How a distant land of fire and ice cast threatening shadow over UK airspace

Thousands of passengers at airports from Glasgow to Heathrow were left stranded after the Eyjafjallajokull volcano erupted in southern Iceland, sending a giant plume of volcanic ash 11km high into the atmosphere. This moved south into UK airspace forcing the Air Traffic Control Service (Nats) to suspend all flights in or out of the UK, in what was the biggest airspace restriction in living memory. We weren't the only ones to suffer, though. Norway, Sweden, Denmark and Finland were among the other countries hit as more than 4,000 flights across northern Europe were affected.

Ironically, though, passengers flying from Iceland to the United States didn't face any problems. Experts say this is because of the direction the volcanic ash is travelling. Weather forecasters expect the ash, which is moving southwards, to have drifted across the UK by the end of today and say it could eventually reach France and Southern Europe.

Brendan Jones, a forecaster with MeteoGroup, said: "The ash that will come over the UK will not be a huge plume but will feature small ash particles. It will be difficult to detect and the only visible sign could be lurid sunsets that often are a feature after an eruption.

"Ash particles from eruptions can spread widely which is why Sweden and Norway could get ash."

Dr Dougal Jerram, an earth scientist at Durham University, explains how it works.

"Volcanic ash is made up of tiny particles that are created when

bubbles break due to gases in a volcanic eruption. Eruptions which are charged with gas start to froth and expand as they reach the surface, which results in explosive eruptions and this fine ash being sent up into the atmosphere. When the ash is ejected high enough, it can reach the high altitude winds and be dispersed around the globe, for example, from Iceland to Europe. And these winds are exactly where aeroplanes cruise."

Flight restrictions were imposed in the UK after scientists and aviation authorities warned that the ash could cause jet engines to

fail.

Dr David Rothery, from the Department of Earth & Environmental Sciences at the Open University, says the restrictions were a necessary precaution.

"This is not a dense cloud, and is unlikely to be noticed by people on the ground. But if volcanic ash particles are ingested in to a jet engine, they accumulate and clog the engines with molten glass."

This can have potentially disastrous consequences. The sudden loss of power can send a large passenger aircraft into freefall, while at the same time the pilot is likely to be flying blind because of damage to the cockpit windscreen caused by the hard ash.

Even though an aircraft may be hundreds of miles from the scene of an eruption, it can still be in danger because the rising clouds of ash travel vast distances.

When Mount St Helens erupted in the United States in 1980, the plume reached as high as 90,000ft in just 30 minutes.

In 15 hours, it had travelled 600 miles downwind and within two weeks ash had circled the earth.

One of the biggest difficulties facing flight crews is the problem of distinguishing ash clouds from ordinary clouds, both visually and on radar. In 1982, a British Airways Boeing 747 plane from Heathrow to New Zealand flew into a cloud of volcanic ash caused by the eruption of Mount Galunggung in Indonesia. The crew were initially unaware of the danger they faced but within minutes all four engines had failed.

With visibility seriously reduced, the plane managed to glide far enough out of the ash cloud for three of the four engines to restart and the crew, who received several awards for their actions, were able to land safely in Jakarta. It was later discovered that as the ash cloud was dry it did not show up on the weather radar designed to detect the moisture in clouds.

In December 1989, a KLM Boeing 747 flight from Amsterdam to Alaska lost power in all four engines after entering a cloud of ash from the erupting Mount Redoubt in Alaska. The plane dropped more than two miles before the crew were able to restart the engines and the aircraft finally landed safely in Anchorage, although it cost millions of pounds to repair the damage. Two years later, more than 20 aircraft were damaged by the ash cloud from an eruption of Mount Pinatubo in the Philippines. Scientists tracked the cloud which travelled more than 5,000 miles to the east coast of Africa.

Dr Rothery says emergency procedure manuals have been changed in the wake of these volcanic ash incidents.

"Previously, when engines began to fail, the standard practice had been to increase power. This just makes the ash problem worse. Nowadays, a pilot will throttle back and lose height so as to drop below the ash cloud as soon as possible.

"The inrush of cold, clean air is usually enough to shatter the glass and unclog the engines.

"Even so, the forward windows may have become so badly abraded by ash that they are useless, and the plane has to land on instruments."

Stewart John, a fellow of the Royal Academy of Engineering and former president of the Royal Aeronautical Society, says we have to be careful

when it comes to aircraft and volcanic ash.

"This dust really is nasty stuff. It's extremely fine and if it gets into a jet engine, it blocks up all of the ventilation holes that bleed in cooling air. Jet engines operate at about 2,000C, and the metals can't take that. The engine will just shut down."

So for the time being air passengers just have to be patient.

"We do not know how long this will last. It's like a typhoon – because you can't fly through it, you can't directly monitor it, so we have to rely on satellite images and err on the side of extreme caution."