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

• Strong swash, weak backwash

• Builds up beaches, deposits material

• Gentle beach profile

• Common in calm weather

Destructive waves

• Weak swash, strong backwash

• Erodes beach material, removes sediment

• High wave height, short wavelength

• Steep beach profile

• Common in stormy conditions

Spring tides

Sun and moon in line at full moon/new moon (large tidal range)

Neap tides

Moon is at right angles to the sun in first/last quarter of the year. This alignment gives the lowest monthly tidal range (small tidal range).

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

• Transport process moving sediment along the coast

• Caused by prevailing wind direction

• Swash moves material up the beach at an angle

• Backwash pulls material back down the beach vertically (gravity)

• Zigzag motion of sediment transport

• 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.

Creep (mass movement)

Soil particles expand with water and are lifted away from the slope at an angle. When they dry, they shrink, and gravity pulls them down. Over time there is a slow movement of material down the slope.

Fall (mass movement)

Freeze-thaw weathering shatters rocks from the cliff. The rock falls, under gravity, to the base of the cliff, where they form talus/scree slopes.

Slide (mass movement)

The top layer of rock becomes saturated by rain; heavy and under the force of gravity, it may break off and slide over the layer of rock below.

Flow (mass movement)

Fine loose material becomes saturated and flows down slopes

Slump (mass movement)

Soft rock cliffs become saturated with rain, this makes them heavy. With undercutting by the sea, they will slump

Wave quarrying

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