677 
ain scarp ( CROWN ) 
Minor scarp 
\ 
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\ 
Zpnt 0/ dtprtuiti 
Zon, ./ 
bu Iging 
rit 
rip pit 
3S movement 
Ld L. Royster). 
i as indica- 
t because it 
sually few of 
firming a ki- 
{ to be pro- 
ie amount of 
ated from ae- 
le offset of 
icl, 1969). 
for the mass 
be recogni- 
listed bel- 
by thick co- 
an steep slo- 
ting surface 
aorly conso- 
lidated soils and pelitic soils interbedded 
with hard rocks (flysch) are extremely like 
ly to give rise to mass movements (Terzaghi, 
1950). 
Such combination of rocks can be easily 
recognized from aerial photographs, hence the 
cause can be known. 
3.2 Weathering: 
Rocks loose their cohesion due to weathering, 
specially mechanical weathering which incr 
eases the possibilities of water penetration, 
this leads to an increase of the pore press 
ure and consequantly decreases the cohesion 
and internal friction angle. This will trigg 
er the movements on slopes. 
Weathering phenomena are visible in aerial 
photographs of large scales only. 
3.3 Vegetation: 
It is well known fact that vegitation incr 
eases the stability of slopes, as plant co 
ver provides protection against surficial 
slides and erosion (Cotechia,1978). However 
(Prandini et.al. 1977) declear that some au 
thors believe that deforestation helps to 
stabilise slopes. Others believe that the an 
gle of repose of a slope covered by vegita 
tion is 60 but it decreases to 36 when is 
barren from vegetation. 
The roots of plants play role in keeping 
the stability of slopes, on the other ftand 
they play role in désintégration of materials 
during penetration. The weight of large trees 
also might disturb the equilibrium due to 
overloading of slopes. 
Changes in vegetation can be easily obser 
ved from aerial photographs, but their rela 
tionship with mass movements has to be deter 
mined in the field.. 
3.4 Human activities: 
Some mass movements occur due to human activ 
ities like quarrying excavations, terracing 
of slope for agricultural purposes, defores 
tation, blasting etc., such factors can be 
observed on aerial photographs if the photo 
graphy is made after ward. 
3.5 Tectonic activities: 
Any sudden change of slopes due to tectonic 
activity like fault may lead to mass movement, 
especially when the slope is in critical eq 
uilibrium and can be triggered due to any 
reason. 
Obviously faults can be easily recognized 
from aerial photographs, hence the cause of 
any mass movement phenomenon which occur in 
faulted area may be explained due to trigg 
ering of the fault. 
4.PREDICTION OF MASS MOVEMENT 
Aerial photographs help in the prediction of 
different types of mass movement. Their int 
erpretation before starting any engineering 
work is highly reccomended. Construction 
activities for engineering works can trigg 
er the potential areas and as soon as move 
ment has started they can be stopped only 
with great difficulties and high costs. 
Prediction of mass movement from aerial 
photographs can be done by observing the 
following clues (1-9), but it can't be esti 
mated when they will start to move, since 
they may never move: 
1. Cracks on steep slopes, when big enough 
to be visible on the photographs. 
2. Thick colluvial soil on steep slopes. 
(Gray et. al. 1977). 
3. Clear bedding planes dipping towards 
the slope. (Barton, 1977). 
4. Highly saturated areas and seepage zones. 
5. Old mass movement areas. 
6. Active erosion at the foot of slopes. 
7. Areas showing disturbed vegitation. 
8. Hummocky surfaces. 
9. Small depressions on slopes. 
The author believes that most of the above 
mentioned clues are recognizable from aerial 
photographs, but it is neccessary to remined 
that the existance of one of the mentioned 
cues must not be considered as a certain in 
dication for prediction of mass movement. 
5 DATING AND ACTIVITY OF MASS MOVEMENT 
The age of the mass movement can be estima 
ted from aerial photographs; approximately 
by recognizing few aspects which are ment 
ioned below (E.-E,), whereas the activity of 
the movement i.e. wether it is active or not, 
recent or old can be known adequately, spe 
cially in large scale photographs (1:3 000 
and larger): 
5.1 Vegetation 
The age of trees or shrubs can be estimated 
from their heights, which can be measured 
from aerial photographs, hence the age of 
the tree which occur on the movement area 
indicates, roughly the age of the movement. 
Comparision between the age of the trees, 
which occur on the movement area and the 
surroundings, also indicates the age of the 
movement. 
5.2 Erosion 
Erosion processes indicate the activity of 
the movement only. These easily can be ob 
served from aerial photographs, hence jthe 
activity of the phenomenon can be known, 
which is very important in planning differ 
ent human activities. 
5.3 Human activities 
Recent and activé mass movement areas are 
usually abandoned from human activities, Re 
cognition of abandoned houses, roads, farms, 
quarries etc. may indicate and lead to a ro 
ugh estimation of the movement. Obviously 
such recognitions are easily done from aer 
ial photographs, especially recently photo 
graphed photographs. 
5.4 Recognition of sedimentation processes 
If any movement is covered or taken place 
by/in terrace, alluvial fans, colluvial dep 
osits etc. then the estimation of the age of 
the sedimentation processes indicates, roug 
hly the age of the movement. But the estima 
tion of the age must be done very carefully,