Stretching about 1,100 km from east to west astride the South Australia–Western Australia state line, the Nullarbor Plain is a flat, almost treeless limestone plateau of about 200,000 km² on the north shore of the Great Australian Bight, with the Great Victoria Desert to its north. It is the world’s largest single exposure of limestone bedrock, an old seabed covered in low saltbush and bluebush, and its name is Latin for “no tree”. It is arid to semi-arid, with only about 184 mm of rain a year at Cook in the interior and about 320 mm at Eucla on the coast. About 32% of the ecoregion is protected, including Nullarbor National Park, the Nullarbor Regional Reserve and, since 2013, the Nullarbor Wilderness Protection Area in South Australia.
The Mirning and Yinyila peoples, who occupied the plain seasonally, called it Oondiri, a name said to mean “the waterless”. Water, more than distance or heat, is what decides how anything lives here, so this guide tracks the water: when the rain comes, where it disappears to, and what people and animals have done about it.
Winter on the Great Australian Bight, May to August: fronts, whales and wombat warrens
The Nullarbor sits far enough south to catch the cold fronts that sweep east across the Southern Ocean in winter. Close to the coast they bring more rain in the cool months than most of inland Australia ever sees, and at Cook, on the railway in the South Australian interior, most of the 184.1 mm average falls between May and August. Winter nights on the open plain often drop well below freezing; the coldest temperature ever recorded in Western Australia, −7.2 °C, was measured at Eyre on the Nullarbor coast. At Eucla the mean temperature falls from 22.1 °C in January to 13.0 °C in July.
The coastal station shows how thin and evenly spread that rain is: no month at Eucla averages more than 33 mm, and a winter month is barely wetter than a summer one. On the coast the seasons differ little in rainfall; inland at Cook the winter peak is much sharper, and the cool months are when that rain does most good.
The animal most tuned to this is the southern hairy-nosed wombat, South Australia’s state animal, which lives from the eastern Nullarbor to the New South Wales border. Wombats live in warrens of linked burrows shared by up to ten animals, where the air stays around 14 °C in midwinter and 26 °C in midsummer while the surface swings from about 2 °C to 36 °C or more. Their breeding depends on winter rain. If enough falls to germinate the grasses, females ovulate between August and October, gestation lasts only 22 days, and most young are born in October. In dry years neither sex comes into breeding condition at all. The wombat also saves water through its gut, producing droppings that can be as little as 40% water.
Offshore, winter is the calving season. Southern right whales come into the Head of Bight, at the northernmost point of the Great Australian Bight, one of only two places on Australia’s south coast where they gather to calve. The waters lie within the Far West Coast Marine Park, and the land behind is part of the Yalata Indigenous Protected Area. West of there, the Bunda Cliffs run for 210 km to Eucla, rising 60 to 120 m straight out of the Southern Ocean, with an unbroken 160 km stretch in the middle.
Summer, December to February: 49.9 °C at Nullarbor Roadhouse and the rare deluge
On updated Köppen maps the Nullarbor falls into the “cold desert” and “cold semi-arid” classes rather than the hot desert type of central Australia, but its summer days can still be ferocious. On 19 December 2019 the automatic weather station at Nullarbor, the roadhouse settlement in South Australia, recorded 49.9 °C, the highest maximum anywhere in Australia that year, the hottest December temperature on the national record and the fourth-highest ever measured in the country.
Summers are generally very dry, with rain coming from scattered thunderstorms. Every so often, though, a decaying tropical system drifts far enough south to deliver a heavy fall in the middle of the dry season, briefly pooling water on ground that normally swallows it at once.
This is also a plain that only recently became dry. Research from Curtin University published in 2023 dates the Nullarbor’s shift to arid conditions to between 2.4 and 2.7 million years ago. The landscape it left is one of the best places in the world to find meteorites, which the dry climate preserves; many have been collected around Mundrabilla, some weighing several tonnes.
Into the limestone: where the Nullarbor’s rain goes
The plain has no permanent rivers. That is not only because of the low rainfall but because of what it is made of. The Nullarbor is a former shallow seabed built from the skeletons of bryozoans, foraminifera, sea urchins and red algae. Its rocks run from the Wilsons Bluff Limestone of the middle to late Eocene at the base to the Nullarbor Limestone of the early middle Miocene on top. One theory is that crustal movements lifted the whole area in the Miocene and that wind and rain have only worn it down since; the plain has probably never had major relief, which is why it is so flat.
Rain that falls on such rock sinks through cracks and dissolves its way down, turning the plain into one of the world’s significant karst regions. Underneath lie caves with underground rivers and lakes, home to crustaceans, spiders and beetles adapted to darkness. Large colonies of the chocolate wattled bat roost in them, and so does a subspecies of the Australian masked owl found only on the Nullarbor. Near the coast, the Southern Ocean pushes air through the cave systems and out of blowholes up to several hundred metres inland.
One cave shows what the water table looks like. Cocklebiddy Cave, near the roadhouse of the same name in Western Australia, is a single passage more than 6 km long, of which about 90% is flooded and can only be explored by diving. A French team set the world record for the longest cave dive there in August 1983; two months later Hugh Morrison of Western Australia pushed 280 m further, South Australian Christopher Brown added 20 m in 1995, and in 2008 Craig Challen and Richard Harris, later part of the 2018 Tham Luang rescue in Thailand, mapped its far reaches with rebreathers. During the Second World War, army engineers tried to draw fresh water from these underground lakes and found only a thin skin of fresh water floating on a vast body of salt water.
Bores, brackish water and the Trans-Australian Railway, 1917–1996
That salt is the problem every settler on the plain has met. The Trans-Australian Railway, whose two halves met at Ooldea on 17 October 1917, runs 1,691 km from Port Augusta to Kalgoorlie and includes the world’s longest stretch of straight track, 478 km across the plain. At no point does it cross a permanent freshwater stream. Bores and reservoirs were sunk along the route, but the water was often too brackish for people and wrecked locomotive boilers: at one stage boiler repairs made up 87% of all maintenance, until barium carbonate treatment plants were installed. In the steam era about half of a train’s load was water for the engine, and condenser plants were later built at several stations. The Tea and Sugar supply train kept the isolated railway settlements stocked until 1996.
Ranchers have done the same arithmetic. Rawlinna Station, founded in 1962 on the Western Australian side, covers about 1 million hectares and is the largest sheep station in the world, with Madura Station of 690,000 ha nearer the coast. The plain’s grasslands can carry some sheep, though introduced rabbits damage the same pastures.
From Eyre’s waterless crossing of 1841 to the dunes that buried Eucla
The first European crossing was decided by water. Edward John Eyre left Fowlers Bay heading west on 17 November 1840 and turned back when three of his horses died of thirst. He set out again on 25 February 1841, reached Caiguna by 29 April, and there, short of food and water, two of his Aboriginal companions killed John Baxter and took the supplies. Eyre and the third man, Wylie, kept going, resupplied by a French whaling ship at Rossiter Bay, and reached Albany in June 1841. Edmund Delisser gave the plain its Latin name in August 1865.
Eucla became an important telegraph station when the Albany–Adelaide line opened in 1877, translating between the two Morse codes used by the colonies on either side. Rabbits and sand then took the town apart. In the 1890s a rabbit plague stripped the plants from the Delisser Sandhills, the dunes began to move, and sand drifts engulfed the townsite. Eucla was rebuilt about 4 km north on top of the escarpment, and the ruins of the old telegraph station still stand among the dunes.
Seen from the train or the highway, the Nullarbor can look like empty ground, but almost everything on it is a response to how little water reaches the surface and how quickly it disappears. For how it fits into the rest of the continent, read our guide to Australia’s geography, and for the processes that dissolved its caves, see what karst topography is.