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Managing river and coastal environments: A continuing challenge 2.4How do coastal processes shape the processes shape the land? land? Part B.

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Presentation on theme: "Managing river and coastal environments: A continuing challenge 2.4How do coastal processes shape the processes shape the land? land? Part B."— Presentation transcript:

1 Managing river and coastal environments: A continuing challenge 2.4How do coastal processes shape the processes shape the land? land? Part B

2 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? AErosional landforms Wave-cut platform Stack Sea arch Geo Sea cave Sea cliff Blow- hole

3 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? BDepositional landforms Beach Spit Bar Tombolo

4 Managing river and coastal environments: A continuing challenge Is wave action the only factor in shaping the coast? No, there are several factors interacting with each other to create coastal landforms.

5 Managing river and coastal environments: A continuing challenge Is wave action the only factor in shaping the coast? 1Tectonic movement Tectonic movement can cause land to rise or fall. The uplifting or lowering of the coastline changes the zone of active wave erosion. Compressional force Sea Plate Uplifting (or lowering) of land Subject to active wave erosion

6 Managing river and coastal environments: A continuing challenge Is wave action the only factor in shaping the coast? 2Nature of rocks Horizontal bedding plane Sea Wave undercutting enlarges the notch and causes collapse of rock above the notch. Parallel retreat of cliffs is resulted. Land Notch

7 Managing river and coastal environments: A continuing challenge Is wave action the only factor in shaping the coast? 2Nature of rocks Bedding plane dipping seawards Sea Rocks loosened by wave erosion and mass movement slide down along the bedding plane. Land

8 Managing river and coastal environments: A continuing challenge Is wave action the only factor in shaping the coast? 2Nature of rocks Bedding plane dipping landwards Sea The slope is more resistant to wave erosion. Land

9 Managing river and coastal environments: A continuing challenge Is wave action the only factor in shaping the coast? 3Weather and climate Global warming leads to a rise in sea levels because of the thermal expansion of water and melting of polar ice caps. Changes in sea levels are changing the position of the zone of active wave erosion.

10 Managing river and coastal environments: A continuing challenge Is wave action the only factor in shaping the coast? 3Weather and climate A warmer world would generate more storm surges, thereby affecting coastal landforms.

11 Managing river and coastal environments: A continuing challenge Is wave action the only factor in shaping the coast? 4Fluvial processes Rivers bring sediment to the coast as they flow to the sea. Deposition occurs at the coast where wave action is weak. Sediment may gradually build up to form depositional landform such as a delta. Delta The River Nile, Africa (Credit: NASA) Red Sea River Nile

12 Managing river and coastal environments: A continuing challenge Is wave action the only factor in shaping the coast? 5Marine organisms Some marine organisms protect the coast from wave erosion and favour deposition. For example, coral reefs and mangroves. Mangroves

13 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? AErosional landforms Sea cliffs and wave-cut platforms Waves repeatedly pound against the coast.The waves erode the part of the coast between high tide and low tide. A notch is formed by undercutting.Undercutting continues and the notch is enlarged. The overhanging part above the notch collapses. It forms a sea cliff.

14 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? AErosional landforms Sea cliffs and wave-cut platforms Erosion continues, the sea cliff retreats inland.Over time, a gently sloping or flat surface called a wave-cut platform is developed at the base of the sea cliff.

15 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? AErosional landforms Sea cliffs and wave-cut platforms Ping Chau in Mirs Bay Sea cliff Wave-cut platform

16 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? AErosional landforms Sea caves and geos A line of weakness in the cliff is exposed to waves.Active wave erosion widens the line of weakness to form a sea cave. When waves splash against the roof of a narrow sea cave, the roof may collapse. A geo is formed. Block diagram Cross-section Sea Land High tide level Low tide level Land High tide level Low tide level Line of weakness Sea cave Collapse of cave roof Geo

17 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? AErosional landforms Sea caves and geos A sea cave in Sai Kung A geo in Sai Kung

18 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? AErosional landforms Sea arches and stacks When a sea cave gets eroded from time to time, it might cut through to form a sea arch. Further erosion may cause the sea arch to collapse.This leaves a mass of rock with steep sides standing offshore. This is the stack.

19 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? AErosional landforms Sea arches and stacks A sea arch and a stack in Canada (Credit: Getty Images)

20 Managing river and coastal environments: A continuing challenge w What landforms are created by coastal processes? AErosional landforms Blow-holes A sea cave is developed along a horizontal line of weakness. When waves break into the sea cave, hydraulic action of waves takes place along the vertical weakness in it. A vertical or near vertical tunnel is formed along the vertical weakness as a blow-hole.

21 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? AErosional landforms Blow-holes During storms, waves breaking into the sea cave may force water or just air out of the blow-hole. Halona Blow-hole in Hawaii (Credit: Getty Images)

22 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? BDepositional landforms Beaches Wave energy is dispersed in sheltered bays. Deposition takes place to form beaches. Sand and shingle are built up between the lowest and the highest water levels.

23 Managing river and coastal environments: A continuing challenge Waikiki Beach, Hawaii What landforms are created by coastal processes? BDepositional landforms Beaches

24 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? BDepositional landforms Materials are transported along the coast by longshore drift. Where the coastline changes, the materials are deposited in slack water. The sediment accumulates and builds up into a spit, with one end attached to the land, and the other end extending out to the sea. The spit extends as sediment continues to accumulate. Land Change of coastline Wind direction Sea Materials are built up to form a spit Longshore drift Wave crest Longshore drift Spit extends Marshland Area behind the spit is of low energy, mud and marshland begins to develop Longshore drift Spits

25 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? BDepositional landforms Spits As the waves are refracted, the end of the spit becomes hooked. Longshore drift Sea Longshore drift Marshland Land End of the spit is bent or recurved Wave crest A Spit in Greece spit (Credit: Corbis)

26 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? BDepositional landforms Bars When a spit develops and extends across a bay, a bar is formed. A lagoon is formed behind the bar.

27 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? BDepositional landforms Bars Chesil Beach in England is formed from a bar (Credit: Corbis)

28 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? BDepositional landforms Tombolos When the spit builds up and joins an island to the mainland or two islands together, a tombolo is formed.

29 Managing river and coastal environments: A continuing challenge What landforms are created by coastal processes? BDepositional landforms Tombolos The Cheung Chau tombolo is formed when two spits join together.


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