1. Topic: Rivers 2
1. Formation of River
Landforms
I. Upper Course:
a) Valleys
b) Gorges Formed by Erosion
c) Waterfalls
II. Middle Course:
a) Meanders Formed by Erosion &
Deposition
III. Lower Course:
a) Meanders
b) Floodplains
Formed by Deposition
c) Deltas
1

2. LANDFORMS FORMED BY EROSION

3. 2.1 A Valley

4. 1. 2. Lateral erosion
River
Hard Rock Hard Rock
3.
V‐shaped
Valley
Hard Rock

5. 2.1 Formation of Valleys
1. River flows over an area of hard rocks.
2. Due to the steep gradient and resistant
rocks, vertical erosion is faster than lateral
erosion.
3. Over time, the river channel deepens by
hydraulic action, abrasion and sometimes
solution.
4. Eventually, a steep‐sided valley is formed.

6. 2.2 A Gorge
A Gorge is an
exceptionally deep and
narrow valley.

7. 1. 2. Vertical erosion > Lateral erosion
River Lateral erosion
Very Hard Rock
Very Hard Rock
3.
Gorge
Very Hard Rock

8. Formation of Gorges (Method 1)
1. River flows through an area of very hard
rocks.
2. Due to the rock hardness and steep gradient,
vertical erosion dominates.
3. Over time, a deep, narrow and steep‐sided
(almost vertical) valley called a gorge is
formed.

9. Side View Front View of Waterfall
1. 2.
Waterfall retreats backwards
Soft
rocks
Hard
rocks
Soft
rocks
3. 4.
Waterfall retreats backwards
A gorge is formed

10. Formation of Gorges (Method 2)
1. As the soft rocks at the base of the waterfall
get undercut by the river water,
2. the tip of the waterfall loses support beneath
and collapses into the water.
3. Overtime, the cycle repeats and the waterfall
retreats backwards
4. leaving behind a deep, narrow and steep‐
sided valley called a Gorge.

11. 2.3 A Waterfall

12. 1. 2.
Soft rock Soft rock
Hard
Hard rock Soft
rock
Soft rock rock
3. 4.
Waterfall
Soft
Soft rock rock
Plunge
Hard rock Hard rock Soft Pool
Soft
rock
rock

13. 2.3 Formation of a Waterfall
1. As rivers flow through bands of hard and soft rocks.
2. Softer rocks gets eroded faster than the hard rocks.
3. This causes the gradient to steepen.
4. Over time, the river plunges from a great height, hitting
the base with great force.
5. This sudden, steep vertical flow of fast moving water
from a great height is called a waterfall.
6. Repeated pounding of the water against the water bed
7. will create a depression at the base of the waterfall called
a plunge pool.

14. LANDFORMS FORMED BY EROSION
& DEPOSITION

15. 2.4 A Meander

16. 1. 2. Deposition
Outer Inner convex (D)
concave bank Erosion
bank (E)
River D
Outer
Inner convex Cliff
concave
bank E
bank
Outer Slip‐off
concave Inner convex D slope
bank bank
3. Separated 4.
Ox-bow
by a narrow
lake
D neck
E D
Legend
Cut-off
Erosion D
Deposition

17. 2.4 Formation of Meanders
1. As a river flows around a bend, river speed is faster on the outer
concave bank.
2. Hence, erosion by undercutting occurs.
3. Over time, a steep‐sided bank called a RIVER CLIFF is formed on the
outer bank.
4. As the river speed is slower on the inner convex bank, deposition
occurs.
5. Over time, a gentle SLIP‐OFF SLOPE is formed on the inner bank.
6. With repeated erosion and deposition, the meander becomes
more and more pronounced, eventually separated by a narrow
neck.
7. Eventually, the river breaks through the neck and flows in a
straight channel.
8. The cut‐off forms an ox‐bow lake.

18. Deposition at the
Erosion on the inner convex bank
outer concave forms a gentle slip‐
bank forms a off slope.
river cliff.

20. Meander
Ox‐bow
lake

21. LANDFORMS FORMED BY
DEPOSITION

22. 2.5 A Floodplain

23. 1. 2.
Heavy and continuous rain, Finer load
river overflows its banks
Coarser
load
3.
Floodplain
Levee

24. 2.5 Formation of Floodplain and Levees
1. After a heavy and long period of rain, the river may
overflow its banks causing a flood.
2. As the water spreads over a larger area, the
friction increases causing the river lose energy and
deposit its load.
3. The coarser and heavier sediments are deposited
on the immediate river banks whereas finer and
lighter sediments are carried further away.
4. Over a series of floods, these layers of sediments
forms a floodplain and the coarser materials that
have accumulated on the immediate banks form
Levees.

25. 2.6 A Delta

26. 1. 2. Land Sea
Land Sea
River River
Distributaries
3. Land Sea
River Delta

27. 2.6 Formation of a Delta
1. When river enters a larger water body such as a
sea, its speed of flow and hence river energy is
reduced. Hence, it starts to deposit its load.
2. At the river mouth, heavier sediments such as
sand is deposit close to the shore whereas lighter
sediments such as silt and clay are carried further
out before being deposited.
3. The layers of deposition at the river mouth block
the flow of water into the sea, hence the river
branches out into smaller streams called
distributaries.
4. Over time, an extensive depositional landform
called a delta is formed at the river mouth.