The Himalayas

The Himalayas are the greatest mountain range on Earth. They stretch for 2,400 km across South Asia, passing through five countries, and contain all 14 of the world's highest peaks. The Himalayas were built (and are still being built) by the slow but relentless collision of the Indian and Asian tectonic plates. The range is so high and so wide that it shapes the climate of the entire continent, controlling the Asian monsoon.

• Length2,400 kmAcross South Asia
• Countries5India, Nepal, Bhutan, China, Pakistan
• Highest peakMount Everest8,849 m
• 8,000-m peaksAll 14Of the world's 14 are here
• Ageapprox. 50 million yearsAnd still rising
• Famous forSherpas, snow leopardsPlus the Buddhist culture of Tibet and Bhutan

How the Himalayas compare to other ranges

Length (km)

Andes7,000

Rockies4,800

Himal.2,400

Atlas2,500

Alps1,200

The Himalayas are not the longest range (the Andes are) but they are by far the highest, containing all 14 of the world's 8,000-metre peaks.

What are the Himalayas?

The word "Himalaya" comes from Sanskrit and means "abode of snow". The range arcs across South Asia from Pakistan in the west through India, Nepal, Bhutan and into China (specifically the Tibet Autonomous Region). The Himalayas separate the dry Tibetan Plateau in the north from the warm wet Gangetic Plain of India in the south. Their high peaks block much of the moisture from the Asian monsoon, which is why their southern slopes are wet and green while the northern slopes are dry and bleak.

How were they built?

The Himalayas began forming approx. 50 million years ago when the Indian tectonic plate crashed into the Asian plate. Before that collision, India was a separate landmass moving north through the ocean. As India crashed into Asia, the rocks where they met had nowhere to go but up. The collision is still happening: India is still being pushed northward at approx. 5 cm per year, and Mount Everest is still growing by approx. 4 mm each year.

The collision is also responsible for the high Tibetan Plateau north of the Himalayas. The plateau is the largest and highest plateau on Earth, averaging around 4,500 metres above sea level. It is sometimes called "the roof of the world".

Fact All 14 of the world's mountains above 8,000 metres sit in the Himalayas or the closely related Karakoram. Climbing all 14 is one of the great achievements in mountaineering. Only approx. 50 people have ever done it.

The monsoon and water

The Himalayas drive the Asian monsoon. During the summer, warm moist air from the Indian Ocean is sucked north towards the warm continent. When this air hits the southern face of the Himalayas, it is forced to rise. As it rises, it cools, and the moisture condenses and falls as rain. Parts of the eastern Himalayan foothills get over 11,000 mm of rain a year, the wettest places on Earth.

The Himalayan glaciers also feed all of South Asia's biggest rivers: the Indus, the Ganges, the Brahmaputra and (to the east) the Yangtze and Mekong. Over a billion people depend on water from the Himalayas for their daily lives. Climate change is now shrinking the glaciers fast, which threatens the water supply for hundreds of millions.

Culture of the Himalayas

The mountains are home to unique cultures shaped by isolation and altitude. The Sherpa of Nepal are famous as climbers and guides on Everest. Tibetan Buddhism dominates the eastern Himalayas in Tibet, Bhutan and parts of Nepal, with its ancient monasteries perched on remote ridges. Hinduism dominates the western Himalayas and considers many peaks sacred. The kingdom of Bhutan famously measures national success not by GDP but by "Gross National Happiness".

Did you know? The snow leopard, the elusive big cat of the high Himalayas, was virtually never photographed in the wild until the 1970s. Today camera-trap surveys have revealed perhaps 4,000 to 7,000 left in the mountains of Central Asia. They live so high (3,000 to 5,500 m) that they almost never see humans.

Deeper dive: continental collision, the Tibetan Plateau and the climate role

The collision of India and Asia is one of the most striking events in geological history. About 70 million years ago, India broke away from the supercontinent of Gondwana (which contained Africa, South America, Antarctica and Australia) and began drifting northward through the Tethys Ocean. India moved fast (around 15 to 20 cm per year for some periods) until it slammed into Asia approx. 50 million years ago. The collision is now slower (around 5 cm per year) but is still ongoing. The total compression so far is around 2,500 km of shortening, which has produced both the Himalayas (as compressed mountain belts) and the Tibetan Plateau (as thickened crust).

The Tibetan Plateau is the largest and highest plateau on Earth, covering approx. 2.5 million square km at an average elevation of 4,500 metres. The plateau is essentially Asian crust that has been thickened to approx. 70 km deep (double the normal crustal thickness) by the underthrust of the Indian plate. The high altitude means the plateau is cold and dry, with much of it being high-altitude desert or grassland. The unique high-altitude ecosystem supports species like the wild yak, the Tibetan antelope and the Tibetan wild ass, all adapted to thin air and extreme weather.

The Himalayas play a huge role in regulating Earth's climate. Beyond the monsoon system, the range affects atmospheric circulation patterns far beyond Asia. The thickening of the continental crust during the collision exposed vast areas of fresh rock to weathering, which absorbed huge amounts of CO₂ from the atmosphere over millions of years. Many scientists believe that the rise of the Himalayas was a major factor in the long-term cooling of Earth's climate over the past 50 million years, eventually triggering the ice ages of the Quaternary period. The current rapid melting of Himalayan glaciers under modern climate change threatens to disrupt the water supply for around 1.5 billion people downstream.

The highest peak is Mount Everest. The second is K2. The longest range is the Andes.