Marine erosion creates coastal landforms and landscapes

Waves

↳ Result from direction between the wind and the sea surface

↳ Potential energy of a wave is proportional to its height, direction, duration of wind and fetch

Constructive and destructive waves

Beaches can experience both constructive and destructive waves. This can change:

• Daily (storms)
• Seasonally (summer vs winter)
• Long term (climate change) | Constructive waves | Destructive waves | |---|---| | • Build beaches
  • Have longer wavelengths and lower in height
  • Less frequent
  • Swash is greater than backwash so beach materials are added meaning a gentle sloping beach
  • Upper part of beach has berms (small ridges) • each represents the highest point the wave reached at the previous high tide | • Backwash is greater than swash so sediment is dragged offshore
  • Create a steeper beach profile initially, but over time the beach flattens as material is drawn backwards
  • Storms create storm beaches (shingle ridges at the back of the beach) |

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Erosional processes

↳ Erosion is not a constant process Most erosion occurs when:

• Waves are at their largest (influenced by wind speed and fetch)
• Waves approach the coast at 90° to the cliff face
• High tide
• Heavy rainfall = ↑ increase in percolation through strata and surface runoff = weaker cliff
• Debris from previous erosion as been removed from the cliff base

PROCESS	EXPLANATION	INFLUENCE OF LITHOLOGY
Hydraulic action	• Air trapped in cracks is compressed by waves crashing against the cliff face • Pressure forces cracks open so more air is trapped & greater force experienced each time	Heavily jointed rocks so very vulnerable
Abrasion	• Sediment picked up by breaking waves is thrown against the cliff face • Over time, the cliff face is gradually worn down	For abrasion to occur loose sediment has to be available ↳ Softer sedimentary rocks are more available than hard igneous ones
Attrition	• Acts on already eroded sediment • As sediment moved around by waves, numerous collisions between particles slowly chip fragments off the sediment • So over time the sediment becomes smaller & more rounded	Softer rocks = rapidly reduced in size by attrition
Corrosion /solution	• Carbonate rocks are vulnerable to corrosion by rainwater and seawater • Visors (overhangs) on tropical coastlines often indicate where limestone has been dissolved	Mainly affects limestone which is vulnerable to solution by weak acids

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Coastal landforms

Wave-cut notches

• At high tide, destructive waves can reach the base of a cliff
• Abrasion & hydraulic action erode the rock at the cliff base
• A curved, wave-cut notch forms along the length of the cliff Caves can also form at weaker points along the wave-cut notch

Wave-cut platform

• Above the wave-cut notch, an overhang of unsupported rock is formed
• As the overhang is further undercut, less support for the overhang, eventual mass movement
  • Leads to cliff retreat
• As the cliff retreats, a flat platform is left behind

Cave → arch → stack → stump

• Mainly hydraulic action & abrasion form caves & eventually meet in the middle forming an arch
• Weathering causes the centre of the arch to eventually collapse
• Leaves a stack which is then further eroded into a stump