In Britain, the closures curtailed some campaigning for the May 6 national election. Monarchs from Norway and the Netherlands traveling to a 70th birthday celebration for Denmark's Queen Margrethe found their plans up in the air.
Swedish Foreign Minister Carl Bildt resorted to driving home to Sweden from Brussels. "We'll arrive sometime tomorrow," his spokeswoman Irena Busic said.
Eurostar train services to France and Belgium and Channel ferries were packed as travelers sought ways out of Britain. P&O ferries said it had booked a passenger on its Dover-Calais route who was trying to get to Beijing — he hoped to fly from Paris instead of London.
It was unclear whether the ash cloud would affect the arrival of President Barack Obama and other world leaders planning to attend the state funeral Sunday of Polish President Lech Kaczynski, who died in a plane crash.
The Icelandic plume lies above the Atlantic Ocean close to the flight paths for most routes from the U.S. East Coast to Europe, and was moving over Europe itself.
Meteorologists from the AccuWeather forecasting service in Pennsylvania said the current ash plume will threaten air travel over Europe through Sunday at the least. Einar Kjartansson, a geophysicist at the Icelandic Meteorological Office, said the problem might persist for weeks, depending on how much wind carries the ash.
Explosive volcanic eruptions inject large amounts of highly abrasive ash — essentially very small rock fragments — into the upper atmosphere, the cruising altitude of most jet airliners. It can cause significant damage to both airframes and engines.
The U.S. Geological Survey said about 100 aircraft have run into volcanic ash from 1983 to 2000. In some cases engines shut down briefly after sucking in volcanic debris, but there have been no fatal incidents.
In 1989, a KLM Royal Dutch Airlines Boeing 747 flew into an ash cloud from Alaska's Redoubt volcano and lost all power, dropping from 25,000 feet to 12,000 feet (7,500 meters to 3,600) before the crew could get the engines restarted. The plane landed safely.
In another incident in the 1980s, a British Airways 747 flew into a dust cloud and the grit sandblasted the windscreen. The pilot had to stand and look out a side window to land safely.
Gideon Ewers, spokesman for the International Federation of Airline Pilots Associations, attributed the extent of the disruption to amount of air traffic in the area where the plume was drifting.
"Normally, these volcanic eruptions affect air travel in areas of thin traffic such as the Aleutian islands in Alaska, or in Indonesia and the Philippines," he said.
Ironically, Iceland's Keflavik airport remained open Thursday. Flights to Europe were canceled but those to North America were operating normally.
Iceland, a nation of 320,000 people, sits on a large volcanic hot spot in the Atlantic's mid-oceanic ridge, and has a history of devastating eruptions.
AP reporters Robert Barr, Jennifer Quinn, Paisley Dodds, Danica Kirka and Chonel LaPorte in London, Slobodan Lekic in Kabul, Ian MacDougall in Oslo, Louise Nordstrom in Stockholm, Shawn Pogatchnik in Dublin, Jan Olsen in Copenhagen, Gretchen Mahan in Brussels, Mike Corder in Amsterdam, Adam Schreck in Dubai, Bradley Klapper and Frank Jordans in Geneva and Matti Huuhtanen in Helsinki contributed to this report.
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