MOUNTAINS: Fold Mountains, Block, Volcanic & Residual Mountain

Mountains are great elevated land surfaces resulting from intense action of internal forces. They have steep slopes and show distinct peaks. Mountains are classified according to their mode of formation, resulting in four major types of mountains. These are (i) Fold mountain (ii) Block Mountain (iii) Volcanic Mountain (iv) Residual mountain

(a) Fold Mountains

Characteristics: They contain old hard rocks with steep sides. They have wrinkling or folding appearance and show distinct peaks of great heights. Fold Mountains exist in layered form. They are soft, and have anticlines and synclines.

Folding shortens the earth’s crust. They form most wide spread type of Mountains and are noted for active volcanoes. They form the highest Mountain ranges. Examples of Fold Mountains include Himalayas, Rockies, Andes, Alps and Atlas Mountains.

Mode of formation: They are formed by large-scale horizontal earth movement as a result of stress and compressional forces which cause expansion or contraction of some parts of the earth. Such stresses therefore subject the rocks to compressional forces.

The compressional forces produce wrinkling or folding of the earth. The up folds of the wrinkles are anticlines while the down folds are called syncline.

A fold may be simple, but where the compressional forces are complex, it results in asymmetrical folding. When pushed further, it forms an over-fold. An over-fold later forms a recumbent fold. In some cases, faults or cracks result in extreme folding to form over thrust fold.

Evaluation Questions

What is a mountain?
State the types of mountains.

(b) Block Mountains

Characteristics: Block Mountains are made up of old hard rocks with flat or slightly sloping surfaces. They have steep sides. They are associated with rift valleys. Examples of Block Mountains include Hunsruck Mountain, Voges Mountain and the Black Forest of the Rhine land. Example of rift valley is the East African rift valley system which is about 4.800km.

Mode of formation: Block Mountains are formed when the earth cracks due to faulting. Faulting may result from tensional forces or compressional forces. Tensional forces are those that tend to pull the earth’s crust apart and they result in a normal fault while the Compressional forces are those that shorten the crust to produce a reverse or thrust fault. Therefore, if a block of rock between two normal faults rises or the land on either sides of the block subsides, a Block mountain or Horst is formed. At times, a block in between two faults may subside so that rift valley or graben is formed. The slopes and height of Block Mountains are modified by agents of denudation.

Evaluation Questions:

Mention any three types of mountain.
Block mountain is also called……
Rift valley is associated with …….Mountain?

(c) Volcanic Mountain

Characteristics: Volcanic Mountains are made up of lava. They have irregular sides with conical shape. Materials that make up volcanic mountains include ash, volcanic bombs, and cinders which are arranged in layers. Examples include Mt. Fuji (Japan), Mt. Mayon (Philippines), Mt Kilimanjaro, Kenya, Elgon, Ruwenzori and Cameroon (all in Africa).

Mode of formation: Volcanic Mountains are formed from volcanoes which are built from materials (molten magma) ejected through fissures or vents in the earth’s crust. The materials also include molten lava, volcanic bombs, cinders, ash, dust and liquid mud. They fall around the vent in successive layers, building up an extensive volcanic cone. Volcanic mountains are also called mountain of accumulation.

(d) Residual Mountain

Characteristic: Residual Mountains are formed from the remains of already existing mountains. They have irregular surfaces with steep sides. They occur in varying heights and sizes and are caused by agents of denudation. Examples include Mt Manodnock (U.S.A), Highlands of Scotland, Highlands of Scandinavia and Decon Plateau.

Mode of formation

Residual Mountains are formed from already existing mountains which are lowered or reduced by agents of denudation such as running water, ice and wind. Residual mountains are therefore, the remains of the existing mountains. Some hard and very resistant parts of the existing mountains remain after the lowering of the upper part. This remaining part is called residual mountain which is also called mountain of denudation.

Importance or uses of mountains

Sources of minerals. 2. Formation of rainfall.
For transhumance. 4. Climatic barriers.
For defence. 6. As tourist centers.
Construction of Hydro-Electric Power. 8. As wind-breaks.

Disadvantages of Mountains

Barriers to Communication.
Prevent Human Habitation.
Mountains Promote Soil Erosion.
Mountains Occupy good land that could have been used for other useful things.
Mountains soil is poor in nutrients.