Geological structure: concordant and discordant coasts

Concordant and discordant coasts

• On a discordant coast, bands of different rock run at right angles to the coastline. Less resistant rock is eroded faster into bays; resistant rock is left as headlands. Example: Studland to Swanage in Dorset, where chalk forms Old Harry Rocks, clay was eroded into Studland Bay and limestone forms a headland further south (Cognito, June 2026).
• On a concordant coast, bands of rock run parallel to the coastline. A resistant outer band protects the softer rock behind, so the coast stays fairly straight. Where the outer band is breached, the sea erodes the softer rock behind into a rounded cove. Example: Lulworth Cove, where the sea broke through the hard Portland Stone and scooped out the softer Wealden Beds and chalk behind it (Cognito, June 2026).

Structural features

Within a rock mass, small-scale structure strongly affects erosion:

• Joints: cracks formed as rock cooled or was unloaded; waves exploit them by hydraulic action.
• Faults: larger fractures where rock has moved; the shattered rock along a fault erodes quickly into narrow inlets called geos and is often where caves start.
• Bedding planes: boundaries between layers (strata) in sedimentary rock.
• Folding: rock layers bent by tectonic pressure; tight folding fractures the rock and weakens it.
• Dip: the angle at which strata are tilted.

Dip and cliff profiles

Dip controls cliff shape:

• Horizontal strata: steep, near-vertical cliffs with a stepped face.
• Strata dipping seaward (towards the sea): the cliff face follows the bedding planes, giving a lower-angle cliff; blocks can slide down the bedding planes, so it is prone to rockfalls and slides.
• Strata dipping landward (into the land): steep, stable cliffs, often overhanging slightly, because blocks are held in by the dip.

The June 2025 mark scheme credited exactly this: seaward dip gives gentler cliffs prone to rockfall; landward dip gives steeper cliffs. Micro-features such as caves, notches and blowholes form along joints and faults.

Worked example

Explain why a cliff with strata dipping steeply towards the sea is less stable than one with strata dipping into the land.

1. With seaward dip, bedding planes slope out of the cliff face.
2. Blocks above each bedding plane have nothing holding them, so gravity pulls them down the plane, especially when waves undercut the base or water lubricates the plane.
3. With landward dip, blocks are tilted back into the cliff and supported.

Answer: Seaward dip lets blocks slide along bedding planes into the sea; landward dip holds them in, so the cliff is more stable.

Check yourself

1. A coastline where bands of chalk, clay and limestone meet the sea at right angles is
   • concordant
   • discordant
   • emergent
   • a sediment cell
   Show answer

   discordant. Bands at right angles to the coast give a discordant coast of headlands and bays.

2. Lulworth Cove formed where the sea
   • deposited sand in a sheltered bay
   • flooded a glacial valley
   • eroded a fault in granite
   • broke through a resistant outer band and eroded softer rock behind
   Show answer

   broke through a resistant outer band and eroded softer rock behind. On a concordant coast, a breach in the hard Portland Stone exposed softer Wealden Beds and chalk.

3. A narrow inlet eroded along a fault line is called a
   • spit
   • geo
   • tombolo
   • bar
   Show answer

   geo. Shattered rock along a fault erodes quickly into a geo.

4. Strata dipping landward usually produce
   • low-angle cliffs prone to sliding
   • wide sandy beaches
   • steep, relatively stable cliffs
   • salt marshes
   Show answer

   steep, relatively stable cliffs. Blocks are tilted into the cliff and supported.

5. On a discordant coast, headlands are made of
   • the more resistant rock
   • the less resistant rock
   • unconsolidated sand
   • salt-marsh mud
   Show answer

   the more resistant rock. Resistant rock erodes more slowly and is left jutting out.

6. Explain how joints and faults increase the rate of cliff erosion.
   Show answer

   Joints and faults are lines of weakness; waves force water and air into them by hydraulic action and abrasion widens them, so blocks are loosened and removed faster.. Weakness, then a process, then the effect.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Geography specification, Issue 3 (September 2025)
• Cognito blog: Discordant vs concordant coastlines (16 June 2026)
• Pearson WGE02/01 mark scheme, June 2025
• Pearson IAL Geography Getting Started Guide

Last updated 8 November 2026. Spotted a mistake? Tell us.