Laki formed from Grimsvötn magma. And in 1783, the rift again gave way and the largest Icelandic eruption since Eldgja devastated the country. It is called Laki, although Laki mountain itself did not take part. After the Laki eruption, the listed population of Iceland had decreased by 25%. This volcano packs a punch.


In spite of its hidden nature, the Icelandic people were well aware of this invisible volcano. The ice-covered lake of the Grimsvötn caldera was known very early on. It may have been more accessible in the past, before the major glacier growth of the little ice age overran the local farms.

Grímsvötn is first mentioned in an Icelandic letter dating from around 1600:

`… fire from within the lake […] that is called Grímsvötn in our language, flinging out, higher than the highest mountains and with tremendous power and destruction, huge amounts of pumice and gravel that is catapulted and dispersed to the most far-flung parts of the country, damaging meadows and terrifying the inhabitants’

A description of an eruption of Katla in 1625 mentions Grimsvötn in passing:

… there is also a common rumour that to the north of Glómagnúpssandur , next to Skeiðarárjökull, there is a lake called Grímsvötn, which flows with fire, ice and water like this glacier [i.e. Kötlujökull] and what so often happens is that the fiery eruption first bursts forth from the centre of the aforesaid Grímsvötn, from which flames burn like a pyre or bonfire’

So it was clear that Grimsvötn was known and had been visited. The Atlas Danicus (1684) contains an account of a volcanic eruption in Grímsvötn and Grímsfjall in the so-called Gríms Vatna Jökull glacier. Maps which for the first time showed the caldera at the right location appeared in 1730. But as the glaciers advanced, the stories became less clear, and began to sound almost mythical: ‘Men have seen 15 separate fires burning on the surface of the lake; what the cause of this can be, people find hard to say, except perhaps that it is caused by an overabundance of sulphur deep in the Earth, for whenever folk ride by these glaciers there is the most powerful odour of sulphur there could ever be’.

After Laki, it seems that the memory of Grimsvötn was completely lost, even though the jökulhaups and eruptions continued. Everyone who knew the stories had either died or moved away during this disaster. In June 1903, pastor Magnús Bjarnason wrote about an on-going jökulhaup, showing how little was left known. He attributes the eruption to the southern edge of the glacier:

[the jökulhaup] occurred at the same time as an eruption in Skeiðarárjökull (?) [nearer Þórðarhyrna] which often happens, to a greater or lesser extent, when there is an outburst in Skeiðará river. Flames arose north and west of the so-called Grænafjall mountain, which lies to the north of Eystrafjall, on Thursday 28 May, upon which the floodwaters increased as the glacier melted, searching for channels with such power that they burst open the front of the outlet glacier and surged forwards with blocks of ice that, according to the post bearer, were 60 feet high, and over a wide area there were others on top of them another 25– 35 feet thick. [..] The most terrifying jökulhlaup was on Thursday and Friday night, when the eruption had begun and was at its peak. Water spurted up in high columns through cracks opening up in the glacier and all the ground and houses in Skaftafell and Svínafell in Öræfi shook so much in an earthquake that windows were broken in Skaftafell, and thuds and bangs were heard as far east as Hornafjörður, for there was a westerly wind. The evening and night sky were lit up by the volcanic flames that stretched high into the sky and from its smoke came flashes of lightning that brightened the land and rivers all the way out to Álftaver, and this was later than ten o’clock at night. A cloud of smoke lay over the Öræfi district, concealing the mountain tops above Sandfell and Hof in black billowing waves with flashes of fire and lightning streaking from them above the farmsteads. Even the earth itself shook when the glacier was cracking open and the explosions louder than the firing of any canon. All of this combined was so terrifying that the folk of Sandfell (Pastor Ólafur himself had recently just left to the west with two children) fled eastwards to Fagurhólsmýri. Fortunately, there was no consequent ash fall, and the cloud and eruption were much milder the next day, indeed the jökulhlaup itself was beginning to abate.

In 1919, two Swedish students, Hakon Wadell and Erik Ygberg, set out to explore the possible causes of the jökulhlaups that frequently emerged from beneath Skeiðarárjökull, unaware that they were retracing the past. They found the glacier very difficult to traverse: they had four horses pulling the sledge, but this was hard going because of a 10-cm thick cover of tephra, which had come from the large eruption of Katla. Suddenly, the front horse stopped, refusing to budge or go any further forward no matter how hard the students beat it. A slight break in the fog appeared, and they found they were standing on the edge of a precipitous cliff. The horse had sensed the up-draught at Grímsfjall! ‘When we came to the head of the horse, there appeared below us a crater comparable to the side of hell in size, though even that would have been expanding in these recent and most difficult times.’ The crater welcomed them with ‘… the rumbling of ice rocks that continually crashed from the cliff walls, hundreds of metres high, down into the crater’s basin where they melted in warm, emerald green water.’ Typical students, they toasted their discovery with cognac and christened the caldera Svíagígur (‘Swedish crater’), a name that did not catch on.

They continued to cross Vatnajökull but had to abandon their horses due to the conditions. The went back afterwards and two of the horses were recovered; the other two and a dog are presumed to have died. The atrocious conditions of the ice and the weather left their mark: Ygberg never fully recovered his health after this trip. And they failed to convince the world that there really was a major volcano hidden in the icecap, something they both reportedly felt bitter about in later life. Who believes students?

Grimsvötn erupted again in 1934, and this time people were able to travel to the caldera during the the eruption. It left no doubt that this was the origin. The travel was as difficult as it had been in 1919: the thick layer of ash made sledging and skiing impossible so the explorers had to walk for 20 kilometers towards the eruption plume. There may have been some health and safety violations: ‘Clumps of slag, pieces of lava and chunks of the crater bed lay in heaps and mounds, in some places as if raked together like haystacks, and the nearer we reached the edge of the crater, the more grandiose everything became.’ And more dangerous: they reported that plumes of steam, yellow, green and steel-coloured, billowed up through a gaping wound in the ice sheet while black pillars of smoke were flung into the air from the pillar lava. Clouds of steaming sulphur seared their lungs as cinders rained down onto the glacier and hissing and sucking sounds were heard all around them as well as a loud rumbling from the deep. Their observations confirmed that the two Swedish students, 15 years earlier, indeed had discovered Iceland’s most active volcano.

Grimsvotn seen from the air in 1938. Photo by Pálmi Hannesson


The icecap that covers Grimsvötn is Europe’s largest glacier (by volume; by area it is the second largest). Snow and ice have a way of smoothing over the cracks and calderas. This glacier indeed covers a multitude of sins.

Remove the glacier and no fewer than five volcanic centres appear: Öræfajökull, Bárðarbunga, Kverkfjöll, Grímsvötn, and Hamarinn. They sit on a 700-meter tall massif, bisected by a deep valley. The valley runs runs south-southwest to north-northeast, parallel to the main spreading axis. The main volcanic activity is in the ridge west of this valley, where Grimsvötn has pride of place.

Vatnajökull without the jökull (icecap). Source: Helgi Björnsson

The glacier around Grimsvötn contains a detailed record of previous eruptions, in the form of layers of ash. This has been used to derive the eruption history. Between the years 1200 and 1800, there are 66 separate ash layers, each from a local eruption within the icecap. Five of these layers indicate that two different volcanoes were erupting in the same year, so the total number of eruptions in these 600 years was 71. Eruptions on the fissures outside the glacier will not be included. Adding the 15 more recent eruptions bring us to 86 eruptions between 1200 and 2000. Two thirds of the ash layers come from Grimsvötn: it erupts more than twice as often as Bardarbunga. In fact, Grimsvötn is responsible for over a third of all eruptions in Iceland. Not bad for a volcano only officially discovered in 1919!

Going back in time, the frequency of the ash layers further increases. The peak activity was between 1000 and 2000 years ago. This was a time when the glaciers were less extended, and perhaps this made eruptions easier.


Recent eruption were in 1903, 1922, 1934, 1954, 1938, 1983, 1996, 1998, 2004, 2011. In spite of the high frequency, there were no eruptions in Vatnajökull between 1938 and 1983, 45 years of quiescence. It now seems unbelievable. But this is part of a pattern. The ash layers show that times of frequent eruptions were interspersed with times of less frequent ones: these two phases alternate every 50-80 years. Around 1950 was the depth of a period of infrequent activity. Large eruptions, such as the 2011 one and 1873, seem to occur about every 140 year, i.e. once in a combined high/low frequency period.


Eruption volumes are not well known because so much is intercepted by the ice, but are in the range 0.01 to >0.5 km3. The 1996 Gjalp eruption produced 0.45 km3. Over the past 1000 years, Grimsvötn has produced an estimated 15km3 of lava and14km3 of tephra, or 21km3 DRE in total (remembering that tephra is three times less voluminous as DRE). Of course, the lava output is almost entirely due to Laki!


The minerals that are found in the ashes trace the conditions under which the magma crystallized. Certain minerals form at certain pressures and temperatures. The ones found in the ashes formed at a depth of 15-17 km, and that is where the main Grimsvötn magma chamber appears to be. The crystals in the Laki eruption formed at the same depth and a temperature as those found from the 1823 Grimsvötn eruption, further strengthening the hypothesis that Laki lava came from Grimsvötn (other evidence is the lava composition and the fact that Grimsvötn itself erupted at the same time as Laki). The summit eruptions themselves come from much shallower magma, fed from the deeper magma storage. The most recent eruptions have minerals from a wider range of temperatures and pressures, more so than during the 19th century. The model for this is a series of dikes and sills, of different depths, fed from the 15-km reservoir, where the efficiency with which magma moves from the deeper reservoir to the sills has been decreasing with time. The 15-km deep reservoir is likely fed from a neutral buoyancy layer at the mantle-crust boundary, 30 km deep.

Holuhraun had a more primitive magma, but with similar crystallization depth as Grimsvötn. The eastern volcanic region may well have a series of such magma reservoirs at 15+-5 km deep, which stores magma for a shorter time for Bardarbunga, and longer for Grimsvötn. Laki was fed from such a reservoir, either directly or indirectly, where the data shows that the same reservoir also feeds Grimsvötn.

A deep connection between Bardarbunga and Grimsvötn seems possible. A paper in the last year pointed out that in the year before Holuhraun, Grimsvötn stopped inflating. It implied that magma was being diverted. The amount of magma involved was rather small (0.015 km3), but it indicated a connection. Either magma was transferred from Grimsvötn to Bardarbunga, or there was a pressure imbalance in a deep common reservoir (30 kilometer deep). The latter seems more likely. As Grimsvötn 2011 showed some evidence for a magma recharge of the deep reservoir, it is possible that the same recharge also was the ultimate cause of the Holuhraun eruption.


Vatnjokull magma plumbing. From Bato et al. 2018, Scientific Reports 8, 11702


The minerals found in the ash indicate the temperature at which crystalization occurred, i.e. the main storage chamber. This shows an interesting effect: the Grimsvötn magma system appears to be slowly cooling. The temperature of the Laki magma (1783) was 1140 C. The composition of the Saksunarvatn ash indicates the same temperature. But eruptions in 1823 and 1873 indicate magma temperatures of 1130 C, and the 2004 and 2011 eruptions gave 1110 C. A paper by Hadadi et al. (2017) find a cooling rate of around 0.1C per year over the past 200 years. The 2011 eruption was the first to show evidence for FeTi particles, a lower temperature mineral: previously the magma had been too hot for this mineral to form.



So how does an eruption proceed? A description of events leading up to the 2004 eruption by the IMO gives an idea what we might expect. Earthquake activity began to increase in the middle of 2003. Tremor was first seen at Grimsfjall in August 2004, each burst lasting 30 minutes. In October, the earthquakes increased in strength from mostly M1 toM2.

The IMO report notes that in October 2004, the GPS station at Skrokkalda (SKRO) started rising, by 40 mm in three weeks, and moved west. This was seen as evidence for strong inflation. But in hindsight (a popular alternative to insight), it is not so clear. SKRO is 56 km from the eruption site, and the the magma reservoir supply would have had to be enormous to give such an effect. Inflation is commonly seen around the glacier in late autumn, due to the increasing weight of the snow. Looking at the SKRO signals now, its motion was probably nothing to do with Grimsvötn. 

On 30 October 2004,a jökulhaup occurred. This is in itself not unusual. The autumn snows can trigger them. For instance, the jökulhaup in 2010 occurred on almost the same date, 31 October. But it is quite possible that the increasing heat accelerated the snow and ice melt, filling the lake. However, the ice above the lake floats, and therefore melting it does not change the pressure on the surrounding ice. For that to happen, either ice from the surrounding glacier needs to flow down and fill the basin (a slow process which happens after every eruption), or ice and snow further away need to melt and flow towards the caldera lake. This requires activity on the short fissures around Grimsvötn, and in fact several times a jökulhaup came after an eruption north of Grimsvötn, causing melt water to flow into the caldera. This happened in 1861, 1867, 1892 and 1938.  A summit eruption should not trigger a jökulhaup because it melts already floating ice. However, it is possible that a jökulhaup can trigger a summit eruption. It quickly removes a lot of weight from the caldera, and the lower pressure can initiate an eruption.

Two days after the jökulhaup, on November 2, the mountain erupted and Grimsvötn had again made its existence known to the world.

Current events

Now let’s get back to the topic of this post. Can we make a prediction as to when the next eruption is likely to happen? How well did it follow the predictions from a year ago? Earthquake activity has significantly increased since last year. Tremor has not yet been seen: even Friday’s (23 November) M3.2 event (unusually strong for the caldera) was purely tectonic in nature. That would suggest that we are at least a month away from the next eruption, if it follows the 2004 path, and it could still be years.

I modelled the earthquake activity with an equation also used for fatigue failure:

Here, tc is the time when things actually break, measured in days since the previous eruption. A larger tc means a slower build-up to the eruption. The factor k is a scaling constant, and M is the total cumulative moment, as plotted daily by IMO. The equation is normally used for number of events rather than moment (strength), and this version basically assumes that all individual events (earthquakes) are of similar size. That makes it rather difficult to deal with much a single much stronger earthquake, such as the recent M3.2. Should it count as a single quake, should it count for its strength, or should it be deleted from the data?

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

The Grimsvotn eruptions. Plotted is the cumulative seismic moment (total energy released by earthquakes) since the previous eruption. Click on image for more detail.

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

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

Looking back at what I wrote a year ago, I missed one aspect. Perhaps the 2011 eruption being ahead of schedule was because of the jökulhaup? Was the 2011 eruption triggered rather than purely spontaneous?

But let’s get back to the current events. How does it look like now?

The up-to-date cumulative seismicity plot (25 Nov 2018)

Over the past year, initially the progression was slow. There was continuing earthquake activity, but it was not particularly strong and the total cumulative moment rose slower than predicted. But over the past few weeks, the mountain has kicked into action. Friday’s M3 quake has brought to total seismic moment to within a factor of two or eruption values.


Now let’s compare the progression with the predictions from last year. The plots below show the two figures, one with the large quake at day 1850 included and one with it subtracted, together with the two original fits. (If you wonder why the data doesn’t look as crisp as in the IMO version, I do not have the actual data so had to digitize the plot to get the values. This procedure is not perfect for a step function. The ‘big quake’ took place some distance from Grimsvötn and its relation to it is unclear, so there is a case for discounting it. Last week’s M3, on the other hand was within the caldera and is harder to ignore.)

Updated plots with the two fits

On the left is the ‘fast’ fit. The fit is not great with the data continuously falling below the projections since the time the fit was made. The burst of quakes of last week has brought the curves closer, but it is not a convincing fit. On the right is the ‘slow’ fit. Here the fit is better, with the two curves staying closer together. The M3 earthquake has brought the data from below to above the curve, but it remains not far off.

It is interesting that in both cases, the data stays well below the model until mid 2014, after which it sharply increases. This change coincides with the onset of the Bardarbunga eruption. This was interpreted above as a possible diversion of magma. The plots here show that Grimsvötn recovered once Bardarbunga erupted. This shows that the issue was pressure, not magma transfer. As magma rose into Bardarbunga, it sucked magma in from a wider area and reduced the pressure underneath Grimsvötn. Magma does not flow from one reservoir to the next: the communication is through a deeper region.

So far, no reason to change the predictions of an eruption around 2021. But the fits are not great. Can we do better? There are two things we can change. First, during 2018, the activity at Grimsvötn was very low. In a way, this looks similar to the pre-Bardarbunga episode. Is it possible that Grimsvötn was affected by the magma rising into Öræfajökull? If I discard this phase, and just fit the recovery last week, it gives me the left plot below. Now the eruption is predicted for early 2021.

The second try is by assuming that the 2011 eruption removed so much stress that the onset of the build-up to the next eruption did not start immediately. Picture the Grimsvötn magma chamber as being surrounded by en elastic band (a bit like stretchable trousers). The build-up to the next eruption begins when the elastic band begins to expand. After the eruption, the band was larger than the remaining chamber, and so there was no stretch – compare your loose-fitting trousers after a crash diet. After some time, enough weight magma has been added that the band begins to stretch. This is the moment that the clock begins to count. This situation with a no-stretch-phase is depicted in the plot on the right. I get a decent fit with an 800-day delay. The fit is not bad, and based on appearance (‘goodness of fit’) it seems better than the others. It has much less of a dip prior to the Bardarbunga eruption. However, the 2018 quiet months are still notably discrepant. In this fit, the eruption is predicted for mid-2020.

Left: fit to the cumulative seismic moment, fitting the peaks. Right: fit assuming that there was an 800-day hiatus after 2011

So there are still a range of possibilities. The next few months will tell us what will happen. All the models here predict that the flurry of earthquakes of last week won’t continue at that rate. There will be a decline again in activity, although perhaps not to the very low levels of last summer. If the rate continues at the high rate, then it is clear that the models here do not work well, and an earlier eruption can be on the cards. Otherwise, I find that mid 2020 to late 2021 is the most likely window.

One final point. In addition to the earthquakes, the local GOS (GFUM) showed sharp inflation over the past month. It looks convincing. But is it?

The main problem here is that there the area has a lot of snow in autumn, and snow and ice on GPS systems introduces errors in the output. GPS system on the icecap often show large variations in their readings this time of the year. The plot below shows a multi-year GFUM curve. The jump seen in recent weeks is exceptionally large. But it happens at a time of the year when this GPS is normally out of action, so there is not a lot of comparison data. So again it is too early to tell. We will have to wait for spring to see whether the inflation is real, or is caused by the onset of winter.

And that is where we are. We have a model, and we have a prediction. It suggests that we still have two to three years to wait. But somehow, I doubt that volcanoes feel any obligation to predictions. They do their own scheduling. They are complex systems. Perhaps what we need is not so much physics, but a study of volcano psychology. Grimsvötn still has ADHD.

Albert, November 2018 

This post made heavy use of the book “The Glaciers of Iceland: A Historical, Cultural and Scientific Overview” by Helgi Björnsson, published by Atlantic Press in 2017 and translated into English by Julian Meldon D’Arcy. It has a wealth of information. I used it in particular for the historical background, and parts of the post follow the book very closely as I could not find a better way to phrase it.



Fun activity: how many Icelandic volcanoes black dots can you see simultaneously?


190 thoughts on “Living dangerously: another Grimsvotn prediction

  1. LoL There is trolls and goblins hiding in Grimsvötns magma chambers
    The brain illusion black dot game you posted in the Article drives me Insane!
    Albert how does that graphics work? !! placing a finger on the black dot and yet more appears
    This is driving me crazy LoL … and the dots seems to be graphics yet they dont exist at all!

      • I like optical illusions and I looked at the grid illusion link, but I think the interesting thing is this may be a fake illusion. The linked ones do jump around as you change your view, but in the one above they stay in the same place, as in they are part of the puzzle/illusion. Stick you mouse pointer on one and look away, then look back. there is still a black dot. stick your mouse pointer on an intersection without a dot, and none appear. I think it’s a reverse illusion, but based on the grid illusions you noted.

      • Short answer, these are always at the same intersections. I count twelve, but only see one, maybe two, at a time.

        • I can see 4 at the same time if I look at the center of a square formed by the intersections with dots.

          • If you look for larger square and rectangle patterns formed by lines between the dots you can see 4 at once at the corners of a large square, like thedustdevil; 4 in any straight line across the picture; 6 at corners of a rectangle formed by 6 dots, with a glimpse of 8 at once bounding the larger picture-wide rectangle.

          • If I look at the screen from above then the net gets blurry and I am able to see the 12 dots at the same time, maybe it’s cheating but I feel accomplished.

      • You can see more if you cover part of the picture up (slide a piece of paper across the screen). Your brain can’t cope with the grid: it fills in the dots based on expectation rather than what you actually see. It plays on this, perhaps plus the fact that your black/while vision has less acuity than colour vision. Anything away from the centre of your vision is seen fuzzy (try looking at a word on a page and read the read of the sentence while keeping your eye fixed on that word). Your brain does a lot of papering over the cracks. And brains can be fooled.

        • I have tried convincing my brain to focus on the dots and ignore the grid but it seems to be just too stubborn.

  2. 2011 Grimsvötn magmas cannot have been only 1110 C
    2011 was extremely fresh and gas rich and NO crystals at all in that ash.
    Have in mind Holuhraun was 1185 to 1195 C thats more likley for a powerful plume that haves the strenght as Iceland have. Grimsvötns magma chambers is likley above 1175 C to more correct.
    I guess Grimsvötns deep roots haves temperatures of almost 1500 C deep down.
    And most of the magma at Grimsvötn in depth likley is little above 1200 C.
    Laki that came from deep source must have been almost 1200 C or above that.
    But if your sources says how it is then its accepted then.

    At 1110 c most basalts contains quite alot of crystals and Hawaii becomes a crystal mush at these temps.
    Puu Oo was 1150 C and already quite crystal rich yet still very very very fluid.

    • Note that Grimsvotn produces very little lava. It is all tephra. This temperature is that of the crystalization depth, not the near-surface temperature. Crystalization also depends on pressure: you can’t compare it to surface conditions.

      • There is NO crystals in the ash.
        Had it been crystals in the depth they woud have been carried upwards and ended up in the ash mix. 1110 C seems too cold for a crystal free ash glass

      • 1110 C deep inside Grimsvötn at Icelands hotspot focus?
        I belived it was good above 1200 C inside there and even hotter at the roots
        ( I says around 1200 C and Grimsvötns deeper magma chambers

        The general temperature deep inside Vatnajökull at the roots is generaly accepted to be around 1485 C to 1510 C as most geologist sources. ( plume head )

        Thank you posting this information beacuse I becomes very curious

      • You makes me very curious indeed! and thank you for keeping me little more happy

        My opinion again
        The extremely quick cooling in 2011 explosive ash fragmentation preserves the original 2011 Grimsvötn magma chamber composition very well. NO crystals suggest the basalt magma was above olivine melting points, ( little above 1200 C ) not 1110 C

        • Hadadi et al find that the Grimsvotn tephra is 95% glass and 5% crystals. This was collected from close to the caldera as was ejected very early in the 2011 eruption. MgO is around 5%, and the 2011 tephra contains sulfur globules FeTi oxides which older tephra does not. The temperature and pressure come from the melt inclusions.

          This does not necessarily ontradict a magma recharge before 2011. It only says that the ejecta had spend time in a cooling deep chamber before moving closer to the surface

  3. My own opinion about Grimsvötns superfresh crystal free and superdeep origin of 2011 ashes
    is that they erupted at over 1200 C at bubble nucleation froth depth
    There was not even olivine crystals in that 2011 ash .. suggesting it was pretty hot.
    Holhuraun at 1185 C had only olivine crystals and rest of the mix was molten glass matrix

  4. 2011 was completely free of crystals what I have learned
    At 1110 c the 2011 ashes and erupted materials woud have been quite crystal rich for a basaltic melt.
    many minerals in a basaltic mix solidify and crystalizes at 1100 C ( a basaltic magma at 1110 C coud be quite crystal rich ). Grimsvötn 2011 had no crystals at all looking at ash particles and shards.
    Holuhraun that came from Vatnajökull at 1180 to 1190 C had most minerals melted at Norman L. Bowen
    reaction mineral seriers. ( Holuhraun was very rich in small olivine crystals I think ).

    2011 with NO crystals at all in the quickly cooled exploded glassy ash, sourley cooked up at 1200 C.
    Grimsvötn 2011 must have been little above 1200 C to be so crystal free.
    My own opinion at 2011 bubble nucleation froth depth is 1200 C , not 1110 C

    But I coud be wrong ; ) you are the boss and haves the source materials

    • Not an expert either, but just throwing out for discussion. Olivine is one of the highest-temp. minerals to crystallize out of a basaltic melt. However,something that is quickly cooled, like a glassy ash, cools so quickly that crystals don’t have time to form (hence, glass). Obsidian is the glassy equivalent of granite (or close compositions) and makes great arrowheads. No crystals may not necessarily be representative of the temperature of the magma/lava, but a function of how quickly it cooled.

      • Had it been below olivine temperatures there woud have been crystals of olivine that formed in the magma chamber before the eruption

  5. Loots of talk
    But the point is that I dont belive that 2011 was erupted at 1110 C
    thats too cold for souch very crystal free mafic ash

    But I coud be wrong Im not a real geologist/volcanologist

  6. Being Faroese, it always bugs me when people write it Faroer Islands, instead of Faroe Islands. Both are technically right/wrong, Faroe Islands is just by far the most common way to write it.

    Far is obviously an anglicisation of Før, which is commonly held to come from Fæ, meaning sheep.
    Oe/r is just ø/er meaning Island/s. So Faroe Islands, is actually Sheepisland Islands, while Faroer Islands is Sheepislands Islands.

    Another theory has it that Far/Før has the same origin as Fair in Fair Island in Shetland, so it would be “Fair Islands” instead of “Sheep Islands”, both are correct when thinking description wise, but I prefer the former 😉

    Personally I prefer to just write it Faroes, when writing in English, as it it doesn’t go into the double “Island/s Islands” thingy.

    • I have changed it to Faroe islands which is the common english form. However, should it be Faroes in english? The wikipedia page makes quite a hash of it, listing the proper names but using different ones as well.

      • I would add that in Scotland we tend to refer to Orkney or Shetland rather than The Orkney Islands or Shetland Islands

      • Personal opinion: It should be Faroes in english, no need for the “Islands” part. Without having really thought about it, I’d say there’s a 50/50 divide among locals wether it should be “Faroes” or “Faroe Islands” in English, it’s not a big subject of discussion though.

  7. Im pretty soure Grimsvötn 2011 was much much much hotter than 1110 C in the magma conduit gas nucleation bubble froth level. As I told before 2011 was completely crystal free ash and lava pieces as far as I knows. A crystal free basalt cooled very quickly and.. was very hot at birth. The huge gas content and crystal free nature suggest a very fresh origin for the 2011 materials.

    ( my own opinion on 2011 temperature in the conduit just before when the gas blows magma to pieces is around 1200 C to explain the completely crystal free nature of the ash glass shards ). The extremely quick cooling in 2011 explosive ash fragmentation preserves the original 2011 Grimsvötn composition very well.
    2011 basaltic ash and materials had all minerals melted at Norman L. Bowen
    reaction mineral seriers for that Grimsvötn magma and that requires little above 1200 c.
    2011 likley asceded quickly from the deeper resovair in Grimsvötn and erupted with force.

    Crystals in erupted magmas are often very small ( erupted rocks are fine grained cools quickly )
    Had the 2011 magma been 1100 C there woud be numerous small phenocrysts ( tiny crystals of olivine and other plagioclases ) under the microscope in the magma. 2011 that was not the case, it was pure glass with all the minerals molten at start. ( at 1100 c many basaltic magmas contains tiny crystals, 2014 Pahoa viscous pahoehoe flows was a crystal mess at 1130 C where they stopped ).
    I have only seen very few eruptions with pure glass in erupted materials, ( Nyiragongo 2003 sampled, Grimsvötn 2011, Kilauea Iki at hottest )

  8. Great pair of articles Carl & Albert as usual!

    I really like the blend of magic and math ;), in the end they will both end up being correct by the same amount, my prediction

    I’m really interested in seeing if there is any influence on BB if Grims goes off

  9. I enjoyed many parts of your post:

    That 45cm tephra layer in the Faroe islands
    The magma chamber connecting both volcanoes
    The historical adventures into the ice cap

    But I do think that 2011 magma was partially primitive.

    Whether it will erupt in 2019 or 2020… What if it erupts towards the southwest fissure swarm?

  10. I definitely see 2. With lateral vision.
    Learnt the technique as an astronomer.

    Not sure if I am seeing 3 at same time. Does not look like it. I have to move my eyes to see them.

    • For a while, I saw five (5), then realised it was due to my eyes’ very rapid saccades playing tricks on me…

  11. only one but happy to see that one….. i’m old and so are the eyes…. 😉 Best!motsfo

  12. Ok I could use your help, somehow I got shanghai’d into a short talk on volcanos. Let me see if I got it close. No I didn’t want to and when I found out it was a private boys school I was frankly, less so. I have attended and hated them and they are filled with nitwits and ne’erdowells. The class I entered where 17-18 yr boys, so idiot savants for a few more years yet. So I had to come up with something that would stay with them and not stress their limited capacity for learning anything else but what comes out smutty sites. So I struck on this and it sort of went down like this as far as I remember.

    ” Your attention please, you at the back. What are you doing”
    ” I made a bet I could go the whole class without using my hands and I’m Itchy.”
    Of course now I know I’m in in a class that at the moment has little chance to average over a 70 IQ. Still their might be a gem in these rock heads. After the snickering dies down I get my voice.
    ” Yes well sit down. Today I have come to talk about volcanos”
    A hand appears and beckons my attention I follow the arm down, it’s a lad that looked like the guys hiding in the universities while the Vietnam War was going on. Several years past the average by the facial growth. Not a good specimen by any means.
    ” Yes?”
    ” What is a volcano?”
    This is a new low, dumb like a Alabama Senator! After a moment contemplating what to do and looking at the faces I hit on it.
    ” What’s your name?”
    ” Zephrane Buck Buckles the third.”
    Now I am absolutely convinced I am next door to Bedlam and the school is an outreach centre. Poor kid probably never had a chance with a handle like that. His father or grandfather either. They must have hurt their Moms during childbirth for that name to go through three generations. Women tend to remember inflicted pain and seek revenge. And a husband is well advised to make himself scarce at such a time when their sweet wives reveal their true nature by the glowing red eyes. But I degress. Poor Zeph’s father likely stayed and compounded the Mother rage. Zeph likely had a beating or two and a short lifetime of verbal abuse just because of his name. I know kids are cruel. Abuse starts in the School Yard sometimes. Sometimes at birth. I felt sorry for him and was determined to at least help him understand a simplified version that he could grasp. The boy ahead of Zeph had a huge nightmare out of a Dr. Pimplepopper show.
    ” Zeph who’s the boy ahead of you?
    ” Bill.”
    ” Bill, Please come up.”
    He did and I stood him where everybody could see. I hated to put him on the spot. I know the feeling of being in the spotlight. Stand there and everyone run their eyes over you. I could see my mental IQ metre twitch for the class and Zeph had opened another eye. Interest, progress.
    ” Now this is not at all like a volcano other than they both must come through the surface and have an outward resemblance. Go ahead sit down, Bill. Please don’t do that Bill.”
    I heard a few groans of disappointment but I continued. The boy near the window had lifted his face out of a visible drool puddle. Braces and a flicker of interest. Another young fellow that would need a few years to mature enough to tie his shoes but interest, good.
    ” Do you know who Andrei the Giant was. Anybody not know?”
    They all knew of course. This is young guy stuff. In the mind I see a hook, and worm is wiggling. They were nibbling. Now to set the hook and land them.
    ” Now a volcano works kind of like this. Andrei could drink prodigious amounts of alcohol and eat huge amounts of food.”
    They all nodded except the drool boy who had hooked his braces in his sweater and was shaking his head side to side not seeming to know what his hands were for. I could see his plight and didn’t take offence. I left him to it and continued for the greater good. I see the IQ metre solidly nudge 70
    ” Now Andrei is near the end of the night and he’s finished 6 to 10 12 beer cases and lots of other alcohol too and used a handy machete to make sandwiches from a twenty pound roast and a 10 pound tub of potato salad and you know the legends. Thats got them. They sure did know the legends and most of them would try to replicate Andrei’s feats of culinary gluttony and try to drink the bar dry, but of course that is impossible. Still such are the simple needs and dreams of teenage boys
    ” Well now Andrei has been eating and drinking and what do you suppose happens?”
    Blank looks all around but they have a taste of the worm now. Finally ‘Brace Boy’ mumbles something.
    ” Yes, your name.”
    He mumbled either Joe or Moe or… my old ears aren’t for dancing any more. Steady plodding only. I faked it by mumbling the whatever and emphasizing the O on his name. Worked
    ” MfjOOO.” It sounded close so I continued. “What happens?”
    Of course he couldn’t work the barb wire fence. I do hope he grows up to be a JTF force guy and finds this cruel dentist and settles the score. Finally he motioned with his hands an explosion. For this bunch this was like a foreign language and ‘Brace Boy’ slammed 80 hard. The rest knew too. A couple slipped out I think because they remembered it had to be done by themselves and Mom wasn’t here to help.
    ” Yes pressure. Now all of Andrei’s buddies have gone to bed and someone locked the door and Andrei is getting desperate. He tries the door. No go, solid. He looks around and the machete is there and he starts to chop on the walls, the door, the ceiling. Soon it’s now or ohoh and he runs into the wall and escapes knocking down chunks of the wall. That is a Volcano.”
    Just base enough for the little monsters to stir from their boredom and I landed them. The IQ metre rocked past 75 and hit 100. I left before they could ask questions. Small steps I always say

    • I was going to take offence at the “Alabama Senator” comment, but I know better, I’m from the next state over.

      BTW, a colloquialism used by a fellow instructor of mine was that his class room was literally, “A box of rocks.” It sounds like you found one also. 😀

      For the visually impaired: Classroom = The Box, Students = The Rocks.

      Side note, the term “students” may a bit too generous. Usually they are just bags of various hormones competing for dominance. Some more gracefully than others.

      IF you want to get adventurous, use the Mentos™ and Soda analogy. It might garner more attention, and on the brighter side, a few of them may try it at home. {Evil? Nah… Let their natural curiosity play it out. Learning by experience is half the fun.} Just make sure you caveat it with “Don’t try this at home” so you can’t be blamed for the mess. Volcano connection → Gas nucleation phase.

    • One thing I can advise against, is drawing a circle on the Dry Erase board labeled “PFM” and calling it the “I believe” button. Kevin (the guy mentioned earlier) got in trouble doing that. The course supervisors wanted him to actually explain the material behind what he was discussing and if he couldn’t, then to place the class on hold and go get an instructor who could explain it. Not a whole lot of help when you hit things like “Why do electrons tunnel?”

      (Hint: That gets into the realm of quantum mechanics and probability functions A topic just a bit beyond what is needed in general electronics theory.) And if you think that’s fun, try explaining spinning magnetic domains in a Yttrium-Iron-Garnet device.

      At some points, “PFM” is almost an appropriate response.

      When I was originally in training in the same course, my questions would occasionally wander off into the same realm. The response I got was “That is beyond the scope of the course material.” (What a wonderful non-intimidating way of saying “PFM.”)

      Note: I was an Instructor, not a Teacher. Instructors have a ridged lesson plan that guides the topic of instruction. (Criteria-Based Instruction → students have to meet a minimum criteria or skill-set to pass each module)

    • There is a saying in the UK that boys who attend these exclusive (and expensive) schools are the very cream of the population. That is: “rich, thick, and full of clots”

      • Sorry I misled you. Mearly fiction. Trying to write a portfolio for a job and sometimes the madness strikes. Apologize for the Alabama thing though it did have a ring. Have you read Sunshine Sketches of a little Town by Stephan Leacock? He was a contemporary of Twain and wrote similar satire.

  13. Ahem, there’s 7 volcanoes under Vatnajokull not 5! Btw the 2011 eruption was its largest since Laki- 1873 barely made it to VEI-4.

    • It is ‘volcanic centres’ which includes rift systems and satellites with the main peak. Bu of course, that is based on interpretation. A volcano may be considered a satellite or rift peak by one and a separate volcano by others. We even had that discussion about Holuhraun.

  14. The extremely quick cooling in 2011 explosive ash fragmentation preserves the original 2011 Grimsvötn magma chamber composition very well. NO crystals suggest the basalt magma was above olivine melting points, ( little above 1200 C ) not 1110 C

  15. Yup rapidly cooling forms crystal free glass as Phil R says.
    But that rapidly cooling also preserves the original magma compostion of the 2011 s magma chamber enviroment. Had temperatures been below olivine solification points, there woud have already been small olivine crystals in the magma chamber and other crystals too in that magma batch if it was 1110 C. The reality was crystal free basalt glass, The extremely gas rich and rapid acent of 2011 is in line with a very fresh hot crystal free melt from the plume enviroment. It haves to be much much hotter than Alberts 1110 C ( Most likley1200 c in my opinion ).
    2011 was a respectable VEI 4 ( more than 700 million cubic meters was erupted )

    Gjalp 1996 was similar in size but little slower in eruptive rates ( still extremely fast eruptive rates ) and that one was a hot Icelandite compostion, 1996 came from magma thats likley been sitting in the ground since 1938 it was much more evolved than Grimsvötns fresher 1998, 2004, and 2011 melts.

  16. I really enjoyed reading this post. Regarding the prediction, I have a couple of ideas I would like to share if I can just free a couple of hours needed to do the necessary work.

    I think it’s probably right to leave out the ‘big quake’ on day 1850. The area used to collect the quake data is a rectangle where the upper left corner includes a small part of the Loki ridge. This is where that large quake happened. If it is included, then I think the last week’s M3 on the Loki ridge, just outside the rectangle, should also be included.


    For the questions about lava temperature, this is what lava at <1100 C looks like, compared to ~1200 C a month later.
    This was fissure 17 on the day that things started getting really intense, May 18. Earlier in the night the lava fountain exceeded 100 meters tall and I remember watching all of that live 🙂
    Fissure 17 had lava temperatures of as low as 1030 C, the lowest temperature observed in hawaii, and was also the first case known of olivine andesite. Fissure 17 lava had large olivine crystals in it, meaning its original source was a deep intrusion. This indicates it was probably from 1924 or maybe 1840. It also could have been much older and maybe from the 1500s event. The later lavas from fissure 18 to fissure 7 had less olivine and were like pu'u o'o composition, fissure 7 erupted lava that was very low in olivine apparently, but fissure 8 had very high olivine that made large visible crystals in the lava, so it was probably draining out of a part of the volcano that pu'u o'o was not reaching during its eruption, either the force of the magma flow dredged up olivine from the magma chamber floor or fissure 8 was fed out of a deeper part of kilauea that was not completely the same as pu'u o'o.

    Fissure 17 is what I imagine hekla to look like when it becomes effusive. I imagine grimsvotn to be more like fissure 8, or kilauea iki, both of which had lava temperatures getting close to 1200 C (kilauea iki probably exceeding that considerably at times).

    • The ERZ gets particularly wide in the LERZ, vents run parallel but leaving distances of in some cases 3 km between the fissure rows. The vents tend to concentrate in the nothern and southern parts of the rift zone leaving a “valley” (aided by graben structures) in the middle but some vents also have erupted in this central gap. If we are talking of narrow parallel dikes then there is a very good chance that few will come into contact with others. For example the lavas of fissure 17 didn’t came from 1840 magmas because the 1840 dike followed the northern row while this year’s eruption used the southern one. I am not aware of which path did the 1924 intrusion follow but there is a prehistoric vent right next to where fissure 17 erupted and I think there might have been some magma remaining from the dike of that old eruption and was what came out of fissure 17, or maybe not. This prehistoric vent is a kipuka in Puu Honualua lavas so it must be 1500-1600 AD or older.

      • I think it probably came from the ~1500s eruption then, the one that was probably linked to the formation of the wider caldera. Like you have said before, that lava as well as halekamahina cone further down rift are picritic and probably the result of a pretty deep intrusion that lead to subsidence and deflation of a lot wider area than this year, if fissure 17 had large olivine crystals then it is probably the result of picritic magma turning into andesite, I think this is probably the same sort of magma that erupts on mauna kea as mauna kea lavas often contain a lot of olivine but are generally considered evolved and sometimes andesitic. Actually there are a lot of pretty big flows that are all clustered around that age (p4o on the USGS map) and so maybe flows like this year are not actually the final act of every rifting episode but that a number of large eruptions could happen in the next century before a really huge event leads to total caldera collapse. Then again, that map is from 2005 and also lists aila’au as being an eruption that happened in 1620 when it is around 200 years older, as well as kane nui o hamo being in the p4o age when it is likely also a lot older as you have said too.

        Fissure 17 could have been from some leftover 1924 magma though, the lower set of 1955 vents are believed to have been 1924 magma and had little to do with the summit, the summit deflation actually only started 8 days later when the kii flow had already stopped and the vents were basically dead. Fissure 17 was only 200 meters away from the main vent of the kii flow. The kii fissures also went down the kapoho graben which was affected in 1924. Some more 1924 magma probably erupted in 1960, it isn’t shown in any of the videos but small vents that were offset from the main 1960 fissure, and in line with the 1955 vents, were observed erupting near an old cone (the one that is a kipuka now) as well as near the lighthouse and just offshore there was an up welling inconsistent with the ocean entry at that time. All were later buried though.

        This is also something I noticed, in this current rifting episode (1955-now) there has not been an eruption in the area north of this years eruption, starting from heiheiahulu, and this gap overlaps with the end of the area that is currently inflating slightly, so going with the idea that eruptions are more likely to happen where there hasn’t been an eruption in recent time before then this is an area to watch out for. I think that the next rift eruption will probably be in the area just downrift of pu’u o’o, and it might evolve into another shield, but a large eruption is quite possible in the area to the north of this years eruption, near the 1840 vents. A worst case scenario is a several time repetrition of this year, with shields building ever closer to the LERZ until everything just breaks, and then is followed by a massive eruption and caldera collapse below the water table. That is unlikely right now but rather plausible in this century.

  18. Near Vatnajökull plume foucs there should be a large and hot molten partial melting zone at around 35 to 45 kilometers depth thats over 200 km across. This melt lens caused by the decompressing hotspot plume, feeds all the Central vatnajökull and highlands volcanoes. Under that there is molten diapirs that rise up from the solid mantle and into that melting zone. Melting there is also caused by the 1485 to 1500 C plume temps.
    Thats the source that feeds Grimsvötn – Bardarbunga – Kverkfjölls – Katla -Askjas very lowest depths.
    The magma then rises upwards and cools and collects large resovairs in the thick Iceland crust where it feeds the central volcanoes as it gets pushed into sill sytems and laccolits and smaller magma chambers.
    As the magma makes it over 35 km journey upwards it cools from almost 1500 C to around 1180 C.
    Vatnajökulls interior likley contains a huge dense intrusive sill – laccolith complex of gabbros.

    • Interesting. But perhaps not representative. The Pacific has been an ocean for longer than life has greened the continents. The floor must be thoroughly wetted by now! This should be confirmed in other oceans, e.g. the deepest parts of the Atlantic or Indian ocean.

  19. The subducted seawater comes back out… as magmatic water vapour in the Subduction Zone Volcanoes togther with co2 gas from subducted carbonate sediments.
    The water vapour is one reason that gives Subduction Zone volcanoes their explosive power
    Thick sillica rich magmas and loots of water and co2 = kabooooooooooooom

    • And as serpentinized rock when the seafloor is scraped off in an accretionary wedge (Hello California, Oregon, Washington State… BC etc.)

      What else can you get from Serpentine rock? → Asbestos

      • Like the south coast of Oregon.. One area of HWy 101 (Rocky Point to Humbug mountain is built on nothing but Serpentine. also known as”The
        Million dollar mile” (back in 1976…) probably close to a billion now.

  20. Herdubreid continues to be rather noisy, I notice. A 2.5, and a few 1.5 quakes at around 4.5 km depth. More random creaks and groans or is something going on? After watching a stack form there about 7-10 days ago I’m wondering if this isn’t a small pulse of the hot stuff, rising.

  21. regarding best fit curve – how about we ignore time for the 2018 quiet months (when we suspect magma which would normally be arriving was diverted/prevented due to other circumstances) so the eventual best fit curve would be broken by a horizontal line during the quiet months, and then resume fitting from there.

    a bit like trying to work out when the waistband snaps – if the chap starts off gaining weight at 1cm a day – and like you suggest is wearing trousers whose waistband is a few cm bigger than his waist, no stretching occurs until his waist reaches the band, then the waistband stretches by 1cm a day, but if during 2018 quiet months the chaps was in hospital and so couldn’t eat quite as much as normal, the waistband wouldn’t be increasing the stretch – so ignore those months (however long that horizontal line is), and then as soon as he’s out – the +1cm a day returns, and the curve continues where it left off.

    so the graph a bit like this


    might have a best fit curve that matched this (if you ignore the horizontal section)?


  22. Iceland should have a lava lake
    Erta Ale is almost the same Rift – Hotspot combination, Iceland is just purely oceanic.
    North Rift Zone and close Vatnajökull I imagines often an Icelandic Erta Ale there.

    In Iceland its very easy for the magma to get to the surface
    You haves a slow spreading ridge and a very very powerful hotspot in Iceland.
    I dont understand why there is not a lava lake in Iceland right now.
    The large holcene shield eruptions in Iceland almost certainy produced lava lakes that feed lava tubes.

    But lava lakes are indeed incredibely rare and requires perfect conditions of open conduit and constant magma inflow and convection and supply. Very very few volcanoes haves these specs.
    Icelands magma stealing rifts that intrudes alot of whats supplyed. Maybe one of the things that makes it very hard for long lasting lava lakes to form in Iceland.
    I think the high sheet intrusion rate and underground emplacement in the spreading ridge in Iceland makes it a bit tricky for lava lake comduits to form. Iceland erupts little of what magma it makes yearly.

    But the country have had lava lakes before, the longest lived lava lake episode in Iceland was likley the Theistareykjarbunga eruption phase, that one was a long and slow shield eruption that almost certainly had lava lake actvity. Theistareykjarbunga resembled alot Erta Ale when it was active I think

  23. Skjaldbreidur shield is second biggest shield in Iceland and when I hiked to the to, a crater is visible and prominent there. Surely a lava lake when it erupted.

    Biggest shield in Iceland is Trolladyngja north of Kistufell and Bardarbunga.

    There are other equally large shields but older especially in the West of the country, such as Ok volcano.

    Last shield eruption happened with Icelanders already on the country, about 1000 AD in tye west side of Lanjokull. A quite large lava eruption little documented and rather unknown to most here in the blog.

  24. Skjaldbreidur.. was for soure a long lived slow Puu Oo like eruption.
    It coud have lasted 100 s of years and produced mainly pahoehoe lavas.
    The whole thingvellir area is Pahoehoes from Skjaldbreidur.

    There is a lower very wide and large prehistoric monogenetic lava shield just east of Skjaldbreidur
    Thats called eldborgir. There is also many nameless more eroded lava shields in upper Reykjanes part.
    When Holuhraun was going… I belived it woud last for many years.. slow down to a crawl and start pahoehoe and tube action and building a new lava shield.
    Instead it stopped as the magma chamber drained and pressure in the dyke lowered.

    A new large shield eruption in Iceland woud be very fun indeed

  25. More space geology.

    NASA’s OSIRIS-REx mission approaches Bennu on Monday.

    NASA Provides Live Coverage of Spacecraft Arrival at Asteroid That May Have Answers to the Origin of our Solar System

    NASA’s Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer (OSIRIS-REx) spacecraft is scheduled to rendezvous with its targeted asteroid, Bennu, on Monday, Dec. 3 at approximately noon EST.

    NASA will air a live event from 11:45 a.m. to 12:15 p.m. EST to highlight the arrival of the agency’s first asteroid sample return mission. The program will originate from OSIRIS-REx’s mission control at the Lockheed Martin Space facility in Littleton, Colorado, and will air on NASA Television, Facebook Live, Ustream, YouTube and the agency’s website. NASA TV also will air an arrival preview program starting at 11:15 a.m. EST.

    OSIRIS-REx launched in September 2016 and has been slowly approaching Bennu. The spacecraft will spend almost a year surveying the asteroid with five scientific instruments with the goal of selecting a location that is safe and scientifically interesting to collect the sample. OSIRIS-REx will return the sample to Earth in September 2023.

    Bennu has a small chance of colliding with Earth sometime after 2175. Let’s just hope they are not upsetting the Egyptian gods with all these wacky names!

    • A seamonster seems to have eaten the brains of certain seismologists.
      What happened is not that uncommon. The only surprising thing is the amplitude.
      I will get back to that in an article that explains monokromatic earthquakes and Gandalfs Smokerings.

  26. Spiffing article Albert!

    I enjoyed how we both came to the pressure conclusion from two completely different ways of wading through the data. I came through via studying GPS-trajectories and you via mathematical analysis.

    I had never heard about Nutty Swedes (re)-discovering Grimsvötn. I actually didn’t know that it had gotten lost. The Icelandic history books is inundated by recollections of Grimsvötn farting off, and there is even a recollection in the Lloyd’s of London archives from 1783. I guess it was more lost in the Universities than among the Icelandic population.

    I do though have to make a minor correction about the 1903 eruption.
    It is more of an eruptive phase, and a long one to boot.
    The eruptive phase started in December of 1902 and lasted until 12th of January 1904. It racked up to a total of a VEI-4, but it was probably more unassuming a VEI-4 eruption than even Eyjafjallajökulls slow clawing to VEI-4-doom.
    Both from historical sources and petrochemical tests of the ash we know that the phase involved both Grimsvötn and Thordarhyrna. The shear length of the eruption, the slow cooking eruption at Grimsvötn and the more vigorous and short lived eruption of Thordarhyrna leaves us with a haunting possibility known from the Skaftár Fires (Lakí). And that is that those two tend to co-erupt, and the eruptions are longer during rift eruptions.
    Could it be that deep and unseen in the ice of Vatnajökull there was a small rifting fissure eruption, perhaps like Holuhraun, but with intermittent central volcano eruptions?
    It is not impossible, but we would need to get samples of lava and date them from deep under the ice to be certain. So, at best this is just an intriguing (perhaps feverish) idea from my mind.

    My point in the end was just that there was indeed an eruption in the southern (nether) regions of Vatnajökull in 1903, but obviously this did not cause the Jökulhlaup since Thordarhyna lacks a lake to hlaup out of.

    Another interesting tidbit, both of us are sticking fairly close to our original forecasts. Are we just stubborn? Or do we have a point, and if we are pointy, who of us is the most Pointificious? Now over to Grimsvötn for the answer.
    Albert made a great case, so I am feeling inclined to go and jump ontop of Grimsvötn during 2019 until it coughs up a ashy fur-ball. Nah, I will swing by Manchuria and pick up my celebratory beer methinks.
    And even if the unlikely thing happens I will get to poor a beer or five in Albert and good fun will be had. 🙂

    • Carl Im pretty soure Grimsvötn 2011 was much much much hotter than 1110 C in the magma conduit gas nucleation bubble froth level. As I told before 2011 was completely crystal free ash and lava pieces as far as I knows. A crystal free basalt cooled very quickly and.. was very hot at birth. The huge gas content and crystal free nature suggest a very fresh origin for the 2011 materials.

      ( my own opinion on 2011 temperature in the conduit just before when the gas blows magma to pieces is around 1200 C to explain the completely crystal free nature of the ash glass shards ). The extremely quick cooling in 2011 explosive ash fragmentation preserves the original 2011 Grimsvötn composition very well.
      2011 basaltic ash and materials had all minerals melted at Norman L. Bowen
      reaction mineral seriers for that Grimsvötn magma and that requires little above 1200 c.
      2011 likley asceded quickly from the deeper resovair in Grimsvötn and erupted with force.

      Crystals in erupted magmas are often very small ( erupted rocks are fine grained cools quickly )
      Had the 2011 magma been 1100 C there woud be numerous small phenocrysts ( tiny crystals of olivine and other plagioclases ) under the microscope in the magma. 2011 that was not the case, it was pure glass with all the minerals molten at start. ( at 1100 c many basaltic magmas contains tiny crystals, 2014 Pahoa viscous pahoehoe flows was a crystal mess at 1130 C where they stopped ).
      I have only seen very few eruptions with pure glass in erupted materials, ( Nyiragongo 2003 sampled, Grimsvötn 2011, Kilauea Iki at hottest ) My own opinions

    • Alberts data there in the article supprised me: But there is alot we still dont know about the Vatnajökull volcanoes

    • Not more than a half-mile from Albert’s place of work there is a famous pub called the ‘Albert Inn’ That would be a fine place for your beer or five (of course, getting there from Guatemala might be a drag)

      • I am in Sweden most of my time to the detriment of my sunny disposition since I have to be away from my wife. So it would be a rather short hop from Copenhagen Airport.
        Albert Squared would be fine with me 🙂

    • A beer or five might be a bit much.. sounds pre-eruptive, and collapsable. It would be interesting to find written documents from the 19th century on Grimsvotn: what I found showed that around 1900, memory of this caldera had been lost. Perhaps not by everyone, but by people who lived next to the glacier and who were well familiar with the frequent jokulhaups. I blame Laki, as all evidence I could find dated from before that eruption. Funnily, it seemed similar to Eldgja where all reports of the eruption itself were lost: it suggests a wipe out of the local population.

      A rifting event around Grimsvotn would seem not impossible. More likely to the south than to the north, I would guess. It is located in the general rifting zone, so the stress field will allow for dikes to form to the south-southeast. It is notable how little lava Grimsvotn has produced. Perhaps that is because there is an escape route.

      We will just have to wait! Tremor would be a warning sign of an impending event.

  27. A while ago there was a discussion regarding the temperature of erupted lava, as well as nyiragongo having the hottest lava erupted today at 1350 C, and kilauea coming in second at 1250 C. However I remember reading that the lava erupted by west mata volcano in the Lau basin is the hottest lava observed erupting, it was a rock called boninite that is basically an ultramafic lava with the silica content of andesite, and I think it was also in excess of 1300 C although I have never been able to find an exact number. However given that the lava was glowing bright white in the cracks in that video of the eruption, this is indicative of an extreme temperature, the only time I have seen bright white lava temperatures was in a video of the kilauea iki fountains, and only in the core of the fountain at night. Generally magnesium and iron rich rocks are hard to melt, and boninite is the most MgFe rich rock that has been historically erupted. I think it has something like 14+% Mg, compared to kilauea which usually has less than 10% and is considered a very mafic basalt.

    I think any place capable of erupting lava in excess of 1200 C is quite exceptional on earth today, only really deep plumes can do that, like Hawaii or the African rift complexes. Iceland likely also joins this although it might be on the rise still. I think above a certain temperature the composition of the lava is pretty meaningless, silicates usually melt at around 1200 C so anything much hotter than that will probably look the same, this might be important as if the idea of toba being a rhyolite lava flood is true then it might have been like a superheated lava that was much less viscous than expected. That also means humans technically have actually seen a flood lava eruption, though not a flood basalt. Some of the silicic rocks in flood basalt provinces could have been erupted this way too, as lava flows. Really if this is the case then most or all VEI 8s are actually not very explosive at all and just flood basalts without the basalt.

    • Nyiragongo was 1370 C ! at upper fissures in 2002
      It woud be a white hot fluid in daylight as it emerged from the steep flanks

      yes west mata was a superhot boninite, the submarines sampled the liquid lava from there at hades went and promethous vents at Matas summit


      Sampling the active boninite pillow lavas from West Mata
      On steep slopes they forms looong tube pipes finger pillows
      Like rooots on a tree. Souch pillow pipes can drains into hollow pipes.
      But often pillows are solid through with a glassy outer rim and slowly cooled more crystaline interior.
      At 1300 C the sillica is mostly molten as you say and this highly mafic andesites flows like runny basalts

  28. Carl got to see Holuhraun when Baugurs fury was alive
    Im jealous

    When eldgosið í holuhrauni was going… I wanted so badely to visit the eruption site
    I missed it all sucks… and I missed puna 2018 too

    • At 1:42, I measured one piece of tephra to take 34 seconds to fall from its maximum height. it must have (10 + (10+10) + (10+10+10) + (10+10+10+10) ) meters high, or 100 meters high (actually a bit less but 10 is easier to add then 9.8). That piece was about twice the height of the cone, so the cone must be 40-50 meters high.

      Again this isn’t perfect, but for some reason there is still no actual number for how tall fissure 17 cone (or 22 cone) is, unlike fissure 8 which is 35 meters tall now and quite widely circulated.

  29. Thats very much as #birdman says overheated andesite
    Andesite thats so hot, it behaves like a viscous etna basalt.
    At 1060 C the sillica polymers in the Andesite is much more broken than at normal ( 800 c ) andesites
    Thats why it behaved like a viscous basalt. Fissure 17 looked like Hekla, Etna, Stromboli.

  30. The hottest Komatities emerged at close to 1650 C or more in late hadean
    Thast so hot it woud almost look like liquid sunlight ( look like it )
    Completely white hot and liquid like water almost.
    Very much like molten iron slag or liquid iron in apparence.
    Souch runny lavas woud form small low very flat shields and large flood provinces. depending on eruptive
    A cooled Komatite lava flow woud look like spilled molten slag or iron, or very very thin pahoehoe.
    rates. Today the mantle is generaly too cold to make 1650 C ultramafic magmas.
    Molten steel and slag are nightmarish stuff! a liquid so hot it can burn through skinn and bone like a hot knife through butter.

    But some strong plumes at peak may be able to do a 1500 C Komatite as the youngest Koamtites are 90 million years old.

  31. Scary stuff, even molten tin hurts like mad.. when it gets on my fingers
    Now imagine molten Iron or molten titanium

    • Molten titanium is pyrophoric and burns at the temperature of 4000 C, that goes far beyond the point of white hot, but more like ultraviolet hot…

      Ti+O2 is one of the most exothermic reactions between two atoms you can get out of touching two atoms together. Think magnesium but twice as hot… It also rips the oxygen out of of anything else that has oxygen in it, including the oxygen in your body and in water (and CO2, and other metal oxides except a couple like Li2O and Al2O3).
      Titanium is a monster in disguise, its legendary corrosion resistance is entirely reliant on the fact that TiO2 sticks to the metal and is as chemically inert as glass, and Ti(IV) forms no stable aqueous solutions and doesn’t bond strongly to any common ions like chloride, a significant difference to other reactive metals.

      • my nieces husband works for a company that does titanium printing. It’s like the machines that use plastic to make 3D model but in titanium done with an electrical current. I saw some samples he had that were so intricate I could not believe they came from a 3D printer! My mind was blown by the small hollow ball with a complicated grid pattern.

        • That is done in a vacuum or under argon to protect from oxidation. If it was done in air you would have a very expensive fire

  32. Yup very hot 4000 C is beyond white hot.
    And thats why ALL stars are white… there is NO thing souch as a “red dwarf”
    The coolest M class dwarf stars ( less than 3000 c ) will still be brillant white
    at 1300 C hot things start to turn white

    The hotter stars are simply just much brigther and harder too look at upclose, but in general are true stars are white.

    Only cool Brown Dwarfs will shine the furnace orange as often red dwarfs are painted too look like

    • Here goes with my first comment (from a long time lurker).

      You cannot really estimate temperature from a visual inspection – and certainly not to within a few tens of degrees at 1100C. Colour perception varies too much depending on all sorts of factors. You most certainly can’t estimate temperature (via how ‘white’ a hot object appears) on any form of recorded media (photo or video) as the ‘whiteness’ depends on even more factors (exposure being the most obvious).

      No – not all stars are ‘white’ as any astronomer will tell you.

      Take our sun. It’s colour tempeature is around 5700K – much hotter than a halogen lamp (c 3000K – and this appears brilliant white in the context of our living rooms). But look at the sun outside and it appears somewhat yellow (against a blue sky) – and in fact astronomically it is considered a yellow star. Blue stars have colour temperatures in excess of 20,000K – and, yes, they really do look blue!

      Our eyes have an amazing ability to adjust our colour balance automatically, often rendering the brightest object in view as ‘white’ even when it can be pretty far from that colour spectroscopically. It makes them very suspect in all but the very roughest measurement of temperature of glowing objects.

      This comment was quarantined by the spam deamon: it doesn’t trust new commenters. You got to spend time in the famous VC dungeons! (Hope you enjoyed the cookies). Hereby released; deamon told off and it shouldn’t happen again – an admin

      • Oh boy. Where to start?

        pcb is correct, and those values that Jesper enumerates are nonsense I’m afraid. So first let’s start by going through a bit of the physics. How can something that is glowing due to its temperature be described mathematically? The formal name is a black body emitter. The equation describing the spectrum of the emissions can be derived and was first described by Planck. If you’re thinking that name sounds familiar from quantum mechanics you are correct. In fact that derivation of Planck’s law was the thing that really kick-started the progress towards quantum mechanics as it solved something called the ultraviolet catastrophe which is related to the amount of energy emitted by really high temperature black body emitters. So what does Planck’s law look like?

        Bν(ν, T)=2hν^3/c^2e^Y-1

        Y in this case being equal to hν/kT

        Bv is the spectral radiance, which has the units of W m^-2 sr^-1 Hz-1, or watts per metre squared per steradian per hertz. Steradian is a unit of angle used for three dimensional situations. Essentially it’s the amount of energy hitting you during a given time period. h is Planck’s constant, ν is the frequency of the radiation, c is the speed of light., k is Boltzmann’s constant and T is the temperature. When spectral radiance is plotted against wavelength the function starts low at small wavelengths, passes through a peak and then tails off at large wavelengths. Small wavelengths are towards the blue end of the spectrum and large wavelengths towards the red end of the spectrum.

        The peak of the spectral radiance, ie the wavelength where the most light is being emitted, shifts as the black body temperature increases or decreases. Lower temperatures mean a longer wavelength, and higher temperatures mean a shorter wavelength. The equation that defines this peak is called Wien’s law. It’s much simpler than Planck’s law and is defined as:


        λmax is the maximum spectral radiance, b is a constant of proportionality and T is the temperature. That’s why a “black body temperature” can be discussed as concept as the temperature is directly related to the frequency of the maximum spectral radiance.

        As pcb says the black body temperature of the sun is about 5700 K and its λmax is about 500 nm. That’s green. Red dwarfs and red giants are M stars and have black body temperatures from 2600 K to 3850 K. Their λmax really does lie in the red part of the spectrum. O stars on the other hand actually can have their λmax in the ultraviolet. However since we can’t actually see ultraviolet light (by definition!) they appear to be releasing most of their light in the blue part of the spectrum.

        So why does something appear “white hot” when it is an awful lot cooler than an O star? Simple. Our eyes get overwhelmed by the number of photons hitting them. They do not have the dynamic range to cope with the input they are receiving. How can this be demonstrated for stars? The easiest way is to look at the two brightest stars in the constellation of Orion. Betelgeuse is a red supergiant and Rigel is a blue supergiant. Both are luminous, and both are easily visible to the naked eye. Betelgeuse has a black body temperature of 3590 K. Rigel has a black body temperature of 12100 K. Even in sky conditions at the edge of a town of tens of thousands of people you can clearly see the colour difference between them. Rigel is distinctly blue and Betelgeuse is distinctly red. To give you an idea of just how big Betelgeuse is, it is sufficiently large that is is one of the few stars that is not a point source when viewed through large telescopes. In fact only the sun itself and R Doradus subtend a greater angle on the sky than Betelgeuse.

        So lava is most definitely red by that definition. 1200 Celcius lava has a λmax of 1967 nm. That’s well, well into the infrared. An incandescent light bulb at 3000 Celcius has a λmax of 885 nm. Even that’s still in the infrared. Visible light is about 380 nm to 700 nm.

        • Red Giants and Supergiants are loots of show over matter
          They are so huge and swollen and pretty much a red hot vaccum for the outer parts. Betelguise haves a density of only 0,00000139 kg/m³
          thats why the size and edges of these enromous gasbags are often debatable.
          ( I think UY Scuti is the largest giant for now )
          The largest red hypergiants haves outer layers so low in density that you can fly a spaceship through the outer layers ( with thermal protection ) there is almost NO drag at all. The superhot and superdense core is hidden deep inside. The sun will turn into a smaller version of souch a bloated bag in 5 billion years.
          Old stars outer parts loose so much mass and is so loosely bound by gravity it forms huge gas clouds that shrouds and hides the hot inner star planetary nebula.
          Red giants go planetary nebula, red supergiants go supernova

      • Not all stars are white in the spectral spectrum
        But for the eyes… even a red dwarf is bright white

      • One addition to this. Stars show the full range of colour. Red dwarfs are very red to the eye, blue supergiants are blue and the sun is yellow. But the eye can not see colour at low light level: with night vision we switch to grey vision (try it!). To the eye, very few stars are bright enough to see in colour; the rest looks white to us. Doesn’t mean they are.

        • And meanwhile we await Betelgeuse’s upcoming supernova death. Now that WILL be bright. Sadly, it is not likely in our lifetimes. But…one never knows. It’s pretty unstable.

          A new Volcano Cafe bet: will Grimsvotn erupt before Betelgeuse explodes? I suspect we all know the answer to that.

          • But will grimsvotn self destruct before betelgeuse? That is actually a matter of argument. Also remember -500 years for when betelgeuse explodes

          • Betelgeuse is similar in age to Iceland. And its end could still be a million years away or more. By that time, none of the currently active volcanoes in Iceland will still be alive.

        • A red dwarf at 3200 C will appear white

          Liquid steel at 1570 C is pretty much white hot

          • No, it won’t. A 3200-K star looks red to the eye. You can see it by looking at Betelgeuze, in Orion: it is notably red. And the sun, much hotter than this does not look white either. It looks yellow. Liquid magma is red, not white.

          • As a backyard (not even amateur) astronomer (or more correctly beer drinker and star gazer), I must say I really enjoyed this little discussion on temperatures, colors and eye perception. Bonus, this is the time of year when Orion starts coming up for the winter.

        • Grimsvötn will likley erupt in the comming 3 years
          Iceland most active volcano

        • The sun is NOT yellow from space
          Its so white and intense that astronauts haves sun google gears on their helmets ( tanned glass ) to make the light less intense

          • That is called blinding. It says nothing about the colour. There is no such thing as a ‘white’ star. To the eye, the hottest ones are blue.

  33. Hot colours in black room

    490 C= very dull red
    570 c= deep dark red
    660 C= deep cherry red
    740 C = clear cherry red
    800 C = strong clear red
    880 C = clear orange
    920 C = strong bright orange
    1080 C = strong orange yellowish
    1140 C = strong bright yellow orange
    1200 C = clear yellow strong
    1250 C = bright yellow
    1300 C = almost white
    1350 C = white
    1400 C = intense white hard to look at
    1600 C and hotter more intense white and getting blinding

    • Another problem is that you forget that different atoms emit light at different wavelength at the same temperature. This means that the colour will be dependent on the chemical composition of the lava.
      Let us say that we come up with something as ludicrous as tungsten-lava. Even at 1600 degrees it would be rather a boring and dark sight.
      Between 2500 and 3000 degrees it would start to glow (depending on amount of trace minerals in the tungsten), but it would still be a solid.
      I guess everyone is getting my point by now.

      But, Jesper has a point. And that is that colour of the lava is a rough indicator of the temperature, but at best you would be in the +/- range of a couple of hundred degrees Celcius.

    • Here’s a (doctored, as the original flow on the left is one those probably from Pu’u O’o) image of what a molten komatiite lava flow would look like compared to a normal basaltic flow.

      • Like this.

        Komatiite would have also been thinner and probably looked more like oil than typical basaltic lava on kilauea, the lava flows would have been very thin and probably quite small unless a lot of it erupted at once then it would flow very far and very fast like any low viscosity liquid.

        Also that picture is from mauna loa in 1984, but on kilauea also erupted, as episode 17 of the pu’u o’o eruption, there arent any pictures of the double event as far as I know though, which is surprising.

  34. Yes – in a black room! In any other context they will not appear the same.

  35. i’m ok but i need to change my pants 😉 that was the worst one ever…. really thought the house might be coming down….. stuff offf the walls…. have connected with all family members and all ok.

  36. AND Thank You, God….. now under tsunami warnings but i’m too far off the water for that..

  37. Getting pictures out of AK showing some destroyed roads with surface displacements 10 feet or more. Possible liquefaction? The usual smashed store shelves and ceiling collapses. Many aftershocks up to M5.7. At least one school building cut in two, no casualties reported as of now.

    • Got to be liquifaction, max displacement for a mag 7.0 quake on a reverse mode fault is about 1.5 meters.

      At 40 km deep, it’s unlikely that there was a surface manifestation of the event. Not impossible, just unlikely.

  38. Wasn’t the Good Friday Earthquake in 1964 one of the strongest, if not *the* strongest to strike a populated area of the US? It reached a magnitude of 9.4 or so. Anchorage’s population was only ~40,000-45,000 at the time. It’s now just over 290,000. And not to mention that most of the Municipality of Anchorage is sitting on a mudflat, IIRC (feel free to correct me if I’m wrong!). Another earthquake of a similar strength would be very, very bad news for that area. Or other parts, esp. the Pacific Northwest, California and the Tennessee Valley.

    I’ve heard/read that a megathrust quake like the one which hit the Pacific Northwest in 1800 could cause ground shaking so intense that a fully grown adult wouldn’t be able to stand up without support.

    • Ask me why I now live three mountain ranges away from the Oregon coast.
      -and on a near solid slab of Columbia River Basalt..

    • I don’t think support would help much. The g acceleration would be quite strong.

Comments are closed.