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 $3.9billionhttp://highered.mcgraw-hill.com/sites/0072402466/student_view0/chapter16/animations_and_movies.html#

Some Earthquake damage

• Loma Prieta, 1989

• Paso Robles, 2004

• Northridge, 1994

http://earthquake.usgs.gov/eqcenter/recenteqsus/

Earthquake theory

• Stresses build up due to plate motion

• Rocks distort and store more energy

• Rocks rupture, an earthquake occurs

• Final offset along the fault

http://earthquake.usgs.gov/eqcenter/recenteqsus/

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

• Hawaiian volcanic flow

• Mt. Lassen vents

• Hawaiian

Visitor’s

Center

http://www.sci.sdsu.edu/volcano/

Volcano Cross sectionPartial 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/visualization/collections/tsunami.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

http://www.geology.sdsu.edu/how_volcanoes_work/Thumblinks/lahar_msh_page.html

Evolution of Landslides

• 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…)

http://www3.interscience.wiley.com:8100/legacy/college/strahler/0471238007/animations/ch15_animations/animation1.html

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 Cross section of beach cliff

B Wave begins undercutting the base of a cliff

C Cliff falls due to removal of supporting base

D Newly exposed cliff is subject to ongoing erosional attack