IGCSE Geography / Coastal environments

Waves and coastal erosion

Edexcel International GCSE Geography (4GE1), chapter 2: Coastal environments, specification point 2.1a. Free lesson.

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Waves form as wind transfers energy to the sea, then change as they reach shallow water. Their swash and backwash affect beaches, while destructive waves wear away the coast through four processes of marine erosion.

How waves form and break

Wind transfers energy to the sea through friction between the air and the water. This first makes ripples, which grow into waves as the wind continues to push them. Near the coast, shallow water slows the wave’s base against the sea bed, while the top keeps moving. The top gets ahead and topples forward, so the wave breaks. Fetch is the distance of open water that the wind has blown over. A longer fetch gives the wind more distance to build waves. Bigger waves need a strong wind blowing for a long time over a long fetch. Swash is water rushing up the beach after a wave breaks.…

How constructive and destructive waves affect beaches

The effect a wave has on a beach depends on how much material its swash carries up the beach compared with how much its backwash drags back down. Constructive waves build beaches, while destructive waves remove material. Constructive waves are low and long, and arrive at a low frequency, so they are well spaced out. They have a strong swash and weak backwash. They carry more material up the beach than they drag back, so they deposit material and build the beach. They usually occur in calm weather. Destructive waves are tall and steep, and arrive at a high frequency, so they are close…

Four processes of marine erosion

Marine erosion is the sea wearing rock away and removing it. Destructive waves erode the coast through four processes. To explain erosion in an answer, describe how the rock is worn or broken, not just the process name. Hydraulic action: waves force air into cracks in a cliff. The pressure widens the cracks until pieces of rock break off. Abrasion: waves throw sand and pebbles against a cliff. These scrape and chip the rock away, like sandpaper. Attrition: rocks and pebbles carried by the sea knock into each other. They become smaller and rounder. Attrition wears down the…

Explain how a destructive wave erodes a cliff

For a three-mark explanation, choose one process and link the action of the waves to what happens to the rock. For example, abrasion explains how destructive waves can wear back the base of a cliff.

More lessons in Coastal environments

• Longshore drift and coastal deposition
• Weathering and mass movement on the coast
• Headlands, bays, cliffs and wave-cut platforms
• Caves, arches, stacks and stumps
• Beaches, spits and bars
• Geology and the shape of the coast
• Vegetation, people and sea-level change
• Coastal ecosystems: coral reefs and mangroves
• Coastal ecosystems: sand dunes and salt marshes
• Inside one coastal ecosystem: the Sundarbans mangrove
• Coastal ecosystems under threat
• Case study: managing the mangrove
• Conflicts at the coast
• Why coasts flood
• Predicting and preventing coastal flooding
• Hard engineering at the coast
• Soft engineering and shoreline management plans
• Case study: coastal management in The Gambia
• Case study: coastal management in Sri Lanka
• Case study: coastal management in the UK
• Coastal fieldwork: collecting the data
• Coastal fieldwork: results, conclusions and evaluation