Published: May 08, 2010 6:28 PM EDT

BRUSSELS (AP) - Travelers flying across the Atlantic Saturday can expect a longer flight.

Ocean winds are carrying the ash cloud from an Icelandic volcano south.

The 1,200-mile-long cloud now stretchesfrom Iceland to northern Spain, where it's forced the closure of 15 airports.

Europe's flight control agency is rerouting trans-Atlantic flights north over Greenland and south of the cloud, adding up to an hour of flying time in either direction.

The plume of ash is expected to expand into southern France during the day.

On average, 600 airliners make the ocean crossing every day.