Coasts
A coast is found where the land meets the sea. Coasts are constantly shaped by the sea, air and the action of waves. Waves act in different ways, through the processes of erosion, transportation and deposition.
Each of these processes involves the power of the sea and the effect of waves that are carried to shore. However, other factors also change and shape our coasts:
Human Activity and Land use
The way in which humans manage and use coastal areas helps shape the coast. Some areas of coast are valued more than others. This will influence the way coasts are used and managed.
Weather and Climate
The weather and climate of coastal areas can contribute to the process of erosion and weathering.
Geology
The geology and rock types found in coastal areas influence how coastal processes work ie hard rock resists erosion.
Waves
The power of waves is one of the most significant forces of coastal change. Waves are created by wind blowing over the surface of the sea. As the wind blows over the surface of the sea, friction is created - producing a swell in the water. The energy of the wind causes water particles to rotate inside the swell. This moves the wave forward.
The size and energy of a wave is influenced by:
- the length of time that the wind has been blowing
- thestrength of the wind
- how far the wave has travelled (called the fetch)
Destructive waves
- operate in storm conditions
- are created from big, strong waves when the wind is strong and has been blowing for a long time
- occur when wave energy is high and the wave has travelled for a long time
- tend to remove material from the coast and associated with erosion
- backwash is stronger than the swash
Constructive waves
- operate in calm weather
- are less powerful waves
- break on the shore and tend to deposit material, building up beaches
- are responsible for transporting material
- swash is stronger than the backwash
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.
Erosion
The sea changes and shapes the coastal landscape. Erosion is the wearing away and breaking up of rock and beach material found along the coast. Destructive waves will erode the coastline in the following four ways.
- The constant force of waves crashing on the shore damages it. This is called hydraulic action.
- Waves bring with them bits of rock and sand. These help to grind down cliffs. This is called abrasion.
- Waves cause rocks and pebbles on the shore to smash into each other and break down. This is called attrition.
- Acids contained in sea water will slowly dissolve certain types of rock. This is called corrosion or solution.
Transportation and deposition
Waves tend to approach the coast at an angle; this is because of the direction of the prevailing wind. This causes the waves to break on the beach at an angle. The swash of the waves carries material up the beach at an angle. The backwash then flows back to the sea in a straight line. This movement of material is called transportation.
On many coasts the combined effect of continually repeating swash and backwash is to transport material sideways along the coast. This movement of material along coasts is called longshore drift.
Deposition
When the sea loses energy, it drops its load of sand, rock particles and pebbles, that it has been carrying. This is called deposition. Deposition happens when the swash is stronger than the backwash.
Deposition is likely to occur when:
- waves enter an area of shallow water
- waves enter a sheltered area
- there is little wind
Coastal features are caused either by the processes of erosion (the wearing away of rocks) or deposition (movement of eroded material by the sea to a new location).
Coastal features created by erosion
Along a coastline there are often many features created by erosion. The most common of these are:
cliffs headlands bays caves arches stacks
Cliffs
One of the most common features of the coastline in Britain and around the world are cliffs. Cliffs are shaped through a combination of erosion and weathering. The weather attacks the cliff top. The waves attack the cliff foot, causing a wave-cut notch at the bottom.
Soft rock erodes easily and creates gently sloping cliffs. Hard rock is more resistant and erodes slowly and creates steep cliffs.
Headlands and bays
Another group of features shaped by erosion are headlands and bays. Headlands are formed when the sea attacks a section of coast consisting of alternating bands of hard and soft rock.
The bands of soft rock, such as sand and clay, erode more quickly than those of more resistant hard rock, such as chalk. This leaves a section of land heading out into the sea; this is called a headland. The areas where the soft rock has eroded away, next to the headland, are called bays.
Caves, arches and stacks
Erosion can create caves, arches and stacks along a headland. Again weathering can also help to create these landforms.Caves occur when the waves force their way into cracks in the cliff face. The water contains sand and other materials that help to grind away at the rock until the cracks become a cave.If the cave is formed in a headland, it may eventually break through forming an arch.The arch will gradually become bigger and bigger until it can no longer support the top of the arch. When the arch collapses, it leaves the headland on one side and a stack (a tall column of rock) on the other.
Coastal features created by deposition
Along a coastline you can find features created by deposition. These include:
beaches spits barssand dunes
Beaches
Beaches are one of the most common features of a coastline. Beaches are made up of eroded material that has been transported from elsewhere and deposited here by the sea.Constructive waves help to build up beaches. The type of material found on a beach ie sand or shingle) is influenced by the geology of the area and wave energy.
Spits
Spits are also created through the process of deposition. A spit is an extended stretch of beach material that projects out to sea and is joined to the mainland at one end.Spits are commonly formed where there is a prevailing wind and where there is a longshore drift.
Bars
A bar is a long stretch of beach material (sand or shingle) that joins together two headlands. A lagoon usually forms behind the bar.
Sand dunes
A sand dune is a small hill of sand found at the top of a beach. The waves do not usually reach this area of the beach. Vegetation may be found on sand dunes and such areas can be important ecosystems.
Fiord
In valleys created by glaciers. They are very deep.
Rias
In valleys formed by rivers. They are more winding with low, gentle sides.
Physical management of the coast
Physical management of the coast is concerned with natural processes such as erosion and longshore drift. Management techniques fall into two categories: hard engineering and soft engineering.
Hard engineering- options tend to be expensive and short-term options. They may also have a high impact on the landscape or environment(wooden croynes, concrete walls, artividial breakwaters).
Soft engineering- options are often less expensive than hard engineering options. They are usually also more long-term and sustainable, with less impact on the environment.
Beach nourishment - this replaces beach or cliff material that has been removed by erosion or longshore drift.The main advantage is that beaches are a natural defence against erosion and coastal flooding. Beaches also attract tourists.While it can be a relatively inexpensive option it requires constant maintenance to keep replacing the beach material as it is washed away.
Managed retreat - this is where areas of the coast are allowed to erode and flood naturally. Usually this will be areas considered to be low value.The advantages are that it encourages the development of beaches (a natural defence) and salt marshes (important for the environment) and cost is low.While this is a cheap option, it will not be free as people will need to be compensated for loss of buildings and farmland.