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EROSION-

EROSION-. The transport of weathered materials…. Major Erosive Agents:. Running Water GLACIERS WIND OCEAN CURRENTS AND WAVES MASS WASTING (GRAVITY!). EROSION by gravity. Also known as MASS MOVEMENT Avalanches or rock falls Land or Mud Slides Slump or Flows Creep.

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EROSION-

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  1. EROSION- The transport of weathered materials…

  2. Major Erosive Agents: • Running Water • GLACIERS • WIND • OCEAN CURRENTS AND WAVES • MASS WASTING (GRAVITY!)

  3. EROSION by gravity • Also known as MASS MOVEMENT • Avalanches or rock falls • Land or Mud Slides • Slump or Flows • Creep

  4. 1995 Landslide in La Conchita, CA.

  5. The two forces involved in all mass movements are GRAVITY (pulling the material down) and FRICTION (keeping the material in place).Typically excessive amounts of water lessen the force of friction and lead to a landslide.

  6. New York City’s Henry Hudson Parkway in Upper Manhattan A 75 foot retaining wall collapsed on May 12th, 2005.

  7. Running water move more sediment than any other agent of erosion.

  8. What happens to rainfall when it hits earth???? • Some evaporates • Some is absorbed and becomes ground water • Some is run off

  9. What determines if rainwater becomes runoff or groundwater? Ground Conditions: • Saturated vs. unsaturated • Vegetation – amount of plants • Slope or Gradient of the Land

  10. Running Water – Most of North America is above sea level. Water flows high to low sea level due to gravity

  11. When Runoff becomes confined to a channel – Stream Exists

  12. Watersheds or Drainage Basins • Smaller stream that flows into a larger stream is called a tributary • Tributaries and land that contribute to the stream is called a drainage basin or watershed (COMPARED TO A BATHTUB. WATER THAT COLLECTS IN A BATHTUB FLOWS TOWARD THE DRAIN.) • The drainage basin of one stream is separated by a drainage divide (ridges or mountains – higher elevations)

  13. HOW WATERSHEDS/DRAINAGE BASINS FORM – RED LINE IS DRAINAGE DIVIDE

  14. Watersheds: Continental Divide and Appalachian Mountains Water goes from high sea level to low sea level

  15. Watershed Regions of New York State

  16. 3 factors affecting Stream Velocity • Gradient – slope of the stream • Discharge – volume of water • Stream channel shape

  17. Stream Velocity in a Straight ChannelFastest – middle just below surface

  18. The velocity changes in the S-shaped curves called MEANDERS. Fastest on the outside of the curve – erosionSlowest on the inside of the curve - deposition

  19. STREAMS CARRY MATERIAL IN … • Solution: dissolved material (includes salts) • Suspension: particles carried in the flow of the water (Clay, silt, sand) • Bed load: particles carried by rolling, bouncing, or dragging along the stream bed (Pebbles, cobbles, boulders)

  20. THE GREATER THE VELOCITY OF A STREAM… • THE LARGER THE SEDIMENT PARTICLES IT CAN CARRY • THE MORE TOTAL SEDIMENTS IT CAN CARRY

  21. Water Velocity determines the size particle that can be moved via suspension and bed load

  22. Stream Development – Early Stage • The landscape is continuously being reshaped by stream erosion. Plateaus can be cut by rivers to form canyons. Valleys can be carved in mountains as rivers flow through them. • As the stream begins to down cut into the land – waterfalls and rapids form

  23. Stream Development – Young Stage • V-Shaped Valley • Rapids and Waterfalls • No Flood Plain – a level plain that borders stream

  24. V-SHAPED VALLEY…

  25. RAPIDS AND WATERFALLS • Rapids - Different resistance among rocks cause FAST-FLOWING WATER • Waterfalls – Rapids develop into waterfalls as softer rock erodes

  26. Stream Development - Mature Stage • Lateral erosion widens the valley profile – slope decreases • River meanders pronounced • A FLOOD PLAIN develops

  27. As the stream grows larger – it begins to shift its course in a series of bends or curves called meanders seeking out the lowest elevation

  28. Point Bars show depositionCut Banks show erosion

  29. Cut bank on outside of curve due to higher velocity of water – more erosion Cut bank on outside of curve Point Bar on inside of curve

  30. Stream Development - Old Age • Very Wide Flood Plain • Land worn down to flat surface • Oxbow Lakes

  31. Stream Development – Old Age

  32. Eventually, it takes too much energy to keep meandering, so rivers will cut off a bend, resulting in an OXBOW lake…

  33. What is the correct sequence in stream development?

  34. Levee Formation

  35. SEDIMENTS ERODED BY RUNNING WATER WILL HAVE THESE CHARACTERISTICS • ROUNDED and SMOOTH • SORTED AND LAYERED

  36. SEDIMENTS ERODED BY RUNNING WATER WILL BE … • SORTED – all materials are about the same size

  37. Contour lines showing head of the stream to the mouth of stream with delta Velocity slows when entering a large body of water

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