Coastal Processes (Cambridge (CIE) IGCSE Geography)

Coastal Processes

Coastal regions

• The coast is the area where land and sea meet

• The shoreline is the boundary of the land defined by the high water mark on a low-lying coast or the base of a steeply sloping coast

• The shore is the area between the highest and lowest tide points

• Tides are usually twice a day but vary from coast to coast and with the time of the year

• The difference between low and high tide is known as the tidal range

• The tide determines the waves' height and depth

• The movement of waves and currents affects coastal features

Waves

• Winds blowing across the sea's surface create waves, which are marine processes that erode, move, and deposit material 

• The size of a wave depends on:

  • The speed of the wind

  • The fetch (distance the wind travels)

  • The amount of time the wind blows (in the same direction)

• The wave size increases with wind speed, strength, and fetch

• Friction from the seabed pushes a wave forward as it gets closer to the coast and into shallower water, where it will finally crest and crash onto the beach

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

• There are two types of waves:

  • Destructive waves erode the beach and have:

    • 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 shingle beaches

  • Constructive waves are beach builders and have:

    • 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 sandy beach

Marine erosion

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

• They cut into the coastline in four ways:

  • Hydraulic Action 

  • Attrition

  • Corrosion 

  • Abrasion 

• A large, rough boulder is gradually reduced into round sand grains (quartz) the longer it remains in the ocean and the farther it travels along the shore

• The effects of attrition are amplified when the waves carry material farther and longer

• Rounded pebbles on a beach are known as shingle

Marine Transportation

• The sea transports sediment that it gets from erosion in the same way rivers do

• 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 (LSD)

• Longshore drift (LSD) is the main process of 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

• Beach sediment is carried farther down the coast on coasts where longshore drift is one way; if it is blocked, sediment cannot move and the area farther down the coast is deprived of sediment. This results in two problems:

  • Smaller beaches are less attractive to tourists, causing a loss of income

  • Removes natural coastal protection 

Marine Deposition

• The 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

• The backwash loses water and energy as it travels because of the sand's porosity, resulting in smaller and smaller deposits.

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

• During a storm, large shingle is thrown above the usual high tide level to form a ridge at the top of the beach called a berm