Fold (geology)

Folding is one of the endogenetic processes.

When two forces act towards each other from opposite sides, the rock layers will be bent into folds. The process by which folds are formed due to compressional force is known as folding.

There are large-scale and small-scale folds. Large-scale folds are found mainly along destructive plate boundaries.

Structure of the fold

The upfold is called an anticline. The downfold is called the syncline.

The imaginary line joining the highest points along the upfold is called the crest line.

The flanks of the fold are known as the limbs.

The central line from which the rock strata dip away in opposing directions is called the axis of fold.

According to the degree of folding of the layers, folds can be classified into five main types.

• symmetrical fold: two limbs are of equal steepness
• Assymmetrical fold: one limb is steeper than the other
• overfold: one limb is pushed over the other
• Recumbent fold: two limbs are nearly parallel
• Overthrust fold: compressional force is so great that the rock strata are broken and slide over the other.

Landforms formed by folding

Large-scale folding will develop parallel ranges of round-top mountains along destructive plate boundaries. These mountains are known as fold mountains.

Examples of fold mountain ranges:

• Himalaya
• Alps
• Andes
• Rocky Mountains

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