coastal landforms and change

waves

• main source of energy at the coastline

• generated by wind

• friction between wind and water surface

Fetch

The distance of open water the wind blows over

strength

how forceful the wind is

duration

how long the wind has been blowing

Constructive waves

• lower wave height

• strong swash and weak backwash

• build up the beach

Destructive waves

• higher height

• weak swash and strong backwash

• break down the beach

beach morphology in summer

Beach profiles are steeper in summer when there are fewer destructive waves

• 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 morphology 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

erosional processes

• abrasion

• hydraulic action

• corrosion

• attrtion

abrasion

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

• Wave type

• Wave size

• Lithology

wave type and size affecting 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 affecting erosion

• Weaknesses in rocks erode more quickly

• More resistant rocks erode more slowly

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

cave , arch, stack

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