If the cave is formed in a headland it may break through to the other side forming an arch, the arch will gradually become bigger until it can no longer support the top or the arch, when the arch collapses it leaves the headland on one side and a stack on the other
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.
