Geoscience Reference
In-Depth Information
Figure 13.1. Mount Badda, Ethiopia, showing evidence of late Pleistocene glacial
erosion.
that glacial and periglacial processes can exert on river discharge and sediment load
(see
Chapter 10
), as was the case with the Blue Nile (Williams,
2012a
)andtherivers
of south-east Australia (Williams et al.,
2009b
).
13.2 Chronology of glacial-interglacial cycles
Before considering the history of desert glaciations, it is necessary to discuss one other
point of possible confusion. Mountain glaciers by their very nature tend to erode and
destroy the evidence of previous glacial advances. As a result, the early attempts to
develop a chronology of Alpine glaciations in Europe depended almost entirely on the
evidence left by glacial outwash fans, notably the
Deckenschotter
gravel terraces in
the Alpine foreland mapped over many years by Penck and Bruckner (
1909
). Arising
from this monumental work was the erection of the once classic fourfold Alpine
glacial sequence: Gunz, Mindel, Riss and Wurm, with older glaciations identified as
the Donau and Biber glaciations. Later work revealed that the Alpine
Deckenschotter
were in fact polygenic or composite features, each incorporating the sediments and
buried soils of several glacial and interglacial stages (Williams et al.,
1993
). Away from
the Alps, in Europe and North America, a number of regional glacial chronologies
were constructed (Flint,
1971
, pp. 624-625). These were based on the identification
