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Processes and Causes of Degradation

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Higher Geography: Applications Rural Land Degradation Processes and Causes of Degradation Positive wind effects Pollination Reduce humidity in canopy - reduce disease ... – PowerPoint PPT presentation

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Title: Processes and Causes of Degradation


1
Processes and Causes of Degradation
  • Higher Geography Applications
  • Rural Land Degradation

2
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

3
Human Causes of Soil erosion
  • Using table 2.1 on p.70. Answer the following
    questions.
  • What is the largest human cause of soil erosion?
  • What continent is the most affected by human
    activities on soil erosion.?
  • Which continent do human activities have the
    least impact on soil erosion?
  • What human activities are LEDCs mostly affected
    by?
  • What human activities are MEDCs mostly affected
    by?

4
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.

5
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.

6
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.

7
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.

8
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.

9
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

10
Chemical Action (2)
  • Soil contamination can also occur through
  • acid rainfall
  • the dumping of hazardous industrial waste
  • overuse of fertilisers and pesticides

11
Your Turn
  • Using textbook p.70 and p.71
  • Answer Q. 1b and 2.

12
Soil Erosion by Water
13
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.

14
COPY DIAGRAM LEAVE ENOUGH ROOM FOR ANNOTATIONS
15
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.

16
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
17
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18
RAINSPLASH
19
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.

20
SHEETWASH
21
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.

22
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23
GULLY EROSION
24
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.

25
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26
Soil Erosion by Wind
27
WIND EROSION
  • Most common in arid or semi-arid areas.
  • What conditions do you think encourage this?
  • Loose, dry and finely grained.
  • Relatively flat land
  • Little or no vegetation
  • Large fields
  • Strong winds

28
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

29
Mechanisms of wind erosion
Suspension
Wind
Saltation
Creep
30
Light areas show where topsoil has been eroded.
Deposition of topsoil along fence lines.
31
Dust Bowl - US 1920s-30s
32
Effects of wind on plants
  • Includes
  • Stunted growth -wind pruning
  • Physical damage - especially if carrying sand
    particles (tall plants may be flattened)
  • Transporting pests

33
Wind pruning
Prevailing wind
34
Positive wind effects
  • Pollination
  • Reduce humidity in canopy - reduce disease
    potential

35
Your Turn
  • Read page 67 - 69 from the applications book.
  • Answer questions 5 8 on page 69..
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