Volcanic Hazards and its Effects to the Community

Senior High School _ Disaster Readiness and Risk Reduction Subject for STEM Students

1. DISASTER
READINESS AND
RISK REDUCTION
Volcano Hazards

2. At the end of this lesson, you
are expected to:
Learning
Outcomes
Explain various volcano-
related hazards;
Differentiate among
different volcano
hazards;
Recognize signs of an
impending volcanic
eruption;
Apply appropriate
measures/interventions
before, during, and after
a volcanic eruption.

3. What naturally-occurring event
creates the amount of damage
shown in the photo?
Introduction
In this lesson, you'll learn about
the different types of volcano-
related hazards.

4. Volcanology is the study of volcanoes.
Volcanology

5. A volcano is an opening or vent on the earth’s surface
where molten rocks, gases, and ashes are ejected.

What is a
volcano?

7. Different types of
volcanoes

8. These are considered as the
simplest type of volcanoes.
They are formed from lava
particles emitted in a vent.
Cinder cones

9. These volcanoes are created
because of continuous lava flows
coming from the vents. As the
lava flows cool down, they
produce a warrior’s shield-like
sloping flat cone.
Shield cones

10. Also known as
“stratovolcanoes”, this type of
volcanoes are often steep-
sided and the cones are
closely symmetrical. These are
also covered with layers of
lava flows and ash that rise up
to 2500 meters.
Composite
volcano

11. Classification of
volcanoes

12. According to Smithsonian
Global Program, it is an active
volcano has at least one
eruption within the last 10 000
years.
Active
volcano

13. An active volcano erupts, distinguished as
either explosive or quiet. An explosive
eruption happens because of a
formation of gases under viscous flow of
magma. This kind of eruption is often
violent and rapid. It ejects volcanic
materials, lava flows, and ash onto a
large area. Meanwhile, a quiet eruption
is classified only when it emits low viscous
lava where gases can easily escape.
Erupting
volcano

14. A volcano is dormant if it has not
erupted within the last 10 000 years.
It is not certain when this kind of
volcano will erupt, but is expected
to occur in the future. For instance,
Mount St. Helens was considered
dormant before it erupted in 1980.
Dormant
volcano

15. This kind of volcano has not had an
eruption within historic times and is not
expected to erupt again in a comparable
time scale of the future. One such volcano
is Kohala in Big Island, Hawaii. The last
time that Kohala erupted was close to 60
000 years ago. As of now volcanologists
do not believe that Kohala will ever be
active again. However, there are
volcanoes that are considered extinct but
became suddenly active like Mt. Pinatubo,
which erupted in 1991.
Extinct volcano

17. Signs of an impending volcanic
eruption

18. There are changes in
geochemical and geophysical
characteristics of a volcano,
such as increase in volume and
temperature of gas
composition and increase in
the frequency of volcanic
quakes. The color of steam
emission changes from white to
gray due to ash. Also, the crater
glows due to the presence of
magma at or near the crater.

19. Deformation of the ground
because magma intrusion and
appearance of fractures on the
sides of volcano can be
observed. There is also an
increasing frequency of
landslides and rockfalls from
cliffs. Moreover, increase in the
extent of drying up of
vegetation around the volcano’s
upper slopes becomes
noticeable.

20. Continuous increase in the
temperature of hot springs,
wells (e.g. Bulusan and
Canlaon), and lakes on
craters (e.g. Taal) near the
volcano. There is also
noticeable variation in the
chemical content of springs
and crater lakes around the
volcano.

21. Tools for recognizing volcanic
hazards

22. Part of mitigation initiatives of
PHIVOLCS is assigning permanent
danger zones around volcanoes.

25. Volcanic Hazards

26. Volcanic gas is one of the basic
components of a magma or lava.
Active and inactive volcano may
release gases to the atmosphere in
the form of water vapor, hydrogen
sulfide, sulfur dioxide, carbon
monoxide, hydrogen chloride, and
hydrogen fluoride. Aside from the
major constituents, minor amounts of
nitrogen, methane, argon, and helium
may be also present in volcanic
gases.
Gas emissions

27. Volcanic ash is made up of rock,
mineral, and fragments created during
explosion and separation of magma
into smaller pieces. Ashfalls can cause
the collapse of roofs and damage
houses if accumulated ash will not be
cleared immediately.
Ashfall

28. Tephra refers to fragments of volcanic rock ejected into air
by explosion. It consists of different rock particles that vary in
size, shape, and composition, among others.
Tephra can irritate eyes, throats, and cause respiratory
problems due to fine particles when inhaled. It also causes
burns and destruction of buildings and infrastructure.
Moreover, it causes disruptions in road and air traffic.
Tephra Falls and
Ballistic Projectiles

29. Lahar is an Indonesian term for mudflows or flows of volcanic
debris. Lahar is flowing mixtures of volcanic debris and water.
It is formed due to pyroclastic flow mixed with water, snow
mixed with debris, and rainfall on ash.
Lahars are classified into two. First is the primary or hot
lahar which is caused by direct volcanic eruption. The
other is called secondary or cold lahar which is caused
by rainfall on and mixture of snow with debris. Lahar can
be produced by the sudden draining of a crater lake,
caused by either an explosive eruption or collapse of a
crater fall. It can also be caused by the mixture of
pyroclastic flow into a river or lake water.
Lahar

30. It is typically a landslide that was triggered by
intrusion of magma, earthquakes, heavy rainfall, or
explosion from volcanoes. It can generate
tsunamis when entering the ocean and bury river
valleys with debris.
Debris avalanche

31. Tsunami is a series of high
water waves triggered by
disruption of seafloor. It can
occur even without volcanic
eruption.
Volcanic
tsunamis