Deposition and Coastal Landforms Revision Notes | GCSE AQA Higher Geography

1. Why Does the Coast Build Up as Well as Wear Down?

You have probably studied how waves erode cliffs and carve out caves and arches. But the coast is not only being destroyed — material is constantly being moved and dropped elsewhere, building entirely new landforms. Understanding deposition is the other half of the coastal story, and it is just as important for your exam.

The key question is: why does sediment get dropped at all? The answer comes down to energy. When a wave loses energy, it can no longer carry the material it has been transporting, so that material is deposited. This happens in sheltered bays, behind headlands, or where a river mouth slows the water down.

Several conditions trigger deposition. Waves entering a sheltered bay lose energy as they spread out. Shallow water also slows waves, causing them to drop their load. Calm weather reduces wave power, and a large supply of sediment from eroding cliffs or rivers gives the coast plenty of material to work with.

• Sheltered locations, such as bays, reduce wave energy
• Shallow water causes waves to slow and deposit sediment
• A change in the direction of the coastline interrupts longshore drift
• Large sediment supply from eroding cliffs or river mouths feeds depositional landforms

2. Longshore Drift — The Engine Behind Depositional Landforms

Before looking at specific landforms, you need a firm grip on longshore drift, because it is the mechanism that moves sediment along the coast and ultimately builds up depositional features. Think of it as a conveyor belt running along the shoreline.

Waves rarely approach the shore at a perfect right angle. They arrive at an angle determined by the prevailing wind. The swash (the rush of water up the beach) therefore travels diagonally up the beach, carrying sediment with it. The backwash, however, runs straight back down the beach under gravity. The net effect is that sediment moves along the coast in a zigzag path, in the direction of the prevailing wind.

This matters enormously for landform formation. When longshore drift reaches a point where the coastline changes direction — such as a river mouth or a bay — the sediment continues moving in its original direction rather than following the new coastline. That is where spits, bars, and other features begin to grow.

3. Beaches and Sand Dunes — Where Deposition Begins

The most familiar depositional landform is the beach. A beach forms when sediment — sand, shingle, or a mix of both — accumulates between the high and low tide marks. Beaches are dynamic: they grow when deposition exceeds erosion and shrink when the reverse is true.

The profile of a beach varies with the type of sediment. Shingle beaches tend to be steep because large particles are not easily moved by the backwash, so they pile up near the top. Sandy beaches are much gentler in gradient because fine particles are spread more evenly by the swash and backwash.

At the back of a beach, where sand is blown inland by the wind, sand dunes can develop. Wind picks up dry sand from the upper beach and deposits it when an obstacle — often a clump of marram grass — slows the airflow. Over time, dunes build up and are stabilised by vegetation. This is a good example of how physical processes and biological factors work together to create a landform.

4. Spits, Bars, and Tombolos — Longshore Drift in Action

Now that you understand how longshore drift transports sediment, you can see exactly how more complex depositional landforms are built. These features all form where longshore drift continues past a change in the direction of the coastline.

Worked example: How a Spit Forms — Step by Step

Describe and explain the formation of a spit at a river mouth.

1. Waves approach the coast at an angle driven by the prevailing wind. Swash carries sediment diagonally up the beach; backwash returns it straight down. Sediment moves along the coast in the direction of the prevailing wind. — This is the engine of spit formation. Without longshore drift, there is no sediment supply to build the feature.
2. The coastline meets a river mouth or bay. The land curves away, but the sediment continues moving in its original direction — out into open water. — Sediment does not 'turn the corner' with the coastline. It keeps going in the direction of drift, extending into the sea.
3. Wave energy decreases as waves enter the sheltered water beyond the river mouth. Sediment is deposited and accumulates, building up a ridge that extends from the land. — The drop in energy is the trigger for deposition. The ridge grows longer over time as more sediment is added.
4. Secondary winds from a different direction cause waves to refract around the end of the spit. This curves the tip of the spit landward, creating a characteristic hooked or recurved end. — The curved end is a key feature to mention in exam answers. It distinguishes a spit from a straight ridge and shows the influence of changing wind directions.
5. The sheltered water behind the spit is protected from strong wave action. Fine sediment settles here, and salt-tolerant plants colonise the area, forming a salt marsh. — The salt marsh is evidence of the sheltered, low-energy environment behind the spit. Mentioning this in an exam answer shows strong understanding of the whole system.

Answer: A spit forms through longshore drift transporting sediment past a change in the coastline direction. Sediment is deposited in open water, building a ridge that extends from the land. Secondary winds curve the tip, and a salt marsh develops in the sheltered water behind.

A bar forms when a spit extends all the way across a bay, cutting off the water behind it to form a lagoon. This happens where the bay is relatively narrow and there is no strong river current to keep the mouth open. Slapton Ley in Devon is a well-known example of a bar in the UK.

A tombolo is a related feature — a bar of sediment that connects the mainland to an offshore island. The island acts as an obstacle that disrupts wave patterns, causing deposition in the sheltered zone between the island and the shore. Over time, sediment builds up until the two are linked.

5. Rock Type and Structure — Why Coastlines Look Different

Deposition alone does not explain the full variety of coastal landforms. The shape of a coastline is also controlled by the type of rock present and how that rock is arranged — its structure. This is where geology meets geography.

Hard rocks such as granite and chalk are resistant to erosion. They erode slowly and tend to form prominent headlands that jut out into the sea. Soft rocks such as clay and sand erode much more quickly, forming bays that are set back from the headlands. The contrast between hard and soft rock is the key driver of the classic headland-and-bay coastline.

Compare this with a concordant coastline, where the rock bands run parallel to the sea. Here, the same type of rock faces the waves along the whole stretch of coast, producing a more uniform, straight shoreline. If the outer band of hard rock is breached — for example through a fault or weakness — the sea can break through and erode the softer rock behind, creating a circular bay called a cove. Lulworth Cove in Dorset is a classic UK example.

Rock structure also matters beyond just the type of rock. The angle at which rock strata (layers) are tilted affects how quickly cliffs erode. Strata that dip towards the sea are more vulnerable because water can penetrate along the bedding planes, weakening the cliff face. Strata that dip away from the sea are more stable. Joints, faults, and cracks in rock also create lines of weakness that waves exploit through hydraulic action and abrasion, eventually forming caves, arches, and stacks.

6. Putting It Together — Processes, Rock, and Landforms

Earlier in this lesson, you saw how deposition and longshore drift build features such as spits and bars. Now you can see that rock type and structure add another layer of explanation. Distinctive coastal landforms are never the result of just one factor — they emerge from the interaction between physical processes (erosion, transportation, deposition) and the geology of the coastline.

For example, a headland forms because hard rock resists erosion. But once that headland exists, it changes the wave patterns around it — waves refract around the headland and lose energy in the sheltered bay behind. That lower energy environment then encourages deposition, which may build a beach in the bay. The geology sets the stage; the processes play out on it.

7. Exam Technique — Getting Full Marks on Coastal Questions

Coastal landform questions are among the most predictable in the AQA paper, which means they are also among the most rewarding to prepare for. The examiners follow consistent patterns, and knowing those patterns is half the battle.

When a question asks you to explain the formation of a landform, you must give a cause-and-effect chain, not a list of facts. Each sentence should connect to the next using words like 'therefore', 'which means', or 'as a result'. A common trap is to describe what a spit looks like rather than explaining the process that formed it — description alone will not earn the higher marks.

For describe questions about a map or photograph, focus on what you can actually observe: the shape, size, direction, and location of the feature. Avoid explaining why it formed unless the question asks you to. Mixing command words is one of the most common ways students lose marks.