The Himalayas: Formation and Divisions

The Himalayas are young fold mountains, formed when the Indian plate moved northwards and collided with the Eurasian plate. The collision crumpled the sediments of the ancient Tethys Sea that once lay between the two plates, pushing them upwards into a great mountain arc. Because the plates are still moving, the Himalayas are still rising, and the region remains prone to earthquakes. This geological youth explains the rugged relief, steep slopes, deep valleys and fast-flowing rivers that distinguish the Himalayas from India's much older peninsular hills.

From west to east, the Himalayas stretch for about 2,400 kilometres, from the Indus gorge in the west to the Brahmaputra gorge in the east. From south to north they are usually divided into three parallel ranges. The Shiwaliks, or outer Himalayas, are the lowest and youngest foothills. North of them lie the Lesser Himalayas, or Himachal, with well-known hill stations and valleys. Furthest north are the Greater Himalayas, or Himadri, which carry the highest peaks and the largest glaciers. Beyond the Greater Himalayas lie the Trans-Himalayan ranges, including the Karakoram, Ladakh and Zanskar ranges.

The highest peaks illustrate the scale. Mount Everest, at 8,848.86 metres on the Nepal–China border, is the world's highest peak. Kanchenjunga, at 8,586 metres on the India–Nepal border in Sikkim, is the world's third-highest peak and is commonly described as the highest peak within India's undisputed territory; the status of K2 in the Karakoram is disputed, since the territory is administered by Pakistan while India claims it. Peaks, passes and valleys have therefore always been more than scenery: they are routes, boundaries and strategic ground.

The Himalayas also work as a climatic and hydrological barrier. They block cold winds from Central Asia, helping to keep northern India warmer in winter than places at similar latitudes elsewhere, and they force moisture-laden monsoon winds to rise and rain. Their glaciers and snowfields feed the Indus, Ganga and Brahmaputra river systems, which support agriculture and settlements across the northern plains. For civil studies, the Himalayas link geology, climate, water, borders and disaster risk in a single system.