1. Unit 1
Introduction to Natural Hazards
EES A05 H3
Marco A. Belmont
2. Nevado del Ruiz, Colombia, 1985
• In 1845, the Colombian volcano erupted
and a mudflow killed approximately 1,000
• Deposits from this event produced rich soil
in the Lagunilla River valley, enticing
people to move there and establish farms.
• The town of Aramero became the
agricultural centre for the valley and in 1985
had grown to a population of 23,000.
3. Nevado del Ruiz
• On November 13,
1985, a small
eruption of the
mudflow that buried
– 21,000 people death
– $200 million in
4. Nevado del Ruiz
5. Nevado del Ruiz
6. Nevado del Ruiz
7. Nevado del Ruiz
• A review of the history of Nevado del Ruiz
– The 1985 eruption and mudflows were
predicted, the hazard identified, and the risk
– Population growth since the last mudflow in
1845 greatly increased the number of people at
– The tremendous loss of life could have been
significantly reduced if warnings had been
8. Importance of studying natural
• The world can experience devastating
natural events like earthquakes, tsunamis,
volcanic eruptions, hurricanes, tornados,
• This events are the result of enormous
forces that are at work both inside and on
the surface of our planet.
• In this course we will study these forces,
how they interact with our civilization, and
how we can better adjust to their effects.
9. Internal and External Processes
• Process.- the physical, chemical, and
biological ways by which events such
as volcanic eruptions, earthquakes,
landslides, and floods, affect Earth’s
10. Internal Processes
• Some processes, such
as volcanic eruptions
and earthquakes, are
the result of internal
forces deep within
• Most of these internal
explained by the theory
of plate tectonics.
11. External Processes
• Other processes associated with natural
hazards result from external forces that are
at or very near Earth’s surface.
• An example of these external processes is
the fact that the energy from the Sun
warms the Earth’s atmosphere and surface,
producing winds and evaporating water.
12. External Processes
• Wind circulation and water evaporation are
responsible for forming Earth’s climatic
zones and for driving the movement of
water in the hydrologic cycle.
• These external forces are in turn directly
related to hazardous processes, such as
violent storms and flooding, as well as
13. Internal and External Processes
• Therefore, hazardous processes result from
internal heating of Earth or from external
energy from the Sun.
• The energy released by natural processes
varies greatly. For example:
– the average tornado expends about 1,000
times as much energy as a lighting bolt,
– the volcanic eruption of Mount St. Helens in
May 1980 expended approximately 1,000,000
times as much energy as a lighting bolt.
14. Internal and External Processes
• Events such as earthquakes, volcanoes,
floods, and natural fires are natural
processes that have been occurring on
Earth’s surface since long before it was
populated by humans.
• These natural processes become
hazardous when human beings live or work
in their path.
15. Hazard, Risk, Disaster, and
• A natural hazard is any natural process
that poses a threat to human life or
– The event itself is not a hazard; rather, a
process becomes a hazard when it threatens
16. Hazard, Risk, Disaster, and
• Risk may be expressed as the probability
that a destructive event may occur
multiplied by the event’s likely impact on
people and property.
• Risk thus integrates hazard and social
17. Hazard, Risk, Disaster, and
• A natural disaster is the effect of a hazard
in society, usually as an event that occurs
over a limited time span in a defined
– The term disaster is used when the interaction
between humans and a natural process results
in significant property damage, injuries, or loss
18. Hazard, Risk, Disaster, and
• A natural catastrophe, simply put, is a
massive disaster, requiring significant
expenditure of time and money for
19. Major hazards in the USA
(not including blizzards and ice storms)
20. Example of a disaster
21. Example of a disaster
22. Death and damage caused by
• Natural hazards vary greatly in their
potential to cause a catastrophe.
– Floods, hurricanes, tornadoes, earthquakes,
volcanic eruptions, and large wildfires are the
hazards more likely to create a catastrophe.
– Landslides have only a moderate catastrophe
potential because they generally affect a small
area. Drought also has a moderate potential
because although it may cover a large area,
there is plenty of warning time before its worst
effects are felt.
– Hazards with low catastrophe potential include
coastal erosion, frost, and lightning.
23. Death and damage caused by
24. Role of History in Understanding
• A fundamental principle of understanding
hazards is that they are repetitive events.
• Knowledge of historic events and recent
geologic history of an area is vital to our
understanding and assessment of the
• Linking the prehistoric and historic records
extends our perspective of time when we
study repetitive natural events.
25. Role of History in Understanding
• To understand the nature and extent of a
natural hazard, we must study in detail its
historic occurrence as well as any geologic
features that it may produce or affect.
• Any prediction of the future occurrence and
effects of a hazard will be more accurate if
we can combine information about historic
and prehistoric behaviour with a knowledge
of present conditions and recent past
events, including land-use changes.
26. Geologic Cycle
• Geologic conditions and materials largely govern
the type, location, and intensity of natural
• Continuous processes produce the Earth’s
material, land, water and atmosphere, necessary
for our survival. These processes are referred to
as the geologic cycle, which is actually a group of
– The tectonic cycle
– The rock cycle
– The hydrologic cycle
– Biogeochemical cycles
27. The tectonic cycle
29. The tectonic cycle
30. The tectonic cycle
31. Plate Tectonics
32. The tectonic cycle
33. Subduction zone off Canada’s west
34. San Andreas Fault
35. The tectonic cycle
36. The rock cycle
37. The hydrologic cycle
38. The hydrologic cycle
39. The hydrologic cycle
40. Biogeochemical cycles
41. Fundamental concepts for understanding
natural processes as hazards
1. Hazards can be predicted through scientific
2. Risk analysis is an important element of
understanding the effects of hazardous
3. Linkages exist among different natural hazards
and between hazards and the physical
4. Damage from natural disasters is increasing.
5. Damage and loss of life from natural disasters
can be minimized.
42. 1. Hazards can be predicted
through scientific analysis
• Science and natural hazards
• Hazardous processes are natural
• Prediction and warning
43. Hazardous processes are natural
44. Prediction and warning
• The effects of a hazardous event can be
reduced if it can be forecast and a warning
issued. This involve:
– Identifying the location of a hazard
– Determining the probability that an event of a
given magnitude will occur
– Identifying any precursor events, predicting the
event, and issuing a warning
45. Prediction and warning
46. 2. Risk analysis is an important
element of understanding the
effects of hazardous processes.
• The risk of a particular event is defined as
the product of the probability of that event
occurring times the consequences should it
• Determining acceptable risk is complicated.
47. 3. Linkages exist among different
natural hazards and between
hazards and the physical
• Linkages between natural process that are
hazardous to people generally fall into two
– Many hazards themselves are linked
– Natural hazards are linked to earth materials
48. 4. Damage from natural
disasters is increasing.
• Examples of disasters in densely populated
• Human population growth
• Magnitude and frequency of hazardous
49. Human population growth
50. Population growth and the future
51. 5. Damage and loss of life from
natural disasters can be
• Reactive response: impact and recovery
– Direct and indirect effects
• Proactive response (Anticipatory response):
avoiding and adjusting to hazards
52. Reactive response: impact and
recovery from disasters
53. Proactive response (anticipatory)
• Proactive response: avoiding and adjusting
– Land use planning
– Disaster preparedness
– Artificial control of natural processes
54. Many Hazards Provide a Natural
55. Many Hazards Provide a Natural
56. Climate Change and Natural
• There is strong evidence that on a global
scale Earth’s climate is now warmer than in
the previous 40 years since records began
• The 1990s appear to be the warmest
decade in the last 1,000 years
57. Climate Change and Natural
• Mean sea level has risen by between 10 to
20 cm from 1860 to 2000.
• Snow cover has decreased by 10% since
• Evidence of thawing of permafrost.
58. Climate Change and Natural
• Evidence of thawing of permafrost.
59. Climate Change and Natural
• Extreme weather events such as drought,
floods, and storms are likely to become
more frequent and more intense in the
• Since 1970s, El Niño events have
increased in frequency, magnitude and
60. Signals of Climate Change
• Global warming is projected to
increase both temperature and
rainfall at high latitudes and high
• Migration of species
• Retreat of glaciers
• Rise of sea level
61. Potential health impacts of climate
• Problems associated with other global
– In 1997-1998, El Niño brought widespread
respiratory illnesses to Indonesia and Brazil
due to haze from uncontrolled forest fires.
– After hurricane Mitch in Central America
(1998), deforested areas experience flooding
and landslides, and the aftermath spawning
clusters of water-, insect- and rodent-borne
diseases (cholera, malaria, dengue fever, and
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disasters, and catastrophes – Canadian Edition.
Keller, Edward A., Blodgett, Robert H., and
Clague John J. Pearson Prentice Hall, 2007.
• Dangerous Earth: An introduction to geological
hazards. Murck BW, Skinner BJ, and Porter SC.
John Wiley & Sons Inc. N.Y. 1997.
• Life support: the environment and human health.
Michael McCally. The MIT press. Cambridge,