The Blast from Hell?

The city of St. Pierre, before the 1902 eruptions. [LaCroix 1904, p. 232

From [LaCroix 1904

Glowing avalanches, pyroclastic flows or nuees ardentes, or whatever you want to call them, are probably the most feared and deadly of the volcanic solid products pouring down the flanks at speeds up to 100km/h+ at temperatures of 500°C or more (lead melts at 330°C, glass softens at 550°C). They are composed of incandescent rock fragments varying from lapilli to large blocks suspended as a continually cominuting rock-particle emulsion. Water does not stop them, the intense heat vapourises water and the whole mass is supported on superheated steam that acts as a lubricating film thus propagating the flow. The eruption of Krakatoa in August 1883 witnessed flows reaching landfall on southern Sumatra 40km from the volcano across the Sunda Strait and hot enough to kill 2000 people.

Nuees ardentes were first described by Lacroix in connection with the 1902 Mt Pelee eruption, these comprise a mixture of everything from fine ash to massive blocks. They are associated with Dome collapse – the instantaneous collapse of a developing lava dome in a vent, dome development being usually associated with the more acidic lavas, also these have a high volatile content and are thus have the potential for highly explosive eruptions. The avalanche comprises two parts, the lower incandescent rock fall and the dust cloud rising above; in general the density of the fall tends to confine the avalanche to valleys, but can extend for many miles from the source.

Eruption column collapse

Picture from

Eruption column collapse is usually the result of the gravity collapse of a column where the density of the column becomes greater than the explosive strength of the eruption and the thermal convection lift effect. It was a combination of collapse of the Plinian eruption column (named in honour of Pliny the Younger who first described the appearance of the column in the AD79 Vesuvius eruption – as looking like a Stone Pine) and heavy ash fall that buried Pompeii and Herculaneum, many of the remains showing evidence of high-heating.

Lateral base surge or pyroclastic surges are formed when an eruption releases large volumes of pressurised high gas content material. these have a high gas:solids ratio and are highly turbulent enabling them to cross all terrains, (unlike nuees confined to valleys). Temperatures range up to 1000°C (hot surge); interaction of magma with water may form cold surges with temperatures around 100°C…


Photograph by courtesy of Peter Francis.

Unwelded ignimbrite, Argentina — This photo is a typical example of an unwelded ignimbrite. It consists of fist-sized dacitic pumice fragments and small, sparse lithic fragments in a fine-grained matrix of dacitic lapillia and ash. This example is from the 4.6 million year old Real Grande ignimbrite which has a volume of over 55 km3.

The picture below is from Santorini – see Carl’s post ‘Santorini – the end of civilisation’ and is taken from

Photo by Lee Siebert, 1994 (Smithsonian Institution).

This spectacular outcrop shows light-colored deposits from the 3500-year-old Minoan eruption of Santorini volcano filling a valley cut in darker, bedded ashfall layers of Pleistocene age. The lower, beige-colored unit filling the ancient valley is a pumice-fall deposit from vertical explosions early in the eruption. It is overlain by laminated pyroclastic-surge deposits produced when water gained access to the magma reservoir as the volcano collapsed into the sea. The upper whitish layer truncating both these deposits is a pyroclastic-flow deposit.

The pictures of ignimbrites above show unwelded tuffs where the rock fragments are relatively poorly cemented (in recent deposits, older deposits that have undergone diagenesis will obviously be compacted and ‘solid’ but still retain each fragment’s form) Welded tuffs are those formed where the pyroclastic flow retained sufficient heat for the fragments, particularly those of vessicular pumice, to partially melt and collapse; experimentally, temperatures of c600°C are sufficient to produce collapse. These collapsed and elongaed pumice fragments are Fiamme (welded tuffs give a Eutaxitic texture to the rock) and are characteristic of welded tuffs of all geological ages.

Welded tuff with Fiamme – in centre – in thin section. From

Whilst most ignimbrites are confined to the area around the source, occasional very large eruptions yield enormous amounts of ignimbrite. The June 1912 eruption of Katmai and Novarupta in Alaska, the most powerful eruption of the 20thC produced an ignimbrite ‘sheet’ up to 200m thick near the source and 120sq km in extent. Miocene eruptions in central Turkey produced similar large deposits, some may be associated here with caldera collapse.

The yellow line delineates the extent of the ignimbrite deposits from

You never know what’s behind you!!



199 thoughts on “The Blast from Hell?

  1. @All:

    Hello everybody!
    Lately there has been quite a lot of copy/paste going on. Why this is not always good was made abundantly clear today when I found that a blogpost of mine (old) had been translated into spanish and posted on AVCAN, and then it got retranslated back and posted in here as a comment. This is not good, for so many reasons.
    I have also received a bit of complaints about this from others. So, I feel that I have to adress this somehow before it goes to far. I thought it would be enough with the rules for posting things in here, or to take text-snippets and posting them in other places. But it seems it was not enough.

    So here are some new guidelines. Please note that I am not banning copy/paste, just giving a heads up on how to filter things:
    1. Official reports are fine to post and translate in any way, as long as they are attributed and commented in the CarlosB style.
    2. Parts of posts from other blogs as long as they are commented and attributed in the CarlosB way.
    3. Very interesting comments from par example AVCAN, must be attributed and commented in the CarlosB style. Please, do only post things from this category if you find it really interesting. It should be about a big change in things. Examples for this would be the harmonic tremoring increasing massively, Bob shooting large stones into the air, lava pouring out on the island. You all understand what I intend here I hope. It should be something noteworthy.
    4. And for the love of Gódabunga, could we cut down on the Bing, Giggle translations? At least clean them up significantly before posting them. (Posting humorous tidbits of maltranslations are of course okay).

    I hope I am not coming through as a grumpy bastard here, but if the amount of copy/paste does not diminishe I (and the other moderators) will have to start cleaning the copy/pastes away.

    Kindest Regards

  2. Thank you, Alan C., for a very informative article on ignimbrite. 🙂

    There are some interesting tuffs from the infamous Laacher See Vulkan: – BTW: @ Daily Mail: No, it’s n o t erupting!

    Rather famous are in Iceland esp. the tuff layers from the last Tindfjallajökull eruption all over Thórsmörk (up to 5 m in thickness), aged about 57.000 years. The ash of this eruption seemingly made it as far as Wisconsin: So even our American friends may walk on Icelandic ash! 😆

    It is interesting to see that these ignimbrite layers are not only grey in colour, but can – depending on the minerals included – also take on red colouring (eg. at the foot of Skarðsheiði, a central volcano in the west of Iceland which was last active about 4 mill. years ago) or even green (famous layer in Berufjördur).

    This is really the most dangerous phenomenon of volcanic activity. A pyroclastic flow also caused the death of a famous couple of French volcanologists named Krafft in 1991.

    • GVP on Tindfjallajökull: Here they say, the big eruption was 54.200 years ago. It has been dormant since, but Holozene eruptions have perhaps just not yet been discovered, because traces are covered up by ash of all these other active volcanoes around it, like Hekla, Katla, Torfajökull etc.

      Anyway, it is still considered being dormant, not extinct, as there are no less than three active high temperature fields in the vicinity connected to it.

      The big eruption about 55.000 years or so ago, was a caldera forming event and covered big parts of the south of Iceland with ignimbrite, but the thickest layer is found in Þórsmörk. This ignimbrite layer even got its name from it and is called Þórsmörk ignimbrite.
      On this photo, the valley to the north of Tindfjallajökull is the a.m. Þórsmörk and to the north of this valley we have the well known volcano Eyjafjallajökull.

      • Sorry, got a bit confused here: The picture is taken from the northeast of the mountain, so the valley Þórsmörk and Eyjafjallajökull are of course to the south of it. 😳

  3. Carl

    As I am the predominately number one poster whom your comments in blue are talking about I am at a loss on how I can cut down on my Bing translations as my HP Pavilion G6 Laptop has Bling pre installed and this is what I use to do my translations. My Spanish is not good enough for me to personally translate from Spanish to English so how do I now translate?.

    Regarding only posting comments that are interesting again we are all different and what seems interesting to me which I have shared and posted on this site it seems have not been interesting enough for others so how do any of us now know what we now are supposed to post?

    Your comments were picked up and must have been found interesting to post on Avcan Facebook page by a Spanish Male person and were being discussed on Avcan Facebook page and I thought this must have been something interesting and I translated the post by Bing and posted the comments on this site and then realised I had read them before and were infact your comments which I added a post to advise of this.

    It seems that for some reason my posts are causing unrest unease problems and this is something I had and certainly have no itention to cause to anyone on this site .

    • Hello Judith!

      First of all I must point out that I wrote the guidelines for all to follow. It was not directed to a person per se.

      Of course I do not have anything to do with how people get their translations. Personaly I read and write Spanish (at least a bit) and do my own translations, but I never meant that everyone should learn Spanish. What my point was, and is, that we should cut down on copy and paste indescrimenatly from all possible sites. For instance, most people that read the comments also check AVCAN from time to time if they have interest of it. So my point was that it would be good if we could kind of cut down a bit of reposting the less interesting comments on AVCAN. I think you have noticed by now that far from everything posted there is neither interesting, nor actually true.

      Regarding what is interesting or not, well I leave quite a lot of leeway regarding what that would be. But let us make it clear, it should contain something new. There are not 20 comments that contain new things there. And also, what makes news interesting is if it is followed by a question, or a comment by the person that reposts in here. We cannot comment in there, from here, so we can only answer questions and comments in here.

      Problem with the male in question was that he did not post a link here, nor did he post my name. If he had done that, you would have noticed that emediatly. You see my point?

      As I said, my guidelines where general and apply to everyone. For an example of how reposts should be done, feel free to study how CarlosB does it.

    • I just lost a really lost post on how to use google translate for you (sorry my fault for using an old machine that crashed out).

      Basically if you try to translate the whole block of text you want to translate, then read it and break up any confusing sections of the text you are trying to translate into small chunks – of 4 or 5 words, then bits that previous don’t translate into ‘sense’ mostly work.

      It should even point out typos in the original spanish most of the time. Clicking on bits in the translated text that look a bit odd often gives alternative translations – and suddenly a whole sentence may make sense where it didn’t before. Two particular things that get translated incorrectly are ‘El Hierro’ which comes back as ‘the iron’, and ‘eruption’ which comes back as ‘rash’ – I tend to fix those by hand at the end. I did notice one more the other day “depths of the sea” – came back as “fond of the sea” (as ‘fondo’ is deep – from the same root as pro’found’).

      So, when you do put that extra work in and get it so that everything you have translated reads nicely , and doesn’t have any bits you don’t understand (unless it is technical wording) then you will automatically be cutting down the amount you copy and paste – because (unless you have a lot of spare time) you won’t find the energy to translate something ‘properly’ unless you think the content is ‘really interesting’ .

      • Actually a good and helpfull tip there…
        That i why I so seldom do translations, it takes me a long time to do it well. So, as a consequence I only do it if it is really important. And surprisingly often CarlosB beats me to it since he cheats through being Spanish 🙂

  4. Thanks Alan C.
    This is a very interesting (and scary) subject.
    I’ve been wondering why Dr. Clive Oppenheimer in his book “Eruptions that shook the world” uses the term “pyroclastic currents”, instead of “surges” or “flows”.
    Could there be an explanation for that?
    And also he refers to the eruption of Katmai, not Novarupta, I know that it was first attributed to Katmai and later, to Novarupta. Is this really so, or both volcanoes were involved, or are both of them part of the same system?
    Thanks again for your attention and excellent blog post!

    • Reynato – sounds like Oppenheimer is using a version of the term “density current” which also applies to pyroclastic flow. Take a look at the link below.

      Katmai and Novarupta are part of the same system. AVO describes the “plumbing” connecting them and other close volcanoes in the vicinity as complex. Cheers –

      • Thanks, Agimarc.
        Anyways, no matter the name, I wouldn’t like to have one of these things rushing towards me!

  5. Earthquake-Report has an update! hot lava at 70meters
    ER reader Roland (see comments) has given us the lead to a report of the University of Las Palmas de Gran Canaria showing the still erupting submarine El Hierro volcano at a depth of 70 meter (this is 18 meter less than the last published data from the IEO High Tech bathymetry equipment!). What nobody could accomplish so far, has been done by the quite simple ROV E-Wally on board of the SOS-Oceanos, Q-Star, Atlantic Explorer ship by the scientists of the Universidad de Las Palmas the Gran Canaria.
    – The images have been captured on March 14 as the date on the images reveal. The images are of course foggy as a lot of suspended material is polluting the water.

    read the rest here

      • @Lurk.

        Presumably even if the force (pulse rate) were constant from Bob the rate of erupted material would increase the closer Bob got to the surface as the overlying pressure would decrease. Not sure what the equation is for that as it is long time since I studied Physics but I bet you know it. For others, a dig about in this site may be interesting;

        @ Alan C

        You “rock”! Thanks muchly. X

        @ Renato

        Bom dia! Nice to see you in here.

        • I don’t know if it would increase or not.

          One thing you have to consider is that as Bob approaches the surface, the ambient pressure from the water decreases, but the overlying pressure from amount of lava gets greater.

          Seawater ≈1030 kg³ Lava… somewhere higher than that but less than about 2700 kg³ (solid granite)

          The lower density for being molten, and the lower density from whatever gases remain would affect that.

          Personally, my gut feel is that the rate would decrease as it approached the surface, but with lower density water, eventually you will get to a point where the system will be more violent as the water gets transformed to steam. That would be the start of the Surtseyan phase.

          Once that happens lord knows what the system will do as far as the pressure dynamics.

          • Assuming constant cone shape and constant lava flowrate, the rate of growth would slow down significantly the taller it gets. Does reduced water pressure change rate of lava solidification and thus, the shape as it nears the surface? I’m guessing better heat transfer/extraction from the lava when reduced pressure allows the water to flash into steam–so steeper cone and relatively fast growth.

            Then you have slumping from the weight depending on plasticity and strength and a natural angle of repose if loose material…. Too may factors to guess emergence but I’d be very surprised if it (change in Bob height) was linear.

            There’s a question for you vulcanologists: How does plasticity vary as lava cools? with type of lava? abruptly? Any pointers to an article on this?

          • @ Lurk

            Yes absolutely agree about the Surtseyan phase.

            As for the build up from the eruption – not so convinced, as eruptile material constantly falls away from the summit leaving a clear throat as long as the pulse is still there (which gets into a cycle. We have witnessed this in the seismograms: Bob gets blocked and constantly cleared.

            At depth, underwater, the magma cools much more rapidly as it is so much cooler.The pressure at depth is unimaginable too!! I’ve watched some great clips on Youtube (@ All google it!) and some science programmes on undersea eruptions.

            It will be a very interesting process to observe when relatively shallow but not yet breaking the surface.

            • Hi
              Pressure at depth is not that big. One bar ( 14 psi) for each 10 meter (30 feet) depth, give or take seawater density. So at 70 meter, 7 bar or 7 kg/cm2. Your mains water comes outof the faucet at around 4 bars….

          • @ Lurk

            @ mnsteve

            @ dfmorvan

            Re: pressure at 2.5 miles deep

            Here is a Youtube video showing an underwater eruption in the Artic Ocean from Woods Hole Oceanographic Institution. The subtext states:”scientists did not think volcanoes submerged under such pressure were capable of such violent eruptions.” Guess that sheds light on the pressure question.

            Here it is:

            Re: Plasticity and cooling from water

            Pillow lava is what you need to look at. Here is a start.

            See here:

    • Fantastic news!! Many thanks for the link to earthquake-report eswviva. I had intended to check out that website after reading on here but I often forget after being on here so great to have the news and the link.
      Also many thanks for the graph from Carl, a lot of food for thought there. As I hate to be disappointed I will look for things happening from 6th April but expect more likely from later. Great news that things are still happening underwater and we mustn’t forget how much we owe these researchers as well as the webcams.

        • Haha, loved the “plotically challenged”. I am most things challenged except curiosity! So Many thanks Lurking for the graph, it gives me a time-frame to look out for at least and so I am wondering how soon me may be seeing substantially more surface agitation?

          • Well, I guess that if we follow the standard depth for hydromagmatic activity depth of 50 to 30 meters we will see things starting to happen for real anywhere between 21st of this month to 16th of april. At least as long as the activity corresponds to Lurkings given growth rates. Since there are 2 factors in the span in the graph the timeframe get’s rather large.
            If I should be totally unscientific and pick a date I would go for 29th this month.
            Time for a competition?

          • OK then, I will go for 5th April based on Murphy’s Law (being PC here 😉 ) as my son will be home for Easter and with one more in the house I will have less time and energy that ever for volcano watching!

          • 1st of April for me. Did I read somewhere that to get interesting, the cone only had to reach a depth of 20 meters?

          • Normaly the depth needed for it to get interesting is given to be 50 to 30 meters of depth. But I guess 20 would do if it is a small eruption.

          • I am sure it will be the 12 April, as that is when I am moving and will be without internet for a while, just when things get interesting… 😛
            *Waves from hotel internet, which is very patchy, so won’t be around for long*

          • Still curious about wheres in the big blue yonder ye are moving.

            Waves towards the internetaly challenged hotell 🙂

          • I’ll let you know when I’m actually there (unless I get crazy first from all the multimultitasking I’m doing to close shop in my current place and organise this whole thing), but it’s not far from one of the places mentioned on this blog. 🙂

          • Ah, so you are moving anywhere in the solar system? I think there are not many places that has not been mentioned in here 🙂

            You’ve got mail…

          • the last reading at 88m was on the 11th of march (16 days before it was 120m) going from there………

            also I read somewhere that gases are projecting 40-60 m from vent

            I am sorry for not being more precise, my brain is on holidays at the moment from exhaustion

    • @eswviva. Thank you for the link to ER’s post. Looking at the pictures from Q-Star, ULPGC & Atlantic Explorer, you can’t tell which direction the lava is going – projected upwards or flowing downwards. If it is the latter, it may be sourced at a depth of less than 70m.

  6. This was a really good post, any post that teaches is always a welcome read.

    The description of the Santorini deposits hints at just how nasty Thera was…. and slap dab in the middle of a major population center.

    For all:
    I noticed in the initial sentence… “glass softens at 550°C”

    Ya know what glass is? “composed of about 75% silica (SiO2)”

    And on the explosive magma end of the scale:
    “Rhyolite is an igneous, volcanic (extrusive) rock, of felsic (silica-rich) composition (typically > 69% SiO2”

    The reason is that one of the last things to solidify is the silica rich material. That’s why long periods of residence in the chamber make the resulting magma more and more silica rich.

    At El Hierro, the period in the “chamber” leads to mostly Trachyte, which contains less silica by percentage. That’s also why there was some contention about what was actually in the restolingas (Bob’s floaters).

    The increased viscosity of the high silica rhyolite means that gases don’t come out of it very well, and that the mix could achieve a state where the gas finally comes out at a catastrophic rate… driving an explosive eruption.

    • I have a usual caveat for this…
      I actually think that the original evolved magma is now finished, and that now it is a more unevolved fresh magma that is being erupted. But, on this I might be wrong. I guess we will see better when it starts to get close to the surface.

      Now the question, will it start to make hydromagmatic explosions at the usual 50 to 30 meters range from the surface..? Hm…

      • With regards to Bob, I agree. What is coming out now hasn’t sat down there for any length of time. The floaters were the clearing out of the phlegm.

        If you remember, the IGN guys and some of the University guys were at odds about what was in them.

        • I think that pretty much everyone was correct about what was in them because they changed wildly in between samples.
          I though think that Bob is just a vent of Tanganasoga as you know, so I do believe that the magma chambers(s) under Tanganasoga is also pretty much cleared out of old stuff too.

          • “a report of the University of Las Palmas de Gran Canaria showing the still erupting submarine El Hierro volcano with glowing lava seen floating at a depth of 70 meter.”
            from ER:
            So this is not stating the depth of the vent as -70metres but that glowing lava has been seen floating at -70 metres… the vent may actually be deeper, we’ve seen lava float all the way to the suface from greater depths…
            Still, Nemisio and Co will be schquirming right now 😀

          • From Saint to Sir to Serf in 2 days. Talk about Bell curve social climbing here 🙂
            I also note the massing of “S” titles here. Neither Lords, nor Earls are used yet.

          • Could be Baldrick to keep the Blackadder theme 🙂 or would Henmaster be more appropriate? 😉
            Thought you were off somewhere oh King of the Plots?

          • King of the Plots? Nah, I am the Plotically challenged Buffoon 🙂

            I am ever so slowly to go to where the sun does shine to look at oddly shaped and coloured objects and say… “Hm…” in a very sagely way.

          • “look at oddly shaped and coloured objects” – must refer to Brits sunbathing and turning lobster coloured!! I follow you tho’ 😉
            Worked out the rock yet??
            Have a good trip!

          • Since I am also geologically challenged my much more beautifull and geologicaly adept fiancée took over mulling over the picture…

            Nah, no sunbathing brittons for me, I am just going to hold elongated yellow and green objects in my hands. Not forgetting the red round balls. As you see, a lot to go “hm…” about.

          • @ Carl

            You may of course be right but it could also be that the vent is as you describe:more free-lowing newer material precisely because Tanganasoga is in the same way as Lurk described ” full of phlegm”!! The venting has occurred as a result, and Tanganasoga is currently ” a maid in waiting”.

      • Evolved magma finished in Bob as he (?) is a “vent” – most probably. Thank goodness for ‘ Bob the Vent’ for so far relieving the pressure on the system. Hurray for Bob! : – )

        Some of the other volcanoes on El Hierro are, however, most likely to be full of Lurkings lovely term: ” phlegm”!

  7. Does anyone have a link where I can learn about the currents around el Hierro? The surface of the water in Frontera look so different from the waters off la Restinga, even with the 45mph gusts. I can tell there’s a strong current from the left, wind from the N. usually the current from the right makes it almost to the harbor, but not the last few stormy days.

  8. For the followers of the dead zone.
    Somethings seems to have happened on the 15th, but I do not have the records for the high resolution for it. But it looks like a magmatic intrusion.

  9. What was the answer to “Name that Lava II” ?

    See Talla did amazingly well; but Carl wanted to know the specific eruption. Did anyone identify it?

    • Not sofar… 🙂
      I will give the answer when I put up the next instalment. Unless of course someone cracks it before that.

      • Ursula mentioned the Permian-Triassic boundary and you said it was close. Is it the actual Permian-Triassic Catastrophe/Mass Extinction?

        • Well, yes it is associated (blamed upon) the poor Siberian Traps.
          I though have my doubts that it would have been able to actually whack that many species on its own.

          • Well, Siberian trap formation allready gave you a point… but it is divided up into quite a few actual eruptions. Think veidivötn, several overlaying eruptions. I am out for the most famooooos one 😉

    • All I can find so far is: the Aldan Shield which is close to where Talla’s source is and closer than the Siberian Traps. But if we are talking the Siberian Traps, I would go for the Siberian Craton.

      • & I have now found the Aldan Craton and Olondo Volcanoes. The Aldan Shield even has rocks from the Siberian Craton in it.

        But fascinating as all this is, going back that far there is no discussion of single eruptive event. Unless we are talking the breakup of supercontinents.

        • But found this:


          “The Murun massif, situated at the boundary fo the Siberian platform and Aldan shield, has been formed in some phases. The massif is composed of tra­chytes, phonolites, pseudoleucite trachytes, pseudoleucitites, pseudoleucite, nepheline, calsilite and aegirine syenites and pegmatoid varieties of these rocks. Both the intrusive massif rocks and host rocks have been subjected to metasoma-tosis. Three stages of metasomatic transformations have been distinguished: potassium metasomatosis, sodium metasomatosis, potassium-calcium metaso-matosis. The last stage resulted in the formation of charoite rock, which compri­ses, besides kali feldspar, quartz, aegirine and other minerals, considerable amounts of rare minerals such as charoite, canasite, tinaxite, pectolite.”

          Unfortunately the rest of the paper is in Russian. But you can find it here:

          • Gently poking you in the right direction…

            And which large lava-flood is associated with Murum, Siberian Craton and “?”…

            If the Siberian Traps was involved in the mass extinction this particular flood is the most likely culprit. 🙂

  10. Carl, great site. Thank you all of the time and work gone in to this site.

    I have been stalking the site for a few months on and off. Just a shot in the dark, seems like the lay of land has change some what.

    Does this new active spike meet your assessment for this zone to warrent a closer look? Not saying anything is going to happen, just Heka had deflation, a pause in EQ’S around Katla after a semi active Winter. The spike in the GPS stations around Gódabunga.

    Just some obversions.

    • Well, Hekla has more had a transferal of magma, than a pure deflation. Parts of Hekla is actually inflating (see Lurkings amazing plot in the apropriate blogpost).

      The Dead Zone has shown a bit of activity lately with among other things a line of quakes forming following the Veidivötn fissure. So, yes I think that the general area merrits attention. Also one should remember that statistically it about “the right time” for a rifting fissure eruption. But, one should remember that it can happen anytime the next 50 or so years, or not at all.
      I do though wish that IMO had a bit more equipment in the general area. A couple of SILs and a couple of GPS:s should help a bit with the monitoring. One should though remember that the signs we are looking for are tectonic strain build up, and that is very hard to see. The tectonic strain release is though very obvious when it happens.

      Nice to see a post from one of our “stalkers/lurkers”.

      • Ref The Dead Zone™

        You don’t happen to have a graphical chart/map/overlay that delineates the extent of the known and historical fissure eruptions between Katla/Torfajökull and the Bárdarbunga/Grímsvötn systems do you?

      • Its Rick, from Jon’s blogg, just been getting to know the site, agree with you nothing to worry about until it there is something to worry about. You have built a fine Hekla character, looking forward to see what happens or not happens.

        • Yepp, and to see if I will have to BBQ my hat… but still it looks like Katla is resting so I guess my hat is safe still.

  11. Very informative post, Alan. Thanks. The Santorini photo is amazing – do you know how it has been exposed so perfectly? Landslide? Cliff erosion?

  12. Great article – this reminds me of a link in an earlier blog posting to a video of a recent pyroclastic flow on Etna and another one at Unzen volcan – very similar in nature where the flow is suddenly halted and appeared to be sucked up into the larger mushroom cloud above.
    Etna:–march-04–2012-/3233 Courtesy of ‘Etna Walk’
    Unzen :

    Fascinating and dramatic footage

    • Thank you. I guess that the flow stops progressing downwards when:

      a) the updraught from rising hot gasses pulls the lighter ash upwards, aided by the fact that the lighter stuff is hot and may contain gasses as well; and,

      b) the heavier stuff is stopped by friction and / gravity.

      • Yes – I’m leaning towards a). Just when it seems to have such a momentum – the hot gases above must take over and pull the whole lot up. What amazing forces at work ! Of course, in other instances the volume of debris and momentum is just too much and the flow keeps going as in Carl’s article above.

  13. Thanks for the post Alan. It reminds us of the deadly power of these fast travelling volcanic events. Fascinating to watch from the safety of distance but certainly not something I would like to experience up close and personal. I think most of us volcano addicts know the result of the pyroclastic flows from Vesuvius in 79 AD.

    My date for Bob’s appearance is 14th April.
    Do we get a prize for guessing right? 😀

    • I guess it is the standing prize, a beer at the Dalek BBQ 🙂

      It is going to be held at a slightly lower altitude though due to transportation problems up Búrfell. 14th or 21st of July if the crowd can join up on a date.

    • Diana, that date of 14th April is what I was going to guess. Not that I am very smart, but because that is my grandson’s birthday 😦

        • Interesting date to pick, Bobbi, especially in the context of this thread. May 8, 1902, was the date when Mont Pelée in Martinique erupted in a pyroclastic flow that obliterated the town of St-Pierre and killed 30,000 people. Fortunately Bob or Bobette is not capable of that!

      • And I will guess May 29 because that is when (hopefully) I will be leaving for France. Last summer I flew over the Atlantic while Grímsvötn was erupting. I got a seat on the correct side of the plane to look toward Iceland but was told by the pilot that they would changing course several hundred miles to the south because of a possible ash cloud. Go figure!

      • Lol Bobbi !It’s my Mum’s Birthday! She was born as the Titanic sank! My grandmother was pressured into calling her Titania but she refused saying she wan’t calling her baby after a disaster. They called her Ethel instead! She would have been 100 years old this year.
        So I own up to no great scientific reasoning behind the date chosen! We could share the date and you can have my beer if I win…I don’t like beer!!!

        • Well, wine could be arranged too of course 🙂
          Personaly I will probably go for the English gift to civilisation and culture, a Gin & Tonic. At least then I will not catch Malaria on Iceland 🙂

          No Daily Mail, you can not in any way get Malaria on Iceland…

  14. BTW – questions on volcanoes in tonight’s programme of ‘University Challenge’ – the final. Impressed the family with my knowledge of everything volcano with answers (can’t exactly remember the questions) : ‘strombolian’ + ‘Pliny’ – which I must thank Carl, for being so timely with his post. Did I own up to having just read about Pliny ? What do you think ?! A guy’s gotta just be cool sometimes 🙂

  15. err – oopsie – sorry Alan. I skim too easily – saw your posting Carl on what and how to reference postings and missed his name above. Well – time for my shuteye. Before I go…..there seems to have been a few references to bubbling at the harbour entrance at Restinga. It has been difficult to see on the webcam because of the high swells. Has this been confirmed ?

    • I have not found any confirmation from anyone who is really there.
      If there is any bubbling I guess that Joke will write about it tomorow.

      My tentative guess is that it is normal foaming around the entrance, I have seen quite a bit of foaming and bubbling harbours in my days. But we will have to wait and see for a reliable source to confirm it or not.

  16. Bolus n. pl. bo·lus·es

    1. A round mass: “A dense bolus of trapped dolphins fills the frame” (Kenneth Browser).
    2. a. A single, relatively large quantity of a substance

    A while back, either here or on Jon’s blog, the idea of “boluses” of magma feeding into an eruptive system came up.

    I think this pdf version of a ppt slide set covers that topic.

    Specifically, it examines the eruptive rate during the 1783-1784 Laki-Grímsvötn eruption and attempts to get a handle on the supply mechanism.

  17. part of an article of in Australia, must be a slow news day, I hate the stuff including Vegemite
    In a culinary crisis that has been dubbed “Marmageddon”, the country’s only Marmite factory in Christchurch closed in November due to earthquake damage and will not resume production of the thick, black savoury concoction until July.

    Read more:

    • Mmmmmm Toast spread with marmite and peanut butter. Oh how childish is that? But so very tasty! You love it or you hate it.
      Poor people in Christchurch seem to be having a major problem with the ongoing quakes there.

    • Well, Ursh, most people I’ve met who say they hate Marmite have not had it served correctly!

      It is full of vitamin B which is so good for the brain so I hope sceptics will give it a try.

      First toast some bread – or better still some crumpets – and whilst it is still really hot ( i.e.just removed from the heat) smother it with lashings of butter so it melts. Now quickly spread over a minute/hardly visible bit of marmite. Et viola – delicious and nutritious!

      Brainy people everywhere – B vitamins are your maintenance.

      @ Carl
      Off topic but just had to comment!

    • What amazing pictures. The lightning is astonishing! If you watch the bottom left screen it shows the speed at which the explosion occurred. Sakurajima is one of the world’s most active volcanoes. The present eruption started in 1955 and has been ongoing since then with Moderate explosions every 1-5 days during most of 2006-10″………. and still going strong!.

      Good morning everyone…. busy day ahead… with husband, preparing the base for my new shed for the allotment. my best to everyone, may today be easy for you all.
      Group hug 😀

      • Nice to hear you are back to feeling well again Diana, hug returned.

        Judith, thanks for posting the video, fantastic, made my morning, what an explosion!

    • Thanks Judith for these very interesting videos
      I particularly like the lightning bolts.

      As for Bob manifestation, if we are speaking about surface manifestations, I will put my bet on 15/4 (just like that). I am pretty sure that the eruption rate is low.
      The other interesting point is that the university of Las Palmas goes on providing information.
      The other intriguing point is that it is the university of Gran Canaria and not the one from Tenerife that supplies info. Sort of By passing the local authorities ?
      The last point is the always top communication skills of these guys. THey are getting better and better. One says the eruption is over. The other one says no it is not (but supplies proof). Well, go on guys ! (or should I say Go on Bob !)

      • I think go on Bob is the best phrase.
        Currently I think one would have to supply a lot of evidence before saying that Bob is dead, after all the erroneous death messages. On friday it is time for IGN to declare Bob dead again. At least it is the usual time and date for it.

    • @ Judith

      Thanks a lot for sharing this with us.

      These webcams are brilliant, aren’t they – we get to see all this from the comfort of our armchairs. No risk,no flights or accommodation costs!

  18. Talking about birthdays, today is the second anniversary of Eyjafjalajökull (Fimmvórduhals) eruption.
    This is a date to be remembered, since many of us were first reunited around this awesome event.
    Greetings to all!

  19. Sorry folks I will not be able to post any more comments on this site as I have tried at least four times to post different things this morning since the youtube video and none have been allowed on the site.

    I have recieved an email from Carl for one to say I was breaching the rules of posting but the three other postings as far as I could see were not in breach of anything.


    • There where 2 messages caught in the spam-filter. I released one of them.
      The other with the following content I deleted:
      “Avcan this morning are saying there could be a stain again near the pier La Restinga.

      10: 45 UTC – Juan Ramon Bello Garcia the last data of the IEO is 88 m of February 21-24… After that there is nothing more, hopefully they do another batimetria and give us a new more updated information… There follows the boat… I believe that it is the patrol of the guardia civil… Incidentally on the WEBCAM it seems it shows something of stain in the vertical of the right Pier in the eruptive area and drifting westward… (Henry)
      2 minutes ago · Like

      This one broke rule number 3.
      3. Put in a link to the original place where you got it.
      And guidelines 3 & 4:
      3. Very interesting comments from par example AVCAN, must be attributed and commented in the CarlosB style. Please, do only post things from this category if you find it really interesting. It should be about a big change in things. Examples for this would be the harmonic tremoring increasing massively, Bob shooting large stones into the air, lava pouring out on the island. You all understand what I intend here I hope. It should be something noteworthy.
      4. And for the love of Gódabunga, could we cut down on the Bing, Giggle translations? At least clean them up significantly before posting them. (Posting humorous tidbits of maltranslations are of course okay).

      Why was it a breach of guideline 3? Because it did not contain any material that actually proved or disproved a stain at La Restinga. It also contained no question or personal comment from you Judith that people could discuss. As I have said, AVCAN comments that are reposted in here generaly do not create any discussion in here.

      In the future you would be advised to ask about Moderations in a letter to me at the email appropriate for this site. I posted this for the benefit of all.
      Another thing, it takes 2 moderators for a message to be permanently deleted.

      Suggestion, just stop the copy/paste thing, with the possible exception if the Sky falls down. That should put you in the clear pretty quickly.
      I hope that this helped.


  20. Anyone have a good timeline on the dates that Bob has been decalred dead, is there a pattern we could look for in those dates, and could that be used to predict the next time bob will be due to be declared dead (and if that falls inside the timeframe when Bob may decide to go surtseyan). If so I’d like to nominate the day after that prediction is due.

  21. Another lurker breaks her silence…just wanted to let you know what a fascinating blog this is — I have followed along since its inception. I now wish I would have majored in Geology instead of Finance – I’ll have to settle for being an armchair geologist! Thanks for such an interesting site!

    • Helena, welcome. I also know very little and in fact didn’t major in anything but I am well tolerated by the clever ones. That is what I love so much about this blog, there is no snobbishness from the clever ones toward the interested ones.

    • Welcome Helena

      what makes the quality of this blog is the technical quality of the posters. No need to major in anything, but you learn things here. By the way thanks to Alan for this post. Montagne Pelée is one of my favorite volcanoes.

      I will add that Lacroix is one of the founders of modern volcanology (at the beginning is was known as a famous mineralogist). Also he was sent there because of the complete destruction of Saint Pierre which was at the time famous troughout the carribean.
      He was also quite unlucky beacause he missed both eruptions (the one in 1902, the other one in 1929-32). But he gave witness to the “nuées ardentes” sometimes at the peril of his life.

      you have here a link video from ina. Notice the dacite lava neddle at the beginning which collapsed finally (height around 300 m max)

    • Hello Helena!
      Welcome to the blog. Personally I majored in Physics (and a couple of others), but ended up in economy instead.
      So, I just try to use the physics part (and reading all I can find on volcanoes) to understand what is happening.

      • Welcome Helena, to the flock!
        Don’t forget, if you don’t understand or want to know more ASK!! In fact it does we ‘oldies’ good to refresh explanations etc!! 🙂

    • Thank you for the tip off and congratulations on your first video capture. Can you select part of the area of the screen to capture with the software you are using?

      Checked out the waves & bubbles just now, mainly on the Eruption cam as this is giving the best view. At the moment there are both waves and bubbles. My guess is that what is happening is the normal currents are meeting rising water (either direct from Bob or heated by lava from Bob) causing waves that are contrary to the usual current. The currents to the north of the Island look normal.

      • that’s my theory too. the current from the left is definitely meeting some kind of chaotic resistance, and superheated water/gas bubbles rising to the top makes the most sense.
        we also have some surface waves from the wind helping to make it a little more visible, I think.

    • It wasn’t always the middle of a continent.

      The mechanics behind this type of volcanic activity has a lot to do with subduction zones and the melting of hydrated rock which then percolates to the surface, forming the volcanic arc. Related, but further along in that process, you can get back arc basins as the crust thins.

      I don’t know, but I’m guessing, that the island arc info that you found relates to a period older than the trap formation.

      One thing I ran across while spelunking that… Is that in the layers near the bottom of the sequence are marine sequenced interspersed with the tephra and flows. Clear signs that the area once was a shallow sea near the start of the traps.

      Later, the marine sequences disappear, and there are remains of land critters in the upper layers.

      This points at the really long period of time that built the Siberian traps

        • It was… and actually seems to have started before the traps… by a few million years.

          This adds credibility to a series of impact events setting up the whole process. At least one of which was likely a Shoemaker–Levy 9 style multi-impact.

          Shoemaker–Levy 9 was that “squashed comet” that broke up on close approach to Jupiter, then hit it on the next pass as a series of fragments.

          There are other impact crater lineaments on the Moon and possibly in Australia that show this as not being a rare event.

          • The Siberian Traps seem to have been located exactly opposite of a very large asteroid strike on Pangea at the point where Africa, South America and Antarctica were joined, which is why you find parts of the same humungous lava flow in Brasil, Uruguay and South Africa/Namibia as well as Antarctica. Alas, the name of the effect that causes severe damage diametrically opposed to the point of impact currently escapes me.

  22. Earthquake Report have reported:

    “Update 20/03 – 09:51 UTC
    – All political parties of the Cabildo of El Hierro have unanimously approved a motion to ask the government of the Canary Islands for a return to the pre-July 2011 situation (green status). The motion refers to the report of PEVOLCA, published on March 5, the the eruption was over.”

    This appears to be based on PEVOLCA’s declaring the eruption to be over and the need for tourist income. For the full update see:

    • Not a motion I would be comfortable to approve: Bob may quieten down, on the otherhand she may not. It is too soon to tell.

    • That is not a good thing to do.
      In all likelyhood all scientific reports point towards Bob getting closer to the surface. And if they go to “Green” and Bob starts to surface with hydromagmatic explosions? Hm, well I for one would stone any politician responsible for lowering the guard.
      As of now it looks like more a question of time before they have to abandon La Restinga, and they want to abandon precaution.

      Only a man named Perfidio Armas could come up with something so perfid.

      • Like I’ve said before, it’s the Mammoth Mountain Syndrome all over again. The current activity hurts people’s purses, they wish for it to be over and put enormous pressure on the scientists to say so – “Your duty as a public servant is to say what is good for the nation” (losely from BBC “Supervolcano”).

        • And they have not thought through the fact that if the eruption on Hierro gets larger but the authorities have said it has stopped – despite evidence to the contrary, tourism on the other volcanic islands could suffer – an additional and possibly bigger financial loss to the Canaries.

    • Well I would mitigate this one.
      Of course saying the eruption is over is a big mistake. I do hope nothing wrong happens except that it could rid us of some people who do not seem very effective in their assignements.
      However my thought is the following. Bob is not strong enough now to send restingolitas up.
      So it can mean that the flow of lava is too small to heat water enough and have the lava bombs floating. On an other hand it could also mean that there is less gases in the lava, this fact corroborated by the near absence of jacuzzi.
      So if (when) Bob begins to show her muzzle near the surface it could be that the sursteyan phase would be rather meek. After all, if you look at the contact between lava and warter in hawaii sometimes it is not that much explosive….

      • It is just that even a weakish surtseyan eruption would be bad news as it would happen 1 km away from the nearest house.

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