Erosion and Deposition Agents, Forces, and Results Mrs. Sherry Giarrusso Palo Alto Science h"p://commons.wikimedia.org/wiki/ File:Water_erosion_below_Hay_Bluﬀ_-­‐ _geograph.org.uk_-­‐_1074175.jpg h"p://commons.wikimedia.org/wiki/ File:Wind_erosion_Seminole_Canyon.JPG h"p://commons.wikimedia.org/wiki/ File:BavenAan_Clay_Beds_-­‐_geograph.org.uk_-­‐ _1776748.jpg What is 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 What Is Wind 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_Features_in_Wadi_Al-Hitan.jpg What Is Water Erosion? • Water – most influential force in erosion – Moves materials – Transports – Wears large objects with fast moving streams away rocks: • rivers • lakes • oceans http://commons.wikimedia.org/wiki/ File:Water_erosion_below_Scarsoch_Bheag__geograph.org.uk_-_1367808.jpg What Is Wave 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,_Downpatrick_Head_-_geograph.org.uk_- What Is Gravitational Erosion? • Mass Movement downward movement of rock and sediments, due primarily to the force of gravity – – Streams and glaciers • move material from higher é to lower ê elevation – Occurs continuously on all slopes » slow moving and sudden movement until equilibrium is reached http://commons.wikimedia.org/wiki/ File:Purbeck_,_Old_Harry_-_geograph.org.uk_- What Is Glacial 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 What is 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 u Wind speed can be related to variations in heating and cooling. u 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 - Water • 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 - Ice • 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 What’s the Difference? • • • WEATHERING – Think of weather wearing rock down. EROSION – Think of a road and traveling. DEPOSITION – Think of depositing money into a bank.