A relief tormented by the impact of two tectonic plates
70 million years ago, the enormous mass of the continent Gondwana (Indian tectonic plate) completed a long journey from southern Africa to Eurasia. The ensuing shock over the following millennia is the most powerful our earth has ever known. Gondwana slides under the continental plate, lifting the seabed to prodigious heights. At the chance of an altitude trail, you can perfectly well discover a marine fossil: originally, Tibet was indeed a sea, the Theetys, whose sediments are still visible. But the gigantic pile-up doesn't stop there: the Indian subcontinent continues its formidable underground bursts at a speed estimated today at 2 cm per year. Compressed between the two continental masses, the granitic rocks escape and rise in altitude to give birth over the millennia to the Himalayan chain. Five million years ago, its peaks reached 3,000 m. Today Nepal is a high seismic risk zone and fourteen peaks are over 8,000 m high. These are, from west to east, the Nanga Parbat (8,125 m), K2 or Chogori (8,611 m), K3 or Phalchen Gangri, Gasherbrum I (Hidden Peak 8,068 m) and II (8,035 m), Dhaulagiri (8,167 m), annapurna (8,091 m), Manaslu (8,156 m), Shishapangma or Gosainthan (8,013 m), Cho Oyu (8,153 m), Everest (8,850 m), Lhotse (8,571 m), Makalu (8,481 m), Kangchenjunga (8,598 m).
5 natural regions on an extreme altitude range
From virgin forest to high altitude desert, Nepal is a gigantic staircase. In barely a hundred kilometres, this staircase takes you from the torrid plains of India to the arctic cold of the Great Range, before descending steeply to the Tibetan plateau. On a relatively short south-north route, you will experience a succession of climates, vegetation, wildlife and lifestyles of exceptional variety. Within this tiering, it is customary to distinguish five major natural regions that correspond to five levels: the Terai, which is a low-lying tropical zone not far from the great plain of the Ganges; the Siwalik, which are the first mountainous formations to be encountered going from south to north, the low-lying ridges separate wide valleys covered with virgin forest and this region is sparsely inhabited; then comes the Mahabharata Lekh, an intermediate mountain range; the Nepalese plateau which is the heart of the country, the richest, most populated and developed region, we find the big cities of Nepal; and finally the Great Himalayas or Himalayan range which is the area of high and very high mountains, 9 peaks exceed 8 000 m. However, there are forests and crops up to 4,000 m, with pastures above.
The Terai plain and the Siwalik foothills, which stretch south of the massif, give an idea of the natural landscape that has long since disappeared in India: large tropical forests sparsely populated by man, where the unicorn rhino, tiger, antelope and, until recently, malaria, have survived. After the Siwalik, we enter the Middle Country, crossed in Nepal by the Mahabharat mountain range. This area is directly under the monsoon regime, which becomes more intense as you head east and approach the Bay of Bengal. Here, the world record rainfall (12 m per year on average in Cherapunji) is recorded east of the Nepalese border in the Meghalaya Hills of southern Assam. Depending on the altitude, the natural environment varies from subtropical to temperate to alpine. Up to 2,000 m above sea level, frost and snow are unknown. Note that this zone is located at the latitude of Mauritania. 90% of the rains fall between June and October. They radically transform the landscape: the arid yellow gives way to soft green. But the monsoon is capricious; it sometimes likes to be kept waiting, jeopardizing harvests, or, on the contrary, taking away crops, villages and roads when it rains. Erosion problems are often a cause for concern: the multiplication of cultivated fields and the retreat of the forest have weakened the slopes and, as a result, landslides are on the increase. Indeed, this area of average altitude, from 700 to 2,000 m, was, until the last few years, the most populated part of the Himalayas, before the mountain people in search of land began to rush to the malaria-free plains in the second half of the 20th century. Forty per cent of the forests still covering the territory of Nepal are being reduced year by year in favour of rice and maize cultivation.
A hydrography as tormented as the relief
The consequence of the clash of continents: seas and rivers are subject to the chaotic evolution of the relief. Saltwater lakes persist on the Tibetan plateau. Rivers follow a curious path parallel to the ridge lines, before finding an exit to the ocean by digging gigantic canyons. The result is also a series of basins (Kathmandu, Pokhara...) where water has remained trapped before escaping thanks to a collapse. The legends have kept the memory of it: the god Manjushri freed the waters of the Kathmandu valley with a sword stroke, giving birth to the Bagmati river.
Nepal's main rivers originate on the Tibetan plateau before crossing the formidable Himalayan barrier and flowing into the Indian plain where they become important tributaries of the Ganges. Prior to the erection of the range, they dug countless furrows in the middle mountains that form the bulk of Nepal's territory before being able to flow at low altitude by crossing the last obstacle, the Mahabharat Lekh. The river system consists of three main basins. In the west, the Karnali is formed by the confluence of the Mugu and Humla rivers in the north, and the Seti and Bheri rivers in the south. In the centre of the country, the Gandaki includes Kali Gandaki, Seti, Marsyendi, Buri Gandaki and Trisuli, while the Sapta Kosi, in the east, forms a set of seven rivers, as its name suggests, with the junction of the Sun Kosi, Bhote Kosi, Tamba Kosi, Dudh Kosi and, finally, the Arun and the Tamur. You only have to see the canyon dug by the Kali Gandaki, between the thirty or so kilometres that separate two peaks over 8,000 m high, to imagine the power of these rivers, whose flow is multiplied tenfold during the monsoon season.
