New Delhi, Aug. 28 -- One of earth's peculiarities as a planet is that its surface temperatures hover near the melting point of water, meaning some parts of it are covered by that substance in its liquid form and some by it in its solid form, ice. One consequence is that life in the transition zone is precarious. Just how precarious, the inhabitants of the Bhote Koshi and Trishuli valleys in Nepal and Tibet discovered on August 26th, when an unheralded surge of water swept all before it. More than 1,300 people are missing.

The explanation for this catastrophe seems to have been a phenomenon called a glacial avalanche. A 600-metre-wide section of a glacier in the Himalaya mountains broke free and dropped 1.2km into the valley below. The k...