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wetter than today and the regional and local water-tables were close to the surface
(Hoelzmann et al.,
2004
).
The focus of this chapter is on what such lakes can tell us about past climatic
changes in areas now arid. We attempt to show how desert lakes have been used to
reconstruct past hydrologic and climatic changes, noting instances where purely local
factors may outweigh or obscure regional climatic signals. Because this chapter is
primarily designed to illustrate some general principles with selected examples and
does not aim to be an encyclopaedic compendium of desert lake histories, we will
confine our attention to a few specific case studies from different arid and semi-arid
areas in Africa, the Near East, Asia and Australia. The desert lakes of the Americas,
the Kenya Rift and north-west India are discussed in some detail in the next chapter
(
Chapter 12
) when we come to the long-debated issue of pluvial lakes and their
relationship to glacial events.
11.2 Use of lakes to reconstruct past hydrologic changes in deserts
There is an abundant literature dealing with the reconstruction of environmental
(including climatic) changes using lake sediments (Haworth and Lund,
1984
; Timms,
1992
; Last and Smol,
2001a
; Last and Smol,
2001b
;Smoletal.,
2001a
;Smoletal.,
2001b
). The vast majority of these studies concern lakes in humid temperate and sub-
arctic latitudes, while studies of desert lakes are far less common (Gilbert,
1890
; Gasse,
1975
; Degens and Kurtman,
1978
; Wasson et al.,
1984
; Tiercelin,
1986
; Williams,
2000
; Yang and Williams,
2003
; Burrough et al.,
2009a
; Burrough et al.,
2009b
;
Currey and Sack,
2009a
; Currey and Sack,
2009b
; Sylvestre,
2009
;Yangetal.,
2010
).
In contrast to many big rivers that flow into or through deserts and are often millions of
years old, desert lakes tend to be ephemeral features of the landscape with a lifespan
in thousands rather than millions of years. They occupy depressions in the landscape
that eventually become filled with sediment. Currey and Sack (
2009a
;
2009b
) provide
a comprehensive overview of sediment types and depositional processes in desert
lakes. Desert lakes may also form as a result of the damming of a drainage channel
by a landslide, dune, tufa deposit or a lava flow. Once the lake reaches overflow level,
a spillway will be cut into the dam and the lake will soon be drained as the river
re-establishes itself. Exceptions to the generalisation that lakes are ephemeral are the
deep fault-controlled lake basins of the African Rift Valley, which originated as a
result of Miocene and Pliocene tectonic events (Gasse,
1990
; Talbot and Williams,
2009
), but many of these late Cenozoic lakes dried out well before the onset of the
Quaternary period 2.6 million years ago, and much of the earlier evidence has long
been faulted, tilted, buried or eroded (Tiercelin,
1981
; Tiercelin,
1986
; Williams et al.,
1986
;Cohenetal.,
1997
; Talbot and Williams,
2009
).
Some of the most detailed desert lake records we possess come from the Ethiopian
and Afar rift valleys, but here again it is often hard to distinguish between changes
