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Interview with volcanologist Peter Diethelm

© Remo Nägeli

The eruption of the Icelandic volcano Eyjafjallajökull in early 2010 held the world spellbound, generating headlines across the globe as its ash cloud disrupted international air traffic. Swiss volcanologist Peter Diethelm analyses the 2010 eruption and talks to us about the unique fascination of volcanoes.

Eyjafjallajökull had a dramatic impact on international air traffic. Is the danger now over?
Peter Diethelm: A simple yes or no would imply that we can predict the volcano’s behaviour. And in this case we can’t, because we only know of three previous eruptions, in 920, 1612 and 1821. We simply don’t have enough information about Eyjafjallajökull’s “personality” as a volcano. In fact, last year’s eruption posed more questions to volcanologists than it answered. We can, though, give the all-clear for the short and medium term, because the volcano has recently been kitted out with a large number of new measuring instruments. They should give us a few months’ advance warning of any major activity.

Were the scale of the eruption and the extent of its consequences foreseeable?

Peter Diethelm: It was possible to predict the timing of the eruption relatively precisely.
GPS measurements had shown significant surface deformations caused by upwelling magma more than a year earlier. And a fortnight before the actual eruption, around 3 000 earth tremors were recorded in the vicinity in a single day.

However, it’s impossible to predict either the scale or the consequences of a volcanic eruption. To do this you would need details of the volcano’s internal structure and of the precise chemical events occurring within its magma. Even the best of today’s measuring instruments can’t give us this type of information.

The unpredictable nature of volcanic eruptions was made abundantly clear by Eyjafjallajökull. The initial eruptions that took place between 20 March and 12 April produced streams of magma which made for a truly amazing sight. But it was the second phase of eruption, from 14 April to 9 July, that affected air travel. When the magma came into contact with ice and melt-water it shattered into tiny glassy particles – volcanic ash – that was then thrown 9 000 metres into the air by steam explosions. The eruption occurred directly under the jet stream, which drove the ash with unusual persistence in a south-easterly direction, straight into the heart of the busy European air traffic network. It was the combination of all these factors – explosive eruption, location under the jet stream, south-easterly wind, continuousness of the jet stream – that produced the serious consequences with which we all became so familiar.