1. 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
barchanoid ridges
HIGH
transverse dunes
linear dunes
(seif dunes)
reversing dunes
star dunes or network dunes
LONG
complex dunes
(two or more superimposed forms) |
draas
ergs
(sand seas)
VERY
LONG
DEPOSITIONAL
BASIN OR SINK
TOTAL SAND
ACCUMULATION
DUNE FORMS RELATED TO VEGETATION
SAND ACCUMULATION ……………..……. STABILIZED SAND ……..……… SAND DEFLATION
LOW
MEDIUM
HIGH
coppice dunes (nebkhas)
foredunes
or lunettes
precipitation ridges
stabilized dunes
deflation hollows
blowouts
parabolic dunes
DEFLATION
UNIMODAL WIND ….. BIMODAL WIND
vegetated
linear dunes
UNIMODAL WIND
DUNE FORMS RELATED TO TOPOGRAPHY
MOUNTAINOUS TERRAIN
UPWIND ………………………………………………………… ……….………………………………………………. DOWNWIND
FLAT
SLOPED
STEEPLY SLOPED
sand sheet
sand ramp
climbing dune
falling dune
leeward dune
CLIFFED TERRAIN
WINDWARD CLIFF
MESA TOP
LEEWARD CLIFF
echo dunes
cliff top dunes
UPWIND …………………………………………………………………………………………………………….……. DOWNWIND
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
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
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