Alastair Stewart presents the first of two programmes featuring incredible eyewitness footage shot by members of the public on mobile devices. This episode includes an American tourist who films his narrow escape when tonnes of rocks hurtle down the mountainside as he descends Aconcagua - a peak in Argentina nicknamed the Mountain of Death. The programme also features a couple who capture on camera a catastrophic collision when a train crashes into a truck at a level crossing in Louisiana, and a man's heart-stopping race against time to find a skier buried deep in the snow after an avalanche in the French Alps.
