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Edexcel IGCSE Geography 復習筆記 1.2.1 Fluvial Processes

Category: IGCSE課程, 國際課程, 教材筆記, 福利干貨 Date: 2022年7月22日下午3:56

Edexcel IGCSE Geography 復習筆記 1.2.1 Fluvial Processes

Weathering & Mass Movement

River valley processes

Both?fluvial?and landscape processes shape the river and surrounding land in the drainage basin
The landscape processes of?weathering?and?mass movement?shape land surrounding the river channel
Fluvial processes shape the river channels and the landforms linked to them. They include:
- Erosion?
- Transportation
- Deposition
Most (about 95%) of a river's energy is used in overcoming friction
There is more friction in the upper course of the river where it is shallow and narrow
The rest of the energy is used in erosion and transportation
Energy in the river depends on the river discharge and?velocity

Weathering?and mass movement

There are three types of weathering. These happen?in-situ:
- Physical?- rock is broken down into smaller pieces. This occurs due to changes in temperature - such as?freeze thaw?and?exfoliation
- Chemical?- rocks disintegrate and dissolve in slightly acidic rainwater
- Biological?- rocks are broken apart by the roots of plants
There are a number of types of mass movement where large scale movement of material occurs
In river valleys there are two main types of mass movement:
- Slumping?- where the slope is eroded by the river. This undercuts the slope causing large scale movement of material down the slope
- Soil creep?- the influence of gravity causes weathered material to slowly move down the slope towards the river

Factors affecting weathering and mass movement

Factor	Effect
Climate?	In hot, wet climates, chemical and biological weathering are dominant
Weather	Heavy rain increases mass movement
Slope	Any slope over 5o experiences mass movement. The steeper the slope, the more mass movement there will be
Geology	Different rocks have different levels of resistance to weathering
Altitude	At higher altitudes, freeze-thaw weathering occurs frequently due to the low temperatures
Aspect	Physical weathering is more common on a colder, north facing slope due to a higher likelihood of freeze-thaw
Vegetation	Roots bind the soil together which limits mass movement

Worked Example

Explain two factors which influence mass movement (4)

Identify the command word
The command word is 'explain'
The focus of the question is 'mass movement'
You can select any?two?factors from climate/weather, geology, vegetation, slope, altitude or aspect
For the second mark for each factor you must explain why it increases or decreases mass movement

Answer?

- All slopes which have a gradient of more than 5^o?experience mass movement (1). The steeper the slope, the more mass movement (1)
- Where rock types are less resistant to weathering (1), there will be more mass movement as there will be more loose material (1)
- Vegetation decreases the amount of mass movement (1) as the roots bind the soil together holding the slope in place (1)
- On the north facing slopes there will be more physical weathering (1) leading to more mass movement as there will be more loose material (1)
- At higher altitudes freeze-thaw weathering may be more common (1) ?leading to more mass movement as there will be more loose material (1)

Exam Tip

Students often confuse weathering and erosion. Remember, weathering is the physical, biological or chemical breakdown of the rock where it is located - 'in-situ'. Erosion is the wearing away and movement of the material, usually by wind, water or ice.

The Process of Erosion

Erosion is the wearing away of surfaces
There are four erosion processes which change the shape of the river channel:
- Hydraulic action
- Abrasion
- Attrition
- Corrosion (solution)

types-of-erosion
Types of erosion

Erosion can be mainly vertical or lateral:
- Vertical erosion?is dominant in the upper course of rivers. It increases the depth of the river and valley, as the river erodes downwards
- Lateral erosion?is dominant in the middle and lower course of rivers. It increases the width of the river and valley as it erodes sideways

Processes of Transportation & Deposition

There are four processes of transportation:
- Traction
- Saltation
- Suspension
- Solution

Processes of Transportation

Deposition

When a river does not have enough energy to carry materials it drops them. This is deposition
The causes of reduced energy include:
- Reduced discharge due to a lack of precipitation or?abstraction?upstream
- Decreased?gradient
- Slower flow on the inside of a river bend
- When the river enters a sea/ocean or lake
The heaviest material is deposited first, this is known as the?bedload
The lighter materials, gravel, sand and silt are known as?alluvium?and they are carried further downstream
The dissolved materials are carried out to sea

Exam Tip

It can sometimes help to remember a word and the process it refers to if you know what the word means.

Traction - the action of pulling something over a surface

Saltation - leaping or jumping

Factors Affecting Processes

Factors	Impact on Processes
Climate	Heavy rainfall and/or low temperatures leads to higher discharge which increases erosion and transportation; below average rainfall and/or high temperatures lead to lower discharge and decreased erosion and transportation
Slope	Rivers on a steep slope will be fast flowing and there will be increased erosion; gentle slopes will result in more deposition
Geology	Softer, less resistant rocks erode more rapidly than harder, more resistant rocks
Altitude	Melting snow and ice increase discharge and therefore erosion and transportation
Aspect	South facing slopes have higher rates of evaporation and transpiration which decreases discharge