What forms when eroded sediments are deposited as a river slows?

• A. Dune
• B. Delta
• C. Moraine
• D. Ridge

Answer: (B)

When a river slows down, it loses the energy needed to carry the sediment it has eroded from its watershed. That sediment then settles out of the water and accumulates where the river meets a still body of water, like an ocean or a lake. Over time this deposition builds up land that fans out into the water, forming a delta. The coarsest material tends to drop first near the mouth, while finer material can be carried farther, helping create the network of channels and silt deposits that characterizes a delta.

Dunes are shaped by wind rather than water, moraine is formed from glacial debris left behind as a glacier advances or retreats, and a ridge is a long, elevated crest formed by tectonic or glacial processes. These features aren’t the result of a slowing river depositing sediment at its mouth.