The stacks of the Twelve Apostles

The stacks are susceptible to further erosion from the waves. On 3 July 2005, a 50 metre tall stack collapsed, leaving eight remaining. On 25 September 2009, three years after our visit, 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. It is expected however, that due to wave action eroding the cliff face, existing headlands will become new limestone stacks in the future.