| Reference Book | Ratna Sagar Integrated Social Science |
| Class | Class 7 |
| Category | Geography |
| Chapter Number | Chapter 4 |
| Chapter Name | Major Landforms |
A) Tick (✓) the correct answers.
1) Which of the following is not an agent of erosion ?
a) Sea waves
b) Glaciers
c) Volcanoes ✓
d) Rivers
2) The highest waterfall in the world is
a) Salto Angel ✓
b) Niagara
c) Gersoppa
d) Victoria
3) Ox-bow lakes are usually formed in
a) deserts
b) snowfields
c) U-shaped valleys
d) river valleys ✓
4) The depositional feature of glacier is
a) moraines
b) waterfalls
c) meanders ✓
d) cirques
5) Mushroom rocks are mostly found in
a) flood plains
b) deserts ✓
c) beaches
d) mountains
B) Name the agents of erosion or deposition responsible for the creation of the following landform features.
1) Delta – Distributaries
2) Natural levee – Running water
3) Sand dunes – Wind
4) Flood plain – Meanders
5) Loess – wind
6) Sea cave – ocean wave
7) Sand bar – high tides
8) U- shaped valley – glacier
9) Moraine – glacier
10) Beach – ocean waves
C) Give short answers for the following questions.
Que 1) Name the factors and agents which help in weathering.
Ans A number of factors and agents such as heat, cold, frost action, plants, animals and chemical reactions help in weathering.
Que 2) How are ox-bow lakes formed?
Ans Due to continuous erosion and deposition, the meandering loops become almost circular and come very close to each other. In due course of time, the river is able to cut the strip of land between the two loops, and takes a straight course. The circular loop that is left behind, completely cut-off from the main channel, forms an ox-bow lake.
Que 3) How are flood plains formed?
Ans During floods, the river generally overflows its banks. The fine alluvial soil brought by the river is deposited on the valley floor. This fertile part is called flood plain. In the flood plain, the coarse materials are deposited along the banks of the river.
Que 4) Why is the work of wind limited to a few metres above the ground?
Ans The work of the wind is limited to a few metres above the ground. This is because the wind is unable to carry the rock particles high up in the air. Near the ground, its work slows down due to friction with the surface.
D) Give long answers for the following questions.
Que 1) How does running water carry out its work?
Ans The running water in the river carries out its work in three ways:
a. It erodes the rocks over which it flows.
b. It transports the eroded materials.
c. It deposits the materials which it has transported.
The erosional work of the river results in the widening and deepening of the river valley. Such a valley is called a V-shaped valley. In hilly areas, the river moves swiftly. Thus, there is more erosion and transportation of the sediments and practically no deposition.
a) When the water of the river falls almost vertically down a steep valley side, a waterfall is formed.
b) When the river leaves the mountain and enters the plains, the flow is no longer swift.The floor of the river valley widens due to continuous erosion along its bank.The river twists and turns to form large bends or loops.These are called meanders.
c) Due to continuous erosion and deposition, the meandering loops become almost circular and come very close to each other. In due course of time, the river is able to cut the strip of land between the two loops, and takes a straight course. The circular loop that is left behind, completely cut-off from the main channel, forms an ox-bow lake.
d) During floods, the river generally overflows its banks. The fine alluvial soil brought by the river is deposited on the valley floor. This fertile part is called flood plain.
e) Long ridges of low height are formed along the banks.These are called natural levees.
f) When the river reached its mouth, it carries a large volume of water and alluvium. The excess load is deposited as sand bars in the wide river channel. This divides the main channel into several channel, which are called distributaries.
Triangular shaped land that is formed between the distributaries due to deposition of sediments is called a delta.
Que 2) Explain the erosional and depositional work of sea waves.
Ans Sea water performs erosional and depositional work through sea waves. It is also aided by currents, tides and storms.The work of sea waves is also known as marine erosion and marine deposition. It is confined to a narrow belt along the coast. The erosional and depositional work of sea waves give rise to coastal landforms.
Strong sea waves dash against the coast and dissolve or break down the rocks into fragments. Many large and small cracks develop on the rocky surface. In due course of time, these cracks become wide and form large cavities. With the continuous action of sea waves, these cavities develop into sea caves.
When a headland projecting into the sea is attacked by sea waves from both sides, a thorough passage is created. This is called a sea arch. When the roof of the sea arch is further eroded, it collapses. The pillars of rocks are left standing in the open water. These are called stacks. A steep vertical wall facing the sea is called a sea cliff. The depositional work of the sea waves is a slow process.
Beaches are formed by the – deposition of sand, gravel and pebbles on the shore. They are generally formed when the sea is calm and winds are of low velocity. When the broken rock materials are deposited on the sea floor near the coast, sand bars are formed. Sometimes the sea water is enclosed between the coast and the sand bar. It then becomes a partially enclosed lake, which is called a lagoon.
Que 3) Explain the erosional work of glacier.
Ans The river of snow and ice, which move very slowly is called glacier. When the glacier passes through a valley, rock fragments fall into moving ice from the mountain slopes. It also picks up rock pieces from the valley floor. These rocks act as tools of erosion. These rocks rub against the sides and the valley floor. This creates a U-shaped valley with a flat bottom and almost vertical sides. The glacier carves out deep hollows along the slope of a mountain. It develops an armchair like depression, called cirque.
Que 4) Describe the depositional work of wind.
Ans The depositional work of wind starts when its speed declines or some obstruction like trees, bushes, forest, buildings, etc., come in its way. The fine dust particles deposited extensively is known as loess. It is porous and rivers cut deep valleys through it. The most extensive loess deposits are in north China. The coarse particles are deposited in the form of hillocks known as sand dunes. They are formed when there is some obstruction in the path of the wind. Sand dunes vary in height from a few metres to as much as 300 m. The windward slope is gentle, while the leeward slope is steep.
HOTS
Que 5) Why is the work of erosion and transportation of a river more in the mountains than in the plains?
Ans The work of erosion and transportation is more in the mountains than in the plains because a river flows very fast in the highlands and that leaves more scope to deposit water and finally cause erosion. But in the plains, the flow of river is slower.
Que 6) Why is the wind the most important agent of erosion in the desert?
Ans The wind is the most important agent of erosion in the desert because in the absence of moisture , rock fragments lie loose on the surface. Moreover , the absence of vegetation in the desert also enables the wind to blow freely.
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