Physical erosion often causes rocks to get smaller or smoother. Physical Erosion Physical erosion describes the process of rocks changing their physical properties without changing their basic chemical composition. This transported material is called sediment. The brown color indicates that bits of rock and soil are suspended in the fluid (air or water) and being transported from one place to another. If the wind is dusty, or water or glacial ice is muddy, erosion is taking place. Most erosion is performed by liquid water, wind, or ice (usually in the form of a glacier). Erosion is the opposite of deposition, the geological process in which earthen materials are deposited, or built up, on a landform. A similar process, weathering, breaks down or dissolves rock, but does not involve movement. Video Clip by Dr.Erosion is the geological process in which earthen materials are worn away and transported by natural forces such as wind or water. The clip also explains how threshold velocity varies depending on the nature of the soil surface. This video clip explains the three steps in wind erosion (detachment, transport, and deposition). Wind erosion most commonly occurs in arid and semi-arid regions, because of the frequent occurrence of dry and windy conditions. As the wind speed decreases, deposition of soil particles begins. While larger particles rolling along the soil surface move shorter distance and also shatter other soil particles along the way. Fine sands, silt or clay size particles can be transported for great distances by strong winds. Once detached these particles are transported by either suspension into air and/or rolling along the soil surface. Wind detaches soil particles from the surface. Similarly, wind erosion is a world-wide problem that occurs when strong winds blow across dry soil on unprotected surfaces. As the water velocity slows down it loses the energy needed to continue carrying the detached suspended soil particles, and the soil particles are then deposited in their new location. How many particles and how far they are transported depends on the velocity and volume of the running water. If the rainfall rate exceeds the rate at which water can infiltrate the soil, the excess water runs off and often carries the detached soil particles with it.ĭetached particles (sediment) are carried with flowing water down the slope. This can clog and seal soil pores and result in reduced water entry (infiltration) into the soil. Some of the detached particles float into soil pore spaces. Raindrops can splash soil particles, moving them up to three feet away. Raindrop impact is the primary cause of particle detachment. The impact of raindrops shatters surface aggregates and detaches soil particles from them. The impact of a water droplet dislodges and scatters soil particles. Clay or silt size particles can be carried a great distance before deposition, while larger sand-size particles will be carried only a short distance. This action deposits the sediment when the wind and water energy subsides. DEPOSITION of particles in a new location: This action carries soil particles in the moving wind or water.ģ. This action dislodges the particles from the soil by the impact energy of the rain or wind. The three steps common to both water and wind erosion: Accompanying Exercise: (For Students to print off, complete and turn in for a grade) How Water and Wind Erosion Occur- Exercise (pdf) Objective By the end of this section the student/user will be able to: Describe the mechanisms/processes of how water and wind erosion occur.
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