FOLDING AND FAULTING

Introduction:

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 and folding.

External forces operate on the earth’s surface leading to denudation , glaciation river action and wave action.

Earth movements 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.

Brief description:

This subtopic describes the two processes of folding and faulting ,the features produced and their importance to human activities.

Lateral forces

Earth 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.

Earth 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 cause faulting.

The process of folding

The 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.

A simple fold

The 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.

A symmetrical fold

One limb steeper than the other.

An over fold or recumbent fold

An 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 side.

An over thrust fold

When 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 shape.

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.

The results of folding(features formed)