Mass Move Class

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Rock Mechanics 4, 71--78 (1972)

(g) by Springer-VerIag 1972

Classification of Landslides and Other Mass Movements

B y

A . N emeo k , J . P a~ ek , an d J . R y b M "

With 4 Figures

(Received Septe mbe r 30, 1971)

S u m m a r y - - Z u s a m m e n f a s s un g - - R ~ s u m d

Classi f icat ion of Landslides and Other Mass Movements. This paper presents

a new universal classif icat ion of slope movements, dest ined for the purpose of '

engineering geological mapping. This classification was compiled after critical eva-

luation of the classifications used by now, on the basis of the experience gained by

systematic study of slope movements in Czechoslovakia.

The fol lowing 4 types of slope processes are recognized regarding to the geo-

mech anical characte r and ve locity of the move me nt: cree p, sliding, flow and fall.

C r e e p is a geological ly long-term mov em ent of n on-increasing veloci ty witho ut

well-defined sliding surfaces. Sliding is a slope movement of coherent masses

along one or more well-defined shear surfaces. Flow represents slope movementsin rocks and soils, analogous to the movements in liquids. Fall is a sudden slope

movement; the moving mass loses its coherence and, for a short time, also its

contact with the underlying rock.

The pictures show the elementary types of movements that are obvious in

the European cl imatic condit ions. Graphical representat ion of dimensions and

veloci ty of the phenomena is included.

Klassi f ikat ion yon Rutschungen und anderen Hangbewegungen. Die vorge-

schlagene Klassifikation geht zurtick auf systematische Untersuchungen an Rutsch-

gebieten in der CSSR. Sie lehnt sich an die besten gebr/iuchlichen Klassifikationen

an, wobei letztere einer kri t ischen Beurtei lung unterzogen werden. Ziel des neuen

Vorschlages ist die Erarbeitung yon Kriterien ftir die ingenieurgeologische Kar-

tierung.

Auf Grund des geomechanischen Charakters der Bodenbewegungen werden

folgende vier Vorg/inge unterschieden: K riechen - - geologisch langandauernde,

nicbt beschleunigte Bewegungen ohne ausgepr~igte Gleitfl/ichen; Gleiten -- Hang-

bewe gungen zusamm enh~ingender Mass en l~ings einer od er m ehr ere r Gleitfl~ichen;

Flief~en - - Ha ngb ew egu nge n yon fliissigkeits~ihnlichem Cha rakte r; Fallen - - pl6tz-

l iche Hangbewegungen, wobei d ie bewegte Masse den inneren Zusammenhang und

kurzfrist ig auch den Kontakt mit dem Liegenden verl iert .

Die Grundtypen werden an Hand europ/i ischer Beispiele graphisch dargestel l t

und durch Angaben t iber Gr6tgenordnung der Massen und deren durchschnit t l iche

Geschwindigkeit erg/inzt.

Classification des glissements et autres mouvements de terrain. D'aprhs les

exp&iences acquises pend ant les 6tudes de gl issements en Tch& oslovaq uie et d 'apr6s

Rock Mechanics, Vol. 4/2 6



7 2 A . N e m ~ o k , J . P a ~ e k , a nd J. R y b l i ~ :

l 'examen critique des classifications employ6es jusqu'ici, on a recommend6 laclassification suivante, destin6e avan t tou t au le v4 de g6ologie de l 'ing6nieur.

En relation avec le caract6re g4om4canique des mouvements de pente et de leu r

vitesse, quatre processus sont distinguds: fluage, glissement, 4coulement, dcrou-

lement. Le fluage - - mo uvem ents g4ologiquem ent d e longue durde, sans acc416-ration et sans surfaces de glissement exprim6es. Le glissement -- mouvements depente de masses coh4rentes, le long d'une ou de plusieurs surfaces de glissement.L 'dcoulement -- mouvements de pente dans les roches et les sols , analogues auxmouvements dans les l iquides. L '&roulement -- mouvements de pente soudains,au cours desquelles les masses en mouvement perdent enti&ement leur connexionint&ieure et, pour un temps aussi, le contact avec le sous-sol.

Les exemples sur les figures repr& entent les types principaux des mouvements

courants dans les conditions climatiques d e l 'Europe. O n indique aussi les dimen-sions et la vitesse moyenne des types individuels.

T h e i n c re a s in g a m o u n t a n d e x t e n t o f e n g in e e ri n g s t r u c tu r e s s u c h a s

l a r g e d a m s , h i g h w a y s , a n d p o w e r s t a t i o n s a s w e l l a s o p e n - p i t m i n i n g o f t e n

r e q u i r e s l a r g e - s c a l e h u m a n i n t e r f e r e n c e i n n a t u r e . I n t h e s e c i r c u m s t a n c e s w e

o f t e n e n c o u n t e r a n u m b e r o f o b s t a c l e s c a u s e d b y n a t u r a l f e a t u r e s . O n e o f

t h e m i s t h e p r o b l e m o f s l o p e s t a b i l i t y a n d r e l a t e d p r o c e s s e s , n a m e l y l a n d -

s li de s a n d o t h e r m a s s m o v e m e n t s . R e c e n t l y c o n c e n t r a t e d a t t en t i o n h a s b e e n

g i v e n t o e n g i n e e r i n g g e o l o g i c a l r e s e a r c h o n t h e s e p r o c e s s e s t h a t r e s u l t f r o m

t h e d i s p l a c e m e n t o f s o i l s a n d r o c k s i n d u c e d b y g r a v i t a t i o n f o r c e i n c o n s e -

q u e n c e o f t h e d i s t u r b a n c e o f t h e n a t u r a l s t a b il it y .

E x t e n s iv e k n o w l e d g e a n d i n te n s iv e c o n t i n u o u s s t u d y o f t h e se p r o c e s se s

a n d o f t h e ir o r i g in a n d d e v e l o p m e n t is n e e d e d in o r d e r t o b e a b l e t o m a k e

a c o r r e c t d ia g n o s i s a n d p a r t i c u l a r l y t o e f f e c t t h e n e c e s s a r y p r e v e n t i o n i n d u e

t i m e . F o r t h e s e r e a s o n s , t h e c o m p i l a t i o n o f a n u n i v e r s a l c l a s s i f i c a t i o n i s

e s s e n t i a l a n d i n d i s p e n s a b l e . T h i s w i l l b e , h o w e v e r , a h a r d a n d t h a n k l e s s

ta sk .

T h e m o r p h o l o g i c a l a n d g e o l o g ic a l s t r u c tu r e o f C z e c h o s l o v a k i a c r ea t es

f a v o u r a b l e c o n d i t i o n s f o r t h e o c c u r e n c e o f t h e s e p h e n o m e n a . T h i s e x e r t s ,

o f c o u r s e , a n u n f a v o u r a b l e i n f l u e n c e o n t h e n a t i o n a l e c o n o m y . F o r t h e s e

r e a s o n s , s l o p e p r o c e s s e s h a v e b e e n s u b j e c t o f i n t e n s i v e s t u d i e s i n C z e c h o -

s l o v a k i a f o r m a n y y e a r s . T h e r e s e a r c h w a s b a s e d o n t h e r e s u l t o f t h e r e g i s -

t r a t i o n o f a l l l a r g e l a n d s l i d e s o n t h e t e r r i t o r y o f C z e c h o s l o v a k i a , c a r r i e d o u t

in 1962--1963 ( R y b ~ i~ , P a ~ e k a n d R e p k a , 1 96 5) a s w e l l a s o n th e o ld

t ra d it io n o f t he l if e w o rk o f Q . Z f i r u b a ( Z f i r u b a a n d M e n c l , 1 96 9).

A f t e r m a n y ea r li er c l as s if ic a ti o n s ( A l m a g i a , 1 9 1 0 ; E c k e l , 1 9 5 8;

H e i m , 1 88 2 ; H u t c h i n s o n , 1 96 8 ; J e m e l j a n o v a , 1 9 63 ; K l e c z k o w s k i ,

1 95 5; L a d d , 1 93 5; N e m ~ o k a nd R yb f i~ ' , 1 96 8; R o d i o n o v , 1 93 9;

S h a r p e , 1 9 38 ; S t i n y , 19 41 ; T e r - S t e p a n i a n , 1 96 6; T e r z a g h i , 1 959 ;

Z f i r u b a a n d M e n c l , 1 96 1; Z o l o t a r i e v , 1 96 3) a n d a n al yz in g c rit ic al ly

( S p f i r e k , 1 9 6 6 ) , t h e a u t h o r s s u g g e s t t h e f o l l o w i n g cl a s si f ic a t io n , t h e p r i n -

c i p l e s o f w h i c h a r e g i v e n b e l o w .

I n g e n e r a l , w e s p e a k o f s l o p e m o v e m e n t s i n r o c k s , i n i c e a n d i n s n o w .

F o r t h e u s e o f p r a c ti c a l e n g i n e e r i n g g e o l o g y w e s h a l l d e a l w i t h t h e s l o p e

m o v e m e n t s i n t h e r o c k s o n l y , n a m e l y i n t h e n o n - s o l i d r o c k s ( so il s) , s e m i -



Classification of Landslides and Oth er Mass Movem ents 73

so l id rocks ( sof t rocks) and in so l id rocks , desp i t e the fac t tha t in ce r t a in

r e g i o n a l c o n d i t i o n s t h e m o v e m e n t s o f s n o w a n d i c e a n d o f f r o z e n r o c k s a r e

a l so o f i m p o r t a n c e .

A c c o r d i n g t o t h e g e o m e c h a n i c a l c h a r a c t e r a n d v e l o c i t y o f t h e m o v e -m e n t w e d i s t i n g u i sh t h e f o l l o w i n g 4 t y p e s o f p r o c e s se s :

E n g l i s h G e r m a n F r e n c h R u s s i a n

c r e e p K r i e c h e n f l u a g e p o l z u ~e s t'

s l id ing Gle i t en g l i ssem ent opo lzan i j e

f low F li et~en 8co ulem ent t e~en i j e

f a ll F a l le n 8 c r o u l e m e n t o b r u ~e n i je

F r o m t h e k i n e t i c a l p o i n t o f v i e w o f t h e k i n e t i c s o f t h e m o t i o n , t h e sep h e n o m e n a c a n b e d e f i n e d a s f o l l o w s :

C r e e p - - g e o l o g i c a l l y l o n g - t e r m m o v e m e n t s o f n o n - i n c r e a s i n g v e l o c i t y

w i t h o u t w e l l - d e f i n e d s l i d i n g su r f a c e s . I n m o s t c a se s w e c a n sp e a k o f d e e p -

se a t e d ( o r v i sc o u s ) fl o w . T h e m o v e m e n t s a r e d e s i g n a t e d a s c r e e p i n g m o v e -

m e n t s , t h e r e su l t i n g p h e n o m e n o n i s r o c k c r e e p , t a l u s c r e e p o r so i l c r e e p .

I f i t ach ieves a c r i t i ca l acce le ra t ion , the c reep becomes s l id ing , f low or fa l l .

In th i s case , c reep i s a p repa ra tory s t age to s l id ing , f low or fa l l .

S l i d i n g - - s l o p e m o v e m e n t s o f c o h e r e n t m a s s e s a l o n g o n e o r m o r e w e l l -

d e f i n e d sh e a r su r f a c e s . W e d e f i n e th i s m o v e m e n t a s a l a n d s l id e .

F l o w - - s lo p e m o v e m e n t in r o c k s a n d s oil s, a n a l o g o u s t o t h e m o v e m e n t s

i n l iq u i d s. W e r e f e r to m u d f l o w s o r e a r t h f l o w s a n d r o c k s t r ea m s .

F a l l - - s u d d e n s l o p e m o v e m e n t ; t h e m o v i n g m a s s e s l o s e t h e i r c o h e r e n c e

a n d f o r a s h o r t t im e a ls o t h e i r c o n t a c t w i t h t h e u n d e r l y i n g r o c k. W e r e f e r

to rock fa l l s .

I n e a c h g r o u p , t h e e l e m e n t a r y p h e n o m e n a c a n b e f u r t h e r s u b d i v id e d

a c c o r d i n g t o d i f f e re n t ty p e s d e t e r m i n e d b y r e g io n a l, m o r p h o l o g i c a l , g e o lo g -

i c a l o r c l i m a t i c c o n d i t i o n s . F o r t h i s r e a so n , w e a b s t a i n f r o m m o r e d e t a i l e d

c lass i f i ca t ion , a s we rea l i ze tha t we a re no t ab le to cons ide r a l l poss ib le

v a r i a t i o n s .

A n u m b e r o f e x a m p l e s a r e p r e s e n t e d o n l y i n o r d e r t o m a k e c l e a r t h e

p r in c i p le s o f t h e e l e m e n t a r y d i v is io n o f t h e s e p h e n o m e n a . T h e y d o n o t

r e p r e s e n t a n y t h i n g b u t a s e t o f e x a m p l e s o f e l e m e n t a r y ty p e s , k n o w n e s-

p e c ia l ly f r o m E u r o p e .

E a c h p i c t u r e c o n t a i n s a l so a g r a p h i c a l r e p r e se n t a t i o n o f d i m e n s i o n s a n d

v e l o c i t y o f t h e p h e n o m e n o n . T h e e x p l a n a t i o n i n t h e t e x t i s v e r y b r i e f ; i t

e x p l a i n s n o t h i n g b u t t h a t w h i c h c a n n o t b e e x p r e s s e d g r a p h i c a l l y . T h e t e r m s

u s e d a r e p r o p o s e d f o r t h e p r o f e s s i o n a l u s e ; t h e y r e p r e s e n t o n l y a v e r b a l

t r a n s l a t i o n o f t h e Cz e c h t e x t .

E x a m p l e s N o s . 1 - - 9 d e m o n s t r a t e c r e e p ( F i g . 1 ) . N o s . 1 - - 8 a r e e x a m p l e s

o f d ee p - se a te d cr ee p ( N e m ~ o k a n d R y b f i ~ , 1 96 8), N o . 9 is e x a m p l e o f

super f i c i a l c reep .

6*



74 A. N em ~o k , J . Pa~e k, and J. Ryb~i~:

No. 1 - - loosening of the rocks in the val ley slope by cracks paral lel to

the surface. This phenomenon is typical of br i t t le rocks.

No. 2 - - ini t ia l s tage of disturbing of the stabil i ty of the slope by open-

ing of tension cracks in i ts upper par t .

Nos. 3 and 4 - - deep-seated creep grading into sl iding in the upper par t

of the s lope . I t i s the same phenomenon of ten descr ibed under the old te rms

"Talzu schu b" and "Bergzerrei tgung". I f a geologist f inds a crack in a mo un -

~'-2/-' - l- ,- ~ 4 - ~ - ~

S++,<I

4 5 6

r , - - ~ ~ ~ / / I ' " I .,,---~'/_ ~ - . ~ ~ / ~ . . ~ - _

):~ ,)'15# 1>,[/.11/ /" / / Z /" ---~"-~"-- /~'~'~'~ '

i

7 8 9

^ r - r".qF#7 ~ - . - ! - :

~ 5. -. 2 - £ - -- - - - . . . . .. . . . . . " , " \ x \ \ . \ \ \ \ \ ~ \ x ' \

i

Fig. 1 . Examples Nos. 1- -9 belonging to the group "creep"

Beispiele Nr . 1- - 9 zur Grup pe , ,Kr iechen"

E xemples Nos . 1 - -9 concernan t l e g roupe " f luage"

ta in r idge, he cal ls this phenomenon "Bergzerreigung". I f a civi l engineer

ascer ta ins some deformat ion a t the toe of a s lope , in a foundat ion pi t or

in tunnels, he speaks o f "Talzus chub ". Ex amp le No. 3 is typical of br i t t le

rocks, examp le No. 4 of cleaved ro ck s - - i t is the so-cal led Sackung

( Z i s c h i n s k y , 1 9 6 6 ) .

No. 5 - - par t ly ana logous to the example No. 4 i s gravi ta t iona l folding

observed in coa ly and c layey complexes a long the margins of the Ter t ia ry

basins in Czechoslovakia and in Germany, occuring also in l imestones with

marly inter layers in geosynclinal mountains.



Class if ica tion of Lands l ides and Other Mass Mo vem ents 75

N o s . 6 a n d 7 - - b l o c k - t y p e m o v e m e n t s a l o n g a p r e - e x i s t i n g s u rf a c e o r

p r e - d i s p o s e d z o n e o n a p l a st i c u n d e r l y i n g r o c k . T h e d e v e l o p m e n t o f b l o c k -

t y p e m o v e m e n t s c o n n e c t e d w i t h t h e r o t a t i o n o f t h e b l o ck s is c o m m o n , w h e r e

t h e u p p e r p a r t o f th e s l o p e is m a d e u p o f s o li d r o c k s a n d t h e l o w e r p a r t o f

p la s t i c c l a y s .

N o . 8 - - r e l at i v el y m o r e p l a s ti c r o c k s a r e sq u e e z e d o u t i n th e b o t t o m

o f a n e r o s i o n v a l l e y a n d f o r m a n a n t i c l i n a l v a l l e y .

N o . 9 - - s u p e r f i c i al c r e e p i n t h e z o n e o f s e a s o n a l c h a n g e s ( b e n d i n g o f

b e d s ) .

P i c t u r e s N o s . 1 0 - - 1 3 i l l u s tr a t e s l i d i n g o n a s h e a r s u r f a c e ( Fi g. 2 ). T h r e e

b a s i c t y p e s a r e d i s t i n g u i s h e d a c c o r d i n g t o t h e t y p e o f t h e s l i d i n g s u r f a c e .

N o . 1 0 - - s l i d i ng a l o n g a s i m p l e r o t a t i o n a l s l i d i n g s u r f a c e . T h i s t y p e o f

s l i d i n g i s r a r e l y f o u n d i n n a t u r e ; t h e o r e t i c a l l y i t s h o u l d o c c u r o n l y i n a

h o m o g e n e o u s r o c k w i t h o u t a n y i nt e rn a l a n i s o t r o p h y .N o . 1 1 - - a l a n d s l i d e a l o n g a p l a n a r s l i d i n g s u r f a c e . T h e s l i d i n g s u r f a c e

i s a l i t h o l o g i c o r t e c t o n i c b o u n d a r y o r o n b e d d i n g , s c h i s t o s i t y o r j o i n t i n g .

N o . 1 2 - - a n a n a l o g o u s l a n d s l id e i n s o li d r o c k s ( M i i l l e r , 1 9 64 ) .

N o . 1 3 - - s l i d i n g a l o n g a c o m b i n e d s l i d in g s u rf a c e . T h i s t y p e o f s l i d i ng

c a n b e o f v a r i o u s f o r m s . T h e p i c t u r e s h o w s a c o m b i n a t i o n o f b o t h c y l i n dr i c a l

a n d p l a n e s u r fa c es . I t o c cu r s o f t e n i n h o r i z o n t a l l y b e d d e d a r g i ll a c e ou s , m a r l y

o r c a l c a r e o u s s e d i m e n t s .

N o . 1 4 - - h o r i z o n t a l t r a n s l a t i o n o n a p r e - e x i s t i n g s li d i ng s u r fa c e . T h e

s li d m a s s e s a r e l im i t e d b y p l a n e s u r f a c e s o f d i s t u r b a n c e . T y p i c a l o f th i s c a se

i s t h e e x i s t e n c e o f a n o n - s t a b l e l a y e r o r z o n e a t t h e t o e o f t h e s l o p e . T h i sl a y e r c a n b e b u i l t o f a s o f t o r s t r u c t u r a l l y s e n s i t i v e c l a y . I t c a n b e , h o w e v e r ,

a l s o a p o s i t i o n o f si l ty s a n d p r o n e t o l i q u e f a c t i o n o r a f o ss i l, t e c t o n i c a l l y o r

g r a v i t a t i o n a l l y c o n d i t i o n e d s u r f a c e o f d i s p l a c em e n t . O n t h e c o n t r a r y , h o w -

Symbols used in figures 1 to 4

A = Dim ension of the zone affected by slope moveme nt: 1 - surface dimension; 2 - per-pendicular dimension. The typical dim ensions of individual examples in following draw ings

ar dotted

B = Order of the average velocity of the slope movement: 3 - ram/da y; 4 - m/ hour ;5 - km/ hour ; 6 - 100 kin/h our

Erl~iuterungen zu den Abbildungen 1 bis 4

A = Gr6 geno rdn ung des yon der Han gbew egun g erfat~ten Bereiches: 1 - in Richtun g dergr6f~ten Ausd ehnung ; 2 - in Richtun g vertikal zur Hangoberflfiche. Die Gr6~en ordn unge n,

die im Gel~inde angetroffen wurden , sind punk tiert eingetragen

B = Gr6i~enordnung der durchschnittlichen G eschwindigkeit der Hangb ewe gung en: 3 -mm /Tag-B ereich; 4 - m/Stunde-B ereich; 5 - km/Stun de-Bereich; 6 - 100km/Stun de-Bereich

Notes explicatives pour les Fig. 1--4A = Ordre de grandeur de la zone affect& d'un mouvem ent de pente: 1 - dimension super-

ficielle; 2 - dim ension perpendicu laire. Les dime nsions typiqu es pou r les diff6rents exemplessuivants sont marqudes de points

B = Ordre de grandeur de Ia vitesse moyenne d'un m ouvement de pente: 3 - en mm /jour;4 - en m/h eure; 5 - en km /heure ; 6 - en 100 km /heu re



7 6 A . N e m S o k , J. P a ~ e k , a nd J. R y b ~ ' :

eve r , t h i s zone can be bu i l t o f r e l a t ive ly e l a s t i c rock , concen t ra t ing the hor i -

zon ta l s t re sses . Be ing un lo ad ed b y a cu t t ing , t h is s t r e ss changes in to an ex-

p a n s i b l e e n e r g y i n f l u e n c i n g u n f a v o u r a b l y t h e s t a b i l i t y o f t h e s l o p e .

j

~ / ~ " ~ . ~ . , . - C ~__._ .4 ._ ~--c

14

F i g . 2 . E x a m p l e s N o s . 1 0 - - 1 4 b e l o n g i n g t o t h e g r o u p " s l i d i n g "

B e i sp i el e N r . 1 0 - - 1 4 z u r G r u p p e , , G l e i te n "

E x e m p l e s N o s . 1 0 - - 1 4 c o n c e r n a n t l e g r o u p e " g l is s e m e n t"

15 16

F i g . 3 . E x a m p l e s N o s . 1 S - - 1 7 b e l o n g i n g t o t h e g r o u p " f l o w "

Be i sp i el e N r . 15 - - 17 z u r G r up pe , ,F li et ~e n"

E x e m p l e s N o s . 1 3 - - 1 7 c o n c e r n a n t l e g r o u p e " d c o u l e m e n t "

Pic tu res Nos . 15 - -1 7 i l l us t ra t e f low (F ig . 3 ) . Th i s p roces s inc ludes a l so

so l i f l u c t i o n a n d s l o p e m o v e m e n t s i n q u i c k - c l a y s . T h e g r a p h i c a l i l l u s t r a t i o n

o f t h e se c a se s wo u l d b e v e r y d i f f i c u l t .

No . 1 5 - - f l o wi n g o f s l o p e d e p o s i t s a s a n e a r t h f l o w .

N o . 1 6 - - a d e b r is f lo w ; a m i x t u r e o f w a t e r a n d f r a g m e n t s o f ro c k s ,

b o u l d e r y , s to n y s a n d y o r l o a m y w e a t h e r i n g p r o d u c t s r u n s d o w n s l o p e .



C l as s if i ca t ion o f Lands l i des and O t he r M ass M ovem ent s 77

N o . 1 7 - - a s u p e r f i c ia l f lo w , a f f e c t i n g t h e s u p e r f i c i a l la y e r s o f s o il s o n

e v e r y m o r e i n c l i n e d s l o p e a f t e r a p e r i o d o f t h a w i n g .

T h e l a s t g r o u p , n a m e l y fa ll s, i n c lu d e s s lo p e m o v e m e n t s p r e d o m i n a n t l y

i n t h e m o u n t a i n s ( Fi g. 4 ) .

\ : ) " . • . . [ -

~ ! ~ . _ / /

. ¢ 1 / i n

2 1 , . ' ; ~# ' i / \

d ~ t ( ~ \ \ ~ </ Z \ . . . x . \

Fig. 4. Exam ples Nos. 18 --21 belonging to the group "fall"Beispiele Nr. 18--2 1 zur Gruppe , ,Fallen"

Exem ples Nos. 18- -21 concernant le groupe "& roulement"

N o . 1 8 - - s u d d e n d i s p l a c e m e n t o f sm a l l f r a g m e n t s b y ro l li n g d o w n -

s l o p e - - a p r o c e s s a n a l o g o u s t o s t o n e f a l l i n re l a t iv e l y s o f te r r o ck s . F o r

i n s t an c e i n y o u n g m o u n t a i n s e x p o s e d t o i n t e n s e m e c h a n i c a l w e a t h e r i n g t h e

l o o s e n e d r o c k f r a g m e n t s r o l l d o w n s l o p e , w h e r e a l a b i l e t a l u s i s f o r m e d .

N o . 1 9 - - s t o n e f a ll , o c c u r i n g o n s t e e p r o c k y s lo p e s .

N o . 2 0 - - r o c k f a ll ; t h is t y p e o f fa l l o c c u r s m o s t l y in m o u n t a i n s o f t h e

A l p i n e t y p e . I t i s a p u r e c a s e o f f r e e f a l l .N o . 2 1 - - f r e e f a l l c o m b i n e d w i t h t r a n s l a t i o n i n t h e f i rs t st a g e . T h i s

t y p e o f m o v e m e n t o c c u r s m o r e o f t e n t h a n p u r e f r e e f a l l .

T h i s c l a s s i f i c a t i o n i s , o f c o u r s e , o n l y g e n e r a l . W e p u b l i s h i t a s a b a s i s

f o r e n c o u r a g i n g f u r t h e r d i s c u s s i o n w h i c h s h o u l d l e a d t o t h e c o m p i l a t i o n o f a

d e t a i l e d c l a s s i f i c a t i o n s c h e m e . T h i s c l a s s i f i c a t i o n s h o u l d i n v o l v e a l l k n o w n

p h e n o m e n a i n o u r f i e l d a n d l a s t b u t n o t l e a s t m a k e p o s s i b l e a l s o t h e c l a s -

s i f i c a t i o n o f a l l s p e c i a l c a s e s o f r e g i o n a l o c c u r e n c e .

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logii i metodiki issledovanij, 1, Moskva, 82- -100 (1963) .

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Ingenieurgeologie, Vol . II, 3-4, 148--212 (1964).

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logy, Prague, 183- -19 8 (1968).

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157--160 (1966) .

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Prag: Verlag der Tsch. Ak. der Wiss. (1961).Z ~i r u b a , Q. , and V. M e n c l : Lands l ides and the i r Co nt rol . A m ste rd am --

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A ddres s o f t he au thor s : D oc . D r . A rno l d N e m ~ o k , C Sc ., S l ovak Techn i calUniversi ty, G ottw ald ov o n~im. 2, Brat is lava, (2SSR. Ing . J a ros l av P aS ek , C S c . andIng. Jan Ryb~i~, CSc. , Geologica l Ins t i tu te of Czechos lovak Academy of Sciences ,Bo~nl II /1401, P rah a 4 -- Spo~ilov, CSSR.

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