When a river flows directly into a shallow sea, sediments may form a large triangular deposit called a...

When a river flows directly into a shallow sea, sediments may form a large triangular deposit called a...

• A. Estuary
• B. Mouth
• C. Delta
• D. Alluvial Fan

Answer: (C)

Sediment carried by a river slows and drops as it enters a shallow sea, and over time this material builds up at the river’s mouth into a landform that extends into the water. Because it forms from ongoing deposition at the boundary between river and sea, the resulting area takes on a triangular shape and is called a delta. Deltas arise from the continuous supply of sediment and the spreading out of the river’s flow as energy decreases in the standing water.

An estuary is the tidal, mixing zone where freshwater meets seawater, not the triangular landmass formed by deposition. The mouth is simply the river’s opening, not the resulting deposit. An alluvial fan forms where a stream exits high terrain and spreads sediment onto flatter ground, not at the interface with a sea.