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Aeolian Geomorphology

Aeolian Geomorphology - Aeolian:1 Aeolian Geomorphology...

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Aeolian:1 Aeolian Geomorphology Wind flow Sediment transport Factors affecting wind erosion Sand Dunes Blowing Dust Aeolian geomorphology is the study of wind processes and the landforms they create. Aeolus was the Greek god of wind. Like running water, wind is capable of transporting sediment and, so, shaping the earth's surface. The two processes are alike in many ways. Both air and water are fluids - liquids and gases behave similarly in many respects. The main difference for our purposes is that water flows down hill under the influence of gravity while gravity has less of an effect on air particles. As you know, air moves because of pressure differences . Air flowing over the ground acts like water flowing over the bed of a stream. The air in contact with the surface is slowed by friction. This air slows the air above it, etc., which results in a progressive increase in the wind speed with height above the surface. Like water in streams, the air flows in a turbulent fashion, with movement in all directions, though the net movement is downwind. ground surface slower faster Feel the wind sometime. You will notice that it is not constant, the speed is always fluctuating- the fast spurts are called gusts and the slow ones lulls. Because the wind speed differs with height, any measure of wind speed makes sense only if the height of measurement is given. The standard height is ten meters. Sediment Transport The decrease in wind speed is because of friction and the result is that some of the kinetic energy of the wind is being applied to the ground surface. This is the force that drives wind erosion. Obviously, this force is positively related to the wind speed.
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Aeolian:2 If wind speed increases over a surface with loose particles, eventually a threshold speed will be reached and particles will be entrained (erosion begins), as shown by the top curve in the diagram below. The speed needed to entrain particles is dependent on size, just as it is for running water. The most easily entrained particle size is about 0.1 mm, which is fine sand. The diagram also shows that sand will continue to be transported even if the wind speed goes below the threshold. This is because it takes a certain speed to start sand moving, but once motion has started, it is the impact of other grains that is causing entrainment and not the direct action of the wind. The bottom curve shows the wind speed needed to keep material moving–below this curve, nothing will move. In other words, for a given particle size, if the wind speed is above the top curve, erosion will occur and below the bottom curve, transport will stop. Between the curves, transportation will continue. Erosion Deposition Transportation Particle Size Wind Speed Wind is not strong enough to move particles larger than sand (>2 mm) except under very strong winds. In physics, the amount of force an object has is related to its mass and its speed . The mass of running water is, essentially, the weight of the water.
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Aeolian Geomorphology - Aeolian:1 Aeolian Geomorphology...

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