A summary about Nishino Shima.

Prior to November 2013 , I think I can safely say that nearly no one knew about this particular island located in the Pacific ocean, about 1000 km south of Tokyo, the nearest islands are part of the Bonin group.
To give an idea of the remoteness of the place, it takes about 26 h by boat from Japan’s mainland to the nearest island.

Much better known due to an historical battle during WWII and an emblematic picture, Iwo Shima, to the south, is itself part of the aptly named volcano islands.

Prior to 1973, the islet was pretty calm as the latest eruption dated back to about 10 000 years. The submarine volcano had been mapped and the island is part of the northwest ridge of the caldera.
The submarine structure is about 3000 m high and 30 km wide at the base.

Image courtesy ot the Japan coast guard

Image courtesy ot the Japan coast guard – Nishino Shima volcano prior to the present eruption

The eruption of 1973-74 lasted apparently from May ’73 to March ’74. A new island was created in the process, but it was partly destroyed by the elements later.

Image courtesy ot the Japan coast guard

Image courtesy ot the Japan coast guard

This is a map (from //www.gsj.jp/hazards/volcano/nishinoshima2013/) showing the bathymetry of the volcano and the location of the initial eruption.

Aoki et al made (La Mer, 22:248- 256) some analysis of rock samples in 1983, collected on and near the island. Their conclusion is that the lavas types are associated with Tholeïtic Basalts.

The present eruption began in November 2013 and was made public on the 20th. At first we saw some pictures and videos of a separate islet, showing the cypressoid jets which are characteristic of a shallow underwater eruption.

Picture dated 20/11/2013 / Japanese Coast Guard

Picture dated 20/11/2013 / Japanese Coast Guard

The eruption went on unabated and soon the new island merged with the older remnants of the ’73 eruption. This evolution is very well shown by this picture from the Japan Geographical Institute. See also: my video using the elevation data.

link obtained from http://www.arukazan.jp/bbs/

link obtained from http://www.arukazan.jp/bbs/

On this picture it is very clear that there was at first only one volcanic cone, but on the picture dated 16/02, a second edifice is visible.

There was also an IR picture taken showing the paths of the lavaflows. (Image dated 11/02/14)



Another set of pictures from


Considering the rate of lava extrustion I found some information on this site.

Apparently the rate of lava extrustion seems quite linear (or regular).

This is a scale of the surface of the island vs time.

Note that apprently in Early January 2014 the island surface was equivalent to the 73-74 eruption



The lava extrustion rate seems to be in the range of 0,5 to 1 x 10⁵ m3 a day.



And the quantity of lava having reached the sea up to 9 January 2014



The latest news we have of the volcanic island date back to April 15 on the Japan coast guard site.



Image JCG

Image JCG

The main cone is still puffing happily away. In fact there are 2 active cones, one is more active than the other.

The lava flows are still reaching the ocean, as we can see some vapour rising from the waves on the left of the picture.

All in all the eruption seems to be continuing unabated. However, some sismological data is missing as there is apparently no seismometer installed on the island, we can only rely on the pictures, videos and satellite data.

About Modis data here is a small animation I made using the Modis thermal alert pictures. Do not pay attention to the date stamp at the bottom of the image, the video shows the different satellite images since April 1st ending today (21st April). There seems to be no active spot since the 18th, but as you will see, this happened also some times since the beginning of the month, so it is not possible to say if this corresponds to a pause or an end to the eruption, or if it is only due to cloud cover for instance.

About the Digital elevation data made available, here is a video which shows the terrain elevation for different dates and so shows the evolution of the volcano on 4 different dates. The last data is for 22/03. The elevation data comes from  http://saigai.gsi.go.jp/2/20131120nishinoshima/nishinoshima_3d

Comments by dfm:

I have exagerated a bit the vertical component, but it is interesting to note that on the last part, the elevation of the new part of the island is clearly much higher than the old remnants of the ’73 eruption. This shows that the new island should stay above the water line for a while.

There is also this last video, which is the latest available from the JCG. It shows very well the 2 active cones and the lava flows getting to the sea on one side of the new island.

This eruption is really something very interesting as we can see a new island building itself. The follow up done by the different Japanese agencies is of high quality. The only point we may regret is the absence of monitoring equipment on site.



112 thoughts on “A summary about Nishino Shima.

  1. THANKS dim for that update on Nishino Shima. That sure was hard work to find all the info especially because the info is japanese!

  2. Very nice summary. Thank you.

    Here’s an interesting annotated view of a recent pic from GSI – note there are four craters (two cones).
    It is also interesting to see how coastal erosion is already at work: many of the lava tongues that stick out into the sea have had their ‘corners knocked off’ when compared with earlier photos, and sandbars are filling the gaps in between.


    By February 16 the larger cone stood at 66 metres above sea level. On that date the GSI estimated the volume of NEW land above sea level was 7,900,000 cubic metres.

    • Minor update: cone height calculated at 71 metres on March 22.

      The Japanese have been using an unmanned air vehicle to take the close-in imagery, flown from Chichijima island. It’s the first time they have used a UAV for volcano monitoring, and allows a much closer look (down to 800 metres altitude) than would be prudent with a manned aircraft

        • I hope there will be another released soon – previously the DEM has followed a flight survey after about 5/6 days. Seems like the last overflight with 3D imaging was on April 15, so there might be more DEM info any day now.

          • I suspect that there are also some other forces at work – the manned flights are almost certainly by Japan Maritime Self-Defence Force P-3 Orions, which will be able to build a very nice 3D radar image of the landmass that will allow more accurate estimations than 3D optical imaging.

            • On second thoughts … it could be one of these (with a nice, fat SAR-capable radar underneath):

              If so … Japanese volcano mapped by Swedish plane!

            • …Yeah.. SAR is fully capable of gathering that data.. it’s capable of quite a number of things…. most of them spooky from my point of view.

              Note, if you ever ask a Hull Technician to fabricate a corner reflector, expect it to be a three man lift when you go pick it up. They made a set for me out of 1/4 inch plate steel. It was really my fault, I should have been more specific.

              Somewhere, on the bottom of the Caribbean, are two rather ungainly chunks of plate steel that may drive some future researcher bat-shit trying to figure out what they are, or were for. Oh… they are about a mile apart. That’s because of how heavy they were to lug them aft and toss em without going in with them.

          • Well, to me, and probably most British folks of “a certain age”, Chi Chi was the name of the panda in London Zoo when I was a kid. Oh, the national excitement when An An was flown in to try and mate with her (unsuccessfully, of course)!
            She’s still around – stuffed and cased in the Natural History Museum.

            • Well, let us put it this way. Lurking referenced to Subic Bay a couple of days ago. It is almost certain that ChiChi could have been witnessed there, and let us not get more graphic on this subject.

              Let us instead pretend it means this:

            • Haha! What happened in Subic Bay (or Po City, or Pattaya) stays in Subic Bay (or etc)
              And no pandas were harmed, etc etc (I hope…)

            • ROFLOL!!!!

              I see he has as much trouble keeping the bottom of his goatee trimmed straight as I do. At that length I trim it back and on occasion, ponder cutting the whole damned thing back and starting over. However, I do carry a lot more gray than he does and my disgust with it kicks in quicker.

              I love his reaction to the end result. “seriously?”

  3. Thank you for this nice post, dfm!
    Placing equipment (and not loosing it) on a constantly growing island is quite challenge I guess.
    Don´t know if this video was posted before, but it shows Nishinoshima in action, seen from a boat about a month ago:

    • Interesting location actually. Could be something poking its way up. If it does we most likely get a new Dom Joao de Castro…

      • 2014-04-21 17:52 38,22 -26,64 4 2,5 Banco D. João de Castro — — –
        2014-04-21 14:10 38,24 -26,57 5 3,1 Banco D. João de Castro — — –
        2014-04-21 12:47 38,18 -26,62 – 2,9 Banco D. João de Castro — — –
        2014-04-21 08:35 38,18 -26,61 – 2,8 Banco D. João de Castro — — –
        2014-04-21 08:16 38,20 -26,60 – 3,2 Banco D. João de Castro — — –
        2014-04-21 07:56 38,23 -26,56 3 2,8 Banco D. João de Castro — — –
        2014-04-21 07:50 38,22 -26,58 – 3,0 Banco D. João de Castro — — –
        2014-04-21 07:48 38,16 -26,62 – 3,4 Banco D. João de Castro — — –
        2014-04-21 07:48 38,20 -26,60 1 3,2 Banco D. João de Castro — — –
        2014-04-18 19:34 40,75 -29,48 8 4,4 Crista Média Atlântico N — — –
        2014-04-18 11:13 38,24 -26,62 2 2,5 Banco D. João de Castro

        • Hm, it was Dom Joao de Castro, and by the looks of depth and other things I would not rule out that we will see Dom Joao de Castro erupting in a little while.

  4. Thank you DFM for nice writing and a very illuminating plot.
    I agree with you, this new land at the Island makes it quite probable that the island will be with us for quite some time. Especially if the Island growth continues like this for a few months more.
    Also, another thing that most people have not pointed out, that is that there is another volcanic peak on this large somma-caldera that is not that far away from Nishinoshima. I think that this volcano will grow significantly over the next thousand years, after all it is not often a brutishly sized caldera volcano emerges out of the water like this.
    What is so interesting is the origin of the magma, tholeitic basalt is normally associated with rift volcanism on sea bottoms, hotspot volcanism or flood basalt volcanism (hotspot).

    • It is not easy to find information for this volcano as (and it’s only logical), most of it is in Japanese. Also there is no Wiki entry to explain the geological settings in the area. The JCG bathymetries are interesting as they show the huge size of the edifice, the emerged isalnd being only a tiny part. The reference article is in a french review (La Mer – The Sea) which is a collaboration between french and Japanese scientists. If you consider the size of the edifice, the eruption could go on for some time. It’s already 5 months, the previous one lasted 10 months at least, I’d keep an eye on Modis (Nothing apparent today – 22)

      • On on of your images one can see the nearby other volcano, it is currently if memory serves 170 something meters below the surface, but that could be done in just a couple of eruptions.

        The Wikipedia article has a huge flaw in it, and I am not sure where it is coming from. It claims that prior to the 1973 eruption the volcano had not erupted for 10 000 years. That is obviously wrong judging from the speed of oceanic decimation. The by then Island was probably erupted in the 40s or 50s… In turn the Island was probably a different one back in 1917 when they did the naval charting. And that would in turn imply that this is a far more active volcano than previously believed. I though think this Island will remain and grow over time as more eruptions occur.

        • Well by looking at the japanese wiki page and translating it with giggle, it would appear that there were maybe some other events in the historical times. The problem with these extremely remote islands is that there were no monitoring means as there are now. I’m wondering how the JCG got the info that the volcano was erupting. I suspect an earlier manifestation because the first videos we get are of the rooster tails eruption phase. What are they using, hydrophones ? By checking on the modis hot spot I got a signal on november 23rd, then you have to wait until the 30th to get another signal.

          • Yes.
            Japanese wates are crawling with hydrophones and infrasound-detectors, they have two reasons for them, one is to protect the japanese waters against foreign subs, and the second to detect even minute changes in their volcanoes. And in some not small measure, to try to find ways to predict earthquakes (not making a lot of progress yet though).

  5. And for you Nordic critters…

    The technology behind the +ulfber+t.

    From Wick yer Pedia: Ulfberht is a name given to unique Viking swords used in Scandinavia in the 1000s. The unique, high-quality steel they incorporated remained unparalleled until the Industrial Revolution. 171 such swords have been found so far, but only a few of these have been proven to be authentic Ulfberht swords. The earliest Ulfberhts date from circa 850.

    • If you wish to see the bulk of the proven swords you would need to meander over to the Historical Museum in Stockholm Sweden. Most of them are in storage, but the one that is on display is well worth the trip.
      After that go to the Royal Armoury (Livrustkammaren) in the Royal Castle and look at a replica that was made as a Masterpiece as the smith Smed-Jan got his Master-Smithing certificate as a Bladesmith (the only westerner with such, and one of 3 on the planet, the other 2 are japanese).
      The replica sword is made from steel produced from a meteorite and the mild steel is made from lake-iron. Total time required to produce the sword was 2 years full time. Estimated price to get a sword like that is well above 500K$. What is interesting is that it is a memory metal, almost any small damage will rapidly disappear as the atoms try to gain their original place. In reallity the steel used in the swords are beyond what could be produced industrially into the mid fifties.
      The expression Swedish Steel is rather old… For those who are not familiar with steel-working. Almost all steel on the planet has a grading starting with the letters SS, that would be Swedish Steel, we’ve been around perfecting it for a long time now. 🙂

      My little way of making my way if all goes to poop is that I have smithing as an interest and skill. I am far from a master smith, but I can bang out pretty much anything and it functions. It should be a tradable knowledge. So let me say it this way, the Smed-Jan Sword and the original Swords are masterpieces on a level closer to magic than anything else. But then a knife to cut sausages with from Smed-Jan costs a normal monthly wage…

  6. Just took a couple of asprin befor bed… In my paranoia about dozing off, I checked the ingrediants to make sure I didn’t just nail myself with a heavy shot of caffine. (many asprins are buffered with caffine). Upon reading the last ingrediant, I imediately thought of volcanoes. See, TiO2 ratios are used in a lot of gas content estimates of magma.

  7. How about the slight low frequency tremor increase at Grimsvotn? I thought that wind noise is usually in the higher freqs. Or is it low freq. noise from the glacier?

    • Two nearby only. The overall scattered auakes in the region between Katla and Torfajokull are more interesting to me, despite the fact they dont mean much, if anything at all. And can some expert please answer my ultimate question, why is Tindfjallajokull so long asleep, while his nearby friends have more or less “regular” eruptions? :/

      • The two ones WSW of Hekla are just on the other side of the Hekla fissure so they might be related, but they could also be purely tectonic. The new one SSE of Hekla is not related, it is in the area of the intrusive 1987 quake of Vatnafjöll (another volcano).

      • Back to your very good questions.

        If we start with the earthquakes between Torfajökull and Katla those are really shallow, and are either due to seasonal motion of the bedrock as the weight-load on the land differs (this case), and deeper earthquakes of tectonic origin.
        Almost all of Iceland suffers from these seasonal quakes, but this area is one of the few with sufficient equipment density to notice them.

        Over to Tindfjallajökull. If you take a look at the surrounding area you can get an inkling of why it has gone dormant (or possibly even gone extinct). The tectonic forces from the South Icelandic Fracture Zone are mainly handled by the two volcanic fissures to north and northwest of Tindfjallajökull, namely Hekla and Vatnafjöll. Both have had a very high rate of eruptions since deglaciation with the height of activity gradualy moving from Vatnafjöll to Hekla. Both these volcanoes are though active. Generally one would assume that the residual energy and rifting is taken care of by them from that direction.
        Torfajökull functions as the end cap for the rifting from the NNE with both Veidivötn and Laki fissures ending inside or close by to the east of the volcano.
        South you have the insular volcano of Eyjafjallajökull that is from the same timeperiod as the ancient Tindfjallajökull, it though seems to be more related to the Vestmannaeyjar volcanic fissure swarm than to anything to the north. Katla on the other hand has a fissure swarm that goes NNE (Éldgja). On can assume that these fissure swarms and volcanoes have created a volcanically dead point where all possible energy (force) is being taken up by the surrounding ones.
        One idea to ponder is that Tindfjallajökull previously filled the function that is now taken by Vatnafjöll and Hekla. One should remember that Vatnafjöll started erupting at the end of deglaciation and that Hekla is even younger, so that direction was up untill then open for force distribution that might have been feeding Tindfjallajökull.
        I should hear state that this is my opinion, and that it is speculative, I though believe that it has at least some merrit. I know of no actual research that would better answer your question.

        • I salute you kind sir, for taking the time to answer my dull questions! I get the whole picture now, and it seems my question was in a way unintentionally rhetorical (answering itself).

          Thanks again!

          • Actually it was a really good question. It is one of those Riddles of Iceland that I hope some student of volcanology will take a look at in the future. There is at least a Masters thesis there. Beccause if you can answer why that volcano have gone silent it would in no small measure help explain why others have come into its place, and also shed light on the entire volcanic area. No small question at all.

  8. Was temporarily confused between Iwo Shima / Iwo Jima. Found the latter on the map a long ways away from Nishino Shima, about 170 mi further south, but along the same volcanic arc. Real interesting post. Many thanks. Cheers –

    • Thanks agimarc

      yes I have also seen the Jima orthograph. I think it’s only a phonetic retranscription problem. I chose Shima….Nishino shima is so small you can find reference about it being on the Volcano chain or Bonin island group-it is nearer to Chichi Jima. But geologically speaking it is part of the same arc as Iwo Jima.

      • Hm, isn’t there a problem with saying that? I thought one was on the main arc and the other on the back-arc? I may though be severely confused again 🙂

          • Main arc for both then, I had Iwo Jima slightly more to the south and on the back arc in my head 🙂

            Now I just have to bend my head around the tholeitic basalt and how come the lava is so hot. But I will leave that for another day 🙂

          • One of those places on earth that definitly get me saying… “What the Fudge” is going on.
            Basicaly to the east of Nishinoshima you have a spreading fault, then comes a main arc (housng Chi Chi shima among others) caused by subduction volcanism.
            Then to really drive you nuts you have the Nishinoshima line of volcanism which most likely are spread volcanism and back-arc volcanism running around holding hands with each other. And to really really compound it all. What on earth is fueling that spread-fault? You do not normally get a spreading fault in a zone that is compressed by the entire oceanic crust of the pacific. Sigh…
            Seriously? I could buy it if there was a hotspot there somewhere, but the direction is just wrong, the track would be meandering straight out into the pacific and not trend towards the south. Meh… This is a really nuts corner of plate tectonic.

            (Warning, all of the above is just a lot of rambling without any real significance)

            • IMO, what you have is a continuing trend of the back arc basin south of there moving slowly to the North. The shimas are just in the leading edge of that trend as the back arc basin moves north.

            • Do you really want to dig deeper into this Fudge? – then go to:
              and then further South to:
              I have got so stuck with my trying to understand this arc-swallows-arc setting that I have even thought of asking someone to write a post on the tectonics of this whole region!
              And yes! Somewhere in my readings I have found out that, at some point, there is crustal stretching and basaltic volcanism as the result of whole plates being subducted under other plates leading to driving mechanisms of mantle upwelling and the formation of mantle plumes which in turn correspond to theories of the recycling of subducted plates at the Earth’s outer core level which would be responsible for cycles of inversion in Earth’s magnetic field!
              Cool stuff indeed!

            • Highly interesting paper that really puts into place the question.
              What comes first, the hen or the egg?
              Seems like the magma acreation in magmatic systems and dykes start a miniscule spread of a few hundred meters on average that grows into a spread zone that gets self-propagating and starts to suck up ever less evolved basalts.
              Sofar it seems like the subduction was the egg and the rift was the hen, but later it still looks like cock came by to make more eggs. Question, how deep does the cock come from?

            • DING!
              Renato found the cock!
              “leading to driving mechanisms of mantle upwelling and the formation of mantle plumes which in turn correspond to theories of the recycling of subducted plates at the Earth’s outer core level”
              What I am getting at is that a self-propagating rift of this size would in the end be likely to create it’s own mantleplume (and if it goes on long enough a hotspot).
              Interesting that Nishinoshima seems to have gone from hen to egg to cock. Isn’t it interesting how nice things become when you penetrate them well and truly.

  9. Thanks dfm, very good summary and update on the little rascal, and well put together!

    The Little Rascals

  10. And here an update on my presently favorite volcano on the other side of the planet, Ubinas:
    I have not seen any lava erupting so far, however, once or twice incandescent tephra in the explosions has been reported. The Peruvian Observatorio Vulcanológico del INGEMMET (OVI) is doing an exemplary job with their comprehensive daily udates, I wish some other institutions would take this as a model!

    Here a short summary from the 21-04-2014 report (pdf, spanish), transl. by Google
    – today, continuing moderate explosions accompanied by significant emissions of ash, gases and ballistic missiles , with eruptive columns more sustained over time, suggesting that gases and ash are being released easily.
    – During the day occured 9 moderate gas emissions and ash, which reached between 600-4100 m above the volcano’s summit .
    – Ash falls were reported in [8 surrounding towns]
    – The Mirova system of the University of Torino – Italy has NOT detected heat anomalies in Ubinas volcano today.
    They also installed another webcam, more reliable then the first one it seems:

  11. Thanks everyone for the enjoyment! dfm, Granya, KarenZ, Matt, Lurking and Carl – fortunately I have you people to give me excellent material to read in my leisure time! (Tomorrow is a local holiday, so…)
    Terranes, slab/trench roll backs, sleeper fishes, hens and the eggs, Ubinas, Sakurajima… Can’t get enough of it all, thanks to you guys! 🙂

  12. And out of left field…

    M4.5 – 18km S of Ulcinj, Montenegro 2014-04-21 21:25:30 UTC

    This is going to be over relatively near that area where “suprasubduction” took place when the Tethys sea still existed. Suprasubduction is where the subduction occured in one direction… then was reversed as the crust dynamics changed and progressed to other direction, then reversed again… etc. Eventually, the whole jumble of rocks became mountins in and around Montenegro/Albania and are preserved in the rather confused morphology of the mountain ranges.

    In my opinon, this is what we are seeing played out in the Philippines area with the opposing subduction trenches. Eventually, they will interfere with each other and another round of tit for tat subduction will take place.

    I sort of wish this had happened 20 years or so ago… I would have been almost on top of it. Our patrol box was only a few nautical miles from the epicenter. I could have gotten the Sonar guys to replay the waveform.

    Suprasubduction zone ophiolites and Archean tectonics Yildirim Dilek and Ali Polat Geology 2008;36;431-432

    Some of the most extensively studied Tethyan ophiolites appear to have developed, for example, in arc-forearc settings within restricted marginal basins, which were nested in older, preexisting oceans (Ishikawa et al., 2002; Dilek et al., 2008).

      • Dunno about Etna, but the Suprasubduction has to do with spreading in the back arc basin that then pushes the trench in the opposite direction of the subducted plate motion as the dangling portion rolls back under itself. That’s just a part or a stage in the development of suprasubduction as I understand it.

        How that relates to Etna is Boris’ department, after all, she is his critter. No one else on here can really hold a candle to his level of knowledge about that entity.

      • Now… a more pressing thing that you should be asking Renato…. is why the hell did I embed a submarine volcano video while talking about suprasubduction?

        Answer: → Boninite. – “Boninite is a mafic extrusive rock high in both magnesium and silica, formed in fore-arc environments, typically during the early stages of subduction. The rock is named for its occurrence in the Izu-Bonin arc south of Japan. It is characterized by extreme depletion in incompatible trace elements that are not fluid mobile (e.g., the heavy rare earth elements plus Nb, Ta, Hf) but variable enrichment in the fluid mobile elements (e.g., Rb, Ba, K). They are found almost exclusively in the fore-arc of primitive island arcs (that is, closer to the ocean trench) and in ophiolite complexes thought to represent former fore-arc settings.”

        And if you will note figures T1 and T2 of the pdf I linked earlier, Boninite is one of the early magmas in a suprasubduction environment. Back to the Wikipedia note: “Eruption of boninite lava was observed in 2009 at West Mata volcano in the Pacific Ocean by scientists using a remotely-operated submersible. Previously, boninite had been found only near extinct volcanoes more than one million years old.”

        I did not embed the figures here since the pdf document specifically states that the authors can use the imagery, and I am not an author. The images at the end of the document give cross sectional schematic layouts for thick and thin crust environments for slab rollback.

        • “An ophiolite /ˈɒfiəlaɪt/ is a section of the Earth’s oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks.” (Wiki)
          As I understand, the supersubduction makes the mantle exposed by folding over itself and the whole being further upwelled, right?

          • Pretty much. It’s a tortured chunk of material that gets pushed up and scraped off onto continental crust or entrained into the accretion prism and then treated like any other bit of terrane that gets plastered onto continental crust. “bugs on a windsheild.” Some of them can be quite exotic and you will spend several minutes staring at them trying to figure out what they were…

            (I actually nailed a bat once while pulling on to state road 20 north of Panama City. Luckily, he just bounced off and didn’t break anything, or get stuck… but he did leave a splat mark in my existing bug accretion. No blood, just disturbed bug carcases. As soon as he got over being stunned, I’m sure he fluttered away. I got away much better than my aunt who hit a buzzard that wound up on the seat next to her after it crashed through the windshield. Her Doberman, riding in the back seat, took the opportunity to decorate the rear seat with feces. She drove her last 150 miles with a hole in the windshield, a dead buzzard beside her, and dog shit in the back seat. Quite stinky. That’s why, when I encounter the more stupid stuff in my travels, I always think to myself.. “Well, it could be worse”)

  13. Back arc basins are interesting. I have another *small* theory about NishinoShima area in regards to the basalt being formed. I would personally guess that the subduction occuring in this area is incredibly steep, which causes much more vigorous back-arc spreading than subduction that would occur at a shallow angle.

    It’s pretty simple from a mechanical perspective – the closer the subducting slab gets towards 90 degrees, the easier it gets for the crust to get dragged down with the subduction as opposed to slipping on by. I believe this is evident given how deep the trench areas are in this arc.

    • An alternate thing that came up while spelunking the net on slab rollback.

      At about 400 km or 600 km, a phase change can slow the dropping slab end (the dangling bit) due to a change in buoyancy. This can also initiate the trench rollback process where the boundary starts tracking in the reverse of subducted plate movement.

      I can’t cite a reference. I was just reading at the time and was not prepping an article.

      • Interesting discussion. I have a fairly strong suspicion from trying to understand the background to NZ and the Havre trough that the Pacific/Australian plate boundary has not smoothly migrated to the east but done it in successive steps. As though the subduction process stalled for whatever reason and suddenly started up again further to the east. This explains a bit past volcanic series like Coromandel and the Colville ridge. I could be way off base on this but it is an idea that came to me while doing the NZ series.

        If the change of buoyancy at the D” boundary leads to the subducting slab stalling this could explain a couple of things. The first is Passerby’s delamination theory and the buckling seen in the deep seismic signals he found and might also propagate to the surface to such an extent that microplates (slabs) form.

        These might in turn help explain those volcanoes that cannot be explained by a volcanic arc or back-arc extension.

        • Hey Bruce! You must be very busy indeed. I have expected you to jump onto this a bit sooner .
          Yes, I have read about this “subduction stalling” – not all plates reach the bottom of the mantle and that has to do with plate’s density reaching a balance with the surrounding mantle. Usually they are colder and heavier, but depending on their mineral compositions and energy gain they get during the subduction process (through friction, radioactivity, etc.), they can stall.

          • 😉 Thanks Renato… but I think there are much better minds than mine here to discuss this!! I’ve been really too busy IRL to follow this which is a shame. Wish I had more time!!

        • Considering that they are all eerily parallel to the Kermadec Ridge, you are probably correct and they represent various stages in the process.

          While poking around at it, I found out that Raoul is quite lethal for researchers. Coincidentally, the two most recent seem to have died while taking water samples or temperature readings in separate incidents. One likely by “drowning” (see my 16:35 below), the other by having it go off while he was present.


          • two? I knew about the DOC worker who got caught in the phreatic blast but not about the other one.

    • Interestingly one of the two current convergence centers of the
      quadrupole model of mantle convection lies south of Nishino-Shima. At the Mariana trench, indeed subduction looks comparably steep, as if some force is pulling the plate straight down.

      IRIS 3D model: http://www.iris.edu/3dv/index.html?caller=IEB&st=1970-01-01&et=2025-01-01&ob=time-desc&li=5000&xla=29.266&nla=10.445&xlo=153.281&nlo=133.770&sbl=1&zm=5&mt=hyb&sz=med
      From: http://www.iris.edu/ieb/

  14. Interesting discussion. http://www.livefromiceland.is/webcams/hekla/
    Here is view of Hekla, if you defocus your eyes you can see “Grimsvötn 2011”. Yep. Still going? No. But its remobilished ash! Blowing in easterly the wind. Snow is mostly gone in south lo-lands, such as in Klaustur areas, and high winds are really de-dusting the countryside (and blowing over here, sigh). This morning I woke up with much of it in my eyes and nosrils. Yuck.
    I feel thats bad for mu health.

    • It has been going for three years now. Won’t it ever stop? I would have thought that after a while ashes would have mixed with normal earth and mud so they wouldn’t be so easily blown.

  15. Dear readers
    Whoever gets an email from me saying you should view a doc… I did not send that mail. The account was hacked.
    Don’t try to open that mail or klick the link, or the same will happen to you, I got it this way, unfortunately i was waiting for a doc from that person… I apologize for the inconvenience. I happened when i edited this post.

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