The action of wave as an important agent of erosion, transportation and deposition of material 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 WAVE
(i) Wave: Wave means turbulent movement of water as a result of wind moving over the water.
(ii) Tide: Tide is the alternate rise and fall of the surface of the sea approximately two times a day.
(iii) Current: Ocean current is the movement of water in the ocean in a particular direction.
(iv) Coast: This refers to the meeting point between the land and the sea.
(v) Shore: This is the part of the land that lies between high water and low water.
(vi) Beach: This refers to the material deposited on the shore by the action of wave.
(vii) Swash: This refers to water thrown up the beach by breaking waves.
(viii) Back wash: This is the water that sucks back and retreats after wash.
(ix) Undertow: This is water which flows near the bottom away from the shore.
PROCESSES OF WAVE EROSION
(1) Corrosion: This is the wearing down of the base of the cliff by wave action.
(2) Attrition: This is breaking down of materials like pebbles, boulders, etc. against cliff faces and against each other, as the wave continues its activities.
(3) Hydraulic action: In this process, fast moving waves force itself into cracks within the base of the cliff under pressure and enlarge the cracks.
(4) Solvent action: This involves the disintegration of rock materials such as limestone in the coast by chemical action of the sea.
- Differentiate between swash and backwash.
- Describe how a beach is formed.
FEATURES PRODUCED BY WAVE EROSION
(1) Capes and Bays: They are features of marine erosion in coastline which can be made of hard rock (cape) or soft rock (bays). A bay usually contains water and could be used as harbour.
(2) Cliff: These are steep rock faces adjoining the coast. They are formed due to the action of waves on the base of headland which cut backward as the wave action intensifies.
(3) Coastal Cave: A cave is a feature of marine erosion.It is an arch-shaped feature found in steep coast or cliff coast.It may contain blow-holes or geo.
(4) Arch: When two caves approach each other from either side of a headland, they meet to form an arch.
(5) Stack: Continuous action of waves makes an arch to collapse. The seaward portion of the highland that remains is called a stack.
(6) Stump: When the stack is seriously eroded to a point that a small portion is just visible above the sea level, a stump is said to be formed.
(7) Geo: Geo develops when a wave cuts into a cliff, resulting into a narrow hole called a geo. It is formed when a cave collapses.
(8) Gloup or Blowhole: Owing to hydraulic action of wave, a hole might develop at the roof of a cave. Continued erosion will result in the hole piercing through to the surface of the cave and water at times may force itself through these holes to form a gloup or blow-holes.
Features of Coastal Deposition
(1) Beaches: Beaches are made up of sand and gravel. They are depositional features on the coast. Beaches are formed when sand and gravel loosened from the land are moved by wavesand deposited along the shore. These deposits of sand and gravel on the shore are called beaches.
(2) Spits: These are ridges of sand and gravel formed by long shore drift across the entrance to coastal inlet by lying on one side to the land and the other side into the ocean.
(3) Bar: Bar is a ridge, usually of sand or rock debris formed by deposition across the mouth of a river or across the entrance of a bay.
(4) Marine dunes and dune belt: Dunes are on shore wind with large force which makes a large amount of coastal sand to move to form marine dunes. Marine dunes will later stretch into dune belts.
- Mention any three features produced by wave erosion.
- What is an arch?
GENERAL EVALUATION QUESTIONS
- Describe a wave.
- Describe a beach.
- What is ocean current?
- Explain attrition as a process of wave erosion.
- What is a bay?
- The water thrown up the beach by wave is known as (a) Swash (b) Backwash (c) Current (d) Tide
- Which of these is not a mechanism of wave erosion? (a) Solvent action (b) Attrition (c) Traction (d) Corrasion
- Steep rocks adjoining the coast are_____ (a) Capes (b) Cliffs (c) Bays (d) Stack
- When two caves meet and unite, they form (a) Stack (b) Stump (c) Arch (d) Bays
- Which of these is not a feature of coastal deposition? (a) Beaches (b) Dunes (c) Spits (d) Bars
- State two differences between Ria coast and Fiord Coast.
- List any three features of coastal deposition.