Final answer:
A long depression in the land containing a river is called a valley, shaped by erosion from flowing water and influenced by environmental factors.
Step-by-step explanation:
A long depression in the surface of the land that usually contains a river is called a valley. Valleys are typically formed over time by the action of the river water eroding the soil and rock, shaping the landscape. Such depressions facilitate the flow of water from higher elevations to lower areas and often lead to the formation of rivers and streams. Factors like precipitation patterns, vegetation, topography, land use, and soil characteristics influence the development and evolution of valleys and rivers within them.
The term is also associated with the concept of a drainage basin, which is the geographic area drained by a river and its tributaries. Additionally, where a river empties into a larger body of water, such as a sea or an ocean, it creates a delta, which is characterized by the deposition of sediments like gravel, sand, and silt.