Distinctively coastal processes: marine: erosion – hydraulic action, wave…

The idea

Coastal landscapes are shaped by an interplay of marine and sub-aerial processes. Marine erosion includes hydraulic action and wave quarrying, where sheer wave force and trapped air widen cliff faults. Cavitation occurs as compressed air bubbles implode, stressing the rock. Corrasion (abrasion) uses sediment as tools to scour the coast, while attrition rounds the sediment itself. Solution dissolves soluble rocks like limestone. Transportation moves this material via traction (rolling large stones), suspension (carrying fine particles), and longshore drift (littoral drift), which moves sediment along the coast in a zigzag pattern until deposition occurs in lower-energy zones. Simultaneously, sub-aerial weathering, mass movement, and surface runoff weaken and transport material down cliff faces.

What earns the marks

• Define specific erosion mechanisms, clearly distinguishing between processes like hydraulic action, wave quarrying, and cavitation.
• Explain the mechanics of longshore (littoral) drift, including the role of prevailing wind direction, swash, and backwash.
• Link sub-aerial processes, including physical, chemical, and biological weathering, mass movement, and runoff, to the supply of sediment to the littoral zone.
• Identify the conditions required for marine deposition, such as a reduction in wave energy, sheltered estuaries, or flocculation.

Common mistakes and how to put them right

• Confusing corrasion (abrasion) with attrition.

  Put it right: Corrasion is the wearing away of the cliff by sediment, whereas attrition is the wearing down of the sediment particles themselves.

• Treating sub-aerial processes as marine erosion.

  Put it right: Sub-aerial processes operate on the cliff face above the high water mark through weathering, mass movement and runoff, not direct wave action.

• Using 'hydraulic action' and 'wave quarrying' interchangeably without distinction.

  Put it right: Specify that wave quarrying involves the scooping action of waves and the compression of air in joints, while hydraulic action is the sheer impact force of the water.

Exam tips

• Use precise terminology when describing erosion; always specify whether the rock face or the sediment itself is being worn away.
• When explaining longshore drift, explicitly mention the role of the prevailing wind in determining the angle of the swash.
• Link sub-aerial processes to marine processes by explaining how mass movement provides a sediment source for marine transportation and deposition.