Sheep raise an ash cloud as they run in a field near Kirkjubaearklaustur 260 km (162 miles) from Reykjav?k, Iceland Tuesday May 24 2011 after the Grimsvotn volcano began erupting on Saturday, sending clouds of ash high into the air that have then been carried toward the European continent on the wind. Experts say that particles in the ash could stall jet engines and sandblast planes' windows. The ash cloud forced US President Barack Obama to shorten a visit to Ireland on Monday, and has raised fears of a repeat of huge travel disruptions in Europe last year when emissions from another of Iceland's volcanos, Eyjafjalljokull, stranded millions of passengers.(AP Photo/Brynjar Gauti )