Dune Processes

Following Warren and Knott (1983 ), aeolian processes can be considered at three spatial and temporal scales. These correspond approximately to the steady, graded and cyclic time scales of Schumm and Lichty (1965). At the steady scale, involving very short or even instantaneous amounts of time and small areas, is the study of the process of sand movement by the wind and the dynamics of small scale bedforms, such as wind ripples. Also probably to be included at this scale of investigations are studies of the primary units of aeolian deposition ( Hunter 1977 ; Schenk 1983 ). The graded scale involves longer spans of time, in this context ranging from months to tens of years, and particularly concerns the dynamics and morphology of dunes, which may achieve or tend towards an actual or partial equilibrium with respect to rates and directions of sand movements generated by surface winds. Form-flow interactions and feedback processes are important at this scale, which is probably the most important in determining the origins and dynamics of dunes and the accumulation of aeolian sand bodies, yet is the least studied and understood ( Lancaster 1984c ; Warren 1984 ). Much of what will be discussed in this chapter concerns the graded scale of process investigations. Study of aeolian processes at the cyclic time scale involves periods of thousands to millions of years and a spatial scale corresponding to that of sand seas and their regional physiographic and tectonic setting. Processes at this scale involve those responsible for the accumulation of the sand sea as a sedimentary body. They will be considered in Chapter 7 .