Folding

What is folding?
Folding refers to the bending of the earth's crust. The rocks in the earth's crust move and bend because several forces are acting upon them.


The main types of forces involved in the movement of the earth's crust are tension, compression and shearing forces.
Compressional forces push btogether, tensional forces pull apart and shear forces  slide past each other.

Compression is the main force responsible for folding. The diagram below shows how these forces affect the earth's crust.

Notice how compression causes the rock to bend? This is called folding. Click "read more" below to see more about folding.



Parts of a fold
The upfold is called an anticline. The downfold is called a syncline and the sides of the fold are called limbs.

The axial plane is an imaginary line that runs down the centre of the syncline or the anticline. Imagine that you could place a thin sheet of paper down the centre of the anticline or the syncline, that paper would be the axial plane.

Types of Folds
There are several types of folds. This is based on how much the rock has folded. Four types of old are shown below.

Symmetrical folds are very simple. As you go more left on the diagram the land becomes more folded in Asymmetrical, overturned and recumbent folds.