The diagram describes stages of an erosion of headlands which is the consequence of the actions of the sea.
Headland erosion is a natural process which is caused by sea waves. The base of a cliff where touches the surface of the sea is much weaker than other parts that don't. As the waves frequently hit the lower part of the cliff, that area is lessened quickly. To some points, rock started to be eroded, creating a hollow on the rock wall and making cave become arch. The real examples of coastal erosion affected by the strong tides are Dordle Door and Dorset.
Sometimes, sea waves can hit till the half-way up or even the top are of the cliff with high tides. Through time, strength of the water beats against the roof, establishing a stack which is a column of rock standing in the sea. Meanwhile, headlands on the top cracks and retreats, the stones and rocks fall into the sea. Simultaneously, the stack is also impacted by the sea waves through the similar stages. It then becomes smaller and creates a stump which is the remain part of the erosion process.
In conclusion, this natural action occuring in a long period of time causes the gradual disappearance of cliffs and headlands over the world