Pakistan, Aug. 28 -- A huge piece of ice that fell thousands of metres from a glacier into a river below may have unleashed the disaster in Nepal and Tibet that killed at least 180 people.

Here is what experts believe happened so far:

Glacier collapse

A glacier collapse in Nepal's mountains near Tibet appears to have triggered the disaster.

"A large chunk of glacier fell from about 5,200 metres (about 17,600 feet). into a valley," said Simon Cox, principal scientist at New Zealand's GNS Science.

It "transformed into this raging mass of debris. where it picks up rocks and sediment and trees and anything in the way and fires it on down through the canyon," he told AFP.

The wall of water first impacted a border post, as documented in t...