Geography of Nepal
Nepal is of roughly trapezoidal shape, about 800 kilometres (500 mi) long and 200 kilometres (120 mi) wide, with an area of 147,516 km2 (56,956 sq mi). It lies between latitudes 26° and 31°N, and longitudes 80° and 89°E. Nepal's defining geological processes began 75 million years ago when the Indian plate, then part of the southern supercontinent Gondwana, began a north-eastward drift caused by seafloor spreading to its south-west, and later, south and south-east. Simultaneously, the vast Tethyn oceanic crust, to its northeast, began to subduct under the Eurasian plate. These dual processes, driven by convection in the Earth's mantle, both created the Indian Ocean and caused the Indian continental crust eventually to under-thrust Eurasia and to uplift the Himalayas. The rising barriers blocked the paths of rivers creating large lakes, which only broke through as late as 100,000 years ago, creating fertile valleys in the middle hills like the Kathmandu Valley. In the western region, rivers which were too strong to be hampered, cut some of the world's deepest gorges. Immediately south of the emerging Himalayas, plate movement created a vast trough that rapidly filled with river-borne sediment and now constitutes the Indo-Gangetic Plain. Nepal lies almost completely within this collision zone, occupying the central sector of the Himalayan arc, nearly one-third of the 2,400 km (1,500 mi)-long Himalayas, with a small strip of southernmost Nepal stretching into the Indo-Gangetic plain and two districts in the northwest stretching up to the Tibetan plateau.
Nepal is divided into three principal physiographic belts known as Himal–Pahad–Terai. Himal is the mountain region containing snow and situated in the Great Himalayan Range; it makes up the northern part of Nepal. It contains the highest elevations in the world including 8,848.86 metres (29,032 ft) height Mount Everest (Sagarmāthā in Nepali) on the border with China. Seven other of the world's "eight-thousanders" are in Nepal or on its border with Tibet: Lhotse, Makalu, Cho Oyu, Kangchenjunga, Dhaulagiri, Annapurna and Manaslu. Pahad is the mountain region that does not generally contain snow. The mountains vary from 800 to 4,000 metres (2,600 to 13,100 ft) in altitude, with progression from subtropical climates below 1,200 metres (3,900 ft) to alpine climates above 3,600 metres (11,800 ft). The Lower Himalayan Range, reaching 1,500 to 3,000 metres (4,900 to 9,800 ft), is the southern limit of this region, with subtropical river valleys and "hills" alternating to the north of this range. Population density is high in valleys but notably less above 2,000 metres (6,600 ft) and very low above 2,500 metres (8,200 ft), where snow occasionally falls in winter. The southern lowland plains or Terai bordering India are part of the northern rim of the Indo-Gangetic Plain. Terai is the lowland region containing some hill ranges. The plains were formed and are fed by three major Himalayan rivers: the Koshi, the Narayani, and the Karnali as well as smaller rivers rising below the permanent snowline. This region has a subtropical to tropical climate. The outermost range of the foothills called Sivalik Hills or Churia Range, cresting at 700 to 1,000 metres (2,300 to 3,280 ft), marks the limits of the Gangetic Plain; however broad, low valleys called Inner Terai Valleys (Bhitri Tarai Upatyaka) lie north of these foothills in several places.