Tsunamis

These massive waves can be taller than the biggest skyscraper, travel at the speed of a jet plane and when they reach land, rear up and turn into a terrifying wall of water that destroys everything in its path. These unstoppable, uncontrollable forces of nature caused the ruin of an entire ancient civilization, may have played a small part in the demise of the dinosaurs, and in World War II were used as a weapon. Yet astonishingly, two men who surfed the tallest wave in history - half a kilometre high - survived.