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Natural Disasters Midterm Study Notes

Natural Disasters Midterm Study Notes - Natural Disasters...

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Natural Disasters Midterm Study Notes INTRO Role of scientists in natural disasters predict natural phenomena and reduce effects Earthquakes local to regional Floods local to regional Hurricanes regional Tsunamis regional to global Meteorite impacts regional to global Levees in New Orleans o City below sea level o Levees designed to keep water out pumping systems pump water back out if it comes in o During hurricane, too much rain and power outages shut down pumping systems caused water to be held in the city o Water had nowhere to go but to remain in the city like a bowl of water Hazard: potential threat to humans and their welfare Risk: probability of loss (death, injuries, damage, economy) Vulnerability: potential degree of loss from event o 0 = no damage, 1 = total loss Disaster: hazardous event affecting a community in adverse way essential social structures and functions are disrupted Prediction/Forecasting: statement that particular natural hazard will occur with a given probability during a certain time frame in a specified geographic area Mitigation: efforts to minimize the effects of a natural hazard on a community People’s reactions to disasters anger, frustration, scepticism, denial, suspicion, refusal to evacuate Long-lived vs. short lived events o Example: tornado = short lived; flooding = long lived Occam’s Razor: when several conflicting hypotheses are proposed for same observations, best explanation is the one with the fewest independent assumptions o Example: Hurricane hypothesis use only one parameter wind speed Determinism cause and effect relationship only for events with 100% probability example, tides (and the flooding it will cause) Unpredictability o Most natural disasters are non-deterministic o Use of probabilities to understand when events might occur o Recurrence interval: average time interval between two events of a given magnitude Based on what has happened over record period Example: there is a 1 in 50 chance of a flood in any one year = 2% probability of occurrence VOLCANOES Molten magma rises within Earth and is erupted either quietly (lava) or violently (pyroclastic) Lava flows: quiet eruptions not so dangerous oozes out from the Earth Explosive eruptions: fragmental/pyroclastic materials dangerous Controls of explosivity o Silica content More silica more viscous higher chance of being explosive Viscosity/Stickiness of magma depends on silica content o Gas content More gas higher change of being explosive o Condition of the conduit
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The same magma of same content can produce very different flows depending on the conditions of strain within the conduit of the volcano Types of magma o Basalt 50% silica and gas-poor lava flows o Andesite 60% silica and gas-rich explosive o Rhyolite 70% silica and gas-rich explosive
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