Weathering

1. Mass Wasting Erosion Soils Weathering

2. Weathering: the physical and chemical breakdown of rock – exposed to wind, water, ice, and living organisms Regolith: loose or broken rock layers resulting from weathering Regolith covers most of the earth. Soil: the upper-most layer of regolith that supports life

3. Do “things” last for ever ? Consider : new concrete a 1955 Chevrolet

4. Rocks can be broken down or chemically altered on the earth’s surface. Mechanical Weathering: Rocks are physically broken down by various surface processes into smaller parts without changing physical properties. Chemical Weathering: Rocks are altered from one form to a completely new form with a different set of physical properties.

5. I weathering Discuss with a friend: • Describe the difference between • mechanical and chemical weathering. • 2. Give two examples of MW and CW you • have observed. I will get an A on my exams and quizzes

6. Mechanical Weathering – the breaking down of rocks How do we expose “more surface” area for chemical weathering to do its job ? Let’s show some surface Rock More surface area Less surface area Increased mechanical weathering accelerates chemical weathering.

7. Frost Wedging • Repeated cycles of freezing • and thawing. • Ice expands 9% of its volume. • Rock is continually broken • down over geologic time • Part of the Yosemite • weathering cycle.

8. Frost Wedging – rocks are broken into plates and split apart.

9. Exfoliation • unloading of overlying rock • material releases pressure • expansion of granitic bodies • causing “sheeting” or slabbing • granite • granite “sheets” break along • planes of weakness or joints • exacerbated by frost wedging • dominant weathering force • in Yosemite

10. Exfoliation Dome – granite is “sheeting” from loss of pressure due to unloading processes.

11. Types of Mechanical Weathering Processes • Biological Activity – breaking down rocks through • animal burrowing • humans • plant roots Human intervention Animal burrowing Plant root weathering

12. I mechanical weathering Discuss with a friend: 3. Why is MW important? 4. Briefly describe how frost wedging, unloading and biological activity contributes to mechanical weathering I will get an A on my exams and quizzes

13. Chemical Weathering Rocks are chemically altered producing a new compound • Why would a perfectly good rock want to change • it’s appearance? • STABILITY! Rocks require stability and achieve • equilibrium with it’s surroundings • Most rocks are not chemically stable at the • earth’s surface • Minerals (compositions) change to become stable • at surface conditions

14. What common agent can begin the process of chemical alteration????? • The Universal Solvent – WATER (H2O) How would we speed up the action of water? Rain + ????? What in the atmosphere is added to water to create a weak acid? H2O (rain) + CO2 (atmosphere) = H2CO3 (carbonic Acid) Let’s weather some granite with the natural acid H2CO3 Granite – the most abundant continental rock weathering the potassium feldspar (orthoclase) bicarbonate potassium silica orthoclase carbonic acid water kaolinite clay 2KAlSi2O8 + 2(H+ + HCO3) + H2O Al2Si2O5(OH)4 + 2K + 2HCO3 + 4SiO2 Granite has been chemically weathered and broken down into individual grains. in solution

15. Reduced to Clay

16. I Chemical weathering Discuss with a friend: 5. What is the universal solvent? 6. How is carbonic acid naturally Produced? 7. How would you describe the “last” or most reduced material ----- the end product of chemical weathering? I will get an A on my exams and quizzes.

17. Soil – product of weathering containing solids, liquids, and gas. CLAY What’s in your soil? Loam – dominant soil fraction Humus – partially decayed organic material CO2/Air – fills the soil voids Water – wets the soil and carries high levels of dissolved substances SAND SILT 50% sand, 20% silt, 30% clay Sandy Clay Loam

18. Soil Profiles: • horizons: a layer of soil with • distinctive physical and chemical • properties. • sequence of soil horizons from • the surface to the underlying • bedrock O A O- Organic matter (humus) E A- Dark layer mixed with mineral and organic matter B E- light colored layer produced from removal of soluble material “leaching” C B- accumulation of clay C- unweathered parent rock

19. Factors that influence soil formation: • Parent Material: • residual regolith – soil forms emplace or “insitu” Soil forms and weathers emplace from parent material. • transported regolith – regolith that is moved by rivers, • wind, and ice transported river deposits transported regolith on Mars

20. Factors that influence soil formation: • Climate – soil profiles differ around the world • which is directly influenced by climate • arid soils vs. tropical soils • Living organisms – a HUGE influence on soils • Plants make organic matter. • (humus) – animals mix the soil • and recycle air and water. • Topography – the contour or “slope” of the land • Time – the longer the time the more mature a • a soil becomes --- 1000’s of years

21. Classification of soils • Soil Taxonomy – Soil classification is based on physical/chemical properties • of a soil profile, influenced by climate, living organisms, • topography, and time. --- How many different soils are there? • Six categories of soil classification: • order • sub-order • great groups • sub groups • family • series Broadest 12-basic soil orders: Names of soils are derived from Latin/Greek. Latin = solum – soil Alfisols (High-Nutrient Soil) Andisols ((Volcanic Soil) Aridisols (Desert Soils) Entisols (New Soils) Gelisols (Permafrost Soils) Histosols (Organic Soils) Inceptisols (Young Soils) Mollisols (Prairie Soils) Oxisols (Tropical Forest Soils) Spodosols (Conifer Forest Soils) Ultisols (Low-Nutrient Soil) Verisols (Swelling Clay Soil) 12-orders Specific 19,000 -series

22. Distribution of Earth’s soils What soil type (order) characterizes the San Joaquin Valley? Alfisols

23. Mass Wasting

24. Mass Wasting What do these pictures have common?

25. What is Mass Wasting ? • down-slope movement of rock, • regolith, and soil under the direct • influence of GRAVITY What force acts alone – to create movements of the earth? GRAVITY

26. The role of Mass wasting– What’s it good for? • Responsible for the evolution of • landforms – features of the earth • Weathering weakens rock – does • not create significant landforms • Need mass wasting to impact • weathering and shape significant • earth features

27. I mass wasting Discuss with a friend: 8. What is mass wasting ? 9. What single “force” acts alone to produce mass wasting processes? 10. What is the sole purpose of mass wasting? I will get an A on my exams and quizzes.

28. So, what “triggers” a mass • wasting episode allowing gravity to • move the mass downward? • The role of water • Slopes to steep • Removal of vegetation • Earthquakes

29. The Role of Water Saturated Sand

30. The Role of Water • Water saturates surface materials. • Particles loose their cohesion (can’t • stick together). • Particles slide past one another and • slip downward under gravity forces.

31. Slopes to Steep • steeper slopes exceed the “angle of • repose” and material moves downward to • stabilize or reach equilibrium. • Angle of repose: • the angle at which particles are overtaken by • gravity and move downward • angle depends on size, shape, and moisture content • of accumulated particles Wet Sand Dry Sand

32. Over steepening exceeding the angle of repose, nature reacts by attempting equilibrium

33. Removal of Vegetation • where plants are lacking – mass wasting • attacking • root systems bind soil • where soil is removed frequent • down slope movements occur

34. The Role of Earthquakes • Areas that have not moved in “years”, • are activated by seismic waves. Mass slide produced by an earthquake dammed a river forming a lake.

35. How would you describe the angle of repose?

36. I Mass Wasting Discuss with a friend: 11. Describe the 4 triggers that enable mass wasting process. 12. What the angle of repose? 13. What is the most dominant “trigger” causing the onset of mass wasting? I will get an A on my exams and quizzes

37. How do geologists classify various mass wasting processes? • Classification is based on Unconsolidated: debris, mud, earth Material Bedrock: rock Fall: freefall of material Slide: material moves cohesively along well defined surface Flow: material moves down-slope as a viscous fluid Motion

38. I Mass Wasting. Discuss with a friend: 14. What two criteria do geologist use to classify mass wasting movements? I will get an A on my exams and quizzes

39. Classification of Mass Wasting Processes

40. SLUMP • downward movement of a sliding • mass, rock or unconsolidated material • that moves as a single unit along a • curved surface • moves very slow • over-steepened slopes (T) • water saturated (T)

41. Rockslide • blocks of bedrock break loose and slide • down a slope Over steepness (T) • Debris slide • unconsolidated material break loose and • slide down a slope Debris slide Rockslide

42. Debris Flow • rapid mass movement containing soil • and regolith with large amounts of • water Water saturation (T)

43. Lahars • debris flows composed largely of volcanic • material from the flanks • flows down existing stream valleys • extremely destructive events’ • water saturation (T) Lahars buried a village

44. Earth Flow • form on hillsides in humid areas with • abundant precipitation • water saturated – hill may break away • under gravity and weight of soil • water saturated (T) • rich in clays and silt • slow moving flows

45. Soil Creep • the gradual downhill movement of soil and • regolith. • soil moves extremely slow • soil disturbed by rain, roots • water saturation (T)