Subdued surface expression of deep cave collapse

Cave systems can be difficult to recognise where karst landforms are subdued or overprinted with other landscape processes. Subtle linear depressions on carbonate platforms are commonly interpreted as fluvial or tectonic landforms, but may also mark collapse above underlying cave systems. We test this on the Nullarbor Plain, southern Australia, a stable >200,000 km² carbonate platform exposed for >14 Myr. Integrating morphometrics, electrical resistivity tomography, passive seismic profiling, cave records, cliff exposures and sedimentology, we show that kilometre-scale, shallow, sediment-filled trenches are surface expressions of vertically propagated collapse and sagging above deep cave conduits. These depressions lack integrated drainage, downstream sediment transport and sedimentological evidence of channelised flow; instead, they overlie vertically extensive low-resistivity zones, align with mapped caves and collapse dolines, and project to cliff-face exposed stratal deformation. The Nullarbor trenches provide diagnostic criteria for recognising subdued cave-collapse systems on Earth and an analogue for interpreting linear depressions on other rocky planetary surfaces. Kilometer-scale linear depressions on Australia’s Nullarbor Plain record collapse and sagging above deep cave conduits, providing criteria for recognizing otherwise subdued cave-collapse systems, according to morphometrics, geophysics, cave records, cliff exposures and sedimentology analyses.