Physiographic divisions and the Himalayas as a whole

Detail

What shapes physiography

• Physiography means the shape of the land surface: its mountains, plateaus, plains and coasts.
• The land of any region gets its shape from three things:
• Structure: the type of rock, its age and how it is folded, faulted or laid flat.
• Process: the forces that wear the land down or build it up, such as rivers, glaciers, wind, waves and earth movements.

• Stage of development: how far these processes have gone. A young landscape is steep and sharp. An old landscape is worn down and gentle.

• India shows all three stages side by side:

• North: high, rugged and young fold mountains. They are still rising.
• South: a stable, old tableland (a high, flat-topped plateau). Rivers have dissected it, which means they have cut it up into valleys and hills. It is edged by scarps (steep cliff faces, such as the Western Ghats edge).
• Between them: the vast, flat Northern Plain, made of river deposits.

Age of the three main blocks

Block	When it formed	Nature of the land
Peninsular Plateau	Archaean (the oldest rocks, more than 2,500 million years old)	Hard, stable block. Worn down and dissected. Bounded by scarps
Himalayas	Tertiary orogeny (orogeny means mountain building)	Young fold mountains. Still rising and earthquake-prone
Northern (Indo-Gangetic) Plain	Quaternary (the most recent period, about the last 2.6 million years)	Flat layers of alluvium (soil laid down by rivers)

• Mountain building, step by step:
• The Tethys Sea lay between India and Asia. About 225 million years ago it separated the two landmasses [4].
• The Indian plate moved north at about 9 metres per century. When India and Eurasia collided 40–50 million years ago, this speed fell by about half [4].
• The crust along the collision line buckled and was pushed upwards. Sea sediments, including fossil-bearing rocks of the Tethys, were raised into mountains [4].
• The Himalayas are still rising by more than 1 cm a year [4]. They are among the world's youngest and fastest-rising mountains [3].

The six physiographic divisions of India (Class 11, Figure 2.2)

1. The Northern and North-eastern Mountains: the Himalayas and the north-eastern hills
2. The Northern Plain: the Indus–Ganga–Brahmaputra plains
3. The Peninsular Plateau: the oldest and most stable block
4. The Indian Desert: the Thar, west of the Aravalli
5. The Coastal Plains: the western and eastern coasts
6. The Islands: Andaman and Nicobar in the Bay of Bengal, Lakshadweep in the Arabian Sea

• Class 7 version: five regions. These are the mountains, the plains, the desert, the southern peninsula and the islands. It is the same frame, but the coastal plains are grouped with the peninsula.

The Himalayas: size and shape

• Himalayas: a series of parallel ranges of young fold mountains along India's northern border (Figure 2.3).
• Great Himalayan range: the central axial range, meaning the main, highest line of peaks at the centre of the system.
• Length: about 2,500 km from west to east.
• Width: 160–400 km from north to south.

• It stands like a wall between the Indian subcontinent and Central and East Asia.

• Ends of the arc:

• West: Nanga Parbat (8,126 m), in Pakistan-occupied Kashmir, near the gorge of the Indus [5][3].
• East: Namcha Barwa (7,782 m), in south-eastern Tibet (China), where the Yarlung Tsangpo (the Brahmaputra) bends sharply [5][6].

• At both ends the ranges bend sharply around the corners of the Indian plate. Each sharp bend is called a syntaxis (a hairpin-like bend where mountain ranges turn back on themselves). The two bends are the Nanga Parbat syntaxis and the Namcha Barwa syntaxis.

• Width compared with height:

• The range is wider in Kashmir (about 400 km) than in Arunachal Pradesh (about 160 km).

• Yet the peaks are higher in the east. Everest, Kangchenjunga and Makalu all stand in the central and eastern part.

• Indian Himalayan Region: stretches over 2,500 km between the Indus and Brahmaputra river systems. It rises from low plains to more than 8,000 m (NMSHE Mission Document, 2010) [2].

Orientation of the Himalayas

• Orientation: the compass direction in which the ranges run. In India, the direction changes along the arc because the ranges wrap around the northward-pushing Indian plate.

Region (west to east)	Direction of the ranges
North-west India (J&K, Ladakh, Himachal Pradesh)	Northwest–southeast
Darjiling (West Bengal) and Sikkim	East–west
Arunachal Pradesh	Southwest–northeast (NCERT misprints this as "southwest to the northwest")
Nagaland, Manipur, Mizoram	North–south (the Purvanchal hills)

• Result: together the ranges form a curved arc. It is convex (bulging outwards) towards the south and wraps around India's northern border.

The Himalayas as a divide

• Climatic divide:
• In winter, the high wall blocks very cold, dry winds from Central Asia and Siberia. This keeps north India warmer than places at the same latitude in Asia.

• In summer, moist south-west monsoon winds hit the mountains and are pushed up. The rising air cools and its water vapour condenses. It rains heavily inside the subcontinent instead of the moisture crossing into Tibet (see indian-climate-monsoon).

• Drainage divide ("Water Tower of Asia"):

• Glacier: a slow-moving mass of ice formed from snow packed down over many years.
• About 17% of the Indian Himalayan Region is under permanent snow and glaciers. Another 30–40% has seasonal snow (NMSHE, 2010) [2].
• This stored ice and snow feeds perennial rivers (rivers that flow all year). They supply water for drinking, irrigation and hydropower [2].

• The big three river systems are the Indus, the Ganga and the Brahmaputra (see india-drainage-rivers).

• Physical divide: high passes are few and snowbound. This made the range a natural wall and a frontier.

• Cultural divide:
• The mountains shaped separate regional identities on either side.
• They are sacred in Indian tradition. Himalaya = hima (snow) + alaya (abode), meaning "abode of snow".

Extent and the "Eight Thousanders"

• Countries crossed (Class 7): India, Nepal, Bhutan, China, Pakistan and Afghanistan.
• Eight Thousanders: the peaks higher than 8,000 m.
• There are 14 in the world, and all of them are in the Himalaya and Karakoram ranges of Asia [3].
• Each mountain range has its own range of highest peaks:

Rank	Peak	Height (m)	Range / location
1	Mount Everest	8,849	Himalaya, Nepal–China (Tibet) [3]
2	K2 (Godwin Austen)	8,611	Karakoram, Pakistan-occupied Kashmir–China border [3]
3	Kangchenjunga	8,586	Himalaya, Sikkim (India)–Nepal [3]
9	Nanga Parbat	8,126	Western end of the Himalaya, Pakistan-occupied Kashmir [3][5]
14	Shishapangma	8,027	Himalaya, Tibet (China), the lowest of the 14 [3]

• The other nine are Lhotse, Makalu, Cho Oyu, Dhaulagiri, Manaslu, Annapurna, Gasherbrum I, Broad Peak and Gasherbrum II [3].

Prelims Hooks

• Six divisions (Class 11): the Northern and North-eastern Mountains, the Northern Plain, the Peninsular Plateau, the Indian Desert, the Coastal Plains and the Islands. Class 7 uses five regions.
• Physiography depends on structure, process and stage. A trap option may list "climate, soil, vegetation" instead.
• Oldest to youngest: Peninsular Plateau (Archaean), then Himalayas (Tertiary), then Northern Plain (Quaternary).
• Great Himalaya: about 2,500 km long and 160–400 km wide. It is wider in Kashmir, but the peaks are higher in the east.
• Orientation, west to east: NW–SE (Kashmir, Himachal Pradesh), then E–W (Darjiling, Sikkim), then SW–NE (Arunachal Pradesh), then N–S (Nagaland, Manipur, Mizoram).
• Ends of the arc: Nanga Parbat (8,126 m, west, Indus) and Namcha Barwa (7,782 m, east, Tsangpo) [5][6].
• Eight Thousanders: there are 14, all in the Himalaya and Karakoram. K2 is in the Karakoram, not the Himalaya. Kangchenjunga (8,586 m) is the highest peak in India [3].
• Six countries: India, Nepal, Bhutan, China, Pakistan and Afghanistan. A trap option may list Myanmar instead.
• Himalaya = hima (snow) + alaya (abode).
• The Himalayas began forming 40–50 million years ago and are still rising by more than 1 cm a year [4].

Mains Points

• Barrier role (GS-I): the Himalayas shape India's climate, rivers and people.
• They block cold Central Asian winds in winter.
• They force the monsoon to drop its rain within India.

• Their glaciers make north Indian rivers perennial, which supports the Indo-Gangetic farming belt.

• Uneven development of the land (GS-I): India's three blocks are at three different stages.

• The young Himalayas are still rising, so they bring earthquakes, landslides and high erosion.
• The old Peninsular Plateau is stable and holds minerals.

• The young alluvial plain is fertile and densely populated.

• Fragile water tower (GS-III): about 17% of the Indian Himalayan Region is under permanent snow and ice [2]. If glaciers shrink, river flow, hydropower and water security downstream are at risk. The National Mission for Sustaining the Himalayan Ecosystem (NMSHE, under the National Action Plan on Climate Change) is India's policy response [2].

• Strategic arc (GS-I and GS-III): the arc changes direction from NW–SE to N–S. Because of this, the Himalayas guard India's borders with Pakistan, China, Nepal, Bhutan and Myanmar, and pass and border infrastructure must be planned for each part of the arc.