How is a wave-cut platform formed?

Wave cut platforms are created as a cliff retreats, due to weathering at the top of the cliff and sea erosion at the base of the cliff. Coastal erosion creates a wave-cut notch at the base of the cliff, as this is where the wave energy is concentrated. This notch gets larger as erosion continues, until the cliff above becomes unstable and collapses. Backwash removes the rubble, and as the cliff retreats a wave-cut platform is left behind.