Nepal, Aug. 27 -- Rasuwa's disaster exposed a deeper gap in Himalayan early warning: We are better at tracking floods once they enter monitored rivers than detecting the high-mountain hazards that create them. By the time a downstream gauge records a catastrophic rise, the most valuable warning time may already have passed.

Wednesday's surge was not triggered by heavy rain in Rasuwa. The strongest evidence now points to a massive debris flow in the high Lhende catchment. Satellite analysis suggests that a section of a glacier over 600 metres wide broke away and plunged nearly 1,200 metres to the valley floor, where the impact shattered the ice and mobilised rock, water and debris, sending a powerful surge into the Bhotekoshi river system...