South American deserts - Climatic Change in Deserts - page 408

Figure 21.1. Major physiographic regions of South America.

and the plateaux, which include the vast forested alluvial plains of the Amazon,
Orinoco and Paran ´ arivers( Figure 21.1 ). The Andes are the dominant feature in the
South American landscape, with an average elevation of 4,000 m, rising to 6,962 m
(Mount Aconcagua), and are high enough to sustain perennial snow and ice for much
of their length. They consist of a single set of mountain ridges in the south, two
sets of ridges separated by broad upland basins in the centre (Helmens and van der
Hammen, 1994 ) and three sets of ridges in the far north, where the Andes change
direction and trend from west to east, parallel to the Caribbean Sea. The hyper-arid
Atacama Desert lies in the western rain shadow of the central Andes between latitudes
15 S. Its origin is bound up with the tectonic evolution of the Andes. The

Patagonian semi-desert lies east of the southern Andes in the rain shadow of the
westerlies and is a land of wind and dust, although far less arid than the Atacama.
In its absence of trees, it is reminiscent of the arid Nullarbor ('treeless') Plain of
southern Australia, but it is a great deal windier. The Bolivian Altiplano ('High
Plain') is an elevated arid plateau, flanked by high mountain ranges which rise to
more than 6,000 m, with scattered freshwater and salt lakes, or salars ,aswellasthe
remains of much larger lakes (Sylvestre et al., 1999 ; Sylvestre, 2009 ). It is 1,200 km
long from north to south, 300 km wide from east to west and has an average elevation
of about 3,800 m. It lies between the Western and Eastern Cordilleras in the central
Andes.

° S and 30 °