Cambridge International AS & A Level Geography (9696): Topic 8 – Coastal environments – Study Guide

This guide covers Topic 8, Coastal environments, of the Cambridge International AS & A Level Geography (9696) syllabus for examination in 2025 and 2026, sections 8.1 to 8.4. Coastal environments is one of the four Advanced Physical Geography Options assessed in Paper 3 (1 hour 30 minutes, 60 marks, 25% of the A Level). Candidates answer questions on two of the four options; for each option they answer a 10-mark structured question and choose one of two 20-mark essays.

Use it with the revision notes and the practice questions. Our earlier coastal environments overview explains the basic process-landform sequences in a different way, and the exam preparation guide covers paper technique. Track your progress on the Cambridge A Level Geography hub and checklist.

Syllabus coverage

Syllabus reference	What you must know or be able to do (from the document)	Where assessed
8.1 Coastal processes	Wave generation and characteristics: fetch, energy, refraction, breaking waves, high and low energy waves, swash and backwash. Marine erosion: hydraulic action, cavitation, corrasion/abrasion, solution, attrition. Sub-aerial processes: weathering and mass movement. Marine transportation and deposition: sediment sources and characteristics, sediment cells, longshore drift.	Paper 3
8.2 Characteristics and formation of coastal landforms	Cliffs and wave-cut platforms, caves, arches and stacks. Beaches in profile and plan, swash and drift aligned beaches, simple and compound spits, tombolos, offshore bars, barrier beaches, coastal dunes, tidal sedimentation in estuaries, coastal saltmarshes and mangroves. The role of sea level change.	Paper 3
8.3 Coral reefs	Characteristics, distribution and formation of fringing reefs, barrier reefs and atolls. Conditions for coral growth. Threats (global warming, sea-level rise, pollution, physical damage) and possible management strategies.	Paper 3
8.4 Sustainable management of coasts	Case study: problems of sustainably managing a stretch or stretches of coastline, and evaluation of attempted solutions, including hard and soft engineering.	Paper 3

Paper 3 gives AO4 (Evaluation) about 40% of its marks, so each section below ends with judgement.

8.1 Waves: generation and energy

Wind transfers energy to the sea surface. Wave size depends on wind speed, wind duration and fetch (the distance of open water over which the wind blows). Wave energy rises with the square of wave height, so a wave twice as high carries about four times the energy.

Key terms

• Wave refraction: the bending of wave crests as they slow in shallow water. On an indented coast it concentrates energy on headlands and spreads it out in bays.
• Breaking wave: as depth falls to roughly the wave height, friction slows the base, the crest steepens and topples.
• Swash and backwash: the uprush and the return flow of water on a beach.
• High energy waves: high, steep, frequent; backwash exceeds swash, so they tend to remove sediment and flatten the beach.
• Low energy waves: low, long wavelength, less frequent; swash exceeds backwash, so they tend to build the beach up.

8.1 Marine erosion and sub-aerial processes

The five marine erosion processes are hydraulic action (water and trapped air forced into joints), cavitation (collapsing air bubbles sending shock waves into rock), corrasion/abrasion (sediment hurled at or scraped across rock), solution (chemical dissolving, especially of limestone and chalk) and attrition (particles wearing each other down).

Sub-aerial processes act on the land above the waves. Weathering (salt crystallisation, wetting and drying, freeze-thaw in cold climates, biological action) loosens rock. Mass movement (rockfall, sliding, rotational slumping, mudflow) then moves it to the cliff foot.

Evaluation: marine erosion explains where a coast retreats, but sub-aerial processes often explain how fast a cliff face changes. A cliff of glacial till can lose more to slumping after heavy rain than to direct wave attack in a calm year.

8.1 Transport, deposition and sediment cells

Sediment sources include rivers, eroding cliffs, the offshore sea bed and biological material such as shell and coral fragments. Its size, shape and sorting reflect its source and distance travelled.

Waves move sediment by traction, saltation, suspension and solution. Longshore drift moves it along the coast when waves arrive at an angle: swash carries particles up the beach in the direction of wave approach, and backwash pulls them straight back down the slope.

A sediment cell is a stretch of coast, usually bounded by large headlands, within which sediment moves between sources, transfers and sinks with little exchange beyond the boundaries. Work at one point in a cell affects the rest of that cell.

Worked paragraph (8.1). “The cliffs of the Holderness coast in eastern England are made of glacial till, which is weak and easily saturated [knowledge]. Waves arriving from the north-east over a long North Sea fetch remove slumped debris from the cliff foot, so the cliff never gains a protective apron [application]. This shows that the rate of retreat depends on the link between sub-aerial slumping and marine removal, not on either process alone [evaluation].”

8.2 Erosional landforms

Cliffs and wave-cut platforms. Erosion concentrated between high and low tide cuts a notch. The overhang collapses and the cliff retreats, leaving a gently sloping platform. As the platform widens, waves lose energy crossing it, so retreat should slow over time. This is a negative feedback loop.

Caves, arches and stacks. Erosion exploits joints and faults on a headland. A cave is enlarged into an arch where it cuts through the headland. The arch roof is weakened from below by waves and from above by weathering, and collapses to leave a stack and later a stump.

8.2 Depositional landforms

Beaches in profile. A typical profile shows a storm ridge at the back, berms marking recent high-tide levels, a steeper upper beach, and ridges and runnels on a flatter lower beach. Shingle beaches are steeper than sand beaches because swash percolates into the shingle and backwash is weak.

Beaches in plan. A swash-aligned beach forms where waves arrive roughly parallel to the shore, so there is little net longshore movement and the beach faces the dominant waves. A drift-aligned beach forms where waves arrive at an angle, so longshore drift dominates and the beach is aligned to the direction of drift.

Simple and compound spits. A spit grows where longshore drift continues past a change in coastline direction. A simple spit has one recurved end or none. A compound spit has several recurves along its landward side, each recording an earlier end of the spit. Hurst Spit in Hampshire is a hook-shaped shingle spit with saltmarsh behind it. Spurn Head on the Humber estuary, over 5 km long and fed by sediment eroded from Holderness, is a drift-aligned spit.

Tombolos, offshore bars and barrier beaches. A tombolo is a ridge of sediment joining an island to the mainland. An offshore bar is a ridge of sand lying parallel to the shore below or near low-tide level. A barrier beach (or barrier island) is a larger ridge above high tide enclosing a lagoon, as along the Outer Banks of North Carolina. Chesil Beach in Dorset is a good test case: it runs 29 km to the Isle of Portland, with the Fleet lagoon behind it. It was long called a tombolo, but it is now usually explained as a barrier beach that rolled landwards until it joined Portland.

Coastal dunes. Onshore winds blow dry sand from a wide beach. Obstacles such as driftwood trap it to form embryo dunes. Marram grass traps and stabilises more sand, giving fore, yellow and then grey dunes as organic matter builds up.

Estuaries, saltmarshes and mangroves. In estuaries, fine sediment settles at slack water around high tide, and flocculation (clay particles clumping in salt water) helps it settle. Mudflats form. Salt-tolerant pioneer plants trap more mud, the surface rises, and a saltmarsh develops with creeks draining it. In the tropics, mangroves occupy the same intertidal niche. Their prop roots and breathing roots slow tidal flow, trap sediment and absorb wave energy.

8.2 Sea level change

Eustatic change is a global change in sea level caused by a change in the volume of ocean water (for example ice sheets growing or melting, or water expanding as it warms). Isostatic change is a local change in land level, such as uplift after an ice sheet melts.

• Rising relative sea level gives submergent coasts: drowned river valleys (rias, such as the Rías Baixas of Galicia, Spain), drowned glacial troughs (fjords, such as those of western Norway) and landward-migrating barrier beaches.
• Falling relative sea level gives emergent coasts: raised beaches and relict cliffs above present wave reach, common where land has rebounded since the last glaciation, such as western Scotland.

Worked paragraph (8.2). “A compound spit forms where longshore drift carries sediment past a bend in the coast [knowledge]. At Hurst Spit, shingle moved east along the Hampshire coast builds out into the Solent, while waves refracted round the tip curve its end [application]. Each change in dominant wave direction leaves a recurve, so the spit records its own growth [analysis]. Yet after nearly being breached in 1989 it was rebuilt with dredged shingle and rock revetment, so its form now reflects management as well as natural processes [evaluation].”

8.3 Coral reefs

Types and formation. A fringing reef grows close to the shore with little or no lagoon between. A barrier reef lies further offshore, separated from the coast by a wide, deep lagoon; the Great Barrier Reef off Queensland is the largest example. An atoll is a ring of reef around a central lagoon with no central island, as in the Maldives and Tuvalu.

Charles Darwin’s subsidence theory (The Structure and Distribution of Coral Reefs, 1842) links the three. A fringing reef grows round a volcanic island. As the island sinks, the coral grows upwards to stay in the light, becoming a barrier reef and finally an atoll once the island is submerged. Strength: 1950s drilling on Enewetak Atoll passed through over a kilometre of reef limestone before reaching volcanic basalt. Limitation: sea level fell and rose by over 100 m during the Pleistocene, so modern reef shapes also reflect growth on older surfaces exposed and eroded at low sea level (the antecedent platform or karst idea).

Distribution and conditions for growth. Reef-building corals live in symbiosis with algae called zooxanthellae, which photosynthesise. So they need:

• warm water, typically about 23-29°C and rarely below about 18°C;
• light, so most growth is in shallow water within roughly the top 30 m;
• clear, sediment-free water;
• normal sea salinity, so reefs are rare near large river mouths;
• wave action to supply oxygen and nutrients, but only brief exposure to air.

These conditions place most reefs between about 30°N and 30°S. They are scarce on western coasts of continents, where cold currents and upwelling cool the water.

Threats.

• Global warming: a few weeks of water above the usual summer maximum makes corals expel their zooxanthellae and turn white (bleaching). Mass bleaching events on the Great Barrier Reef include those of 1998, 2002, 2016, 2017, 2022 and 2024.
• Sea-level rise: healthy reefs can usually grow fast enough to keep up, but stressed reefs may not. Ocean acidification from dissolved CO2 also slows skeleton growth.
• Pollution: farm runoff adds nutrients that feed algae, and sediment cuts out light. Sewage and oil add stress.
• Physical damage: anchors, trampling, blast fishing, coral mining, dredging and storm damage.

Management. The Great Barrier Reef Marine Park (established under a 1975 Act; World Heritage Site since 1981) was rezoned in 2004, raising no-take “green zones” from 4.6% to 33.3% of the park. Other strategies include mooring buoys, crown-of-thorns starfish control and reducing farm runoff. Evaluation: local management can raise reef resilience, but no zoning plan stops a marine heatwave. Bleaching on the Great Barrier Reef has continued since the 2004 rezoning, which suggests that reducing global emissions is the main long-term solution.

8.4 Sustainable management of coasts: case study

The syllabus asks for a case study of a stretch or stretches of coastline, with evaluation of hard and soft engineering. The examples below are one possible choice; your teacher will confirm the case study your class uses.

Holderness, eastern England (hard engineering and its knock-on effects). The coast from Flamborough Head to Spurn Head is cut in glacial till. It retreats about 1.5 m a year on average, among the fastest rates in Europe, and at least 23 settlements have been lost since Roman times. At Mappleton, a 1991 scheme costing about £2 million built two rock groynes and a rock revetment, and reduced the cliff gradient. The village is now protected and its beach is wider. But the groynes trap sediment moving south, so the cliffs immediately south of Mappleton have eroded faster. Spurn Head became a tidal island after a December 2013 storm surge cut its road, and its old defences will not be replaced.

The Sundarbans, Bangladesh and India (soft, ecosystem-based protection). This mangrove forest covers about 10,000 km² of the Ganges-Brahmaputra-Meghna delta, with about 60% in Bangladesh. Mangroves act as a natural barrier against cyclone surges for millions of people. Threats include conversion to shrimp farms and agriculture, rising salinity, sea-level rise and embankments that block natural drainage.

Evaluating solutions.

• Hard engineering (sea walls, revetments, groynes, rock armour) gives reliable local protection of high-value land. But it is expensive to maintain and can starve downdrift beaches. Protecting cliffs also removes the sediment supply to the rest of the cell.
• Soft engineering (beach nourishment, dune stabilisation, managed realignment, mangrove planting) works with natural processes and creates habitat. But it needs repeated renewal and cannot protect every site.
• Sustainability means judging a scheme across the whole sediment cell and over decades, and weighing the views of residents, farmers, conservationists and governments.

Worked paragraph (8.4). “At Mappleton, rock groynes and a revetment have stopped the village being lost [knowledge]. But because Holderness is one sediment cell, sediment trapped at Mappleton no longer reaches the cliffs to the south, which have retreated faster since 1991 [application and analysis]. The scheme is therefore successful for one community but not sustainable at the scale of the cell. It moves the problem rather than solving it [evaluation].”

Common errors

• Writing that refraction “makes waves bigger” on headlands. It concentrates energy there.
• Defining cavitation as hydraulic action. Cavitation is bubble collapse.
• Calling every spit “compound”. Only use the term when there are several recurves.
• Listing coral growth conditions without linking them to zooxanthellae and photosynthesis.
• Judging hard engineering as “bad” by default. Mappleton was successful for Mappleton; the problem lies further down the sediment cell.
• Using an 8.4 case study with no named place, date or scheme.

Where to go next

Test yourself with the practice questions and condense with the revision notes linked above. Revise the core physical topics behind this option in the Paper 1 Core Physical Geography guide and physical geography revision notes.

Official syllabus

Cambridge International AS & A Level Geography (9696) syllabus for examination in 2025 and 2026 (Version 1, published September 2022), section 3.3 Paper 3 Advanced Physical Geography Options, topic 8 Coastal environments.