Short Answer Type Questions. [3 Marks]

Describe the Theory of Plate Tectonics.
Ans. A plausible theory presented by Earth scientists to explain the formation of continents and ocean basins and the various landforms is the ‘Theory of Plate Tectonics’. According to the theory, the crust of the earth has been formed out of seven major and many minor tectonic plates.

According to them, millions of years ago, the world comprised of a super-continent ‘Pangaea’ surrounded by the primaeval ocean ‘Panthalassa’. The present continents and intervening oceans were formed because of the splitting of the crust into plates due to convection currents and drifting of these plates.

Where would one find most of the volcanoes and earthquake zones in the world and why?
Ans. Most volcanoes and earthquake zones in the world are located at plate margins. The movement of these plates due to convection currents results in the building up of stresses within the plates and continental rocks above. This leads to folding, faulting and volcanic activity along the zones of maximum stress, i.e., mostly along the margins of the plates. Earthquake and volcanic activity are maximum at these places.

Define tectonic or lithospheric plates.
Ans. Earth scientists have put forward the view that the earth’s crust or the lithosphere is not a continuous block. It consists of several large and small, rigid, irregularly shaped plates (slabs) which include continents and the ocean floor. These slabs are moving or drifting in relation to each other by about 2.5 cm to 5 cm each year. These crustal slabs are called tectonic, or lithospheric plates. According to the Theory of Plate Tectonics, the earth’s crust has been formed out of seven major and some minor tectonic plates
or lithospheric plates.

Name the different major physiographic divisions of India. Write a note on any one of the physiographic divisions of India.
Ans. The major physiographic divisions of India are as follows:
(i) The Himalayan Mountains (ii) The Northern Plains
(iii) The Peninsular Plateau (iv) The Indian Desert
(v) The Coastal Plains (vi) The Islands
The Coastal Plains:
The Peninsular Plateau of India is flanked by a stretch of narrow coastal plains to its west and east. The Western Coastal Plain is a narrow strip of plain stretching along the Arabian Sea lies to its west and flanked by the Western Ghats to its east. The northern part of the West Coast is called the Konkan (Mumbai to Goa), the central stretch is called the Kannad while the southern part is called the Malabar Coast.
The Eastern Coastal Plain is comparatively wider and level stretch running along the Bay of Bengal lying to its east with the Eastern Ghats rising to its west. It is known as the Northern Circar in the north, while its southern part is referred to as the Coromandel Coast.

How was the Great Northern Plains of India formed? Give a brief description.
Ans. The formation of the Himalayas due to upliftment of sediments out of the Tethys Sea and subsidence of the northern flank of the Peninsular Plateau resulted in the formation of a large basin.
Over millions of years, this depression gradually got filled up with alluvium deposited by the three major river systems – the Indus, the Ganga and the Brahmaputra flowing from the Himalayas in the north. Sediments were also deposited by the tributaries of these rivers rising from the mountains in the north as well as the Peninsular Plateau to its south. As a result, the fertile Indo-Gangetic or Northern Plains, and the Brahmaputra Plain in the northeast was formed. As the Himalayas gained in height, the rivers, glaciers and other agents of denudation became increasingly active in erosion. As a result, a large amount of silt got deposited in the depression, which became the Northern Plains.

Where are the Western and the Eastern Ghats situated? Write a small note on each.
Ans. The Western and the Eastern Ghats are situated in the Peninsular Plateau region. The Western Ghats mark the western edge of the Deccan Plateau and lie parallel to the Western Coast. The Eastern Ghats mark the eastern edge of the Deccan Plateau. They stretch from the Mahanadi Valley to the Nilgiri Hills in the south. The Eastern Coastal plain runs to its east.
The Western Ghats are continuous and regular and can be crossed only through passes like the Thal, Bhor and the Pal Ghats. They are comparatively high in elevation (average 900 to 1600 metres). No major river cuts across the Western Ghats. The Eastern Ghats are discontinuous and irregular. They are of relatively lower elevation (average 600 m). They are dissected by rivers draining into the Bay of Bengal.

Which plateau lies between the Aravali and the Vindhya range? Write a brief note on this plateau.
Ans. The Malwa Plateau lies between the Aravali hills and the Vindhya range. The Aravali hills lie to the west of the plateau and the Vindhya range lies to its south. The part of the peninsular plateau lying to the north of the Narmada river, covering a major area of the Malwa plateau is known as the Central Highlands. The Malwa plateau lies in Madhya Pradesh. It is composed of extensive lava flows. There are rolling plains separated by flat-topped hills. The plateau is largely broken in the form of ravines near the Chambal Valley in its east.

What are corals? Name and describe the island group, which is of coral origin.
Ans. Corals are short-lived microscopic organisms that live in colonies. They flourish in shallow, mud-free and warm waters. They secrete calcium carbonate. The coral secretion and their skeletons form coral deposits.
Lakshadweep islands group lying close to the Malabar Coast of Kerala is composed of small coral islands.

Describe ‘Bhabar’ and ‘Terai’.
Ans. Bhabar is pebble studded formation situated at the base of mountains and plains in the Himalayan region. It is a belt of 8 to 16 km in width lying parallel to the slopes of the Shivalik. Terai is a sloping land at the foothills of the Nepal Himalayas. The Terai receives heavy rainfall and is densely forested with rich wildlife.

Name any three divisions of the Himalayas on the basis of regions from west to east and also write one main feature of each.
Ans. The Himalayas have been divided on the basis of regions from west to east. These divisions have been demarcated by river valleys.
(i) The part of the Himalayas lying between Indus and Satluj has been traditionally known as the Punjab Himalayas. It is also regionally known as the Kashmir Himalaya, the Himachal Himalaya, respectively.
(ii) The part of the Himalayas lying between Satluj and Kali rivers is known as the Kumaon The Himalayas.
(iii) The Kali and Tista rivers demarcate the Nepal Himalayas and
(iv) The part lying between Tista and Dihang rivers is known as the Assam Himalayas.

Why are the Himalayas called young fold mountains?
Ans. The Himalayan mountains are geologically young and structurally fold mountains that stretch over the northern parts of India. It was uplifted from the ‘Tethys Sea’ during the Tertiary period. The whole mountain represents a very youthful topography with high peaks, deep valleys and fast-flowing rivers. That is why it is called the young fold mountain.

The relief of India displays a great physical variation. Explain.
Ans. India is a vast country with varied landforms. It has high mountains, plains, plateaus, islands, deserts, etc. This varied large landmass formed during different geological periods which has influenced her relief. Besides geological formations, a number of processes such as weathering, erosion and deposition have created and modified the relief to its present form. Thus, India displays great physical variation.

What is the Great Himalaya? Write three characteristics of it.
Ans. The northernmost range of the Himalayas is known as the Great or Inner Himalayas or the Himadri.
(i) It is the most continuous range consisting of the loftiest peaks with an average height of 6000 metres. It contains all the prominent Himalayan peaks.
(ii) Its folds are asymmetrical in nature and its core is composed of granite rock.
(iii) It is perennially snowbound and contains many glaciers.

What are the Purvanchal?
Ans. The eastern Himalayas are known as the Purvanchal. These consist of small hills in the north-eastern boundary of India. The Brahmaputra marks the easternmost boundary of the Himalayas. These hills consist of sandstone, i.e. sedimentary rocks. It has dense forests in the hills, like the Naga hills, Mizo hills, Patkai bum, etc. The height of these hills is lower, i.e. not more than 1000 m above sea level.

Mention three important features of the Northern Plains.
Ans. • It is one of the most fertile plains in the world.
• This plain is the most densely populated and agriculturally productive.
• It has a favourable climate and has an extensive network of an irrigation canal.

What do you understand by riverine islands?
Ans. The Himalayan rivers bring great depositional sediments from the mountains and deposit these in the plains. In the lower course of the rivers, these sediments accumulate and form islands in a river. These are called riverine islands. For example, the Majuli river island in the Brahmaputra river is the largest inhabited riverine island.