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Erosion and Deposition

Erosion and Deposition. Two Important Definitions. Erosion : the removal of weathered rock and soil from its original location

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Erosion and Deposition

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  1. Erosion and Deposition

  2. Two Important Definitions • Erosion: the removal of weathered rock and soil from its original location • Deposition: the dropping of eroded material in a different location (when you make a deposit at the bank; you are leaving money; here rock is deposited in a new place)

  3. Gravity • The power behind most erosional agents • Rock is pulled downslope by the force of gravity

  4. 4 Types of Erosion • Erosion by Water • Erosion by Glacier • Erosion by Wind • Erosion by Living Things

  5. 1a. Erosion by Water • Rill Erosion : when a narrow stream cuts a small channel into the land (think narrow stream) • Gully Erosion: stream of water has gone beyond Rill Erosion and now the stream of water is deep and wide (think wider stream)

  6. 1b. Erosion by Water- Rivers and Streams • Each year streams carry billions of metric tons of sediments and weathered material to the coastal areas • Over time, the build up of sediment produces deltas (example: Colorado River Delta-right; Mississippi River Delta - left)

  7. 1c. Erosion by Water- Waves • Sand on an ocean shoreline is repeatedly picked up, moved, and deposited • Constant movement of water is a continuous erosional process • Deposits can lead to sand bars and barrier islands (example: Outer Banks of N.Carolina)

  8. 2. Glacial Erosion • Currently cover 10% of the Earth’s surface • Once covered 30% • Scraping and gouging the earth as they move huge rock and piles of debris over great distances • Glacial movements scratch and grind surfaces and deposit material over long distances

  9. 3. Wind Erosion • Moves fine, dry particles a great distance • Most common in areas without vegetation holding the soil into places • Can be prevented with a wind barrier (stand of trees or other vegetation planted perpendicular to the direction of the wind)

  10. 4. Erosion by Living Things Examples of Erosion by living things: • Excavating land • Planting a garden • Developing land • Building a highway All of these can lead to erosion

  11. Mass Movement • Downslope moving of soil and weathered rock resulting from the force of gravity • ALL mass movements occur on slopes

  12. Factors that Influence Mass Movement • Material’s weight • Materials resistance to sliding or flowing • Trigger (like at earthquake) • Water

  13. Classification of Mass Movement • Creep: slow, steady downflow of loose weathered material a) slowly creep can cause once vertical utility poles and fences to tilt

  14. 2) Flows: slow movements of soil a) mudflows: swiftly moving mixtures of mud and water

  15. Mudflow • http://www.youtube.com/watch?v=n1cCs-S5EKc

  16. 3) Slides: top layers of soil are thin and move downslope rapidly a) Landslides b) Slumps (landslide on a curved surface) c) Avalanche (snow melts in sun, refreezes at night and the fallen snow moves downslope)

  17. Avalanche • http://www.youtube.com/watch?v=99j17GL3qlE

  18. 4) Rockfalls: rocks are loosened by physical weathering, • they then break loose and fall downslope a) less likely in humid climates where a layer of soil and vegetation cover the rock

  19. Rock fall • http://www.youtube.com/watch?v=ZVYGJYnJTi0

  20. People • Humans can minimize the destruction caused by mass movement by not building near the base of unstable slopes • >25o slopes are at the greatest risk of a catastrophic mass movement

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