UNIT 1C - COASTAL LANDFORMS (Caves, arches, stacks and stumps - Caves,…
UNIT 1C - COASTAL LANDFORMS
Case study: Dorset coastline
- Dorset is located in the south of England. Its coastline has examples of many erosional and depositional landforms. For example:
at Chesil Beach there is a bar
- 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.
Old Harry Rocks is an example of caves, stacks and stumps
- 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.
Swanage is an example of a headland and 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.
- When water loses its energy, any sediment it is carrying is deposited. The build-up of deposited sediment can form different features along the coast.
- Sometimes a spit can grow across a bay, and joins two headlands together. This landform is known as a bar. They can trap shallow lakes behind the bar, these are known as lagoons. Lagoons do not last forever and may be filled up with sediment.
- A spit is an extended stretch of sand or shingle jutting out into the sea from the land. Spits occur when there is a change in the shape of the landscape or there is a river mouth.
Waves cannot get past a spit, therefore the water behind a spit is very sheltered. Silts are deposited here to form salt marshes or mud flats.
A hooked end can form if there is a change in wind direction.
When there is a change in the shape of the coastline, deposition occurs. A long thin ridge of material is deposited. This is the spit.
Sediment is carried by longshore drift.
Caves, arches, stacks and stumps
- Caves, arches, stacks and stumps are erosional features that are commonly found on a headland.
The stack is undercut at the base until it collapses to form a stump.
The base of the arch continually becomes wider through further erosion, until its roof becomes too heavy and collapses into the sea. This leaves a stack (an isolated column of rock).
The cave becomes larger and eventually breaks through the headland to form an arch.
As the waves continue to grind away at the crack, it begins to open up to form a cave.
Cracks are widened in the headland through the erosional processes of hydraulic action and abrasion.
Cliffs and wave-cut platforms
- Cliffs are shaped through erosion and weathering. Soft rock erodes quickly and forms gentle sloping cliffs, whereas hard rock is more resistant and forms steep cliffs. A wave-cut platform is a wide gently-sloping surface found at the foot of a cliff.
The process repeats. The cliff continues to retreat.
The backwash carries away the eroded material, leaving a wave-cut platform.
As the notch increases in size, the cliff becomes unstable and collapses, leading to the retreat of the cliff face.
A wave-cut notch is formed by erosional processes such as abrasion and hydraulic action - this is a dent in the cliff usually at the level of high tide.
The sea attacks the base of the cliff between the high and low water mark.
Headlands and bays
Erosional features such as wave-cut platforms and cliffs can be found on headlands, since they are more open to the waves. Bays are more sheltered with constructive waves which deposit sediment to form a beach.
Bands of soft rock such as clay and sand are weaker therefore they can be eroded quickly. This process forms bays. A bay is an inlet of the sea where the land curves inwards, usually with a beach. Hard rock such as chalk is more resistant to the processes of erosion. When the softer rock is eroded inwards, the hard rock sticks out into the sea, forming a headland.
Cliffs along the coastline do not erode at the same pace. When a stretch of coastline is formed from different types of rock, headlands and bays can form.
- The process of erosion can create different landforms along the coastline.