8 Coastal environments 8.1 Waves, marine and sub-aerial processes Features of waves
Revised
Waves result from friction between wind and the sea surface. Wave height is an indication of wave energy. It is controlled by wind strength, fetch (the distance of open water a wave travels over) and the depth of the sea. Waves of up to 12–15 m are formed in open sea and can travel vast distances away from the generation area, reaching distant shores as swell waves, characterised by a lower height and a longer wavelength. In contrast, storm waves are characterised by a short wavelength, high amplitude and high wave frequency.
Wave refraction
Wave height or amplitude is the distance between the trough and the crest. Wavelength is the distance between two successive crests or troughs. Wave frequency is the number of waves per minute.
l
As wave fronts approach the shore, their speed of approach will be reduced as the waves ‘feel bottom’. l Usually, wave fronts will approach the shore obliquely – this causes the wave fronts to bend and swing round in an attempt to break parallel to the shore. l The change in speed and distortion of the wave fronts is called wave refraction (Figure 8.1). l If refraction is completed, the fronts will break parallel to the shore. Reduced wave energy in embayment
Refracted wave fronts Concentration of wave energy on to headland
Concentration of wave energy on to headland
Parallel wave fronts Source: Advanced Geography: Concepts & Cases by P. Guinness & G. Nagle (Hodder Education, 1999), p.294
Figure 8.1 Wave refraction
Wave refraction distributes wave energy along a stretch of coast. Along a complex transverse coast with alternating headlands and bays, wave refraction will concentrate wave energy and therefore erosional activity on the headlands, while wave energy will be dispersed in the bays. Hence deposition will tend to occur in the bays.
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Cambridge International AS and A Level Geography Revision Guide
