Katla: a retrospective

/ 05/07/2023

After our ‘quantum Katla’ post, it is now time to return to the real Katla. For in the real world, Katla has been showing unusually strong shaking. It turned out that Henrik had already done much of the work for us. Here is a resurrected post from the dungeons of 2012 where young Henrik keeps our Katla feet firmly on the ground. It includes an addendum on the current activity.

Rest in peace, Henrik, and when Katla blows we will raise a glass to you. (Clive, 2019)

Part I

Katla is a relatively young volcano which like so many Icelandic volcanoes formed when Iceland was covered by ice. Hence it is a tuya, steep-sided with a broad, flat top. Like other large Icelandic volcanoes, it has a very large summit crater described as a caldera, but one that did not come about as a result of the collapse of the volcanic edifice into an emptied and very large magma chamber as happened at Mount Mazama a.k.a. Crater Lake in Oregon, at Krakatoa or at Long Valley.

Fig. 1. Herðubreið, a subglacially formed tuya with steep sides and a flat top. Post-glaciation, erosion has made the sides less steep and a small post-glacial cone makes the top appear less flat than it once was. The similarity to Katla, once you allow for the vast differences in size, is obvious. (extremeiceland.is)

One of the keys to understand what goes on at Katla is to have an idea of what lies beneath the up to 700 meters thick glacier that covers her crater/caldera. In schematic representations of Katla, a magma chamber at the very shallow depth of three to five kilometres is often displayed. From reading descriptions of other volcanoes that have suffered caldera collapse or looking up a general definition of ”caldera”, it is easy to assume that Katla too must have a magma chamber that spans the entire width of the “caldera” and which, “once-upon-a- time” collapsed to for the present-day caldera. Nothing could be further from the truth, but alas, there is no direct information available that accurately describes what Katla’s magmatic system, the true volcano, looks like. We have to fill this gap ourselves.

The first thing to do is to look at what she has done in the past. If we look up her “Eruptive History” on the Smithsonian Global Volcanism Program website, we find that Katla is listed as having had 27 eruptions during the period Iceland has been settled by humans, some eleven centuries and counting. Of these, only the larger eruptions seem to have been registered prior to the middle of the 20th Century. Thus the 27 eruptions are divided as follows: Two VEI 0 (1955 and 1999), three VEI 3, fourteen VEI 4 (including the AD 934 “Eldgjá fissure eruption”) and four VEI 5 with a further four not assigned a VEI number. Of the four unassigned eruptions, one is listed as “subglacial, lava flows” and three as “subglacial, explosive”. Please take note of the dearth of smaller eruptions, VEI 0 – 2, as this is important and something we’ll return to later.

From this information, it is clear that Katla cannot have a single, caldera-sized magma chamber because such a chamber would contain several tens to even hundreds of cubic kilometers of magma, which in turn would have led to far larger eruptions. None have occurred. Since VEI 5 is assigned to eruptions that eject between 1 and 9 cubic kilometres of Dense Rock Equivalent (DRE) explosively, and Katla’s VEI 5 eruptions are remarkably consistent at between 1.2 and 1.5 cubic kilometres, anything much larger than some 3 – 4 cu km is rather out of the question. A caveat – given the area covered by the crater/caldera, there could be more than one such chamber responsible for her eruptions, in which case it would be fair to ask the question if Katla really is a single volcano or if not a description of her being several volcanoes rolled into one would be more accurate.

If we look at her eruptive history prior to Iceland being settled, deduced by tephrochronology – ash layers deposited being identified by their physical properties, such as chemical composition and grain size, as belonging to Katla and from the size, distribution and time derived for each individual layer of tephra, an eruption responsible for it is inferred – we find that there have been a multitude of eruptions, but only a few of which have been assigned a VEI number. Interestingly in every such case a VEI 3 or 4 has been deduced. Anything much larger must have left such extensive deposits that such a huge eruption cannot have escaped detection, hence we can conclude that no explosive eruptions larger than a small VEI 5 have ever occurred at Katla.

There have been two exceptions to the rule that Katla’s eruptions normally are in the VEI 4 range volume-wise. Both originate on her NE flank, outside the crater/caldera. Around 5550 BC, Katla was the source of the 5 cubic kilometres “Hólmsá Fires eruption” lava flow. In 934 AD, the four times larger “Eldgjá eruption” spewed forth some 18 cu km of lava and five cu km of tephra, or ash. Even if the total volume erupted in 934 AD, about 22 cu km DRE, is on the order of 50 times greater (25 to 200 times), a lowly “VEI 4?” has been assigned.

As the underlying causes and processes that drive “regional fissure eruptions” are vastly different and as they happen very rarely, seemingly with a time interval measured in several millennia in the same-ish location, fissure or rift eruptions should be considered separately – even if the visual appearance of the Katla crater/caldera suggests that a fissure eruption has at some point in the distant past intersected it. They are mentioned here because an article such as this cannot fail to do so, nor can it fail to give a reason why they are not included in the discussion.

Earlier I mentioned the apparent absence of small eruptions from her eruptive record with only two “possible subglacial eruptions” in 1955 and 1999 listed, to which can now be added the equally suspected or “possible” July 2011 subglacial eruption. As I write this, it seems that there may have been yet another, very minor hlaup. That such eruptions were not noted in earlier days is not surprising as the very small hlaups they resulted in were local nuisances rather than regional catastrophes of a major Katla jökulhlaup and would not have been seen as important enough to be recorded, even had they been observed. But how frequent could this type of small eruption be?

Fig 2. Seljansfoss Waterfall during the 2010 Eyjafjallajökull eruption (Binaural Waves Blogspot). Notice evidence of several minor eruptions on the mountainside above the waterfall.

We know from the 2010 Eyjafjallajökull eruption that it was preceded by two fissure eruptions at Fimmvörduhals that intersected each other. If we look at the topography and geography of Eyjafjallajökull, we can see many areas of monogenetic cones. This indicates that eruptions of the Fimmvörduhals type greatly outnumber eruptions at the main vent. At Askja, a similarly sized volcano albeit glacier-free and with a slightly smaller summit crater/caldera, there have been six small eruptions since the great eruption of 1875 and many prior.

Of the 24 eruptions (not counting the AD 934 Eldgjá fissure eruption) listed before it was realised that there were smaller eruptions that would only show as minor jökulhlaups, 20 are listed as VEI 3 or higher and three of the four not assigned a VEI number are listed as (subglacial and) explosive. At least 17 of the 23 explosive eruptions have been assigned a VEI of 4 or 5. The eruptive record of Katla thus indicates that in order to break through the up to 700 meters thick Mýrdalsjökull glacier, an eruption would need to be at least as powerful as to merit a designation of VEI 3. Thus – the reason for the dearth of smaller eruptions observed is that they are not energetic enough to break through thick glaciers such as Vatnajökull or Mýrdalsjökull to be visually obvious and the minor hlaups resulting have been much too insignificant to have been considered as a result of an eruption that never was seen.

Fig. 3. Pits formed by melting from below in the Katla glacier, summer 2011. The glacier was still covered with tephra from the Eyjafjallajökull eruption which made such features stand out unusually well. (ModernSurvivalBlog, picture may originate with Icelandreview)

With the advent of aircraft, it was noted that there were pits in the glacier as if it had melted from below and the collapsed to form an ice crater. These pits are relatively numerous and vary in size. They have been explained as due to either strong hydrothermal activity or, in the case of the larger ones, as the result minor subglacial eruptions.

The obvious conclusion is that in the case of Katla, small eruptions of the Fimmvörduhals type far outnumber the bigger, recorded eruptions. This is vital for understanding how a volcano such as Katla is built and works.

Let us for a moment return to what I like to call “Katla’s defrosted twin”, Askja. Here we can see, side by side, the effects of the two types of eruption. In 1875 she had the big VEI 5 eruption, about four times as great as Katla’s historic VEI 5s, that would eventually form lake Öskjuvátn. Here we have a magma chamber where magma collected over time, partially re-melting and absorbing the chamber walls which together with fractionating led to the body of magma collected being far more silicic than the basalt injected into the chamber, which provided the heat or energy for the process. This went on for centuries, quite likely millennia as GVP lists the preceding very large eruption at Askja as having occurred about 11,000 years ago, until a final basaltic intrusion was energetic enough to unbalance the magma chamber and the big eruption of 1875 followed. Please note that both before and after, there have been many smaller, basaltic eruptions that have evidently bypassed the main magma chamber on their way to the surface, one of which caused the miniscule crater Vítí located immediately north of Lake Öskjuvátn

Fig. 4. “Katla’s defrosted twin”, Askja. Aerial photograph inside and above the Askja caldera with Lake Öskjuvatn and the miniscule crater Viti barely discernible on the near left-hand side of the lake. (uwmyvatn blogspot)

This too is what I believe must have been happening and is going on at Katla. Sturkell and his co-authors in their 2009 paper “Katla And Eyjafjallajökull Volcanoes” note that the products of Katla’s eruptions are bimodal, comprising alkali basalt and mildly alkalic rhyolites “with intermediates very subordinate”. One, or possibly more magma chambers where magma collects, fractionates and grows more silicic, a process that takes hundreds if not thousands of years which is why more than one magma chamber seems to be required in order to account for the relatively frequent eruptions of Katla, until there eventually is an eruption of “mildly alcalic rhyolites”, accompanied by tens to hundreds of smaller, alkali-basaltic eruptions which due to their location under the ice in a watery environment, gouge out small craters and fill in the bigger ones with mostly small, broken fragments of lava, piles of pillow lava or even small lava flows or easily eroded cones. When a big eruption occurs, the glacier first closes the wound, then the crater gets back-filled with loose rubble which gets pasted over with more solid lava flows from later eruptions.

This process has been going on for as long as Katla has existed. Not only has this constant remodelling inside the crater/caldera left a kilometres-deep zone of clastic, i.e. broken or fragmented, rock mixed with water, it also in my opinion explains how the caldera was formed in the first place. This layer extends down to not much above the roof/-s of the magma chamber/-s. As freshly injected basalt from the mantle makes its way up, it will eventually encounter this water-rich zone and result in intense activity, hydrothermal at first, and if the intrusion continues, hydromagmatic. It is primarily this activity we see when we look at the tremor charts of the SIL-stations surrounding Katla, in particular the one located at Austmannsbunga, on the north-eastern crater/caldera wall.

In the next instalment, it is time to take a look at Katla’s neighbours Eyajafjallajökull and the Gódabunga “cryptodome” and try and separate their activity from that of Katla so that we can finally figure out what she may have been up to over the last few years and how likely an eruption in the near future could be.

Part II

It is now time to have a look at what’s going on and try to paint a coherent picture of what she actually is, is up to and able to do, but first let us recapitulate what we found previously:

  • There is a general interest in Katla because she is and has been regarded as a very dangerous volcano by generations of Icelanders.
  • The presentation of Katla in media is skewered by vested interests ranging from scientists who hope to increase their professional and/or public standing, people trying to cash in on the interest generated such as journalists and bloggers, and finally, there are people trying to increase their standing within the subculture of doomsaying and alarmism.
  • Katla is a massive but relatively young volcano, located on the MAR, and formed when Iceland was covered by glaciers.
  • The records include two large fissure eruptions on the NE flank of Katla; the prehistoric 5 km3 Hólmsá Fires of 5550 BC and ~22 km3 Eldgjá eruption in 934 AD. In historic times, the 1100 years or so that Iceland has been settled, there have been 27 listed eruptions (28 if the inferred minor subglacial 2011 eruption is included), 23 of which have been explosive.
  • Of the 23 explosive eruptions, three have been assigned VEI 3, thirteen VEI 4 and four VEI 5.
  • The four VEI 5 eruptions are remarkably alike in size at 1.2 – 1.5 km3, which is at the upper end of what Katla probably is able to do but at the very lower end of VEI 5 eruptions.
  • Tephrochronology (in some cases complemented by radiocarbon dating) has identified a further 103 eruptions going back ~8,500 years, and in the few cases where a VEI has been assigned, none have been greater than a VEI 4.
  • Katla does not possess a caldera-sized magma chamber.
  • In order to account for the great number of explosive eruptions which involve more evolved magmas, Katla could have more than a single magma chamber.
  • The available evidence suggests that in order to break through the up to 700 meters thick Mýrdalsjökull glacier, an eruption must be at least a substantial VEI 3.
  • Direct and (primarily) indirect evidence suggests that smaller eruptions, mainly basaltic VEI 0 – 2 eruptions are severely underrepresented in her eruptive record and ought to exceed the number of observed eruptions.

Fig 5. Mýrdalsjökull showing the main glacier outlets, directions of jökulhlaups and areas affected. E – Entajökull, S – Sólheimajökull, K – Kötlujökull, M – Markarfljot, Ss – Sólheimasandur, MS – Mýrdalssandur. Eyjafjallajökull is to the left and the smaller glacier above is Tindfjallajökull (adapted from Google Maps).

The greatest danger from Katla comes from the very quick and extensive melting of the glacier caused by large eruptions which results in destructive jökulhlaups. There are three major outlets from the glacier: Entujökull to the NW that empties into the Markarfljot river and valley north of Eyjafjallajökull, Sólheimajökull to the SSW that empties onto the Sólheimasandur and finally, Kötlujökull to the SE that empties in a great arc east through south onto the Mýrdalssandur. What ought to be prime farmland and in fact once was settled, is nowadays an unsettled wasteland because of the devastating jökulhlaups unleashed by Katla. This is the true reason why Katla is considered to be such a dangerous volcano.

The fact that one often comes across the reference that in the days before the Hringvegur (ring road), “people were afraid to traverse the Sólheima- and Mýrdalssandur because of the frequent jökulhlaups” is another indication that smaller and unrecorded eruptions that cause only minor hlaups are far more frequent than the 40 – 80 years often given as the interval between main, and thus visible, eruptions.

Fig. 6. The foundations of the old bridge across the Múlakvísl river destroyed by the July 9th 2011 jökulhlaup are visible to the left. The new bridge was laid down a week later. (photo John A Stevenson, GVP website)

Apart from the postulated connection between the Eyjafjallajökull and Katla volcanoes, one question that always crops up is the Goðabunga cryptodome. Many volcanologists maintain that it is a part of the volcanic system of the Katla central volcano. Others, notably Sturkell and his co-workers, claim it is part of the Eyjafjallajökull volcanic system. In order to shed some light on this issue, I asked our own GeoLurking if he could make a plot of all the earthquakes from 1994 up to and including the 2010 Eyjafjallajökull eruption. The results are quite clear and do throw up a surprise:

Fig 7. E-W cross section, view from south, through Eyjafjallajökull, Goðabunga and Katla. Plot by and courtesy of GeoLurking. The “lines” formed at approximately 5, 3 and 1.1 km at Goðabunga and Katla are most likely artefacts caused by quakes being assigned a poorly defined depth. The latter, 1.1 km, is the default depth assigned by the automatic system in case it cannot compute a depth within the predetermined level of certainty and unless they are manually checked, which is not the case of every quake, automatic depth remains uncorrected, hence these artefacts.

From this cross section, it is quite clear that there is no connection between the Eyjafjallajökull volcanic system and Katla. Eyjafjallajökull has its own, well-defined feeder system from the Moho (first molten layer beneath the Earth’s solid crust) as does Katla, thus they are wholly independent of one another. As can also be seen, albeit not as clearly, Goðabunga too seems to be independent of either Eyjafjallajökull and Katla, the ramifications of which will be the subject of a later post by Carl. Sufficient to say that when we contemplate what Katla herself may be up to, we must differentiate between activity at Goðabunga and activity at Katla. Once we do, we see that while Goðabunga is more or less continuously active, Katla operates in bursts and seems to be most active during summer and autumn when the ice cap is at its, relatively speaking of an up to 700 m thick glacier, thinnest.

Fig 8. Activity post-Eyjafjallajökull. Activity at Eyjafjallajökull is minor and has to do with the system settling down after the end of the eruptive phase. Note that at a depth of 0 to 5 km or so, there seem to be three separate areas of activity at Katla. (Plot by and courtesy of GeoLurking.)

After the Eyjafjallajökull eruption, Katla seems to have entered an active phase with a suspected subglacial eruption on July 9th 2011 and several pits or craters forming on top of the glacier. This activity seems to be localised to three main areas within the caldera:

Fig. 9. Earthquake activity at Katla July 9th 2011, the day of the jökulhlaup and suspected subglacial eruption. Both the 1823 and 1918 eruptions occurred close to but just east of this area. The 1823 eruption occurred close to the easternmost red spot while the 1918 eruption was roughly at the rightmost dark blue spot below it. (IMO)

Fig 10. Earthquake activity at Katla July 17th 2011. (IMO)

Fig. 11. Earthquake activity at Katla July 21st 2011. The 1755 eruption was situated in the same area as the three overlapping orange spots.

As can be seen, there are at least three distinct areas of activity inside the caldera with the one associated with the inferred July 9th eruption well to the south. The pits formed in the glacier also align with these three areas, albeit the pits to the northeast seem more drawn out along the caldera wall and not over the center of activity. These three areas seem to tie in with the three areas of activity noted in fig 4 as do the locations of three of Katla’s major eruptions. Thus there is not a single vent, but at least three at surface distances of approximately 5 to 8 km from each other. It is equally likely to judge from Fig 7. and Fig 8. in conjunction, that at great depth, they do have a common source.

I will now present you with my personal view of Katla, but do not be afraid to disagree or draw your own conclusions (within reason please, no Katlatubos here):

Katla is a young volcano and far more active than has previously been thought. Unlike the similarly aged but much less active Eyjafjallajökull, Katla has had more time to develop her system of sills to the point where they are fewer in number than they originally were but have a substantially larger magma-carrying capacity and approach or may have reached the point where they can be considered magma chambers proper. Since cooking evolved magmas takes a long time, usually millennia in the case of cubic kilometre-sized silica-rich magmas and at the very least many centuries for intermediate magmas, it is highly likely that Katla possesses several pockets of magma capable of eruptions ranging from high VEI 3s to small VEI 5s. Not only do the times between such eruptions argue this, their wide spread of location within the caldera does so too.

The most common type of eruption at Katla is the small, subglacial eruption of a few tens of millions of cubic meters of basaltic magmas. These eruptions are not energetic enough to break through the very thick Mýrdalsjökull glacier and the only proofs of their existence are intense earthquake swarms followed by minor jökulhlaups and later observations of deep pits or craters, sometimes water-filled, in the glacier ice. My guesstimate is that there may be many such small eruptions over any given ten-year period, and possibly in the case of a period of high activity, there may even be more than one in a single year. By back-tracking and investigating old accounts over the past few centuries of jökulhlaups in the area not associated with visible eruptions, it ought to be possible to identify many of these minor eruptions.

While a larger “proper” eruption of Katla in the VEI 3 – 5 range cannot be ruled out, I find one unlikely at present as the current activity mostly is in areas already depleted of evolved magmas by geologically speaking very recent major eruptions. Also there is little sign of the uplift required on GPS. If one were to occur, the odds for one towards the upper end of what Katla is able of ought to be better in the Eastern to Northern parts of the caldera.

Finally, what we do see when we look at SIL-stations such as Austmannsbunga, located on the NE caldera rim (not a coincidence, see above), is hydrothermal activity following a period of possibly still ongoing magmatic intrusion and not signs of an imminent, large eruption.

Fig 12. Hydrothermal activity at Katla as shown on the Austmannsbunga SIL (IMO) (Source: https://icelandgeology.net/?p=3291)

I’m sorry to be such a boring old fart, but if this is unsatisfactory, start looking for intense earthquake activity at some 25 – 10 km depth, showing on the IMO map for Mýrdalsjökull as being in the Eastern to Northern part of the caldera, activity that shows a clear upwards trend and spreads when it reaches depths approaching 5 km!

HENRIK, May/June 2012

Addendum

Henrik wrote this in 2012, after the burst of activity at Katla in the summer of 2011. It is now 2023 and we again had an earthquake swarm at Katla. And again it happened in summer. The activity occurred on 30 June, and was all shallow but far larger than might be expected of normal summer activity caused by ice melt. The strongest earthquake was M4.4 and around 10 quakes were M3. Not huge, but significant.

The swarm continued events from 4 May when there was an earlier swarm in the same general area. That swarm was a bit stronger with three quakes of M4. It briefly caused the status of Katla to be set to ‘yellow’ before returning to ‘green’ which it still is. That sequence was rather uncommon for early spring, normally a quiet time for Katla! Katla comes to life in summer. The last time a similar (albeit weaker) swarm occurred in Katla was in September 2016.

Was there any sign of an eruption? If we look at the tremor plot, a bump in blue line is evident on June 29. It is weak but otherwise similar to what was seen in 2011. The peak frequency of 2-4 Hz can be associated with glacial floods, i.e. increased ice melt. A magmatic eruption (bubbly magma moving up in the conduit) would normally show up equally at all three frequency ranges. However, this particular bump occurred a day before the earthquake swarm so is not directly caused by the shaking.

June 2023, Katla

It is worthwhile looking underneath the ice. Katla has a distinct caldera with a deep central depression, a steep rim which has three gaps where water can flow out, and several flow channels feeding the surrounding rivers. The ice cover reaches 700 meters thickness near the northeastern rim. About half the icecap lies above the caldera; a similar area of ice covers the northeastern slopes. The caldera shows geothermal activity. This is nicely shown by the icecap which contains several cauldrons where the heat has melted some of the ice. The hydrothermal activity is mainly located just inside the caldera rim, along the western and eastern edge. This suggests that the heated water is circulating via the ring fault. There are also two active areas within the caldera.

The ice-free caldera map. This view is from the southwest. Image from Helgi Björnsson et al, 2000, Jokull 49, 29 (https://www.researchgate.net/publication/285499559_Surface_and_bedrock_topography_of_the_Myrdalsjokull_ice_cap_Iceland_The_Katla_caldera_eruption_sites_and_routes_of_jokulhlaups).

High resolution map of the caldera. The circles indicate hydrothermal activity. North is up. Image source Björnsson et al.

The recent earthquake swarm was located just inside the northeast rim of the caldera (see Jon’s post: https://icelandgeology.net/?p=11319). The swarm in May was in the same area. The caldera map shows a narrow gorge just outside the caldera, which curves a bit but generally runs north-northeast. This is the rift that fed the Eldgja eruption. The swarm was located a little south of there, within the caldera. Rest assured: last week’s activity had no relation to Eldgja!

Previous activity after the large 1918 eruption occurred on 25 June 1955, 17 July 1990 and 8 July 2011, all in the caldera. All three were hydrothermal events where magma was either not involved at all or was only a minor byproduct. Notably, all were in the summer, which clearly indicates that they were driven by summer melt: Katla is a summer volcano. We might even call it an august volcano, fitting both its size and seasonality. (The eruption of 1918 though was on 12 Oct, showing its magma is not limited by the season.) In 1955, two ice cauldrons formed on the southeast rim and a small jokulhaup occurred. In 1999, the activity was on the southwest rim with tremor and a jokulhaup. The 2011 activity was larger, with strong tremor, earthquakes in the south and east of the caldera up to M3.4, and a jokulhaup which swept away a bridge. The effect was likely amplified by the fact that water had accumulated in the caldera over the preceding year, causing uplift of the icecap.

The 2023 activity fits with these events. The location is a bit north of the 1955 event. The earthquake activity was stronger but it has not caused a jokulhaup – perhaps because the location is a bit away from the immediate drainage channels.

Was it an eruption? Or perhaps a precursor? Katla is a mysterious beast. It has much to hide – it keeps its icecap for a reason.

There is in fact no evidence that the earthquake swarm was related to an eruption. There may have been a small hydrothermal event, as evidenced by the sulphur smell around the rivers. This may have preceded the swarm. However, the size of the earthquakes and the fact they followed on from a similar swarm from two months before does suggest a pressure change around the ring fault. That could be coming from a dike or from increased water circulation. The time of the first swarm may make the first possibility more likely, at least for that event. Perhaps it was the continuation of the intrusions from the deep which happened a decade ago. If you want to know, see the second link below.

My guess for now (and it is only a guess) would be that the earthquake activity is related to (but not coincident with) a small hydrothermal event. — which may not have happened yet! This may be or may become one of Henrik’s missing VEI 0’s. Whether it will become anything more is just a matter of wait and see. Katla is still a quantum volcano – it remains impossible to predict.

Post by Henrik, May 2012; addendum by Albert, July 2023

Henrik Lovén 1958-2019

Deep magmatic roots of Katla…

The Eldgja Eruption: Iceland’s Baptism by Fire

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686 thoughts on “Katla: a retrospective”

  3. There are now some quakes that are under 3 km deep, this thing is rising fast, there must be no more space in the rift underground so the intrusions just go right up.

    Also apparently all of Reykjanes from Hengill out to Eldey is showing inflation and signs of magma accumulation at depth. That is to say it is possibly all connected and more than just being on a divergent boundary. So either Fagradalsfjall is going to turn into Fagrafjall or we are going to see all of the volcanoes wake up in the near future. The whole thing concerning neat progression of the activity going westwatds with time I think can pretty safely be laid to rest, as can the idea Fagradalsfjall was a kind of freak event. Reykjanes has woken up, the rest of the country might as well be an exiting side show.

    • There’s an aseismic layer so activity less than 3km may indicate that magma is approaching that layer.

  4. It’s been rattling along pretty noticeably here at Reykjavík University since about a quarter to eight. The local volcanologists, who were pretty cautious about predicting an eruption in 2021, aren’t in the least bit shy now.

    • 2021 was a big call, first eruption on Reykjanes on land since the middle ages, and Fagradalsfjall was considered an inactive volcano. Fast forward a few years and the impossible happened, and then happened again, seems a much safer bet now 🙂

    • They’re only saying increased likelihood of an eruption. Mind you the aviation code for Reykjanes is orange at the moment.

    • From RUV: “Volcanologist Þorvaldur Þórðarson says there is a high probability that an eruption is imminent at Fagradalsfjall. This series of earthquakes is similar to the one that led to the last eruption, a similar pattern is going on. ‘It’s a matter of hours or days rather than anything else.’ … Þorvalður believes that it will most likely erupt in the same area as the last time, and possibly somewhat further north, but still in a direct line with the craters that formed in the last eruption. ‘This is a continuation of the Fagradalsfjall volcanoes, as I prefer to call them. If everything is as it seems, there will be a third eruption in the Fagradalsfjall volcanoes.'”

      • Turning Fagradalsfjall into Fagrafjall 🙂

        Actually though, we know that cumulatively these eruptions can be pretty big. The fast fissures of Krysuvik and Svartsengi probably involve volumes of magma as much as 1-2 km3 with maybe 1/10 to 1/5 erupting and the rest being huge dikes going nany km underground, there are grabens abd faults going right south of Reykjavik coming from Krysuvik even though no vebts are present. The slow eruptions probably dont create huge dikes in the crust so much more of that couple of km3 erupts, probably almost all of it if the eruption can last long enough. There are lots of large craters and some shields on Brennisteinsfjoll which has the same eruption style as Fagradalsfjall. Perhaps we jumped to conclusions too early to say it has the same style but larger.

        So in the end maybe in a decade or two when Fagraalsfjall finally goes to sleep and one of the others can go, there is probably going to be a couple km3 of new black basalt in the area, that will need a proper name. The lava is Fagradalshraun but the actual vent structure has no name other than the pet names as far as I am aware.

        I will call it Tjadsgigur in the meantime, or maybe Tjadsgigar seeing as there is more than one of them now 🙂

      • It should be seen as a continuation, not a completely new eruption. I would agree with the likely location of the eruption as the north edge of Fagradalsfjall. But not a certainty. This is presumably magma from the intrusion in the spring?

        • The USGS definition of an eruption is anything starting from a new intrusion, or the same intrusion but with a gap of more than either 3 months or 90 days. Kilauea in 2018 was immediately after Pu’u O’o but considered a new eruption. Thos is used worldwide now too, GVP uses it.

          This will be both a new intrusion and more than 3 months since the last so is a new eruption.

          • That is the definition. But it is semantics, not the reality.

    • I haven’t run regression on the quake depths to find when a surface broaching is possible….but every time I’ve run that plot I have missed the date.

      (Probably due to not constraining the quakes to the actual eruption spot)

    • I think the Webb Telescope might be a bit closer to the potential action than this webcam…

      • I can ask them.. it has a resolution of about 1 km for its distance the Earth. You’d be better off with the Hubble

    • It looks to be located in northern Keflavik, looking at the complex of buildings just south of Vogar, (Stofnfiskur?) then at the nice classic cone of Keilir and the higher ground behind.

    • It’s an exciting time like the days before Christmas: You (as a child) know that something is going to happen, but don’t know what Santa Claus exactly will deliver.

    • The location of that webcam has been bugging me all morning. I think you are right! The buildings look to be some sort of educational centre just south of Vogar.

      For another perspective of Keilir, this time from the centre of Reykjavik, here’s this webcam. The two striped silos are at the aluminium smelter, which is one a direct line between Perlan and Keilir. A bonus is the webcam is also a lot clearer in case something happens!

    • Oops, I didn’t mean for that webcam to insert. But now it’s there click the go button and you’ll see a nice view of Keilir from the north east!

    • I agree with your location and probably a fairly robust fissure eruption start. I think that the eruption most likely is only hours away, but I hope some Icelanders get some cameras ready for internet media.

    • I imagine that the experience of a sensible earthquake swarm can be scary. How many earthquakes of the present swarm can humans feel at the present depth of the quakes?

      • Someone posted in a non-geology related social media group from Reykjavik, and upon being asked, said they were feeling the eqs “pretty constantly”.

  9. Hopefully, this eruption is a bit more dramatic than the last (lame) ones, I am desiring something more substantial

      • I especially liked the white smoke coming from the hillside on the north end. Occasionally it would activate. Finally got to see a picture of this, it was pure sulfur fumes creating the white appearance. I was able to make an actual movie from one of the webcams of about 1 minute before the fissure eruption started, to when it actually occurs, it is pretty dramatic and strangely quiet when it happened. There was a sudden cloud of steam which increased, and in less than a minute, the fissure eruption was on.

    • Eh, the 2021 one was exciting. I agree the ’22 one could have done with a bit more flare though.

      • There appears to be some path dependency. It continues as it has begun to do before. But the more pressure magma needs to overcome “anti-pressure”, the more dramatic will the new eruption supposedly be. We may expect a high lava fountain. But I wouldn’t expect a very long eruption. The altitude is too high for Fagradalsfjall’s power.

  12. Question for Fagradalsfjall system: Will it get over the lava watershed between south and north? 2021 and 2022 the eruptions sent flows to the south. Can 2023 lava flow towards the north?

    • That is by far the most likely direction. But on a fairly flat surface (the lava lake), the direction it takes is rather random

      • The Volcano Catalogue says that “Þráinsskjöldur” is on of the largest volcanic shield of Fagradalsfjall’s early holocene eruptions. This shield volcano is the high plain to the northeast from the 2021-2022 eruptions. There the landscape is as flat as Netherlands. Lava would be slowed down a lot if an eruption occurs there.

    • Remember that there was a dyke intrusion that failed in December 2021. It’s not 100% until you see red stuff coming out of the ground. That said, I think the probability that we will see a new eruption in a few days is very high.

      • That’s right, it’s hard to predict whether it will breach the surface or not, there might be factors we cannot know about involved. However, the dyke intrusion is still growing very vigorously. Magma is still coming into it at high rates, despite not lengthening more, so all that growth must be widening or upward. I’d agree that the way the intrusion is evolving, chances of an eruption are much higher than not.

        • Hector, I am watching the https://vafri.is/quake/#close live and there seems to be a bifurcation occurring as regarding quake depths. 5.8 km or so seems to be one common level, but I have noticed 1.1 km or so as the 2nd level. Could this be an indicator of magma getting ready to go the last 1 km or so?

          • 1.1km is often assigned to quakes when the depth is uncertain. You should disregard quakes that have not yet been verified. There is a setting on that page to include them or not. I recommend turning that off.

      • The many cones show that 8000 years ago magma found a way to the surface. We don’t know for sure, whether this present intrusion will get to make an extrusion. But sooner or later one must found a way again.
        The next cone to the north of Geldingadalir is “Kistufell”, it is around 100m above the plain. I’d guess that on its west flank is a good position for the third episode of the “Fagradalsfjall Fires”.

        If we look at Krafla Fires, there were many intrusions and small extrusions until the “Big eruption” happened in the end. Like this we may at Fagradalsfjall get several small extrusive eruptions as we had since 2021. They are precusors for the “Mother eruption” of the Fagradalsfjall Fires which one day in the future awaits us and may even do an Ocean entry on the northern coast.

  15. Very interesting post about Katla, I have not visited this site for quite a long time, Henrik would still have been alive, but the cafe roll’s on. Though I think there may be more to come from the Reykjanes area in the not too distant future.Having now retired, I shall endeavour to visit the cafe more often.

  16. Here’s a livecam from Þorbjörn, looking toward Fagradalsfjall. You can see the crater from the 2021 Geldingadalir eruption on the horizon, just slightly right of center.

  18. If you scrub back a couple minutes in the Live from Iceland stream, they zoomed in on some pretty heavy steam

  19. All of the quakes under 3 km deep are between Keilir and the rest of the mountains, looks like the probable eruption will be out on the plains of Þrainsskjaldurhraun. Coincidentally this is where the 2021 was first predicted to happen before the dike went south 🙂

    • It may be starting right now. Lots of steam right next to kelir on this camera.

    • Chad, please take a look at https://skjalftalisa.vedur.is/#/page/map and zero in on the quake activity. I am going to stick my neck out here and say that the quake activity near Keilir is due to colder underground rock, as the magmatic pressure is still splitting rock along the fissure line. If you carefully balance the northern section with the southern section of quake activity near Grindavik, it still comes out very close to the Fagradsfjall location. Maybe the best guess is just a bit north of the 2nd fissure eruption location?

      • Maybe, we will see. But there are now as many quakes at under 2 km depth as there were under 5 this time yesterday, and now even a couple under 1 km. I think we will know soon enough 🙂

    • I’d bet on the west side of Fagradalsfjall’s Kistufell (not to confuse with other Kistufells). That’s still close to 2021-2022 eruptions, but a little bit towards the northeast. With each eruption the “Fires” move towards the northeast, where once they are going to escalete into a shield eruption. According to the Catalogue, shield eruptions are typical for Fagradalsfjall. So the “Top eruption” of the Fires is still to come.

      • There are a lot of Kistufells, I remember from a GutnTog video in one of the other eruptions that it means ‘coffin mountain’. It was never exactly clarified if it was because of the shape or because many fools met their end there, it is probably a bit of both, depending on the place.

        To me it sounds like it was probably originally a literal description that has been later interpreted as a name by foreigners, or evolved to become one locally.

  20. Have been watching the https://vafri.is/quake/#close website for posted quakes the past 4-5 hours, but there appears to be a slow throttling back of quakes during a 1 hour time period, also there are deeper quakes occurring near Keiler. I am going to assume that this means that the pressure is still not released and is cracking deeper rock. One question, is the rock cracking at 5 km or so depth really due to the breaking of crystalline rock which is colder, on the north side of where the Geldgadalir eruption occurred, while the south side, near Grinavik, is where the underground rock is warmer, hence less cracking? Just an idea as to why we are seeing so much quake activity north of Fagradalsfjall, but this idea might not be that accurate upon careful consideration.

    • Keilir is too distant from (buried) Geldingadalir. But “Little Keilir”, a hill on the half way, should be a better position. Maybe this fire series follows the patterns of the past and moves with each new eruption a little bit towards the Northeast. Little Keilir was a small eruption 8000 years ago. There may be a good position for a new volcanic cone.

    • Photo current around 1:09 am Iceland Time, Thursday July 6th, 2023. Sorry about forgetting the timestamp on this.

      • Google Photo removed the photo. I wrote to the website owner and got permission to post single snapshots to this group. Now if I can get Google Photo to recognize that I obtained permission.

  22. From 9:55 pm my time to 10:06 pm PDT which is 5:06 am Iceland time there has been a drop in quakes of mag >= 0 as recorded by the https://vafri.is/quake/#close website, which went from about 100 quakes an hour down to 0 at 5:07 am Iceland time. I am not sure if this is an artificial artifact or what? Checking both Fagradalsfjall and Langihryggur webcams shows nothing amiss, all seems quiet. https://livefromiceland.is/webcams/langihryggur

    • The “Fagradalsfjall fires” may in the end have a tendency to move with each eruption towards the northeast. The coming 2023 eruption may be a small step, but later eruptions may flood the high plain around Keilir. Past eruptions made shield volcanoes around Keilir. Until now we only may have got the “shy” beginning of the “Fagradalsfjall Fires” which once culminate into another shield eruption.

      8000 years ago Fagradalsfjall showed what it can do. There are many cones left … and a huge shield (238m above sea level). Keilir sits on the northeastern flank of this shield, where the base already is below 200m. Kistufell is an old cone on the southern flank of the shield. Somewhere to the west of Kistufell should we expect the 2023 eruption to happen.

  27. Looks like the intensity of the swarm is reducing. Is it entering the silent period of the final push? Is Keilir once again too tough to crack? Will it try Nátthagi instead, or maybe just go back to Fagradalsfjall and do its thing there? Is it a temporary lull that will soon resume, or will it shut down and come back in a few months?

    Nice to see that there’s good webcam coverage again, in case it does decide to come up.

      • Not so much a lull as a lessening of intensity, Isn’t that what we expected to happen. Now it seems we wait to see if it lessens further leading to an eruption or alternatively a true lull in the activity and possibly a failed eruption. I personally lean toward the former but then I am well and truly biased so put nothing on my judgement.

        • We are all biassed in favour of eruptions.. Activity like this can take 2-3 days to erupt (or not to erupt..), so nothing to it then to watch the live cameras and wait! Luckily Icelandic weather provides very nice eye candy at the moment. Seismic activity is down from the peak but still very high. It is now similar to what it was in first few hours of the swarm. The magma feeder at 10 km depth seems to between Keilir and Fagradalsfjall. My random guess for a break-through would be right at the bottom slope of Fagradalsfjall.

          • Thanks Albert. I have been hoping for a while that any possible eruption would be in reach of the already in situ cameras. Murphys law says it probably wont be but any cam near or far will be a bonus.

  28. And in non-Iceland news: Kilauea has resumed rapid inflation. The GPS is shooting up again

    • In a little over 2 weeks it has refilled 13 microradians. The total drop from the last eruption was 20. So it is 2/3 of the way, at this rate it will be recovered in about a week. The last eruption had a volume of about 15 million m3 so the supply now is probably on the order of 5 million m3 a week, which for context is about double what it was before 2018. The GPS is even more extreme, the caldera has spread further already than it ever contracted in the last eruption. In 2 weeks it has moved 8 cm, about 1 cm every 2 days. Since this time last year the caldera has spread by 53 cm. Since the end of the 2018 eruption, about 1.5 meters… The rate of spread of the caldera is faster than every divergent boundary on the planet, combined.
      1.5 meters since 2018 would bring it about 65% of the way to the high point before that eruption. 65% of 0.9 km3 for the 2018 caldera volume, is about 0.58 km3, or on a yearly basis about 0.12 km3, although the rates of deformation at present are about twice as strong as most of the last 5 years, which ties in pretty well to the prior numbers.

      All of this while it sits in near silence, barely enough quakes to need two hands to count have happened in the caldera sicne the last eruption ended. It is like the calm before the storm…

  29. Interestingly there’s also a swarm going on at Eldey with around 90+ earthquakes mostly between 5-10kmm deep. I wonder if this is somehow related to the activity near Fagradalsfjall or a totaly separate event?

    • That is an interesting phenomena that I have noticed before with the previous Fagradalsfjall eruptions was concurrent swarms of quakes on the furthest tip of the peninsula. What it has signified I have not the knowledge to do more than hazard a guess. I have frequently wondered if there is a cause or effect going on there. Is the magma moving along from Eldey direction? Or is the unrest on the mainland causing the effect on Eldey area?

      I also would be happy to have an explanation of this possible correlation.
      Please anyone.

      • As Albert said, the volcanic systems are totally separate.

        But the increased tension around Fagradallsfjall (think about a dyke with 30-50 cm in diameter trying to break through) has an effect on other plate boundaries, especially if there is already some accumulated tension.

        • Many thanks to Albert and Dirk. You have cleared up one of lifes small puzzles for me!
          🙂

    • Think the link is tectonic. They are both on the Mid Atlantic Ridge; i.e. the plate boundary.

  30. Based on the recent activity this seems to be where the swarm is getting shallower. Which may mean nothing!

    • And they are back.

      Perhaps some quantum strangeness from Katla migrated to Reykjanes 🙂

      • Presumably they were being verified. After all, a quantum quake needs an observer!

        • Most of those won’t be checked or at least not for a while. Think there are too many.

          They are back 😀

    • Or it’s the quieting before the start of eruption number 3…

  33. Hi folks,

    Can someone visualise the dike for me. Length, width, dept, magma source, general rate of propogation and compare to the 3 previous dikes.

    It would help greatly in viewing what’s happening down there.

    Many thanks

    • Nothing precise but a few sources I have seen said this is bigger than the 2021 intrusion. I dont know about that but it is bigger than last years when I tried to map it. And if it erupts where Albert predicted (also where I would guess too) it is more or less right above the deeper origin of the dike and not off to the side like in the past two eruptions.

      That may allow for a significantly higher effusion rate and possibly for a shield to form properly. I have been making assumptions that Fagradalsfjall isnt capable of the sorts of intense fissure eruptions that happen at Svartsengi and Krysuvik but we dont know that for certain, both of those systems did shields in the late Pleistocene like Fagradalsfjall, they just erupted more often. Fagradalsfjall might have been frozen in time and has some extreme catching up to do that we might have only seen the start of yet.

      Also, before this eruption the entire peninsula lifted by a few cm, there is an immense amount of magma available if the intrusion can make it.

  36. Well the swarm seems to be losing intensity, I think this is that calm before the storm moment, where it is in the upper crust.

    Eruption in the next 12 hours 🙂

    • It could also start moving south like it did 2021. Activity is at least shifting back a bit along the dyke. Now the focus is right next to Litli Hrútur as Albert marked on the map above. Keilir once again seems to be a tough nut to crack.

      Does anyone know the satellite trajectories and when we can expect an InSAR picture? Last year, the eruption started within a 100m radius from the center of the intrusion as indicated by the InSAR picture.

      • I would think it isnt really growing laterally at all if the swarm is subsiding. It isnt dead quiet so some cracking is going on but that would be expected of a break for the surface. If it was going sideways significantly from the present dimensions the quakes would be bigger and more numerous probably.

        • If there has been upward migration of the swarm, it could go quiet while magma goes through the aseismic layer. We won’t know until lava eventually emerges, assuming that it does.

        • And that was an M4.2. Not what I would call ‘losing intensity’! Devious, this swarm

  38. 4.7.2023

    Updated 6. July 2023 at 12:30pm
    …
    Based on the present assessment, two outcomes are possible. The seismicity could decrease progressively without magma reaching the surface. Alternatively, the seismicity could still decrease when the magma stops moving laterally but begins to move upward towards the surface (as observed prior to the last 2 eruptions here). This would likely result in an eruption close to where seismicity is currently concentrated. However, magma reaching the surface anywhere in the region between Fagradalsfjall and Keilir cannot be excluded. Of the two possible outcomes, a volcanic eruption occurring within days or weeks is considered more likely.
    …
    https://en.vedur.is/about-imo/news/earthquake-activity-in-fagradalsfjall-area

  39. The tremor is going down, by now the chances of an eruption are diminishing.

    • Way to early to say the chances of an eruption is diminishing!

      • I used to think every small change was significant when I first came on volcano cafe. Now since the initial eruption at Fagradalsfjall I have learned that patience is needed before we can get the full picture,

        • This quake
          Thursday
          06.07.2023 17:01:57 63.937 -22.147 4.2 km 4.0 99.0 1.3 km ESE of Keilir
          I am sure was initially a low 3+ but now has been upgraded to a 4. Quite an upgrade. Reminds me nothing can be taken on face value until the quakes are checked to 99% quality.

  40. The Fagradalsfjall eruption in August 2022 was preceded by a 3 -4 day swarm which was initially very intense. Suspect that that swarm was not as intense as the current one but I did not take enough screen shots at the time to be sure.

  41. Has anyone seen any InSar inflation satellite pictures? Surely someone somewhere has been watching ground inflation on this earthquake swarm set. Is it too preliminary to hope for some ground inflation maps?

    • The Sentinels come over only once every couple of days or so. But Sentinel-1 (radar) did just cover the area today so we may get some result soon

      • Albert, I have been watching the Skajalti earthquake listing site https://vafri.is/quake/#close since yesterday and still seeing quake at around 5 km depth near Keilir. Can we interpret this as continued pressure at depth and that the magma has not yet lessened pressure due to an escape route to the surface? If the quakes at depth continue, it might be a week or two before any surface fissure eruption occurs.

      • Using very crude landmarks from the coastline and simply eyeballing the approximate location of the center of the “body” of the butterfly pattern, it looks like Albert hit the spot more or less dead center. I think RÚV might have placed their webcams in the best possible spot.

    • That looks to be south, out in the Atlantic. I wonder what that is? It appears to be on the European side of the plate. Perhaps stress?
      The 3D Chart nicely shows the magma dike under Keilir!

    • I see what you mean, going east from the red dot at Keilir, making a 90° triangle with the Reykjavik red dot, at about 5-6 km depth?
      I haven’t refreshed my old model from earlier today, and it isn’t there.

    • I’m going to hazard a guess that that is probably just degassing from the lava field of the 2022 and/or 2021 eruptions (that spot looks to be near the overlap region of lava flows from both)

        • I think you may be talking about a different cam view then. The one I’m referencing is on the “Geldingadalur” cam from MBL that Keith posted above. The steam there is clearly coming from the old 2021/2022 lava field.

          There have been some other claims of steam visible on the RUV cams that are pointed at the area south of Keilir that is indeed far from he original lava fields, but as near as I can tell those appear to be smudges on the lens…

    • Good spot though whether it’s anything or not I don’t know. Now examining the screen with a magnifying glass! 🙄

  46. Litli Hrutur North webcam has a smudge on it on the left just by Little Kelir. Is is a smudge, is it mist or could it possibly be gas?

    The distance has gone hazy I guess because it’s evening, but there doesn’t seem much closer. But if there is a subtle difference in air temperature / moisture that could affect mist.

    But most likely just a smudge on the camera.

    Who votes for what?

  47. My employer has seen fit to block YT livestreams, but looking at the EQs they seem to be piling up at the SW foot of Keilir.

    • I’m pretty sure it is innocuous. Sorry, old age creeping up on me. 🙁

  49. Actually I saw the start of last years eruption (viewed from roughly the same place, I think). That churned out dense smoke very quickly. I was going to post about it, but thought someone would have got there first. In fact it took about 10 minutes before the camera zoomed in, so I was probably the only one paying attention. Which is a rarity in itself.

  50. https://livefromiceland.is/webcams/langihryggur definitely has some type of mist being given off, I watched carefully for about 5 minutes to verify that I was watching some type of mist or fog or condensation moving. It is at the upper left hand corner of the screen but it is quite hard to make out distinctly. Timestamp 21:48 pm Iceland time Thu – July 6, 2023.

    • I agree Randal. At that distance though hard to see what is really happening

          • Yes, I saw that one too. After a few minutes staring it seemed this is in the camera. It is not moving. It is not the same as the mist on the other camera.

      • Alice, I believe this is outgassing from the previous volcanic eruption flows. A recent mention from the Iceland Meteorogolical Office mentions 219 deg C temperatures measured of the lava outflows. My video of the 2nd fissure eruption shows that these fissure eruptions are VERY HARD to actually predict and catch, the camera actually happened to pan the area where the 2nd fissure eruption started. I am hopeful that one volcanologist from France can come forth with some revelant information on what the current dike progression near Kielir is actually signalling.

      • apart from the camera flare from the sun it does look like a bit of steamin but could be mist, The jury is stil deliberating. 🙂

    • Fagradalshraun degassing. It’s the area of Geldingadalir that had the perched pond, which drained so dramatically at the end of the 2021 eruption.

      • I agree, after careful watching. But at least people are seeing this and commenting about it.

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