Chhota Shigri Glacier: Its kinematic effects over the valley environment, in the northwest Himalaya

Surendar Kumar

Wadia Institute of Himalayan Geology, Dehra Dun 248 001, India

The relation of surface lowering, net balance and flow dynamics reflects that vertical component of ice flow is downward in and around the equilibrium line while it is upward in the lower part (Ablation zone) of Chhota Shigri Glacier. The submergence velocity in accumulation area is higher than the rise of surface and emergence velocity is lower than that of negative net balance. The basal sliding velocity is responsible for the movement of the glacier. The over extension of the glacier at average snout position is one of the factors in controlling the temperature variation of the main Chandra river valley.

THE Chhota Shigri Glacier valley is a 9 km long narrow valley with about 8.75 km2 of accumulation area which is mostly covered by thick snow and ice sheet (Figure 1 a). The glacier lies on the northern slopes of the main Pir Panjal range 30 km east of Rohtang Pass. The highest peak over the range in the region reaches up to 6428 m. The total drainage area is about 45 km2 and the glacier occupies about 22% of the total drainage area.

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The study revealed a marked diurnal cycle, suggesting that the submergence velocity in accumulation area is higher than the rise of surface and emergence velocity is lower than that of negative net balance.

The Chhota Shigri Glacier valley is a very steep-walled valley. The altitude varies from 3500 m near snout to 6428 m at the top and the Sara Umga Pass at 6000 m (Figure 1 a) and the temperature varies between 15 C to –5 C at snout and 7 C to –15 C near the snow line. The annual 0 C temperature is at an altitude of 4000 m. The very cold condition at the accumulation zone creates an ideal condition for the development of this glacier. The opening up of creavasses on the glacier also create local temperature variations.

It is observed that in the main Chandra valley average wind speed ranges between 8 and 18 km/h whereas that in the Chhota Shigri valley in between 2 and 16 km/h. Near the snout the wind speed is reduced due to the pressure from the main Chandra River Valley wind.

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The surface melt and the lake formation over the glacier body have direct relation with microclimatic effects created by eddies and local stress differences caused by block movements in the ice flow controlled by the bed rock topography2.

For the mass balance of the present Chhota Shigri Glacier, surface balance melted is suitable for determining the annual balance by direct measurements. Net balance has been calculated between 1987 and 1988 (month of reaching September) (Table 1) along 20 stake positions (Figure 2) common to both the years3. The densities are taken at different levels in pits between these stakes (Table 2) to calculate the net balance in cm of liquid water equivalent at each stake (Figure 2)2. Negative mass balance of –157934 m3 a–1 has been estimated (Table 3)5. Mundepi et al.6 on the basis of variation ratio d h/d t have calculated that middle and lower portion of the glacier begin to thin while upper portion thickened. The middle zone between the cross section XII and XIII (Figure 2) shows maximum thinning due to abrupt change in slope.

Since 1985 a continuous decrease in mean surface velocity till 1989 from 73.16 m a–1 to 32.60 m a–1 is observed (Table 4), except from 1986–1987 to 1987–1988 for a brief advance from 26.44 m a–1 to 32.60 m a–1 and was followed by a retreat.

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Mean surface velocity pattern along 10 and 20 cross section (Figure 2) for 1987 and 1988 have been calculated respectively (Table 5). It is so observed that velocity is maximum in the middle of ablation zone (from No. 5 to 7 cross sections), varies from 49.80 to 52.79 and at the equilibrium line (cross section No. 13 and 14) it varies from 42.34 to 49.15 m a–1 whereas at the accumulation zone the mean surface velocity is 34.11 m a–1 and at snout 27.52 m a–1. The velocity variations have also been effected by the valley widening (Table 6) (Figure 2) and shearing of margin from the valley wall in the same way as that of surging at the bend at cross section 9 and 10 (Figure 2).

Surface velocity pattern at the central flow line for short period August–September 1988 and long period 1987–1988 have been shown by direction and amount in Figure 3 along the longitudinal axis. All the vectors are diverging towards its central flow line. Surface velocity is decreasing between height 4750–4800 m whereas the glacier is thickest and the valley is also widened (Figure 1 b). The flow patterns of short period (Figure 3 a) and long period (Figure 3 b) do not vary much.

From the Tables 5 and 6 it is very clear that the glacier near the velocity measurement cross sections X to V, i.e. near the equilibrium line and XIII to XVI, i.e. near snout gets raised by 2.26 m a–1 but remains lower than the negative net balance. Such fluctuations near the snout indicate that the year when maximum vertical velocity component is more, i.e. if the emergence velocity is more near the snout, the main Chandra valley temperature will be less and there will be a lower discharge in the Chhota Shigri stream. This shows that the vertical rise due to vertical velocity in the glacier near the snout has got direct effect on the valley temperature as the Chandra valley temperatures are more than the Chhota Shigri valley. Hence to maintain the latent temperature effect on the valley temperature the extra glacier rise melt near the snout compensates the lower temperatures that year. This lower temperature has got direct effect on the meteorological variations which control the seasons either in lengthening of rainy season or earlier snow in the upper reaches.

 


  1. Kulandaivelu, E., Ray, B. and Sharma, J. K., DST Technical Report No. 3, 1989, pp. 37–57.
  2. Kumar, Surendar and Dobhal, D. P., J. Glaciol., 1997, 43, 467–472.
  3. Dobhal, D. P., Kumar, Surendar and Mundepi, A. K., Curr. Sci., 1995, 68, 936–944.
  4. Kumar, Surendar, Mundepi, A. K. and Rawat, B. R. S., DST Technical Report No. 3, 1989, pp. 109–130.
  5. Vohra, K. K., 1991, DST Technical Report No. 4, 1991, pp. 108–123.
  6. Mundepi, A. K., Kumar, S. and Purohit, K. K., Geosci. J., 1994, 15, 163–169.

 

 

ACKNOWLEDGEMENTS.  I thank the Department of Science and Technology for providing sufficient funds for this study under the Himalayan Glacier program.

 

 

Received 24 August 1998; revised accepted 1 June 1999