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

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.


307 thoughts on “What’s going on at Katla? Part 2

    • Not that widely known, we co-operate a bit. And the idea is to expand that co-operation. It is just that I have had too little time lately to make it happen fully.
      So for the record, any links or republishing done there are done with official permission. Same goes the other way.

      • Shall i change the widget “Essential readings for volcano lovers”, the volcano discovery link is somehow out of date and Bob or better “El Hierro y su transformacion
        Mapa de volcanes activos” might not be as top priority as it used to be, that could be moved to treasury or “wonder what Bob is up to” (or both).

  1. For those who are trying to access the Hekluvöktun to check effects of the Árness earthquake, could you please relax… The server is swamped right now with requests and will only show a Error 503 untill people start relaxing with their requests.
    There is nothing pointing towards anything happening at Hekla.

      • It was just a 1.2M at Árness, it was not related to Hekla.

        But this kind of exemplifies why I am not handing out links to the back-door access.

        • Quite! I hadn’t realised before the hoo-ha earlier this week that what we say here gets spread around so much! 😀

          • Between 3000 and 10000 viewers per day does that you know…
            This is a whale of a blog actually.

          • When next time one of the Icelandic volcanoes erupts I am expecting betwen 30 and 50 thousand viewers per day. That is why we have so many Dragons…

      • Its because no commercial concern will build fossil-fuelled back up for UK’s becalmed windmills that initiatives such as this get aired. It could work if Iceland’s geothermal generation can be turned on/off to match the changing UK wind speed. But steam turbines and area heating dont look to be that flexible temporally to me. Nor do aluminium smelters lend themsleves to hourly reajustment according to UK wind power and demand. So it will I reckon have marginal capacity, within the limitations of the Icelandic grid. More about green posturing than securing a reliable UK grid in the future.
        Live data on UK grid power sources here:

    • no signatures (hope so) but its news here on co-op Britain / Iceland, on Geothermal energy harnessing, as percursor for Power cable to Britain

    • Oh that’s good. “power cable to Britain.” Not that it’s implausible, but it opens up a whole line of jokes that can be made when the power goes out.

      “Someone unplugged Britain”

      “Okay, who tripped over the power cord”

      Tactically, it’s a boon… to an aggressor. Just think of all the kilometers of critical power cable laying the ocean floor, away from prying eyes… as and ROV places a small explosive charge. Hell, some of the more well funded “environmentalist” organizations could pull that off… like GreenPeace.

    • Bad waste of energy – GreenSomething aside – some person on RUV news here today said its only “15% efficiency” in harnessing Geothermal Power to Electricity. How about squadrons of supertankers taking on Hot Water over there for heating London (or any city) Wonder if that could be more efficient?

      • Depends on which ‘efficiency’ they mean. At least geothermal is nearly CO2 -free power. Wind turbines by contrast work out in UK at about 6-7% CO2 -free ( expressed as percentage of their rated power) This is because the wind dosent blow all the time and the use of fossil fuel generation to back them up when wind resource is low.

        Hot water to London-yes! Then they can drink it once cooled. They have official drought down there. A month ago some rivers were only flowing because of water released from sewerage works

        • GeoThermal power does release toxic gases, CO2 included. Forgot heated water is not needed except in wintertime. We use it year round and are always warm 😉

        • Very puzzled by the official drought in London. We have had rain – lots since January; the Thames looks normal; the water table is good; and, a water authority has allegedly closed some reservoirs saying they are not needed. Suspect someone is conserving water for the Olympics. But at least I do not have feel guilty for not cleaning the car 🙂

      • Doesn’t matter. It’s a more efficient idea than the bird chippers, but there are certain strategic and tactical issues that come up in the plan unless some method is taken to allow for them.

        As for line losses and lower efficiency, those can be overcome via voltage and line engineering. The loss is not going to be that much different (IMO) than high tension power lines.

        As for the strategic/tactical point, many times nations have built critical infrastructure and not allowed for belligerency. Always.. always have a contingency plan. Sure, you have this neat thing that allows so-and-so, now what are you gonna do if it goes “poof?” Will it put you out of business? Do you have a back-up plan? A way of working around the issue until you can restore that capacity?

        This is not specifically against the power line issue, but it applies here.

        In Japan, this summer, over-all there will be a deficit of about 4 to 5% of power demand vs capacity. That means blackouts/brownouts. And that is with heightened energy conservation measures. Some districts will have up to a 16% shortfall. (News source NHK World News English language pod-cast)

        • I think its rather bad idea, if water power is concerned (consideriing almost all our Hydro power stations are in Volcanic Active areas, and these can wipe out many of them, if f.e. Thorsárhraun do run again, not impossble), and we all know the (alledged) effect on bringing about the Krafla fires (probably untrue too, but these did affect holes already drilled and them holes cost a lot each).

        • You should note that Europes power-grid is fairly interconnected allready. It at the same time builds in redundancy, and at the same time makes it more of a target. It is as with all things in life, risks and benefits.

    • Carl, ok. , I heard about cable idea already (locally) in the eighties (at least before year 1992, as well as producing Hydrogen and exporting it, but that was not economical). Back them it was a DC cable of quite low voltage (high amperes?) but problems with the other polarity (i.e. at both ends, do not remember the proper tearm) could result in dead fish on quite an area.

      • Thing is that the technology to make it feasible came first this decade with the ABB ultra-lines. There is no risk for the environment at all with this system (power-line).
        The original proposal was Vattenfall AB, but thenn SS&E took it over when Vattenfall pulled out of Iceland.
        I still say it is a brilliant idea for Iceland from an economic standpoint, and for UK from an environment and economy point.
        Why? England is coal powered almost exclusively. Second of all, electrical prices production and sell prices differ a factor of 5 to 10 depending on season. Profits for both parties would be rather stumping. For Iceland we are talking about billions in your favourite currency at any given year.

  2. All praise and accolades to God for making such a fine and useful plant as the Coffea genus.

    I’m gonna miss it when the alien overlords take over and subjugate humanity. At that point I will probably seek out the Yaupon Holly and toast it’s leaves… then brew the crushed leaves into a tea. Just for the caffeine.

    • All I have to do is head for the woods. It grows wild in the Southeast. The water moccasins and ground rattlers might be an issue, but at least the Pythons and Anacondas haven’t made it this far North. (gators might also be an issue, but I stay away from wooded water)

  3. It would be a interesting effect if the HV cable sprung a leak , would Britain back feed it taking the entire power grid with it? to say nothing about the generators feeding it

    • OT: From the “It ain’t always easy memo” : Once upon a time while working on a site in a land far away, we came across some clear oil like fluid near the surface. This 200 acre site had known issues with coal tar, animal waste from slaughter houses and other fun stuff so we made a note and kept on drilling. Some years before two pipe cable casings were installed and one was completed for hi-voltage transmission and placed in service. While installing and testing the second cable some years later the insulating fluid would not hold pressure. A mile of the cable was scraped and the pipe inspected. Turns out that in pulling in the second unit, the centering spiders failed to prevent the cable from grooving the intrados of the upper casing. Some time later the repairs were completed, and the line went live. The guys who did the first one were not around for the second. 500 KV or higher transmission is used but requires a lot of care. Given the depth, length, traverse of the MAR and risk for foul play it would be interesting to see how this solution, is more economical and reliable than upgrading GB’s nukes or coal fired plants. When the
      “nattering nabobs of negativism” (SA) rule the roost fun games are in play.

      • Thanks for this. Its always good to learn something new.

        Out of curiosity, what was the dielectric fluid composed of… mostly. (not asking for proprietary info)

      • Hi ATMJ. Are you talking about HVAC or HVDC lines? The later is quite a different beast. Easier to insulate and solves any synchronisation isues between both ends. The down side is the more costly stations at both ends. Also because the lower loss they are the choice in favour at the moment.
        Just wondering what you’ve been installing 🙂

  4. Pragmatic adj.
    1. Dealing or concerned with facts or actual occurrences; practical.

    Wife: There is a spider in the bathroom!
    Me: Is it alive?
    Wife: It was.
    Me: Is it now?
    Wife: Well, I stepped on it.
    Me: Then don’t worry about it, put down some bug spray and be done with it.
    Wife: I hope it’s not poisonous.
    Me: Did it bite you?
    Wife: No, I stepped on it.
    Me: Then put down the bug spray and don’t worry about it.
    Wife: How did it get there?
    Me: Probably from the drain pipe, we had the tank pumped out yesterday.

    • I got more spiders then you can poke a stick at the present abode, so I had to learn to live with it, it is a bit like the Adam’s Family at this time of the year, winter starts tomorrow, but has been colder then normal for the whole in the last few years.

    • I love hard freezes. It thins off some of the more irritating bugs so that spring and summer are more bearable.

      I used to drive a black truck… in Florida. That was so the @#$ love bugs wouldn’t be so obvious until I could wash it.

  5. Just a Hekla update:
    these last days Hekla has regained again an entire snow cover at its summit. So whatever “heat” was there a few weeks ago (with some snowless patches) it is now gone. This on/off occurs once in a while. Hekla is now in deep sleep I think. I would hike it again. 😀

  6. OT and possibly dumb question, but wasn’t there a historical eruption in the Galapagos Islands that formed a caldera?

  7. Henry, you probably will miss my comment, but I have just realized you are probably right in assuming the 50cm Vedde ash in Norway is due to wind accumulation. Here in south Iceland, Grimsvotn deposited a fine 1mm layer in 2011. But I have found places around here where ash has gathered now up to 10cm, I was shocked by looking at such deposits. They were not there before, and have been carried with wind. Its the same magnetic and brown ash as everywhere else. Even, close to Grimsvotn, in Laki lava fields, the ash is mostly gone now, but you can easily spot patches of half a meter ash there (in eruption day, the ash acumulated was about a widespread 3cm there). So, this supports your point that 50cm does not mean a VEI7.

    • Based on Irpsit’s two anecdotal accounts, that yields an average reduction to about 8% of the measured accumulation. ( 10% and 6% )

      Site topology, prevailing wind at the time, and later scattering by wind make this highly variable.

  8. OT Has anyone else seen this ?? Mila cam at Jökulsárlón won a award from earthcam as one of the most intresting cams of 2011 fair play you may say ,but clicking on the award takes you to the earthcam web site the discription of the cam can be found here……………. http://www.earthcam.com/top25/2011/?page=cams
    The inacurate discription is as follows……..
    This webcam dilivers truely explosive views and we’er not kidding ! See a live view of the Jokulsarlion Volcano in Iceland and watch as the smoke billows into the sky before the grand finale….an eruption
    The picture shown acompanying the text is of the Eyjafjallajökull eruption !!!

    • rofl. yeah sure the Jokulsarlion VOLCANO, spewing ice when the tides roll in and out, or what?
      But the Turiabla cam is not bad either, link leading exacty nowhere.
      Thanks for sharing, made my day.

      • To be fair though; the rock faces you see at the back of the picture on a clear day are associated with a volcano – Snaehetta (central) volcano of the Esjufjöll subglacial volcanic complex which apparently includes a 40 km2 caldera (corresponds to ~7½ km in diameter). During the build-up to the May 2011 Grímsvötn eruption, the eq swarms stretched as far SE as Esjufjöll.

        But I bet that the Earthcam crew have no idea about that!


        • On the Jokulsárlon you can also see Öraefajökull. And that can as we all know become a bit disgusting if it blows.

  9. OT, but Mobile Phone Warning system in Iceland is in place, tested to about 800 phones around Katla yesterday (all phopne companies took part and included were foreign registered ones – Tourist aimed), 70% responded within minutes of sending time, at 16:00 hrs, RUV news said.

    • Gotya beat…

      Via the radio, a man was arrested for holding another man at gun point and forcing him to perform the Moonwalk. (Michael Jackson dance step)

      Alledgedly, this was in Chicago.

      • Oh my, but I would rather do a moon-walk under gunpoint than having my face eaten.
        On the other hand I have done the moon-walk for a beer in a bar once…

  10. Good Morning/evening……. The world is having a quieter moment this morning.
    Maybe time to find out how a volcano works. There seems to be some correlation between sound/tremor waves and eruption magnitude after all.
    Carl et al. be very wary about playing Hard Rock music in the vicinity of Hekla !

    • ….Coffee # 2 (Nice strong Columbian) and I am browsing the world news before getting down to some serious on line work (I tend to procrastinate when the work looks like potentially major hassle)
      I came across this and it sort of links with my comments about human survival …these company directors may survive in the short term but their thinking, or lack of , and greed is of epic- doomsday -disaster – movie- films proportions

    • ah, thanks for this video. interesting volcano art, and yes quiet moment morning today and hekla window about to close … nah … notice Bur strain tonight, first fall this spring, very small, but interesting all te same… ta ta.. *on 1st coffee*

      • Hi Islander! In regard to your comment about the spike at 21.30 last night, there was also one after midnight at about 1am. Any idea what these were? I can’t find any tremors that account for them. I also noted the tiny fall at Burfell, and a slightly thickened line. 🙂

        • Hello, Yes, not expert(TM), but I think they were some sort of “medium to slow” quakes (but automatic programs were unable find single origin), or these even some sort of “serial tremour”, the latter has apparent Katla origin, but 21:30:15 event seems show more up north but may also be from Katla or Dead Zone. I whould be very interested in seeing detailed analyses for such events, their mechanism, as they must have been recorded before and have source indentified. Bur strain is still interesting and Hek strain is still “up” bound to make a dip.

          • Many thanks for replying – the after midnight spikes have been toned down a bit now, I guess they have been corrected. I’d also like to know more about these quakes and what causes them. With regards to HEK – “what goes up, must come down” but no sign yet! 🙂

    • I think nice to know, but not “The Proof” per se. Seems all forgot these events are still not happening that frequent to worry about (all that much).

    • Be interesting to see why the zircon studies show such different results from the quartz studies.

    • Where to start? First of all, the journalist has made the mistake of believing that the findings of research based on zircon crystals and research using quartz crystals are mutually exclusive meaning “If one is right, the other must be wrong.

      Second, magma doesn’t appear in vast pockets in the crust out of nowhere. It starts out as basaltic intrusions from the semi- to fully molten zones tens to hundreds of kilometers below the crust. It takes an enormous amount of time to inject enough of this material into the crust, tens if not hundreds of thousands of years, to collect as a “supervolcano-sized” magma chamber.

      Third, the basaltic magma injected is at a temperature of 1200 – 1400 degrees centigrade. Quartz-rich minerals begin to crystallise when the temperature has dropped below 700 C. The mineral quartz itself in the form of Rock Crystal (coloured varieties Amethyst, Citrine, Rose Quartz and Smoky Quartz) does not begin until the temperature has fallen below 550 C. Thus, before crystallisation of quartz-rich minerals can begin, the temperature MUST drop from roughly 1300 to 700 degrees centigrade and the alkalic mineral MUST have had time to crystallise out of the melt. This process is most likely measured in hundreds of thousands of years.

      What I think has happened here is journalistic misunderstanding. I strongly suspect that what the researchers have found is that when the magma reaches the point where quartz-rich minerals begin to crystallise out of the melt, 700 C, it is also very vulnerable to any injection of fresh, superhot magma which will “instantly” destabilise it and cause an eruption, and that such an injection is likely to occur within a few centuries of the magma chamber reaching this point.

      Take a look at this paper http://petrology.oxfordjournals.org/content/45/11/2197.full and especially “fig. 15.” and what the researchers say caused the magma chamber to erupt. Make not of the fact that they specifically mention the temerature 700 C.

      It does indeed appear as if magma chambers are particularly sensitive at 700 C.

      • In a paper by Sparks (And I forget which one, probably the Volcanic Degassing one) he mentions that active eruptions (ones that are spewing stuff) typically exhibit behavior that resembles a sigmoidal function. This is due to the dynamics of pressurization, pushing the system over to a more energetic phase, then back again to more sedate activity.

        From my experience with saturable reactors (such as used in magnetic amplifiers), the hysteresis of the core of the reactor is loaded and unloaded by a relatively low power signal that dictates how a much larger signal is modulated. A hysteresis curve is also sigmoidal in shape, though it has a different curve depending on if it’s entering or leaving saturation.

        I imagine that this function shows up in a lot of natural processes… even magma fractionation. One of the key characteristics is that while traveling down that curve, it is quite easy to go from sedate to energetic after a tipping point is reached. In other words, it easily avalanches.

        • BTW… one of the scariest pieces of gear that I have had to take test readings on was based on the saturable reactor. It was a metal box about 18 inches across and 25 inches deep, and the test points were in the back half of the box. If the antenna drive circuit failed while you were taking the reading (rare, but entirely feasible) the voltages in that box could jump to several thousand volts as the magnetic fields collapsed, pushing several amps of current into an infinite resistance.

          Try it out.

          Voltage = Current x Resistance
          E=I x R.

          With a constant current (I) as R rises, what do you think voltage does (E).

          It will never reach infinite voltage, either the current runs out or the system arcs. But having your hands anywhere near it is not something you want to occur. This check required double gloves and an extended probe.

          • Interesting chain of thought here, Lurk! Magma chamber failure > sigmoidal function > paper by Sparks > high-voltage arc.

            Where next? Mount Ararat or a scared cat? 😉 🙂

      • Something else also occurs to me. Quartz is also a component of continental crust. Close to very hot magma it would melt and, if the conditions are right, re-crystallise on cooling post eruption. Yellowstone is believed to be / have been a hot spot.

  11. enjoy all, it is good to see all nature has to offer, sometimes we forget how lucky we are living on this planet, good night

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