Geology 105 Geol 105-010
Popular in Geological Hazards and Their Human Impact
Popular in Geology
This 7 page Bundle was uploaded by Tonisha Hurd on Monday February 29, 2016. The Bundle belongs to Geol 105-010 at University of Delaware taught by Kohut,Edward John in Spring 2016. Since its upload, it has received 182 views. For similar materials see Geological Hazards and Their Human Impact in Geology at University of Delaware.
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Date Created: 02/29/16
Week of 10 February 2016 The Earth, An Active World Earth is constantly changing o Matter worked on by energy Energy is either from within (internal) or external Internal energy (heat within Earth) drives deep processes: o Uplift (mountain building) o Formation of continents and ocean External energy (solar) helps drive surface processes o Heat oceans and atmosphere In turn drives water cycle, ocean circulations, weather Erosion Floods Landslides Costal process Earth metals + energy =process Internal Heat From radioactive decay Solar Incoming light converted to heat in atmosphere, oceans and land Gravity Drives landslides, water flow Creates pressure within the earth Mechanical energy Seismic waves, ocean waves and tsunami (energy traveling through matter) Kinetic and potential energy Sources of energy Energy in all geologic processes is conserved But is converted from one form to another Effects of life on Geology Influences erosion and weathering Plays a big role in determining composition of the atmosphere Includes humans People have one of the largest influences of any organism in Earth’s history Disaster Trends Recently there has been a dramatic increase in the number of natural disasters Why? Global populations increase puts more people in harms way Timescale of Hazards Earthquakes – 10 seconds to 5+minutes Eruptions – hours to years Floods – hours to weeks Climate Change – decades to centuries Erosion, weathering – slow, ongoing Recurrence interval: most probable length of time between event of a particular magnitude (size) Calculated statistically Range from a few years to hundreds of thousands of years Cannot be reliably determined for all hazards Magnitude –Frequency Relationships: the larger the event the larger the recurrence interval Earth Materials Minerals, rock and sediment Water also important Elements Basic unit of chemistry 92 naturally occurring Atoms are the smallest units of elements Most common in the Earth’s crust: Oxygen (O): 46% Silicon (Si): 27% Calcium (Ca), Aluminum (Al), Iron (Fe) and Magnesium (Mg) a few % each Rest trace amounts Atoms The major subatomic particles that control chemical characteristics are protons, neutrons, and electrons Protons: in nucleus, positive charge Atoms of each element have a unique number of protons (atomic number) Electrons: nearly mass-less, negative charge Neutrons: in nucleus, no charge, same mass as protons Number of neutron Isotopes all have different atomic weights. Some are stable, others decay and are radioactive Radioactive decay creates heat in the earth Also used in determining age of rocks Compounds Most elements on Earth in compounds and mixtures: Compounds: atoms bound together in molecules, unique properties Example: H2O water Mixtures: elements and molecules together but not bound Example: air (nitrogen, oxygen, etc.) Minerals Most minerals contain silica, a compound of silicon and oxygen These minerals are called silicates Quartz Silicon and Oxygen (SiO2) Harder than glass Resists weathering Potassium feldspar Plagioclase feldspar Silica, aluminum, potassium and or sodium/calcium As hard as glass Abundant Clay Minerals Silicate minerals formed by weathering of other silicate minerals Typically found as groups of very small particles Clay minerals are very weak Important during erosion Carbonate minerals Calcium, carbon and oxygen Carbonates tie up carbon dioxide that would be in atmosphere otherwise Calcite Rocks A rock is an aggregate (solid mixture) of minerals Igneous Rocks Form when magma (molten rock) cools and crystalizes Extrusive (volcanic) cool on the surface Easily weather to turn soil Sedimentary Rocks Rocks exposed at the Earth’s surface are weathered They break down into small pieces called sediments Are transported away Then buried, compacted and cemented to form rock Fine-grained mud may form mudstones and shales Sand deposits may form sandstone Divergent Boundaries Two sub types o Oceanic spreading centers o In ocean basins o Plates pull away from each other (extension, rifting) o Rising hot asthenosphere partially melts at shallow depths o Solidifies to form new oceanic crust at boundary o Seafloor spreading new oceanic crust is continually moved away from boundary o Youngest crust at ridge, oldest furthest away Divergent boundaries may begin under continents o Rift continents apart (rift valleys) o Eventually oceanic crust is formed o New ocean basin may be created Convergent Plate Boundaries o Two types Subduction zones Continental collision zones Subduction zones Cooling lithosphere sinks, one plate sub ducts under another Compressive stress Crust and sediments in sinking plate release water Asthenosphere in overlying plate is fluxed and melts One plate carrying a continent sub ducts under another Transform boundaries Connect convergent and divergent boundaries Transform motion towards or away from boundaries into motion along the boundary Plates slide parallel to boundary Shear stress Transform fault Plates move laterally past each other between seafloor spreading centers Hotspots Areas of extra heat and uplift from mantle Appear to be fixed relative to plates Not part of plate tectonics Could be caused by rising plumes of hot mantle Evidence for Plate Tectonics Magnitude Scales Richter’s method: o Calculated from the amplitude of the largest seismic wave recorded Modern Magnitude Scales Local Magnitude (Ml): Magnitude calculated by updated Richter method Mb: uses only largest body wave Ms: based on larges surface wave Using just amplitude and distance underestimates very large quake magnitudes Seismographs saturate at 8-8.5 o A 9.2 quake would look the same as 8.2 Seismic moment: based on area of fault rupture Larger area = larger moment = larger amount of energy Quake Magnitudes Greater than 10 not possible o Chile, 1960: largest recorded at 9.5 o Alaska, 1964: largest U.S. quake, 9.2 o Indonesia, 2004: 9.1 o Tohoku Japan (2011) 9.0 o Haiti, 2010: 7.0 o San Francisco, CA (1906): 7.9 Intensity Based on effects of earthquake Mercalli scale – invented by Giuseppe Mercalli in 1902, uses observations to estimate earthquake intensity Intensity ranked from I to XII o From not felt (I)… o To total damage (XII) with objects thrown in air and line of sight distorted Foreshocks and aftershocks Foreshocks - quakes on a fault before a larger quake (the main shock) o Sometimes occur in swarms Aftershocks- smaller quakes on a fault after main shock Foreshocks do not always occur, cannot tell they are actually foreshocks or just individual quakes Most damage caused by ground motion Ground-motion amplification: loose and muddy soils amplify ground motions Ground Motion Damage Weakly supported floors, such as bottom floor parking areas or parking garages susceptible Elevated highways also susceptible Disrupt utilities, transportation, building right on fault Liquefaction Saturated granular soils flow like liquid when shaken Fires Not a natural effect of earthquakes o Broken gas mains, spilled liquid fuel, overturned cooking fires and lamps Hazard Mapping Map areas at greatest risk o Use intensities from earlier quakes o Locate landslide and liquefaction prone areas Earthquake engineering Design buildings to withstand earthquake stresses Retrofit older buildings Preparation Educate public on what to do before, during and after quakes Earthquake Forecasting Quakes cannot be predicted But with sufficient data, probabilities of future quakes can be forecast Earthquake Forecast Probability of an EQ on a given fault over a certain time period Based on statistics of how often quakes occur on the fault Require geologic or historic record of activity Earthquake Prediction goal is to predict when and where earthquakes will strike based on precursors: small foreshocks, change in well-levels, electromagnetic waves, even animal behavior not considered possible at this time 2010 Haiti M7.0 Directly hit Port-au-Prince Poor quality concrete buildings crumbled Landslides on steep Most government buildings destroyed UN buildings destroyed and troops killed 46,000 to 300,000 killed 1.5 to 1.8 million homeless Reconstruction is slow There are allegations that poor will be displaced by new project Few rescue and medical resources o What were not destroyed were overwhelmed o Even though US got airport running, international relief was not coordinated New Madrid, Missouri Dec. 1811 – Feb. 1812 EQs on ancient faults Effects Area sparsely settled, little loss of life Shaking felt throughout east Tsunami A long wave that moves the entire depth of the ocean. Experienced on shore as a series of rapid surges flowing for many minutes Cause: any disturbance on seafloor that displaces a large water mass o Incorrectly called tidal waves Most tsunami generated by subduction zone earthquakes A few tsunami are generated by volcanic processes Quake triggered landslides can cause huge mega tsunami in confined waterways Comparison to Wind Waves Wind waves: o Energy: mainly on surface o Periods: typically 10 seconds o Wavelengths: typically 150 m (500 ft) o Height: typically 1-3 meters (3 ft) Tsunamis: o Energy: surface to seafloor Move the entire depth of the ocean (often several kilometers deep) Periods: minutes to hours Wavelength: several hundred km Height: a few meters in deep ocean Not noticeable in deep ocean Travel at speeds from 500 to 1,000 km/h (315-625 mi/h) Tsunami characteristics: In shallow waters: Water piles up at wave front Speed slows to 72 km/h (45 mph) Long wavelength = onshore flow for several minutes There will be several surges of varying heights over many hours Hilo, Hawaii and Tsunami Hilo, Hawaii is very susceptible to tsunami Shape of island and seafloor focuses tsunami on Hilo Destructive tsunami in 1946 and 1960
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