Mountains – SS1 Geography Lesson Note (First Term)

Mountains are greatly elevated land surfaces resulting from the intense action of internal forces. They have steep slopes and show distinct peaks. Mountains are classified according to their mode of formation. The four major types are:

1. Fold mountains
2. Block mountains
3. Volcanic mountains
4. Residual mountains

Behavioural objectives

By the end of the lesson, students should be able to:

• define a mountain;
• name the four major types of mountains;
• describe the characteristics and mode of formation of each type;
• give examples of each type of mountain;
• state the uses and disadvantages of mountains.

What are fold mountains?

Characteristics of fold mountains

1. They contain old hard rocks with steep sides.
2. They have a wrinkling or folding appearance and show distinct peaks of great heights.
3. They exist in layered form.
4. They are soft and have anticlines and synclines.

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

How are fold mountains formed?

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 synclines.

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

What are block mountains?

Characteristics of block mountains

1. Block mountains are made up of old hard rocks with flat or slightly sloping surfaces.
2. They have steep sides.
3. They are associated with rift valleys.
4. Examples of block mountains include Hunsruck Mountain, Vosges Mountain and the Black Forest of the Rhineland.
5. An example of a rift valley is the East African rift valley system, which is about 4,800 km long.

How are block mountains formed?

Block mountains are formed when the earth cracks due to faulting. Faulting may result from tensional forces or compressional forces. Tensional forces tend to pull the earth’s crust apart and result in a normal fault, while compressional forces shorten the crust to produce a reverse or thrust fault.

If a block of rock between two normal faults rises, or the land on either side of the block subsides, a block mountain or horst is formed. At times, a block in between two faults may subside so that a rift valley or graben is formed. The slopes and height of block mountains are modified by agents of denudation.

What are volcanic mountains?

A volcano explodes with smoke and hot red flowing lava.

Characteristics of volcanic mountains

1. Volcanic mountains are made up of lava.
2. They have irregular sides with conical shapes.
3. The materials that make them up include ash, volcanic bombs and cinders, which are arranged in layers.
4. Examples include Mt. Fuji (Japan), Mt. Mayon (Philippines), and Mts Kilimanjaro, Kenya, Elgon, Ruwenzori and Cameroon (all in Africa).

How are volcanic mountains formed?

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.

These materials fall around the vent in successive layers, building up an extensive volcanic cone. A volcanic mountain is also called a mountain of accumulation.

What are residual mountains?

Characteristics of residual mountains

1. Residual mountains are formed from the remains of already existing mountains.
2. They have irregular surfaces with steep sides.
3. They occur in varying heights and sizes and are caused by agents of denudation.
4. Examples include Mt Monadnock (U.S.A), the Highlands of Scotland, the Highlands of Scandinavia and the Deccan Plateau.

How are residual mountains formed?

Residual mountains are formed from already existing mountains which are lowered or reduced by agents of denudation such as running water, ice and wind. They 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. These remaining parts are called residual mountains, also called mountains of denudation.

What are the uses of mountains?

1. Sources of minerals
2. Formation of rainfall
3. For transhumance
4. Climatic barriers
5. For defence
6. As tourist centres
7. Construction of hydro-electric power
8. As wind-breaks

What are the disadvantages of mountains?

1. Mountains cause barriers to communication.
2. They prevent human habitation.
3. They promote soil erosion.
4. They occupy good land that could have been used for other useful things.
5. Mountain soil is poor in nutrients.

Evaluation

1. Define a mountain.
2. Name the four major types of mountains.
3. Explain how fold mountains are formed.
4. What is the difference between a horst and a graben?
5. Give four uses of mountains.

Assignment

1. Describe the mode of formation of volcanic mountains and give two examples.
2. List three disadvantages of mountains.