Concordant coastline

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Aerial view of Lulworth Cove

A concordant coastline occurs where the bands of differing rock types run parallel to the coast. The outer hard rock (for example, granite) provides a protective barrier to erosion of the softer rocks (for example, clays) further inland. Sometimes the outer hard rock is punctured, allowing the sea to erode the softer rocks behind. This creates a cove, a circular area of water with a relatively narrow entrance way from the sea.

Lulworth Cove in Dorset is situated on a concordant coastline. The outer hard rock is Portland limestone. The sea has broken through this barrier and easily eroded the clays behind it. A chalk cliff face at the back of the cove resists further erosion. Erosion is just starting to the west, where the sea has again broken through the Portland limestone barrier at Stair Hole.

The converse of concordant coastline is a discordant coastline.