Landform change – the Dorset coastline

Old Harry Rocks is between Swanage and Bournemouth, on the south coast of England. Chesil Beach is east of Lyme Regis.

Dorset is located in the south of England. Its coastline has examples of large scale landforms. For example:

How does the geology affect the rates of landform change?

The area around Swanage is made up of bands of hard and soft rock. This is called a discordant coastline.

The soft rock is made of clay and sands, and the hard rock is chalk and limestone. As erosion processes take place, the clay erodes away quicker than the limestone and chalk. This forms headlands and bays, creating Swanage Bay and two headlands - Ballard Point and Durlston Head.

Swanage Bay has alternating hard rock (limestone, chalk), and soft rock (clay, sands).

Old Harry Rocks

Old Harry Rocks are located on the headland between Swanage and Studland Bay. The headland is made out of chalk, a hard rock. The headland juts out into the sea, so it is more vulnerable to high-energy waves. This caused the formation of Old Harry, a stack. Over time Old Harry will collapse to form a stump.

Old Harry Rocks is made up of a stack, a cave, a wave-cut platform and a collapsed arch.
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Coastlines where the geology alternates between strata (or bands) of hard rock and soft rock are called discordant coastlines. A concordant coastline has the same type of rock along its length. Concordant coastlines tend to have fewer bays and headlands.
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