30271 Eve DeAngelis February 7, 2014.docx

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Northeastern University
Earth & Environmental Sciences
ENVR 1104
Malcolm D Hill

2/7/14 Natural Disasters and Catastrophes ENVR 1104 CRN: 30271 Chapter 1-7 Overview 1. Overview • What do EQ do that make them hazards? – Shaking- what bad things could that cause? • Is there a specific cutoff size btwn “hazard” and “catastrophe”- no there is no specific cutoff • Some hazards are highly localized, some are large spanning or even global • Forecasting- recurrence interval; magnitude vs. frequency o More energy, larger recurrence interval • Feedback- negative and positive o Positive: a volcano that puts a lot of dust in the atmosphere, reduces the sun light, reduces temperature, more snow, white snow reflects the sunlight (not absorb it)- so the ground will be even cooler as a result o Negative: warming climate melts large icecaps, so sea level rises, and floods onto dry land- that sea water will be shallow- this causes the climate to warm- evaporation rate increases- snow and rainfall increases as well 2. Plate tectonics and physical hazards • Core mantle crust separation (oceanic vs. continental) Oceanic= basalt • Plates= rigid, not much internal deformation (lithosphere) crust and cold upper part of mantle • Asthenosphere= can flow gradually, increased temperatures • Plate Boundaries: o Divergent (Ocean ridge, continental rift)- vertical fault  Decompressed magma melts  Tension stress, normal or reverse faults  Hanging wall- one above the fault  Foot wall- one below the fault  Hazards at divergent boundaries: • Volcanism in a ocean ridge may not cause any hazard to people- especially if they’re far away • Continental ridges cause hazards • Divergent boundaries can cause earthquakes o Convergent (2 oceanic plates, 2 continental, or one of each)-vertical fault  Subduction zone  Compression stress  Hazards: • Subduction zone; causes andocyte volcanoes • People living in subduction zones can cause problems too o Transform fault- strike slip- horizontal fault  Shear stress  Right and left lateral  Hazards: • Ocean- not a problem • Land- potential problem • Plates move because: new magma at divergent plate boundaries (ridge push) vs. weight of dense cold oceanic lithosphere at subduction zones (“trench pull”) • Continental Drift vs. Plate Tectonics: o Continental drift-  Fossils told Wegner about Pangia  Plate tectonics is a better explanation because sea floor muds tell us that older mud is farther away from ridges 3. Earthquakes and their causes • Elastic rebound theory- earthquake waves that spread when rock breaks • Focus (underground where rock breaks) vs. epicenter (point on surface- can be plotted on a map) • Strain= deformed rock- stored energy before breaking point • Interpolate earthquakes- any earthquake not near any plate boundaries- not as frequent • Waves: o P (always move faster) and S waves- formed instantly and spread out o Period (important in understanding whether tall or short buildings will be affected), amplitude, frequency o Seismograph- pendulum-like way to measure EQ- distance btwn the arrival of P and S waves helps determine location of the EQ o Richter, Mercalli, Seismic Moment- EQ size scales • Ground motion and failure: o Acceleration- from shaking o Liquefaction- water saturated sand- lubricated the particles allowing for what appeared to be solid ground to become liquefied 4. EQ prediction, forecasts, mitigation • Precursors: o Foreshocks o Volume of rock increases- due to tiny cracks in rocks o Level of water in wells o Animal behavior • Type one and type two errors (don’t have to know the difference) • EQ Probability: o Trench- look for offset soil o Seismic gap- where a big one hasn’t happened in a while o Migrating EQ’s o Recurrence intervals • Populations at risk- SF bay area • Resonance- period of sway of building vs. period of sway from the waves of the EQ shaking the ground • Preparedness- land use zoning, building codes, emergency response procedures 5. Tsunami • Formed by EQ, Volcanism, Landslides • Water depth is the main factor affecting the tsunami’s speed • Very tall and carry a lot of energy- highly destructive 6. Volcanoes: tectonic environments and eruptions • Magmas form in the earth: o Add water o Decompress o Increase temperature • Basalt (gassiest), andesite and rhyolite are the three types • Lava Flow: o Basalt- pahoehoe vs. Pyroclastic eruptions 7. Volcanoes: hazards and mitigation • Lava flows • Pyroclastic flows/surges • Ash/pumice falls • Volcanic mudflows • Poisonous gases • Landslide risk • Precursors: o Rock bulges- change in shape o Magma rises and temp of rock around it increases o Snow melts o Increase in steam o Temperature of steam vents • Controlling lava flow? Chapter 1 terms: - Catastrophe: a large-scale disaster with economic and human damage - Cyclic events: events that can be predicted based on their recurrence interval - Forecast: predicting that a hazard will occur in a certain area within the next number of years - Fractal: a quality of geologic features when they look the same regardless of size - Insurance: protection from economic troubles after a disaster - Land use planning: redistrict development based on where disasters are likely to occur - Mitigation: preparing for and reducing the damage of a disaster - Natural disaster vs. hazard: hazard is when a process could be a threat to human life or property; disaster is when this actually occurs - Precursor event: small disasters leading up to the large event - Recurrence interval: past recorded disasters that express the probability of a future disaster - Risk: a hazard in the light its recurrence interval and expected costs Chapter 2 terms: - Asthenosphere: inner, hotter, more easily deformed part of the earth - Collision zone: the place where two continental plates collide - Continental drift: the theory that the continents were connected then drifted away through the oceanic crust - Convergent boundaries: where plates move toward each other, includes subduction zones- compression stress, reverse fault - Divergent boundaries: plates move away from each other, usually at spreading zones- tension stress, normal fault - Hotspot volcanoes: volcanoes that erupt not on a plate boundary - Isostacy: the idea of buoyancy, which explains why less dense rocks rise to the surface - Lithosphere: the stiff, rigid outer rind of the earth - Low- velocity zone: the boundary between the asthenosphere and the lithosphere - Magnetic field: the earth has it - Mid- oceanic ridge: a mountain range down the center of the ocean - Mohorovicic Discontinuity: the boundary between the earth’s crust and mantle that has a difference in density - Pangea: the giant super continent that all the continents were originally a part of - Plates: the lithosphere is divided into about 12 plates - Plate tectonics: the movement of the earth’s plates - Plumes: abnormally hot but solid rock that rise within the earth’s mantle and begin to melt as the rock pressure on them drops - Resurgent calderas: depressions where the erupting giant volcano collapsed - Rift zones: an elongate spreading zone in earth’s lithosphere - Seafloor spreading: the process that moved the continents away from each other caused by new oceanic crust forming, spreading and sinking into the oceanic trenches - Spreading centers: source of basalt lava flows that cover the entire ocean floor - Subduction zone: the denser plate descends into the asthenosphere - Transform boundary: two plates slide past each other, shear stress - Trenches: a depression in the ocean floor at a subduction zone between two plates - Triple junctions: where different types of plate boundaries join Chapter 3: - Amplitude: the amount of positive or negative wave motion - Blind thrust: thrust faults that do not break the surface - Body waves: waves that travel through the body of the earth: P and S waves - Creep: when a fault releases stress by moving continuously instead of suddenly snapping, prev
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