HKDSE Geography/M2b/Factors Affecting Coastal Processes

Several factors affect the coast: Atmospheric factors, marine factors and geological factors.

Atmospheric Factors

• Climate: A hot, wet climate facilitates chemical weathering of rocks. This weakens the structure of rocks at the coast, lowering their resistance. This leaves them more vulnerable to wave erosion.
• Wind speed: Higher wind speed creates waves with greater erosive power.
• Wind direction: Wind direction determines the path of a wave. Along with the shape of the coastline and its properties, it determines the fetch. Fetch refers to the distance of open water over which a wave has travelled (i.e. without obstacles). The greater the fetch, the greater the wave energy.
• During during wind has been blowing from a direction: If the wind has been blowing from a single direction for a long time, the waves will have greater erosive power.

Marine Factors

• Shape of coastline: Wave refraction describes how wave energy tends to concentrate at headlands and disperse at bays. At headlands, waves are more concentrated. Destructive waves are formed and erosion usually occurs. At bays, waves are less concentrated. Constructive waves are formed and deposition usually occurs.
• Outlying islands: They reduce fetch. Therefore, an area of the coastline with outlying islands is likely to experience constructive waves and wave deposition.
• Shore gradient: If there is a steeper shore gradient, the waves will break nearer to the coast. Less energy is spent on overcoming friction against the seabed. The energy and erosive power are greater. The waves thus tend to be destructive waves causing erosion.

Geological Factors

• Rocks with many joints or cracks are more vulnerable to hydraulic action. This increases the rate of erosion.
• Rocks with soluble minerals are more prone to solution. This increases the rate of erosion.
• Rocks with minerals of varying resistance are more prone to salt sprays from seas which cause honeycomb erosion.