The history and nature of wind erosion in deserts

摘要

Recently, the importance of wind erosion has been reevaluated. Many low-angle surfaces, developed on susceptible materials, possess closed depressions (pans), and these often have a distinctive morphology and lunette dunes on their lee sides. It has also become apparent that in drylands there are extensive areas of stone pavements, some of which have been molded by deflation; however, it is now recognized that other horizontal sorting processes have played a role, especially movement of fines by overland flow. Vertical sorting associated with wetting and drying, salt heave, bioturbation, frost action, and dust accretion have also played a role. In hyperarid areas, especially with unidirectional winds, bedrock outcrops and old lake beds have been molded to give aerodynamic forms, called yardangs. The study of dust storms by analysis of climatological data and remote sensing has revealed the importance of deflation, especially in hyperacid areas with centripetal drainage. Deflation hot spots, such as the Bodele Depression, have been identified. Analysis of ice and ocean cores and loess deposits has indicated that wind activity was greater during glacial phases than now. There is, however, great variability in the importance of wind at the present day, depending on the wind velocity characteristics of different deserts.