Geomorphic Threshold and Landslide - Semi-quantitative Approaches for Landslide Assessment and Prediction - page 159

100 % certainty. In case of Binomial distribution the 100 % certainty of the major
landslide events are to be expected at the return period of 19 years (Fig. 5.5 ). In the
mountain region physical and anthropogenic processes are active on slope in an
interactive combination. Construction of settlement, road and associated defores-
tation destabilize soil and slope. Slope is steepened, soil becomes loose and friable,
lateral support is removed, soil becomes saturated by hydrological intervention. All
these together lead to instability and threshold condition are achieved. Ultimately
slope failure occurs and that helps to achieve temporary stability (Fig. 5.6 ).

ANTHROPOGENIC
PROCESS

Concentration of
Settlement

Road-cut Bench

Reduction in
soil strength

Plying of vehicles

I
N
S
T
A
B
I
L
I
T
Y

Roof-top & Waste
water disposal

Steepening
of Slope

Deforestation

Increase in
slope length

S
L
I
D
I
N
I
N
G

OR Reduction

Of Slope
Through
Internal
Feedback

EQUILI
BRIUM

Reduction in
lateral and
basal
support

T
H
E
S
H
O
L
D

PHYSICAL
PROCESSES

SLOPE

Increase in
depth of
Saturated of
soil

G
E
N
E
R
A
T
I
O
N

SOIL/DEBRIS

Increase the
depth of soil

Infiltrated
Through
Flow

Soil becomes
loose &
friable

WATER

Reduced
Surface
flow

Fig. 5.6 Homeostatic adjustment through self-organized internal feedback in a complex system of
interaction among physical and anthropogenic process