Volcanic Disruption

Why did Eyjafjallajökull erupt differently than other volcanoes, and what will we learn from it?

The eruption of the Eyjafjallajökull volcano in Iceland this month took Europe by surprise and resulted in losses of at least $2 billion for airlines, substantial personal costs to stranded passengers, and major commercial losses to businesses dependent on air freight (especially those trading in fresh produce, including many African companies that ship fruit, vegetables, and flowers to the European market).

But why the surprise? Iceland is basically formed from a mass of volcanoes and lava flows that have erupted over the last 20-25 million years, and Icelanders are well accustomed to living on this unstable and ever-changing island. Famously, when the Eldfell volcano erupted in 1973 and lava flows threatened to engulf the town of Heimaey, they built dikes and dams that successfully diverted the lava and averted catastrophe. Eyjafjallajökull is a relatively old volcano with a long history of eruptions, so it was no real shock, or even concern, when it first showed signs of new eruptions in early April.

At that time, the authorities were monitoring the volcano for jökulhlaups, a common but relatively localized hazard that affects volcanoes that erupt beneath glaciers. Jökulhlaups are sudden floods of water mixed with rock, caused by the ice cover melting. In 2004, a jökulhlaup from the Grimsvötn volcano in southern Iceland washed away roads and infrastructure. However, volcanic eruptions themselves rarely cause loss of life or more than mere inconvenience in Iceland because the type of lava is normally basaltic, similar to the lava erupted on the popular tourist island of Hawaii. As basaltic lavas are quite fluid, they typically just flow down valleys away from the volcano, slowly enough that people can easily get out of the way.

But Eyjafjallajökull didn’t behave quite like this. Since it’s an older and more established volcano, its magma – the molten rock before it erupts at the surface of the earth – contains more silica (in this case, the erupted material was of trachyandesitic composition, not basaltic). Silica-rich magmas are stickier than basalts and therefore have a greater tendency to explode upon eruption at the surface, rather than just flow quietly down the slopes of the volcano.

Added to this characteristic was the fact that Eyjafjallaj̦kull was capped by a glacier; when meltwater interacts with hot lava, the lava can explode. This combination of more silicic magma plus water caused the volcano to erupt in a way that is not common in Iceland (although it has happened historically). Rather than emitting relatively passive lava flows, or even j̦kulhlaups, the magma exploded and sent a plume of ash and steam up to 10,000 metres into the sky. The last such major eruption, from the Laki volcano in 1783-84, caused spectacular sunsets throughout Europe and starvation in Iceland Рbut that was before the days of air travel.

As was discovered in 1982 after a British Airways Boeing 747 came close to disaster when it flew unwittingly through an ash cloud from the Mt. Galunggung volcano in Indonesia, ash causes serious damage to aircraft jet engines by eroding the turbine blades and clogging critical internal parts such as fuel atomizers. Fragments of volcanic glass are particularly hazardous because the glass melts at temperatures below those at which the engine typically operates, coating the hot engine parts with sticky material. The result is that the engines get clogged up, overheat, and shut down. It was only after the stalled engines on the BA flight cooled down a little and the glass solidified again and became brittle, that the material broke away as the pilots tried repeatedly to restart the engines. Eventually, the pilots succeeded, but not before losing two thirds of their flying altitude and preparing to ditch their aircraft in the sea.

So when the Eyjafjallajökull volcano began emitting ash high into the atmosphere and the plume started blowing southeast towards Europe, aviation authorities throughout the continent decided to close airports and re-route planes already in the air away from the potentially deadly cloud. The precaution was sensible – had they not done so, knowing the risk, and an aircraft had crashed…

But it turns out that the risk might not have been as severe as feared, and after the flight ban had continued for several days and the financial losses had begun to mount, several airlines flew test planes without passengers through the cloud to see what would happen. The result: not much! Recriminations flew, and now there is the usual talk of compensation.

The reason for the apparently lower hazard of the Eyjafjallajökull ash compared to, for example, the Mt. Galunggung ash, may be that the latter volcano is even more silicic, and the bulk of the ash emitted was glass. Early indications are that, in comparison, there was less glass and there were more crystal and fine rock fragments in the Eyjafjallajökull ash, as well as a high proportion of harmless steam. This non-glassy dust can wear away aircraft and engine parts but will not melt so easily and stick to critical components. The volcano now seems to have gone into a more normal eruptive mode, emitting more lava than ash (presumably most of the ice cap has now melted), and the air travel crisis seems to have subsided.

The Eyjafjallajökull eruption tells us once again that we don’t yet (and likely never will) know everything about the way our exciting and sometimes dangerous planet operates. Expect to see a lot of research on more accurate risk assessment from explosive volcanic eruptions in the next few years, because the financial and human costs of overreacting, or failing to act when action is needed, can be enormous.