Final answer:
A delta is a landform commonly formed at the mouth of a river where it deposits silt and sediment into a larger body of water, creating fertile triangular-shaped lands that can support agriculture.
Step-by-step explanation:
The landform often formed at the mouth of a heavily silted stream is called a delta. Deltas are typically created when rivers carry silt and sediment towards the ocean or a large lake. As the river water slows down dramatically upon reaching these larger bodies of water, the silt carried by the river settles and accumulates over time, often forming an often triangular-shaped section of land. This process can lead to the creation of fertile lands that are excellent for agriculture, such as in large deltaic agricultural areas where multiple crops can be supported.
Examples of this process include the Mississippi River delta, which exhibits the deposition of colloidal clay particles as freshwater mixes with seawater, and the formation of fertile delta ponds and associated habitats in places like Eugene, Oregon. Even on other planets, such as Mars, evidence of ancient delta deposits suggests that similar processes may have occurred in the planet's history.