The eruption of a volcano at the Eyjafjallajoekull glacier, about 75 miles east of Reykjavik, has created a plume of ash and debris about 7 miles high. The volcano had been dormant for about 200 years until an eruption last month but Wednesday's event was much larger.
The ash cloud from the volcano drifted east, affecting air traffic across Europe. Particles in volcanic plumes can cause airplane engines to shut down.
Officials predicted about 17,000 flights would be canceled Friday across the northern tier of Europe. Many international flights into that part of the world were also canceled. Air traffic controllers don't expect conditions to improve enough for safe travel until Saturday.
Scientists said the volcanic eruption appeared to be lessening and some airports in Ireland were reopened by midday Friday.
Officials in Poland, however, voiced concern over how flight restrictions would affect the ability of world leaders to reach the country for Sunday's funeral of President Lech Kaczynski, who died in a plane crash last Saturday. No decision was announced on whether to postpone the ceremonies.