The 2010 Eyjafjallajokull eruption, Iceland

A constructive plate margin

Iceland straddles the Mid-Atlantic Ridge, where the North American and Eurasian plates pull apart by a few centimetres a year, and it also sits above a mantle hot spot. Magma rises to fill the gap, feeding frequent eruptions. Eyjafjallajokull itself erupts rarely, and pressure had been building beneath it for months before March 2010.

Magma meeting ice

The April vent opened beneath the volcano's ice cap. Meltwater flooded onto the rising magma, chilling it almost instantly so that it shattered into tiny glassy fragments, while the water flashing into steam made the eruption violently explosive. This combination produced unusually fine ash that could stay airborne for days and travel thousands of kilometres.

Weather that carried ash to Europe

For days after 14 April the jet stream blew steadily from the northwest, pushing the plume straight towards the busiest airspace on Earth. High pressure then kept the pattern stuck in place, so fresh ash kept arriving over Britain and mainland Europe instead of dispersing over the empty North Atlantic.

Strict aviation rules

Volcanic ash melts inside jet engines and can shut them down, and the rules at the time treated any concentration of ash as unsafe. Regulators therefore imposed a blanket ban rather than a partial one. The closure of most of Europe's airspace, more than the eruption itself, is what turned a local event into a global story.

Primary

• Explosions under the ice threw fine ash to about 10,000 metres on the first day.
• Meltwater floods, known as jokulhlaups, surged down rivers and washed out sections of Iceland's ring road.
• Ash fell across farmland in southern Iceland, contaminating pasture and water supplies.

Secondary

• Most European countries closed their airspace in mid April, grounding about 100,000 flights.
• Around 10 million passengers were stranded around the world.
• Air freight stalled, so perishable exports such as Kenyan flowers and vegetables rotted before they could be flown out.

Social

• Travellers were stuck abroad for days, missing work, school, weddings and funerals.
• Several hundred Icelandic farming families were evacuated from the flood zone.
• Trains, coaches and ferries across Europe were overwhelmed as people looked for other routes home.

Economic

• Airlines lost about 1.7 billion dollars of revenue while their fleets sat on the ground.
• Some estimates put cancelled international tourist arrivals at over 2 million, at a direct cost to tour operators of about 1 billion euros.
• Icelandic farmers faced losses from flooded land and ash-covered pasture.

Environmental

• Ash blanketed farmland near the volcano, though it later added nutrients to the soil.
• Glacial floods reshaped river channels and spread sediment across the coastal plain.
• Grounding aircraft briefly cut European carbon dioxide emissions by more than the volcano was emitting.

Immediate

• Icelandic authorities evacuated residents from flood-risk farms and deliberately breached the ring road to save its bridges from the meltwater.
• The Volcanic Ash Advisory Centre at the UK Met Office tracked the plume and forecast its spread for aviation.
• European regulators closed airspace, and airlines rebooked or accommodated stranded passengers.
• Governments and airlines laid on coaches, ferries and even navy ships to bring travellers home.

Long term

• Aviation authorities replaced the zero-ash rule with agreed safe concentration limits, so later eruptions caused far less disruption.
• Engine makers and regulators researched how much ash aircraft engines can actually tolerate.
• Monitoring of Iceland's ice-capped volcanoes was strengthened, with more sensors and better flood warnings.
• Airlines and the EU reviewed compensation rules for passengers stranded by ash closures.