Despite signs the volcanic ash cloud that has crippled air travel may be lessening, its continued drift south and east has forced cancellation of more flights and closed airspace in 13 European countries, officials said.

Parts of airspace in Ireland and Sweden reopened Friday, but London's Heathrow and other airports in Britain are expected to remain closed Saturday, according to a spokesman for the International Air Transport Association.

While there are about 300 trans-Atlantic flights landing each day in Europe, Friday only about 100 to 120 had arrived, according to a statement by Eurocontrol, the European air traffic organization.

The drop-off remains more dramatic for internal European air travel, with around 11,000 flights Friday, compared to a normal 28,000, the agency reported. Thursday there were 20,334 internal flights.

While there are usually 337 daily U.S. flights to Europe, on Thursday 165 flights were canceled while Friday saw 280 cancellations, said David Castelveter, a spokesman for the Air Transport Association of America, an industry group.

Airspace remained fully or partly closed in the United Kingdom, Belgium, the Netherlands, Denmark, Sweden, Norway, Finland, Estonia, part of France near Paris, northern Germany and the Czech Republic, Eurocontrol reported.

Parts of Polish airspace, including Warsaw, were also closed, a factor that could delay the Sunday funeral of Polish president Lech Kaczynski, who died in a plane crash last weekend. President Barack Obama is slated to attend those rites.

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The mushrooming implications of the eruption of Eyjafjallajokull in Iceland showed how vulnerable air traffic can be.

"There are no remote volcanoes," observed Dave Schneider, a research geophysicist for the U.S. Geological Survey in Alaska, referring to the impact an eruption can have.

At Kennedy Airport, the human effects of the travel snafu was evident. Terminal 8 looked like a small shantytown of cots and sprawling travelers.

"The time goes slowly," said a sleep-deprived Dimitri Hovine, 43, of Brussels, traveling with his wife, Isabelle, 40, and their three children ages 10 to 17. The Belgium Consulate has helped them with food vouchers.

To ease travelers' pain, Mayor Michael Bloomberg announced late Friday 30 city hotels would provide discounted tariffs for stranded passengers. Two shuttle services that both serve Newark and JFK would also supply discounted rates to and from the airports for such passengers, he said.

The ash might move closer to southern Europe and the Balkans Saturday, according to a scientific forecast map. Those predictions don't mean volcanic material has actually been observed in those regions, Schneider said.

Advances in satellite technology allow researchers to quickly spot movement of ash and sulfur dioxide from a volcano and check on the accuracy of predictions, Schneider said. While most U.S. volcanoes are on the Pacific "ring of fire," much of American air traffic flies near volcanoes, he noted. For instance, Anchorage, like London, is a major cargo hub and is about 200 miles from Mount Redoubt, which erupted last year.

With Gary Dymski

Some major active U.S. volcanoes

Mt. Redoubt

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Location: Alaska

Height: 10.197ft

Last eruption: 2009


Mt. Saint Helens

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Location: Washington

Height: 8,363.ft.

Last eruption: 2004-08


Kilaue

Location: Hawaii

Height: 4,091.ft

Last eruption: 2010*


Mauna Loa

Location: Hawaii

Height: 13,681.ft

Last eruption: 1984

Note: Kilaue is emitting sulfur dioxide and showing some activity with magma.

Source: U.S. Geological Survey website dealing with volcanoes