Nitin

The Himalaya range runs for about 2,400 km, from Nanga Parbat (Pakistan) in the west to Namche Barwa in the east. The width varies between 250-300 km. The Himalayan range comprises three parallel ranges, arranged by elevation and geological age.

Composite satellite image of the Himalayan range. The Tibetan Plateau is near the centre and the Taklamakan plain is visible as the lighter area near the top.The youngest of the three is called the Sub-Himalayan Range (Shivalik Hills) and has an elevation of about 1,200 m. This range is made up of erosion material from the rising Himalaya. Running parallel to this is the Lower Himalayan Range, which has an elevation between 2,000�5,000 m. The northernmost range is called the Great Himalayas and is also the oldest of the three. It has an elevation of more than 6,000 m and contains a large number of the world's highest peaks including the three highest, Mount Everest, K2 and Kangchenjunga. Much of Nepal and Bhutan lies in the Himalaya. The Pakistani states of Baltistan and Indian states of Jammu and Kashmir, Himachal Pradesh, Uttaranchal, Sikkim and Arunachal Pradesh lie mostly in the Himalaya. A very small portion of southeastern Tibet also lies in the Himalaya. (However, the Tibetan Plateau is by definition beyond the Himalaya, and thereby not part of it). It is in fact just north of India and Bangladesh.

The flora and fauna of the Himalayas varies with climate, rainfall, altitude, and soils. The climate ranges from tropical at the base of the mountains to permanent ice and snow at the highest elevations. The amount of yearly rainfall increases from west to east along the front of the range. This diversity of climate, altitude, rainfall and soil conditions generates a variety of distinct plant and animal communities, or ecoregions.

The Himalayas are among the youngest mountain ranges on the planet. According to the modern theory of plate tectonics, their formation is a result of a continental collision or orogeny along the convergent boundary between the Indo-Australian Plate and the Eurasian Plate. The collision began in the Upper Cretaceous period about 70 million years ago, when the north-moving Indo-Australian Plate, moving at about 15 cm/year, collided with the Eurasian Plate. By about 50 million years ago this fast moving Indo-Australian plate had completely closed the Tethys Ocean, whose existence has been determined by sedimentary rocks settled on the ocean floor and the volcanoes that fringed its edges. Since these sediments were light, they crumpled into mountain ranges rather than sinking to the floor. The Indo-Australian plate continues to be driven horizontally below the Tibetan plateau, which forces the plateau to move upwards. The Arakan Yoma highlands in Myanmar and the Andaman and Nicobar Islands in the Bay of Bengal were also formed as a result of this collision.

The Indo-Australian plate is still moving at 67 mm/year, and over the next 10 million years it will travel about 1,500 km into Asia. About 2 cm/year of the India-Asia convergence is absorbed by thrusting along the Himalaya southern front. This leads to the Himalayas rising by about 5 mm/year, making them geologically active. The movement of the Indian plate into the Asian plate also makes this region seismically active, leading to earthquakes from time to time