- Define and explain Depositional Landforms 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
This lesson focuses on Depositional Landforms: explain how longshore drift builds spits, bars and tombolos.
Explain how longshore drift builds spits, bars and tombolos.
Key ideas
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.
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.
Key term — longshore drift: The zigzag movement of sediment along a beach, driven by waves approaching the shore at an angle.
Explain how longshore drift forms a spit where the coastline changes direction.
Prevailing winds drive waves to approach the beach at an angle. The swash carries sediment up the beach at that angle, but the backwash drags it straight back down under gravity — so sediment zigzags along the shore: longshore drift. Where the coastline bends sharply, such as at a river mouth, the drift continues in its original direction into deeper water. Deposition builds a ridge of sand and shingle out from the coast — the spit. A secondary wind or wave direction may curve the end landward, forming a hooked end, as seen at Spurn Head.
Answer: Oblique waves drive longshore drift; where the coast turns, sediment is deposited in open water, building a spit that may develop a recurved end.
- 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.
- Assuming hard engineering has no downsides Groynes trap sediment but starve beaches downdrift, often shifting the erosion problem along the coast — this knock-on effect is called terminal groyne syndrome.
Practice
Advantage: they trap sediment and widen the beach updrift. Disadvantage: they starve beaches downdrift, increasing erosion there.
Destructive: tall, steep, frequent, strong backwash — erode. Constructive: low, long, less frequent, strong swash — deposit.
The distance wind blows over water; longer fetch allows bigger, more powerful waves to develop.
Cave → arch → stack → stump.
Quick check
Which of these best defines "longshore drift"?
Why might managed retreat be chosen over a sea wall for farmland?
How does a wave-cut platform form?
- Depositional Landforms: explain how longshore drift builds spits, bars and tombolos.
- 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).
- fetch: The distance wind travels over open water — a longer fetch builds larger, more powerful waves.
- Watch out for: saying longshore drift moves sediment straight along the beach