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Midterm

Midterm Review.pdf

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Department
Earth Sciences
Course
ERTH 2415
Professor
All Professors
Semester
Winter

Description
Natural Disasters Midterm Review LESSON 1-INTRODUCTION What is a natural disaster? - Natural Disaster: natural event which large amounts of energy is released in a short time, resulting in a catastrophic impacts on life or environment ∙ usually has high casualties, destruction of infrastructure, disruption of society, economic loss, media coverage, gov't involvement ∙ big focus on if it disrupts society Natural Hazards - Natural Hazards: source of potential hazard that exists in the environment that have the potential to cause harm (eg rock slides) natural hazards vulnerability natural disaster - Vulnerability: likelihood that a community will suffer injuries, deaths or property damage from a hazardous event - Resilience: reduction in likelihood for community suffering by taking various steps (eg burying power lines) Metrics - Frequency: number of occurrences of similar events per unit of time (eg Caribbean storms affect Atlantic Canada 4x per year - Return Period: length of time between similar events (eg severe hurricanes occur in the US about every 6 years.) - Magnitude: amount of energy fuelling a natural disaster event (eg force of hurricane winds, or of an earthquake.) Origin of the Solar System 1. Formation of Solar Nebulla - gravity: force of attraction between masses m &m₂ separated by a distance of r - turbulent cloud filled with dust particles that attract each other and eventually becomes a disk by moving in the same direction(gravity flattens it) 2. Planetary Accretion - accretion into planetestimals - planets ∙ collisions between a small number of large bodies in final stage>impact body ∙ controlling T◦ as you move from the sun ◦ closer: merc, venus, mars, earth>rocky ◦ further giants: jup, saturn, uranus, nep>icy ◦ other very far: comets, stable, water/ice 3. Differentiation of Earth - caused by gravity causing denser materials to gradually migrate to the centre of the planet - centre is hot because of radioactive decay Global Trends 1. Man-made disasters decreasing in recent years - emerging health and safety, economics 2. # of great natural disasters increasing with time - geological disasters staying constant (earthquakes, tsunami) - weather realated going up (drought, flood etc) ∙ result of climate change?? 3. # of natural disaster fatalities increasing with time - communities are more vulnerable (higher populations, degradation of ecosystems, over reliance on technology) 4. Economic losses rising Canadian Trends 1. natural disaster #s increasing overtime - is climate increase responsible? 2. # of fatalities decreasing - improved engineering 3. economic loss most due to weather Risk and Mitigation Risk: product of hazard x valnerability Response: immediate actions taken after a disaster has occurred to put event under control Recovery: middle-term activities to put situation back to normal (not always possible/desireable to return excatly as it was before) Mitigation: long term actions to reduce risk - structural: building retrofitting, etc - non-structural: land use policies, severe weather warnings Preparedness: planning for disasters by putting in place resources to cope with them when they occur LESSON 2: GUEST SPEAKER MATTHEW GODSOE What makes a disaster? - disasters: a social phenomenon that results when a hazard intersects with a vulnerable community in a way that overwhelms that community's ability to cope - Vulnerabilities ∙ Structural ◦ old buildings ◦ critical infrastructure (oil, gas) ◦ urbanization ◦ unsustainable land use planning ∙ Social ◦ health, age and gender of population ◦ language ◦ aboriginal community considerations Emergency Management - focus on managing emergencies and deciding whether it is a disaster later ∙ 4 pillars ◦ Prevention/Mitigation ◦ Preparedness ◦ Response ◦ Recovery ∙ all hazards emergency management ◦ common response to multiple disasters LESSON THREE: IMPACTS WITH SPACE OBJECTS Extraterrestrial Debris Meteoroids: extraterrestrial debris orbiting the sun (potential impactor) Asteroids: small rocky body orbiting the Sun (primary source) - most frequently hit earth - impactor larger than 100m - Main Asteroid Belt ∙ most asteroids are in the belt ∙ range from tiny pebble to massive (more than 900km) Near Earth Asteroids: asteroids crossing the orbits of earth or mars (only 1/1000 the number as the belt) - Apollo and Atens asteroids cross Earth's orbit (2 contact points each) Comet: small object composed of ice and rock debris moving through outer space (secondary source) - very far from the Sun, Mostly past Neptune - "dirty snowballs", famous for having a beautiful tail with passing near the sun - Halley's comet: 76 year orbit. Fringe of Solar System to right near the sun Impact Scenarios - Meteoroids are classified according to size 1. Cosmic Dust (0.001-1mm) - pass through atmosphere unchanged - settles on Earth's surface - mass gains10 5- 10⁶ 2. Shooting Stars(~1mm) - melt when entering atmosphere because of friction ∙ blaze=1s, 100km above ground - tiny glass spheres fall on the Earth's surfact 3. Meteorites (1mm-100m) - pass through atmosphere and fall to earth's surface - can split into fragments mid air - 2 definitions ∙ impactor 1mm-100m ∙ impactor that hits the ground - upon entry, exterior melts and is stripped away - Classification: ∙ Stony Meteories (primitive) [95%] ◦ composition similar to Earth's mantle ◦ Chondrules are solidified droplets of matter from the solar nebulla ∙ Iron & Stony-Iron [2-3%] ◦ composition similar to Earth's core  stony more rare as they are harder to find - Measuring Density ∙ density provides clues about source body ∙ 3D laser imaging to determine volume 4. Asteroids (<100m) - not slowed by atmosphere - explode on contact with surfact - 160 craters on earth (low number due to rain erosion) Mid-Air Explosions - Tungtuska, Siberia 1908 ∙ massive fireball in the sky, blast hear 1000km away ∙ barometric anomelies recorded worldwide ∙ 80 million trees fallen ∙ no crater ever found ∙ no scientists visited site before 1928 ∙ 50m diameter, exploded 6km above ground - K/Pg boundary event (K=Cretaceous, Pg=Paleogene) ∙ major extinction, 65% of all species extinct in short time ∙ 1980 Alverez asteroid impact theory ◦ discovery of a worldwide iridium rich layer at boundary event  rare element on earth, meteorites are rich in iridium  usually associated locally at impact sites ◦ asteroid of 10km diameter need to generate enough iridium to completely disrupt environment  additional stress on life from flood besaults (volcanos in india)  likely a combination of impact and volcanos, unable to fins crate site at the right age until Riviera Mais, Mexico. Right by shore. 1/2 on land and 1/2 underwater  return perioud ~100Ma LESSON FOUR: IMPACT TOURS Impact Craters Astrobleme: synonym for impact crater - Distinctive Features 1 Circular Feature 2 Crater is steep sided and closed 3 Rim rocks tilted away from crater 4 Shattered rocks on crater floor 5 larger angular clocks of rock scattered around 6 presence of meteorite fragments 7 shock minerals 8 shatter cones: conical fragments of host rock fractured by shock wave generated in the impact - Simple Craters: small impacters ∙ diameter >5km ∙ raised rim, no central uplift ∙ concave bottom, would look here for meteorites - Complex crater ∙ <5km ∙ collapsed rim ∙ central uplift, no meteorites Canadian Impact Crater Tour 1. Sudbury, ON (1850 +- 3Ma) - largest and oldest - heavily deformed by regional movements along faults (was originally a complex circular crater, no an elliptical structure) - nickel already present in area, and heat helped to concentrate metals - DF: circular, shatter cones 2. Wanipetei, ON (37 +- 2Ma) - lies within limits of sudbury crater but is much younger - located under Lake Wanapetei (revealed by gravity survey) ∙ measuring gravity done a gravimeter, requires very precise field measurements, very expensive ∙ interpreting gravity data processed to map heterogeneties ◦ low gravity values=cavity ◦ high gravity values=high rock concentration - DF: circular 3. Brent, ON (396 +-20Ma) - stony meteorite 150km in diameter, velocity=20km/s - crater now=simple 3km crater, 2 kidney shaped lakes - 12 boreholes drilled In crater in 1950-60s - DF: semi-circular, crater in steep-sided, shattered rocks on floor, large angular blocks of rock scatter around crater 4. Charlevoix, BC (357 +- 15Ma) - north shore of St lawrence river - heavily eroded - differs from regional topography - associated with earthquake activity (impact scars act as zones of weakness in earths crust - DF: semi-circular, shatter cones 5. Eau claire, QC (290 +-20Ma) - double impact site ∙ binary pair (2 bodies closely bound by gravity>asteroid + little moon bound by gravity) ∙ 32 km and 22 km ∙ DF: circular 6. Manicouagan, QC (214 +- 1Ma) - originally 100km, now 75 km) - hydroelectric resvoir since 1960s, flooding revealed crater structure, complex crater - DF: shock minerals, circular. 7. Haughton, NU (23.4 +-1Ma) - shatter cones found 1974 - mars analog (place on earth that looks and feels like mars) - DF: semi-circular, shatter cones 8. Pingualuit, QC (1.4 +- 0.1 Ma) - aerially found in 1943 - simple crater, 3km, rim ~160 above water, 250m deep ∙ impacticide: glassy material produced by partial fusion of host rocks by the heat generated from impact, rich in iridium, terrestrial rocks. - one of the deepest freshwater lakes in World, water pure and transparent, water stays ~330years. - QC Provincial park, - DF: circular, crater is steep sided, shock minerals 9. Whitecourt, AB (0.036 +- 0.001Ma) - youngest in Canada - discovered 2007, with iron meteorites (only one in canada) - almost perfect bowel shape, only 36m D, 6m deep - DF: circular, steep-sided, presence of meteorite fragments Crater Counting - Absence of radiometric data, surface dated using 'crater counting' (older surface=more craters) - method has been calibrated with lunar data from which radiometric data is available - knowing crater rate, age can be estimated - assumptions ∙ geological record has been preserved ◦ N/A to Earth cause of place tectonics, N/A to Venus due to complete resurfacing effect ◦ little of no erosion LESSON FIVE: PLATE TECTONICS Layered Earth Differentiation of Earth; gravity causes denser material to migrate to cetntre Layers based on 1. Density of 2. Physical Properties 1. Density Layers - inner core: solid iron - outer core: liquid iron - Mantle: Iron and Magnesium - Crust: silicone and oxygen - less dense material 'floats' on top of denser material ∙ continental crust has lower density than oceanic crust ∙ mantle is supported by the very dense core 2. Strength Layers - gaseous atmosphere - liquid hydrosphere (mostly ocean) - rigid lithosphere: thicker than crust, ~ first 100km thick, rigid solid that when put under pressure will crack - plastic asthenosphere: solid but more like toothpaste, from 100-350km, slippery and moves a bit - Plastic mesophere: more viscous than asthenosphere Before "Plate Tectonics" Early Hypotheses - Aristotle (384-322BC) ∙ earthquakes caused by undergound air escaping explosively after being heated by central fire - Kircher, Atheanasius (1602-1680) ∙ witnessed active volcnos in Italy ∙ Drew early cross-sections of earth ◦ fire in core inflame subsurface resevoirs feeding volcanos - Catastrophism (17-18C) ∙ earth;s landscape shaped by great catastrophes (based on Christian thinking at the time) - James Hutton (1726-1797)Uniformitarian's ∙ natural processes operate with the same intensity and under same set of physical contraints with now as geological past ∙ based on erosion rate, concluded Earth was much older ∙ "Present is key to the past" - End of 19C ∙ earths internal structure understood ◦ radiates heat ◦ basic geology of continants known ◦ recycling earth material through Rock Cycle - Rock Cycle ∙ describes process by which older rocks are made into new rocks ◦ Igneous Rocks: form by cooling from molten liquid called magma ◦ Sedimentary Rocks: by erosion and compaction of rock fragments or by precipitation ◦ Metamorphic Rocks: form by alteration of existing rocks by heat and/or pressure ◦ theory fails to describe distribution of rock types and processes on Earth's surface - Alfred Wegener & Continental Drift Theory ∙ hypothesis largely correct but with incorrect details ◦ continents are in motion, not fixed ◦ supercontinent Pangea broke apart starting 200Ma ago ◦ estimated drift rates of 3-10m/year (real=2-10cm/year) ◦ matched rock types, mountain ranges and fossils across Atlantic ◦ Paleoclimatic evidence  fossils of tropical plants found in artic zones ◦ BUT was unable to provide an explanation for HOW  suggested low density continents has moved laterally through denser mantle (impossible!) Tectonic Cycle Tectonic: related to deformation forces acting on Earth's lithosphere and responsible for creation of mountain ranges and faults Tectonic Cycle: episode of large scale deformation of Earth's cycle, one cycle=~250ma) Plate Tectonics - continents move laterally, as part of rigid lithosphere plates that slide over plastic asthenosphere ∙ lithosphere: continental and oceanic crust and rigid upper mantle ∙ athenosphere: convecting upper mantle (convection in asthenosphere is the driving force) ∙ subduction: process which a lithosphere plate descends beneath another, pulled down by gravity ◦ less dense plate=overriding plate ◦ denser plate=subducting plate ◦ avg plate descends at ~45◦ ◦ subducting plate gradually melts into asthenosphere Magnetization Patterns on Seafloor Internal Geomagnetic Field - liquid iron outer core creates field - Earth's rotation, heat transfer by convection at outer-inner core boundary - Magnetic Lines of Force: theoretical representation of the force acting on a small magnet ∙ resembles bar magnet ◦ equator:
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