The Nullarbor Plain is huge arid area, probably the deadliest area of Australia. But despite this waterless climate of today, it is also the biggest karst area of Australia. This seems strange, as karst is characterized by the solution of rock by water. But the explanation is easy: The center of Australia was no desert, long time ago when the caves here were formed.
We need a bit of plate tectonics to understand that. Our Earth has a hard crust, floating on a more or less liquid upper mantle, which consits of lava, molten rock. This lava is heated by thermonuclear reactions inside the Earth and cooled by the surface, so convection starts. This convection streams of molten rock transport the crust along the planets face in huge plates. About 200 Million years ago, all contentinets we know today stuck together and formed one big continent called Gondwanaland.
This continent broke up into pieces, which floated away from each other. The smallest pieces were India, Australia and Antarctica. Australia and Antarctica moved slowly across the South Pole. While Antarctica lies right at the pole, Australia is several thousand kilometers ahead and moves continuously to the north.
During the Pleistocene, about one million years ago the continent was in the southern temperate zone, the latitudinal range between the tropics and the polar circles, with frequent rainfalls and four seasons. It is about the same range, where the USA and Europe are at in the northern hemisphere.
But Australia moved on and reached the latitude of the southern arid area, at the border to the tropics, which corresponds with the arid belt where the Sahara is located in the north. Now the Nullarbor plain lies in the arid zone and karstification almost stopped. But the caves are still there, collecting and storing the water of the rare rains. Shallow dolines with a huge diameter, which are called Uvalas, were first described here (locus typicus aka type locale).
The exploration of the Nullarbor plain is difficult, because of the extreme climate and the remote location. To get there requires some travelling, even for Australians, and is thus time consuming and expensive. The area is not inhabited, and so the caves are not known to locals. It is necessary to scan the area by foot, which is rather exhausting in this arid climate (150mm-250mm annual rainfall and 1,200mm-2,500mm annual evaporation).
At the moment only 130 caves are known in an area of 200,000 square kilometers. Those known caves are generally huge and well decorated, Old Homestead Cave is 30km long and the passages of Abrakurrie Cave reach 45m width and 30m height. Cocklebiddy Cave has about 4km of flooded passages, which makes it the longest cave dive in the world (1996).
Because of the remote location the Nullarbor plain has no tourist caves. If you travel through this area, watch out for other karst features: there are dolines and uvalas all over. In the last years different tour operators started to offer visits to two caves.