1. Geography
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Geological And Natural Hazards
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2. Objectives:
 Define the terms tsunami.
 List major types of geological hazards and describe ways to mitigate their
impacts.
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3. Define the terms tsunami.
 Tsunami: An immense swell, or wave, of ocean water
triggered by an earthquake, volcano, or landslide,
that can travel long distances across oceans and
inundate coasts.
Japan Tsunami (March 2011)
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4. List major types of geological hazards and
describe ways to mitigate their impacts.
• The circum-Pacific belt, or “ring of fire”, spawns most of the world’s
volcanoes and earthquakes.
• Earthquakes result from movement at faults and plate boundaries.
We cannot prevent them, but we can build structures and cities in
safer ways.
• Volcanoes arise from heating by magma at rifts, subduction zones,
or hotspots.
• Landslides and other forms of mast wasting can occur on small or
large scales; damage can be minimized by understanding their risks.
• Tsunamis can flood coastlines and cause immense damage. Early
warning systems will be key in minimizing future losses.
• We often worsen impacts from natural hazards, but we can reduce
them through better land use practices.
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5. Geologic and natural hazards
• Some consequences of plate tectonics are hazardous
• Plate boundaries closely match the circum-Pacific belt
– An arc of subduction zones and fault systems
– Has 90% of earthquakes and 50% of volcanoes
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6. Earthquakes result from movement
• Earthquake = a release of
energy (pressure) along plate
boundaries and faults
• Can be caused by enhanced
geothermal systems
– Drill deep into rock, fracture it
– Pump water in to heat, then
extract it
• Can do tremendous damage
to life and property
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7. Volcanoes
• Volcano= molten rock, hot gas,
or ash erupts through Earth’s
surface
– Cooling and creating a
mountain
• In rift valleys, ocean ridges,
subduction zones, or hotspots
(holes in the crust)
• Lava can flow slowly or erupt
suddenly
• Pyroclastic flow: fast-moving
cloud of gas, ash, and rock
– Buried Pompeii in A.D. 79
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8. Volcanoes have environmental effects
• Ash blocks sunlight
• Sulfur emissions lead to sulfuric acid
– Blocking radiation and cooling the atmosphere
• Large eruptions can decrease temperatures worldwide
– Mount Tambora’s eruption caused the 1816 “year without
a summer”
• Yellowstone National Park is an ancient super volcano
– Past eruptions were so massive they covered much of
North America in ash
– The region is still geologically active
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9. Landslides are a form of mass wasting
• Landslide = a severe, sudden mass wasting
– Large amounts of rock or soil collapse and flow
downhill
• Mass wasting = the downslope movement of soil
and rock due to gravity
– Rains saturate soils and trigger mudslides
– Erodes unstable hillsides and damages property
– Caused by humans when soil is loosened or exposed
• Lahars = extremely dangerous mudslides
– Caused when volcanic eruptions melt snow
– Huge volumes of mud race downhill
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10. Mass wasting events can be colossal
and deadly
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11. Tsunamis
• Tsunami = huge volumes of water are displaced by:
– Earthquakes, volcanoes, landslides
• Can travel thousands of miles across oceans
• Coral reefs, coastal forests, and wetlands are damaged
– Saltwater contamination makes it hard to restore them
• Agencies and nations have increased efforts to give
residents advance warning of approaching tsunamis
– Preserving coral reefs and mangrove forests decreases the
wave energy of tsunamis
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12. One dangerous tsunami
On December 26, 2004 an earthquake off Sumatra triggered a massive
tsunami that hit Indonesia, Thailand, Sri Lanka, India, and African countries
Killed 228,000 and displaced 1–2 million more
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13. We can worsen impacts of natural
hazards
• We face and affect other natural hazards: floods,
coastal erosion, wildfire, tornadoes, and hurricanes
• Overpopulation: people must live in susceptible areas
• We choose to live in attractive but vulnerable areas
(beaches, mountains)
• Engineered landscapes increase frequency or severity
of hazards (damming rivers, suppressing fire, mining)
• Changing climate through greenhouse gases changes
rainfall patterns, increases drought, fire, flooding,
storms
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14. We can mitigate impacts of natural
hazards
• We can decrease impacts of hazards through
technology, engineering, and policy
– Informed by geology and ecology
• Building earthquake-resistant structures
• Designing early warning systems (tsunamis, volcanoes)
• Preserving reefs and shorelines (tsunamis, erosion)
• Better forestry, agriculture, mining (mass wasting)
• Regulations, building codes, insurance incentives
discourage developing in vulnerable areas
• Mitigating climate change may reduce natural hazards
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