An example of a cave, arch, stack and stump is Old Harry and his wife in Swanage, Dorset.

Formation

Lines of weakness (Geo, cracks) in the cliff face are affected by weathering (carbonation) and they become larger and the cliff becomes weaker, thus leaving a small cave. This cave is further weathered and eroded, and it becomes larger. After further erosion from both sides of the cliff face the cave breaks through to the other side and it becomes an arch. After more weathering and erosion lines of weakness appear above the arch and around the edges, which eventually become weaker and weaker so the arch roof collapses and this forms a stack.