Why do deltas form at river mouths?
Show answer & explanation
Answer: Sediment settles out of slowing water and builds new land
Ocean currents push water back and force the river to drop its load — Wrong. The ocean does not push water back to make the river drop its load; the delta forms because the river's own flow slows at the mouth and can no longer carry its sediment.
Sediment settles out of slowing water and builds new land ✓ — Correct! Rivers carry sediment. At the mouth, water slows as it enters the ocean or lake, losing energy to transport particles. Sediment drops and accumulates over time, building new land that extends into the water—a delta. The Nile, Mississippi, and Ganges have massive deltas, and their shape depends on the balance between sediment supply and wave or tide erosion.
Rivers split into branches that each carry water to the sea — Wrong. Rivers do branch into distributaries near the mouth, but that branching is a feature of the delta, not the reason it forms; the land is built by sediment dropping out of slowing water.