Page 323 - Fundamentals of Geomorphology

306 PROCESS AND FORM

Table 12.3 A classification of dunes
Primary dune forms Criteria for subdivision Secondary dune forms Description

Free Morphology or orientation:
Transverse Transverse Asymmetric ridge
Barchan Crescentic form
Dome Circular or elliptical mound
Reversing Asymmetric ridge with slip faces on either side of
the crest
Linear Seif Sharp-crested ridge
Sand ridge Rounded, symmetric ridge, straight or sinuous
Star Star Central peak with three or more arms
Network Confused collection of individual dunes whose
slip faces have no preferred orientation
(Sheets) Zibar Coarse-grained bedform of low relief and
possessing no slip face
Streaks or stringers or Large bodies of sand with no discernible dune
sand sheets forms

Anchored Vegetation and topography:
Topography Echo Elongated ridge lying roughly parallel to, and
separated from, the windward side of a
topographic obstacle
Climbing dune or Irregular accumulation going up the windward
sand ramp side of a topographic obstacle
Cliff-top Dune sitting atop a scarp
Falling Irregular accumulation going down the leeward
side of a large topographic obstacle
Lee Elongated downwind from a topographic obstacle
Fore Roughly arcuate with arms extending downwind
around either side of a topographic obstacle
Lunette Crescent-shaped opening upwind
Vegetation Vegetated sand Roughly elliptical to irregular in plan, streamlined
mounds downwind
Parabolic U-shaped or V-shaped in plan with arms opening
upwind
Coastal Dunes formed behind a beach
Blowout Circular rim around a depression
Source: Based on Livingstone and Warren (1996, 74–101)

upon the slope of the obstacle. When the upwind slope zone of slightly lower wind velocity just beyond the crest
of an obstacle is less than around 30 , sand blows over it. of an obstacle. Falling dunes form in the lee of an obsta-
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When it is above 30 , then sand is trapped and a climb- cle, where the air is calmer. If the obstacle is narrow, then
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ing dune or sand ramp forms. If it exceeds 50 , then an sand moving around the edges may form lee dunes that
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echo dune forms at an upwind distance of some thrice the extend downwind. Lunettes are crescent-shaped dunes
height of the obstacle. Cliff-top dunes may form in the that open upwind and are associated with pans (p. 299).