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Natural Geologic Hazards A visual tour of worldwide natural geologic hazards Earthquakes • Earthquakes can be powerful movers of the Earth’s crust • Annual cost of damages in the US alone is $3.9billion http://highered.mcgrawhill.com/sites/0072402466/student _view0/chapter16/animations_and _movies.html# Some Earthquake damage • Paso Robles, 2004 • Loma Prieta, 1989 • Northridge, 1994 http://earthquake.usgs.gov/eqce nter/recenteqsus/ Earthquake theory http://earthquake.usgs.gov/eqcenter/re centeqsus/ • Stresses build up due to plate motion • Rocks distort and store more energy • Rocks rupture, an earthquake occurs • Final offset along the fault Volcanic Eruptions • There are approximately 3000 active volcanoes • About 50 volcanoes erupt every year • 80,000 people have been killed by volcanoes since 1900 • Mt. St. Helens caused about $1billion in damage • Mt. Lassen vents • Hawaiian volcanic flow • Hawaiian Visitor’s http://www.sci.sdsu.edu/volcano/ Center Volcano Cross section Partial melting of rock occurs at subduction and divergent plate boundaries and at hot spots* • Magma flows upward through weaknesses in the lithosphere Tsunami • Tsunami hit California coastlines in 1946, 1952, 1957, 1960 and 1964 • Over 80 tsunami have been reported in the last 100 years • Damage estimate for the 1964 tsunami was over $10million. • Crescent City Tsunami, April, 1964 • Banda Ache devastation, Dec 24, 2004 Tsunami formation • Ocean floor before the earthquake • Earthquake occurs. Faulting pushes Earth upwards • Tsunami is generated. Waves move outward. • Tsunami wave height grows towards shore http://serc.carleton.edu/ NAGTWorkshops/visua lization/collections/tsun ami.html Landslides • Aka mudslides. avalanches, hillside creep, lahars • Can be fast or slow, dry or watery • Average US annual losses are $2billion and 25 ~ 50 deaths Evolution of Landslides http://www3.interscience.wiley.com:8100/legacy/college/strahler/04712380 07/animations/ch15_animations/animation1.html • Landslides occur due to gravity pulling weak material downhill • Steeper slopes = greater downward pulling-effect • Weakened rock enhances potential of sliding (rain, water, earthquakes, volcanic blasts, ice, weight etc…) Coastal Erosion • 85% of California’s shoreline is actively eroding • El Nino winter poses the greatest threat to coastlines due to increased storms • Ca damages of $116million for the winter of ’82~’83 Coastal erosion Processes of Coastal Erosion A B C D Cross section of beach cliff Wave begins undercutting the base of a cliff Cliff falls due to removal of supporting base Newly exposed cliff is subject to ongoing erosional attack
