On Victoria’s southern coast, giant limestone stacks have been sculptured by waves. Nobody knows for how long they will survive.
On 15 January 1990, a young couple strolled onto a famous rock formation on the Australian coast along the Great Ocean Road. The formation was named ‘London Bridge’ because of its two natural arches that branched out from the mainland. Suddenly the inner arch crashed into the sea. The couple were trapped on an islet. They had to be rescued by a helicopter.
The episode was typical of the coastline stretch known as Port Campbell, situated some 230 kilometres (140 miles) south-west of Melbourne. For thousands of years, powerful waves have pounded against the coastline and gradually torn away the rock. Spectacular sculptures have been left behind. They include London Bridge; now named the ‘London Arch’ for obvious reasons. They also include ‘The Twelve Apostles’: large pinnacles at 50 metres’ height lined up outside the mainland. Some 1.2 million people come annually to see them.
The Apostles have formed through a natural erosion process. At Port Campbell, the 70-metre-tall cliffs are made of Miocene sedimentary rocks. These form in layers – almost entirely horizontally – with the youngest rock facing the bottom. As such, the cliffs are softer at the lower levels. Over time, the Southern Ocean has hammered away until the underlying rock has gone. The result has been a series of caves and rock overhangs.
And this is how the pinnacles were created. “Generally each Apostle has formed as the result of a cave being cut through a narrow protruding headland, forming an arch which then collapses, leaving an outlying stack,” says Eric Bird, a professor at the University of Melbourne. The Apostles survived because they possess a higher concentration of calcium carbonate – which is given to rock that, when created in ancient times, is close to skeletons and shells that are deposited to the ocean floor. As such, they have more substance and are harder to break down.
The name ‘The Twelve Apostles’ should not need explaining, but there is disagreement over how many stacks there actually are. They were first called ‘Sows and Piglets’, then renamed ‘The Apostles’ in 1922. They changed again to ‘The Twelve Apostles’. Some say there were nine large pinnacles and eight smaller ones in 1922. The accepted version today is that eight main stacks remain.
So did one disappear? Yes it did. On 3 July 2005, a giant Apostle crumbled into the ocean. Confusingly, on 10 June 2009, an arch called Island Archway also dissolved, leaving two new pillars. The two collapses were unexpected. The coast is always changing. “Lumps of the cliff subside suddenly from time to time,” says Bird, and gives an example. “In 1939 a section of cliff 70 metres long and up to 12 metres wide near Sentinel Rock, Port Campbell, suddenly fell into the sea.”
Nobody knows when another Apostle will be taken. Some reports say the pillars are eroded at a rate of two centimetres per year. Bird says it is extremely difficult to predict how long they will survive, but believes most of them will survive the next century. “There appears to be no immediate threat to the eight remaining Apostles, but this is a part of the coast exposed to strong swell from the Southern Ocean and to frequent storms, especially in winter, and any of them could collapse at any time.”
Photos: Alberto Loyo, pinggr, Xufang [all via Shutterstock.com].