Bungle Bungle: Tower Karst in Sandstone

Abstract

Although the complex array of towers in the Bungle Bungle massif resembles the tower karst found in tropical limestone terrain, it has been eroded in quartz sandstone. Long-term leaching of silica by chemical weathering has produced a sandstone made up of highly etched and interlocking quartz grains with little intergranular cement. The resultant high compressive strength but low shearing and tensile strengths have maintained very steep slopes but have promoted intricate dissection of the massif. Topographic variation from rounded towers to joint-bounded pinnacles and sinuous ridges separating box valleys is due to variations in rock properties. The spectacular red and grey banding on rock faces is only a surface phenomenon on the intensely weathered sandstone, and results from deposition of iron and clay skins and the growth of cyanobacteria. The prominent pediment near the summit and the vast pediments surrounding much of the massif are erosional surfaces rather than stripped weathering fronts. Similar, though less spectacular, tower assemblages in sandstones occur elsewhere in tropical Australia and in the temperate southeastern part of the continent. As sandstone tower complexes also occur in other continents, it is now clear that long duration of weathering in quartz sandstone can produce landforms similar to those previously believed to be limited to limestone.