1. Weathering Processes

2. Weathering 1.Weathering vs. Erosion 2.Joints: Setting the Stage 3.Physical (Mechanical) Weathering 4.Chemical Weathering

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. s

7. 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

8. Very different!

9. Columnar Jointing From contraction after lava flow cools

10. or faulting/folding stresses the rock

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

12. 3. Physical (Mechanical) Weathering Frost weathering Pressure release weathering Salt Weathering Thermal Expansion/Contraction Wedging (Fissuresols & Calcrete) Wetting/Drying Root pressure

13. Frost Weathering

14. Breaks rock along small fractures

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

16. Aesthetic, so used in commercials

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

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

19. Glacial Erosion Great Way to Generate Pressure Release

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

21. 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.

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

23. Caverns (tafoni – larger cavernous forms)

24. (Goudie and Viles, 1997:168)

25. Caverns (alveoli – smaller cavernous forms)

26. Weathering along bases of rocks

27. Wedging

28. Sequence in Rock Fractures

29. Generalized Process

30. Fissuresol wedging can pry apart bedrock

31. Fissuresol wedging can pry apart mountain sides and giant boulders

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

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

42. Other rocks dissolve too, but slower than limestone

43. Acid Rain Accelerates Decay Crosses political boundaries …

44. Taj Mahal Athens

45. Oxidation

46. 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+

47. 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

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