How does the 'fetch' of a wave affect coastal recession?

Fetch is the distance of open water over which wind blows. A longer fetch allows waves to gain more energy, resulting in more powerful destructive waves that accelerate coastal recession through increased hydraulic action.

What is the difference between lithology and structure in coastal geology?

Lithology refers to the rock type and its chemical/physical composition (e.g., clay vs. granite). Structure refers to how the rock is arranged, including faults, joints, and the angle (dip) of the bedding planes.

Why does a seaward dip in rock strata often lead to lower cliff stability?

When strata dip toward the sea, gravity can more easily pull loosened blocks of rock down the bedding planes. This often results in landslides or slumping, especially when the base of the cliff is undercut by waves.

What is a common mistake when evaluating the impact of sea walls on coastal stability?

A common error is ignoring 'down-drift' effects. While a sea wall protects a local area, it often starves adjacent areas of sediment by stopping cliff erosion, leading to increased recession further down the coast.

Define 'Pore Water Pressure' and its role in coastal recession.

Pore water pressure is the pressure of water held within the gaps of soil or rock. High pressure (often from heavy rain) lubricates grains and reduces friction, triggering mass movements like slumping.

Compare Concordant and Discordant coastlines.

Concordant coasts have rock layers running parallel to the shore, often forming straight coastlines. Discordant coasts have layers at right angles to the shore, leading to differential erosion and the formation of headlands and bays.

How do destructive waves differ from constructive waves in terms of sediment transport?

Destructive waves have a stronger backwash than swash, removing sediment from the beach. Constructive waves have a stronger swash, depositing sediment and building up the beach, which increases coastal stability.

What error occurs if one assumes coastal recession is only caused by waves?

This overlooks sub-aerial processes like weathering and mass movement. In many cases, a cliff collapses because it was weakened from above by rainwater and frost, not just because it was attacked from below by waves.

What is the 'Sediment Budget'?

It is the balance between the amount of sediment entering a coastal system (inputs) and the amount leaving it (outputs). A deficit in the budget leads to beach thinning and increased cliff erosion.

How does a high tidal range affect the rate of erosion?

A high tidal range spreads wave energy over a larger vertical area of the cliff face. While this may reduce the intensity of erosion at a single point, it subjects a wider zone of the cliff to marine processes.

Factors Affecting Coastal Recession & Stability | Pearson Edexcel A-Level Geography

Coastal Landscapes & Change

Factors Affecting Coastal Recession & Stability

Summary

Coastal recession and stability are governed by a complex interplay of geological, marine, and sub-aerial factors. Understanding these variables is essential for predicting land loss and designing effective coastal management strategies to protect human infrastructure and natural habitats.

1. Definition & Core Concepts

Coastal Recession refers to the landward retreat of the shoreline over time, primarily driven by erosion and mass movement processes.
Coastal Stability is the state of equilibrium where the rate of sediment supply roughly equals the rate of sediment removal, preventing significant changes in the coastline's position.
The Sediment Budget is a fundamental concept used to assess stability; it is the balance between sediment inputs (e.g., river discharge, cliff erosion) and outputs (e.g., longshore drift, offshore transport).
A Negative Sediment Budget occurs when outputs exceed inputs, leading to increased recession and instability of the coastal landforms.

2. Geological Influences: Lithology and Structure

Lithology refers to the physical characteristics of rocks, such as their mineral composition and hardness, which determine their resistance to erosion.
Igneous rocks (e.g., granite) are generally highly resistant and recede slowly, whereas sedimentary rocks (e.g., clay or sandstone) are often weaker and recede rapidly.
Geological Structure involves the arrangement of rock layers, including bedding planes, joints, and faults, which create planes of weakness for erosional agents to exploit.
The Dip of Strata significantly affects cliff stability; seaward-dipping strata are prone to mass movement (slumping), while landward-dipping strata tend to produce more stable, steeper cliff profiles.

Diagram showing a coastal cliff profile with landward-dipping strata and the zone of wave attack at the base.

3. Marine Dynamics and Wave Energy

Wave Energy is the primary driver of coastal recession, determined by wind speed, duration, and fetch (the distance of open water over which wind blows).
Destructive Waves possess high energy and a strong backwash, which removes sediment from the beach and exposes the cliff base to hydraulic action and abrasion.
Tidal Range influences the vertical zone over which erosion occurs; a high tidal range spreads wave energy over a wider area, while a low range concentrates it at a specific height.
Storm Surges caused by low atmospheric pressure can temporarily raise sea levels, allowing waves to reach higher up the cliff face and causing rapid, episodic recession.

4. Sub-aerial Processes: Weathering and Mass Movement

5. Key Distinctions: Concordant vs. Discordant Coasts

6. Exam Strategy & Tips