Himalayas history and geography page
The Himalayas are a mountain range in Asia separating the plains of the Indian subcontinent from the tibetan plateau. The Himalayan range is bordered on the northwest by the karakoram and hindukush ranges, on the north by the tibetan plateau, and on the south by the Indo-Gangetic Plain. Some of the world's major rivers, the Indus, the Ganges, and the Tsangpo-Brahmaputra, rise in the Himalayas, and their combined drainage basin is home to some 600 million people. The Himalayas have profoundly shaped the cultures of South Asia; many Himalayan peaks are sacred in Hinduism and Buddhism. Lifted by the subduction of the Indian tectonic plate under the Eurasian Plate, the Himalayan range runs, west-northwest to east-southeast, in an arc 2,400 kilometres long. Its western anchor, Nanga Parbat, lies just south of the northernmost bend of Indus river, its eastern anchor, Namcha Barwa, just west of the great bend of the Tsangpo river. The range varies in width from 400 kilometres in the west to 150 kilometres in the east.
The Himalayan range is one of the youngest mountain ranges on the planet and consists mostly of uplifted sedimentary and metamorphic rock. According to the modern theory of plate tectonics, its formation is a result of a continental collision or orogeny along the convergent boundary between the Indo-Australian Plate and the Eurasian Plate. 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. During the Upper Cretaceous, about 70 million years ago, the north-moving Indo-Australian plate (which has subsequently broken into the Indian Plate and the Australian plate) was moving at about 15 cm per year. About 50 million years ago this fast moving Indo-Australian plate had completely closed the Tethys Ocean, the existence of which has been determined by sedimentary rocks settled on the ocean floor, and the volcanoes that fringed its edges. Since both plates were composed of low density continental crust, they were thrust faulted and folded into mountain ranges rather than subducting into the mantle along an oceanic trench. An often-cited fact used to illustrate this process is that the summit of Mount Everest is made of marine limestone from this ancient ocean. Today, the Indian plate continues to be driven horizontally at the Tibetan Plateau, which forces the plateau to continue to move upwards. The Indian plate is still moving at 67 mm per year, and over the next 10 million years it will travel about 1,500 km into Asia. About 20 mm per 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 per 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. During the last ice age, there was a connected ice stream of glaciers between Kangchenjunga in the east and Nanga Parbat in the west. In the west, the glaciers joined with the ice stream network in the Karakoram, and in the north, joined with the former Tibetan inland ice. To the south, outflow glaciers came to an end below an elevation of 3,300 to 6,600 ft. While the current valley glaciers of the Himalaya reach at most 20 to 32 kilometres in length, several of the main valley glaciers were 60 to 112 kilometres long during the ice age. The glacier snowline (the altitude where accumulation and ablation of a glacier are balanced) was about 4,590 to 5,450 ft lower than it is today. Thus the climate was at least 7.0 to 8.3 °C colder than it is today.