How Australia’s iconic Twelve Apostles fashioned: Study reveals how tectonic plate actions over hundreds of thousands of years lifted and tilted the enormous buildings out of the ocean
They’re the towering limestone stacks that draw visitors from across the world – and now scientists have finally worked out how Australia’s iconic Twelve Apostles were formed.
The immense structures, which can reach up to 230 feet (70m) high, are located off the shore of Port Campbell National Park in Victoria.
Experts have never fully understood how they evolved, and to many it may look like they’ve simply always been there.
But now, a team from the University of Melbourne have discovered that tectonic plate movements over millions of years lifted and tilted the giant structures out of the sea.
This tectonic event helped shape the Apostles into being one of the world’s best-preserved and accessible records of ancient climates and sea levels.
The new research also reveals the layered limestone dates back 14 million years, to a time when temperatures on Earth were around 3°C higher than they are today.
‘Much like an environmental time capsule, each layer of these giant structures preserved information about the Earth’s climate, tectonic activity, plants and animals over millions of years,’ lead researcher Stephen Gallagher said.
‘This includes a key time about 13.8 million years ago when the climate was much warmer than what it is today.’
The immense structures, which can reach up to 230 feet (70m) high, are located off the shore of Port Campbell National Park in Victoria
Experts have discovered that tectonic plate movements over millions of years lifted and tilted the giant structures out of the sea
The researchers used mapping and microfossil analysis to closely study the geology of the stacks.
Like tree rings, the layers provided the scientists with a clearer idea of their evolution.
The study found that the local limestone was pushed out of the sea over millions of years by shifting tectonic plates.
However, it was only in the last few thousand years that coastal erosion exposed and shaped the towering pillars we see today.
‘We also uncovered that the tectonic movements didn’t push up the Apostles perfectly straight,’ Dr Gallagher said.
‘Instead, they forced layers to tilt and break along the way. If you look closely at the cliffs around the Twelve Apostles today, you can see the limestone layers are not flat but are, in fact, tilted by a few degrees.
‘Small fault lines can also be seen, which are records of ancient earthquakes.’
The study, published in the Australian Journal of Earth Sciences, explains that the Twelve Apostles are composed mainly of Port Campbell limestone – a brittle material deposited during shallow marine conditions millions of years ago.
The researchers used mapping and microfossil analysis to closely study the geology of the stacks. Pictured: Microfossils from within the stacks
Like tree rings, analysis of the layers provided the scientists with a clearer idea of their evolution
The current stacks began to form when sea levels rose to their present position. Coastal erosion by waves undercut the cliffs, forming arches and ridges of rock projecting over the sea.
As these arches eventually collapsed, the isolated sea stacks were left behind.
‘We are using this ‘window back in time’ to understand where temperatures and sea levels may be heading on our current path of climate change,’ Dr Gallagher said.
‘With only eight of the Twelve Apostles remaining, we need to study and learn from them while we can.’
A decade ago, five new Apostles were discovered near the famous site – but they were 150 feet (50m) underwater.
Dubbed the ‘drowned Apostles’, these underwater stacks amazed geologists because it was the first time submerged limestone towers had been seen anywhere in the world.
The discovery was made by PhD student Rhiannon Bezore who was analysing preliminary sonar scans of the area.
Melbourne University geomorphologist David Kennedy says the columns were likely preserved because the sea rose so quickly after the last ice age.
Last month, it emerged that millions of tourists could soon be slapped with an admission fee to visit the site.
The aim of the tourist tax is to better manage crowds, protect the coastline and boost local economies along the Great Ocean Road, which attracts 6.8 million visitors each year.
Locals and members of the Eastern Maar Indigenous community will be exempt from the entry fee, which is currently unknown and will be based on consultation with local councils, traditional owners and businesses.
A new booking system will also be introduced to manage visitor numbers and parking during peak periods.
