The river that gave India its name, flowing from the Tibetan plateau through Ladakh to the Arabian Sea.
The Indus is one of the great rivers of the subcontinent. It rises from glaciers near Mount Kailash on the Tibetan Plateau, runs northwest through the high, arid valleys of Ladakh, then bends south and west and eventually reaches the Arabian Sea.
Through Ladakh it holds a remarkably straight northwest line, and there is a reason for that. For much of this stretch the river runs right along the Indus–Tsangpo suture, the crushed, weakened seam where India welded onto Asia. Rivers exploit weakness: sheared, broken rock erodes far more easily than solid rock, so the young river found the join and settled into it.
The Indus is also older than the mountains it crosses. It is what geologists call an antecedent river, one that was already flowing on its course before the land beneath it rose. As the collision of India and Asia forced the ranges upward, the river kept sawing downward at roughly the pace the rock was lifted. So instead of being dammed or pushed aside, it stayed in place and cut a deep slot straight through the growing mountains.
The clearest proof lies far downstream, where the Indus swings around the Nanga Parbat massif and plunges through one of the deepest gorges on Earth, thousands of metres below the surrounding peaks. There the rock is being lifted unusually fast, and dating of the bare bedrock benches the river has left behind shows it is grinding down at a similar rapid rate, on the order of several millimetres a year. That balance, cutting down about as fast as the land rises, is exactly what lets an antecedent river hold its course across a rising mountain belt.
So the Indus records two histories at once. Its straight upper course traces the ancient join between two continents, and its deep gorges record its long contest with the mountains that join threw up. It has been holding its line and cutting down for millions of years. On its lower plains, where the river finally slows and spreads its silt, that fertile ground fed the Bronze-Age cities of the Indus Valley (Harappan) civilisation, among the earliest urban cultures on Earth, and the river gave India its name.
Sources
- Natural Earth
- Burbank et al. (1996), Incision and differential bedrock uplift along the Indus River near Nanga Parbat, from 10Be and 26Al exposure age dating of bedrock straths, Earth and Planetary Science Letters
- Thakur, V. C. Indus Tsangpo suture zone in Ladakh: its tectonostratigraphy and tectonics, Journal of Earth System Science