n April 2010, the eruption of Iceland's Eyjafjallajoekull volcano turned much of the northern hemisphere into an ash-strewn no-fly zone, stranding hundreds of thousands of travelers. But Eyjafjallajoekull was just the start. Now, an Icelandic volcano ten times bigger, Katla, has begun to swell and grumble. Two more giants, Hekla and Laki, could erupt without warning. Iceland is a ticking time bomb: When it blows, the consequences will be global. As CGI takes us inside these geological monsters, meet atmospheric scientists who are working to understand just how devastating an eruption could be.