What you'll learn
This revision guide covers all testable content on coasts from the CIE IGCSE Geography specification. You'll understand how waves shape coastlines through erosion and deposition, the formation of distinctive coastal landforms, and how human activity both threatens and protects coastal environments. This topic frequently appears in Paper 1 and Paper 2, so thorough revision is essential.
Key terms and definitions
Fetch — the distance of open water over which wind blows to generate waves; longer fetch produces more powerful waves with greater erosive energy.
Hydraulic action — erosion process where waves compress air into cracks in rock, creating explosive pressure that breaks rock apart.
Attrition — erosion process where rocks and pebbles carried by waves collide with each other, becoming progressively smaller and rounder.
Longshore drift — the transport of sediment along the coast in a zigzag pattern, caused by waves approaching the beach at an angle but retreating straight down the slope.
Spit — an extended stretch of beach material projecting out into the sea, formed by longshore drift where the coastline changes direction sharply.
Groyne — a wooden or concrete barrier built at right angles to the coast to trap sediment being moved by longshore drift.
Sustainable management — coastal protection strategies that meet current needs without compromising the ability of future generations to meet their needs, often involving soft engineering approaches.
Storm surge — abnormally high sea levels caused by a combination of low atmospheric pressure and strong winds, often associated with tropical storms.
Core concepts
Wave formation and characteristics
Waves are created by wind blowing over the sea surface. The energy transferred depends on wind speed, duration, and fetch. As waves approach the shore, friction with the seabed causes them to slow, become steeper, and eventually break.
Constructive waves:
- Low height (less than 1 metre)
- Long wavelength
- Low frequency (6-8 per minute)
- Strong swash, weak backwash
- Build up beaches by depositing material
Destructive waves:
- High height (over 1 metre)
- Short wavelength
- High frequency (10-14 per minute)
- Weak swash, strong backwash
- Erode beaches by removing material
Wave type determines whether a coastline experiences net erosion or deposition. Storm conditions generate destructive waves, while calm conditions produce constructive waves.
Coastal erosion processes
Four main processes erode coastlines:
Hydraulic action: Wave impact compresses air into rock cracks. When waves retreat, the air expands explosively, widening cracks and breaking rock fragments away. Most effective on jointed rocks like limestone and chalk.
Abrasion (corrasion): Waves hurl sand, pebbles and boulders against cliffs, wearing away rock surfaces. This sandpapering effect is the most powerful erosion process on most coastlines.
Attrition: Rock fragments carried by waves collide and break into progressively smaller, rounder pieces. Produces sand and eventually silt from original boulders.
Solution (corrosion): Chemical weathering where seawater dissolves soluble rocks, particularly limestone and chalk. Operates slowly but continuously, even during calm conditions.
Coastal transportation and deposition
Waves transport eroded material through four processes:
- Traction: Large boulders rolled along the seabed
- Saltation: Smaller stones bounced along the seabed
- Suspension: Fine particles (sand, silt) carried within the water
- Solution: Dissolved minerals transported invisibly
Longshore drift is the dominant transport process on most coastlines. Waves approach the beach at an angle determined by prevailing wind direction. Swash carries sediment up the beach at this angle, but gravity pulls backwash straight down the slope. Over thousands of wave cycles, sediment moves progressively along the coast.
Deposition occurs when waves lose energy due to:
- Entering sheltered areas (bays, behind headlands)
- Friction with shallow seabed
- Reduced wind strength
- Obstacles blocking sediment movement
Erosional landforms
Headlands and bays form on coastlines with alternating resistant and less resistant rock. Destructive waves erode softer rock faster, creating bays. Harder rock remains as headlands projecting into the sea. The Dorset coast (England) displays excellent examples, with chalk headlands and clay bays.
Cliffs and wave-cut platforms develop through marine erosion at the cliff base. Hydraulic action and abrasion create a wave-cut notch. The overhanging cliff eventually collapses. Repeated cycles cause cliff retreat, leaving a gently sloping wave-cut platform exposed at low tide. The White Cliffs of Dover demonstrate this process clearly.
Caves, arches, stacks and stumps form on headlands through a sequence:
- Waves attack weaknesses (joints, faults) in headland rock, enlarging them into caves
- Caves on opposite sides of a narrow headland eventually meet, forming an arch
- Arch roof becomes unstable and collapses, leaving an isolated stack
- Stack base erodes until it collapses, leaving a stump (visible only at low tide)
Old Harry Rocks in Dorset exemplifies all these features in different stages.
Depositional landforms
Beaches are accumulations of sediment (sand, shingle, pebbles) between high and low tide marks. Constructive waves build beaches by depositing material. Beach gradient depends on sediment size: shingle beaches are steeper (8-12°) because water drains quickly through large particles; sand beaches are gentler (2-5°) as water drains slowly.
Spits develop where longshore drift transports sediment along the coast until reaching a river estuary or sharp change in coastline direction. Unable to transport sediment inland, deposition creates a narrow ridge extending into the sea. Recurved ends form when secondary winds push the spit tip landward. Saltmarsh often develops in the sheltered area behind spits. Orford Ness (Suffolk) is a classic spit example, extending 15km along the coast.
Bars form when spits extend completely across a bay, creating a lagoon of trapped water behind. Unlike spits, bars connect two headlands. Slapton Ley (Devon) demonstrates this feature clearly.
Tombolos are beaches connecting the mainland to an offshore island, formed by deposition in the sheltered area behind the island. Chesil Beach (Dorset) links Portland Island to the mainland via an 18-mile tombolo.
Coral reefs
Coral reefs form in tropical waters (minimum 18°C) where coral polyps build calcium carbonate skeletons. Three types exist:
Fringing reefs grow directly from the shoreline, forming a platform extending seaward. Common in the Caribbean, including parts of Barbados and Jamaica.
Barrier reefs parallel the coast but separated by a deep lagoon. Australia's Great Barrier Reef is the world's largest example.
Atolls are circular reefs surrounding a central lagoon, marking where coral grew around a volcanic island that subsequently subsided.
Coral reefs provide natural coastal protection by absorbing wave energy, but face threats from:
- Rising sea temperatures causing coral bleaching
- Ocean acidification from increased CO₂ absorption
- Physical damage from tourism and fishing
- Pollution from coastal development
Coastal management strategies
Coastal management addresses erosion threats to property, infrastructure and farmland. Two approaches exist:
Hard engineering involves building artificial structures:
Sea walls are concrete/stone barriers reflecting wave energy. Effective but expensive (£5,000-10,000 per metre), require constant maintenance, and increase erosion elsewhere by reflecting waves.
Groynes are timber/concrete barriers perpendicular to the shore, trapping sediment moved by longshore drift. Build beaches that absorb wave energy, but starve beaches downdrift of sediment, increasing erosion there. Cost £5,000-10,000 per groyne.
Gabions are wire cages filled with rocks, stacked to form barriers. Cheaper than sea walls (£100-150 per metre), absorb wave energy, but only last 20-25 years and appear unattractive.
Rip-rap (rock armour) uses large boulders placed at cliff base to absorb wave energy. Relatively cheap (£1,000-3,000 per metre) and effective, but boulders may shift during storms, and gaps allow wave attack.
Soft engineering works with natural processes:
Beach nourishment involves adding sand/shingle from elsewhere (often offshore dredging). Creates wider beaches absorbing wave energy naturally. Requires regular replenishment (every 3-5 years) but appears natural. Used extensively along the Caribbean coast and in places like Sandbanks, Dorset.
Dune regeneration plants marram grass and restricts access to allow sand dunes to develop naturally. Dunes provide flexible barriers absorbing wave energy, cost little, create habitats, but require space and time to establish.
Managed retreat (coastal realignment) deliberately allows low-value land to flood, creating salt marsh that absorbs wave energy and protects higher-value areas inland. Controversial but cost-effective long-term. Implemented at Medmerry (Sussex) in 2013, creating 183 hectares of intertidal habitat.
Sustainable coastal management typically combines multiple strategies, prioritizing high-value areas while allowing natural processes to operate elsewhere.
Coastal flooding threats
Low-lying coastal areas face flooding from:
Storm surges: Low pressure (1mb drop raises sea level 1cm) combined with strong onshore winds can raise sea levels 2-3 metres above normal. Tropical storms create particularly dangerous surges affecting Caribbean islands.
High tides: Spring tides (new and full moon) raise water levels significantly. Storm surges coinciding with spring tides create extreme flood risk.
Climate change impacts: Sea level rise (3mm per year currently) increases flood frequency and severity. Predictions suggest 0.5-1 metre rise by 2100, threatening coastal cities and small island developing states (SIDS) in the Caribbean.
Tsunami: Underwater earthquakes generate waves traveling at 800km/h in deep ocean, reaching 10-30 metres height when approaching shore. Rare but catastrophic. The 2004 Indian Ocean tsunami killed 230,000 people.
Bangladesh faces extreme coastal flood risk from monsoon rainfall, storm surges in the Bay of Bengal, and rivers depositing sediment in the Ganges-Brahmaputra delta. The 1970 Bhola cyclone killed 300,000-500,000 people through coastal flooding.
Worked examples
Example 1: Explain how a wave-cut platform is formed. (4 marks)
Model answer: Waves attack the base of a cliff through hydraulic action and abrasion (1), creating a wave-cut notch (1). The overhanging cliff becomes unstable and collapses (1). Repeated erosion and collapse causes the cliff to retreat, leaving a gently sloping rocky platform exposed at low tide (1).
Examiner guidance: This requires a sequence explanation. Each stage earns 1 mark. Use geographical terminology (hydraulic action, abrasion, wave-cut notch) to demonstrate knowledge.
Example 2: Compare the advantages and disadvantages of using groynes and beach nourishment for coastal protection. (6 marks)
Model answer: Groynes trap sediment transported by longshore drift, building beaches that absorb wave energy effectively (1). However, they starve beaches downdrift of sediment, increasing erosion elsewhere (1), and are expensive at £5,000-10,000 per groyne (1).
Beach nourishment creates wide beaches that absorb wave energy naturally and maintains sediment budget along the coast (1). The beach appears natural and supports tourism (1). However, it requires regular replenishment every 3-5 years as storms remove added sediment (1), making long-term costs high.
Examiner guidance: "Compare" requires discussion of both approaches with advantages AND disadvantages for each. Six valid points earn full marks. Specific costs/timescales demonstrate detailed knowledge.
Example 3: Explain how longshore drift transports sediment along a beach. (3 marks)
Model answer: Waves approach the beach at an angle determined by the prevailing wind direction (1). Swash carries sediment up the beach at this angle (1). Backwash returns directly down the slope under gravity, moving sediment in a zigzag pattern along the coast (1).
Examiner guidance: A clear sequence with geographical terminology. A labeled diagram would support this answer effectively.
Common mistakes and how to avoid them
Confusing erosion processes: Students often mix up hydraulic action (air compression) and abrasion (rock hurled against cliff). Learn each process distinctly with clear examples of where each operates most effectively.
Incomplete landform formation sequences: When explaining caves-arches-stacks, include all stages in correct order and use process terminology (erosion, weathering, collapse). Don't just describe the feature's appearance.
Not comparing in comparison questions: "Compare" requires discussing both items. If asked to compare hard and soft engineering, ensure you cover advantages AND disadvantages of BOTH approaches, not just one.
Vague coastal management descriptions: Avoid "it protects the coast" without explaining HOW. Specify that beaches absorb wave energy, or sea walls reflect wave energy, using correct terminology.
Missing case study details: When asked about coastal management, include specific locations (e.g., "Mappleton, Yorkshire" not just "England"), actual costs, and dates to demonstrate genuine knowledge rather than generic understanding.
Forgetting scale in diagrams: If drawing coastal landforms, include scale indicators and labels. A stack without reference to its size or surrounding features gains fewer marks than a fully annotated diagram.
Exam technique for "Theme 2: The Natural Environment — Coasts"
Command word precision: "Describe" requires stating what you observe (features, patterns, trends). "Explain" requires reasons/processes/causes. "Compare" needs similarities AND differences. "Assess/Evaluate" demands weighing up different viewpoints with a judgment.
Mark allocation guides answer length: For 2-mark questions, make 2 distinct points. For 6-mark questions, develop 3 detailed points or provide 6 shorter points. Extended answers (8+ marks) require structured paragraphs with introduction, developed points, and conclusion.
Use case studies strategically: Questions worth 6+ marks often reward specific located examples. Learn 2-3 case studies thoroughly (location, specific features, actual data, dates) rather than many vague examples.
Draw annotated diagrams: For landform formation questions, well-labeled diagrams showing stages often earn more marks than lengthy written descriptions alone. Combine both for maximum credit.
Quick revision summary
Waves shape coastlines through erosion (hydraulic action, abrasion, attrition, solution) creating cliffs, wave-cut platforms, and cave-arch-stack sequences on headlands. Longshore drift transports sediment, forming depositional features including beaches, spits, bars and tombolos. Coastal management uses hard engineering (sea walls, groynes, rip-rap) or soft engineering (beach nourishment, dune regeneration, managed retreat) to protect against erosion and flooding. Sustainable approaches increasingly favor soft engineering working with natural processes. Climate change intensifies coastal flooding through sea level rise and increased storm frequency.