Coasts
The coast or the coastline is the border between the land and the sea. The coasts are very important because they have many uses for humans, but they are also under threat because of humans.
WHY ARE COASTS IMPORTANT AND HOW ARE THEY USED?WHY ARE COASTS UNDER THREAT?
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WHY ARE COASTS UNDER THREAT?
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Waves
Waves are formed because of friction between the wind and the sea. Although it appears that water particles in waves are moving forward, in reality it is only the shape and the energy of the wave that is moving. Water particles tend to move up and down in a circular motion. When waves near the coast, the bottom of the wave is slowed by friction with the sea bed. Because the top of the wave is experiencing less friction, it moves faster and eventually topples over the bottom of the wave and breaks. The size of the wave is effected by three factors:
Waves are formed because of friction between the wind and the sea. Although it appears that water particles in waves are moving forward, in reality it is only the shape and the energy of the wave that is moving. Water particles tend to move up and down in a circular motion. When waves near the coast, the bottom of the wave is slowed by friction with the sea bed. Because the top of the wave is experiencing less friction, it moves faster and eventually topples over the bottom of the wave and breaks. The size of the wave is effected by three factors:
- Duration of wind
- Strength of wind
- Fetch (the distance that a wave travels)
Wave Terminology
Crest: The top of the wave.
Trough: The low area in between two waves.
Wavelength: The distance between two crests or two troughs.
Wave height: The distance between the crest and the trough.
Wave Frequency: The number of waves per minute.
Velocity: The speed that a wave is traveling. It is influenced by the wind, fetch and depth of water.
Swash: The movement of water and load up the beach.
Backwash: The movement of water and load back down the beach.
Crest: The top of the wave.
Trough: The low area in between two waves.
Wavelength: The distance between two crests or two troughs.
Wave height: The distance between the crest and the trough.
Wave Frequency: The number of waves per minute.
Velocity: The speed that a wave is traveling. It is influenced by the wind, fetch and depth of water.
Swash: The movement of water and load up the beach.
Backwash: The movement of water and load back down the beach.
Wave Refraction
Coastlines are very rarely perfectly straight. Coastlines normally have a series of bays and headlands. As you already know, as waves reach shallower water, the bottom of the waves experience greater friction with sea bed. This greater friction causes the waves to slow down.
If you have a series of bays and headland, waves will start to slow down around the headland where the water is shallower, but continue to travel more quickly into the bay area where the water is deeper. Because the section of the wave centred on the headland is travelling slowly and the sections either side are travelling more quickly the wave begins to refract (bend) around the headland. This concentrates the wave energy on the headland and disperses the energy across the bay.
Coastlines are very rarely perfectly straight. Coastlines normally have a series of bays and headlands. As you already know, as waves reach shallower water, the bottom of the waves experience greater friction with sea bed. This greater friction causes the waves to slow down.
If you have a series of bays and headland, waves will start to slow down around the headland where the water is shallower, but continue to travel more quickly into the bay area where the water is deeper. Because the section of the wave centred on the headland is travelling slowly and the sections either side are travelling more quickly the wave begins to refract (bend) around the headland. This concentrates the wave energy on the headland and disperses the energy across the bay.
Coastal Erosion (types of erosion)
Coasts being at the boundary of the land and the sea are extremely vulnerable to erosion. They are attacked by the immense power of the sea and the weather. Later you will look at one of the fastest eroding coastlines in the world; the Holderness coastline in NE England which is eroding at over 2 metres a year. The main ways that the sea erodes the coast are:
Hydraulic Pressure: This is when sea water and air get trapped in cracks. The increasing pressure of the water and air cause the rocks to crack.
Corrasion (abrasion): Rocks been thrown into the cliffs by waves and breaking off bits of the cliff.
Corrosion (solution): The slight acidity of sea water causing bits of the cliff to dissolve.
Attrition: Rocks, sand and stones being thrown into each other by the sea current and waves.
Wave Pounding: This is the immense power of waves crashing into cliffs that causing them to weaken.
Sub aerial weathering: This is the top of cliffs being attacked by the weather, making the cliffs weaker and less stable. Wind, rain, the heat and the cold can all cause the cliffs to be weathered.
Coasts being at the boundary of the land and the sea are extremely vulnerable to erosion. They are attacked by the immense power of the sea and the weather. Later you will look at one of the fastest eroding coastlines in the world; the Holderness coastline in NE England which is eroding at over 2 metres a year. The main ways that the sea erodes the coast are:
Hydraulic Pressure: This is when sea water and air get trapped in cracks. The increasing pressure of the water and air cause the rocks to crack.
Corrasion (abrasion): Rocks been thrown into the cliffs by waves and breaking off bits of the cliff.
Corrosion (solution): The slight acidity of sea water causing bits of the cliff to dissolve.
Attrition: Rocks, sand and stones being thrown into each other by the sea current and waves.
Wave Pounding: This is the immense power of waves crashing into cliffs that causing them to weaken.
Sub aerial weathering: This is the top of cliffs being attacked by the weather, making the cliffs weaker and less stable. Wind, rain, the heat and the cold can all cause the cliffs to be weathered.
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Bays and Headlands
Bays and headlands are formed in a very similar way to rapids (rivers topic). They are formed when you get alternate layers of hard and soft rock. The sea is able to erode the soft rock a lot quicker than the hard rock making a bay. The harder rock forms a headland.
Bay: An indented area of land normally found between two headlands. Bays are usually more sheltered so there is less erosive power, meaning you often find beaches in bays.
Headland: A piece of land that sticks out into the sea. Waves refract around headlands so they experience a lot of erosion forming features like arches and stacks (see below).
Bays and headlands are formed in a very similar way to rapids (rivers topic). They are formed when you get alternate layers of hard and soft rock. The sea is able to erode the soft rock a lot quicker than the hard rock making a bay. The harder rock forms a headland.
Bay: An indented area of land normally found between two headlands. Bays are usually more sheltered so there is less erosive power, meaning you often find beaches in bays.
Headland: A piece of land that sticks out into the sea. Waves refract around headlands so they experience a lot of erosion forming features like arches and stacks (see below).
Wave Cut Notch and Wave Cut Platform
Wave cut platforms are made in a similar ways to waterfalls and gorges (rivers topic). At high tide the power of the sea attacks and erodes the bottom of the cliff. Over time this erosion creates a wave cut notch (basically an eroded hole at the bottom of the cliff). As the wave cut notch gets bigger, the weight of rock above the notch gets greater. Eventually the cliff can not support its own weight and it collapses. The process then starts again, with the erosion of the sea making a new wave cut notch. As the process continues the cliff starts to move backwards (retreat). Because the cliff is moving backwards a wave cut platform (an expanse of bare rock) is created. Wave cut platforms are only visible at low tide.
Wave cut platforms are made in a similar ways to waterfalls and gorges (rivers topic). At high tide the power of the sea attacks and erodes the bottom of the cliff. Over time this erosion creates a wave cut notch (basically an eroded hole at the bottom of the cliff). As the wave cut notch gets bigger, the weight of rock above the notch gets greater. Eventually the cliff can not support its own weight and it collapses. The process then starts again, with the erosion of the sea making a new wave cut notch. As the process continues the cliff starts to move backwards (retreat). Because the cliff is moving backwards a wave cut platform (an expanse of bare rock) is created. Wave cut platforms are only visible at low tide.
Caves, Arches, Stacks and Stumps
Caves, arches, stacks and stumps are usually found on headlands, where wave refraction is causing erosion on three sides. The waves always look for weaknesses in the headland (cracks and joints). If they find a crack or a joint they will start attacking it. Hydraulic pressure will be the main type of erosion. Overtime the crack may turn into a cave. Slowly the cave will get bigger and cut all the way through the headland, making an arch. As the arch gets bigger the weight of the arch roof gets too great and it collapses, leaving a stack. The stack is then eroded by the sea and weathered from the air leaving a stump.
Blowhole: Sometimes the sea may erode through to the top of the headland (following a large crack). If this happens a blowhole is created.
Caves, arches, stacks and stumps are usually found on headlands, where wave refraction is causing erosion on three sides. The waves always look for weaknesses in the headland (cracks and joints). If they find a crack or a joint they will start attacking it. Hydraulic pressure will be the main type of erosion. Overtime the crack may turn into a cave. Slowly the cave will get bigger and cut all the way through the headland, making an arch. As the arch gets bigger the weight of the arch roof gets too great and it collapses, leaving a stack. The stack is then eroded by the sea and weathered from the air leaving a stump.
Blowhole: Sometimes the sea may erode through to the top of the headland (following a large crack). If this happens a blowhole is created.
Transportation (longshore drift)
Longshore Drift: This is the process of waves moving (transporting) material (load) along a coastline.
Swash: The waves breaking and traveling up the beach carrying load. Waves will break and the swash will travel in the direction of the wind.
Backwash: The waves returning to the sea with load. Waves will take the shortest possible route back to the sea (gravity).
Longshore drift only happens when the waves hit the beach at an angle. It is the process of the swash transporting material up the beach at an angle and the backwash returning directly under the force of gravity that causes material to be transported along the beach.
Prevailing (or dominant) Wind: This is the direction that the wind normally hits a coastline.
Groynes: Groynes are wooden or concrete fences (walls) placed out into the sea to stop longshore drift happening.
Sea currents: Currents are the movement of water caused by differences in temperature, changes in wind or tides. Currents can be extremely strong and can transport large amount of material.
Saltation: The wind can also transport sand and even small stones across a beach. The process of the wind bouncing sand and small stones across a beach is known as saltation.
Longshore Drift: This is the process of waves moving (transporting) material (load) along a coastline.
Swash: The waves breaking and traveling up the beach carrying load. Waves will break and the swash will travel in the direction of the wind.
Backwash: The waves returning to the sea with load. Waves will take the shortest possible route back to the sea (gravity).
Longshore drift only happens when the waves hit the beach at an angle. It is the process of the swash transporting material up the beach at an angle and the backwash returning directly under the force of gravity that causes material to be transported along the beach.
Prevailing (or dominant) Wind: This is the direction that the wind normally hits a coastline.
Groynes: Groynes are wooden or concrete fences (walls) placed out into the sea to stop longshore drift happening.
Sea currents: Currents are the movement of water caused by differences in temperature, changes in wind or tides. Currents can be extremely strong and can transport large amount of material.
Saltation: The wind can also transport sand and even small stones across a beach. The process of the wind bouncing sand and small stones across a beach is known as saltation.
Tides
Tides: Tides are the twice daily movement of the sea in and out. Tides are constant and are caused by the gravitational pull of the moon. Some tidal ranges can only be a few metres, others can be several kilometres.
Tidal Range (or intertidal zone): The difference or area between high tide and low tide.
Spring Tides: When the moon and the sun are in complete alignment you get particularly high and low tides.
Neap Tides: When the moon and sun are aligned at right angles to each other so the gravitational pull of the moon and the sun are pulling in different directions. This makes for lower high and low tides.
Tides: Tides are the twice daily movement of the sea in and out. Tides are constant and are caused by the gravitational pull of the moon. Some tidal ranges can only be a few metres, others can be several kilometres.
Tidal Range (or intertidal zone): The difference or area between high tide and low tide.
Spring Tides: When the moon and the sun are in complete alignment you get particularly high and low tides.
Neap Tides: When the moon and sun are aligned at right angles to each other so the gravitational pull of the moon and the sun are pulling in different directions. This makes for lower high and low tides.
Beaches and Sand DunesBeach: The beach is the accumulation of sand between the lowest spring tides and the highest spring tides. Beaches can be made out of sand, shingle and/or pebbles. Beaches receive their material from longshore drift, constructive waves, cliff erosion and river discharge. Beaches cane be divided into backshore, offshore and foreshore. The backshore is the area above the normal high tide level, the foreshore is the area in between normal high and low tide and offshore is the area below the normal low tide.
Berm: The berm is a ridge (long thin hill) that forms at the top of the beach. It is the highest section of the beach and is basically sand accumulated on the strand line (twigs, litter, seaweed, etc. deposited at high tide).
Intertidal zone: The area of land between high tide and low tide.
Strand line: The material (seaweed, driftwood) that is deposited by the sea at furthest point of the high tide.
Sand Dunes are very dynamic, which means they are constantly changing. Sand dunes are found behind berms and are basically an extension of the beach. They are formed by dry sand being blown up the beach.
Embryo Dune: Embryo dunes are the starting dunes of sand dunes. They form in the sheltered area behind the berm and strand line.
Foredunes: Small embryo dunes can join to make foredunes. Foredunes tend to be very yellow because they only have limited vegetation so no real humus layer develops.
Yellow Dunes: Sea couch and marram grass begin to grow on the foredunes so they become more stable and grow. As the dune grows and the vegetation develops a humus layer develops.
Grey Dunes: A developing humus layers starts changing the colour of the dune from yellow to grey.
Mature dunes: As the humus layers grows more, the dunes can sustain more plants, flowers and even trees.
Dune slack: As the size of the dunes develop water can collect between the dunes. Marsh plants can grow in these wet areas.
Blowout: A blowout is a depression or hole in the dune caused by the wind.
Humus: Is the layer of decaying plant and animal matter that adds nutrients to the ground.
Succession: The changing types of plants from basic sea couch to trees is known as succession.
Water table: The line between saturated and unsaturated ground.
Berm: The berm is a ridge (long thin hill) that forms at the top of the beach. It is the highest section of the beach and is basically sand accumulated on the strand line (twigs, litter, seaweed, etc. deposited at high tide).
Intertidal zone: The area of land between high tide and low tide.
Strand line: The material (seaweed, driftwood) that is deposited by the sea at furthest point of the high tide.
Sand Dunes are very dynamic, which means they are constantly changing. Sand dunes are found behind berms and are basically an extension of the beach. They are formed by dry sand being blown up the beach.
Embryo Dune: Embryo dunes are the starting dunes of sand dunes. They form in the sheltered area behind the berm and strand line.
Foredunes: Small embryo dunes can join to make foredunes. Foredunes tend to be very yellow because they only have limited vegetation so no real humus layer develops.
Yellow Dunes: Sea couch and marram grass begin to grow on the foredunes so they become more stable and grow. As the dune grows and the vegetation develops a humus layer develops.
Grey Dunes: A developing humus layers starts changing the colour of the dune from yellow to grey.
Mature dunes: As the humus layers grows more, the dunes can sustain more plants, flowers and even trees.
Dune slack: As the size of the dunes develop water can collect between the dunes. Marsh plants can grow in these wet areas.
Blowout: A blowout is a depression or hole in the dune caused by the wind.
Humus: Is the layer of decaying plant and animal matter that adds nutrients to the ground.
Succession: The changing types of plants from basic sea couch to trees is known as succession.
Water table: The line between saturated and unsaturated ground.