Ash from Iceland's spewing volcano halted air traffic across a wide swathe of Europe on Thursday, grounding
planes on a scale not seen since the 9/11 terror attacks.
Thousands of flights were canceled, tens of thousands of passengers were stranded and officials said it was not clear when it would be safe enough to fly again.
In a sobering comment, one scientist in Iceland said the ejection of volcanic ash - and therefore disruptions in air travel could continue for days or even weeks.
Authorities stopped all flights over Britain, Ireland and the Nordic countries. The shutdown closed London's five major airports
including Heathrow, Europe's busiest, a major trans-Atlantic hub that handles over 1,200 flights and 180,000 passengers per day.
With the cloud drifting south and east across Britain, the country's air traffic service banned all non-emergency flights until at least 7 a.m. (0600 GMT, 2 a.m. EDT) Friday.
Irish authorities closed their air space for at least eight hours, and aviation authorities in Denmark, Norway, Sweden and Finland took similar precautions.
Airport shutdowns and flight cancellations spread across Europe - to France, Belgium, the Netherlands, Denmark, Ireland, Sweden, Finland and Switzerland - as well as around the world.
The volcano's smoke and ash poses a threat to aircraft because it can affect visibility, and microscopic debris can get sucked into airplane engines and can cause them to shut down.
Health officials said the plume, which rose to between 20,000 feet and 36,000 feet (6,000 meters and 11,000 meters), posed no threat to human health.
Airlines in the United States were canceling some flights to Europe and delaying others.