Waves, Weathering and Erosion

Factors affecting wave energy

Strength of wind - the larger the pressure gradient between two area, the stronger the winds. As waves are caused by the wind, stronger winds also mean stronger waves
Duration of wind - if wind is active for longer periods of time, then the energy of the waves will build up and increase
Size of fetch - the fetch is the distance over which the wind blows, and the larger it is, the more powerful the waves will be

Constructive waves

🔨 Constructive waves – think "Construction = Building up"

Key traits:

- Strong swash, weak backwash

- Deposits material onto the beach

- Builds up beaches

- Low wave height, long wavelength

- Usually in calmer weather

Destructive waves

💥 Destructive waves – think "Destruction = Breaking down"

Key traits:

- Weak swash, strong backwash

- Erodes the coastline

- Removes material from the beach

- High wave height, short wavelength

- Often in stormy weather

Spring tides

The largest tidal range, caused when the Sun, Moon, and Earth are aligned (new moon or full moon).

🧠 "Spring = Strong tides"

Neap tides

The smallest tidal range, caused when the Sun and Moon are at right angles to the Earth (first and third quarter moon).

🧠 "Neap = Not much difference"

Low tidal range

• Small difference between high and low tide

• Found in enclosed seas (e.g. Mediterranean)

• Less potential for tidal erosion and deposition

High tidal range

• Large difference between high and low tide

• Wide coastal area influenced by tidal movement

• Greater potential for erosion, sediment transport, and deposition

Rip currents

• Powerful underwater currents near shorelines.
• Caused by plunging waves building up water at the top of the beach.
• Backwash is forced under the surface due to resistance from breaking waves.
• Forms an underwater current moving away from the shore.
• Act as an energy source, transporting sediment away from the beach.

High-energy coastlines

Type of coastline that has:

• Strong prevailing winds and large waves

• Rate of erosion greater than deposition

• May have headlands, bays, cliffs and wave cut platforms

Low-energy coastlines

Type of coastline that has:

• Less powerful (lower energy) waves, occurs in sheltered areas

• Rate of deposition exceeds erosion

• May have beaches/spits, estuaries and sheltered bays

Longshore drift

The movement of sediment along the coast by waves hitting the shore at an angle, carrying material up the beach with the swash and back down with the backwash, creating a zigzag pattern.

• Forms features like spits, bars, and tombolos

Deposition

Occurs when sediment becomes too heavy for water to carry, or if wave loses energy
High-energy coastlines continue to transport smaller sediment, so larger rocks are deposited
Low-energy coastlines have much smaller sediment, which is only deposited in these areas where there is a much lower water velocity

Weathering

Breakdown of rocks over time, leading to transfer of material into littoral zone, where it becomes an input to sediment cells.

Freeze-thaw (Mechanical weathering)

Water enters cracks in rocks and then the water freezes and expands in volume causing cracks to develop

Salt crystallisation (Mechanical weathering)

As seawater evaporates, salt is left behind. Salt crystals will grow over time, forces the cracks to widen. Salt can also corrode ferrous rock

Wetting and drying (Mechanical)

Rocks such as clay expand when wet and then contract again when they are drying and these cycles cause the rocks to break up

Carbonation (Chemical)

A type of chemical weathering where carbon dioxide (CO₂) in rainwater forms a weak carbonic acid, which reacts with calcium carbonate in rocks like limestone, causing the rock to slowly dissolve

Oxidation (Chemical)

When materials become exposed to the air it will become oxidised which will increase its volume causing the rock to crack. Most common with iron materials

Mass movement

Movement of material down a slope under the influence of gravity. Categorised into creep, flow, slide and fall.

Rockfall

• Pieces of rock breaking away from a slope of cliff and falling to the bottom

• Caused by weathering (e.g. freeze-thaw) weakening rock.

• Material falls and accumulates as scree at the base.

Rock slide

• Large section of rock moves downhill along a flat surface (bedding plane).

• Often triggered by heavy rain or earthquakes.

• Faster and more uniform than a slump.

Solifluction

• Slow downslope flow of saturated soil in permafrost areas.

• Caused by melting of surface layers of soil in the active layer which are then lubricated and move under gravity, usually more slowly

Wave quarrying

The mechanical chiselling and removal of rock fragments from cliff faces by the sheer force of breaking waves.