SNOW AVALANCHE PROBLEM IN TURKEY (Türkiye’de Çığ Problemi)

SNOW AVALANCHE PROBLEM IN TURKEY (Türkiye’de Çığ Problemi)

D oç.Dr. İBRAHİM GÜRER*

ABSTRACT

Snow avalanche problem in mountainous parts o f Turkey costs about the lives o f 40 - 50 people ecah year. The econom ic loss to goods and livestock can not be defined accurately because o f present situation o f standards used and news media. In this investigation, the types o f avalanches, their mechanism, and the forecasting methods are summarised and then data on avalanche accidents collectes during 1982 - 1989 from different sources are analysed and a map of avalache sensitive zones o f the countr is presented. The active and passive methods o f prevention o f avalanche hazards are also presented.

ÖZET

Türkiye’deki çığ problem i, her yıl yaklaşık 40 - 50 kişinin hayatına mal olmaktadır. Mal mülk ziyanı ise kesin olarak tespit edilememektedir. Bu araştırmada çığ türleri, oluşum mekanizması, ve tahmin yöntemleri özetlemekte ve 1982 - 1989 döneminde değişik kaynaklardan toplanan çığ kazaları ile ilgili bilgiler analiz edilerek, ülkenin olası çığ bölgelerini gösteren bir harita sunulmaktadır. Aktif ve pasif çığ felaketini önleme metodları sunulmaktadır.

1. SNOW AVALANCHE PROBLEM IN TURKEY

Although Turkey is located in mild climate belt o f the world, especially in mountainous parts o f the country, every year about 40 - 50 people lose their lives in snow avalanches. Snow avalanches occur at hilly, sloping and forest- less parts o f the mountainous zones o f the country. Avalanche starts under the affect o f both internal, and external forces, and due to gravitational acceleration, a huge mass o f snow slides down to the bottom of the valley. Avalanche danger starts with first the snow fall and increases continuosly with snow accumulation and reaches its climax at the beginning o f melting season. Intermittent thaws during the snow pack formation period will cause layering of different densities. The strength o f the snow cover is due to this layering,

* Hacettepe University, Engineering Faculty, Beytepe, Ankara

224 İBRAHİM GÜRER

because with each new snow fall more layers are formed. Snow, itself, has about 80 different crystal structures.

The layering o f snow in prevailing conditions o f Turkey varies from region to region. For example, in eastern Anatolia it starts from the beginning of March whereas in central Anatolia it starts in mid February.

On mild constal regions layering may be observed in very cold periods in January. The completion time o f layering in snow was observed to vary approximately 15 days from one region to anather. Especially, sudden fresh snow accumulation with a snow storm on aged snow pack and sudden rise o f air temperature upon the stop o f storm may cause a melt water layer between the fresh and old snow and consequently sliding o f upper layer on lower one occurs.

When the layering o f snow pack is closely studied just before the avalanche formation seven different layers are observed (Figure 1). The number of these layers may change according to the number o f thaws in a season and the thicknesses are closely related to the snow falls between the thaws.

Figure 1. Different layers o f snow cover before the occurence o f avalanche.

The people who are affected from snow avalanche problem are snow ob servers, skiers, winter vacationers, miners and villagers living in mountains. These people may be prevented from going to avalanche sensitive zones but this is not a long term solution for the problem. For example, energy distribution lines crossing teh mountainous parts o f the country, the people who build and repair them, highway operation and maintanence people and miners under any circumstances can face the problem . Therefore, at planning stage of these types o f projects, it is wiser to stay away from avalanche senistive zones.

SNOW AVALANCHE PROBLEM IN TURKEY 225

Because o f this resaon, it is necessary to prepare avalanche map o f Turkey. Compared to other naturel disasters, the magintude o f human life and property loss in snow avalanches may be considered much less that the others, repetation o f the problem each year forces the people to gent preventive measures.

In defining the potential o f an area in avalanche zone, for tourism, mining, highway and energy line constructions can be defined by comparing;

— Number o f people and the size o f economical investment put in- torisk

— Investment to improve the existing conditions and to replace the existing facilities

— Investment for avalanche preventive measures— Investment to increase confidence against the danger (Tesche, 1977). In

a country like Turkey to make such a comparison, again, it is necassary to prepare an avalanche map.

2. SNOW AVALANCHE RECORDS OF THE PAST

The oldest known avalanche occured in 218 B.C. to Hannibal army triying to cross Alp mountains, he lost 38000 warriors. After a big gap in recording, 890 people lost their lives in an avalanche disaster in 1910, in USA. During the first world war 18000 soldiers were lost at Austria - Italy border, in Alps again. 18000 people were lost both in ice avalanche and earthquake in 1970, in Peru. Starting from 1982, 13 skiers in Austria, 13 in France, 16 in Japan and 15 in Turkey lost their lives in snow avalanches (Cupp, 1982).

According to the survey o f newspapers and Turkish Radio and Television (TRT) news, the avalanche incidents occured during the period 1982 - 1989 in Turkey are listed in Table 1.

Besides, the human lost given in Table 1, at Hakkari - Çukurca; energy line was broken, At Trabzon - Gümüşhane; intercity highway road was closed more than a week. The number o f livestock loss is unknown.

Table 1. Number o f losses in snow avalanches during the period o f 1982 - 1983in Turkey. ____________

Date Location Number of the Source ofpeople lost information

13.12.1982 Ordu-Golkoy 3 Deaths TRT17.01.1983 Sivas-Su§ehri 1 Deaths TRT22.02.1983 Erzurum-Hmis 4 Deaths TRT23.02.1983 K.Mara§-Goksun 1 Deaths TRT


23.02.1983 Hakkari 1 Deaths TRT23.02.1983 Bingöl 1 Deaths TRT28.02.1983 Niğde-Aksaray

Çukurelma Village 2 Deaths TRT01.03.1983 Malatya-Pötürge 2 Deaths TRT05.03.1983 Trabzon-Hamsiköy 17 Deaths TRT05.03.1983 Bitlis-Kebanlar

region 2 Deaths TRT06.03.1983 Road to Karakaya

dam 3 Deaths Paper10.03.1983 K. Maraş-Süleymanlı

village-Hüsnü country 3 Deaths PaperFeb., 1988 Erzurum-Tekman 2 Deaths TRTFeb., 1988 Erzurum-Ispir

Çayırözü 3 Deaths MilliyetFeb., 1988 Erzurum-Tortul

Kireçli 1 Deaths MilliyetFeb., 1988 Hakkari-Şemdinli 3 Deaths MilliyetFeb., 1988 Sivas-Imranlı 1 Deaths MilliyetMarch, 1988 Hakkari-Yüksekova

Ikiyaka village 19 Deaths 8 injured

TRT

03.09.1988 Artvin-ŞavşatSarıgöl 7 Deaths Hürriyet

15.02.1989 Siirt-PervariKışlacık 1 Deaths TRT

27.11.1989 Trabzon-Gümüşhane 2 Deaths TRT

3. MECHANICS OF SNOW AVALANCHE

When the forces acting on a snow mass hang on the slope of a mountain is closely studied, it can be seen that the basic factors affecting snow avalanche are either natural or artificial for the avalanche to occur, accumulation o f extra snow on valley slopes, disappearing o f supporting forces, vibration and internal stresses should exist. But it is hardly possible to observe the trigging mechanism of avalanche at the moment o f occuernce.

As can be seen from Figure 2, for the stable snow mass to slide down it is necessary to have Wp>XM. Here ZM = Me + M f where XM is total shearing force, Me is force due to cohesion, M f is friction force. The componests o f the total weight is shown in Figure 2. When Wp>EM, sliding either starts from a definite line or from a definite surface (Hotchkiss, 1972).


Figure 2. Forces in avalanche mechanism.

When the snow pack ages due to settlement and squezing, the vectors causing deformation are given in Figure 3. Creep, internal plastic deformation and glide vectors cause the down flow o f the snow layer. The magnitudes of the creep and glide vectors vary with the air temperature. If the snow pack is isothermal at 0 °C and consists o f free water in it, thedeformation is very fast. But if the temperature is below 0 °C, then the glide vactor is zero. When the fall temperatures are rather high and snow accumulation is sudden, glide vector is very important. Also viscosity o f the snow is related to the fourth power o f tha snow grain diameter, fine grained snow flows easier that coarse grained snow (La Chapelle, 1969).

Figure 3. Vectors affecting snow pack on valley slope.

Snow accum ulation on hilly areas shows a large variation from one location to another a ccord in g to the topographical slope at locality, exposure and

prevailing wind direction, in a small section, part o f the snow pack will be under tension and the neighbouring part will be under compression (Figure 4).

228 i b r a h i m GÜRER

Figure 4. Sections of snow cover under the effects of compression and tension, on a hill.

That means, snow layer will deform more from both viscosity and elasticity point o f views. Since at low temperetures, snow is not Newtonia fluid but viscid fluid, under tension part it behaves like a rubber due to internal stresses. Due to the extra load o f the new snow fall the stored energy is released as viscous flow. Snow layer on slope is rather brittle material and when it is hanged on a slope, it has a big amount of elastic stress energy. Under the affect of any external force (skier, a piece o f cornice broken from the top, or artificial blasting material to produce sound) will trigger this energy and it will be released with a big explosion and whole snow will come down either as block or powdery avalanche. In eastern Anatolia, snow avalanches are observed on north facing slopes in December and Janurary but on south facing and bare slopes in second half o f March or April. The reasons are;

— The first permanent snow cover is on north facing slopes and in shaded sections.

— Aged and settled snow layers have more variations in their internal forces.

— As the winter advances XM / Wp ratio decreases.At present, the depth, the density and the water equivalent o f snow are

measured at predetermined localities known as snow courses by using Mt. Rose typw snow smapling tubes (Figure 5).

SNOW AVAI.ANCHE PROBLEM IN TURKEY 229

Figure 5. Mt. Rose type snow samling tube used in Turkey.

A: Sampling tube, B: Cylindirical balance,C: Hanger, D: Driver, E: Wernch, F: Cutter,G: Extra tube

These parameters are usefull in defining the weight o f the snow pack. In order to determine the strength of the layer, snow resistographs are necessary, but unfortunately, in Turkey snow strength measurements could not have been started yet. In general, it was found that if (XM / Wp) 4, the snow cover is stable, and if (XW / Wp) < 2 then it is unstable (Bradley, 1969). During the snow measurements done at Uludag between 1975 - 1982, it was observed that the upper surface o f the snow cover melts during the day time and freezes during the night and forms an increasingly thick crust in Spring, the inner part o f the snow cover has less strength than the surface crust. Therefore, new settlements are observed very often. The same mechanism may be one o f the reasons for snow avalanche sensitive zones o f the country.

4. STRUCTURE OF THE SNOW PACKFrom the structural analysis point o f view, snow packs are classified into

two groups:

— W inter snow pack (snow pack in north facing slopes and shaded areas).

— Spring snow pack (on open slopes under the a ffect o f wind and daily melts).


Winter pack is thicker, colder and harder compared to spring pack although not affected by the weight o f a skier but collapses suddenly under its own weight. Winter pack is formed from fine grained snow, less permeable and has free water therefore, structural metamorphism due to day time melt of surface cover is less than the spring pack. Whereas in spring pack, surface crust is hard and internal layering is experienced, greenhouse affect is more dominant. Snow avalanches o f winter snow pack start with a sudden collapse and high explosion noise, and generally the damaged area is rather large. In snow avalanches of spring snow pack, the magnitude of the damage, snow metamorphism are less and usually, there is a line o f fracture at the upper and o f the sliding zone.

5. CLASSIFICATION OF SNOW AVALANCHES

Since the awareness o f snow avalanche problem is rather new in Turkey, there is not etymologically sound terms to define the different terms o f snow avalanches. In Turkish language, some o f the internationally known avalanche terms do not have one to one translation. It is believed that “ Snow and Ice Section of National Hyrology Council” can find the most proper terms, thus it can be possible to avoid the miss uses in future. Snow avalanches may be classifed according to different criteria, such as the type of the release, free water content of the snow cover, and position o f the sliding layer etc (Figure 6). Also, there are slight differences between European, Japanese and Ameri-

Figure 6. Classification of snow avalanches (After La Chapelle, 1969)


can standards for snow classifications. The most destructive type o f the avalanche is the cliamax avalanches because they are produced by more than one snow layers and occur after a series o f meteorological events when tehere is a equi-temperature metamorphism in snow. The temperature gradient is usually more than 1 °C / cm o f snow layer and this is very destructive and produces internal forces resulting avalanche (Hotchkiss, 1972).

6. AVALANCHE OBSERVATIONS

The following observations are based on the studies and experiences of Switzerland State Snow and Avalanche Institue, USA Departmen of Forestry (U.S.D.A., 1958), snow investigation stations o f Japan. r

I — Post avalanche observations

a) Information on trace morphology, ground surface, exposure, magnitude, free water content, and resulting destruction are collected.

b) Number o f Sliding surfaces in distance between upper surface and sliding surface, depth o f sliding surface to the ground, length, age o f sliding surface are determined.

c) Orientation o f the slopes undergone snow avalanche, elevation, geographical location are determined.

d) Depth, density, wate equivalent of snow determined.

e) Qualitative and quantitative magnitude o f avalanche destruction are given in terms o f money.

II — Observations during avalanche occurence

Information on date, time, prevailing meteorological conditions, triggering mechanism, type, and velocity o f flow o f avalanche, is collected by an experienced observer. For example, in a losse snow avalanche, the velocity was measured as 100 mm/second by Martinelli and Davidson, 1966 (Hotchkiss, 1792).

7. METHODS OF SNOW AVALANCHE FORECASTING

At present, remote sensing date, geological investigation and analysis of historical avalanche events are used in determination o f avalanches in macro scale... In m icro scale, i.e. local avalanches, they can easily be defined from the topography, exposure, slope and plant cover o f the area. Especially, in steep sloped (More than 35°), bare slopes are natural avalanche zones. Less slope and forest cover decreases the possibility o f avalanche. Steep, open, south facing slopes are rather suitable to spring avalanches after each snow fall. On the lee side o f the windy hills due to snow drift, more snow is accumulated and those parts are the main source for climax avalanches.


In eastern Anatolia, winter seasons are cold and long. Therefore, avalanche forecasting methods based on the study o f the structure o f the compacted and layered snow pack are more depandable whereas in Black Sea region, even at Istranca mountains, forecasting methods based on the analysis o f meteorological conditions will be more dependable.

8. AVALANCHE CONTROL

In avalanche control, the restriction o f the use o f sensitive zones, use of avalanche barriers, and tunnels are passive methods applied in Turkey. During the last decade, especially, avalanche tunnels succesfully used at Erzin- can - Pülümür, Trabzon - Hamsikôy, Erzincan - Kelkit highways. In Europe and USA, active methods, such as topographical modifications o f the slopes, snow compaction by artificial means, melting and frezzing o f snow to get co mpact layer and use of explosive material to create artificial avalanche, are used. Recently, by investigating the characteristic o f the noise created during the internal metamorphism of the snow pack in the labarotories, it was found that the wave length o f the noise varies between 30 KHz and 300 KHz. So it may be possible to determine the degree o f stability o f the snow pack in the field by recording the noise emitted from the snow in the future. This is planned to be used as early warning system for avalanche disasters.

9. CONCLUSIONS

Although the avalanche problem compared to eartquake and flood damages is less important in mountainous parts o f Turkey, many snow avalanche problems occur as the season’ thaws start. Only those avalanches closing the highways and railroads, damaging the energy lines affecting local people are known. The rest in remote areas can not be recorded. In defining the new routes for highways, railroads, mines and energy lines and re-locating the villages, a detailed map o f the avalanche sensitive zones are given in Figure 7. This map is based on the data obtained from State Highway Department, General Directorate o f Village Affairs, General Directorate o f Natural Disasters, State Hydraulic Works, State Meteorological Organization, Electrical Research Institue and news media. Finalization o f the map still requires micro scale study o f each disaster location. It is believed that data base center in one o f the organizations listed above and the analysis o f the snow and avalanche data will be very usedull. Also, TRT can broadcast daily information about the possibility o f snow avalanche between late March and Early April within the daily weather report. Also, State Highway Department can give information about avalanches within their daily reports on road situations. According to information collected, every year 40 - 50 people, on average, are lost their lives in


avalanches, property loss in monetary terms can not be determined. Therefore, the people should be educated about avalanche danger and a first aid team equipped with proper tools should be form ed to help the victims without panic when the snow avalanche happens.

10. REFERENCES

Bradley, C.C., 1969, “ Collapsing Snow” , Western Snow Conference, USA

Cupp, D., 1982, “ Avalanches” , National Geography Magazine, September 1982 Issue, Washington D.C., USA

Hotchkiss, W .R., 1972, “ Avalanche Awareness and Safety for Snow Scientists in the Field” , Western Snow Conference, USA

La Chapelle, E .R ., 1969, “ Snow Avalanches” , Oregon State University Press, USA

Tesche, T.W., 1977, “ Present Status in Determination o f Snow Avalanche Zones, Difficulties Faced and Future Needs” , Western Snow Conference, USA

U.S.D.A., 1958, “ Snow Avalanches” , Booklet Prepared by Forest Service of United States Department o f Agriculture, Washington D.C., USA


ire 7.

Snow

ob

serv

atio

n lo

catio

ns

of D

SI,

EIEI

, av

alan

che

tunn

els,

pot

entia

l av

alan

che

zone

s of

the

coun

try,

loc

aliti

es

of sno

w av

alan

ches

oc

urre

d du

ring

the

perio

d of

1982

- 19

89

in Tu

rkey

.

Documents

SNOW AVALANCHE PROBLEM IN TURKEY (Türkiye’de Çığ Problemi)