Wave-cut platforms are wide, level areas of gently sloping exposed rock. They are usually found lying below a cliff. Also they may extend to an area of rock debris which accumulates just below low-tide water level. This area of rock debris is called a wave built terrace. Wave-cut platforms develop when high energy waves erode a wave-cut notch in a cliff between high tide and low tide water levels. Abrasion and hydraulic action combine to erode the base of a cliff. The action of compressed air may also occur where the cliff is composed of a rock type which is jointed. Undercutting of the base of the cliff undermines the cliff face and eventually causes it to collapse.
Material eroded from the cliff is transported and deposited below the low water mark (low tide level). As the cliff retreats inland a gently sloping area of exposed rock remains at the cliff base. Eroded rock debris continues to accumulate below the low water mark and attrition smoothens it. This debris increases the area of the platform. Over time the increasing length of the platform reduces the erosive force of the incoming waves because they have a greater distance over which to travel. Eventually the coastline will no longer be eroded because the waves expend all their energy crossing the platform and mainland. Examples of wave cut platforms can be found in Kilkee, Co. Clare.