Coastal systems and landscapes - 3.1.3.2 Systems and processes — AQA A-Level Geography
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Coastal systems and landscapes - 3.1.3.2 Systems and processes explained
Coastal systems are driven by multiple energy sources.
Read the full explanation
Winds generate waves and drive surface currents, with fetch determining wave energy. Constructive waves have a strong swash and weak backwash, building up beaches, whereas destructive waves possess a weak swash and strong backwash, eroding material. Tides, driven by gravitational pull, dictate the range of wave action and generate tidal currents in estuaries. High energy coasts, like Cornwall, face strong prevailing winds and long fetches, resulting in destructive waves and erosional landforms such as cliffs. Conversely, low energy coasts, like the Baltic Sea, experience limited fetch and gentle winds, dominated by constructive waves and depositional features like spits and mudflats.
Sediment sources, cells and budgets.
Coastal sediment originates from various sources, including cliff erosion, fluvial discharge, and offshore deposits. This material moves within sediment cells, which are largely self-contained stretches of coastline where sediment circulates, such as the Flamborough Head to Spurn Point cell. Within these cells, a sediment budget represents the balance between sediment inputs (sources) and outputs (sinks). If inputs exceed outputs, a positive budget creates a surplus, leading to coastal accretion and the formation of depositional landforms like beaches. Conversely, a negative budget causes a deficit, resulting in coastal retreat and erosion. Understanding these interconnected components is vital for effective shoreline management.
Geomorphological processes: weathering, mass movement, erosion, transportation and deposition.
Coastal landscapes are shaped by five key geomorphological processes. Weathering breaks down rocks in situ through mechanical, chemical, or biological means, such as freeze-thaw action. Mass movement involves the downslope transfer of this material under gravity, seen in rotational slumping on clay cliffs. Erosion actively wears away the coastline using energy from waves, through mechanisms like hydraulic action and abrasion. The eroded material undergoes transportation via longshore drift, traction, or suspension. Finally, deposition occurs when wave energy decreases, dropping the sediment to form features like spits and beaches. Together, these interconnected processes continuously modify the coastal system.
Distinctively coastal processes: marine: erosion – hydraulic action, wave quarrying, corrasion/ abrasion, cavitation, solution, attrition; transportation: traction, suspension (longshore/littoral drift) and deposition; sub-aerial weathering, mass movement and runoff.
Coastal landscapes are shaped by an interplay of marine and sub-aerial processes. Marine erosion includes hydraulic action and wave quarrying, where sheer wave force and trapped air widen cliff faults. Cavitation occurs as compressed air bubbles implode, stressing the rock. Corrasion (abrasion) uses sediment as tools to scour the coast, while attrition rounds the sediment itself. Solution dissolves soluble rocks like limestone. Transportation moves this material via traction (rolling large stones), suspension (carrying fine particles), and longshore drift (littoral drift), which moves sediment along the coast in a zigzag pattern until deposition occurs in lower-energy zones. Simultaneously, sub-aerial weathering, mass movement, and surface runoff weaken and transport material down cliff faces.
Your focus
- Describe the formation and characteristics of constructive and destructive waves.
- Explain how winds, currents, and tides provide energy to drive coastal processes.
- Compare the physical characteristics and dominant processes of high energy and low energy coastal environments.
Show all 12 objectives
- Categorise different sources of coastal sediment into terrestrial, marine, and human inputs.
- Define a sediment cell and explain its function as a largely closed coastal system.
- Analyse how changes in a sediment budget affect coastal erosion and accretion rates.
- Differentiate between weathering, mass movement, and erosion using precise geographical definitions.
- Explain the mechanisms of marine transportation and the conditions required for deposition.
- Evaluate the relative importance of sub-aerial versus marine processes in shaping a specific coastal landform.
- Differentiate between the six specified types of marine erosion and explain their distinct physical or chemical mechanisms.
- Describe the processes of marine transportation, including traction, suspension, and longshore drift, and how they lead to deposition.
- Evaluate the contribution of sub-aerial weathering, mass movement, and runoff to overall coastal landscape development.
Coastal systems and landscapes - 3.1.3.2 Systems and processes exam tips
Marking Points
- Identify wind as the primary energy source that generates waves and influences their magnitude through fetch, duration, and velocity.
- Contrast constructive waves (low frequency, strong swash, net deposition) with destructive waves (high frequency, strong backwash, net erosion).
- Explain the role of tides in shifting the zone of wave action and generating tidal currents that transport sediment, particularly in estuaries.
- Characterise high energy coasts by their exposure to strong prevailing winds, long fetches, and dominant erosional processes and landforms.
- Characterise low energy coasts by their sheltered locations, short fetches, and dominant depositional processes and landforms.
- Identify primary sediment sources, distinguishing between terrestrial (rivers, cliff erosion) and marine (offshore bars) inputs.
- Explain the concept of a sediment cell as a closed system with distinct boundaries, typically defined by major headlands or estuaries.
- Calculate or interpret a sediment budget by comparing the volume of sediment inputs against outputs, often measured in m³ per year.
- Link a positive sediment budget to coastal accretion and a negative budget to coastal erosion and shoreline retreat.
- Distinguish weathering as an in situ process from erosion, which involves the active removal of material by a moving medium like waves.
- Explain specific mass movement processes, such as rockfalls or rotational slumping, linking them to cliff lithology and moisture content.
- Detail marine erosion mechanisms, including hydraulic action, abrasion, attrition, and corrosion (solution).
- Describe the four main methods of coastal transportation: traction, saltation, suspension, and solution, alongside the overarching process of longshore drift.
- Explain that deposition occurs when the velocity and energy of the transporting agent fall below the critical threshold required to carry the sediment load.
- Define specific erosion mechanisms, clearly distinguishing between processes like hydraulic action, wave quarrying, and cavitation.
- Explain the mechanics of longshore (littoral) drift, including the role of prevailing wind direction, swash, and backwash.
- Link sub-aerial processes, including physical, chemical, and biological weathering, mass movement, and runoff, to the supply of sediment to the littoral zone.
- Identify the conditions required for marine deposition, such as a reduction in wave energy, sheltered estuaries, or flocculation.
Examiner Tips
- 💡Link wave types directly to beach profiles, explaining how destructive waves create steep, combed-down winter profiles.
- 💡Use specific geographical examples to contrast high energy (e.g., Atlantic coast of Scotland) and low energy (e.g., Lincolnshire coast) environments.
- 💡When discussing energy sources, explicitly mention how wind fetch and duration control the kinetic energy transferred to waves.
- 💡Use a named example of a sediment cell, such as the Holderness Coast (Flamborough Head to Spurn Point), to contextualise your answers.
- 💡When discussing sediment budgets, explicitly use the terms 'positive budget' (surplus) and 'negative budget' (deficit) to demonstrate geographical terminology.
- 💡Evaluate how human interventions, like dam construction on rivers, can disrupt sediment budgets by reducing fluvial inputs.
- 💡Always link specific geomorphological processes to the formation of specific landforms, such as linking abrasion to wave-cut notches.
- 💡Use precise terminology for transportation, ensuring you can differentiate between saltation (bouncing) and traction (rolling).
- 💡Discuss how sub-aerial processes (weathering and mass movement) work in tandem with marine processes (erosion) to cause rapid cliff retreat.
- 💡Use precise terminology when describing erosion; always specify whether the rock face or the sediment itself is being worn away.
- 💡When explaining longshore drift, explicitly mention the role of the prevailing wind in determining the angle of the swash.
- 💡Link sub-aerial processes to marine processes by explaining how mass movement provides a sediment source for marine transportation and deposition.
Common Mistakes
- Stating that constructive waves have a strong backwash; correction: constructive waves have a strong swash and weak backwash, leading to sediment deposition.
- Confusing currents and tides; correction: tides are vertical movements of water driven by gravity, while currents are horizontal movements of water driven by wind, temperature, or tidal flows.
- Assuming high energy coasts only experience erosion; correction: while erosion dominates high energy coasts, deposition still occurs in sheltered bays or during calmer seasonal conditions.
- Error: Confusing sediment cells with open systems. Correction: Describe sediment cells as largely closed systems, though acknowledge that fine sediment can occasionally bypass boundaries.
- Error: Assuming cliff erosion is the largest sediment source globally. Correction: State that fluvial (river) input is typically the most significant source of coastal sediment worldwide.
- Error: Using the terms 'source' and 'sink' interchangeably. Correction: Use 'source' for sediment inputs (e.g., eroding cliffs) and 'sink' for permanent depositional outputs (e.g., deep offshore waters).
- Error: Confusing weathering with erosion. Correction: Define weathering as the breakdown of rock in situ (without movement), whereas erosion involves the wearing away and removal of rock by a moving force.
- Error: Using 'attrition' to describe waves smashing into cliffs. Correction: Use 'abrasion' or 'corrasion' for waves throwing rocks at cliffs, and reserve 'attrition' for rocks colliding with each other in the water.
- Error: Treating mass movement as a marine process. Correction: Categorise mass movement as a sub-aerial process driven by gravity, though it is often exacerbated by marine undercutting.
- Confusing corrasion (abrasion) with attrition; correction: corrasion is the wearing away of the cliff by sediment, whereas attrition is the wearing down of the sediment particles themselves.
- Treating sub-aerial processes as marine erosion; correction: sub-aerial processes operate on the cliff face above the high water mark through weathering, mass movement and runoff, not direct wave action.
- Using 'hydraulic action' and 'wave quarrying' interchangeably without distinction; correction: specify that wave quarrying involves the scooping action of waves and the compression of air in joints, while hydraulic action is the sheer impact force of the water.