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Glacial lakes and glacial lake outburst floods in Nepal (英语)

The world’s climate has been warming for more than a hundred years: there have been fluctuations, notably cooling phases in the 1960s and 1970s, although long-term records indicate an accelerating warming trend from about 1980. Although this has influenced ecosystems worldwide, its effects on glaciers and the duration of winter snow cover have been particularly noticeable, especially in the European Alps and Greenland, and on the reduction of sea ice cover in the Arctic Ocean. The Hindu Kush-Himalayan region has been no exception. One of the more spectacular effects of recent atmospheric warming in the Himalayas has been the creation of meltwater lakes on the lower sections of many glaciers. In an increasing number of instances, especially well-documented in Nepal, several of these lakes have burst their natural retaining dams (usually old end moraines that were formed when the glaciers were thicker and more extensive than today). This has produced catastrophic flood surges (glacial lake outburst floods or GLOFs) that have destroyed infrastructure and taken human lives in the valleys below. The report is based upon information and experience accumulated during collaboration with several partner institutions in Nepal. It outlines a stepwise approach to assessment of risk beginning with an extensive desk study of aerial photographs and satellite images that provided the first reconnaissance mapping of more than a thousand glacial lakes. There followed a provisional identification of six lakes that were considered to be potentially dangerous and that warranted special study. Three lakes, namely, Tsho Rolpa, Thulagi Lake, and Imja Tsho, were selected for detailed field investigation, application of computer dam-break modelling, and assessment of the vulnerability of human life and property for up to 100 kilometres downstream.