Sonapani Glacier of Lahaul

SONAPANI GLACIER OF LAHAUL, KANGRA DISTRICT,
PUNJAB, INDIA *
T. K. KURIEN and M. M. MUNSHI
(Geological Survey of India). Download Original PDF 
ABSTRACT
This paper reports a survey of the Sonapani glacier in the Kangra district of
Punjab State, India. The glacier is 14.72 km long and in situated 6 km N.N.E. of
the confluence of Kulti Nala with the Chandra River. The position of the snout has
been determined with reference to permanent bench marks and is at an altitude of
3,856 metres. The total area occupied by the glacier is 33 square km out of which
28.5 square km form the area of accummulation and the rest the ablation area. The
present study indicates that the glacier has retreated by 899 metres during the past
fifty years, and has lost roughly 142 million cubic metres of ice since the last survey.
The glacier has a fairly steep gradient with numerous crevasses both of the longi-
tudinal and transverse types. The total thickness of the snow cover is about 4.8 me-
tres. The position of the snow line and firn line is at 4,267 metres above mean sea
level and the lower limit of snow in Winter is at about 1,524 metres above mean sea
eve .
Résuivifi
Les auteurs présentent l‘etude du Glacier Sanapani, district de Kangra, Punjab.
Le glacier a une longueur de 14,72 km et il est situé it 6 km au N. N . E. de la confluence
des rivieres Kulti Nala et Chandra. Le front du glacier a été levé. ll est a 3856 m
d‘altitude. Le glacier occupe une surface de 33 kmz de zone d‘accu.mulation et le
reste de zone d’ablation. Le front du glacier a reculé de 899 m durant les 50 dernieres
années et a perdu environ 142 millions de m3 de glace depuis le dernier levé. Le
glacier a une forte pente et presente de nombreuses crevasses longitudinales et
transversales. L‘épaisseur totale de la surface de neige est de 4.8 m. L’altitude de la
limite des neiges et de la ligne de névé est de 4267 m, et la limite inférieure de la neige
en hiver est de 1524 m.
I. INTRODUCTION
A survey of the Sonapani Glacier of Lahaul, in the Kangra district of Punjab,
India, was undertaken by the authors during the months of August and September,
1957. The name “Sonapani” has probably been derived from the golden hue of the
altered biotite-schist over which the glacier stream flows in the lower part of its course.
Physiogruphy : There are two main mountain ranges in the area and they are the
Great Himalayan Range striking roughly N.N. W.-S.S. E. on the north and the Pir
Panjal Range striking NW-SE. on the south. There a.re peaks reaching heights of even
6,100 metres on both the ranges. Lahaul area lies north of the Pir Panjal Range and
the valley has altitudes varying between 3,050 and 3,650 metres above the mean sea
level.
Climate : The climate of the area is characterised be a long and cold winter
extending from October to about the middle of April. During the winter months the
minimum temperature goes down very much below the freezing point. The area enjoys
moderate summer with day temperatures not exceeding 24°C, the night temperature
fl Published by kind permission of the Director of the Geological Survey

239

being above freezing. The area being well over 6,050 metres in altitude has abundant
snowfall during the winter months, when the precipitation is totally in the form of
snow. It is reported that areas lying at altitudes ranging between 3,050 and 3,350 metres
get an average snowfall exceeding 6.1 metres per annum. Lahaul is considered as a
cloudless and rainless country and the average rainfall of the area is 15 centime-
tres, all of which is confined to the months of June and July. The precipitation on the
northern side of the Pir Panjal is negligible compared with that on the southern, the
reason being that the hill ranges act as an afl’ective barrier against the rain clouds.
Months of July and August are considered to be very favourable for carrying out
surveys in this region.
The line of perpetual snow, above which summer heat and rain fail to melt the
snow, is about 4,260 metres in Lahul, but on the southern side of the Pir Panjal,
inspite of the higher precipitation of snow,it is above 4,260 metres. The lower limit
of snow-fall on the south face, however, is as low as 1,525 metres.
Previous work t The one and only earlier survey of the Sonapani glacier including
its snout was carried out by H. Walker and E. H. Pascoe (1907) during September,
1906. Besides surveying the Sonapani glacier they undertook the survey of the Bara
Sbigi Glacier also and even made an attempt to survey the Perad Glacier. The excel-
lent sketch map accompanying their report was extremely useful in the location of
the previous snout. The present survey of the Sonapani Glacier is after a lapse of over
fifty years and an attempt was made to prepare a similar sketch rnap which will
help future Workers in the location of the present snout even in the absence of cairns.
I1. THE sonsrmr GLACIER
Location : The Sonapani glacier lies roughly N.N.E. of the old rest house at
Khoksar, with the glacier snout and the ice caves being situated at a distance of about
5.6 kilometres from it. The glacier snout is at present on longitude 77° 19’ 4” E and
latitude 32″ 25’ 53″ N, see Fig. l.
Type of Glacier : The Sonapani is a valley glacier fed by many converging moun-
tain tributaries. The trend of the ranges in the area is NE-SW and the glacier flows
in this direction for about 5.6 kilometres in the lower regions. The flow of some of
the tributaries is not particularly controlled by the trend of the ranges.
The main glacier has two tributaries meeting about 3 kins above the snout. The
branch from the south-east is fed by a large snowfield amidst some of the prominent
peaks of the area. The other branch is fed by a number of radiating tributaries. Besides
the above, there is at least one minor tributary glacier seen on the south-east of Sara-
garu with its confluence one and half kilometres up the snout.
A number of hanging valleys form a prominent feature of the glacier, especially
towards its higher reaches; and even near the snout an icefall with a drop of about
24 metres and having numerous tributary glaciers With fairly steep gradients join
the main glacier.
Gradient : The Sonapani glacier has an uneven gradient and is interrupted by
falls. The total fall of the glacier is about 1,430 metres in a distance of eight kilometres
along the lower reaches. At places, there are abrupt falls of the glacier and one such
is seen in the vicinity of Saragaru.
Crevasses occur most commonly at places where comparatively thin ice is flowing
over an abruptly steepened slope. Ordinarily the central areas of the ice sheet having
thick ice and very gentle slopes are characteristically devoid of crevasses and even
when present they do not generally extend beyond depths of 30 to 60 metres. The large
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.MAP
number of longitudinal and transverse crevasses are characteristic of the Sonapani
glacier. It can be duduced that th.is glacier has a rather steep bed rock gadient. Howe-
ver, towards the snout the gradient is less steep.
Length : The glacier has its source in the ranges SSW of the 19,229 foot peak and
its present snout is in the vicinity of Saragaru, covering a total distance of 14.72 kilo-
metres. Besides the main glacier, there is at least one subsidiary glacier, as has already
been mentioned, flowing in a Westerly direction, for a total length of about 6.4 kilo-
metres.
Area : It has not been possible to estimate accurately the total area of the glacier
Without a detailed survey. The Sonapani glacier and snow-fields which feed it, lie
amidst the 18,199, 19,481 19,229 and 18, 678 foot peaks and the area of the glacier is
almost 33 square kilometres.
The snour 1 The snout of the glacier has a concave shape and has a width of 225
metres. It is situated at a height of 3,856 metres above mean sea level. The ice cliff
in the snout region measures 46 metres in height. There are two ice caves, centrally
situated, which are 103 metres apart, and streams emerge from them.
Position of the firn line : During the period of the present survey, there were inter»
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mittent snowfalls at high altitudes in this region and the exact position of the firn line
could not be determined. However, an attempt was made and the results indicate
that the firn line lies at an altitude of 4267 metres.
Approximate areas ofaccumularion and ablation : The area of accummulation of
the Sonapani glacier is about 28.48 square kilometres and the area of ablation is about
3.88 square kilometres.
Lower limit ofsnow in winter: In winter the lower limit of snow in the Kulu valley
is about 1,674 metres above the mean sea level. Manali, which is at an altitude of
about 1,707 metres, has an average snowfall of about 1.2 metres per annum. It is,
however, noteworthy that Manali and adjacent areas lie on the south face of the Pir
Panjal range where the precipitation is more extensive than in the Lahaul area lying
on the north of the Pir Panjal ranger All the areas in Lahaul lie at altitudes exceeding
3,048 metres and they get abundant snowfall during the winter months. Khoksar
and the neighbouring areas have an annual snowfall exceeding about 8 metres. The
lower limit of snow in winter for this area can be assumed to be at about 1525 metres.
Inferred from mnrpholugical evidence : That the glacier during the early part of
its history extended up to the Chandra valley is clearly indicated by the remnants of
the moraine seen near the confluence of the Kulti Nala with the Chandra River.
This is the oldest terminal moraine of the glacier and its position probably represents
the position of the snout during Pleistocene times. The second oldest terminal moraine
is at a distance of about 1.6 kilometres north of the confluence, but only scattered
remnants ofit are seen. The third and the largest terminal moraine is known as Rataskal
and is situated at a distance of 2.5 kilometres from the oldest terminal moraine. A
terminal moraine, partly covered by grass, is noticed on the left bank of the stream
at a distance of about 2,438 metres from the Rataskal moraine. This moraine is
younger than those mentioned earlier and the thinness of the grass cover shews
it is recent. Further upstream at a distance of about 1,220 metres terminal moraines,
thinly covered, are seen on both the right and left banks of the stream.
Whereas all the other moraines are considerably eroded by the glacial stream, these
have not been much affected. The younger terminal moraines are seen on the south-
west of the red clifi” and they stand out as small ridges amidst the ablation moraines
of an earlier period. The glacier snout during the early part of the present century
was very near the red clifi” on the left bank. The area between the clifl and the present
snout is covered by moraines of various types. Some of the terminal moraines in
this locality are of small dimensions. It is often difficult to locate the terminal moraines
of the more recent times and it can only be inferred that the glacier, in spite of its
pronounced retreat during the early part of its history, has been only retreating rather
sluggishly during the past few hundred years.
The snout of the glacier is concave and the ice-cliffs at the snout are nearly
vertical. A concave snout indicates retreat of a glacier, whereas the vertical ice-cliffs
indicate advance. These indications by themselves are not very significant, but when
coupled with the other important evidences mentioned above, they go to prove beyond
doubt that the glacier has retreated.
It may be hypothetically stated that the snow line in this area had commenced
to rise by about the period when the snout started to retreat. Recession of the snout
is common to most of the glaciers in the Himalayan region; but such retreats are rather
irregular in amount, rate and time of occurrenoe. This may partly be attributed to
the large annual fluctuations in the snowfall. An unusually long terminal retreat or
advance in a glacier may be due to the ice being rather thin in the zone of ablation,
especially at the snout and neighbourhood. The thickness of the ice at the snout of the
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Fig. 2
Sonapani glacier is only 46 metres and consequently variations in the thickness of
the ice in the ablation zone will have a pronounced effect on the position of the snout.
Change in the volume of the glacier : The Sonapani glacier shows a total terminal
recession of 899 metres, but it has not been possible to estimate the total thinning in
the terminal zone. It is generally accepted that far more ice is lost owing to the thinning
of the glacier below the firn line than by the inward migration of the snout itself.
Ablation thins the ice in the zone where it operates and consequently the rate offiow
of the glacier is aflected. lt has been found that the rate of flow varies approximately
as the square of the thickness and hence even a small decrease in the thickness tends
to decrease the flow of the glacier rather disproportionately. It has been estimated
fairly accurately that out of the total ablation measured about 99 per cent is due to
thinning of the terminal zone alone. The Sonapani glacier has lost a volume of about
I42 million cubic metres during the past fifty years owing to terminal retreat alone,
and from this one can easily visualise the loss of volume of the glacier due to thinning.
Morphological rhamcters : The glacier follows a valley more or less uniform in
width up to the locality _|ust above the icefall and at the fall the valley narrows down
considerably. Transverse crevasses are a prominent feature of the icefall. At the bottom
of the icefall the glacier fans out into a broader valley and assumes a piedmont form
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with longitudinal crevasses. The interrupted gradient below the icefall has been respon-
sible foranumber of transverse crevasses and this has resulted in a number of seracs.
Marginal crevasses due to the higher velocity at the middle portions of the glacier are
prominent on the left bank of the ice fall and they sometimes extend up to the middle of
the glacier.
Streaks of lateral moraines are seen on either side of the glacier above the snout
and below the icefall.
Snow feature: : The newly-fallen snow which has been superficially melted and
refrozen into a crust, known as sun crust, is a common feature of the snow in this
area. Thin ice found on the top of old hard snow, but separated from it by small
air space is known as film crust. This has been noticed in the snow near the snout
and is due to the high contrasts between night and day temperatures.
For about three days there was heavy snowfall in the area during the month of
September. Initially, when the temperature of the atmosphere was near the freezing
level, moist, dense type of snow was observed, but later when the temperature went
below the freezing point, dry, powdery snow was noticed.
According to the Forest Research Division of the Punjab Government the actual
average depth of snow accummulating at the end of the season, is about 3.05 metres
at an altitude of 2,985 metres and 5 metres at 3,962 to 4,876 metres, above which
precipitation does not increase perceptibly with increase in height. The measurement
of accummulated depth of snow tends to be rather inaccurate, because of the rapid
shrinkage at depth of newly-fallen snow, and hence the total amount of snowfall in
the region should be more than the measurements taken at the end ofthe season. No
systematic measurements of the total thickness of snow cover were made and only the
total thickness of the accummulated snowfall is all that has ever been measured.
Hence the figures available for this area may be considered as very approximate.
REFERENCES
WALKER, H. and PASCOE, E.H. Notes on certain glaciers in Lahaul, Rec. Gen]. Surv.
1na’., Vol. 35, Pt. 4, 1907.
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