CH-10: WEATHERING AND MASS MOVEMENT
 
4-10-2002

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ADVISORY

  • Lecture is illustrated with 35mm film slides.  These are not those in your textbook.  Lecture is the only place to see these and receive an interpretation.  Some of your textbook graphics illustrate the same things.
  • Tildes (~~) indicate where film slides will be shown in lecture.
  • P 331-335:  This is target material for Exam-3.  It will not be lectured.  You are responsible for it.
  • "Amateurs make cave discoveries:"  Exam candidate.  Study it.
  • "Vaiont Reservoir landslide disaster:"  Exam candidate.  Study it.
  • This is a "short" chapter; especially after one subtracts the illustrations.

OVERVIEW

  • INTERNAL VS. EXTERNAL FORCES ~
    • Remember, "roughening" the surface -- previous chapter,
    • Versus "smoothing" the surface -- this and later chapters
  • EXTERNAL FORCES
    • DENUDATION  
      • A collective term, to reduce down, the landscape, an "unclothing"/uncovering of the surface  ~
      • DENUDATION = WEATHERING + MASS WASTING + EROSION
    • WEATHERING:
      • BREAKING DOWN OF ROCK INTO SMALLER PARTICLES
      • Boulders, cobbles, stones, gravel, sand, clays, silt
    • MASS WASTING: DOWNHILL MOVEMENT, BY FORCE OF GRAVITY
      • Has to be weathered or broken apart first (WEATHERING)
    • EROSION:  Removal -- erosion, itself
  • LANDFORMS OF EROSION:
    • COMBINED EFFECTS OF CARRYING AWAY WEATHERED AND WASTED MATERIAL
    • TRANSPORTATION -- actual act of carrying away
  • LANDFORMS OF DEPOSITION:
    • WEATHERED, ERODED AND TRANSPORTED MATERIAL IS DEPOSITED ELSEWHERE
    • If removed and transported, it must be placed somewhere!

SLOPES AND REGOLITH

  • A SERIES OF INTER-RELATED ELEMENTS  ~
  • SLOPE:
    • A PATCH OF LAND NOT FLAT -- INCLINED
    • GUIDES FLOW OF WATER
    • GUIDES MOVEMENT OF REGOLITH (broken rock)
  • BEDROCK:
    • UNDERLYING, UNWEATHERED ROCK
  • OUTCROP:
    • BEDROCK EXPOSED AT THE SURFACE
  • JOINTS:
    • CRACKS IN BEDROCK, NOT FAULTS  ~
    • PERMIT PENETRATION OF AIR AND WATER  ~
    • PERMIT WEATHERING UNDERGROUND
  • JOINT SETS
    • HORIZONTAL AND VERTICAL JOINT SETS
    • BRYCE AND ZION NAT'L PARKS  ~ ~
  • REGOLITH  
    • SURFACE LAYER OF BROKEN DOWN ROCK
    • RESIDUAL REGOLITH: FROM ROCK BELOW SURFACE
    • TRANSPORTED REGOLITH  
      • ALL "SEDIMENTS"
      • BOTH COARSE AND FINE MATERIALS
      • TRANSPORTED BY WATER, ICE, WIND, WAVES, COASTAL CURRENTS
      • CAN BE ABSENT, OR, HUNDREDS OF FEET THICK
  • SOIL -- ON TOP OF REGOLITH
    • THICKNESS:
      • VARIES FROM NONE TO MUCH
      • ABSENT, OR A FEW INCHES, OR A FEW FEET THICK
    • INCLUDES VEGETATIVE RESIDUE AND "CRITTERS"
    • TAKES A VERY LONG TIME TO MAKE SOIL

PHYSICAL WEATHERING

  • THE BREAK DOWN OF ROCK BY FRACTURING  ~
  • FROST ACTION (S) ~
    • ALTERNATING FREEZING-THAWING -- SHATTERS ROCKS
    • OCCURS IN MOUNTAIN/ALPINE LOCATIONS  ~
  • TALUS CONES ARE FORMED FROM FALLEN ROCK
    • A TALUS CONE IS A LANDFORM
    • ANGLE OF REPOSE /SLOPE STEEPNESS IS A SPECIFIC CHARACTERISTIC  ~ ~
    • FALLEN MATERIALS PILE UP ONLY SO STEEPLY
  • ICE NEEDLES  ~
    • RAISE SOIL AND SMALL ROCK FRAGMENTS  ~
    • THEREFORE SOIL AND PARTICLES ARE DISLODGED/DISPLACED, CANDIDATES FOR "EROSION", TO BE TRANSPORTED AWAY

PHYSICAL WEATHERING: SALT CRYSTALS

  • SALT-CRYSTAL GROWTH
    • A DRY CLIMATE PHENOMENON IN SANDSTONE
    • WATER MOVES UPWARD BY CAPILLARY ACTION
    • WATER EVAPORATES LEAVING SALT CRYSTALS
    • SALT CRYSTAL GROWTH BY EXPANSION BREAKS SAND GRAINS
    • OR, GROUND WATER
      • FLOWS DOWN, AND OUT  ~
      • EVAPORATES AND FORMS SALT CRYSTALS
    • OCCURS AT BASES OF CLIFFS ~

PHYSICAL WEATHERING: UNLOADING

  • UNLOADING: BREAKING OF ROCK AS PRESSURE IS UNLOADED
    • REMOVAL OF OVERLYING LAYERS, OVER TIME
  • EXFOLIATION -- BREAKING AWAY IN SHEETS  ~
    • LARGEST OF LANDFORMS MADE BY PHYSICAL WEATHERING
      • "HALF DOME" -- YOSEMITE NATIONAL PARK
      • EXFOLIATION ON GRANITE  ~ ~
  • OTHER PHYSICAL WEATHERING PROCESSES
    • HARD TO PROVE, BUT SUSPECT THAT THEY TO OCCUR
    • EXPANSION/CONTRACTION
      • FROM TEMPERATURE
      • FROM PLANT ROOTS

CHEMICAL WEATHERING

BREAKDOWN OF ROCK BY CHEMICAL CHANGE, NOT BY PHYSICAL BREAKAGE/SHATTERING

  • DIFFERENT ROCKS AND MINERALS HAVE DIFFERENT SUSCEPTIBILITY
    • FELDSPARS AND MAFIC MINERALS SUSCEPTIBLE
    • QUARTZ ALMOST IMMUNE

HYDROLYSIS AND OXIDATION

  • HYDROLYSIS AND OXIDATION ARE CHEMICAL REACTIONS WHICH CONVERT ROCK MATERIAL INTO DIFFERENT CHEMICALS
    • CHANGE "STRONG" ROCK TO "WEAK" REGOLITH
    • THEN MASS WASTING AND EROSION CAN OCCUR

TROPICAL CLIMATES

  • CHEMICAL WEATHERING DEEP BENEATH SURFACE: OCCURS UP TO 300'
  • CONSTRUCTION OF FOUNDATIONS IS DIFFICULT

DRY CLIMATES -- GRAIN BY GRAIN BREAKDOWN

  • STRANGE ROCK AND LAND FORMS  ~

CARBONIC ACID ACTION

  • CARBON DIOXIDE DISSOLVED IN WATER = WEAK ACID
  • ATTACKS CARBONATE SEDIMENTARY ROCKS
    • ACID PRECIPITATION (RAIN) IN URBAN AREAS
    • ATTACKS BUILDING MATERIAL; STATUARY ~
    • LIMESTONE AND MARBLE -- BUILDINGS, ETC
    • DISSOLVES ROCK AND CARRIES AWAY IN WATER
    • MAKES RILLS AND CUPS  ~

MASS MOVEMENT/WASTING

MASS WASTING: THE COLLECTIVE DOWNHILL MOVEMENT OF REGOLITH AND SOIL

  • IMPORTANT
    • A LANDFORM BUILDING PROCESS
    • LOWERS A LANDSCAPE
  • SOMETIMES FAST; SOMETIMES IMPERCEPTIBLY SLOW
    • BROKEN MATERIALS MORE SUSCEPTIBLE TO GRAVITY
  • SOIL CREEP:
    • SLOW, DOWNHILL MOVEMENT
    • SOIL AND REGOLITH  ~ ~
    • ROCK LAYERS SEEM TO BEND  ~
  • HILLSIDE TERRACETTES  ~
    • PROCESS OF FORMATION IS NOT FULLY UNDERSTOOD
  • EARTHFLOW  ~
    • IN HUMID CLIMATES WITH SATURATED SOIL/REGOLITH
    • FLOWS DOWN STEEP SLOPES -- IN A FEW HOURS
    • HAS STEP-LIKE TERRACES; SCARPS; BULGING TOE
    • COVERAGE = FEW SQUARE FEET TO ACRES
    • MAY BLOCK RAILROADS; HIGHWAYS
    • REMEMBER SOUTHERN CALIFORNIA EVENTS?
  • SOLIFLUCTION 
    • HILLSIDE SOIL CREEP  ~
    • ARCTIC AND ALPINE TUNDRA SITUATIONS ~
    • UNDERLYING ICE MELT ACTS AS A LUBRICANT
  • MUDFLOW
    • VOLUMINOUS PRECIPITATION CANNOT BE ABSORBED
    • OCCURS IN STEEP AREAS,
    • RUNS DOWNSLOPE RAPIDLY  ~
    • IN DESERTS, MAY BE LITTLE OR NO GROUND COVER TO ABSORB PRECIPITATION
  • ALLUVIAL FANS  ~
    • MUDFLOW EMERGES FROM DESERT CANYONS
    • SLOWS DOWN, SPREADS OUT
    • CAN MOVE BOULDERS  ~
    • VOLCANIC ERUPTION MAY PRODUCE MUDFLOW  ~
  • LANDSLIDE -- RAPID SLIDING OF MASSES OF BEDROCK ) ~
    • WHERE MOUNTAIN SLOPES ARE VERY STEEP
    • EARTHQUAKES CAN TRIGGER  ~
    • CAN DESTROY VILLAGES; KILL PEOPLE, ETC  ~
    • DIFFICULT TO STUDY: WHEN AND WHERE TO OBSERVE?

MASS WASTING: HUMAN FOSTERED

INDUCED MASS WASTING -- HUMAN CAUSED

  • REMOVE SUPPORT MATERIALS
    • BY EXCAVATING IN CONSTRUCTION PROJECTS
    • CONSTRUCTION; MINING
    • ROAD CUT SLOPES: SLUMPING ~
  • BUILD UNSTABLE PILES
    • TOO STEEP
  • UNDERGROUND LUBRICATION
    • SUBSURFACE WATER IS A LUBRICANT
    • PALOS VERDES  ~

SCARIFICATION

  • LAND EXCAVATIONS FOR SURFACE MINING  ~
  • ALSO TAILINGS, PILES OF MINED MATERIALS ON THE SURFACE

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