1. SLOPE,
PROCESSES &
DEVELOPMENT
Lesson 8

2. SLOPE
 A small strip or patch of the land surface
that is inclined from the horizontal
 is mantled with regolith, which grades down
into, unaltered rock called bedrock
 Regolith provides the source f sediment,
which consists of rocks and mineral particles
 Soil and regolith blanket the bedrock, except
in a few places where bedrock is particularly
hard projects in the form of outcrops

5. Slope Models
1. Convex slope segments
2. Concave slope segments
3. Rectilinear slope segments

6. Convex slope segments
 Form on the upper parts of slopes
 Inresponse to soil creep and rain
splash
 When slopes are below the
threshold for rapid mass wasting

8. Concave slope segments
 Slopesegments that form near the base
of slopes
 Inthe absence of removal waste (e.g.
river downcutting)
 With increasing run off
downslope, velocity and sediment
transport can be maintained over
increasingly lower slope

11. Concave or convex?

12. Concave or convex?

13. Rectilinear Slope segments
Straight section of a profile
May develop on uniform rock
type where there is only very
thin covering debris

15. Factors controlling slope
form and development
1. Climate
2. Geological structure
3. Nature of regolith
4. Vegetation

16. Climate
 Different processes operate in different climate
zones and produce different slope forms and shapes
 Humid areas – slopes are frequently rounded due to
chemical weathering
 Arid region – slopes are jagged or straight owing to
mechanical weathering and sheetwash
 Heavy rain and meltwater both add volume and weight
to the soil  increases erosive power  make slope
less stable
 Heavy snowfall add weight  conducive to rapid
movement (Avalanche)

19. Geological structure
Rock type
affect
vulnerability to
weathering 
resistant
to down
slope
movement

20. Nature of the regolith
 Includes soil, scree, weathered bedrock and deposited
material.
 Unconsolidated nature  prone to downslope movement
 Increase weight of deep regolith will increase the
likelihood of instability
 Clay rich regoliths – unstable because the ability to retain
water
 In a non saturated soil- increases cohesion and reduce
soil movement
 In saturated soil – the pore water pressure forces the
particle apart, causing soil movement

24. Vegetation
 Can decrease
overland run off
 Lack of vegetation
means there are
fewer roots to bind
the soil together

25. How do we get slope failure?
 When the
gravitational
force acting on
a slope exceeds
its resisting
forces, slope
failure (mass
wasting occur)

26. What is a shear strength?
 The resisting forces that help to
maintain slope stability include the slope
material’s strength and cohesion
 The amount of internal friction between
grains and any external support of the
slope known as shear strength

28. How does the force gravity
resulted in slope failure?
 Gravity operates vertically
but has a component acting
parallel to the slope causing
instability
 The steeper the slope angle
the greater the component of
force acting parallel to the
slope and greater the chances
for mass wasting

30. Define angle of repose
 The steepest
angle that a
slope can
maintain
without
collapsing
 Angle of
repose for
unweathered
solid rock
steeper than
40 degrees

31. What does it mean by “when a
slope is in a constant state of
dynamic equilibrium”?
Means that they
are constantly
adjusting to new
conditions