Geog 1113- Week 3
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This 3 page Class Notes was uploaded by Victoria Koehl on Thursday September 8, 2016. The Class Notes belongs to GEOG 1113 at Georgia State University taught by Larry Kleitches in Fall 2016. Since its upload, it has received 15 views.
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Date Created: 09/08/16
Geog 1113 Notes Fire Lake Plates are driven by the cooling of Earth, gravity provides additional force Important principle: In the big picture, Earth gives off heat to cool, the heat energy from the Earth's interior produces the melt that makes oceanic plates and moves them The heat in Earth's interior is 50% residual from the formation of Earth, and 50% from radioactive decay; mainly the elements Uranium, Thorium, and Potassium Convection cannot take place without a source of heat Tectonic plates, or lithospheric plates, rigid and brittle, 100 km thick, fractures to produce earthquakes, plates move 110 cm per year The deepest quakes occur in subduction zones Volcanoes appear along plate boundaries All continents have a nucleus of old crystalline rock; cratons are the cores of the continental crust, they are low in elevation, preCambrian Regions where cratons are exposed at the surface due to erosion are called continental shields Each major plate is a collage of many crustal pieces Accretion or Accumulation when crustal fragments of ocean floor, curved chains of volcanic islands, and other pieces of continental crust have been swept aboard the edges of continental shields These migrating crustal pieces are called terranes At least 25% of the growth of western North American can be attributed to the accretion of terranes since early Jurassic Period Faults Fractures in rock along which displacement has taken place; sudden movements along faults are the cause of most earthquakes Faults are classified by their relative movement: normal faults, thrust and reverse faults, and strikeslip faults Fracking is the process of pumping water, sand, and other materials under high pressure into a well to fracture rock for oil/natural gas; has been linked to earthquakes Scientists believe that putting fracking wastewater in underground disposal wells, called "flowback water", is more strongly linked to seismic activity Orogenesis 'Birth of mountains', the process of mountain building Orogeny is a mountainbuilding episode that thickens continental crust; can occur through large scale deformation and uplift of crust during continental plate collision, it may also include the capture of migrating terranes and cementation of them to continental margins Uplift is the final act of the orogenic cycle Orogen Major chains of folded and faulted mountains Major orogens: Rocky Mountains (Laramide orogeny), the Appalachians and the Valley and Ridge Province (Alleghany orogeny), and the Apls (Alpine orogeny) An earthquake is a vibration of Earth produced by the rapid release of energy; energy released radiates in all directions from its source, the focus Vibrations occur as the deformed rock springs back to its original shape after slippage at the weakest point (focus) Earthquakes produce smaller ones called aftershocks; foreshocks are small earthquakes that often precede a major earthquake by hours, days, even years Seismology is the study of earthquake waves, and dates back almost 2000 years to China Seismographs record the movement of Earth in relation to a stationary mass on a rotating (drum Scientists monitor the San Andreas Fault by bouncing laser beams off a network of reflectors Two types of seismic waves: Primary (P) waves pushpull motion, changing the volume of intervening material, travels through solids, liquids, and gases Secondary (S) waves Shake motion at right angles to their direction of travel, travels only through solids, slower than P waves Two measurements that describe the size of an earthquake: Intensity The degree of earthquake shaking based on the amount of damage Magnitude Estimates the amount of energy released at the source of the earthquake Richter magnitude Concept introduced by Charles Richter Richter scale based on the magnitude of the largest seismic wave recorded, accounts for the decrease in wave amplitude as distance increases Magnitudes less than 2.0 are not felt by humans, each unit of Richter magnitude increase corresponds to a tenfold increase in wave amplitude and 32fold energy increase Liquefaction unconsolidated materials saturated with water turn into mobile fluid Tsunamis, or seismic seas waves Destructive waves, results from vertical displacement along a fault on the ocean floor or large undersea landslide created by an earthquake, height can get up to 30 meters A volcano forms at the end of a central vent or pipe that rises from the asthenosphere through the crust into a volcanic mountain, usually forming a crater; magma rises and collects in a magma chamber deep below the volcano until conditions are right for an eruption Calderas large basinshaped depressions formed when summit material on a volcanic mountain collapses inward after eruption Volcanic activity occurs in three areas: along subduction zones at continentaloceanic plate or oceanicoceanic plate convergence; along seafloor spreading centers on the ocean floor and areas of rifting on continental plates; and hot spots (like Hawaii) where individual plumes of magma rise through the crust Effusive eruptions are the relatively gentle eruptions that produce enormous volumes of lava on the seafloor and in places like Hawaii; direct eruptions from the asthenosphere produce a low viscosity (thickness) magma that is very fluid 2 A mountain formed from an effusive eruption tends to be gently sloped, gradually rising from the surrounding landscape to a summit crater, similar in outline to a shield of armor lying face up, therefore called a shield volcano Volcanic activity along subduction zones produce explosive volcanoes, the magma is thicker, it tends to block the magma conduit inside the volcano which allows pressure to build and lead to an explosive eruption Composite volcano is a term used to describe mountains formed from such an explosion Composite volcanoes tend to have steep sides and are more conical than shield volcanoes, they are also known as composite cones 3
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