Structure and Physiography (India) — Practice

Question 1

Identify the physiographic division of India for each description:
(a) A narrow, continuous mountain range forming the western edge of the peninsula, running from the Gulf of Khambhat to Kanyakumari
(b) Fertile alluvial plains formed by the Indus, Ganga, and Brahmaputra river systems
(c) Coral reef islands in the Arabian Sea, formed atop the Lakshadweep Ridge

Accepted Answer

(a) **Western Ghats** (part of the Peninsular Plateau physiographic division). They run ~1,600 km along India's west coast, average 1,000–1,500m height, and act as a watershed — rivers draining west (to Arabian Sea) are short; those draining east (to Bay of Bengal) are longer. Anamudi (2,695m) is the highest peak in peninsular India, located in Western Ghats.

(b) **Northern Plains** — formed by alluvial deposits of three major river systems over millions of years. Stretched ~3,200 km from Punjab to Assam, the plains have depth of alluvium up to 8,000m. They are India's most important agricultural region, supporting wheat, rice, sugarcane cultivation.

(c) **Lakshadweep Islands** (part of the Islands physiographic division). These 36 coral islands and atolls sit on a submarine ridge. Coral formation requires: warm shallow water, clean water, and active coral growth. The islands are India's smallest Union Territory and a Ramsar-notified wetland.

Question 2

Describe the three Himalayan ranges from north to south. For each range, give: (a) alternate name, (b) average elevation, (c) one distinguishing characteristic, and (d) one specific example (peak, hill station, or feature).

Accepted Answer

**1. Greater Himalayas / Himadri (northernmost)**:
(a) Also called: Main Himalayan Range, Himadri
(b) Average elevation: 6,000m+ (reaches 8,849m at Everest)
(c) Distinguishing characteristic: Always snow-capped; contains the world's highest peaks; steep asymmetric profile — gradual slope on Tibetan side, steep escarpment on south side; core of granite intrusions
(d) Example: Mount Everest (Nepal-China border), Kangchenjunga (Sikkim-Nepal border, 8,586m), K2 (Pakistan-controlled Kashmir)

**2. Lesser Himalayas / Himachal (middle range)**:
(a) Also called: Himachal, Middle Himalayas
(b) Average elevation: 3,700–4,500m
(c) Distinguishing characteristic: Composed of highly compressed and altered rocks; contains famous valley resorts (Kullu, Kangra, Bhagirathi valley); forests of oak, rhododendron, pine; glaciers are smaller and temporary
(d) Example: Shimla (1,400m, Himachal Pradesh), Mussoorie (2,000m, Uttarakhand), Nainital (2,000m). Kashmir Valley lies between Himadri and Himachal ranges.

**3. Shiwaliks / Outer Himalayas (southernmost)**:
(a) Also called: Shiwaliks, Outer Himalayas
(b) Average elevation: 900–1,100m (900–1,800m range)
(c) Distinguishing characteristic: Youngest range, composed of unconsolidated sediments (sand, gravel, boulder) — very susceptible to erosion; flanked on south by alluvial foothill plains (Terai); separated from Himachal by longitudinal valleys called 'Duns'
(d) Example: Dehradun (famous Dun valley between Shiwaliks and Himachal); Terai region of Uttarakhand and UP lies along the Shiwalik southern foothills

Question 3

Explain the formation of the Northern Plains of India. Why are they India's most important agricultural region? Describe khadar and bhangar with their differences and significance.

Accepted Answer

**Formation of Northern Plains**:

The Northern Plains occupy the structural depression (foredeep) that formed between the rising Himalayas and the ancient Peninsular Block when the Indian Plate collided with Asia ~50 million years ago. As the Himalayas rose, rivers originating from them (Indus, Ganga, Brahmaputra and their tributaries) carried enormous quantities of sediment southward and deposited it in this depression.

Over millions of years, the foredeep filled with alluvial deposits 8,000–15,000 metres deep in places. Today, the plains stretch ~3,200 km from Punjab (Indus) to Assam (Brahmaputra), covering 7.5 lakh km² — 22% of India's land area.

**Why they are India's most important agricultural region**:
1. **Fertile alluvial soil**: Rich in minerals (silt, clay, sand from Himalayan glaciers and weathered Peninsular rocks) and renewed annually by river flooding.
2. **Flat terrain**: Easy mechanisation, irrigation canals, road and rail connectivity — unlike hilly or plateau regions.
3. **Perennial rivers**: Himalayan rivers (Ganga, Yamuna, Indus) are glacier-fed — they flow year-round even in dry season, enabling irrigation. Peninsular rivers are seasonal (rain-fed).
4. **Dense population + agricultural labour**: Concentrated workforce in Bihar, UP, Punjab, Haryana — India's breadbasket.
5. **Green Revolution heartland**: Punjab and Haryana plains (flat terrain + canal irrigation + HYV seeds) drove India's food revolution.

**Khadar vs Bhangar**:

| Feature | Khadar | Bhangar |
|---|---|---|
| Type | New, younger alluvium | Old, older alluvium |
| Location | Active floodplains, low-lying riverbanks | Higher terraces, above flood reach |
| Soil texture | Finer, loam-like, sandy | Coarser, contains kankar (calcareous nodules) |
| Flooding | Flooded annually — nutrients renewed | Not flooded — nutrients less frequently replenished |
| Fertility | Higher — fresh nutrient deposition | Lower — kankar impedes water retention |
| Cropping | Best for rice, jute, sugarcane | Better suited to wheat, millets |

**Significance**: Khadar soils of the Ganga-Yamuna doab (land between two rivers) are among India's most productive agricultural lands. Bhangar, though less fertile, is more stable for settlement (not flooded). The UP-Bihar Khadar zone is critical for rice production.

Practice — Structure and Physiography (India)

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