CHAPTER 13: NATURAL
HAZARDS, MITIGATION, and
ADAPTATION
Prepared by: Anna Crizza Castillo IV BSED English
Objectives:
• describe the various hazards that may happen in the event of earthquakes,
volcanic eruptions, and landslides (S11/I2ES -If-30)
• using hazard maps, identify areas prone to hazards brought about by
earthquakes, volcanic eruptions, and landslides(Sl1/12ES-If-31)
• give practical ways of coping with geological hazards caused by
earthquakes, volcanic eruptions, and landslides (S11/12ES-If-32)
LESSON: HAZARD FROM GEOLOGIC PROCESSES
• Refer 379-388. Read and analyze the geological processes and hazards.
• Please watch the provided video about "hazard caused by geological
processes”
• Source: https://www.youtube.eom/watch?v=cqCHtePMC8E
Geologic Processes and Hazards
Hazards, Risk, Vulnerability, and Disasters
Hazards are phenomena that have the potential to bring
damage to humans and properties.
Exposure is the potential of humans and properties to
become exposed to hazards.
Vulnerability encompasses the mitigation efforts to reduce
the effects of hazards which is dictated by a number of
factors such as poverty indices, etc.
Hazards, Risk, Vulnerability, and Disasters
Risk is simply the collective effects of hazards, exposure,
and associated vulnerabilities.
Exposure is the potential of humans and properties to
become exposed to hazards.
Earthquake
Earthquake is the intense ground shaking or movement caused
by a sudden release of energy. Earthquakes can be generated
by a bomb blasts, volcanic eruptions, and most commonly,
slippage along faults and subduction zones.
Generating Earthquakes
Elastic Rebound Theory
The theory simply states that the generation of earthquakes goes into four stages:
(1)
Original Position
(2)
Build-up of strain
(3)
Rupture or slippage
(4) The release of energy
Seismology: The study of seismic waves
Earthquakes release tremendous amount of energy in the form of seismic
waves.
.These seismic waves travel through the medium (rocks) and are recorded by
an instrument called the seismometer.
Two Types of Seismic Waves
Body waves come from the focus and emanate in all
directions through the interior of the Earth.
Surface waves travel only on the surface similar to water
waves.
Two Subtypes of Body waves
P-waves
are
capable
through solid and liquid medium
S-waves can only travel through solids.
of
travelling
Describing an Earthquake
Magnitude
estimation of the amount of energy released at the source of the
earthquake.
Intensity
refers to the degree of ground shaking at a given locality.
Describing an Earthquake
I
Not felt.
II
Felt indoors by persons.
III
Vibration at rest, on like upper passing floors of ,light or favorable trucks. placed.
IV
Vibration like passing of heavy trucks.
V
Felt outdoors. Small unstable objects displaced or upset.
VI
Felt by a II, Furniture moved. Weak plaster/masonry cracks.
VII
Difficult to stand. Damage to masonry and chimneys.
VIII
Partial collapse of masonry. Frame houses moved.
IX
Masonry seriously damaged or destroyed.
X
Many buildings and bridges destroyed
XI
Rails bent greatly. Pipelines severely damaged.
XII
Damage nearly total.
Epicenter
Epicenter is defined as the geographic (inapt-locatable) location where the source
of the earthquake or energy release is.
Earthquake Effects
1. Wave amplitude. It refers to the highest point of shaking recorded on
seismographs.
2. Duration of vibration. Earthquakes usually last for a few seconds to
minutes. With an increase in earthquake duration, the ground shaking
intensifies and will have detrimental effects to structures.
3. Nature of bedrock. Bedrock refers to the nature of the material where
structures are built. Material could range from solid rocks to
unconsolidated sediments and soil.
Earthquake Effects
4. Design of Structure. Design of structure refers to the integrity of buildings
to resist ground motion during an earthquake.
The Future of Earthquake Studies
The occurrence of earthquakes throughout human history has
brought immeasurable damages to lives and property. At the
same time, their occurrence has provided us with a picture of
what goes underneath the planet. Earthquakes are reflections
that geologic processes are at work and will continue to affect us
in the future.
Volcanic Eruptions
Volcanoes have been one of the most visible evidences that there
is so much heat at the Earth's interior. It compose of glowing lava,
ash, and rock debris that are ejected by volcanoes during their
eruption.
Volcano Hazards
Communities living near an active volcano should be aware of the
different hazards accompanied with living close to such geologic
feature. This does not necessarily mean that anyone living far from
a volcano should feel safer than those who are close.
VOLCANO HAZARDS
1. Lava is a mixture of dominantly molten rock that is several hundreds of degrees
in temperature.
2. Pyroclastic flows have high temperatures and are generally gas-rich making
their transport down the slopes of a volcano very fast compared to lava flows.
3. Lahar is a special term for a volcanic mudflow. It is similar to a mudflow but
only involving volcanic materials (pyroclastic).
VOLCANO HAZARDS
4. Gas contributes to the overall greenhouse gases aside from oxygen and water
vapor, volcanoes which is present in the atmosphere during its activity (carbon
dioxide, sulphur dioxide, hydrogen sulphide, etc.).
5. Ash is the smallest the pyroclastic unit (<2mm) produced from the fragmentation
during a volcanic activity. Being small and produced at large volumes, ash is
considered one of the most widespread hazard from volcanic eruptions.
Volcano monitoring
Volcano monitoring involves the assessment of
different volcanic phenomena that may point out to a coming
eruption. It is a very important tool that can lead to the safety
of lives around an active volcano.
Signs that a volcano will erupt:
1. Ground movement
2. Gas release
Magma that is moving underground will show
Being the lightest component of
subtle to obvious changes on the surface prior
magma, gas can easily exsolve or
to an eruption. This sign can
be monitored through GPS (global positioning
systems) and remote sensing of areas around
the volcano.
separate from the magma and travel
through fissures and cracks in the
rocks and soil.
Signs that a volcano will erupt:
3. Anomalous thermal signatures
Magma slowly reaching the surface will
4. Chemical changes in nearby bodies of
water
Bodies of water near an active volcano
heat up rocks and warm the surface.
(including lakes formed at the vent or crater)
Sometimes, if a body of water is present,
will absorb the gases exsolved from the
the increased temperature can dry up the
magma. This "taking in" of gases will
surface water in a matter of days.
change the chemistry of the water that can
be attributed to a coming eruption.
Volcanic Hazards and the Survival of Man
Monitoring the activity of volcanoes has
prevented the loss of lives and properties. With the fast
development of technology that allows us to have a
greater understanding of magmatic processes, reduction
of risks from volcanic hazards is inevitable but we are
still far from this bright future.
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