Geography presentation of fold moutains in kenya

LESSON 2: FLUVIAL PROCESSES AND LANDFORMS
1

Fluvial processes refer to the geological processes
related to the flow of water, particularly in rivers and
streams, and their effects on the landscape.
Fluvial processes play an essential role in the denudation
of land surfaces and the transport of rock detritus from
higher to lower levels.
Key fluvial processes include;
2

EROSIONAL PROCESSES
Rivers erode in four ways:
a) Attrition
Attrition involves the collision and breaking down of
sediment particles carried by the river.
As these particles interact with each other during
transport, they become smaller and more rounded
through repeated impacts.
3

b) Abrasion
Abrasion occurs when rocks and sediment carried by
the river wear away the riverbed and banks.
This is often a result of the particles in the water
colliding with the riverbed, causing the gradual wearing
down of the substrate.
4

c) Hydraulic Action
This process involves the force of moving water itself.
The pressure and turbulence of flowing water can
dislodge and remove rocks, soil, and sediment from the
riverbed and banks.
It is particularly effective during periods of high water
flow, such as floods.
5

d) Solution or corrosion
In areas where the river water is slightly acidic, certain
types of rocks, such as limestone, can dissolve over
time.
This dissolution process contributes to the overall
erosion of the river channel.s
It involves transportation of dissolved chemicals.
6

RIVERS TRANSPORTATION PROCESSES
River transportation processes involve the movement of
sediment, rocks, and other materials within a river
system.
Rivers transport materials in various ways, influenced by
factors such as water velocity, channel morphology, and
the size of the transported particles.
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Rivers transport material in four ways:
a) Solution
In the solution mode, dissolved minerals and ions are
carried within the water as a solution.
This mode is particularly relevant for soluble substances
like calcium carbonate in limestone.
The water acts as a solvent, gradually dissolving these
materials and transporting them downstream.
9

b) Suspension
Suspension occurs when smaller particles, such as silt
and clay, are lifted and carried within the water column
without direct contact with the riverbed.
These fine particles can remain suspended for extended
periods, especially in turbulent water.
Suspension is a mode of transportation associated with
slower river flows.
10

c) Saltation
Saltation involves the bouncing or hopping movement
of medium-sized particles, such as sand and small
pebbles, along the riverbed.
These particles are lifted and carried by the current
before falling back to the bed due to gravity.
This is a common transportation mode in rivers with
moderate flow.
11

(d) Traction
In traction, the largest and heaviest particles are rolled
or dragged along the riverbed by the force of the
flowing water.
This mode of transportation is more common during
periods of high flow or flood events when the river has
enough energy to move large rocks and boulders.
12

Rivers Transportation Processes
13

RIVERS DEPOSITION PROCESS
River deposition is the process by which rivers and
streams deposit sediment, rocks, and other materials
that they have eroded and transported downstream.
Deposition occurs when the energy of the flowing water
decreases, causing it to release or deposit the sediment
it was carrying.
Several factors influence the deposition process in
rivers: 14

Reduction in Water Velocity
As a river flows downstream, it may encounter areas
where the water velocity decreases.
This reduction in flow energy can occur due to factors
such as widening of the river channel, decrease in
gradient, or the presence of obstacles.
When the water velocity decreases, the river loses its
ability to transport and carry sediment, leading to
deposition. 15

Losing Competence
The competence of a river refers to its ability to
transport particles of a certain size and weight.
When the river's velocity decreases, it may lose
competence for larger and heavier particles.
As a result, these particles settle and accumulate on the
riverbed.
16

Channel Friction
Friction between the flowing water and the river
channel can slow down the water, causing deposition.
This is particularly evident in areas with irregularities in
the channel, such as meanders or sudden changes in
slope.
17

Lateral Erosion and Bankfull Stage
During periods of high flow, rivers may erode their
banks through lateral erosion.
As the riverbanks are eroded, sediment is transported.
When the river returns to its normal or bankfull stage,
it may deposit some of the transported sediment along
the banks and floodplain.
18

Mouth of the River (Deltas)
Rivers often deposit sediment at their mouths, forming
features known as deltas.
Deltas are triangular-shaped landforms created when
rivers empty into oceans, seas, or lakes.
The decrease in water velocity as the river meets a
larger body of water causes sediment to settle and
build up, creating delta formations.
19

Floodplains
During periods of flooding, rivers can deposit large
amounts of sediment on their floodplains.
Floodplains are low-lying areas adjacent to rivers that
receive sediment deposits during floods.
The sediment deposition contributes to the development
and fertility of floodplain soils.
20

Features of Fluvial Processes
a) Upper course of a river
In the upper course of a river gradients are steep and
river channels are narrow.
Vertical erosion is greatest in the upper course of a
river.
As the result of this typical features include V-shaped
valleys, interlocking spurs, rapids, gorges and
waterfalls. 21

b) Middle course of a river
The middle course of a river has more energy and volume than
in the upper course.
The gradient is gentler and lateral (sideways) erosion has
widened the channel.
The river channel has also become deeper.
U-shaped valleys and Meanders are typical landforms found in
this stage of the river.
A meander is a winding curve or bend in a river.
25

They are typical of the middle and lower course of a
river.
This is because vertical erosion is replaced by a
sideways form of erosion called LATERAL erosion,
plus deposition within the floodplain.
26

c) Lower course of a river
The volume of water in a river is at its greatest in the
lower course.
This is due to the contribution of water from tributaries.
The river channel is deep and wide and the land around
the river is flat.
Energy in the river is at its lowest and deposition occurs.
Features associated with old stage of a river include;
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Well-developed floodplain
Meanders
Meander scars
Oxbow lakes
Levees
Meander scars
Cutoffs
Deltas
estuaries 28

ASSIGNMENT (WHICH REQUIRES NO SUBMISSION)
In the context of river geomorphology, how does the
character of sediment transport change as a river
progresses from its upper course to its lower course,
and what specific landforms are associated with each
stage.
29

CHAPTER 3: AEOLIAN PROCESSES AND LANDFORMS
Aeolian processes, involving erosion, transportation, and
deposition of sediment by the wind, occur in a variety of
environments, including the coastal zone, cold and hot
deserts, and agricultural fields.
Common features of these environments are a sparse or
nonexistent vegetation cover, a supply of fine sediment (clay,
silt, and sand), and strong winds.
Aeolian processes and the associated landforms: 30

AEOLIAN PROCESSES
Suspension
Fine-grained particles, such as silt and clay, are lifted into
the air and transported over long distances by the wind.
Suspended particles can remain airborne for extended
periods, traveling with the wind at various altitudes.
This process is particularly effective in regions with
relatively low wind speeds.
31

Saltation
Small to medium-sized particles, such as sand, are lifted
and bounced along the ground by the wind.
Saltation involves a hopping or skipping motion of
particles on the surface.
It is the primary mode of transportation for sand-sized
grains and is most effective close to the ground.
32

Creep
Larger particles, such as pebbles, may be slowly
moved along the ground through a rolling or sliding
motion.
Creep is a less common mode of transport for larger
particles, and it generally occurs when wind speeds
are not sufficient for saltation.
33

Abrasion
Abrasion, as an aeolian process, refers to the wearing
down and shaping of rocks and surfaces through the
abrasive action of wind-blown particles.
It is a key mechanism through which wind contributes
to the erosion and modification of geological features.
The process involves the impact of wind-carried
particles, such as sand and dust, on exposed surfaces,
gradually wearing away the material over time.
34

AEOLIAN PROCESSES AND LANDFORMS
Deflation hollows and desert pavements
Deflation Hollows: Depressions in the landscape formed by
the removal of fine particles.
Desert Pavement: A surface layer of closely packed, larger
rocks left behind after the finer particles have been
deflated.
Process: The lifting and removal of loose, fine-grained
particles (such as silt and clay) from the ground surface by
the wind.
35

Ventifacts
Ventifacts are geological formations that result from
the abrasive action of wind-blown particles,
typically sand, on exposed rock surfaces.
These are rocks shaped and polished by wind-blown
sand abrasion.
Process: The wearing down of rocks and surfaces by
the impact of wind-blown particles.
36

Zeugens and Yardangs
Zeugens are elongated landforms formed through the
selective erosion of resistant rock layers by wind-driven
sand.
They often have a streamlined, elongated shape,
resembling ridges or low walls.
The direction of elongation corresponds to the
prevailing wind direction 38

Yardangs are streamlined, wind-eroded landforms
carved from soft rock or sedimentary layers.
Yardangs often have a ridge-and-valley morphology,
with elongated ridges separated by concave
depressions.
The ridges align with the prevailing wind direction.
39

Inselbergs
Inselbergs are characterized by their isolated nature,
rising conspicuously from the surrounding landscape.
They are often surrounded by relatively flat or gently
undulating terrain.
The formation of inselbergs is often associated with
erosion and differential weathering.
41

Inselbergs can represent more resistant rock
formations that have withstood erosion while the
surrounding softer rock has been weathered away.
42

Loess Deposits
Loess deposits are widespread accumulations of wind-
blown, fine-grained sediment, primarily consisting of silt-
sized particles.
These deposits are typically loosely compacted and can
form thick layers covering extensive areas.
Loess deposits are known for their high fertility due to
their mineral composition and the presence of nutrients.
43

Sand Dunes
Sand dunes are prominent landforms shaped by the
wind-driven movement of sand.
These dynamic structures are commonly found in arid
and coastal regions where there is an ample supply of
loose sand and prevailing wind directions.
Sand dunes exhibit distinct forms and characteristics,
and their morphology is influenced by factors such as
wind speed, sand availability, and vegetation cover45

Sand Sheet and Sand Ripples:
Sand Sheets: Thin, widespread deposits of sand
covering large areas.
Sand Ripples: Small, short-wavelength ridges or waves
formed on the surface.
Process: Wind deposits thin layers of sand (sand
sheets) and forms small, low-profile sand waves (sand
ripples) on the ground. 48

ASSIGNMENT (WHICH REQUIRES NO SUBMISSION)
In regions with prevalent aeolian processes, such as
desert environments, how does the interplay between
wind-driven erosion and deposition shape the
distinctive landforms observed.
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Next Lecture
CHAPTER 4: COASTAL PROCESSES AND
LANDFORMS
51

Geography presentation of fold moutains in kenya

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