Processes and Causes of Degradation

Higher Geography: Applications

Rural Land 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 :PhysicalBiologicalChemical

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 replacedthe soil become less able to support plantsthe organic content of the soil is reducedits structure is loosened and more easily removed by rain and wind

Chemical Action (2)

Soil contamination can also occur through :

acid rainfallthe dumping of hazardous industrial wasteoveruse of fertilisers and pesticides

Your Turn

Using textbook p.70 and p.71Answer 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 DIAGRAMLEAVE ENOUGH ROOM FOR ANNOTATIONS

Soil erosion3 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 2.7p. 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.Loose, dry and finely grained.2.Relatively flat land3.Little or no vegetation4.Large fields5.Strong winds

• Loss of topsoil in one area

• deposition of material in another area where it can:

• form topsoil

• clog waterways

• cause air quality problems

Wind erosion has two types of impacts:

Suspension

SaltationCreep

Wind

Mechanisms of wind erosion

Light areas show where topsoil has been eroded.

Deposition of topsoil along fence lines.

Dust Bowl - US 1920’s-30’s

Includes: •Stunted growth -wind “pruning”

•Physical damage - especially if carrying sand particles (tall plants may be flattened)

•Transporting pests

Effects of wind on plants

Reduce crop yields and/or quality

Prevailing wind

Wind pruning

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..