Bárðarbunga – everything you need to know (well, almost). 21 August 2014   5 comments

Yesterday a colleague decided to hold a ‘mock’ interview with me during our lunch break, which she recorded and I’ve just written up and tidied up. You may find it informative.

Q. So Dave, stop the 50:50 stuff when asked ‘will it erupt’. What do you really think?

A. It’s still 50:50! Whether it will erupt or not depends on a number of factors, some of which cannot be monitored. So that people can better understand why predictions are so difficult let me list some:

The magma is sitting at depth in a vertical fissure and slowly moving NE. It’s a dyke intrusion.

A key question is whether new magma is joining the magma in the dyke. If not (or it’s just a small amount), then there is unlikely to be an eruption. It will stall and cool.

However should a fracture suddenly appear above the dyke, then the magma is going to move upwards, and then it’s more likely to erupt.

Because as it moves up, it will reach a level where any dissolved gases (mostly water) will stop being dissolved, expand dramatically and accelerate upwards, and ‘push’ the magma to the surface. This is actually how eruptions are powered – bubbles.

Another scenario is if magma keeps being pumped into the dyke. The dyke has a number of choices: use the extra energy to keep moving NE; expand by moving to the SW, or grow up and/or down.

Get the picture?

Q. Thanks Dave, and stop calling me Bubbles. Right, we all love an apocalyptic story, so what’s the worst case scenario?

A. Ah, well, there’s more than one with this particular volcano – sorry. But these are nowhere on the horizon at the moment. Here are three.

  1. This presently benign little dyke intrusion is the forerunner to the uprise of large packets of melt from below (from the mantle) and it suddenly turns into a Laki-type flood basalt eruption. There’s still controversy over how these massive eruptions are fed in Iceland, but they always occur in fissures, and they have to involve the mantle because we have no definitive evidence that 10s of cubic kilometres of melt are stored under each central volcano just waiting to erupt. A little puzzle to solve is why these flood basalts (if they are fed directly from the mantle) have ‘shallow’ pressure signatures, but this might just mean they spend enough time at shallow dept in transit to ‘equilibrate’ to lower pressures.
  2. This event triggers activity within the heart of Bárðarbunga, beneath the summit, where there’s almost certainly some melt and or mush (melt+crystals) stored. This could be all basalt, or there could be some more ‘sticky’ magma around, such as rhyolite. Evidence from ash layers in Iceland indicates that explosive basalt eruptions from Bárðarbunga do happen, and that they are powerful. The good news is – and myself and John Stevenson have said this many times – is that we have less to worry about if this happens because we’ve already had one – Grímsvötn 2011. So we know that fewer flights will be cancelled simply because the old “ash in the sky you don’t fly” rules no longer exist. Everyone is much better prepared for a big and powerful explosive eruption. I’ve seen a few geologists say things like “Icelandic magmas do not contain enough gas to drive powerful explosive eruptions”. This is utter rubbish, incorrect, and misleading. These are invariably geologists who lack a true understanding of Icelandic volcanism because they have done little or no research there.
  3. Probably the worst-case scenario for Iceland is that this leads to a massive volcano-tectonic event in the fissure system to the SW of Bárðarbunga, as this is where a number of large flood basalt eruptions have occurred. The hydroelectric power plants on the rivers near to this fissure system would be in trouble, and we know that in the past large ash piles have dammed the rivers. The abundant water in this area results in spectacular (but fairly local) explosions and a high production of fragments as the abundant river water cools the erupting magma.

Q.Final question. You mentioned over coffee that you’d been very active on Twitter trying to get what you called the ‘right information’ out there. But isn’t there a danger that others will pinch your work and re-cast it as their own?

A. That comes with Twitter territory. I’d much rather try and provide an informed and scientifically-based set of views and ideas that can be pillaged and re-used (usually without credit) than leave it to those who don’t understand Icelandic volcano-tectonics to mislead (not always deliberately I hasten to add). I appreciate it when folks give me credit, but I don’t expect it. If you are being paid from public money to do your science, then put your knowledge to good use for the benefit of the public. Getting credit for it is a bonus, not a right.

Q. OK – late for the next meeting Dave. Maybe continue with a pint or two later?

A. Only if it’s a real ale acceptable to my palate.

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Posted August 21, 2014 by davemcgarvie in Uncategorized, Volcanism

5 responses to “Bárðarbunga – everything you need to know (well, almost). 21 August 2014

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  1. I leave for Iceland in 3 weeks so have been following the earthquakes there with great imterest.
    I started following you on Twitter when I saw you emerge as an intelligent, science-based voice of reason as opposed to the crazy, fear mongerimg media outlets.
    Keep up the good work

  2. as usual very much to the point – well done

  3. Pingback: Bárðarbunga ruskar på sig | Erika Groth

  4. Thank you
    Blog fantastic
    ………………….
    http://www.8ii.in

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