Soil erosion is when the land surface gets worn away by water, wind, ice, and other natural forces. Water erosion is a big problem because it not only makes soil less fertile, but also pollutes water with sediment and nutrients. Erosion is a natural process, but human activities can make it worse. Some soils erode more easily than others, even under the same conditions. The shape and steepness of the land affect how much soil gets washed away. Researchers are trying to understand erosion better by breaking it down into smaller parts that can be explained physically.