Which of the following is NOT a process of overland erosion?

The correct response is based on the understanding of erosion processes. Gully erosion, rill erosion, and sheet erosion are all types of overland erosion.

Gully erosion occurs when water concentrates in small channels on the landscape, which deepen and widen over time as runoff increases. Rill erosion involves the formation of small channels, typically less than 30 cm wide, when water flows over the soil surface, detaching and transporting soil particles. Sheet erosion is the removal of thin layers of soil over large areas, often happening when rainwater flows across a sloped surface.

In contrast, thermal erosion is not classified as an overland erosion process. It instead refers to the erosion caused by temperature changes, which can lead to the melting of ice or thawing of permafrost, resulting in the movement of soil and sediment. This process does not stem from the typical runoff and surface water flow associated with overland erosion. Understanding these definitions helps clearly distinguish between the different types of erosion and their causes.