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Eyjafjallajökull

Britain – the perfect location!

In Britain, we are very lucky to have our spot on the globe. We have no active volcanoes, any earthquakes are absolute tiddlers and hardly ever cause any structural damage. Our weather is also very gentle as we very rarely get extremes of temperature.

Minus 10C (50F) is considered to be very cold here in the UK, but it would be a mild day in Moscow. If temperatures reach just over 30C (86F), Brits start running for the shade whilst people in North Africa would be reaching for their jumpers.

This explains why almost any kind of natural event that impacts on us here in the UK tends to be blown a bit out of proportion. This because we are used to things being quite mild.

Distance between Iceland and UK

Travelling aerosols

Iceland is the closest highly volcanic region to Britain and it was this that caused chaos in the skies over Britain this spring. In fact, the Icelandic volcanoes are a lot closer than most people think and do give us a pummelling at pretty regular intervals, geologically speaking that is. They are only about 1609Km (1000 miles) away. This is about the same distance as the Costa Brava in Spain, about about two hours by jet!

We also regularly get material from the Sahara blown up as far as Britain. If you've ever found a thin layer of dust on the car in the morning, then have just seen a bit of the Sahara Desert.

Saharan Wind

Aerosols can travel many thousands of miles. An aerosol in this case is not something you squirt under your arms to make you smell less like a buffalo, but any kind of fine particles that can be carried high into the atmosphere. Volcanoes can be really good at producing aerosols. Eyjafjallajökull (a mouthful for a volcano eh!) was really good at it because it started to erupt under a glacier.

Did we experience an Icelandic aerosol?

All volcanoes produce ash. Pompeii was buried under tens of metres of volcanic ash, but it was made of large, heavy particles that fell out of the air after travelling only a few miles from the volcano.

Pompeii

To make really fine ash that travels hundreds miles you need water, and Eyjafjallajökull has loads of it! As the volcano came to life under a glacier the heat started to melt the ice and boil the water. The steam gets hotter and hotter until the pressure gets so great that it blasts its way out of the glacier. Very spectacular!

Eyjafjallajokull

Also, it's potentially deadly. As the melted glacier fell down the mountain, it turned into a river as big as the Amazon. Thankfully, no towns were in the way or they would have been instantly destroyed.

Aerosols and Eyjafjallajokull

The ash formed was incredibly fine, the same size as flour grains. The lava that was blasted to pieces is made mostly of Silica. This is the same stuff that sand and window glass is made of. So the dust that settled over Britain in the weeks that followed the eruption was really very fine glass particles!

Why is this so dangerous to aircrafts?

Actually it's only dangerous for a jet aircraft. Old fashioned piston engine aircraft can fly quite happily. Just like a car engine, they have air filters that clean out any potentially damaging particles before they can pass into the engine. A jet sucks in so much air that you could never filter the particles out. In fact jet engines are incredibly robust. They are one of the most reliable machines ever made. An airline pilot that flies every day for twenty years may never experience a single engine failure. Amazing! The safest form of travel really is the aeroplane.

So why all the panic?

Jet engines can cope with quite staggering amounts of rubbish being pushed into them. A large jet can swallow several birds the size of chickens, chew them up and spit them out the back without incident. So why should a little bit of ash cause problems?

Bird Strikes

The reason is that the ash is made of these fine glass particles and glass has a very low melting point. You can soften a glass rod by sticking it into the hottest part of Bunsen burner flame. The temperature inside a jet engine is a lot hotter than that, over 1500C (2732F). This is well above the melting point of some glass. What happens is that the volcanic ash is drawn into the engine, melts and then sticks to the turbine blades. This can cause the engines to shut down.

Speedbird 9

This is what happened to a British Airways flight over Indonesia in 1982. It was flying at 37,000 feet, about 6 miles up, when it flew through an ash cloud produced by the Galunggung volcano on the Island of Java. Nothing appeared on the planes radar as the ash particles were too fine to reflect any radio waves back.

Speedbird 9

The first time the crew knew that something strange was going on was when they noticed a terrific display of 'St.Emlo's' fire on the outside of the plane. This is a form of static electricity and it isn't unsual to see this at high altitudes.

But this time it was because the aircraft was flying through a cloud of very fine ash particles that were charging up due to the friction with the aircraft.

On that day though, there was worse to come. Smoke started to appear though the ventilation system and there was a strong smell of sulphur. A few minutes later the number 4 engine shut down. Within a minute or so the other three engines did the same. Speedbird nine was the biggest glider the world had ever seen.

Luckily, the captain calculated that from 37,000ft, the aircraft could glide for about 23 minutes and cover 146Km (91 miles). There were two clear options: clear the high Indonesian mountains and make it to an airfield, or a sea landing. But a sea landing was something that had never been attempted in a 747 before.

As the cabin pressure failed, it was clear that the aircraft would have to descend rather quicker to keep the 248 passengers breathing. All this time they had been trying to restart the engines. At about the 15th attempt one of the engines restarted followed shortly by the other three. Speedbird 9 landed safely sometime later. This is why aviation people tend to be a little touchy about volcanic ash clouds.

Was it a stroke of luck?

Remember that it is a coating of molten glass that causes jet engines to fail. As the plane descended to lower altitudes, masses of cold air rushing into the engines cooled the glass and caused it to solidify. As it froze solid it contracted and fractured, shattering into thousands of tiny pieces. This unlocked their grip on the engines and they could fire up again. It is an amazing story and one that should not need to be repeated!

The big questions:

Why is volcanic ash such a big deal to aircraft?

How do they cause engines to fail?

Are Icelandic volcanoes likely to stay a threat?