Geoscience Reference
In-Depth Information
were due to the presence of earlier faults in the bedrock that moved again during the
later episode, often in the opposite direction.
As soon as the Weald uplift produced high ground, patterns of local river and
stream drainage started to develop, particularly by cutting valleys back from the coast-
lines into the areas of newly formed high ground to produce a generally radial drainage
pattern. The variable resistance of the bedrock to erosion has strongly influenced the
landscape, creating some of the most spectacular scenic features. The other variable in
this valley erosion was the climate, which influenced the amount of rainfall and the
occurrence of the floods that do much of the work in eroding and removing material
from the landscape. Valley slopes are also critically affected by climate changes, which
determine vegetational cover and, during cold episodes of the Ice Age, the permeabil-
ity and stability of the bedrock. It seems likely that the dry valleys visible today on the
South Downs formed during cold phases when the ground was frozen.
Sea-level change, particularly in response to vigorous changes of climate during
the Ice Age, is the other major factor that has influenced the scenery. It is now under-
stood that, about 20,000 years ago, sea level was some 120 m lower than at present.
Since then it has invaded the land, rising to within 10 m of its present level approxim-
ately 6,000 years ago, although minor fluctuations more recently have been important
in local coastal development, both natural and man-made. Over the previous 2.6 milli-
on years of Pleistocene time, sea-level changes between about 100 m below and 10 m
above present sea level have occurred many times, at approximately regular intervals
(see discussion of this under Area 7).
Figure 136 shows the present coastline of Area 6, and the present land up to an
elevation of 20 m above sea level as the 'coastal flooding zone'. Sea level may not
have reached as high as this 20 m level, but river and stream systems of the past would
certainly have been influenced by invading seas, causing ponding-up of their flow to
about this level at some earlier times. The whole of the South Coastal Plain (Landscape
E
) and the Pevensey Levels (Landscape
F
) are clearly within this coastal flood zone,
and it is also interesting to note how the 'water gaps' of the rivers Arun, Adur, Ouse
and Cuckmere allow the flooding zone to extend inland, to invade Landscapes
B
and
C
and even parts of Landscape
A
. One conclusion is that anywhere within this zone
will have been influenced by coastal advance and retreat processes over the past few
million years of the Ice Age. Another conclusion is that anywhere within this zone is
liable to be influenced by future rise of sea level.
