Influence of Geological Structure (Edexcel A Level Geography)

Discordant coastlines

• A discordant coastline is one where the rock structures meet the coast at an angle - run perpendicular to oncoming waves
• Alternating rock types lead to the formation of headlands and bays
• Discordant coasts are also known as Atlantic coasts

Concordant coastlines

• Concordant coastlines are where the rock structures run parallel to the coast
• Dalmatian and Haff coastlines are examples of concordant coastlines

Discordant and concordant coastline

• The shape and form of the coastline is known as coastal morphology
  • This is influenced by the rock type (geology) and structure

Concordant coastlines - examples

Dorset, UK

• 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 in South Dorset

Dalmatian coastline

• The Dalmatian coast in Croatia is another example of a concordant coastline
• Formed as a result of tectonic forces and sea level rise 
• Tectonic activity forms anticlines and syncline which run parallel to the sea 
• Sea level rise after the Devensian Glacial then flooded the synclines leaving the anticlines standing above the water
• The result is a series of islands which run parallel to the coast

Example of a Dalmatian coastline

Haff coastline

• Located along the southern Baltic coastline
• During the Devensian Glacial large amounts of sand and gravel were deposited offshore
• After the glacial period had ended the material was then deposited nearer to the land by constructive waves
• This formed bars across bays and river mouths trapping the water behind to form a lagoon (Haff)
• These are a feature of low-energy coastlines

Haff coastline on the Baltic coast

Discordant coastlines - examples

Dorset, UK

• 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
• This leads to the formation of headlands and bays

Headland and bay formation

• The area is also affected by wave refraction
  • Wave refraction changes the amount of energy reaching the shore on a small local scale
  • Wave energy concentrates at the headland and increases the rate of erosion

Wave refraction around headlands

• The geological structure is the way that rocks are folded or tilted - this is known as its lithology
• Lithology can refer to any of the following characteristics:
  • Strata - layers of rock
  • Bedding planes - horizontal cracks created by pauses in rock formation
  • Joints - vertical cracks caused by tectonic movement or contraction
  • Folds - the result of pressure during tectonic movement causing the rock strata to fold
  • Faults - the result of stress or pressure causing it to fracture
  • Dip - the angle of the rock strata

Cliff profiles

• Cliff profiles are the angle and height of the cliff face
• A profile also includes any features such as wave cut notches
• Different lithology creates different cliff profiles

Impacts of lithology of cliff profiles