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 mountains (ii) Block Mountains (iii) Volcanic Mountains and
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(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 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 overfold, an overfold later forms a recumbent fold. In some cause, faults or cracks result in extreme folding to form over thrust fold.
(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 pf 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.
- 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 etc which are arranged in layers. Examples include Mt. Fuji (Japan), Mt. Mayon (Philippines), Mts 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 material also includes 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 Mountain 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 reduces by agents of denudation such as running water, ice and wind. Residual mountains are therefore, the remains of the existing mountains. Some hard and the very resistant parts of the existing mountains remain after the lowering of the upper part. This remaining parts is called residual mountains which are also called mountains 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
- It causes barrier to communication
- It prevents human habitation
- Mountains promote soil erosion
- Mountains occupy good land that could have been used for other useful things
- Mountain soil is poor in nutrients.
GENERAL EVALUATION QUESTIONS:
- Volcanic and residual mountains are also called……… and………….
- Mention two examples of a volcanic mountain.
- Give four importance of mountains to man.
- What is a highland?
- Give an example of a highland.
- The unfolds of the wrinkles produced in Fold Mountain is known as
(a) synclines (b) anticlines (c) push ups (d) push downs
- Which of these is not a fold mountain (a) atlas mountain (b) Himalayas
(c) mountain Kenya (d) alps
- Which of these mountains is produced by faulting (a) fold mountain (b) residual mountain (c) block mountain (d) volcanic mountain
- Another name for “mountain of accumulation” is (a) residual mountain (b) fold mountain (c) volcanic mountain (d) block mountain
- Mountain Manodnock in USA is an example of (a) fold mountain (b) block mountain (c) volcanic mountain (d) residual mountain
- With diagram, explain the formation of any one type of mountain.