Giant caves beneath sinkhole reveal origin of mystery trenches that score Australia's Nullarbor Plain

Mysterious trenches stretching across Australia's Nullarbor Plain appear to be the surface result of ancient caves collapsing deep underground, according to new research. These seemingly river-like trenches, found along the eastern edge of the Nullarbor, a vast arid expanse, have long puzzled scientists. Despite their considerable size ranging from several miles to over 12 miles long, they are not always visible, blending in with the plain's almost-treeless landscape.

The cause of these trenches remained unclear until researchers used digital elevation models and electrical resistivity tomography to investigate. The findings revealed that these trenches are actually dips at the tops of canyons, plunging more than 130 feet below the surface, filled with sediment, predominantly sand, with finer particles of silt and clay beneath.

The researchers discovered a series of large, deep caves along the trenches, often accessible through sinkholes, with passages extending hundreds of meters. These caves, formed in the porous karst limestone by groundwater flow during the Oligocene and Early Miocene epochs, likely collapsed over time, creating the shallow depressions on the surface.

The team confirmed their theory by exploring a cave within one of the trenches, finding its features matched those of the others. The study, published in Communications Earth and Environment, suggests that these collapses might still leave undiscovered large caves beneath the surface. The research also has implications for understanding caves and potential habitable environments on other planets, such as Mars, where similar elongated depressions have been interpreted as collapsed lava tubes.