- Define and explain Coastal Processes in your own words
- Use key terms such as longshore drift accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
Coasts are among the most dynamic landscapes on Earth, where waves, weather and human decisions collide. In this chapter you will compare wave types, follow erosion from crack to stump, explain deposition by longshore drift, and evaluate how we defend — or retreat from — the sea.
This lesson focuses on Coastal Processes: examine destructive and constructive waves, weathering and mass movement at the coast.
Examine destructive and constructive waves, weathering and mass movement at the coast.
Key ideas
Waves come in two types
Destructive waves are tall, steep and frequent, with a powerful backwash that drags sediment down the beach — they erode. Constructive waves are lower, longer and less frequent, with a strong swash that pushes sediment up the beach — they build. Winter storms bring destructive waves; calm summer conditions bring constructive ones, so beaches often shrink in winter and recover in summer.
Coasts work as systems
A coastal system has inputs (weathered cliff material, river sediment), transfers (longshore drift), stores (beaches, dunes) and outputs (sediment lost offshore or to another cell). Building a groyne or sea wall interrupts the transfers, which is why protecting one stretch of coast can starve beaches further along the sediment cell.
Key term — longshore drift: The zigzag movement of sediment along a beach, driven by waves approaching the shore at an angle.
Describe two differences between destructive and constructive waves.
Destructive: tall, steep, frequent, strong backwash — erode. Constructive: low, long, less frequent, strong swash — deposit.
Answer: Destructive: tall, steep, frequent, strong backwash — erode. Constructive: low, long, less frequent, strong swash — deposit.
- Confusing swash and backwash Swash is water rushing up the beach; backwash is water draining back down. In constructive waves the swash is stronger; in destructive waves the backwash dominates.
- Saying longshore drift moves sediment straight along the beach The movement is a zigzag: swash up at an angle, backwash straight down. The net result is alongshore, but the path is not straight.
Practice
Farmland is low value, so an expensive wall is hard to justify; managed retreat is cheaper, creates natural habitats like salt marsh, and works with coastal processes.
The distance wind blows over water; longer fetch allows bigger, more powerful waves to develop.
Waves erode the cliff base by hydraulic action and abrasion, undercutting it until the overhang collapses; as the cliff retreats, a rocky platform is left behind at the high-tide level.
Cave → arch → stack → stump.
Quick check
Which of these best defines "longshore drift"?
Give one advantage and one disadvantage of groynes.
- Coastal Processes: examine destructive and constructive waves, weathering and mass movement at the coast.
- Waves come in two types: Destructive waves are tall, steep and frequent, with a powerful backwash that drags sediment down the beach — they erode.
- fetch: The distance wind travels over open water — a longer fetch builds larger, more powerful waves.
- Watch out for: confusing swash and backwash