Structure and Physiography - Solutions

 CBSE Class 11 Geography

NCERT Solutions
Chapter 18
Structure and Physiography

1. Choose the right answer from the four alternatives given below:
(i) In which part of Himalayas do we find the Karewa formation?

(a) North-eastern Himalayas
(b) Himachal-Uttarakhand Himalayas
(c) Eastern Himalayas
(d) Kashmir Himalayas

Ans. (d) Kashmir Himalayas

(ii) In which of the following states is Loktak lake situated?

(a) Kerala
(b) Uttarakhand
(c) Manipur
(d) Rajasthan

Ans. (c) Manipur

(iii) Which one of the water bodies separates the Andaman from the Nicobar?

(a) 11° Channel
(b) Gulf of Mannar
(c) 10° Channel
(d) Andaman Sea

Ans. (a) 10° Channel

(iv) On which of the following hill range is the 'Dodabeta' peak situated?

(a) Nilgiri hills
(b) Anaimalai hills
(c) Cardamom hills
(d) Nallamala hills

Ans. (a) Nilgiri hills

2. Answer the following questions in about 30 words.
(i) If a person is to travel to Lakshadweep, from which coastal plain does he prefer and why?
 Lakshadweep islands are situated in the Arabian Sea. These islands are located at a distance of 280 km-480 km off the Kerala coast. Its distance is shortest from the Malabar Coast. Therefore, if a person is to travel to Lakshadweep, he will prefer the western coastal plains.

(ii) Where in India will you find a cold desert? Name some important ranges of this region.
 The north-eastern part of the Kashmir Himalayas is a cold desert, which lies between the Greater Himalayas and the Karakoram ranges. Main ranges of this region are Laddakh, Karakoram, Zasker and Pir Panjal.

(iii) Why is the western coastal plain is devoid of any delta?
 The western coastal plain is narrow and has steep slope. The slope of rivers of western coast is very steep. Therefore, these rivers do not flow in different parts but in one part and hence they do not form any delta. As a result, we do not find any delta in the western coast.

3. Answer the following questions in not more than 125 words.
(i) Make a comparison of the island groups of the Arabian Sea and the Bay of Bengal.

Ans. Lakshadweep islands are in Arabian Sea and Andaman and Nicobar islands are in Bay of Bengal.

BasisAndaman and Nicobar islandLakshadweep Island
DistanceIt lies far away i.e., 1200 km away from Indian land in Bay of BengalThese island lie opposite to the coast of Kerala in Arabian Sea approximately at a distance of 280-480 km.
LocationThey are extended between 6° N to 14° N latitude and between 92°E to 94 ° E longitude.Their extent is 8°N - 12° N latitude and 71°E- 7 4 °E longitude.
OriginThey are volcanic in origin.They are coral in origin and are coral islands.
FormationThey are located on submerged hill ranges.They are formed by of skeletons, Microscopic species or coral polyps on the sea bed. These species are flourishing on the shallow water, many of them are atoll ( horse -shoe shaped) ringed shape.
CapitalPort Blair is its the capital.Kavarati is its capital.
NumberThey are approx. 572 islands.They are approx. 36 islands out of which 11 are inhabited.
PartsThey has 2 volcanic islands Barren island-active volcano Norkandom island- extinct volcano.Minicoy is the largest island, of 453 sq km area, which is known for tourist attraction.
SeparationThe water body separating Andaman and Nicobar islands is ten degree channel.The group of island is divided by eleventh degree channel as north of which is Amini islands and the south is Canannore islands.

(ii) What are the important geomorphological features found in the river valley plains?

Ans. Alluvial fans are formed when streams flowing from higher levels break into foot slope plains of low gradient. Normally very coarse load is carried by streams flowing over mountain slopes. This load becomes too heavy for the streams to be carried over gentler gradients and gets dumped and spread as a broad low to high cone shaped deposit called alluvial fan. Usually, the streams which flow over fans are not confined to their original channels for long and shift their position across the fan forming many channels called distributaries.

Alluvial fans in humid areas show normally low cones with gentle slope form as a low cone. Delta is like alluvial fans but develop at a different location. The load carried by the rivers is dumped and spread into the sea. If this load is not carried away far into the sea or distributed along the coast, it spreads and accumulates. Such areas over flood plains built up by abandoned or cut¬off channels contain coarse deposits. The flood deposits of spilled waters carry relatively finer materials like silt and clay.

The flood plains in a delta are called delta plains. Floodplain is a major landform of river deposition. Large sized materials are deposited first when stream channel breaks into a gentle slope. Thus, normally, fine sized materials like sand, silt and clay are carried by relatively slow moving waters in gentler channels usually found in the plains and deposited over the bed and when the waters spill over the banks during flooding above the bed. These river valley plains have a fertile alluvial soil cover which supports a variety of crops like wheat, rice, sugarcane and jute, and hence, supports a large population.

The geomorphological features of the valley plains are :
1. The valley plains are formed by the alluvial deposits brought by the rivers.
2. Bhabar : It is a narrow belt ranging between 8 km and 10 km parallel to Shiwalik foothills at the break up of the slope.
3. Tarai : South of Bhabar is the belt of Tarai with a width about 10 to 20 km where the most of rivers re-arrange without having any properly demarcated channel creating a marshy and swampy condition known as Tarai.
4. Bhangar : It is composed of old alluvium and forms the alluvial terraces above the level of the flood plains.
5. The Khadar : The flood plain which has newer alluvium is called Khadar. A newer layer is deposited by river floods every year.
6. Delta : The mouth of mighty rivers also form the delta. Sunderban delta is an example.

(iii) If you move from Badrinath to Sunderbans delta along the course of the river Ganga, what major geomorphological features will you come across?

Ans. Badrinath is situated along Ganga river in Uttaranchal Himalayas. The Sunderban delta is on the mouth of Ganga and Brahmaputra in the Bay of Bengal. If we move from Badrinath to Sunderbans delta along the course of the river Ganga, following major geomorphological features we will come across:
(a) V Shaped Valleys: The V-shaped valley is typical of one that has been carved by flowing water. The erosion is more pronounced when the water flow is a heavy one, and the water carries suspended particles (sedimentary load). Valleys start as small and narrow rills; the rills will gradually develop into long and wide gullies; the gullies will further deepen, widen and lengthen to give rise to valleys. Depending upon dimensions and shape, many types of valleys like V-shaped valley, gorge, canyon, etc. can be recognised.
(b) Gorge: A gorge is a narrow valley with steep, rocky walls located between hills or mountains. The term comes from the French word gorge, which means throat or neck. A gorge is often smaller than a canyon, although both words are used to describe deep, narrow valleys with a stream or river running along their bottom.
(c) Canyon: A canyon is characterised by steep step-like side slopes and may be as deep as a gorge. A gorge is almost equal in width at its top as well as at its bottom. In contrast, a canyon is wider at its top than at its bottom. In fact, a canyon is a variant of gorge. The movement of rivers, the processes of weathering and erosion, and tectonic activity create canyons. The most familiar type of canyon is probably the river canyon. The water pressure of a river can cut deep into a river bed.
(d) Waterfall: When the rivers start falling in pits in mountainous regions, it makes waterfall. A waterfall is a place where water flows over a vertical drop or a series of drops in the course of a stream or river. Waterfalls also occur where meltwater drops over the edge of a tabular iceberg or ice shelf.
(e) Plunge pools: Once a small and shallow depression forms, pebbles and boulders get collected in those depressions and get rotated by flowing water and consequently the depressions grow in dimensions. A series of such depressions eventually join and the stream valley gets deepened. At the foot of waterfalls also, large potholes, quite deep and wide, form because of the sheer impact of water and rotation of boulders. Such large and deep holes at the base of waterfalls are called plunge pools.