Dust and Soil Landscapes in the Southwestern United States.

Dust plays a critical role in aridland soil formation, given an abundant supply of dust and limited chemical weathering. The recognition that virtually all calcium in pedogenic carbonate in calcic horizons is derived from calcium-bearing dust demonstrates that soil formation in aridlands differs substantially from that in other settings. Studies of soils on basaltic volcanic flows show that the nature of soil development below desert pavements constrasts markedly from that proscribed by the “canonical” A/B/C Dokuchaev model (the model most familiar to many Earth scientists). The vesicular A horizons and thickening clay and calcium carbonate-enriched B horizons mainly form in parent materials composed of entrapped dust that is subsequently translocated below the pavement, resulting in accretionary and inflationary profile (AIP) development. Soil chronosequence studies show that AIP and desert pavement formation also are favored on other landforms (e.g., alluvial fans) if pavement-forming, weathering-resistant rock types are present. Once formed, desert pavements commonly survive exposure to one or more “glacial” periods. The hillslopes of aridland hills and mountains are excellent dust traps, and in favorable circumstances, AIP promotes vegetated and smooth, soil-mantled transport-limited hillslopes. Toposequence studies indicate that the presence of dust-entrapping colluvium is probably necessary to maintain AIP on aridland hillslopes. Certain rock types in aridlands weather rapidly, also favoring the development of transport-limited hillslopes in many areas; however, the typically thin, weakly developed soils are prone to rapid erosion triggered by centennial scale drought cycles. The  results of a half century of soil geomorphological research in aridlands, relying largely on the “CLORPT”-based approach, indicates that maintaining two necessary conditions fundamental in the application of “soil production functions” in studies of hillslopes (transport solely by diffusive processes and steady-state soil thickness) for thousands to tens of thousands of years is unlikely in most aridlands.