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11-12. Earthquakes 

13-14 Deformation and Mountain Building

15. Earth's Internal heat

17. Weathering
   

18. Mass Wasting
     

 Physical Geology Lecture Outlines # 2

Lecture 10 - Volcanos

Reading: Chapter 5 of Tarbuck and Lutgens, 8th ed.

Topics

Shield volcano/stratovolcano comparison

8. Anatomy of a volcano

Magma chamber

Vent


Lecture 11- Earthquakes
Reading: Chapter 11 of Tarbuck and Lutgens, 8th ed.
 
Topics:
1. The Great San Francisco Earthquake of 1906
2. Plate Tectonics and Earthquakes
3. Elastic Rebound Theory
5. The Size of Earthquakes
4. Earthquake waves
P-waves
S-waves
Surface Waves
5. Locating an earthquake
6. Earthquake Damage
7. Seismology and the interior of the Earth

 
1. The great San Francisco Earthquake of 1906
Important because:

 

Casualties and damage

Dead - More that 3,000

Homeless - 225,000 from a population of about 400,000

  • Buildings Destroyed - 28,000
  • Monetary Loss - More than $400 million

    San Francisco Burning
     
    SF Hotels
     
    Length of the rupture
     
    Fault offset
     
    Slip along the fault
     
    Can it happen again?

    Bay Area Map
    Probabilities
     
    Loma Prieta 1989
    Bay Bridge
    Building collapse
     
    Hayward Fault

    2. Plate tectonics and earthquakes

     
    The plate boundaries are marked by a concentration of Earthquakes
     
    Direct evidence of the plate motions
     
    The type and size of earthquake depends on:
    • the type of plate boundary
    • the rate of plate motion
    • the length of the fault that slips
     
    Biggest Earthquakes found in subduction zones and continental transform boundaries
     
    People like to live near the coast
     
    Along the Pacific rim the plate boundary follows the edge of the continents.
     
    Billions of people are at risk of earthquakes

     3. Elastic Rebound Theory

     
    At geological scale the plates behave like a leaf springs
     
    Deformation (strain) is stored as the plates try to move past each other
     
    When the plate boundary fails there is an earthquake
     
    Strain is released
     
    Deformation begins to accumulate again
     
    Stick-slip behavior
     
    Size of quake depends on the amount of strain stored
     
    Earthquake size and frequency variations are systematic
    Small quakes are frequent
    Big quakes are rare
     
    The earthquake cycle may be 100's of years for big quakes
     
     Magnitude  Effects Example  Number per year
     <2.5  Not felt  900,000
     2.5-6.0  Moderate damage  31,000
     6.1-6.9  Destructive Northridge (1994)  100
     7.0-7.9  Serious damage Loma Prieta (1989)  20
     >8.0  Total destruction Alaska (1964)

     1 every 5 years
     

    4. Earth quake waves

    P-waves
    Primary waves
    Pressure waves
    Fastest (first to arrive)
    Sound is a type of P-wave
    Transmitted through both solids and liquids
    Particles move in the direction the wave travels
     
    S-waves
    Secondary waves
    Second to arrive
    Shear waves
    Transmitted only by solids
    Particles move perpendicular to teh direction the wave travels
     

    6. Earthquake Damage

    Ground Shaking
    Structural collapse
    Turkey 99_1
    Turkey 99_2
    Oakland Freeway
    Liquefaction
    Fire
    Landslides
    Tsunamis


    The Earth's Interior

    Reading: Chapter Chapter 12

    Topics:
     
    1. Observations
    2. The geothermal gradient
    3. Physics of heat transfer
    4. Second Law of Thermodynamics
    5. Lord Kelvin and the age of the Earth
    6. Radioactive elements in the crust and mantle

    1. Observations
    In oil wells, the deeper you drill, the hotter it gets
    Deed gold mines (Witwatersrand (South Africa))
    Temperature increases with depth
    At 3200 m depth -> 150 deg. F (65 deg. C)
    Areas with permafrost :
    If you cover the ground, the permafrost melts
    Heat is coming off the ground everywhere

     

     
    2. Geothermal gradient
    Temperature increaces at 10 to 50 deg. C/km
    Average geothermal gradient: 25 deg. C/ km
    Rate of increase is less at depth
    Otherwise most of the Earth would be molten
    Mantle geotherm
     

     

    3. Physics of heat transfer
    Temperature:
    Thermal state of matter: degree of aggitation of atoms
     
    Heat:
    Energy transfer due to movement of atoms
     
    Heat flow:
    Amount of heat transfer per unit area
     
    Coffee cup experiment 1 :
    Leave coffee on counter
     
    Heat always flows from hot to cold
    This is governed by the Second law of Thermodynamics
    It is a fundamental property of our universe
    It distinguishes future from past
    It gives a definite direction to time
     
    Coffee cup experiment 2 :
    Drink out of a metal cup
    Drink out of a china cup
    Why do we burn our lips with the metal cup if coffee is at the same temperature?
     
    Thermal conductivity of materials (k)
    Iron 80
    Rock 2
    Wood 0.2
     
    Determines how fast heat flows through a material
     

     

    5. Lord Kelvin and the Age of the Earth
     
     
     


    Lecture 13 and 14- Deformation and Mountain Building

    Reading: Chapter 10 and 24 of Tarbuck and Lutgens, 8th ed.

    Topics:

    1. Mountain Ranges & Orogenic systems
     
    2. Crustal Deformation
    Stress
    Strain
     
    3. Types of deformation
    Elastic behavior (brittle deformation)
    Plastic Behavios (ductile deformation)
     
    4. Faults (brittle)
      Tension ->Normal Faults
      Compression ->Thrust faults
      Horizontal Shear -> Strike-slip faults
     
    5. Folds (ductile)
      Synclines
      Anticlines
       
    6. Structures and Tectonic Settings
     
    7. Isostacy
     
    8. The Appalachian Orogen
     

    1. Mountain Ranges & Orogenic systems
    Alps
    Matterhorn
    Himalayas
    Nepal Himalaya
    DEM
    Andes
    Central Andes Map
    United States
    Shaded Relief Map
    Appalachians
    Cordillera
    Rocky Mountains
    Basin and Range Province
    Sierra Nevada
    Coast Ranges
     
    Folded rocks
     
    2. Crustal Deformation
    Stress
    What causes deformation?
    Stress=force/area
    Stress acts in all directions
     
    Strain =deformation
     
    3. Types of deformation
    Rock behavior depends on:
    Temperature
    Strain rate (how fast the deformation happens)
     
    Elastic behavior (brittle deformation)
    The rocks break
    Generates Earthquakes
    Shallow in the crust
     
    Plastic Behavios (ductile deformation)
    The rocks flow under stress
    No earthquakes
    Deep in the crust
     
     
    4. Faults (brittle)
      Tension ->Normal Faults
      Compression ->Thrust faults
      Horizontal Shear -> Strike-slip faults
     
    5. Folds (ductile)
      Synclines
      Anticlines
       
    6. Structures and Tectonic Settings
    Divergent Plate Boundary:
    Rifts
    Normal faults
    Thin crust
    Volcanism
    Example: East African Rift
     
    Convergent Plate Boundaries
    Big Mountains
    Thrust Faults
    Fold belts
    Thick crust
    Volcanism
    Example: The Himalayas, the Appalachians
     
    Transform Boundaries
    Complex deformation
    Strike slip faults
    Example: San Andreas Fault System
     
    7. Isostacy
    What is down?
     
    Gravity Anomalies
     
    The crust floats on the mantle
       Density
     Mantle  3300 kg/m^3
     Continental Crust  2700 kg/m^3
     Oceanic Crust  3000 km/m^3
     
    Because the continental crust is lighter it is higher than oceanic crust
     
    Thicker continental crust results in higher topography
     
    Isostacy was one of the paradigms of geology before plate tectonics
     

     

    8. The Appalachian orogen
     

     


    Lecture 17 - Surficial Process-Weathering

    Reading: Chapter 6 of Tarbuck and Lutgens, 8th ed.

    Topics:

    1. Intro to Surficial Process
    2. Mechanical Weathering
    3. Chemical Weathering
    4. Soils
    1. Intro to Surficial Process
     
    Processes that shape the landscape
    Landscape appears immutable
    Actually it is constantly changing
    Normally slow cummulative change
    Sometimes catastrophic change
     

     

    Geomorphic process
    Wear down the mountains
    Carve valleys
    Create soil -> Permits vegetation to exist
    Make the stuff sedimentary rocks are made of
    Interaction between lithosphere and hydrosphere-atmosphere
    (Interaction between rocks, air, and water)
     

     

    Processes:
    Weathering- Break down of rocks
    Mechanical-disintegration of rock
    Chemical-decompositiono f minerals
     
    Mass wasting- Down slope movement of rock masses due to gravity
     
    Erosion- Removal and transport of material by water, wind, ice
     
    Why does West Virginia look so different from Utah or Alaska?
    Different Tectonic Setting
    West Virginia- Continental interior far from plate boundary
    Utah- Continental interior, closer to plate boundary
    Alaska - Active plate margin- bigger mountains, young mountains
     
    Different Climate
    Different Vegetation
    Different Geomorphic processes in action
    West Virginia -temperate, wet climate
    Strong chemical weathering
    Erosion- Streams
     
    Utah- temperate, dry climate
    Strong mechanical weathering - water
    Erosion- water
     
    Alaska- Arctic, wet climate
    Strong mechanical weathering - ice
    Erosion - Glaciers and streams
     

     

     
    2. Mechanical Weathering
    Frost Wedging
    Glass bottle in the freezer
     
    Water seeps into cracks
    Freezes and expands 9%
    Pushes the crack open
    Very powerful over the centuries
    Problem for structural geologists in Alaska
     
    Elastic Rebound
    Rocks srings back when pressure is released
    Enough to crack the rock
    Exfoliation of granite
    Yosemite:
    Half Dome
    Glacier Point apron
     
     

     

    3. Chemical Weathering
    The minerals suffer chemical attack when exposed to near surface conditions
    Changes in mineralogy
    Changes in composition
     
    Controlled by:
    Moisture
    Temperature
    Plants
    Geochemical Environment
    Rock type
    composition
    particle size
    Time
     
    Main agents:
    Water, Oxigen, organic acids

     

     
    Dissolution
    Greatly enhanced by acids
    Example:
    Limestone (made of calcite) disolves to Ca++ ions and CO2 gas.
    Many sedimentary rocks are held together by calcite cement
     
    Sources of acid:
    Plants
    Acid rain (polution)
    Volcanoes
     
    Oxidation
    Geochemical conditions in the subsurface reducing (low oxygen)
    Minerals are stable under those conditions
    Near surface the environment is oxidizing, some minerals react with oxygen and break down to oxides and hydroxides
    Oxigen is a very active chemical agent
    Most living things are burning continously (breathing=controlled oxidation)
     
    4. Soils
     
    Surface of the Earth is covered by a layer of decomposed rock
    Regolith:
    Chemically Weathered rock (soil)
    Rock fragments (mechanical ly weathered)
    Soil:
    Organic Layer (humus) (0)
    Zone of leaching (A)
    Zone of accumulation (B)
    Parental material (C)
     
    Soil formation takes place from the top down
    Thickness and nature depends on:
    climate (rainfall, temperature),
    vegetation
    rock type
    slope
     
    Tropical soils:
    Very thick
    Amazon:
    High rainfall during rainy season
    Little rainfall in dry season
    Hot climate
    Organic layer-very thin
    Very active chemical weathering
    Difficult to find solid rock
    Zone of leaching- very thick (depleted in nutrients)
    Poor soil for sustained agriculture
    Cutting the forest leads to rapid erosion of Organic Layer
    Forest is replaced by grassland
    Amazon natives have to abandon gardens after a few years and clear a new patch of forest
     
    Andes Highlands
    Moderate rainfall through the year
    Thick Organic layer
    Very good for sustained agriculture
     
    Laterite soils:
    Mostly in the tropics
    Complete leaching
    Only the most insoluble componds are left behind:
    Aluminum hydroxide
    Iron Oxide
    Clay
    Aluminun and Nickel mineral deposits are laterites
    Start with an igneous rock with no quartz (basalt, syenite, pyroxenite, etc)
    Initially:
    Al -- 15% (in plagioclase mostly)
     
    Mafic minerals are easily decomposed chemically
    After Leaching :
    Al --50% (in Aluminum hydroxides (bauxite))

       

    Lecture 18 - Mass Wasting
    Reading: Chapter 15 of Tarbuck and Lutgens, 8th ed.
     
    Topics:
    1. Intro Mass Wasting and Video
    2. Driving and Resisting forces
    3. Angle of Repose
    4. Causes
    6. Mitigation of slope failure (not covered in lecture)
    5. Types of Mass Wasting Process
    Rock Fall
    Slides
    Flows
    Creep

    1. Intro Mass Wasting and video

    Mass wasting = mass movement, downslope movement

    Movement of Earth materials (rock, regolith, soil, debris, snow) downslope as a result of the pull of gravity.

    Examples:

    Landslides
    Avalanches
    Debris flows
    Rock Falls
     
    Mass wasting can be very slow or catastrophic

    In the US alone, landslides cause about $1.5 billion in economic losses and 25-50 deaths each year.

    In West Virginia because of steep slopes and wet climate landslides are an important problem.

     
    2. Driving and Resisting forces
     
    Gravitational force acts vertically down
    Slope angle causes a component of the force to act down-slope
    Magnitude of down-slope component depends on steepness of slope
     
    G= gravitational force
    F= down-slope component
    a= 90 - slope angle
    F= G Cos a

     

     
    Resisting resisting forces:
    Friction
    Cohesion
    Cohesion between material and substrate
    Internal cohesion of material
     
    SHEAR STRENGTH - measure of the ability to with stand a change in shape.

     

     
    3. Angle of Repose
    Demo with sand and flour
    Steepest angle a slope can sustain
    Driving and resisting forces are perfectly balanced
    Dynamic equilibrium
    Critical State
    Angle of repose is 25 to 40 degrees depending on internal cohesion
    For sand it is about 30 degrees

     

     
     
    4. Causes
     
    Change in slope
    Undercutting of slope
    by rivers
    by ocean waves
    by ground water
    by humans
     
    Weakening of material
    Chemical weathering
    Mechanical weathering
    Water
    Water saturated soil is weaker
    Water adds to the load on the slope
     
    Thawing
    Frozen water holds the soild together
    Example: Today there is rapid erosion of the Arctic coastlines due to melting of the permafrost
     
    Changes in vegetation
    Plants holds the soil together
    Plants absorb water

    Factors that influence slope stability:

    1. Shear strength of the material (rock, soil, regolith, sediment)
    2. Gradient, steepness of the slope
    3. Weathering and Climate
    4. Water content
    5. Undercutting
    6. Overloading
    7. Vegetation
    8. Geology and Slope Stability
    9. Slope modification by human activities -- roadcuts, quarries, etc.

    Factors that can trigger a slope failure or landslide:

    1. Excessive rain or melting snow
    2. Earthquakes, seismic activity
    3. Volcano eruption
    4. Rapid undercutting by waves, streams, or humans

    5. Mitigation and Prevention of Slope Failures

    Do not build on or near steep slopes.

    Not always possible: Highways need roadcuts: there will always be slope failures.
    People like a view, they will build on slopes or sea cliff despite the high risk of slope failure.
     
    Engineering techniques:
    Retaining walls, rock bolts, weep holes, drainage pipes, diversion walls, slope shallowing, etc.}
     
     
    6. Types of Mass Wasting Process

    Rapid Mass Movements

      Rockfalls

    Rocks falling from near-vertical cliffs, the rockfall is the smallest, most common, and most rapid from of mass wasting.

    Yosemite Rock Fall

    Talus

    Slides:

    Rapid transport of mixture of soil, rock, and vegetation down a moderate to steep slope.

    Rock and snow avalanche, Mount Huascaran, Peru. In 1970, an earthquake-induced rock and snow avalanche on Mt. Huascaran, Peru, buried the towns of Yungay and Ranrahirca. The total death toll was 66,000. The avalanche swept about 11 miles to the village of Yungay at an average speed of more that 100 miles an hour. Photograph by G. Plafker, U.S. Geological Survey.

    Sinkhole

    Debris slides (Rather dry)
    Rock Slide
    Avalanches (Snow and Ice)
    Landslides
    La Conchita, CA
    Colorado
    Thisle, UT
    • Rock and snow avalanche, Mount Huascaran, Peru. In 1970, an earthquake-induced rock and snow avalanche on Mt. Huascaran, Peru, buried the towns of Yungay and Ranrahirca. The total death toll was 66,000. The avalanche swept about 11 miles to the village of Yungay at an average speed of more that 100 miles an hour. Photograph by G. Plafker, U.S. Geological Survey.
     

      Flows:

    Debris flow (Wetter than slides): Mix of water, rock, soil, mud moving rapidly downslope.

    Debris Flow, Colorado 1994

    Mudflows:

    Fluid, rapid flow of mud, mixed with rocks and other debris.
     
    Occur following heavy rainstorms in arid regions
    Associated with volcanic eruptions
    Usually follow preexisting channels ( streams or valleys).
    Mt. St. Helens
      
    Earthflows: Slow flowage of water saturated soils down moderate to steep slopes.
    More fluid, shallower, and smaller than slumps.
     
    Earthflow, OH
     
    Slow Mass Movements
    Slumps - Intermittent movement of a mass of earth or rock along a curved plane.
    Usuallyo occur after a heavy rain, on a steep slope with deep, clay-rich soils.
     
    Creep - The slowest but most widespread of the slow mass wasting.
    Creep involves the entire hillside.
    Evidence: tilted trees, fence posts, utility poles, tombstones
    Soil behaves like a very viscous fluid. It slowly flows down hill.
     
    Frost heaving - Earth material pushed outward due to ice expansion during cold episodes then downward during thawing.
     
    Solifluction - Slow downslope movement of soil and regolith in tundra and alpine areas due to thawing of permafrost