Coastal Processes And Landforms


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Coastal Processes And Landforms

  1. 1. Coastal processes and landforms. 1. Terms 2. Wave actions 3. Landforms 4. Coral reefs 5. Sediment cells 6. Storm & swell profiles. 7. Coastal management.
  2. 2. Terms <ul><li>1. Waves is open water are called oscillatory waves. </li></ul><ul><li>2. The crest and the trough are respectively the highest and lowest points of a wave. </li></ul><ul><li>3. Wave height is the distance between the crest and the trough </li></ul><ul><li>4. Wave length (L) is the distance between two successive crests. </li></ul><ul><li>It can be determined by the formula: </li></ul><ul><li>L = 1.56 T2 </li></ul><ul><li>5. Wave period (T) is the time taken for a wave to travel through one wave length. </li></ul><ul><li>6. Wave frequency is the number of waves per minute. </li></ul><ul><li>7. Wave fetch is the amount of open water over which a wave has passed. </li></ul><ul><li>8. Wave velocity (C ) is the speed of movement of a crest in a given period of time. </li></ul>
  3. 3. Wave action. <ul><li>Explain how sea wave generated & describe </li></ul><ul><li>Destructive and constructive waves. </li></ul>2. Describe the processes of marine erosion. Using examples, explain how marine erosion can affect cliff coastlines. 3. Describe the processes of marine erosion and explain how these processes can influence the formation of a wave-cut platform. 4. Explain how waves can transport and deposit Sediment in coastal areas.
  4. 4. <ul><li>Sea wave is generated by the drag effect of wind producing orbiting </li></ul><ul><li>water particles. Height, length and velocity are all dependent upon wind </li></ul><ul><li>speed, fetch and depth of water. </li></ul><ul><li>Constructive wave : </li></ul><ul><li>Constructive waves are low energy waves with a stronger swash than </li></ul><ul><li>backwash. Where there are less than 8 waves breaking each minute </li></ul><ul><li>they tend to be constructive waves. Constructive waves tend </li></ul><ul><li>to deposit material and build up a beach. </li></ul><ul><li>Destructive waves : </li></ul><ul><li>By contrast, destructive waves have much higher energy. They are </li></ul><ul><li>much larger in height. They have a weak swash but a strong backwash, </li></ul><ul><li>and they therefore erode the beach by pulling sand and shingle (beach </li></ul><ul><li>materials) down the beach as water returns to the sea. </li></ul><ul><li>* Draw diagrams. </li></ul>Sea waves generated & types of waves.
  5. 5. Constructive & destructive waves. Constructive waves Destructive waves
  6. 6. <ul><li>2. Marine erosion processes include hydraulic, quarrying (cavitation), </li></ul><ul><li>corrosion and solution. </li></ul><ul><li>Hydraulic action : the constant force of waves crashing on the shore damages it. </li></ul><ul><li>Abrasion : waves bring with them bits of rock and sand. These help to grind down cliffs. </li></ul><ul><li>Attrition : waves cause rocks and pebbles on the shore to smash into each other and break down. </li></ul><ul><li>Solution/corrosion : acids contained in sea water will slowly dissolve certain types of rock. </li></ul><ul><li>examples, explain how marine erosion can affect cliff coastlines. </li></ul><ul><li>(Formation of wave-cut platform e.g. Durdle Door (arch), Stair Hole, </li></ul><ul><li>Lulworth Cove) </li></ul>Marine erosion and wave-cut platform.
  7. 7. <ul><li>Destructive waves at an exposed coast erode a steep coastal slope </li></ul><ul><li>through processes like hydraulic action and abrasion . </li></ul><ul><li>2. The waves erode along lines of weakness in the rock face to form a </li></ul><ul><li>notch. </li></ul><ul><li>3. Continued erosion enlarges the notch and causes its roof to </li></ul><ul><li>collapse, and a cliff is formed. </li></ul><ul><li>4. Further undercutting at the base of the cliff results in an overhanging </li></ul><ul><li>cliff which eventually collapses </li></ul><ul><li>5. As the steep cliff retreats landwards, a flat terrace at the foot of the </li></ul><ul><li>cliff is exposed to form a wave-cut platform. </li></ul>Wave-cut platform
  8. 8. Explanation on how waves transport and deposit sediment in coastal areas
  9. 9. Landforms <ul><li>Using diagrams, explain formation of spits & coastal salt </li></ul><ul><li>marshes. Describe the effects of human activities can have </li></ul><ul><li>upon these landforms. </li></ul>Describe the main features of spit and salt marshes and explain formation. Explain why spits and salt marshes are subject to change and are considered fragile environments. Suggest ways in which they can be protected. With the help of diagrams, describe the features of 3 different types of coastal depositional landform and explain the formation of each.
  10. 10. Spits & salt marshes. <ul><li>Formation: </li></ul><ul><li>A spit is a bank of sand or shingle protruding from the coast into the sea, or partially across a river estuary. </li></ul><ul><li>It results from the movement of sediment along the coast by the process of longshore drift. </li></ul><ul><li>The tip of the spit is curved by powerful wave action or wave refraction to form a lateral at A. </li></ul><ul><li>Over time, the spit extends further, often with the development of several laterals. Sediment is deposited in the shelter of the spit and a saltmarsh develops. </li></ul><ul><li>In places, spits can grow to extend right across an estuary joining two headlands to form a bay bar. </li></ul><ul><li>Where a spit links the mainland to an island, it is known as a tombolo. </li></ul>
  11. 11. Diagrams of spit and salt marshes.
  12. 12. Features of spits and salt marshes. <ul><li>Spit is an accumulation of sand and shingle that is attached to a </li></ul><ul><li>coastline. </li></ul><ul><li>2. Behind the spit are accumulations of silt and mud that are anchored </li></ul><ul><li>by vegetation to produce marsh and creek areas. </li></ul><ul><li>3. The laterals represent periods of growth of the spit are formed from </li></ul><ul><li>beach sediment transported by longshore drift which accumulates </li></ul><ul><li>where the coastline changes direction or where drift is held up by a </li></ul><ul><li>river mouth or estuary. </li></ul><ul><li>4. Accumulations of mud occur in the shelter of the spit and is </li></ul><ul><li>colonised by halophytes. </li></ul>
  13. 13. Fragile environments (spits and salt marshes) & ways in which they can be protected. <ul><li>Spit and salt marshes are subject to change and are considered fragile environments because Spits can change shape due to both growth (laterals) or erosion. </li></ul><ul><li>Storms or removal of sediment supplies can have severe impacts such that these features can be considered fragile. Salt marshes are equally responsive if the shelter of the spit is removed or pollution affects the estuarine or river silts and mud. </li></ul><ul><li>Development or changes of sea level can also have severe consequences. </li></ul><ul><li>Protection can be afforded by trapping sediment (groynes) or guaranteeing continuous sediment supplies. * Case study: Breaching of spit during storm (Chesil Beach) & Dredging (Poole Harbour) </li></ul>
  14. 14. Coastal depositional landform and formation. Coastal depositional landforms: Spits, bars, dunes and salt marshes and beaches <ul><li>Beaches Beaches are the main feature of deposition found at the coast, </li></ul><ul><li>these consist of all the material (sand, shingle etc.) that has built up between </li></ul><ul><li>the high and low tide mark. There are number of different sources of beach material </li></ul><ul><li>the main source being rivers, where fine muds and gravels are deposited </li></ul><ul><li>at the river mouth. Other sources of beach material include longshore drift </li></ul><ul><li>(bringing material from elsewhere along the coast); constructive waves </li></ul><ul><li>(bringing material up the beach from the sea) and from cliff erosion. As constructive waves build up beaches, they often form ridges in the beach </li></ul><ul><li>known as berms. The berm highest up the beach represents the extent </li></ul><ul><li>to which the water has reached during high tide. </li></ul>
  15. 15. Bars: These form in the same way as a spit initially but bars are created where a spit grows across a bay, joining two headlands. Behind the bar, a lagoon is created, where water has been trapped and the lagoon may gradually be infilled as a salt marsh develops due to it being a low energy zone, which encourages deposition. Example of a Bar: Slapton Sands - Devon.
  16. 16. <ul><li>TOMBOLOS Tombolos are formed where a spit continues to grow outwards joining land to an offshore island. Example of a Tombolo: - Chesil Beach - which joins the South Dorset coast to the Isle of Portland. </li></ul>
  17. 18. Cliff profile affected by nature of rocks.
  18. 19. Factors that affect cliff profile. <ul><li>Cliff profiles owe their form to the geology (Lithology and structure), sub-aerial processes and wave energy along a given stretch of coastline. It takes thousands of years for the cliffs profile to form from complex processes, there are many complicated processes taking place on coasts that affect the profile of a cliff. </li></ul><ul><li>Wave action causes three erosional processes, abrasion, hydraulic action and corrosion. These processes are most effective when high energy waves, associated with storm conditions strike coast profiles made of less resistant rocks. Concentrated wave action on cliff leads to undercutting. The three types of wave erosion processes play an important part in forming cliff profile. </li></ul>
  19. 20. Factors that affect sea cliff profiles. <ul><li>(b) The factors that can affect sea cliff profiles are wave </li></ul><ul><li>action (dependent upon fetch etc.), marine erosion </li></ul><ul><li>processes, geology and sub-aerial weathering and erosion. </li></ul><ul><li>These combinations can be shown to produce distinctive </li></ul><ul><li>profiles and answers should demonstrate some of these </li></ul><ul><li>and not merely generalise the cliff forms (‘any cliff’). </li></ul><ul><li>Clearly there is a lot of material available so we will expect </li></ul><ul><li>some selectivity. Even so there should be some </li></ul><ul><li>representation in each of the factor areas as well as some </li></ul><ul><li>idea of impact. </li></ul>
  20. 21. Coral reef <ul><li>1(a) With the aid of diagrams, describe the nature </li></ul><ul><li>of fringing reefs, barrier and atolls. </li></ul><ul><li>(b) Give a brief explanation of the theories that </li></ul><ul><li>have been advanced for their formation. </li></ul><ul><li>(c) How can changes in sea level affect the </li></ul><ul><li>formation and continued existence of coral </li></ul><ul><li>reefs and atolls? </li></ul><ul><li>(d) What are the condition required for coral reef </li></ul><ul><li>formation? </li></ul>
  21. 22. Fringing, Barrier and Atoll. <ul><li>Good annotated diagrams will probably be the key here and could receive </li></ul><ul><li>the bulk of the marks. If well done could receive 3 marks each. Fringing </li></ul><ul><li>reef should show (be described as) a coral reef that is attached to a shore </li></ul><ul><li>either as a continuous wave washed erosion platform or separated by a </li></ul><ul><li>shallow lagoon. Barrier reefs are of great thickness (e.g. Queensland) and </li></ul><ul><li>are separated from coast by a wide and deep lagoon or strait. Atolls are </li></ul><ul><li>ring-shaped islands surrounding a central lagoon. </li></ul>
  22. 23. Theories of formation
  23. 24. Changes in sea level affect the formation and continued existence of coral reefs and atolls Coral is sensitive to heat and light it is also sensitive to changes in sea level as reefs cannot survive long periods of sub-aerial exposure. Falls in sea level can lead to the death of coral and to the emergence of the reef above high water forming low lying land such as keys. The islands become colonized by vegetation. To a certain extent reefs can contend with sea level rise leading to the growth of thick reefs (Darwins model). However rapid rise consequent upon global warming may result in inundation and destruction.
  24. 25. Condition for coral reef formation <ul><li>As a marine organism coral requires: </li></ul><ul><li>Temperatures generally above 20C with optimum 25–30 C; </li></ul><ul><li>Sufficient light (depth) for photosynthesis to occur; </li></ul><ul><li>Salinity within range 27–40 (i.e. not extreme). </li></ul><ul><li>Suitable surface to develop upon (firm base); </li></ul><ul><li>Limited amount of turbulence for oxygen and nutrient supply; </li></ul><ul><li>Lack of sediment (clear water); </li></ul><ul><li>Not too great a tidal range or large changes in sea level; </li></ul><ul><li>Gentle Currents ; </li></ul><ul><li>food supply (zooplankton). </li></ul>
  25. 27. Sediment cell and landforms. <ul><li>A coastal sediment cell is a system by which sediments </li></ul><ul><li>are sourced, transported and deposited within a part of a </li></ul><ul><li>coast and offshore area. </li></ul><ul><li>They appear as a coastal system, thus sediments are </li></ul><ul><li>derived from estuaries and coastal erosion, transported by </li></ul><ul><li>Such features as longshore drift and deposited in the form </li></ul><ul><li>of beaches, bars, spits etc. </li></ul><ul><li>The nature of the landform thus depends upon the </li></ul><ul><li>nature of the cell, as well as the configuration of the coast. </li></ul>
  26. 28. Describe and explain the features shown below and account for the Differences between the storm and swell profiles. STORM & SWELL PROFILES.
  27. 29. Storm and swell profile.
  28. 30. Coastal management Explain how human activities have affected the physical environment in a coastal area or coastal areas you have studied. Explain the problems of the sustainable management of a stretch or stretches of coastline you have studied.
  29. 31. Problems of coastal management and evaluate the solution <ul><li>Groynes are low walls built out into the sea, usually at right angles to the coastline. They help break the power of the incoming waves and slow down the process of longshore drift. </li></ul><ul><li>Steel and rock walls. Steel walls are sunk vertically into the beach to stop the sand moving. Rock walls stop waves removing sands and gravel from the beach. </li></ul><ul><li>Embankments. These are high walls that are situated where a beach meets the land or cliff. They are usually made of concrete or stone and bounce back storm waves. </li></ul><ul><li>Beach slopes are made shallower to keep the sand and shingle stable. </li></ul><ul><li>Dumping sand and shingle offshore to reduce the power and height of the incoming waves. </li></ul><ul><li>Building a barrier across an estuary of a river to reduce the risk of flooding (for example the Thames Barrier). </li></ul><ul><li>Setting up a storm tide early warning system which provides information about extra high tides. </li></ul><ul><li>Preventing building on high flood risk areas. This would minimise the loss of life and damage to property. </li></ul>
  30. 32. Human activities affecting coastal environment.
  31. 33. Sustainable management of coastlines. <ul><li>Sustainable management will be defined along the lines of encouraging Improvement of coasts but within the capacity of the supporting physical systems i.e. minimising environmental degeneration. </li></ul><ul><li>In coastal terms this can mean the preservation both of the coastal environment and its exploitation. Thus protection schemes that have severe knock on effects are of limited usefulness. </li></ul><ul><li>Similarly ado nothing approach may also have repercussions for the long term coastal environment (loss of fishing, tourism landforms etc). These aspects can be illustrated by reference to a particular case study or more disparate examples. </li></ul><ul><li>* Examples: </li></ul>