The Coastal Zone

Features and Processes:Types of Erosion:Corrosion: Fragments of rock picked up and thrown at the cliffs acting as an erosive tool.Attrition: Material carried by the waves, bump into each other and so are smoothed and broken down into smaller particles.Abrasion: 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.Solution: 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.Transportation Methods:Although Long Shore Drift is the main process of transportation the material moves in four different ways. These are:Traction: Larger materials is rolled along the sea floor.Saltation: Beach material is bounced along the sea floor.Suspension: Beach material is suspended and carried by the waves.Solution: Material is dissolved and carried by the water.Weathering:Weathering is the process of weakening and breaking up rocks caused by water, frost, temperature change, flora and fauna and it is sometimes wrongly twinned with erosion.It is the physical and chemical breakdown of rocks and minerals at or near earth's surface.Mechanical Weathering:Mechanical weathering takes place when rocks are broken down without any change in the chemical nature of the rocks. The rocks are essentially torn apart by physical force, rather than by chemical breakdown. The forces that break rocks down can be numerous, and include such things as pent up energy as the Earth’s crust slowly moves. When great amounts of pressure build up, the resulting mechanical effect can be that very large joints, or faults are created.Freeze-Thaw:Most rocks are very hard. However, a very small amount of water can cause them to break. When water seeps into cracks and freezes it then expands. This powerful force can increase the size of cracks. Over time the repeated freeze-thaw action of water can break rocks apart. Eventually, pieces of rock break off creating scree.Exfoliation:This type of erosion is common in warm areas. As the sun shines on rocks during the day it causes them to expand. During the night the rock contracts due to the colder temperature. Over time this continued process causes small pieces of surface rock to flake off.Chemical Weathering:Chemical weathering causes an alteration to the chemical composition of rock due to a reaction. Water that is slightly acidic can dissolve rock. An example of this would be slightly acidic rain changing the chemical composition of limestone to form a limestone pavement. This occurs on the surface and along the joints and bedding planes of limestone. You can also see evidence of this on buildings made from limestone.Biological Weathering:Biological weathering is the effect of living things. For example as the roots of a tree extend into the ground they can prise rocks apart. Ivy growing up a building can cause bricks to loosen. It also occurs on a much smaller scale through lichen and moss.Flower Power:One of the ways a plant spreads its seed is by the wind. Seeds carried by the wind may drop into cracks in rock. The crack proves to be an ideal place for the seed to germinate as the crack unwittingly provides moisture and shelter.Coastal Environments, Mass MovementMass Movement:The downhill movement of weathered material under the force of gravity.The speed can vary considerably, from soil creep, where the movement is barely noticeable, to slumps, slides and mud flows, where the movement becomes increasingly more rapid.Rotational Slip:Here, water can build up in soils and add weight to it.The material moves down slope along a curved surface, leaving behind an exposed scarp face below the head of the slump, and producing a hummocky toe at the foot.Mud flow:Occurs on steep slopes over 10°. It's a rapid sudden movement which occurs after periods of heavy rain. When there is not enough vegetation to hold the soil in place, saturated soil flows over impermeable sub soil, causing great devastation and endangering lives.Rock Fall:Is the rapid, free-fall of rock from a steep cliff face. Rock fragments fall from the face of the cliff because of the action of gravity. This is made worse by freeze-thaw action loosening the rock. Bare, well-jointed rock is very vulnerable to rockfall - water enters the joint, freezes and expands, cracking the rock. A scree slope of fallen rock is formed at the bottom of the cliff.Land Slide:Landslides take place when dirt, pebbles, rocks and boulders slide down a slope together. Sometimes these landslides are small, and hardly noticeable. Other times however, they can be substantial, involving the entire side of a mountain.Features of the Coast:Bay, Headland, Arch, Stack and Stump.Long Shore Drift:The process whereby material is moved along a stretch of coastline. Waves approach the shore at an angle (usually in line with prevailing wind direction) and swash moves material up the beach in this direction. Backwash pulls material straight down the beach.The result is that material is transported in a zig-zag fashion. It is important to remember that long shore drift can act on a beach in more than one direction, depending on the approach of waves and wind direction. Deposition:When the sea loses energy, it drops the sand, rock particles and pebbles it has been carrying. This is called deposition. Deposition happens when the swash is stronger than the backwash and is associated with constructive waves. Types of Waves:Destructive Waves: Destroy beaches. The waves are usually very high and very frequent. The back wash has less time to soak into the sand. As waves continue to hit the beach there is more running water to transport the material out to sea. these waves are most common in winter. Constructive Waves: Build beaches. Each wave is low. As the wave breaks it carries material up the beach in its swash. The beach material will then be deposited as the backwash soaks into the sand or slowly drains away. These waves are most common in summer. Wave Refraction: Wave refraction refers to what happens to waves when they approach an uneven coastline.  Very few coastlines are perfectly straight, and few sea beds have uniform height and shape. Headland and Bays: The bands of soft rock, such as sand and clay, erode more quickly than those of more resistant rock, such as chalk. This leaves a section of land jutting out into the sea called a headland. The areas where the soft rock has eroded away, next to the headland, are called bays. Wave Cut Platforms: They really are platforms of rock created by waves cutting away at the cliffs, leaving just a rock surface at beach level.When cliffs are being worn away, the processes of weathering and erosion only act on the parts of the cliff that are above the level of the beach. Once the cliff has been worn down to the same level as the beach, the ability of the sea to continue to erode the remaining rock becomes much reduced. Under the right conditions the continuous erosion and landward retreat of the cliff line produces a wide, flat, area of rock, looking as if the foundations of the cliff have been exposed. Wave cut platforms are often most obvious at low tide when they become visible as huge areas of flat rock. Sometimes the landward side of the platform is covered by sand, forming the beach, and then the platform can only be identified at low tides or when storms move the sand. Caves, Arch, Stack, Stump sequence:Caves occur when waves force their way into cracks in the cliff face. The water contains sand and other materials that grind away at the rock until the cracks become a cave. Hydraulic action is the predominant process.If the cave is formed in a headland, it may eventually break through to the other side forming an arch.The arch will gradually become 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.The stack will be attacked at the base in the same way that a wave-cut notch is formed. This weakens the structure and it will eventually collapse to form a stump.One of the best examples in Britain is Old Harry Rocks, a stack found off a headland in the Isle of Purbeck.Beach:Beaches are a common feature of a coastline. Beaches are made up of eroded material that has been transported from elsewhere and deposited by the sea. Constructive waves help to build up beaches. The material found on a beach (i:e sand or shingle) depends on the geology of the area and wave energy. A cross-section of a beach is called a beach profile. The shingle ridges often found towards the back of a beach are called berms.The material found on a beach varies in size and type as you move further away from the shoreline. The smallest material is deposited near the water and larger material is found nearer to the cliffs at the back of the beach. Large material is deposited at the back of the beach in times of high energy, for example during a storm. Most waves break near the shoreline, so sediment near the water is more effectively broken down by attrition. Sandy beaches have gently sloping profiles and shingle and pebble beaches are steeper.Coastal Environments, SpitCase Study: Blakeney Point Spit, North Norfolk.Blakeney point is located in the East of England. It is controlled by the National trust and part of the national nature reserve. Blakeney is a spit that was formed by a process called Long shore drift because of erosion along the coastal line. The process of deposition happens, the movement of sand along the coast by sea waves. That's why the land is made of sand. Coastal Management    As things like coastal tourism have become more frequent, humans have found it increasingly necessary to attempt to control the effects of the sea. The main reasons for coastal management are: to protect the coast from the erosive effects of the sea and to increase the amount of sand on the beach. Many strategies have been tried around the world, and these can be divided into two main groups, hard and soft engineering. Hard engineering methods aim to stop the coastal processes from occurring. Soft engineering methods try to work with nature to protect the coast.Hard Engineering:Building a sea wall: A wall built on the edge of the coastline. AdvantagesProtects the base of cliffs, land and buildings against erosion. Can prevent coastal flooding in some areas. Disadvantages: Expensive to build. Curved sea walls reflect the energy of the waves back to the sea. This means that the waves remain powerful. Over time the wall may begin to erode. The cost of maintenance is high.Building groynes: A wooden barrier built at right angles to the beach.AdvantagesPrevents the movement of beach material along the coast by long shore drift. Allows the build up of a beach. Beaches are a natural defence against erosion and an attraction for tourists. Disadvantages: Can be seen as unattractive.Costly to build and maintain. Rock armour or boulder barriers: Large boulders are piled up on the beach.Advantages: Absorb the energy of waves. Allows the build up of a beach.Disadvantages: Can be expensive to obtain and transport the boulders. Soft Engineering: Beach management: This replaces beach or cliff material that has been removed by erosion or long shore drift. The main advantage is that beaches are a natural defence against erosion and coastal flooding. Beaches also attract tourists. It is a relatively inexpensive option but requires constant maintenance to replace the beach material as it is washed away.Managed retreatAreas of the coast are allowed to erode and flood naturally. Usually this will be areas considered to be of low value - eg places not being used for housing or farmland.The advantages are that it encourages the development of beaches(a natural defence) and salt marshes (important for the environment) and cost is low. Managed retreat is a cheap option, but people will need to be compensated for loss of buildings and farmland.Global Warming:Global Warming is a rise in temperature over the earth's surface, thoughts to cause extremes of weather, this is thought to be caused by human activity. Possibly caused by pollution, chiefly the amount of carbon we add or leave in the atmosphere. It may increase temperature levels world wide.Global warming happens because of burning fossil fuels releases harmful gases into the atmosphere, carbon dioxide is one of these gases - it is called a greenhouse gas because it stops heat escaping from the atmosphere causing global warming.The consequences of Global Warming: Polar ice caps could melt - evidence suggests this is already happening. Causes flooding to low lying land - particular problems for countries like Netherlands. Less water vapour in the atmosphere leading to more drought.Waves and Coastal Erosion:Hydraulic Power: The sheer weight and impact of water against the coastline, particularly during a storm. Abrasion: Breaking waves throw sand and pebbles against the coast during stormsAttrition: The rocks and pebbles carried by the waves rub together and break down into smaller pieces.Solution: Chemical action on rocks by seawater dissolve some rocks, especially limestone.   

New Page