Coastal Erosion: Waves, Factors, and Landforms

1. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Waves • Responsible for erosion, transportation and deposition of material along coastlines • Generated by wind passing over the surface of the sea • Fetch is the open area of the sea that a wave travels over • The longer the fetch, the stronger the wind speed, the stronger and greater the waves generated

2. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Factors affecting the rate of coastal erosion Where the breaking of a wave occurs • Steepness of the wave • Rock resistance

3. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Types of waves • Constructive waves • Destructive waves

4. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Wave refraction • Waves slow down as water becomes shallow • Waves bend and change their direction as they approach the shore • Causes waves to move towards the headland where their erosive force is released

5. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Longshore drift – a process of coastal transportation The sea transports its load of sand and shingle in two main ways: • Up the shore in swash • Back down the shore in backwash

6. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Processes of coastal erosion • Geology of the coastline determines the rate of erosion • Soft rock, e.g. chalk, is eroded faster than harder more resistant rock, e.g. igneous rock

7. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Processes of coastal erosion • Hydraulic action • Compression • Abrasion/corrasion • Attrition • Solution/corrosion

8. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Landforms of coastal erosion • Cliffs • Cliffs are vertical slopes on a coastline • Form as a result of a combination of coastal processes of erosion, such as hydraulic action, compression, abrasion, solution and attrition • Destructive waves attack an area of weakness in rocks • Crack/joint forms • Crack/joints are attacked by hydraulic force of the water and by compression • Notch forms

9. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Landforms of coastal erosion • Cliffs (continued) • Notch gets bigger, eventually the rocks above the notch are unsupported and collapse to form a cliff • Shattered rock falls into the sea • Sea uses this shattered rock to further erode the cliff through abrasion • Solution also erodes the cliff face • These events continue over time and the cliff face retreats • Wave-cut platforms – surface of rock that remains in front of the retreating cliff • Wave-built terraces – deposited pieces of rock that are deposited below low-tide level

10. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Landforms of coastal erosion 2.Bays and headlands • Differential erosion – rocks along coastlines are eroded at differing rates depending on whether they are soft or hard • Sections of coastline that are composed of soft rock will erode faster than areas composed of hard, more resistant rock • Stretches that are composed of soft rock will form bays • Harder more resistant rock will take longer to erode and will remain jutting out into the sea as headlands

11. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Landforms of coastal erosion 3. Sea caves, sea arches, sea stacks and sea stumps • Caves form in an area of weakness on a cliff face or headland • Processes of coastal erosion act on this area of weakness and enlarge it to form caves • Caves are further eroded by abrasion, resulting in them becoming larger • Sea arches form when continued erosion occurs in a sea cave causing it to extend right through the headland • A sea arch may also form when two sea caves form back to back on the opposite sides of a headland

12. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Landforms of coastal erosion • Sea caves, sea arches, sea stacks and sea stumps(continued) • A sea stack is a rock which is standing out in isolation in the sea away from the coastline • Sea stacks form when erosion continues on a sea arch, widening the sea arch and causing the roof of the sea arch to eventually collapse • When the roof of the sea arch collapses, it leaves the former section of headland isolated or cut away from the main headland/coast. What remains standing out in the sea in isolation is called a sea stack • A sea stump is the eroded remains of a sea stack

13. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Landforms of coastal erosion 4. Blowholes • Blowholes form at areas of weakness, for example, where a hole forms on the surface of a cliff top joins with a roof of a sea cave. They are formed as a result of compression • Air may become trapped in a sea cave by waves • Results in a build up of pressure which leads to rock shattering the rocks of the cave roof • Rock eventually collapses creating a ‘blowhole’

14. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Processes of coastal deposition • Coastal deposition occurs when waves lose energy and therefore their ability to carry material • Sea deposits its load on the coastal area • Constructive waves have an ability to move the load inland • Wave refraction in bays result in wave energy decreasing and this results in deposition occurring • Deposited material may include shingle, sand and sediment

15. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Landforms of coastal deposition 1. Beach • A beach is an area of sand and gravel located in an area between high tide and low tide mark • Waves move up the sea shore, slow down and their load of sand and rocks is deposited • Heavier load of rock and shingle is deposited on the backshore • Finer, lighter material such as sand is deposited on the foreshore • Over time a beach is formed • A storm beach forms when waves are strong enough to push large rocks and boulders above the high tide mark

16. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Landforms of coastal deposition 2. Sand spit • A sand spit is a long narrow ridge of deposited sand and shingle that is connected to the coast at one end • Sand spits develop due to longshore drift and deposition • Sand spits form where the process of longshore drift is interrupted • Sediment is deposited in sheltered and shallow water • Over time this sediment builds up and becomes visible above the level of the sea

17. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Landforms of coastal deposition 2. Sand spit (continued) • On the seaward side of the sand spit constructive waves deposit fine sediment such as sand and form a beach • Over time the sand spit gets wider • As sand spits grow the area of water behind it is often then sheltered by waves and wind • This often leads to the formation of a salt marsh • Wave refraction may occur at the end of a sand spit which results in the sediment being carried around the end of the sand spit to form a recurved spit (i.e. hook)

18. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Landforms of coastal deposition 3. Sand bar and lagoon • A sand bar forms when a sand spit extends across a bay and over time connects two land masses • Sand bars will eventually seal off an area of coastline and the water directly behind the sand bar will then be called a lagoon

19. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Landforms of coastal deposition 3. Sand bar and lagoon (continued) There are two types of sand bar: • Offshore bar • Located away from the coastline • Parallel to the coastline • Generally only exposed at times of low tide • Breaking waves deposit sand on the offshore bar • Size of the offshore bar increases over time • May eventually block or close off the bay creating a lagoon

20. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Landforms of coastal deposition 3. Sand bar and lagoon (continued) 2. Baymouth bar • Sand spit extends from one side of a landmass across a bay and reaches the other landmass • Blocks/closes off the bay

21. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Landforms of coastal deposition 4. Tombolo • Tombolos are formed due to wave refraction and longshore drift • Result from a sand spit extending out to an island and connecting the island to the mainland • Waves approach the island, wave refraction occurs • Sediment is deposited • Results in the spit connecting the island to the mainland and – a tombolo is formed

22. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Human activities can impact on the operation of coastal processes • The impact of recreational pressures • Caravan parks, camping sites and hotels or even apartments may be unwisely and hastily built • Sand dunes damaged • Sewage and litter • Pollution

23. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Coastal defence work • Groynes • Rock armour • Sea walls • Breakwaters • Gabions

24. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Conservation and management case study Increasing rates of coastal erosion may be attributed to a number of factors: • Rising sea levels • Increasing storm frequency • Increasing wave energy

25. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Erosion may be caused by the following: • People • Nature

26. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Advantages of beach nourishment • Restores and widens existing beaches • Infrastructure and property at the back of the beach is protected • Beach nourishment places sand on the beach

27. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Disadvantages of using beach nourishment • Sand pumped onto beaches through beach nourishment usually erodes faster than the natural sand • Expensive and must be repeated • Visitors and marine life impacted during beach nourishment pumping

28. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Sand dune management Erosion and damage may be caused by the following: • Wind • Water • Human activity

29. Chapter 12: Coastal Processes, Patterns and Associated Landforms, and Human Interaction • Protection of sand dunes • The action taken includes the following: • Planting/re-establishment of vegetation • New sand dune formation encouraged • Screens and fences trap sand that is blown inland • Grass and shrubs are planted on the sand dunes to ensure stability • Timber pathways laid down