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This 26 page Class Notes was uploaded by Sigmund Corwin on Saturday September 19, 2015. The Class Notes belongs to GEOL108 at University of Delaware taught by EdwardKohut in Fall. Since its upload, it has received 46 views. For similar materials see /class/207146/geol108-university-of-delaware in Geology at University of Delaware.
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Date Created: 09/19/15
GEOL 108 972011 110800 PM Scientific Inquiry 0 Science a rational process for examining and explaining the natural world 0 Explains events in nature as results of known physical causes 0 Uses observations and measurements data 0 Explanations are developed and tested I Always can be revised with new evidence 0 Hypothesis an initial explanation 0 Based on limited evidence 0 Needs to be tested and adjusted 0 Theory a welltested explanation based on abundant data 0 Atheory is NOT speculation or unproven Physical Framework 0 Matter 0 Something that occupies space 0 Smallest units in chemistry are atoms 0 4 common states I solid I liquid I gas I plasma 0 Mass an amount of matter 0 Volume lengthquot3 0 Density massvolume 0 Energy 0 Ability to do work on matter I Many forms of energy I One form can be converted to another 0 Forms of energy I Electromagnetic heat light radio waves I Gravity I Potential and kinetic 0 Time and space 0 Velocity distancetime o Acceleration velocity change over time 0 Units The Earth Heat 0 Science uses the metric system 0 Force Newton N I 1N1kgxms2 0 pressure pascal pa I 1pa1Nmquot2 I 1 atmosphere 101325 pa I 1 bar 100000pa Force and stress 0 Force mass X acceleration 0 Stress force X area or volume 0 Differential stress opposing forces acting on a point or surface I Tension pulling I Compression pushing I Shear opposing stress parallel to surface Diameter 12742 km gt70 ofvolume is rock 71 is covered by water has active tectonics 0 formation of mountains valleys continents ocean basins 0 two byproducts of tectonics eruptions and earthquakes Form of electromagnetism Also known as infrared light Lower frequency than visible light higher frequency than radio waves Sources of heat 0 Heat ofaccretion I Earth was formed by accreting smaller rocky planetoids and meteors I Impact between planetoids produced heat Originally cold protoEarth heated up and partially melted I Most iron melted and moved to core Earth still losing some of this heat Plate tectonics Processes 0 Three exist that can cause differential stress andor melting I Plate tectonics I Hotspots I Isostasy Compositional layering 0 Three layers I Metallic core I Rocky mantle I Rocky crust o Mantle and crust are mostly silicon and oxygen in compounds 0 Magnesium iron aluminum are also important in these compounds 0 Mantle highest Mg and Fe density34 56 gcmquot3 o Oceanic crust high Mg and Fe density33 gcmquot3 0 Continental crust lowest Mg and Fe highest Si density27 gcmquot3 Physical layering o Lithosphere crust and upper mantle behaves rigidly o Asthenosphere middle of the mantle solid but plastic Plate tectonics o A general theory about how the solid earth operates I Tectonics result from movement and interaction of rigid plates of lithosphere o Convection in hot plastic mantle 0 Pull of sinking plates Plate boundaries 0 Where plates meet 0 Boundaries are actually regions offaulted crust 0 Stress forcearea concentrated along boundaries 0 Active deformation and movement along faults in boundary regions 0 Three types I Divergent tension and rifting extension Melting formation of oceanic crust I Convergentcompression Subduction zones and continent continent collision crust Melting and creating of continental crust mountains I Transformshear Plates slide past each other Little or no melting Some deformation Not destructive or constructive 0 Pre plate tectonics ideas 0 There was no consensus and no universally accepted theory 0 Geosyncline sea oor along continents sinks from weight of sediments I Edge of continents buckle and create mountains o Shrinking and cooling Earth I Racking and wrinkling creates mountains 0 Expanding earth I Pulls continents apart Continental drift 0 Alfred Wegener 0 German meteorologist o Noted fit of South America and Africa 0 1912 and 1915 presented his hypothesis of continental drift 0 Envisioned continents plowing through solid oceanic crust Faults and Melting Rock What is an earthquake o Vibrations through the Earth due to 0 Movement along faults tectonic o Volcanic eruptions I Movement ofmagma I Movement on faults in volcano o Explosions I Volcanic I Conventional explosives I Nuclear explosions o Impacts Seismology study of earthquakes Seismograph an instrument that records horizontal or vertical movements of the earth Magnitude a standard scale of the amount of energy released by a quake Intensitya relative scale of the shaking effects felt by people and structures Faults and Quakes 0 Fault fracture in the crust along which there has been movement 0 If stress is applied to an area 0 Blocks of crust will move along faults o Ifmovement is sudden vibrations result 0 Movement begins at an initial point and spreads outward Fault Orientation 0 Need to show how fault surface is oriented o Vertically o Horizontally o Strike orientation of imaginary horizontal line on fault 0 Dip angle of fault from horizontal 0 Fault plane area of fault on either block 0 Fault line where fault intersects surface 0 Scarp fault plane above surface Types of faults o Classified by movement direction 0 Movement direction depends on stress conditions in the crust 0 Compression pushing toward fault o Tension pulling away from fault 0 Sharing horizontal movement parallel to fault Normal fault 0 Vertical or near vertical movement quotdip slip o Tensional stress 0 Common in divergent margins 0 Hanging wall moves down footwall up Reverse 0r thrust fault 0 Compression one side thrusts under the other 0 Common in convergent margins 0 Hanging wall moves up footwall down Blind thrustfault Transform 0r Strikeslip o Crustal blocks slide past each other horizontally along strike due to shear stress 0 Common along transform boundaries Oblique 0 Combination of horizontal and vertical movement Earthquake Mechanisms 0 Two described 0 Elastic rebound 0 Window of opportunity Elastic rebound mechanism 0 If fault is under stress block want to move 0 But blocks are often locked in place 0 Crust deforms around locked fault Strain storing potential energy 0 When strain overcomes locking force 0 Crust moves along fault o Deformed crust snaps back into original shape 0 Energy is released quotWindow ofopportunity mechanism 0 Rupture begins at a small weakpoint and spreads o If conditions are right 0 Rupture may spread to cover a larger area than expected 0 Will release large amounts of energy even without a large amount of accumulated strain m 0 Energy released by earthquake travels in waves 0 Wave height amplitude re ects amount of energy Seismic Energy 0 Energy travels in body and surface waves 0 Body waves through earth 0 Surface waves travel along surface 0 All seismic waves lose energy as they travel due to 0 Absorption o Spreading o Scattering 0 Re ection 0 Energy may also be locally intensified amplified o Magnitude energy released then is only one factor in determining felt effects intensity Body Waves 0 Primary or Pwave 0 Pressure wave like sound 0 Crust alternately compressed and stretched 0 Pass through all layers but change speed 0 Secondary or Swave o Shear wave Wave shears crust from side to side Cannot travel through liquid do not pass through the core 0 O O Slower than pwave Sur ace waves 0 Love waves 0 Energy travels near surface 0 Side to side motion decreases with depth 0 Rayleigh wave 0 Energy travels near surface 0 Rolling motion Like wind wave on water Foreshocks and aftershocks o Foreshocks quakes on a fault before a larger quake the main shock 0 Sometimes occur in swarms o Aftershocks smaller quakes on a fault after the main shock Locating a quake 0 Focus hypocenter point where rupture begins 0 Epicenter point on surface above focus 0 Difference in arrival time at seismic station can be used to calculate distance 0 Triangulating location using at least 3 seismic stations Where do earthquakes occur 0 Primarily along or near plate boundaries 0 But some earthquakes do occur with in plates intraplates 0 But Subduction zone quakes can be up to 600km deep Melting Styles and Magma Types Composition of crust and mantle 0 Most abundant element is Oxygen 0 Found combined with other elements 0 Silicon neXt most abundant Iron Magnesium Calcium 0 O O 0 Aluminum 0 And many others in small amounts 0 Composition described as percentages of oxides 0 Example SiOz Magma and igneous rocks 0 Molten rockis magma o Rocks formed from crystallization of magma are igneous rocks Composition ofMugmus and Igneous Rocks 0 Mafic 0 lt5 2 SiOz 0 520 FeO and MgO o hottest temperature and lowest viscosity 0 intermediate 0 5263 SiOz o lt10 FeO and MgO o Felsic 0 gt63 SiOz 0 Very little FeO and MgO o Coolest and highest Viscosity magmas o Oceanic Crust o Mafic Crust 0 Continental crust o Felsic and intermediate rocks 0 Also other types How melting occurs 0 Three main mechanisms 0 Pressurerelease bring hot mantle rock up to a depth or pressure it will melt at o Flux melting add water to mantle rock to lower its melting temperature 0 Secondary crustal melting from contact with preeXisting magma Magma type and melting style 0 Dry pressurerelease melting produces o Mafic magma low silica 0 Low viscosity 0 Low amounts ofwater and C02 0 Occurs at hotspots and divergent plate boundaries 0 Wet ux melting produces 0 Intermediate magmas 0 Higher Viscosity 0 Higher amounts of silica water and C02 0 Occurs in Subduction zones 0 Secondary melting of continental crust produces o Felsic magma 0 Highest amounts of silica 0 Very high viscosity 0 Can occur anywhere hot magma intrudes continental crust 0 Gas cannot easily escape high Viscosity intermediate and felsic magma o Builds up 0 Volcanoes with high silica magmas erupt Violently Flux melting o Ifwater is added to the mantle its melting temperature will change 0 Wet or ux melting o Occurs in Subduction zones Pressure release melting 0 When hot mantle rises its temperature may hit the melting point at shallow depths 972011 110800 PM Prescientific ideas on quakes and volcanoes 0 Oral vs Written Why folklore and myths 0 Early people had knowledge of limited areas 0 Earthquakes and eruptions were very unusual and inexplicable 0 People sought explanations 0 Some unseen force or being thought to be responsible 0 Led to folklore and myths Pre history 0 People have long lived in tectonically active regions 0 Fossils and footprints of human ancestors found in ash deposits in East African Rift 0 These can be favorable locations 0 Volcanic and uplifted peaks may provide water sources and forests o Lava ash and freshly exposed rock break down to form rich soil 0 The drawback destructive eruptions and quakes 0 Whole cultures disrupted o Incorporated into folklore and legend Animal explanations 0 World sits on some enormous animal whose movement caused quakes o Norseteutonic serpent Nidhog gnaws at root of World Tree Indian myth world sits on head of Great Elephant Other asian traditions world on back of a giant frog fish or tortoise O O 0 Japan giant eel Jishin Uwo moves beneath Japanese islands Deities o More sophisticated societies blamed specific gods or other beings o Gods were often seen to be punishing humans 0 Examples 0 Norse Loki responsible o Greeks Poseidon responsible I Athena buried monster Engeladus beneath Sicily o Mayan and also Aztec kizin was god of underworld and quakes 0 Specific volcanoes of considered gods 0 Sacrifices offered to appease volcanoes o Aztec Mayan and Incan civilizations sacrificed children or captives o In central Africa one group sacrificed 10 of their best warriors Mythology o Elaborate stories created to explain volcanoes o Often attributed to monsters or gods 0 Greek and Roman Mythology o Zeus imprisoned Typhon below Mt Etna o Jailkeeper was Hephaestus Greek god of metalworking 0 Roman version of Hephaestus was Vulcan Early Rational Explanations o Aristotle 384 322 BC quakes resulted from subterranean winds 0 Quake locator invented by Chang Heng in China 130 AD 0 Philosophers and volcanoes o Philosophers in the West and East Asia did attempt rational explanations in ancient times 0 Some explanations from Greeks and Romans I Empedocles all natural events the interaction of Fire Air Water and Earth I Aristotle internal fires create winds which interact with water and earth I Plato a subterranean river of fire supplies volcanoes I Seneca combustion of sulfur and tar drives volcanoes Ancient Quakes the Bible 0 Old and New Testament contain stories of quakes or events that could be interpreted as quakes 0 Usually depicted as signs of God s displeasure Ancient Eruptions Thera Santorini 0 Island in the Aegean Sea 0 Site of colossal eruption and collapse in 1620 BC 0 May have damaged Minoan civilization 0 Possible source of Atlantis legend 0 79 Vesuvius o in Pompeii people were asphyxiated then buried in ash in Herculaneum people were caught in pyroclastic flows 1000s killed Towns buried and forgotten O O O O Buried ruins of Pompeii and Herculaneum began to be uncovered in the 18th century Port Royal 0 0 Still being excavated today Not only provide details of Pompeii s death but also its life and the Roman world at the time Pre modern Quakes with gt100000 deaths 0 526 Antioch Present Turkey 0 1138 Aleppo present Syria 0 856 893 present Iran 0 1556 Shaanxi Ming Dynasty in China Considered to be the deadliest quake in history 830000 500 1700 0 Quakes would create sudden destruction and high death tolls in Middle East and Asia 0 Combination of densely populated cities collapse of stone and masonry buildings and fires 0 After collapse of Rome476 knowledge diminished in the western Europe I People returned to supernatural explanations 0 Arab scholars kept alive rational Greek and Roman ideas added their own o In China some philosophers still worked on rational concepts I Most people still relied on folklore and myth 0 Modern scientific revolution would begin in Western Europe during the Enlightenment The Wrath of God O In western civilization I Quakes seen as evidence of God s displeasure I Since some crime or immortality always is occurring I Easy to link human misbehavior to God s presumed displeasure 1600s main town in English Jamaica built on sand spit in today s Kingston Harbor major trading port for new plantations also a port for privateers and pirates reputed for lawlessness Considered wicked June 7 1692 0 Major earthquake 0 Much spit slid into harbor Lisbon 0 2000 killed outright quake seen as God s punishment 0 1700s Lisbon Portugal 0 Capital of global empire 0 Prosperous 0 Very important Catholic city 0 Many churches and libraries 0 Considered favored by God Nov 1 1755 All Saints Day Earthquake in Atlantic I 200km from Lisbon Estimated magnitude approaching 9 0 Large cathedrals collapsed onto worshippers Many important palaces libraries museums also destroyed O O O 0 Fires began destroyed homes of wealthy and poor alike 0 Tsunamis swept in after quake Theologians speculated on why God would destroy Lisbon But others considered more rational natural explanations 0 Quake occurred during Enlightenment Age of Reason Led to beginnings of seismology o Kant speculated it was caused bys shifting of gas filled caverns 0 Prime Minister spent questionnaire to parishes I Seeking info on effect of quake and any odd events noted beforehand Destabilized Portuguese politics Affected European Philosophy Measuring Quakes and Quake Effects Toward a scientific understanding 0 Science of geology began during the Enlightenment I Particularly in Britain 1780s through 1820 o Branched out into seismology and volcanology in 19th century 0 Understanding and technology rapidly increased in the 20th century Toward scientific view 0 Late 1700s many looked for natural causes 0 Developed into scientific discipline in 1800s 0 Seismometers first developed by Europeans living in Japan Seis o A religious order the Jesuits were pioneers in seismology mometer Principles 0 How to measure how much Earth vibrates I Need something non vibrating for comparison I A large suspended mass will not move due to inertia 0 adding a marker on the mass and something to record on 0 creates a seismograph o seismographs developed in late 19th century 0 calculations to concert amplitudes to energy developed later 0 at first no standard way to easily compare sizes of quakes Magnitude Dr 0 Energy released by quakes covers a large range 0 Need more convenient and simpler way of expressing vales over large ranges 0 Numbers can be expressed using exponential notation I 10quot110 I 10quot2100 I 10quot61000000 o the logarithm of an exponential number reduced to he exponent I loglOquot22 I loglOquot66 I Every whole log number increase reflects a 10 fold increase in the actual value Charles F Richter o Caltech seismologist o Often asked by reporters to compare sizes of recent quakes o In 1935 with Beno Gutenberg developed a simple scale to do so Magnitude Scales o Richter Scale a logarithmic scale to compare the sizes of earthquakes Calculated form the amplitude of the largest seismic wave recorded Calculation corrects for distance from epicenter O O 0 Every whole number increase10x increase in amplitude on seismograph 32x increase in energy Greater than 10 not really possible 0 2 mircoquakes 2 39 small minor quakes 4 59 light to moderate O O O O o 6 79 strong 0 8 89 major 0 Modern Magnitude Scales o Richter s method really only meant for I Shallow quakes in California 0 Does not distinguish between body and surface waves 0 Local magnitude ML magnitude calculated by Richter s method 0 MB largest body waves 0 MS based on surface waves 0 Moment Magnitude 0 Seismic moment based on area of fault rupture 0 Larger area larger moment larger amount of energy 0 Moment magnitude based on amplitude of waves and area of fault rupture 0 Used for the largest quakes o Intensity 0 Based on effects of earthquake o Mercalli scale invented by Giuseppe Mercalli in 1902 uses observations to estimate intensity 0 Intensity marked from to XII o Earthquake effects 0 Ground motion I Seismic waves create ground motion I Close to epicenter surface waves can be the strongest I Most damage is caused by ground motion I Ground motion amplification soft soils amplify ground motions I The local geology and soil play very important roles in earthquake damage I Unreinforced masonry very susceptible to ground motion I Soft stories weakly supported floors such as bottom floor parking areas or parking garages I Resonance all structures have a natural frequency they will vibrate at I Similar to tuning fork structure will vibrate if it feels its resonant frequency I Increases risk of structural failure 0 Surface rupture I Movement along fault breaks surface O O O O O O O Landslides I Ground motion can trigger collapse of unstable slopes Slumping I Ground motion can cause soft soil on slopes to slump in cohesive pieces Liquefaction I Water saturated soft sandy soils behave like liquid during strong ground motion Fires I Not a natural effect of earthquakes I Broken gas mains spilled liquid fuel overturned cooking fires and lamps Tsunamis I Series of surges in the water column I Cause any disturbance on seafloor that displaces a large water mass Areas of great stress I Convergence compression I Mainly thrust faulting I Large vertical movements even in a single quake I Some strike slip movement as crust squirts out of collision areas Continental Collision Zones I Uplift on thrust faults builds mountains I Actively growing mountains are steep and unstable I Prone to landslides during quakes o Assam Tibet O O O O 1950 Largest M 86 recorded in a continental collision zone 70 villages destroyed by landslides Rivers blocked debris dams later gave way I Major flooding o 1988 Armenia 0 O 0 Then part of the USSR M 68 Shoddy Soviet construction collapsed I 25000 killed 500000 homeless Further destabilized Soviet Union o Armenia now independent still shows effects 0 Subduction Zone Quakes 0 Top 10 all occurred in convergent plate boundaries 9 out of 10 were all in subduction zones 0 Megathrust quakes I Thrust faults in both plates I Large slips during quakes I Rupture lengths can be 100s of km I Can be gtM 9 largest on Earth I May generate tsunami Tsunami Comparison to Wind Waves 0 Wind waves 0 Energy mainly on surface 0 Periods typically 10s 0 Wavelengths typically 150 m 500 ft 0 Tsunamis 0 Energy surface to seafloor I 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 O O O 0 Characteristics I Not noticeable in deep ocean I Travel at speeds from 500 to 1000 kmh 315 625 mih I In shallow waters I Water piles up at wave front I Speed slows to 72 kmh 45 mph I Long wavelength onshore flow for several minutes Megathrust examples 0 1960 Chilean Quake 0 May 22 1960 o Largest quake recorded M 95 o Preceded by strong foreshocks one the day before was M 79 I Alarmed population may have saved lives during main shock Tsunami O Distant effects 0 O I tsunami caused destruction across Pacific I Teletsunami I Hit Hilo Hawaii 15 hrs after quake I Biggest wave was 10 m 35 ft U 61 killed I 540 homes and businesses were destroyed or severely damaged I Hit Japan 22 hours later I 138 fatalities I California hit by smaller tsunamis One of the first well documented examples of a megathrust I Provided evidence that help reveal subduction zones Demonstrated that tsunami could affect entire ocean basins o 1964 Alaska 0 O O O O O O O O O O O O O O O 0 Prince William Sound Alaska Large thrust offshore due to subduction zone March 27 1954 Good Friday 536 pm Magnitude 92 strongest recorded in US Shaking lasted nearly 3 minutes 123 killed tsunami 113 earthquake 15 property damage over 300 million 18 billion in 2007 dollars Many new buildings in Anchorage collapsed Vertical movement during quake caused fissures ot open Major slumping occurred Tsunamis devastated coastal towns Highest waves in Valdez lnlet were 67 meters 220 feet high Most deaths caused by tsunamis These hit Oregon N CA and Hawaii hours later Had a major impact on the development of Alaska Provided more evidence that help reveal subduction zones 0 2004 Sumatra EQ O O 0 December 26 2004 magnitude 91 93 quake off Banda Aceh Sumatra Lasted 500 600 seconds 10 min I Longest recorded quake Whole planet shook Area of seabed 1200x100 km displaced 16 m 53 feet upward Created teletsunami No warning system existed for the Indian Ocean The toll I 225000 dead or missing I 168000 in Indonesia I 13 children 0 Case Study 2011 Tohoku 0 March 11 2011 o Strongest recorded Japanese quake Mw 90 o Generated teetsunami I Peak heights in Japan 405 metres 133 ft I Traveled up to 10 km 6 mi inland 0 Quake was more powerful than expected for where it occurred 0 Tsunami damage would lead to meltdowns and radiation leaks at Fukushima nuclear plantnon Seismic Gap 0 Length of an active fault that has few quakes 0 Strain builds along the gap 0 High probability the next large quake will be in the gaps o This allows probability estimates to be made Quake sequences 0 When a quake occurs stress may be shifted to other locations 0 These locations may be the site ofthe next significant quake 0 Over timedecades to centuries the quake locations may move or shift along the fault Plate and Stresses 0 Plate boundaries 0 Differential stress I Movement along faults occurs in boundary areas of an ideal plate 0 But real plates are not perfect o Zones of weakness exist within plates 0 Plate moves at different rates and directions in these zones I Creates differential stress within plate Stress Concentrators 0 Effects of intraplate quakes are often felt over larger areas than plate boundaries 0 Why 0 Plate interiors are colder more rigid 0 Plate boundaries have loose blocks of crust Intraplate quakes from Hotspots o Magma pushes up into plate 0 Volcanoes grow push down on plate 0 Both local tension and compression result Intraplate quakes on old ocean fractures 0 Charleston SC Quake 0 1886 largest recorded quake in the south east US 60 killed due to old ocean fracture zone Estimated M 73 0 Max intensity ofX 10 Quakes on old plate boundaries 0 Many old plate boundaries along the East Coast 0 Occasional random small quakes 0 But some faults are more active 0 Difficult to determine why this is the case sostatic rebound 0 Ice sheets add mass to continents 0 When ice melts mass is removed 0 Continent slowly rises or rebounds I Takes thousands of years to reestablish equilibrium 0 Creates differential stress and quakes 0 Parts of Canada New England and Scandinavia still rebounding Failed rifts 0 Sometimes rifting stops 0 Rift valley is later buried o Divergent boundaries may begin in continents o Create rifts such as the East African Rift Valley 0 But a zone of weakness left in continent 1811 1812 New Madrid Quake 0 Largest quake series in US history 0 Three or four main shocks 0 1st December 16 1811 2AM estimated M 77 0 2nd quake same day at dawn M7 I some consider this an aftershock o intensity VII 0 3rd quake January 23rd 1812 M75 0 4th and largest on February 7 1812 I estimated magnitude 77 82 I intensity X XI 0 Estimated 200 moderate quakes 0 Ground constantly trembled from Dec Feb Effects 0 Area sparsely settled little loss of life 0 Shaking felt throughout eastern US 0 Uplift and dropping ofland 0 Massive liquefaction many sand boils Impact 0 Loss of life was small 0 Region was sparsely settled 0 Most buildings were simple and small 0 Economic impact was minimal 0 Little infrastructure or trade at the time Impact of a M 77 today 0 Results today would be far worse 0 Most building not seismically sound 0 Area is very prone to liquefaction o Densely populated and traveled 0 Possibly 0 86000 casualties o 2 million homeless 0 would affect entire nation Case Study 2010 Haiti 0 11210 0 M70 o Directly his Port au Prince 0 Poor quality concrete buildings crumbled o Landslides on steep bare hillsides Most government building destroyed UN buildings destroyed and peacekeepers killed 46000 to 30000 killed 15 to 18 million homeless gt95 of city still in piles of rubble Cholera outbreak in October Societal Contributions to the Tragedy Haiti has a legacy of great wealth disparity and corrupt oppressive regimes Present government barely has enough money to operate let alone prepare for quakes Vast majority of Haitians live day to day with little opportunity to improve their lives 972011 110800 PM Subduction Zones Concluded Calderas and Undersea Volcanoes o Collapse ofvolcano during Plinian eruption 0 May form in a stratovolcano or a large region of the crust o Calderaforming eruptions include the largest on Earth Simple calderas 0 Many calderas that form in stratovolcanoes are onetime events Resurgent Calderas o Other volcanoes have repeated caldera forming eruptions 0 Many resurgent caldera may be part ofa caldera complex 0 Occur in subduction zones continental hotspots and continental rifts A Tale of Two Volcanoes o Tambora and Krakatatu 0 Both erupted in 19th century 0 68 years apart 0 Tambora o Erupted in 1815 o Largest eruption in past 500 years 0 gt50 kmquot3 ofash o 200 million tons of 502 0 villages buried 0 outside world knew little of the eruption o Tambora a year without summer 0 Average northern hemisphere temp decrease 47 degrees C o 1816 abnormally cold throughout North America and Europe 0 in New England there was a killing frost every month Snow in New Hampshire Vermont and Maine in July 0 people at the time were not able to link eruption to climate changes 0 Krakatau 0 Small island between lava and Sumatra o Became active in 1883 0 Events very well documented 0 Climatic phase in August 0 4 large explosions o loudest noise ever reported 0 also produced devastating tsunamis O O O 0 Long Valley Island collapsed into caldera Unlike Tamb ora I News of eruption transmitted around the world I Local and global effects well documented Spectacular optical effects Global knowledge of events allowed people to understand that Krakatoa eruption was the cause Caldera complex in Eastern California Formed 76000 years ago Followed by O O Yellowstone Rhyolite ows every 200000 years Smaller eruptions every 200700 years Wyoming Created by quothotspotquot below North America Caldera forming eruptions 6 to 2 million years apart Last one was 62000 years ago Yellowstone is now monitored A calderaforming eruption today would 0 Produce pyroclastic ows 100km around Yellowstone 0 Cover surrounding states in very thick 10100s ofmeters ashfall 0 Cover farms in Great Plains in cm s to meters ofash o Inject ask and 10s ofbillions tons ofS02 into atmosphere 0 This would I Render Wyoming and part ofneighboring states uninhabitable for centuries I Wipe out crops in central US for many years I Produce eXtreme global cooling I Kill millions I Threaten civilization 0 However I Probability is low in any given year I Other eruptions around the world are much more likely Lonely Volcanoes Geographically isolated Most due to hotspots Some have provided important ports or refuges in otherwise empty oceans Bouvet Island 0 Maybe the most inactive isolated volcanic island Submarine Volcanoes Most volcanic activity occurs on midocean ridges o Erupt pillow basalts In between there may be intense geothermal activity Associated with unusual organisms Life may have originated around such vents Eruptions on midocean ridges have never been observed First active submarine eruption observed in Marinas a Subduction zone North West Rota seamount Benefits of Volcanoes Recycle chemicals necessary for life Replenish soil Gather water in snow rain and ice Create valuable ore deposits Consider Australia the most geologically inactive continent 0 Does not have volcanoes o Rarely receives ashfall o No uplift few quakes but no new rock is exposed to erode and form new soil Result Australian soil is among the most infertile on Earth Final Thoughts Earth is an active planet Allows planet to support life Also produced quakes and eruptions The largest quakes and eruptions are the most infrequent Very large eruptions and quake generated tsunami can have global effects Quakes and eruptions have affected human history Have caused much suffering Modern science allows us to identify and evaluate the risks In the modern world death tolls are not controlled by the size of the event alone Other human factors 0 Dense populations O O O 0 Poor construction Poor preparation Poor response Political corruption
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