What's New Mountains, plateaus, valleys, and plains are examples of Earth's various landforms. Some of these landforms were formed as a result of rocks breaking down and erosion. Soil erosion is a naturally occurring phenomenon that affects all landforms. Soil is a non-renewable resource that cannot be renewed after it has been eroded. Soil erosion is the irreversible change of the characteristics of the soil. In agriculture, it refers to the natural physical forces that wear away the topsoil. 4 CO_04_Science5 Mod