Which of the following is an example of erosion?

• A. Sediment carried away by a river.
• B. Freeze-thaw cycles causing rock to crack.
• C. Rainwater dissolving minerals.
• D. Wind-blown sand abrading a rock surface.

Answer: (A)

Erosion is the process of moving soil or rock from one place to another by natural forces such as water, wind, or ice. When sediment is carried away by a river, it means material has been removed from its original location and transported downstream—this transport is what erosion is all about. The other options describe weathering or abrasion: freeze-thaw cycles crack rock in place (mechanical weathering), rain dissolves minerals (chemical weathering), and wind-blown sand wears away a rock surface (abrasion, a form of weathering). Erosion requires movement, whereas weathering describes the breakdown that often happens before erosion can carry the material away.