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
- 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 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.
- Atrrition: 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
- Sources of the load include:
- Rivers entering the sea
- Landslide on cliffs
- Wave erosion
- Types of material transported include:
- 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.