Caves, arches & stacks: how they're formed
Stage 1: waves attack a weakness in the headlands- this creates a crack.
Stage 2: As wave attack a weakness, an opening begins to grow and a cave is formed on the sea cliff.
Stage 3: Arches are formed by continuous growth of sea caves. Many times, arches form by the meeting of two sea caves.
Stage 4: The roof of the arch becomes weak enough to collapse & be a sea stack. Sea stacks are tall, steep sided islands near shore. Over time it'll erode to become a stump.
The wave and wind direction controls the movement of material. Sand is carried up the beach by wave action called swash. When the water returns to the sea it does so at right angles to the coast. This is called the backwash. This happens several times and so the material is moved along the coast.