This unit deals
with the formation of features on the earth's surface. The forces, which produce
physical features, are of two types: internal forces and external forces.
Earth movements e.g. folding, faulting, down warping and up warping, volcanicity
and earthquakes have formed features on the earth's surface.
These are movements which are lateral and vertical, they exert great forces of
tension and compression and although they usually take place very slowly they
eventually produce very impressive features like the rift valley escarpment in
FOLDING AND FAULTING
The forces which produce physical features are of two types i.e. internal
forces and external forces.
Internal forces are lateral and vertical
forces within the earth surface leading to earthquakes, vulcanicity, faulting
External forces operate on the earth’s surface leading
to denudation , glaciation river action and wave action.
have led to the formation of features on the earth's surface of East Africa. Major
features such as mountains plateaus, plains, rift valley and others.
The movements are lateral and vertical and exert great forces of tension and compression,
though take place very slowly they eventually produce impressive features.
This subtopic describes the two processes of folding and faulting ,the features
produced and their importance to human activities.
movements cause sedimentary rocks to be displaced i.e. to be pushed out of the
horizontal plane so that the rocks are tilted or inclined.
movements can also cause folding and faulting of the sedimentary rocks. Folding
results from lateral forces (compressional forces).
Lateral forces of compression
cause folding while either lateral or vertical forces of tension or compression
process of folding
nature of folds
The layers of rock which bend up form an up fold or anticline.
Those which bend down form a down fold or syncline. The sides
of a fold are called the limbs .if compression continues the
simple folds are changed first to a symmetrical folds, then into
over folds and finally into over thrust folds.
centre line of the up fold or down fold is called the axis. In simple folding,
the folding process is never intense.
The process gives rise to mountains
and valleys. The anticlines became the mountains and synclines the valleys. The
sides of a fold are called the limbs.
limb steeper than the other.
over fold or recumbent fold
over fold is formed when one limb is pushed over the other limb. This process
occurs when the compressional forces from one side are greater than from the other
over thrust fold
pressure is very great a fracture occurs in the fold and one limb is pushed forward
over the other limb forming an overthrust fold.
In east Africa folding
did not cause high mountains as the crust consists of hard basement rocks which
fractures when folded.
However minor folds are found at the boarder between
Uganda and Tanzania/Karagwe where layers of mudstone were compressed into a U
There is also some folding in the layers of limestone on the
East Africa coast. Folding is evident in Bukaba region in the North of Tanzania.
results of folding(features formed)
Fold Mountains can be found in the North West Africa i.e. Atlas Mountains and
in South Africa i.e. Cape Ranges.
of Fold Mountains on human activities
Mountains often receive heavy rain or heavy snow falls which may give rise to
important rivers. For example the Alps in Europe.
process of folding was not significant in East Africa and therefore didn't create
any significant land forms.