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CHARACTERISTICS OF THE SEASONAL SNOW COVER OF PIR PANJAL AND GREAT ... H.S. Gusain*, Amreek Singh, Ashwagosha Ganju and Dan Singh.
Proceedings International Symposium on Snow Monitoring and Avalanches (ISSMA)-2004, Manali, India, 97-102 CHARACTERISTICS OF THE SEASONAL SNOW COVER OF PIR PANJAL AND GREAT HIMALAYAN RANGES IN INDIAN HIMALAYA

H.S. Gusain*, Amreek Singh, Ashwagosha Ganju and Dan Singh Snow and Avalanche Study Establishment, Manali, Himachal Pradesh, India

ABSTRACT: Pir-Panjal and Great Himalayan ranges in Western Himalaya of India fall in low (2000-4000m) and mid (3500-5300m) altitude ranges respectively and gets extensively covered by seasonal snow-cover during winters. While winter climate of Pir-Panjal range is close to maritime snow climate characterized by heavy snowfall, mild temperatures and deep snow cover, Great Himalayan range has continental type winter climate characterized by relatively lesser snowfall, colder temperatures and shallow snow cover. In the present work an attempt has been made to understand the evolution pattern, properties and structure of the seasonal snow-cover in these two ranges having different climatic and topographic conditions. The study highlights the temporal variability in snow-cover composition during its evolution in two ranges in terms of the formation of different metamorphosed layers and respective properties. The results exhibit that equi-temperture layers dominate in Pir-Panjal range snow-cover up to mid-winter and melt-freeze layers in late winter. While Great Himalayan range snow-cover is dominated by depth hoar and faceted crystals layers till late March and melt-freeze layers dominate thereafter. The relationship between snow-cover properties and associated avalanche activities in the area has also been established. KEYWORDS: Snow Cover, Pir Panjal range, Great Himalayan range, Avalanches 1. INTRODUCTION Snowfall and avalanche activity is a common feature in upper reaches of western Himalaya, causing the loss of many precious lives of troops and civil population as well as property worth millions every year. Thus it becomes very essential to predict avalanches well in advance so that necessary preventive measures could be taken in time. Avalanche prediction needs knowledge about evolution, stability, composition, ablation and properties of the snow-pack of concerning area. These information can be obtain by regular monitoring of the deposition of the snowstorm on the ground and regular pit observation of the snow-pack till its ablation and metamorphism.

*Corresponding author address: SASE-RDC, Himparisar, Sector 37A, Chandigarh, India.Pin-160036 Tel: +91-172 - 2699804, 2699805, Ext-275, Fax: +91- 172 – 2699802 E-mail: [email protected]

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Very few attempts have been made in past ( N. Mohan Rao, 1983) to understand the evolution pattern of the seasonal snow cover in the snow bound areas of Himalaya. This paper highlights the evolution pattern, properties and structure of the seasonal snowcover in Pir Panjal and Great Himalayan ranges of Western Himalaya. 2. DATA COLLECTION OBSERVATION SITES

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For the present work, s tr at i gr a p h y an d s n o w m ete or o lo g i c a l da ta of t he pas t 8 wi n t er s f r om 19 9 3- 94 t hr ou g h 20 0 0- 01 we r e a n al yze d . Stratigraphy data, also named as Snow Profile data, is recorded every week and after every major snowstorm, once the snow pack starts building up till its ablation by melting. Data used for this study was collected at two well-instrumented observatories of SASE having diverse topographic and climatic conditions. The first station Dhundi is located in a valley bottom of Pir Panjal range at an altitude of 3050m above mean sea level on windward side. The observatory is set up on a flat open area of about 1500-sq.m. The second station Patsio is located in Great

Proceedings International Symposium on Snow Monitoring and Avalanches (ISSMA)-2004, Manali, India, 97-102 Himalayan ranges at an altitude of about 3800m above mean sea level on a flat place at the junction of two valleys.

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Figure 1: Maximum and Minimum temperatures in °C during 2002/03.

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Sharma and Ganju (2000) classified the snow climate of Himalayas from the point of view of avalanche activity into three classes: Lower Himalayan zone or subtropical zone, the middle Himalayan zone and the upper Himalayan zone or high latitude zone. According to their classification Pir Panjal range fall into the category of lower Himalayan zone or subtropical zone and Great Himalayan region falls into the category of Middle Himalayan zone or Mid- Latitudinal zone. However the figures 1, 2 3 and 4 show the weather pattern of these two ranges. Figure 1 and 2 show temperature, snow-fall and standing snow data for two ranges during the winter 2002/03 while Figure 3 and 4 show mean temperatures and mean snow-fall of past 14 years. General weather pattern of the regions can be shown by the following parameters: 1. Mean maximum temperature for Pir Panjal range vary between 3.9°C (lowest) during the month of February to 11.6°C (highest) during the month of April. While the lowest and highest values for mean minimum temperature are -4.1°C (during Feb) and 2.5°C (during April) respectively. In Great Himalayan ranges mean minimum temperature vary between -6.4°C ( during April) and -15.4°C( during Jan) while mean maximum temperature vary between -1.4°C ( during Feb) and 6.5°C (during April). 2. Total snowfall in Pir Panjal range during the winter 2002/03 recorded was 1053cm and normal snowfall of past 14 years is 1178cm while for Great Himalayan ranges these are 537cm and 511cm respectively. 3. Mean snow-fall is higher in Pir Panjal range compare to Great Himalayan ranges for all winter months except the month of April. January, February and March are the months with higher snow fall in both the ranges.

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Proceedings International Symposium on Snow Monitoring and Avalanches (ISSMA)-2004, Manali, India, 97-102

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considered. For analysis of the properties of the snow cover the whole winter season is divided in to Pre winter (Nov, Dec), Mid winter (Jan, Feb) and Post winter (Mar, Apr) period.

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5. RESULTS & DISCUSSION

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Figure 4: Mean Snow Fall (In cm) of past 14 years.

4. ANALYSIS METHODOLOGY: For each range, the stratigraphy data records were first segregated into month-wise weekly symbolical groups, according to their time of observation. For simplicity, from Jan to April, each month was represented by four symbolical weeks. This way we divided the whole duration from Jan to April into 16 symbolical weeks. Under every week, each stratigraphy record was then analyzed in detail to identify ET, TG, and MF layers present in the snow pack. The thickness of ET, TG and MF layers of all stratigraphy records under a week were then added. Similarly, the snowpack heights in all records under each week were also added. The snow-pack heights used here were achieved by subtracting the amount of fresh snow from actual standing snow value. The ratio of total thickness of individual type of layer to the total of snow-pack heights gives the percentage of snow-pack height comprised of that kind of layer under the week 99

5.1 Evolution and ablation pattern of the snow cover In the Pir Panjal ranges, the peak accumulation period of the seasonal snow cover is generally from mid December to mid March. The snow cover depth increases with every spell of snowstorm and maximum depth occurs during late February or first week of March. The maximum snow cover depth th reported in Pir Panjal range is 442cm on 5 March1998. Figure 5 shows the evolution of the seasonal snow cover of Pir Panjal range under mild ambient temperature conditions during pre and mid winter period and ablation during post winter period. Snow cover start ablating from mid march and the whole snow-pack ablates by late April or first week of May. While in Great Himalayan ranges the evolution period of the seasonal snow cover is longer under cold climatic conditions up to mid April and there after snow-pack starts ablating. The maximum snow cover thickness generally lies in the range of 1.5-2.4 m in the Great Himalayan ranges and 2.0-4.5 m in the Pir Panjal ranges, with a multi-year average of 1.9 m and 2.4 m respectively. 5.2 Structure of the snowpack In the seasonal snow cover of Great Himalayan ranges temperature gradient is large and may reach up to 61.9°C/M th (Observed on 5 Feb 1997). So the metamorphism of the snow is dominated by sublimation-recondensation process(Mc Clung D.et all, 1993). Therefore, the accumulation of the snow layers with the different grain sizes has a certain regularity and the deposition is in a sequence of new-fallen snow (or surface hoar), felt like grains, equi-temperature grains, sugar grains and depth hoar from the top to the bottom (Figure 6). While in the snow cover of Pir Panjal ranges the deposition is in a sequence of newly fallen snow, felt like grains and equi- temperature grains from top to bottom (Figure 6).

Proceedings International Symposium on Snow Monitoring and Avalanches (ISSMA)-2004, Manali, India, 97-102

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Figure 5: Evolution and ablation pattern of the snow cover in Pir Panjal and Great Himalayan ranges Snow-pack of Great Himalayan ranges is dry up to mid march and become moist onward due to rise in ambient temp and Wet snow pack is found during late April and onwards. While the snow pack of Pir Panjal range is found moist from early winter and it becomes wet during the month of March and convert into very wet/ slush during late April. 5.3 Properties of the snow cover Analysis of snow-pack structure show that in snow-pack of Pir Panjal range equitemperature grains are found in abundance from the beginning of the evolution of snowpack and during the first week of January equi-temperature layers comprises more than 90% of the snow-pack thickness (Fig 7). Rest of the snow-pack is shared by melt-freeze grains. As the time proceeds share of melt freeze grains in the snow-pack start increasing gradually and it becomes more than 60% by

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Figure 6: Snow-pack structure at Pir Panjal and Great Himalayan ranges Legends: A: Ice Layer, B: Melt Freeze grains, C: Surface hoar grains, D: Depth hoar grains, E: Sugar grains, F: Rounded grains, G: Felt like grains, H: Fresh snow grains

the end of April as the equi-temperature grains start converting into melt-freeze grains after the process of melt-freeze metamorphism. In Pir Panjal ranges temperature gradient grains were not found at all due to low temperature gradient inside the snow-pack. In Great Himalayan ranges temperature gradient layers are found in abundance and the share of TG grains straddles between 40% to 60% of the snowpack thickness up to mid March and rest of the thickness is shared by equi-temperature grains. Mid March onwards melt-freeze grains start appearing and their share increases gradually up to mid April, thereafter growth of the melt-freeze layer is fast and by the end of April more than 50% thickness comprises of melt-freeze layers. Observations show that density of the snow-pack of Pir Panjal ranges are higher than that of the Great Himalayan ranges while the temperature gradient inside the snow-pack observed higher in Great Himalayan ranges through out the winter season and the

Proceedings International Symposium on Snow Monitoring and Avalanches (ISSMA)-2004, Manali, India, 97-102 optimum values are given in the tables 1 and 2. Pir Panjal Range Standing Snow Temperature gradient

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Figure 8: Ram profiles before few avalanches in Great Himalayan ranges (A) Ram Profile16 Feb94, Avalanche release16 Feb 94 (B) Ram Profile 18 April 95 Avalanche release 20 April 95 (C) Ram Profile 21 March97 Avalanche release 21 March 97

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Table 1: Snow-pack density Period Pir Panjal Mid Winter Post Winter

0.240.40gm/cc 0.320.52gm/cc

Great Himalaya 0.20.32gm/cc 0.250.45gm/cc

Table 2: Temperature gradient Period Pir Panjal Great Himalaya Mid Winter 2-15°C/m 10-62°C/m Post Winter

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Figure 9: Ram profiles before few avalanches in Pir Panjal range (A) Ram Profile 9March94 Avalanche release 9 March 94 (B) Ram Profile 27 March 95 Avalanche release 26 March 95 (C) Ram Profile 14 Feb 98 Avalanche release 15 Feb 98

5.4 Avalanche Activities in the Regions During the period 1993-2001, 77 avalanche occurrences reported in the region of Patsio observatory. Out of which 54

Proceedings International Symposium on Snow Monitoring and Avalanches (ISSMA)-2004, Manali, India, 97-102 avalanches (around 70%) triggered during snow-storm or within 24 hours after storm. Snow-pit data just before 17 avalanche occurrences is available and analysis show that in most of the cases ram-resistance at the bottom most 20 cm of the snow-pack is quite low i;e less than 20 Kg , comprising depth hoar grains. This indicates the existence of weakest layer and probable failure at the depth of the snow-pack near ground resulting in to cold-climax avalanches.

Most of the avalanches are DirectAction avalanches in both the ranges while presence of fairly low ram resistance at the bottom most 20 cm of the snow pack just before the avalanche infer occurrence of ColdClimax avalanches in the Great Himalayan ranges. However more information about the snow pack properties from formation zone of avalanches is required for accurate deductions about the avalanches. 7. ACKNOWLEDGEMENT

In Dhundi observatory region comparatively the less avalanche occurrence data is available. Only 18 avalanche occurrences reported during the data period in this region. Out of which 17 avalanches triggered during snowstorm or within 24 hours after the storm. Analysis of stratigraphy data before few avalanches show that the ram resistance is quite high at the bottom of the snow-pack but resistance is low at the top due to the presence of new snow. This indicates that failure layer of the snow-pack contains new storm snow resulting in to direct-action avalanches. 6. CONCLUSION The paper has presented some characteristics of the seasonal snow cover of Pir Panjal and Great Himalayan ranges on the basis of observations from two stations, one in each range. As both the ranges are quite broad, analysis of some more observational stations are recommended for further deductions. However on the basis of present study following can be deducted: Because of the higher temperatures, low temperature gradients developed inside the snow pack of Pir Panjal range as a result, rapid densification occurs which tends to cause a stable snow pack comprised largely of equi- temperature and melt freeze snow with higher densities and higher ram resistances. This reflects the basic features of the snow cover that accumulates under maritime climatic conditions. Shallow snow pack and low temperatures developed higher temperature gradients inside the snow pack of Great Himalayan ranges resulting in to development of sugar grains and depth hoar crystals after temperature gradient metamorphism, reflecting the features of accumulation under continental climatic conditions. 102

The authors are thankful to Maj. Gen.(Retd) S S Sharma KC, VSM, Director SASE for continuous encouragement. We also express thanks to all technical staff of avalanche forecasting group for their sincere efforts in data observations. 8. REFERENCES Ganju Ashwagosha et.al., Characteristics of avalanche accidents in Western Himalayan region, India, National snow science meet-01, 07-10 Nov, 2001, Manali, India Mc Clung D., Schaerer P., 1993. The avalanche handbook, Mountaineers, 1001 SW Klickitat Way, Seattle, WA 98134, USA Rao N Mohan, 1983, Some observations on the seasonal snow cover, First National symposium on seasonal snow cover, 28-30April 1983, New Delhi Rangachary N, et.al., 1983, Density of snow and its variations in central and western Himalaya, First National symposium on seasonal snow cover, 28-30April 1983, New Delhi Sharma S S, Ganjau A, 2000, Complexities of avalanche forecasting in Western Himalaya- an overview, Cold Region Science and Technology 31(2000) 95-102. Ward R G W, et.al., 1985, Snow Profiles and Avalanche Activity in the Cairngorm Mountains, Scotland, Journal of Glaciology, Vol 31, No.107, p18-27. Wenshou Wei, et.al., 2001, Properties and structure of the seasonal snow cover in the continental regions of China, Annals of Glaciology, Vol. 32, p93-96