New Hebrides – Ambrym

This really should be Ruminarian VI, but I got delayed/sidetracked in writing it. (or just plain burnt out). Someone posted a Vanuatu quake and… well, they are sort of common. Poking around at it I ran across Ambrym, and one of my discarded post ideas came back to lend an intro to this. For the sake of sanity, I hopped out of the Ruminerian sequence to the coordinating Dragon won’t pop a gasket trying to keep it straight. Ruminerian VI will logically follow V when I get around to finishing it.

I’ve sought calderas now for several weeks… I find them quite entertaining. I always get a hoot when some media bobble head yammers about “Supervolcanoes.” I’m not a geologist, and I also detest the term. My preference is “large caldera structure.” One or two media oriented sites stated that there were six known “supervolcanoes,” which is total B/S when you get right down to it. Some in the geologic community have actually adopted the term, more out of making something useful out of it rather than fight the phrase. There still isn’t a clearly defined set of standards that make one eruption super and another not super. I’m pretty sure that the residents of Yakima Washington thought Mount St Helens was pretty “super” at the time it went off… though even with the widest pseudo definition, Saint Helens was far from a “Supervolcano.” I’m sure the residents around Merapi feel the same way about their recent volcano encounter.

One breakpoint that I’ve seen mentioned, is 500 km³ of ejecta. Okay… then what about the 200 km³ eruptions? They aren’t “super?” At 200 km³ I’m pretty sure that those affected may not really give a rats arse what the definition is. So… if you break it down into “large caldera” events… they are everywhere.

The one I’m going to look at shows up in earthquake lists all of the time. It’s the system that usually pops up with the Vanuatu quakes. The name of it… is Ambrym. Mt Marum and Mt Benbow are in a state of eruption… but they are just features inside the Ambrym caldera. At 12 x 14km, Ambyrm caldera has an extent of about 132 km². It’s last major event was about 50 AD ± 100 years with a bulk Tephra volume of 7.0 (±1) x 10^10 m³. That’s not DRE (Dense Rock Equivalent), that’s bulk. You can estimate the DRE by multiplying that against the ratio of bulk density vs rock density… or about 1000 kg/m³ over 2700 kg/m³. That’s about 0.3704. That gives us a rough DRE of about 2.59 x 10^10 m³. (GVP’s generic conversion routine when you don’t have the actual densities)

Doing a quick conversion to km³, it comes out to about 2.59 km³ 25.9 km³. Not small, but hardly that impressive. Far less than what the 132 km² area of the caldera hints at. Using that formula that you guys here on VC helped to gather the data for, it comes out at 155 km³ of material associated to a caldera of that size.

Since the caldera is supposed to have formed in conjunction with that eruption, there seems to be a huge disconnect with the formula. Something on the order of around a factor of six. Why the disconnect? Because Ambyrm caldera is a collapse structure… not an eruption structure.

McCall et al note:

“The Ambrym caldera appears to have formed by quiet subsidence or by subsidence accompanied by eruption of scoria lapilli little or no different from the material that was erupted prior to and subsequent to caldera formation.”

And given that their observations indicate that the caldera walls have a youthful appearance (little erosion in a tropical environment) it is easy to see where they came up with that conclusion.

They also note that the non-collapsed slopes tend to represent the pre-collapse gradient… working off of that, I calculate that the summit max height could have been as high as about 1600 meters.

So, where is all that missing 129 km³ of material? It’s not really missing. That was part of what built the island to begin with.

Now for something that hasn’t been touched on since way before Eruptions moved to its current site. One of the users there, “Passerby” and I would trade info back and forth about processes. My knowledge was inferior to his, but I did pay attention to the stuff he put forth. One of the ideas is best described as “pleating.” Passerby noticed that in some of my plots, the quaked in the Benioff zone (aka Wadati–Benioff zone) seemed to describe a shape similar to the folding of a piece of fabric as it hit the floor… bending back and forth. This is from the nose of a subducted plate encountering resistance (either from density or from buoyancy) and folding up like slow moving molasses/taffy. It’s really remarkable when you think about it, and actually comes from the fact that rock is not the hard substance that we think it is when you get to really high pressures and temperatures. It oozes. Carrying this a bit further, as a plate subducts, it doesn’t do so in a simplistic fashion. It can bend, fold, pleat or move in any fashion that you can imagine a semi-ridged slab of not quite ridged material can. Clay, Fudge, toffee… all show similar movement characteristics.

You can see this best illustrated of you yank out all of the quakes above 50 km and look at just those associated with the Benioff zone in the area of Ambrym. Notice that the subducting slab is folding and pleating as it goes down. This is a combo graphic of a fitted poly-sheet to those quakes. This indicates roughly where the quakes are at based on what their history was, and fills the gaps so that we can mentally picture where that surface it at.



“The Geology and Geophysics of the Ambrym Caldera, New Hebrides” McCall et all (1969)


128 thoughts on “New Hebrides – Ambrym

  1. Neat! You misplaced a decimal – the tephra conversion works out at 25.9 km³, not 2.59 km³. That’s a fair-sized VEI 6 and with an area of 132 km² area, it corresponds to an average collapse depth of ~200 m from tephra-DRE alone. But I do agree, there seems to be a “performance gap” here.

    As for terminology, we’ve discussed this before and an alternative is to link it with the area of effect; local, regional or global. Laki 1783 would be in the second category as it led to famine in many parts of Europe even if it wasn’t all that impressive volume- or explosivity-wise.

    • Corrected. (Thanks!)

      As for Laki, I noted a pathway for Sulfur from non-tropopause bumping eruptions to get it to the stratosphere. It’s still a work in process and bears further reading.

      Carbonyl Sulfide – OCS. It’s a long lived molecule that becomes SO2 and eventually Sulfate, that can get into the stratosphere via the tropical Hadley cells

      I don’t have a good handle on the OCS to SO2 ratios in volcanic gas release. From what I have seen.. it’s pretty low. But being long lived, it can probably fit the bill.

    • Probably missing the point here, as this is just a quick visit. Laki was mainly flood basalt from a fissure system – how does that fit the caldera model?

      • Flood Basalts, by their nature, don’t generally loft stuff past the tropopause.

        If not, then how can a Flood Basalt have much of an effect on the global climate. Tropospheric SO2 is short lived. There just is not enough time for the molecules to have time to drift up to the stratosphere. As soon as SO2 becomes sulphate, it starts to precipitate out as the particles grow in size. The principal way that sulphate is removed from the atmosphere is sedimentation.

        So… what mechanism is available that can allow a flood basalt to affect the global climate? Tropospheric effects will tend to be localized and regional… or at the most, hemispherical.

        The answer? Carbonyl sulfide. (OCS) Well, I think that’s the answer, but I’m not sure. I have found (via reading) that Carbonyl sulfide is a long stay time molecule. It has a turnover period measured in years. That gives it time to be lofted to the stratosphere and take part in the sulfur reactions that generate a persistent background haze. Provided that the release is large enough to have an effect in the global budget of the stuff.

        As for how “flood basalts” came up, that is due to Tolbachik. Grumpybear noted (last thread) that the stated flow rate, and the length of the eruption are getting close to the 1970’s event in size. Tolbachik is doing what amounts to a flood basalt. A bit slow… maybe, but a flood basalt in form.

      • The debate about terminology. It all depends upon which criteria you select as the defining one(-s). If you choose volume, as Lurk points out, you end up with colossal eruptions not considered “super ereptions” because they fall below the arbitrary 500 km³, eruptions that may actually have been far more devastating than some that made the grade. If you select area affected, you end up with eruptions such as Laki that have devastating regional effect, yet don’t fit our idea of what constitutes a “supereruption”.

      • A bit more context for Tolbachik. Grumpybear mentioned that the flow rate is 400 m³/s.

        Looking at Laki’s entire event, it’s 15km³ over 742 days works out to about 234 m³/s. But you have to remember, that most of that 15km³ probably happened over a much shorter time.

        The spray height of the magma from Tolbachik is comparable to that reported from Laki… 800 to 1000 meters in height.

        • Should Tolbachik continue for another 23 months, the big difference would be what is/was being spewed. Tolbachik seems, thankfully, to be free of the flourine ejected by Laki.

        • I guess it is pretty conservative to assume 10km3 over the first 3 weeks. That is 5511 m3/s (Laki first 3 weeks). Roughly twice compared to 0.7 cu km3 released in 3 days of Grimsvotn 2011 eruption.

          But probably, in Laki, there was a much larger initial release rate in the first few days. Its a totally different scale of eruption

          • GeoL: Carbonyl Sulfide, is that produced during the eruption or later, when it reaches the high atmosphere?

            I wonder if the amount of Carbonyl Sulfide is related or not to sulphur gases (hydrogen sulphite and SO2)

          • Carbon disulfide – CS2, Carbonyl sulfide – COS, Carbon dioxide – CO2, Sulfur dioxide – SO2, Hydrogen sulfide – H2S, Water – H2O

            Are just a few of the gases that are involved in volcanoes.

            CO2, H2O, SO2 are the lions share, and based on what I can find so far, COS will come in around 0.2% of what the SO2 tonnage turns out to be.

            That’s not a lot.

            But noting that the conversion SO2 leaves you with about 0.001 percent remaining after 400 days, even with a 5000 Mt release, that (roughly estimated) 10 Mt load of COS will be around for about 7.1 to 11.6 years before it is all gone. That’s 6.5 to 10.5 times longer than the SO2 stay time.

            In a nutshell, if the volcano doesn’t punch the tropopause during it’s eruption, the SO2 remains as mainly a tropospheric phenomena, any haze that is produced (sulfate) will get sedimented out pretty rapidly as the clouds and rain and turbulence interact with it.

            Sulfate in the stratosphere… that’s where the screening takes place… the air is not as turbulent and the sedimentation of sulfate takes up to about 1500 days before you are down to 0.01 percent of the sulfate produced from a 5000 Mt injection.

            Most of the COS in the atmosphere, gets to the stratosphere via the tropical Hadley cells. The brunt of it is anthropogenic, but oceans, marshes, swamps produce it. And natch, some volcanoes.

            Where the volcanic component of it gets important, is when you get a humongous “once in a forever” eruption that heavily loads the atmosphere. SO2 that doesn’t reach the stratosphere? It will be gone quick enough to not be much of a factor. The COS however, even if it is 0.2% of the SO2 level, has 7.1 to 11.6 years of residence time, and amply opportunity to get there via the Hadley cell circulation.

            Some things to think about.

            Since Flood Basalt events can be large emitters of gas, more so that strombolian or subplinian eruptions, is there a cooling signal that takes a bit longer to show up than with the plinian and ultraplinian erupitons? VEI-3 can reach the tropopause, but barely. VEI-4 can punch it… but not well. VEI-5 and 6 are solid stratosphere reaching events. Did the winters following Laki or Eldga get worse two to four years later? I don’t have the resources to check that… and there are some authors that claim that there was no effect. I wonder how this sits with that.

            A not so well known circulation occurs in the stratosphere. (not well known to the general public) It’s call the QBO (Quasi-biennial oscillation)

            It’s a zonal flow (meaning east to west or west to east) that changes with altitude in the stratosphere over a period of 28 to 29 months. How does that sit with the SO2 / COS → Sulfate rate of production and subsequent sedimentation?

            Well… other than a few graphics, I’ve pretty much let the cat out of the bag with regards to Ruminarian V.

            Cat out of the bag? That’s why you check it before you buy pig in a poke.

          • According to this paper COS has an atmospheric lifetime of 2.5 years, mainly due to rapid uptake by vegetation, seen by seasonal variations.

            It is produced in volcanic fumaroles from CO and elemental sulfur or CO2 and H2S
            (Carbon disulfide, carbonyl sulfide: literature review and environmental assessment. Peyton, Steele and Mabey 1976. Available on Google Books)
            and is positively correlated with the emission temperature of the volcanic gases.

            You can access the Geophysical Research Letter papers by login in without username and password.

          • Yay! Dueling papers… 😀

            “A Three Dimensional Global Model Study of Carbonyl Sulfide in the Troposphere and
            the Lower Stratosphere” Kjellström (1998) places the turnover time at 7.1 years for the Northern Hemisphere, 11.6 for the Southern Hemisphere, and 8.9 years globally.


            By “turnover time,” I think they mean that that is how long it takes for a quantity to leave the biosphere once emitted.

          • Junge Layer, also known as “The Stratospheric Aerosol Layer” (I guess some of them don’t like Junge) is where the majority of Earths stratospheric sulfate is at.

            I’m still working on nailing down where this thing lives at, but background OCS is one of the major contributors to it.

            My thoughts about OCS, have to do with the large scale monster gas releases that accompany Flood Basalts, or that weird huge SO2 plume that happened two weeks after Grimsvotn erupted.

            What concentration of it could have been OCS, and how did that affect the stratospheric load.

            One thing I don’t have, is a conversion rate to sulfate for OCS. Your paper link may help with that.

            Thank You!

          • Atmospheric lifetime or turnover tau is the ratio of the total amount of a molecule to the removal amount (+deposition +chemical loss). If supply seizes, after tau years the total amount is reduced by 50%.

            Duelling papers is fun! With rising complexity of the matter it becomes increasingly ridiculously easy to find a supportive report 😉 (at least my experience from the life sciences)

          • Yer drafted.

            What is the proper definition of turnover time?

            How can I find or determine the e-fold rate, or any form of decay rate from it?

            Inquiring minds want to know…

          • You are right, something is weird and missing in my formula. But it was too late yesterday to think I guess. These are the sites where I digged it out from yesterday:

   leading to this:
   (naming it T, time)

            And the “Atmospheric lifetime” section (which is referencing Jacob, Daniel (1999). Introduction to atmospheric chemistry.) calls it tau (time constant). There is a link to the pdf.


          • Ahh, there the problem. Skeptical Science and the IPCC site.

            Skeptical Science is not skeptical, and their science usually doesn’t even agree with itself.

            “I’m not a climatologist or a scientist but a self employed cartoonist…”

            – John Cook, Skeptical Science


            As for the IPCC, they have a major problem with their models not agreeing with empirical data. In part, it is due to them not adhering to their own criteria for data and information sources. It will be interesting to see what gets edited out of the leaked draft of AR5 when the final report is released. Much of the thing is couched in caveats and vague wording to the point that even if the equator freezes solid it could still be covered as a plausible argument for global warming.

            When you start dealing with gases in the atmosphere, it is difficult to find source material that is not tainted from some rabid psuedo-religious anti-human ideology. That realm tends to stray from actual science.

          • Well, taking a linear fit to the decay, and then locating the 1/e point is strait forward… but most (if not all) real world decay rates are logarithmic.

            That means that doing the linear fit is error ridden if not flat out wrong. Natural systems hate a straight line.

            (BTW, I like that link, at least it’s backed by something of some caliber rather than a cartoonist)

  2. People!!!
    Carl and Ursula founded this blog. Not in the sense that people fight each other but in the sense of learning about volcanoes.
    They both left this site.

    • Eh? I made an error, it was pointed out. I corrected it. Fight? Only with the metric system…

      ( 1 x 10^9 m³ per km³ )

      As for Oliver St John-Mollusc’s missives on the last thread, they clarified what to me was an infuriating topic coupling. The points that he made are well founded and illustrated the intentions of the post.

      I have an issue with petty dictators, not with the people here.

    • I’m here and reading, but no time for posting or dragoning, sorry. Just overwhelmed by current events, but hopefully it will not be long before things return to somewhat normal…
      Happy Holidays to everyone!
      Not sure what happened to Carl though – I tried to reach him a while ago through both emails that I have and no reply. 😦

      • Happy holidays 🙂

        Sissel said Carl had been very busy and also unwell (pneumonia ?). Hopefully, he will be back in circulation again.

          • Oh, that is good news, I was really starting to worry about Carl.
            As for me, it’s a combination of a deadly semester (worst I’ve ever had) plus problems with parents’ health, so all this didn’t leave much mental space for anything else lately. I’m hoping next semester will be easier, if nothing else, because I’ve more or less learnt how things work (and hoping I didn’t just jinx myself :-P).

          • And I was starting to worry about you too Ursula and very much so about Carl as well.
            Great to hear you are OK Ursula even if very busy (I know the feeling of busy, as a carer for three family members with depression and anxiety problems sometimes even my housework has to be left for a while,) and I am so happy to learn Carl is still in touch with somebody. All my best wishes to everyone on here who is struggling with any bad problems at the moment. Let’s hope next year is a better one for everyone and another brilliant one for the volcano cafe.

    • Any reason why they left? & is it for good? – if yes, sad to see friends leave; but, if no, look forward to seeing them again.

  3. Large eruptions from arcs like the New Hebrides are interesting because they are highly likely to become hydromagmatic eruptions similar to Santorini, Krakatoa, or other huge water-infused eruptions.

    I believe there are several massive submerged caldera systems in the hebrides similar to how there are several massive submerged caldera systems in the Kermadecs (worth reading about if you’re looking for more obscure and lesser known caldera systems).

    To me, a “supervolcano” is anything that can erupt a decent sized VEI 7 event. If we’re going by apocalyptic style Toba-Eruptions, then it’s probably true, that there are only a select few volcanoes that can even dream of putting out an eruption of that size, but by normal standards of what would be super devastating, mid to high vei 7 events would be catastrophic beyond belief if there is any reasonable population nearby.

    So as a result, I typically classify caldera systems that are roughly larger than 12×12 (or 10×15, 11×14 etc) to be “super”. That puts Campi Flegrei and Santorini on the very low end of “super”.

      • Again, Laki had a far more devastating impact on human history as the poisoning of crops contributed to the collapse of the French economy which in turn led to the French Revolution (etc). While no one would consider a VEI 6 eruption a supereruption, imagine one at, say, Nisyros that results in a 50-foot (15 m) tsunami across the Eastern Mediterranean basin. Not a supereruption per definition, but the consequences would be far more dire than a caldera-forming VEI 7+ in the Andes. Just where do we draw the line?

        • Not only France, the UK and other European countries were badly affected by Laki in addition to Iceland.

          From Francis and Oppenheimer’s “Volcanoes” (2nd edition), Lake generated over an 8 month period: 14km^3 of basaltic lava; some tephra; 60 Mt of sulphur (120 Mt of SO2), which generated 200 Mt of acid aerosol; 7 Mt HCl; and, 15 Mt HF. Observations of the volcanic cloud at various points in Iceland indicate that the cloud may have reached the stratosphere.

    • And the calderas of Bárdarbunga and Katla (which roughly have that size). But -so far- they have never been showed to produce anything larger than a mid VEI6.

  4. “Opening to the sea”

    Yeah, that would be bad. We have Santorini as a fine example of what could happen in a worst case scenario.

    In the last thread, Rabaul figured prominently in the topic. It is a fitting example of one of the many nastys that lurk out that but were overlooked at the onset of the Decade Volcano program. I noted that Rabaul is actually a nested system with a few neighbors.

    And just a short jaunt away… as the albatross flies, (295 km), Garove and Dakatura.

    Both volcanic systems… both open to the sea.

    Yee Haw. They’re everywhere, They’re everywhere….

    • …and we do need to know more about them! While I’d expect a country such as Italy to investigate an monitor the dozen or so areas where calderae have formed, there’s no way that Papau New Guinea or Vanuatu could do the same. This, IMHO, is where the international effort should be directed. I like Karen’s idea about a mobile response team, but first there would have to be a minimum of monitoring installed to alert such a team.

      • I think the USGS may have a psuedo team like that. I know that they have, on occasion, sent people to systems that were getting restless. Donno about their scope though.

        IGNs temp stations have helped conciderably, with El Hierro, and have enen stepped in to provide coverage when station CHIE was eaten by a lizard.

      • Haraldur Sigurdsson – who was everywhere, it seems – visited New Guinea last year. And he tells on his own blog, that there are just 5 geologists working in a country with around 60 active volcanoes and a very limited financial budget. (“Yfirvöld í Papaua Nýju Gíneu reka eldfjallastöð í Rabaul, og starfa þar fimm jarðvísindamenn, (…). En þeir bera ábyrgð á eftirliti með öllum virkum eldfjöllum landsins (um 60 að tölu), og hafa því miður mjög takmarkaðan fjárhag til sinna starfa.” )

      • That’s why I want to write a book about volcanoes in the south pacific. I mean, look at all these large caldera systems with almost no information about them for the general public!

        Rescued by Schteve

    • Wow! They are really a lot of these “opened to the sea” calderas. Examples of the worst case scenario.

      It seems most are subduction region volcanoes, that probably started undersea, and they eventually went a large caldera event caused by water flowing inside the magma chamber. Just like Krakatoa.

      But the largest calderas of all seem to be inland and sometimes also not related to subduction. Toba, Yellowstone, etc…

      • Krakatau was also so enormous because of a strange kind of magma mixing (basalt and granite): An interpretation of the 1883 cataclysmic eruption of Krakatau from geochemical studies on the partial melting of granite, by Noboru Oba Dr., etal. (1992, abstract)

      • Actually, most of the “largest of all” calderas ARE related to subduction. What most people are unaware of, is that Yellowstone is the redheaded stepchild in that it ISNT related to subduction. That’s part of what makes Yellowstone so interesting to me.

        Toba, Altiplano Puna Complex, Taupo Volcanic Zone, Kyushu Caldera Systems (aira, ata, kikai, aso), Kurile Lake Caldera zone, along with a few other massive caldera systems all sit within Subduction arcs. I’m not entirely sure, but I do believe there is a relationship between extensional faulting near subduction zones and the creation of large rhyolitic caldera systems (aka supervolcanoes).

        • Be interesting to know more of the history of Yellowstone. Perhaps there was a subduction zone there many millions of years ago. Having found a least two (currently inactive) in the UK while researching Snowdon’s lively past, I would not rule out one out for Yellowstone, even if it is now inactive.

        • There are some that believe Yellowstone is slab gap volcanism related to Farallon plate remnants sinking from west to east after the Laramide orogeny.

          • Sort of. The Farallon was sliced in two as it slid by.

            There is a section of what seems to be dangling crust off to the west… roughly in the vicinity of the SE end of the OWL but south of the Wrangellia Terrane.

            And if you really want a mind bender… The Pacific NorthWest was constructed by the subduction and demise of the Intermontane Plate, the scraping off of a volcanic island arc, then the subduction of the Insular plate, the scraping of of another volcanic island arc, then the subduction of the Farallon plate.

            Those island arcs and a collection of other terrane and super terranes… all (if I got it right) components of the Wrangellia Terrane… If i’m wrong, then the Wrangellia was just another collection of volcanic islands that were splattered into the North American plate like the Insular and Intermontane before it.

            You can get lost reading this… but I highly recommend it.


            BTW…after all that island scraping… the Farallon took it’s final plunge, was sliced in two, and the Columbia flood basalts formed (starting about 21 mya). And they flowed on top of the previous Crescent Basalts (about 50 to 57 mya) that flowed into the Columbia embayment.

            I give that link three thumbs up for knowledge.

            In fact, I’m gonna link it again it’s so good.


    • Psst… check this out…

      From that same site… this:

      Notice anything peculiar about the alignment of the “active margin / subduction zone” with relation to modern day odd-ball lineaments that don’t have a ready explanation?

      Also remember, the San Andreas is an active strike-slip that denotes the location of where the subduction line was when that zone stopped (and the Farallon slipped away…)

      Perhaps the OWL is just a “no longer active” strike slip of a similar construct.

      • I said that a few posts back in my “best guess” as to what the OWL actually is. By its nature, it resembles a strike-slip fault, but there are other anomalies associated with it, namely the fact that it is present on land masses that are both thousands of years old as well as hundreds of thousands of years old. The time-frame of the lineament doesn’t quite add up.

        To me, the American west coast is as big of a geologic mystery as there is. Yes, there is a lot of known facts as to what has or hasn’t happened, but we still don’t REALLY know the true nature of Yellowstone, we still aren’t positive why the farralon plate subducted at such a shallow rate, and we still don’t know the whole history of the tertiary ignimbrite flare up. Add in other anomalies such as Long Valley Caldera, the Rio Grande Rift zone, the OWL, and other random oddities, and it’s a simple, yet very strange area of the world that has a lot of oddities that seem to be related to the farralon plate’s subduction.

  5. Glad to see you back Ursula. Hope things will get sorted out for you to the best.

    Lurking, I like your last plot a lot.

    I repost my latest video of El Hierro which is a summary of all events since July 2011 day by day as it was the last post on the previous topic.

    On YT there is also a fast version which shows also some things….The quakes move are quite sudden in fact.

    Most interesting part are @ around 13′ (swarm), 19-20′ (eruption day), 30-34 (new deep swarm), 1’29 (shape), 1’37 and 1’57 (new activity).

    • dfm says:
      December 27, 2012 at 20:44

      Lurking, I like your last plot a lot.

      Which one? Christmas tree plot, the people plot, the volcano profile plot, or the caldera plot?

    • I’m an idiot. You’re talking about the surface for the Benioff zone quakes.

      I pulled the USGS data for the area, all quakes back to 1973. Sliced off the top 50 km of quakes and plotted what was left. Then I fit a poly surface to it, regridded to 200 x 200 without extending it outside of the data point area. Shifted it to a scatter plot, took a screencap and georeferenced it into Google Earth, second screen cap, sized it and uploaded.

      I bumped up the size of the points in order to make them stand out.

  6. I think in the next few weeks, I’m going to start a project to make a custom google earth overlay that highlights known caldera systems, and outlines them as such in the google earth display. I’ll have to learn how to do it, but it doesnt seem like it would be all that difficult, and I would think it would be entertaining enough to learn anyway.

    • My method is to find a research paper with a caldera system diagram in it.

      Screen cap it, then trim off what I don’t need.

      Import it into Google Earth as an overlay, then referencing it. (rivers, roads, coastlines, towns, lat and lon if it’s on the graphic.

      Add a polyshape or poly line for the caldera extents.

      I’ve been working on this for about two months as I find them. I need to get them organized.

      Once you have the caldera shapes into a folder, you can save that as a kmz or kml file.

      I don’t think WordPress supports them, or else I would share what I have. A really decent version would include references to the source documentation… at the very least a citation.

  7. Hi All, I hope you all had a really nice Christmas..My husband who has been working all Christmas asked me to accompany him today to visit his family in the North of Tenerife and to put some flowers on his mothers grave…I have made that trip so many times, we have to drive up through the mountains from the South of Tenerife to the North, and to be quite honest all the curves in the road usually makes me feel quite queasy..but today was significantly different for me..the whole time..all I could think about was you Volcanoholics.and how you might appreciate this regular trip that I do a lot more than me and wished I had taken my camera so that I could show you some amazing scenery…..I was trying to look at the scenery with your eyes, thinking how you could all probably identify each and every lava type so easily.. but one thing that struck me was (and I have seen it hundreds of times before) how huge the lava flows are, we were driving on the road that has been cut out in the middle of these old lava flows.. and it really made me realise what a huge and devastating effect that the previous erruptions in Tenerife have had on this small makes me appreciate that even if the “decade” volcano programme is not “perfect” at least we are on the list…

    • Welcome back. 🙂

      Here the Christmas was nice, joyful, social, but totally snowless. There is a big lack of snow in south Iceland, while the north is having piles of it!

      And also we are feeling very much the winter blues…. little daylight, mostly not so much to be done, not even the common act of shoveling snow (eheh), and only we, people, to support each other in this mellow times.

      • Hi Irpsit, here in the south of Tenerife, Christmas was a hot and sunny one. but I am sad to say that the sunny weather does not bring about any of the common acts you are missing this year…I suppose we could try shovelling sand..but not quite the same..usually at this time of year there is at least snow on Teide, but not this far..when there is snow on Teide, the locals go mad and all take a trip up there to just put their footprints on the snow and to throw the odd snowball at each other, the only problem with that is that due to the altitude at Teide, the snow is not soft and fluffy, it is hardened like ice, so that the snowballs could quite easily knock you out!

    • How nice that you were thinking of us all Debbie, Iceland no snow, England too much rain, it has been a strange year so I for one am really looking forward to a new start again in a few days time. 2013, the year the doom-sayers said we wouldn’t see. ROFL

      • As I was typing this morning… I heard a tell tale metallic “crunch” and then the squeal of tires. I put on a coat went outside and looked up and down the road, but saw nothing.

        I don’t know why I went to go look. I guess in order to make sure it was no one that I knew… and secondly, in a previous past-time I was a Volunteer Firefighter… with extrication experience. Not that I could have done anything to assist. The one thing that came to mind was how much I hate holidays. Well… not the holidays itself, but some aspects of them. A few people will not make it to 2013. You can rest assured of that. That’s the part about holidays that I don’t like.. and one reason I stopped doing the fire-fighter thing.

        Everybody stay safe, okay?

        • I often wonder if statistically more people are killed in car accidents than were killed in horse and carriage accidents. Sadly the holidays seem to encourage too many people to drink and mix that with driving. Add in a generous dollop of bad weather in the Northern hemisphere and it is a recipe for disaster.

        • I think that motor vehicles would be statistically higher. At least with the Horse, you had a designated driver (of sorts) who wouldn’t intentionally harm themselves unless spooked.

          The greatest hazards would be getting scraped off on a limb or falling off of it while drunk.

          Though you don’t have to be drunk to fall off of a donkey. I was laid up for two days due to a back injury playing donkey basketball when I was a teenager.

          • Coming from a Ranching back ground I think you are right Lurk. However the chances
            Broken bones is probably higher along with spinal cord injuries. Personally I prefer
            riding Mules in rough country, Less likely to spook or, a good Morgan -something
            with some smarts and sense. My Pop always liked Thoroughbred/Quarterhorse
            cross and paid for it sometimes like walking 6 miles back to Cow Camp in Cowboy boots..Couldn’t beat the cross for good cutting horses …

  8. Seems to me that the definition of “super” is completely subjective. 10m3 would be fairly “super” if it was in my lounge room 🙂

    IMHO the whole “supervolcano” thing has been blown right out of proportion by the media (invented by BBC wasn’t it?). A very large eruption can have minimal impact if it is in the “right” place, whereas even a modest eruption could be catastrophic in the “wrong” place (say downtown Auckland, or in the suburbs of Naples).

    As to tagging eruptions as “super” based on some threshold on the kind of subjective & useless VEI scale, I say phooey! (Was it Carl who said that the VEI is “completely horked”?)

    (Aside – is there a guide to posting features somewhere? Couldn’t figure out how to do a superscript “3” above. Apologies if I’ve overlooked it.)

  9. OT: But I have to leave for Nebraska tomorrow to see my grandma for one last time. The doctor’s are only giving her 2 to 3 days to live.

  10. Wow, Tolbachik is really cranking now, and looks to me to be consolidating on a single vent. Possibly we are entering a more explosive phase now?

      • Thanks from me too. Very impressive! 🙂

        BTW: I took a screenshot from the webcam. Seems to me that there are still at least two vents active at Tolbachik.

    • Just awesome. Thank you very much Johan! Make sure you click on the ultra high resolution version, which is the small inset on the lower right (just to the left of the orange helicopter inset). The definition in the view of the crater is just stunning.

          • Yes, but…

            a) the old magma chamber responsible for the caldera-forming eruption was destroyed by that eruption
            b) the current magma reservoir is described as a “sill” (flat, lenticular shape) measuring 7.5 by 5.5 km
            c) the current rate of inflation, 30 cm per year, corresponds to an annual influx of 60 cm or – at the very greatest if evenly spread across the entire sill – 0.0162 km^3 (1 cu km per 60 years if sustained)

            Unless there’s a “premature”, stratovolcano forming period, it will take the magma sill thousands if not tens of thousands of years to evolve to the stage where a caldera-forming eruption is likely.

            Still, it is interesting!

          • In response to Oliver, wouldn’t that be only true if the influx & uplift were starting just now? If we’re assuming that the only inflation Laguna del Maule has undergone is since 2007, then yeah, we would need to wait a long time. However, there is no saying that this system hasn’t already inflated a ton in the past, and is just going through another period of magma influx.

          • Cbus, it says “sill” which rather rules out it having inflated for the very long time required to be anywhere near a caldera-forming eruption. As you see here, a sill is a very thin “wafer” of magma between layers of rock. At the size given in the article, 5.5 by 7.5 km (two-dimensional), it would take an average thickness of approximately 35 meters (3rd dimension) for every cubic km, thus even if 1000 m thick (i.e. 5.5 x 7.5 x 1 km) it would only contain some 28 km^3 of magma.

            Before there can be a caldera-forming eruption, the sill will have to go through a long period of gestation before it has built a large enough magma chamber and more likely than not, there will be a period of eruptions that build a stratovolcano before the roof is again strong enough to contain such a growth. Even so, the next caldera-forming eruption will most likely be smaller because of the fragmented state of the rocks filling the present caldera.

          • Oh, even at the present high rate of influx it would have taken a sill ~500 m thick about a thousand years to form so yes, the growth began long before 2007.

            Your best bet for a very large eruption would still be Iótó (Iwo-Jima) which has been growing at a rate of 25 cm/a for at least 700 years with a guesstimated total inflation on the order of 150 – 200 meters.

          • Ah, thanks Oliver, that provides some context which I was missing. GVP is silent on when the caldera forming eruption may have occurred, noting only that the more recent cinder cones are Pleistocene. As you say, the amount of magma involved is unlikely to do anything huge. However, with that rate of inflation it appears the area is ripe for a resumption of eruptions, even if it is only a small cinder cone forming event.

            When I first read the article I incorrect inferred that it was a candidate for another huge eruption, like I have also seen claimed for Uturuncu. Still, I wouldn’t be surprised if the next VEI 6+ comes from some obscure locale that is just a footnote in a textbook somewhere, if recognized at all.

          • And if you want to read about the area in more detail…


            Some of the non-paywalled stuff from that search term:

            Petrogenesis of the Laguna del Maule volcanic complex, Chile (36° S)” Frey et al (1984)

            Plio-pleistocene volcanism in the Andean Cordillera of Central Chile (33° – 40° S. L.)” Davidson et al (1988)

            Andesites and high-alumina basalts from the central-south Chile high Andes: Geochemical evidence bearing on their petrogenesis” Lopez-Escobar et al (1977)

            Metamorphic facies series of the crystalline basement of Chile” González-Bonorino et al (1970)

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