A wall of grey, silted water tears through a Himalayan Valley. People look on in shock, disbelief and fear as buildings are swallowed. Cars are swept away and people run as the flood surges down below.

In its aftermath, more than 800 people are dead and thousands are missing, including 43 Australians.

In the search for answers, scientists now believe the disaster began high in the mountains, when an enormous mass of ice and rock, weighing around 500 million tonnes, collapsed and unleashed a torrent of water down the valley.

Today, glaciologist at University of Sunshine Coast Adrian McCallum, on how this disaster unfolded, and why the Himalayas and some of the world’s other great mountain ranges are becoming more vulnerable to events like it.

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