30 comments on “Unzen Conduit Drilling Project

  1. Thanks agimarc, this is so interesting! So, it shows that magma in those near-surface conduits cools much faster than expected, making it *not ready* to erupt with the next upwelling of heat from below. > Means that the next eruption initiated in the mantle has to create its own path up through new conduits, or re-using and re-melting the older stuff as in a completely new eruption. > For a setting like Unzen this would implicate that fresh magma always comes up very fast from greater depth.

    Q 1: How does that reconcile with the volcano being dacitic? Dacite is an evolved, more felsic magma. I understand such magma should have a history of long stop-and-go periods on its way up to evolve from basaltic to dacitic. Does that not imply magma chambers near the surface for repose times?

    Q 2: Re fast cooling near the surface: Does that mean that volcanoes with very shallow magma reservoirs (at 2-3 km depth) are NOT more prone to quicker eruption than other volcanoes with their chambers at, say, 20 km depth? As the mush in a very low chamber can not stay hot enough to be readily eruptible?


  2. Howdy Granyia –

    Good questions all. Real answer: I don’t know. Second real answer: This project is a single data point.

    Speculation: I think the clue here is the stacked dikes of eruptible material in the conduit. We have come across a couple theories of volcanic reservoirs. The oldest and simplest is the notion of some sort of magma chamber(s) below the vent. This is the one that most people think about and use.

    A new one which source I cannot immediately recall is the action of multiple dikes and sills – hot magma accumulating along multiple planes of weakness in the rock below the vent. This one is a lot more complex and probably has some real holes in it (how do you re-mobilize crystal mush?).

    We’ve seen action of magma moving along dikes at Eyjafjallajokul and Holuhraun. This drilling project discovered dikes stacked like vertical plates in the conduit of Unzen.

    A large dike / sill would allow what we see with an injection of magma; cooling / formation of crystal mush; remobilization of the dike / sill upon the injection of a new slug of magma.

    It makes a certain amount of sense if you look at a volcano as a combination of weak spots in the rock and some quantity of hot magma. The magma is buoyant. It’s upward travel is also pushed by depressurization of it’s volatile content. Combine enough hot magma with weak spots in the overlying layers of rock and you get a volcano or another expression of subsurface heat of some sort. And what are dikes and sills but the interaction of hot magma with weak planes in overlying rock?

    I don’t have this thought out well enough to do much more than head scratching and arm waving. But the more I think about it, the more sense it seems to make, at least until the next shiny object comes along. Best to you and yours. Cheers –


  3. Fascinating stuff Agimarc. This ties in really well with the finding at Chaiten that rhyolite can rise at astonishingly fast rates (guess it is all just a question of requisite pressure coupled with the degassing you refer to). I bet that was also a dike/sheet structure in the conduit allowing such a rapid ascent.
    Here it sounds like they wanted to explore the zone where water, which had already exsolved from the melt, flashes to steam, so I am not sure what this should imply for the melt itself or the deeper magma chamber and its evolution.
    Consequently, they only drilled to 1000 meters under the summit, which might still be far too shallow to tell us much about the chamber. What it did show was that the conduit in the upper edifice cools down faster than previously assumed, at least in this case.

    The fact that shallow chambers / reservoirs of crystal mush exist is proven by the number of calderas around (you don’t get calderas from deep chambers based on the 1:1 chamber width to depth ratio). Secondly, the volume of erupted material also indicates that some of these chambers/zones of crystal mush must but be quite extensive.
    My preferred model is a zone of crystal mush that is near a tipping point reached when the zone depressurises suddenly turning pretty solid mush into fluid eruptive melt, although there are ignimbrites displaying very little zonation which must therefore be sourced from very homogenous chambers of fluid melt, at least that is the way I have understood it so far. I am still pretty low on the learning curve on this one.


    • Gotta correct myself… apparently water only starts to exsolve from rhyolite at about 1000 meter depth (25 MPa) and I guess dacite only a little deeper than that.


      • isn’t it crazy, as soon as you think you know something and put it down in writing, you realise you know so little..
        Anyway, sheeted dykes seems to be the phrase of the week. After reading Erik’s piece on kimberlite pipes, I followed it up on Wikipedia and found this:
        “The morphology of kimberlite pipes, and their classical carrot shape is the result of explosive diatreme volcanism from very deep mantle-derived sources. These volcanic explosions produce vertical columns of rock that rise from deep magma reservoirs. The morphology of kimberlite pipes is varied but includes a sheeted dyke complex of tabular, vertically dipping feeder dykes in the root of the pipe which extends down to the mantle.”
        Now, by my understanding, bubble nucleation (be it CO2 or H2O) only starts when the pressure gets low enough, which is just some 1 to 2 kms depth and not lower, so this cannot be driving the rapid ascent from the depth of the mantle to the zone where bubbles start to form. Buoyancy alone doesn’t explain the speeds involved either. So what is it? Is it just the combination of top pressure forcing a fluid melt to exploit propagating fissures? Am I missing something? The way Erik described it, it sounded as though the magmatic foam started at depth but this is not possible, is it? The Unzen drilling project also found no bubbles in the conduit magmas, implying that the foam is a near-surface phenomenon.


        • need an editing function.. “which is just some 1 to 2 kms depth and NOT lower”..

          Fixed 🙂 -Gr


        • Howdy Bruce –

          The only two things that I know of that can make magma rise are heat (buoyancy) and volatile content flashing to gas somewhere along the way up. There may be others, but right now, today, I only know of two. It is the weakness in the overlying rock that allows the magma to rise. That could be due to previously existing faulting or new faulting due to the rising injection of new magma. Get the magma hot enough, and you melt your way thru to the surface.

          So if the only players (major variables) are heat of the melt, weakness of overlying rock layers, chemical composition (viscosity) of the melt, and volatile content of the melt, how do we get the wide variety of eruptive styles? Better yet, how do you end up with a Kimberlite pipe which to me looks a whole lot like a natural shaped charge.

          I think Erik is on to something that a foamed melt may from time to time happen a lot deeper than we think it can today, all of which leads us directly to figuring out how that can happen. Your comment above makes me wonder if it also happened at Chaiten. Probably would go hand in hand with figuring out what destabilizes a magma chamber.

          It is not outside the realm of possibility that Unzen magmas flashed at different depths with more explosive eruptions being generally deeper flashing. Our job is to figure out why and how.

          Still arm waving and head scratching here. Fun stuff, though. Cheers –


  4. Had some local news reports yesterday about recent earthquakes near Gareloi near the end of the Aleutian Islands. Here is the AVO report from Monday:

    51°47’21” N 178°47’46” W, Summit Elevation 5161 ft (1573 m)
    Current Volcano Alert Level: NORMAL
    Current Aviation Color Code: GREEN

    The magnitude 6.0 earthquake that occurred this morning at 09:00 AKDT (17:00 UTC) near Gareloi volcano was part of an ongoing swarm of shallow earthquakes that has been active between Gareloi and Tanaga Islands since April 30. At this time, the event and ongoing swarm appear to be tectonic in nature, and there is no indication that the earthquakes are related to volcanic activity. Convergence between the down-going and overriding plates produces deformation in the upper plate which results in shallow crustal earthquakes. Aftershocks are also typical of such events. AVO will continue to monitor the volcanoes closely for indications of volcanic activity.

    For more information, see the AEC website: http://earthquake.alaska.edu/


    Cheers –


    • That is a really strange swarm: Since last Wednesday there were 44 quakes, all from M3.1 to M6.4, most of them M4-5. The depths are odd: most of them were at a single-digit depth of 2-10 km, then a few up to 20, two 30, 37 and one 40 km deep. The M6.4 yesterday was 10 km deep. Some of the deepest happened yesterday and today (the last one was 40 km deep) – not at the beginning of the swarm.

      It’s sort of hard to imagine what’s going on there, with the strongest happening in the middle (time-wise) and all the very shallow ones interspersed with deeper ones.

      The last 20 (today and some yesterday)

      All quakes since last wednesday


  5. Eruption warning and raise to alert level 2 issued today for Iwo-yama (Iozan, Mt. Io), NW part of Mt. Kirishima. Continued strong inflation and growing steam plumes had been noted for some time, also thermal areas have increased in size. The rest is lost in translation… but it seems there have been emissions of some sort as it says “…and ejectables have been confirmed in the Iwozan crater.” Further: “The field investigation conducted by the University of Tokyo Earthquake Research Institute on May 8 confirmed the ejecta in the Iwan volcano crater.” The danger zone is 1 km around the crater and a warning for caution has been issued for Ebino City.


    • As in eruptive activity? Anyway it seems strange to have separate alerts for parts of a volcano, at least in this case two areas are on Yellow but the volcano as a whole is on Green/White.


      • Ah, that’s what they mean, ash emissions: “…grayish spewed material was confirmed in the Iwozan crater.” and this: “Ejecta collected in the Iwozan crater on May 9”

        https://tinyurl.com/l4l8xho (.pdf) If I understand the illustrations right, the inflation has been significant, and is still going on.


    • looking at the topology of the cone (short, steep, with a wide flattened crater) this looks like it might be a re-run of Shinmoe Dake


      • I don’t know, Bruce, Iozan is a young lava dome that has grown within the scar of a flank eruption of Karakuni-dake, I always thought it may be a feature of that volcano. GVP has Shinmoedake as a separate volcano of the complex.


        • but it does have a wide flat crater, unlike most domes. I think it probably once hosted the same kind of cow-pat lava that Shinmoe Dake has – something between a dome and a lava lake. This looks relatively fluid for a more felsic lava. What does that indicate? Heat, entrained bubbles or a more mafic melt after all? Shinmoe had some pretty impressive explosions so obviously there is a fair bit of gas involved as opposed to the classic degassed lava dome that gets extruded like toothpaste, usually in the latter stages of an eruption.


      • True, I never noticed it had that cowpad shape too. 😉

        But then, all of Kirishima’s volcanoes erupt the same intermediate lava type, Andesite, fed by a common source at ~6km below the NW part. (Each “volcano” seems to have an own smaller reservoir half way up from there. At least, Shinmoedake has one. When it erupted in 2011 volcanologists were surprised about it’s explosive power, but one professor said that was due to the long repose time. Kirishima had not emitted lava for 300 years. – http://www.nature.com/news/2011/110209/full/news.2011.79.html)


  6. Wow! A before and after of Fuego’s pyroclastic flow path a few days ago:


    • Wow, that is pretty impressive. Makes you realise why these things can induce tsunamis when they hit the ocean.


  7. More detailed report w/ photos on the field survey of Mt. Io of May 9. Two new fumaroles and “fumaroles with roar” have been found coming from big pits. The “ejectables” are said to be a first layer of sand and on top of that comes mud – caused by the expansion of the fumaroles first and then the hot water containing mud sprayed out (called sandy and siltic volcanic ash resp. in the translated report. Japanese rep.: http://www.eri.u-tokyo.ac.jp/2017/05/11/iouyama/).


  8. Something I have never seen on Etna tremor graphs… chugging… Wonder what’ll come of it?


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