Marine processes and the coast (WJEC Eduqas GCSE Geography B): Revision Note

The notes on this page cover part of 2.1.1 of the WJEC Eduqas B specification – How do people and processes contribute to the development of distinctive coastal landscapes in the UK?

• Erosional marine processes must include:

  • hydraulic action, abrasion, attrition and solution.

• Processes of transportation and deposition, including:

  • longshore drift, traction, saltation, suspension and solution.

Waves

• Waves are marine processes

  • They erode, transport and deposit material

• Waves are formed by winds blowing over the surface of the sea 

• The height and strength of a wave are dependent on three factors:

  • the fetch 

  • the amount of time the wind blows

  • the strength of the wind

  

• As a wave approaches the coast, it enters shallower water; friction from the seabed causes the wave to lean forward and eventually crest and break onto the beach 

• The movement of water up the beach is called the swash, and the return movement is the backwash

Types of waves

• There are two types of waves:

  • Destructive waves erode the beach

  • Constructive waves are beach builders

Constructive waves

• Constructive waves, also known as beach builders, have the following characteristics:

  • A long wavelength with low height

  • A low-frequency wave rate of 6-8 per minute

  • A shallow wave gradient

  • Low energy

  • A stronger swash that carries material up onto the beach and deposits a gently sloping, sandy beach

Destructive waves

• Destructive waves erode the beach and show the following characteristics:

  • A steep wave gradient

  • A short wavelength with high height

  • A high-frequency wave rate of 10-12 per minute

  • High energy

  • A strong, abrasive backwash that drags material out to sea and forms steep, shingle beaches

Wave refraction

• Coastlines have different depths of water and reflect waves

• The depths vary because headlands and bays have formed over time

• As waves travel into shallower water near the beach, they slow down

• This makes the wave bend or refract to fit the shape of the shoreline

• When waves are refracted, the energy is focused on the headland

• This causes more erosion to the headland than bays, where sediment is deposited

Marine erosion

• Destructive waves are responsible for the majority of erosion that occurs along a coast

• They carve the coastline in four ways:

  • Hydraulic power/action 

    • When a wave hits a cliff, seawater and air are forced into any joints or cracks in the rock

    • This air is then compressed within the crack

    • As the wave retreats, the pressure on the air is released, opening the crack

    • The process repeats with each wave, widening the cracks and breaking off pieces of the cliff

  • Attrition

    • Pebbles and rocks carried by waves smash into each other, breaking down into smaller, smoother, and rounder pieces

    • This type of erosion doesn't really erode the coastline, but forms shingles and sand 

  • Abrasion (corrasion)  

    • Rocks and sand carried by waves grind against the cliff face, acting like sandpaper and wearing it away

  • Corrosion (solution) 

    • Because seawater is slightly acidic, limestone and chalk dissolve over time

    • Wave action speeds the processes by removing dissolved material and exposing fresh rock surfaces

    • Salt crystals can also form and expand, causing the rock to disintegrate

Marine transportation

• Material in the sea arrives from many sources:

  • Eroded from cliffs

  • Transported by longshore drift along the coastline

  • Brought inland from offshore by constructive waves

  • Carried to the coastline by a river

• Once in the water, the material is moved in different ways:

  • Traction 

  • Saltation

  • Suspension

  • Solution 

Longshore drift

• This is the main process of deposition and transportation along the coast 

• Waves approach the beach at an angle due to the prevailing wind

• As the waves break, the swash carries material up the beach at the same angle

• As the swash dies away, the backwash carries the material down the beach at right angles (90°) 

• The process repeats, transporting material along the beach in a zig-zag movement

Marine deposition

• Deposition occurs when material is dropped from seawater

• This happens when the water flow's speed (velocity) decreases

• This means the force is no longer strong enough to keep the material suspended in the water, so it drops to the ground

• Sediment deposits in bays form beaches

• Salt marshes and mudflats form in sheltered estuaries, typically behind spits

• Waves carry sand or shingle as they travel

  • Backwash carries it away, while swash carries it onto a shore

  • The largest material is deposited along the upper reach of the swash when a constructive wave carries sediment up the beach