Weathering and erosion processes in the natural environment Exposed rock surfaces undergo a constant degradation by physical chemical and biological processes that is called weathering. The degraded rock particles are subsequently carried away and deposited through the actions of wind and rain in a process called erosion. Key examples of such erosion materials are the silt and sediment carried by rivers. The speed and volume of erosion as well as the chemical composition of the eroded material largely determines the build up and the quality of soil and groundwater. Weathering and erosion processes therefore are of key interest for environmental scientists and managers.