Earth 20: Weeks 7-10
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Date Created: 05/29/14
Earth 20 Weeks 710 Notes Final Exam Information See Week 6 Notes II III IV VI VII 4 worst eruptions since 1700 a Volcanic hazards rarely erupt without warning tsunamis kill more b Mount Tambora i Stratovolcano Ash clouds and pyroclastic ow ii Became caldera caused tsunami and agricultural loss Krakatoa i Became caldera Ash clouds and pyroclastic ow ii Tsunami part of island disappeared d Mount Pelee i Stratovolcano formed high velocity pyroclastic ow that destroyed town of St Pierre e Mount Ruiz i Stratovolcano killed 25000 people surge of meltwater and mud ows ii Town of Armero buried under mud ow Mid Ocean Volcanism a Lava comes from here b Asthenosphere rises pressure is reduced and decompression melting starts new oceanic lithosphere forms World Wide Hot Spots a Comes from a plume endless magma b Non explosive c Hawaii produces chain of volcanoes Yellowstone caldera a Explosive due to volatiles and silica content viscosity b Basaltic then rhyoltic land explodes ocean doesn39t Flood Basalts largest eruptions large igneous province a Forms earth surface brings a lot of CO2 b Columbia River ood Basalts closest to US c Largest is Ontong Iava Plateau Mass Movement a Landslides aren39t dependent on seasons b Range in speed and material costly c Downslope movement of material slow to fast water to dry and anything in between d Optimal Conditions i Occur onnear bases or tops of slope ii Fractured bedrock rock falls boundaries between layers with different mechanical properties slides destroyed vegetation followed by rain old landslides volcanoes seismic activity Stability P VIII IX Gravity force pulling slopes downhill cohesion and friction hold slope in place Steeper than 31 degrees is generally unstable Forces on Slopes The force holding must be greater than pulling force i Driving forces move material downslope resisting forces oppose downslope movement ii Safety factor ration of resisting forces to driving forces stable when gt1 iii Mineral composition shale or weak pyroclastic materials occur as creep earth flows debris ows or slumps resistant rock overlies weak rock iv Degree of consolidation slumps uncommon in unconsolidated materials unconsolidated materials are over bedrock v Presence of zones ok weakness slip planes natural breaks in consistency rotational slides have curbed slip surfaces translational slides have planar slip surfaces vi Permeability ability to transmit water soil slip occurs when layers contrast this vii Steepness of slope 1 Steeper greater driving force rock falls avalanches and soil slips 2 Moderate earth ows 3 Gentle creep Topographic relief height of hill above land mass wasting occurs more in high relief areas viii d Angle of repose when pulling force is equal to holding force e Affected by i Increase pulling erosion removing lateral support adding mass construction adding weight saturation lateral pressure in cracks freeze thaw regional tilting tectonics and ground vibrations quakes ii Decrease pulling weak materials interplay with clay minerals chemical weathering faults water pore pressure erosion decrease in cohesion clearing of vegetation Cohesion a The internal strength for material to stick together holds mass b Adds to the stability c Angle of repose is max angle for slope to be stable without cohesion Pore Pressure a Water pressure at a given depth weight of the water b Decreases normal force pushing against the slope enables instability Landslides a People don39t advertise caution areas for real estate b Rock falls slope failure and shallow debris ow c Caused by gravity erosion saturation earthquakes volcanoes and excess weight accumulation XI XII XIII XIV II d Slopes are dynamic and evolving e Depends on underlying rock type climate regional tectonics and regional drainage pattern f Falling free fall of earth material i Rockfall fall thru air and accumulate as talus rock rubble not much mass ex cliffs at beach g Sliding moves as coherent block i Slump clocks of soft earth slide on curved surface ii Soil slip soil slides on titled surface debris slide iii Rock slide large blocks of bedrock slide on planar surface easy to slide from water frequent h Flowing unconsolidated material i Avalanche granular ow of snow etc that moves rapidly downhill ii Creep very slow downward movement of rock dangerous near large houses iii Earth ow wet deformed mass of soil and rock iv Debris ow uid mix of rock mud water etc that is intermediate between a landslide and ood lahars i More than one i Complex combo of two types of the above Factors in uencing Landslides a Permanent characteristics of the landslide that are constant over time eg Steepness of the slope type of rock b Variable characteristics that change quickly from an event eg Ground shaking water level soil moisture Rotational and Translational slides a Sliding along a curved surface rotational slide slump b Often caused by erosion at slope s base Mamayes Puerto Rico greatest casualties from landslide in N America Thistle Utah most costly landslide in N America from water Weather and Climate a Weather day to day response to energy imbalance in earth b Climate long term and worldwide the average of weather Processes fueled by the sun a Hydrologic cycle and erosion with gravity b Weather tornados heat waves hurricanes cyclones oods c Climate ice ages droughts atmosphere changes ocean circulation shifts d Sun heats unequally i Equator receives 24 times more than poles ii Earth39s spin and gravity create circulation patterns to even out heat in ocean and atmosphere 1 Gravity is 1 thing driving climate and giving energy along with slope III IV VI 2 Sun provides most of energy iii Circulation patterns determine weather and climate Heat transfer mechanisms a b Radiation transfer by electromagnetic waves like a crowded room Conduction transfer by molecular collisions touching a hot pot from the stove diffusion c Convection transfer by circulation of a uid most efficient i Happens in mantle and magma chambers ii Move mass and takes heat with it iii Like iceberg oating or a car radiator iv Leads to balancing of globe v Infrared greenhouse gases visible light energy is radiation and is redistributed thru convection vi Radiation and temp are related Radiation a Solar radiation some re ected some absorbed reabsorbed part are greenhouse gases i Relative amounts reflected used in hydrologic cycle and converted to heat that differ at diff latitudes ii Equatorial belt faces sun directly absorbs iii Polar regions receive solar radiation at low angle re ects net cooling iv Excess heat at equator is transferred to polar regions b Works with wavelength c With temperature observe spectra of electromagnetic waves to find temp and composition d Electromagnetic Radiation i Sun39s Energy radiant energy reacts in 3 ways ii Re ectivity albedo ex sand on beach iii Reflection only changes direction not wavelength or amplitude iv Transparent no change in radiant properties v Absorption radiant energy transferred to the matter increase in molecular energy e Mew Re ectivity a Lighter surfaces have higher albedo re ect more b Darker and rough surfaces have lower albedo absorb more c Earth about 30 moon about 7 Water and Heat a Ability to absorb or release heat is controlled by water b Water stabilizes temperature and conserves energy thermodynamics c Specific heat required amount of heat to raise temp of water high d Convection transmission of heat in owing water air e Conduction direct transmission of heat through contact VII VIII IX f Water absorbs stores and releases solar energy solid liquid and gas g Latent Heat ice melting absorbs about 80 calories per gram h Latent Heat of Vaporization liquid vapor absorbs 600 cal g Heating land vs water a Low heat capacity of rock land heats up and cools down quickly b Winter land cools quickly so air sinks towards ground high pressure region i Oceans retain warm so warm moist air rises ii Cold dry air from land ows over oceans c Summer land heats up quickly so hot dry air rises low pressure i Ocean warms more slowly so cool moist air sinks over ocean ii Cool moist air over ocean is drawn inland warms over land and rises to cool condense and form rain summer monsoons General circulation of the oceans a Surface Circulation climate b Surface and near surface ocean waters absorb and store huge amounts of solar energy i Mainly driven by wind ii Top layer of water drags on lower layer iii Wind driven ow affected by Coriolis effect and deflection of continents currents 1 Surface currents take about 1 yr to make full circuit deep currents take around 1000 yrs iv Caries heat from low latitudes toward poles c Some solar heat transferred deeper by tides wind d Surface and deep ocean circulation transfers heat thruout oceans affects global climate e North Atlantic warm surface water blown west from Africa into Carribean Gulf of Mexico path blocked by continents and forced northward along east coast to Europe warms Europe f Thermohaline Circulation moves energy and carbon i Driven by cold salty dense sinking water ii lt 1 year in upper water deep ocean takes 1000 yrs Earth39s Atmosphere a Where energy is transferred b Thin collection of mainly gases N2 78 O2 21 Argon 9 H20 vapor up to 4 and CO2 038 c Important trace and ultra trace components OH CH4 qzone nitrogen oxides CFCs and more d Lower Atmosphere i Disturbed by convection partially random but has pattern ii Hadley cell near equator dry air coming down deserts iii Troposphere 1 Lowest layer warmer at base and colder above XI XII XIII XIV XV 2 Instability as warm air rises and cold air sinks constant mix leads to weather 3 Tropopause top of troposphere iv Stratosphere 1 Stable configuration of warmer air above colder air Energy Balanced by convection a Energy imbalance insolation amount of solar radiation received differ with latitude causing diff heating in atmosphere b Atmosphere and oceans work together to redistribute solar energy from equator to higher latitudes Atmospheric circulation and pressure gradients a Pressure gradient created by diff heating of atmosphere i Cause wind weather at local scales ii Cells are circulation of moisture jet streams b Flow of atmospheric gases from high to low pressures causes wind and weather on local and regional scales Coriolis Effect a Earth rotates west to east b Velocity of rotation varies by latitude 1000 at equator and O at poles and helps define circumference c Bodies moving to diff lats follow curved paths i Northern hemisphere veers right southern veers left d Magnitude increases with increasing speed of moving body and increasing lat et Streams a Relatively narrow bands of wind b Turns air ow near cell boundaries into high speed jet streams c At high altitudes wind goes west to east polar jet and subtropical jet d Factor in creating tornadoes with wind shear and supercells Severe Thunderstorms a Conditions i Large changes in wind shear and moisture ii High water vapor content moist air in lower troposphere iii Updraft of air iv Existence of dry air above moist air mass b Wind Shear gradient in wind speed rolling motion i Causes problems with planes drop in pressure c Supercell Storm defined by presence of upward spiraling column of air mesocyclone i Source of most large tornadoes ii Thundercloud titled by wind shear may grow into supercell thunderstorm iii Rainfalls with downdrafts in forward ank of storm warm air rises updrafts in middle of storm downdrafts of cool dry air in trailing side of storm Tornadoes a Average Tornado Distribution i Air masses collide in interior US world tornado capital ii Occur at any time most common in late spring early summer May is most common month b Deaths i 3 main destructive actions high speed winds winds throw debris like bullets or shrapnel fast winds blowing into building rapidly increase air pressure inside and sometimes blow off roofs and walls ii Declining numbers of tornado deaths recently 1 At risk elders mobile homes exterior rooms with windows those unaware of alerts 2 Safer in car than mobile home lower center of gravity c Facts i Rapidly rotating column of air from large thunderstorm ii Highest wind speeds of any weather phenomenon more intense and localized than hurricanes iii About 70 occur in central US move SW to NE iv Travel up to 100 kmhr wind speeds up to 500 kmhr v Core of vortex lt1 km wide suck up objects vi Form hundreds of meters high in atmosphere may never touch ground d How to make a tornado i Warm air mass from Gulf of Mexico collides with fast moving cold polar air ii Collision causes updrafts which are caught by Ietstream iii Shear created by air masses causes rotation iv Added energy from rainfall and lightning e How a tornado forms i 3 air masses warm humid low Gulf air cold dry mid altitude air fast high altitude jet stream winds moving in diff directions give shear to thunderstorm ii Form between middle updraft and rear downdraft iii Rotation develops in wide zone core pulls into tighter spiral as speed increases dramatically and angular momentum is preserved iv Downward moving air in center surrounded by upward spiraling funnel v Wind speeds highest few hundred meters above ground slowed by friction at ground level vi Rising Gulf air is spun one way by mid altitude cold air then spun around another way b jet stream corkscrew effect 1 Warm air rising on leading side 2 Cold air descending on trailing side f Fujita wind damage scale F O is light F 6 is unexpected see table 91 i Can39t define until after XVI g Largest known Tri state Tornado moved about 100 kmhr leaving a 2km path of destruction h Super outbreak of 1974 i 147 touched ground 16 hours in 13 states 335 killed 1200 hospitalized gt75000 houses destroyed 6000 other homes damaged i In urban areas i Urban heat islands up to 10 degrees C warmer than surrounding ii Warm air rising creates low pressure convecting cell forms thunderstorms iii Few strike cities iv Safe rooms traditional cellar or interior closet with concrete walls and roof with steel door safe even when rest of house is destroyed Hurricanes a Large topical cyclones b Heat engines converting heat of tropical ocean into winds waves c Generate winds over 240 kmhr d Push massive amounts of water onshore as surges up to 6m over sea level e Heavy rains cause dangerous oods well away from coastlines f Sandy largest Atlantic hurricane 2nd to Katrina for loss g Form a hurricane i Warm H20 in upper 200ft of tropical ocean ii Seawater at greater them than 80 F in upper 60m iii Unstable warm humid air iv Upper level winds need to be weak and in same direction of storm movement v Begins with tropical disturbance low pressure zone drawing in cluster of thunderstorms with weak surface winds h Stages of Development 1 Tropical disturbance low pressure zone that draws in thunderstorms ii Tropical depression surface winds strengthen and ow into center develops iii Tropical storm surface winds reach a sustained speed between 39 and 74 mph iv Hurricane surface winds reach 74 mph v Becomes tropical depression receives identifying number 1 Surface winds strengthen and ow around into core counterclockwise in N hemisphere vi Converging surface winds ow up into central core and send warm moist air into stratosphere vii Rising air cools to dew and condenses releasing latent heat XVII II III viii Released heat warms surrounding air stronger updrafts increase rate of upward ow of warm surface air ix Winds spiral upward with increasing speeds 1 Tropical Storm over 63 kmhr Hurrican over 119 km hr 2 Main energy source is latent heat released by water vapor condensation 3 Weaken rapidly when move onto land i AKA Hurricane Atlantic ocean Cyclone Indian and South Pacific or Typhoon in N Pacific Ocean j The Saffir Simpson Scale i Ranges hurricanes from category 15 ii Based on barometric pressure and wind speed iii Larger storms have lower pressure than smaller standard is 1 bar iv Wind speeds increase with category see table 101 k Geographic Percentage about 84 each year The Eye of the Hurricane i As more wind blows into center spiraling upward cylindrical wind mass in center of storm ii When surface wind speeds reach about 119 kmhr no wind reaches center calm clear eye iii Inside eye cool high altitude air sinks and absorbs moisture iv Eye wall cylinder shaped area of spiraling upward winds around eye strongest winds here v Storm Surge is most significant cause of damage most affected by winds across sea surface 1 Greater the area of the winds the greater the water height p a Storm Surges a Rise in sea level due to i Winds push water to pile above normal levels especially on right hand side of storm where highest wind velocities occur ii Low atmospheric pressure causes water to mound up under eye of hurricane iii Also large waves blown from hurricane winds iv Sometimes already astronomical tides Moore Oklahoma part of larger outbreak Urban Areas a Partially the cause more pop means hot ground b Death not due to winds but from storm surge Life Cycle of a Hurricane a Tropical Disturbance low pressure zone draws in storms IV VI VII VIII IX XI XII XIII b Tropical Depression surface winds strengthen and a ow to center develops c Tropical Storm surface winds reach a sustained speed and storm receives a name d Hurricane surface winds about 74mph Do not form along Equator and cannot cross equator once formed No shear relies on the Coriolis force 0 at the equator Energy Transfer a Heat transfer from the warm moist air above tropical seas into the core of hurricane Latent heat is released in staggering amounts upon condensation c Creates about 200x more energy than out ability to generate electricity d Energy released from cloudsrain is 400x greater than hurricane winds energy Hurricane Paths a In uences are trade winds blowing cyclone west Coriolis effect forcing a curved path to the right stronger with distance from equator and location of Bermuda High Hurricane Season 2005 a 28 storms named une to November Katrina Category 5 125 mph Flooding most expensive natural disaster in US history Made landfall in SE Louisiana New Orleans i Billions spent on levees which failed ii City built on delta loose mix of sand mud and water deposited from Mississippi River Human Control of Rivers has Impacts a Building levees and diverting the river diminish sediment deposition that creates a protective barrier for New Orleans b Also susceptible to breach during strong storm seasons Typhoon Haiyan a Super typhoon change in vegetation b Winds responsible for change Factors affecting Climate a Extraterrestrial Factors i Solar Output Earth Sun Geometry and Stellar Dust b Ocean Atmosphere and Land Factors i Volcanic Activity Mountain Building Continental Drift Ocean Heat Exchange Surface Albedo Atmospheric Albedo and Atmospheric Chemistry Climate History of the Earth a Timescale in Millions of Years P F793 i Climate depends on balance between incoming and outgoing heat ii Earth divided into belts of frigid temperate and torrid lat iii Ice Age 1 Frigid zone expands to larger area 2 Torrid zone shrinks but doesn39t disappear iv Torrid Age 1 Torrid zone expands to larger area 2 Frigid zone shrinks but doesn39t disappear b Atmospheric CO2 declined due to i Photosynthesis ii Dissolution in the oceans iii Precipitation of calcium carbonate shells algae skeletons etc iv Results greenhouse effect and lower global temps c Earth39s Climate Throughout Time i Fluctuates change is normal XIV Tectonics and Climate a Tectonically active periods i Supercontinents break up rapid plate motion ii Divergent zones have increased volcanism iii Volcanoes release large amounts of CO2 iv Sea levels rise b Tectonically quiescent periods i Continental collisions slow plate movement ii Mountain build exposes fresh rock at surface iii Weather of silicate rocks less CO2 iv Sea levels fall c Configuration of continents effects ocean circulation XV Paleoclimate Records a Oxygen Isotopes i Oquot16 evaporates quicker than Oquot18 ii Organisms use oxygen to make their shells iii Ratio of 8 to 16 records ocean temp and global ice volume iv Big ice caps more 18 in ocean 1 Cold temp less evaporation less snowfall more 16 on the ice caps 2 Less 18 means hot temps more evaporation and more snowfall XVI The Late Paleozoic Ice Age a Large landmasses near poles accumulate snowfall built continental ice sheets i Pangea moved across south polar region b Continents blocking equatorial ocean circulation i Warm tropic water doesn39t build much heat ii Warm water evaporates more easily than cold XVII XVIII XIX XX XXI XXII If continents divert warm currents north and south then more water will evaporate to form clouds and snow iv Polar continent allows snow and ice to build Paleocene Torrid Age a General Heating trend b Equatorial zones similar to today pole ward lat much warmer c Absence of strong seasons evenly distributed rainfall warmer and wetter d No ice caps e Dinosaurs roam Antartica Shifting to Warmer Temperatures a Enormous release of lava from opening of Mid Atlantic Ocean sea levels rise b Equatorial zones get covered by oceans 9 more solar absorption i Tethys seaway opens allowing heat to build in tropics c As oceans warm snow melts and albedo lowers i Positive feedback lower albedo means more warming d Warming oceans melts methane hydrates i Positive feedback e All related to breakup of Pangaea tectonics i Separation of Antartica allows circum polar current ii Landmasses move towards poles and accumulate ice iii Tethys Seaway closed iv Himalayan Mountains and Colorado Plateau uplift 1 Disrupted E W atmospheric circulation 2 Caused rock weather uses up CO2 v Formation of Central American Land Bridge Quaternary Glaciation a When permanent ice sheets are established at poles Determining Temp a Tree rings growth rings of corals tax records almanacs grape crops changes in glaciers weeks year of sea ice in Iceland writings and paintings Climate on Timescale a About 10 glacial advances and retreats b Advances last almost 1000000 years retreats are faster few thousand Caused by cycle s in orbit that affect areas receiving solar energy Most data from Vostock Ice Core Representative of entire Quaternary Glaciation Fluctuating temps result in advances slow and retreats fast g Reproducibility the hallmark of good science Milankovitch Theory and Scale a Eccentricity varies from circular to elliptical less solar radiation when elliptical main control of glacial changes b Tilt 215 to 245 degrees off vertical in cycle iii nrnon XXIII XXIV II III IV c Precession of Tilt direction of tilt chances in double cycles d Changes in Earth39s orbit tilt and wobble correlate to changes in amount of Earth39s solar radiation received e Amount of solar radiation at high lat in summer affects snow of winter Complex Climate Systems Feedbacks a Strong Correlation between high CO2 and high sea surface temp global warming Last Glacial Max a AKA the Ice Age glaciers at max extent b We are still in Quaternary Ice Age interglacial period c If all ice melts sea levels rise 65m d Antarctica has 90 of world39s ice Temperature Records Solar Radiation a All sunlight passes through atmosphere but only 51 is used b 4 re ected back to space c 26 scatteredre ected by clouds and atmospheric particles d 19 absorbed by atmospheric gasses and clouds Greenhouse Gases a Begins with absorption of shortwave radiation which is converted into sensible eat at Earth39s surface b Some heat transferred into lower atmosphere convection conduction c Surfaces become radiators d Absorption of this energy adds heat energy to atmosphere and cycles back and forth between ground and atmosphere e Examples CO2 methane Nitrous Oxide Hydro ourocarbon Per ourocarbon Sulpher hexa uoride f Water vapor is most common methane is most potent g People didn39t worry about CO2 before because they thought the ocean absorbed it h We would freeze without them Human s contribution to Greenhouse gases a Cutting burning forests CO2 b Wetland techniques of rice growing methane c Agricultural practices d Changes occur over thousands of years and are relatively minor Temperature of the Earth a Milankovitch Cycles cause glacial changes b Predict a rise in sea level mainly affect east coast c Climate forcing factors page 420 lol i Positive and negative numbers some balance out ii Range between 16 and 28 wmquot2 iii Can we engineer the environment 1 No can39t just do one thing environmental feedback iv Methane leveling out yet still in atmosphere d Consequences in near future e Amundsen Sea Sector of W Antarctica Break up i 12m increase in sea level II Ozone layer in the Stratosphere Blocks ultraviolet radiation that causes skin cancer Disappearing but has hit its max if we all work together it can rebuild Ozone on earth causes smog health hazard at ground level Natural level is balance between sunlight creating it and chemicals destroying it e Used to use Chloro uorocarbons in fridges cars and aerosols i Can39t be washed out in troposphere ii Chlorine atoms form with oxygen atoms and break up ozone f Concentration Antarctica confirmed that not only has hole gotten smaller but has split in 2 P F793 I Extinction a Processes i In both land and sea mainly affects animals ii Disappearance of tropical life forms iii Tendency for certain groups to experience them repeatedly iv Alleged equal spacing between events v Cause remains relatively unknown b Agents i Catastrophic meteorite impacts and comet showers ii Earth volcanism glaciations sea level changes global climatic changes changes in ocean levels of oxygen or salinity c Possible Causes of Mass Extinction i Plate tectonics 1 Rates of Sea Floor Spreading 2 Position of Continents and Glaciation 3 Number and Size of Continents 4 Sea Level Changes ii Volcanoes 1 Flood Basalts Change in Atmospheric Composition 2 Examples Ontong ava Broken Ridge North Atlantic Deccan Traps Columbia River Ethiopian Traps a Deccan Traps 30 trillion tons of CO2 6 trillion tons of S 60 billion tons of halogens possible reason for dinosaur extinction iii Climate Changes 1 Cooling heating volcanic sources iv Ocean Composition Causes Competition Reduction in food resources Extraterrestrial II 5 Largest Extinctions a Late Ordovician period i 100 families extinct b Late Devonian Period i 30 of animal families extinct c End of Permian Period i Trilobites go extinct 60 of all animal families and 95 of marine species die out also many trees ii Formation of Pangaea iii Sea level fall climate changes less shoreline ocean comp changes lack of oxygen iv Siberian Traps ood basalt duration of extinction events v Tropical seas eliminated less shallow marine waters arid interiors warmed atmosphere d Late Triassic Period i 35 of animal families die out early dinosaurs die out most synapsids died except for mammals ii 75 extinct by the end iii possibly from asteroids ood basalts or gradual climate change e Cretaceous Tertiary K T boundary i About half of all life forms die out ii Impact Event 1 Rocks have iridium rich clay layer that matches with changes in fossils 2 Shocked quarts high pressure tektites meteorite fragments and spherules melted rock or glass 3 Chicxulub impact asteroid caused earthquake and tsunami 4 Global wildfires acid rain dust and soot blocked sunlight prevented photosynthesis tsunami atmospheric CO2 increase 10C temp rise iii End of Cretaceous 1 Sea level fall rapid sea oor spreading followed by slower spreading and cooler climate 2 Deccan Traps ood basalt 3 Chicxulub Impact Bolide impact capable of causing nuclear winter 4 60 of species extinct including pterosaurs but some survive mammals birds turtles and other reptiles amphibians and insects 5 Possible causes of extinction bolide impact Deccan Traps climate change trace element poisoning egg eating mammals supernova disease III Impacts a Civilization Threatening IV VI VII b Mass Extinction c Earth Sterilizing d Meteor Crater outline tends towards square shape Tunguska a Something exploded and destroyed large amount of land b Fires burned for weeks c Don39t know if it was comet or asteroid Asteroid Comet Predictions a Measured on the Torino Scale What happens at an impact a Bolides i Sometimes just great fireworks with no damage ii Globally catastrophic stratospheric dust and smoke iii Only known natural hazard that can destroy a civilization iv Tunguska class impact 1 Damage similar to nuclear bomb 2 Average interval for whole earth 100 yr 3 Minor risk relative to other natural disasters b Larger local regional catastrophes i Destroys area equivalent to small country ii Average interval 100000 yr iii Moderate risk relative to other natural disasters c Global Catastrophes i Global environment damage threaten civilization ii Average interval 1 million yr iii Major risk relative to other natural disasters Hazards of Impacts a Compared to other risks minor b Most happen in oceanunpopulated areas
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