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. Types of Mechanical Weathering Processes Frost Wedging: repeated cycles of freezing and thawing Water Water Freezes (expands) pieces break off (watch for falling rock) rock rock Dominantly takes place in freezing / thawing areas Unloading – reduction of pressure from overlying rocks -- take the pressure off me. overlying rocks Sheet like structures granite pluton Sheet like structures eroded and uplifted granite pluton

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

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

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

11. I mechanical weathering Discuss with a friend: • Why is MW important? • 2. Briefly describe how frost wedging, • unloading and biological activity • contributes to mechanical weathering I will get an A on my exams and quizzes

12. 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

13. 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

14. Reduced to Clay

15. I Chemical weathering Discuss with a friend: • What is the universal solvent? • 2. How is carbonic acid naturally • Produced? • 3. 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.

16. 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

17. 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- weathered parent rock

18. 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

19. 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

20. Mass Wasting

21. Mass Wasting What do these pictures have common?

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

23. 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 River Valley widened by mass wasting Example: River Valley from weathering

24. I mass wasting Discuss with a friend: 1. What is mass wasting ? 2. What single “force” acts alone to produce mass wasting processes? 3. What is the sole purpose of mass wasting? I will get an A on my exams and quizzes.

25. 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

26. 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.

27. 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

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

29. 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.

30. I Mass Wasting Discuss with a friend: • Describe the 4 triggers that enable • mass wasting process. • 2. What the angle of repose? • 3. What is the most dominant “trigger” • causing the onset of mass wasting? I will get an A on my exams and quizzes

31. 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

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

33. Classification of Mass Wasting Processes

34. 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)

35. 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 flow Rockslide

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

37. 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

38. 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

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