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

Previous Dune Classifications

Hack, 1941

Livingstone and Warren, 1996

Thomas, 1997 Lancaster, 1995

Pye and Tsoar, 1990

Cooke, Warren and Goudie, 1993

McKee, 1979