Costline Formation

The influence of geological structure

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

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

• This forms a concordant or discordant coastline, such as the Dorset coastline

• Geology, therefore, determines the coastline vertically through the height and profile of a cliff and horizontally with bays and headlands

Concordant coastlines

Concordant coastlines

• Concordant coastlines are made up of the same rock type, running parallel to the sea

• This causes even rates of erosion along the coastline

• These coastlines typically produce coves 

  • 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

Discordant coastlines

Discordant coastlines

• Discordant coastlines have alternating bands of rock perpendicular (90°) exposed to the sea

• This causes uneven rates of erosion along the coastline

• These types of coastlines form headlands and bays

  • For example, 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