Explain how stacks and stumps form

Stacks and stumps form when waves erode a weakness in a headland using abrasion or attrition. The crack widens until a cave is formed. Waves continue to erode the back of the cave until eventually it pushes all the way through the headland forming an arch. Sometimes two caves, one on each side of the headland join to form the arch. Weathering weakens the top of the arch and eventually it collapses this leaves s stack. The stack is then also weathered and eroded over time until a stump forms. An example of a stack and a stump is old harry and old harry's wife.