Major Landforms of the Earth: 6th Social Science

Question: Distinguish – (i) Tectonic and gradational forces, (ii) Erosion and deposition, (iii) Mountain range and mountain system.

Answer: (i) Tectonic and gradational:

Tectonic:

1. Tectonic forces originate from within the earth.
2. It create irregularities on the surface of the earth.
3. Tectonic or the internal force is responsible for the upliftment and subsidence of the earth’s surface.

Gradational:

1. Gradational forces originate from outside the earth.
2. The gradational fores or the external forces continuously wear down and rebuilds the surface of the earth.
3. It modifies the irregularities on the surface of the earth.

(ii) Erosion and deposition:

Erosion: The wearing away of the surface of the earth is called erosion. It causes the lowering of the surface.

Deposition: The rebuilding of the earth’s surface is done by deposition.

(iii) Mountain range and mountain system:

Mountain range: It is system of mountains, hills having peaks and valleys, arranged in line.

Mountain system: It has several mountain ranges, separated by valleys.

Question: Classify mountains on the basis of their origin. Explain each type.

Answer: There are three types of mountain:

1. Fold Mountains:

1. Mountains that have been formed recently are known as young fold mountains.
2. Mountains that were formed much earlier are known as old fold mountains.
3. The fold mountains are formed when the sediments deposited the water bodies are uplifted by the horizontal compressional forces which crumpled the top layer of the sediments into arches and troughs.
4. For eg: Aravallis are old fold mountains and The Himalayas are young fold mountains.

2. Block Mountains:

1. Block mountains are formed by the horizontal tensional forces which causes cracks or faults in the earth’s crust. These faults can break the crust into blocks. When these blocks are raised, block mountains are formed.
2. The block mountains have flat tops and steep slopes.
3. A block mountain can also be formed if the blocks on either side of the fault sink downward.
4. For eg: Black Forest in Germany, the Vosges in France.

3. Volcanic Mountains:

1. Formation of a volcanic mountain is associated with volcanic activities.
2. When a volcano erupts, hot magma is thrown out with great force. This magma accumulates around the vent of the volcano and generally forms a tall cone-shaped mountain known as the volcanic mountain.
3. For eg: Etna and Vesuvius in Italy, Kilimanjaro in Africa.