badlands The word ‘badlands’ originated in North America, where extensive areas of badlands occur in the north-western Great Plains, such as in Badlands National Monument, South Dakota, and Dinosaur Provincial Park, Alberta. It seems likely that early French explorers in this region translated Plains Indian descriptions of these areas into the phrase
‘les mauvaises terres á traverser’ meaning ‘land bad (hard) to cross’. In fact, badlands occur in a wide range of environments, and on various materials, from marine silts in valleys of the Canadian Arctic to mine-spoil heaps in New Guinea. Badlands can, therefore, form as purely natural landscapes or as human-created features resulting from unwise agricultural or industrial practices.
Badlands are usually associated with arid or semi-arid regions where occasional intense rainstorms cause highly erosive rainsplash and run-off on exposed, weak rock surfaces. Erosion rates in excess of 20 mm a year have been recorded in some badlands. Relatively impermeable sedimentary rocks, such as mudstones and clay-cemented sandstones, are particularly susceptible to such rapid erosion and most badlands develop on such materials. Generally, the infertile nature of the rock and the rapid erosion inhibit the establishment of a vegetation cover and the landscape becomes a barren, often spectacular, and seemingly impenetrable maze of deep winding gullies, steep sharp-crested slopes, and an assortment of weirdly shaped hoodoos, rills, and tunnels. The steep slopes are often scarred by a network of closely spaced rills, which form as a result of rainstorm run-off. Rill incision deepens downslope as rills amalgamate into larger channels to form gullies. Wind may assist the processes of badland formation by removing fine grains and causing minor sandblasting effects.
While surface erosion caused by water can produce dramatic landscapes in many badlands, a considerable amount of subsurface erosion in the form of tunnels can also occur. Sedimentary rocks such as mudstones often contain a variety of clay minerals, including swelling clays such as bentonite. The swell–shrink effects of these clays, resulting from alternate wetting and drying, creates deep desiccation cracks which help to channel surface flow underground (see
subsurface flow and erosion). Extensive subsurface drainage networks may develop, producing an effect that resembles, in some respects, the caves and shafts that form by chemical solution in limestones. In badlands, however, solution processes are minor and tunnel systems are almost entirely erosional in origin as the rock particles are washed away. The tunnels become enlarged and their sides and roofs collapse to form gullies which, in turn, direct flow into newly forming tunnels in a complex interlinked surface and subsurface drainage system.
Ian A. Campbell
