The 1783 Laki volcanic eruption in Iceland did not only devastate the Icelandic landscape. Dr John Grattan describes how the poisonous sulphuric gas emitted from the volcano engulfed Europe, killing huge numbers of people. Clip taken from the BBC documentary series Timewatch: Killer Cloud. Watch more high quality videos on the Explore YouTube channel from BBC Worldwide here: http://www.youtube.com/bbcexplore