Question 1.
Explain the theory of Plate Tectonics. HOTS
Answer:
According to this theory, the crust of the earth has been formed out of seven major and some minor plates. The movement of these plates led to folding, faulting and volcanic activity. These are classified in three categories:

• Convergent Boundary: When plates come .towards each other, also called folding movement.
• Divergent Boundary: When plates move away from each other, also called faulting movement.
• Transform Boundary: In the event of coming together, they may collide or may slide under each other.

Question 2.
What is the difference between a tributary and a distributary?
Answer:
A Tributary: A tributary is that river which joins the main river, and increases the volume of water. It is generally found in the upper or the middle course of a river. For example, the Yamuna is the main tributary of the river Ganga.

A Distributary: It is that river which originates from a main river. It is formed near the river’s mouth before it falls into the sea. It is found in the lower course of the river. For example, the Hooghly is the main distributary of the Ganga.

Question 3.
Name the three major divisions of Himalayas from the north to south.
Answer:
The three major divisions of Himalayas from north to south are:

• The northernmost range which is known as the Great Himalayas or Inner Himalayas or Himadri. It is the most continuous range consisting of the loftiest peaks. It has an average height of 6000 meters. It consists of all the prominent Himalayan peaks.
• The southern range of Himadri which is known the Himachal or the lesser Himalayas lies to the South of Himadri. It forms the most rugged mountain system. The ranges are mainly composed of highly compressed and altered rocks. The altitude varies between 3700 and 4500 meters and its average width is 50 kms.
• The outermost range of the Himalayas is known as Shiwaliks. Its height varies between 900 meters and 1100 meters. This range is composed of unconsolidated sediments brought down by rivers from the main Himalayan ranges. These are also called foothill ranges. They represent the southernmost divison of Himalaya.

Question 4.
Name the southernmost range of Himalaya. Mention any four features of this range.
Answer:
The southernmost range of Himalayas is called Shiwaliks.
Features:

• The outermost range of the Himalayas is called the Outer Himalayas or Shiwaliks.
• They extend over a width of 10-15 km.
• Their altitude varies between 900-1100 metres.
• They are discontinuous ranges and are composed of unconsolidated sediments, gravel and alluvium brought down by the rivers from main Himalayan ranges located farther north.
• Longitudinal valleys known as Duns lie between the lesser Himalayas and Shiwaliks. e.g., Dehradun, Kote Dun, Path Dun. (any four)

Question 5.
How is Himadri range different from Himachal range? Mention any three differences.
Answer:

	Himadri	Himachal
(i)	This range is the highest of Himalayas with an average height of 6,000 metres.	Himachal is not so high as Himadri. Its average height is between 3,700 and 4,500 metres.
(ii)	This range contains loftiest peaks. Example: Kanchenjunga and Nanda Devi.	This range contains hill stations Example: Shimla and Nainital.
(iii)	This range is always covered with snow.	It snows here in winter.

Question 6.
Differentiate between Western Himalayas and Eastern Himalayas.
Answer:

S. No.	Western Himalayas	Eastern Himalayas
(i)	These are spread over Jammu & Kashmir, Himachal Pradesh, Uttarakhand and Uttar Pradesh.	These are spread over West Bengal, Sikkim, Bhutan and Arunachal Pradesh.
(ii)	The Western Himalayas are very high.	These are of medium height.
(iii)	The Indus and the Sutlej are main rivers which pass throught the Western Himalayas and fall into the Arabian Sea.	The Brahmaputra is the main river which passes through these and falls into the Bay of Bengal.
(iv)	The average annual rainfall is less than 100 cm.	The average annual rainfall is more than 200 cm.
(v)	Srinagar, Shimla, Manali are the famous hill stations found in the Western Himalayas.	Darjeeling and Shillong are the famous hill stations found in the Eastern Himalayas.

Question 7.
Write about the main features of the Shiwaliks.
Answer:

• It is the outermost range of the Himalayas.
• The average altitude of the Shiwalik range varies between 900 m and 1,100 m above the sea level, and extends over a width of about 10-50 km.
• This range is made of unconsolidated material such as mud, silt and soft rocks and is prone to earthquakes and landslides.
• Some narrow valleys are found between the Shiwaliks and the Himachal. They are called ‘duns’. For example, Dehradun, is situated in one such valley.

Question 8.
How did the northern plains come to existence? Write two points briefly. Also mention two features of these plains.
Answer:
(i) The northern plains have been formed by the interplay of the three major river systems, i.e., the Indus, the Ganga and the Brahmaputra.
(ii) The northern plain is formed of the alluvial soil brought by these rivers.
Features:

• These plains are very fertile.
• These are densely polulated.

Question 9.
Why are Northern Plains agriculturally productive parts of India? Explain.
Answer:

• The deposition of alluvium in a vast basin lying at the foothills of the Himalaya over millions of years, formed this fertile plain. It spreads over an area of 7 lakh sQuestion km.
• The plain being about 2400 km. long and 240 to 320 km. broad, is a densely populated physiographic division.
• With a rich soil cover combined with adequate water supply and favourable climate, it is agriculturally a very productive part of India.

Question 10.
Which three river systems form the northern plains of India? Mention main features.
Answer:
The northern plain has been formed by the interplay of the three major river systems—the Indus, the Ganga and the Brahmaputra.
Features:

• The river Indus and its tributaries form the western part of the northern plain which is referred to as the Punjab plains. The larger part of this plain lies in Pakistan.
• The Ganga plain extends between Ghaggar and Teesta rivers. It spreads over the states of North India; Haryana, Delhi, U.P., Bihar, partly Jharkhand and West Bengal.
• The Brahmaputra plain particularly lies mainly in Assam. It forms the largest riverine islands in the world.

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