COMBINING REMOTE SENSING, GEOPHYSICAL AND "OLD -SCHOOL" GEOMORHOLOGICAL TOOLS TO ASSESS WEATHERING RATES OF THE WORLD'S LARGEST EXPOSED CARBONATE PLATFORM: THE NULLARBOR PLAIN, AUSTRALIA

Geomorphological studies of remote, extensive landforms have traditionally relied on air-photographs and extrapolation of few ground observations. This is especially true of the Nullarbor Plain, Australia, a ~200,000 km2 limestone plateaux with subdued topography and relative paucity of karst features. The presence and distribution of palaeo-channels and shallow depressions in the interior has previously been examined using air-photos and isolated ground observations. These features are barely discernible on the ground and it they have not been considered in detail in the karst development in this now semi-arid environment.

The advent of high (vertical) resolution SRTM (radar) elevation data, coupled with new multi-spectral satellite data allows a much more detailed landform analysis than has hitherto been possible. Coupled with ground observations using microgravity and traditional survey techniques such an analysis for Nullarbor Plain reveals a number of unexpected findings: (i) the plain does not rise continuously to its north, but instead dips north over a large area; (ii) an extensive palaeo-channel network is identified, which did not drain south onto the plain from the interior, but instead drained from the plain towards this depression; (iii) large areas of numerous small (<200 m) shallow depressions (<4 m deep) can be identified: those examined exhibit significant gravity anomalies and some are actively draining, suggesting they are karst dolines with sediment fill; (iv) subsurface karst weathering has generated substantial cavernous porosity, which connected via surface blowholes exhibit strong barometric draughts, allowed total void volume to be assessed using micro-meteorological techniques. The results suggest that not only the southern margin, but the entire plain has undergone significant modification through limestone dissolution and tectonic processes. Current weathering rates in this dry climate are low, however, it is clear that karst weathering during wetter climates has been the main factor shaping this platform since its emergence 15 Ma years ago.