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What are the risks of prolonged volcanic activity?

Paul Hudson | 16:53 UK time, Wednesday, 5 May 2010

Latest projections for tomorrow at 7am indicate that Ireland, Wales and the Southwest of England may well be affected by ash. Whether it affects flights of course depends on its density. Upper level winds suggest that the ash should start to clear southwards, with most of Ireland and the UK clearing accordingly through tomorrow and into Friday. With a general northerly persisting into the weekend and into the first half of next week, the volcanic ash should stay clear of the UK, although it may be a close run thing for parts of Ireland at times, especially into next week.


I have been asked numerous times just how long we could be affected by volcanic ash.

Dr Dave McGarvie who is a Volcanologist at the Open University told me earlier today about what history can tells us about Icelandic volcanic eruptions in the past.

"The current volcano (Eyjafjallajokull) erupted for just over a year from December 1821 till early 1823. It didn't erupt constantly all this time though, as after a week or so of intense activity it just sent out occasional minor explosions until end-June 1822 - when another sequence of substantial explosive eruptions started and lasted for a month till early August. It was quiet from then on (occasional explosions) and activity gradually died out early in 1823.

On June 26, 1823 the bigger volcano next to it (Katla, 25 km to the E) erupted. This was a small eruption by Katla standards and lasted for 28 days.

Historical record (last 1100 years) shows that three times Eyjafjallajokull erupted Katla has erupted soon after (c.920 AD, 1612, and 1821-1823). But it could be pure coincidence! After all Katla has erupted 20 times in that same time period. And each of the Eyjafjallajokull eruptions were different, so there's no common thread there. But the volcanoes are close to each other, and the lavas etc from both volcanoes overlap on the surface, so there could be a subterranean connection. Bottom line - we don't know enough.

The last substantial Katla eruption started 12 October 1918 and lasted 24 days. It produced an eruption plume an estimated 14 km (46,000 feet) high. A nice little injection of ash into the stratosphere of course, with a different set of problems to what we experienced in mid-April.

Katla is Iceland's second most active volcano, after Grimsvotn which lies within the Vatnajokull glacier. Katla has a habit of erupting twice a century, so that's why the Icelanders are a bit anxious about the length of time that's passed since 1918 - and whether this might mean a bigger eruption is due. However there's no correlation between the length of time that's passed and the size of the eruption because (for example) both of the eruptions in the 1600s and in the 1700s were amongst the largest recorded."


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