Deserts of the World - Design with the Desert: Conservation and Sustainable Development - page 6

FIGURE 1.5
Photograph of the Namib Desert (Soussusvlei). (Courtesy of N. Lancaster.)
contains two major dune fields separated by inselberg-studded gravel plains: the Skeleton
Coast erg 26 and the great Namib erg to the south of the Kuiseb Valley. 27
The most striking feature of the Namib is the 13,400 miles 2 sand sea that stretches for
over 188 miles between Luderitz and the Kuiseb River (Figure 1.5). Three major dune types
occur: transverse and barchanoid dunes * that occur aligned normal to SSW to SW winds in
a 12.5 miles wide strip along the coast; linear dunes on N-S to NW-SE alignments, reach-
ing heights of 490-568 ft in the center of the erg; and dunes of star form that occur along the
eastern margins of the erg (Figure 1.5). †
The Namib seems to be a desert of considerable antiquity, for the character of most
Tertiary sediments in the Namib is suggestive of arid or semiarid conditions. The cross-
bedded Tsondab Sandstone Formation represents the accumulation of a major sand sea in
the central and southern Namib over a period of 20-30 million years prior to the mid to late
Miocene. 29 In addition, extensive calcrete formation seems to have occurred at the end of the
Miocene, while in the Pliocene, a climate of modern affinities was developing in the region.
Seisser's 30 investigation of offshore sediments has indicated that upwelling of cold waters
intensified significantly from the late Miocene (7-10 million year BP) and that the Benguela
Current developed progressively thereafter. Pollen analysis of such sediments indicates
that hyperaridity occurred throughout the Pliocene and that the accumulation of the main
Namib erg started at that time. For much of the Pleistocene, aridity was also the norm, and
although there have been periods of increased fluvial and lacustrine activity, most of the
sedimentological and faunal record suggests that moist phases were relatively short-lived
and of limited intensity. However, fossil silts caused by ponding of river waters in the dune
field occur in the Kuiseb Gorge, the Sossus Vlei, and the Tsondab Valley, 31 but no coherent
picture emerges as yet from the few dates that are available. There are also speleothems ‡
in the Rössing cave of the central Namib that indicate phases of greater hydrological
activity in the late Pleistocene before 25,000 year BP. 32 The last glacial maximum (c. 18,000
year BP) may have been dry. 33 To the east of the Great Western Escarpment is a second
major desert: the interior desert of the Kalahari, 34 a word derived from the Setswana word
* Names of sand dune types are extensive and descriptive. For example, barchan dunes tend to have a parabolic
form.
† Detailed morphometric and sedimentological data on the Namib Desert are provided by N. Lancaster. 28
‡ Speleothems (aka dripstone) are calcium carbonate accumulations in caves (e.g., stalactites, stalagmites).