The Flow of Glaciers in the Khumbu Region*
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Seppyo, 1976 H. Kodama and S. Mae 31 The Flow of Glaciers in the Khumbu Region* Hideo Kodama** and Shinji Mae*** Abstract The results of measurements of the surface velocity of the glaciers in the Khumbu region showed that the surface velocity underwent a seasonal variation in the upper parts of the ablation area of the Khumbu and the Nuptse glaciers, that is, the velocity from May to August was higher than that of the rest of the year. It was found that the surface of the Kongma Glacier moved upward and this strange motion of the ice was discussed. The thickness of the Khumbu and the Nuptse glaciers was estimated using the theory of glacier flow to be 110 m and 70 m, respectively. The discharge of the Khumbu Glacier was also estimated to be 7.5 •~ 106, 3.4 •~ 106, 1.6 •~ 106 and approximately 0 •~ 106 tons/year at the elevations of 5340 m, 5280 m, 5140 m and 4960 m, respectively. Using these values and measured ablation rate, the increasing rate of the thickness of the Khumbu Glacier was obtained as follows, 1 m/year between 5340 m and 5280 m, 0.3 m/year between 5280 m and 5140 m, and -1.5 m/year between 5140 m and 4960 m. These results indicated that the Khumbu Glacier was not in equilibrium. basis of them the glacier flow is discussed. The 1. Introduction thickness and discharge of glaciers are estimated In 1956 Mailer (1968) carried out the first and the thickness change of the Khumbu Glacier measurements of flow velocity in the Khumbu is obtained. Glacier and found that the flow velocity increased in the premonsoon season, especially in May. 2. Measurements of flow velocity From his observation he concluded that the 2.1. Measured glaciers increase in the flow velocity was caused by the The measurements were carried out in the enhancement of basal sliding due to the percola- Khumbu, the Nuptse, the Kongma, and the tion of melt water stored as glacier ponds down Kongma-Tikpe glaciers which are shown in Fig. to the glacier bed. However, Muller measured 1. The morphology of the glaciers where the the flow velocity in only the Khumbu Glacier, measurements were performed are described as though there are various and complicated types follows. of glaciers in the Nepal Himalayas, even in the 2.1.1. The Khumbu Glacier Khumbu region. The glacier is 18 km long and 1 km wide. The In the spring of 1973 the Glaciological Expedi- accumulation basin of the glacier is called the tion to Nepal (GEN) started measurements of West Cwm which is separated by a big ice fall flow velocity in many glaciers of the Khumbu from the ablation area. From 1 km down-glacier and the Dhaulagiri regions in order to determine of the ice fall to the glacier terminus the glacier the mechanism of glacier flow and the effect of is covered with a debris. climate on glaciers. In this paper the results of The velocity measurements were made at 4 the measurements are summarized and on the stake lines called the Everest Base camp line * Glaciological Expedition to Nepal (5340 m), the Pumo Ri line (5280 m), the Gorak , Contribution Shep line (5140 m) and the Lobuche line (4960 m) No. 10 as shown in Fig. 1. At each stake line which was ** Water Research Institute , Nagoya University (present address, Chubu Region Development located in the ablation area, 5 to 7 stakes were Research Center, Sakae 2, Naka-ku, Nagoya) set. Near the Everest Base Camp line ogives of *** Water Research Institute , Nagoya University, which the height and wave length are about 5 m Chikusa-ku, Nagoya 464 and 10 m were observed. At other lines no 32 The Flow of Glaciers in the Khumbu Region Fig. 1. Glaciers in the Khumbu region. ogive was observed but irregular undulations were were set at each stair of this stair-type glacier. observed. Below the Lobuche line the glacier is 2.1.4. The Kongma-Tykpe Glacier covered with a thick debris. This glacier is the smallest among the measured 2.1.2. The Nuptse Glacier glaciers and the surface is smooth. The stakes The Nuptse Glacier is a valley glacier. It is were set along the center line of the glacier from covered with a debris, as is the Khumbu Glacier, the highest point to the terminus including the but there are no big ice fall and no ogives. The ablation and accumulation areas. altitude of its terminus is the same as that of 2.2. Method of measurement the Khumbu Glacier and is 4900 m. The Nuptse Using a Sokkisha's No. 10 theodolite or Wild Glacier is 6 km long and 500 m wide. The ac- T-2 theodolite, the position of stakes were cumulation area is very steep, but in the ablation measured by triangulation method from fixed area the surface gradient is about 5 degrees. points located usually on a side moraine. The Two stake lines for the velocity measurments positions of the lines were determined on a were set and are called the upper (5380 m) and topographical map from the photographs near lower (5210 m) lines as shown in Fig. 1. At the lines. The directions of the lines were deter- each line 4 or 5 stakes were set. The upper line mined from measurements of the angles between is located just below the accumulation area and the lines and magnetic north using a Sokkisha's the surface gradient is 5 degrees, and the lower No. 10 theodolite. line is located near the terminus and the gradient Bamboo and alminium poles were used as is 8 degrees. stakes in the measurements. Bamboo stakes 2.1.3. The Kongma Glacier were successfull, but alminium stakes were a The Kongma Glacier is very small and com- little bit weak and sometimes bended strongly as pletely different from the Khumbu and the a consequence of some accidents. Therefore, the Nuptse glaciers. The morphology and the strati- position of the stakes were measured at their graphy of the Kongma Glacier were investigated foot. Errors in the stake position are caused in detail (Wushiki, unpublished). A few stakes by uncertainties in the setting of the theodolite, Seppyo, 1976 H. Kodama and S. Mae 33 in measuring the base line length, in reading the surveying instrument and by the effect of refrac- tion of light. These uncertainties are independent but their contribution to the error of the stake position is not independent. The error was, therefore, estimated using the law of propagation of errors. The flow velocity was calculated from the displacement of the stake position and the time interval between the measurements. 3. Results of measurements The flow velocities were represented in the Data Report of 1973 and 1974 GEN and in this section simple features of the glacier flow is described. 3.1. The Khumbu Glacier The directions of the flow are almost parallel to the center line of the glacier except at the Lobuche line where the directions deviate to left side of to glacier. At the Lobuche line, however, the error of the velocity magunitude is slightly larger than the calculated velocity. Therefore, it is concluded that at least the part below the Lobuche line is stagnant. The flow velocity at the Everest Base Camp line and the Pumo Ri line show a remarkable Fig. 2. Seasonal variation of surface velocity in seasonal variation consistent with Mailer's results. the Khumbu Glacier. Though Mailer (1968) reported that the velociey in 1956 increased only in May, the velocity in 1973 was large in May, June and July as shown in Fig. 2. This difference may be caused by the difference of ablation in 1956 and 1973. The difference between the velocities at the Everest Base Camp line in May, June, July and August and in winter is almost the same as that at the Pumo Ri line or a little smaller than it. This is consistent with Mailer's results. It is very interesting that such a seasonal varia- tion of the velocity as those at the Everest Base Camp line and the Pumo Ri line is not observed at the Gorak Shep line. This indicates that the flow mechanism at the former lines is not com- pletely the same as that at the latter line. 3.2. The Nuptse Clacier In this glacier, the directions of the flow Fig. 3. Seasonal variation of surface velocity velocity is parallel to the center line at both the in the Nuptse Glacier. upper and the lower lines. From the measure- ments a stagnant part is not observed in the Therefore, near the terminus a stagnant part glacier, but the velocity at the lower line contains might be observed. a stagnant component as will be discussed later. The velocity at the upper line indicates a 34 The Flow of Glaciers in the Khumbu Region seasonal variation which is smaller than that at paratively large seasonal variation of the velocity the Everest Base Camp and the Pumo Ri lines is derived by the basal sliding. Theoretical work in the Khumbu Glacier as shown in Fig. 3. A on the basal sliding was begun by Weertman seasonal variation was not detected at the lower (1957), but the observations of it were not enough line. to obtain a relation between h and Vb until 3.3. The kongma Glacier Paterson (1970) obtained a following relation The Kongma Glacier has a flow completely different from that of the Khumbu and the (3) Nuptse glaciers.