Influences on Landscapes (OCR GCSE Geography B)

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

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

Biological weathering

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

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

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

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

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

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