“Popocatépetl provides an excellent example of how the perception of risk is strongly influenced by the recent eruptive history and not by a full geological record, particularly among the people dwelling in the endangered areas and the media.”

I think the above is probably a good quote that describes one of the biggest issues that geologists face when trying to properly educate the public about volcanoes, and more specifically Popocatepetl. In 1994 when Popocatépetl reawakened from it’s 60+ year slumber, it was only natural for the media to be in an uproar thinking only of the worst case scenario. Almost 20 years later, the opposite is more likely to be true where it’s hard to get locals excited or worried about the gigantic volcano lurking right next door to Mexico’s two largest cities.

Popocatepetl Steaming Away From Space

Popocatepetl’s Recent History

While some locals near Popo may (improperly) believe the giant volcano to be a sheep in wolf’s clothing, it’s not hard to see why they might think this. Since reawakening, Popocatépetl has been in a state of almost constant eruptive activity, mostly consisting of small explosions, daily exhalations of ash, and the occasional vulcanian eruption that occurs when a lava dome collapses. Activity of this nature may occasionally appear like a larger eruption during a dome collapse, but the largest eruption since 1994 has been a small VEI-3 eruption that forced evacuation of nearby towns, yet resulted in very little actual disruption.

Since the initial evacuation, there have been subsequent evacuations that were largely unnecessary due to weak explosions causing very little damage. This causes problems for local authorities as they enter into a “boy who cried wolf” situation, in which locals may be reluctant to leave in the event of an actual larger eruption. The problem here, is the evacuations are important since it’s not really possible to predict whether a small explosion will occur, or a much larger eruption, which Popocatepetl certainly is capable of.

Popocatepetl’s Rather Violent Past

While Popocatepetl has been frequently active with smaller eruptions throughout it’s entire history, the smaller eruptions are likely a cyclical part of an eruption process that leads towards much larger plinian eruptions. In the last 23,000 years, there have been at least 7 Plinian eruptions from Popocatépetl that have been determined by finding ash flow deposits and pumice falls in the region around the volcano (Siebe et al., 1996; Siebe & Macías, 2004). Prehistoric and historic eruptions repeatedly formed large volumes of hot pyroclastic flows and air falls that extended 20 km southeastwards and 10 to 15 km northeastwards (Source).

For some volcanoes, sending pyroclastic flows 20km away would simply be an awesome and exciting event to watch from afar. For Popocatepetl, this is a very different scenario as 30 million people live within view of the volcano. Puebla (2 million population) is situated approximately 45km from the volcano’s eastern flank, and Mexico City (8+million population) sits approximately 55km Northwest of the volcano.

How Lateral Blasts and Landslides Change Everything

So if the pyroclastic flows only reach on average 15-20 km from the volcano during a large eruption, the major cities should be okay, right?

This is largely true with a few very relevant exceptions. First, there is still a large population living much closer to the volcano, including towns directly on the slopes of the edifice. But more importantly, Popocatepetl likes to aim it’s eruptions like cannons, instead of shooting straight out from the top. In other words – the massive peak likes to lose it’s side, forming lateral blast eruptions similar to Mt. St. Helens in 1980.

Flank Collapse from Mt. St. Helens - Popocatepetl has 3 instances of this, on a significantly larger scale than what was seen here. National Oceanic and Atmospheric Administration (D. Wellman).

Flank Collapse from Mt. St. Helens – Popocatepetl has 3 instances of this, on a significantly larger scale than what was seen here. National Oceanic and Atmospheric Administration (D. Wellman).

Lateral blast eruptions are interesting since much more of the eruptive power is directed in a single direction radiating sideways from the edifice. Whereas a normal eruption goes straight up, then disperses around the edifice, a flank eruption can send debris flows, pyroclastic flows, and landslides an incredibly far distance from the point of eruption.

The first large Plinian eruption that occurred roughly 23,000 years back created a debris avalanche that is simply massive. To form a comparison, Mt. St. Helens’ 1980 plinian flank eruption traveled approximately 23km from the summit, with the total volume approximating 2.5 cubic kilometers of material. Popocatepetl’s debris avalanche traveled as far as 70 km southeast of the summit, and totaled a volume of roughly 30 cubic kilometers of material, more than 10 times the size of St. Helen’s 1980 landslide eruption. The flow covered an area over 300 square kilometers, and the ensuing flank collapse produced a caldera structure roughly 6.5 x 11 kilometers in size. Source. Since the first episode, there have been at least two more flank collapse eruptions of the edifice, likely on a smaller scale than the original.

So while it’s unlikely that any normal pyroclastic flows from an eruption would reach Mexico City or Puebla, if a flank collapse occurs pointing to either the northwest or the east, all bets are off in terms of how far the eruption and debris flow would reach. Also, given the current height of the edifice, it would be pretty safe to assume that any collapse of a mountain as large as Popocatepetl would be nothing short of enormous.

What Causes the Frequent Flank Collapses?

As with most things relating to volcanoes, there are many factors that influence events of this nature. With that said, Popocatepetl has the age old issue of being too big to carry it’s own weight. Unlike skyscrapers, volcanoes aren’t engineered to stay standing upright. They’re built by somewhat random outpouring of lava (lava flows), intrusions within the edifice, dome building and collapse, and other similar events. Over the years, all that material piles on top until it can’t hold it’s own weight any more.

For some volcanoes, they’ll never collapse since the slopes are at such a shallow angle, the edifice is rather stable – think of Icelandic or Hawaiian shield volcanoes here. Some volcanoes simply aren’t active enough to ever collapse. Other volcanoes have magma that is too sticky and brittle to ever form a large edifice before blowing itself apart – think of Pinatubo or Taupo here. For Volcanoes like Popocatepetl, you get the perfect storm of edifice building, where the magma is runny enough that it can flow out and build a large edifice, but sticky enough that it forms a tall, steep, and brittle edifice.

Popocatepetl currently is the second highest mountain in Mexico, and one of the most prominent volcanoes in the world, standing 3,020 meters from it’s base with a pretty steep slope. When you add in earthquakes, erosion, and magmatic intrusions, you get a very instable mountain that likes to topple over when a decent sized blob of magma rises from depth. This results in the lateral blasts that have been much more common at Popocatepetl than most volcanoes.

Other Risks to Surrounding Cities and Villages

In the grand scheme of things, a large flank eruption is fairly unlikely to happen any time soon, and in the event that it does, it probably won’t be aimed directly at one of the major cities in the area. But that doesn’t mean there aren’t major risks from a standard large or mid-sized eruption of Popo. Ancient archaeological sites have been discovered beneath lahar deposits caused by the large eruption that occurred around approximately 800 a.d.

More than just lahars and ash flows, ash-fall is often an overlooked problem from large eruptions. If significant ash were to fall in a city such as Mexico City, how would they accomodate for it? Most buildings are not designed to carry an additional 2 foot layer of rock on their roofs, which results in the collapse of many small or mid-sized buildings. Would clean drinking water be available for the population of 8+ million residents in the municipality alone? These are some of the questions that become much more relevant when thinking of eruptions near large urban populations.

Example of how light ash-fall can cause structural collapse – From Pinatubo 1991

Geological Environment and Ruminations on Future Activity

Popocatepetl has been studied extensively since it’s reawakening in 1994. While there have been many detailed studies performed, there hasn’t been a lot of conclusion reached on how large the magma chamber is, and exactly how deep the chamber is. What is known however, is that the magma chamber is deeper than normal, sitting more than 6km below the edifice. Above the magma chamber, most geologists have concluded that there is a complex system of sills and dikes above the primary magma chamber.

Seismicity occurs in two primary areas below the volcano. The first area is predictably in a pocket below the summit vent. Interestingly, there is another pocket of seismicity that occurs to the southeast of the main cone, close to the base of the volcano. This seismicity sits near a northeast trending fault. While the fault is thought to be tectonic in nature, it’s formation and activation relates directly to rising magma within the edifice, or relaxation of the mountain as a whole (source). It’s not yet known whether this fault is a sign of growing instability or not, but it leaves some room for speculation at the bare minimum.

Red Circle represent nests of high seismicity beneath the volcano. Yellow lines represent fault structures. The northwest trending fault below cluster b is the area that may represent some potential instability. Image by GeoLurking.

While the volcano has reawakened since 1994, there has interestingly been very little inflation despite the renewed volcanic activity. The lack of inflation is a bit of a mystery, but some speculate it may be a result of the extra-deep magma chamber, and the lack of a shallow reservoir for magma to accumulate.

One interesting note is that most volcanologists consider the current activity of the volcano as a continuation of a cycle that started after the last plinian eruption occurred roughly 1100-1300 years ago. Eruptions have seemed to be cyclical in this regard with Plinian eruptions occurring around 800 AD, 400-800 BC, and 3100 BC. This leaves an approximate interval period of 1200-1800 years between large eruptions, which is somewhat similar to Krakatoa and Pinatubo, although this time period is subject to change at any given time.

Another interesting thing I noticed which is 100% speculation is that there appears to be a vent of some sort opening at the base of the volcano. This may just be fire or fumaroles degassing more vigorously during an eruptive sequence, or it may be the initial start of a ring fracture. It may be nothing, but it’s at least worthy of discussion. Look carefully at the base of the edifice during the eruption, and you can see an area where gas seems to be vigorously outpouring through cracks in the mountain. The area this occurs in is slightly north on the eastern flank of the edifice. See the video below for reference.

Yellow Lines represent approximate fault structures on the edifice. This view is from the same location as the webcam, which came from East, and slightly north of the Popocatepetl. Image by GeoLurking.



155 thoughts on “Popocatepetl

  1. Very nice article Cbus, thanks! From the video, it is clear that glowing material rained down from the cone and it looks as if they also set the forest of fire. No ring fault here I’m afraid!

    • Yeah, the more I learned about the volcano, the less likely it seemed any ring fault would be forming. The magma chamber is likely too deep for a ring fracture to build up prior to a very large eruption, and there seems to be a pretty complex mishmash of dikes and sills in the roughly 6 km area between the magma chamber and the summit.

      Large flank eruptions and collapses are the biggest risk here, although it’s pertinent to know that a large flank collapse would likely be pretty similar to a caldera forming eruption anyway, just with more of a directional force, and huge landslide.

      The southeast zone seismic nest is an area of interest as it’s pretty active, and represents a tectonic fault that’s activated by inflation and the movement of magma in the volcano. This is also in the area where most of the flank collapses have occurred, so it potentially could represent an area of weakness.

      One article I read mentioned that a shallow magnitude 4-4.5 summit earthquake would have a pretty good chance at triggering a landslide event (citing st. Helens as an example). I didn’t include this, since in reality, it’s the rising wad of magma that triggers the landslides as it’s the root cause behind the instability as well as earthquakes.

    • Great post Cbus! I’m afraid I was one of those thinking it was a fairly “harmless” volcano that is entertaining to watch on webcam. We can only hope that any flank collapse will be towards the least populated area.

  2. Ahh, I love this place. The way so many different people come up with such great articles and input. Great stuff cbus.

    The history of Popo reminds me of Taranaki, another really symmetrical cone which has a huge debris fan out to the west of it. (note to self: write a post on Taranaki one day). Maybe a lot of these youthful perfect cones do this self-implosion thing when they hit puberty.

    • Yes! Looking forward to that post 🙂

      Edit: Never ever look at Jan Mayen on Google earth on 32 inch screen hooked up to a quad-processor quad-core computer on a 250megabit line and punch in Bouvetöya… My head is reeling. Yuck!

        • Yeah, Bouvetöya has collapsed in so many weird ways that I can’t get my head around it. But the side cliffs of the island is beautifull with all the different coloured lava.

          • hey, I was talking of Taranaki, but whatever moves your Bouvetöya.

            Btw, is she any relation of Bouvet Island? A daughter perhaps who just happened to wander 10,000 km to the north? That would fit with Taranaki, who according to legend also wandered off after losing the battle for the love of a cute little cone to the east of Taupo.

            • Öya = Island
              I just used the original Norwegian version of the name. Bouvetöya and Jan Mayen are the only two active volcanoes the Norwegians have.

            • As a paid up member of the Bouvet Island Land Rights for Gay Whales Liberation Front I should have known that. Goes to show, activists aren’t worth the seat of their pants.

              But I am glad Norway has two active volcanoes. I mean compared to Sweden two is pretty good really.

            • Now now, we should not persecute us volcanically dysfunctional Swedes. We generally blame the Finns for our lack of volcanic provess.

  3. Thanks for the great post cbus!
    Could the missing inflation be due to the quite frequent eruptions? 6 km depth of the magma volume, or 3 km beneath the base, is actually not so deep.

  4. Thanks for a wonderful post, cbus. Popo is one of my favorite volcanoes. Not only is it beautiful, it has a great webcam. Popo is like Sakurajima in that the people living in close proximity seem to take them for granted. I suppose if you live your whole life by something so beautiful and it just occasionally has flu-like symptons, it is pretty easy to be complacent.

  5. Interesting post. Thank you, CBUS.

    Not sure that I would call the local populations for Popocatepetl and Sakurajima complacent. The former do evacuate and the latter do have regular evacuation drills.

  6. I for one, was certain that a ring fault structure was in a formative stage there. After poking around in the provided papers, it became apparent that the known fault system transversing the area were likely responsible. The papers even note that much of the seismicity seen along them are reflective of magmatic activity of the volcano. In other words, should the need arise, they could become dike locations.

    “Caldera formation by magma withdrawal from a reservoir beneath a volcanic edifice” Pinel & Jaupart (2005) {Earth and Planetary Science Letters 230 (2005) 273– 287}


    An eruption starts when the reservoir pressure increases and reaches the threshold for tensile failure of wall rocks. This allows dyke formation, eruption and hence magma withdrawal from the reservoir. As a consequence, the reservoir pressure decreases. As long as the reservoir walls are in tension, feeder dykes can remain open. Once they are in compression, however, the dykes close, which stops the eruption.

    BOLD added

    Even though I had prior knowledge of what this post was about, it turned out to be one seriously fine and informative piece of writing. Thank you CBUS!!

    • Why do you think there was an eruption? I couldn’t see any popcorn on EBCN seismogram during today, tremor is and has been abt 2 to 3 which is nothing, There is nothing hot on the thermal cams, in short, nothing is indicating anything…

      • Popcorn on EBCN during the last few hours. Not the largest on the planet, but visible. Press F5. There has been reports of one small explosion that I know.

        I never said it was big. I just said there was a small explosion.

        • Cool, the dude is really good. The original was the first song ever made on a sequencer, an analogue beast of a sequencer. The reason why it was sequenced was that the melody was considered to hard to play. And back then the musicians were pretty good.

          Only other time I’ve heard it played live was when Florian did it on a kid’s flute at a party. That is one dude not credited for being one of the best musicians of our time, everyone thinks he did it with computers. Thing is he never did, except on stage.
          Everyone still thinks he played keyboard, he didn’t he was a flutist all along. Here is an early piece that nobody today could ever play on flute today, classicaly trained or not.

          Look at the audience 90 percent goes, “What the fudgepuck is this???” and about five look like “This is the best shit ever”.

          And if anyone wondered A) what this has to do with volcanoes, and B) what the heck is he doing now, here is logically C) The answer:
          http://faszination-islandpferde.de/adressen/schneider-florian (For those who are slightly germanically challenged, Pherde means horse and Island is Iceland. Icelandic horses are weird, they have a different gearbox than normal horses)

            • The precission he get’s out of that flute is awesome. I once told one of the flutists at the symphony orchestra about the piece, she listened to it, spent about a month and then gave up on playing what he did.

  7. Hello all! Looking forward to reading Cbus’ article but it has to wait for now. Currently, I am busily fiddling with my website moving it to a new host. The old one has not survived several hacking attacks… This is so despicable, I’ll never understand what it does for those hackers.

    Meanwhile, for all who miss the webcam pages, they can be accessed here temporarily: http://tinyurl.com/lwgzm38 As soon everything is “in Sack und Tüten”, I will post the new permanent URL here. I hope it works properly this way, if not let me know.

    • Why? Simple. A feather in someones cap.
      If they were rally skillful, they would go take down NAMBLAs site… again. My guess is that they don’t have the “5klizz” to do so.

      (however the 733t wannabe’s spell it today.)

      A group I used to chat with reveled in how fast they cold drop that site. It was almost a competition with them. I never gave them any greif for it, since doing so would infer that I supported NAMBLA… which I don’t. And if I made too much noise, I know for a fact that they would have dropped my servers offline.

      It was a humorous quip when I thought it up, but I would not be surprised if NAMBLA were the labor union for the TSA.

  8. Does Popo ever stop? Its seems to keep going and going.
    I read somewhere that Popo has a history of occasionally collapsing and having to rebuild. I don’t remember the source though.

  9. Yay. Some F@#$ wad shoots up the Historic Washington Naval Yard.

    Description of (the now dead) shooter.

    Former Military. Specialty Advanced Electronics (Aviation Electronics)
    Doesn’t like to get up in the morning.

    Me: Former Military, Advanced Electronics (Electronic Warfare)
    And, I don’t like to get up in the morning.

    Nothing like fitting a profile to lighten your day eh?

      • I have always been low key. The whole idea of EW is not being seen… or if you are, not being noticed.

        My one difference is that I am not a Buddhist like the shooter is alleged to have converted to. I do find it odd that a Buddhist would consider his actions to be appropriate.

        The other odd thing… is that most of the people interviewed by the “knews” has an account of sending text messages back and forth to each other to see what are is safe or who is okay. I can just see it now, a citation of valor for calmly texting under fire. In fact, I have an informal bet with a friend that someone will show up with something like that.

        Elsewhere, when shots rang out at near the White crack House, I noted to the same friend that the secret service must have gotten fed up with the dog digging holes in the yard. (allegedly, they were fireworks set off by a future Darwin Award candidate. It was a really bad time to pull a stunt like that.)

        • I would not be surprised if someone got a medal for that. “For outstanding Tweeting under fire”…

          To be honest, I am always surprised at the little fact that it is always religious people who get out and do things like this. I still wait for the “knews” to give a biography saying, “the renowned atheist Horgan Rune MacFugglesSon shot and killed 10 people”.

          The (sofar) only tower shooter we had was a Baptist junior officer who did not get to have sex with his equally baptist girlfriend. Apparantly this lack of getting any made his latent mental illness go into full bloom (in combination with large amounts of alcohol) and he went and killed 7 people and injured 3.

          The two local police-men who in the end gunned him down and apprehended him did not tweet about it. They though got medals of valour.

          • They don’t advertise it but I doubt most of your college shooters were religiously motivated. Rather they were atheist but for some peculiar reason, atheist media aren’t as keen to expose and advertise that fact as when a religious nut goes berserk.

            Skewd data Carl!

            • I would be very surprised if a majority of the college shooters was atheists. Maybe the finnish one, but most definitely not a majority of the US ones. If memory serves the Columbine shootings where performed after visiting church and bowling. Remember that unlike us a huge majority of the US citizens are religious. We are the odd ones in that respect.

            • Carl, careful here! Statistically, atheists are just as likely to be fanatical about their religion as religious people are about god. In practice they are more so as they are a) far more intolerant and aggressively so, and b) believe that because they do not believe in a god they are immune to fanaticism. You are making several assumptions here, assumptions based on the mistaken ideas that atheists are more sane, more well-adapted and less prone to reprehensible acts. They’re just the same bag of good, bad and messed up as everyone else, Carl.

            • Actually, that is not my experience, of course with the fantastic exception of the Fanatical Moroon who leads The Humanistiska Föreningen. He really needs medication. But sofar he is the grand exception.
              But, perhaps we should keep this discussion private. My belief is after all that everyone should have the right to have whatever belief they wish without having others opinions thrust upon them. And discussing religion seems to end up in bloodshed most often…

    • So they decided against the ping pong ball idea…. hmm…

      Whoah! She has some serious structural damage. That’s gonna get pricey.

      Gurgle Earth

      42.365539°N 10.921536°E

      • Yeah, and according to what I have heard, that rock cut her up below water the entire length. It hurts hitting reef at full speed.

        Edit: It is raised to go to a scrap yard. Only reason to lifting it is to cut the pollution and to get rid of the ungodly sight.

          • Actually, it is pretty good for tourism. People enjoy to watch catastrophies…
            Thing that is really whacked out is that getting rid of the thing cost more than the ship did when brand spanking new…

            • Actually people love to basque in the glory of old death… People go a goodly bit to go oh, and ah in place where there have been catastrophes. The oddest tourist attraction I have run across was an old soviet river tug that had capsized outside of Gotland in Sweden drowning 27 refuges. People went there for years to look at the tug after it had been lifted.

            • Humans are wired to find novel experiences interesting. Add in drama, learning, and a bit of “safe” fear, and I think it’s why people are drawn to disasters. So I could absolutely understand why it would be good for tourism.

              To a large degree, it’s the same reason why volcanism is so interesting.

  10. Hey cbus, I was just thinking, maybe we could (over time) string together a catalog of stratovolcanoes around the globe that have suffered flank collapses (not just lahars, I mean real sector collapses) in the last 20,000 years or so, similar to the catalog of calderas.

    I’ll start the ball rolling with NZ: hmm.. it is harder to get accurate data than I thought.
    Ruapehu: last major collapse was over 45k years ago
    Tongariro: can’t find any dates but there have been frequent smaller slides, compounded by the multiple craters
    Taranaki: the volcano is 2500 meters high and started erupting 130,000 years ago. In that time there have been five major landslides.

    • Hm, perhaps a shorter list involving less work would be one of volcanoes that haven’t. Another way to look at it would be to regard all stratovolcanoes as volcanoes that eventually will suffer a flank collapse and just take a look at composite and shield volcanoes?
      Or were you after volcanoes that have suffered a St Helenesque flank eruption-collapse?

    • Sinabung is potentially very nasty as there were emissions along one of the deep gorges below the peak the last time it erupted – it has a flank weakness.

      • The eruption looks rather weak, but that doesn’t mean it won’t get stronger and turn into a “real” eruption.

        Has this volcano ever had larger eruptions?

        • It is right now about the size of 2010 eruption. The columnal height puts it into a VEI-2 sofar. Problem with Sinabung is that nobody knows really. The only known holocene eruption is the 2010 eruption, and that was more like a throat clearing. Volcanoes like Sinabung are worysome not due to them being known as big blowers, no it is more that nothing is known about their behaviour. For all we know it could have a maximum sized eruption now, or it could go in Pinatubo style in a couple of weeks. Unknown volcanoes is a bother. But, judging from the next one over it could have a large one.

          • I think the GVP or some other resource did mention it has quite a few flank lava flow, but I don’t think I saw anything outside that.

            • Hrm, interesting. That’s a lot taller than it looks on google earth, although I suppose sitting next to Toba has a way of making anything look small.

          • Looking at it on google earth, it has the look of a small youthful volcano that hasn’t really done anything all that explosive ever. I would personally believe that it would need to grow before doing anything on a larger scale, but looks can be deceiving.

            While it’s easy to think of Pinatubo as it was also a small volcano prior to erupting, it’s important to remember Pinatubo also had a few previous edifices near it that were also blown up, along with voluminous ash flow tuffs surrounding the volcano. This little guy does not seem to have any of those, and instead has small lava flows around the summit.

            I believe Pinatubo also was primarily dacitic, which explains the smaller edifice, but explosive eruption. This little guy on the other hand is apparently primarily andesitic like most Indonesian volcanoes, which would explain the lava flows.

            • Erupts andesitic dacite. It is rising 2000 meters above the plain with a total height of more than 2400 meters, so I do not know if it is realy that small. It is also interestingly elongated (quite like Hekla) and the eruptions are progressing towards the south, and it has 4 different craters.
              Sibayak is far smaller, and still the side of it has been gutted.

            • Sinabung is andesitic, which isn’t as viscous as dacite. Thus, it holds onto less gas. Pinatubo had a few hundred years or dormancy, allowing magma to collect and gas pressure to build. Andesite doesn’t hold onto it as well.

            • A thought:

              Sinabung is andesitic and erupts andesitic dacite. Prior to the 2010 activity, it hadn’t erupted during the Holocene. So if what’s going on now and in 2010 is “throat-clearing” of pre-Holocene andesite to andesitic dacite, what has been cooking below for over more than 10,000 years?

              10,000 years is long enough to cook anything, even basalt, to rhyolite…

            • To be precise. The mountain is listed as having had andesitic to pure dacitic magmas, but prevailing and most normal seems to be dacitic andesite.

            • It takes a long time to produce rhyolite in large quantities, and I doubt that 10 thousand years is enough time. Silicic magma is produced by differentiation of magma and by melting and mixing of continental crust with mafic magma.

              The GVP says andesitic to dactic. There is no dactic andesite(I doubt magma of that composition exists).

            • Thank you mdatc! Sometimes it takes an assertive but obviously inaccurate statement to elicit the correct information. As 80,000 years is long enough to render even a large body of magma ineruptible (Torfajökull, 3 by 4 km diameter) and 10,000 are years not long enough to form a large body of rhyolite, if we assume that the andesitic to dacitic lavas is a) what was erupted by Sinabung prior to the holocene, and b) a fair reflection of the composition of the magmas present in Sinabung’s magmatic system more than 10,000 years ago, in your (professional) opinion how far could those magmas have evolved since then?

            • To be fair, I’m pretty sure this volcano HAS erupted in the last 10,000 years. Doing just a light bit of research shows a potential eruption around 1600. and It wouldn’t be entirely surprising if it had many smaller eruptions before history.

              I think much of it is just the fact that this volcano is under-studied as it hadn’t erupted in historical Indonesia.

              But it is relevant to believe that the andesitic-dacitic magma may have evolved to something more explosive, but that’s all speculation. Another relevant consideration is that this does seem to be in the same graben as Toba, which as we well know, cooked an insane amount of rhyolite throughout it’s history of 3 VEI-8 eruptions, so I suppose we can’t really discount the fact that there may be some very evolved magmas from this volcano.

            • MDATC, sorry, but you are wrong. It does not take long time to convert basalt into rhyolite. Eyjafjallajökull proved that it can take as short a time as 173 years.

              And to confound things even more, when they drilled by accident into the magma chamber under Krafla they found rhyolite and that is 24 years.

              If you wish you can argue this with Erik Klemetti (Eyjafjallajökull and his famous rhyolitic mush) and with the IDDP and the Univeversity of Reykjavik on the Krafla findings.

              MDATC, what you are forgetting is that volcanoes do not have one homogenous chamber, they often have pockets of more evolved magmas at hand, or even multiple chambers. So, you can juvenile magma nextdoor to rhyolite. Or as happened in both the case of Askja and in Eyjafjallajökull, hot basalt finds a pocket of rhyolite and a small nice effusive affair goes off with a roar.

    • Thank you Carl! 🙂 I did not mean to say I didn’t believe you, I am sorry if you took it like that. I just wanted to express my surprise that there wasn’t anything at all to see on the instruments (when I was watching right at the time of the last explosion – as I know now from your link).

      • Problem is that it takes a bit of getting used to finding the traces of what is happening on the instruments when the activity is so small. I guess next time you know exactly what to look for now that you have seen it 🙂

          • To say it in the favourite word of a 4 year old…. *poop*

            And if you are into sailing, poop get a completely different meaning!

            Edit: And at sea things are not pronounced as it is written. Forecastle is actually pronounced fo’c’sle, and even the landlubbing variant of English is rather bizarre. Worchestershiresauce would be pronounced “Woosteriresauce”. What? Is swedish odd? Nooooo… We have the sensible åöä to help us 😉

  11. Found a few pictures that show a spire (similar to the ones of Mount Pelée 1902 and Soufrière Hills 1995- albeit smaller) that I do not recall from the 2010 photographs of the summit. The best one apparently is from 2012:

    • Interesting! Did a search myself and found some more similar pics –

      And speaking of landslides and edifice failure…. that’s a seriously steep summit.

      • combine that with incandescence seen out of what looks to be a newly opened flank vent (thanks cryphia!), and you definitely have to consider risks for landslides.

        • If one look closely one can see the pipe leading up to the eternal flame that is the “flank vent”. It fooled me no end untill I compared a daylight and a nightlight image. Then Google Earth. I laughed a lot when I figured it out. 🙂

  12. MAUNA LOA VOLCANO (CAVW #1302-02=)
    19°28’30” N 155°36’29” W, Summit Elevation 13681 ft (4170 m)
    Current Volcano Alert Level: NORMAL
    Current Aviation Color Code: GREEN

    No significant deformation was recorded; seismicity rates were slightly elevated.

    Deformation: There were no changes in deformation rates or patterns on Mauna Loa; deformation continued to be dominated by southeasterly motion of the south flank.

    Seismicity: Seismic activity within the southwest rift zone was elevated above background levels. HVO seismic networks detected 1 shallow event below summit area , several scattered events (0-10 km) across the NW flank, 10 shallow events on the upper southwest rift, 5 shallow events on the lower southwest rift, 2 shallow events on the NE rift zone.

  13. One thing that tends to trip you up, is working on a model of equipment that you have never been inside of… or had apart.

    Had one of them today. I honestly felt that I had run across transmissions that were less complicated to replace. (Other than weighing a hell of a lot more)

    • Hi Lurk been there, helped rebuild a nose case on a Wright 3350 once- put it on the
      engine, wrong dash number- Navy case, which is OK but Airline/Civilian Engine. no match…
      different bolt holes and crank.Arrrgh!!!

  14. You spoke too soon GeoLurking! 10 “Bob” quakes in one hour


    1233520 09/17/2013 23:17:09 27.7178 -18.0306 12 1.5 4 W THE PINAR.IHI [+] Info
    1233521 09/17/2013 23:18:46 27.7309 -18.0208 10 2.1 4 SW FRONTERA.IHI [+] Info
    1233522 09/17/2013 23:20:05 27.7373 -18.0239 11 1.1 4 SW FRONTERA.IHI [+] Info
    1233523 09/17/2013 23:22:38 27.7288 -18.0311 11 0.5 4 SW FRONTERA.IHI [+] Info
    1233524 09/17/2013 23:24:02 27.7237 -18.0260 8 0.5 4 SW FRONTERA.IHI [+] Info
    1233525 09/17/2013 23:27:18 27.7193 -18.0274 10 0.9 4 W THE PINAR.IHI [+] Info
    1233526 09/17/2013 23:27:59 27.7229 -18.0244 11 1.0 4 SW FRONTERA.IHI [+] Info
    1233527 09/17/2013 23:31:57 27.6783 -18.0357 11 0.6 4 SW THE PINAR.IHI [+] Info
    1233534 09/17/2013 23:37:16 27.7252 -18.0203 11 1.4 4 SW FRONTERA.IHI [+] Info
    1233538 09/17/2013 23:49:24 27.7277 -18.0247 11 0.9 4 SW FRONTERA.IHI [+] Info

    • That will be handy if I ever get off my arse. 😀

      From the link.

      Depletion of the magma from the margins of the ellipse collapsed the ring-grabens, rather like a mega-caldera. The ellipse continues to extend. Its widening minor axis parallels North American plate motion.

      This thing contains parts of seven States…

      Spookshow baby… spook show… {BOSEG} That makes the entire Yellowstone large caldera sequence nothing more than a sort of feature of this mega feature.

      Now here is a question. Not “the” question, just “A” question. How does the OWL figure into this? (Olympic-Wallowa Lineament)

      • The OWL is a source of fascination. Living around the thing and and Occasionally using
        its features to navigate across the Cascades to Seattle. I have held that it is an old
        plate boundary but this makes me wonder….
        I live on the Northern edge of the “Peak Ring.” of the three rings featured Between the Blue and Wallowa mountains-and they are not geologically related, at least closely. Just south into the Strawberries it gets worse.. . This does look like one freaking big caldera….

      • Well, an important point before some alarmist comes along and shit his pants.

        Not all “calderas” are explosive. Some are simply collapse structures, formed when whatever material under them, became no longer under them.

        Per the site, magma escaped via different pathways and eruptive sequences. The Columbia Flood Basalts are a lot of material, that and eruptions for the Large Calderas of the Snake River plain would have removed a lot of material, this can (in part) account for the formation of the collapse structure “ellipse” as the material was vented over millions of years.

        Now.. I wonder if this thing is antipodal to an impact structure>

        • Agreed but-impact structure-hmm. First thing I thought when I saw that illustration…
          Any fracture/shock ring features from an impact would be buried under may gigatons
          of igneous rock of all types. Basalt in particular..
          Big rock to do it too..
          Straight in …

          • Which is why I was revisiting that antipode idea. The idea is that the shockwaves refocus on the opposite side of the impact.

            And I thought Japanese game shows were weird…

            Carry out a simple task, and sing Karaoke. While getting the shit knocked out of you with electrodes.

            (Note, in all likelihood, this is pretty safe. A 9VDC battery run through a multivibrator configured relay will zap the bejeevous out of you if the wires are applied to the skin. I think this one is remotely activated. It’s a buzzer type circuit and you do react accordingly. What you get is a high voltage, low amp pulsed DC. But your skin doesn’t’ know that, and neither does your brain. Done right, you can make someone hurt themselves while trying to get away from it.

        • Just brilliant Lurk! If this was FB, I’d be reduced to a simple “like” as I have nothing clever to say at this point except to convey my feeling of having been exceptionally impressed.

        • “Now.. I wonder if this thing is antipodal to an impact structure”

          Not really, but it is at the bottom of the ocean:
          rougly (long axis is good I think, the short axis is more ‘guess’work):
          Image and video hosting by TinyPic
          I don’t know if you could make something out of it.

          • I think Lurking meant anitpodal to a meteor crater. Lurking is fond of a theory that has a bit of merrit to it, and I think it sometimes does explain the larger plumes and hotspots. And that is that Mantleplume with an associated hotspot will well up antipodaly to a large meteor impact.

            Kerguelen is sweet though 🙂

      • From the article on that –

        “Geologists debate the origins of hot spots and associated large igneous provinces. Morgan (1972), Richards et al. (1989), and Ernst & Buchan (2001) think that hot spots and large igneous provinces represent outbreaks of deep mantle plumes. In contrast, Anderson (1994) and authors in Foulger et al. (2005) and Foulger & Jurdy (2007) propose that these features may form where lithospheric attenuation triggers decompression melting.”

        Personally, I think it works both ways. As I’ve mentioned a bit, most ginormous yellowstone sized calderas are not related to hotspots or mantle plumes. If they were, there would be a “track” as the crust slides over the mantle (similar to Hawaii, Yellowstone, or the Azores).

        As a result, most enormous calderas (toba, taupo, taal, aso, long valley, etc) are built through decompression melting caused by crustal thinning. The ignimbrite flareup of the great basin greatly supports this idea (not that you need much more support).

        With that said, if you get a huge mantle plume that can melt through tons of granite, you end up with a second way to get a very large caldera – which explains the dynamics of Yellowstone. If you put that plume over an ocean bed, you get an effusive island arc similar to hawaii.

        • With that said, an interesting conundrum comes up. If we’re to assume the Yellowstone hotspot is the parent of the Columbia river basalts, why did it switch from flood basalt, to explosive caldera volcanism driven by Rhyolitic eruptions?

          I have no clue if this has been researched or studied (so a more conclusive answer may have already been reached), but I generally believe that it has to do with the crust material that yellowstone was sitting above as it tracked below the north american plate. You’ll notice one glaring difference in the land above where the Columbia river basalts lie, and where the current track lies. When Yellowstone was erupting the Columbia river basalts, it was erupting through accreted terrain. I would guess that much of that terrain is oceanic material, and more than that, the hotspot most likely didn’t have to melt through much of anything to reach the surface as the accreted terrain was most like a piecemeal floor of faults, oceanic crust, and small island arcs, allowing the magma to flow right through the cracks with little resistance.

        • The last paragraph has interested me. Basaltic LIPs should melt a lot of continental crust, and thus there should be a huge amount of silicic magma produced. But where does all of this magma go?

          • It probably just stays un-erupted, but that’s just a guess. Oceanic crust is really easy to punch through in comparison to crustal rock.

          • Look for volcanic sediments / clays nearby. From memory when I researched SLIPs, LIPs do have silicic magmatism but the ash etc are easily eroded so the subaerial structures have been lost.

    • Here is a novel idea. How about an upstrike zone?

      We know the mantleplumes start at some point, and then the continent moves onwards and the plume and hotspot moves onwards. While it does so it uplifts things and occationaly does as it has done here, created large as calderas as it punched through.

      Now, take Iceland, general uplift of Iceland is 54 meters, as Iceland moves over the hotspot areas sink down, and it creates a horkload of sprungur. But thing here is that Iceland has thin crust, so it can do so uniformly with stacked areas like a bookshelf.

      Now, imagine that the hotspot/plume strikes in the middle of the area in the image Lurking plastered in above and and at a geological breakneck speed lifts it up 50 – 100 meters, Since this is harder and thicker material than in Iceland it will be a less neat affair.

      And as the pressure gets to high it ejects the Columbia plain LIP deflates and then moves on into a craton to hard to uplift and the area just falls down like a bad souflè (Bublé). Then moves onwards, finds a crack, blast. Move, find crack, blast. Move find yellowstone crack, blast blast blast. Move on, searching for crack today (should probably go to Washington DC and ask the mayor where to buy it).

      And as presumably the upstrike zone would be hit harder than anything else by the mantleplume. Think inverted impact zone. An area first uplifted like a souflé, then deflated.

      Ie, not a caldera at all.

      • I have a question for all of you: Do you think of hotspots as physical plumes of hot material that rises all the way from wherever they were generated or do you think of them as an outbreak of surplus energy that rises through matter?

        The way you think about it will greatly affect your models and explanations for these very large volcanic features.

        • Hello!

          Best question in a loooooong time Henrik!

          There is actually a difference between the hotspot = transfer of energy in the form of heat
          And a plume = transfer of material.

          I think mantleplumes are used to often as a term. First we must differentiate between the two types that we know exist, the deep plumes and the shallow plumes.
          I think the deep plumes originating from the mantle/core boundary or even the core are fairly rare and only happen where you have massive intrussives. Take the Malmfälten Iron Ore body, here we have Iron slamming through the craton like it was just so much butter, probably at temperatures far higher than anything else ever seen. That Iron did not come from the mantle, it came straight from the core. So in that case we have evidence for material moving up. There are others known too like for instance the Siberian Trap formation. We know from the Norilsk deposit that at least a fair amount of what was erupted is core material, this from the insane amount of nickel that was deposited.
          There seems to have been a few others like that, and we have one active today, the African plume. But, they are rare ducks indeed, really they are Lurkings Black Swans.

          Then we have smaller possible plumes with only mantle material, we have that for instance in Iceland where we know that the material originates at cirka 500km depth from REM isotope readings. If the rest of the hotspots also are plumes? Hell know, and probably hell no.

          • Hm,
            Agree with the difference between hotspot and plume, but won’t any hotspot, if it lasts, lead to a kind of at least local “upwelling” of material and turn into some kind of plume?

          • “There is actually a difference between the hotspot = transfer of energy in the form of heat and a plume = transfer of material.”

            I would argue that it is a matter of different energy potentials. In the case of the hotspot, the amount of energy generated is released slowly and more or less continuously, given a few hiccups, over a long period of time which gives the hotspot time to to transfer energy on the passage.

            In the case of the mantle plume, the energy generated greatly exceeds that of a hotspot and also, it is concentrated over such a short period of time that there is not time for energy transfer on a big scale. The end result is that the matter affected is “shot out like a bullet going through a barrel and energy transferal is minimal.

            • You are absolutely correct that it is a matter of different energy potentials.

              What though differs is that one would have impact energy and the other not.

              Why I am so hard at differentiating them is that you get different magmas from them. The deeper the magma come from the more goodies it carries so to speak (Swenglishism on purpose).

              And here is another Swenglishism:
              -Will Yellowstone Supererupt?
              -Seldomly the Woodpecker Coughs!
              (Henrik will explain that one, over the head taken (Swenglishism) he is better than me in English).

            • Speaking a second language using the grammatic structures and idioms of your native language, in this case Swedish.

        • Well argued, Carl. Now consider this:

          a) If you have a basaltic eruption, the basalt always originates from below the crust. But where does the energy required to break through mantle and crust to deposit that basalt originate from and how did it get there?

          b) Evolved magmas such as Dacite and Rhyolite come from either subducted crust or, most commonly, from the crust itself. Where did the energy come from that caused the silicic magma reservoir to go supercritical?

          As far as matter is concerned, I think we all can agree that any eruption contains material that has travelled from a) the point where the energy responsible for the eruption originated, and b) the subsequent journey through different strata. Whichever and irrespective of the actual percentages of distribution, I would argue that it’s all about energy transferal from the point of origin to and beyond the point of eruption, the point where it breaks through the Earths crust.

          • a) Well, I can see 3 mechanism that can act individually or in combination. 1) Energy in the form of heat acts as a blow-torch and melt through the crust (hotspot function). 2) Mass of the upwelling material breaks through via its cinetic energy, ie. it punches through (plume function). 3) Rift function, as two plates separate decompression melt occurs and the basalt travels up through the tiny crack leaving a larger low pressure area that decompressively melt creating pressure upwards widening the original crack, rinse repeat. This is the Rifting fissure eruption function. One could say that it forms its own localized plume.
            In the case of the Kirunawaara Iron Ore it was a function of 1 and 2 on a massive scale. Icelandic central volcanism is a function of 1 and 2 also, but then we come to Theistareykjarbunga for instance, there it is mainly 3 only, and it can still do copious eruptions. And a Laki/Veidivötn event that draws power from all 3 functions… Well, there is actually no limit to what it can do. I think this was what happened at Alpha Ridge, Endekka/Parana and maybe at the Siberian Trap. And it sure as heck is what is going to happen next time that African Superplume (core probably), Megahotspot, Heinous Rift punches into high gear when that Craton is shattering or it all comes out on the other side.
            As far as I know it is the only spot on earth that really could do what the Nibiruists hope for. But, most likely it will take about 2 – 5 million years before it happens.

            Oh hork, I have B to answer too…

            b) I think we here have several functions that could do it. 1) A highly pressurized magmatic storage unit that suffers a minor breach causing a regular eruption causing decompression melt and decompression degassing causing an accelerating eruption that finally breaches the roof over the chamber. If then there is water (or ridiculous amounts of gas) nearby… “boom”. There are probalby more functions like andesite with a huge amount of water.

            Now, here comes Jonny! My questions is this. Yellowstone is caused by a hotspot finding rifts. The hotspot delivers basalt in large amounts. The hotspot/plume have caused a long series of large basaltic eruptions creating mostly nice unexplosive calderas. But then it arrives at Yellowstone, take a look around and all of a sudden that same basalt goes Kabloy. How the hork?

            • The Yellowstone hotspot has done that on many occasions as it passed through what is now the Snake River Plain. My guess is that first, there’s a huge emplacement of basaltic magma over a long period of time that gouges out a large magma chamber. In doing so, it melts the old, more silicic crust that sits on top of the basalt wad like the layers of an onion. as time goes on, the silica-rich melt moves to the top as it is not as dense as basalt. Now plunk another huge wad of hot basaltic magma into the equation. It will quickly blast through the more basaltic bottom layer and come in direct contact with the rhyolites and dacites swimming on top. KA-BLOOOEY!!! As most of the accessible high-silica rocks in the crust have already been “consumed”, I’d venture a guess that Yellowstone won’t do much more before the hotspot moves on to its next location within the next ½ – 1 million years.

              As for the rifts – what came first? The hen or the egg? Are you certain that the hotspot (which arrived at Yellowstone a very long time before the first mega-eruption 2.1 MY ago) had nothing to do with the creation of the rifts?

    • Interesting idea. It may be a bit far-fetched, but it definitely presents some arguments for consideration.

      A few things that to my limited knowledge don’t seem to add up however.

      1. If the yellowstone hotspot was created by decompression, and it’s initial outbreak was the Columbia River Basalts, it shouldn’t still be active as rifting and decompression melt stopped around 13-14 million years ago as it tracked further into Idaho. Even if the magma chamber was huge, if it was just a byproduct of decompression melt, it shouldn’t be active anymore, especially considering the fact that it’s had multiple massive eruptions, including the columbia river basalt, which would aid in depleting any reservoir.

      2. Can torsion really trigger crustal thinning, and decompression melting as a result? I don’t doubt some minor spreading and decompression can occur, but would there be enough to trigger a flood basalt? That seems far-reaching to me.

      3. If decompression halts, the magma production should coincide, effectively ending any “hotspot” formed by decompression melting before it can track (since rifting does not track). If decompression oriented hotspots had the ability to track, we would already see a hotspot track for Toba, Aso, Taupo, and other similar sized “supervolcanoes” that are created mostly due to decompression melting. But they don’t track, which is why Yellowstone is the outlier, and why it’s pretty clear that it’s heat and magma source is derived from a mantle plume not related to thinning of the crust and decompression melt.

      I would think the only other explanation for a possible decompression oriented scenario with Yellowstone is that the snake river plain is a rift that is more or less “unzipping”, with the caldera volcanism sitting at the forefront of the actively rifting plain, but that’s not likely, and I’ve never seen that brought up in anything before.

      • 1. How on earth could you start a hotspot by decompression melt? Decompression melt does not raise temperature at all, actually it lower temperature. A hotspot starts at far greater depth as a heatwave moves away like a solar corona standwave from the core. Personally I think that a hotspot is created as a magnetic flareline rises up from the core. But that is just a theory. But one thing is sure, there is no way the hotspot started as decompression melt. A hotspot normally raise the temperature and pressure under untill something breaks apart and the decompression melt take place, and in some brutal cases the temperature get so hot that it just melts anyhow like under Africa and in the Kirunawaara emplacement.

        2. It probably can, but here we are talking about a hotspot/mantleplume crashing into the plate at high speed and high temperature, and we know that such things can do spectacular things. Just look at what the African superplume is doing under Ol’Donyo Lengai. And to be brutal, take a look at what the Siberian Trap Hotspot/mantleplume did to the Siberian Craton. It just punched it pieces and created the Siberian Traps.

        3. Is made redundant since 1 was a faulty premis. No decompression created the hotspot.

  15. Slightly OT: I am going to have to get a new screen to read these very interesting debates! After a few replies to replies I am seeing long paragraphs which have only two words per line which my poor eyes and what is left of my brain don’t like.

    The debates are great but is there any way to make them easier to follow, please 😀

    • Hello Karen!
      The idea is to do some radical changes to the appearance of the blog. One of them should be to increase readabilty. We have no come so far that Lurking have discovered a way of making the blog 3 letters wide… Let us say that our headway have been excruciatingly slow. Please bare with us, we are getting there as soon as we can.

    • not bad 🙂 . But this organ sound a little bit too ‘clean ‘for me. I grow up in Herent, 5 km of Leuven. The church here has an original Robustelly organ from 1770. So I’m used to an other timbre for organs 😉

      to give you an idea: This is from the (bigger) Robustelly organ of Helmond (1772):

  16. Great debate going on here!
    And “Bublé! and “Kablloooey” are yet two nice words I have learned! Keep on doing your great jobs!
    BTW Sakurajima seems to be back to action!

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