Geographical distribution of seasonally frozen ground and permafrost

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Geographical distribution of seasonally frozen ground and permafrost

Baranov, I. Y.; National Research Council of Canada. Division of Building

Research

PREFACE

This t r a n s l a t i o n i s t h e t h i r d arranged by t h e Permafrost Subcommittee of the Associate Committee on S o i l and Snow Mechanics of the National Research Council of t h e Russian permafrost p u b l l - c a t i o n , " P r i n c i p l e s of ~ e o c r y o l o g y " . The f i r s t t r a n s l a t i o n i n t h i s group was of Chapter V I e n t i t l e d

eat

and Moisture T r a n s f e r i n Freezing and Thawing S o i l s " by G.A. Martynov (TT-1065). The second i n t h e group was Chapter

N ,

" ~ e n e r a l Mechanisms of t h e

Formation and Developrr~ent of ~ e r ~ n a f r o s t " by P .F. Shvetsov (TT-1117). The f i r s t s e c t i o n of t h i s translation of Chapter

VII

by

I.Ya. Baranov d i s c u s s e s the globa 1 d i s t r i b u t i o n , with emphasis on t h e U.S.S.R., of s e a s o n a l l y frozen ground. The l a r g e s t p o r t i o n of t h e t e x t d e a l s with t h e d i s t r i b u t i o n of permafrost throughout t h e world. It includes Information on t h e a r e a l e x t e n t , t h i c k n e s s and temperature of permafrost, and v a r i a t i o n s i n t h e s e c h a r a c t e r i s t i c s from one p h y s i c a l region t o another.

The Division of Building Research

i s

g r a t e f u l t o M r . A. Nurkllk,

Research and T r a i n i n g Division, Meteorological Branch, Department of Transport, Toronto, f o r t r a n s l a t i n g t h i s c h a p t e r i n response t o t h e r e q u e s t of t h e Permafrost Subcommittee.

Ottawa

R.F.

Legget

NATIONAL RESEARCH COUNCIL OF CANADA

Technical Translation 1121

Title

:

&!ographical distribution of seasonally frozen ground and

parmaf

roa t

(~feograficheskoe

raeprostranenie

sezonnopromerzayushchlkh pochv

1

mnogoletnemerzlykh gornyk porod

)

Author

:

I.Ya. Baranov

Reference

:

Principles of geocryology (permafrost studlee

), Part

I,

Qeneral

geocryology, Chapter VII. Academy of Sciences of the

U.S.S.R.

Moscow 1959. p.193-219

(0snovy geokriologii (merzlotovedeniya

)

,

Chas

t pervaya,

Obshchaya geokriologiya, Olava VII. Akademiya Nauk SSSR. Moskva

1959

9 s

193-2191

Translator: A.

Nurklik, Meteorological Branch, Department of Traneport,

Toronto

GEOGRAPHICAL DISTRIBUTION

O F

SEASONALLY

FROZEN GROUND

AND

PERMAFROST

Introduction

The phenomenon of the f r e e z i n g of the e a r t h ' s c r u s t occurs not only

in

two circumpolar regions of the e a r t h but a l s o i n i t s temperate and t r o p i c a l

zones near and above t h e "permanent" snow-line

.

I n

the northern hemisphere the a r e a s of seasonally frozen ground and

permafrost encompass p a r t s of the Eurasian and North American c o n t i n e n t s , the

A r c t i c Ocean i s l a n d s , Greenland and Iceland.

In

t h e southern hemisphere t h e

area comprises the A n t a r c t i c continent and the a n t a r c t i c i s l a n d s i n t h e

P a c i f i c , Indian and A t l a n t i c Ocean

.

The depth of the f r e e z i n g of the e a r t h ' s c r u s t depends, i n the f i r s t

place, on the duration of f r o s t period (seasonal o r p e r e n n i a l ) and t h e severity

of f r o s t .

It

a l s o depends on t h e composition, p r o p e r t i e s and condition

(moisture) of s o i l and bedrock, some physical and o t h e r processes t a k i n g place

i n the ground and the heat flow from i n s i d e the e a r t h , e t c . Consequently, the

formation, duration and depth of frozen ground depend on t h e l a t i t u d e and

a l t i t u d e of a l o c a l i t y , 1 . e . on t h e p e c u l i a r i t i e s of zonal and v e r t i c a l ex-

change of heat between the ground and the atmosphere and t h e i n t e r a c t i o n s of

heat and moisture between the continents, seas and oceans.

The

p e c u l i a r i t i e s

of t h e v e r t i c a l exchange of h e a t and t h e i n t e r a c t i o n s of h e a t between t h e

continents and oceans d e s t r o y the s o l a r zonal heat regime of the ground and

produce an i r r e g u l a r form t o t h e boundaries of a r e a s of seasonally and per-

manently frozen ground i n t h e circumpolar regions (Fig. 21) of t h e e a r t h .

Periods of f r e e z i n g and thawing of the e a r t h ' s c r u s t and t h e existence of

frozen l a y e r s and depths vary from s e v e r a l hours i n low l a t i t u d e s t o many

years t o thousands of years

In

high l a t i t u d e s .

I n

the near e q u a t o r i a l zone

the f r e e z i n g of s o i l a s

a

r e g u l a r seasonal phenomenon

i s

p o s s i b l e only I n high

mountains. Over

i t s c o n t i n e n t a l d e s e r t s , the seasonal f r e e z i n g

of

:toil

i s

replaced

by

s h o r t - l i v e d r a d i a t i o n a l cooling of s o i l below t h e f r e e z i n g p o i n t .

However, no t y p i c a l f r e e z i n g of s o i l with t h e development of i c e t e x t u r e

occurs

here s i n c e t h e s o i l moisture does not exceed the hygroscopic l e v e l .

Purely seasonal f r e e z i n g of ground (not r e l a t e d t o permafrost) occurs i n

c e r t a i n regions surrounding t h e circunipolar permafrost a r e a and under d i f f e r e n t

c l i m a t i c conditions.

In

mountainous t e r r a i n s of these regions frozen ground

i s

d i s t r i b u t e d i n

a

v e r t i c a l zonal p a t t e r n .

Between t h e main a r e a s of s e a s o n a l l y frozen ground and permafrost,

f r o z e n ground may e q u a l t h e d e p t h d u r i n g a complete thawing season. North of t h i s sub-zone, o r above t h i s v e r t i c a l zone i n mountains, t h e pernlafrost b e g i n s l o c a l l y a t f i r s t , i n pJ.?ces where c o n d i t i o n s a r e most f a v o u r a b l e f o r I t s

development and then becomes continuous a t some h i g h e r l a t i t u d e and e l e v a t i o n .

In

t h e n o r t h e r n hemisphere t h i s z o n a l l y o r i e n t e d t r a n s i t i o n a l sub-zone s e p a r - a t e s t h e a r e a s of p u r e l y s e a s o n a l l y f r o z e n and p e r e n n i a l l y f r o z e n ground.

D i s t r i b u t i o n o f S e a s o n a l l y Frozen S o i l s

A s a r e s u l t of t h e heterogeneous p h y s i c a l g e o g r a p h i c a l c o n d i t i o n s of t h e h e a t exchange between t h e ground and t h e atmosphere, t h e boundary between t h e a r e a s of s e a s o n a l l y f r o z e n ground and t h e pernlafrost a r e n o t d e f i n i t e l i n e s b u t , a s was s t a t e d above, t r a n s i t i o n a l sub-zones o r b e l t s which l i m i t season- a l l y f r o z e n ground o r where i t and t h e pernlafrost o c c u r o n l y s p o r a d i c a l l y .

Line-boundaries d e f i n i n g a r e a s of d i f f e r e n t f r o z e n ground t y p e s d i s c u s s e d above may be used o n l y on s m a l l - s c a l e c h a r t s . T r a n s f e r of t h e s e line-boundar- i e s on a l a r g e - s c a l e c h a r t has n o t meaning a t a l l s i n c e t h e boundaries on t h e s e c h a r t s must a l r e a d y o u t l i n e t h e i s l a n d s of s e a s o n a l l y f r o z e n grounds and p e r m a f r o s t i n t r a n s i t i o n a l sub-zones. Line-boundaries on c h a r t s w i t h

a

s c a l e s m a l l e r t h a n 1 : 5,000,000 I n d i c a t e o n l y t h e g e n e r a l d i r e c t i o n s o f t h e t r a n s i - t i o n a l sub-zones and t h e mountain b e l t s and g i v e an i d e a o f t h e b a s i c d i s t r i - b u t i o n o f f r o z e n ground.

The l i n e - b o u n d a r i e s o f s e a s o n a l l y f r o z e n ground have n o t been e s t a b l i s h e d a s y e t . Even t h e method o f d e t e r m i n i n g t h e s e boundaries on l a r g e - s c a l e c h a r t s has n o t y e t been worked o u t . It

Is

e v i d e n t t h a t a method based on a c t u a l o b s e r v a t i o n a l d a t a would be most a p p r o p r i a t e f o r t h e purpose. However, i t

i s

p r a c t i c a l l y impossible t o have such a dense o b s e r v a t i o n a l network a s t o be guided o n l y by a c t u a l d a t a In p l o t t i n g t h e boundaries o f s e a s o n a l l y f r o z e n ground even on s m a l l - s c a l e c h a r t s .

N e v e r t h e l e s s , t h e a c t u a l observed d a t a niust be t h e b a s i s o f a combined method which t a k e s i n t o account laws governing t h e s e a s o n a l f r e e z i n g o f s o i l

i n

v a r i o u s p h y s i c a l - g e o g r a p h i c a l r e g i o n s of t h e e a r t h . U n f o r t u n a t e l y s u f f l c - l e n t o b s e r v a t i o n a l d a t a a r e n o t y e t a v a i l a b l e f o r working o u t such a method.

Owing t o a lirnited number of o b s e r v a t i o n a l d a t a a v a i l a b l e i n many f o r e i g n c o u n t r i e s on t h e d i s t r i b u t i o n of s e a s o n a l l y f r o z e n ground i t was n e c e s s a r y t o use some i n d i r e c t i n d i c e s which would p e r m i t one t o o u t l i n e , a l t h o u g h approxi- mately, t h e a r e a s of s e a s o n a l l y f r o z e n ground. Two c l l n l a t o l o g i c a l i n d i c e s were used t o determine t h e p o s s i b i l i t y of s o i l f r e e z i n g and t h e d e p t h o f t h e f r e e z i n g . The f i r s t of t h e s e i n d i c e s was t h e January mean a i r t e m p e r a t u r e in

t h e n o r t h e r n hemisphere and t h e J u l y mean a i r temperature i n t h e s o u t h e r n hemisphere. The second i n d e x used was t h e d u r a t i o n o f f r o s t p e r i o d ( p e r i o d of

below f r e e z i n g t e m p e r a t u r e s ) i n p a r t i c u l a r and t h e p r o b a b i l i t y of below f r e e z i n g temperatures i n g e n e r a l .

These i n d i c e s , p a r t i c u l a r l y t h e d u r a t i o n o f f r o s t p e r i o d a l s o r e f l e c t t h e e f f e c t o f t h e e l e v a t i o n o f a l o c a l i t y .

The u s e o f t h e s e i n d i c e s i s j u s t i f i e d by t h e f a c t t h a t t h e r e i s a n

e s t a b l i s h e d r e l a t i o n s h i p between t h e a i r and s o i l temperatures. Furthermore, c o n s i d e r a b l y more long-term d a t a a r e a v a i l a b l e on t h e a i r temperature and t h e d u r a t i o n of f r o s t p e r i o d s t h a n on t h e s o i l temperature and t h e d e p t h of f r o z e n ground. The disadvantage of u s i n g a i r t e n ~ p e r a t u r e s in s t e a d o f s o i l tempera- t u r e s i s t h a t t h e former cannot r e f l e c t t h e p e c u l i a r i t i e s i n t h e f r e e z i n g depth caused by t h e conlposition of s o i l and o t h e r phy3lcal-geographical f a c t o r s (snow cover, s u r f a c e water, p l a n t cover, e t c . )

.

Analysis of t h e s e two i n d i c e s i n d i c a t e s t h a t t h e y form

a

uniform a l t h o u g h i n d i r e c t b a s i s f o r o u t l i n i n g t h e a r e a s of s e a s o n a l l y f r o z e n ground on t h e e a r t h ' s s u r f a c e . Mean a i r temperature c h a r t s cannot be used f o r t h i s purpose s i n c e t h e y do n o t r e f l e c t t h e t r u e p i c t u r e of t h e temperature d i s t r i b u t i o n which depends on t h e e l e v a t i o n of t h e t e r r a i n and o t h e r p h y s i c a l - g e o g r a p h i c a l f a c t o r s .

The zone of s e a s o n a l l y f r o z e n ground and t h e sub-zone of t r a n s i t o r y f r o z e n ground a r e shown i n Fig. 22. The dashed l i n e i s o l a t e s t h e a r e a of s e a s o n a l l y f r o z e n ground (heavy s h a d i n g ) , 1 . e . t h e a r e a where t h e s e a s o n a l f r e e z i n g of s o i l f o r varying l e n g t h s of time i s an a n n u a l l y r e c u r r i n g phenom- enon and where t h e s e a s o n a l l y f r o z e n ground i n patchy, o r i n a more continu- ous form, p r e v a i l s over a r e a s where s o i l does n o t f r e e z e each y e a r . The d o t t e d

l i n e

i n

F i g . 22 o u t l i n e s t h e sub-zone of t r a n s i t o r y f r o z e n ground ( l i g h t shading), 1 . e . t h e a r e a where t h e s e a s o n a l f r e e z i n g ( c o o l i n g ) of d r y s o i l

i s

s h o r t - l i v e d (from some hours t o some d a y s ) and does n o t occur each y e a r . I n t h i s sub-zone, i s l a n d s of s e a s o n a l l y f r o z e n ground a r e widely d i s t r i b u t e d and a r e l o c a t e d i n r e g i o n s where t h e p h y s i c a l - g e o g r a p h i c a l c o n d i t i o n s a r e most

favourable f o r t h e f r e e z l n g of ground.

South of t h e sub-zone of t r a n s i t o r y f r o z e n ground i n t h e n o r t h e r n hemi- sphere and n o r t h o f t h i s sub-zone i n t h e s o u t h e r n hemisphere, s e a s o n a l f r e e z -

i n g of s o i l may occur o n l y i n h i g h mountain ranges a s t h e r e s u l t of t h e p e c u l i a r i t i e s of t h e h e a t exchange between t h e s u r f a c e and t h e atmosphere.

A c o n s i d e r a b l e p o r t i o n of t h e a r e a of s e a s o n a l l y f r o z e n ground i n t h e n o r t h e r n hemisphere i s s i t u a t e d on t h e E u r a s i a n c o n t i n e n t . Here s e a s o n a l f r e e z i n g of ground o c c u r s o v e r almost t h e e n t i r e t e r r i t o r y o f t h e USSR, t h e Scandinavian c o u n t r i e s , c e n t r a l , western, s o u t h e r n and s o u t h e a s t e r n Europe, Asia Minor, middle and c e n t r a l Asia and t h e f o r e i g n p a r t of t h e F a r E a s t .

In orestern and s o u t h e r n Europe t h e s e a s o n a l f r e e z i n g o f ground o c c u r s o n l y I n l i m i t e d a r e a s on t h e I b e r i a n , Apennine and Balkan p e n i n s u l a s . On t h e I b e r i a n Peninsula s o i l seldom f r e e z e s i n t h e southwcstcrn c o a s t a l lowlands of P o r t u g a l and s o u t h e r n Spain because of t h e warming i n f l u e n c e of t h e A t l a n t i c and t h e b a r r l e r e f f e c t of t h e S i e r r a Morena and Andaluslan ranges which

o b s t r u c t t h e southward p e n e t r a t i o n o f n o r t h e r n cold waves.

There i s a l s o no s o i l f r e e z i n g on t h e c o a s t a l lowlands o f t h e

Mediterranean i s l a n d s ( ~ a l e a r i c I s l a n d s , Corisca, S a r d i n i a , S i c i l y , N a l t a , Crete, Cyprus, e t c . ) .

Owing t o t h e f a c t o f warm s e a c u r r e n t s , t h e s o i l almost n e v e r f r e e z e s I n t h e s o u t h e r n p a r t of t h e Apennine Peninsula a l o n g t h e c o a s t s o f t h e A d r i a t i c and Ionian Seas. The same can a l s o be s a i d f o r t h e s o u t h e r n p a r t o f t h e Grecian Archipelaeo, e a s t c o a s t of t h e Mediterranean Sea, Arabian P e n i n s u l a

( w i t h t h e e x c e p t i o n of some mountain r a n g e s ) , c o a s t a l a r e a s o f t h e P e r s i a n Gulf and t h e Arabian Sea.

On t h e I n d i a n Peninsula, t h e boundary of s e a s o n a l l y f r o z e n ground c o i n - c i d e s w i t h t h e southernmost r i d g e s of t h e Kinlalayas. From t h e r e it swings eastward under t h e i n f l u e n c e of t h e n e a r l y m e r i d i o n a l l y a l i g n e d Szechwan Alps t h e upper reaches of t h e Merkong and Yangtse r i v e r s s o u t h t o t h e l a t i t u d e o f t h e Tropic of Cancer.

In

t h e c o a s t a l a r e a s of t h e South China Sea, s e p a r a t e d from t h e main c o n t i n e n t by mountains, t h e ground does n o t a p p a r e n t l y f r e e z e . North of t h i s boundary t h e sub-zone of t r a n s i t o r y f r o z e n s o i l h a s a v e r y v a r i a b l e width and a complex c o n f i g u r a t i o n .

Owing t o t h e warming I n f l u e n c e o f t h e Gulf Stream t h e f r e e z i n g of s o i l i n England, even a t l a t i t u d e s 50

-

52ON, and on t h e west c o a s t o f France,

is

r a t h e r s h o r t - l i v e d and n o t a n a n n u a l l y r e c u r r i n g e v e n t . The sub-zone of

t r a n s i t o r y f r e e z i n g of ground a t t a i n s a c o n s i d e r a b l e width i n t h e lowlands o f t h e Apennine Peninsula under t h e warming i n f l u e n c e of surrounding s e a s and t h e b a r r i e r e f f e c t of t h e Alps t o t h e n o r t h and t h e D i n a r i c (Balkan) Alps t o t h e east. I n mountainous r e g i o n s o f I t a l y and t h e Mediterranean i s l a n d s s e a s o n a l f r e e z i n g of s o i l i s a r e g u l a r phenomenon.

F u r t h e r e a s t in Asia Minor t h e a r e a of s e a s o n a l l y f r o z e n ground i n c r e a s e s because of t h e mountainous c h a r a c t e r of t h e t e r r a i n . Owing t o t h e deep south- ward p e n e t r a t i o n of p o l a r a i r e v e r t h i s r e g i o n , t h e s e a s o n a l l y f r o z e n ground a t t a i n s i t s southernmost p o s i t i o n (namely i n t h e Zagros Mountains i n western I r a n , i n Asia Minor). S t i l l f u r t h e r e a s t i n s o u t h e r n and s o u t h e a s t e r n China and s o u t h e r n Japan t h e width of t h e sub-zone o f t r a n s i t o r y f r e e z i n g i s

c o n s i d e r a b l e .

The s o u t h e r n boundary of t h e a r e a o f r e g u l a r s e a s o n a l f r e e z i n g of ground on t h e Eurasian c o n t i n e n t h a s a r a t h e r odd form. Its p o s i t i o n depends on t h e

i n f l u e n c e s of t h e A r c t i c and t h e c o n t i n e n t . In r e g i o n s (western Europe,

s o u t h e a s t e r n China) where these e f f e c t s a r e modified by warm s e a s , it recedes northward and advances south where t h e c o n t i n e n t a l and a r c t i c i n f l u e n c e s p r e v a i l . The s h i f t i n g of t h i s boundary i s a l s o a s s i s t e d by t h e e l e v a t i o n of the t e r r a i n .

Comparison of f r e e z i n g depths i n western Europe and i n t h e European U.S.S.R. i l l u s t r a t e s the diminishing e f f e c t on t h e s e a s o n a l f r e e z l n g of ground, of warm s e a s and l a t i t u d e , and t h e i n c r e a s i n g e f f e c t of t h e c o o l i n g of t h e c o n t i n e n t by outbreaks of a r c t i c a i r .

In western Europe t h e t h i c k n e s s of s e a s o n a l l y f r o z e n p o u n d i s r a t h e r small (10

-

20 cm). From t h e r e i t i n c r e a s e s s l o v ~ l y northward and eastward.

In t h e European U.S.S.R. i t a l s o i n c r e a s e s from south and soutvrest t o n o r t h

-

and n o r t h e a s t . For i n s t a n c e , the depth of s e a s o n a l l y f r o z e n ground i s 10

-

20 cm on t h e south c o a s t of Crimea, 2

-

2 . 5 m a t t h e A r c t i c C i r c l e and l o c a l l y

3

-

3.5

m i n the low snowfall regions of t h e Ural Mountains.

I n

mountainous regions of Europe and Asia, t h e thicknesa of t h i s l a y e r i n c r e a s e s independently of t h e l a t i t u d e . On t h e C e n t r a l Asian p l a t e a u s where t h e s o i l i s r e l a t i v e l y dry, t h e depth of s e a s o n a l l y f r o z e n ground even I n

middle l a t i t u d e s

(45

-

4 7 ' ~ ) i s

4

-

5

m.

The a r e a of s e a s o n a l l y f r o z e n ground a t t a i n s i t s g r e a t e s t north-south e x t e n t ( n e a r l y 4000 km)

i n

t h e European p a r t of t h e U.S.S.R. F u r t h e r e a s t ,

i t

s h r i n k s considerably (2000

-

2100 km along t h e g0'E m e r i d i a n ) .

On t h e North American c o n t i n e n t s e a s o n a l l y frozen p o u n d i s widespread. Only a narrow zone along t h e c o a s t of t h e Gulf of Mexico ( i n c l u d i n g F l o r i d a ) and along t h e P a c i f i c c o a s t up t o t h e l a t i t u d e of San Francisco escape t h e r e g u l a r seasonal f r e e z i n g of ground. In t h e C o r d i l l e r a s t h e boundary of

s e a s o n a l l y frozen ground must be located a t a c e r t a i n a l t i t u d e and must extend southward t o the l a t i t u d e of the Tropic of Cancer. A wide sub-zone of t r a n s i - t o r y frozen ground l i e s n o r t h of t h e d o t t e d l i n e boundary shown i n F i g . 22.

Eastward from the Rockies t o t h e A t l a n t i c c o a s t t h e s e a s o n a l f r e e z i n g of ground occurs under c o n d i t i o n s of f l a t t e r r a i n . In t h e western p a r t of t h e

-

North American c o n t i n e n t t h e e x t e n t and t h e t h i c k n e s s of s e a s o n a l l y f r o z e n ground a r e influenced by t h e Rockies and t h e p l a t e a u s . The b a r r i e r e f f e c t of t h e C o r d i l l e r a s and Rockies i n c r e a s e s t h e c o n t i n e n t a l i t y of c l i m a t e . I n t h i s connection t h e a r e a of s e a s o n a l l y frozen ground a l o n g t h e Rockies extends t o 3000 km. In t h e e a s t e r n p a r t of t h e c o n t i n e n t

i t

a l s o widens meridionally, although t o a l e s s e r e x t e n t , under t h e I n f l u e n c e s of t h e cold Labrador c u r r e n t and t h e Appalachian range.

Judging from t h e c l i m a t e of t h e North American c o n t i n e n t , t h e depth of the frozen l a y e r n u s t i n c r e a s e from south t o n o r t h and from s o u t h e a s t t o

northwest. I f one conlpares t h e c l l m a t o l o ~ l c a l p e c u l i a r i t i e s of t h i s c o n t i n e n t with those of western Europe and t h e European U.S.S.R. one may assume t h a t t h e maximum depth of s e a s o n a l l y f r o z e n ground, p e c u l i a r t o s t e p p e regions, must occur I n t h e Rockies i n t h e northwest p a r t of t h e c o n t i n e n t (Canada), where i t

may be 2 t o

3

m.

I n t h e southern and southwestern p l a i n s a s f a r n o r t h a s t o t h e southern shores of the Great Lakes, s e a s o n a l l y f r o z e n p o u n d has a r a t h e r l i m i t e d t h i c k n e s s ( l e s s than 0.5 111) and patchy distribution p a r t i c u l a r l y I n the

M i s s i s s i p p i v a l l e y .

In

Greenland and Iceland s e a s o n a l l y frozen ground I s a r e g u l a r phenomenon.

I n

more s o u t h e r l y c l i m a t i c zones i n d i v i d u a l i s l a n d s of s e a s o n a l l y f r o z e n ground a r e located i n the A t l a s range (northwestern ~ f r i c a ) and on e l e v a t e d t e r r a i n s of Indonesia and blexico.

Such i s t h e general p i c t u r e of t h e d i s t r i b u t i o n of s e a s o n a l l y f r o z e n ground and bedrock i n t h e n o r t h e r n hemisphere.

The e x t e n t of s e a s o n a l l y f r o z e n ground I n the southern hemisphere i s

d i f f e r e n t from t h a t i n t h e n o r t h e r n hemisphere owing t o d i f f e r e n c e s i n t h e s i z e , l o c a t i o n and o u t l i n e s of t h e i r c o n t i n e n t s . In t h e southern hemisphere t h e a r e a of s e a s o n a l l y f r o z e n ground i s very l i m i t e d and i n s i g n i f i c a n t a s compared t o the northern hemisphere.

Seasonal f r e e z i n g of s o i l a s an annual phenomenon on t h e African continent i s o n l y p o s s i b l e i n i t s southermnost e x t r e m i t i e s , namely i n t h e Drakensberg range where i t may extend t o t h e l a t i t u d e of t h e Tropic of Capricorn. A s

a

t r a n s i t o r y phenomenon i t may occur on t h e e l e v a t e d t e r r a i n a l o n g t h e south- western c o a s t of the c o n t i n e n t and I n t h e southex-n p a r t of t h e K a l a h a r i Desert. Seasonal f r e e z i n g of s o i l i n a b e l t i s p o s s i b l e i n mountains i n t h e e a s t e r n p a r t of t h e e q u a t o r i a l - t r o p i c a l zone: in t h e region of V i c t o r i a Lake and

Tanganyika Lake and a l s o probably i n t h e Ethiopian highland. I n t h e s e r e g i o n s the f r e e z i n g of s o i l may only be caused by the a l t i t u d e of a l o c a l i t y , i . e . by t h e p e c u l l a r i t i e s of h e a t exchange between t h e atmosphere and t h e upper p a r t a of mountains extending t o an a l t i t u d e of 4000

-

6000 m. For the n:i;:ie reason even the e x i s t e n c e of permafrost on KilimanJaro (6010 rn) i s l i k e l y .

On the A u s t r a l i a n c o n t i n e n t , which i s mainly south of t h e Tropic of

Capricorn, t h e r e g u l a r s e a s o n a l f r e e z i n g of s o i l Is p o s s i b l e o n l y in t h e south- e r n and s o u t h e a s t e r n s e c t i o n s where the A u s t r a l i a n Alps reach an e l e v a t i o n of 2200 m and t h e g r e a t e r Dividing Range 1800

m.

For t h e c e n t r a l p o r t i o n of t h e c o n t i n e n t only i r r e g u l a r t r a n s i t o r y s e a s o n a l f r e e z i n g of ground o r Its r a d i a - t i o n a l coo l i n g be low O0C seems probable.

Seasonal f r e e z i n g of ground i s a l s o p o s s i b l e on t h e Tasmanian and New Zealand i s l a n d s . k h i l e only t h e r e g u l a r s e a s o n a l f r e e z i n g of ground is

p o s s i b l e on New Z e a l a n d s s North I s l a n d where t h e t e r r a i n r i s e s t o an e l e v a t i o n of 2737 m ( ~ a u k u m a r a ~ a n g e ) , th e e x i s t e n c e of permafrost ln a d d i t i o n t o sea- s o n a l l y f r o z e n ground i s probable on Mount Cook (2797 m) on South I s l a n d . G l a c l e r s on Coolc Mountain wl~ich descend t o an a l t i t u d e of 115

-

215 rn a r e evidence of t h i s . Seasonal and p e r e n n i a l f r e e z i n g o f mountain bedrock i n t h i s r e g i o n depends d i r e c t l y on t h e e l e v a t i o n of t h e t e r r a i n . The warming influence of t h e ocean i s suppressed by t h e dominance of cold s e a c u r r e n t s .

On t h e So~uth American c o n t i n e n t s e a s o n a l l y f r o z e n ground i s more wide- spread than on any o t h e r c o n t i n e n t i n t h e s o u t h e r n hemisphere. Judging from c l i m a t i c d a t a , s e a s o n a l l y f r o z e n ground on p l a i n s and p l a t e a u s may extend t o t h e l a t i t u d e of t h e Tropic of Capricorn and in t h e system of t h e Andes even t o t h e e q u a t o r . The f r e e z i n g of s o i l on t h e South American c o n t i n e n t

i s

due t o t h e e l e v a t i o n of t h e t e r r a i n and t h e i n t r u s i o n o f cold a n t a r c t i c a i r masses W t o i t s s o u t h e r n p a r t .

Seasonal f r e e z i n g o f ground a l s o occurs i n T i e r r a d e l Fuego and t h e entLre t e r r i t o r y of Pa t a g o n i a .

Numerous i s l a n d s of s e a s o n a l l y f r o z e n ground probably o c c u r a t an e l e v a - t i o n of 2800 m w i t h i n t h e boundaries of t h e B r a z i l i a n p l a t e a u .

Near t h e lower r e a c h e s of t h e Parana R i v e r I n t h e lowlands between t h e Andes and t h e B r a z i l i a n p l a t e a u and i n t h e i n t e r i o r of t h i s p l a t e a u , s e a s o n a l s o i l f r e e z i n g

i s

probably s h o r t - l i v e d and does not occur each y e a r .

The e l e v a t i o n of t h e Andes p r o v i d e s s u i t a b l e c o n d i t i o n s n o t o n l y f o r t h e s e a s o n a l f r e e z i n g of .pound but a l s o f o r t h e p e r e n n i a l f r e e z i n g o f bedrock. The depth of t h e f r o z e n ground on t h e South American c o n t i n e n t may be v a r i a b l e , p a r t i c u l a r l y I n t h e Andes. Seasonal f r e e z i n g of ground a l s o o c c u r s on t h e Falkland I s l a n d s

.

D i s t r i b u t i o n o f Permafrost

A l l t h a t was s a i d about t h e l i n e - b o u n d a r i e s o f s e a s o n a l l y f r o z e n ground a l s o a p p l i e s t o t h e line-boundaries of pernlafrost.

Many e f f o r t s have been made i n t h e p a s t t o p l o t t h e p o s i t i o n of t h e permafrost boundary. Works of A.F. Middendorf (1848, 1862) and K.M. Baer

(1855)

of t h e Russian Acadeniy of Sciences undoubtedly gave t h e f i r s t impetus t o t h e s e e f f o r t s . These a u t h o r s were f i r s t t o i n d i c a t e on t h e b a s i s of s c a n t y o b o e r v a t i o n a l d a t a t h e boundaries of t h e a r e a s o f "permanently f r o z e n ground". F r i t z (up t o 1879) attempted t o p l o t t h e permafrost boundary i n t h e n o r t h e r n hemisphere. H i s boundary i s weakly founded however and has o n l y h i s t o r i c a l s i g n i f i c a n c e . The same i s a l s o t r u e of t h e permafrost boundary p r e s e n t e d i n t h e 3erghauoen A t l a s (1892). The l a t t e r boundary i s a modified v e r s i o n of

F r i t z s s boundary. The p e r r n a f r o s t boundary i n A n d r e e 1 s A t l a s a g a i n c l o s e l y a p p r o x i ~ n a t e s th e Berghausen boundary.

F o l l o w i n g A.F. Middendorf,

K.M.

B a e r and L. Y a c h e v s k i i ( 1 8 8 9 ) , a u t h o r s M . I . Sunigin ( 1 9 3 7 ) , Sutngin e t a l . ( 1 9 4 0 ) , L.A. B r a t t s e v (13'10) and V . F . Twnelf

(1911.6) had more b u t s t i l l i n s u f f i c i e n t o b s e r v a t i o n a l d a t a a t t h e i r d i s p o s a l . T h e i r s u g g e s t e d s o u t h e r n boundary o f t h e p e r m a f r o s t a r e a i s c l o s e t o i t s

a c t u a l p o s i t i o n . However, i n many a r e a s t h e d e t e r n l i n a t i o n o f t h i s boundary was s t i l l guided by g e n e r a l c o n s i d e r a t i o n s based on t h e p e c u l i a r i t i e s o f t h e topography and c l i n ~ a t i c d a t a (Tumel # , 19146).

Many r e s e a r c h workers have deterniincd t h e s o u t h e r n boundary of p e r m a f r o s t u s i n g c o r r e l a t i o n s between q u a n t i t a t i v e c 1 i m a t o l o e ; i c a l i n d i c e s and t h e temper- a t u r e regimes of s o i l and t h e l i t h o s p h e r e . To t h i s group b e l o n g G . I . Wild

( 1 8 8 2 ) ) V.B. S h o s t a k o v i c h ( 1 9 2 8 ) , A . A . G r i g o r t e v ( 1 9 3 0 ) and o t h e r s .

A group o f a u t h o r s h a s emer1ged i n r e c e n t y e a r s who a d v o c a t e t h e p l o t t i n g o f t h e p e r m a f r o s t boundary on t h e b a s i s o f a c t u a l o b s e r v a t i o n a l d a t a and some t h e o r e t i c a l c a l c u l a t i o n s based on s t u d i e s o f t h e i n t e r a c t i o n o f a number o f p h y s i c a l - g e o g r a p h i c a l f a c t o r s which d e t e r m i n e b a s i c a l l y t h e development o f f r o z e n b o d i e s . T h i s p r i n c i p l e h a s been used by V.A. Kudryavtsev ( 1 9 5 4 ) and I.Ya

.

Baranov ( 1952 )

.

The p e r m a f r o s t b o u n d a r i e s o f v a r i o u s a u t h o r s a r e p r e s e n t e d i n F i g .

23.

The p e r m a f r o s t a r e a s o f t h e g l o b e based on contemporary o b s e r v a t i o n a l d a t a and t h e t h e o r y o f t h e f o r m a t i o n o f p e r m a f r o s t a r e p r e s e n t e d i n F i g . 22. The p e r m a f r o s t boundary w i t h i n t h e U.S.S.R. h a s been determined by V.A.

Kudryavtsev ( 1 9 5 4 ) i n 1949 and I.Ya. Baranov ( 1 9 5 2 ) i n 1950. The p e r m a f r o s t boundary and t h e o u t l i n e s o f p e r m a f r o s t i s l a n d s on t h e North American c o n t i - n e n t and Greenland i n F i g . 22 a r e based on s p e c i a l c a l c u l a t i o n s c a r r i e d o u t b y I.Ya. Baranov.

The p e r m a f r o s t boundary on c o n t i n e n t s i n t h e s o u t h e r n hemisphere is n o t shown i n F i g . 22 because c o n t i n u o u s p e r m a f r o s t t h e r e i s c o n f i n e d t o t h e A n t a r c t i c c o n t i n e n t . The p o s i t i o n o f p e r n ~ a f r o s t is l a n d s and l a r g e r a r e a s shown i n F i g . 22 a r e based mainly on c a l c u l a t l o n s s i n c e a c t u a l o b s e r v a t i o n a l d a t a a r e v e r y s c a r c e .

A s c a n be s e e n from F i g . 24, t h e s o u t h e r n boundary of t h e p e r m a f r o s t a r e a i n t h e n o r t h e r n hemisphere h a s

a

r a t h e r odd form. On the E u r a s i a n con- t i n e n t , i n n o r t h e r n Fenno-Scandia and t h e European U.S.S.R. i t o u t l i n e s a narrow zone of l a n d which widens c o n s i d e r a b l y when a p p r o a c h i n g t h e U r a l r a n g e where i t swings s h a r p l y t o t h e s o u t h .

In

w e s t e r n S i b e r i a t h e p e r m a f r o s t boundary encompassing a wide a r e a o f l a n d f o l l o w s a n e a r l y l a t i t u d i n a l c o u r s e t o t h e Y e n i s e i R i v e r . Because of t h e i n c r e a s i n g c o n t i n e n t a l i t y o f t h e c l i m a t e and t h e g e n e r a l r i s e o f t h e t e r r a i n e a s t o f t h e Y e n i s e i which f a v o u r t h e

c o o l i n g of t h e l i t h o s p h e r e i n w i n t e r i t t h e n swings s h a r p l y southward a l o n g t h e Y e n i s e i R i v e r . A f t e r rounding t h e A l t a i range i t l e a v e s t h e U.S.S.R. t e r r i t o r y and c o n t i n u c s eastward through Mongolia and China. Curving around t h e Mongolian A l t a i , Hangay and Hentey r i d g e s and t h e Great and L i t t l e Khingan Mountains i t r e t u r n s t o t h e U.S.S.R. n e a r Khabarovsk. Here t h e p e r m a f r o s t boundary f o l l o w s t h e l e f t bank of t h e Aniur River t o t h e Gulf o f T a t a r y where i t t e r m i n a t e s . It appears a g a i n o n l y i n t h e extreme n o r t h o f S a k h a l i n I s l a n d (cape Y e l i z a v e t a ) and on Kanchatka Peninsula where a f t e r rounding t h e s o u t h e r - l y extremes of t h e middle and e a s t e r n mountain ranges i t r u n s t o t h e Sivuch Cape i n t h e Bering Sea.

The b a s i c c o n d i t i o n f o r t h e development and e x i s t e n c e of p e r m a f r o s t i n Kamchatka a s w e l l a s i n o t h e r mountainous r e g i o n s ( U r a l , A l t a i , Sayan, e t c . )

-

i s t h e presence of h i g h mountain r i d g e s . Numerous p e r m a f r o s t i s l a n d s i n t h e Karnchatka mountain ranges and on sumn~its of volcanoes form a p e r m a f r o s t a r e a l a r g e enough t o be considered a s an e x t e n s i o n of t h e c o n t i n e n t a l p e r m a f r o s t a r e a

.

On t h e North American c o n t i n e n t t h e s o u t h e r n boundary of p e r m a f r o s t f o l - lows t h e s o u t h e r n s l o p e of t h e Alaska range and t h e n swings southward a l o n g t h e western s l o p e of t h e Rockies t o 53ON t h e n t u r n s back northward a l o n g t h e e a s t e r n s l o p e of t h e Rockies t o 57ON. From,there i t swings t o t h e s o u t h e a s t , i n t e r s e c t s Lake C h u r c h i l l and t h e n o r t h e r n p a r t of Lake Winnipeg, p a s s e s

through s o u t h e r n e x t r e m i t i e s of Hudson Bay (James ~ a y ) , rounds t h e s o u t h s i d e of t h e Labrador highland and t h e n swings n o r t h t o l a t i t u d e 53ON where I t

d i s a p p e a r s a t t h e c o a s t . It a p p e a r s a g a i n i n t h e s o u t h e r n p a r t of Greenland where i t f o l l o w s t h e s o u t h e r n and s o u t h e a s t e r n c o a s t ( F i g . 2 5 ) .

Thus t h e p e r n ~ a f r o s t a r e a i n t h e n o r t h e r n hemisphere c o v e r s c o n s i d e r a b l e p o r t i o n s of t h e E u r a s i a n and North American c o n t i n e n t s , t h e l a r g e i s l a n d s

Greenland and I c e l a n d , and t h e i s l a n d s i n t h e A r c t i c Ocean.

Outside of t h i s a r e a o n l y s p o r a d i c p e r m a f r o s t ( l a r g e o r s m a l l i s l a n d s of p e r m a f r o s t ) i s encountered i n h i g h inountain s y s t e m s . These p e r m a f r o s t i s l a n d s owe t h e i r e x i s t e n c e t o t h e e l e v a t i o n and t h e p e c u l i a r i t i e s of h e a t exchange i n t h e f r e e atmosphere. On t h e E u r a s i a n c o n t i n e n t such p e r m a f r o s t i s l a n d s a r e l o c a t e d i n t h e Alps and Pyrenees i n w e s t e r n Europe, i n t h e Scandinavian

mountains between t h e l a t i t u d e 60°N and t h e A r c t i c C i r c l e in n o r t h e r n Europe, i n e a s t e r n Europew i n t h e U r a l s (on I r e m e l ' p e a k ) i n t h e Great and L i t t l e Caucasus; on Great A r a r a t i n Asia Minor and on E l b u r z i n I r a n .

*

The p o s s i b i l i t y of t h e e x i s t e n c e of p e r m a f r o s t i n t h e C a r p a t h i a n Mountains and on peaks of t h e Balkan Mountains i s n o t excluded.

In S o v i e t c e n t r a l * Asla c o n s i d e r a b l e p e r m a f r o s t a r e a s a r e l o c a t e d on t h e Tarbagatay Mountains, i n western Tlcn-Shan i n t h e Parnir and i n t h e Hindu Kuoh range i n Af ghanis t a n .

In C e n t r a l Asia wide a r c a s of p e r n ~ a f r o s t a r e s i t u a t e d i n t h e e a s t e r n p a r t s of Tangshan i n t h e Altyn Tagh, Nan-Shan and Kunlun r a n g e s , i n t h e Himalayasj Szechwan Alps and a l s o on t h e T i b e t i a n p l a t e a u .

I n t h e F a r East, p e r m a f r o s t i s l a n d s can be found i n t h e S i k h o t e A l i n range, on h i g h peaks of t h e North Korean mountains, on Fujiama i n Japan, i n mountains and i n swamps on S a k h a l i n I s l a n d and on i n d i v i d u a l i s l a n d s of t h e K u r i l I s l a n d c h a l n .

I n t h e western hemisphere, t h e occurrence o f s p o r a d i c p e r m a f r o s t i s

p o s s i b l e in some mountain r a n g e s i n Mexico ( ~ o p o c a t e p e t l , O r i z a b a ) and i n t h e North American C o r d i l l e r a s and t h e Rockies.

Large p e r m a f r o s t i s l a n d s a r e l o c a t e d i n mountaln ranges i n s o u t h e r n S i b e r i a and i n t h e n o r t h e r n p a r t s of C e n t r a l Asia ( ~ o n g o l i a ) .

Although t h e perrnafrost a r e a s i n t h e mountain r a n g e s of s o u t h e r n S i b e r i a and i n t h e n o r t h e r n p a r t of C e n t r a l Asia ( ~ o n g o l i a ) were included i n t h e continuous p e r m a f r o s t a r e a of E u r a s i a t h e y s t a n d a p a r t from i t because of topographic p e c u l i a r i t i e s and t h e c o n d i t i o n s o f f o r m a t i o n . In t h e above- n~entioned mountains t h e a l t i t u d e of t h e lower boundary o f p e r m a f r o s t i s ex- tremely v a r i a b l e . Judging from calculations and from a v a i l a b l e o b s e r v a t i o n a l d a t a t h e lower boundary of p e r m a f r o s t i n middle l a t i t u d e mountains under t h e i n f l u e n c e of moist ocean a i r masses must be a t a r a t h e r low a l t i t u d e , p o s s i b l y between t h e 1800 and 2100 m ( s c a n d i n a v i a n r a n g e ) . Under c o n t i n e n t a l c o n d i t i o n s t h e e l e v a t i o n of t h i s boundary i s v a r i a b l e : i n t h e Tien-Shan range ( C h i n a ) a t an a l t i t u d e of about 2500 m, i n t h e Turkestan and Pamir ranges a t a b o u t 4200

-

4300 m and i n T i b e t a t e l e v a t i o n s r a n g i n g from 3700 t o 5400 m.

Thus, t h e a l t i t u d e of t h e lower p e r m a f r o s t boundary i n mountains depends on t h e p e c u l i a r i t i e s o f t h e h e a t exchange i n v a r i o u s r e g i o n s of t h e E u r a s i a n c o n t i n e n t . I n n ~ o u n t a i n ranges i n f l u e n c e d by moist o c e a n i c a i r masses it

i n c r e a s e s from n o r t h t o s o u t h and i n t h e d i r e c t i o n of i n c r e a s i n g c o n t i n e n t a l i t y o f c l i m a t e . In mountain ranges under c o n t i n e n t a l c l i m a t e t h i s incr12ase o c c u r s b a s i c a l l y from n o r t h t o s o u t h .

It must be p o i n t e d o u t t h a t t h e widespread b e l i e f i n t h e c o i n c i d e n c e of t h e lower l i r n i t s of p e r m a f r o s t and t h e permanent snow-line i s e r r o n e o u s ( ~ u m e 1 I ,

191~6).

I n v e s t i g a t i o n s i n t h e A l t a i and Pamir Mountains have shown

t h a t t h e lower boundary of perriiafrost i n mountains Is a t a lower a l t i t u d e t h a n

t h e permanent snow-line. For i n s t a n c e , i n t h e A l t a i mountain range t h e lower boundary of permafrost i s l o c a t e d a t an a l t i t u d e of 1000 - 1100 m a s compared

t o an a l t i t u d e of 2300

-

3200 m f o r t h e permanent snow-line.

It h a s been e s t a b l i s h e d t h a t t h e mean a i r temperature a t t h e permanent snow-line i s 1 . 5 O C a t t h e e q u a t o r , +0.5OC on t h e s o u t h e r n s l o p e s of t h e IIin-ialayas and about -2.O0C on t h e n o r t h e r n s l o p e s ; -3.g°C i n t h e Karakorom range, -b°C i n t h e Alps, - 6 O C i n t h e Turkestan range (and Pamir p l a t e a u ) and - l l ° C on h i l l s of Novaya Zemlya.

Thus i t can be concluded t h a t t h e mean a n n u a l temperature and t h e a l t i - tude of t h e permanent snow-line a r e n o t r e l a t e d d i r e c t l y and t h a t t h e pernman- e n t snow-line i s n o t a r e l i a b l e c l i m a t i c index.

One may assur~je t h a t t h e p e r m a f r o s t boundary i n n ~ o u n t a i n s i n t h e t r o p i c a l - e q u a t o r i a l zone i s l o c a t e d above t h e snow-line. Depending on t h e change of c l i m a t o l o g i c a l c o n d i t i o n s w i t h l a t i t u d e , t h e e l e v a t i o n of t h e p e r m a f r o s t boundary d e c r e a s e s with i n c r e a s i n g l a t i t u d e w i t h r e s p e c t t o t h e e l e v a t i o n of

t h e snow-line. The p e r m a f r o s t boundary and z e r o i s o t h e r m i n t e r s e c t t h e snow- l i n e between t h e e q u a t o r and t h e p o l e s .

The a l t i t u d e of t h e lower boundary of p e r m a f r o s t i n mountains on t h e North American c o n t h e n t has been determined by rneans of c l i ~ n a t i c d a t a . It

r i s e s a l o n g t h e P a c i f i c c o a s t from 75 rn a t t h e Gulf of Alaska t o 2400 m a t l a t i t u d e 50°N. F a r t h e r s o u t h it r i s e s s t e a d i l y t o 5400 m i n t h e Mexican

mountains a t t h e l a t i t u d e of t h e Tropic o f Cancer. Along t h e e a s t e r n s l o p e of t h e Rockies t h e e l e v a t i o n of t h e lower boundary of p e r m a f r o s t r i s e s from

80

m

i n t h e r e g i o n of Great Bear Lake t o 4600 m i n t h e r e g i o n of Mount E l b e r t (39ON

In t h e n o r t h e r n hemisphere t h e p l o t t i n g of t h e s o u t h e r n boundary of

p e r m a f r o s t i s based, t o a g r e a t e x t e n t , on known laws governing

i t s

f o r m a t i o n . Actual s u r v e y d a t a of s u f f i c i e n t q u a n t i t y t o p e r m i t one t o determine i t s e x a c t p o s i t i o n a r e n o t y e t a v a i l a b l e , even f o r t h e

U.S.S.R.

S e v e r a l Russian c r y o l o g i s t s have p l o t t e d t h e p e r m a f r o s t boundary a s a z o n a l b e l t s o u t h of v!hich, w i t h o u t s i g n i f i c a n t changes i n n a t u r a l c o n d i t i o n s , t h e fornlation o f permafrost i s n o t p o s s i b l e .

Let u s c o n s i d e r sonme t h e o r i e s concerning t h e n a t u r e of t h e c o n d i t i o n a l boundary of t h e p e r m a f r o s t a r e a .

M.I.

Sumgin (1937, 1940) c o n s i d e r e d t h a t t h i s boundary could o n l y be determined on t h e b a s i s of a c t u a l o b s e r v a t i o n a l d a t a . He was faced with a dilemma: whether t o i n c l u d e numerous b o r d e r i n g p e r m a f r o s t i s l a n d s i n t h e p e r m a f r o s t a r e a , t o l e a v e them o u t and o u t l i n e them s e p a r a t e l y , o r t o o u t l i n e t h e thawed a r e a s w i t h i n t h e p e r m a f r o s t a r e a .

M.I.

Sumgin used t h e f i r s t c h o i c e , 1 . e . he drew t h e p e r m a f r o s t boundary a l o n g t h e g e o g r a p h i c a l p o s i t i o n of t h e southernmost p e r m a f r o s t i s l a n d s .

Pl. I. Sunlgin (1933) p r e s e n t i n g t h e 1;heory of t h e d e g r a d a t i o n and aggrada- t i o n of t h e depth of permafrost was f i r s t t o p o i n t o u t t h e dynamics of t h e permafrost boundary. L a t e r on (1937) he a t t a c h e d g r e a t importance t o t h i s problem.

V.A. Kudryavtsev (1954) considered t h e permafrost boundary a s an average l i n e c o i n c i d e n t w i t h t h e geographical p o s i t i o n of t h e z e r o amplitude of long- term annual bedrock temperature. According t o h i s concept t h e p e r m a f r o s t boundary i s t h e a x i s of a zone o f continuous and p e r i o d i c s h i f t i n g of perma- f r o s t from n o r t h t o s o u t h and v i c e v e r s a . In o t h e r words, a c c o r d M g t o Kudryavtsev t h e southern boundary of permafrost i s a t r a n s i t i o n zone from s e a s o n a l l y f r o z e n ground t o p e r n a f r o s t . Such a boundary may be considered v a l i d o n l y f o r a c c r t a l n time i n t e r v a l . T h i s p e r m i t s one t o p l o t i t on a c h a r t a s a mean boundary of t h e t r a n s i t i o n zone. To d e t a i l t h e p o s i t i o n of t h i s boundary he used t h e long-term mean ground temperature. This permafrost boundary does n o t c o i n c i d e with t h e p o s i t i o n of t h e z e r o isotherm of ground temperature.

I.Ya. Baranov (1952) a n a l y s i n g t h e problem o f t h e s o u t h e r n boundary o f permafrost a r r i v e s a t t h e conclusion t h a t t h e concept " s o u t h e r n boundary" h a s n o t y e t been s a t i s f a c t o r i l y e s t a b l i s h e d . According t o o u r view, p l o t t i n g o f t h e permafrost line-boundary has p r a c t i c a l meaning o n l y on s m a l l - s c a l e review c h a r t s . The s c a l e of such c h a r t s must n o t exceed 1 : 5,OOO,OOO. On l a r g e - s c a l e c h a r t s l a r g e r p e r n a f r o s t i s l a n d s may be o u t l i n e d o r i n d i c a t e d by conven- t i o n a l symbols. T h i s would e l i r n l n a t e t h e n e c e s s i t y o f drawing t h e conventional line-boundary.

There a r e t h r e e p o s s i b i l i t i e s o f p l o t t i n g a line-boundary depending on how we d e f i n e i t .

1. One may draw a line-boundary a l o n g t h e z e r o i s o t h e r m of long-term

annual s o i l temperature i n t y p i c a l p h y s i c a l - g e o g r a p h i c a l r e g i o n s . A s a m a t t e r of f a c t , t h e formation of permafrost begins a t t h i s p o i n t . It i s obvious t h a t such a boundary may be c a l l e d c o n d i t i o n a l l y t h e geophysical boundary o f t h e p e r m a f r o s t a r e a . T h i s boundary r e f l e c t s t h e r e l a t i o n s h i p between t h e perrna- f r o s t temperature and t h e contcmporary h e a t exchange between t h e e a r t h ' s c r u s t and t h e atmosphere. I n t h e n o r t h e r n p a r t of t h e European U.S.S.R. t h i s

boundary c o i n c i d e s with t h e t r a n s i t i o n zone from s o u t h e r n tundra t o n o r t h e r n tundra, i n Western S i b e r i a from f o r e s t tundra t o s o u t h e r n t u n d r a , i n Mid-

S i b e r i a from s o u t h e r n t a i g a t o n o r t h e r n t a i g a , i n t h e Trans-Baikal r e g i o n and i n t h e F a r E a s t of t h e U.S.S.R. from f o r e s t s t e p p e s t o v a s t S i b e r i a n f o r e s t s .

The geophysical boundary of permafrost a l s o encompasses t h e a r e a s of s p o r a d i c permafrost inasmuch a s t h e l a t t e r a r e d i s t r i b u t e d among s o i l s w i t h a p o s i t i v e mean annual temperature and owe t h e i r formation t o some l o c a l

2. The permafrost boundary may be drawn a l o n g t h e most s o u t h e r l y l i m i t of permafrost i s l a n d s which, independently of t h e i r l i t h o l o g i c a l composition, remain s t a b l e d u r i n g s h o r t p e r i o d warmings of c l i m a t e . T h i s boundary,

c o n s i d e r a b l y s o u t h of t h e geophysical boundary, may be c a l l e d t h e l a t i t u d e zone and v e r t i c a l zone o r simply t h e p h y s i c a l - g e o g r a p h i c a l boundary of permafrost.

Unlike t h e geophysical boundary, t h e p h y s i c a l - g e o g r a p h i c a l boundary o f t h e permafrost a r e a i n t h e western p a r t of t h e

U.S.S.R.

(west o f t h e Y e n i s e i R i v e r ) i n c l u d e s permafrost i s l a n d s i n p e a t s o i l s which a r e i n t h e s t a g e of d e g r a d a t i o n . The same Is a l s o v a l i d f o r t h e p e r m a f r o s t boundary i n t h e s p h e r e of maritime i n f l u e n c e e a s t of Great Khingan range r e g i o n . In t h e c e n t r a l p a r t of t h e permafrost a r e a ( i n Mongolia and c h i n a ) t h i s boundary i n c l u d e s t h e permafrost i s l a n d s i n mountains. S i n c e t h e l a t t e r a r e s i t u a t e d i n t h e r e g i o n c h a r a c t e r i z e d by t h e c o n t i n e n t a l regime of t h e h e a t exchange between t h e e a r t h and t h e atmosphere, t h i s p h y s i c a l - g e o g r a p h i c a l boundary i s l e s s dynamic w i t h time, t h u s , t h e p h y s i c a l - g e o g r a p h i c a l boundary d i f f e r s from t h e g e o p h y s i c a l boundary i n t h a t

i t

i n c l u d e s i n t h e continuous p e r m a f r o s t a r e a t h e zone of permafrost i s l a n d s . On review c h a r t s w i t h a s c a l e of 1 : 5,000,000 and l e s s b o t h boundaries may be i n d i c a t e d sinlultaneously

.

3 .

For p r a c t i c a l c o n s i d e r a t i o n s t h e p e r m a f r o s t boundary may be p l o t t e d t o i n c l u d e a r e a s where t h e f o r ~ n a t i o n of permafrost i s probable b u t non-exis t e n t a t t h e p r e s e n t time because of c e r t a i n f a c t o r s (ground water, snow c o v e r ) h i n d e r i n g i t s forrnations. T h i s boundary v ~ i l l l i e s t i l l f a r t h e r s o u t h t h a n t h e p h y s i c a l - g e o g r a p h i c a l boundary, p a r t i c u l a r l y i n t h e r e g i o n west o f t h e Y e n i s e i River. In t h e c e n t r a l - c o n t i n e n t a l p a r t of t h e p e r m a f r o s t a r e a t h i s boundary c o i n c i d e s with t h e p h y s i c a l - g e o g r a p h i c a l boundary b u t t a k e s a more s o u t h e r l y p o s i t i o n i n t h e e a s t ( S a k h a l i n I s l a n d , S i k h o t e A l i n range, Amur lowland). T h i s boundary may be c a l l e d t h e p o s s i b l e o r p o t e n t i a l p e r m a f r o s t boundary.

It can be seen from t h e above c o n s i d e r a t i o n s t h a t p l o t t i n g t h e s o u t h e r n boundary of t h e p e r m a f r o s t a r e a i s n o t o n l y c o n d i t i o n a l w i t h r e s p e c t t o i t s

n a t u r e b u t a l s o t o i t s form and depends on t h e s o l u t i o n of a number of a s s o i c a t e d problems of prime importance.

Taking i n t o account t h e e f f e c t of human a c t i v i t i e s on t h e h e a t exchange between t h e s o i l and t h e atmosphere, t h e p h y s i c a l - g e o g r a p h i c a l boundary of t h e perrnafrost i s most important from t h e p r a c t i c a l p o i n t of view. There i s no doubt about t h e dynamics of t h i s boundary, however i t s movement i s r e l a t i v e l y slow. F l u c t u a t i o n s i n t h e p o s i t i o n o f t h i s boundary a r e caused by considerahle changes in t h e c h a r a c t e r and c o n d i t i o n s of t h e h e a t exchange between t h e s o i l and t h e atmosphere i n i n d i v i d u a l s e c t o r s and f r e q u e n t l y s i m u l t a n e o u s l y i n t h e

e n t i r e perrnafrost a r c a

.

During r i s i n g o r d e c l i n i n g l e v c l o of h e a t exchange, c o n s i d e r a b l e v a r i a t i o n s t a k e p l a c e I n t h e permafrost a r e a and i t s depth. However, s h o r t - l i v e d v a r i a t i o n s i n t h e c h a r a c t e r an6 c o n d i t i o n s of t h e h e a t exchange a r e incapable of s h i f t i n g t h i s boundary.

S e v e r a l papers have d e a l t w i t h t h e p l o t t i n g of t h e s o u t h e r n p e r m a f r o s t boundary on t h e North American c o n t i n e n t . The boundaries known t o us a r e p r e s e n t e d I n P i g . 25.

Let us now b r i e f l y r e v i c v ~ th e p e c u l i a r i t i e s of t h e d i s t r i b u t i o n and t h e depth of t h e permafrost i n t h e n o r t h e r n hemisphere. We s h a l l f i r s t c o n s i d e r t h e Eurasian continent.

According t o A. Cajander (1902-1303), K. Rathjens and H . b!eisslnann ( 1 9 2 9 ) ~ Lapland l a p a r t l y s i t u a t e d i n t h e p e r m a f r o s t a r e a . W. Bodmannrs (1901-1903), B. ~ 6 ~ b o r n ' s (1927) and W. Ule I s (1922) o b s e r v a t i o n s show t h a t p e r m a f r o s t

i s l a n d s a r e encountered I n n o r t h e r n Norway and n o r t h e r n Sweden, p a r t i c u l a r l y on t h e e a s t e r n s l o p e of t h e Scandinavian r i d g e n o r t h of t h e A r c t i c C i r c l e . However, a number of' pernmfrost I s l a n d s a r e a l s o l o c a t e d on s l o p e s s o u t h of t h e A r c t i c C i r c l e . For i n s t a n c e , a t Lynger

(750

m above s e a l e v e l ) f r o z e n nloralne l a y e r s up t o 20 m t h i c k have been encountered Fn mines. According t o P. Smith ( ~ r a t t s e v , 1940) h i l l y swamps a t a n a l t i t u d e of 800

-

900 m have been

discovered i n n o r t h e r n Sweden.

S i m i l a r i t y of p h y s i c a l - g e o g r a p h i c a l c o n d i t i o n s i n Fenno-Scandia and t h e Kola Peninsula s u g g e s t s t h e e x i s t e n c e o f perrnafrost i n n o r t h e r n Finland

( ~ a r a n o v , 1953).

I n t h e U.S.S.R. permafrost a r e a s a r e l o c a t e d i n t h e t u n d r a zone, i n forest tundra and p a r t l y I n t h e sub-zones of t h e n o r t h e r n S i b e r i a n f o r e s t . The d i s - t r i b u t i o n of t h e permafrost changes from west t o e a s t and from southwest t o n o r t h e a s t .

Permafrost i s encountered Fn l i m i t e d a r e a s on t h e Kola P e n i n s u l a . In

t h e western p a r t o f t h e p e n i n s u l a it i s l i m i t e d t o p e a t s o i l s , i n t h e e a s t e r n p a r t t o g l a c i a l and a l l u v i a l c l a y and sandy c l a y s o i l s , l e s s f r e q u e n t l y t o sandy s o i l s . The d e p t h of permafrost i s about 20

-

25 m. C r y s t a l l i n e and metalnorphic s o i l s t r u c t u r e s f a v o u r permafrost developnlent Ln t h e Lovozersk h i g h l a n d s and i n some o t h e r " t u n d r a s " a s w e l l a s i n t h e s o u t h e a s t e r n p a r t of t h e Kiev highlands.

I n t h e t u n d r a and c o n i f e r o u s f o r e s t zone between t h e White Sea and t h e Ural range, permafrost has a l s o a patchy d i s t r i b u t i o n . Only i n t h e n o r t h e r n p o r t i o n of t h e B o l ~ s h e z e m e l l s l r t u n d r a do t h e p e r m a f r o s t i s l a n d s for111 a Inore o r l e s s c o n t i n ~ ~ o u s a r e a s e p a r a t e d by t a l i k s i n r i v e r v a l l e y s , l a k e b a s i n s and i n w a t e r - r i c h t e c t o n i c d e p r e s s i o n s . 1;lthin t h e n o r t h e r n p a r t of t h e t u n d r a zone, t h e t h i c k n e s s of perrnafrost i n c r e a s e s s h a r p l y . In t h e v i c i n i t y of t h e v i l l a g e

of Amderm i t e v i d e n t l y reaches a t h i c k n e s s of

285

rn i n c o n t r a s t t o 25 t o 30 m

i n a r e a s of Infrequent permafrost i s l a n d s . A ternperatme drop ancl I n c r e a s i n g t h i c k n e s s of permafrost a r e observed I n c r o s s i n g from t h e southern h i l l o c k tundra t o t h e northern s p o t t e d tundra.

I n t h e Ural region t h e boundary of the a r e a c o n t a i n i n g permafrost i s l a n d s s h i f t s considerably southward.

In t h e northern f o r e s t zone of liestern S i b e r i a where the snow cover

is

r e l a t i v e l y deep (60

-

90 cm and more), the zone of permafrost i s l a n d s i s very wide, The t r a n s i t i o n zone from sporadic t o almost continuous permafrost c o i n c i d e s with t h e northern boundary of the coniferous f o r e s t and is accom- panied by a sharp Increase i n t h e t h i c k n e s s of permafrost ( ~ o p o v , 1953). For Instance, t h e thickneso of sporadic permafrost within t h e coniferous f o r e s t zone i s a t most 25

-

30 m a s compared l o c a l l y t o a t h i c k n e s s of 300 m i n t h e f o r e s t tundra and 1400 m i n t h e tundra.

The thickness of sporadic permafrost i n the western Cis-Baikal r e g i o n ( i n t h e southern p a r t of Mld-Siberia) l o c a l l y reaches 35

-

40 m and exceeds t h i s depth i n t h e e a s t e r n Cis-Baikal.

In t h e c e n t r a l p a r t of t h e Mid-Siberian p l a t e a u the permafrost i s sporadic in t h e southern p o r t i o n and continuous i n t h e n o r t h . T a l l k s under r i v e r

channels, lakes and a t s p r i n g s of subterranean water a r e c h a r a c t e r i s t i c of t h i s region. In t h e zonal s e c t i o n of t h e Nlzhnaya Tunguska River v a l l e y t h e

t h i c k n e s s of permafrost exceeds 100 m.

In

t h e Taymyr depression, t a l l k s a r e p o s s i b l e under l a r g e r i v e r channels and l a k e s . The t h i c k n e s s of permafrost reaches 400 m on t h e Taymyr peninsula and 450

-

500 m i n t h e lov~land of t h e Khatanga River.

In t h e most c o n t i n e n t a l p a r t of S i b e r i a , namely i n t h e s t e p p e s e a s t of Lake Baikal, permafrost Is encountered only i n c e r t a i n p l a c e s .

I n

c o n t r a s t t o

t h e c e n t r a l p a r t of kIestern S i b e r i a t h e permafrost i s l a n d s a r e confined t o v a l l e y s , b a s i n s and northern s l o p e s of mountains u s u a l l y overgrown with f o r e s t . The southern s l o p e s of mountains a r e c h a r a c t e r i z e d by t a l l k s owing t o h i g h e r s o l a r i n s o l a t i o n on t h e s e s l o p e s , s p r i n g s of ground water o r by shallow bed- rock. Here the t h i c k n e s s of permafrost v a r l e s from 10 t o 25

-

30 m.

The g r e a t e s t thicltness and the lowest temperatures of permafrost occur In

r i v e r v a l l e y s , o l d lava beds and on t h e n o r t h e r n s l o p e s of mountains. The e f f e c t of a l t i t u d e on permafrost development i s apparent above the temperature i n v e r s i o n l a y e r . I n the v i c i n i t y of t h e c l t y of Chita t h e Lnversion extends t o an a l t i t u d e of 1000 m . Above t h i s l e v e l t o approximately 2500 ni t h e e f f e c t of a l t i t u d e decreases g r a d u a l l y .

Frequent t a l i k s s e p a r a t i n g frozen a r e a s a r e confined t o southern s l o p e s of mountains, v a l l e y and b a s i n s e c t i o n s c h a r a c t e r i z e d by s u r f a c e run-off,