What’s going on at Katla? Part III

Image from Wikimedia. Aerial picture of Katla.

Trying to make sense of complex phenomenae

In the first two instalments, we had a look at Katla as she appears through media and what she has done historically. 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 1. 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. 2. 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 3. 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 4. 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. 5. 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 6. Earthquake activity at Katla July 17th 2011. (IMO)

Fig. 7. Earthquake activity at Katla July 21st 2011. The 1755 eruption was situated in the same area as the three overlapping orange spots. (IMO)

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 3. and Fig 4. 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 8. Hydrothermal activity at Katla as shown on the Austmannsbunga SIL (IMO)

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

What’s going on at Katla? Part 2

Part 2, A view of Katla

Fig. 1. Katla from Háfell looking NNW (RUV webcam capture)

So what really is going on at Katla? Well, we’re not really there yet. In this instalment, I will summarise what I have learnt from reading various scientific or otherwise papers and articles and my current understanding of it. At certain points I will supplement this with what I believe to be or could be the explanation, but when I do, I will say so. Again, I emphasise that I am not an expert in any way.

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. 2. 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 “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 3. 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. 4. 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. 5. “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.

HENRIK

What’s going on at Katla?

Part 1, public awareness background

Fig. 1. Katla from the south, webcam capture.

The current hysteria over Katla started at the same time as the ash from the Eyjafjallajökull played havoc with European air travel. Some journalist noted that Iceland’s, at least publicly, most respected volcanologist Professor Páll Einarsson, the man who nailed down the February 2000 Hekla eruption to within 30 minutes, had made claims that Eyjafjallajökull and Katla were linked and that an eruption of the former would lead to the eruption of the latter within a few months. And Katla was a huge volcano whose unavoidably upcoming eruption would be tens of times greater… …at least in the minds of journalists trying to further their professional standing.

The basis for the supposed linkage is that the last two eruptions of Eyjafjallajökull, 1612 and 1821 to early 1823 were in both cases followed by eruptions of Katla a few months later, in October 1612 and June 1823. The previous eruption of Eyjafjallajökull in 920 AD, just after Iceland was settled, was not followed by an eruption near Katla until 934 AD even if Katla had erupted ahead of Eyjafjallajökull in 920. Also, while there have been only four eruptions of Eyjafjallajökull over the past 1000+ years, Katla has erupted at least 27 times during the same period.

It cannot be claimed that the hypothesis that an eruption of Eyjafjallajökull is always followed within months by an eruption of Katla is particularly strong or convincing. The historical evidence tells us that in at least 25 of 27 instances, Katla has erupted irrespective of what Eyjafjallajökull has done. Denison Professor Erik Klemetti succinctly says that “correlation does not equal causation” and Dr Boris Behncke of INGV Catania gave us an example of a volcano that simultaneously erupted magma of two distinctly different chemical compositions as an example of how difficult it is to correctly identify what goes on at depth below a volcano.

Fig. 2. Katla erupting in 1918. Origin of picture unknown.

Let us return to Professor Páll Einarsson. If he had been quoted out of context, as so often happens when journalists interview scientists, especially since the former have no concept of the differences between human and geologic time scales, Professor Einarsson has had plenty of opportunities to correct such misrepresentation. He has not done so. Instead he has repeated his assertion in front of other volcanologists at a conference in the United States. Early last autumn he reiterated his belief that Katla would erupt within 18 months of the end of the Eyjafjallajökull eruption, and this in spite of the minor subglacial eruption assumed last summer after a small jökulhlaup, which implies that he did not think this episode substantial enough to merit to be credited as the predicted eruption.

To me, this looks like a clear-cut case of a scientist, confident in his own ability after previous successes, going out on a limb and then not have the courage of his convictions to stand up and admit that his pet theory has been proven wrong. As long as he refuses to do so, the 2012, Grub Street or otherwise inspired Katla-mongering has an extremely reputable figurehead and spokesperson, albeit an unwitting one.

The most prolific source for information about Katla is the “Iceland volcano and earthquake blog” hosted by Jón Frímann Jónsson. If you google Katla, alone or accompanied by key words or phrases, you will find that his blog comes up frequently. As an example, I googled “Katla tremor” and the top three results refer you to entries in his blog. He is even credited on the Wikipedia entry for Katla as the source for volcanic unrest in 2010 and the minor eruption of 2011 that led to a minor jökulhlaup in 2011.

Now Jón to his very great credit has made no secret of the fact that he tries to make money from his blog, primarily to support the purchase of more instruments for his hobby but also himself. One of the forms this takes is renumeration for advertisments carried based on the number of visits to his site. As he is a clever young man, he cashes in on the current interest in Katla – he would be a fool not to – and posts topics about her on an almost weekly basis. It is in his interest not to antagonise his visitors with either claims that every minor twitch was a sure sign of impending doom or that nothing was going on. Thus he couches his statements in ambiguous terms such as “time will tell” and it comes as no surprise that he is sometimes quoted as the source for the latest “unrest” at Katla by less reputable sites.

Fig. 3. Katla-mongering “at its finest”.

When it comes to the question of reliability, Jón is not a professionally trained volcanologist. He is self-taught. He always supports his topics by screen captures of IMO maps and charts or with print-outs from his own set of seismometers, or “geophones” as he calls them. However, he does make claims that there have been harmonic tremor pulses in named volcanoes or that a certain pattern of earthquakes portents something volcanic, without any professional corroboration of his interpretations whatsoever. Much as I respect Jón, I am not always satisfied with the scientific accuracy of his interpretations. This situation is unfortunate as Jón reaches a very wide audience, one that in many cases is not as critical as it should be, one that accepts as fact what it chooses to believe Jón’s latest word to be.

Unfortunately, there is one aspect of the human psyche that professional volcanologists sometimes seem to blissfully oblivious to. If we are interested in something and feel a need to understand what is going on but cannot obtain reliable facts, we look to the opinions of others whom we often absurdly assume must be better informed than ourselves. If not even that is available or if there are still gaps left, we fill those in with our own, invented, “facts” and/or interpretations. Unfortunately, scientific institutions tend to care more about what other scientific institutions think of their work than about supplying accurate and up-to-date information to, and education of, the general public.

If we apply this to Katla, it is easy to see why so many people are convinced that Katla not only will, but “must” erupt within the very near future: We have Iceland’s most respected volcanologist repeatedly saying that Katla will, is bound to, erupt very soon and really should have done so by now. We have little, verging on none, official information about her true state. We have Jón Frímann Jónsson almost continuously feeding us updates of dubious scientific accuracy with the intent of guaranteeing a steady traffic to his blog, updates couched in suitably ambiguous language that can be interpreted as support for Professor Einarsson’s hypothesis as well as Doomsday prophecies. And Mila have just repaired their Katla webcam at the same time that a very minor flow from the glacier has been reported, an occurrence gratefully seized upon by Jón Fríman Jónsson to proclaim “Katla volcano warming up for an eruption. Small glacier flood continues”

Fig 4. “Katlatubo” (montage), the Katla-mongerers’ favourite scenario…

But as I have pointed out, we have had no official statement, which in itself ought to be a good indication that nothing alarming is going on. Or are there really people out there, intelligent people at that, who believe that Allmannavarnír with their excellent track record would say nothing or even cover up such vital information if available?

HENRIK

Editors comment:

Páll Einarsson have been notified via email that he was mentioned in here and also been informed that he is more than welcome to comment the issue in here. Jón Frimann has also been notified.

Sheepy Dalek – Name that Lava XII

This week’s competition

There has been a small change in the leadership board. Diana Barnes and Lughduniense is now sharing the leadership together with DF Morvan.
This week will be the name of the volcanic system (1 point), the name of the volcano (1 point), the lava (1 point). And since people love odd volcano related facts, three famous beverages from the area (1 point). So, 4 points are out there for grabs.

This weeks picture is unknown to me, and the sender said that I was allowed to compete. To be honest though I am not quite as good at this as the crowd in here is.

The Score is:
3 Diana Barnes
3 Lughduniense
3 DFMorvan
2 Talla
2 Ursula
2 Doug Merson
2 Hattie
2 Schteve42
2 Birgit
2 Irpsit
2 Stephanie Alice Halford
1 Jim
1 Luisport
1 Heather B
1 Jamie
1 Henri le Revenant
1 UKViggen
1 Alan C

As usuall I will not hand out the answers untill tomorrow.

Alan’s Evil Riddle

This riddle is about one (1) volcanic feature. There are 3 riddles and 3 answers, but all of them are about the same volcanin feature.

In the land of the griffin and truck we will be found, by the tower twig zone. Ah, but where!
A)  What are we made of?
B)  How many – at least – are we?
C)  What is the ‘zone’?

CARL

Adriatic Bop – Italian Quakes

Picture from IB Times. End of Time.

Recently there was a rather significant Earthquake in Northern Italy along the Po valley. Rescue and recovery efforts are still underway. With luck there will be no additional injuries due to aftershocks and building/infrastructure failure. Though unfortunate, this quake does afford us the opportunity to look around to see what is going on… geologically.

I would like to thank KarenZ whose plots put me on to this line of inquiry.

There is a lot going on in this region, and the structures there are somewhat complicated (to me) but in essence, the Adriatic or Apulian Plate broke off of the African plate and is wedged between the two. Where it is pushed North , the Alps were formed, to the Southwest, the Apennine Mountains formed and make up the familiar “spine” that runs down the Italian peninsula. The northern section of this range between the Po Valley and the Ligurian Sea is the region of interest. It seems that there is a pretty ancient subduction structure here that has a plate section hanging almost vertically underneath the mountains. (see Fig 1 of Margheriti et al). It is suggested that this is not a classic “subduction zone” but could be some exotic structure made up of continental crust fragments frozen in place in said paper.

Why do I bring that up? Well, the focal mechanisms for the two largest quakes show faulting similar to that of a subduction zone… specifically reverse faulting. The dangling slab in the last paragraph is not it.

USGS Moment focal tensor solutions (beach balls) of a fore-shock, the main-shock, and an after-shock of the large Italian earthquake.

In reverse faulting, the headwall is pushed up over the other side of the fault (relative to the other side) or the other side is being pushed under the headwall. (same motion, just different ways of looking at it) For this quake, it is actually oblique reverse faulting since it is pushing off to one side a bit. (the ball isn’t perfectly lined up).

The question about the Bulgarian quakes came up , but those have a completely different solution. They show normal faulting where one side slides down and away from the other. (or up and away). The only things those two quake sets have in common is.. um.. nothing. They were along the northern boundary region of the Agean Sea plate and the Eurasian plate. There may be some regional stress that caused them both, but as for fault lines, totally unrelated.

So.. what is with the Apulian Plate and how did it get there? Well, that’s the really wild thing. It seems (according to diagrams in reference 4) that the toe and heel of Italy, and part of Greece, originated in the gap in the North African coast down around Tripoli. During this drive north the Alps were formed. Massive folding and crumpling occurred as the land was tortured into position. Anticlines and Synclines formed and eroded, and the leading edge of the collision warped and formed a basin…much like the Persian Gulf between the Arabian and Eurasian plate collision or the Ganges valley on the Indian Plate to Eurasian Plate collision. As some of you know, the top of the Matterhorn is African crust. Did you also know that it is upside down? That’s how extreme the collision is. (pg 14 of Ref 5) In fact, one anticline was an island in a shallow northern Adriatic sea during the Pleistocene, the Ferrara Anticline, buried about 20 km northeast of Modena in the Po river plain. (ref 2 and 3).

Okay, enough rambling.

From reference 3, a modified Figure 1.

In this document I noticed that the study area covered a rectangle directly covering the quake area. Taking a position on the Northeast end of that box, I was able to calculate the distance to each quake and plot them in relation to the cross sectional strata of the study area. As you can see, the fore shock and mainshock occurred in the Mesozoic era limestone that was laid down when this area was part of the sea. Most of the aftershocks are along the interface of that layer and a lower ancient Tethyan crust. Only one quake in the USGS set shows as being in that part of the crust.

The dangling slab is not shown in this plot, and I did yank the mountains off the top. (They were represented in a different scale).

Thank You for your time.

GeoLurking

References:

1) “The subduction structure of the Northern Apennines: results from the RETREAT seismic deployment” Margheriti et al, ANNALS OF GEOPHYSICS, VOL. 49, N. 4/5, August/October 2006

http://earth.geology.yale.edu/~jjpark/Margheriti_etal_Annali_2006.pdf

2) “HYDROGEOLOGICAL FEATURES OF THE PO VALLEY (NORTHERN ITALY)” Bortolami et al

http://iahs.info/redbooks/a120/iahs_120_0304.pdf

3) “A new active tectonic model for the construction of the Northern Apennines mountain front near Bologna (Italy)”, Picotti et al JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113, B08412, doi:10.1029/ 2007JB005307, 2008

http://www.ees.lehigh.edu/ftp/retreat/outgoing/preprints_and_reprints/picotti_pazzaglia_2008_Apennines_final.pdf

4) “FROM THE TETHYS OCEAN TO THE MEDITERRANEAN SEAS: A PLATE TECTONIC MODEL OF THE EVOLUTION OF THE WESTERN ALPINE SYSTEM” Biju-Duval et al lNTERATlONAL SYMPOSIUM ON THE STIUCTUIAL HISTORY OF THE MEDITERIANEAN BASINS. SPLIT (YUGOSLAVlA) 15.29 OCTOBER 1976.

http://archimer.ifremer.fr/doc/1977/publication-5197.pdf

5) “Tectonic evolution of the Alpine orogen” Jacques Charvet

http://www.sklable.ac.cn/uploads/file/Jacques%20Charvet.pdf