Why Is a Bird- Foot Delta Like That of the Present-

Multiple Choice

Why is a bird- foot delta like that of the present- day Mississippi below New Orleans likely to change naturally toward one with the shape of an equilateral triangle like the upper- case, Greek letter delta (A) ?

A) Present- day distributaries have higher gradients than potential new ones.
B) Potential, new, distributary channels have higher gradients, causing downcutting of the existing channels.
C) Increased sediment loads since the mid- nineteenth century have caused the major distributaries to be filled with sand.
D) Potential, new, major distributary channels have steeper gradients than existing channels.