Question

The picture below shows a floodplain alongside a river channel. A floodplain is a flat landform created by deposition on the bottom of a wide river valley.
Over time, a river gradually shifts its position back and forth across a valley bottom. As it shifts, it drops sediment to gradually build up a flat floodplain.

As the landform's name implies, another process plays a role in floodplain formation. Which of the following describes this process?Glaciers move through a river valley every winter and flatten out the landforms.

 A. Glaciers move through a river valley every winter and flatten out the landforms.

 B. A river may flood its valley and form a permanent inland sea.

 C. Acid rain weathers large rocks until they form a broad, flat plain.

 D. A river floods over its channel banks and deposits sediment on the wide valley bottom.

Answer 1

The appropriate answer is D. a river floods over its channel banks and deposits sediment on the wide valley bottom. 

Flood plains usually develop along the lower course of the river. The lower course has a gentle gradient and so the flow of water is not fast and therefore the bed load of the river gets deposited. Rivers carry materials such as boulders, pebbles, gravel, sand, silt and clay. The larger size materials will get deposited upstream while the finer material will travel to the lower course. 
The glacier melt each year increases the volume of the river so it will overflow its banks and deposit materials in layers on the flood plains. Materials on the flood plain are usually fine such as sand and silt. 

Answer 2

Answer:

D. A river floods over its channel banks and deposits sediment on the wide valley bottom.