Arid geomorphology

Abstract

The past year has been one in which the subfield of the geomorphology of aeolian processes and landforms has finally matured. There have been two important books: one is a general text on aeolian landforms , which should make the field much more widely understood and accessible to students; the other is a review of the geomorphology of desert dunes (Lancaster, 1995a). collections of articles on the research frontier and illustrate the diversity of approaches. I Changing paradigms in aeolian process studies Studies of sand transport by wind have traditionally concentrated on wind tunnel experiments in which controlled conditions of airflow and sediment size have allowed precise quantification of relations between transport rates and boundary layer winds. As commented on by Anderson et al. (1991), there is a need to relax these constraints to deal with more realistic conditions of unsteady flow and variable surface conditions so that geological and environmental problems can be addressed. Important aspects of surface conditions include moisture content (Arens, 1996) and vegetation cover (Musick and Trujillo, 1996;Wolfe and Nickling, 1996), both of which act to increase the transport threshold, slope (Iversen and Rasmussen, 1994;Rasmussen et al., 1996) and surface roughness (Greeley et al., 1995). Recent field studies have documented the spatial and temporal variability of actual transport rates in a variety of environments (beaches, simple dunes, agricultural lands and playas). They provide valuable insights into the appropriate methodology and instrumentation surface changes in time and space. The dynamic nature of surface conditions coupled with interactions between the wind, the surface, and the developing saltation cloud give rise to a 'fetch effect' or the change in sediment flux with distance downwind (Gillette et al., 1996). The effects of gustiness and turbulence on sediment transport are now being increasingly recognized (Butterfield, 1993), and instrumentation to detect and measure them is becoming more widely available (Jackson,