S44E23 : Killer Volcanoes

NOVA follows a team of volcano sleuths as they embark on a worldwide hunt for an elusive volcanic mega-eruption that plunged medieval Earth into a deep freeze. They look for the signature of a volcanic eruption big enough to have blasted a huge cloud of ash and sulfuric acid into the atmosphere, which chilled the entire planet. Across the globe, it turned summer into winter.