Geoscience Reference
In-Depth Information
Table 5.2
Free, simple dunes. Note that surveys of dune types indicate that linear dunes are the most common, followed by: transverse, parabolic (Table 5.3) and star dunes. Features such
as dome dunes are comparatively rare (see data reported in Fryberger & Goudie (1981) and Thomas (1997b)). For an illustration of morphology see Figs 5.13 & 5.16.
Category
Type
Slip faces
Major control on form
Nature of movement
Internal structure
Transverse (consistent
unidirectional winds)
Some directional variability in the
wind and abundant sand supply
Less directional variability in the
wind and abundant sand supply
Limited sediment supply
Transverse
ridge
Barchanoid
ridge
Barchan
1
Forward migratory
High angle cross-beds inclined downwind (more
tabular sets in transverse dunes and a tendency to
wedge shaped sets in barchanoid dunes). Narrow
range of orientations of cross-beds. Cross-beds
frequently truncated by low-angle erosion surfaces
that dip gently downwind
When viewed in cross-section perpendicular to the
wind, sets of cross-beds are seen to dip in opposite
directions from the crest
As above but with more complex bedding pattern
due to the sinuous crest
Mix of cross-bed orientations reflecting the
bi-directional movement, although one direction
may dominate
Linear (bi-directional
winds and more variable
wind direction)
Other (various
wind directions)
A variable unidirectional or
bi-directional winds, more limited
sand supply than transverse dunes
Bi-directional winds
Linear
ridge
1-2
Extending
(sandpassing
forms)
Seif
2
Reversing
2
Opposing bi-directional winds
Will show a net
migration if one
wind direction is
dominant
Sand accumulating,
vertical forms
Star
3
+
Wind directions may vary
seasonally, or where transverse
dunes migrate into a region with
multidirectional winds. Sand supply
is abundant and wind direction
unstable
Composed of course sand, which
limits movement to highest
velocities. Various wind directions
Various wind directions
Variable and complex cross-beds
Zibar
0
Limited
?Weak
Dome
0
Limited
?Weak
