Smoke rises from Iceland's Grimsvotn, the island nation's most active volcano, on Saturday, May 21, 2011. (AP Photo/Halldora Kristin Unnarsdottir)

Photo by: Halldora Kristen Unnarsdottir

Smoke rises from Iceland's Grimsvotn, the island nation's most active volcano, on Saturday, May 21, 2011. (AP Photo/Halldora Kristin Unnarsdottir)