Systems and Processes (AQA A-Level Geography): Revision Notes
Systems and Processes
Introduction to coastal systems
Coastal environments operate as natural systems with distinct inputs, stores, flows, and outputs. Understanding these systems is essential for explaining how coastal landscapes develop and change over time. Energy from various sources drives processes that shape coastlines through weathering, erosion, and mass movement.
These systems constantly seek dynamic equilibrium, where the balance between inputs and outputs shapes the characteristic features we observe along coastlines. By examining coastal areas through a systems approach, we can better understand how different elements interact to create the landforms and features found in coastal zones.
The nearshore zone
The nearshore is the coastal area that extends seaward from the High Water Mark (HWM) to the point where waves begin to break. This zone is characterised by active wave processes and can be subdivided into three distinct areas:
Swash zone
This is the area where turbulent water washes up the beach following a wave breaking. As waves break and release their energy, water rushes up the beach face. This rushing water carries sediment with it, playing a crucial role in beach formation and sediment distribution.
Surf zone
The surf zone lies between the point where waves initially break and where they move up the beach. In this area, waves form a foamy, bubbly surface as they break and release energy. The water movement in this zone is highly turbulent, creating the characteristic white water and foam that we associate with breaking waves.
Breaker zone
This is the area where waves approaching the coastline begin to break. Wave breaking typically occurs where the water depth is between 5 and 10 metres. At this depth, the wave base (the lowest point affected by wave motion) begins to interact with the seabed, causing the wave to become unstable and break.
Understanding the Nearshore Zones
Each of these three zones plays a distinct role in coastal processes. The breaker zone initiates wave energy release, the surf zone continues energy dissipation through turbulent flow, and the swash zone directly shapes the beach face through sediment transport. Together, they form an integrated system of wave energy transformation.
Coastal systems framework
System inputs
Coastal systems receive energy and materials from various sources:
- Energy sources: waves, wind, tides, and sea currents all provide the energy needed to drive coastal processes
- Sediment: material enters the system from various sources including rivers, cliff erosion, and offshore sources
- Geology: the underlying rock structure and composition of the coastline influences how the system operates
- Sea level change: variations in sea level affect the position and intensity of coastal processes
System components
The stores and features within the coastal system include:
- Characteristic erosional landforms such as cliffs, wave-cut platforms, caves, arches, and stacks
- Depositional landforms including beaches, spits, bars, and sand dunes
- These features represent the temporary storage of energy and sediment within the system
System outputs
Energy and materials leave the coastal system through several mechanisms:
- Dissipation of wave energy: as waves break and interact with the coast, their energy is gradually released and absorbed
- Accumulation of sediment: material may be deposited above the tidal limit where it is no longer actively moved by marine processes
- Sediment transfer: material may be removed beyond local sediment cells, effectively leaving the immediate coastal system
The Dynamic Nature of Coastal Systems
It's crucial to understand that coastal systems are dynamic and interconnected. Changes in inputs (such as increased storm frequency or altered sediment supply) will affect the components (landforms) and outputs of the system. This interconnectedness means that human interventions in one part of the coastal system can have significant and sometimes unexpected effects elsewhere along the coast.
Sources of energy in coastal environments
The energy driving coastal processes comes from four main sources: waves, wind, tides, and currents. Each plays a distinct role in shaping coastal landscapes.
Wind as an energy source
Wind serves as a vital input into the coastal system, functioning both as a direct agent of change and as the primary generator of wave energy.
Spatial variations in wind energy
The energy available from wind varies considerably across different coastal locations. Where wind speeds are persistently high and uninterrupted, wave energy is likely to be significantly higher. This creates more energetic coastal environments with greater potential for erosion and sediment transport.
Local weather patterns may cause short-term fluctuations in wind speed and direction. However, most coastlines experience a prevailing wind direction - the direction from which wind generally approaches the coast most frequently. This prevailing direction is particularly important because it controls the dominant direction of wave approach, which in turn influences the direction of sediment transport along the coast.
The importance of fetch
Fetch is the distance of open water over which a wind blows uninterrupted by major land obstacles. The length of fetch directly determines the magnitude and energy of waves reaching the coast.
A longer fetch allows winds to transfer more energy to the water surface, generating larger, more powerful waves. This is why coastlines facing large ocean basins typically experience more powerful wave action than those facing smaller, enclosed seas.
Worked Example: Comparing Fetch Effects
Consider two coastal locations in the UK:
Location A: A beach on the east coast of England facing the North Sea
- Fetch: approximately 600 km across the North Sea
- Result: Moderate wave energy, typical wave heights of 1-2 metres
Location B: A beach on the west coast of Scotland facing the Atlantic Ocean
- Fetch: over 5,000 km across the Atlantic Ocean
- Result: High wave energy, typical wave heights of 2-4 metres (can exceed 10 metres during storms)
This example demonstrates how longer fetch produces significantly more powerful waves, explaining why Atlantic-facing coasts generally experience more erosive conditions than North Sea coasts.
Key terminology
Erosion is the wearing away of the Earth's surface by the mechanical action of processes including glaciers, wind, rivers, marine waves, and wind.
Mass movement refers to the movement of material downhill under the influence of gravity, though it may also be assisted by rainfall. This process is particularly important on coastal cliffs and slopes.
Weathering is the breakdown and/or decay of rock at or near the Earth's surface, creating regolith that remains in place (in situ) until it is removed by later erosional processes. Weathering can be mechanical, biological/organic, or chemical in nature.
Distinguishing Between Related Processes
While weathering, erosion, and mass movement are closely related, it's essential to understand their differences:
- Weathering breaks down rock but leaves material in place
- Erosion involves the active removal and transport of material
- Mass movement specifically refers to downslope movement under gravity
These processes often work together sequentially: weathering weakens rock, making it more susceptible to erosion or mass movement.
Key Points to Remember:
- The coastal system operates with inputs (energy and sediment), components (landforms), and outputs (energy dissipation and sediment removal)
- The nearshore zone consists of three distinct areas: swash zone, surf zone, and breaker zone, each with different wave characteristics
- Wind provides energy directly and generates waves, with prevailing wind direction controlling the dominant direction of coastal processes
- Fetch (the distance of open water) determines wave size and energy - longer fetch produces more powerful waves
- Weathering, erosion, and mass movement are distinct but related processes that work together to shape coastal landscapes