Coast Flashcards
What are waves?
Waves are a disturbance on the surface of the sea or ocean in the form of a moving ridge or swell.
How are waves caused?
Waves are caused by energy transfer from the wind to the sea. As the wind blows over the surface of the sea, it creates friction forming waves. In deep water, water molecules within a wave move in a circular movement. It is only in shallow areas that the water itself moves forward, which occurs along the coastline where the land meets the sea.
What does the size of a wave depend on?
The size of a wave depends on its fetch. The fetch of a wave is the distance it travels. The greater the fetch, the larger the wave.
Wind speed also has a significant effect on the size of waves. The stronger the wind, the larger the wave because of the energy transfer. Finally, wind duration also affects the size of a wave. The longer the wind blows over the sea or ocean, the larger the wave.
What are constructive waves?
Constructive waves build beaches.. Constructive waves predominate in calmer weather conditions when less energy is transferred to the water. Each wave is low. As the wave breaks, it carries material up the beach in its swash. Beach material is deposited as the backwash soaks into the sand or slowly drains away. When the next wave breaks, its swash will deposit more material without it being ‘captured’ by the backwash of the preceding wave.
What are some of the characteristics of a constructive wave?
Constructive waves have a long wavelength and a low frequency (8–10 waves per minute). Constructive waves are low and are typically under one metre in height. The wavefront is gently sloping and gains a little height, breaks and spills onto the beach. Water spreads a long way up the gently sloping beach.
Constructive waves are typically found in sheltered bays and spits, where they build up sandy beaches.
What are destructive waves?
Destructive waves destroy beaches. The waves are usually very high, have a short wavelength and are very frequent. They have a steep front and are typically over 1 metre tall. As destructive waves approach the coast, they gain height, plunge onto a steep beach, and do not travel far up it. The swash is very weak, whereas the backwash is strong. This leads to a net loss of beach material. Although a destructive wave’s swash is much stronger than a constructive wave, its swash is much weaker than its backwash. This means that these waves can transport beach material back into the sea creating a steep beach profile.
What are the characteristics of a destructive waves?
Short wave legnth so high frequency (10-14 waves per minute). Steep wave front. Waves over 1 meter in Hight. Breaking wave gains much height. Waves plunges onto the steep beach energy directed downwards so does not travel far up the beach. Weak swash, very strong bash wash erodes sand. Offshore bar where sand is deposited.
What is weathering?
Weathering is the breakup and breakdown of rock in situ by the action of rainwater, extremes of temperature, and biological activity.
What is mechanical weathering?
Mechanical weathering is the breakup of rock without changing its chemical composition. Freeze-thaw weathering is the primary type of mechanical weathering that affects coasts.
Freeze-thaw weathering occurs when rocks are permeable . Water enters the rock and freezes. The ice expands . This causes pressure on the rock until it cracks. Repeated freeze-thaw can cause the rock to break up.
How does freeze thaw weathering take place?
Water enters the crack in the rock tempretures fall at night. Causes water to freeze. When water turns to ice it expands by 10 percent. This puts pressure on the rock, prising the crack apart. Ice melts water seeps deeper into the crack and freezes again. Over a period of time large locks of rock can be shattered by freeze thaw.
Recently weathered rock can be seen at the foot of chalk and limestone cliffs and is easily identified because it is angular. Over time it will become smoother, forming peddles and then eventually sand.
What is Biological weathering?
Biological weathering involves the roots of vegetation, causing the breakup of rocks.
Roots enter a small crack in the bedrock, growing roots put pressure on the rock causing it to became larger the rock breaks away from the cliff face.
What is salt weathering?
Salt weathering is when salt spray from the sea gets into a crack in a rock. Water then evaporates, depositing salt crystals that expand when heated, putting pressure on the surrounding rock and weakening the structure.
The end product can be granules or blocks of rock.
What is chemical weathering?
Chemical weathering is the breakdown of rock by changing its chemical composition. When rainwater hits a rock, it decomposes This is known as carbonation. This occurs when slightly acidic (carbonic) rain or sea water comes into contact with sedimentary rock, such as limestone or chalk, and it causes it to dissolve.
Hydrolysis is when acidic rainwater breaks down the rock, causing it to rot.
Oxidation is when rocks are broken down by oxygen and water.
Weathering weakens cliffs, and this then speeds up rates of erosion.
What is mass movement?
Mass movement is the downhill movement of cliff material under the influence of gravity. There are a range of different types of mass movement
What is slumping/ rotational slip?
Cliffs formed from boulder clay, material deposited by glacial periods, are susceptible to high rates of coastal erosion.
The soft boulder clay is quickly eroded through hydraulic action and abrasion. However, this is not the only way it is being eroded. Sub-aerial processes, such as rainfall, also cause erosion. This often happens when layers of boulder clay, left behind by melting glaciers, become saturated and cause the cliff to slump. The debris on the beach is then eroded by the sea, leaving the cliff exposed once more.
What are landslides?
In areas of more resistant cliff material erosion is greatest when waves break at the foot of a cliff. This causes erosion at the base of the cliff. This creates a wave-cut notch in the base of the cliff. As the notch increases in size, the weight of the cliffs above becomes too much to support, leading to a landslide. This material will provide temporary protection for the cliff behind. However, once the sea has removed it, this process will occur again. Wave-cut platforms will be created where cliffs are made of more resistant material.
What is rockfall?
A rockfall involves rock fragments breaking away from the cliff face, often due to freeze-thaw weathering.
What is mudslide?
Mudslides occur when saturated soil and weak rock flow down a slope. These typically occur where cliffs are made up of boulder clay.
What is costal erosion?
Coastal erosion is the wearing away of the land by the sea often involves destructive waves wearing away the coast (though constructive waves also contribute to coastal erosion)
