1. Weathering and Soils

2. Weathering & Soils 1.Weathering vs. Erosion 2.Joints: Setting the Stage 3.Physical (Mechanical) Weathering 4.Chemical Weathering 5.Weathering Products 6.Weathering Landscapes 7.Soils: Introduction

3. 1. Weathering vs. Erosion Common Error Made in K-12 Earth Science Teaching: these are synonyms No! Weathering – chemically dissolving candy or physically crunching candy – breakdown in place Erosion – moving pieces (dissolved or as fragments)

4. 1 st - Weathering = decay in place 2 nd - Detach = break off 3 rd Erode = move

5. 1 st – decayed 2 nd – detached 3 rd – eroded

6. The balance between weathering and erosion defines the landscape

7. In deserts – transport is faster

8. Humans can upset the balance and accelerate erosion. So when transport (detachment and erosion) becomes faster than weathering, landscapes are not sustainable.

9. s

10. 2. Joints: Setting the Stage Joints – fractures (that allow water to penetrate and weather the rock) Many ways to make joints: Cooling & contraction Tectonic Stresses

11. Very different!

12. Columnar Jointing From contraction after lava flow cools

13. or faulting/folding stresses the rock

14. Joints can even fracture sedimentary strata from regional tectonic pressures

15. 3. Physical (Mechanical) Weathering Frost weathering Pressure release weathering Salt Weathering Thermal Expansion/Contraction Wetting/Drying Root pressure

16. Frost Weathering

17. Classroom Resources Clip of freezing exploding metal Spin-around showing fractured rock in Antarctica

18. Breaks rock along small fractures

19. Breaks rock along large fractures & produces jagged alpine topography

20. Aesthetic, so used in commercials

21. Pressure Release Sometimes called “exfoliation” (like exfoliating skin) – incorrect usage pressure release shells

22. Erosion removes overburden & shells pop off as pressure is released

23. Glacial Erosion Great Way to Generate Pressure Release

24. Salt Weathering Salt is common in deserts Salt is common along coasts

25. Mechanics of Salt Weathering Salt Crystal Growth: Extreme pressures in cracks and rock pores are caused by salt crystal growth from solution. There are varying causes of and extents to which salt growth occurs. Hydration: The hydration of various salts causes expansion & contraction, pushing apart the silicate host minerals Thermal Expansion: During temperature fluctuations, salts trapped in pores may expand to a greater degree than the surrounding rock minerals.

26. Caverns (tafoni) Base of rock notching (basal weathering) Wedging

27. Caverns (tafoni – larger cavernous forms)

28. (Goudie and Viles, 1997:168)

29. Caverns (alveoli – smaller cavernous forms)

30. Weathering along bases of rocks

31. Wedging

32. Thermal Expansion/Contraction

33. A bit of moisture & sudden heat makes the rock pop

34. Vermillion Cliffs Wetting/Drying

35. Root Pressure

36. Online Animations Physical Weathering Visualizations http://serc.carleton.edu/NAGTWorkshops/vis ualization/collections/physical_weathering. html

37. Physical weathering “sets up” chemical weathering

38. Why do you ground coffee? to increase surface area

39. Classroom Resource Animation of physical weathering exposing more surface area for chemical weathering

40. 4. Chemical Weathering Egyptian Obelisk – chemically weathered when brought to wetter environment, so water matters!

41. Classroom Resource Clip introducing chemical weathering

42. Dissolution Sugar & Salt Dissolves – so do rocks Best example: limestone

44. Other rocks dissolve too, but slower than limestone

45. Acid Rain Accelerates Decay Crosses political boundaries …

46. Taj Mahal Athens

47. Classroom Resources Dissolution from dropping a weak acid on limestone Close-up of dissolving mineral in electron microscope

48. Oxidation

49. Hydrolysis Water molecules at the mineral surface dissociate into H+ and OH- and the mobile H+ ions penetrate the crystal lattice, creating a charge imbalance, that causes cations (important nutrients) such as Ca 2+, Mg 2+, K + and Na + to diffuse out. For example, the feldspar reacts to decay and leaves a residue of clay mineral. H+H+ OH - H+H+

50. Hydration Water alters structure Complexation Metals released from primary minerals such as iron and manganese build complexes with organic components, such as fulvic acids and humic acids, causing an imbalance between cations and anions – that leads to mineral decay

51. Online Animations Chemical Weathering Visualizations http://serc.carleton.edu/NAGTWorkshops/vis ualization/collections/chemical_weathering.html

52. 5. Weathering Products Quartz Sand: quartz is one of the last minerals to decay – it survives weathering & erosion to be deposited in

53. Rock Coatings

54. Nutrients - released from mineral weathering Calcium Sodium Magnesium Potassium

55. Clay Minerals Formed

56. Clays represent Earth’s ultimate decay of rock

57. If have too much clay, it shrinks & swells

60. Classroom Resources Feldspar turns to clay

61. 6. Weathering Landscapes Consider a common rock – granitic rocks (granite, granodiorite, tonalite, diorite …) made up of interlocking minerals

62. Decay of weak minerals (biotite, feldspar) separates grains and makes granite sand called - GRUS

63. Grus produced most rapidly where joints intersect

64. Grus erosion from joints creates rounded forms at Mt Rushmore

65. Core stones made when corners of granite blocks weathered into grus

67. Core stones in subsurface are “emerge” onto the surface as the grus washes away with rain and flowing water, because they are too big to be carried by water

68. Grus washes away easily with rain, leaving piles of core stones - tors

69. Tors (piled up core stones) very common in the Sonoran Desert

70. Tors often take on significance to people

71. Granite weathering took a long time in the subsurface (from groundwater) – spheroidal forms were then exposed by erosion of grus

72. Dome forms produced the same way: subsurface weathering in joints Granite that is not heavily joined becomes domes after grus washed away Rio de Janeiro - Sugar Loaf

73. Half dome was made in the subsurface in tropical times and exposed by erosion of grus

74. Karst Topography: entire landscape made by dissolution weathering

75. Other rocks can also dissolve to form karst (gypsum, rock salt)

77. If exposed see grooves (karren)

78. Solution doline – dissolve fastest in joints

79. “Sinkhole” (doline)

80. Can also create doline by collapse

81. Florida – lots of groundwater pumping & roof of cave collapses Before Development After solution doline

82. Sinkholes merge to form Uvale valley

83. “Blind” rivers flow down sinkholes into cavern systems

84. Caves Formation Limestone Cave

85. Caves Features

86. Stalagtite Stalagmite Speleothems: Cave formations

87. Limestone Caves Step 1: Groundwater dissolves limestone, most aggressively at the water table. Also, groundwater follows lines of weakness in the limestone enlarging caves. Step 2. When the water table drops, stalactites and stalagmites can form on the roof and floor, respectively.

88. The water table usually drops when the stream has “cut down” to a lower level

89. Stalagmite – requires lots of time with water table much lower

90. Classroom Resources Cave Formation “Spin Around” Blind River

91. The southwest China karst region has “tower” karst” forms

92. 7. Soils: Introduction Soils are more than just weathered rock

93. Soils organize themselves into layers

94. Online Free Resource URL

101. Classroom Resources Important in making humus & aerating soil Biomantles show Dynamic nature of soils

102. Classroom Resources: Soils Soil Horizons Visualizations http://serc.carleton.edu/NAGTWorkshops/visualization/collections/soil_ horizons.html Soil Orders Visualizations http://serc.carleton.edu/NAGTWorkshops/visualization/collections/soil_ orders.html Physical Properties of Soils http://serc.carleton.edu/NAGTWorkshops/visualization/collections/soil_ physical_properties.html

103. Online Resources

104. Imagery seen in this presentation is courtesy of Ron Dorn and other ASU colleagues, students and colleagues in other academic departments, individual illustrations in scholarly journals such as Science and Nature, scholarly societies such as the Association of American Geographers, city,state governments, other countries government websites and U.S. government agencies such as NASA, USGS, NRCS, Library of Congress, U.S. Fish and Wildlife Service USAID and NOAA.