1. Erosion and Landscape Evolution

2. How Do We Know Rivers Cut Their Valleys? John Playfair, 1800 Tributary valleys almost always join the main valley at exactly the same elevation, even though the valleys may begin many miles apart. This is very unlikely unless the rivers have cut the valleys. How Rivers Widen Valleys

3. Constructive and Destructive Processes Highlands Erosion Dominates Destructive Processes History not Preserved Little Geological Record Transport Lowlands, Coastal Plain, Lakes and Seas Deposition Dominates Constructive Processes History Preserved Good Geological Record

4. Stream Abrasion, Marathon County

5. Stream Potholes, Marathon County

6. Mega-Potholes, St. Croix Valley

7. Anatomy of a Drainage System

8. The Continental Divide, Colorado

9. Stream Order

10. The River That Did This….

11. Looks Like This Near Its Source

13. The Ideal Stream Cycle (W.M. Davis, 1880) Not a Literal Time Sequence Youth Maturity Old Age Rejuvenatio n

14. Youth V-Shaped Valley Rapids Waterfalls No Flood Plain Drainage Divides Broad and Flat, Undissected by Erosion Valley Being Deepened General Agreement on this stage, lots of examples

15. Youthful Landscape, Arizona

16. Maturity (Early) V-Shaped Valley Beginnings of Flood Plain Sand and Gravel Bars Sharp Divides Relief Reaches Maximum Valleys stop deepening General Agreement on this stage, lots of examples

17. Young-Mature Landscape, California

18. Mature Landscape, Kentucky

19. Maturity (Late) Valley has flat bottom Narrow Flood Plain Divides begin to round off Relief diminishes Sediment builds up, flood plain widens River begins to meander Many geologists believe slopes stay steep but simply retreat.

20. Old Mature Landscape, Tennessee

21. Old Age Land worn to nearly flat surface (peneplain) Resistant rocks remain as erosional remnants (monadnocks) Rivers meander across extremely wide, flat flood plains

22. Monadnock, Colorado

23. Monadnocks, Maine

24. Old Age Landscape, South America

25. The Onset of Old Age? Indiana

26. Old Age? Or Maybe Not: Nebraska

27. Old Age? No! (Wisconsin)

28. Rejuvenation Some change causes stream to speed up and cut deeper. – Uplift of Land – Lowering of Sea Level – Greater stream flow Stream valley takes on youthful characteristics but retains features of older stages as well. Can happen at any point in the cycle.

29. Rejuvenation, Utah

30. Rejuvenation of an old-age landscape

31. Rejuvenation, San Juan River, Utah

32. Rejuvenation of an early mature landscape

33. Machu Pichu, Peru

35. Why the Stream Cycle Doesn't Explain Everything Rises and falls in sea level during the ice ages rejuvenated most landscapes to some extent. Climate changes mean that mass-wasting processes in temperate regions may have undergone radical changes repeatedly in the last few million years. In places where conditions have remained uniform for long times, like the stable interiors of Africa, Australia and South America, the ideal stream cycle seems to work best.

36. Sea Level and River Profile

37. Superposed (Antecedent) Drainage Streams Cut Right Through High Topography

38. Rejuvenated Peneplain: the Northeastern US

39. Rejuvenated Peneplain

40. Superposed Drainage, Delaware Water Gap

41. Water Gap, Pennsylvania

42. Cumberland Mountains, Virginia

43. Cumberland Gap

44. Devil’s Gap, Wyoming

45. Approach to Devil’s Gap

46. Rivers and Crustal Movement, California

47. Tectonic Uplift, Colorado

48. Tectonic Uplift, Grand Canyon

49. The Ultimate Antecedent Drainage, India- Nepal- Tibet

50. Drainage Diversion

51. The Huang He: “China’s Sorrow” 1887: 2,000,000 dead 1931: 3,700,000 dead 1938: The Chinese dynamite levees to slow the Japanese; half a million Chinese died.

52. River Diversions in the Caspian Region

53. Stream Piracy: Northeast England

54. Why is the Danube Blue?

55. Piracy on the Danube

56. Flood, Ecuador

57. Flood, Green Bay, June 1990

59. Building Smart in a Flood Plain

60. Channeled Scablands, Washington

61. Fluid Flow is Scale-Invariant

62. Erosion of Bedrock River Beds

63. Scabland Terrain, Oregon

64. Erosion of Soft River Beds

65. Mega-Gravel Bar, Washington

66. Mega-Flood Deposits, Washington