Abstract
The deposition of fine aeolian sediment profoundly influences the morphology of several different landscapes of the arid and semi-arid western portion of South Africa. Such landscapes and features include: (1) regularly-spaced mounds known as heuweltjies of the succulent Karoo region, (2) barren stone pavements in the more arid regions, and (3) hillslopes with smooth, curvilinear slope profiles that are mantled with coarse, stony colluvium. Investigations of each of these are presented, together with comparisons of similar features found within arid and semi-arid portions of Western North America. Recent findings suggest that the formation of the distinct, regularly-spaced heuweltjies involves a linked set of biological and physical processes. These include nutrient accumulation by termites and the production of dense vegetation patches, which, in turn, serve as a trap for aeolian sediments. Dust deposition is also responsible for the formation of stone pavements as demonstrated by research conducted principally in the Mojave Desert region of the United States. Mineralogical and geochronological studies have demonstrated that the stone clasts remain on the surface as fine aeolian sediments are translocated downward beneath the clasts resulting in a silt-rich soil horizon directly beneath the clasts. Pavements examined in South Africa have the same morphological features that can only be explained by the same process. The formation of soils on hillslopes mantled with stony colluvium are commonly viewed as having formed through the in-situ weathering of the stony colluvium. However, like pavements, mantles of coarse, stony colluvium are effective dust traps that provide the long-term stability required for advanced development of thick, fine-grained soils. This process contributes to the evolution of smooth, vegetated, curvilinear slope profiles. In each of these examples, the accumulation of dust has a profound influence, not only in soil formation, but also on the development of dominant landform characteristics. A greater awareness of these processes will contribute considerably to the growth of knowledge about soils and landscape development in the drylands of South Africa.
Highlights
Aeolian processes and Aeolian geomorphology are terms that typically evoke mental images of extensive landforms created by the movement and deposition of large amounts wind-blown sediments.expansive dune fields and thick periglacial loess deposits create distinct, extensive landforms that have long been recognized and much studied
In stark contrast to hummocky landscapes dotted with regularly spaced heuweltjies, some of the more arid portions of western South Africa contain barren, low-relief landscapes covered by stone pavements (Figure 6)
That example is compared with recent research conducted in western North America where multiple lines of evidence demonstrate the profound influence of aeolian dust accumulation on soil- and hillslope-forming processes in drylands
Summary
Aeolian processes and Aeolian geomorphology are terms that typically evoke mental images of extensive landforms created by the movement and deposition of large amounts wind-blown sediments. The quantity of over centuries to millennia, the accumulation and subsequent modification of those sediments profoundly centuries to millennia, the accumulation and subsequent modification of those sediments profoundly influence soils and and landforms landforms of of arid aridand andsemi-arid semi-aridenvironments. Biological processes contribute protective mantles of coarse, stony colluvium. Biological processes contribute to the development to of the development of some of thesepotentially features. Comparisons made withwith similar landscape features foundfound in other and semi-arid regions, regions, . Western are made similar landscape features inarid other arid and semi-arid . With the intent of highlighting similarities or differences that may exist in processes. Western North America, with the intent of highlighting similarities or differences that may exist in of development
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