The diagram illustrates a headland, the area of hard rock which juts into the sea, erode slowly in stages.
At the first time, a headland stood much further in the sea. Continuously, the waves attack the base of the cliff which has the weakest area. Then, the rock eroded into cracks and over the time it becomes larger and larger.
These cracks which created by erosion develop into a cave. The process erosion continuous widens the cave and it undercuts through the headland until shaping an arch. There is an impressive example of natural arch just Durdle Door in Dorset.
Next, the water continues to wipe the structure of an arch. Therefore, it makes the arch unstable and cannot support its roof. Further, it collapses into the sea when a mass of rock higher than the mainland so it becomes a stack.
Moreover, the stack continually eroded until it finally leaves behind a stump. As a result, it creates the headland retreating but stack standing independently besides the headland.
Overview, headland slowly disappear from the surface our planet, it is caused by erosion which waves against the cliff of coastal.

Theo mình là vậy