Caves, arches, stacks and stumps are the landscape features of waves. Caves occur when waves force their way into cracks in the cliff face. When the cave is formed in a headland, it may eventually break through to the other side forming an arch. When the arch collapses, it leaves the headland on one side and a stack (a tall column of rock) on the other.
The stack will be attacked at the base in the same way that a wave-cut notch is formed. This weakens the structure and it will eventually collapse to form a stump.