SCIENCE 9

Lesson : VOLCANOES

The Philippines is located along the Ring of Fire. As a result, it is a home to many volcanoes. The most famous
among our volcanoes is the Mayon Volcano that has erupted last May 7, 2013 while a group of hikers were
exploring its beauty.

Who could forget the terrible eruption of Pinatubo Volcano in 1992 after 600 years of inactivity? Based on
statistics, in the first five years following the eruption, lahars destroyed the homes of more than 100,000
people. Lahars also covered about 120,000 hectares with sediment to an average depth of about one meter,
and floods spread rock debris over a larger area.The eruption also affected other countries as its emissions in
the atmosphere lowered the air temperature.

According to the Philippine Institute of Volcanology and Seismology (PHIVOLCS), our country is an ideal site
for any volcanic activity. It is therefore, important for us to know how this natural phenomenon happens to
reduce the risks and effects it may cause.

Pre Assessment

A. Choose the letter of the best answer.

1. Which characteristic of magma mainly determines its explosiveness?

a. color
b. amount
c. temperature
d. silica content

2. Which of the following characteristics of a volcano depends on its magma

emission?
a. age
b. size
c. shape
d. location

3. Which of the following factors associated with huge volcanic eruptions may cause the
decrease in the Earth’s average temperature for a few years?
a. heat
b. light
c. acid rain
d. volcanic ash

4. A thick layer of volcanic ash can be heavy enough to collapse the roofs of
buildings because ash .
a. is solid.
b. cannot be blown by winds.
c. becomes heavier as it cools.
d. consists of tiny fragments of rocks that becomes heavy as they pile up.
 5. Which of the following is an active volcano in the Philippines?
a. Apo in Davao b.Bud
Datu in Sulu
c.Isarog in Camarines Sur d.Kanlaon in
Negros Oriental

B. Answer the following questions briefly.

6. Aside from Mayon Volcano, name another Philippine volcano that has erupted
recently.
7. What causes a shield volcano to be shaped like a broad dome?
8. By what process can a volcanic eruption affect temperatures around the world?
9. Give one positive effect and one negative effect of volcanic eruptions.
10. How is energy from volcanoes tapped as source of electricity?

In Grade 8, you have learned about the relationship between the occurrence of earthquakes and the
location of the Philippines along the Ring of Fire. Due to its location, the Philippines is a home to many
volcanoes. This module will guide you through the study of volcanism in the Philippines.

What is a volcano?

Since you were in elementary, you have heard about volcanoes. But do you know what a
volcano is? To find out, let’s do the following activity.

Activity 1. Volcano concept map Objective

 characterize a volcano

DRAFT
Fig. 1. Mayon Volcano(pls re-draw in your notebook)

Materials: pictures of a volcano, paper and pen

Procedure: Q1. Based on the picture, give five descriptions of a volcano. Present your answer in a concept map as

VOLCANO

shown

Fig. 2. Concept map in volcano

In activity 1, you have described what a volcano is. The next thing to do is to classify them. Do
you have an idea how they are classified? Let’s find out in the next activity.

Classification of volcanoes

There are several ways by which volcanoes can be classified. PHIVOLCS have adapted a
systemwherethe Philippine volcanoes as active or inactive. Active volcanoes are those that have a
record of eruption within the last 600 years or those that erupted 10, 000 years ago based on
analyses of their materials.

Inactive volcanoes, on the other hand, are those that have not erupted for the last 10, 000
years and their physical form is being changed by agents of weathering and erosion through
formation of deep and long gullies.

According to PHIVOLCS,our country has more than a hundredvolcanoes as of 2013. Twenty-

three are active while the rest are inactive. Some of these volcanoes will be mentioned in the next
activity.

Perform the next activity to classify the volcanoes according to their record of eruption.
 Activity 2. Volcanoes in the Philippines Objective

 classify volcanoes as active or inactive

Materials: Philippine map colored pens triangle ruler

Procedure:

1. Using the Philippine map (fig. 3), plot the location of thefollowing volcanoes. Assign
colors for the volcanoes. Indicate this in the legend.

Table 1. List of some volcanoes in the Philippines

Number of Latest
Volcano Latitude Longitude historical eruption or
eruptions activity
Cabaluyan 15° 42′ 120° 19′ 0 -
Cocoro 10° 53′ 121° 12′ 0 -
Iraya 20° 29′ 124° 01′ 1 1454
Kanlaon 10° 24′ 123° 7′ 26 2006 June
Mayon 13° 15′ 123° 41′ 49 2013 May
Pulung 7° 55′ 124° 38′ 0 -
Smith 19° 32′ 121° 55′ 6 1924
Taal 14° 120° 59′ 33 1977
Tamburok 11° 33′ 124° 26′ 0 -
Urot 5° 59′ 121° 15′ 0 -

Source: Philippine Institute of Volcanology and Seismology, accessed Sept. 30, 2013)
 Fig. 3. Map of the Philippines (Source: Gr 8 LM, UPNISMED)

Legend:

= volcano that has no record of eruption

= volcano that has erupted 1 to 5 times

= volcano that has erupted 6 to 10 times

= volcano that has erupted more than 10 times

Q1. Are all the volcanoes found in the same location?

Q2. Which of the volcanoes had the most number of eruptions? least number of eruptions? no
record of eruption?

Q3. How will you classify the volcanoes that have records of eruptions? Q4. How will
you classify volcanoes with no record of eruption?

Q5. In your own words, differentiate an active volcano from an inactive one.

Now that you have differentiated an active volcano from an inactive one, the next question
could be: what causes volcanoes to erupt? Let’s find out in the next activity.

Activity 3. Under pressure Objective

 describe the effect of high temperature to the formation of gas

Materials

two 300 ml bottled softdrinks(must be sealed before using) two 300 ml

bottled cooking oil

two identical small basins hot water

Procedure

1. Hall-fill basin A with hot water and basin B with cold water.

2. Put one bottled soda in basin A and another one in basin B. Wait for three minutes.

3. Slowly unscrew the caps from the bottlein each basin and observe.

Q1. What did you observe in each bottle? Q2. Explain

your observation.

Q3. What is the role of hot water in the setup?

What if we use another liquid such as oil instead of softdrinks? Will we have the same
observation? Let’s find out in the next procedure.

4. Replace the hot water in basin A.

5. Put one of the bottled cooking oil in hot water and the other one in cold water. Wait for three
minutes.

6. Slowly unscrew the caps and observe.

Q4. Do you have the same observation as in the soda drinks?

Q5. Explain your answer.

 In the activity, you have seen the effect of temperature on the amount of gas that can be
produced in a liquid. How does this affect the pressure inside the bottle? What is the role of pressure
in the setup?

Let us relate this concept to what is happening inside the volcano. Magma inside the volcano
has high temperature. As the magma is continuously heated, it goes up. As it rises, gas bubbles are
developed. The gas bubbles are trapped and expand causing the molten material to swell also,
resulting in a gradual increase in pressure within the volcano. When the pressure exceeds the
strength of the overlying rock, fracturing occurs. The resulting breaks lead to a further drop in
confining pressure, which in turn causes even more gas bubbles to form.

Lava may appear to be the primary material ejected from a volcano, but this is not always the
case. Aside from lava, broken rocks, lava bombs, fine ash and dust are also ejected. Does this have
any effect on the volcanic shape? Let’s find out how.

Volcanic landforms and eruptive styles

Volcanoes come in different shapes and sizes, and each structure has a unique history of
eruption. However, volcanologists have been able to classify them according to their landforms and
eruptive patterns. We have considered the three general volcanic types according to the shape of
their cones: namely: shield volcanoes, cinder cones, and composite cones.

Before we go further, let us discuss the external parts of a volcano. summit

slope

base

Fig. 4. Parts of a volcano(Source: Project EASE Module 12)

A volcano usually has a summit, slope, and base. At the summit, there is an opening which
may either be a crater or a caldera. A crater is a funnel-shaped opening at the top of a volcano while a
caldera is formed when a part of the wall collapses following an explosive eruption as shown in Figure
5. A volcano can have one crater, like Mayon Volcano, or more than one, like Taal Volcano that has 47
craters.
 Fig. 5. A crater and a caldera(pls. re-draw)

Volcanic activity can be very fascinating. After an explosive eruption, a scenic cone-shaped structure may be
produced or changes on its slope can be observed. The emissions of a volcano provide us with clues on what
materials are found inside the Earth. Some eruptions are very explosive, while many others are not.

What determines the nature of eruption? There are primary factors affecting the volcanoes’ eruptive style,
namely: the magma’s temperature, its chemical composition, and the amount of dissolved gases it contains.
These factors can affect the magma’s viscosity in different ways. Viscosity is the property of the material’s
resistance to flow. It is also described as the liquid’s thickness and stickiness. The more viscous and thicker the
material is, the greater is its resistance to flow. For instance, syrup is more viscous than water.

Let us discuss how each factor affects the viscosity of magma. First, let’s look into how
temperature of magma affects its viscosity. The viscosity of magma decreases with temperature. The
higher the temperature of magma is, the lower is its viscosity. Aslava flows, it cools and begins to
harden, its ability to flow decreases and eventually it stops.

Next, let’s look at how the composition of magma affects its viscosity. Magmas with high silica
content are more viscous than those with low silica content as shown in Figure 6.The magma that
contains less silica is relatively fluid and travels far before solidifying.

Lastly, the amount of gases contained in the magma affects its viscosity. Other factors being equal, gas
(mainly water vapor) dissolved in magma tends to increase its ability to flow. Therefore, in near-surface
environments, the loss of gases makes magma more viscous, forming a dome or a columnar as shown in
Figure 6.
 can travel a great distance, forming a thin sheet.

Lava with high silica content is too

viscous to travel far, and tends to
break up as it flows.

Lava with low amount of gas and high silica content is very
viscous and does not flow out at all as it rises forming, a
columnar plug in the vent.

FT
Lava with low amount of gas as it rises has high
viscosity that it piles up at a vent resulting in a
dome.

Fig. 6. Viscosity of magma in different conditions (Source: Project EASE Module 12)

Types of volcanic eruptions

Volcanoes erupt differently.They are generally classified as wet or dry depending on the magma’s water
content. Volcanoes are described according to the style of eruption as follows:

a. Phreatic or hydrothermal – is a stream-driven eruption as the

hot rocks come in contact with water. It is short- lived,
characterized by ash columns but may be an onset of a larger
eruption. Shown on the right is our Taal Volcano in Batangas.

Fig. 7. Taal Volcano (Photo credits: USGS)

b. Phreatomagmatic – is a violent eruption due to the contact between water and magma. As a result, a large
column of very fine ash and high-speed and sideway emission of pyroclastics called base surges are observed.

c. Strombolian - a periodic weak to violent eruption

characterized by fountain lava, just like the Irazu Volcano in
Costa Rica.

Fig. 8. Irazu Volcano (Photo credit: USGS)

d. Vulcanian – characterized by tall eruption columns that
reach up to 20 km high with pyroclastic flow and ashfall
tephra like that of Paricutin Volcano in Mexico.

Fig. 9. Paricutin Volcano (Photo credits: USGS)

e. Plinian – excessively explosive type of eruption of

gas and pyroclastics, just like our Pinatubo Volcano in
Zambales.

Fig. 10. Pinatubo Volcano (Photo credits: USGS)

how will you describe the slope of Pinatubo Volcano? Infer the type of materials from which it was formed.

Fig. 12. Pinatubo Volcano

(Source: https://www.google.com.ph/url/mt-pinatubo-things-that-matter)

Although volcanologists have different basis for classifying volcanoes, one way to classify volcanoes is by their
cones.Now that you have learned about the relationship between volcanic emission and the shape of its slope,
let’s discuss the three volcanic cones, namely: shield, cinder, and composite cones.

Shield volcanoes are formed by the accumulation of lava that oozes out from the volcano.
Since non-viscous lava can flow freely, a broad, slightly domed structure that resembles a warrior’s
shield is formed as shown in Figure 13. An example of this type is the Mauna Loa in Hawaii.

Cinder cones, on the other hand, are built from ejected lava fragments. They have a steep
slope, wide crater and are the most abundant of the three major volcano types. One example of this
type is the Paricutin in Mexico.
 Composite cones or stratovolcanoes are large, nearly perfect sloped structure formed from
alternate solidification of both lava and pyroclastic deposits. One perfect example of this type of cone
is ourMayon Volcano.

Fig. 13. Types of volcanic cones(pls re-draw)

Energy from the volcano

Since our country is a home to more than a hundred volcanoes, energy has been tapped from
them. Actually, the Philippines ranks second in the world’s production of geothermal energy.
According to the Department of Energy, 14.4% of the country’s total power generation is produced
from geothermal energy. The production of electricity from geothermal energy is cheaper than the
electricity production using natural gas, coal, and hydropower.

How do volcanic eruptions affect society?

Volcanic eruption is often associated with negative effects. It can cause loss of lives and
properties. As the lava flows or pyroclastic materials are ejected in the air, they can destroy anything
in their way. Actually, it has a good and a bad side. For example, the eruption of Pinatubo in 1991,
one ofthe longest volcanic eruptions, has caused the decrease in the Earth’s surface temperature
foralmost two years. The strong winds during its eruption spread the aerosol particles from the plume
around the globe. The result was a measurable cooling of the Earth’s surface for a period of almost
two years.

Volcanoes also affect people positively. For example, the eruption of Pinatubo Volcano has
created spectacular scenery in its wake. Likewise, the eruption of Musuan Volcano in Bukidnon has
produced very rich soils for farmingyears after its eruption in 1867. People became creative also by
making earthenware out of the ashfall from the Pinatubo Volcano eruption.

Fig. 15. The Pinatubo caldera

 Despite the advantages that people get from volcanic eruption, the major concern now is
how to reduce the negative effects of disasters to reduce loss and save lives.

Zzz

. The aftermath of Pinatubo Volcano eruption (Photo credits: USGS)

Are you prepared?

Signs of an impending volcanic eruptionAccording to the Philippine Institute of Volcanology and Seismology
(PHIVOLCS), the government agency tasked with monitoring earthquakes and volcanoes in the country, the
following are commonly observed signs that a volcano is about to erupt. These may vary from one volcano to
another.

1. Increase in the frequency of volcanic quakes with rumbling sounds; occurrence of volcanic
tremors;
2. Increased steaming activity; change in 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 inflation), ground tilt and ground fissuring due to magma intrusion;
5. Localized landslides, rockfalls and landslides from the summit area which not attributable
to heavy rains;
6. Noticeable increase in the extent of drying up of vegetation around the volcano's upper
slopes;
7. Increase in the 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, crater lakes within the vicinity of
the volcano;
9. Drying up of springs/wells around the volcano; and,
10. Development of new thermal areas and/or reactivation of old ones; appearance of
solfataras.
SCIENCE 9

Lesson : VOLCANOES

Assessment Answer the following questions:

For numbers 1 to 3, choose from the illustration below. (pls re-draw without the labels)

Which among the following volcanoes is formed from: a

1. cinders and ash? b

2. mostly lava?
c
3. alternate solidification of lava and cinders?

4. Which of the following are active volcanoes?

I. Mayon in Albay II.Taal in

Batangas
III. Vulcan in Camiguin
IV. Kanlaon in Negros Oriental

a. I and II only
b. II and III only
c. I, II, and III only
d. I, II, and IV only

5. Which of the following characteristics of magma mainly affect the explosiveness of a

volcanic eruption?

a. color
b. amount
c. temperature
d. silica content

6. How does the eruption of a volcano lower the atmospheric temperature?

7. Give one positive effect and one negative effect of volcanic eruption.

Subject Teacher: MS. MILDRED I. CABULISAN LPT

09050411140/09207730625 Facebook/messenger: Mildred I. CabulisaN

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