Science
The (really) big Australian rock trip: take a tour of the nation's geological behemoths
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A few years ago, Solomon Buckman and his family went on a six-month road trip to check out Australia's rocks.
"It was the best thing I ever did," says Dr Buckman, a geologist at the University of Wollongong.
On his list was one of Australia's most iconic tourist destinations.
Uluru's massive red dome rises above spinifex and desert-oak dotted plains on Anangu country in Central Australia.
Covering an area of around 3.3 square kilometres, and standing more than 340 metres tall, Uluru is listed by the Guinness World Records as the "largest sandstone monolith in the world".
But is it? By definition a monolith is a massive single rock without fractures.
"People want to call big rocks 'monoliths', but it's a funny term," says Dr Buckman.
"I steer clear of the term monolith because it never quite applies properly to any feature."
While many big rocks appear to be standalone lumps towering above their surrounds, they are often connected to other rocks underground, are fractured or are made up of different types of material.
That's why Dr Buckman prefers the term inselberg or "island mountain" to describe most of Australia's rocks.
Australia has many island mountains, some of which are bigger than Uluru, monoliths (depending upon your definition) and massive geological wonders that don't quite fit either definition.
If you're planning a road trip, here are a handful of big rocks to add to your list.
Uluru, which is made up of fine-grained sandstone, is connected underground to nearby Kata Tjuta, which is made up of coarse-grained conglomerate rocks.
"Uluru is more resistant to weathering [than Kata Tjuta] so it sticks up above the landscape," Dr Buckman says.
The formation of Uluru is a story of creation, destruction and reinvention over a very long time.
Both formations are remnants of a geological process that began around 550 million years ago with the rise and fall of an ancient mountain range.
"Uluru is actually part of a whole sequence of sedimentary rocks that have been tilted on their side and folded and you are just seeing the tip of the iceberg," Dr Buckman says.
But Ross Cayley, senior geologist at the Geological Survey of Victoria, believes it still ticks both boxes.
"Uluru is a virtually unjointed, flawless, absolutely ginormous single lump of rock, and an inselberg," he says.
Burringurrah, in Wajarri country about 1,000 km north of Perth in Western Australia, is claimed by some to be the "world's largest monolith" and "biggest rock in the world".
Standing more than 800 m high, 14 km long and with a circumference of 39 km, it is much bigger than Uluru.
"It is probably not as striking because it's not as steep-sided as Uluru," Dr Buckman says.
Like Uluru, it is an inselberg, but it contains different types of rock so it's not a monolith.
It is largely made up of ancient sandstone that was laid down more than 1.6 billion years ago, then lifted and folded into an anticline or '"A" shape.
However, some sections of the bedrock contain rocks made up of solidified magma such as granite laid down 1.8 billion years ago, as well as much more recent veins that pushed into the sandstone sediment about 700 million years ago.
Is it the biggest rock in Australia? That's debatable, according to Mr Cayley.
"In the inselberg department, Mt Buffalo is way, way larger than Mt Augustus plus Uluru combined," he says.
Mt Buffalo in Minjambuta country in the Victorian Alps stands between 600 to 900 m proud of all the hills that surround it.
"Mt Buffalo certainly has the classic ‘inselberg’ profile when viewed from places like Mt Feathertop or Mt Hotham," Mr Cayley says.
Like many other rock masses in the Victorian Alps, Mt Buffalo is made up of granites — huge bubbles of igneous rock that pushed up into Earth's crust around 400 million years ago.
As the Great Dividing Range formed, the rocks were lifted and then exposed by millions of years of weathering.
Mt Buffalo is three times bigger than Pine Mountain, further to the north, near Corryong in Jaitmatang country.
Pine Mountain is part of a thin belt of granites that span the Victorian/New South Wales border.
Standing around 1,080 m tall, it is claimed to be 1.5 times the size of Uluru and one of Australia's largest monoliths.
While it's definitely a big rock, like Mt Buffalo, it is highly fractured.
"Victoria can't really compete in the 'monolith' department," Mr Cayley says.
"All our big rock masses are internally jointed, which is why they have a vegetated, more disrupted appearance."
The cracks of Pine Mountain, and the nearby Mt Burrowa massif which is even taller, provide homes to many species of rare and threatened plants such as phantom wattle and the Pine Mountain grevillea.
Dyurrite rises 140 m above Victoria's Wimmera plains on Wotjobaluk country.
This rock climber's paradise ticks all the boxes as an inselberg and is the Victorian version of Uluru.
"From above, Dyurrite/Arapiles even looks a bit like Uluru, but with bonus trees on top," Mr Cayley says.
Dyurrite is made up of sandstone laid down by ancient rivers and shallow seas some 430 million years ago that also makes up Gariwerd (the Grampians) 50 km away.
"So there are direct parallels to the relationship between Uluru and Kata Tjuta as well."
But it formed in a different way to Uluru.
The shape we see today was sculpted around 10 million years ago when Dyurrite was an island in an inland sea that extended into the Murray Basin.
If you look closely you'll see coastal cliffs, sea stacks and wave cut platforms.
Pildappa Rock on the Eyre Peninsula is best known as "South Australia's Wave Rock" for the 2-to-3m-high curved surface that runs 100 m along its edge.
It is one of a number of large rocks including Mt Wudinna and Polda Rock all within a stone's throw (in outback terms) of each other, near Minnipa on Barngarla country.
"These rocks are part of the Gawler Craton, one of the major building blocks of the western two-thirds of Australia," says Tom Raimondo of the University of South Australia.
"The Gawler Craton represents a block of very ancient rock that dates back over 2 billion years.
"Most of the outcrops you see throughout the Eyre Peninsula are these very old, very durable, very resistant rocks that are still preserved."
These rocks, as well as Murphy's Haystacks, a much smaller inselberg further south on Wirangu country, are made out of red Hiltaba granite that has been sculpted over time, Professor Raimondo adds.
Holes or gnamma weathered out of many of the large rocks provided an important source of water in the arid area for local groups of the Barngarla, Wirangu and Kokatha people for thousands of years.
Some of these rocks also have walls built by European settlers to capture the water running off their sides.
Katter Kich is a massive wave-shaped rock on Noongar country in Western Australia's wheatbelt.
Around 14 m high and 110 m long, it is the sculpted northern face of Hyden Rock.
It is one of a number of large inselbergs in the area that provide permanent supplies of water.
"There are a whole bunch of these inselbergs through the wheatbelt which are really important Aboriginal sites or landmarks," Dr Buckman says.
The 2.7-billion-year-old light-coloured granite is streaked by the greys, reds and yellows of chemicals such as carbonates and iron hydroxide leaching out of the rock by water.
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So how did the wave form? Some scientists believe it is due to the base being eroded away by water.
But Dr Buckman believes the curved shape of Wave Rock, as well as Pildappa Rock, Murphy's Haystacks and the caves around the base of Uluru, are caused by fire.
"Fires come in near the ground where the vegetation is really thick and then spalls the rock off; over time that creates a wave impression," Dr Buckman says.
This effect was commonly seen in east coast granites following the Black Summer bushfires, he adds.
Bald Rock, which straddles the New South Wales/Queensland border near Tenterfield, is said to be Australia's largest exposed granite surface.
"I personally doubt that's correct," Mr Cayley says, pointing to other examples such as Frenchman Peak and Cape Le Grande in WA.
"But it's certainly a contender, and looks spectacular."
About 750 m long and 500 m wide, it stands about 200 m above everything else around it.
An important meeting place for the Jukambal, Bundjalung and Kamilaroi people, the rock formed around 250 million years ago.
It is in part of the Great Dividing Range known as Stanthorpe Granite.
Even though this granite formed about 150 million years after the rocks in Victoria, the uplift that created the Great Dividing Range began around 90 million years ago, says geologist Nathan Daczko of Macquarie University.
The range was created by the rifting of Zealandia off Antarctica, and while most of Zealandia sank, eastern Australia was pushed up.
"That's what would have controlled the eastern highlands of Australia, and brought these [large granite rocks] close to the surface, and part of these mountain areas."
Further south, you'll find the most spectacular rocks in Mr Cayley's books.
Federation Peak on Tahuni Lingah country and Frenchman's Peak on Toogee country in south-west Tasmania are remnants of some of the oldest rocks in eastern Australia.
These stunning rocks are made from 1- to 1.6-billion-year-old metaquartzite — sandstone converted into quartzite by the heat and pressure of mountain building in the same process that also created the Great Dividing Range.
But the sharp spires and dramatic cliffs we see today were carved much more recently by glaciers that covered Tasmania until about 20,000 years ago, Mr Cayley says.
"South-west Tasmania in particular wras festooned with glaciers."
These glaciers carved out spectacular lakes and huge U-shaped valleys. In the process, the most resistant of the older rocks got left behind as glacial horns.
"Frenchman's Cap is a huge, hulking, isolated monolithic block of metaquartzite with a gigantic vertical ice-carved cliff looming over an epic glacial valley," Mr Cayley says.
"Those young landscapes would hold their own if teleported into the Dolomites, and there aren't too many Australian mountains that can claim that."
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