676 
most common movement of this type is the ro 
ck fall. The size of the fallen blocks may 
reach up to tens of metres, whereas the in 
volved area may reach up to hundreds of me 
tres. "Usually rock falls are small but they 
occur at extremely high velocity and thus 
are capable of damage or to generate fairly 
large moves" (Schuster, 1978). 
2 RECOGNITION OF MASS MOVEMENT FROM AERIAL 
PHOTOGRAPHS 
Without any doubt the interpretation of ae 
rial photographs is one of the most promi 
ssing methods in recognition the mass move 
ments, especially the large scale aerial ph 
otographs. 
M a ny mass movement phenomena can not be 
recognized in the field without the help of 
aerial photographs, specially when they are 
old, inactive and big enough that the limits 
can not be seen. 
The main procedure for recognition of mass 
movement from aerial photographs is to look 
for the three main parts of it (fig.1), whi 
ch are : 
1. The root area or the crown (scarp area). 
2. The tongue area (displaced materials). 
3. The toe. 
The recognition becomes more difficult wh 
en these parts are already removed or flatt 
ened by erosion processes. On the other hand 
the recent and active phenomena are easily 
recognizable, because the morphology often 
reflects the occurance of mass movement ph 
enomena by an irregular slope form which is 
not in harmony with the surroundings. 
Another difficulty arises in recognition 
of mass movement phenomena when the moved 
mass is very large and old that it might be 
missed and explained as another geological 
process such as faults. 
The clues which could be observed from ae 
rial photographs in mass movement recogni 
tion are: 
1. Existance of cracks on steep slopes 
(when big enough). 
2. Hummocky slopes. 
3. Erosion front in the foot of a steep 
slope which faces stream. 
4. Existance of bulges in the foot of sl 
opes. 
5. Existance of steep scarps on a slope. 
6. Existance of concave or spoon-shaped 
slope. 
7. Existance of accumulated mass at the 
bottom of a steep slope or cliff. 
8-.- Steep slope having large mass(es) of 
loose soil and rock (Varnes, 1978). 
9. Steep break(s) in a slope giving it a 
steeped shape. 
10. Existance of ponds on slopes. 
11. Narrowing of a valley which faces a 
steep slope and has no apparent relation 
with underlying bedrock. 
12. Changes in the direction of a valley 
in arch shape, facing the instable slope wi 
th a clear widening of the valley, both be 
low and above the arched section. 
13« Assymetrical valley with active eros 
ion on the steeper side. 
14. Internal drainage on slope. 
15. Existance of highly saturated areas 
which show a different tone on slopes 
(Nossin, 1973). 
16. Seepage zones (Harold & Taliang, 1978). 
17. Sudden change in valley gradient. 
18. Accumulation of scree on slopes. 
The existance of only one of the above 
Mam scarp t CROWN I 
Zant af dtprtsu,. 
Figure 1. Showing details of mass movement 
(after George F. Sowers and David L. Royster). 
mentioned clues can not be taken as indica 
tion for recognition of movement because it 
may indicate another process. Usually few of 
the clues have to exist for confirming a ki 
nd of movement, which is finally to be pro 
ved by adequate field check. (The amount of 
the movements also can be estimated from ae 
rial photographs by observing the offset of 
any linear feature, Zaruba & Mencl, 1969). 
3 CAUSES OF MASS MOVEMENT 
Although there are many causes for the mass 
movements, only those which can be recogni 
zed from aerial photographs are listed bel 
ow : 
3.1 Geological conditions: 
Peletic rocks when are overlain by thick co 
mpetent rocks and are situated on steep slo 
pes tend to behave as a lubricating surface 
below the competent rocks. 
Fine grained clastic rocks, poorly conso- 
lidated 
with har 
ly to gi 
1950). 
Such c< 
recogniz« 
cause cai 
3.2 Weatl 
Rocks lo< 
speciall; 
eases th< 
this leac 
ure and < 
and inte] 
er the m< 
Weathea 
photograj 
3.3 Vege 
It is v/e. 
eases th> 
ver prov 
slides ai 
(Prandih: 
thors be! 
stabilise 
gle of r 
tion is i 
barren f: 
The ro 
the stab 
they pla; 
during p< 
also mig 
overload 
Change 
ved from 
tionship 
mined in 
3.4 Huma 
Some mas 
ities 11 
of slope 
tation, 
observed 
graphy i 
3.5 Tect 
Any sudd 
activity 
especial 
uilibriu 
reason. 
Obviou 
from aer 
any mass 
faulted 
ering of 
4.PREDIC 
Aerial p 
differen 
erpretat 
work is 
activiti 
er the p 
ment has 
with gre