The Inland Sea

David Cook — 7 June 2019
Exploring the mileposts of a long forgotten sea can be the basis of many great camping journeys.

At the beginning of the 19th Century, the first European explorers who crossed the mountain barrier to the west of the foundling settlement of Sydney, opening their path to the continent’s interior, noted that most of the inland rivers ran towards the west. This soon sparked the notion that they were draining towards a vast inland sea and this became a magnet that drew them, one after the other, to push ever further to the westward. What they found was an ever drier landscape, and it cost the lives of many and left all manner of clutter across a parched land, from whaleboats to pianos.

The big trouble for them all was that they were about sixty million years too late. That’s when the centre of Australia, as with many of the world’s continents at the time, was covered by a vast shallow sea. The world’s temperature was warmer than it is today, and sea levels were much higher. It was a time when the great supercontinent of Pangaea – in which all the world’s land masses had welded themselves together – was breaking apart and without the collision of land masses the necessary mountain building processes were much less active, so the landscape was generally flatter.

The ancient Australian seaway flooded from what is today the eastern side of the Gulf of Carpentaria and western Cape York, down through western Queensland into what is now northern NSW and across into South Australia almost to the Western Australian border. It wasn’t very deep but it did become a home for numerous forms of life and though the lands around weren’t of great elevation there were numerous rivers carrying in loads of sediment. At its southern edge it was a cool temperate zone, probably equivalent to southern New Zealand today, but at its northernmost reaches it was close to sub-tropical.

Now known as the Eromanga Sea, this inland ocean has given Australia great riches. The bowl-like depression in which the sediments from the sea lie is the main watercourse for the Great Artesian Basin, which has been the lifeblood for so many small outback settlements and watering places and directed the pace and direction of much of the outback’s development. And for campers such as us it has set out mile posts that define our nation and the outback – the lonely watering holes where uniquely eclectic pubs sustain life around huge pastoral properties, where wetlands both natural and artificial sustain existence for thousands of birds and small animals and storied tracks connect places that are a part of our national heritage – and exploring these waypoints can form a bucket list of great camping adventures.

The Basin covers over 1.7 million square kilometers – nearly a fifth of the Australian mainland – and consists of alternating layers of sandstone and fine grained shales, adding up to 3000 metres in thickness at its centre. The clay-like shales prevent the downward passage of water, and it instead flows along the more porous sandstone aquifers under gravity, following its south-western dip.

The Eromanga Basin is the name given to the southern half of the Great Artesian Basin and is home to Australia’s largest onshore oil deposits, around Roma, Qld, and the rich oil and gas fields around Moomba in northern South Australia. Surprisingly, little exploration has been undertaken in the Eromanga sediments of northern NSW.

The surface signs of that subterranean water course were well known to the aboriginal residents of the land. These mostly outcrop in areas which are traditionally, at best, poorly watered and, at worst, hardened desert. The surface seeps of water were, in places, little more than that: bone dry sandy landscapes with no other regular supply of water. These were thus very valuable resources for the native groups moving through the area, and they became just as vital to the early explorers and those who would try to eke a living out of the land.

It was explorer Benjamin Babbage who noted aboriginal people travelling in from what was assumed to be dry and unlivable waste land to the north and west to the north of Adelaide and in 1858 he and Peter Warburton found each their first mound springs. These are build-ups of mineralized crust around a spring that stand several metres above the surrounding plain and support rich green growth with a pool of clear water at the top. Mound springs have been found across the basin, though the greatest number are in the south-west. These springs exist throughout the Basin and continued to be found as recently as 1951.

The almost linear alignment of the South Australian mound springs was used by explorer John McDouall Stuart as launching pads to enable his northerly pursuit of the crossing of Australia. When the colony of South Australia won the right to build the first telegraph line from Darwin, where it reached the Australian mainland, the engineers used the mound springs as stepping stones for the establishment of repeater stations and as a guide to the line’s passage almost to the halfway point in its passage south.

Then the railway was extended north from Part Augusta through to Marree and a maintenance track was built alongside. The railway has now fallen into decay – though creating some great bridges, old watering towers, railway sidings and other relics, and the old wooden sleepers have fuelled many a camp fire – but that maintenance road, now known as the Oodnadatta Track, is one of the great drives of the outback and probably the most accessible of introductions to the desert country of Central Australia.

From the north the Birdsville Track is likewise an easily accessible and well driven journey. Its route was surveyed in the early 1860s to open a path for cattle from the huge properties of the south-western corner of Queensland through to Port Augusta and then later to the railhead at Marree. This was a huge journey, crossing three deserts – the Tirari, Sturts Stony and the Strzelecki – but it was a thousand kilometers shorter than trying to reach the markets in Brisbane. The blinding sandstorms and total lack of water most of the time, however, cost cattle and drovers’ lives, so bores were drilled at regular intervals, many of which remain active. Even as recently as 1963 a family of five lost their lives when their car broke down and they tried to walk to safety.

The Strzelecki Track is another easily accessible route that again passes a Great Artesian outlet, at Montecollina Bore, an oasis of life in a sea of sand.

Much of that subterranean water, some of which dated back as far as two million years old, has now been drained away by uncontrolled use in places, but this water is still restocked, mainly from rainfall along its northern and eastern margins and is extraordinarily valuable in many agricultural pursuits today.

Over the years more than 4700 bores were drilled down into the aquifers to release water under the pressure of the overlying rocks, along with another additional 2500 bores which required the use of pumps, mostly driven by the wind. Some proved very wasteful. For example, at Coward Springs, on South Australia’s Oodnadatta Track, a bore was put down to augment the natural flow, but the resulting gush was so great that it flooded the plain for a great distance all around until the bore was capped to reduce the flow again. This sort of waste has resulted in the gradual decline in the water pressure in the aquifers and a drying up of some outlets. In places – such as at Strangways Springs further up the Oodnadatta Track from Coward Springs – the flow of water from the springs, which once sustained this important settlement, has declined to almost zero.

This doesn’t mean that there still isn’t plenty of water left to the desert sands at Coward Springs. Like so many other places along the edge of the aquifers water bubbling to the surface has been tapped and directed into low points in the landscape. This has left the country dotted with small wetlands, even in the midst of parched summer heat, and now we can drive along some of the major roads of the outback and enjoy these spots of wildlife plenty. The Birdsville Track, for example, brings us examples at Clayton Station, Mungerannie and even where the Cooper Creek crosses the Track in times of heavy rain. These lush green ecosystems teem with birds and other small animals and make great places to camp.

Also of great value are the rich deposits of opal which occur mostly through the southern margin of the basin. Australia supplies over 80 percent of the world’s opal. The biggest problem today is meeting market demand, with some fields reportedly almost exhausted. For example, in Coober Pedy there was, in the 1970s and 80s as many as 800 operating miners but that number was in 2016 down to as few as 80. The opal industry is estimated to be worth in excess of $100 million per year and increasing rapidly as prices for this rare gem rise.

Ticking off the opal fields can be another bucket list trip possibility. With most of the major fields lying around the southern margin of the basin you could make up a unique journey, starting at Lightning Ridge, in NSW, and heading north and west to Eulo and Quilpie in Queensland, then down back south to White Cliffs in NSW, across the border into South Australia and west to Coober Pedy and Mintabe.

Opal Mining towns are great places, like an Aussie version of the wild west. There are people living underground, signs threatening all manner of punishments to trespassers, strange characters, weird constructions, old buses and cement mixers and a seemingly complete disregard for the normal rules of life. These are the realms of the individualist. Notionally Lightning Ridge has some 2600 residents, but that’s a number which fluctuates wildly as people admit they live there and then seemingly drop off the known list. There’s a lot of cash and a lot of living under the radar.

Each of these towns has its mines you can visit, piles of mullock heaps you can pick over, underground shops and hotels, underground homes you can inspect and any number of places that will sell you a souvenir gem fresh out of the ground.

The Eromanga Sea was a great national asset long before this was a nation, and its remains in the Great Artesian Basin continue to shape the outback and the nation’s wealth. Taking a few journeys around the mileposts of this hundred million year-old prehistoric theme park will take you to some of the greatest destinations in the Australian Outback.

And for what it’s worth, scientists think that if we allow global climate change to run rampant that by the time all the ice melts – in several hundred years - the sea levels will have risen far enough to reestablish the Eromanga Sea, so that not only will all our coastal cities be flooded by the consequent 70 metre sea level rise, but so will some of the driest sections of our desert interior. Maybe then the dinosaurs and swimming and flying reptiles will make their comeback.


inland sea desert destination geography geology