The ash cloud produced by the eruption of a sub-glacial volcano in Iceland brought chaos to the European air industry between 14 and 21 April. Since then, disruption to flights has continued sporadically depending on the varying intensity of ash cloud and weather patterns. Here we explain how and why the crisis developed.
Iceland is a country of fire and ice, home to several volcanoes and straddling two tectonic plates. The Eyjafjallajokull volcano began erupting in March. On 14 April, the eruption entered a new explosive phase which was to bring European airspace to a standstill.
The eruption threw thousands of tonnes of mineral ash into the air - forced higher by steam plumes created as glacial ice melted. Most of it was very fine particles which formed an ash cloud, rising 6-10km (20,000-35,000 feet) into the atmosphere.
Test shows how ash affects a jet engine
Ash clouds pose great danger to aircraft and can lead to engine failure. The fine, abrasive particles erode metal, clog fuel and cooling systems and melt to form glassy deposits. Flight instruments, windows, lights, wings and cabin air supply can also be affected.
As the ash cloud spread south and east, air traffic controllers responded by closing airspace due to safety fears. First Scottish airspace closed, then the whole of UK airspace, then most of northern European airspace. It was the biggest disruption to flights since 9/11.
The cloud moved with the weather systems, some of it drifting over the Atlantic. Test flights allowed aviation authorities to identify safe thresholds of ash concentration in the atmosphere and most flights were given the all clear to resume on 21 April.
It was business as usual for a while, until another major eruption. This time, weather systems also carried the cloud to Spain and the Mediterranean causing widespread cancellations. Since then, ash clouds and flight disruption have continued sporadically.
The knock-on effects have been huge: thousands of passengers have had to make their way home overland, air operators have lost millions of pounds a day and some trade sectors have ground to a halt. It is unclear for how long the volcano will continue to erupt.