May 17, 2010

expert reaction to continuing volcanic eruption

The Icelandic volcano Eyjafjallajökull has continued to erupt sporadically over the past month, causing intermittent disruption to air traffic across parts of Europe

Dr David Rothery, Dept of Earth & Environmental Sciences, The Open University, said:

“It is now nearly five weeks since the eruption of Eyjafjallajökull migrated to beneath the ice-cap (14 April) and began to produce a high ash cloud that led to closures of European airspace. The eruption has continued ever since. The rate of ash eruption and the height that it reaches have both decreased over time, though now and then they temporarily re-intensify. This is a pattern that we can expect to continue. Major disruption to air traffic is likely only when the ash column is high and the wind carries it southeastwards, so from now on I think we’re looking at a few days every month.

“We can expect the eruption to become less intense over time, though there are likely to be episodes of renewed intensity, for example when melt water from the icecap gains access to the volcano’s magma-plumbing system via newly-opened fractures. There is no sign of the current eruption ending. The previous eruption of Eyjafjallajökull lasted twelve and a half months*. We cannot assume that this eruption will be the same, but we at least know that the present eruption could drag on for several months.

“There is no sign of Eyjafjallajökull’s neighbouring volcano Katla coming back to life, and I think we would mostly likely have several weeks or months warning of a Katla eruption. However Katla had nine ash-producing eruptions between 1560 and 1918. These were mostly bigger but shorter-lasting than what Eyjafjallajökull is currently doing. Now that the potential of Icelandic volcanoes to do disrupt air traffic – something that volcanologists have been warning of for decades – has been demonstrated, it is up to the airline industry and the air traffic regulatory authorities to develop a strategy to cope with such a situation in a way that balances the risks of flying against the disadvantages of not flying.

*19 Dec 1821- 1 Jan 1823 (http://volcano.si.edu/world/volcano.cfm?vnum=1702-02=&volpage=erupt) This has been erroneously reported as ‘two years’ in various news stories, presumably because people have just taken note of 1821-1823 without looking at exact dates.”

Dr David McGarvie, Dept of Earth & Environmental Sciences, The Open University, said:

“Q1. Because the last Eyjafjallajökull eruption lasted for 2 years (1821-23), does this mean that the current eruption could go on for 2 years?

A1. It’s not a valid comparison, because the eruptions are not the same.
1.,A widely quoted error is that the 1821-23 eruption lasted for 2 years, whereas records show it lasted for no more than 15 months, which is just over one year. Of greater importance is that during these 15 months there were only two sustained periods of explosive ash-producing eruptions, one lasting 1-2 weeks in December 1821 and a second lasting about a month in late June 1822. The rest of the time there were only occasional explosions.
2.,The 1821-23 eruption definitely did not involve 2 years of continuous ash-producing eruptions!
3.,Both eruptions occurred at the summit of the volcano, but that’s the main similarity.
4.,The lava (magma) type that erupted in 1821-23 is also different to what is erupting now. The 1821-23 magma was more silica-rich, which means it is more ‘sticky’ (viscous) and richer in gases (volatiles), and hence more likely to produce ash more readily.

Q2. Could the current ash-producing Eyjafjallajökull eruption could go on for many years?

A2. Possibly, but unlikely.
1.,This would only happen if (everything else being constant) the storage system beneath the volcano contained/produced enough of the ’sticky’ ash-producing magma to feed an eruption that lasted many years.
2.,However there is usually a finite amount of ‘sticky’ magma available at a volcano like this (because it usually takes a long time to produce it), and so it can reasonably be anticipated that once the eruption of ‘sticky’ magma ends, we’ll see an end to the ash-producing activity that has been closing airspace.

Q3. In late April the eruption seemed to be getting weaker and dying out, but it’s kept erupting, so what’s changed?

A3. The simple answer appears to be that more energy has been added to the eruption.
1.,This appears to be related to pulses of new magma entering the deep plumbing system beneath the volcano.
2.,Icelandic scientists have recorded swarms of earthquakes that have started deep (20-24 km depth) and then migrated upwards into the volcano, which they have interpreted as pulses of new magma being injected into volcano’s plumbing system.
3.,This new magma provides extra energy which can fuel and prolong an eruption.
4.,The first deep earthquake swarm occurred around 3 May, and soon afterwards the eruption became more energetic and explosive, with more ash being carried to higher altitudes. (And soon afterwards Irish and Scottish airspace was closed, but of course it was necessary for the winds to be carrying the ash in the ‘right’ direction.)
5.,There have been two further earthquake swarms since 3 May, suggesting that new magma is periodically being injected into the deep plumbing system beneath the volcano.

Q4. How good is the evidence suggesting that Eyjafjallajökull eruptions always trigger Katla eruptions?

A4. It’s circumstantial.
1.,The three historic eruptions of Eyjafjallajökull (i.e. past 1100 years) are all quite different to one another. The c.920 AD eruption produced a long lava ridge that would have taken weeks-to-months to form; in 1612 a small summit eruption apparently lasted for only 3 days; and in 1821-23 a 15-month eruption only had two short (fortnight-to-month long) periods of sustained ash-producing explosive activity. There’s no clear reason why these eruptions – especially the apparently tiny and short-lived 1612 eruption – should have triggered eruptions at Katla.
2.,Crucially, Katla erupts independently of Eyjafjallajökull. In the c.1100 year historic period Katla has erupted about 20 times and Eyjafjallajökull only 3 times. So it could be pure coincidence that three of Katla’s eruptions have occurred within about a year of the three historic Eyjafjallajökull eruptions.”