A huge cloud of volcanic ash from Iceland has forced authorities to shut down air travel across much of northern Europe, with delays and cancelations spreading quickly.
Officials in Britain Thursday canceled all non-emergency flights, including those to and from London's Heathrow Airport. Heathrow, Europe's busiest airport, averages about 1,200 flights and 180,000 passengers a day.
A statement on Heathrow's Internet site said officials had yet to decide whether to allow flights to resume Friday morning.
Authorities in Ireland, Denmark, Norway, Sweden and Finland also have stopped all air traffic. The massive plume is also causing delays and additional cancelations in France, Belgium, the Netherlands and Switzerland.
U.S. authorities say some outbound traffic from the eastern United States also has been disrupted.
In addition to reducing visibility, authorities warn that volcanic ash contains small particles of glass that cause jet engines to malfunction.
In some cases, airplanes flying into ash plumes have dropped thousands of meters before their crews were able to restart stalled engines.
The current cloud of ash is the result of a volcanic eruption Wednesday under a glacier in southeastern Iceland.
The eruption melted part of the glacier, causing flooding that has forced hundreds of locals to flee their homes. It also shot a plume of ash about eight kilometers into the atmosphere.
Police say no lives or property are in immediate danger and that the worst of the flooding appears to have subsided.
The volcano has now erupted twice since March 20. Until then, it had been dormant for nearly 200 years.
Iceland sits on a North Atlantic volcanic hot spot.