Landforms of the Earth
ICSE Class 9 · Geography · Chapter 5
What this chapter covers
- Landforms and the forces that shape them
- Mountains: definition and types
- Fold mountains
- Block mountains
- Residual mountains
- Plateaus: definition and types
- Intermont plateaus
- Volcanic plateaus
- Plains: definition and types
- Structural plains
- Depositional plains
- Examples from the world and India
Key points
- A landform is a natural feature of the earth's surface with a recognisable shape; the three major landforms are mountains, plateaus and plains.
- Endogenic forces from inside the earth build up relief; exogenic forces on the surface wear it down by denudation and fill low land by deposition.
- Fold mountains form when compression squeezes thick sediments in a geosyncline into anticlines and synclines; examples are the Himalayas, Alps, Andes and Rockies (young) and the Aravallis, Appalachians and Urals (old).
- Block mountains form along faults: a horst stands high between faults and a rift valley (graben) sinks between them; examples are the Vosges, Black Forest, Sierra Nevada and Satpuras.
- Residual mountains are the worn-down remains of older high land; examples are the Aravallis, Eastern Ghats and Parasnath.
- A plateau is a raised, broad, flat-topped landform with steep sides.
- Intermont plateaus are enclosed by fold mountains and are high, cold and dry, like the Tibetan and Bolivian plateaus.
- Volcanic plateaus are built by sheets of basic lava from fissure eruptions, like the Deccan Traps and the Columbia Plateau; their basalt weathers into fertile black soil.
- A plain is a large area of flat, low land, usually below 200 m.
- Structural plains are raised sea floors or evenly moved blocks of crust, like the Great Plains and the Russian Plain.
- Depositional plains are built by rivers (alluvial plains and deltas), glaciers, wind (loess) and lakes (lacustrine); the Indo-Gangetic Plain and the Ganga-Brahmaputra delta are the chief Indian examples.
Questions answered
Define a landform and name the three major landforms of the continents.
A landform is a natural feature of the earth's surface with a recognisable shape. The three major landforms are mountains, plateaus and plains.
Distinguish between endogenic and exogenic forces, with one landform produced by each.
Endogenic forces start inside the earth and move the crust, building up relief; fold mountains are produced by them. Exogenic forces act on the surface through water, wind, ice and temperature change, and wear down or fill up the land; residual mountains and depositional plains are produced by them.
What is a fold mountain? Explain how fold mountains are formed.
A fold mountain is a mountain formed by the bending of rock layers under compression. Sediments collect in a geosyncline and harden into layered rock. Movements of the crust push the landmasses on either side together, and the layers are squeezed into anticlines and synclines and raised to form a range.
Why are fossils of sea animals found high in the Himalayas?
The rocks of the Himalayas formed from sediments laid down in the Tethys Sea. When India pressed against Asia, the sediments, with the remains of sea creatures in them, were folded and lifted thousands of metres above sea level.
Differentiate between young fold mountains and old fold mountains, with one example of each.
Young fold mountains were raised in the last 50 million years or so and have high, sharp, snow-capped peaks, for example the Himalayas. Old fold mountains were formed hundreds of millions of years ago and have been worn into low, rounded ranges, for example the Aravallis.
Explain the terms horst and rift valley, and name one example of each.
A horst is a block of land standing high between two faults, forming a block mountain, such as the Vosges or the Satpuras. A rift valley is a long, narrow valley formed when a strip of land sinks between two parallel faults, such as the Narmada valley or the Rhine valley.
Why do block mountains have flat tops and steep sides?
The block is moved up or down as a whole along faults, so its original level surface is preserved, giving a flat top. The sides follow the fault lines, so they are steep and straight.
How are residual mountains formed? Why are they low and rounded?
Residual mountains are what is left of older, higher land after denudation has removed the softer rocks over a very long time. Because erosion has worked on them for tens or hundreds of millions of years, their peaks have been lowered and rounded and their slopes made gentle.
Past board exam questions
ICSE 2019 sample paper · 2 marks
(i) Differentiate between intermont plateau and volcanic plateau. (ii) Give an example of residual mountain and an example of depositional plain.
Show answer
(i) An intermont plateau is enclosed partly or fully by mountain ranges and is formed along with them by folding (e.g. the Tibetan Plateau); a volcanic (lava) plateau is formed by the spreading and solidifying of layers of lava poured out of fissures (e.g. the Deccan Plateau).
(ii) Residual mountain: the Aravalli Range (or the Nilgiris / Eastern Ghats). Depositional plain: the Indo-Gangetic Plain.