Chapter 16: Natural Disasters and Catastrophes
Hazards, Disasters, and Catastrophes
• Natural processes are physical, chemical, and biological changes that modify the landscape.– Common denominators of vastly destructive
natural events are transport of material (water, air, and earth) and expenditure of energy.
Earthquake
• Earthquakes result when the rocks that are under stress from the internal earth processes that produce our continents and ocean basins rupture.– mostly at depths of 10 to 15 km along faults
• Earthquakes release vast amounts of energy.– they can release more energy than a large
nuclear explosion.
Volcanic Eruption
• Volcanoes are the result of extrusion at the surfaces of molten rock (magma). – May be explosive and violent, or they may be less
energetic lava flows.
– Generally occur at boundaries between tectonic plates
– Some volcanoes also occur in more central parts of tectonic plates where hot spots deep below heat the rocks.
• E.g. Yellowstone National Park and the Hawaiian Islands.
Landslides
• A general term for the down slope movement of soil and rock. – Occur when the driving forces that tend to move
materials down a slope exceed the resisting forces that hold the slope material in place.
– Resisting forces are produced by the strength of the material on slopes.
– The dominant driving force on slopes is the weight of slope materials influenced by the force of gravity. The steeper the slope and the heavier the slope materials, the greater the driving forces.
Landslides
– Human processes that add to or increase the slope angle increase the drive forces.
– Resisting forces reduced by increasing the amount of water on or in a slope, or by removing vegetation that reduces the root strength of the soil or rock.
Hurricane
• A hurricane is a tropical storm with circulating winds in excess of 120 km (74 mi) – Move across warm ocean waters of the tropics.
• Hurricanes gather and release huge quantities of energy– Water is transformed from liquid in the ocean
to vapor in the storm
Tsunami
• A series of large ocean waves produced after the ocean water is suddenly disturbed vertically by processes such as – Earthquakes, volcanic eruptions, submarine
landslides, or the impact of an asteroid or comet– Over 80% of all tsunamis are produced by
earthquakes.
Wildfire
• A rapid, self-sustaining, biochemical oxidation process that releases light, heat, carbon dioxide, and other gases and particulates into the atmosphere.
• Fuel is rapidly consumed during wildfires – helps maintain a balance between plant productivity
and decomposition in ecosystems.
• The primary cause is vegetation built up– When microbes are not able to decompose plants fast
enough to balance the carbon cycle.
Tornado
• A tornado is a funnel-shaped cloud of violently rotating wind – Extends downward from large cells of thunderstorms to
the surface of Earth. – May occur when a cold air mass collides with a warmer
one. • Water vapor in the warmer part of the atmosphere is forced
upward where it cools and produces precipitation. • As more warm air is drawn in, the storm clouds grow higher
and thunderstorm activity increases in intensity.
– Tornadoes concentrated in the Plains States
Flood
• The inundation of an area by water.• Produced by a variety of processes ranging from
– Intense rainstorms to melting of snow, storm surge from a hurricane, tsunami, and rupture of flood protection structures, such as levees or dams.
• River flooding– Shapes the landscapes through erosion and deposition.
– Erosion has produced features as small as gullies and as large as the Grand Canyon of the Colorado River.
Heat Wave
• A period of days or weeks of unusually hot weather– A recurring weather phenomenon related to
heating of the atmosphere and the moving of air masses.
• Hypothesized that human-induced global warming has increased the number and intensity of heat waves in recent years.– Now considered the most deadly of all weather
hazards
Drought
• A period of months, or years, of unusually dry weather.– Related to natural cycles of wet years that
alternate with series of dry years. – Thought to be related to the heating of ocean
waters and the moving of major air masses.
Hazards, Disasters, and Catastrophes
• These processes are natural– Become hazards, disasters or catastrophes when
people interact with or live and work where they occur.
• Natural hazard– Any natural process that is a potential threat to
human life and property.
Hazards, Disasters, and Catastrophes
• Disaster– A hazardous event that occurs over a limited
time span in a defined geographic area
• Catastrophe– A massive disaster that requires significant
expenditure of money and time for recovery.
Hazards, Disasters, and Catastrophes
• No area in the world is hazard free– Average annual loss of life around 150,000– Financial losses exceeding many billions of $$
• Hazards that produce extensive property damage are not necessarily the same ones that cause the greatest loss of life.– Economic cost increasing because people
moving to the coast.
Taking a Historic Point of View
• Natural hazards are repetitive events– To evaluate the flooding of a particular river we
can evaluate the history of flooding for that river
– Need to link the historic record with prehistoric records and modern measurements to gain greater insights into the flood hazard.
Fundamental Concepts Related to Natural Hazards
• How natural processes and hazards, might be reduced, minimized or eliminated:– Natural processes have service functions.– Hazards are predictable.– Linkages exist between hazards.– Linkages exist between different hazards and
between the physical and biological environment.
Fundamental Concepts Related to Natural Hazards
– Hazards that previously produced mostly disasters are now producing catastrophes.
– Risk from hazards can be estimated.– Adverse effects of hazards can be minimized.
Natural Process Have Natural Service Functions
• Nature provides a number of natural service functions– Clean air, water purification, mountain
building, etc.– Fault can produce springs and seeps
• Habitat for animals and plants
Natural Process Have Natural Service Functions
• River and flatland adjacent to it form a floodplain. • Many benefits for the environment
– Water and nutrients are stored on the floodplain.– Deposits on the floodplain contribute to the formation
of nutrient-rich soils.– Wetlands on the floodplain provide an important
habitat for many birds, animals, plants, and other living things.
– The floodplain functions as a natural greenbelt that is distinctly different from adjacent environments and provides environmental diversity.
Natural Process Have Natural Service Functions
• Volcanic eruption produce new land– Over millions of years volcanoes produce the
Hawaiian islands
Natural Process Have Natural Service Functions
• Dust storms carry nutrient rich soil
• Landslides may form lakes.
• Physical processes linked to a varied landscape– W/o diversity in land diversity of life would be
reduced.
Hazards are Predictable
• Most hazards can be mapped – Where they have occurred in the past– Monitored for present day activity
• Predictability– Spring snow melt and flooding– Earthquakes often clustered– Volcanic eruption from dormant volcanoes
usually preceded by precursor events
Hazards are Predictable
• Statistic and probability useful in evaluating the frequency of a particular event. – “100 year flood”– Used to determine flood insurance and restrict
development
• Another important variable in predicting hazardous events is geography
• Forecasting events like tsunamis
Linkages Exist
• Understanding the links between hazards and between the physical and biological environment is a important part of understanding the consequences of natural hazard.
• Hazards can be linked– Volcanic eruption-landslides
– Landslides-flooding
– Hurricanes-flooding-landslides
– Submarine earthquake-tsunamis
Linkages exist
• Links to biological environment– Global scale; comet-extinction– Regional scale; hurricane-beach erosion and
vegetation destruction– Wildfires remove vegetation-landslides– Erosion-loss of fish habitat
Hazards that previously Produced Disasters are now Producing Catastrophes
• During the last 10,000 years human population grown exponentially– >6.6 billion today– Now have 15 cities exceeding 10 million
people• Most in areas vulnerable to natural hazards
Hazards that previously Produced Disasters are now Producing Catastrophes
• Nevado del Ruiz in Colombia– Mudflow in 1845 killed 1,000 people– Mudflow in 1985 killed 21,000 people– Events predict and even mapped but warnings
largely ignored
Land Use Transformation and Natural Hazards
• Landscape transformations– From forest to agriculture or urban– May turn a disaster into a catastrophe– E.g. flooding after deforestation along Yangtze
River in China– E.g. landslides after Hurricane Mitch and
deforestation in Honduras
Risk from Hazards Can Be Estimated
• Risk is defined as– The product of the probability of that event
occurring times the consequence should it occur.
– Determining consequence fairly straightforward• Property damage, loss of life
– More complicated is determining acceptable risk
Risk from Hazards Can Be Estimated
• Acceptable risk– The risk that individuals or society are willing
to take– E.g. millions of people choose to live in CA
even though high probability of earthquakes
Adverse Effects of Hazards can be Minimized
• Active vs. reactive response– Response include search and rescue,
firefighting and provision of emergency food, water and shelter following an event.
Adverse Effects of Hazards can be Minimized
• Proactive choices– 1. land-use planning to limit construction in hazardous
locations
– 2. construction of hazard-resistant structures, such as floodwalls and levees
– 3. protection of ecosystems on coastal floodplains and wetlands that provide natural protection from hazards
– 4. well-thought-out plans for evacuation and relief following a disaster.
Impact and Recovery from Disasters and Catastrophes
• Direct effects– People killed, injured, dislocated, made
homeless or otherwise damaged by the event.
• Indirect event follow a disaster– Donations, shelter, taxes to help finance
recovery and emotional distress.– May effect society as a whole
Perceiving, Avoiding and Adjusting to Hazards
• People generally optimistic about natural disasters.
• Laws and regulations designed to control development in particular areas.– Land-use planning is one of the best tools we
have to avoid some hazards.
• Insurance may be required for flooding and earthquakes– People often rebuild in the same spot
Perceiving, Avoiding and Adjusting to Hazards
• Evacuation– Hurricanes can often be spotted days or weeks out
• Disaster preparedness also minimizes impact of hazards– Requires working chain of communication
• Control of hazards– Many people have been led to believe they are
protected by levees
– E.g. Sacramento area
What does the Future Hold with Respect to Disasters and Catastrophes?
• Every year we seem to set new global records– Economic losses from disasters and
catastrophes– # of disasters has increases significantly in the
last ½ century• In part because of human population pressure
– Urbanization affects severities of events– Oceans getting warmer effects severity of
storms
What does the Future Hold with Respect to Disasters and Catastrophes?
• Anticipating hazards rather than simply reacting to them will help minimize economic losses and reduce pain and suffering.– E.g. large earthquake in China
