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Contents 1 Definitions 2 Factors Determining the Nature of Coasts 3 Formation of Waves 4 Wave Erosion 5 Features Produced by Wave Erosion 5.1 Cliffs, Wave Cut Platforms and Offshore Terraces 5.2 Caves, Geos, Arches and Stacks 5.3 Headlands and Bays 6 Factors Affecting the Rate of Wave Erosion 7 Wave Transport 8 Wave Depositional Features 9 Comments

Definitions

• Coast: The strip of land where it meets the sea
• Coastline: The margin of land. The limit to which wave action takes place.
• Shore: The strip of land lying between the high and low water levels.
• Shoreline: The limit of the shore. The line where the shore and the water meet.
• Beach: A shore covered by a deposit of sand and/or pebbles.

Factors Determining the Nature of Coasts

• Wave action
• Tidal currents
• Nature of the rocks forming the coast
• Height of the coast
• Nature of the climate
• Work of man

Formation of Waves

• Wind blows over the sea surface.
• The surface of the sea exerts frictional drag on the lower layer of the wind.
• The top layer (with the least drag) moves faster than the lower layer and hence tumbles over it.
• This causes a circular motion of wind energy that acts on the sea to create waves.

Wave Erosion

• Wave erosion like river erosion involves 4 processes:
• Abrasion/Corrasion: The wearing away of the sides and the bed of a river by the impact of the load.
• Hydraulic Action: Erosion by the force of moving water.
• Attrition: The breaking down of the load by particles hitting against each other.
• Solution/Corrossion: When minerals dissolve in water.

Features Produced by Wave Erosion

Cliffs, Wave Cut Platforms and Offshore Terraces

• A notch is cut by waves at high tide level and developed further.
• As this notch is developed, a cliff is formed.
• The cliff steepens as weathering attacks the base further.
• As the cliff retreats, the rock debris is swept by the backwash creating a wave-cut platform.
• Some of the debris collects along the seaward edge of the wave-cut platform forming and off-shore terrace.

Caves, Geos, Arches and Stacks

• Holes in the cliff face are enlarged by wave action
• A tunnel like opening called a cave is formed.
• The cave may develop further forming a long narrow inlet known as a geo.
• An arch is created when a cave in a headland is eroded right through i.e. the inlet has two openings
• When the arch collapses, the end of a headland stands up as a stack.

Headlands and Bays

• These are formed in areas of alternating resistant and less resistant rocks.
• Erosion/wave action acts less on the more resistant rock creating headlands and more on the less resistant rock creating bays.

Factors Affecting the Rate of Wave Erosion

• Breaking point of the wave.
• Wave steepness
• Configuration of the coastline
• Depth of the sea
• Supply of beach material
• Beach width
• Nature of the rock

Wave Transport

• Sources of the load include:
  • Rivers entering the sea
  • Landslide on cliffs
  • Wave erosion
• Types of material transported include:
  • Sand
  • Shingles
  • Mud
• Process: Swash (forward moving waves) and backwash push and drag material up and down the shore resulting in longshore drift.

Wave Depositional Features

• Beach: Formed by deposition of mud, sand or pebbles along the coast.
• Barrier Beach: A long ridge of sand parallel to but separated from the coast ridge by a lagoon.
• Spit: A narrow ridge of sand joined to the mainland with the other end terminating in the sea
• Bar: A ridge of material (usually sand) lying parallel to the coast
• Tombolo: A ridge joining an island to the mainland
• Offshore Bar: Developed on the gently sloping seabed. Occurs when sand is thrown up by waves breaking close to the coast.
• Mudflat: Developed when tides/waves deposit fine sand along gently sloping coasts particularly in bars and estuaries.

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