Processes and Causes of Degradation

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Processes and Causes of Degradation

• Higher Geography Applications
• Rural Land Degradation

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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

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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?

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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.

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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.

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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.

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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.

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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.

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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

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Chemical Action (2)

• Soil contamination can also occur through
• acid rainfall
• the dumping of hazardous industrial waste
• overuse of fertilisers and pesticides

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Your Turn

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

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Soil Erosion by Water
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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.

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COPY DIAGRAM LEAVE ENOUGH ROOM FOR ANNOTATIONS
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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.

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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
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RAINSPLASH
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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.

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SHEETWASH
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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.

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GULLY EROSION
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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.

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Soil Erosion by Wind
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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

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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

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Mechanisms of wind erosion
Suspension
Wind
Saltation
Creep
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Light areas show where topsoil has been eroded.
Deposition of topsoil along fence lines.
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Dust Bowl - US 1920s-30s
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Effects of wind on plants

• Includes
• Stunted growth -wind pruning
• Physical damage - especially if carrying sand
  particles (tall plants may be flattened)
• Transporting pests

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Wind pruning
Prevailing wind
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Positive wind effects

• Pollination
• Reduce humidity in canopy - reduce disease
  potential

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Your Turn

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