15 comments on “ARDOUCÔBA – the Seven-Day-Wonder in the AFAR TRIANGLE

  1. fascinating article once again Graniya! I wonder if the mantle plume theory and plate tectonics are not just two aspects of the same thing: i.e. the plume is driving the tectonics, particularly in light of the fact there is no slab pull going on either east or west of the rift (both plates are bordered by mid-ocean ridges on the other side – the Atlantic to the west and the Indian ocean to the east:
    http://africa-arabia-plate.weebly.com/somali-plate.html

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    • Thanks Bruce! It’s too bad that I could not find access to this paper: Demange, J., and Tazieff, H., 1978, The “tectonic” eruption of the Ardoukoba (Djibouti): C.R. Acad. Sci. Paris, Ser. D, v. 287, p. 1269-1272; I would have loved to read what his idea had been. (I bet, even if I had found it, the French would have seen to that it wasn’t translatable 😉 ) The question seems to have been whether magma was “squeezed” upwards by tectonic processes or came by upwelling of mantle plume.

      That the rifting and volcanism is driven by magma plumes seems to be generally agreed upon; I am not so sure about the plates’ movements. There are more processes in the mantle that make the cratons drift. The uplift by the plume seems not that strong, it is said that the power is considerably greater in a narrow rift (as in shooting up through a restricted diameter pipe) like the East African than in an older, widened rift like the Red Sea. If the plumes are so quickly exhausted they would not be able to move (or help moving) continents, methinks.

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    • Hi agimarc, just measured the distance to Anchorage to be 680 km – think you are safe enough from any stray lahar! 😉 But there is a big cold front coming to you, I read something about -32°C tomorrow, so, you’d better get a double layer of sheep wool sweaters on you and a double helping of hot whisky into you!

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      • Howdy Granyia – that might be wind chill, as it is blowing nicely. Not quite as bad down here. Only around 0 F this morning. Interior is going to be way cold, though.

        When Aniakchak blew 5,000 years ago or so it put centimeters of ash on the North Slope some 1,550 km north of the caldera. While I am far enough away to dodge the lahars and PF’s, should it do its thing in a big way and the winds are blowing toward us, we may be shoveling ash for a while. Plants love it. Rotating machinery and filters, not so much. Though slugs hate volcanic ash which tends to protect the garden from them for a while at least. Cheers –

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    • We can take this one with a very large grain of salt. The size of the caldera makes it a decent but not huge eruption (M6.8 has been calculated, Krakatoa-size). The ice core record puts limits on the sulphur emissions (not much is left after subtracting Eldgja). The reason why there was no climate shift is that this eruption was not large enough.

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      • Howdy Albert – Good point, that. Baitoushan has always been something of an oddball, at least to me. Big eruption – Krakatau to Tambora depending on your sources. Dusts Japan. No noticeable climate shift. Why? Northern latitude volcano? Maybe. Blows during winter? Even better reason as the winter jet will tend to keep stuff in the upper atmosphere confined depending on its relative location when the injection took place. Blows during the latter part of the Medieval Warm Period? Of course, if you are a Willis Eschenbach fan (WUWT) eruptions don’t have much of an impact on climate. It is such an odd duck, that I keep my eyes open for anything new about it. Best to you and yours. Cheers –

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  2. Nice overview. Perhaps the most surprising aspect is how slow the Ethiopian rift has developed. The hot spot developed more than 25 million year ago. The other two arms of the junction became mid-oceanic rifts (albeit not particularly fast). The southern arm has grown much slower. It is a tough, deep lithosphere which is hard to split, perhaps. Geological activity does not change over decades: that requires a million year or more. But it can go through cyclic changes with pent-up spreading released over a short time. There is a lot more thinning/extension needed before a mid-oceanic rift can form here though. Give it another 10 million year.

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      • Yes, it all began with huge flood basalts erupting all over the place. So far, everyone seems to agree. Since 1998, the apple of discord seemd to be the Where, When and How. Some believed there is a single huge blob of a super plume and others wanted it to be a chain of small “normal” plumes down the rift. In 2011 there is still disagreement over it. Maybe most scientists now favor the chain version, in my research for the post I have only seen maps with red spots lined down the EARS, the Afar plume being the biggest by far. Would be interesting to know if the question is solved.

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    • Thanks Albert! I think the reason for the slow rifting is still not solved. The lithosphere should not be as homogeneously tough and deep as the parts are breaking off along lines where once, in Gondwana times (?), terranes had been pasted onto the continent, which itself was made up of a cluster of smaller cratons. But that’s only me thinking, I haven’t read up on it yet.

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