Coasts: processes and landforms

Last time

Before we start: last time, in Rivers, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Where land meets sea

Waves batter cliffs, carry sand along beaches, and build spits across bays. The coast is always changing. This lesson covers waves, coastal erosion, transport and deposition, the landforms they create, and coral reefs and mangroves.

Waves

Waves are made by wind blowing over the sea. Their power depends on wind speed, how long it blows, and the fetch: the distance of open water. Destructive waves are tall and frequent, with a strong backwash that removes material: they erode. Constructive waves are low and gentle, with a strong swash that pushes material up the beach: they build beaches.

Coastal erosion

Hydraulic action: waves force air into cracks, breaking the rock. Abrasion: waves throw sand and pebbles at the cliff. Attrition: rocks knock together and become smaller. Solution: sea water dissolves rocks such as limestone. Weathering and mass movement also weaken cliffs from above.

Cliffs and wave-cut platforms

Waves erode the foot of a cliff, forming a wave-cut notch. The cliff above is undercut and collapses, so the cliff retreats inland. A flat rocky wave-cut platform is left at the base, exposed at low tide.

Caves, arches and stacks

On a headland, waves erode a crack into a cave. The cave is eroded through to form an arch. The arch roof collapses, leaving a stack. The stack is eroded to a stump. Each stage takes many years.

Longshore drift

When waves approach at an angle, the swash carries material up the beach at that angle. The backwash returns straight down the beach, under gravity. So material zigzags along the coast: longshore drift.

Depositional landforms

Beaches form where constructive waves deposit sand and shingle, often in sheltered bays. A spit is a long ridge of sand or shingle built by longshore drift, sticking out where the coast changes direction. A bar forms if a spit grows across a bay; a tombolo joins an island to the mainland.

Coral reefs

Coral reefs are built by tiny animals, polyps, in warm, shallow tropical seas. Conditions: water about 18 degrees or warmer, clear and shallow so sunlight reaches the coral, salt water, and little sediment. Types: fringing reefs, barrier reefs, and atolls. They protect coasts and support many fish.

Mangroves

Mangroves are trees that grow in salty, muddy water on tropical coasts. Their roots trap sediment and break the force of waves, protecting coasts from storms. They are threatened by clearing for farming, fish farms and building.

Mistakes that lose marks

Mistake one: mixing up constructive and destructive waves. Mistake two: getting the cave, arch, stack sequence out of order. Mistake three: listing coral reef conditions without explaining why each matters. The fix: the right wave, the right sequence, and reasons.

The full-marks tip

The full-marks tip: explain a landform as a sequence, with the processes named at each step. For coral reefs, explain why each condition is needed: sunlight for algae, warm water for growth.

On one card

So, on one card: coasts. Keep it for revision.