The document provides information about volcanoes, including how they are classified and signs of impending volcanic eruptions. Volcanoes can be classified based on their activity as active, dormant or extinct. They can also be classified by their composition and structure as shield, cinder or stratovolcanoes. Signs of an impending eruption include increased seismic activity, changes in steaming and gas emissions. The document also outlines hazards from eruptions like lava flows, pyroclastic flows, ash falls and lahars. It provides guidance on preparing for, during and after an eruption, such as evacuating, sheltering indoors and wearing protective equipment.

1. Signs of
impending
Volcanic
Eruption

2. What are Volcanoes?
Underneath Earth’s surface, magma or molten rock
is slowly being forced through the cracks or
weaknesses on Earth. Overtime, the pressure
builds up and ultimately causes eruptions of lava
and ash.
This event slowly forms volcanoes. Volcanoes are
generally conical in shape. When magma is outside
the volcano, it is called lava.
The repeated eruptions causes the volcano to rise
and shape its shape.
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3. Classification of
Volcanoes
When studying volcanoes, it is important to note that
scientist often classify them according to certain
criteria: Activity, Composition and Structure, and
Eruption
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4. By Activity
A volcano may be classified as Active, Dormant, or
Extinct based on its life cycle.
➝ An Active Volcano is one that has a tendency to
erupt or is already erupting.
In the Philippines, Mount Mayon and Mount Bulusan
are examples of an active volcanoes.
Out of the estimated 1500 known active volcanoes
in the world today. About 50-70 erupt annually.
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5. By Activity
Volcanoes may be classified according to the
periodicity of their eruption.
➝ A volcano that is not erupting or is not going to
erupt sometime in the near future is considered
Dormant.
➝ Dormant volcanoes are considered as active
threats even if they have not exhibited any
activity for a long time.
Mount Pinatubo, for example erupted in 1991 after
being dormant for 600 years.
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6. By Activity
Some of the volcanoes in the world are considered
Extinct.
➝ Extinct volcanoes have not erupted in the last
30 000 to 40 000 years, and are not expected to
erupt anytime soon.
One such volcano is Mount Kohala in Hawaii that
has it’s last eruption 60 000 years ago.
Even though extinct volcanoes will ever be active
again, scientist believe that a phenomenon called
Rejuvenation may revive a volcano.
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7. By Composition and Structure
Classification of Volcanoes can also be due to their
composition and structure. They can be Shield,
Cinder and Stratovolcanoes.
➝ A Shield volcano is generally low and has a dome
shape, like the shield of medieval knights, hence
the name
➝ These volcanoes are mountains that have been
slowly shaped by lava flows. As lava flows from a
central vent or set of vents, it gently builds a
broad-sloping, coned-shaped form covering a
large area
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8. Example of Shield Volcano:
Mauna Loa is one of the worlds largest shield volcano
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9. By Composition and Structure
The Cinder cone type of volcano is considered to be
the simplest type.
➝ These type of volcanoes are the result of eruption
from a single vent.
➝ Eruption on a single vent results in a bowl-shaped
crater which form at the summit.
➝ Cinder cone volcanoes are typically viewed as
hardened lava which piled up around the vent
and then formed a mountain.
➝ Cinder cone volcanoes are small compared to
others and they are known as “Coned Shaped
Volcanoes” 9

10. Example of Cinder Volcano:
Mauna Kea, a volcano on the American island of Hawaii
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11. By Composition and Structure
The most common type of volcano is the
Stratovolcano or Composite volcano.
➝ They are called as such because they are formed
by alternating layers of lava and pyroclastic
materials from multiple eruptions that occurred
through time.
➝ These type of volcanoes are typically tall
mountains that have steep sides
➝ The eruption from a stratovolcano may be a
pyroclastic flow that is composed of hot steam,
ash, rock and dust.
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12. Example of Stratovolcano or Composite Volcano:
Mayon Volcano, a famous stratovolcano that can be found in the Philippines
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13. By Eruption
Volcanoes can also be classified according to the
type of eruption they have exhibited in the past,
which is controlled by the chemistry of the magma.
Eruptions can be Explosive (Central), or Quiet
(Fissure).
➝ Explosive eruptions happen due to the build up
of thick magma with high silica content. It is slow
flowing and very viscous.
➝ These eruptions are very violent. Volcanoes spew
lava, ash and other volcanic material over large
distances. 13

14. By Eruption
A Quiet or fissure eruption, on the other hand, emits
a lot of lava coming from a fissure or a crack on the
surface.
Lava derived from magma with slow silica content
has low viscosity, allowing gas to escape.
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15. Signs of Impending
Volcanic Eruption
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16. Signs of Volcanic Eruption
1. Increased frequency of volcanic quakes with
rumbling sounds; occurrence of volcanic tremors
2. Increased steaming activity; change color of
steam emission from white to gray due to
entrained ash
3. Crater glow due to presence of magma at or near
the crater
4. Ground swells (or inflammation); ground tilt and
ground fissuring due to magma intrusion
5. Localized landslides, rock falls, and landslides
from the summit area not attributed to heavy
rains 16

17. Signs of Volcanic Eruption
6. Noticeable increase in the extent of drying up the
vegetation around the volcano’s upper slopes
7. Increased temperature of hot springs, wells (e.g
Bulusan and Canlaon) and crater lake (e.g Taal)
near the volcano
8. Noticeable variation in the chemical content of
springs and crater lakes within the vicinity of the
volcano
9. Drying up of springs/wells around the volcano
10. Development of new thermal areas and/or
reactivation of old ones; appearance of Solfataras
(shallow volcanic craters) 17

18. Hazards from
Volcanoes
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19. Lahar
➝ Lahar is a mudflow composed of rocky debris,
water, and pyroclastic material. Lahar flows down
from a volcano, often along a river valley.
➝ Lahar has a cement-like consistency which
makes this more dangerous
➝ Also Lahar has a maximum temperature of 100°
(the boiling point of water). The Movement of
lahar may cause much devastation compared to
that of a lava flow.
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20. Ash Fall
➝ Volcanic ash or tephra is a hard type of ash,
extremely abrasive, mildly corrosive, conducts
electricity when wet, and does not dissolve in
water.
➝ It is made up of small jagged pieces of rocks,
minerals and volcanic glass less than 2 mm in
diameter (about the size of sand)
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21. Pyroclastic Flow
➝ Pyroclastic flows are high-density mixture of hot,
dry rock fragments and hot gases that move
away from the vent that erupted them at high
speed.
➝ Pyroclastic flows have the ability to cover large
distances. To make things worse, with the
combination of rain or melted snow and ice,
pyroclastic flow can transform into lahar and
cause greater damage as they flow to farther
distances.
➝ Pyroclastic flows are considered to be the
greatest volcanic hazards.
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22. Ballistic Projectile
➝ Ballistic projectiles are basically rocks that an
erupting volcano sends into the air. The rocks cab
vary in size and density – some can be small as
ash, others can be as big as boulders.
➝ The impact of large projectiles can penetrate
wooden and concrete buildings. It can also
deposit in agricultural lands near volcanic vents,
making these unsuitable for farming
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23. Volcanic gases
➝ Volcanic gases are dangerous due to their
temperature and toxicity.
➝ Volcanic gases are composed mainly of water,
carbon dioxide, and sulfur dioxide. During violent
eruptions, these gases are injected into the
stratosphere.
➝ These acids are very toxic and damaging to the
skin, eyes and lungs of animals and human even
in small concentrations. It can destroy fabrics,
metals, and vegetation.
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24. Lava Flow
➝ Lava flow is described as a steam of molten rock
that flows out of a volcano or volcanic vent.
➝ Lava flows can be very fluid or very sticky,
depending on its composition and temperature.
➝ Lava flows can and will destroy anything that is
blocking its path but compared to pyroclastic
flow people and animals can move safely out of
the way because it moves slowly.
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25. What to do before,
during and after a
Volcanic Eruption
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26. Before a Volcanic Eruption
➝ If there is a high risk, putting up of building
structures should not be done and consider
relocating when you live inside the danger zone
➝ Familiarize yourself and your family with hazard
maps, evacuation areas, evacuation routes and
evacuation protocols set by the authorities.
➝ Make sure that you are updated to the current
status of the volcanic activity in your area, and
learn any special signals that are used to issue an
evacuation order.
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27. Before a Volcanic Eruption
➝ Prepare yourself for the other hazards that
accompany a volcanic eruption.
➝ Make sure that you have a family emergency
communication plan and emergency supply kit to
use in case the eruption happens during the day.
➝ Prepare yourself and your family with your own
survival pack.
➝ Your survival pack should at least contain:
flashlight and extra batteries, first aid kit,
emergency food and water, essential medicines,
dust mask (preferably N95), and googles.
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28. Before a Volcanic Eruption
➝ Prepare yourself for the other hazards that
accompany a volcanic eruption.
➝ Make sure that you have a family emergency
communication plan and emergency supply kit to
use in case the eruption happens during the day.
➝ Prepare yourself and your family with your own
survival pack.
➝ Your survival pack should at least contain:
flashlight and extra batteries, first aid kit,
emergency food and water, essential medicines,
dust mask (preferably N95), and googles.
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29. During a Volcanic Eruption
➝ Listen to the emergency information and follow
the evacuation order issued by authorities.
➝ You should avoid areas near the volcano,
especially those which are downwind and
downstream from the volcano
➝ To protect yourself from as fall, wear long sleeved
shirts and pants
➝ .
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30. During a Volcanic Eruption
(Indoors)
➝ You should close all windows, doors and
dampers. This could provide a barrier between
you and the debris brought by the volcano
➝ Put all machinery inside a garage or barn, and
cover them with cloth if there is still time so that
they are not exposed to dust or ash.
➝ Bring animals or livestock into closed shelters.
This prevents asphyxiation due to toxic gases.
➝ Check if everybody is present.
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31. During a Volcanic Eruption
(Indoors)
➝ Call your emergency contact person and inform
them of your whereabouts.
➝ You may also fill your bath tubs and other water
containers with water to be used for washing and
drinking.
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32. During a Volcanic Eruption
(Outdoors)
➝ Seek shelter indoors as soon as possible.
➝ Roll into a ball to protect your head, if you are
caught in a rock fall.
➝ If you are near a stream, be aware of mudflows.
Move to a higher ground, especially if you hear
the roar of mudflow.
➝ Keep your car or truck engine off; ash fall could
clog engines and this would just add to the toxic
gases already present in the air due to eruption
➝ Remember to stay out of the defined danger
zones. The effects of volcanic eruption can be
experienced even if you are miles away. 32

33. After the Eruption
➝ Stay away from volcanic ash fall areas as much
as possible.
➝ When you have to go outside, make sure to cover
your mouth and nose, always wear googles to
protect your eyes; do not wear contact lenses.
➝ Keep your skin covered to avoid irritation from
contact with ash --- wear long sleeved shirts .
➝ Clear roofs of ash only when it is safe to do so,
Ash fall can cause a building or house to collapse
because of their weight.
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34. After the Eruption
➝ It is unsafe to drive in or after a heavy ash fall.
Doing so will lead to clogged engines and stalled
vehicles.
➝ If you have respiratory or cardiac ailment, avoid
contact or exposure with ash as it could make it
hard to breath.
➝ It would be best to stay indoors until local health
officials advise that it is safe to go outside
➝ When going outside to help, however, do so with
caution.
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35. After the Eruption
➝ When going outside to help, however, do so with
caution.
➝ Report to the authorities and your relatives at the
soonest time possible for them to know you are
safe and so that the government can update their
headcount for search and rescue purposes.
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36. 36
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