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Natural Disasters Tornadoes, Flooding, and Avalanches Tornado Facts • Mainly occur east of Rocky Mountains in US – Spring/summer • 800 tornadoes reported nationwide • Speeds up to 250 MPH; damage paths 150 miles long Tornadoes – What Causes Them? • Develop in warm, moist air as they are met with cold fronts • Creates atmospheric instability, which causes a spinning updraft Supercell Thunderstorms • Long line of thunderstorms whose updrafts/downdrafts are in perfect balance • Deadly: Perfect conditions for many tornadoes Wall Cloud • Rain-free clouds that accompany tornadoproducing thunderstorms Waterspouts • Tornadoes that form over water The “F” Scale • • • • • • F0: Winds less than 73 MPH F1: 73-112 MPH F2: 113-157 MPH F3: 158-206 MPH F4: 207-260 MPH F5: 261-318 MPH Floods • Most often, caused by overflow of rivers/lakes for a variety of reasons • Farmhouses, vehicles and farmland ruined • Can contaminate water Why Live Near Water? • Humans value the proximity to water • Land cost is cheaper near water; easier access to transportation Flood Control • Levees/Reservoirs • In emergencies, sandbags Benefits of Flooding • Egypt benefits from silt/clay deposits; soil becomes very fertile • Indus/Ganges in Bangladesh • Humans thrive off of rich soil for crops Deadliest Flood • China Flood, 1931 • Est. deaths: 400,000-4,000,000 • Left 80,000,000 homeless Three Gorges Dam • Built to help control flooding and control China’s 3 main rivers
