What makes an avalanche so dangerous?

There are around 250 thousand avalanches in the Alps each year. But the size and the speed of the one that struck the climbers on Mont Maudit would have left them with little chance of survival.

Ninety per cent of avalanches are triggered by the people caught up in them.

They're certainly very dangerous - about 150 a year die in avalanches around the world, and that's because they're just so fast.

This video from the Swiss Avalanche Research Centre shows a speedometer detailing the speed at which the avalanche moves. By the time the snow reaches the camera, it's travelling at more than 100 mph.

It seems incredible that anyone could survive being buried in that.

There's an 80 per cent chance of surviving after 15 minutes but only a 20 per cent chance after 90 minutes.