1. The transport of weathered materials…
EROSION-
The transport of weathered materials…

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

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

5. 1995 Landslide in La Conchita, CA.

6. 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.

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

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

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

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

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

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

13. 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)

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

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

16. Watershed Regions of New York State

17. 3 factors affecting Stream Velocity
Gradient – slope of the stream
Discharge – volume of water
Stream channel shape

18. Stream Velocity in a Straight Channel Fastest – middle just below surface

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

20. 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)

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

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

24. 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

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

26. V-SHAPED VALLEY…

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

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

31. 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

34. Point Bars show deposition Cut Banks show erosion

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

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

39. Stream Development – Old Age

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

45. What is the correct sequence in stream development?

46. Levee Formation

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

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

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

51. Alluvial fans form when streams come out of mountains onto flat land – velocity slows and deposition occurs

52. Erosion by Waves and Long shore Current
Where lake or ocean waters meet land, waves and currents act as agents of erosion, creating unique landscape features

53. Winds at the ocean’s surface cause waves

55. Longshore Current
Waves are refracted or bent in the shallow water of the shore
Water near the shore is pushed in one direction along the shore – called longshore current
Sediments are carried in a zig-zag pattern in the SAME direction as the longshore current

60. The sand trapping effect of the jetties to the north at Charleston, South Carolina has deprived Morris Island of needed sand. As a result, the island has eroded to the point that this previously land based lighthouse is now 400 meters out to sea.

61. Which direction is the long shore current carrying sediment????

62. Barrier Islands Wave Action creates sand bars
Waves and Longshore current - can form barrier islands Ex. Fire Island

64. Wind Erosion Sediment – sand or smaller
Arid regions or ocean coastlines
2 types:
1. Deflation – lowers the land
2. Sandblasting and Abrasion

65. Sandblasting and Abrasion
Wind can only lift sand to about 1 meter high - results in “Mushroom Rock”
Frosted or Pitted sediments – rocks with flat sides

68. Windward side
Leeward side