48 comments on “The Sacred Mountain – G. AGUNG, Bali (ID) + ACTIVITY UPDATES + Webcams

  1. latest bulletin shows continued high levels of seismicity :

    “On September 27, 2017 at 00:00 WITA to 06:00 WITA, recorded 106 times Shallow Volcanic Earthquake (VB), 165 times In Volcanic Earthquake (VA), 27 times Local Tectonic Earthquake (TL).
    Recommendation: Communities around G. Agung and climbers / visitors / tourists not to be on, do not climb and do not engage in any activity in the danger zone that is within the G. Agung crater area within a radius of 9 km from the top crater of G. Agung and plus sectoral expansion to the North-Northeast, Southeast and South-Southwest for 12 km.”

    I guess that last sentence is an indication they think they eruption might mirror the 1964 eruption.

    I see at some other sites people getting excited about the prospect of a caldera forming eruption. I think that is still highly unlikely for the following reasons.

    Although the region is dotted with large (and recent) calderas there is an absence of flank collapses, which is astounding, given the height of the edifices.

    This suggests to me that the structural components of the volcanoes are relatively firmly welded. At Agung this ties in with the more mafic magmas and despite the explosively (high volatile content) of the magmas, it suggests there are frequent lava flows and probably relatively hot lava flows (particularly if the magmas do not reside in shallow storage very long and are sourced almost directly from the mantle).

    Over time, the shallow chambers will evolve and due to the height of the edifice intrusions will find it increasingly difficult to reach the surface. Volatiles will build up in the shallow storage chambers and due to crystal fractionation, the magmas will get more silica rich.. Only when this phase is reached and the shallow magma storage chamber has reached the requisite size will there be any likelihood of a large caldera forming eruption.

    At Agung it appears the system is relatively open from the mantle source through to the vent so I doubt that the shallow magma chamber is anywhere near being primed for such a large event. The one caveat to this is that I haven’t found any information about the size of the shallow chamber (which is tricky to assess at the best of times)

    Another observation: Although G. Agung is a huge mountain, proto-Batur next to it must have been about one order of magnitude bigger (by volume) in other words, Agung could still grow a lot yet. Moreover, if you consider how many small eruptions it takes for something to grow that big, you can get an idea of the relative likelihoods of a small to moderate (up to VEI 5) eruption to a VEI 7 eruption.
    So my bet (and this is all pretty wild speculation) is for an eruption of between VEI 3 to VEI 5 up to but not exceeding the size of the 1964 eruption.

    and while I am here: hat tip to Mike Ross for his voice of reason.

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    • With so many volcanoes on Bali (3-5), and esp. active Batur near Agung, I thought there might be a number of shallow magma chambers beneath them, perhaps stacked in hight as well. Agung already erupted (more evolved) Andesite in ’63, and researchers think it was intruded during the eruption by basalt. The andesite could have come from a batch in longer repose, and, by pressure release, newer magma from a lower chamber followed up? They expect a smaller eruption this time because they don’t expect further andesite to erupt.

      This paper has been tweeted as open access, but it is not open for me. Got it on sci-hub, though. https://link.springer.com/article/10.1007/s00445-012-0615-z?no-access=true

      Where did Mike say what?

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  2. btw there was a strong and unusual signal at JAGI about 30 min ago (0815 UTC). Not your usual tectonic P/S double cone wave but more spherical. Wonder what that was!

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    • Googled JAGI, found (Korean) for Jagiya: honey, sweetie, love, darling. 😀 So, where is JAGI?

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  3. The Government of Vanuatu has ordered complete evacuation of all (more than 11 000) residents of Ambae island yesterday. Most of them are going to the island of Pentecost, but more possible evac. centers are considered.

    A few bold young people ventured to the summit of Mt Lombenben for a better view of erupting Manaro volcano. They noted that they saw some “fire” and that the second lake (nearere to them) had changed water color. Video by by N. G. Tambeana:

    https://twitter.com/i/videos/tweet/913553878070706176

    Sat. img of Manaro volcano via NASA-worldview today shows constant heat signature again. I wonder if the lake is dry now and if there might be a lava lake?

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  4. Hi Graniya, only just saw your replies above..
    here’s the link to JAGI (seems to be the closest online plot but is unfortunately a long way away from the mountain. I am not sure it will pick up harmonic tremor from that distance):
    http://geofon.gfz-potsdam.de/waveform/liveseis.php?station=JAGI

    Looks like seismicity is increasing this morning (report from Oct. 1 run through giggle):

    “-29 September 2017 recorded 198 times Shallow Volcanic Earthquake (VB), 565 times Inner Volcanic Earthquake (VA), 26 times Local Tectonic Earthquake (TL).

    -30 September 2017 recorded 252 times Shallow Volcanic Earthquake (VB), 542 times Volcanic Earthquake In (VA), 4 times Local Tectonic Earthquake (TL).

    -01 October 2017 (00: 00-06: 00 WITA), recorded 100 times of shallow volcanic earthquake (VB), 180 times of volcanic earthquake (VA), 7 times local tectonic earthquake (TL) and felt 1 times.

    Recommendation:

    Communities around G. Agung and climbers / visitors / travelers to avoid, do not climb and do not engage in any activity in the danger zone of deep within the G. Agung crater within a radius of 9 km from the summit crater of G. Agung and added expansion sectoral to the North-Northeast, Southeast and South-Southwest for 12 km.”

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  5. yippee! a seismogram! no HT yet. But a lot of brittle fracture… ties in nicely with the “pyroclastic veins” that they talked of at Unzen. I get this image of the volcanic gases decomposing the rock in the conduit above the magma column to a point where it is so weak that the magma can make the final push to the surface.. Big question will be how gaseous that first charge will be (the “throat-clearing phase”). Will it be an effusive lava flow or a vulcanian explosion?

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    • I was wondering if those little bursts were the brittle fractures people talked about. Some look like they may have gases pushing through after them?

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      • Hi Clive, that is the precisely the question I have been pondering for years and still have not found any definitive answer: how can you distinguish from a seismic signal if it involves just gas or if it involves the movement of fluid magma? Both harmonic tremor and tornillos are attributed to the movement of “gas or fluid” which implies they could be caused by magma, exsolving gas or geothermal activity. How can you tell the difference? As of the time of writing this, there has been a noticeable uptick in seismic activity at Agung over the last two hours (0300 -0500 UTC) but I can’t see any tornillos or HT.

        We know Agung erupts more mafic magmas (basalt to andesite)
        The less silica in the magma the less gas can be contained in solution. (btw CO2 exsolves at much greater depth than H2O)
        The magmas at Agung are quite explosive hence they contain a relatively high concentration of volatiles. I couldn’t find any data on this but let’s guess at 4%. This would mean H2O starts exsolving at a depth of roughly 5km (although the initial bubbles at these depths will be tiny due to the confining pressure).
        Agungs shallow magma storage is thought to be at roughly 5 km depth.
        We are seeing a shipload of brittle fracture going on.
        Brittle fracture is attributed to pyroclastic veins of gas/ash fracturing the host rock in advance of ascending magma. But we haven’t seen any sign in the signal yet of the magma directly.

        So what do we make of all this?

        My guess is that the magma column is ascending from the shallow storage but is still at some depth between the shallow storage and the crater.
        There seems to be a LOT of fracturing going on which suggests there is quite a lot of gas involved, implying that the body of magma is not just of marginal volume. The big questions are if magma can exploit one of these pyroclastic veins feeding the fumaroles and if so when, and how rapidly. Looking at other eruptions over the past ten years or so I have been watching this stuff, sustained HT sometimes only started immediately before the eruption. And according to Erik there is a positive correlation between the number of tornillos and the volume of the eruption.

        So while an eruption is looking increasingly likely, I think we still have to see HT and/or tornillos before getting too excited. However, once we do see these the eruption might only be hours away.
        Disclaimer.. I could be completely wrong on all of this!

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        • actually, I will retract what I said about there not being any tornillos.. in the last hour or two some of those signals have durations of up to 80 seconds.. that could qualify them as tornillos. I at first just thought they were largish volcanic/tectonic quakes. Not an expert on this, so don’t quote me on this! But 80 seconds is quite long

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  6. I wonder why they think the eruption at Aoba/Manaro is going to ramp up so much? You can see lava in the video so it obviously already is erupting. They must be expecting a large new pulse of magma or maybe they are worried about a phreatomagmatic eruption and accompanying base surge.

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    • S. Cronin, one of the expert Volcanologists on Ambae matters, said he did not expect a very damaging eruption, a few days ago. Today, Vanuatu scientists thought that the volcano has “stabilized”.

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  7. Bruce, it seems you are quite right about the magma source below Agung not being small:

    “Devy Kamil, the head of a sub-section of PVMBG, said on Sunday, October 1, 2017: “The magma is not scattered, but is a single mass of magma that’s on the move. The magma is seeking cracks and weaknesses through which to escape to above the surface.”

    News article on an assesment of the magma storage underneath Agung. Doesn’t sound hopeful for a quiet eruption 😦

    http://www.balidiscovery.com/messages/message.asp?Id=17446

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    • ha 😉 though 15,000,000 cubic meters is only 0.15 cubic km so we are not talking about a huge volume. I wonder if they calculated that by inferring from the inflation using the Mogi formula like Geolurking does.. if so they induced a spherical body with a radius of 150 m (diameter 300m) .. though I am not sure this actually tells us much.

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      • well, I guess it tells us the intrusion is not that big after all though I have my doubts about the direct correlation of inflation to the ensuing size of an eruption. I am not sure if that data warrants the strong language of the article. An intrusion of that size is not likely to be a “huge” eruption or “extraordinary” but I guess you never know.

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        • 15 Mill. m³ is even only 0.015 km³… but, “Our estimates and analysis indicate that there is, in fact, more than 15 million cubic meters of magma that is moving below the surface. That amount is limited to only that causing the earth tremors… The estimate of the magma’s volume is extrapolated by converting the magnitude of the tectonic earthquakes emanating from Mount Agung, permitting the PVMBG to calculate the pressure and size of the deposit of subterranean magma” (emphasis by me).

          So they just account for the already risen (“moving”) amount of magma that is causing the tremors within the mountain – and perhaps will be erupted with the first explosions. Certainly not the entire reservoir below. (1963 had erupted 0.95 km³ DRE)

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          • Well, they are walking on the small edge between mollification and justification, the most difficult task.

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            • ha, nicely put. It is hard to know what the 0.015 km³ is actually referring to when they say “magma on the move” All I can think of is extrapolating from the measured inflation of the edifice. I don’t know of any model that calculates magma volumes from the magnitude of seismic activity.. do you?

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              • No, I do not, but my knowledge is not a yardstick for anything… esp. not for anything mathematical, haha. But I guess it could be possible to extrapolate something from the cumulative energy of quakes (which should be calculated constantly anyway) for a given time frame, figuring in rock density, temp. and pressure… You’d still have to account for amount of gas content which would be crucial… In such cases I’d rather become religious and *believe* what experts say. 🙂

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              • Nothing wrong with a bit of faith in the experts! … certainly beats flying by the seat of your pants like I do
                (not sure if this reply is going to appear at the right place!)

                Liked by 1 person

  8. am cate from kenya coming from nakuru london where there is menengai crater……..so on the night of 1st december i dreamt of eruption taking place on menengai ……….i was so scared coz i new the dream was real and it had to take place or was taking place somewhere……so i pleaded with Jesus christ our king in the dream not to let it happen………
    so still on the same dream i found myself having travelled in a foreign country which i didnt recognize it and i found myself asking people starting with the president why they had foreseken Christ……….
    what i know about myself i do see revelations in dreams……..
    so next day i was shocked to see that in deed somewhere in this world volcanic eruption was taking place…….so i just had to post this coz i was shown and i had to pass it out…..if its related to your country u will know that Jesus is talking to u people……..

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    • Hi Cate, thank you for your comment! It inspired me to write an entire post on the Menengai Crater volcano, I hope you like it!

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