Evolution of the Peninsular drainage
Topic: Drainage System of India: Rivers, Basins and Patterns · NCERT: Class 11, Ch 3 "Drainage System"
Meaning
The Peninsular rivers are much older than the Himalayan rivers. Three events in the past shaped how they flow today.
- In the early Tertiary period, the western flank of the Peninsula subsided (sank) below the sea. This upset the old, balanced arrangement of rivers on both sides of the central divide.
- When the Himalayas rose, the northern part of the Peninsula sank and trough faults formed. These are long, sunken strips of land between cracks in the crust. The Narmada and Tapi now flow in these faults.
- The whole block tilted slightly from northwest to southeast, so most rivers now flow to the Bay of Bengal.
Example
The Narmada flows west in a rift valley between the Vindhyas and the Satpura. It fills its fault trough with debris and reaches the Arabian Sea south of Bharuch through an estuary, not a delta. Meanwhile the Mahanadi, Godavari, Krishna and Kaveri follow the tilt east.
Don't confuse with
- Indo-Brahma hypothesis: this explains the Himalayan drainage. It says one great Miocene river was broken up into the Indus, Ganga and Brahmaputra systems. It does not explain the Peninsular rivers.