Coastal Landscapes: The Interaction Between Human & Physical Processes (Edexcel GCSE Geography A)

Coastal Case Study - The Dorset Coast

• The geology of the Dorset coast has both erosional and depositional landforms

• There are bands of sedimentary rock, consisting of soft clay and harder limestone and chalk

• These rocks, which erode at different rates, create a range of landforms, including:

  • Headlands and bays

  • Arches

  • Stacks

  • A tombolo 

• This stretch of coastline forms part of the commonly known Jurassic Coast

• It stretches for 155km from Exmouth in Devon to Poole in Dorset

How has the coast changed?

Rock Formation along the Jurassic Coast

Erosional landscape 

• Durdle Door is an example of an arch formation

  • Wave erosion opened a crack in the tough limestone headland

  • It is unusual as it has formed parallel to (along) the coastline 

  • Further erosion has led to a cave, which has developed into an arch in the headland

  • Softer rocks behind the limestone have been washed away, leaving a line of chalk cliffs

  • These are being eroded by mechanical, chemical and biological weathering

• Lulworth Cove is a small bay which formed when a gap was eroded in the band of tough limestone 

  • Lying behind the limestone is a band of soft clay, and this has been eroded to form a bay 

  • The entrance to the cove is narrow because the harder band of limestone is more resistant to erosion

  • The limestone cliffs forming the back wall of the cove are vulnerable to mass movement and sometimes experience small slides and slumps

• Old Harry and his wife sit at the end of The Foreland

  • This chalk headland has eroded to form caves, arches and a stack (Old Harry)

  • Further erosion has resulted in a stump called Old Harry's Wife

  • Chemical weathering and erosion have gradually eroded these features

  • Biological weathering, through surface vegetation on the headland, is also weakening the rock

Main features along the Dorset Coast, UK

Map showing main features of the Dorset Coast, UK

• Swanage sits on two beach bays called Studland Bay and Swanage Bay

  • The cliffs behind the bays are areas of soft sandstone and clay

  • Between the two bays is The Foreland, a headland of harder chalk

  • 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 depositional beach losing material year on year

Depositional landscape

• Chesil Beach is an 18-mile-long pebble/shingle barrier beach

• The beach has moved landwards and is often referred to as a tombolo (spit that joins an island to the mainland)

• It stretches northwest from Portland to West Bay.

  • The formation of Chesil Beach is still debated but it is thought to be the result of glacial deposition

  • There is a shallow saltwater lagoon called The Fleet Lagoon that separates the beach from the mainland 

• Studland Bay has four miles of sandy beaches within sheltered waters and backed by sand dunes

• Studland’s dunes are unusual because:

  • Sand only began to be deposited about 500 years ago

  • A freshwater lake has formed inland, called the Little Sea

  • The dunes are made of acidic sand that has a low shell content

    • This acidity means that the dunes will be colonised by dune heather and not grass

Impacts of the 2014 Valentine’s Day storm

• On 14 February 2014, a large storm battered the coastline with winds of up to 80mph and storm waves of more than 30 feet high

• Sea defences were breached and huge waves threw rocks from Chesil Beach into the streets behind the seafront

• Portland Beach Road was under 4 feet of water from flooding at Hamm Beach

• Parts of Chesil Beach were lost and the 150-million-year-old Pom Pom Rock collapsed

• West Bay cliffs retreated by a few metres after the cliffs collapsed

Potential effects of climate change on the coast

• As global sea temperatures increase, water levels rise due to melting ice caps and seawater expansion

• A warmer atmosphere leads to more intense and frequent storms, creating powerful and destructive waves

• A warmer atmosphere can hold more water vapour, which will lead to higher levels of precipitation and increased rates of weathering and erosion. This will lead to increased cliff instability, leading to increased levels of landslips and falls

• Climate change can impact the whole of the UK's coastline, particularly those areas where the cliffs are made from softer rock and clay or are lying close to sea level and can, therefore, flood