26 comments on “A Spare Volcano in the Desert – OLLAGÜE (CL)

  1. More absolutely fantastic armchair reading Graniya! Hope you guys one day get the recognition you deserve!
    Speaking of the Andes there was a wonderful photo of Quilotoa in the Guardian yesterday:
    https://www.theguardian.com/travel/2017/dec/07/andes-mountains-south-america-readers-tips

    Another very productive little volcano I know little about.

    And while we are at it. I sure as hell hope they have dialled up the reading on the TMKS seismogram at Agung. It is looking positive frightening at the moment with another intrusion on the way by the look of it. I wonder what depth it has got to?

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  2. The recent photo via Marc Szeglat’s blog is fascinating.
    http://www.vulkane.net/blogmobil/
    Many thanks to the guy who took it, who was aware of the risks (we are told – he wouldn’t be the first volcanologist to risk their life for this kind of thing).
    I guess the risk is similar to a snail crossing a highway with medium traffic. It is certain that a car or truck is going to come down the road sooner or later. If it does, you don’t have a snowflake’s chance in hell of getting out of the way, so you will be a goner. If you are lucky though, you can get to the other side unscathed. This guy was lucky and knew the risk he was taking. I don’t have any trouble with that but I do worry about idiots who don’t know what they are doing trying to emulate him and getting killed.

    Back to the photo:
    We see two things that seem contradictory: A flat lava dome, implying fluid lava, made up of ʻaʻā lava in concentric rings but, secondly, there is an open vent in the middle.
    How on earth can we make sense of this? The flatness and concentric rings indicate low viscosity which suggests the lava was hot and/or mafic enough to remain flat instead of doming, and it looks like it was effused in pulses of molten mass, which explains the rings. But, despite the low viscosity, it must have solidified enough so as not to run back into the crater mouth when the pressure dropped and thereby plug it. Further, the lava must have been cool enough for the surface to solidify and get broken up as the lava continued its forward creep, creating the ʻaʻā look. Moreover, there are no signs of blocks or bombs in the lava field, at least no big ones, suggesting that the eruption is purely effusive at this stage. Quite possibly the pulses that created the concentric rings correlate with the pulses of strong tremor we saw. If I recall correctly, these did not have any correlating gas/ash cloud, which makes sense. The subsequent puffing is reminiscent of Stromboli and I imagine it is due to vent blockage and regular clearance from small blasts of gas.

    It is quite fascinating. Obviously this lava has a low gas content, which suggests this is still older lava left behind after the 1963 eruption. Moreover it must be cool enough to create an ʻaʻā field yet not so viscous to create a steep dome, suggesting it is more on the mafic side of things rather than felsic.

    Always amazes me the vast range of forms that volcanos are capable of.

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    • Hi, Bruce, many thanks for posting the link, I’m following Marc on Twitter but it seems he doesn’t tweet his new posts.

      As to the dome, hm, here’s my take: The lava certainly was quite liquid, but, as it had nowhere to flow after reaching the crater walls, it was pushed up. That alone would explain the concentric ridges, every batch would make a new ridge, regardless of what we see on the seismogram, or so I think. The surface of lava cools very quickly, so the relatively small pieces we see must be broken bits of the relatively thin solidified skin. I don’t know about lava flowing back in, perhaps, when it has lost a few hundred °C, it has become too viscous to do so? Anyway, I would like to know what rock it is, the last in 1993 was andesite, which is more viscous than basalt. How would you know it has low gas content? Satellite images show a fairly big SO2 cloud over Agung. I hope he who took the photo took some hundred more and a few samples as well! 🙂

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      • Hi Graniya, yep, the shape is very reminiscent of Shinmoedake, which had some very explosive burps as I remember as the pancake dome cooled and plugged the vent. So you are right, the shape of this dome does not preclude the presence of gas. But I think this lava is low in gas because there is no sign of any explosive activity (assuming the first ashy phase was phreatic from groundwater interaction). Of course it might simply be that the magma is of such low viscosity that the gas escapes before fragmenting the lava but somehow I doubt it. Rather, I think there is not much gas in this batch. The initial SO2 cloud was most likely from a volume of gas that had gathered in the upper reaches of the volcano over time, i.e. during the magma intrusion and was released in one go during the initial throat-clearing stage, rather than being an indication of the gas content of the magma that is currently getting extruded. If 1963 is anything to go by, the really gassy stuff is still on the way.

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        • PS.. I agree with you on the concentric rings being the product of batches / pulses of sticky magma getting injected into an enclosed space (the crater walls) and the ʻaʻā field being from the surface cooling and then moved incrementally by fluid flow underneath it. What is puzzling is why there seems to be a vent in the middle. If the lava is that fluid, why hasn’t it flowed back to cover the vent?

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        • The most simple reason might be that there has grown a small spatter/cinder cone around the vent, preventing the lava running back in. Or that the whole “cow pad” is slightly cone shaped – it’s hard to see on the images.

          My pet idea is that quite strong effusions continued all the time over the “quiet” period, so perhaps no time for clogging up. I was really amazed when reports came in, around 7/8 Dec., that the crater should be something like half full already, when there was “nothing happening” for 8 days since Nov. 28/29. Mirova shows thermal anomalies on 1+3+5 Dec., Suomi NPP on 4+5 Dec. The rest may have been obscured by clouds. Also, a distinct cloud of SO2 was tweetet on 4 Dec., I guess strong degassing has been going on all the time.

          MIROVA, btw., has stopped updating Agung on Dec. 6.

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  3. It’s so sad that most countries keep their volcanoes under cover like a holy grail, making people guess, speculate and risk lives.

    Dr. Behncke said in reply to Marc Sz. on Twitter: “there is no point in publishing EVERYTHING, especially in a volcanic crisis situation. That is NOT important for those at risk, they just want to be safe, but it can also lead to a lot of false interpretations from people who don’t correctly understand the data.”

    This, of course raises the old question in me again: Why then do countries like Iceland and Japan fare so much better by publishing everything, if there’s no point in doing so? We rarely hear of any hoaxes, cries of doom or panic from those countries. Just look at the amount of fake Agung videos on YT! They would not have so many believers if there had been updates with good drone or satellite footage.

    I really condemn the adventurous photographer for risking the lives of an entire SAR team in the case of an accident, because he must have backed up his trip somehow. But, sure, it must have been the chance of his life to be The First to take those shots, and I can understand that, too. If there had been satellite images as clear as the ones from Planet Lab (link below), there would have been no reason for risky adventures in the first place.

    https://medium.com/planet-stories/21st-century-landscapes-7799a3680d0b

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    • Comments by volcanologists:

      MC: “This plug may explain the intermittent Vulcanian explosions observed as exsolved gases try to escape.”
      GW: “Shows incandescent central vent within lava pond covering base of crater. Consistent with persistent night-time summit glows. Also ash distribution mainly on southern flanks.”
      GW: “Yes [images] are of the lava pond in Agung’s crater (not a dome).”
      (Other person: “Asked and was told by Willow, a volcanologist based at Amed Bali, it’s a lava dome in Agung crater rather than a lava pond.”)
      GW: “Lava domes are typically convex, or hemispheric, due to high viscosity of the magma, such as dacite or rhyolite. Magmas which are less viscous, such as basalt or basaltic andesite, spread easily and form relatively flat pools or ponds. The crater lava looks flat to me.”
      (Other person: “Just passing on what was told to me by the volcanologist based at Amed.”)

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  4. Hey Bruce, you were right with this:
    “The volcanic ashes released today is generated from the old magma five to 10 kilometers beneath the crater”; also: “deformation is still occurring on the volcano”. (Gede Swantika, today on AntaraNews)

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  5. Cool, puzzle solved. There is no open central vent and we are looking at a pancake dome or sticky (basaltic/andesitic) lava lake, whatever terminology takes your preference. Those new pictures tell a fantastic tale. Look at that central vent area before it erupts. You can even see a block that looks almost like a lava spine. I bet this bit glows red at night (and the rest of it a dull red (because of the cooled crust on it). So the vent is open and the volcano can degas relatively easily (which it is doing in steady puffs). The big question is IF new gassy magma will make it to the surface, and if so, how much. Obviously it is still on the move. It could lack the buoyancy to push out this old gas-depleted magma first and the eruption will stall. I wouldn’t be surprised if that is what happens. It could however also follow the pattern of 1963. I’d love to know if the quakes registering on the seismogram are deep quakes or just the occasional blast from the crater..

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    • PS: by open central vent in the first sentence, I mean an open crater like the very first photo we saw suggested.. Of course the vent as such is open, the lava lake is an expression of it!

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    • very interesting! I wonder when that caldera formed. 5 km diameter is pretty sizeable. Sounds a bit like McCauley Island further south in the Kermadecs.

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      • Maybe you’d like to look a bit into that matter and make a teeny-weeny post about it? (Not that I’m waving a lamp-post… would I ever?)

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  6. New drone video today of G. Agung. Yes, it is a lava dome, with an elevated center. And the material could be andesite (says Erik K.).

    Turn your volume down! 🙂

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    • Very nice, thank you dfm! Quite a large dike! And, if the yellow dots were in a more contrasting colour, one could clearly see how the quakes concentrate along, and outline, the caldera rim towards the end. So, perhaps the cauldron isn’t just from drained meltwater but from the caldera floor subsiding? If so, would that mean, lava has been ejected somewhere underneath – or did the floor cave in just because of the pressure release through the ring fault? Who knows… not even the scientists would agree on one interpretation, sigh. It has beeen said, yesterday?, that seismic activity is declining now…

      That second activity center to the left (WNW), is it just stress related earthquakes or another intrusion? As far as I can see there isn’t a volcano in that area. But then, you never know with the rift, I suppose a new one could spring up in any place.

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  7. Thank you for your constructing comments. I agree with you about the colors, I still have some (many) things to get better. I’ll try some plot also for Bardarbunga maybe.

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