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Dave Rothery on volcanoes

Updated Monday 4th October 2010

In this video, Dr David Rothery talks about the 2010 eruption of Eyjafjallajökull in Iceland and the likelihood of future eruptions around the globe

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The 2010 eruption of Eyjafjallajökull in Iceland caused chaos for the aviation industry. Dave Rothery talks about the eruption and how some of the problems caused by the volcanic ash could have been avoided.


Copyright The Open University


Copyright The Open University


The eruption in Iceland of the Eyjafjallajokull volcano didn’t actually catch volcanologists entirely by surprise. There’d been signs of unrest at the volcano for several months. As far back as December, there were small earthquakes deep beneath the volcano that began to become shallower. There was ground deformation. The students on my Volcanoes, Earthquakes and Tsunami course had been watching the earthquakes since at least February waiting for the eruption to happen, and they were expecting a volcanic flood to happen with meltwater because the volcano’s underneath an icecap, and we were expecting what the Icelanders call a jökulhlaup, a glacier burst, a big flood of meltwater to escape, which has happened in the past under similar circumstances.

What was surprising was when the eruption began it actually burst out beyond the edge of the ice cap. So it didn’t cause any melting of meltwater at first; it caused what the Icelanders refer to as a touristic eruption. It was low viscosity lava basalt fountaining out, very pretty fire fountains, little sprays of molten basalt magma going hundred feet into the air and flopping back to the ground and forming lava flows, very pretty, it didn’t do anybody any harm, and this was in March. But in April that’s when things really began to go pear shaped because the eruption beyond the ice cap sealed up, and it burst out again right underneath the ice cap, and sure enough all that magma coming out under the ice melted a lot of glacial ice, caused a big flood, which destroyed the coastal road and destroyed some bridges and ruined some farmland.

That was expected, that had been prepared for, but what caught most people on the hop was so much meltwater got into the volcano plumbing system, but it turned what had been an effusive eruption, or very low-grade explosion eruption, into a very, very big explosive event. The meltwater was turned into steam very quickly deep within the volcano plumbing, and the expansion of this steam and the shockwaves generated fractured or fragmented the magma into very fine particles that we call ash, and these ash particles were shot out at great speed and still quite hot into the sky forming a big high column of ash, and that ash got carried up to a height of 20,000 feet at some times.

Now the reason why you can’t fly when there’s ash is that if ash gets into a jet engine it can coat the surfaces of the engine. It will melt because the engines are hot inside, and this molten ash turns into glass, which just stops the engines working basically. There were two near fatal incidents in 1982 when first of all the British Airlines jumbo jet and two weeks later a Singapore Airlines jumbo jet flew into the downwind ash cloud from a volcano in Indonesia called Galunggung, and in both those cases the plane lost all four of its engines and were just gliding down towards a crash landing in the sea when the engines were able to be restarted fortunately. The cold air rushing through the dead engines shattered the glass and enabled the engines to restart.

So after those incidents, people began to be aware of flying into ash clouds, but then in 1989 it happened again over Alaska. A KLM flight lost its engines over Mount Redoubt. Again fortunately the engines were restarted. But it would be dreadful to actually lose a plane. You can’t guarantee you’re going to restart your engines if it gets clogged with ash, and after that network of volcanic ash advisory centres were set up around the world to take charge of reporting ash clouds, tracking them and passing the information on to basically the civil aviation air authorities to direct planes away from ash clouds. The airlines complained pretty loudly about not being allowed to fly, but really they were part of the problem.  They had been asked for a long time to decide a safe limit for flying through ash, and nobody had agreed how much ash could be tolerated.

So the rule that was in place was that if there’s any ash in the sky, you mustn’t fly through it, and most of the world you can live with that because you can fly around, but with this ash cloud over the whole of Europe, planes just couldn’t operate, and this was clearly not sustainable indefinitely. I’m glad we stopped flying because it would have been dreadful to lose a planeload full of people.  The airlines and the engine manufacturers did some tests, and it took them six days to get an agreement that a limit of ash of two milligrams of ash per cubic metre was a safe limit. So once that limit had been agreed and approved by the authorities flights were cautiously able to begin again. They were stopped once or twice later when the ash re-intensified. But they brought in this limit of ash that was declared safe to fly.

Now I wish they’d worked out how much ash they could tolerate in advance rather than having to work out this safety threshold in a tearing hurry during a crisis.

In this second video, Dave explains the effects of plate tectonics and how eruptions occur, and warns about the deadliest volcanic eruption - the supervolcano - such as the Yellowstone Caldera.


Copyright The Open University


Copyright The Open University


When a volcano erupts explosively, what drives it is the force of expanding gas. As magma rises to the surface, gases that have been dissolved within it at depth are subject to less and less confining pressure. And they come out of solution and form bubbles, and if these bubbles expand sufficiently rapidly, it can drive fragmented volcanic material out of the vent of the volcano with a fair degree of explosive force; stuff can be thrown thousands of metres into the air in the most explosive cases.

Now some magmas carry a lot of gas with them, particularly above subduction zones where one tectonic plate is pushed below another because you’ve got ocean water getting involved in the melting there, which is obviously going to turn to steam and come out through the volcano. Other volcanoes, which are not above sites rich in magmatic gas, can still erupt explosively if water can get in near the surface.

Now this happened very famously this year in Iceland where the Eyjafjallajokull volcano erupted below a glacier and glacial meltwater got into the volcanic plumbing system, and turning that to steam caused explosions which drove a big column of ash into the sky, which closed down European airspace for several days.

The volcanoes that have the biggest explosions tend to be those that erupt least often. If you go to a volcano like Stromboli, where I’ve worked myself on many occasions, if you’re lucky you can see an eruption every twenty minutes or every half hour, but it’s just a small burst. A bubble bursts and throws a rock out hundred feet above the vent, and it falls back down to the ground and it’s over. But volcanoes that do nothing for hundreds of years and then let rip are the most dangerous ones.

I mean the most dangerous, biggest eruption of the last century was a place called Mount Pinatubo in the Philippines, which erupted in 1991, and the eruption column there got to about 60,000 feet into the sky. Hundreds of people were killed by mud flows and ash falling onto roofs which weren’t cleared, and a lot of people were evacuated.

Of course, Mount St Helen’s is a very famous eruption of the last century as well. What happened there as well as stuff going skyward, the flank of the mountain gave way at the start of the eruption, and the trapped gases blasted out sideways. So this directed blast flattened the surrounding forest in a very spectacular fashion and showed us a new style of eruption which we hadn’t been aware of.

The biggest explosions we can get from a volcano is something called a supervolcanic eruption. Now a supervolcano is something which typically only erupts once every 100,000 years or something like that, only not as regular as clockwork, but on average something like that. The most famous supervolcano is in Yellowstone in Wyoming in the North West USA.

Now Yellowstone’s had three eruptions about two-and-a-half, one-and-a-half and about three-quarters of a million years ago, something like that, and each time it’s produced an enormous column of ash into the sky, which has been showered down onto the ground and caused very hot searing pyroclastic flows. If this were to happen today, you would lose most of the Midwest of the United States, and there would be so much muck in the sky that photosynthesis would shut down over much of the globe for weeks or maybe months.

Supervolcanoes are really very nasty events. Now they’re not going to wipe out life on Earth, they’re not going to make species go extinct, but a large proportion of individuals would die as a result of a supervolcanic eruption. So we need to be prepared for these. As I say, they’re not that frequent, if every supervolcano erupts every 100,000 years and we’ve got half a dozen supervolcanoes lurking somewhere on the planet, every 10,000 years or so we could get a very, very nasty eruption, which we need to learn how to cope with.


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