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GRIMSVOTN, ICELAND – MAY 23: The eruption of the Grimsvotn volcano sends thousands of tonnes of volcanic ash into the sky on May 23, 2011 above Iceland. The cloud has forced the closure of Icelandic airspace and spread fears of a repeat of the global travel chaos that was caused by last year’s Icelandic eruption, although authorities inisist that this Grimsvotn poses a lesser threat. (Photo by Jon Magnusson/Getty Images)