The Action of Waves

• 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

1. Wave action
2. Tidal currents
3. Nature of the rocks forming the coast
4. Height of the coast
5. Nature of the climate
6. Work of man

Formation of Waves

1. Wind blows over the sea surface.
2. The surface of the sea exerts frictional drag on the lower layer of the wind.
3. The top layer (with the least drag) moves faster than the lower layer and hence tumbles over it.
4. 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:
  1. Abrasion/Corrasion: The wearing away of the sides and the bed of a river by the impact of the load.
  2. Hydraulic Action: Erosion by the force of moving water.
  3. Atrrition: The breaking down of the load by particles hitting against each other.
  4. 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

1. Breaking point of the wave.
2. Wave steepness
3. Configuration of the coastline
4. Depth of the sea
5. Supply of beach material
6. Beach width
7. 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

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