Overview: Sam Champion, ABC News Weather Editor, Jeff Piotrowski (Storm Chaser) (via telephone), Tom and Olivia Rogers (Tornado Survivors), Zach Tusinger (lost aunt and uncle in tornado) and Jacqui Jeras (CNN Meteorologist) discuss the deadly tornado that struck Joplin, Missouri. CNN's Anderson Cooper (Host, AC 360) and T.J. Holmes (anochor) report from Joplin. Also, the President of Iceland, Olafur Ragnar Grimsson, is interviewed regarding an erupting volcano in his country and the potential effects on European air traffic.