Deserts of the World - Design with the Desert: Conservation and Sustainable Development - page 22

salars; nitrates and iodates are distinctively concentrated, especially on the eastern side of
the coastal cordillera 105 ; and the salt domes occur in the precordillera of the Norte Grande.
The evolution of the Peru-Chile deserts is still a matter of considerable speculation, but
a few observations are in order. First, and contrary to common opinion, it seems likely that
there has not been enormous Andean uplift during the Quaternary. One study, based on
K-Ar dating of ignimbrite flows, suggested that in the high Andes of the Norte Chico, the
pediplain topography * has suffered remarkably little erosion since the Upper Miocene and
that over the past 9-12 million years there has been entrenchment only in the canyons of
c. 328-650 ft. 106
Second, the Atacama Desert is probably very old. It is generally believed that it
has been arid since at least the late Eocene, with hyperaridity since the middle to late
Miocene. 107 The uplift of the Central Andes cordillera during the Oligocene and early
Miocene was a critical palaeoclimatic factor, providing a rain-shadow effect and also
stabilizing the southeastern Pacific anticyclone. However, also of great significance
(and analogous to the situation in the Namib) was the development 15-13 million year
BP of cold Antarctic bottom waters and the cold Humboldt current as a result of the for-
mation of the Antarctic ice sheet.
Third, it is a widely held view that much of the region is a “core desert,” where climatic
change has been quite limited during the Quaternary. Certainly much of the Atacama
gives this impression. Although there is some evidence of glaciation in the high Andes
of the desert during the Quaternary, it was very local and only on the highest mountains.
Morainic deposits showed that short glaciers extended to c. 13,800 ft. Morainic deposits
and associated features have been identified in the northern Atacama, east of the Salar de
Atacama. 108 Farther south, in the Norte Chico, glacial features suggest three or four glacial
“periods,” although their ages are uncertain. 109
Detailed research leaves no doubt that there has been a series of roughly synchronous
glacier fluctuations of similar magnitude in the Andes during the late Pleistocene and
that these events were preceded by glaciations of similar magnitude during the past 3.5
million year BP. 110 Clapperton 110 recognized significant glacial episodes in the Holocene
(c. 16,000-10,000 year BP), the last glaciation (c. 18,000-16,000 year BP), the penultimate gla-
ciation (c. 170,000-140,000 year BP), the prepenultimate glaciations (<1.9 million year BP),
and the pre-Pleistocene glaciations (1.9-5 million year BP). The glacial episodes undoubt-
edly reflect climatic changes. In the Atacama region, the glacial features were minor, but
the impact of the climatic changes on the evolution of landforms is not yet clear, except in
so far as there is evidence of fluctuations in lake levels in the salars.
Evidence of precipitation changes is provided by lake basins in the Altiplano. Hastenrath
and Kutzbach, 111 for example, have shown that in the late Pleistocene (before 28,000 year
BP and from 12,500 to 11,000 year BP) lakes in the Peruvian-Bolivian altiplano were four
to six times more extensive than today and that this implies rainfall increases of around
50%-75%. By contrast, in the mid-Holocene (c. 7700-3650 year BP), Lake Titicaca was at a
very low level. 112
Along the perennial river valleys and the coast, there is also evidence of Quaternary
evolution in the form of marine and fluvial terraces and their associated deposits. Because
the number of these surfaces and deposits varies from sector to sector along the coast, it
seems probable that the sequences may reflect differential tectonic movements as well as
fluctuating sea levels. As a result, clear generalizations are difficult, but it seems likely that
the highest major surface of erosion-aggradation is at least Pliocene in age and possibly
* Pediplain topography refers to coalesced pediments or slopes overlying bedrock created by scarp recession.