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GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
GEOG 100--Lecture 15--Weathering and Mass Wasting
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GEOG 100--Lecture 15--Weathering and Mass Wasting

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  • 1. Weathering and MassWeathering and MassWastingWastingChapter 10
  • 2. 22External vs. Internal ProcessesExternal vs. Internal Processes(the dynamic equilibrium model)(the dynamic equilibrium model)(the dynamic equilibrium model)(the dynamic equilibrium model)
  • 3. 3DenudationDenudation—Large-scale removal of material—Large-scale removal of materialthat lowers the overall profile of thethat lowers the overall profile of thetopographytopography
  • 4. 44Denudation ProcessesDenudation Processes• Weathering—Rock disintegrating in place• Mass wasting—Eroded rock moving downslope• Erosion—Extensive removal of rock material,generally transported long distances
  • 5. 5The Grand CanyonThe Grand Canyon
  • 6. 66WeatheringWeathering• The combined action of all atmospheric andbiologic processes that cause rock todisintegrate physically and decomposechemically because of exposure near Earth’ssurface– From bedrock to regolith
  • 7. 7Weathering of BedrockWeathering of Bedrock► Wherever bedrock isWherever bedrock isexposed to the naturalexposed to the naturalelements, it weatherselements, it weathers► Any crack, joint, orAny crack, joint, orcavity in the rock willcavity in the rock willallow weatheringallow weatheringagents to penetrateagents to penetrateand break it apartand break it apart
  • 8. As rocks weather, surface area increases,offering more surfaces to be weathered…
  • 9. …producing this result.
  • 10. 1010Mechanical WeatheringMechanical Weathering• Physical disintegration of rock as a resultof natural phenomena, without a changein its chemical composition– Pounding, pushing, cracking, breaking,wedging apart
  • 11. Mechanical WeatheringProcesses• Frost wedging• Salt wedging• Unloading/pressure-release jointing• Thermal expansion and contraction• Biologic weathering
  • 12. Frost Wedging• Repeated growth and melting of ice crystals in pore spaces ofrock fractures or joints• Expanding ice exerts pressure, breaking rocks apart• Most effective where there is repeated freeze and thaw (as inarctic or tundra environments)
  • 13. Frost Wedging
  • 14. Salt Wedging• Similar to frost wedging• Growth of salt crystals breaks rocks apart• Most effective in coastal environmentsand semi-arid environmentsHoneycomb (called“tafoni”), Salt Point,Sonoma Coast
  • 15. 15Unloading or Pressure-release jointing• Rock brought near the surface relievesconfining pressure and allows the rock toexpand slightly, forming cracks
  • 16. Thermal Expansion andContraction• Heated rock expands slightly, cooled rock contracts• Rapid expansion and contraction of the surface of the rockcauses cracks to form and propagate• Most effective in regions with large differences intemperature between daily highs and nightly lows
  • 17. Thermal Expansion andContraction
  • 18. 18Biologic Weathering• Growth of plant roots,burrowing animals loosenand break apart rocks
  • 19. Chemical Weathering• Rocks forming at depth are stable underthose conditions• Once rocks are exposed to surfaceconditions many of the minerals becomeless stable and may undergo a slowchemical change that weakens theirinternal structures
  • 20. Chemical Weathering• Decomposition of rock thorough thechemical alteration of its minerals– Air, soil water solutions, and groundwatersolutions contain dissolved oxygen, carbondioxide, or other reactive elements– Water is the greatest agent of chemicalweathering– Chemical weathering is most effective inwarm, moist climates
  • 21. Chemical Weathering:The Influence of Temperature andPrecipitation
  • 22. Oxidation• Oxygen dissolved in soil water orground water can bond with thechemical elements of the minerals toform new minerals• Causes expansion and exertspressure that breaks the rocks apart• Example: iron (Fe) turning to rust(Fe2O3) in the presence of oxygen andwater
  • 23. Hydrolysis and Hydration• Hydrolysis--Water combines with someminerals, breaking down the rocks into newmineral compounds– granite: fedspar turns to clays + quartz sand– contributes to spheriodal weathering
  • 24. Hydrolysis and Hydration• Hydration--Water molecules become part ofthe chemical composition of the rock (nobreakdown). Mineral alteration and expansionresults in grain-by-grain destruction of rocks.Formation of gypsum from anhydrouscalcium sulfate (the mineral anhydrite)which has absorbed water into itschemical structure
  • 25. Carbonic AcidLimestone and marble are mostsusceptible to this type of weatheringCarbon dioxide dissolved inwater creates a weak acidcalled carbonic acid which candissolve some minerals,especially calcium carbonate
  • 26. Acid Precipitation• In urban areas withpollution from sulfur andnitrogen oxides, thesegasses can mix withatmospheric water,forming acid precipitation• Dissolves limestone andmarble and other types ofbuilding stones
  • 27. Organic Acids• Decaying vegetation mixes w/ water to formsoil water w/ complex organic acids that canreact to dissolve or chemically alterminerals
  • 28. 2828Mass WastingMass Wasting• Spontaneous downslope movement of soiland eroded rock fragments under theinfluence of gravity, but without the actionof moving air, water or ice
  • 29. Angle of Repose• The steepest angle that loose fragmentscan lie without movement if undisturbed
  • 30. 30
  • 31. Mass Wasting• The type of masswasting eventthat occurs willdepend uponspeed and thedegree ofsaturation
  • 32. Mass Wasting(another view)
  • 33. Types of Mass Wasting• Rock fall• Rock slide andTopple• Debris flow• Earth flow• Mudflow• Slump• Solifluction• Creep• Induced mass wasting
  • 34. Rock FallTalus slopes—Regolith whichhas fallen down steep slopes,funneled into “blankets” of rockcalled talus conesFresh slopes are very unstable
  • 35. Rock Fall
  • 36. Rock Slide
  • 37. Mudflow and Debris Flow• Mudflow—Rainwatermixed with soil flowingvery quickly downslopeas a river of mud• Debris flow—More rockfragment than mudflow,but similar in othercharacteristics
  • 38. Earthflow• Water-saturated soil orrock material• Moves a limited distancedown slope as one largemass• Generally slower inmotion (over the courseof hours)• Common form of earthmovement causing roadclosures and propertydestruction during heavyrains
  • 39. Near La Conchita Slide, alongHwy. 101 in Ventura CountyHwy. 101 in Ventura County
  • 40. La Conchita Slide (Earthflow)Hwy. 101, Ventura County
  • 41. La Conchita Slide (Earthflow)Hwy. 101, Ventura County
  • 42. Slump—Slow, concave sliding
  • 43. Slump
  • 44. Slump
  • 45. Solifluction• Continuous freeze andthaw cycles slowly moveweathered particlesdownslope• Over time, the entireslope moves downhill
  • 46. Solifluction
  • 47. Solifluction
  • 48. Solifluction LobesEmphasized by Animal Trails
  • 49. Soil Creep
  • 50. Induced Mass WastingMass wasting caused by human activity• Moving weathered rock material downslope duringconstruction on steep hillsides– Carried away as debris flows or mudflows during heavy rains• Removal of material supporting the base of a slope• The wetting of weathered rock material and soil frompipe breakage, lawn watering, etc. causing slippage• Debris removal by heavy rains after fire may alsoremove stabilizing vegetation

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