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Grimsvötn eruption, Iceland

Submitted by Claire on Mon, 05/23/2011 - 12:00

A new eruption began on Iceland on 21 May, from Grimsvötn volcano. Volcanic ash fell on Iceland and the Volcanic Ash Advisory Centre, London ( www.metoffice.gov.uk/aviation/vaac)/) issued advisories predicting an ash cloud over northern UK, Ireland and parts of Scandinavia from early Tuesday (24 May) morning (see image below). The eruption had ceased by 30 May.


IVHHN Statement: Ash fallout from Icelandic eruptions across the United Kingdom and Europe

As we saw with the Eyjafjallajökull eruption of April-May 2010, and now the Grimsvötn eruption of May 2011, explosive eruptions of Icelandic volcanoes can occasionally inject volcanic ash particles into the atmosphere under conditions where the windfields may then bring that ash across the United Kingdom and Europe.  In April-May 2010, the Eyjafjallajökull eruption was unusually violent (probably because of the thick ice cap on the volcano, and the explosive interaction of molten rock with this ice), and produced an unusual quantity of fine to very fine ash, which was then transported across the UK and Europe at relatively low levels in the atmosphere (less than a few kilometres altitude), with well documented consequences for aviation.  The current eruption of the Grimsvötn volcano is likely to produce a far smaller proportion of fine ash;initial reports from Iceland suggest that less than ten percent of the ash is ‘fine ash’, which is about half the value during the Eyjafjallajökull eruption.

In the early stages of the Grimsvötn eruption, the ash layer was injected at a higher altitude in the atmosphere than in the 2010 eruption, but the ash level will typically descend to lower altitudes as the cloud is blown further away from the volcano. The coarser ash particles will probably fall out of the plume much closer to Iceland, and as a consequence there may be very little ash fallout across the UK and Europe when the ash plume passes over.  Our experience from last year’s Eyjafjallajökull eruption is that even in areas of the UK where the fine ash from the eruption fell out of the plume and was deposited on the ground, there were no unusual consequences: most of the ash particles were too coarse (20 – 50 microns) and at too low a concentration to have any detectable impact on air quality.  In fact, in most ‘dust’ samples which were collected at the time (whether on sticky tape, or on car windscreens, or at air sampling sites), most of the dust particles were not of volcanic ash at all, but a mixture of natural mineral grains and pollen grains, both of which are usually found in airborne dust.

Written by Prof. David Pyle, Oxford University, for IVHHN on 23 May 2011, updated 24 May 2011.


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