Toward a Genetic Classification of Aeolian Sand DunesKevin R. Mulligan, Department of Economics and Geography, Texas Tech University Lubbock, TexasVatche 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 ProcessesIn 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 VegetationIn 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 TopographyLastly, 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.
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.
DUNE FORMS RELATED TO TOPOGRAPHY
MOUNTAINOUS TERRAIN
UPWIND ………………………………………………………… ……….………………………………………………. DOWNWIND
FLAT SLOPED STEEPLY SLOPED STEEPLY SLOPED SLOPED FLAT
sand sheet sand ramp climbing dune falling dune leeward dune sand sheet
CLIFFED TERRAIN
FLAT WINDWARD CLIFF MESA TOP LEEWARD CLIFF FLAT
sand sheet echo dunes cliff top dunes leeward dune sand sheet
UPWIND …………………………………………………………………………………………………………….……. DOWNWIND
TOTAL SANDACCUMULATION
DUNE FORMS RELATED TO VEGETATION
SAND ACCUMULATION ……………..……. STABILIZED SAND ……..……… SAND DEFLATION
LOW
MEDIUM
HIGH
coppice dunes(nebkhas)
foredunesor lunettes
precipitation ridges
stabilized dunes
deflation hollows
blowouts
parabolic dunes
TOTAL SANDDEFLATION
LOW
MEDIUM
HIGH
UNIMODAL WIND ….. BIMODAL WIND
coppice dunes(nebkhas)
vegetatedlinear dunes
stabilized dunes
stabilized dunesvegetatedlinear dunes
UNIMODAL WIND
SAND SUPPLY
LOW
MEDIUM
HIGH
EFFECTIVE WIND REGIME
UNIMODAL ………………….……..… BIMODAL …………..…….. OPPOSING .….. // …… MULTIDIRECTIONALLOW ANGLE …………………… HIGH ANGLE
barchans
barchanoidridges
transverse dunes
compoundbarchans
asymmetricbarchans
seif dunes
linear dunes(seif dunes)
linear dunes(seif dunes)
reversing dunes
reversing dunes
reversing dunes
TIME(MEMORY)
SHORT
MEDIUM
LONG
simple star
star dunes ornetwork dunes
star dunes ornetwork dunes
DUNE FORMS RELATED TO AUTOGENIC PROCESSES(BEDFORM SELF-ORGAINZATION)
complex dunes(two or more superimposed forms)
|draas
|ergs
(sand seas)
VERYLONG
DEPOSITIONALBASIN OR SINK