Himalayas

Topic: Structure and Physiography of India: Himalayas, Plains, Peninsula, Coasts and Islands · NCERT: Class 6, Ch 3 "Landforms and Life"; Class 7, Ch 1 "Geographical Diversity of India"; Class 9, Ch 2 "Shaping of the Earth's Surface"; Class 11, Ch 2 "Structure and Physiography"; Class 11, Ch 4 "Climate"; Class 11, Ch 6 "Natural Hazards and Disasters: Causes, Consequences and Management"

Meaning

The Himalayas are a young fold mountain system (mountains made when layers of rock are squeezed and bent upwards) that formed when the Indian plate collided with the Eurasian plate. They are a series of parallel ranges in an arc about 2,500 km long and 160–400 km wide along India's northern border. They are still rising and often have earthquakes.

They matter because they act as a wall that shapes India's climate, rivers, borders and culture. They are also the "water tower" behind the farming belt of north India.

Explanation

How the Himalayas formed

• Before the collision:
• The Tethys Sea lay between India and Asia. About 225 million years ago it separated the two landmasses [4].

• Sediments (layers of sand, mud and shells) built up on the floor of this sea.

• The collision:

• The Indian plate moved north at about 9 metres per century [4].

• India and Eurasia collided 40–50 million years ago, and the speed of the plate fell by about half [4].

• The result:

• The crust along the collision line buckled and was pushed upwards. Tethys sea sediments, including rocks with fossils, were raised into mountains [4].

• The building of these mountains is called the Tertiary orogeny (orogeny means mountain building).

• Still active:

• 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].
• Because the plates are still pushing, the region has earthquakes and landslides and wears away quickly.

Shape, size and orientation

• Parallel ranges: the system is made of several ranges running side by side. The Great Himalayan range is the central axial range, meaning the main and highest line of peaks in the middle.
• Size: about 2,500 km from west to east and 160–400 km from north to south.
• Width and height do not match:
• The system is wider in Kashmir (about 400 km) than in Arunachal Pradesh (about 160 km).

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

• Ends of the arc:

• West: Nanga Parbat (8,126 m), near the gorge of the Indus [5][3].
• East: Namcha Barwa (7,782 m), where the Yarlung Tsangpo (Brahmaputra) bends sharply [5][6].

• At each end the ranges turn sharply around a corner of the Indian plate. This hairpin-like bend is called a syntaxis. The two bends are the Nanga Parbat syntaxis and the Namcha Barwa syntaxis.

• Orientation (the compass direction in which the ranges run) changes along the arc:

• North-west India (J&K, Ladakh, Himachal Pradesh): northwest–southeast
• Darjiling and Sikkim: east–west
• Arunachal Pradesh: southwest–northeast

• Nagaland, Manipur, Mizoram (Purvanchal hills): north–south

• Result: the ranges form an arc that is convex to the south (it bulges outwards towards the south) and wraps around the northward-pushing Indian plate.

The Himalayas as a divide

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

• In summer, moist south-west monsoon winds hit the mountains and are pushed up. The rising air cools, its water vapour condenses and it rains heavily inside India. The moisture does not cross into Tibet.

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

• A glacier is 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, and another 30–40% has seasonal snow [2].

• This ice and snow feeds perennial rivers (rivers that flow all year). They give water for drinking, irrigation and hydropower [2].

• Physical divide: there are few high passes and they are snowbound, so the range has long been a natural wall and frontier.

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

Place among India's landforms

• Physiography (the shape of the land) depends on structure, process and stage of development.
• The Himalayas are the young stage. They are high, rugged and still rising.
• They form part of the first of India's six physiographic divisions (Class 11), the Northern and North-eastern Mountains.

Block	Age	Nature
Peninsular Plateau	Archaean (oldest)	Stable, worn down, dissected
Himalayas	Tertiary	Young fold mountains, still rising
Northern Plain	Quaternary (youngest)	Flat layers of river alluvium

Where it occurs

• Indian states and UTs along the arc: J&K, Ladakh and Himachal Pradesh (NW–SE), Darjiling (West Bengal) and Sikkim (E–W), Arunachal Pradesh (SW–NE), and Nagaland, Manipur and Mizoram (N–S, Purvanchal).
• 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 [2].
• Countries crossed (Class 7): India, Nepal, Bhutan, China, Pakistan and Afghanistan.
• Western end: Nanga Parbat, in Pakistan-occupied Kashmir, near the Indus gorge [5][3].
• Eastern end: Namcha Barwa, in south-eastern Tibet (China), at the great bend of the Yarlung Tsangpo [5][6].
• Major peaks:
• Mount Everest (8,849 m), Nepal–China (Tibet) [3]
• Kangchenjunga (8,586 m), Sikkim (India)–Nepal [3]

• Shishapangma (8,027 m), Tibet (China), the lowest of the 14 eight-thousanders [3]

• Rivers fed: the Indus, Ganga and Brahmaputra systems.

Don't confuse with

• Karakoram: a separate range that holds K2 (8,611 m), the world's second-highest peak [3]. K2 is not in the Himalaya. The 14 eight-thousanders are spread across the Himalaya and the Karakoram.
• Great Himalayan range: only the central axial range (the highest middle line of peaks), not the whole system of parallel ranges.
• Purvanchal hills: the north–south hills of Nagaland, Manipur and Mizoram. They belong to the Northern and North-eastern Mountains but are not the east–west main Himalayan arc.
• Peninsular Plateau: an Archaean, stable, worn-down block. The Himalayas are a Tertiary, young, still-rising and earthquake-prone fold system.

Prelims Hooks

• Wider in Kashmir (about 400 km), higher peaks in the east. A trap option may say "wider where peaks are higher".
• Orientation, west to east: NW–SE (J&K, 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].
• Oldest to youngest: Peninsular Plateau (Archaean), then Himalayas (Tertiary), then Northern Plain (Quaternary).
• Six countries (Class 7): India, Nepal, Bhutan, China, Pakistan and Afghanistan. A trap option may list Myanmar instead.
• The collision happened 40–50 million years ago, and the Himalayas still rise by more than 1 cm a year [4]. Kangchenjunga (8,586 m) is the highest peak in India [3].

Mains Points

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

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

• Young and unstable (GS-I and GS-III, disasters): the Himalayas are still rising because the plates keep colliding.

• This brings earthquakes, landslides and fast erosion.

• Roads, dams and towns in the hills must be planned with these hazards in mind.

• Fragile water tower (GS-III): about 17% of the Indian Himalayan Region is under permanent snow and ice [2].

• If the glaciers shrink, river flow, hydropower and water security downstream are at risk.
• India's policy response is the National Mission for Sustaining the Himalayan Ecosystem (NMSHE), under the National Action Plan on Climate Change [2].

Related concepts

• Physiographic divisions of India
• Orientation of the Himalayas

Read more

• Physiographic divisions and the Himalayas as a whole