A Colossal Cave System lurking Beneath Australia’s Desert: The Nullarbor Caves

The Hidden World Beneath the Nullarbor

On Australia’s Nullarbor Plain, the landscape above seems hostile and barren: a flat, almost treeless expanse under a merciless sun. It appears as an arid, flat desolation, stretching to every horizon without relief. But looks are deceiving. Scattered across this plain are mysterious openings – sinkholes, blowholes, and gaping dolines – that puncture the hard crust. These holes are gateways to an astonishing subterranean world.

Beneath the sun-baked surface lies an enormous, honeycombed labyrinth of caves. In fact, the Nullarbor Plain sits atop the world’s largest arid limestone karst system, a single massive slab of limestone roughly 200,000 square kilometres in size that is completely riddled with voids and passages. Down there in the darkness, a hidden geological wonderland sprawls for tens of thousands of kilometres – truly one of Earth’s great cave networks.

Origins of a Subterranean Labyrinth

To understand how this underground wonderland came to be, we must picture the Nullarbor as it was millions of years ago. During the Miocene epoch, 23 to 5.3 million years ago, this region was not a desert plain at all, but the bed of a shallow sea. The ocean teemed with corals, molluscs, echinoderms, and foraminifera, all of which left their calcareous shells and skeletons behind. Layer upon layer of marine limestone was deposited then, forming a thick platform of carbonate rock geologists now call the Nullarbor Limestone.

Eventually, as Australia’s continental interior rose and seas retreated, the limestone seabed was left high and dry – an emerged platform as flat as a table. But the real transformation began after the plain was exposed to the elements.

Limestone, though hard, is highly reactive to slightly acidic water. Any rain that falls on the Nullarbor today doesn’t collect into streams or lakes on the surface. Instead, the water vanishes, seeping straight down into the ground. Over hundreds of thousands to millions of years, those trickles of rainwater – enriched with carbon dioxide from the soil and atmosphere – became nature’s miners. They dissolved the limestone grain by grain, carving out minute voids.

The water exploited weaknesses in the rock: joints, fractures, and bedding planes. With patience beyond comprehension, these small cracks were widened into channels, and the channels into tunnels. Inch by inch, drip by drip, the limestone was hollowed out from within.

The southern edge of the Nullarbor ends abruptly at the sea cliffs of the Great Australian Bight, where vertical limestone walls drop straight into the ocean.

Thus, the Nullarbor cave system was born – an immense karst network forged by groundwater. The process was gradual but relentless, etching out tunnels, chambers, and galleries on a continental scale.

The Scale of the Underground World

Today, the Nullarbor cave network is staggering in scale. Around 10,000 caves and karst features have been identified so far, and new ones are still being discovered. Because the plain is so flat, entrances often appear suddenly as collapsed dolines – massive sinkholes that yawn open in the otherwise featureless landscape.

Imagine walking across the stony desert and suddenly coming upon a hole 40 m deep and 80 m wide. From the bottom of such pits, enormous tunnels radiate outward. Some passages reach 20–30 m in diameter, resembling subway tunnels constructed by nature herself. Others twist and narrow, forcing explorers to crawl through labyrinthine passages.

The caves reach about 90 m below the surface in places and extend astonishing distances. The longest mapped cave, Weebubbie Cave, snakes beneath the Nullarbor for over 35 km.

Many of these tunnels terminate in lakes, where crystal-clear groundwater fills the passage. In fact, some caves are completely submerged for long distances, accessible only to cave divers with specialized training. These flooded caves are among the most pristine on Earth, their waters so still and transparent that divers appear to float in mid-air.

Beauty in Darkness

Step inside one of these caverns and you enter a world of silence and wonder. In the hushed darkness, the beams of an explorer’s torch reveal stalactites dangling like teeth from cathedral-high ceilings, while stalagmites rise to meet them like ancient pillars.

Over millions of years, drip water has sculpted an ornate gallery of calcite. Soda-straw stalactites grow so slender and fragile that they can break at the lightest touch. Flowstone sheets cascade across walls like frozen waterfalls, while helictites twist in impossible directions, defying gravity.

Some chambers are so vast they feel like underground cathedrals. The air is cool and still. Where collapses have punched shafts to the surface, a single beam of sunlight may lance into the darkness, illuminating turquoise pools or shimmering crystal draperies. It is an alien beauty, untouched and hidden in one of the harshest environments on Earth.

The Fossil Treasure Trove

But the Nullarbor caves are not just geological marvels – they are also time capsules. Because the caves are isolated and dry, they preserve organic remains with extraordinary fidelity.

In 2002, cavers exploring a chamber stumbled upon one of the greatest fossil finds in Australian history: a nearly complete skeleton of the marsupial lion, Thylacoleo carnifex. This powerful Pleistocene predator, roughly the size of a leopard, had likely tumbled into a hidden chasm and perished. Its remains lay undisturbed for tens of thousands of years. Protected from scavengers and weather, its skeleton was preserved in exquisite detail, allowing scientists to reconstruct its anatomy and hunting behaviour more accurately than ever before.

And this was not an isolated find. Across the Nullarbor caves, palaeontologists have uncovered a menagerie of extinct megafauna: giant kangaroos with flat faces, enormous flightless birds, oversized wombat-like Diprotodons, and more. Many of these fossils are still articulated, their bones lying in life position as though the animals had died only yesterday.

The caves thus serve as vaults of deep time, preserving an Ice Age ecosystem that vanished long ago. They offer rare insights into Australia’s lost giants and the environments they inhabited.

Signs of the First People

Beyond fossils, the caves also hold evidence of early human presence. Aboriginal people have lived in the Nullarbor region for tens of thousands of years, and some caves were visited or used by them. Archaeologists have found stone tools, hearths, and ochre markings in certain caves, suggesting they were not only shelters but also sites of cultural and possibly spiritual significance.

In a land where surface water is scarce, caves with underground lakes would have been vital refuges. For the first Australians, the caves were both a source of life and places imbued with story and meaning.

Science and Exploration

Today, the Nullarbor caves continue to draw scientists, cavers, and adventurers. Cave divers have mapped kilometres of submerged tunnels, pushing the limits of endurance and technology. Geologists study the speleothems – stalagmites and stalactites – because their growth layers record ancient climates like tree rings, providing a record of rainfall and drought stretching back hundreds of thousands of years.

Biologists, too, have been astonished. Isolated pools harbor unique stygofauna – tiny, blind creatures that live in complete darkness. Some are found nowhere else on Earth. These organisms, adapted to an eternal night, underscore the biological as well as geological significance of the Nullarbor caves.

A Paradox of Landscapes

What makes the Nullarbor so compelling is its paradox. Above ground, it appears lifeless, harsh, and flat beyond imagination – the very word “Nullarbor” comes from the Latin nullus arbor, “no trees.” Yet just beneath this barren veneer lies one of the planet’s most intricate and spectacular subterranean landscapes, alive with geological artistry, fossil treasures, and unique ecosystems.

The plain is often dismissed as an empty crossing by motorists driving the Eyre Highway between Western and South Australia. Few realize that under their wheels stretches one of Earth’s great hidden worlds.

The Story the Caves Tell

Ultimately, the Nullarbor cave network tells a story of transformation. It is the story of water’s patience, of rain carving a continent-wide labyrinth from stone. It is the story of lost oceans turned to desert, of extinct beasts preserved in perfect repose, of early people finding refuge in the deep.

The Nullarbor above may be harsh and forbidding, but below, it is a realm of wonder. Together, they form one of the most striking contrasts in all of Australia: desolation above, beauty and history below.

The next time one crosses that endless, treeless horizon, it is worth remembering that the real marvel of the Nullarbor is not the plain itself, but the unseen kingdom it conceals – a vast, silent underworld, sculpted by water and guarded by time.

Here's the video we made on this on the OzGeology YouTube Channel: