Physical Influences on Coastal Landscapes (SL IB Geography)

Waves

• Waves form our coastlines through erosion, deposition and transportation
• Wind causes waves to move over the surface of the sea:
  • Wind creates friction, causing the water to ripple
  • These ripples grow into waves
• Waves can have different energy levels depending on:
  • Wind strength
  • The length of time the wind blows
  • The fetch (the distance the wave has travelled)
• If the fetch is larger, the wave will be more powerful
• If the wind is powerful and blows over a longer period, the wave will be larger
• The swash is when a wave moves up the beach
• The backwash is when the wave pulls back out to the ocean
• Waves slow down as they reach a coastline and the water becomes shallower: 
  • The bottom of the wave experiences friction with the seabed below
  • The top part of the wave (crest) gains momentum, pushing over the bottom of the wave
  • This is when the wave will break

Diagram of a wave

Diagram of a wave

• There are two types of waves:
• Constructive waves – constructive waves construct or build up beaches through deposition processes
• Destructive waves – destructive waves destroy the coastline through erosion processes

Table comparing constructive and destructive waves

• Waves can reflect, refract, diffract and interfere:
• Waves can change direction when they slow down through refraction, often seen at headlands and bays

Diagram showing wave refraction

Wave refraction

• • Waves can reflect, typically seen if a wave collides with a cliff
  • Two waves from different directions may meet, causing wave interference
  • Waves can also bend, or diffract, when they meet an obstacle or a gap

Tides

• Tides are when the surface of the sea moves up and down
• Gravitational pull (from the moon) controls tidal movements
• The rotation of the earth causes different tidal patterns across the globe
• When the water reaches its highest level, this is high tide:
  • As different areas of the earth face the moon, gravity will pull the ocean in the moon’s direction 
  • Directly on the other side of the earth, high tide will also occur 
  • High tide causes ocean waters to bulge outwards
  • High tide causes the water to spread up the coastline
• As the water sinks back to its lowest level, this is low tide:
  • Low tides are located between the two high tides
• The difference between high and low tide is the tidal range
• Spring tides occur if the moon, earth and sun all line up, causing tides to be higher
• Neap tides occur when the moon, earth and sun are at right angles to each other, causing tides to be lower

Tidal differences as the earth rotates

Tidal differences as the earth rotates

• Sediment is the material on a coastline, e.g. sand, shells, silt 
• The coast is a system of inputs, transfers and outputs of sediment:
• Sediment cells (littoral cells) are areas of coastline where this system takes place
• Sediment moves around in each cell
• Each cell is typically a closed system that recycles sediment

Diagram of a sediment cell

A sediment cell

• Sediment supplies and sources (inputs) come from:
  • Rivers
  • Erosional processes and mass movement
  • Onshore currents
  • Subaerial processes (weathering)
  • Aeolian processes (wind)
  • Biological processes (particles from dead marine life)
  • Human activity (hard and soft engineering)
• Sediment transfers occur along the coastline by:
  • Longshore drift
  • Swash and backwash
  • Wind
  • Ocean and tidal currents
• Output of sediment occurs through:
  • Deposition. It produces sinks (depositional landforms)
  • Ocean currents

Sediment cells of England and Wales

Map showing the sediment cells of England and Wales

• The sediment budget is the balance of sediment that enters and exits the system
  • If more sediment enters than exits the system, this will produce a positive sediment budget
  • A negative sediment budget occurs when more sediment exits than enters the system
  • The system is in equilibrium when inputs and outputs are in balance. Sediment moves equally through the system
  • Changes to inputs and outputs affect the sediment budget
  • Positive and negative feedback loops can alter the equilibrium by heightening and balancing changes within the system:
    • Positive feedback can cause instability, moving the system out of equilibrium
    • Negative feedback brings the system back into equilibrium

• Lithology is the study of the physical characteristics of rocks
• Discordant coastlines contain both hard and soft rock types:
  • Discordant coastlines have more bays and headlands 
• Concordant coastlines contain one type of rock

Map showing concordant and discordant coastlines on the south coast of England

Concordant and discordant coastlines

• The rate of recession describes the speed at which coastlines retreat 
• Sedimentary rocks, like sandstone, erode more easily:
  • Softer rocks contain more faults, like cracks, which increase the rate of erosion 
  • Rocks like limestone are more vulnerable to chemical weathering 
  • They are clastic rocks 
  • Rocks like gravel or sand are not cemented well together, making erosion easier
  • Sedimentary rocks will likely form bays or beaches as waves easily erode the cliff
• Igneous rocks, like granite, are harder to erode:
  • They are formed of interlocking crystals which are more resistant to erosion
  • There are fewer weaknesses and faults
  • Headlands will more likely to form due to erosion resistance 
• Metamorphic rocks are not eroded as easily:
  • They contain crystals, which reduce the rate of erosion
• The type of rock on a cliff face can also impact the shape of the cliff

Table showing rock type and its effect on cliff shape

• Vegetation is vital for stabilising coastlines 
• Vegetation reduces the coastline’s vulnerability to erosion and increases deposition:
  • Roots of plants can bind the sediment together
  • Stems and leaves protect the ground
  • Plants shelter the sediment from the wind
  • Plants can help to slow down wind and water, increasing deposition 
  • Once vegetation dies, organic matter is recycled back into the soil 
  • Vegetation protects coastal landforms like sand dunes, salt marshes and mangroves
• Coastlines are harsh environments for vegetation e.g. high salt levels
• Hardy, adaptable plants colonise areas like this
• If a landform has existed for a long time, plants will more likely colonise
• Plant succession is the colonisation and development of new plants: 
  • Pioneer plants colonise in bare environments, e.g. sediment
  • They help to stabilise the sediment and improve the fertility of the soil
  • Other species can then begin to colonise 
  • As more species colonise, the hardier they become
  • The climax community settles at the end of the succession