Stack, near Old Harry Rocks.
Old Harry Rocks
is a geological landform
. Stacks are steep, often vertical, sided columns of rock in the sea, near coasts. Stacks are formed when part of a headland
leaving a small island
. These also form when a natural arch
collapses due to sub-aerial processes and gravity
. A stack may collapse or be eroded leaving a stump
. Stacks form most commonly on chalk
cliffs, because of the medium resistance to erosion
. Cliffs with weaker rock, such as clay
tend to slump
and erode too quickly to form stacks, while harder rocks, such as granite
erode in different ways.