Himalaya

I

Introduction

Himalaya, also Himalayas (Sanskrit for “abode of snow”), mountain system in Asia, comprising a series of parallel and converging ranges and forming the highest mountain region in the world. More than 30 peaks of the Himalaya rise to heights of 7,620 m (25,000 ft) or more, and one of these, Mount Everest (8,850 m/29,035 ft), is the world's highest mountain. The vast Himalayan complex extends in an arc of about 2,400 km (1,500 mi) from the River Indus in northern Pakistan eastwards to the Brahmaputra River, across Kashmir in northern India, part of southern Tibet, most of Nepal, the Indian state of Sikkim, and Bhutan; the system covers an area of about 594,400 sq km (229,500 sq mi). The extreme climate and challenging landscape of the range have made it the goal of many mountaineers.

II

Geological Formation and Structure

During the Palaeozoic and Mesozoic eras (65 million to 570 million years ago) the area that is now the Himalaya occupied the floor of the ancient Tethys Sea on the northern part of the Indian Plate of the Earth's crust. The mountains were formed by the action of plate tectonics as the Indian Plate, moving north, pressed against the stationary Asian land mass. The principal uplift occurred during the middle or late Tertiary period (12 million to 65 million years ago). The ranges of the Himalayan system developed from north to south in a series of stages. Even today the system has not reached a state of equilibrium, and earthquakes are frequent.

The Himalaya consists primarily of metamorphic rocks; extensive areas of igneous rocks are in the south. Palaeozoic and Mesozoic marine sediments are found in several regions.

III

Topography

The Himalaya can be divided into four parallel, longitudinal mountain belts of varying widths. From south to north these belts are the Outer Himalaya, or Sub-Himalaya; the Lesser Himalaya; the Great Himalaya; and the Tethys, or Tibetan Himalaya. The Outer Himalaya comprises the Siwalik Range, which rises steeply from the northern Indian plains and descends gently to flat-floored basins. To the north is the Lesser Himalaya, where the mountains rise to 4,572 m (15,000 ft) and the valleys lie at elevations of about 915 m (3,000 ft). The Great Himalaya, which forms the backbone of the Himalayan system, contains the main ranges and highest peaks and rises above the snow line to an average elevation of about 6,100 m (20,000 ft). The maximum height of these mountains is in Nepal, where 9 of the world's 14 highest peaks are found. Among these are Kanchenjunga, Dhaulagiri, and Annapurna in addition to Everest. The world's second highest mountain, K2, is in the Karakorum Range in the border area between Pakistan and China. To the north are the more complex Tibetan ranges and plateaux.

The passes in the Himalaya, which often lie along or across glaciers, are the highest in the world, with an average height of about 3,050 m (10,000 ft). All passes above about 4,880 m (16,000 ft) are closed by snow from November to May.

IV

Rivers, Lakes, and Glaciers

The Himalaya is drained by several major Asian rivers, including the Brahmaputra, Indus, and the Sutlej, as well as by many of their important tributaries. The headwaters of the River Ganges are also in the Himalaya. Numerous small glacial lakes are found at the heads of gorges, but the largest lakes lie at comparatively low elevations. Above the snow line, in all parts of the Himalayan system, small glaciers are found. Several glaciers are as much as 48 km (30 mi) long; the majority, however, are less than half that size.