UNIT 113 AVALANCHES

Structure
13.0 Learning Outcome
13.1 Introduction
13.2 Avalanche: Formation and Classification
13.2.1 Avalanche Formation
13.2.2 'Qpes of Avalanches

13.3 Avalanche Prone Areas

13.4 Avalanche Disasters in India
13.5 Avalanche HazardMitigation and Management Plans
13.5.1 Passive Methods
13.5.2 Active Methods
13.6 The Snow and Avalanche Study Establishment (SASE)
1 3.7 Lessons Learnt
1 3.8 Conclusion
13.9 Key Concepts
13.10 References and Further Reading
13.11 Activity

13.0 LEARNXNG OUTCOME

After studying this Unit, you should be able to:
0 understand the phenomenon of avalanches;
e explain the formation and classification of avalancl~es;
0 identify the avalanches prone area;
e discuss the avalanche hazard mitigation and management plans;
e highlight the role of SASE ;and
e bring out the lessons learnt.

13.1 INTRODUCTION
Ayalanches are the events of snow bound mountains and have been occurring during winter months
in the snowbound areas of the Himalayas, taking a heavy toll of lives and property, year after yea.
A number of lives are lost and millions worth of property is destroyed. Besides loss of lives,
avalanches also destroy forests and disrupt road communications, thereby hindering the hill ama
developmentand affecting installations in the area. This Unit definesthe phenomenon of avalanches,
describes its genesis, classification and magnitude of the destructive power. Vdrious techniques for
mitigating the avalanche disaster are described. The Unit also brings out the work being done in
India in this regard, specially the role of the Snow and Avalanche Study Establishment (SASE). It
 Avalanches 161

has been observed that heavy snow accumulation due to snow precipitation and avalanche
movements are the twin problems of high mountain areas. While the former is a problem of snow
clearance, which by no means is an insurmountableproblem with the availability of the latest types
of snow clearing equipment, the latter problem remains a problem of scientific study, research,
engineering and organisation.
Definition
An avalanche is the downwardmotion of a large mass of snowlice on a slope with high speed and
great force causing widespreaddestruction on its way downhill and in the valley region below. The
downward motion may be in the form of gliding or sliding along the slope like a rodk fall, or flowing
along the ground like fluid or whirling through the air like a whirl wind. An avalanche comprises
three zones i.e. Starting Zone, Run out Zone, and the AvalancheTrack. Avalanches occur when
the weight of the upper snow layers exceeds the bond with the material underneath. The snow can
break loose in chunks or as a wall sweeping victims down the mountain. Many a times, vibrations
caused by loud noise, such as, artillery fire, thunder or rock blasting can set the snow mass in
motion, thus triggering an avalanche.

AVALANCHE: FORMATION AND CLASSEIFICATION

13.2.1 Avalanche Formation
The three factors that contribute to avalanche formation are snow, nature of ground and
I meteorological or weather conditions.Snow forms when water vapour in the atmosphere condenses
at a tehperature below the freezing point of water and passes directly from the vapour (gaseous)
state to the solid state in the form of very tiny ice crystals which unite into small snow flakes.
Obviously, because of the height and/or weather conditions, there are areas in mountainous regions
that have snow cover either throughout the year or for large part of the year. These areas are
demarcated by the lower edge of the snow cover (called snow-line). The region above the snow
I line comprises more or less continuous snow cover. There is a high permanent snow line in the
iI summer and alower variable snow line in winter. Snow being light weight is highly winddriven and
I winds areusually strong in hills, specially during snow storms. The drifting snow can accumulate in
large quantity in certain areas, may be against an obstacle and result in an unstableaccumulation or
overhang,This is called Snow Drift. Thus snowfall starts due to meteorological (weather)conditions,
which also contribute to excessivesnowfall, snow accumulation or snow drift; Ground conditions
i determine whether the accumulated snowmass can remain stuck at the place or overcome the
I friction and start moving to generate an avalanche. As stated earlier, external conditions (like
i

loosening of the bond at ground due to melting or even extraneous vibrations) can trigger an
1
I
avalanche.
The role of the weather condition does not end with the snowfall, snow accumulation or snowdrift.
Ii .
Even when the snow accumulation or ground is in an apparent stable equilibrium, it is undergoing
transformations, which are primarily temperature dependent and are classified as thermal
1 metamorphism. The thermal metamorphism with transformation of vapours from convex surface
I to concave surface within a snow crystal at temperatures close to O0C results in the formation of
felt grains and round grains. Formation of such grains is called Equi-Temperature (ET)
Metamorphism or Destructive Metamorphism. Likewise, freezing of water vapours through
sublimation from the snow -ground interfaceonto the snow crystal within the snow cover due to
temperature gradient between the ground and the atmosphere during a cold spell results in the
. formation of hollow cup crystals. This process is known as Temperature Gradient (TG)
metarnorphisrnorConstructive Metamorphism. Also, melting and freezing of a snow crystal due
162 Ut~derstundirlgNatural Disasters

to rise and fall in temperature above and below the freezing point is called Melt-Freeze (MF)
Metamorphism.
The above types of metamorphisms, make the snow cover either strong or weak. For example,
formation of round grains during ET rnetalnol-phism improves cohesion and thus the snow cover
becomes'stronger. On the other hand, the formation of cup crystals due to TG metarnorphisrn
weakens the snow cover. Also, occussence of melt-freezecycles during MF metamorphism results
in the loss of cohesion during melting cycle and formation of hard slab during the freezing cycle.
Also, when snow is soft and fluffy, i t has very low angle of repose of the order of 17" - 30°, and
when it is cohesive, it has high angle ~)l'scposeofthe order of 30'-35'. As aresult of this, formation
of avalanches is largely due to hcah snow cover lying on slopes close to the angle of the response
of snow. It is generally seen that avalanche occurrence is more predominant on slopes between
35O to 49, though any slope mol-ethan 30" and less thai155ucangive birth to avalanches.
Avalanchesoccur when the weight of upper snow layers exceeds the bond with material underneath.
Being a visco-elastic ~naterial,the snow lying on the slope, because of its self-weight,expel-iences
stresses which causecreep and glide in the snow cover. These movements cause further stresses
in the snow cover. Initially, a primary fracture 1sinitiated which later extends into a secondary
fracture, resulting in themovement of the snow slab from afew mm per second to afew metres per
second. This is the principal cause of avalanche formation.

13.2.2 Types o f Avalanches

There are basically two types of avalanches viz., Ice Avalanche andSnow Avalanche. Ice avalanches
occur generally on slopes covered with glaciers. They occur due to development of weaknesses
in the ice Inass deposited as integral part of aglacier. The weakening of the ice mass takes place
due to various changes taking place in the atmosphere time to time. Since the material involved is
ice which has low co-efficient of friction, these avalanches are capable of travelling even on flat
slopes for long distances. Such avalanches have not very rn~~ch been seported in the Indian~llountains
since most of the glaciers in India lie in the remote areas and so there are not Inany reports.
However, occurrence of such avalanches has been observed on the Siachen glacier. Scientifically,
the mechanics of ice/glacier avalanches are similar to that of snow avalanches.
Snow avalanches involve snow as the pri~narymate~iai,which consists of ice, air, water and impurities.
Snow avalanches, due to high friction between snow and snow and snow and ground, travel with
comparatively low velocity ( 1 0 to 30 mlsec)and generally come to a halt on slopes less than 12O.
Snow avalanches can be of dry or wet type. Dry snow avalanches involve fresh i,e. dry snow
sliding over a surface of snow which has congealed and become fixed and stable. Wet snow
avalanches occur when rainfall or walm wei~therfollows iintnediately after aspell of heavy snoMdll.
In that case, snow avalanche consists of melting snow mixed with water and carrying along any
other material enroute. Wet snow avalanches also occur during spring season when snow
accumulated in winter staits melting.
Snow Avalanche Classification
Formation of snow avalanche largely depends on the type of snow, terrain and the prevailing
weather conditions. The snow avalanches can be classified as Loose Snow avalanche, Slab
avalanche and Airborne/Powder avalaliche.
i) Loose Snow Avalanche
I

The two most important pre-requisites for the formation of loose snow avalanches are: (a) the ,

snow is weak in cohesion; and (b) it is lying on a steep slope When the above two conditions
-a'
 Avalanches

prevail, small crystallgrain on snow loses contact with its neighbouringcounterparts due to lack of
cohesionand gathers speed and momentum. As the particle descends with increased mass, it
disturbs other crystalslgrains, which also start moving down. The motion contjnues, gathering
Inore mass as long as the movement is on steep slope. The avalanche comes to halt once it
reaches flat slopes where its kinetic energy is absorbed by the frictional energy. A Loose Snow
Avalanche is triggered when a force sufficient to overcome the internal cohesion and frictional
resistance gets applied. This may bedue to falling of stones in the folmation zone, falling of chunks
of snow from the trees in the formation zone, shock waves due to explosives or otherwise, and
movelnent of skiers.
Steepness of a slope has got adirect bearing on triggering of loose snow avalanches. Slopes
between 40 to 60" are more prone to loose snow avalanches.
Types of Loose Snow Avalanches
The newly fallen snow crystals at the startof ET metamorphism change into felt-like (felty) grains
before reaching the end of ET metamosphism. The snow cover consisting of fresh snow crystals
and felty gl;ains is acohesionless inass and is pmne to dry loose snow avalanches. Similarly, old
metamorphosed snow in the shady slopes loses cohesion due to TG metamorphism and becomes
prone to dry loose snow avalanches.
When freshly fallen snow or even old snow is subjected to high Lemperutures, the snow grains get
transformed into melt grains, which lack cohesion and the resulting snow cover becomes prone to
wet loose snow avalanches. Since loose avalanches consist of loose dry/wet snow, they have low
velocity and force. On the basis of obse vations made in field in India and abroad, speed of loose
snow avalanches is of the order of 1 mls to 10 m/s and density is of the order of 100 (dry snow)
1 to 500 (wet snow) kg/m3. r
ii) Slab Avalanches
The failure or separation of a snow slab lying on a slope and its downward descent with high
I momentum is known as a slab avalanche. The zone demarcating the ruptured snow and the un-
I
~upturedsnow on the slope is in the form of a well-defined zigzag line. The three pre-requisites for
I
the formation of a slab avalanche are (a) the snow has had time to gain cohesion; (b) it has gained
some strength; and (c) it is lying on a steep slope.
Slab avalanche occurs when either there is an increase in stress or there is decrease in strength or
there is simultaneous increase i n stress and decrease in strength.
Types of Slab Avalanches b

The slab avalanches could be dry slab or wet slab avalanches. D1.y slab avalanches generally
occur in the early part of winter and during peak winter when fallen snow crystal undergoes a
quick rate of ET inetamoi-phis~n,or TG metamorphism, under sustained sub-zero temperatures.
The resulting slab is dry slab, which triggers into an avalanche on occurrence of rupt~~re.
Wet Slab Avalanches generally occur in the latter part of winter when a slab is subjected to above
O0C temperature, which causes formation of thin water film around the crystaIs, thereby making
the snow slab wet. Such slab, when triggered due to occurrence of ~upture,results in the ,Formation
of a wet slab avalancl~e.Dry slab avalanches have speeds of the order of I0 - 20 m/s and density
100-250 kg/m%and wet slab avalanches have speeds of the order of 10-30 m/s and density 200
- 500 kglm3.
iii) AirborndPowder Avalanche
When a dry snow avalanche moves along the ground with high speed, the air surrounding the
moving avalanche column experiences a sudden vilcuum, which results in the neighbouringsnow
I
 Under.standing N~zturulDisasters

particles getting airborne. Thus, one part of the moving avalanche moves along the ground and the
other part with the snow pal-ticlesinoves in the air. During movement, the air column initially lags
behind the ground colu~nn,and later overtakes the ground column and travels to a long distance,
rnuch ahead of the ground column. The poi-tion that moves in the air is termed powder avalanche
or airborne avalanche. Such avalanches, which are more commonly seen during the early part of
winter, when snow is d ~ ysoft
, and fluffy,are more predominant and visible when amoving avalanche
comes across a sudden steep descent.
Such avalanches have low density of the order of 2-10 kgfin3 and very high speed of the order of
50 to 75 mlsec. These avalanches are less destsuctive than the ground avalanches but they cause
severe destruction to forests.

13.3 AVALANCME PRONE AlRlEAS

Snow and Avalanche problem is a problem of high altitude lnountainous regions, which receive
heavy snow precipi tation and are either inhabited or are used fequently by human beings for
communication, winter sports, mountaineering, defence, natural sesourceexploration,etc. The
avalanche areas of our country lie along the Northern parts of Jammu and Kashmir, Himachal
Pradesh, I--Iillsof Uttaranchal and up to Sikkiin i n the Eastern region. These areas, due to
colnmunicationdifficulties and remoteness from the rest of the country, are very thinly populated
and under-developed and hence a lot of incidents of this nature in these areas go unnoticed and
they do not receive media attention. Nevertheless, there lies a great polential for development,
which needs our careful attention for mitigating such disasters. Every yeas, avalanches in these
areas take a heavy toll of lives and cause considerable dainage to pl-operly.

AVALANCHE DISASTERS IN LNDEA

In hldia, snow avalanches occur in the Himalayan ranges and more so in the mountainous regions
of J&K ,H.P. and Uttasanchal. The incidence is much less in theeastern and north-eastern Himalayas
because the.denseforest and vegetation cover these act as a binding force and inhibit the slippage
of snow mass. However, these do occur in Sikkim. An averageof 50 to 60 human lives is lost and
assets worth millions of ~upeesare destroyedevery year in the snow-bound regions of the country
due to avalanches. Thougll no systematic record is available for the years before 1970, the locals
in the areas report a number of serious avalanche disasters which can be compared with those
anywhere in the world. On January 7,1973, an airborne avalanche came on one of the Avalancl~e
Research teams of the Snow and Avalanche Sh~dy Establishment (SASE), at Sonamarg in J&K.
The airborne avalanche, after travelling adisaster of riearly 2 kin in ail; hit the Research Statjan
with tremendous force, killed two men, seriously injured 20 and buried 18 barracks. In the same
year, over 70 lives were lost in J&K due to avalanches.
The maximum number ~Ccasualtiesd ~to~avalanches
e were reposted during the winter of 1978-79
when over 600 hurnan lives were lost in J&K, HP and UP Wills. In November 1986, an early
I
snowfall event triggered a few avalanches and blocked a large convoy of vehicles at Zojiia Pass in
J&K. ~his,followedby a severe snow blizzard, claimed over il hundred lives and a good deal of
property. Avalanches have also affected the settlelnents around the shrines of Badrinath and
Kedarnath in Uttaranchal, In December 1994 and Januwy 1995, the atmy suffered severe losses
in J&K andsiachen areas due to intense snowfall, sudden b d weather andavalanches.In February
2005, z\ series of avalanches, triggered by very heavy snowfall, hit lnountainous areas of the J&K
State. The population affected was approximately 2.35 lakh. 278 persons lost their lives and I

more than 260persons were missing due to snowfall and avalanches.

Avalunches 165

In JGrK, the most affected areas are in lhe higher reaches of the Kashlnir and Gurez valleys, Kargil
andLadakh and sorne of the major roads. Thus in H.P., the vulnerable areas are: Chamba, Kullu,
Lahol-Spiti and Kinnauc In the Garhwal Himalyas in Uttaranchal, parts of Tehri Garhwal and
Chamoli districts are vulnerable. About 2500 kn-1of lnajor roads in the Himalayas are exposed to
the damages of snow avalanches.The Ja~mu-Srinagar,Srinagar-Leh and Manali -Leh roads are
particulmly vulnerable.

AVALANCHE HAZARD NTITIGATION ANI)

NAGEMENT PLANS
Avalanche is a recurring phenomenon. Avalanche hazard mitigation is done through Active and
Passive methods. Efficient control of avalanches is possible only through active methods,comprising
essentially, structures, afforestation and artificial controlled release/triggering. These methods,
besides being costly, are also very difficult to execute due to the peculiarities of the terrain. At
some places these methods cannot be implemented at all because of logistic problems. In any
case, cost effectiveness versus facility to be protected need to be weighed properly before execution
of any of the active methods of control of avalanches.
While methods like stluctural control or afforestation arrest the creep and glide motions of snow
on slopes; and retarding and diversionary structures, as the name i~nplies,retard and divert a
flowing avalanche, artificial triggering helps in bringing down the avalanches before they reach
stupendous proportions. The latter method is relatively cheapec The Passive and Active methods
are described below.

13.5.1 Passive Methods

Passive methods include increasing awareness about the avalanche hazard; timely forecasting the
avalanchedanger and imparting training on safety and rescue ~nethods.
i) Awareness
There is a general lack of awareness about the avalanche phenomenon and the safety and rescue
measures to be taken against it. A study conducted in H.P. during the early nineteen eighties
revealed that people prefer to stay indoors all through the winter or carry out movements with
precautions. However, in vi6w of winter tourism and increasing usage of the snowbound regions
in winter for trade, tourism, spoils and defence, this concept is out-dated. It is therefore imperative,
that the inhabitants of the local area and other agencies responsible for traffic regiilation, winter
sports and other connected user organisations are made more' aware about various aspects of
avalanche disasters. The awareness enhancement efforts should include conducting awareness
workshops at various levels with various training aids like multimedia,films, classes, posters and
demonstrations. The awareness programme may d dealt on the lines inentioned in the succeeding
paragraphs.
a) Pre-winterAvalanche Awareness ProgrLmme:Prior to the onset of winter, some courses
of 2 to 3 days duration may be organised at the district or village level for educating the users
about the types of avalanches, avalanche sites and their past history, avalanche incidents and
accidents observed and the precautions to be taken to avoid mishaps. During such courses,
some training on conduct in the avalanche prone area, rescue techniques, method of reporting
the casualties,medical attention, etc., may also be imputed. Some details about the organisation
of the avalanche service in the general area with the set-up of observations and the system of
issuing avalancheforecast bulletins and their interpretation should be coveivd. Simultaneously,
talks and discussions by expests in this field should be organised through the media, specially
i;
 Understuncling Nat~iralDisasters

Doordarshan and the All India Radio. Such talks should be regular with demonstration of the
past cases through multi-media. Any money spent on developing awareness amongst the
users, is worth it, since a vigorous programme run in an organised manner before the winter
can result in saving of number of lives.
b) Mid-winter appraisal report: It is seen that most of the avalanche events occur in the
initial phase of the winter, since there is a general erroneous feeling that unless sufficient snow
cover is built-up, there is a less likelihood of avalanche occurrence. Also, during the first few
spells of snow precipitation, users generally rush up at the last minute to safe places and also
continue attending to the unfinished tasks. All such incidents should be noted and an analysis
report prepared by a central organisation like SASE responsible for avalanche research and
prediction. During mid-winter, such reports should be published in brief, thiough newspapers
and also through TV media with cornments from the experts. An outlook about the remaining
part of the winter indicating the likely amount of precipitation and the temperature trend
should also be attempted. This will help various organisations in learning important lessons
from the recent incidents as well as getting ready for the remaining part of the winter.
c) Post-winter appraisal report: Once the winter is over, the research organisation should
conduct criticd evaluation in which the entire winter snow and avalanche activities should be
discussed. Feedback on what was taught before the winter and what actually happened,
how useful the training programme was, etc., should also be discussed.
d) Avalanche Forecasting: Since every winter follows a different trend and the types of
accidents seen are also viuying in nature, it is imperative that theresearch organisation publishes
'
a detailed account of the snow precipitation experienced, warning issued, and accident9
observed during the past season.
e) Publication of Hazard Maps and Avalanche Atlases: The research organisation should
publish detailed avalanche maps marking avalanche sites, accumulation of snow due to such
avalanches and also the history of such avalanches. Such [naps should be updated every
year and compiled in an avalanche atlas for aparticular area. These atlases should be made
available to vasious organisations and the local panchayats and district authorities.
Multimedia and Users' Guide: The multiinediapresentation of the avalanchephenomnenon,
their classification, the common types of accidents, safety and rescue and other measures
shduld be prepared by the research organisation and distributed to various user-organisations.
Small pocket size handbook with pictures covering important aspects of avalanche activity
and remedial measures to be taken should be published and distributed in sufficient nurqbers
.I
to the users. Also, poster? p i n g pictures on do's and don'ts and other safety aspects should
be published in sufficiait numbers and displayed at important locations in the general area.
It is our experience that a number of Iides can be saved if the awareness progranlme and aids
mentioned above are followed in thktrue spirit in u mission mode, year after year. This will
certainly savemany lives of the local population. Besides, it will also develop a sense of confidence
in the minds of the local inhabitants,traffic police and touristsfor moving in the avalanche prone
areas without any fear. This will greatly boost the economy and will also strengthen the confidence
of the local people of the hill states.
ii) Avalanche Forecasting
~ i t i ~ a t i of
o navalanches through avalanche forecasting is the best and most cost-effective method
available. However, the methodology somewhdt lacks objectivity,and Libove all requires knowledge
of the antecedent conditions. This also requires continuous monitoring andupdating.
Occurrence of an avalanche is the result of a catastrophic fracture in the snow on a slope and its
downward descent to the lower region due to gravity. The principal factors, which affect the
 Avalanches 167

health of the snow cover are, snow precipitation, standing snow, type of snow stratification,
atmospheric temperature, wind conditions, etc. These factors can also make the snow cover
stronger which can conveniently rest on the slopes, and they can also make the snow cover weaker,
which with slight initiation can trigger an avalanche. Thus, avalancheforecastinginvolves assessment
of the present stability of snow cover and its continuous monitoring with the changing meteorological
conditions.
The ideal methodology for forecasting an avalanche is to climb up the avalanche formation zone
and measure the stability of the snow cover and also that of the various layers present in it, by
physically measuring through instlurnents. This involves opening of pits in the snow and measuring
the strength properties of different layers and also the overburden over each layer and the resultant
stresses caused in them. Thus, if at any site, the stress over the layer exceeds the strength of the
layer, the probability of occurrence of an avalanche is very high. EIowever, the above is easier said
than done, as the slopes where the avalanches form are inaccessible and carrying out the
measurements as mentioned above is most hazardous. Thus, the workable method is to extrapolate
the conditions of the snow cover on the slopes through various measurements of the snow cover at
a representative observatory. The measurements involved, ase the thickness and density of each
layer, shape and size of the crystals present in the layer, temperature of each layer and overburden
over the layer, and moisture content, Theprjncipal factors contributing to avalanche occurrence in
a given area are, amount and type of snow precipitation and its intensity, snow and atmospheric
temperatures wind conditions, and intensity of sunshine. Having done the measurements of these
parameters at the representative observatories, certain models are developed for estimating the
snow conditions on the slopes through extrapolation. Having done so, the health of the snow
cover is continuously assessed with the changing ~neteorologicalconditions. Even this task of
I taking measurements in a representative observatory is not an easy task. Also, to have a realistic
I
estimation,the number of observationsrequired is very high and difficult to establish. To overcoqe
I

I
this difficulty, Snow Cover Simulations Models are developed to estimate the condition of the
I
snow cover by continuously measuring the external parameters like fresh snow, temperature, wind
and water content of snow. Such models give afttir estimate of various paraineters relevant to the
1
forecasting of an avalanche.
Mathematical models have been developed for avalancheforecasting by taking into account the
external and internal parameters of snow and meteorological factors which give a fair estimate of
the probability of avalanche activity. Some of the models, which arecommonly in use a, Discriminatr:
Analysis Model, Nearest Neighbour Model, Expert System, and Process Oriented Approach.
All these models though provide effective tool to a forecaster, but issuing final forecast for anarea
for different types of users still largely depends upon theaskill of the forecaster. Thus, the modern
! technique of using the snow cover siinulation model coupled with differentforecast models holds a
i
I
I
good promise for achieving higher accuracy. However, the ground truth and the skill and experience
of the forecaster in interpreting the output of the models continue to be important. Nevertheless,
1 the forecasting models available today, supported by the fast computational techniques, provide a
1
I
promising tool in this field.
Having assessed the degree of avalanche danger for a particular area, the avalanche danger is
i i classifiedin the four categories;like low danger, medium danger, high danger and all round danger.
I A brief description of each is given in table 13.1.
i
1 iii) Safety and Rescue Methods
Safety, in terms of preparedness in clothing, equipment, safe route, projected weather, physical
fitness, etc., is the basis for any'backcountry travellers to be prepared about while negotiating an
avalanche prone area. The do's and don'ts while crossing an avalanche path should be known
and the actions to be followed on being hit by an avalanche should be well rehearsed - in advance.
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 Understanding Natural Disasters
I

Table 13.1: Scale of Avalanche Danger

a
Degree of Danger Implications' Suggestions/Precrrutions

Low o Generally favourable condition. e Valley movenlents are safe.

e Triggering is generally possible Movement on slopes with care.
only with high additiollal loads and
on very few extreme slopes.
a Only snuffs possible and reach
valley in small sizes.
Medium o Partly unfavourable condition. e Avoid steep slopes.
0 Triggering possible from the most e Route should be selected with care.
avalanche prone slopes with low
e Valley movement with caution.
additional loads and inay reach the
valley in medium size. a Movement on slopes with extreme
care.
High o Unfnvourable condition. e Suspend all movements.

e Triggering possible froin a1 1. e Airborne avalanche likely.

avalanche prone slopes even with
low additional loads and reach the
valley in large size.
A11 round e Very unfavourable condition. e Suspend all movements.
e Nu~nerouslarge avalanches are a Airborne avalanche likely.
likely from all possible avalanche
slopes even on moderately steep
terrain.

Even with all preparedness, avalanches strike and claim lives year after year. his calls for efficient
rescue operations. In case of avalanche victims, it becomes even more important, because survival
chances reduce by 50 percent after the first 30 minutes. Immediate responsibility of rescue thus
falls on the survivors. They, besides attempting to rescue the buried victims, simultaneously try to
inform the rescue organisations, which calls for an efficient communication system. An organised
rescue with trained avalanche dogs and proper equipment and organisation is very essential in
locating the buried avalanche victims.
-.
13.5.2 Active Methods
Active methods include control of avalanches by structures, affol-estationof fornition zones and
controlled release of avalanches. ;

i) Structural Control: Structural control of avalanches is a positive method and provides a

very high degree of protectionfrom avalanche danger. Stmcturil control can be carried out
in the formation zone (starting zone) by retaining ban-iers and drift control structures, in middle
path or Avalanche Track by diversion structures, like diversion wall, wedges and galleries
and in run-out zone by catch dams and mounds. The retaining barriers in the formation zone
arrest the creep and glide of the snow mass and thus create back-pressure zones, which
prevent fracture in a snow slab. The drift control structures help in altering the pattern of
accumuiation of blowing snow, thereby preventing creation of cornices and excessive snow ,
. accumulation. Diversionary structures divert a flowing avalanihe away from the object to be
protected, Retarding structures generally shorten the run-out zone of an avalanche short of
the object to be protected. Different types of struhres with their estimated costs for Indian
mountains, wherever available, are given in table 13.2.
 Avalanches

Table 13.2 : Avalanche Control Structures: Types and Estimated Costs

Avalanche Control Type of structures Cost Sites where such

Zone construction done
I. Formation Zone Retaining barriers I Crorelhectare D 10 site on
like snow bridge, Jawahar Tunnel,
snow net, snow NH-1A
rakes, etc.
2. Middle Zone Diversionary D I I site NH-1A
Structures
- Gallery Rs. I0 lacslm
- Diversion dam Rs. l lac/m
- Wedge Rs. 2.5 laclwedge
3. Run-out Zone Catch dam Rs. l lac/m Badrinath
Mounds Rs. 1 laclmound Uttaranchal

ii) Afforestation: Forests arrest the formation of avalanches in a number of ways. A forest
with thick growth of high trees in the stilting zone inhibits the formation of avalanches. The
processes involved are: supporting the snow cover and providing anchors to the potential
slab avalanches through tree trunks; eliminating the snow drift and retaining the snow on the
tree canopies and releasing it gradually. Forest canopy moderates variability in the energy
exchange with the snow surface, which tends to produce u uniform snow temperature
distribution and stable snow cover,
In India, the timberline is maximum up to 3500 m. About fifty per cent of avalanche sites in
the Pir Panjal range have fortnation zone (FZ)altitudes below 3000m..Similarly, about 31
per cent of avalanche sites in the Gseat Himalaya ranges have FZ altitudes below 3000111, and , ,
avalanche sites in Karakora~nhave FZ altitudes above 4500 m. Furthermore, the tree-line is
confined to certain pockets only near the water bodies. Afforestation can be taken up at all
sites where formation zone altitudes of avalanche si tes is below 3000 m and thus mitigate the
avalanche danger. The only drawback with afforestation is that saplings cannot sustain cneep
and glide forces of the snow and die in the very first winter. Afforestation in conjunction with
control measures is good, provided wood available for erecting structures is available in
I
plenty. This method though being most effective is quite expensive.
I

iii) Controlled Relwe/Artificial Triggering: This method attetnpts at pre-empting the release
of an avalanche by explosivesor by controlled skiing before it triggers naturally. This method
inhibits the build up of snow cover on slopes to disastrous proportions. The method is
generally adopted in conjunction with avalanche forecasting because unless the snow pack
on the mountain slope is unstable, no amount of firing would bring it down as an avalanche.
Hence artificial triggering of avalanches is an extension of avalanche forecasting. It can be
done by pre-planning the explosion, dropping the explosive by hand or by some other
mechanical device, or dropping the explosives by guns. However, though this technique is
simple and economical, it requires great amount of planning, co-ordination and training for
successful execution.
 170 Ulzderstanding N u t ~ ~ r Disasters
al

13.6 SNOW AND AVALANCHE STUDY

ESTABLISHMENT (SASE)
The Snow & Avalanche Study Establishment (SASE), right from its inception in 1969, has carried
out studies of various aspects of snow and avalanche related subjects, like avalanche formation,
snow mechanics andphysics, avalanche dynamics, avalanche forecasting techniques and safety
and rescue measures for various areas in Jammu & Kashmir, Hitnachal Pradesh and Uttaranchal.
It is a specialisedestablishment of the Defence Research &Develop~nentOrganization (DRDO)
and has its headquarter in Manali (H.P.).SASE has prepared seven avalanche atlases and has
established the Avalanche Forecastingand Mountain Meteorology Centres at Srinagar for Kashmir
valley, at Sasomafor Siachen and Nubra valley, and at Manali itself for Himachal Praclesh from
where regular avalanche forecasts and mountain-weather forecasts are issued. They also conduct
avalanche awareness training courses and publish various reports, like pre-winter appraisal reports,
mid-wirlter appraisal reports and post-winter appraisal reports, and send them to the users for
their infarmation and comments. SASE also pl-epares a detailed winter report at the end of the
winter season where they bring out a general summary of the snow and meteorological conditions
of the winter and the types of forecasts issued by them for various areas. This is published in a
special report known as 'Avalanche Forecasting - Successes and Failures', where various accidents
reported are described and their investigations discussed.
SASE has found that keeping in view the frequent turn-over of the troops in the snow-bound belt
of our country, trainingcourses, year after year, pay a very rich dividend. Keeping this in view, the
SASEorganises regular training courses during September- October every year where practical
training with the help of multi-niedia presentiitions is given to the defence personnel serving in high
altitude areas. These have greatly helpedin reducing the number of mishaps. SASE has established
over 32 observatories in the Army areas of Jarnmu & Kash~nirand Hiinachal Pradesh, which
record round the year snow and meteorological data and transmit the &:me to the Avalanche
Forecasting and Mountain Met Centres. SASE has developed the appropriate technology for
control of avalanches by structures. Consultancy projects for civil and army are taken up by
SASE for such tasks regularly as a help to the uses agencies. They have successfiilly been able to
develop different types of avalanche control structures and demonstrated their usef~rlness.As an
extension to the work done by SASE for armed services, the avalanche forecast bulletins for
different areas are broadcast on AIRand Doordarshan regulnrly. This has developed awareness
amongst civil users who frequently requestSASE for extending their work to different areas.

13.7 LESSONS LEARNT

The activities in the avalanche prone regions are definitely on the increase. Not only are the local
population and habitats increasing, civil and defence officials are more in numbel; scientific and
academic centres are coming up, pilgrims are coining in larger nurnbers not to speak of wild life
enthusi~uts:mountainneers and tourists. They know about avalanches but quite often the risk taken
by them is more due to lack of fill1information.The problem of uncel-tainty associated with avalanche
phenomenon is unique and the accidents as a result bring more agony, and this cannot be acceptable.
There are many variables required in assessing the avalanche danger at any time. Assessing
avalanche danger at my time is difficult as behaviour of snow as a material is still not fully known.
Hence, travellers in avalanche prone area always mn arisk of accident. The accidents generally
take place ilnmediateiy after the cessation of snowfdll when people venture out in clear day. Since
most of the movements in Indian Himalaya are generally thr&gh the valley bottom region, most of
the accidents take place in the run-out-zones of avalancl~es.Of late, some movements have
started taking place in the middle and formation zones of an avalanche also but the number is still
small. Since day time or early morning movelnent is prefesred while traversing through avalanche
terrain in India, most of the accidents have taken place during the day time.
While natural avalanches have been the main cause of conce1.n till date, the scenario is likely to
change soon when the recreationist and mountaineers would start going on to the slopes and
release avalanches themselves. A study has also revealed that the release of avalanches from
southern slopes far exceeds the number on northern slopes. This is likely a consequence of wind
loading and sunshine. Southerly slopes receive inaxi~numsunshine, and after each snow spell,
such slopes release avalanches, which have been seen many tirnes coinciding with the lnovement
of the people. The northerly slopes, besides being in unstable state for longer duration, do accumulsite
drift snow from windward slopes due to southwesterly winds that genesally prevail during disturbed
weather. Such slopes, due to presence of sufficientsnow till late winter, will attract more and more
winter sport activities and that may result in n1ol.e casualties.
There has been significant decline in the avalanche accidents of the civilian people in the past
4ecade or so. Among other factors, which could be attrib~~ted to the decline of accidents among
civilians, is general awareness, safe consll-uctionsand fairly dry weather conditions that have been
prevalent during the past few years. However, a proactive approach needs lo bc talcen to mitigate
the threat. While encouraging people to go to hills, en-joy winter sports and take tourism to new
areas deep within Himalayan ranges, the avalanche accidents siiould also be minimiserl,This can
be achieved through awareness programmes,controlled release of avalanches, encouraging winter
tourism industry to grow and bringing the fruits of basic research to the affectedmilsses.
Above all, the excellent work (both research and operational) done by SASE should be expanded
and replicated to cover the entire region vul~iernbleto avalanche hazards.

13.8 CONCLUSION
In this Unit, we have observed that avalanche occurrence is a ~.egularphenomenon which occurs
every year in winter months in the north-westem and central Himalayas. 1 is rnainly terrain and
weather dependent. Mitigation of this disaster requires study of snow as amaterial and terrain as
a base over which the snow falls and avalanche formation takes place. Occurrence of fracture in
,
the snow cover lying on a slope is mainly governed by ~neteorologicalfactors. In addition, the
mechanics of the subject and mitigation techniques have been discussed. The role of the Snow and
Avalanche Study Establishment (SASE) has been described detailing the excellent work, both
research and operational, being done by them. There is need to expand arid replicate the work of
SASE, especially when the activities in the avalancl~eprone areas are on the increase.

113.9 -KEYCONCEPTS
Avalanche : It is a rapid and sudden sliding of masses of incoherent and
unsorted mixtures of snow and ice with rock material.
Avalanche Track : It is also called Slide Path or Avalanche Path, which i s the
middle path or middle part between the Starting Zone and the
Run Out Zone.
Diversionary Structures : Stluchlres that help in diverting the rnovelnent of snow mass
Retarding Structure : Structures that help to slow down the movement of.snowmass.
172 Understanding Natural Disasters

Run Out Zone : It is also known as deposition zone, which is the lowest end
or the destination area of a snow avalanche where it will
ultimately come to astop.
Starting Zone : This zone is also called Release Area, or Formation Zone, or
Origin Zone or Accumulation Zone, or Rupture Zone or
Fracturezone or Catchment Basin. Snow avalanche begins
in this area.
Thermalmetamorphism : The transformation that snow on the ground undergoes due
to temperatureconditions on the ground.
Tree Canopies : Tops of tall trees in a dense forest area.

REFERENCES AND FURTHER READING

Government of India, Ministry of Agriculture, 2001, Manual on Natural DisasterMarzagernent
in India, NCDM, IIPA, New Del hi
McClung, David and Schaerer, Peter, 1993, The Avalanche Handbook, Mountaineers, Seattle,
Washington.
Perla, R and M. Martinelli, 1976, Avalanche Handbook, Forest Service publication, USDA.
Sil-omony,I? Michael Vetha (Ed.), 2000, Source Book On DistrictDisasterManagement, Ministry
of Agricul~re,Government of Itldia, New Delhi.

ACTIVITY
1) List the regions and seasons prone LO snow avalanches in India, and discuss the causes for
the formation of snow avalanches.
2) List and discuss the essential elements of preparedness to meet the avalanche hazard.
3) Describe the role and work of the Snow and AvalancheStudy Establishment(SASE)
4) How would you distinguish between:
(a) Ice avalanche and snow avalanche; and
(b) Dry snow avalanche and wet snow avalanche?