Toward a Genetic Classification of Aeolian Sand Dunes

1. DUNE FORMS RELATED TO VEGETATION TOTAL SAND ACCUMULATION SAND ACCUMULATION ……………..……. STABILIZED SAND ……..……… SAND DEFLATION TOTAL SAND DEFLATION UNIMODAL WIND ….. BIMODAL WIND UNIMODAL WIND LOW coppice dunes(nebkhas) coppice dunes(nebkhas) stabilized dunes deflation hollows LOW MEDIUM foredunes or lunettes vegetated linear dunes stabilized dunes blowouts MEDIUM HIGH precipitation ridges vegetated linear dunes stabilized dunes parabolic dunes HIGH DUNE FORMS RELATED TO TOPOGRAPHY MOUNTAINOUS TERRAIN UPWIND ………………………………………………………… ……….………………………………………………. DOWNWIND FLAT SLOPED STEEPLY SLOPED STEEPLY SLOPED SLOPED FLAT sand ramp climbing dune leeward dune sand sheet sand sheet falling dune CLIFFED TERRAIN UPWIND …………………………………………………………………………………………………………….……. DOWNWIND FLAT WINDWARD CLIFF MESA TOP LEEWARD CLIFF FLAT sand sheet echo dunes cliff top dunes leeward dune sand sheet Toward a Genetic Classification of Aeolian Sand Dunes Kevin R. Mulligan, Department of Economics and Geography, Texas Tech University Lubbock, Texas Vatche P. Tchakerian, Department of Geography and Geology & Geophysics, Texas A&M University, College Station, Texas Aeolian sand dunes occur in a wide variety of forms in many different environmental settings. Although several notable attempts have been made to classify dune forms (e.g. Hack, 1941; McKee, 1979; Pye and Tsoar, 1990; Cooke et. al., 1993; Lancaster, 1995; Livingstone and Warren, 1996; Thomas, 1997), the problem of dune classification is complicated by the diverse terminology used in the literature and a lack of consensus among geomorphologists. More importantly, most dune classification systems fail to emphasize the genetic linkage between different dune types. In many situations dune morphologies can be represented as part of a continuum from one dune type to another. The purpose of this paper is to outline a simple dune classification system that stresses the genetic linkage between the different types of dunes controlled by autogenic processes, vegetation and topography. Dunes Related to Autogenic Processes In the first case, dunes controlled by autogenic processes reflect bedform self-organization and the nature of dune morphology is largely a function of the wind regime, sand supply and time. Over very long time scales these dunes can become part of larger draas or ergs in depositional basins or sinks. Dunes Related to Vegetation In the second case, vegetation is considered to be an important controlling variable and dunes are classified as part of a continuum reflecting the degree of sand accumulation or deflation. In the absence of vegetation (either natural or human induced), these dunes can take on the form of autogenic dunes. Dunes Related to Topography Lastly, dunes are classified in relation to topography, expressed as either sloped terrain or cliffed terrain. In this case, dune forms are controlled by their relative position with respect to the dominant wind direction and slope. DUNE FORMS RELATED TO AUTOGENIC PROCESSES (BEDFORM SELF-ORGAINZATION) EFFECTIVE WIND REGIME SAND SUPPLY UNIMODAL ………………….……..… BIMODAL …………..…….. OPPOSING .….. // …… MULTIDIRECTIONAL TIME (MEMORY) LOW ANGLE …………………… HIGH ANGLE LOW barchans asymmetric barchans seif dunes reversing dunes simple star SHORT compound barchans MEDIUM linear dunes (seif dunes) reversing dunes star dunes or network dunes MEDIUM barchanoidridges HIGH transverse dunes linear dunes (seif dunes) reversing dunes star dunes ornetwork dunes LONG complex dunes (two or more superimposed forms) | draas | ergs (sand seas) VERY LONG DEPOSITIONAL BASIN OR SINK REFERENCES Cooke, R., Warren, A., and Goudie, A., 1993, Desert Geomorphology, UCL Press, London, p. 526. Hack, J.T., 1941, Dunes of the western Navaho county, Geographical Review, v. 31, p. 240-263. Lancaster, N., 1995, Geomorphology of Desert Dunes, Routledge Press, London, 290 p. Livingstone, I., and Warren, A., 1996, Aeolian Geomorphology, Longman, Essex, 211 p. McKee, E.D., 1979, Introduction to a study of global sand seas. In E.D. McKee (ed) A Study of Global Sand Seas, U.S.G.S. Professional Paper 1052, p. 1-19. Pye, K., and Tsoar, H., 1990, Aeolian Sand and Sand Dunes, Unwin Hyman, London, 396 p. Thomas, D.S.G., 1997, Arid Zone Geomorphology, John Wiley and Sons, London, 713 p.

2. Previous Dune Classifications Hack, 1941 McKee, 1979 Livingstone and Warren, 1996 Pye and Tsoar, 1990 Thomas, 1997 Cooke, Warren and Goudie, 1993 Lancaster, 1995