The arid zones
239
yardangs, and ergs. The relief features common to these deserts are caused mainly by the
long crustal stability observed in these regions.
The mountain and basin deserts are constituted by long mountainous alignments
separated by depressed areas. This relief in a number of places was shaped during
the Alpine orogeny in the Mesozoic and Cenozoic ages. As a consequence of the
topographical contrast the high zones have suffered a constant denudation and the
resultant materials have lodged in the depressions, in the form of coalescent alluvial fans.
In the distal areas of the alluvial fans the run-off waters are collected in closed
depressions that form ephemeral lakes (Figure 10.9) in which takes place an evaporitic
sedimentation (playa-lake). The contact between mountains and basins commonly is
due to an existing active tectonic front, along which rise the high zones together with
the subsequent subsidence of the deeper parts. Therefore, these are areas of intense
subsidence in which there have accumulated an important amount of sediments during
the Tertiary and Quaternary. On the other hand, in the depressions aeolian activity of
some importance occurs. The deserts of the western United States and those in the
Precordillera and Central Cordillera of the Andes present these characteristics. Similarly,
the deserts of Central Asia have similar features, although they also develop to a major
altitude, for which the climatic contrasts are more marked.
239
yardangs, and ergs. The relief features common to these deserts are caused mainly by the
long crustal stability observed in these regions.
The mountain and basin deserts are constituted by long mountainous alignments
separated by depressed areas. This relief in a number of places was shaped during
the Alpine orogeny in the Mesozoic and Cenozoic ages. As a consequence of the
topographical contrast the high zones have suffered a constant denudation and the
resultant materials have lodged in the depressions, in the form of coalescent alluvial fans.
In the distal areas of the alluvial fans the run-off waters are collected in closed
depressions that form ephemeral lakes (Figure 10.9) in which takes place an evaporitic
sedimentation (playa-lake). The contact between mountains and basins commonly is
due to an existing active tectonic front, along which rise the high zones together with
the subsequent subsidence of the deeper parts. Therefore, these are areas of intense
subsidence in which there have accumulated an important amount of sediments during
the Tertiary and Quaternary. On the other hand, in the depressions aeolian activity of
some importance occurs. The deserts of the western United States and those in the
Precordillera and Central Cordillera of the Andes present these characteristics. Similarly,
the deserts of Central Asia have similar features, although they also develop to a major
altitude, for which the climatic contrasts are more marked.