Geoscience Reference
In-Depth Information
more and more smooth. Acting against these flattening processes are periodic move-
ments of the ground surface caused by forces within the Earth, producing new moun-
tains and hills, and so creating new landscapes (Fig. 5).
Continuing research into the processes operating within the Earth shows that
movements of the Earth's crust are taking place continuously, even though the rates in-
volved are generally too slow to be noticeable. The discovery that the Earth's surface
consists of a large number of tectonic plates in continuous relative movement was one
of the major breakthroughs in the earth sciences, and has fundamentally changed our
understanding of the planet. More on this topic will be considered in Chapter 3, but at
this point it is important to realise just how slow the rates of movement are: at most a
few centimetres per year on average (often compared to the rate at which fingernails
grow). Occasionally, movements of centimetres or metres occur within seconds along
faults during earthquakes, but the average rate of movement is still rather slow. Most of
us living in stable areas are totally unconscious of any movement at all because we are,
ourselves, moving slowly with the landscape that we live on. Slow though the move-
ments may be in a particular landscape, so also are the rates of surface modification,
and the balance between the two is a delicate one. In much of Southern England modi-
fication by surface processes is dominant, but this has not always been the case.
FIG
5.
Landscapes are changed by surface modifications (Chapter 2) and solid earth
movements (Chapter 3).
Our next chapter deals with the timescales represented in the landscapes of South-
ern England and the processes that have been modifying them. Chapter 3 deals with the
movements from below - from within the Earth's crust - that are ultimately creating
major landscape patterns.
