A river widens its valley by removing sediment. This process is called:

• A. Weathering
• B. Erosion
• C. Deposition
• D. Compaction

Answer: (B)

Erosion is the process at work here. It describes how natural forces, like a river, wear away and transport soil and rock from one place to another. In this scenario, the flowing water removes sediment from the valley walls and channels, widening the valley as material is carried away downstream. Weathering would break down rocks in place but not move them away. Deposition would occur if the sediment were dropped off and accumulated elsewhere, and compaction is about sediments being pressed together over time, not about removing material. So removing sediment to widen the valley is erosion.