A headland is an area of hard rock which sticks out into the sea. Headlands form in areas of alternating hard and soft rock. Where the soft rock erodes bays are formed either side of the headland. As the headland becomes more exposed to the wind and waves the rate of its erosion increases. When headlands erode they create distinct features such as caves, arches, stacks and stumps.
The diagram below shows the sequence in the erosion of a headland.
An animation showing the erosion of a headland
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.