The extent of coastal erosion depends on the

Analyze the question: It asks which factor determines how much coastal erosion takes place. Coastal erosion is the wearing away of land along the shoreline.

Explain the concept: Waves are the main agent of coastal erosion. They erode in several ways:

• Hydraulic action: the force of water and compressed air pushing into cracks in rocks.
• Abrasion (corrasion): waves hurl sand, pebbles and rocks against the cliff face.
• Attrition: the eroded particles knock against each other and break into smaller, rounder pieces.
• Solution (corrosion): some rocks, such as limestone, dissolve in seawater.

The strength of these processes depends on the type and energy of the waves. Destructive waves have a strong backwash, a high frequency and a steep form, so they erode a lot. Constructive waves are gentle and tend to deposit material. Wave height and the length of the fetch (the distance the wind blows over water) also affect wave energy.

Solution, option by option:

• A. Fresh water from tributaries: Rivers can bring sediment to the coast, but the amount of fresh water does not control erosion along the shore.
• B. Depth of ocean water: Depth has some influence on wave energy near the shore, but it is not the main factor in the extent of erosion.
• C. Salinity: Salt content has almost no effect on how much erosion occurs.
• D. Nature of the waves: This is correct. Wave energy, height and type (destructive or constructive) directly determine how much material is removed.

Tip: In coastal geography questions, think "waves first". Remember WAVES = erosion energy. Other factors that matter are rock type and the shape of the coastline, but they are secondary to wave action.