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 among the most destructive and deadly events in nature. But as Iain Stewart reveals, there is far more to volcanos than death and destruction - they are actually one of the keys to life on Earth.
(First shown on BBC4)