Waves attack a weakness in the headland. The video below shows cracks in the chalk cliffs at Flamborough.
A cave is formed.
Eventually the cave erodes through the headland to form an arch.
The video below shows an arch at Flamborough.
The roof of the arch collapses leaving a column of rock called a stack.
The video below shows a stack at Flamborough.
The image below shows Old Harry, a stack on the Dorset Coast. You can view more images of this stack in the Old Harry gallery.
Od Harry Rocks
The base of the stack is then eroded which causes it to collapse leaving a stump.