Geology

Geology

1. Plate Tectonics

   • Steps leading up to plate tectonics:
     • Location of earthquakes and volcanoes
       • Hess: seafloor spreading at ocean ridges
         • Bathymetry: ocean floor mapping
           • Polarity and paleomagnetics: alignment of magnetic particles in rock responded to Earth's magnetic field at the time
             • Alfred Wegner: Continental Drift Hypothesis
               • Evidence: fossils matching, puzzle-like fit, climactic belts shifting, mountain belts, rocks the same in S America and Africa
                 • People still didn't believe in him until after he died because it couldn't explain how the continents moved-- observation not explanation
             • Showed that continents had moved across Earth over time
           • Ocean floor is not flat
         • Marine magnetic anomalies: positive (normal polarity), negative (reversed polarity)
           • Paleomagnetic reversal chronology: rate of seafloor spreading
   • Proof: Plate Boundaries
     • Divergent
       • Seafloor spreading: new ocean floor is formed by lava erupting from a rift, pushing the existent floor outward. CRUST IS CREATED HERE.
       • Characteristic features: mid-ocean ridges, valley rifts, EQ activity, volcanic activity-> pillow basalts, hydrothermal vents
       • Ex: Mid-Atlantic Ridge, East Pacific Rise
     • Convergent
       • Ocean-Ocean Subduction: crust is recycled
         • Characteristic features: trench, volcanic island arc, EQ activity, back-arc basin, accretionary prism
         • Ex: Japanese Islands
       • Ocean-Continental Subduction: crust is recycled
         • Characteristic features: volcanic arc, deep sea trench bordering continent, EQ activity, accretionary prism
         • Ex: Andes Mountains
       • Continental-Continental Collision: crust is deformed
         • Characteristic features: high continental mountain chains, EQ activity
         • Ex: Himalayas
     • Transform: shearing, CRUST IS DEFORMED
       • Characteristic features: EQ activity, faults, absence of volcanism
       • Ex: San Andreas Fault, North Anatolin Fault in Turkey

2. Rock Types

   • Sedimentary
     • Weathering
       • Mechanical weathering: physical break-up of rock into pieces
         • Jointing: natural cracks in rocks b/c of removal of weight, changes in pressure, or changes in thermal setting
         • Frost wedging: process where water freezes in the cracks of rocks and wedges it apart, eventually breaking the rock into smaller pieces
         • Abrasion: wearing away of rock by grinding action
         • Biological weathering: root wedging, animal burrows
       • Chemical weathering: process when rocks are decomposed, dissolved or loosened by chemical processes to form into new material (involves water)
         • Hydrolysis: chemical reaction between minerals in the rock and hydrogen in rain water
         • Dissolution: minerals in rocks dissolve directly into water
         • Oxidation
         • Hydration: absorption of water into crystal structure of minerals and causes them to swell
       • Factors that influence:
         • The more quartz content the more resistant to weathering
         • More acid of water the more weathering
         • Adjacent rock type/structure
         • Slope and climate
     • Lithification: burial compacting, cementing
     • Classes
       • Clastic: made from weathered rock fragments
       • Biochemical: derived from living organisms
       • Organic: made from organic carbon
       • Chemical: made of minerals precipitated from water solution
     • Sedimentary features
       • Stratification: caused by changing conditions during deposistion
       • Cross bedding: created by ripple and dune migration; sediment moves up gentle side of ripple, piles up, then slip face continually moves downstream
       • Graded bedding: bedding layers that fine upward
       • Fossils
       • Ripple Marks: indicate flow direction; asymmetrical or symmetrical
       • Dunes
       • Mudcracks
     • Depositional Environments
       • Alluvial fan: sediments pile up at base of mountain and rapid drop in stream velocity creates cone-shaped wedge
       • Fluvial: channelized flow transports sediment
       • Beach
       • Shallow marine: finer beach sediment
       • Swamp: coal is found here
   • Igneous
     • Formation of magma
       • Heat Transfer Melting: rising magma brings heat up with it and melts overlying rock
       • Flux melting: melting caused by addition of volatiles (happens at convergent)
       • Decompression melting: melting of hot mantle rocks due to decrease of pressure during migration towards Earth's surface (happens at divergent and convergent)
     • Magma differentiation
       • Source rock variations: total melting of continental forms felsic/intermediat magma, total melting of mantle forms ultramafic
       • Magma mixing
       • Assimilation
       • Partial melting: felsic minerals melt first
       • Fractional crystallization: felsic minerals crystallize first
     • Extrusive features: lava sheets, domes, pillow basalts, ash, pyroclastics
     • Intrusive features: dike, sill, laccolith, pluton, batholith
   • Metamorphic
     • Metamorphosis
       • Heat: energy breaks and reforms atomic bonds
       • Lithostatic pressure: mineral stability is highly dependend on T and P
       • Differential stress: pressure that's greater in one orientation
     • Metamorphic processes
       • Recrystallization: minerals change size and shape
       • Phase change: different minerals form with same chemical formula, different crystal structure-> POLYMORPHS
       • Pressure solution: mineral grains partially dissolve
       • Plastic deformation: mineral grains soften and deform
       • Neocrystallization: new minerals form when P-T changes
     • Increased grade: Slate, Phyllite, Schist, Gneiss

3. Earthquake: earth shaking caused by a rapid release of energy

   • Factors: sudden formation of new fault, sudden slip on existing fault, sudden change in the arrangement of atoms in rock minerals, movement of magma in a volcano, landslide, meteorite impact, underground nuclear bomb test
   • Seismic waves measured by seismometers and recorded on seismograms
     • Primary: fastest; compressional body wave; pushing and pulling end of spring
     • Secondary: second-fastest; shear body waves; moving rope up and down (can't go through water)
     • Love: second-slowest; surface wave; ground surface moves back and forth
     • Rayleigh: slowest; surface wave; ground surface goes up and down
   • Scales
     • Mercalli Intensity Scale: measures intensity in roman numerals, subjective, different intesenties for the same EQ depending on location
     • Richter Scale: measures magnitude, only works well for shallow EQs
     • Moment Magnitude Scale: measures magnitude and is most accurate
   • Shallow focus: divergent and transform boundaries, Intermediate/Deep focus: convergent boundaries
   • Hazards
     • Landslides and Avalanches: shaking causes slopes to fail
     • Liquefaction: waves liquefy H2O sediments-> land slumps and buildings topple
     • Fires: shaking topples stoves, candles and powerlines
     • Tsunamis: EQ change the shape of the seafloor
     • Disease: EQs cut off water and sewer lines so people are exposed to bacteria
   • Prediction
     • Short term: not really possible
     • Longterm: estimates probability an earthquake will happen during a specified time range based on recurrence interval and seismic zones
   • Mitigation: EQ engineering & EQ zoning

4. Volcanoes

   • Types of magma
     • Basaltic: low viscosity, causes pahoehoe flows (glassy, rope-like ridges), form pillow basalts under water
     • Andesitic: high viscosity, forms large mound above vent that slowly runs down volcano and stops at the bottom. Forms blocky lava
     • Rhyolitic: most viscous, accumulates above a vent in a lava dome, broken and blocky surfaces
   • Characteristic features
     • Magma chamber: located in upper crust containing large amount of magma
     • Vent: lava outlet on a volcano
     • Craters: bowl shaped depression at top of volcano because erupted lava piled up around vent
     • Caldera: volcanic depression that a volcano collapses into
   • Types of Volcanoes
     • Cinder cones: conical, made of cinders, explosive eruption
     • Stratovolcanoes: lower slopes, made of lava and pyroclastics, explosive eruption
     • Shield volcanoes:gentle slopes, made of fluid lava, erupt quietly, effusive
   • Hazards
     • Lava flows: destroys immovable objects but rarely people
     • Tephra: ash and lapilli falling around the volcano
       • Lahars: water that moves tephra
     • Pyroclastic flow: clouds of rolling ash and gas that race downslope (immediately deadly)
     • Landslides: eruption-related slope faliure
     • EQ: moving magma causes earthquakes
     • Tsunamis: water explosions that create giant waves
     • Volcanic gases are poisonous
   • Mitigation: evacuation and diverting flows

5. Hydrosphere

   • Surface Water
     • Drainage Basin: land area that drains into specific trunk stream
       • Dendritic: uniform resistance
       • Trellis: alternating resistance and weakness (valley)
       • Rectangular: zones of weakness perpendicular to each other
       • Radial: streams flow inward/outward from a point (dome/basin/volcano)
     • Types of Streams
       • Permanent: water flows all year, at/below water table, humid/temperate, discharge varies seasonally
       • Ephemeral: don't flow all year, above water table, dry/arid, flow during flash floods
     • Sediment loads
       • Dissolved load: ions from mineral weathering
       • Suspended load: fine particles in the flow
       • Bed load: larger particles roll, slide and bounce along
   • Groundwater
     • Zones
       • Unsaturated: interstitial spaces can't be pumped
       • Saturated: water completely fills the voids between rocks and soil particles
     • Aquifers
       • Confined aquifer: transmits water easily and is separated by overlying aquitard
       • Unconfined aquifer:transmits water easily, and intersects surface of Earth
       • Aquitard: sediment or rock that doesn't transmit water easily so retards the motion of water

6. Climate Change

   • Climate: long term weather patterns of an area; Weather: current state of the troposphere/short term variations
   • Climactic zones
     • Tropics: warm throughout the year
     • Temperate: mild temperatures
     • Polar: cold temperatures
   • Layers of atmosphere: Troposphere, stratosphere, mesosphere, thermosphere; temperature and pressure increases w/ elevation
   • Long-term change
     • Greenhouse: warmer climates
     • Icehouse: colder climate
     • Causes: plate tectonics, volcanic gases trap heat, orogenic uplift consumes CO2, formation of organic deposits removes CO2, greenhouse gases, supercontinent cycle, volcanoes,
   • Short term change
     • Causes: abundance of sunspots, Milkovitch cycling, oceanic currents, atmospheric currents, volcanic eruptions, tsunamis, mass extinctions
   • Predicted effects of global warming: shift in climactic belts, stronger storms, rise in sea level