18 Distributions and Grain Sizes of Supraglacial Debris in the , Khumbu Region

Distributions and Grain Sizes of Supraglacial Debris in the Khumbu Glacier, Khumbu Region, East ***

Hiroji Fushimi***, Minoru Yoshida***, Okitsugu Watanabe*** and Bidur Prasad Upadhyay****

Abstract

The Khumbu Glacier, Khumbu region, east Nepal, is a typical debris-covered glacier on the south side of the Great .

The occurrences, distributions and grain size measurements of the supraglacial debris of the Khu- mbu Glacier show the following results. 1 ) The longitudinal zonal distributions with different kinds of debris can be traced even down to

the glacier terminus. 2) The traverse zonal distributions of the schistose debris are found. 3) The

schistose debris are mainly composed of pebbles and cobbles, while the granitic debris contained many boulders coarser than -8ƒÓ (256 mm in diameter). 4) The measurements of debris grain sizes shows that there are high contents of coarser debris found from area IV near the ice fall down to area II near

the present active terminus, while there are low contents of coarser debris found in the area I of the stagnant ice body. 5) The supraglacial round debris are found in the area II near the present active

terminus and in the area I of the stagnant ice body. 6) Layered englacial debris are also found at the ice cliff in the down-stream part of the Khumbu Glacier.

I. Introduction There are 664 glaciers listed in the glacier in-

The Khumbu Glacier is located to the south of ventory (Higuchi et al., 1978) of the Dudh Kosi

Mt. Sagarmatha (Chomo Lungma, Everest), north- region, east Nepal, and 47 are the D-type glaciers ern Khumbu region on the south side of the which are relatively few, but the area occupy nearly

Great Himalayas, and the glacier is surrounded by 50 % of the total glacier area. Since the supraglacial lofty 8,000 m peaks with steep cliffs producing a debris give strong effects to the ablation processes, large amount of debris by periglacial phenomena, the D-type glaciers account for one of the most im- avalanches and geological fault structures. The portant characteristics of the glacial phenomena Khumbu Glacier is a kind of debris-covered glacier, among the temperate "Nepal type glacier group" especially in the down-stream part. in contrast to the cold "Tibet type glacier group"

Moribayashi and Higuchi (1977) classified glaciers classified by Watanabe (1976). in the Khumbu region into two types : debris-covered The observation of glacier flow (Kodama and glacier, namely a large glacier with the down-stream Mae, 1976) and structural studies (Fushimi, 1977) part covered by debris, which is called a "debris- showed that the down-stream part of the Khumbu covered type glacier (D-type glacier)", and debris- Glacier can be considered as an inactive ice body free glacier, which is called a "clean type glacier having no direct relation to the present glacier flow. (C-type glacier)". The Khumbu Glacier is classified The present active terminus is situated in the debris- in the D-type glacier. covered part between Gorak Shep and Lobuche and

this inactive ice body is thought to be a fossil ice * Glaciological Expedition of Nepal, Contribution No. 64 of which the age is 410•}110 years at most (Fushimi, ** Project Report No . 3 on "Studies on Supraglacial 1978).

Debris of the Khumbu Glacier" D-type glaciers have huge glacier ponds and *** Water Research Institute , Nagoya University, Nagoya 464 lakes near the terminus, and when the ground **** Meteorology Instruction Committee , Trichandra around those ponds and lakes occasionally collapes, Campus, Tribhuvan University, Kathmandu a catastrophic flood occurs like as the case of the Seppyo, 1980 H. Fushimi, M. Yoshida, O. Watanabe and B.P. Upadhyay 19 glacier flood which originated from the Mingbo mal characteristics of glaciers of the Nepal type Glacier, Khumbu region, in 1977. glacier group with large quantities of debris. It is The study of the D-type glacier is fundamental also necessary to find out the relationship between to clarify the characteristics of the supraglacial the ablation process and the hydrological charac- debris such as distributions, occurrences and grain teristics of the D-type glacier in relation to the sizes of the debris, in order to understand the ther- glacier floods. However, there has not been much

Fig. 1. Distribution of the supraglacial Debris and the rock types, Khumbu Glacier, Khumbu region, east Nepal. 1) granitic rocks, 2) schistose rocks, 3) supraglacial granitic: debris, 4) supraglacial schistose debris, 5) debris-free part, 6) snow cover, 7) side- and end-moraines and 8) ponds and lakes. 20 Distributions and Grain Sizes of Supraglacial Debris in the Khumbu Glacier, Khumbu Region research done on those subjects in the Nepal Him- to the fossil ice area. alayas, except for the work of Nakawo (1977) who In the 1978 field observations, 4 detailed survey observed on the structure of the D-type glacier in areas were chosen : area I (4,950 m) in the fossil relation to the glacier flow and the size distributions ice part near Lobuche, area II (5,050 m) near the of the supraglacial debris in the Hidden Valley, present active terminus between Lobuche and Gorak central Nepal. Shep, area III (5,150 m) in the mid-stream part In 1978, the Glaciological Expedition of Nepal between Gorak Shep and Base Camp and area IV (GEN) sent a field party to the Dudh Kosi region, (5,300m)at Base Camp just below the equilibrium east Nepal, and we have made observations of glacier line, from down-stream to up-stream (Fig. 1). topography, ablation, discharge, heat budget and On the Khumbu Glacier, the equilibrium line is supraglacial debris of the Khumbu Glacier as a located at about 5,600 m at the lower part of the typical Nepal type and D-type glacier in the sum- ice fall. The supraglacial debris in the accumula- mer monsoon season (Watanabe et al., 1980; Iwata, tion area are buried in the firn snow and the debris Watanabe and Fushimi, 1980; Inoue and Yoshida, appear below the equilibrium line. The schistose 1980). debris are mainly seen on the right side of area IV This paper mainly deals with the characteristic and the granitic debris on the left side. distributions and grain sizes of the supraglacial There is an ogive structure developed below the debris on the Khumbu Glacier (Fig. 1). ice fall in area IV and the supraglacial debris is distributed along the transverse valley-topography 2. Distribution and Occurrence of Supraglacial of the ogive structure (see the logitudinal profile of Debris the lower ogive zone in the appendix), and a huge The Great Himalayas are thought to have been transverse schistose debris-hill (schist hill) is seen rising since the Late Cenozoic era, and weakly meta- (Fig. 2). Below the ice fall, two lines of ice pin- morphosed rocks (Tibetan Formation) are found nacles are developed with the height difference of near the summits of the 8,000 m peaks and granitic 20-30 m. The ice pinnacle on the right side has rocks (Himalayan Gneisses) along the southern flank rich schistose debris and that on the left side mainly of the Great Himalayas. granitic debris. Fig. 1 shows the rock types around the Khumbu The another ice bodies from Mt. , Mt. Glacier and the areal distributions of the spraglacial , (pass) and the west of the Mt. debris. The weakly metamorphosed sedimentary have rich granitic debris. The supraglacial rocks are a kind of schistose rock composed of river system originates from area IV. black schist, schistose hornfels and marble-like There still exist two lines of the longitudinal ice limestone, and the granitic rocks are composed of pinnacles with weak transverse ogive structure be- typical granite, migmatites and gneisses. The tween areas IV and III, but no clear lines of ice schistose rocks are well developed to the south of pinnacles are seen in area III. However, the supra- Mt. Sagarmatha and to the west of Mt. , glacial schistose debris is mainly distributed along and the remainder of the area is mainly composed the right side of area III as the continuation of the of granitic rocks. right side ice pinnacles (B in Fig.. 3), and granitic The Khumbu Glacier is a kind of a compound debris along the left side as the continuation of the glacier and there are tributary glaciers from Mts left side ice pinnacles (A in Fig. 3). The ice bodies Lingten, Khumbutse, Nuptse and the other moun- from the west of Gorak Shep and Mt. Nuptse have tains nearby. The ice body, coming from the West rich granitic debris. The supraglacial rivers general- Cwm basin (the main stream), has supraglacial ly flow along the boundaries of the different ice schistose debris mainly accumulated from the south bodies. face of Mt. Sagarmatha and granitic debris mainly In the down-stream part, supraglacial ponds and from the of Mt. Nuptse. So, the schis- ice cliffs are well developed near area II (Fig. 4). tose deris are distributed on the right side of the There is a kind of foliation structure with clays, West Cwm ice body and the granitic debris on the sands, gravels and even huge boulders seen in this left side. The zonal distribution of the schistose area (Fig. 5-A). Though the boundaries of the debris can be traced even down to the terminus, different ice bodies are not clear and the supraglacial though the zonal distribution becomes slightly weak rivers strongly meander in this area, the zonal dis- as it comes down from the present active terminus tributions of the schistose rocks are still found near Seppyo, 1980 H. Fushimi, M. Yoshida, 0. Watanabe and B.P. Upadhyay 21

Fig. 2. Photograph of the upper part of observational area IV near the Base Camp for the Mt. Sagarmatha Expedition. A: ogive structure, B: schist hill, C: ice fall, D: Mt. Nuptse, E: and F: ice pinnacles. The width of the glacier is about 1.5 km.

Fig. 3. Photograph of the area between observational areas IV and III near Gorak Shep. A, B: ice pinnacles, C, D: supraglacial schistose debris, E, F: supraglacial granitic debris, G: schist hill and H: Gorak Shep. The height differences of the ice pinnacles range from 10 to 30 m, and the width of the glacier is about 1 km.

Fig. 4. Photograph of observational area II between Gorak Shep and Lobuche. A: ice cliffs, B: ponds, C: side moraine, D: Mt. , E: Mt. Ligtren and F: Mt. Khumbutse. The height difference between the side moraine and the glacier surface has a maximum of about 100 m in the Khumbu Glacier. the center line of this area. Angular debris as well the glacier surface is situated above the level of the as rounded debris are observed in area II (Fig. side and end moraines (Fig. 6), and at some places, 5-C and D). lake deposits and rounded pebbles are found. The The zonal distribution of supraglacial schistose englacial river finnally appears as a spout on the and granitic debris becomes weak when one comes left side of this area. down from area II and the supraglacial rivers be- We did not observe the distributions and occur- come englacial. In the area I, there are very thick rences of debris in the accumulation area and at debris covering the fossil ice body and a part of the bottom of the glacier, but it is important to 22 Distributions and Grain Sizes of Supraglacial Debris in the Khumbu Glacier, Khumbu Region A. B.

C. D.

Fig. 5. A. the foliation structure of huge boulders, sands and clays in the down-stream part of Khumbu Glacier. The height difference of the ice cliff is about 10 m. B: occurrence of debris at the bottom of the Gyajo Glacier. C: angular granitic debris in area II. D: rounded granitic debris with angular debris in area II.

Fig. 6. Photograph of observational area I near Lobuche. This area is covered by thick sapraglacial debris and show gentle undulating topography. The width of the glacier is about 1 km.

Fig. 7. Snow beds at a cliff in the accumulation area of the Gyajo Glacier, Khumbu region, east Nepal. A: stratifications, B: debris layers. The height difference of this cliff is about 20 m as shown by a man (C) standing in the right center. Seppyo, 1980 H. Fushimi, M. Yoshida, 0. Watanabe and B.P. Upadhyay 23

know the stagte of debris at those locations. Fig. of debris finner than 8 mm.

7 and 5-B show the occurrences of debris in the 3.1. Size distributions of debris coarser than 8 accumulation area and at the bottom of the Gyajo mm

Glacier to the north of Namche Bazar. Dirt bands More than 100 samples of debris were measured composed of clays, sands and organic materials along a fixed direction at each location by two were observed in the firn snow of the accumulation methods: one measurement was for debris 8 mm to area as well as in the glacier ice of the upper ice 10 cm in diameter and other for that larger than 10 body and there is a large debris layer even in the cm. firn snow, possibly caused by a rock fall (Fushimi, Fig. 8 shows the areal distributions of the grain

1977) (Fig. 7). It was not possible to observe on size coarser than 8 mm and the locations of obser- the subglacial debris at the bottom of the Khumbu vations on the Khumbu Glacier. In the diagrams,

Glacier. The foliation structure with clays, sands, the grain sizes are shown as the abscissa by a gravels and boulders has a lineation parallel to the phi scale (-3ƒÓ = 8 mm, -5.5ƒÓ= 45 mm, -8ƒÓ= 256 glacier flow (Fig. 5-B). mm and -10.5ƒÓ= 1448 mm) as the average grain size of the major axis, and the histograms of the

3. Grain Size Measurements debris area percentage are shown as the ordinate

Size distributions of debris coarser than 8 mm by a logarithmic scale. The areal ratio of the were measured at 38 locations from areas I to IV schistose debris (shaded) to the granitic debris and the supraglacial debris were sampled at 36 (open) having the same grain size is shown in the locations in order to know the size distributions same bar by a linear scale. For example, the ratio

IV

III

II

I

Fig. 8. Distributions of debris size coarser than 8 mm in diameter. The grain size is shown as the abscissa on a phi scale and the areal percentage as the ordinate on a logarithmic scale. The area ratio of the schistose debris (shaded) to the granitic debris (open) is shown in this diagram. 24 Distributions and Grain Sizes of Supraglacial Debris in the Khumbu Glacier, Khumbu Region,

will be 1 if half of the bar is shaded and the other 3.2. Size distributions of debris finer than 8 mm half open. The more the shaded areas, the more To analyse the areal distributions of the finer the relative content of schistose debris. grain sizes, 36 debris samples were well dried and The grain sizes of supraglacial debris coarser passed through 4 different sieves: 8 mm, 1.190 mm, than 8 mm are classified into pebbles (-3ƒÓ to 0.297 mm and 0.074 mm, thus the debris are clas- 5.5ƒÓ), cobbles (-5.5ƒÓ to -8ƒÓ) and boulders - sified as gravel (1.190 to 8 mm in diameter), coarse

(coarser than -8ƒÓ). sand (0.297 to 1.190 mm), fine sand (0.074 to 0.297 In area IV, 15 measurements showed the differ- mm) and fine particles (silt and clay) less than 0.074 ence in the size-area distributions between the mm. granitic zone and schistose zone. The schistose In the diagrams (Fig. 9), the grain sizes are shown debris are composed of pebbles and cobbles, while as the abscissa by a phi scale (-3ƒÓ=8 mm, 1ƒÓ= the granitic debris have rich in boulders. 0.5mm and 5ƒÓ= 0.03 mm) and the weight percentage Eight measurements in area III and seven measu- are shown as the ordinate. rements in area II indicate the zonal distributions In area IV, 13 measurements showed high con- of the schistose and granitic debris. The typical tents of gravel and low contents of the finer debris size-area distributions of the granitic debris are in both granitic and schistose zones, while the shown in III-1 and 8 and II-1 and 7, and those of contents of the finer debris such as coarse sand and the schistose debris in 111-3 and 6 and 11-3 and 5. fine sand increased in sub-areas IV-b and IV-c as The schistose debris are mainly composed of peb- compared with that in sub-area IV-a. bles and cobbles, but, in a rare case, schistose Eight measurements in area III and 7 measure- boulders are found as seen in 111-7. The granitic ments in area II show the contents to have less debris still have rich boulder content. gravel and the more sands and fine particles as Eight measurements in area I showed nearly compared with that of area IV in the granitic zone, similar patterns in their size-area diagrams, due to while the contents of gravels are still high in the the weak zonal distribution of the schistose debris. schistose zone.

IV

III

II

I

Fig. 9. Distributions of the debris grain size finer than 8 mm in diameter. The grain size is shown as the abscissa on a phi scale and the weight percentage at the ordinate. Seppyo, 1980 H. Fushimi, M. Yoshida, O. Watanabe and B.P. Upadhyay 25

There are, in area I, 8 measurements showing the Lhakpa Sherpa, Mr. J. Inoue, Mr. S. Iwata, Mr. low contents of gravels and the high contents of K. Ikegami and Mr. Y. Tanaka for their help coarse sands, fine sands and fine particles in both during the field observations. granitic and schistose zones. References 4. Concluding Remarks Fushimi, H. (1977): Structural studies of glaciers in The occurrences, distributions and grain size the Khumbu region, Seppyo, Vol. 39, Special measurements of the supraglacial debris of the Issue, 30-39. Fushimi, H. (1978): Glaciations in the Khumbu Khumbu Glacier show the following results. Himal (2), Seppyo, Vol. 40, Special Issue, 71- 1 ) The longitudinal zonal distributions with dif- 77. ferent kinds of debris, related to geological condi- Higuchi, K., Fushimi, H., Ohata, T., Iwata, S., Yoko- tions, can be traced even down to the present active yama, K., Highchi, H., Nagoshi, A. and Iozawa, terminus, though the zonal distributions become T. (1978): Preliminary report on glacier inventory in the Dudh Kosi region, Seppyo, Vol. 40, Special slightly weak in the stagnant ice area. Issue, 78-83. 2 ) The transverse zonal distributions of the schi- Inoue, J. and Yoshida, M. (1980): Ablation and Heat stose debris are found on the right side of the West Exchange over the Khumbu Glacier, Seppyo, Vol. Cwm ice body. 41, Special Issue, in this issue. 3 ) The schistose debris are mainly composed of Iwata, S., Watanabe, O. and Fushimi, H. (1980): pebbels and cobbles, while the granitic debris con- Surface Morphology in the Ablation Area of the tained many boulders coarser than -8ƒÓ (256 mm Khumbu Glacier, Seppyo, Vol. 41, Special Issue, in this issue. in diameter). Kodama, H. and Mae, S. (1976): The flow of glaciers 4 ) The measurements of debris grain sizes show in the Khumbu region, Seppyo, Vol. 38, Special that there are high contents of coarser debris found Issue, 31-36. from area IV near the ice fall down to area II near Moribayashi, S. and Higuchi, K. (1977): Characteris- the present active terminus, while there are low tics of glaciers in the Khumbu region and their contents of coarser debris found in area I of the recent variations, Seppyo, Vol. 39, Special Issue, stagnant ice body. 3-6. 5 ) Supraglacial round debris are found in area II Nakawo, M. (1977): Studies on structure and flow of near the present active terminus and in area I of a glacier related to elongated bubbles, Low Tem- the stagnant ice body. perature Science, Ser. A, 35, 180-219 (in Japa- nese). 6 ) Layered englacial debris are also found at the Watanabe, O. (1976): On the types of glaciers in the ice cliff in the down-stream part of the Khumbu Nepal Himalayas and their characteristics, Seppyo, Glacier. Vol. 38, Special Issue, 10-16. Watanabe, O., Fushimi, H., Ikegami, K., Tanaka, Y., Acknowledgements Yoshida, M., Iwata, S., Inoue, J. and Upadyay, The present authors express their appreciation to B.P. (1980): Outline of Studies on Supraglacial Prof. S.R. Chalise, Dr. S.P. Adhikary, Mr. D.D. Debris of the Khumbu Glacier, Khumbu Region, Mulmi, Mr. Pasang Dawa Sherpa, Mr. Tawa Seppyo, Vol. 41, Special Issue, in this issue.