19 comments on “A VOLCANO WITH A TRAPDOOR – SIERRA NEGRA CALDERA (Galápagos, EC)

  1. Thank you! What a fascinating article! It will be interesting to see if the upcoming eruption will fit the trapdoor model.

    I’m also curious to know if that model could fit some of the larger Icelandic volcanoes, or if the trapdoor best suits the large shield volcano.

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    • Historical eruptions came from Yugama which is intensively monitored and people are prepared for. This time, it is erupting from Moto-shirane which has had almost no activity & is less understood. Apparently its last eruption was ~1500 years ago.

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  2. Hi Agimarc, hope you are on higher ground! It took 26 minutes for the Tsunami warning to appear on the TWC website. That is a hell of a long time for a relatively shallow major earthquake on a known subduction zone. It is the middle of the night I guess, but still. Hope this quake hasn’t generated any major tsunami. fingers crossed.

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    • Howdy Bruce –

      Thanks for thinking of us. Woke last night to dresser drawer pulls rattling. Went on for a while before surface wave hit. House rolled a while. Was not gentle but not as violent as the 7.1 a few years ago. Did not feel any aftershocks. Did not move anything in the house or otherwise rearrange the furniture or items on the shelves. Based on the delta between the arrival of P / S waves and the surface wave I figured it was large and a long ways away. Surprised this morning that it was as far away as it was – 580 km south. No tsunami warning here. We are on top of a 20 m bluff and whatever is generated has to rattle up Cook Inlet to get to us. If tides are low, no problem. If they are high, things may be exciting. A 10 m total tidal throw is not uncommon, though they are not all that large. West Coast Tsunami office is online but the page doesn’t load due to internet traffic. Looks like there were at least 10 aftershocks in the M 5+ range. Interested in seeing what caused the quake as there is not a lot out of there and perhaps 100 km south of where the plate starts down. Cheers –

      http://earthquake.alaska.edu/event/18173527

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      • My last info was 17 aftershocks in the 4-5 range abt an hour ago. The quake was a strike-slip, so not much up-down motion:

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      • Interesting thread by seismologist S. Hicks on the AK M7.9 (begins just after quake happened). Click on it and scroll down:

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  3. Mount Motoshirane (the main peak of Mt. Kusatsu-Shirane) from a helicopter after the eruption this morning:

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  4. Hi
    thanks for showing us some glimpse of the Galapagos
    about the phreatic eruption in Japan some footage from La culture Volcan blog. The guys filming were very near.

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  5. Kusatsu-Shiranesan:
    Yes, they say it was a phreatic eruption similar to Ontakesan in… when, 2015?… because the analysis says ash is 80% base rock material. What about the other 20%? And there was no avalanche, it was the eruption cloud that hit the people. The one who died was hit in the chest by a rock, while together with others trying to shield a family. Flying rocks were up to 1 m big.

    Photo taken by the Kyodo News Agency helicopter about two hours after the eruption. One plus 4 craters in a row. The craters are near the ropeway summit station. There a number of people were stuck for half an hour when the power failed during the eruption. (They must have soiled their pants, waiting, waiting, – at least I would have, I guess)


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    • The craters extend about 220 meters on a line that runs almost east to west. Each depression is between 10 and 15 meters in diameter. A professor from Tokyo University, Toshitsugu Fujii, said that a surveillance of this area is necessary, because these new craters could result from different eruptive mechanisms. – Soo… not phreatic, perhaps?

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  6. I would keep it Phreatic. If you look at the shape of the plume it is cypressoidal. Also the color of the ash is whitish, so a lot of steam in this. Also there was no forewarning I suppose this volcano is well equiped as it is in Japan.

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    • Yes, of course you are right, and I should have said: not *just* phreatic. My idea behind it was that it could perhaps have been phreato-magmatic. As the volcano had been restless for a long time, there might not have been a distinct rise of magma necessary. A prolonged presence of magma near the surface could have caused cracks to open, by heat and pressure, that eventually allowed hydrothermal fluids to get deeper and explode. The crater row speaks for that hypothesis, imho: a purely phreatic eruption would happen too fast and in a more chaotic manner. There might not be time to create a neat row of craters. I think the fissure might have been “prefabricated”.

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        • well, I guess phreatic eruptions like this should just be taken as one of a suite of possible signs of “restlessness” that includes fumaroles, gas emissions, seismic unrest, inflation, etc. It appears that in the vast majority of cases the period of unrest dies away again quietly without anything more happening. Occasionally it doesn’t and the activity builds up to an actual eruption of fresh magma. But even in this case most eruptions are small affairs like we have seen recently and only a few make it to the big league like Pinatubo – thankfully!! I am quite happy if eruptions stay in the small category – although even these can be fatal, as we see here, sadly.

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