P. Chapter 15 - Chapter 15 Wind and Deserts Wind an...

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Chapter 15 Wind and Deserts Wind – an important geological agent in eroding, transporting, and depositing loose sediment. - deserts - along shorelines - plains Wind Transport Wind is a turbulent fluid, so transports sediment in much the same way as running water. Wind typically has a greater velocity, but lower density, than water which affects the particle size it can transport. 1. Bed Load – sand-sized particles and larger. 2. Suspended Load – clay- and silt-sized particles Bed Load Saltation – bed load moves by intermittent bouncing. Sand grains are set rolling and bouncing by the wind, a grain is lifted and carried a short distance, as it falls to the surface, it strikes other grains causing them to bounce. Once saltation begins, it sets off a chain reaction of collisions between sand grains. Grains continue to move, even if the wind speed drops below that necessary to start the sand moving in the first place. Suspended Load Even though the clay- and silt-sized particles are much smaller and lighter than sand-sized, the wind usually moves the sand-sized first. A thin layer of motionless air lies next to the ground, so clay- and silt-sized particles remain undisturbed. The sand-sized particles stick up into the turbulent air, so are set in motion. The clay- and silt- sized particles only move if this stationary air layer is disturbed. Ex. A dirt road on a windy day. Once in suspension, these fine particles may be carried many kilometers from their source.
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Wind Erosion Abrasion Def’n: the impact of saltating grains on an object Effects (geologically) are usually minor because the sand particles are rarely lifted higher than 1 meter. Wind abrasion may produce many bizarre features. 1. Ventifacts – stones whose surfaces are polished, pitted, grooved, or faceted by the wind 2. Yardangs – elongated and streamlined ridges. Generally grouped in clusters aligned parallel to the prevailing winds. Probably form by differential erosion. These features have been observed on Mars. 3. Deflation – removal of loose surface sediment - deflation hollows or blowouts – caused by differential erosion - desert pavement – fine particles are removed leaving a close-fitting mosaic of larger particles that protect the underlying soil from further erosion. (See fig. 15.8, p. 435) Wind Deposits Two Types 1. Dunes – typically sand-sized particles deposited close to their source. 2.
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This note was uploaded on 04/16/2008 for the course GEOL 1403 taught by Professor Teague during the Spring '08 term at Tarrant County.

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P. Chapter 15 - Chapter 15 Wind and Deserts Wind an...

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