Which process is demonstrated by the formation of a sand dune?

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

Answer: (C)

Forming a sand dune shows deposition—the laying down of sediment as the transporting force loses enough energy that grains can no longer be carried. Wind moves sand in small jumps and rolls (saltation), and when it slows down or encounters a barrier, those grains settle out of the flow and accumulate. Over time, this ongoing deposition builds up a pile that becomes a dune, with layers of deposited material forming the body of the dune.

Erosion would remove material rather than build it up, and weathering is the breakdown of rocks into smaller pieces rather than the transport and accumulation of loose sand. Condensation has to do with water changing from a gas to a liquid, which isn’t involved in dune formation.