Mysterious trenches stretching for miles across the vast Nullarbor Plain in Australia are the surface scars of huge ancient caves collapsing deep underground, according to new research."They look like some kind of river channel, but they start and end so abruptly that it triggered us to investigate them," Matej Lipar, a researcher at the Anton Melik Geographical Institute in Slovenia and first author of the study, told Live Science.The Nullarbor Plain is an arid, flat, almost-treeless expanse in southern Australia. Nestled between the Great Victoria Desert and the Great Australian Bight coast, it has existed for more than 14 million years. Along the eastern edge of the Nullarbor Plain are fi...