The apostles were formed through erosion due to the extreme weather conditions from the Southern Ocean over time eroded the soft limestone forming caves in the cliffs, eventually they became arches. These arches then collapsed and left rock stacks up to
45 metres in height. This was commonly identified as the Sow and Piglets until 1922 (Muttonbird Island, near Loch Ard Gorge, was the Sow, and the smaller rock stacks were the Piglets); after which it was renamed to The Apostles for tourism purposes.
The rocks eventually became known as the Twelve Apostles, despite only ever having nine stacks. In 2002, the Port Campbell Professional Fishermens Association
unsuccessfully attempted to block the creation of a proposed marine
national park at the Twelve Apostles location, but were satisfied with the later Victorian Government decision not to allow seismic exploration at the same site by Benaris Energy; believing it would be harmful to marine life.
The stacks are susceptible to further erosion from the waves. On 3 July 2005, a 50 metre tall stack collapsed, leaving only eight remaining. On 25 September 2009, it
was thought that another of the stacks fell, but this was actually one
of the smaller stacks of the Three Sisters formation. The rate of erosion at the base of the limestone pillars is approximately 2 cm per year. Due to wave action eroding the cliff face existing headlands are expected to become new limestone stacks in the future.
