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Erosion and Landforms

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New Unit: Managing Coasts We are moving onto a new unit called ‘Managing Coasts’. This topic will cover processes and features of the UK coastline. L1: Features of different types of wave. L2 & L3: Different erosion processes and associated features. L4 & 5: Different depositional processes and associated features. L6: Coastal defences L7: UK Case study Starter – what do you remember about waves? Tick the correct box in the table below. Cons = constructive wave Des = destructive wave Feature Cons Des Generally high waves Strong backwash Generally long low waves Break 6 to 9 times per minute Can cause erosion on cliff faces Frequently break between 11 and 15 times per minute Weak backwash Can form beaches Consider what might cause this to happen? Coastal Erosion Learning Objectives: - to know the different coastal erosion processes - to know the different types of landforms created by coastal erosion. What is Coastal Erosion? Task: Fill in the missing vowels (a,e,i,o,u) Coastal Erosion _s th_ w_ _r_ng _w_y _f m_t_r_ _l by s_ _ w_t_r. Th_r_ _r_ 4 pr_c_ss_s _f _r_s_ _n. Th_s_ _r_ * Hydr_ _l_c _ct_ _n * _br_s_ _n * _ttr_t_ _n * S_l_t_ _n. What is Coastal Erosion? Answers Coastal Erosion is the wearing away of material by sea water. There are 4 processes of erosion. These are * Hydraulic action * Abrasion (sometimes called corrasion) * Attrition * Solution (sometimes called corrosion) The processes of erosion. Task: Look at the information on the following 4 slides to match each of the images below with the correct process. Abrasion Attrition Solution Hydraulic action The waves FORCE water into cracks in the rocks. This is called HYDRAULIC ACTION Rough seas fling pebbles against the cliff The pebbles act like sandpaper. This is called ABRASION The waves knock chunks of rock together. The rocks end up as pebbles on the beach This is called ATTRITION The water DISSOLVES soluble material from the rocks. This is called SOLUTION How is the coast eroded? Task: Use the information on the following 4 slides to complete the table that is on the slide after them. Success criteria: 1. Define the type of erosion and insert correct diagram to show the process 2. Show you can explain how your type of erosion works 3. Use the key terms highlighted correctly and extension information in your explanation The wearing away of pebbles which are in the sea. Pieces of rock and pebbles are eroded by the sea, from the cliffs. These pieces of rock fall into the Pebbles sea and are thrown around by the crash into waves. As they are thrown around each other by the waves they collide with in the waves each other. Over time the pebbles are worn down by each other and become smaller in size, smoother and more rounded. Extension information This is why on the part of the beach nearest to the sea you will always find the smaller rocks and pebbles. A chemical reaction caused by the salt and acids in the sea water. The waves cause erosion by solution in two main ways. Firstly, the sea contains salt. The waves break off material from the cliffs, which falls into the sea. Some Soluble of this material is then dissolved by material is the salt water in the waves. dissolved by the salty and acidic Secondly when the waves crash at sea water the cliff, the salt and other acids in them causes a chemical reaction to happen with soluble rocks in the cliff. This causes parts of the cliff to be eroded by being dissolved. Extension information This can be seen particularly on limestone and chalk cliffs where the water is a milky blue at the bottom of the cliffs due to the dissolved lime. Rocks in the waves wear away the cliff face. The waves contain material (pebbles Rocks are rocks and sand) that has been eroded thrown at from cliffs. the cliff. When the waves are destructive they have enough power to throw the materials that they carry with great force against the cliff face. The material acts like sandpaper and wears away and breaks off more rocks, which in turn are thrown against the cliff by the breaking wave. The force of the waves wear away the cliff. When the waves are destructive they have enough power to throw themselves against the cliffs. This Air in the cracks is happens repeatedly until the cliff compressed develops cracks. Once the cracks have developed the power of the waves continues to widen them. Extension information The water also gets into the cracks in the cliff, and it causes the air to be compressed (squashed). This all puts even more pressure on the cracks and pieces of rock break off. Erosion Process Description of process Diagram What questions can you ask about this photograph? My questions are….. Landforms of coastal erosion Now we know about the different types of erosion that happen at the coast, let’s look at what the erosion does to our coastline over time…. Landforms of coastal erosion Headlands and Bays Headlands and bays formation: follow the arrows… This is a ‘bird’s eye view’ What does of a coast line. ‘bird’s eye view’ mean? Imagine you are flying above the land and looking down – what would it look like? Headlands and bays formation: This is a ‘bird’s eye view’ of a This is a ‘bird’s eye view’ of the coast line 10,000 years ago… same coastline today… Headlands are usually formed of more resistant (harder) rock types than bays. If there are different bands of rock along a coastline, the weaker or softer rock, such as clay, is eroded fastest. This leaves more resistant rock types, such as granite, sticking out Headlands and bays formation: Use the sentence starters and the word bank to write a short paragraph to tell me how headlands and bays have formed – write in complete sentences 1. A coastline has areas of…. 2. The hard rock is… 3. This leaves a … (describe it) 4. The soft rock is…. 5. This leaves a… (describe it) eroded quicker hard and soft rock not eroded quickly headland bay sticks out to sea as it is too strong as it is too weak with a beach in Headlands and bays formation: A coastline has areas of Your short paragraph Write five words which you will use to remember how headlands and bays form Headlands and Bays Landforms of coastal erosion Wave-cut platforms • These photographs show a cliff collapsing… • Why do you think this has happened? Cliff erosion and wave-cut platforms 1.Waves attack the bottom of the cliff, particularly during storms and at high tide. 2.Eventually a wave-cut notch is formed. 3.At the same time weathering attacks and weakens the top of the cliff. 4.The weakened cliff is left unsupported and eventually collapses. 5.Once the sea has removed the fallen rocks it can start the process again. 6.The cliff will move back and leave a rocky platform at the base called a wave- cut platform. C F B A E D Match the statement to the diagram to show the complete process – use the letters A – F to put the statements in the correct order The notch gets larger until the rock above collapses Waves attack the base of the cliff again and the whole process repeats The sea will remove the lose rock that has fallen. Destructive waves attack the base of the sea cliff by hydraulic action and abrasion Waves undercut the cliff and create a wave cut notch. Over time the whole cliff moves inland called retreat and a flat area of rock is left behind called a wave cut platform. Landforms of coastal erosion Cave to Stump Features of a headland Draw lines to match the words with the features on the photograph Where are they on the image? Cave Arch Stack Stump Crack to stump - joint • Cracks and joints in the rock between the high and low tide mark (the wave attack zone) form and become enlarged due to hydraulic action, abrasion and solution. Joint • Weathering processes such as chemical weathering can also speed up this widening. Joint Crack to stump - cave • These cracks and joints eventually widen into smaller caves through continued hydraulic action and abrasion. The larger surface area exposed to weathering and erosion processes leads to an increase in the rate of rock removal. • Weathering processes continue as before. Crack to stump - cave • Wave refraction (where waves bend in around the sides of a headland) leads to increased erosion along the side of the headland, forming a very large cave. • The large area exposed within the cave means more hydraulic action and abrasion can table place. Crack to stump - arch • Caves developing on opposite sides of a headland may erode deeper as a result of these erosional processes. • Eventually they meet, combine, and form an arch. • Biological and chemical weathering on the top or roof of the arch begin to weaken it. Crack to stump - stack • The arch roof becomes narrower as it is weathered from above by biological and chemical weathering. It becomes thinner until it eventually collapses, leaving an isolated pillar of rock known as a stack. • Material that falls into the sea is eroded away by attrition. Crack to stump - stump • The resultant stack is weathered from above by chemical and mechanical processes, as well as eroded by the sea at it base. It will reduce in both height and width until it collapses and leaves behind a stump. • The collapsed material is eroded by attrition and transported away.
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