|Chhota Shigri Glacier: Its kinematic effects over the valley environment, in the
Wadia Institute of Himalayan Geology, Dehra Dun 248
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.
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
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.
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
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 a1 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 a1 to 32.60 m a1
is observed (Table 4), except from 19861987 to 19871988 for a brief
advance from 26.44 m a1 to 32.60 m a1
and was followed by a retreat.
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 a1 whereas at the
accumulation zone the mean surface velocity is 34.11 m a1 and
at snout 27.52 m a1. 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
Surface velocity pattern at the central flow line
for short period AugustSeptember 1988 and long period 19871988 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
47504800 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 a1
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.
Kulandaivelu, E., Ray, B. and Sharma, J. K., DST Technical Report No.
3, 1989, pp. 3757.
Kumar, Surendar and Dobhal, D. P., J. Glaciol., 1997, 43,
Dobhal, D. P., Kumar, Surendar and Mundepi, A. K., Curr. Sci.,
1995, 68, 936944.
Kumar, Surendar, Mundepi, A. K. and Rawat, B. R. S., DST Technical
Report No. 3, 1989, pp. 109130.
Vohra, K. K., 1991, DST Technical Report No. 4, 1991, pp.
Mundepi, A. K., Kumar, S. and Purohit, K. K., Geosci. J.,
1994, 15, 163169.
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