Marine Erosion (Edexcel A Level Geography)

Wave Types

• The main source of energy at the coast is the waves 

• Waves are mainly generated by wind 

• The friction between wind and the water surface which transfers energy from the wind to the water

• Wind occurs because of the rotation of the earth and differences in atmospheric pressure when different parcels of air are heated differently by the sun

• Various features of the wind will affect how much energy a wave has: fetch, duration and strength of the wind.  

• Wave height is the distance from the peak to the trough

• Wave length is the distance from crest to crest

• Wave frequency is the number of waves which pass a specific point over a given time

Types of wave

• There are two main types of wave, constructive and destructive

Impact on beach morphology

• Beaches are formed from loose material 

• Waves alter the morphology (form/shape) of the beach

• The morphology is also affected by the size and shape of the beach material

• The type of wave in an area can vary depending on the time of year or coastal management

  • Beach profiles are steeper in summer when there are fewer destructive waves and gentler in winter

  • Storm berms may develop in winter when large destructive waves carry larger sediment further up the beach than normal

  • In winter beaches may also have a greater variation in pebble size as larger pebbles are deposited by the destructive waves and smaller pebbles are removed

  • Offshore ridges/bars are formed due to material being eroded from the beach by destructive waves and deposited offshore

Types of Wave and Their Characteristics

Erosion Processes

• Erosion leads to the formation of a range of landforms at the coast

• There are four types of erosion

  • Abrasion (corrasion) - sediment and stones are picked up by the waves and wear away at the cliff/headland

  • Hydraulic action - this is the shear force of the waves forcing air at high pressure into cracks in the cliff over time this weakens the rock and causes the joint to widen

  • Corrosion - weak acids in seawater dissolve the rock particles

  • Attrition - as rocks are moved around by the water they knock into each other gradually becoming smaller and rounder

Factors affecting erosion

• The amount of erosion is influenced by a range of factors

  • Wave type

  • Wave size

  • Lithology

• Wave type and size affects the seasonal changes in the amount of erosion 

  • Erosion tends to happen more during the winter due to a greater number of destructive waves

  • The size and type of waves affects the amount of hydraulic action and abrasion

• Lithology influences the rate of erosion

  • Weaknesses in rocks erode more quickly

  • More resistant rocks erode more slowly

Coastal Landforms

Wave cut platforms

• At high-energy coastlines, hydraulic action and abrasion can cause the formation of wave-cut platforms 

  • Powerful destructive waves attack the base of the cliff at high tide 

  • The hydraulic action and abrasion create a wave-cut notch which over time increases in size 

  • This is called undercutting 

  • Eventually, the overhang created by the undercutting collapses due to weathering and gravity 

  • The cliff retreats, leaving a wave cut platform that is exposed at low tide

• At a headland, where the rock is hard, erosion is slow and can lead to a variety of landforms

• Wave refraction concentrates wave energy onto the headland and can contribute to the formation of caves, arches, stack and stumps

  • Joints in the headland are susceptible to erosion by hydraulic action

  • Over time the joints widen forming a cave that is enlarged by hydraulic action and abrasion

  • Eventually, erosion cuts through the headland forming an arch

  • The roof of the cave will eventually collapse due to gravity and the lack of support

  • This leaves a stack that will over time be eroded by weathering, abrasion, and hydraulic action to form a stump