Jurassic Coast Geography Case Study

Dorset - case study of a UK coastal landscape

Dorsert is located on the southern coast of the UK. It is called the Jurassic Coast as it has lots of fossils dating back to the Jurassic period.

How are geomorphic processes creating coastal landforms?

Swanage Bay: the cliffs backing Swanage Bay are made of clay, which is a soft rock. Towards the northern end of the bay the cliffs are covered in vegetation, stablising them and protecting them from erosion. Elsewhere, the cliffs are not covered by vegetation, so wet weather weakens them causing slumps. Longshore drift affects the bay carrying material (mainly gravel) from the south to the north of the beach. Erosion is the dominant process in the bay with the beach losing material year on year.

 

The Foreland, Old Harry and his Wife: in between the two bays (Studland and Swanage Bays) is a headland named the Foreland. This is made of chalk which is a harder rock. An arch at the end of the headland has collpased to form a stack called Old Harry and a stump called Old Harry's Wife. Chemical weathering and erosion are gradually wearing down these down. Biological weathering caused by the vegetation on the top of the headland is also breaking up the rock.

 

 

Durdledoor: this is an arch which has formed on a hard limestone headland. It is unusual as it has formed parallel to the coastline. Erosion by waves opened up a crack in the headland, which then became a cave and eventually an arch. The arch is gradually being worn away by mechanical, chemical and biological weathering.

 

 

 

Lulworth Cove: this is a cove formed when a gap was eroded in a band of limestone. Behind the limestone is a layer of clay which is softer so more easily eroded. The limestone cliffs forming the back wall of the cove are vulnerable to mass movement and sometimes experience small slides and slumps.

 

 

 

 

Chesil Beach: this is a tombolo (spit which connects mainland to an island). It connects the Isle of Portland to the mainland. It has been created by longshore drift. Behind Chesil Beach is a lagoon called The Fleet Lagoon.

 

 

 

 

 

 

How do climate and geolgy influence geomorphic processes?

 

How is human activity, including mangement, working in combination with geomorphic processes to shape the landscape?

As areas of the Dorset coast are being eroded, properities and infrastructure are at risk. There is also a risk for people from landslides and rockfalls. Coastal management strategies are being used along the Dorset coastline to prevent erosion in some areas but they have impacted the landscape and caused changes to the natural environment.

Groynes
  • Groynes are wooden or stone barries which are built at right angles to the coast. They trap material being transported by longshore drift to create larger beaches which can then absorb wave energy to reduce erosion rates.
  • New timber groynes were installed on Swanage beach in 2005-6 and have reduced the loss of beach material. But, by stopping the movement of beach material along the coast beaches further down the coast are becoming narrower and subject to more erosion (due to reduced ability to absorb wave energy).

Sea wall

  • Concrete sea walls are in place along most of Swanage beach. They reflect waves back out to sea preventing erosion of the cliff. However, this creates a strong backwash which removes sediment from the beach and can lead to erosion under the wall. Because there's no erosion, there is no material to replenish the beach meaning the beach level will become lower.

Beach replenishment

  • In the winter 2005-6, sand and shingle were dredged from the sea bed at Poole Harbour and added to the upper parts of Swanage beach creating a wider beach. This means waves are slowed, reducing erosion and will help to protect proprties and cliffs. However, this cost £5 million and it will need to be repeated roughly every 20 years.

 

Case study: coastal landforms - Dorset coastline

Dorset is located in the south of England. Its coastline has examples of many erosional and depositional landforms. For example:

Durdle Door, Dorset

Swanage Bay

The area around Swanage is made up of bands of hard and soft rock. 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.

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.

Chesil Beach

Chesil Beach is an example of a bar. Sediment has been deposited over time to form a spit. The spit has continued to join to the Isle of Portland. Behind the spit there is The Fleet, a lagoon.

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