Fluctuations of Sedimentary Environments of the Gyajo Glacier, Khumbu Region, East Nepal

Abstract

Studies on the snow-layer stratigraphy were carried out at the Gyajo glacier, Khumbu region, East Nepal from 1973 to 1978. The ages of the snow layers were determined by stratigraphy and tritium analyses, and the fluctuations of sedimentary environments of the Gyajo Glacier, the lower type of a glacier located below 6,000 m in the Nepal Himalayas, were clarified from 1940s to 1975 in relation to the climatic changes. The results are: (1) It is likely that one snow layer per year is preserved divided by dirt bands: there are depositional periods ranging for 4-9 years, interrupted by depositional gaps (lacuna) lasting several years. Such stratifications contrast with such higher glaciers as the Khumbu Glacier, where two snow layers per year are formed with continuous deposition. (2) The ages of snow layers were determined by variation of tritium concentrations due to the thermonuclear tests series of 1950s-1970s. From 1940s to 1960s, the net annual balances have a decreasing trend from 450 to 45 mm, while annual balances are relatively large at the start of the 1970s, ranging from 540 to 270 mm, due to the increased precipitation.