3-1-2-influence-of-geological-structure

Discordant & Concordant Coast Formation

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

Influence of Geology on Coastal Morphology

• 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

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

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

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

• 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

Influence of Geological Structure

• 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