Tsunami of dirt: what caused Nepal’s deadly glacial flood?

Prakash Mathema/Getty More than 150 people are dead and hundreds more missing after an enormous wave of water, ice, mud and rock cascaded more than 170 kilometres down the Bhote Koshi River valley in Nepal.

The valley is the main link between Kathmandu in Nepal and Lhasa in Tibet.

At least 34 Australians are missing.

There was little warning.

Footage of the debris-laden flash flood is shocking.

It is, unfortunately, not surprising.

As an expert in glaciers, I have tracked their accelerating retreat around the world as they melt – and the disasters that can follow.

Early analysis suggests the abrupt collapse of a glacier triggered the disaster.

As climate change intensifies, glaciers worldwide are melting – even in high regions such as the Himalayas .

The Himalayas are especially vulnerable, because the steep slopes of many of these very tall mountains are made of permafrost – rock and soil frozen for centuries.

As temperatures rise, these slopes are beginning to melt or destabilise.

If an earthquake or slope failure occurs, it can trigger a sudden and devastating debris flow.

It’s too early to say this was the exact cause.

But we know that the great ice stores of the Himalayas – known as the world’s “ third pole ” because it contains the largest amount of snow and ice after the Arctic and Antarctic – are no longer safe.