Coastal Structure (Edexcel GCSE Geography A)

Concordant & Discordant Coastlines

The influence of geological structure

• Geological structure influences the shape of the coastline 

• A coastline made up of softer rocks such as sands and clays will be more easily eroded

• Coastlines of more resistant, harder rock will take longer to erode and produce rugged landscapes 

• Joints and faults expose rock to erosion and weathering

• The differences between hard and soft rocks will also impact the shape and characteristics of cliffs

The Effects of Rock Type on the Coastline

Discordant and concordant coastlines

• The angle of the rocks at the coastline determines the shape that the coastline will take

• There are discordant coastlines and concordant coastlines

Dorset coastline

Discordant coastlines 

• A discordant coastline is one where the rock structures meet the coast at an angle; they run perpendicular to the oncoming waves

• Alternating rock types lead to the formation of headlands and bays

• To the east of Lulworth Cove in Dorset, the coastline runs north to south and so the rocks meet the coast at an angle, creating a discordant coastline

Headland and bay formations on a discordant coastline

Concordant coastlines 

• Concordant coastlines are where the rock structures run parallel to the coast

• An example of a concordant coastline can be found in the area around Lulworth Cove in Dorset

• More resistant Portland Limestone runs parallel to the sea, with less resistant Purbeck Limestone and Wealden Clay behind it

• The formation of coves has occurred where the water has broken through at weaker points in the Portland Limestone

Concordant coastline

Concordant coastline in South Dorset

Wave Types & Characteristics

• The coast can be defined as:

The meeting point between land and sea

• Coastal processes are divided into two parts:

  • Marine processes: Offshore (water-based)

  • Terrestrial processes: Onshore (land-based)

• These processes are further divided into:

  • Wave action

  • Erosion

  • Transportation

  • Weathering

  • Mass movement

• These processes produce the distinctive landforms found around our coastlines 

Wave action

• Waves are marine processes that erode, transport and deposit material

• Waves are formed as winds blow over the surface of the sea 

• The height and strength of a wave are dependent on 3 factors:

  • The fetch 

  • The amount of time the wind blows

  • The strength of the wind

• The greater the strength, time and fetch of the wind, the larger the wave

• As a wave enters the shallow water of the coast, friction from the seabed causes the wave to lean forward and eventually crest and break onto the beach 

• The movement of water up the beach is called the swash, and the return movement is the backwash
  

• There are two types of waves:

  • Destructive waves erode the beach

  • Constructive waves are beach builders

Comparison of Wave Type

Constructive waves are beach builders and destructive waves are the destroyers