摘要：We carried out multi-date morphological mappings to document the development of the glacial lake ‘Chamlang South Tsho’ in the eastern Nepal Himalaya over four decades. High-resolution Corona KH-4A and Advanced Land Observing Satellite (ALOS) PRISM stereo-data taken in 1964 and 2006 were processed in the Leica Photogrammetric Suite (LPS) to generate digital terrain models (DTMs). The DTMs produced topographic maps representing elevations and morphology of the glacier surface with a maximum error of +/- 10 m. A bathymetric map was also produced based on sonar sounding data obtained in November 2009. Extensive surface lowering was found to have occurred since 1964, as high as 156.9 m in the upper glacier area. The average lowering of the glacier for the entire 42-year period from 1964 to 2006 is 37.5 m, with the average surface-lowering rate calculated at 0.9 m/year. The average surface lowering for the 45 years from the glacier surface in 1964 to the lake bottom in 2009 was 99.5 m at a rate of 2.2 m/year. The minimum and maximum surface lowering during that period were 12 m and 153.8 m, respectively. The area surrounding the largest supraglacial pond in 1964 exhibited a low surface gradient, and there had already been a large degree of ice melting that favoured further lake expansion. The larger lowering rate at the lake area supports the previously presented idea that ice calving into the pond triggered the larger and faster up-glacial lake expansion.
