Geology Reference
In-Depth Information
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Figure 14.11
Flandrian transgression in north-western Europe. Notice the rapid rise between about 9,000 and
7,000 years ago; this amounted to about 20 m, an average increase of 1 m per century.
Source:
Adapted from Mörner (1980)
The lowering of the sea was substantial. During the
Riss glaciation, a lowering of 137-59 m is estimated,
while during the last glaciation (the Würm) a figure of
105-23 m is likely. A fall of 100 m or thereabouts during
the last glaciation was enough to link several islands with
nearby mainland: Britain to mainland Europe, Ireland to
Britain, New Guinea to Australia, and Japan to China.
It would have also led to the floors of the Red Sea and
the Persian Gulf becoming dry land.
Of particular interest to geomorphologists is the rise
of sea level following the melting of the ice, which started
around 12,000 years ago. This rise is known as the
Holocene or
Flandrian transgression
. It was very rapid
at first, up to about 7,000 years ago, and then tailed
off (Figure 14.11). Steps on coastal shelves suggest that
the rapid transgression involved stillstands, or even small
regressions, superimposed on an overall rise. The spread
of sea over land during this transgression would have
been swift. In the Persian Gulf regions, an advance rate
of 100-20mayearislikely and even in Devon and
Cornwall, England, the coastline would have retreated
at about8mayear.
SUMMARY
Fluvial system response to environmental change is usu-
ally complex. Large changes occur in the wake of shifts
from glacial to interglacial climates. Changes in historical
times, as deciphered from sequences of alluvial deposits
sequences, suggest that the response of the fluvial sys-
tem to climatic change may vary place to place, partly
owing to regional variations of climate and partly to
thresholds within the fluvial system itself. In places where
human occupancy has affected geomorphic processes, as
in the Mediterranean valleys, it is difficult to disentangle
climatic effects from anthropogenic effects. Many aeo-
lian landforms are inherited from the height of the last
ice age, some 18,000 years ago, when the planet was drier
and windier. The geological record registers colder times
