N O T I C E 

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IN THE INTEREST OF MAKING AVAILABLE AS MUCH 

INFORMATION AS POSSIBLE 
ICAL MEMORANDUM NASA IN-77911

LAWS OF DISTRIBUTION OF THE SNOW COVER

ON THE GREATER CAUCASUS (SOVIET UNION)

Ye. Ye. Gurtovaya, G.K. Sulakvelidze

and A.V. Yashina

Translation of "Zakonomernosti raspredeleniya snezhnogo

pokrova na bol'shom kavkaze", IN: Geografia Snezhnogo

Pokrova (Geography of Snow Cover), Academy of Sciences of

the Soviet Union Press, Moscow, 1960, pp. 7-20

(NASA-TM-77911) LAWS OF DISTRIBUTION OF THE

SNOW COVER 011 THE GREATER CAUCASUS (SOVIET

UNION) (National Aeronautics and Space

Administration) 24 p HC A02/MF A01 CSCL 08L

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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

WASHINGTON, D.C. 20546 AUGUST 1985

0011955

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STANDARD TITLE PAGE

1^ Report No.

NASA TM-77911

2, Gay ernment Accession No. 3, Recipient's Catalog No.

4. Title snd Subtitle

LAIVS OF DISTR,IBUTION Or THE SNOW COVER ON THE

5. Report Date

AUGUST 1985

GREATER CAUCASUS (SOVIET UNION) 6. Performing Organization Code

7. Author(s)

Ye. Ye. Gurtovaya, G.K. Sulakveli.dze and

t1, Performing Organization Report No,

A.V. Yashina 10. Work Unit No.

Contract or Grant No,

NAM-400.5

11,

9, Performing Organization Nome and Address

Leo Kanner Associates 13. Type of Report and Period Coyered

Redwood City, CA 94063 TRANSLATION

12. Sponsoring Agency Name and Address

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

WASHINGTON, D.C. 20546

14. Sponsoring Agency Code

15. Supplementary Notes T

Translation of "Zakonoteraosti raspredeleniya snezhnogo pokrova na

bol'shom kavkaze", IN: Geografia Snezhnogo Pokrova (Geography of Snow

Cover), Academy of Sciences of the Soviet Union Press, Moscow, 1960,

pp. 5-7

16, Abstract

The study of the laws of the distribution of the snow cover on the

mountains of the greater Caucasus is discussed. It is shown that

an extremely unequal distribution of the snow cover is caused by

the complex oeography of this territory, the diversity of climatic

conditions and by the difference in altitude. Regions of constant,

variable and unstable snow cover are distinguished because of the

clearly marked 6ivision into altitude layers, each of which is

characterized by climatic differences in the nature of the snow

accumulation.

17. Key Words (Selected by Author(s)) 18, Distribution Statement

Unclassified - Unlimited

19, Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price ',

Unclassified Unclassified 22

a 9

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M

NASA-HQ

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H.
f;

LAWS OF DISTRIBUTION OF THE SNOW COVER ON THE GREATER CAUCASUS

(SOVIET UNION)

Ye. Ye. Gurtovaya, G,K. Sulakvelidze and AX. Yashina

The study of the saws of the distribution of the snow cover

on the mountains of the greater Caucasus is of definite interest.

The complex orography of this territory, the diversity of climatic

conditions and the great difference in altitudes above sea level

cause an extremely unequal distribution of the snow cover, while

as a result of tPo. diversity of its inherent physical and

geographical conditions considerable structural differences

are created, Meanwhile on the territory of the greater Caucasus

because of the clearly marked division into altitude layers

regions of constant, variable and unstable snow cover are

clearly distinguished (Rikhter, 19481, each of which is

characterized by climatic differences in the nature of snow

accumulation.

Re qions of Constant Snow Cover

The limit of the region of permasnow corresponds to the

lower limit of this region.

The snow limit according to the determination of P. V.

Kovalave (19551 has now risen as compared with 1916 by 50 to

60 m, In the western portion of the greater Caucasus it

now occurs at the altitude of 2800 to 3400 m and gradually

increasing towards the east, reaches in the Central Catc asus

an altitude of 3500 to 400.0 meters, Starting from the altitude

of 3500 to 4000 m above sea level, great areas are occupied

by thick glaciers, which form a large center of contemporary

g.i.aciation of the Caucasus,

tN ^ has

y

'E

The snow distribution in mountanous countries. depends to

a great extent on the orographic conditions and the direction of

the wand, The factor of the wind redistribution of snow is

particularly important factor, In connection with the fact that

the upper belts of the mountain of the greater Caucasus are

3 Ps 2CEDING PAGE BLANK NOT FILMED

'M

1
in the region of A certain circulation of the atmosphere t here

the western tranverse prevails, On the leeward slopes, large

masses of snow accumulate, whereas the ridges and windward

slopes remain without snow for a large portion of the winter,

Snowfalls are possible all year round, The snow layer is characterized by low density and fine-grained structure, From November

to April the average density of snow cover is less than 0,23g/cm3,

while in the areas sheltered from the wind as a rule it does not

exceed 0,10 to 0,15 g/cm 3 j the minimum value of the density was

observed in February. Starting from the end of April,, the density of the snow cover increases as a result of melting under

the effect of solar radiation and. in August it reaches at the

lower limit of the zone 0,35 to 0,40 g/cm 3 , and at the upper

limits it is less than 0,30 g/cm3,

In summer the which has condensed into firn does not melt at

all. Gradually slipping under the effect of its own gravity and

the pressure of freshly falling masses, and also under the effect

of solar radiation, the snow increases in density, is converted

into firn and then into ice, From September because of the new

snowfalls the average density of the entire thickness of the

snow cover decreases, Studied seasonal, changes of density,

related with the metamorphosis snow thickness under the aspect

of solar radiation and meteorological factors, refer only to

the snow falling during one year, The density of the snow cover

of the previous years, partly converted into firn and ice, does

not undergo great changes.

The temperature conditions. of the: region is peculiar.

The summer temperature maximum is. low, as a result the average

annual amplitude decrease sharply, reaching values of average

annual amplitude of the Black Sea coast, Thus for example, at

the altitude of 4150 m on r, -,he slopes of the Elbrus the average

annual amplitude of temperatures („17. 6 0 1 is equal, to the amplitude, fixed at the meteorological stations of Gagr G17,5 Q and

Gudaut (.17.60 1, The temperature fluctuations in the snow cover

are small,

4

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Regionn of Variable. Snow Covex

This pa_V ,on covers, the texxi=toriea where the %tAble

snow cover occurs for several months; no winters without

snow occur in it, The position of the sower limit of the

region varies within wide ranges, In conditions of the

Western Caucasus it occurs at the altitude of between

500 tit (;valley of the river Bvipi) to 1,000 to 1,200 m

(valley of the river Ingur ), and in the Central Caucasus

between 1,000 m (,valley of the Rioni river) to 1,500 to

2,000 m (valley of the river Rargdi)

The thickness of the snow cover in this region and its

structural characteristics; may be judged according to the

data of the snow measuring photographs taken in the Abkhaz

Spanetikya, in the valley of the river Bakafan, and in the

region of the Military--Georgian road and refe,2,ring to the

normal distribution of precipitations. To explain the

characteristics of the distribution of the snow cover on the

slopes, of different exposure and at a different altitude

above sea level, snow measuring photographs as a rule were

related to the transversal. and longitudinal profiles of the

mountain valleys. At altitudes of between 2,000 and 3,000

meters more details of the observations were carried out.

The distribution of the thickness. of the snow cover

fluctuates within wide :Limits as. a function of the absolute

altitude of the place, the exposure of the slope and the

nature of the flora. The factor of wind transfer is very

important just as in the region of constant snow cover. Hare

the plant cover and wind transfer cause great diversity in

the distribution of the snow, within the limits of one altitude

belt, and the exposure of the slope of the Main Cau(-asian

ridge and the alt;i;ti de above sea level have left their imprint

t

on the general laws of s.now. built,-up, chaxacteristi:c of the i

entire territory of the greater Caucasus,

In the opinion of V. Ya, $h.arovaya (.1958) the exposure of

ti^

5

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slopes of the Vodorazdel l niy ridge plays a particularly important

role. In connection wa;th the activation in winter of the

southwest and western air flows,, the precipitations fall more

often on the wa;ndward southern and western slo es Thi L, . n the

southern slopes of the Vodorazdel t niy ridge, the western and

southwestern slopes of the Bokoviy ridge, turn towards the

direction of the main a.4:r flows, intercept in winter a great

portion of the precipitation, and the northern slopes fall in

the region of the decreased amounts of precipitation. On the

northern slope we alsc observe a low .recurrence of precipitation

as compared with the southern slopes. This interception

occurs in the region where both ridges are adjacent to each

other.

The difference between the northern and southern slopes ^ 9

of the same altitude above sea level reaohes. 60 to 70 cm in

the region of the Krestoviy Pass and somewhat to the west in {

the region of the Priel l brus, it increases to 1 m, In the

western region of the greater Caucasus the precipitations

in winter are more frequent and abundant as compared with other M

seasons of theear. y The maximum number of days of y precipitation

in winter is .observed here on the southern slope (.Achishkho

Mountain, at the altitude of 1885 m above sea level, 95 days,

on the El"brus fountains at an altitude of 4250 above sea level,

92 days). with the shift to the east the amount of winter

precipitations and the recurrence of their fall decreases, which:

is exp?ained by the characteristics of the cyclonic processes

and to a certain extent by the phenic phenomena (.for example in

the Bylin region east of the Eltbrus).

The stable snow cover is never established immediately. j4

The free winter period is in places, fairly long, but its duration

decreases with the Altitude, At an altitude of 2,1Q0 - 2,2Q0 m Ii

in the wall%y of the Baksan River, the first snowfalls may be

observed in October, but the snow-falling during that month.melts

3

I( qu:,ckly, and the constant snow cover is established as a rule j1

i

6.,

i

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from the middle to the end of November Caccording to many years

of data of the Terskol, Observatory). Thus the prewi nter period

covers here 1,5 to 2 months,

The periods of formation of stable snow cover onthe northern

and southern slopes of the main Ca°acasian ridge differed somewhat. For the northern slope Clayo;lt of the Military-Georgian

road), a more extensive prewnter period and higher temperatures

of the air during the period of the first snow fall are char#-

acteristic. In the first winter nonths the height of the snow

cover does not exceed here 5 to 10 cm, A further increase

of its thickness is noted only from the end of December to

the beginning of January, On the southern slope with stable

snow cover, 30. to 50 cm thick, is ,established already in the

Middle of November, in December its height reaches 60 to 70 p.m.

A stabile .snow cover is formed on the territory of the greater

Caucasus for positive average monthly temperatures l : in the

Western Caucasus for an average monthly temperature of nearly

5 o and an average monthly minimum of 0 0 in the region of the

Central Caucasus at 1.82 0 and 0 0 respectively, and on the

slopes of the Eastern portion of the greater Caucasus, for

positive average monthly temperature 0.8 to 0.3 0 . In certain

regions (for example in the region of the Military-Georgian

Road), in individual winters it was possible to establish a snow

cover for positive average daily air temperatures.

As a result of the effect of the. wind, solar radiation and

snow avalaches, a redistribution of the snow takes place between

the slopes of different exposure and between the sections of

different altitudes above sea level. The wind factor has a

particularly active effect in the longitudinal valleys and ravines,

with, west-east orientation, where the effect of mountain-valley

winds is amplified by the effect of the winds on the side of the

An exception was the late winter of 2957-1958,

7
Black Sea (western and southwestern direction),

In the transversal valley the primary importance must be

attributed to mountain-valley wind, because of which a snow

exchange is implemented from the leaward to the windward sections

of the slopes. The wind induced snow transfer in the some ravine

is so great in some places that the d.tffere"ce in the thickness

of the snow between the western and. eastern slopes reaches in

the middle of winter (February-March) 1 m or more. On the eastern

slopes of the ridges thick snow ledges and drifts appear, /10

characterized by great density of the snow ("Table 1).

Table 1 Height of the Snow Cover (In cm) in Eastern and Western Sections of the Slopes of River Valleys

Region and Time of Altitude Eastern Western

Observation Above Sea Slope Slope

.Level

Valley of the Avadkhari 2000 480 360

River (,basin of the Bvipi river)

March

River of the xnguri River 2200 180 120

(upstream) February

Valley of the Pskhenis-Tskali 2200 160 110

River (,upstream) February

Valley of the Gudamkari River 2000 120 60

(basin of the Rargvi River).

February

Valley of the Baksan River 2500 210 100

(.upstream) March

The most active processes of redistribution of the snow occur

in the first two or thxe.e. days after the snow falls., With. the

increase of the absolute level the factor of the wand induced

redistribution of the snow increases•. For example in the Priel"brusle

for example, already at an altitude of 3,000 m the snow-cover shows.

an alternation of large snow drifts, of height 4 m or more and

Is

8
i

;sections completely bear of snow.,

The data of the snow measuring photographs showed that the

greatest height of the snow cover is reached in the Western

Caucasus, where its thickness fluctuates as a function of the

altitude above sea level within the limits of 2-8 m, In the

region of the Abkjz Spanet ya according to the profile plotted

from the nvipi River to the Avadkhari Pass and from the

I;odori Ri^3er to the Klukhori Pass, in April at an altitude of

280a m the thickness of the snow cover reached 790 cm, At the

altitude of 2000 m above sea level., the maximum height of the

snow cover (410 cm) was observed in March. according to the data j

of many years. With the decrease of the absolute levels

the maximum of the snow cover shifts to February and its thick- .

ness also decreases accordingly, At the altitude of 1500 to 1000

m the February maximum of the snow cover is 195 to 1.305 cm (Table

2)

Table 2 Average Monthly Height of the Snow Cover (in cm) as a

Furn::tion of the Altitude above Sea Level in the Region of 3i Abkhaz Spanetiya

Altitude Month 1

Above Sea

Level m 1X X XT XII 1 II 111 IV V VI VII

No I

1000 - • • 25 90 135 125 65 Data --

1500 0* • 5 55 13 0 195 190 125 25 - - q

2000 1 1 40 110 170 210 410 360 110 • -

2800 • 20 200 310 410 600 760 790 310 120

* • indicate that in the given months the snow cover was unstable.

In the basin of the Inguri River the snow cover is somewhat

Less thick, Thus at the altitude of 2000 m above sea level its

maximum height occurs in March and does not exceed 130 cm, The i

decrease of the thickness of the snow cover according to profile

'f

is observed over the territory and in other altitude belts. For

example at the level of 1,000 m the February maximum of the snow

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cover does not exceed 45 cm according to the data of many /11

years, and at th.e. altitude of 1 { 500 m, 75 cm (Table 3),

Table 3 Average Monthly Height of the Snow Cover (in cm) as

-" a r"unction of the Altitude above Sea Level in the Basin of

of 'the Ingrui River

Alti{=ude Months

Above Sea

Level, m xX X X1 XI1 1 11 111 1V V V1 VI

1000 • 10 30 45 15 i -- -

1500 ., • 25 55 75 50 12 119 -

2000 7 29 65 115 130 65 5 ti

2200 0 • 8 35 30 150 190 90 10 • -

A certain decrease in the thickness of the snow cover in

the valley of the Inguri River as compared with the other regions

of the Western Caucasus have been explained by the extension

with regard to the latitude of the valley in its upstream and

higher ridges (Melgrel'skiy and Svanetskiy 3,000 to 4,000 m),

located on the path of the winter southwest flow of air.

In connection with the :fact

in winter at altitudes exceeding

with the winds of the south-west

moisture from the Black Sea, the

the duration of its ► stay and the

are determined to a ,great extent

the increasing distance from the

of the stable snow cover becomes.

decreases.

that the fall of precipitations

1,500 to 2,000 m is connected

and west directions, carrying

thickness of the snow cover,

number of days with snow fall

by the distance from it. With

Black Sea the period of occurrence

shorter and its altitude

l

The greatest duration of the occurrence of stable snow cover

is. obse"'ed also in the Western Caucasus. Within the limits of

the Abkhaz Svanetiya, the snow rover remains longest at the

altitude of 2800 m (,from October to June). In the valley of

the Inguri Rj,'ver the maximum period of stay of the stable snow

10 a

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w
{ cover at the altitude 2,20Q m is decreased to 7 months, November

to May) and at the altitude of . j QOQ m to 4 months (December to

March) The average number of flays Ydth stable snow cover is

approximately 175 in the We3tersn Caucasus, 150 in the Central.

Caucasus and 130 in the Eastern Caucasus.

The characteristics of the air circulation and cyclonal

processes, in the winter season may explain also the unequal degree

of stablity of the snow cover in different altitude belts of

t

the Western and Eastern Caucasus, In the Western Caucasus

the wind from the western direction is capable of forming the

f stable snow cover at high altitudes. on the Eastern Caucasus

at the same altitudes the snow cover is less stable. Meanwhile in the lower belts of the mountains, whtre in the cold

season of th.e year winds of eastern direction occur predominant .y,

in the western i,* ,oucasus the snow cover (u,:) to the altitude 1,000

to 1 1 500 m) is less stable than in the Eastern Caucasus.

Certain differences are also observed in the dimensions of

the snow flakes. It was observed that on the Black Sea Coast,

and in the south-west slopes of the main Caucasus ridge the

size of the :falling snowflhkes are often Larger than 5 cm and

on the rest of the territory of the Greater Caucasus are larger

than 5 cm and on the rest of the territory of the Great Caucasus

it :Fluctuates between 1 and 5 mm (Sharova, 1958).

In the Centr?l Caucasus in the region of the Eastern

Priel'brus (galley of the Baks.an River) the snow cover reaches, its

maximum thickness (250. cm) at the altitude of 3 1 000 m, The

maximum of duration of the occurrence of the snow cover is also

observed at this altitude. The stable snow cover remains here

for 7 months (November to May),, Below, 3,000 m the duration of

the stable snow cover and its; thickness fl,ucturates within wide

limits as- a function of the relief, the flora and the exposure of

the slopes. The greatest masses of snow are accumulated in depressions in plain areas sheltered from the wind, whereas the

ridges and folds of the slope remain without snow almost the entire

A.

11
winter, ii

As a ale in this region time maximum height of this snow cover

is observed in summer masses and on the northern slope, For

example in the valley of the Baksan River at the altitude of

2 1 000 to 2 1 500 m in the middle of winter (February to March),

the height of the snow cover at the bottom of the valley is

80 cm (in individual years 100 to 130 cm) and on the northern

slope at the level.. of 2,500 m, 130 to 160 cin, On the slopes

of the southern exposure, the height of the snow cover is low,

30 to 40 om, and the lower sections of the slopes, as a result

of the radiation-induced thaws, are periodically free from snow,

In the eastern portion of the Central. Caucasus (region of

the Krestoviy Pass) the thickness of the snow cover (averaged

over many years) at the altitude of 2,380 m does not exceed

250 em. With the de grease of latitude its thickness increases,

This law is manifested particularly clearly on the northern

slope (Table 4).

Table 4 Average Monthly Height of the Snow cover (in cm) as a

Function of the Altitude Above Sea Level in the Region of the

Krestoviy Pass

Altitude Months

Above Sea

Level X XI X11 1 11 111 1V V

2000 No Data 12 45 90 120 137 105 10

1500 '" No 17 65 90 97 30

Data

1000 " "" 10 45 ^2 45 5

The establishment of the snow cover for positive monthly

temperatures, and also the great thickness of the snow layer

protect the soil from Jeep freezing, 'thus for example at the

altitude of 3,0.Q0 m at the depth of 30, cm the temperature of the

snow cove-,, does not go below -10, -150 , and at the altitude of

2, 000. m, less than --7, '7.0 0 (Figure 1) ,

12
The. analysis of variation of the temperature mj-ni.ma according

to the profile of the fresh layer makes it possible to draw the

conclusion that in the studied regions on conditions that there

is uniform distribution of the snow cover the soil is protected

from deep freezing during the whole year. A certain freezing

of the soil is possible only in the falls months, when the

average temperature of the air drops below Oo , and the stow

cover has not yet been established, This is most probable

for the Central Aegion of the Caucasus,

In connection with, the great fluctuations of altitude and 14

physical and geographical differences within the limits of

the Greater Caucasus, the density of the snow cover varies

greatly. We should mention first of all the regular decrease

of the density of the snow cover with the increase of the

altitude above sea level observed over the entire territory.

Thus from 0,40 g/cm 3 at the altitude of 1 1 000 m, it drops to0.15 to 0,20 g/cm3 at the altitude of 3,000 m (February-March),

For Western Caucasus in February and March it is characteristic

to find a high density of the snow cover, 0.30 to 0.40 g/cm3,

But it is not constant and varies within wide limits as a function

of the meteorological conditions and the exposure of the slope,

On the northern slopes the snow density as a rule is lower by

0.05 to 0,15 g/cm 3 than on the southern slopes for the entire

winter. At the beginning of the thaw and in fair weather the

difference in density of snow cover on these slopes may reach

0.20 g/cm 3 . The considerable increase of density occurs

uniformly over all slopes during the wet snowfall and in advective

thawing processes.

^,

I

According to the data of the snow measuring photographs in

the basins of the rivers. Bva:p , .ioorodi, Inguiri and Rioni, a

very clear law was, revealed for the variation of the density in

time and according to the altitude. The density of the snow

cover decreased from 0,30 g/cm3 at the altitude of 1,000 m to

0.18 g/cm3 at the altitude of 2,800 m and from 0.33 g/cm3

in December -- January to 0,40 g/cm3 in Pebruary-March, A

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AV tijpi OWO& OZOAMM4 man.7mg

Figurexe I VAr^Ation of the Tomperture Within the Thiokness

the Snow Cover in the Priel lbrus Region at the Altit

of 2,25a m on JAnuAgy 5 and 6, 1557,

Key; 1) Height of the Snow Cover, cm; 2) Time of day

ORIGINAL pjGE IS ODE POOR QUALITY

14
15

particularly clear increase in the snow density takes plAce in

spring montha t In MArch the density of the snow At the upper

level of this zone is on the average higher by 0,1Q-0,12 9/cm3

than in December, In the sower belt o g these Mountains this

difference decreases to 0,05 to 0,10 g/cm 3 (:Table 51.

Table 5 Density Distribution (in g/cm 3 ) of the Snow Cover in the

Western Caucasus

Altitude Months

Above Sea

Level, m XII r I I - III

2800 0,18-0.20 0,28-0,30

2300 0.21 0,33

2000 0.22 0,35

1700 0.23 0,34

1500 0,25-0.28 0.35•-0,37

1000 0,30 0,40

500 0.35 0,40

Table 6 Density Distribution (in g/cm 3 ) of the Snow, in the

Central Caucasus

Altitude Months Above Sea

Level, m XII-I II-ii

3000 0118 0.21

2500 0,20 0.210,28

2200 0,26 0.26-0.30

200.0 0,240.26 0.31

On the territory of the Central Caucasus the density is

relatively low and reaches high. values only during the period

of thawing or in the lower portion of the region CTable 6)t
in the region of Oast Priel l bxusr at the bottom o.f the valley

of the BAks:an river, the dens$, ty of Q,25 g/cm3 is most characteristic for winter, decreasing greatly during the time of

snowfalls because of the freshly falling snow, At the end of

March--beginning of April,, when the snow begins to melt, the

density of the snow-cover rises to 0,35 g/cm 3 The difference

in the density of the snow cover on the northern and southern

slopes is clearly manifested, In January the snow density is

greater by-0,07 g/cm 3 because of the greater insulation on the

southern slope than on the northern one, and in March it is

greater by 0.05 g/cm3 . The density of the snow at the bottom

of the valley has a middle value as compared with this density

on the northern and southern slopes,

The values of density of the snow cover indicated are /15

average data for these regions. The detailed snow measuring

photograph reveals considerable differences in its density

in connection with the nature of the plant cover and the micro

climatic conditions. In the forest the snow density is usually

less than in open sections. A certain increase of the density

of the snow cover is observed on the windward slope because or

its consolidation by the wind and snow brought by blizzards.

Snow avalanches, characteristic for the entire territory of

the Great Caucasus have a considerable effect on the nature of

the occurrence of a snow cover, Dry snow avalanches (,in the

middle of winter) and wet ones (in spring) clear systematically

the upper sections of the mountain slopes and cause its accumulation

a the foot of the slopes and at the bottom of the deep ravines and

valleys. The snow avalanches: occur particularly often starting

from an altitude of 1,400 m,. which. is explained by the great

thickness; of the snow cover and the process of metamorphosis

of the snow layer. On mountain ravine and valleys in the

Georgian republic in winter avalanches carry more than 0.5 million

m3 of snow (:in each. ravine. or valley).,

4h

y

16
G'

4

I

ORIGINAL PAGE IS

OF POOR QUALITY

Figure 2 Crystals of Deep-Seated Snow. Photo by A. V, Yashina.

The accumulation of large masses of snow of high density

(0.50 to 0.60 g/cm 3 ) of average thickness in the snow cone up

to 10 to 15 m delays the melting of the snow in the spring and

regulates the discharge of mountain rivers in summer.

Besides the variation of the thickness and density of the

snow layer differences are also observed in its structure.

Immediately after the establishment of the stable snow cover

under the effect of solar radiation and temperature gradients

processes of recrystallization of the snow cover start. At the

end of January, it is characteristic for the profile of the

snow layer on afforested and open sections of the bottom of valleys

and northern slopes to find in the presence of thawed soils, a

clearly marked free flowing level of deep-seated frost, up to

45 to 50 cm thick. The crystals of the deep-seated frost have

a clearly marked shape of hexadral prisms and caps, hollow inside

(Figure 2). The dimensions of other crystals fluctuates

within the limits of 2 to 5 mm, and on rare occasions they

reach 7 mm. Usually crystals near the soil surface become larger.

The transition from the level of the deep-seated frost may be

i.

17

r
18 yr

I

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gradual. (in the. case of great th^:ckness of the snow coyer) or

abrupt, limited on the, top by An ice layer, The vertical

orientation of the crystals predominate Cthe basis of the prisms

are at the bottom), The vertical texture with suspended clusters

of crystals and large number of gaps between them (the dimensions /16

of the gap reach 0,5 to 1 cm 3 ) is well marked. The structure of

the upper levels is less clearly marked, it is characterized by

crystals of dimensions 1-2 mm of nonclearly outlined shape. The

le-, 'els are usually separated by ice layers, which correspond to

periods. with thaws between snowfalls.

An example of a clearer differentiation of the snow layer

on stratigraphic strata may be the description given below of

the cross-section of the snow cover in the upper reaches of

the Baksan ravine (Central Caucasus) in the middle of February

1957. For an average height of the snow cover of 45 to 50 cm,

the upper 0 to 5 cm were represented by freshly fallen fraiable

ones, consisting of fragments with snowflakes (density 0.10 to

0.15 g/cm3 ); below at a depth of 5 to 25 cm a firm dense wind

slab occurs (,density 0.38 to 0,40 g/cm 3 1 of fine-grained snow,

The thickness of the wind s1 ab fluctuated between 10 and 25

cm. At the depth of 25 to 50 cm a layer of free-flowing deepseated frost was observed, The crystals of the deep--seated

frost were large (5--7 mm) of prismatic shape, hollow inside and

of vertical orientation. They were firmly bound in clusters.

The vertical texture with suspended clusters of crystals and

large number of gaps between them was particularly clearly marked.

Underneath at the limit with the grass cover, the crystals became

larger (up to 10 mm), the number and size of the gaps increased.

The crystals freezing firmly had their sides touching and gradually acquired a cylindrical shape and 4 horizontal orientation.

The porosity of the lower layer was so great that the freezing

cylindrical crystals. created the i:znpression of a brittle lattice;

the s001 was melted,

A

The physical principle of metamorphosis of the snow layer may

be explained as follows, Snow as: a , good insulator, causes a sharp
16

- a

drop in temperature betwcaen the surface of the snot cover and

the surface of the melted soil, as; a result of which a pressure

gradient of water vapor is created between the upper and lower

levels of the snow layer, In the above described case, as a

result of the formation on the surface of the snow cover of a

firm wind slab of relatively large thickness the decrease of temperatures between the lower level and the surface of the snow

covex became so large that between the upper and lower 19vels of

the snow cover a pressure gradient of water vapor arose. Under

the effect of the gradient the migration of water vappors began

from the warmer sower levels to the cooler upper levels. The

migration of vapor created conditions of incomplete saturation

and decreased the relative humidity in the lower layer, as a

result of which the evaporation started from the surface of

snow grains, the growth of some crystals at the expense of others

and the formation of gaps. The vertical orientation of migration

of the water vapors is indicated by the vertical orientation

of the crystals. The largest crystals of the deep-seated

frost were observed in sections with thick layer of last year's

turf, which under the effect of the processes of decomposition

created an additional thermal effect. The metamorphosis of

the snow coven, leading to the formation of a free--flowing

level of deep-seated frost, causes the occurrence of avalanches

on the steep sections of the slope,

In the spring, when the soil underneath begins to thaw,

the process of migration of vapor from the lower levels to the

upper ones is intensified and the growth of the crystals of the

firn level takes place particularly intensely, At the same time

the thickness of the firn layer increases. The levels lying on

top become more dense (Figure 3),

The variation of the density of..the density of the snow

cover over the structural layers on the afforested and open

sections take place unequally, On the bear sections the upper

layer of the snow cover have a relatively higher density (.Q,21

19
. w

--0,28 g/cm3 ) than the lower one (0.,15-Q,23 g/cm3 1 bemuse of

consolidation by the wand and radiation thawing processes, In

the afforested sections because of the layer being covered by

tree trunks there is no increase in the density of the upper

layer, Therefore in the shady sections of the wood we observe

A staggered nature of the density distribution over the profile

of the snow cover and specifically the increase of density from

the upper layers to the middle ones and its decrease in the

layer of free--flowing deep.-seated frost (Figure 4) ,

FigureT 3 Distribution of the Density of the Snow Cover According

to the Structural Layers in the Forest in Spring

1) Melting snow, consisting of sb.apeless lumps of ice; 2) Deposit of dry snow, becoming denser under the effect of the force

of gravity; 3) Deep-seated frost (crystals of different dimensions);

4)_ Fine grained and medium grained snow with inclusion of crystals

of deep-seated frost; 5) Ice layers and ice formations

Key; 11 Height of the snow cover cm

/Ii^omaocma, p/cn►^

Q Q , 2 ^

I • •

p X 0 0 0 O•

:t QQ -0 o o o oopo

G o o °a°° oo

C s. ^A, p•rA A ^•sd

4 3r 

6 A ..y A. '•A.D•d.A•

0 70 A^ e e l 1IA ^

M

20
1

I

n

Because of the high temperature gradient f the recrystAllization

of the snow cover takes place more intensely on the southern

slope than on the northern one, This process is observed

particularly clearly inthe establishment of a stable snow cover

in clear frosty weather, In this case the entire 3040 centimeter

snow cover has a clearly marked crystalline structure, The

crystals. of 3-4 mm, free-flowing, are weakly bound to each other.

In bright sunny weather the crystals on the surface of the snow

cover have a structure of melted grains of frost. On cloudless

days the effect of solar radiation is so great that the snow

cover acquires from the surface a cellular structure, and on the

surface of the soil because of the seepage of the water produced

by the thaw an ice crust 1-2 cm thick is formed.

The snow measuring photograph made it possible to determine

the reserves of water in the snow cover according to the individual

basins of the rivers of the Great Caucasus (Table 71.

Table 7 Reserves of Water (in mm) in the Snow Cover on the

Greater Caucasus

River Basin Altitude Above Sea Level

1000 1500 20.00 2800

Bvipi and Kodori 450 670 1100 2400

Inguri 100 250 440 1600

Rioni. 150 390 410 1500

Aragvi--Liakhvi 150 390 410 1500

The analysis of the data shows the sharp decrease of the 18

water supply with increase for the distance from the Black

Sea and their increase with.the increase of the absolute altitude.

A certain exception may be observed for the Inguri River basin

where in spite of its closeness to the sear the water reserve in

the snow cover on the lower levels are less than in the basin

of the Rioni. River, which. is further away from the Sea, The

21
t

Figure 4 Distribution of the Density of the Snow C pver According

o the. Structure, 7 4yera in the Forest (l) and in A Dare

Section (11)

1-5 See Figure 3; 6-• Fine Grained sandy snow with inclusa:ons of

ice

Key: 1) Height of the snow cover, cm; 2) Density g/'cm3 ?`

)kl

1

/1nomNncme, t/cN^

G / 2 J

,f

PO •"•^.,...

I ^ • ♦ • I••

^+'—^ ^ ^

^

/

/j//0117I/OC/llb, P/CH9

is

Vii`

I

oA m {lm m o 11°m !^^ 0 0 I 2 9.

Ai m

•• 1{ • • • ^, ' •

a

`fit

®m,p^^! /^•^•;•;•• ?^^

;,k30

a ®'

Q

110 0 °°°0 ^ 0 p

V 0 °° oo °p

m

A A

4 SO

100

^^

^7.4

99 e a

90

s

difference in the reserves of water in these basins is, explained

by the different thickness. of the snow cover.

In the western Priel'brua region the results of water from

the snow cover are low'and according to the profile in the valley

of the Bak.san River at the altitude of 2,20Q m they constitute

228 mm, gradually increasing with.th.e increase of the absolute

altitude up to 279 mm at the altitude 2,500 m and 45Q mm at

the altitude of 3 F OQa m,

2

2
Region of Unstabla Snow Cover

The region of unstable snow cover includes the fo,,ath,illa

and '-he lower sections of the slopes, In the periods, between

snowfalls,, the snocover here usually falls ;ompletely, remaining

not more than several days,, and It may lie for about 2 to 3

months only in individual winters with most snowfall, in

connection with the shortness of the stay of the snow cover

no interesting laws were observed in the distribution and

structure,

More frequent and abundant snowfalls are characteristic 119

for the Western Caucasus in the region of the unstable snowcover

than in the Eastern one. Wet snowfalls accompanied by rain

are very common. The density of the snow cover as a rule is

higher here than the density of snow in the region of the

variable snow cover,

General Conclusions

1, The stable snow cover on the territory of the Greater

Caucasus is formed for positive average monthly air temperatures.

2. The maximum height and water reserves of the snow cover

are observed in the Western Caucasus; with the increase of the

distance from the Black Sea, they decrease gradually.

3. The snow cover in the Western Caucasus is less stable

up to altitudes of 1,000 to 1,500 m, than in the Eastern Caucasus,

and starting from the altitude 1,500 to 2,000 m it is more

stable.

4. The density of the snow cover on the territory of the

Greater Caucasus decreases with the increase of the altitude

above sea level and with. the increase. of the distance from

the Black. Sea,

5. In the region of the variable snow cover the height of

the snow. cover increases with. the increases of the altitude

above sea level, and the time of occurrence of the maximum

thickness shifts from aanuary-February, to March.-April,

6, The height of the snow cover in the region of the variable

snow cover exceeds to a considerable extent the height which can

r^

23j
i

i

t s

protect the coil Xrom deep freezing,

Literature

Kovalev, P, V. Certain Characteristics of the Modern G1aciEication

of the Upper Reaches of the Paksan, Soovshch_AN Grt,

SSR Vol, 16 no, 6, Tbilisi, 1955,

Richter, G,L. Role of the Snow Cover in the Physical and Geographical

Process. Proceedings of the xnatitute of Geography of

the USSR Academy of Sciences, Vol 14, Moscow-Leiningrad,

1948,

Sharova, V. Xa.: "Chislo Gney s Soedkami Razlichnoy Velichiny

Na Territorii Xevropeyskoy Chasti SSSR E Kavkaza"

(Number of Days with Precipitations of Different Amount over

the Territory of the European Part of the USSR and Caucasus)

Leiningrad, 1958.

24