River Deltas Are Built by Sediment Deposition, Not Weathering

Weathering does not create river deltas. Weathering breaks down rock in place; it's a source process, not a depositional one.

River deltas form when sediment transported by a river is deposited at its mouth — where the flow velocity drops upon entering a standing body of water (lake, sea, ocean). The river loses energy, drops its load, and builds outwards in a characteristic fan shape.

Key factors: sediment supply, river discharge, wave/tide energy, basin geometry. The Mississippi Delta, Nile Delta, and Mekong Delta are classic examples built over millennia by deposition, not weathering.