Hidden Geology of Australia: Paroo-Darling Mound Springs, Tasman Abyssal Plain and the Woodleigh Impact Crater

3 Strange Geological Wonders in Australia

Most people think of Australia’s geological wonders as the big, obvious ones – Uluru, the Great Barrier Reef, or the Twelve Apostles. But some of the most fascinating stories are tucked away in places you’d never expect or even hidden deep beneath the surface. In this video, we’re going to explore three of those lesser-known gems. We’ll start out in the outback, where strange little green mounds bubble with water from deep underground. Then, we’ll take a plunge into the dark, silent depths of the Tasman Sea to visit a vast abyssal plain. And finally, we’ll head to Western Australia to uncover the buried scar of one of the largest asteroid impacts in Earth’s history. These aren’t the everyday tourist spots – they’re the hidden chapters of Australia’s deep-time story.

Paroo-Darling Mound Springs – New South Wales

An Oasis of “Mini Volcanoes” in the Outback

Imagine driving for hours through red, dusty outback New South Wales and suddenly coming upon a shimmering lake surrounded by clusters of lush green mounds. At Peery Lake in the Paroo-Darling National Park, usually a dry salt pan, you’ll find these odd little hills covered in vegetation. They were once described by early travellers as looking like “miniature volcanoes” popping up from the flat lakebed. In reality, these are artesian mound springs – one of the rarest landforms in Australia. They form when ancient water from the Great Artesian Basin (a massive underground reservoir) finds its way to the surface through cracks in the bedrock. As the water bubbles up and evaporates in the desert air, it leaves behind minerals and sediment that slowly build into mounds over millennia. Incredibly, the groundwater feeding these springs may have trickled underground for up to 30,000 years before emerging here – a true vintage Aussie outback brew!

Stumbling across these emerald-green spring mounds in such an arid land feels surreal. From above, they even look like fuzzy green pom-poms dotting the lake’s surface. Each mound is an oasis of life. The pools of fresh water and rich soils support unique plants and animals found nowhere else. You might spot waterbirds, frogs, and little lizards thriving around the moist fringes of the mounds, a stark contrast to the dry scrub just meters away.

But not all of Australia’s geological wonders are on dry land – one of the biggest is hiding under the ocean!

The Tasman Abyssal Plain – Exploring the Deep Blue Unknown

Off the east coast of Australia, beneath the Tasman Sea, lies the Tasman Abyssal Plain (also called the Eastern Australian Abyss). You can’t see it without sonar or submarines, but picture a vast, pitch-dark plain almost 5 kilometres below the waves, stretching from roughly southern Queensland to Tasmania. It’s absolutely enormous – about 1.1 million square kilometers in area. That’s bigger than Texas, all of it under water. This deep-sea plain is like an alien world on Earth: frigid water, crushing pressure, and no sunlight. Yet it’s a geological wonder because it preserves clues to Australia’s ancient past and harbors strange forms of life that endure in extreme conditions.

*Image Depicts The Tasman Abyssal Plain

Geologically, the Tasman Abyssal Plain is a product of tectonic drama. Between 90–50 million years ago, Australia and the precursor to New Zealand (Zealandia, a mostly submerged continent) were joined; then the earth’s crust tore apart, opening the Tasman Sea. As the continents rifted, a new ocean floor was born between them – and that became the abyssal plain. For tens of millions of years, underwater volcanoes on the spreading ridge spewed out lava, but eventually the tectonic activity died down, leaving a broad expanse of flat oceanic crust blanketed in sediments. Today, the plain lies 4,000–5,000 m deep on average, covered by fine mud and tiny skeletons of plankton that rained down over eons. It’s so deep that sunlight never reaches the bottom; the world down there exists in permanent midnight.

In 2017, scientists conducted a cutting-edge sonar mapping of this remote seabed – a “world-first” close look at the abyss – and discovered the undersea landscape is more rugged than anyone thought. The continental slope where Australia’s landmass falls away into the abyss isn’t a gentle decline; it’s incised with steep canyons, cliffs and landslides where huge chunks of the margin collapsed long ago. The sonar revealed craggy escarpments and sediment slumps at the edge of the abyssal plain, like an underwater Grand Canyon system, all hidden beneath the waves. Beyond the foot of the slope, the abyssal plain itself is relatively flat, made of deep-sea clay and oozes. It’s punctuated by the occasional seamount (underwater volcano) from old hotspot activity – for instance, the north–south line of the Tasmantid Seamounts formed as Australia’s plate drifted over a hotspot millions of years ago.

Life down on the Tasman Abyssal Plain might not be abundant, but it’s there – and it’s weird. In the darkness, blind crustaceans, sea cucumbers, starfish, and polychaete worms populate the sediments. In fact, when researchers sampled the area, they found that bristly polychaete worms were among the most common critters crawling through the mud, forming a major part of the benthic (seafloor) ecosystem. Many species discovered are microscopic or invertebrate, and most are scavengers or filter-feeders adapted to scarce food. Any organic material (like the carcass of a fish or whale that sinks from above) is a feast in this “marine desert”.

Sailing on the surface of the Tasman Sea, you’d never guess that nearly 6 km below your boat lies a plain that has remained largely unexplored and unchanged for millions of years. It’s humbling to think that the Earth’s biggest unexplored frontier isn’t remote islands or jungles, but the deep ocean floor.

The Woodleigh Impact Structure – Western Australia

A Buried Remnant of a Mega-Meteor

Our next stop takes us back to dry land – well, sort of. Woodleigh Station in Western Australia’s remote Gascoyne region looks like typical outback cattle country at first glance. You wouldn’t know that deep below the red dirt lies the scar of a catastrophic meteor impact – one of the biggest ever to hit Australia. The Woodleigh Impact Structure is a massive, ancient asteroid crater now completely buried by younger sedimentary rocks. It doesn’t have a neat bowl shape like smaller craters; instead, geologists had to play detective to find it. But what they discovered is astonishing: Woodleigh could be up to 120 km in diameter and roughly 364 million years old, dating back to the Devonian period. If the largest size estimates are correct, Woodleigh ties as the fourth-largest confirmed impact crater on Earth – truly a hidden giant under the Aussie bush.

*Image Depicts The Estimated Crater Extent

How did they figure this out? In the late 1990s, geologists drilling for oil and studying gravity data noticed something unusual under Woodleigh Station. Deep in a drill core, they found telltale signs of an extraterrestrial collision: shocked quartz crystals and veins of melted rock (impact glass) that only form under immense pressures, far beyond any normal volcanic or earthquake activity. The rocks had been hit so hard that their crystal structure was deformed – a microscopic “smoking gun” for a meteor strike. Further evidence came in 2018 when scientists identified reidite in the core – an extremely rare mineral that forms when the mineral zircon is smashed by the pressure of a huge impact. This was only the sixth time reidite had ever been found on Earth, and its presence strongly suggests Woodleigh’s crater was over 100 km wide.

Let’s pause to imagine the scene 364 million years ago: it’s the Devonian period, long before dinosaurs, when Earth’s life was mostly in the oceans (with some early amphibians and forests on land). Suddenly, a rock from space 5–10 km across hurtles into the shallow sea covering what’s now Western Australia. The meteor came in at tens of thousands of kilometres per hour. The impact explosion would have been apocalyptic – releasing more energy in a second than all the world’s nuclear arsenals combined. It blasted a crater possibly 120 km across and shattered the crust to depths of several kilometres. If you’re thinking “mass extinction event,” you’re on the right track. Scientists note that craters over 100 km can cause global climate upheaval. In fact, Woodleigh’s timing roughly coincides with a severe extinction at the end of the Devonian. Coincidence? Maybe not! An impact this big would have vaporized everything at ground zero and sent shockwaves, wildfires, and tsunamis across the planet.

Today, none of that violence is visible on the surface – Woodleigh’s grand crater has been eroded and buried over hundreds of millions of years. You could camp on Woodleigh Station and have no clue you’re atop a giant impact structure. The “smoking guns” are all beneath your feet. Geophysical surveys have mapped a circular gravitational anomaly and a central uplift zone under the ground, consistent with a multi-ring impact crater. The central uplift (the rebound mountain that often forms in the middle of very large craters) is about 20 km wide and was first detected in old drilling logs from the 1970s. When cores were brought up, that’s when those shocked minerals were found, clinching the impact theory.

What’s exciting is that we’re still learning about Woodleigh. Because it’s not exposed, estimates of its true size vary – some scientists argue it might be on the smaller side (~60 km), while others cite evidence for the larger (~120 km) figure. The recent reidite discovery favors the larger scale, implying a colossal impactor ~6–12 km wide. If so, Woodleigh’s crater is in the same league as Chicxulub (the 180 km crater from 65 million years ago that killed the dinosaurs) – just a bit smaller. It’s mind-blowing to think Australia had its own “dinosaur-killer”-class impact (albeit before dinosaurs existed). The Woodleigh event would have dramatically changed the environment; researchers are now investigating if it triggered any of the Devonian extinction pulses.

So there you have it – three places that remind us just how weird and wonderful geology can be. From the mound springs in the desert, to the silent abyss beneath the Tasman Sea, to a hidden impact crater the size of a small country – each one tells a story that stretches way beyond human history.

There are dozens more strange and spectacular geological wonders out there, many of them just as overlooked as these. So next time you’re thinking about Australia’s natural wonders, don’t just picture the famous landmarks – remember the hidden ones too. They’re just as extraordinary, if not more so.

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