2.2.+Coastal+features

2. How are the main coastal features formed?

**Bays and Headlands**


1. Headlands and Bays can form where rocks outcrop at 90degrees to the coast 2. Here there are alternate bands of resistant and less resistant rock 3. Where there is soft rock (e.g. clay), erosion is rapid - and bays are formed (indent in coastline) 4. Where there is more resistant rock (e.g. chalk), erosion is much slower - headlands are formed as the harder rock is left sticking out into the sea 5. Exposed headlands then become vulnerable to destructive waves but help to shelter neighbouring bays.

The Foreland or Peveril Point in Dorset are good examples of headlands with Swanage Bay between them. Headlands are hard rock outcrops, sticking out into the sea and bays are indents in the coastline. These features are formed when there are alternate bands of hard (e.g. chalk - pale green) and soft rock (e.g. clay) exposed to wave attach. The rocks are attacked by the waves which are armed with pebbles (abrasion) and is gradually undercut. It may also be eroded by solution (dissolved) or by hydraulic action (when waves compress air in small cracks in the rock). Wave pounding (the sheer force of waves hitting against the cliffs) can also exert huge forces against the hard rock, particularly in storms. The hard chalk however is not eroded as easily as the clay which is less resistant and erodes quickly forming a bay with a sandy beach. The more resistant hard chalk i

is left sticking out as a headland which now becomes vulnerable to the full force of the waves.

The formation of Stairhole – a cove
The cove has formed because there are bands of rock of alternating resistance running parallel to the shore. On the seaward side the clays and sands have been eroded away. A narrow (less than 30 metre) band of rockers Portland limestone forms the shoreline. Behind this is a narrow (less than 50 metre) band of slightly less resistant Purbeck limestone. Behind this are 300-350 metres of much less resistant clays and greensands (Wealden clays, Gault and Upper Greensand). Forming the back of the cove is a 250 metre wide band of chalk, which is considerably more resistant than the clays and sands, but less resistant than the limestones. The entrance to the cove is a narrow gap in the limestone bands. This was formed by an erosional processes by wave action. The wide part of the cove is where the weak clays and greensands have been eroded. The back of the cove is the chalk, which the sea has been unable to erode as fast.

Cliff erosion
1. Wave erosion is greatest where waves break at the base of a cliff. 2. A wave-cut notch is formed at the base of a cliff due to undercutting by wave erosion (e.g. abrasion / hydraulic action) 3. As undercutting continues, the cliff will eventually collapse and retreat. 4. The gentle sloping rocky platform left behind when the cliff retreats is called a wave-cut platform. This feature is only exposed at low-tide. A good named example of an eroding cliff face and well developed wave-cut platform would be: Flamborough Head (North Yorkshire Coast) or Wave-cut platform at Runswick Bay (North Yorkshire)

Erosion of a Headland


1. The sea attacks the foot of the cliff (through processes of erosion such as abrasion and hydraulic action), eroding areas of weakness (e.g. joints - cracks in the rock) 2. These cracks get larger developing into small caves 3. Further erosion widens and deepens the cave until it is eroded through the headland forming an arch (this process may occur quicker where two caves erode back to back along the same line of weakness) 4. Undercutting of the arch occurs and the roof of the arch is weakened by weathering, eventually collapsing leaving a stack (column of rock isolated from the headland) 5. The stack continues to be eroded and eventually collapses forming a stump (covered at high tide). Named Examples include: Erosion of "The Foreland" (Headland) on the Dorset Coast - which has produced: On the Dorset Cpast is Durdle Door (Arch) and Old Harry - Stack and Old Harry's Wife - Stump

Although some material eroded at the coast is washed out to sea, most of the material is transported along the coast by longshore drift. Deposition will occur when the waves are now longer able to transport material due to a loss of energy. This is the case with constructive waves, where material is moved up the beach in the strong swash, but the weak backwash means material is deposited to build up the beach.
 * Deposition commonly occurs:** [[image:2.2K_Deposition_diag.png align="right"]]
 * where the water is sheltered (e.g. a bay) and the waves lack enenrgy.
 * where the coast is shallow and the increased friction between the water and the sea bed reduces the energy available for transport

Coastal Deposition Features:
Deposition of material results in the formation of a number of distinctive features: beaches; spits; bars and tombolos. You must be able to describe and explain the formation of each of these features with named examples (it is useful to be able to back up your explanation with a labelled diagram).

Beaches are made up of material lying between the high and low tide mark. There are four main sources of beach material: 1. Material deposited at the mouth of rivers 2. Cliff erosion, provides rock fragments that will build up the beach 3. Constructive waves have a strong swash pushing sands / pebbles up the beach 4. Longshore drift carries material from elsewhere along the coast.
 * Beaches** are the main features of coastal deposition. A beach is defined as the gently sloping area of land between the high and low water marks. Remember, beaches are not permanent features as their shapes are altered by waves.

**Spits** are long narrow ridges of shingle and sand extending out into the sea or across a river estuary.

The material initially deposited is the largest material, dropped due to the reduction in energy. Finer material is then deposited, helping to build up the rest of the spit. As the spit continues to grow outwards, a short term change in wind direction may result in a change in the direction of the spit forming a curved end (recurved laterals). If growing across a river estuary,
 * How are Spits formed?[[image:2.2M_Spit_diag.png width="463" height="266" align="right"]]** Longshore drift transports material along the coastline. Spits are formed in areas of relatively shallow and sheltered water where there is a change in the direction of the coastline. Deposition occurs resulting in the accumulation of sand and shingle

the length of the spit will be restricted by the river outlet washing sediment away. A salt marsh may form in the sheltered, low energy zone behind the spit. Named examples of spits: 1. Spurn Head, Humberside 2. Orford Ness (near Aldeburgh)

Tombolo's are ridges of sand and shingle which join the mainland to an island. Tombolo's are created through the process of longshore drift. Where there is a change in the shape of the land, a spit forms in the shallow / sheltered water. A tombolo is formed where the spit continues to grow until it reaches an island, forming a link with the mainland. Named Example: Chesil Beach (joins the South Dorset Coasts to the Isle of Portland)
 * What are tombolo's and how are they created?**

[[image:2.2W_Thames_Estuary_map.png width="215" height="158" align="right"]]
There are a few features that have occurs as result of the the Ice Ages ending.

An estuary
Is larger than a river mouth, for example the river Thames, and resulted from a river that flowed out into the sea from a valley with low hills on either side. When the ice melting further north, the sea level rose causing an entry to the sea considerably wider than its former mouth.

A **Ria**
During the Ice Ages, the sea level dropped as so much ice was piled up on the land, that there was less left in the sea, so the UK was joined to Europe and Alaska was joined to Russia ( we think the Baring Straits was still a land bridge that the Native Americans cross from Asia into North America) With the lower sea level, rivers that were still flowing eroded vertically making their flood plain at a lower level. When the ice melted and re-entered the sea the lower flood plains and the lower parts of the middle course were flooded, frome xample the River Tamar in Cornwall

Raised Beaches
Raised beaches are another way that show that sea level has changed. A raised beach is an elevated area of sloping ground, sitting above the present tide line. In the past this area was at sea level.

There are many examples of this feature throughout Britain, particularly along the West coast - this is because the area experienced the greatest weight of ice during the last Ice Age (about 10,000 years ago).

During an Ice Age, the massive weight of ice bearing down on a landmass caused it to sink. Over time, as the earth's temperature rose and the weight of ice decreased, areas of land began to slowly rise back out of the sea. This ‘bounce back' motion - the localised change in sea level, relative to the land - is known as isostasy, or isostatic uplift.

Some raised beaches may consist of several different levels, each indicating a different stage in the shoreline's development.

The picture of East Prawle in South Devon shows the old cliffs and the wave cut platform that was created at the timethe land was lower than it is today.

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 * ==What do you need to remember?  == || == == ||
 * * **Know that many features of coastline have been caused by primarily erosion, deposition or the aftermath of the Ice Ages **
 * **Know which features are largely due to erosion, how they are formed (often with a labelled diagram) and an example of each **
 * **Know which features are largely due to deposition, how they are formed (often with a labelled diagram) and an example of each **
 * **Know which features are largely an aftermath of glaciation, how they are formed (often with a labelled diagram) and an example of each **
 * **When describing a particular erosional feature remember to include an example or 2 relevant types of erosion with an explanation e.g. ** The rocks are attacked by the waves which are armed with pebbles (**abrasion**)