Edexcel Geography A-level Coastal Landscapes and Change: Classifying Coasts

Classifying Coasts

• A coast can be considered as an open system, receiving inputs from outside the system and transferring outputs away from the coast and into other systems.
• These systems may be terrestrial, atmospheric or oceanic and can include the rock, water and carbon cycles.

Sediment Cells

• Coasts can be split into sections called sediment cells.
• Sediment cells are typically considered a closed-system in terms of sediment.
• There are eleven sediment cells in England and Wales.
• A sediment cell has:
  • Sources: where the sediment originates from (e.g. cliffs, offshore bars).
  • Through flows: the movement of sediment along the shore through longshore drift.
  • Sinks: locations where deposition of sediment dominates (e.g. spits, beaches).
• The coastal system operates in a state of dynamic equilibrium, where input and outputs of sediment are in a constant state of change but remain in balance.

The Littoral Zone

• The littoral zone is the area of the coast where land is subject to wave action.
• The littoral zone is constantly changing and varies due to:
  • Short-term factors like tides and storm surges.
  • Long-term factors like changes in sea level and climate change.
• There are several subzones within the littoral zone:
  • Backshore: area above high tide level and only affected by exceptionally high tides.
  • Foreshore: this is land where most wave processes occur.
  • Offshore: the open sea.

Valentine’s Classification

• Valentine’s Classification describes the range of coastlines that can occur.
• An advancing coastline may be due to the land emerging or deposition being the prominent process.
• Alternatively, a coastline may be retreating due to the land submerging or erosion becoming the prominent process.
• Emergent or submergent coastlines may be due to post-glacial adjustment (the land ‘wobbles’ as the glacier above it melts, causing isostatic sea level change), as well as other causes.

Coastal Processes and Land Formations - Erosional Processes

• Erosion is a collaborative process which involves the removal of sediment from a coastline by different types of erosion, not one type acting by itself.
• Corrosion (Solution): mildly acidic seawater can cause alkaline rock such as limestone to be eroded, similar to the process of carbonation weathering.
• Wave Quarrying: breaking waves that hit the cliff face exert a pressure up to 30 tonnes per m².
• Erosion rates are highest when:
  • Waves are high and have a long fetch.
  • Waves approach the coast perpendicular to the cliff.
  • At high tide, waves travel higher up the cliff.
  • Heavy rainfall occurs, water percolates through permeable rock, weakening cliff.
  • In winter, destructive waves are the largest and most destructive.
• The main processes of erosion are:
  • Corrasion: sand and pebbles are picked up by the sea and hurled against the cliffs at high tide.
  • Abrasion: sediment is moved along the shoreline, causing it to be worn down over time.
  • Attrition: wave action causes rocks and pebbles to hit against each other, wearing each other down.
  • Hydraulic Action: as a wave crashes onto a rock or cliff face, air is forced into cracks, joints and faults within the rock, causing it to fracture.