Erosion is the movement of materials from one place to another, usually accomplished by wind, ice or water. Eventually, these materials including different sized sediments are deposited in a distant location. Also, if there is a mountain, the force of gravity causes soil and sediments to "creep" downhill. Living things can sometimes remove sediments and transport them as well--think of prairie dogs digging underground burrows. Sometimes, humans can cause erosion to speed up when we remove trees and native plants from an area and replace those with crops. If there is a natural disaster such as flooding or drought, these non-native plants which are not adapted for these areas die and the soil is easily eroded by wind or by water. This occurred in the 1930's in the American Dust Bowl. Farms in the midwest experienced several years of drought and because the native grasses were no longer present, the soil eroded creating dust storms as far as the East Coast. Native plants have underground root systems to hold soil in position.