At the mouth of which of the following rivers, the 'bird's foot' type delta is formed?

The correct answer is D, the Mississippi. Its delta in Louisiana is the textbook bird's foot delta. The river carries a very heavy sediment load into the Gulf of Mexico, where wave and tidal action are weak, so sediment builds up quickly at the mouth. This pushes long, finger-like distributaries (passes) far out into the sea, giving the shape of a bird's foot.

• Huang Ho (A): Its delta in the Bohai Sea is fan-shaped and shifts its course often, so it is not the classic bird's foot form.
• Danube (B): Its Black Sea delta is a large wetland delta with many channels, but it is not the textbook bird's foot case.
• Nile (C): The Nile delta is the classic arcuate (fan-shaped) delta in the Mediterranean, where wave action smooths the coastline.

Core concept: delta shape depends on the balance between sediment supply from the river and marine forces such as waves, tides and currents. Sediment-dominated deltas with weak marine energy become bird's foot, wave-dominated ones become arcuate, and tide-dominated ones become estuarine. For Mains, this links to coastal geomorphology and to land loss in Louisiana, where levees have cut the sediment supply to the delta.

Trap: Aspirants pick the Nile because it is the most famous delta. The Nile is arcuate; the bird's foot shape belongs to the Mississippi.