Mysterious trenches stretching for kilometres across southern Australia\u2019s Nullarbor Plain have been revealed as the surface footprints of deep, hidden ancient cave systems.<\/p>\n\n\n\n
New research involving Curtin University has found that shallow, sediment-filled trenches formed when underground caves gradually collapsed, eventually reaching the surface. This challenges the idea that they were carved out by flowing water, as their appearance might suggest.<\/p>\n\n\n\n
The findings provide a new way to identify hidden cave systems in dry landscapes on Earth and could help scientists interpret similar features on Mars and other planetary surfaces.<\/p>\n\n\n\n
Lead author Dr Matej Lipar, who at the time of the research was an Adjunct Research Fellow in Curtin\u2019s School of Earth and Planetary Sciences<\/a>, and is now at the Anton Melik Geographical Institute at the Research Centre of the Slovenian Academy of Sciences and Arts (ZRC SAZU), said the trenches were difficult to recognise as evidence of underground caves because their surface features were so subtle.<\/p>\n\n\n\n \u201cFrom the surface, these features can look remarkably like shallow valleys or drainage channels, but our evidence shows they have a very different origin,\u201d Dr Lipar said.<\/p>\n\n\n\n \u201cBy combining mapping, geophysical surveys, cave records and sediment analysis, we found these trenches are linked to deep cave systems beneath the Nullarbor Plain.<\/p>\n\n\n\n \u201cOver time, the cave roofs progressively collapsed causing sagging of overlying material, eventually creating shallow depressions at the surface.\u201d<\/p>\n\n\n\n Dr Lipar said the trenches can range from several kilometres to more than 20 kilometres long and are generally 100 to 500 metres wide, but at less than nine metres deep are hard to see on the huge expanse of the Nullarbor Plain.<\/p>\n\n\n\n \u201cBecause the landscape is so vast, it appears to be a flat, endless plain. But when we created exaggerated digital models of the terrain, the trenches became much easier to see and identify.\u201d Dr Lipar said.<\/p>\n\n\n\n \u201cUnlike typical valleys, the trenches don\u2019t have connected streams or other signs that water once flowed through them. Instead, geophysical surveys found deep underground cavities, while several trenches lined up with known caves and areas where the ground has collapsed.\u201d<\/p>\n\n\n\n The researchers also identified a progression from obvious cave-connected collapse features in the west to wider, more subtle trenches further east, showing how cave collapse can progressively reach the surface depending on the thickness of rock.<\/p>\n\n\n\n Curtin co-author Associate Professor Milo Barham<\/a>, from the Curtin Frontier Institute for Geoscience Solutions (CFIGS)<\/a> and School of Earth and Planetary Sciences, said the findings could change how scientists interpret similar subtle landscape features elsewhere.<\/p>\n\n\n\n \u201cCave systems are not always obvious from the surface, but the dry and stable landscape of the Nullarbor is excellent for removing a lot of \u201cnoise\u201d to allow us to recognise subtle landscape characteristics,\u201d Associate Professor Barham said.<\/p>\n\n\n\n \u201cThis gives us a useful set of indicators for identifying hidden cave systems elsewhere \u2013 including on other planets such as Mars.<\/p>\n\n\n\n \u201cCaves are important as they can preserve evidence of past environments on Earth and impact our engineering and access to clean drinking water, while potential caves on other planets could provide protected subsurface environments relevant to the search for evidence of extraterrestrial life or act as bases for future astronauts.\u201d<\/p>\n\n\n\n The study was supported by the Slovenian Research and Innovation Agency and also involved researchers from The University of Western Australia, La Trobe University, the University of Ljubljana, and The University of Queensland.<\/p>\n\n\n\n