The extent of a coastal erosion depends on the______?

Step 1: Analyze the question The question asks what determines how much coastal erosion takes place, that is, how much the sea wears away the land along the coast.

Step 2: Explain the concept Coastal erosion is mainly caused by wave action. The sea erodes the coast through:

• Hydraulic action: the force of the water and compressed air pushing into cracks in rocks.
• Abrasion (corrasion): waves hurl sand, pebbles and rock fragments against the cliff.
• Attrition: rock fragments knock against each other and break into smaller, rounder pieces.
• Solution (corrosion): soluble rocks such as limestone are dissolved.

The strength of these processes depends on the wave's energy, which is determined by the wave's height, steepness, and frequency, and by whether the waves are destructive or constructive. Destructive waves are high and steep with a strong backwash, so they erode. Constructive waves are low with a strong swash, so they deposit material.

Step 3: Evaluate the options

• A. Fresh water from tributaries: this affects river flow and deposition at estuaries, not the force of the sea against the coast.
• B. Depth of ocean water: this has some influence on wave energy near the shore, but it is not the direct factor. The question asks for the main factor, which is the waves themselves.
• C. Salinity of the ocean: salt content has negligible effect on how much erosion occurs.
• D. Nature of the waves: correct. The type and energy of the waves determine how much rock is worn away.

Step 4: Answer The extent of coastal erosion depends on the nature of the waves, which is option D.

Exam tip: Remember "waves do the work." In any question on coastal erosion, think of wave energy first. Also link destructive waves = erosion and constructive waves = deposition, because this contrast appears often in WASSCE and NECO.