Chapter 12
Desert surfaces: pavements, patterned ground,
varnishes and crusts
1. Introduction
The surface materials of arid zones and their existence at shallow depths are subjected
to numerous processes that act together or separately, depending upon lithology, climate,
relief, and so forth. The result of this activity leads to the generation of desert pavements,
patterned ground, varnishes, and crusts.
2. Desert pavements
2.1. General characteristics
Desert pavements consist of rounded or angular rocky fragments within a matrix of finer
sand, silt, and clay-sized material (Mabbutt, 1965b, 1977). They develop not only on low
relief surfaces such as alluvial fans, terraces and pediments, but also on slopes. They can
occur in other morphoclimatic settings, but it is in arid zones where they reach their
maximum expression, going on to occupy significant areas.
Locally they are given many names: gibber in Australia, sai" in central Asia and
hamada, reg, and serir in the Sahara, the Near East, and India. Hamadas are tabular relief
structures, pedimentation, or glaciplanation surfaces of negligible slope. The surface can
be devoid of fragments, in which case it is denoted a rocky hamada, or it can be covered in
angular blocks (boulder hamada) (Figure 12.1) that have not suffered any transport. In
some cases the blocks have suffered intense weathering in which a continuous flaking has
rounded the fragments (Evenari et al., 1971a,b). Reg or serir can develop, however, on
alluvial surfaces with a slight or negligible slope and in these cases the stones are rounded
as a consequence of their transport (Figure 12.2). At the present time many reg or serir
appear as relict surfaces that are remote or left away from the current drainage network.
A well-developed pavement consists of a stable surface, but when altered by
anthropomorphic action (e.g. all-terrain vehicle traffic in the SW USA and Saudi Arabia;
Webb and Wilshire, 1983) water and aeolian erosion can lead to substantial modification.
Similarly, the famous Nazca Trails, southem Peru (Figure 12.3), which date from
thousands of years ago, are desert pavements partially mobilised during their construction.
Elsewhere, the pavement's constituent stones can be prehistoric artefacts, and other times
the rocks are painted or carved (petroglyphs) (Brakenridge and Shuster, 1986),
circumstances by which it is possible to gain information about the relative age of desert
pavements.
Desert surfaces: pavements, patterned ground,
varnishes and crusts
1. Introduction
The surface materials of arid zones and their existence at shallow depths are subjected
to numerous processes that act together or separately, depending upon lithology, climate,
relief, and so forth. The result of this activity leads to the generation of desert pavements,
patterned ground, varnishes, and crusts.
2. Desert pavements
2.1. General characteristics
Desert pavements consist of rounded or angular rocky fragments within a matrix of finer
sand, silt, and clay-sized material (Mabbutt, 1965b, 1977). They develop not only on low
relief surfaces such as alluvial fans, terraces and pediments, but also on slopes. They can
occur in other morphoclimatic settings, but it is in arid zones where they reach their
maximum expression, going on to occupy significant areas.
Locally they are given many names: gibber in Australia, sai" in central Asia and
hamada, reg, and serir in the Sahara, the Near East, and India. Hamadas are tabular relief
structures, pedimentation, or glaciplanation surfaces of negligible slope. The surface can
be devoid of fragments, in which case it is denoted a rocky hamada, or it can be covered in
angular blocks (boulder hamada) (Figure 12.1) that have not suffered any transport. In
some cases the blocks have suffered intense weathering in which a continuous flaking has
rounded the fragments (Evenari et al., 1971a,b). Reg or serir can develop, however, on
alluvial surfaces with a slight or negligible slope and in these cases the stones are rounded
as a consequence of their transport (Figure 12.2). At the present time many reg or serir
appear as relict surfaces that are remote or left away from the current drainage network.
A well-developed pavement consists of a stable surface, but when altered by
anthropomorphic action (e.g. all-terrain vehicle traffic in the SW USA and Saudi Arabia;
Webb and Wilshire, 1983) water and aeolian erosion can lead to substantial modification.
Similarly, the famous Nazca Trails, southem Peru (Figure 12.3), which date from
thousands of years ago, are desert pavements partially mobilised during their construction.
Elsewhere, the pavement's constituent stones can be prehistoric artefacts, and other times
the rocks are painted or carved (petroglyphs) (Brakenridge and Shuster, 1986),
circumstances by which it is possible to gain information about the relative age of desert
pavements.