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:
- Fold mountains.
- Block mountains.
- Volcanic mountains.
- Residual mountains.
- FOLD MOUNTAINS
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, have anticlines and synclines. Folding shortens the earth’s crust. They form the 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.
Fold Mountains 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 crust 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 recumbent fold. In some cases, faults or cracks result in extreme folding to form over thrust fold.
- BLOCK MOUNTAINS
Block Mountains are made up of old hard rocks with flat or slightly sloping surfaces. They have steep sides. They have steep sides. They are associated with rift valleys. It is a block between two faults. It has fairly steep, straight edges. Block Mountains are usually very high. Examples of Block Mountains include Hunsruck Mountain; Voges Mountain and the Black forest of the Rhine land.
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 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.
Characteristics of Rift Valley
- There is a trough between two parallel faults.
- It has steep – sided walls.
- It also has flat bud, at times, irregular floor.
- Rift valleys are usually very deep.
Examples are Rhine valley, Dead sea, Jordan valley, Great East African Rift valley which is about 4,800km.
It should be noted that land forms produced by faulting are Rift valley and Block Mountain.
Rift valley occurs when there are tensional and compressional forces operating. Two parallel faults occur and there will be gravitational force leading to the sinking of the land between the faults. The side blocks will be uplifted. The rift valley will be steeped or steep-sided where there are senses of parallel faults.
- VOLCANIC MOUNTAINS
Volcanic Mountains are made up of lava. They are irregular sides with conical shape. Materials that make up volcanic mountains include ash, volcanic bombs, and cinders etc. which are arranged in layers. Examples include Mt. Fuji (Japan), Mt. Mayon (Philippines), Mt. Kilimanjaro, Kenya, Elgon, Ruwenzori and Cameroun (all in Africa).
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 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 mountains of accumulation.
- RESIDUAL MOUNTAINS
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.
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 already existing high mountains. Some hard, and the very resistant parts of the existing mountains remain after the lowering of the upper part. This remaining part is called residual mountains which are also called mountains of denudation.
IMPORTANCE OF MOUNTAINS
- Rocks from highlands are used for construction, e.g. rocks of the Shai Hill were used to construct the Tema Habour in Ghana.
- Mountains of the world do serve as tourist attractions or holiday resorts such as the Olumo rock, Idanre hills and the Swiss Alps.
- The presence of mountains in some parts of the world makes possible the practice of transhumance on mountain pasture as can be seen in Switzerland and Australia.
- Mountains do serve as sources of rivers in the world e.g. River Niger from the Guinea Highlands in West Africa, the Blue and White Nile from East Africa highlands.
- Mountains are usually source of minerals. The common minerals from these highlands include tin and columbite (Jos Plateau), coal (Udi Hills), gold from Rockies.
- Mountains modify climate thereby making it ideal for human settlement. Such mountains include Kenya Mountain, Mountain Elgon, Kilimanjaro Mountain and Jos Plateau (Nigeria).
- Mountains do present natural boundaries as clearly shown by Cameroun Mountain between Nigeria and Cameroun.
- Mountains of the world serve as haven against invaders especially in the olden days when slavery was the order of the day.
- Mountains do encourage lumbering along their slopes as clearly shown in Scandinavia for timber, paper and pulp and matched industries.
- Mountains do encourage terrace farming, a system of agriculture practiced in Biu Plateau, Jos Plateau and Udi Hill (Nigeria).
DISADVANTAGES OF MOUNTAINS
- Mountains are barriers to communication as they prevent roads, railway and airports construction.
- High mountains are known to be associated with cold weather which prevents good human and animal habitation.
- Areas close to mountains are usually associated with soil erosion due to the speed of running water down the steep slopes of mountains.
- Mountains at times do occupy good land that should have been used either for farming or settlement.
- Mountainous areas are not good for agriculture as the soils are poor in nutrients and difficult to work on.