Influences on Landscapes (OCR GCSE Geography B)

Revision Note

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Jacque Cartwright

Written by: Jacque Cartwright

Reviewed by: Bridgette Barrett

Weathering

Geomorphic processes

  • Geomorphic processes are the methods involved in changing the shape of the landscape 

  • The Earth's surface is continually being made, destroyed and reformed

  • This is achieved through various methods of erosion, weathering, mass movement, transportation and deposition

Weathering

  • Weathering is the break-down of rock in its place of origin (in situ)

  • It is not erosion, as the rock does not move

  • Types of weathering include:

Types of Weathering

Type of weathering

Process

Mechanical 

Temperature changes cause rocks to break down

Biological 

Rock breakdown due to action of plants and animals

Chemical 

Rock decomposes due to chemical reaction

Mechanical (physical) weathering

  • Also called freeze-thaw or frost shattering 

  • This happens in places where night temperatures often reach below freezing 

Process of Freeze-thaw Weathering

process-of-freeze-thaw-weathering

Biological weathering

Process of Biological Weathering

The process of biological-weathering
  • Nesting birds and small burrowing animals like rabbits can also cause rock to breakdown through biological weathering

Chemical weathering

  • There are few ways that chemical weathering can occur:

    • Carbonation - rain is slightly acidic and reacts with limestone, causing them to dissolve

    • Oxidation - iron minerals in the rock react with the air to cause rust and breakdown the rock 

    • Solution - when salt minerals in the rock are dissolved 

Weathering in the UK

  • The UK's climate is considered to be temperate - there are no extremes of weather

  • Physical weathering of the UK's landscape is usually slow

  • However, areas that receive more precipitation and fluctuations in temperature, such as the mountains of Wales and Scotland, see higher rates of chemical weathering and freeze-thaw weathering 

Table Showing Climatic Conditions of the UK

Part of the UK

Climate

North-west

Cool summers, mild winters and high rainfall

North-east

Cool summers, cold winters and low rainfall

South-west

Warm summers, mild winters and high rainfall

South-east

Warm summers, cold winters and low rainfall

Mass Movement

  • Mass movement is the downhill movement of material under the influence of gravity

  • Throughflow and runoff caused by heavy rain can also make cliffs more unstable and increase the likelihood of mass movement

    • It includes landslides, slumping and rockfalls

  • The type of movement is influenced by:

    • The angle of slope (steeper is faster)

    • Nature of regolith

    • Amount and type of vegetation

    • Water

    • Type and structure of rock

    • Human activity

    • Climate

  • Soil Creep:

    • Speed is below 1cm per year

    • Common in humid climates 

    • When soil expands, individual particles are lifted up at right angles to the slope

    • Soil also expands when it freezes, gets wet or is heated up in the sun

    • When the soil shrinks again, the particles fall straight back down

    • Soil creep takes a long time because the soil moves only a millimetre to a few centimetres at a time

  • Flow:

    • Occurs on slopes between 5° and 15°

    • Usually after the soil has become saturated with a flow of water across the surface

    • Vegetation can be flattened and carried away with the soil

    • Speeds range from 1 to 15km per year

  • Slide:

    • A movement of material 'en masse' which remains together until hitting the bottom of a slope

  • Fall:

    • Slopes are steep and movement is rapid

    • Caused by:

      • Extreme weathering - freeze-thaw action can loosen rocks that become unstable and collapse

      • Rainfall - too much rain will soften the surface leading to the collapse of the slope

      • Earthquakes can dislodge unstable rocks 

      • Hot weather can dry out soil causing it to shrink and allow rocks to fall

  • Slump:

    • Usually found on weaker rock types (i.e. clay), that become saturated and heavy

    • This is common at the coast and is also known as rotational slip

    • It involves a large area of land moving down the slope in one piece

    • Due to the nature of the slip, it leaves behind a curved surface

Types of Mass Movement

Diagram showing the most common types of mass movement

Erosion

  • Erosion is the process by which water breaks-down rock and sediment from rivers and coasts

  • There are four processes that contribute to erosion:

  • Hydraulic action:

    • This is when the sheer force of water compresses air into cracks, that expand and fracture over time

      • In rivers this is seen along the banks and beds and causes vertical (downward) erosion in the upper part of a river and lateral (sideway) erosion to the banks in the lower course

        • This action also helps to form the outside bend in a meander in the middle-lower course 

      • On coasts it is when waves smash against the cliff face 

  • Abrasion/corrasion:

    • This is the process when sediments/rocks/pebbles grind against a river's bank, bed, shoreline or cliffs in a sand-papering effect

      • Responsible for a river's lateral and vertical erosion 

      • Angular rocks are more effective at 'grinding/rubbing' 

  • Corrosion/solution:

    • All water is slightly acidic and dissolves soluble rocks, such as limestone or chalk, and carry the dissolved material away, leading to erosion

  • Attrition:

    • This is when sediment particles knock against each other and break into smaller, more rounded pieces 

      • In rivers, this action occurs along the river bed and within the water, it does not affect the river bank as this would be abrasion

      • On coasts, rocks and stones carried by waves hit and knock against each other wearing them down into rounded beach pebbles and sand on beaches

  • These processes can interact with each other, leading to complex erosion patterns and changes in the shape and form of rivers and coasts over time

  • Erosion can have significant environmental, economic, and social impacts, such as loss of habitat, damage to infrastructure, and increased risk of flooding and storm damage

Types of erosion

types-of-erosion

Transportation

  • Material in rivers and the sea arrives from many sources:

    • Eroded from cliffs and river banks

    • Transported by longshore drift along the coastline

    • Brought inland from offshore by constructive waves

    • Carried to the coastline by a river

    • Mass movement 

    • Scree from weathered rocks

  • Once material is in the water, it is moved in different ways:

    • Traction 

    • Saltation

    • Suspension

    • Solution 

Methods of Transportation by Water

Diagram showing four methods of transportation by water

Longshore drift

  • This is the main process of deposition and transportation along the coast 

  • Influenced by the prevailing wind, waves approach the beach at an angle

  • As the waves break, the swash carries material up the beach at the same angle

  • As the swash dies away, the backwash carries the material down the beach at right angles (90°) 

  • The process repeats, transporting material along the beach in a zig-zag movement

The Process of Longshore Drift

Image showing the process of longshore drift along a coastline

Worked Example

Describe and explain the process of longshore drift

(4 marks)

  • Identify the command words and link to the key term 

  • Command words are 'describe and explain' - say what you see and why

  • Your focus is on 'longshore drift' - what is it?

Answer

  • Longshore drift is the process where the waves transport material [1], such as sand along the beach in the direction of the prevailing wind [1]. The swash moves material up the beach at an angle [1], as the waves approach in a similar direction to the wind. The material then moves back down the beach at 90° due to gravity [1], this is the backwash. This movement continues along the beach in a zig-zag motion [1] in the direction of the prevailing wind. 

Deposition

  • Deposition is where sediment is dropped and occurs when a river or the sea loses energy

  • Sediment that is carried by rivers can be deposited at the coast or on the inside of a river bend

  • Constructive waves deposit material at the shoreline to build the beach and sand dunes

  • Conditions that encourage deposition in a river include:

    • A lack of precipitation or over abstraction, will reduce a river's overall discharge 

    • Decreased gradient - the flatter the gradient the less energy there is

    • Slower flow on the inside of a river bend or where the river is shallower 

    • When the river enters a sea/ocean or lake

  • Conditions that encourage deposition along the coast include:

    • Too much material in the water

    • Too little wind

    • Waves enter a sheltered area such as a bay and form beaches or mudflats behind spits 

    • Waves enter shallow water

  • The heaviest material is deposited first, this is known as the load - carried the least distance

  • The lighter materials; gravel, sand and silt, are known as alluvium - carried at a distance

  • Dissolved materials are carried out to sea - carried the furthest distance

Worked Example

Name one geomorphic process that erodes landforms.

(1 mark)

Answer

  • Hydraulic Action [1]

  • Abrasion / Corrasion [1]

  • Attrition [1]

  • Corrosion / Solution [1]

Commentary:

  • The question asks for one method of erosion, so there would be no extra marks for multiple answers

  • If weathering had been written, no marks would be awarded - weathering is the break-down of rock in situ, and is not erosion

  • The same would go for any method of transportation or deposition

  • Although weathering, transportation and deposition are geomorphic processes and change the shape of the landscape they do not do this through erosion

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Jacque Cartwright

Author: Jacque Cartwright

Expertise: Geography Content Creator

Jacque graduated from the Open University with a BSc in Environmental Science and Geography before doing her PGCE with the University of St David’s, Swansea. Teaching is her passion and has taught across a wide range of specifications – GCSE/IGCSE and IB but particularly loves teaching the A-level Geography. For the past 5 years Jacque has been teaching online for international schools, and she knows what is needed to get the top scores on those pesky geography exams.

Bridgette Barrett

Author: Bridgette Barrett

Expertise: Geography Lead

After graduating with a degree in Geography, Bridgette completed a PGCE over 25 years ago. She later gained an MA Learning, Technology and Education from the University of Nottingham focussing on online learning. At a time when the study of geography has never been more important, Bridgette is passionate about creating content which supports students in achieving their potential in geography and builds their confidence.