Overview:Iain Stewart takes a grand tour of the world's most extraordinary volcanoes. With explosions that dwarf atomic bombs, waves of hot turbulent gas that travel at the speed of sound and rivers of hot molten rock that destroy everything in their path, volcanic eruptions can literally move mountains in minutes and are rightly thought of as among the most destructive and deadly events in nature. But there is far more to volcanoes than death and destruction, because without them the planet would be a very different place - there would be no atmosphere and no life.