This document discusses different types of water erosion and slope processes. It describes four main types of water erosion: 1) splash erosion caused by rain drop impact, 2) sheet erosion where a thin layer of water flows overland carrying soil particles, 3) rill erosion where small channels are formed by flowing water, and 4) gully erosion where rills deepen into trenches. It also discusses various mass wasting processes including creep, falls, topples, flows, slides, and landslides, which involve downslope movement of soil and rocks under gravity. Mass wasting ranges from very slow to very rapid downslope soil and sediment movement.

1. Unit 4

2. SLOPE PROCESSES

3. 3
Types of Water Erosion
1. Splash Erosion
2. Sheet Erosion
3. Rill Erosion
4. Gully Erosion

4. Splash erosion
 This kind of erosion is caused by the impact of rain
drops striking the ground surface (rain splash).
 It can be takes place in two steps.
1 as initial precipitation is absorbed by the ground
surface, it fills the pore space, loosening the soil
particles and moving them apart.
2 the impact of subsequent rain drops hitting the surface
splash and sends sand and other types of particles of
the soil away from the point of impact.

5. Raindrop Erosion
This is where
it starts
 Rain drops
act as
bombs
 They
dislodge
soil
particles
and allow
for
transport
Photo credit USDA NRCS

7. 7

8. Overland flow and sheet
erosion
 Over land flow: water runoff across the
ground surface.
 Sheet erosion is the detachment of soil particles
by raindrop impact and their removal down-slope by
water flowing overland as a thin sheet.
 As the velocity of overland flowing water increases,
additional soil particles are detached and transported
causing sheet erosion.
 thin layer of water flowing across the surface referred to
as “sheet flow”.

9. Sheet Erosion
 The water moves in
broad sheets over the
land and is not
confined in
concentrated flow
paths.
Photo credit NRCS Bourbonnais

10. 10
Sheet
Erosion

11. Does not occur over long lengths of
time; it quickly goes to rill and gully
erosion.

12. Rill erosion
 Rill –a small channel …………
 Rills are formed by the minute stream of
water cutting separate flow channels.
 Rill erosion refers to the development of
small, ephemeral concentrated flow paths
which function as both sediment source and
sediment delivery systems for erosion on
hillslopes.

13. 13
Photograph of rill erosion
RILL EROSION

14. Gully erosion
 Rills that continue to receive concentrated flows can
eventually turn into gullies of varying widths and depths.
 Gullies are Steep-sided trenches formed by the
coalescence of many rills.
 The distinction between a rill and a gully is one of
depth.
 A gully is sufficiently deep that it would not be obliterated
by normal tillage operations, whereas a rill is of lesser
depth and would be smoothed by use of normal tillage
equipment.

15. 1. Raindrop erosion
2. Sheet erosion
3. Rill and gully
erosion
4. Streambank and
bed erosion

16. 16
Stages in Erosion &
Sedimentation
1.
Detachment
2. Transport 3. Deposition

17. Colluvium
The loose, unconsolidated earth materials that
accumulate at the base of hillslopes by the processes of
sheet erosion, splash erosion and slow continuous
down-slope movements of rock particles or a variable
combination of these process is colluvium.
It is a heterogeneous mixture of earth materials ranging from silt to
larger rock fragments of various sizes.
Colluviation: the process of building up
of colluvium at the base of a hillslope.

18. Mass
Movements
/Wasting

19.  The downslope transfer of material through
the direct action of gravity
Mass
Wasting

20.  Mass wasting is the process of down- slope
movement of rock debris and soil mainly under the
influence of gravity.
 This process may be slow and gradual or very
rapid.
 Mass wasting is a process of erosion and here the
agent involved is gravity.
 Gravity is considered as a passive agent therefore it
requires no medium for its erosive action.

21. Angle of repose is the
natural angle at which a granular material,
such as sand or gravel, will rest without
slipping.
 The forces of gravity and friction are in
balance at the angle of repose.

22. Angle of Repose Varies for Different Materials

24. A
A
R
R

25. What are they?
On the basis of the nature of
movement involved, Mass
movements include:
Landslides
• Rock falls
• Avalanches
• Mud flows
• Debris flows
• Creep
. topples

26. Creep
 Creep is the slowest form of mass
movements.
 The process of creep along slopes cannot
be monitored in a short interval of time and
is undetectable by the eye.
 The slow down-slope movement of soil and
regolith is termed soil-creep or solifluction.

28. Falls
 Rapid mass movements.
 Falls are abrupt movements of masses of
geologic materials , such as rocks and
boulders that become detached from steep
slopes or cliffs.
 Falls are further subdivided into rock fall,
debris fall, etc., based upon the type of rock
materials involved.

29. Rock Falls

31. Topples
 Toppling movements are characterized by
the forward rotation of a rock unit or rock
unit about some pivotal point, located below
or low in the unit, under the action of
gravity and forces exerted by adjacent units
or by fluids in cracks.

33. Flow
 Rapid movement.
 Mixture of rocks, mud, &
water.
 Moves as a viscous fluid
 Based upon the type of
rock materials…..flows
are included….debris
flows, mud flows, earth
flows etc.,

34.  Subsidence:- is the another type of mass
movement.
 it is the direct sinking or lowering of a mass of earth
material below the surrounding ground level.

36. Slides
 Slides are down-slope movement of
coherent block of earth material
 The movement take place along a clear-cut
or distinct surface of detachment that
separates underlying stationary material
from the moving mass of rock material
above.

37.  Slides can be either (a ) translational slide or
(b) rotational slide

38. Land-Rock Slide

40. Rotational landslide

41. Slump
 Slow to rapid movement
 Slumps are rotational slide,
Material moves as a coherent
unit along a curved surface
(spoon-shaped)
 Blocks of material rotate..

42. Landslide
 The term “landslide” describes a wide
variety of processes that result in the
downward and outward movement of slope-
forming materials including bedrock,
regolith, soil, artificial fill, or a combination
of these.
 The materials may move by falling,
toppling, sliding, spreading, or flowing.

43. Avalanches
 Avalanches is the another type of mass
movement where the downward moving
mass of material comprises mostly of snow
and ice.
 This type of mass movement occurs along
mountain slopes especially in cold countries
and at high mountain altitudes covered with
snow is known as avalanche.

44. thanks