) -- A volcano in Iceland has forced London's Heathrow, the busiest airport in Europe, to shut down while hundreds of flights across Northern Europe have been canceled.
The ash clouds from the Eyjafjallajokul volcano in Iceland forced authorities to close the air space in the U.K. and Scandinavia.
British airport operator
said Heathrow and Stansted airports in London would close around 7 a.m. EDT. Gatwick, the U.K.'s second-busiest airport, also planned to close, the
Authorities didn't say when flights might resume Thursday.
The volcano was sending up smoke and ash that posed "a significant safety threat to aircraft," Britain's National Air Traffic Service said,