Which one of the following east flowing rivers of India has rift valley due to down warping?

Answer: (a) Damodar

The Damodar flows through a rift valley (graben) — which is why it holds Gondwana coal.

The idea

A tectonic trough can guide a river irrespective of whether the river flows east or west. Faulting and broad bending of the crust create low ground that drainage can follow. Do not transfer the westward direction of familiar rift rivers to every river in a trough.

Why the others are wrong

(b) The Mahanadi flows in a normal valley.

(c) The Son follows the Vindhya scarp.

(d) The Yamuna is a Himalayan river.

The trap

Rift valleys are usually associated with west-flowing Narmada and Tapi — the Damodar is the east-flowing exception.

Also know

The Damodar coal belt includes Jharia, Bokaro and Raniganj, with coal in Gondwana sedimentary basins. Its tributaries include the Barakar and Konar. Compare the west-flowing Narmada and Tapi with the eastward Damodar system. Down-warping is broad downward bending; a graben is specifically a down-dropped block between faults.