Coastal Dynamics and Landform Development
- Coastal landscapes are shaped by the interplay of erosion, transport, and deposition.
- These processes create distinctive landforms that evolve.
Understanding these landforms helps us appreciate the dynamic nature of coastlines and their vulnerability to change.
Erosional Landforms
Wave-Cut Platforms: Evidence of Cliff Retreat
- Wave-cut platforms are flat, rocky surfaces found at the base of cliffs.
- They form as cliffs erode and retreat, leaving a platform exposed at low tide.
Formation Process
- Hydraulic Action and Abrasion: Waves crash against the cliff, compressing air in cracks and dislodging rock fragments.
- Undercutting: Erosion creates a notch at the cliff base, weakening its structure.
- Collapse: The unsupported cliff top collapses, and debris is washed away by waves.
- Platform Exposure: As the cliff retreats, a flat platform is left behind.
Wave-cut platforms are typically less than 500 meters wide and slope gently seaward at an angle of about 1°.
ExampleThe wave cut platform at Flamborough Head, UK, is a classic example, showcasing the relentless power of wave erosion.
Cliffs and Stacks: Sculpted by Wave Action
- Cliffs are steep rock faces formed by the continuous erosion of coastal land.
- Over time, they can evolve into dramatic features like stacks and arches.
Formation of Cliffs
- Wave Erosion: Waves attack the base of the rock, creating a notch.
- Collapse: The overhanging rock collapses, forming a steep cliff.
- Repetition: The process repeats, causing the cliff to retreat.
Formation of Stacks
- Caves: Erosion exploits weaknesses in the rock, forming caves.
- Arches: Caves deepen and break through the headland, creating an arch.
- Stacks: The arch collapses, leaving a pillar of rock called a stack.
- Stumps: Continued erosion reduces the stack to a stump.
The Twelve Apostles in Australia are iconic stacks formed by the relentless action of the Southern Ocean.
Common Mistake- Don’t confuse stacks with arches.
- Stacks are isolated pillars, while arches are bridges of rock with an opening beneath.
Depositional Landforms
Spits: Curved Ridges of Sand and Shingle
- Spits are long, narrow ridges of sand or shingle that extend from the coast into the sea.
- They form in areas where wave energy decreases, allowing sediment to accumulate.
Formation Process
- Longshore Drift: Waves approach the coast at an angle, moving sediment along the shoreline.
- Deposition: When waves lose energy, sediment is deposited, forming a ridge.
- Curved End: Wave refraction or changes in wind direction cause the spit’s end to curve.
Spurn Head in the UK is a well-known spit, with a distinctive curved shape at its distal end.
TipSpits often form near river mouths or in areas with indented coastlines, where wave energy is reduced.
Beaches: Dynamic Accumulations of Sand and Shingle
- Beaches are the most familiar coastal landforms, formed by the deposition of sediment along the shore.
Formation Process
- Sediment Supply: Sediment is delivered by rivers, eroding cliffs, or offshore sources.
- Wave Action: Constructive waves (with strong swash and weak backwash) deposit sediment on the shore.
- Sorting: Waves sort sediment by size, with finer sand settling in sheltered areas and coarser shingle on exposed beaches.
Bondi Beach in Australia is famous for its fine sand and gentle slope, shaped by the action of constructive waves.
Common MistakeAvoid assuming all beaches are sandy. Many beaches are composed of shingle, pebbles, or even boulders, depending on local conditions.
Reflection and Broader Implications
- Coastal landforms are not just aesthetic, they have practical and environmental significance.
- Wave-cut platforms can protect cliffs by dissipating wave energy, while beaches act as natural buffers against storms.
- However, these landforms are vulnerable to human activities and climate change.
How do human activities, such as coastal development or the construction of sea defenses, impact the natural processes that create and maintain these landforms?
