Outline of Debris Cover Project in Khumbu Glacier:Glaciological Expedition of Nepal Contribution No. 62 Project Report No.1 on "Studies on Supraglacial Debris of the Khumbu Glacier"

One of the most conspicuous morphologic features on the southern slope of the Himalayan range is the dominant distribution of debris covered glaciers. It has often been pointed out that there is relationship between the geographical distribution of glaciers and climatic conditions in the Himalayas. In consideration of these feature, Watanabe (1976) has classified the glaciers of Nepal Himalayas into the following two types based on geographic location and surface morphologic conditions: Nepal type glaciers and Tibet type glaciers. The identifying feature of the former types is the extensive cover of debris in the ablation area. From a similar point of view, Moribayashi (1974) has proposed another glacier classification in the Nepal Himarayas : clean type (debris-free type) and debris type. Furthermore, the progress of glaciological studies in Nepal Himarayas reveal that, those debris feature are related not only to the recent environmental conditions surrounding the glaciers, but also to the glaciation process. Great attention has also paid to the important role of air-surface interaction. In the GEN Project since 1973, study of the debris cover has included study of the Rikha Samba glacier, a so-called clean-type glacier, in central Nepal by Nakawo (1977), and of the Khumbu glacier and others in the vicinity by Fushimi (1977 and 1978). 2. General aspect of Khumbu Glacier Khumbu Glacier is situated in the Khumbu region, east Nepal. In this region many debris covered glaciers, such as Nangpa, Summa, Ngozumpa, Lhotse and Imja, are found. The largest among those is the Ngozumpa where the debris covered area now occupies 16 km in length and 2 km in width. Khumbu Glacier is relatively smaller in comparison. These glaciers have similar topographic characteristics. Upstream of these glaciers are surrounded by 7-8000 m ridges so the accumulation basin is directly adjacent to steep slopes having and large height differences. The Khumbu Glacier is a type of valley glacier with compound basins such as the West Cwm, the Lho La, the Lingtren-Khumbutse and the basin to the west of Nuptse. At one time, the Khumbu Glacier had other tributaries from the Pumori and the Changri Glacier (Fushimi, 1977) . The latest expansion of the glacier is presumed to have been 400 years ago as determined by radiocarbon dating (Fushimi, 1978). The upper limit of the glacier is around 6800 m on the SW face of Sagarmath (Mt. Everest, 8848 m) and 8000 m on the Lhotse (8511 m) face. The equilibrium line which divided the area of accumulation and ablation of the glacier is around 5600 m. In the area above this line, accumulation processes by which mass is added to the glacier occur through the deposition of snow fall, blowing snow and avalanches. Mixing of the debris from surrounding wall with the ice mass may be performed through those processes. Although a detailed study of the mass balance of this glacier has not been done, a preliminary estimate was made by Inoue (1977). The result showed that recent conditions may by in nearly equilibrium with a value of 3.8 •~ 1012g in accumulation and 3.5 •~ 1012g in ablation. Topographic features of the ablation area are characterized by rows of ice pinnacles, ridges and cliffs, glacier pond and depressions and a com-