Action of Wave – SS2 Geography Lesson Note (First Term)

Wave action is the work of sea and ocean waves in eroding, transporting and depositing material along the coast. Waves are formed by wind moving over water. They wear down cliffs through corrosion, attrition, hydraulic action and solvent action, and they build beaches, spits, bars and dunes by deposition.

Behavioural objectives

By the end of the lesson, students should be able to:

1. Define the terms associated with waves, such as wave, tide, current, coast, shore, beach, swash, backwash and undertow.
2. State the factors that affect the rate of marine erosion.
3. Describe the four processes of wave erosion.
4. Describe the features produced by wave erosion, such as cliffs, caves, arches, stacks and stumps.
5. Describe the features of coastal deposition, such as beaches, spits, bars and marine dunes.

What is wave action?

The action of waves is an important agent of erosion, transportation and deposition of material. It is confined to the coast of seas and oceans. The rate of marine erosion depends on the nature of the rocks, the amount of rock exposed to the sea, the effects of tides and currents, and human interference in coast protection.

Terms associated with waves

1. Wave: the turbulent movement of water as a result of wind moving over the water.
2. Tide: the alternate rise and fall of the surface of the sea approximately two times a day.
3. Current: the movement of water in the ocean in a particular direction.
4. Coast: the meeting point between the land and the sea.
5. Shore: the part of the land that lies between high water and low water.
6. Beach: the material deposited on the shore by the action of waves.
7. Swash: water thrown up the beach by breaking waves.
8. Backwash: the water that retreats back down the beach after the swash.
9. Undertow: water which flows near the bottom away from the shore.

What are the processes of wave erosion?

1. Corrosion: the wearing down of the base of the cliff by wave action.
2. Attrition: the breaking down of materials such as pebbles and boulders against cliff faces and against each other, as the waves continue their activities.
3. Hydraulic action: fast-moving waves force themselves under pressure into cracks at the base of the cliff and enlarge the cracks.
4. Solvent action: the disintegration of rock materials such as limestone on the coast by the chemical action of the sea.

Which features are produced by wave erosion?

1. Capes and bays: these are features of marine erosion along the coastline. A cape is made of hard rock and a bay of soft rock. A bay usually contains water and can be used as a harbour.
   
   
   
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2. Cliff: a steep rock face adjoining the coast. Cliffs form when waves attack the base of the headland and cut it backwards as the wave action intensifies.
3. Coastal cave: a cave is a feature of marine erosion. It is an arch-shaped feature found on steep coasts or cliff coasts. It may contain blow-holes or geos.
4. Arch: when two caves approach each other from either side of a headland, they meet to form an arch.
   
   
5. Stack: the continuous action of waves makes an arch collapse. The seaward portion of the headland that remains is called a stack.
6. Stump: when a stack is eroded so much that only a small portion is visible above sea level, a stump is formed.
7. Geo: a geo develops when a wave cuts into a cliff, resulting in a narrow hole. It is formed when a cave collapses.
8. Gloup or blowhole: through the hydraulic action of the waves, a hole may develop in the roof of a cave. Continued erosion makes the hole pierce through to the surface above the cave, and water at times may force itself through the hole to form a blowhole.

Which features are produced by coastal deposition?

1. Beaches: depositional features of the coast, made up of sand and gravel. They form when sand and gravel loosened from the land are moved by waves and deposited along the shore.
2. Spits: ridges of sand and gravel formed by longshore drift across the entrance to a coastal inlet. A spit is joined to the land at one end and extends into the water at the other.
3. Bar: a ridge, usually of sand or rock debris, formed by deposition across the mouth of a river or the entrance of a bay.
4. Marine dunes and dune belts: onshore winds of large force move a large amount of coastal sand to form marine dunes. Marine dunes later stretch into dune belts.

Evaluation

1. Define swash and backwash.
2. List the four processes of wave erosion.
3. Describe how an arch, a stack and a stump are formed.
4. State the factors that affect the rate of marine erosion.
5. Name two features of coastal deposition and describe one of them.

Assignment

1. State two differences between the Ria Coast and Fiord Coast.
2. List any three features of coastal deposition.