study guide for test 2
study guide for test 2 GEO 101
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This 14 page Study Guide was uploaded by Amber Butler on Tuesday October 6, 2015. The Study Guide belongs to GEO 101 at University of Alabama - Tuscaloosa taught by Rezene Mahatsente in Fall 2015. Since its upload, it has received 241 views. For similar materials see Dynamic Earth in Geology at University of Alabama - Tuscaloosa.
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Date Created: 10/06/15
Test 2 Study Guide for Geo 101 with Rezene Mahatsente Terms to know Alfred Wegener Father of quotcontinental drift he suggested once had supercontinent Pangaea that broke apart to form modern continents Wegener39s lines of evidence quotJigsaw puzzlequot fit of the continents All assembled would fit into one large landmass Evidence of past glaciations a Striations scratches on rock produced by ice moving over it b Locations of glacial deposits not in polar locations c Striations pointed outward from a common point d Tropicalsubtropical climates across southern N America NW Africa Other evidence Coal deposits formed by swamps and jungles Tropical reef environments Distribution of fossils and their correlation Correlation of geologic units Ex rocks in Appl Mts Resemble rocks found in mountains in Scandinavia and Great Britain Not initially believed Problems with Wegener39s theory Continental rocks fairly weak compared to oceanic rock Rotational forces too small to move massive chunks of land Importance of thickness of ocean oor Sediment Variable thickness of sediment across sea oor Even where sea oor sediment was thickest still too thin to have been accumulating for all of Earth39s history Oceans much younger than continents Importance of Sea Floor Spreading making of new oceanic plates New ocean crust made at midocean ridges thin sediment gets older as it moves away thick sediment Sea oor consumed at trenches History of Magnetic Reversals Preserved magnetic records are symmetrical around a midocean ridge spreading center Can be used to identify the spreading center Oldest oceanic and continental crusts Oceanic about 200 million years Continental 4 billion years Earth39s Compositional Layers The crust Oceanic and continental The mantle 0 Below crust surrounds core 0 Plastic not molten consistency The Core 0 Solid inner core 0 Liquid outer core 0 Both composed mostly of iron and nickel Earth39s Rheological Mechanical Layers Lithosphere 0 Crust and upper mantle 0 Rigid brittle Asthenosphere 0 Mantle down to 660 km 0 Plastic ows very slowly 0 Not molten Oceanic vs Continental Lithosphere i Continental 0 About 150 km thick crustal part 3540 km thick 0 Composed primarily of granite less dense ii Oceanic 0 Varies from 10100 km thick crustal part 10 km thick 0 Composed of basalt and gabbro more dense Pieces of the Lithosphere Plates Types of Plate Boundaries Divergent Convergent Transform Divergent Boundaries Constructive 0 Where two plates are moving away from one another spreading center 0 Between Ocean PlatesMidocean ridge sea oor spreading 0 Between continental platescontinental rift 0 Constructive making new plate material Convergent Boundaries Destructive 0 Where two plates are running into one another 0 OceanOcean OR OceanContinent collision Subduction zone 0 ContinentContinent Collision Mountain building 0 Destructive destroying plate material Transform Boundaries Conservative 0 Where two plates are moving past one another sidebyside 0 Plate material is neither created or destroyed Strikeslip faults move horizontally with respect to each other Know leftlateral and rightlateral Hotspots Hawaii is caused by a hotspot underneath an oceanic plate Hotspots can also come up underneath continents eX Yellowstone Active Margin 0 At edges of continents where you have an active plate boundary subduction or mountain building going on Passive Margin 0 Transitional area between oceanic and continental crust minimal tectonic activity 0 EX Gulf of Mexico Bathymetry Wilson cycle Describes how continents rift apart and then come back together again through time Convective Flow in the Mantle Mechanism of Plate Tectonics i Heat from the core rises creating convection cells in the mantle ii Asthenosphere is plasticlike so it can ow but it is NOT molten iii Convective ow from heat in mantle is basic driving force of plate tectonics How Plate Motion is Measured i Plate motions are measured in relation to hotspots ii Hotspots are thought to be stationary through time iii Plates move hotspots don39t Earthquake Shaking of the Earth caused by a sudden release of energy Focus Different types Shallowfocus less than 70 km deep Generally the most destructive earthquakes Intermediatefocus 70300 km deep Deepfocus greater than 300 km deep Earthquakes occur at every type of plate boundary Faults i Fracturescracks along which movement has occurred ii Most earthquakes occur due to movement on faults release of energy during movement Types of Faults DipSlip and Strike Slip DipSlip Faults Primarily accommodates vertical motion 4 types Normal Reverse Thrust Oblique Normal i Hanging wall moves down relative to footwall ii Accommodate extensional forces Reverse i Hanging wall moves up relative to footwall ii Dip angle greater than 45 degrees iii Accommodates compressional forces Thrust i Hanging wall moves up relative to footwall ii Dip Angle less than 45 degrees iii Accommodates compressional forces Oblique i Orientation can be such to accommodate either compression or tension ii Some component of horizontal motion as well StrikeSlip Faults a Types Rightlateral and leftlateral b Accommodates horizontal motion c Transform Boundary type of strikeslip fault i Large cuts through the lithosphere ii Accommodates motion between 2 plates Elastic Rebound Theory i Developed by Harry Fielding Reid following the 1906 San Francisco earthquake ii Describes how energy builds up and is released during an earthquake Displacement i Movementdisplacement occurs along fault segments This can happen in 3 ways 3 ways 0 Fault creep slow gradual displacement 0 Numerous small earthquakes periodic energy release 0 Store up energy until major earthquake occurs Foreshocks and Aftershocks Foreshocks small earthquakes before the major event generally in days or months leading up to the main earthquake fault is starting to move ii Aftershocks Small earthquakes generated by adjustments after a major earthquake Earthquake Triggering i Earthquakes setoff far away from the main earthquake outside aftershock area ii Landers triggered earthquakes up to approximately 1300 km away Types of Waves 2 main Body and Surface Body waves Compressional and Shear Compressional P waves a Pressure wave or primary wave b Particle motion is parallel to the wave propagation direction Shear S waves a Shear wave or secondary wave b Particle motion is perpendicular to the wave propagation direction Surface Waves Rayleigh and Love Rayleigh waves a Named for Lord Rayleigh who mathematically predicted this wave type in 1885 b Also known as quotground rollquot very damaging to structures c Counterclockwise elliptical particle motion that decreases with depth Love waves a Named for AEH Love a mathematician who worked out the model for this type of wave in 1911 b Sidetoside particle motion that also decreases with depth How Earthquakes are Recorded and Measured i Seismometer 0 Instrument used to measure the intensity direction and duration of an earthquake ii Seismograms 0 A record of the ground motion at a measuring station as a function of time Locating an Earthquake i Earthquake locations can be determined using the SP time from several seismograms ii Must have at least 3 records to locate the earthquake Earthquake Depth i Ranges from 5700 km Classi ed as a Shallow less than 70 km b Intermediate 70300 km c Deep greater than 300 km WadatiBenioff zones a Dipping seismic zones common to convergent plate boundaries where one plate is subducted beneath another Magnitude A measure of the energy released during an earthquake several different scales Richter Magnitude or local magnitude i Developed by Dr Charles Richter for southern California earthquakes recorded by a speci c type of seismometer ii Uses the maximum amplitude of shear waves recorded iii MLlog10Amplitudemm 3log10SP time 292 Moment Magnitude MW i Independent of seismometer type ii Based on the total amount of energy released during an earthquake iii MW 23log10M0 107 where M0 seismic moment which depends of fault and rock properties and the amount of slip can be estimated from the ground motion recordings Earthquake Hazards Ground Shaking Liquefaction Ground Displacement Landslides Fires Tsunamis Ground Shaking Controlled by multiple 3 factors a Magnitude i How much energy is released b Distance i Shaking decays with distance from the earthquake c Local soil and bedrock conditions i Affects the ampli cations of shaking Liquefaction Mixing of soil and groundwater during an earthquake Ground becomes very soft and loses strength Mercalli Intensity Scale i Based on data gathered from people who experienced the earthquake ii Quantifies the effects of an earthquake on humans and manmade structures based on a scale from 112 Can earthquakes be predicted i Although we know where earthquakes are likely to occur there is no reliable way to predict when an event will happen at any specific location ii We cannot quantify the frictional forces at plate boundaries nor the quotweaknessquot of points where failure may occur both of which can change over time Fault interaction also complicates the situation Stress and Strain i Stress force applied to a speci c area note pressure is a kind of stress 3 types a Compression b Tension c Shear Strain a change in volume andor shape of a rock body caused by stress 4 types of strain 1 Elastic Deformation Strain is proportional to stress Rock returns to original shape once stress is removed 2 Plastic Deformation Rock is permanently deformed will not return to original shape Two types 1 Brittle 2 Ductile Factors Controlling Deformation Temperature and Pressure Conditions amp Amount of time the stress is applied amp Rock CompositionStrength Temperature and Pressure Conditions 0 Higher temperature and pressure results in ductile deformation 0 Lower temperature and pressure results in brittle deformation Amount of time the stress is applied 0 Stress applied slowly leads to ductile deformation 0 Stress applied quickly leads to brittle deformation Geologic Structures Faults Joints and Folds Faults 0 Result of brittle deformation Joints 0 Result of brittle deformation 0 Different than faults 0 Fractures along which no movement has taken place quotnatural cracksquot 0 Tend to occur in groups 0 Help advance chemical weathering Folds 0 Result of ductile deformation 0 Series of wavelike undulations caused from ductile deformation and compressive stress Types of Folds a Syncline b Anticline Types of Anticline i Upright anticline ii Plunging anticline c Domeupwarped rock layers d Basindownwarped rock layers Strike 0 Compass direction of the line produced by the intersection of a rock layer or fault with a horizontal plane 0 Generally expressed as an angle relative to north measured clockwise Dip 0 Perpendicular to strike 0 The angle of inclination of a rock unit or fault measured from a horizontal plane 0 Includes both an angle measurement ie how much its tilted and a direction ie which direction it39s tilted Foliation i Alignment of mineral grains due to differential directional stress ductile deformation ii Higher metamorphic grade more extensive ductile deformation Orogenesis i Term used to describe an episode of mountain building Accreted terrains i added to a continent though convergent margins ii EX western US made up of about 100 accreted terrains Isostasy i Gravitational balance between the lithosphere and the asthenosphere ii Tectonic plates quot oatquot at a height dependent on their thickness and density iii EX Iceberg Interior Continental Structure Craton i Craton crust that hasn39t experienced an orogeny for at least 1 billion years Parts of a craton 0 Shield where Precambrian igneous and metamorphic rocks are eXposed 0 Platform where Precambrian rocks are covered by thin layer of sediment Volcanoes Chapter 5 General Features Summit Opening Vent Fumarole Summit opening 0 Crater less than 1 km diameter 0 Caldera greater than 1 km diameter produced by the collapse following an eruption Vent 0 Connection between summit opening and magma chamber Fumarole 0 Emits gas and smoke Mafic is first to crystallize at high temperatures 0 Gases easily escape low viscosity 0 Mild eruption 0 Broadshaped volcanoes 0 Rock types include basalt andesite and rhyolite Felsic is last to crystallize at lower temperatures 0 Gases trapped high viscosity 0 Explosive eruptions 0 Steep sided volcanoes 0 Rock types include gabbro diorite and granite Controlling Factors on Volcano Type Shape and explosivity of a volcano controlled by lava viscosity Viscosity determined by Compression Temperature and Volatiles Composition Si02 content a Complex Si02 minerals higher viscosity b Simple Si02 minerals lower viscosity 0 Temperature High temp less viscous Volatiles a Dissolved gases expand due to decreasing pressure b Explosivity of eruption related to how easily gases escape Products of Eruptions Lava Pyroclasic material Nuee Ardente Lahar Lava 0 Ex Pahoehoe ropy texture and Aa rough blocky texture Pyroclastic material 0 Debris extruded from volcano a Bomb greater than 64 mm b Lapilli 264 mm c Ash less than 2 mm Nuee Ardente quotglowing cloudquot 0 Hot gases infused with ash and debris 0 Avalanchelike speeds of approximately 200 kmhr Lahar volcanic mud ow 0 Mixture of volcanic debris and water 0 Moves down volcanic slopes and stream valleys Types of Volcanoes Shield Volcano Composite Volcano Cinder Cone Shield Volcano 0 Broad slightly domeshaped 0 Cover large areas 0 Mild eruptions of large volumes of mafic lava 0 Ex Mauna Loa and Kilauea Hawaii Composite Volcano Stratovolcano 0 Large classicshaped volcano steep sides 0 Alternating layers of lava and pyroclastic material 0 Violent eruptions of felsic lava 0 Ex Mt Saint Helens Mt Fuji Japan Cinder Cone 0 Built from ejected pyroclastic material 0 Steepslope angle 0 Small size 0 Occur in groups VolcanicRelated Features Caldera Lava Domes Lava Tubes Columnar Joints Pillow Lava Caldera 0 Steepwalled depression at summit formed by collapse Lava domes 0 Bulbous mass of congealed lava associated with explosive eruptions Lava Tubes 0 In an insulated tube lava can ow faster approximately 50 kmhr Columnar Joints 0 Lava contracts as it cools opening joints 0 Form hexagonal 6sided joints that extend downward into ow Pillow lava 0 Lava rapidly chilled through contact with water 0 Composed mostly of igneous rock in the upper part of the oceanic crust Plate tectonics and Volcanoes i Volcanoes are found at rifts and ridges subduction zones and above hotspots ii Generally Oceanic settings mafic volcanoes Continental settings intermediatefelsic volcanoes LOOK OVER THE STUDY GUIDE HE POSTED
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