One of the greatest diagnostic features of geomorphology is the character of river cross profiles. The cross-profile of the Himalayan Rivers is marked by gigantic gorges especially in the higher Himalayas. Gansser shows the Kiogar gorge in a tributary of the Alaknanda carved out in a limestone anticline of the Great Himalayan Range on the northern border of the U.P. The great Himalayan rivers like the Arun Kosi, the Gandak, the Karnali and the Sutlej cut across the Great Himalayan gorges which are 2000-4000 meters deep, while the width of these gorges between summits is 10-25 km. There are stupendous gorges at interval of 80 or 100 km forming ‘the wonders of this part of India’.
The cross-profiles of the valleys in Inner Himalayas show abrupt change in their form. There may be broad V-shaped cross-sections in some reaches but these suddenly give place to narrow U or I-shaped gorges. The latter occur in hard crystallines while the former occur in soft rocks. The Indus valley near Gilgit has gravel terraces. The valley is some 5000 meters deep.
The Sutiej flows in a 1000-meter deep SE-NW canyon parallel to the Himalayan axis through the region called Hundes. This chasm has been cut in Pleistocene sediments consisting of boulder, gravel and clay. Onwards of Shipki pass, the river adopts a southerly course cutting 2000-meter deep rock-walled gorges across the Zanskar and Great Himalayan ranges.
The Sutiej has numerous terraces built in lacustrine silt along its course. Similar terraces also occur along the course of the Chenab and Jhelum. These are indicative of the former existence of numerous lakes in their courses, when the Himalayas were in the young stage of the cycle of erosion.
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V-shaped cross-sections are common in the Himalayas. The idea of their form in the three successive belts of the Great Himalaya, Lesser Himalaya and Outer Himalaya may be obtained from some specific figures. A cross-profile of the Bhagirathi, 25 km to the west of the Gangotri glacier shows valley flanks of 30%. Eastward where relief is higher the slope angle of ‘V’ increases. Thus, about 20 km south of Mt. Everest the slope angle of the flanks of the Dudh Kosi is 55%.
The ‘V’s become wider in the Lesser Himalayas. Thus the Bhagirathi (upper Ganga) c. 10 km above Devaprayag has a cross-section, the angle of whose slope is 23%. In the Siwaliks ‘V’s are still wider. Thus the approximate slopes of the gorges where the Yamuna (Maira), Ganga (Hardwar), Sarda (Barmdeo), Gandak (Bhainsalotan) and Kosi (Chatra) cross the Himalayan foothills respectively are 3%, 7%, 15% and 20%.
The Himalayas are higher and more compressed (along a N-S line) in the east. This explains the greater gradients of rivers as well as the higher angles of valley flanks.
The Himalayan river valleys are marked by some of the steepest thalwegs in the world. There is a drop of as much as 6,000 meters within a distance of 150 km, giving a gradient of 1 in 25 in the case of such larger streams as the Gandak, Ghaghara and Yamuna.