Higher Geography: Applications
Rural Land Degradation
Processes and Causes
of Degradation
Introduction (1)
RLD is usually the result of unreliable
climate (eg : periods of drought with
occasional heavy rain), combined with poor
agricultural practice.
There are three kinds of action that
commonly lead to land degradation :
Physical
Biological
Chemical
Human Causes of Soil
erosion
• Using table 2.1 on p.70. Answer
the following questions.
1. What is the largest human cause of soil
erosion?
2. What continent is the most affected by
human activities on soil erosion.?
3. Which continent do human activities have
the least impact on soil erosion?
4. What human activities are LEDC’s mostly
affected by?
5. What human activities are MEDC’s mostly
affected by?
Introduction (2)
The impact of human activity on the land
intensifies these three actions,
contributing to accelerated land
degradation.
These human activities include
deforestation, overgrazing (both linked to
population pressure) and poor agricultural
practice.
Physical Action (1)
Physical action can cause the soil to
become more compact - where land is
frequently used by humans (walking,
animal hooves, heavy machinery etc.)
This wear and tear destroys plants
and leaves bare earth open to the
weather and erosion.
Physical Action (2)
Compact soil without vegetation cover
often prevents water from penetrating the
soil, causing run-off at the surface which in
turn accelerates soil erosion.
Extreme physical damage where quarrying
and open-cast mining are found.
Biological Action (1)
Biological action usually takes the form of
removing the living cover of vegetation
(trees, grass etc.)
The removal of vegetation means that less
rainfall can be intercepted. More rain falls
directly on to the soil and it can be washed
away much more rapidly, increasing soil
erosion.
Biological Action (2)
In dry areas of the world, any
removal of vegetation will increase
the power of the wind to cause soil
erosion.
Other biological action can result
from plant diseases or locust attacks.
Chemical Action (1)
Chemical action occurs where farmers
overuse soil, this means that :
minerals are often not replaced
the soil become less able to support plants
the organic content of the soil is reduced
its structure is loosened and more easily
removed by rain and wind
Chemical Action (2)
Soil contamination can also occur
through :
acid rainfall
the dumping of hazardous industrial waste
overuse of fertilisers and pesticides
Your Turn
Using textbook p.70 and p.71
Answer Q. 1b and 2.
Soil Erosion by Water
There are 4 types:
Rainsplash is concerned with the impact of
raindrops on the surface of a soil.
Sheet wash is the removal of a thin, almost
unseen, layer of surface soil.
Rill erosion is the creation of a very small eroded
channels across a soil surface.
Gully erosion is the creation of large gullies by
large quantities of water flowing over the soil
surface.
COPY DIAGRAM
LEAVE ENOUGH ROOM FOR ANNOTATIONS
Soil erosion
3 step process
1. Detachment
- Soil particles detached from the main
body of soil mass.
2. Transportation
- Soil particles carried downhill. Float,
roll or be dragged by water.
3. Deposition
- Deposited in a downhill location 
river bed or sea bed.
Rain Splash
The bigger the raindrop, the faster it
hits the soil.
A drop of rain causes soil to splash.
Gravity causes more particles to move
down than up slope.
Copy diagram 2.7
p. 72
RAINSPLASH
Sheetwash
The rainsplash effect can also clog up the soil,
leading to a form of soil erosion called sheet wash.
The tiny soil particles which are displaced during
rainsplash find their way into soil pore spaces
located between soil crumbs and clog them up.
The result is the formation of a surface crust
(1mm thick), but the rate at which rainwater can
now infiltrate the soil is now reduced.
SHEETWASH
Rill and gully erosion
These are the most serious form of soil erosion by
running water.
Most land surfaces are irregular, with natural
depressions, slopes and channels. A sudden burst
of rainwater, which is unable to soak into the soil
will flow over the surface, finding its way into
natural channels.
Here it will gather in volume, power and speed as it
makes its way down slope. Dislodging and moving
soil particles down slope as it goes.
GULLY
EROSION
The difference between Rill and Gullies
Gullies are steep sided water
channels which carry water only
during rainstorms and , unlike rills,
are a permanent feature on the
landscape.
Soil Erosion by Wind
WIND EROSION
Most common in arid or semi-arid areas.
What conditions do you think encourage
this?
1.
2.
3.
4.
5.
Loose, dry and finely grained.
Relatively flat land
Little or no vegetation
Large fields
Strong winds
Wind erosion has two types
of impacts:
• Loss of topsoil in one area
• deposition of material in another area
where it can:
• form topsoil
• clog waterways
• cause air quality problems
Mechanisms of wind erosion
Suspension
Wind
Saltation
Creep
Light areas show
where topsoil has
been eroded.
Deposition of
topsoil along
fence lines.
Dust Bowl - US
1920’s-30’s
Effects of wind on plants
Includes:
•Stunted growth -wind “pruning”
•Physical damage - especially if carrying sand
particles (tall plants may be flattened)
•Transporting pests
Reduce crop yields and/or quality
Wind pruning
Prevailing wind
Positive wind effects
Pollination
Reduce humidity in canopy - reduce
disease potential
Your Turn
Read page 67 - 69
from the applications
book.
Answer questions 5 –
8 on page 69..