© boardworks ltd 2004 1 of 35 coastal processes and landforms

© Boardworks Ltd 20041 of 35

Coastal Processes and Landforms


Why are waves generally larger in the south west than in the south east?

Wave energy depends on the fetch, the strength of the wind and the length of time over which the wind has blown.

Look at an atlas or a wall map to find out the largest fetch around the British Isles.

fetch = the distance over which the wind has blown


Why do waves break?

wavelength

the bottom of the wave touches the sand, slows down and the top of the wave topples over


Why do waves break?


Backwash

Swash

Note: Backwash is always at right angles to the beach

Swash and backwash


Waves can be destructive or constructive.When a wave breaks, water is washed up the beach - this is called the swash. Then the water runs back down the beach - this is called the backwash. With a constructive wave, the swash is stronger than the backwash. With a destructive wave, the backwash is stronger than the swash.


Types of waves

Destructive Waves

Constructive Waves

Backwash stronger than swash

Swash stronger than backwash


Attrition

Hydraulic action

Abrasion

Corrosion

Processes of erosion

Processes of erosion


Attrition

Material carried by the waves bump into each other and so are smoothed and broken down into smaller particles.

Abrasion/Corrasion

This is the process by which the coast is worn down by material carried by the waves. Waves throw these particles against the rock, sometimes at high velocity.

Hydraulic action

This process involves the force of water against the coast. The waves enter cracks (faults) in the coastline and compress the air within the crack. When the wave retreats, the air in the crack expands quickly causing a minor explosion. This process is repeated continuously.

Corrosion

This is the chemical action of sea water. The acids in the salt water slowly dissolve rocks on the coast. Limestone and chalk are particularly prone to this process.


Dorset coastline


Landforms of coastal erosion

1) Headlands and Bays

2) Cliffs and Wave Cut Platforms

3) Caves, Arches, Stacks and Stumps


Headlands and bays


An example of headlands and bays on the Dorset coastline…

chalk

clay

limestone

Swanage Bay


Cliffs


The waves attack the base of the cliff through the processes of abrasion, corrosion, hydraulic action and attrition.

Over time the cliff will be undercut and a wave-cut notch is formed.

Eventually the cliff becomes unstable and collapses. Further cliff retreat will form a wave-cut platform.

Wave-cut platform


Wave-cut platform – Burgh Island, Devon


Caves, arches, stacks and stumps



1. The waves erode FAULTS (cracks) in the headland.

2. The waves eventually erode through the headland to form an ARCH.

3. The arch becomes unsupported and collapses to form a STACK.

4. A STUMP is formed from the collapsed stack.

C DBA

Match the image with the most appropriate label.

1 23 4


If these photos were taken of one headland over time, which of these landforms would be the first to be formed?


Coastal processes – transportation


This movement of sediment along the coastline is called longshore drift.

Direction of movement

swash

Backwash

Backwash is always at right angles to the beach

Longshore drift


Landforms of coastal deposition

1) Beaches

2) Spits

3) Tombolos and Bars


Spit formation


The wind direction changes and moves the spit inland. In storm conditions the spit may be breached.

Why doesn’t the spit grow across the estuary to form a bar?

The river’s current stops deposition across the estuary.

Why is the spit curved?

Spit formation


If a spit joins the mainland to an island it is called a tombolo.

This diagram show the tombolo – Chesil Beach.

The mainland is joined to the Isle of Portland.

Tombolos and bars


Chesil Beach

Isle of Portland

Chesil beach


If a spit joins one part of the mainland to another it is called a bar.

For example, there is a bar at Orford Ness in Devon.

Tombolos and bars


Groynes are used to stop LSD


Humans are affected by the retreat of the cliff (loss of land, housing, etc.) They erect sea defences which stop the erosion (groynes).


How do groynes work?

Groynes trap the sand which is carried along the coast by longshore drift.

The sand acts as a natural protection against the force of the waves. The waves break on the beach and not the cliffs.


c) Points for Groynes construction:•It protects the coastline and preserves peoples: property•Groynes encourage a beach to grow which can help tourism and bring money to the areaAgainst: Groynes•Looks very ugly•Very expensive to build•No guarantee it will last forever•Some people suffer if groynes are built and sediment is trapped .•Divide the beach up into unnatural sections


Explain the processes that have caused this cliff to collapse.

C

C


Erosion or deposition?


8 Coastal Landscapes and Processes(a) Study Figure 12a, on the insert, a photograph of Flam borough Head on the east coastof England. Figure 12b is a sketch of the photograph.Figure 12b

(i) On Figure 12b, mark with an arrow and label three coastal features shown inFigure 12a.


Bays and Headlands

Ans 4) Headlands and Bays form along DISCORDANT coastlines where rocks outcrop at 90o to the coast2. Here there are alternate bands of resistant and less resistant rock3. 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 sea5. Exposed headlands then become vulnerable to destructive waves but help to shelter neighbouring bays.


d)What is a spit formation? SPIT = is a hooked shaped landform which typically runs along a coastline formed where a river estuary meets the coast. It is formed by the process of Longshore Drift bringing material along the coastline in a zig-zag fashion. A saltmarsh often forms behind the spit as the sediment can build up here in shallower waters.


Key Ideas

Waves are the result of the wind blowing over the sea. They break as they approach land.

Swash and backwash describe the movement of a wave on the beach. Fetch is the distance that the wind has travelled.

Sub-aerial processes such as weathering and mass movement occur on the cliff face.

Coastal processes of erosion include hydraulic action, attrition, corrosion and solution.

Landforms created by erosion include headlands and bays, caves, arches, stacks and stumps.

Longshore drift is a method of coastal transport.

Landforms created by deposition include beaches, spits, tombolos and bars.

© boardworks ltd 2004 1 of 35 coastal processes and landforms

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