Types of Mountains

Mountains make up a large proportion of the earth's surface. Based on their mode of formation, four main types of mountains can be distinguished.

1.     Fold mountains. These mountains are by far the most widespread and also the most important. They are caused by large-scale earth's movements, when stresses may be due to the increased load of the underlying rocks, flow movements in the mantle, magnetic intrusions into the crust, or the expansion or contraction of some part of the earth. When such stresses are initiated, the rocks are subjected to compressive forces that produce wrinkling or folding along the lines of weakness. Folding effectively shortens the earth's crust, creating from the original level surface a series of waves. The upfolded waves are called anticlines and the troughs or downfolds are synclines.
The formation of up and down folds closely resembles that of the wrinkles of a table cloth when it is pushed from either one or both sides of the table.
The relief of a part of Ghana provides good examples of folding and faulting in West Africa. Earth movements have been so intense in the Akwapim-Togo mountains and the adjacent areas (including the Togolese part of the mountains) that the earth's crust has been overfolded and thrusted, with both shear and thrust-faults. This has led to the presence of very sharp mountain edges, the ridges and valleys show folds and faults. The weakness and instability caused by these movements in the crust were responsible for earthquake shocks and tremors in Accra in 1906, 1930, 1933 and 1939.
In the great fold mountains of the world such as the Himalayas, Rockies, Andies and Alps, due to the complexity of the compressional forces, the folds developed much more complicated forms. When the crest of a fold is pushed too far, an overfold is formed. If it is pushed further, it becomes a recumbent fold. In extreme cases, fractures may occur in the crust, so that the upper part of the recumbent fold slides forward over the lower part along a thrust plane, forming an overthrust fold. The overriding portion of the thrust fold is termed a nappe. Since the rock strata have been elevated to great heights, sometimes measurable in kilometres, fold mountains may be called mountains of elevation. The fold mountains are also closely associated with volcanic activity. They contain many active volcanoes especially in the Circum-Pacific fold mountain system. They also contain rich mineral resources such as tin, copper, gold and petroleum.

2.     Block mountains. Folding occurs when the earth's crust bends, but faulting takes place when the crust bends, but faulting takes place when the crust cracks or features with a displacement on either side of the crack or fracture. The lower Gongola valley and the Benue trough of Nigeria show some evidence of faulting. In Guinea, the Fouta Djallon rises on the west and north by a series of fault-steps, while the Tarkwa Hill region between Konongo and Tarkwa (Ghana) contain faults which have been responsible for the presence of transverse valleys and a number of gaps.
Faulting may be of two sorts - one caused by tension and one caused by compression in the crustal layers. Tensional forces lengthen the crust while compressional forces Shorten it. A fault caused by tension is known as a normal fault while one which is caused by compression is termed a reserve, or thrust fault.
A normal fault occurs when one block moves or slips down relative to the other, but in a reserve fault, one block slips underneath the other block.
Earth movements generate tensional forces that tend to pull the crust apart, and faults are developed. If the block enclosed by the faults remains as it is or rises, and the land on either side subsides, the upstanding block becomes the horst or block mountains. The faulted edges are very steep, with scarp slopes, and the summit is almost level, e.g. the Hunstruck Mountains, the Vosages and black forest of the Rhineland. The western arm of the rift valley of East Africa, on the Zaire-Uganda border, contains an uplifted