Nullarbor mapping reveals surface signs of deep, hidden cave systems

The vast, flat plains of the Nullarbor, stretching over 200,000 square kilometres across southern Australia, are home to a remarkable, largely hidden underground world. Formed when an ancient shallow sea retreated 14 million years ago, the region is composed of limestone, which has been gradually dissolved by water over millions of years, creating a Swiss-cheese landscape with cave openings and shallow depressions.

While valleys were previously thought to be formed by river activity, recent research has revealed that these features are actually the result of cave formation. Scattered across the Nullarbor are long, shallow trenches – up to 20 kilometres long and a few metres deep – that trend roughly north-south and appear to be unrelated to existing rivers or drainage networks. These mysterious trenches, invisible from the ground, can be identified through modern digital landscape models.

Using a combination of mapping techniques, borehole measurements, and geophysical methods, researchers have been able to "see" inside the Earth and determine the thickness and disturbance of the geology within these mysterious features. These findings not only shed light on the formation of the Nullarbor Plain but also provide a new way to identify hidden caves elsewhere, potentially offering insights into the formation of cave systems on other planets.