volcano

1. VOLCANO
having a crater or vent in which
lava, rock fragments, hot vapor,
and gas are or have been erupted
from the earth's crust.

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4. Parts of a Volcano
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Summit is the highest point or the
apex of the volcano. At the summit,
you have an opening called vent.
Slopes are the sides or flanks of a
volcano that radiate from the main
or central vent.
Base is lower outer part of the
volcano.

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6. Other Geologic features of a volcano:
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Magma Chamber is a region beneath the vent of
a volcano where molten rock or
Main Vent is the main opening or outlet on the
surface of a volcano that emits lava, gases, ash
or other volcanic materials.
Conduit is an underground central tube-like or
pipe-like structure of a volcano that connects
the magma chamber to the crater through which
the magma travels.
Side Vent is a smaller outlet through which
magma escapes.

7. Other Geologic features of a volcano:
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Crater is the mouth of the volcano which
is a funnel-shaped or bowl-shaped hollow
at the top of the vent from where magma,
ash and gas comes out.
Lava is a molten rock which is given off
onto the surface of the Earth when a
volcano erupts.
Ash and Gas Cloud is a of mixtures of
rock, minerals, glass particles and gases
expelled or pushed out of the volcano

8. Types of Volcanoes
Based on Activity

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ACTIVE VOLCANOES are
those volcanoes that have
had at least one eruption
during the past 10,000 years.
They are those that erupted
recently and still showing
regular activity like emission
of gases, lava and ash flows.

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INACTIVE VOLCANOES, on the other
hand, are those that have not erupted
for the last 10,000 years and is not
expected to erupt again in a
comparable time scale of the future.
There are no signs of volcanic activity
for a long period of time because
magma supply is cut off. Also, the
physical form of the volcano has signs
of intensive weathering and erosion

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POTENTIALLY ACTIVE
volcanoes are those that
have no records of
volcanic activity but are
morphologically young-
looking.

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Another way of classifying
volcanoes according to the
Philippine Institute of
Volcanology and Seismology
(PHIVOLCS) is based on
their activity as indicated by
their behavior and historical
records.

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Our country has more than
a hundred volcanoes.
Twenty four (24) are active
while the rest are either
potentially active or inactive
volcanoes. Below are some
examples of active
volcanoes.

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Mount Banahaw, boundary of Laguna and
Quezon (Lucban)

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Mount Hibok Hibok, Camiguin, Region 10,
Northern Mindanao

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Mount Apo, Davao Del Sur, Mindanao

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Mount Kanlaon, Negros Occidental

18. Types of
Volcanoes Based
on Structure

19.  CINDER CONE VOLCANOES are the
simplest type of volcano. They are
built from particles and blobs of
solidified lava ejected from a single
vent. Lava is thrown into the air,
which breaks into small fragments
that solidify and fall as cinders
around the vent to form a circular or
oval cone. Most cinder cones have a
steep slope, wide crater and are the 19

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Cinder Volcano
Smith Volcano Taal Volcano

21.  COMPOSITE VOLCANOES OR
STRATOVOLCANOES are large, typically
steep-sided, symmetrical cones of large
dimension formed from alternating layers
of lava flows, volcanic ash, cinders,
blocks, and pyroclastic materials. One
important feature of a composite
volcanoes is the conduit system from
which magma rises to the surface of the
Earth. They are formed from viscous, or
sticky, lava that does not flow easily. The 21

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CompositeVolcano
Kanlaon Volcano

23.  SHIELD VOLCANOES are large, broad
volcanoes that look like shields from
above – hence the name. These
volcanoes are built almost entirely of fluid
lava flow thus these volcanoes are not
steep. They can be easily identified
because they are tall and broad, with flat,
rounded shapes. The lava is not
accompanied by pyroclastic materials,
which makes shield volcanoes relatively
safe. Eruptions at shield volcanoes are 23

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Mauna Kea, Hawaii -- Shield Volcano

25. Types of Volcanic
Eruptions

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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 a beginning of a larger

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Phreatic
Eruption

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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 pyroclastic
materials called base surges

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Phreatomagmatic Eruption

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STROMBOLIAN a
periodic, weak to
violent eruption
characterized by
fountain lava

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Strombolian Eruption

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VULCANIAN is
characterized by tall
eruption columns that
reach up to 20 km high
with pyroclastic flow
and ash fall tephra like

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Vulcanian Eruption

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PLINIAN is
excessively
explosive type of
eruption of gas and
pyroclastic materials,
like in Pinatubo

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Plinian
Eruption

36. MAGMA AND
ITS
COMPOSITION

37. Magma
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•is the molten rock which lies
underneath volcanoes. It is
formed at destructive plate
boundaries and is rich in silicate.
These are products of crustal
rocks (which are richer in silica
than the rock of the mantle).

38. Crystal Content
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•Some magmas begin to
crystallize as they reach the
surface. High temperature
minerals are formed as magma
slowly cools down followed by
low temperature minerals.
Magma always contains crystals
of high temperature.

39. Viscosity
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•The magma’s silica content affects its
viscosity, the resistance of the fluid to
flow. Low viscosity magma has low silica
content and is composed mostly of
basalt. While magma with rhyolite is
viscous or high in viscosity due to its
high silica content. Temperature also
affects the viscosity of the magma.
Magma with high temperatures have low
viscosity while magma with low

40. Temperature
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•Temperature of magma reflects the
melting points of their mineral
components. Magmas formed by
partial melting of mantle rocks are
much hotter over 1200⁰C for some
basalts. Rhyolites that reached the
surface have temperature of less than
900⁰C, and have a much higher

41. Volatile Content
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•Magma contains small amounts of
dissolved gas (water vapor,
Carbon dioxide, etc.) which is
released as pressure is removed.
Magmas formed by melting of
mantle rocks have generally low
volatile contents, but those
formed by partial melting of
crustal rocks are often volatile-

42. Volatile Content
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•The degree of concentrations of different
volcanic gases are different from one volcano
to the other. Water vapor is the most abundant
volcanic gas, followed by carbon dioxide and
sulfur dioxide. There are other volcanic gases
such as hydrogen sulfide, hydrogen chloride,
and hydrogen fluoride. Trace gases are also
found in volcanic emissions and these are:

43. Volatile Content
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•The movement of this volatile
content is affected by the
viscosity of the magma. As the
gas continues to precipitate from
the high viscosity magma, the
bubbles will be prevented from
rapidly breaking out resulting to
the increase in pressure on the
magma column. This causes the

44. CLASSIFICATIONS OF MAGMA
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45. PROCESS OF
VOLCANIC
ERUPTION

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1. High temperature inside the Earth melts
the solid rocks in the mantle and turns it
into a thick molten mixture commonly
known as magma.
2. The continuous melting of solid rocks and
accumulation of additional magma push it
to the vent of a volcano, called magma
chamber.
3. Magma contains dissolved gases mostly
water vapor, carbon dioxide, and sulfur
dioxide. As dissolved gases are released
from the magma, bubbles will begin to

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1. This can occur by decompression or
crystallization. In decompression, the
confining pressure is lowered when
magma rises which promotes bubble
formation. This process is like bubble
formation in soda bottles when opened.
2. In the process of crystallization of
anhydrous minerals, the vapor pressure of
the residual liquid of the cooling magma
increases leading to vesiculation. Bubbles
frozen in a porous or frothy volcanic rock
are called vesicles.

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1.As the magma reaches
the Earth’s surface it
explodes due to the
presence of dissolved
gases. The type of
explosion of a volcano is
dependent on the

49. VOLCANIC HAZARDS AND THEIR
EFFECTS
Ash fall – pulverized rocks, sand, gritty and
harsh glasses shoot out in the air by volcano.
Mud flow – mixture of water, molten rocks and
debris flowing down from the side of volcano to
the ground. It is also called as Lahar.
Lava flow – streams of molten rocks and other
fragmented materials emitted by erupting
volcano.
Pyroclastic flow – fast moving hot mixtures of
gas, ash, and molten rocks moving away from

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52. Benefits of living by a volcano
People choose to live in volcanic areas despite the
risks of an eruption. Volcanoes can provide people
with many benefits such as:
volcanic rock and ash provide fertile land which
results in a higher crop yield for farmers
tourists are attracted to the volcano, which increases
money to the local economy
geothermal energy can be harnessed, which
provides cheaper electricity for locals
minerals are contained in lava, eg diamonds - these
can be mined to make money

53. Yellowstone Supervolcano,
Western United States.
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54. thank you