COMPEXITIES OF AVALANCHE FORCASTING IN WESTERN HIMALAYA - AN OVERVIEW

Maj. Gen. SS Sharma, KC and A Ganju*

Abstract: Himalaya, the longest chain of mountains in the world shows complex variations in snowand meteorological conditions as one traverses from east to west and from south to north. The paperpresents the analysis of the past 25 years of snow precipitation and avalanche occurrence data of thewestern Himalaya region and delineates the region into three principle zones, Lower, Middle, andUpper. While Upper Himalaya Zone is close to polar region characteristics, Lower and MiddleHimalaya compares well with the Maritime and Continental Zones.Avalanche forecasting in the Himalayan region is biased toward conventional knowledge-basedapproach. The variation in three zones on avalanche activity in the region has been discussed.Different approaches of avalanche forecasting developed so far, however, require experiencedobservers and forecasters, which causes a problem because of the temporary nature of avalanchejobs. It has been seen that each zone warrants separate treatment and models for prediction ofavalanches at anyone-time.

1. INTRODUCTION

Indian Himalaya stretches from east to west forabout 2500 km across nOE to 96°E longitudesand 26°N to 37°N latitude Fig1. The complexfolding pattern that it has been subjected toduring the upheaval of Himalaya in Pleistoceneand subsequent period leading to thrusting ofIndian plate with Eurasian plate has produced along chain of mountain ranges having deepfurrows in between. This major-geological eventhas lifted the rock structure to 8847 m above sealevel. The interaction of global atmosphericcirculation system with the tallest geologicalfeature of the earth has produced diverseclimatological, biological and snow climaticzones within Himalaya. This complex variation isunparalleled in the world. The diverse variationin snow climatic conditions makes it difficult foran avalanche forecaster to apply a unified codeto predict avalanches even in .westernHimalayan region.

2. CLASSIFICATION OF SNOW CLIMATEIN GENERAL

For the purpose of classifying the avalancheactivity with respect to weather pattern, McClungand Schaerer (1993) have classified theavalanche areas into two categories Le.Maritime and Continental. As per them relativelyheavy snowfall and mild

*Maj. Gen. SS Sharma, Director, Snow andAvalanche Study Establishment Manali,Himachal Pradesh India; tel.: 0091-1733-53311;fax: 0091-1733-53510; email:root@Sasehg.ernet.in

temperatures characterize the maritime snowclimate. Snow covers are deep while rain mayfall at any time during the winter, and cold arcticair can also appear several times per winter.Avalanche formation in maritime snow climatesusually takes place during or immediatelyfollowing storms, with failures occurring in thenew snow near the surface.The prevalence of warm temperature promotesrapid stabilization of snow near the surface onceit falls, thereby, limiting the instability period. Dueto deep snow covers and warm snowpacktemperatures, the persistence of buriedstructural weaknesses deep within the snowpackis . less usually common in maritime snowclimates as compared to continental snowclimates. Weather observations are primarytools for predicting avalanches in a maritimesnow climate. Typical examples are CascadeRange of western US, the Coastal range ofBritish Columbia and the mountains of westernNorway. The average annual snowfall in themaritime ranges of North America is about 15 to25m.On the other hand, continental snow climate ischaracterized by relatively less snowfall, coldtemperature and location is considerably inlandfrom coastal areas. Snow covers are relativelyshallow and often unstable due to persistence ofstructural weaknesses. Typical examples areRocky Mountains (Canadian and Colorado), theBrooks Range of Alaska and the Pamir of Asia.The annual snowfall in the continental ranges ofNorth America is usually less than 8 m. Theavalanches in continental ranges occur mostlydue to buried structural weaknesses in the snow

154

THE HIMALAYA I .

Fig1. The Himalayan Ranges

cover as well as due to the weather conditionsthat cause the failure of these layers. Theavalanche frequency is generally low and thelow temperatures generally allow structuralweaknesses to persist for longer duration.

3. CLASSIFICATION OF SNOW CLIMATEFOR WESTERN HIMALAYA

The classification given by McClung et al (1993)is generally applicable to the USA and Europe.In India due to widespread mountains covering26 degrees of longitudes and 11 degrees oflatitudes with snow precipitation and avalancheactivity 'experienced from 2000 m to 6000 m, theclassification given by McClung does not applyfor Himalaya in its present form. In the opinion ofthe authors, the snow climate from the point ofview of avalanche activity of Himalaya may be

TABLE-1

Terrain and Meteorological Factors: LowerHimalayan ZoneTerrain (Avalanche Sites)*Altitude : 3200-4100 m (76%)*Slope : 30-38° (64%)

: 38-42° (13%)*Aspect : SE-SW (63%)

: S (34%): N (19%)

*Ground : Tall grassy cover up to300m, forested, Bushes, BouldersMeteorology*Snowfall in Major Storms: 20-80 cm (56%)

: 80-200 em (30%)*Average P.I. (nunIbr) : 0.5-3.5 (90%)

: 3.5-5.5(10%)*Temperature in winter (OC):Highest Max. 19 Mean Max. 10.8Mean Min. 10.8 Lowest Min. - 11

155

classified as, Lower Himalayan Zone orSubtropical Zone, Middle Himalayan Zone andUpper Himalayan Zone or High latitude zone. Abrief description of each of them is given in thesucceeding paragraphs.

4. LOWER HIMALAYAN ZONE OR SUBTROPICAL ZONE

This zone could be classifi~d as the zone ofwarm temperature, high precipitation and shortwinter periods of three months. The precipitationis generally concentrated between December­March with the periods before and afterexperiencing wet snow precipitation or rains.Due to prevalence of warmer temperatures, thesnow cover very soon changes into isothermalsnow pack at zero degrees Celsius.The avalanche actiVity is quite high, with most ofthe avalanches triggering during, snowfall asdirect action avalanches due to excessiveoverburden or within 24 hours after a majorsnow fall on a clear sunny day. The peak winteravalanches are generally moist slab avalanchesand late winter avalanches are melt avalanches(Thaw avalanches) containing snow, mud andstones.The mountainous areas falling in this categoryare the Pir Panjal ranges in Jammu and Kashmirand lower altitudes on the windward side of thesame range in Himachal Pradesh Fig 2. Theseareas have an average height of 2000m to4000m with seventy six per cent of the totalregistered avalanches between 3200-4100 m.This semi-arcuate range has about sixty per centavalanches slopes in the slope range of 30°-38°.Most of the hazardous avalanche slopes havesouthern aspect and only 20 per cent havenorthern aspect. Most of the slopes up to 3000mare forested. Avalanche slopes have tall grassysurface with occasional bushes and boulders intheir paths.These areas are heavily populated because ofprevalence of pleasant climatic conditions. Themoist snowstorms that this area receives frommid December to February end are generallymoderate in nature with 50% of snow spells inthe precipitation range of 20-80 cm and 30%touching 200 cm.The salient points describing the characteristicsof Lower Himalayan zone are given in Table-1.

4.1 Deductions:Major avalanches occur:-During snowstorm when overburden exceeds200-Kg m-2 after terrain irregularities get filled up

75 76 77 78

I .- ,.1' .,1"". .. .. I""" ""I,· "" '..... _~

31

33

32

,._ 34

LEGEND

Lower'Himalayan Zone

~:'I I, Middle

'~:"" "':::~,.'L\layan Zone I"':.~ S .... Upper fllmalayan Zone :r

:'-; '- .<.,

, Himachal Pradesh:;'

"I'

INDIA

rl

fI:~

f

r Il I I ' I '

-

V1

'" Fig 2. Snow Avalanche Climatic Zones of Himalaya

...-. MeaDMax

devoid of vegetation except in few preferredareas where slopes up to 3000 m is sparselyforested. The zone has an -average height of3500 m with maximum avalanche slopes in 3500- 5300 m ranges. This mid-latitudinal Himalayanrange has almost seventy five percenthazardous avalanches in the slope range of 32­40 degrees. About 58 per cent of theseavalanche slopes have southern aspect and asizeable number (35 per cent) have northernaspect. Avalanche slopes in western flank of thisrange have grassy ground cover, open forest upto 3000 m whereas the eastern flank of samerange has generally barren slopes with scree orboulder filled.The areas falling in this zone are windward sideof the Great Himalayan range in Jammu andKashmir and upper reaches of Pir Panjal rangein Himachal Pradesh Fig 2. This zone is sparselypopulated by virtue of being rugged, cold andmostly glaciated. This range receives goodamount of total snowfall during winter, eighty percent of which is through moderate snow spell of20-80 cm. Entire middle Himalayan rangereceives. dry snow between mid December andend January. The general rise in temperaturefrom mid February onwards generally moistensfresh snowfall, and after March the freshsnowfall is often accompanied with light rain orwet snow precipitation. Unlike in lowerHimalayan zone, where sudden spurts of highprecipitation intensity are observed occasionally.this range generally receives precipitation atmoderate rate throughout the winter. Severewind activity redistributes snow from avalancheslopes very frequently in this zone.Severe avalanche 'activity is reported in thisrange throughout the winter. The initialavalanches are mainly due to the failure of TGlayer, which gets formed in the shallow snowpack during early winter. The massive slabavalanches from drift loaded slopes are alsoobserved. Thaw avalanche activity is alsoobserved from a few slopes in the months ofApril and May.The salient points describing the characteristicsof Middle Himalayan zone are given in Table-2

5.1 Deductions:_*Initial Avalanches occur:-Due to the failure of TG layer formed in shallowsnowpack.*Subsequent avalanches occur:-From steep formation zones-Due to creep deformation of metamorphosedsnow.

-30

-20

N DJ FMA

9.//

/

0._-0,. p-_J:f.&.& " '"

.& ''0''''' .&.& ..

200

­o

6 6 Highest Max

'. • LowestMax

0---0 MeaD MiD

with 150 cm of standing snow.- Within 24 hours of storm on a clear

sunny/windy day.- Radiation may cause loose snow

surface avalanches- In spring-after snowpack becomes O°C

isothermal, full depth or even surfaceavalanches trigger

- Few delayed actions avalanches onnorthern slopes trigger.The climograph of a representative observatoryin Pir Panjal range along with frequencydistribution of avalanche activity observed in arepresentative area is given in Fig-3.

Fig 3. Climograph of a representativeobservatory in Pir-Panjal Range along wittfrequency distribution of avalanche activit)observed.

5. THE MIDDLE HIMALAYAN ZONE ORMID LATITUDINAL ZONEThe middle Himalayan zone is characterized bythe highest mountain peaks and numerousglaciers. The terrain is rugged and is generally

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6. UPPER HIMALAYAN ZONE OR HIGHLATITUDINAL ZONE

The average height of this zone is about 5000 mand it houses some of the longest glaciers of theworld. This zone is characterized by steep peaksand glaciated valleys. The rugged terrain andextremely cold climate makes it the mostinhospitable area in the Himalaya. All hazardousavalanche slopes in this range have formationzone altitudes more than 5000m. A good percent of avalanche slopes (33%) have slopeangles of 32-40 degrees. Almost all avalancheslopes have northern aspect and thus, remaindangerous throughout the season.The areas falling in this category are a fewslopes in the leeward side of Great Himalayanrange (Jammu and Kashmir and HimachalPradesh), Zanskar range, and KarakoramRange Fig 2.This part of the Himalaya is very thinlypopulated. Small villages are located insheltered valley regions, where congenialenvironment supports growth of single cropduring brief summer period. The climaticconditions are closer to polar conditions.Snowfall in this zone is generally scanty but it isextended almost throughout the year. About fiftyper cent of the storms precipitate less than 20cm snow in a stretch, however, fresh snow up to80 cm in a storm has also been reported at anobservatory in this region. The snowfall is mostlydry and bonds poorly with the glaciated surfaceor with old snow. Although steep rise intemperatures has been observed to commencefrom mid February onwards but that hardlycrosses freezing level on glaciated terrain. Itrarely rains in this region, and whatever littleliquid precipitation takes place during peaksummer period, is in the valley region only. Thetotal precipitation as well as the precipitationintensity remains low in this region. However,whatever little precipitation that takes placeremains for longer duration till the melt seasonstarts in May. Since snow on slopes remainsmostly loosely bonded, the redistribution due towind activity takes place very frequently.Avalanches occur from steep slopes in thisregion, however, their frequency is not very high.Since the ground conditions are not conducive toanchor good snow pack, avalanches fromglaciated and steep rocky surfaces start with aslittle as 30-40 cm of fresh snow. However, incertain areas where rugged, undulatingavalanche slopes offer good anchorage, delayedaction avalanches have been observed.

0 ~

~<

·-10 cor::

i-20

-30

Mean Max. 0.5Lowest Min. -27

: 12-15m: 0.5-3.5 (98%): 3.5-5.5 (2%)

: 32-40°(75%): SE-SW (58%): SE (37%): NE-NW (35%): Scree , Boulders

*Slope*Aspect

*Ground coverMeteorology*Snow in Major Storm: 20-80 cm (81 %)Average totalsnow fall in a year*Average P.1. (mm/hr)

Temperature in (OC):Highest Max.13Mean Min. -11.7

100

N D J F M A

<:>--0 MeaD. MiD

Fig 4. Climograph of a representativeobservatory in Great Himalayan Range alongwith frequency distribution of avalanche

...--. Meaa Max

Terrain and Meteorological Factors:Middle Himalayan ZoneTerrain (Avalanche Sites)*Altitude : 3500-5300 m (100%)

-Loose snow avalanches and sloughing is alsoprevalent.-Spring avalanches. Thaw avalanches are inApril-May.TABLE 2

The climograph of a representative observatoryin this zone lying in Great Himalayan rangealong with frequency distribution of avalancheactivity observed in a representative area isgiven in Fig 4.

158

The salient points describing the characteristicsof upper Himalayan climatic zone are given inTable-3.

..-. MeanMax

0---0 Mean Min.

TABLE 3

*Snow in Major Storms: 10-20 cm (51%): 20-30cm (25%): 30-80 cm (24%)

Terrain and Meteorological Factors: UpperHimalayan ZoneTerrain*Altitude : 5000-5600m(100%)

*Slope : 28-32 (0C) (67%): 32-40 (OC) (33%)

*Aspect : NW (42%): N-NW (34%)

*Ground Cover: Rocky, Scree, and GlacialMeteorology*Average Total snowfall in a year : 700-800 cm

-30

o

N D J F M A

too

! 300

~Co) 200

~CI.l

.6.

./::; /::; Highest Max

• • LowestMax

: Mean Max. -8.1: Lowest Min. 41

*Temperature (0C): Highest Max. 9: Mean Min. -27.7

The snow conditions in Himalaya are complexand require continuous monitoring of snow andmeteorological parameters with a densernetwork of observatories. Also, the observatorylocations for correct assessment of snowconditions have to be meticulously planned inorder to obtain realistic data for avalanche

assessment of avalanche danger. This warrantsa very accurate monitoring of meteorologicalparameters in accessible as well as ininaccessible areas. The very fact that this area isoften in use by civil population and troops,accurate models for timely warning for thepedestrians on winter routes are required.The conditions encountered on UpperHimalayan range are somewhat close tocontinental snow conditions with the salientdifference being in altitude, unstable terrain, andabsence of vegetation and total absence ofliqUid precipitation throughout the year. Thiswarrants continuous study of snow not onlyduring the winter periods but also throughout theyear.

6.1 Deductions:

Avalanche occur:- When overburden exceeded 30 Kg/m2

- Due to failure of TG layers (Delayed action)

The climograph of a representative observatoryin this zone lying in Upper Himalayan rangealong with frequency distribution of avalancheactivity observed in a representative area isgiven in Fig 5.

7. INFERENCE

From the above the following is inferred:The conditions prevailing in lower HimalayanZone are somewhat closer to maritime snowconditions, the short winter with heavy moistsnow precipitation during winter cautions aforecaster to remain on continuous watch forforecasting avalanches during snow storms.Since this zone is heavily popUlated andcontinuous traffic plies on highways, a veryaccurate continuous avalanche forecast iswarranted.The conditions encountered in Middle HimalayanZone warrant a detail study of snow cover fromits inception to ablation for an accurate

Fig 5. Climograph of a repre.sentativeobservatory in Karakoram Range

7. RECOMMENDATIONSCONCLUSION

AND

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forecast. This can be conveniently implementedin lower Himalayan region, but for other tworegions automatic weather stations have to beinstalled.Various models developed so far in Europe andNorth America cater for the areas wheremeteorological conditions are fairly stable andpredictable, and where educated-trainedobservers are available who are very sincere inrecording and transmitting data. This aspect istotally absent in India. In order to accuratelypredict avalanches for Indian conditions,separate models for separate areas catering forthe quality of observations and gradation ofobservers have to be developed.Remote sensing through satellite photographsand other means provide a great promise. Suchmeans should be developed and utilized.A very accurate weather prediction can greatlyinfluence forecast. In order to cater for this,

. mountain meteorology as a science with meso­scale models to cater for 1Ox1 O-km resolution issuggested.

8. ACKNOWLEDGEMENT

The authors are thankful to the scientists and thescientific assistants of Avalanche ForecastingGroup (SASE) for helping in compiling theinformation from archives of SASE. Thanks arealso due to Patron for allowing publication ofpaper.

9.REFERANCES

1. McClung, D. Schaerer P (1993) TheAvalanche Handbook: Published by theMountaineers 1001 SW Klickitat Way, Seattle,

. _'and Washington 98134. P 17, 18.. ¥-2. Annual Reports of SASE (1971 to till

date)

160