Ch-ch-ch-changes!

Eruption Report #12 - This here eruption is one unstable beast
20.4.2010
Words by James Ashworth
As so often happens with volcanoes, a lot has changed in the past day or so, so I will try to sum up the recent activity as of Tuesday afternoon. If something changes before this even gets published, then so be it - volcanoes are often incredibly unstable beasts!

Firstly, it seems as if the eruptive activity was at its most severe around the time we were there on Saturday. I have heard reports of a 'pyroclastic surge' on Saturday, and I believe we actually witnessed this, although I sort of didn't believe it at the time, as I didn't think this eruption was really capable of producing them. A pyroclastic surge is a sort of 'blast' of gas and rock fragments, which can travel very quickly over the ground, and can be extremely dangerous. It certainly looked like the ash column collapsed on Saturday, which could give rise to a surge, so it's certainly very possible. If so, we shouldn't underestimate the potential power of this quite small eruption.

In the last couple of days, the eruption column has become much smaller, and the activity has changed towards more 'Strombolian' eruptive activity (the name is taken from Stromboli volcano in southern Italy, which erupts in this way). Strombolian eruptions are characterised by intermittent small eruptions from the crater, throwing incandescent blocks and bombs of lava up into the air, and with much lower ash production than the previous phreato-magmatic activity.

This change in activity is definitely a good thing for humans (and animals!), both in Iceland and abroad. In Iceland it means that less ash is being generated, and so a lot of the old ash fall can be cleared up. Route 1 is back open all along the south coast as I write this - the old breaks in the road have been filled in, so presumably the risk of jökulhlaup has been considered minimal (scientists believe any meltwater being formed by the eruption is draining away steadily and not building up beneath the ice). It also means much less disruption to air travel, as has previously been reported - air routes are beginning to reopen as the air begins to clear a little over Europe.

So what's in the future? Well (you guessed it!) we really don't know. Strombolian activity can continue for months or even years (in the case of Stromboli itself, over 20,000 years, although this is an exceptional case!) with minimal disruption to surrounding areas. There were theories kicking around in the scientific community that the current decrease in activity could be due to an injection of very thick, silica-rich magma blocking things up as it makes its way to the surface. If this turned out to be true, there would be two possible outcomes. If the magma was very rich in gases, a large explosive eruption could occur if it reached the surface. If it was gas-poor, a passive dome-building eruption would occur, where a new hill of lava would be built with no real explosive risk at all (but would bring with it risks of its own, best discussed elsewhere).

Really, any talk of the future of this volcano is pure conjecture. It may die out tomorrow, Strombolian activity may continue for years, or a large explosive phase could set in. We have no idea. I think the most likely possibility is that activity will continue as it is now for an indefinite period of time, and then simple wind down. Whatever happens, be sure to keep an ear to the Grapevine!



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