Coastal Processes & Landforms

1. Coastal Processes & Landforms Ms Carr 5th year Geography

2. Learning Intention • Understand how coastal processes transform the landscape • Examine the landforms created by these coastal processes • FEEDs for these landforms • Feature • Explanation • Example • Diagram • Identify coastal landforms on OS Maps and in Photographs

3. Today we will...... • Recall what we already know about coastal processes. • Examine what influences coastal erosion. • Discuss two types of waves. • Recap on processes of coastal erosion. • Textbook pages 122-124.

4. Mind Map..What I already know..

5. Chapter 12: Coastal Processes, Patterns & Associated Landforms, & 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

6. Factors affecting the rate of coastal erosion • Where the breaking of a wave occurs • Highest energy at moment of collapse • If it hits a cliff before or after it breaks it won’t erode as much - Steepness of the wave - Formed nearer coast, steeper & stronger - Rock resistance

8. Chapter 12: Coastal Processes, Patterns & Associated Landforms, & Human Interaction Types of Waves • Constructive waves Deposit more than they erode Carries material in Swash up the shore Most common in summer • Destructive waves Erode more than they deposit Steep waves Strong Backwash Most common in winter

10. Chapter 12: Coastal Processes, Patterns & Associated Landforms, & Human Interaction Wave Refraction • Waves slow down as water becomes shallow. • This change in speed causes the wave to bend and change their direction as they approach the shore, this is called Wave Refraction. • This causes waves to move towards the headland where their erosive force is released. • Erosion is stronger on the headland and deposition occurs in the bay.

11. Change of wave direction Debris

12. Processes • Erosion • Transportation • Deposition

13. Chapter 12: Coastal Processes, Patterns & Associated Landforms, & Human Interaction Processes of coastal erosion • Hydraulic Action • Compression • Abrasion/Corrasion • Attrition • Solution/Corrosion

14. Erosion • Hydraulic Action; direct force of the waves on the coast. • Abrasion; rock debris is hurled by the waves against the coastline. • Attrition; fragments of stone are rounded and eroded by hitting off each other. • Solution; minerals in certain rocks are dissolved by water. • Air Compression; breaking of rock as a result of being trapped by waves in rocks. • Wave Refraction; bending of waves concentrates erosion at headlands, this then leads to the formation of cliffs, caves, arches and stacks.

15. Chapter 12: Coastal Processes, Patterns & Associated Landforms, & 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

16. Transportation • Longshore Drift • Movement of material along the coast • Zig zag path • Swash and Backwash

18. The movement of material along the coastline in a zig zag manner due to the angle of the approaching waves and the slope of the coastline. Deposition occurs because the swash is more powerful than the backwash. The bending of waves due to a headland causing the waves to lose energy and deposition to occur. Erosion occurs because the backwash is more powerful than the swash Constructive Waves ? Destructive Waves ? Wave Refraction ? Longshore Drift

19. Learning Intention • Recap on coastal processes. • Examine landforms of coastal erosion. • Answer a FEED style question on one landform.

20. Recap • The return movement of water downshore is called _____________. • ____________________ deposit more than they erode and are most common in summer. • When a wave slows down, bends and changes direction it is called _________________. • __________________ is the zig-zag movement of material along the coast. • _____________ happens when fragments of rock are rounded and eroded by hitting off each other. • When rock breaks as a result of being trapped by waves in rocks, it is called ____________________.

21. Landforms of Marine Erosion • Cliffs • Wave-cut Platform • Bay • Headland • Cave • Blowholes • Sea Arches • Sea Stacks

22. Chapter 12: Coastal Processes, Patterns & Associated Landforms, & Human Interaction 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

24. Chapter 12: Coastal Processes, Patterns & Associated Landforms, & Human Interaction • Notch gets bigger, eventually the rocks above the notch (overhang) 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 rockthat are deposited below low-tide level

26. Cliffs • Example; • Cliffs of Moher, Co Clare • Hook Head, Co Wexford OS Map- Textbook page 125

27. Chapter 12: Coastal Processes, Patterns & Associated Landforms, & Human Interaction 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

28. Baysand Headlands

29. Bays and Headlands

30. Bays and Headlands

31. Malin Head, Donegal

32. Bays & Headlands • Example; • Dublin Bay • Wicklow Head • OS Map; Textbook page 126

33. Chapter 12: Coastal Processes, Patterns & Associated Landforms, & Human Interaction 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

34. Cave, arch, stack, stump

35. Cave, arch, stack, stump

36. Chapter 12: Coastal Processes, Patterns & Associated Landforms, & Human Interaction • 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

37. Cave, Arch, Stack, Stump • Examples; • Hook Head, Co Wexford • Caves; Ballybunion, Co Kerry • Arch; The Bridges of Ross, Co Clare • Sea Stack; Dun Briste, Co Mayo

38. Chapter 12: Coastal Processes, Patterns & Associated Landforms, & Human Interaction 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’. • During stormy weather, sea spray blasts out through the blowhole. • Example; Hook Head, Co Wexford. • Geo: a long narrow inlet that forms when the roof of a cave, that was once connected to a blowhole collapses.

41. Landforms of Coastal Erosion on OS Maps • Textbook- page 128.

42. Pairwork Quick Questions • List 5 processes of coastal erosion. • List the 3 main landforms of coastal erosion. • Name an Irish example of each of the above landforms. • What does a sea stack look like on an OS map? • Explain the term ‘differential erosion’. • What is a ‘geo’?

46. Exam Question; FEED • Caves, arches, stacks, stumps and blowholes are features of coastal erosion. • Caves: what are they? • Type of rock they are formed in • Why hard rock? • Hydraulic Action (P) • Compressed Air (P) • Weakness in the roof of the cave • Formation of a blowhole • Continued erosion on roof and back wall • Formation of an arch • Weathering and erosion of the roof of arch • Creation of a stack • Erosion of stack • Abrasion (P) of stack – why • Creation of a stump

47. E: Caves are open hollows usually found near the base of a headland on the cliff face. They tend to form in areas of hard rock along the coastline. Soft rock erodes too quickly for a cave to maintain its shape therefore they tend to form slowly in hard rock and can be deep and large. Caves occur due to the main marine processes of erosion such as hydraulic action (the power and the force of the seas waves pounding the coastline) and Compressed air (where air is trapped between the cliff face and the wave and causes the air to expand. This in turn causes the cracks to enlarge and the coastline to erode). Over time the sea will continue to erode the back wall of the cave and in stormy times cracks in the roof of the cave will be further eroded by solution and compressed air. This creates an area of weakness such as a tunnel or vent in the roof all the way to the surface of the headland. If a vent opens from the roof of the cave to the top of a headland a blowhole is now formed. During times of high tide or storms water will force its way up the vent and spray out on the surface. As this feature is formed the cave continues to erode backwards through the headland. Sometimes one cave will erode the whole way through or sometimes two caves will meet from either side of the headland. As this happens an arch is formed. However, the roof of the arch (with the blowhole) is weakened and continuous erosion will cause the roof to collapse. Once an arch collapse the headland appears smaller and the remaining outer wall is called a stack. However there is an increase of broken rocks and debris in the area and the processes of abrasion (the scraping of the seas load against the coastline) will continue to erode the stack. Over time it is eroded down to a stump. This is an area of rock barely visible over the waves and dangerous for incoming boats. The creation of these features are responsible for the coastline appearing to ‘retreat’ and appear smaller on maps/photographs. E: Examples x 3 D: Diagram (frame, title, details, colour, labels) • Caves are open hollows usually found near the base of a headland on the cliff face. They tend to form in areas of hard rock along the coastline. Soft rock erodes too quickly for a cave to maintain its shape therefore they tend to form slowly in hard rock and can be deep and large. Caves occur due to the main marine processes of erosion such as hydraulic action (the power and the force of the seas waves pounding the coastline) and Compressed air (where air is trapped between the cliff face and the wave and causes the air to expand. This in turn causes the cracks to enlarge and the coastline to erode). Over time the sea will continue to erode the back wall of the cave and in stormy times cracks in the roof of the cave will be further eroded by solution and compressed air. This creates an area of weakness such as a tunnel or vent in the roof all the way to the surface of the headland. If a vent opens from the roof of the cave to the top of a headland a blowhole is now formed. During times of high tide or storms water will force its way up the vent and spray out on the surface. As this feature is formed the cave continues to erode backwards through the headland. Sometimes one cave will erode the whole way through or sometimes two caves will meet from either side of the headland. As this happens an arch is formed. However, the roof of the arch (with the blowhole) is weakened and continuous erosion will cause the roof to collapse. Once an arch collapse the headland appears smaller and the remaining outer wall is called a stack. However there is an increase of broken rocks and debris in the area and the processes of abrasion (the scraping of the seas load against the coastline) will continue to erode the stack. Over time it is eroded down to a stump. This is an area of rock barely visible over the waves and dangerous for incoming boats. • The creation of these features are responsible for the coastline appearing to ‘retreat’ and appear smaller on maps/photographs. • E: Examples x 3 • D: Diagram (frame, title, details, colour, labels)

48. Coastal Landforms Deposition

49. Learning Intention • Examine landforms of coastal deposition. • Review a sample answer on one landform. • Answer a FEED style question on another landform.

50. Chapter 12: Coastal Processes, Patterns & Associated Landforms, & Human Interaction • Textbook page 129-132