A PowerPoint Presentation for Grade 9 teachers. This presentation is ONLY suggested guide for teachers to assist them on the discussion after the activities as suggested in the Learner's Module were performed. Please feel free to add comments and suggestions. Thanks!

1. VOLCANOES
Grade 9, Module 3 Lesson 1.1
(Teachers’ Guide for Discussion)
Author:
MA. RACHEL B. ESPINO
Teacher I, Science
Buhatan NHS, Sorsogon City

2. What is a volcano?
• A volcano is a mountain where lava (hot, liquid
rock) comes from a magma chamber under the
ground. A volcano usually has a summit, a slope
and base.
• Most volcanoes have a volcanic crater at the top.
When they are active, materials pour out of it.
This includes lava, steam, gaseous compounds of
sulphur, ash and broken rock pieces.
• Volcanoes erupt when magma and pressure
come together, and the pressure blows off the
top of the solid rock, and the magma pours out.

3. Types of Volcanoes: SHIELD VOLCANOES
• Shield volcanoes are built out of layers of lava from
continual eruptions (without explosions). Because the
lava is so fluid, it spreads out, often over a wide area.
Shield volcanoes do not grow to a great height, and the
layers of lava spread out to give the volcano gently
sloping sides. Shield volcanoes can produce huge areas
of basalt, which is usually what lava is when cooled.
• Even though their sides are not very steep, shield
volcanoes can be huge. Mauna Kea in Hawaii is the
biggest mountain on Earth. If it is measured from its
base on the floor of the sea, Mauna Kea is even taller
than Mount Everest, the tallest mountain on land.

5. Types of Volcanoes: STRATOVOLCANOES
• A stratovolcano, also known as a composite volcano, is
a tall, conical volcano. It is built up of many layers of
hardened lava, tephra, pumice, and volcanic ash.
• Unlike shield volcanoes, stratovolcanoes have a steep
profile and periodic eruptions. The lava that flows from
stratovolcanoes cools and hardens before spreading
far. It is sticky, that is, it has high viscosity. The magma
forming this lava is often felsic, with high-to-intermediate
levels of silica, and less mafic magma. Big
felsic lava flows are uncommon, but have travelled as
far as 15 km (9.3 mi).

7. Types of Volcanoes: CALDERA
• A caldera is what is left when a huge
stratovolcano blows its top off. It leaves a
crater where the top of the volcano was
before. Krakatoa, best known for its
catastrophic eruption in 1883, is much smaller
now.

9. How are volcanoes formed?
There are two main processes.
• Volcanoes are made when two tectonic plates come
together. When these two plates meet, one of them
(usually the oceanic plate) goes under the continental
plate. This is the process of subduction. Afterwards, it melts
and makes magma (inside the magma chamber), and the
pressure builds up until the magma bursts through the
Earth's crust.
• The second way is when a tectonic plate moves over a hot
spot in the Earth's crust. The hot spot works its way
through the crust until it breaks through. The caldera of
Yellowstone Park was formed in that way; so were the
Hawaiian Islands.

10. FORMATION OF VOLCANOES
http://youtu.be/6Z4as_imJfM

11. Classification of Volcanoes
A traditional way to classify or identify volcanoes
is by its pattern of eruptions. Those volcanoes
which may erupt again at any time are called
active. Those that are now quiet called dormant
(inactive). Those volcanos which have not
erupted in historical times are called extinct.

12. ACTIVE VOLCANOES
• An active volcano is currently erupting, or it
has erupted in the last 10,000 years. An
example of an active volcano is Mount St.
Helens in the United States (US).

13. DORMANT VOLCANOES
• A dormant volcano is "sleeping," but it could
awaken in the future. Mount Rainier in the
United States is considered dormant

14. EXTINCT VOLCANOES
• An extinct volcano has not erupted in the past
10,000 years. Edinburgh Castle in Scotland is
located atop an extinct volcano.

15. What determines the nature of
eruption?
• There are many primary factors affecting the
volcanoes eruptive style, namely: the
magma’s temperature, its chemical
composition, the amount of dissolved gases it
contains. These factors can affect the
magma’s viscosity in different way.

16. VISCOSITY
• 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.

17. Effect of Magma’s Temperature to
Viscosity
• The viscosity of the magma decreases with
temperature. The higher the temperature of
magma is, the lower is its viscosity. As lava
flows, it cools and begins to harden, its ability
to flow decreases and eventually stops.

18. Effect of Magma’s Composition to
Viscosity
• Magma’s with high silica content are more
viscous than those with low silica content .
The magma that contains less silica is
relatively fluid and travels far before
solidifying.

19. Effect of the Amount of Gases
Contained in Magma to Viscosity
• 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 a dome or a
columnar.

20. Lava with low amount of
gas as it rises has high
viscosity that piles up at a
vent resulting into a dome.
Lava with less silica
content is too viscous to
travel far, and tends to
break up as it flows
Lava with less silica
content has less silica
content has low viscosity
that it can travel a great
distance, fow=rming a thin
sheet

21. Volcanic Eruption
• Eruption of Mayon Volcano last 2006 in Albay,
Philippines
http://youtu.be/MEI1BTjxmok
• Eruption of Mt. Kilauea in Hawaii, USA
http://youtu.be/488BkTUsMa4

22. Types of Volcanic Eruption
• PHREARIC 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 for a larger
eruption. Example is Taal
volcano eruption in
Batangas (as shown on
the right)

23. Types of Volcanic Eruption
• PHREATOMAGMATIC
- is a violent eruption due
to the contact between
water and magma. As a
result, a large column of
very fine ash, high speed
and side-way emission of
phyroclatics called based
surges are observed.
Example is the eruption
of Mt. Fukutoku-Okanoba
in Bonin Islands, Japan

24. Types of Volcanic Eruption
• STROMBOLIAN
- a periodic weak to
violent eruption
characterized by
fountain lava. Example
is Mt. Irazu Eruption in
Costa Rica

25. Types of Volcanic Eruption
• VULCANIAN
- characterized by tall
eruption coulmns that
reach up to 20 km high
with pyroclastic flow
and ash fall tephra.
Example is Mt. Paricutin
in Mexico.

26. Types of Volcanic Eruption
• PLINIAN
- excessively explosive
type of eruption of gas
and pyroclastics.
Example is Mt. Pinatubo
in Zambales.

27. Examples of Volcanoes found in
the Philippines

36. Suggested Videos
• Naked Science: Volcanoes (it provides
discussion about the formation of new
volcanoes in Yellowstone National Park, USA)
http://youtu.be/G1pa6afh8o4
• BBC: Iceland Volcanoes Erupts (it shows
eruption of Iceland volcanoes, its effects and
how people in Iceland adapts and survive
along the volcanic areas)
http://youtu.be/MlH7pCK4H-s