Rivers shape landscapes through erosion by gradually wearing down rocks and soil along their banks and beds as they flow downstream. This erosion process is mainly caused by the force of the flowing water, which picks up and carries away sediment. Deposition occurs when rivers slow down, allowing sediment to settle and accumulate along the riverbanks or in areas such as river deltas. Over time, erosion and deposition can create various landforms such as river valleys, floodplains, and deltas, ultimately shaping the landscape.