Srinagar, Sept. 7 -- Mohan Bahadur Chand, a Himalayan glaciologist with Kathmandu University, was in a discussion on glaciers, permafrost, snow and mountain hazards on the morning of 26 August when reports of the disaster arrived.

A torrent of water, mud, rock and debris was barrelling down the Lhende Khola valley along the mountainous Nepal-Tibet border, killing thousands as it tore through three major Nepali districts spanning roughly 100km.

Early accounts suggested a glacial lake outburst flood, or GLOF, in which a glacial lake suddenly releases a large volume of stored water. But as Chand and his colleagues reconstructed the event, a different sequence emerged. There had been no lake at the point of failure. A massive ice-rock the s...