Weathering

1. Weathering

2. Weathering Lectures • Weathering vs. Erosion • Joints: Setting the Stages • Physical (Mechanical) Weathering • Chemical Weathering • Products and Forms Made by Weathering • Weathering Landscapes

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

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

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10. 2. Joints: Setting the Stage Joints – fractures (that allow water to penetrate and weather the rock) Not what you are thinking!

11. 2. Joints: Setting the Stage Joints dependent on lithification (sedimentary & foliated metamorphic rocks) – where fractures occur along bedding planes or along foliations Joints independent of lithification (all rock types) – all other fractures

12. Joints dependent on Lithification • Sedimentary Rocks – where fractures occur along bedding planes

13. Joints dependent on lithification • Can also be Foliated Metamorphic Rocks – where fractures occur along bedding planes or along foliations

14. Joints dependent of lithification Rocks can be cracked by cooling, leading To columnar jointing

15. Columnar Jointing From contraction after lava flow cools

16. Joints independent of lithification Rocks can be cracked by Tectonic Stresses

17. or faulting/folding stresses the rock

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

19. Sandstone fractured across bedding planes

20. Can have both together • Along bedding (& foliation) weaknesses and cutting across

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

22. Abrasion • Often see abrasion by sediment or soil transport by water over rock… this both weathers (decays) and erodes by abrasion (like sand paper)

23. Anthropogenic Abrasion • carving chiseling, bullet impacts

24. Frost Weathering

25. Check out these links Click here to see a 360 degree view of fractured rock in Antarctica by frost weathering Click here to see a fun movie clip about frost weathering

26. Breaks rock along small fractures

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

28. Aesthetic, so used in commercials

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

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

31. Glacial Erosion Great Way to Generate Pressure Release

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

33. 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. • Thermal Expansion: During temperature fluctuations, salts trapped in pores may expand to a greater degree than the surrounding rock minerals. • Hydration: The hydration of various salts causes expansion & contraction, pushing apart the silicate host minerals

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

35. tafoni – larger cavernous forms

36. (Goudie and Viles, 1997:168)

37. Alveoli – smaller cavernous forms: alveolization is the process

38. Alveolization can occur from more than salt weathering, including insects & bird activity!

39. Weathering along bases of rocks:basal notches

40. Salt Efflorescence

41. Salt subflorescence(salt under the surface)

42. Salt subflorescence(salt under the surface – usually see when look at undersides of eroded flakes)

43. fissuresol wedging & calcrete wedging

44. Order from innermost crack out:calcrete – white calcium carbonateiron film – orange clays and ironrock varnish- outer edge black clays & manganese/Iron

45. Wedging can split small rocks and giant boulders – carbonate & dust washes away – leaving iron film and rock varnish

46. Thermal Expansion/Contraction • Thermal Expansion/Contraction

47. A bit of moisture & sudden heat makes the rock pop – typically flakes (fingernail thick)but sometimes scales (thicker)

48. “flaking”Wyomingrock artsite

49. Wetting/Drying Vermillion Cliffs

50. Root Pressure creates weaknesses