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Erosion and Deposition http://commons.wikimedia.org/wiki/File:Water_erosion_ below_Hay_Bluff_-_geograph.org.uk_-_1074175.jpg http://commons.wikimedia.org/wiki/File:Wind_erosion_ Seminole_Canyon.JPG http://commons.wikimedia.org/wiki/File:Bave ntian_Clay_Beds_-_geograph.org.uk__1776748.jpg Erosion •Erosion – moving of rock material from one place to a new location – Three processes must take place: • detachment of particles • lifting them • transporting them – Agents of erosion: • flowing water • moving ice • waves • gravity • wind – Sand is composed of small pieces of rock that have been: • weathered from a parent rock • eroded • deposited somewhere else Erosion •Wind – wears away rocks and is responsible for the creation of deserts such as the Sahara and the Gobi - Most effective in moving loose material – Main effects: 1. Wind lifts small particles and moves them away. 2. Suspended particles may cause erosion on solid objects by abrasion (rubbing). – Occurs in areas where there is not enough rainfall to support vegetation http://commons.wikimedia.org/wiki/File:Wind_Erosion_Featu res_in_Wadi_Al-Hitan.jpg Erosion •Water – most influential force in erosion –Moves materials –Transports large objects with fast moving streams –Wears away rocks: • rivers • lakes • oceans • Ground/sinkholes http://commons.wikimedia.org/wiki/File:Water_e rosion_below_Scarsoch_Bheag__geograph.org.uk_-_1367808.jpg Erosion • Waves – relentless pounding • Erodes: • softer/weaker rock first • harder/more resistant left behind • Can take over 100 years to erode a rock to sand • Energy of waves and chemicals contained in the water erode the rock off the coastline. http://commons.wikimedia.org/wiki/File:Wave_Erosion,_Downpatri ck_Head_-_geograph.org.uk_-_369272.jpg Erosion •Mass Movement – downward movement of rock and sediments, due primarily to the force of gravity –Streams and glaciers • move material from higher to lower elevation – Occurs continuously on all slopes » slow moving and sudden movement until equilibrium is reached http://commons.wikimedia.org/wiki/File:Purbeck_,_Old_Har ry_-_geograph.org.uk_-_1711962.jpg Erosion • Ice – moves and carries rocks, grinding the rocks beneath the glacier – Plucking occurs when water enters cracks under the glacier. • freezing • breaking off pieces of rock that are then carried by the glacier – Abrade (abrasion) • cuts into the rock under the glacier • smoothing • polishing the rock surface http://commons.wikimedia.org/wiki/File:Ushaped_valley_at_the_head_of_Leh_valley,_Ladakh_(2).JPG Deposition •Deposition – laying down of sediment that has been transported by a medium such as wind, water, or ice –Process of erosion stops: • when the moving particles fall out of the transporting medium and settle on a surface –Speed of the medium slows or the resistance of the particles increases, the balance changes and causes deposition –Speed can be reduced by large rocks, hills, vegetation, etc. Deposition Wind speed can be related to variations in heating and cooling. Transportation of particles in wind: – Fine particles in suspension hundreds of km from its original source in the desert – Heavier material may be blown along the ground. – Material is deposited when the wind changes direction or loses its strength. http://commons.wikimedia.org/wiki/File:Desert_Chihuahuan_Big_Bend.JPG Deposition • Running water enters a large, fairly still body of water and its speed decreases • SPEED • As the speed of the water decreases, the water's ability to carry sediment also decreases. • Deposited in streams, rivers, and oceans: • Running water deposits sediments where the slowing water can no longer move them. • Largest particles are deposited near the shore. • Increasingly smaller particles settle out farther from the shore where the water is calmer. http://commons.wikimedia.org/wiki/File:Enchanted_Rock,_stream.jpg Deposition • Glacial flows of ice – become slower when the ice begins melting – Deposits left by glaciers: – Outwashes are deposits similar to those left by rivers. – Large chunks of broken rock deposited at the base and sides of the glacier as it melts and recedes are called Moraines. – When the glacial ice melts, smaller material is carried by the rivers. http://commons.wikimedia.org/wiki/File:Cavell_Glacier_with_Crevices_and_Annual_Rings.jpg • WEATHERING – Think of weather wearing rock down. • EROSION – Think of a road and traveling. • DEPOSITION – Think of depositing money into a bank. Running Water Deposits Well-Sorted Particles Vertical Sorting – When sediments are suddenly deposited into water. The particles separate by size with the largest on the bottom and smallest on top. Horizontal Sorting – When rivers empty their sediments into quiet bodies of water. Particles are sorted by size with larger particles being found closer to the shore and smaller particles being carried out into the body of water to be deposited. Delta – A fan-shaped deposit of sediment at the mouth of a river