2. Lesson Objectives:
Describe the basic shapes of volcanoes.
Compare the features of volcanoes.
Describe the shapes in the formation of volcanoes.
3. Review
What are Volcanoes?
Volcanoes are openings in the planet’s crust that allow
molten rocks (magma) and gasses trapped beneath to
escape. The forceful ejection of lava and gasses often
result in a relief on the planet’s surface, which appears in
the form of a hill or mountain. The resulting structure is
what we call a volcano.
Note: The thick blazing hot liquid made up of molten
rocks beneath the surface is called magma. When
magma reaches the surface, it is called lava.
4. Types of Volcanoes
When most people think of volcanoes, they think of a tall
mountain with a crater on top, maybe a little snow at the
summit and some trees scattered around the base. There are
many volcanoes like this, but volcanoes exists in many forms
as well. Each type of volcano has characteristic features that
distinguish it from other types. Volcanoes differ in appearance
because of the composition of their magma and the processes
that originally created them.
The tall cone shape you usually think of when you think of
a volcano describes a composite volcano, one common form of
volcanoes. Other types of volcanoes, includes the shield
volcanoes include the shield volcano, the cinder cone, fissure
volcano, caldera volcano.
5. What Are the Characteristics of Volcanoes?
Volcanoes are elevated structures formed due to the magma moving to the
surface.
Volcanoes can vary in shape but generally consist of a conical structure formed
due to the accumulation of erupted material.
When magma reaches the surface, it’s called lava. Lava cools down over time
and solidifies into rocks.
Depending upon the activity, volcanoes can be active, dormant, or extinct.
Volcanoes are formed where there is a fracture in Earth’s crust. These fractures
allow magma to rise to the ground, pushing rocks and forming volcanoes.
6. What Are the Main Parts of a Volcano?
A volcano may seem like a single structure rising
above the ground from the outside. However, it
consists of several parts, from the top of the
opening to the magma chamber inside. Let’s learn
about different parts of the volcano in detail.
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11.
12. How Does a Volcano Form?
Volcano formation is linked with the functioning of tectonic plates. Earth’s
crust is not uniform throughout its length – it consists of layers.
The topmost layer is where we live, and beneath it is the mantle. Mantle
comprises very hot molten rocks known as magma. The top layer, also
known as the tectonic plates, floats over the mantle.
These tectonic plates could move towards each other or away from each
other. Volcanoes form at the boundaries of these tectonic plates where
there are fractures in the Earth’s crust, allowing the magma to escape to the
surface.
13. How Does a Volcano Form?
The resultant movement of tectonic plates gave rise to two types of plate boundaries;
Convergent Plate Boundaries
Divergent Plate Boundaries
When two tectonic plates collide with each other, they create convergent plate boundaries.
During the collision, the denser plate’s edge is often pushed beneath the less dense plate in a
process known as subduction.
The edges of the downward-moving plate heat up due to enormous friction, which causes the
rocks to melt, forming magma. Pressure build-up forces the magma to move towards the
surface and results in an eruption forming a volcano.
The Ring of Fire in the Pacific lies in the subduction zone and hosts around 425 volcanoes or
more.
14. Divergent Plate Boundaries
When two plates move away from each other, they form
divergent plate boundaries.
Moving plates often result in vents or fissures that give
way to magma and allow it to move upward, forming volcanoes.
Example:
Mount Kilimanjaro in Kenya and Mount Nyiragongo in
Congo are located at divergent plate boundaries.
20. Depending upon their shape and
formation, volcanoes can be of six types;
• Fissure Volcano
• Shield Volcano
• Dome Volcano
• Ash-Cinder Volcano
• Composite Volcano
• Caldera Volcano
21. Fissure Volcano
Fissure Volcanoes or linear volcanoes
are usually found along the oceanic
ridges and, in rare cases, on land.
22.
23. Fissure Volcano
have no central crater at all
giant cracks are open in the ground and expel vast quantities of lava.
This lava spreads far and wide to form huge pools that can cover almost
everything around.
When these pools of lava cool and solidify, the surface remains mostly flat.
Majority of these volcanoes are found near the ocean ridges.
Example of these is the fissure eruption that occurred in Los Pilas volcano in
Nicaragua in 1952 and along Taal volcano.
24. Fissure Volcano
They differ from other volcanoes due to their lack of central structure
that forms around a crater.
Instead, these volcanoes consist of a series of fractures that run deep
underground.
Lava escaping these volcanoes is of low viscosity; therefore, lateral
development of fissure volcanoes is more profound than vertical
development.
Examples of Fissure Volcanoes:
Eastern African Rift, Cordón Caulle, Holuhraun.
29. Shield Volcano
The main characteristic of a
shield volcano is its shape of an
inverted shield.
30.
31. Shield
Has wide gentle slopes.
It is low in height
Formed by the accumulation of lava that oozes out from the
volcano.
They look like low, broad, dome shaped mountains.
Almost flat like a warrior’s shield.
Example: Mt. Biliran in Philippines
Mauna Loa Volcano in Hawaii
32. Shield Volcano
The height of a shield volcano is much less than its width.
Therefore, these volcanoes have low slopes.
The lava flow is effusive that is slow-moving due to less viscosity
(low in silica).
Being less viscous, lava flows to a greater distance before cooling.
Accumulation of such a type of lava flow over a long period gives
rise to a shield volcano.
Examples of Shield Volcano: Mauna Kea, Mauna Loa, Kohala
volcano, Killauea, Tamu Massif.
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34.
35.
36.
37. Dome Volcano
Very thick lava that could not
move too far beyond the crater
gave rise to the dome volcano.
38.
39. Lava Dome
rounded, steep-sided mound
is formed by smal, bulging masses of lava
Lava coming from a dome is too viscous to flow from
the vent, hence, when it cools down and piles up
around the vent it solidifies
Examples:
Unzen Dome in Japan and
Novarupta Volcano in Alaska
40. The escaping lava moves sluggishly, cools down and piles around
the vent giving the characteristic dome shape to the volcano.
Lava domes are typically low in height. Similar to composite
volcanoes, they can cause violent eruptions.
Examples of Dome Volcanoes:
Mount Merapi, del Caribe volcano, Soufrière Hills and Chaitén lava
dome,
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44.
45. Cinder Volcano
Cinder cone volcanoes typically rise 300m
to 500m and form by the fragmented and
fragmented and erupted ash that falls near
the chimney or vent.
46.
47. Cinder Cone volcano
Simplest type of volcanoes
Has a single opening
Wide crater
Has a short and steep slope
Composed primarily of loose pyroclastic materials.
Are formed from the ejected lava fragment
Examples:
Taal volcano in the Philippines
Mt. Paricutin in Mexico
48. Cinder cone volcanoes lack horizontal layers, unlike
stratovolcanoes. Instead, they form a rather steep conical
hill of tephra or pyroclast (volcanic debris).
The loose volcanic debris escapes from the vent
and collects around it, giving rise to ash-cinder cone
volcanoes.
Examples of cinder-cone volcanoes: Mono-Inyo Craters,
California, Paricutín in Mexico
49.
50.
51.
52.
53. Composite Volcano
Composite volcanoes are also known as strato
volcanoes due to their peculiar characteristics of
layers of solidified material.
54.
55. Composite Volcano
Also called Stratovolcano
It is tall, has wide base and a steep-sided symmetrical cone
Sometimes rising 10,000 feet high
Composed of ash and cinders.
It has a nearly perfect sloped structure-formed from solidified lava and
pyroclastic materials.
Some of the most beautiful mountains in the world
Examples:
Mt. Mayon in Bicol and Mt. Vesuvius in Italy
56. • They form from consecutive eruptions and lava flow over thousands of
years.
• Composite Volcanoes often have a steep side and very pronounced
volcanic cones.
• Lava coming out of composite volcanoes is usually viscous and sticky due
to the greater quantity of silica. It flows slowly and forms a towering
structure.
Example of Composite Volcano:
Pico del Teide, Arenal volcano,
Krakatoa, Monte Helena, Monte Vesubio
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58.
59. Mayon, also known as Mayon Volcano or Mount Mayon, is an active stratovolcano in the
province of Albay in Bicol Region, on the large island of Luzon in the Philippines.
60. Kanlaon, also spelled as Kanla-on or sometimes Canlaon, is an
active stratovolcano on the island of Negros, Philippines. It is
the highest point in Negros, as well as the whole Visayas, with
an elevation of 2,465 m above sea level.
61. Mount Apo is a large solfataric, potentially active
stratovolcano in the island of Mindanao, Philippines.
62.
63. Caldera Volcano
Caldera is a cauldron-like structure formed
when a volcano erupts and creates a
depression.
64.
65. Caldera (Ryolite Caldera
Complexes)
are the most explosive volcanoes on Earth but they do
not look like volcanoes.
Their explosions are usually so strong that the volcano
will collapse. And when they collapse they create a
large caldera.
Example: Laguna Caldera
66. • When the magma chamber empties following an eruption, the support due to
magma vanishes, and the chamber collapses inward, forming calderas.
• There are resurgent calderas too that form due to refilling of the magma chamber.
The refilling magma pushes the caldera floor upward, hence the name, resurgent or
‘rise again.’
• Caldera often forms a lake as the depression formed fills with water.
Examples of Calderas:
Oregon crater lake, Mt Mazama, Kilauea.
67. Crater Lake Caldera: A satellite view of
Crater Lake, one of the world's most famous
calderas. Crater Lake formed about 7700
years ago when a massive volcanic eruption
of Mount Mazama emptied a large magma
chamber below the mountain. The
fractured rock above the magma chamber
collapsed to produce a massive crater over
six miles across. Centuries of rain and snow
filled the caldera, creating Crater Lake. With
a depth of 1949 feet (594 meters), Crater
Lake is the deepest lake in the United
States and the ninth-deepest lake in the
world. The image above was produced using
Landsat GeoCover data from NASA. Enlarge
image.
68.
69. What is Volcanic Eruption?
The forceful and violent ejection of lava, gasses,
and rocks from a volcano is known as a volcanic
eruption.
The eruptions result from the pressure build-up
due to magma moving from the mantle to the
magma chamber inside the volcano.
70. How Are Volcanoes Classified?
Volcanoes are classified depending upon their activity. By
this definition, volcanoes can be;
• Active
• Dormant/Inactive
• Extinct
71.
72. Active Volcanoes
These are volcanoes that erupt occasionally. These
are volcanoes that erupted with in the last 60O years and
those that 10,000 years ago, based on the age of volcanic
rocks. Most active volcanoes have erupted in the recent
past and have a very high chance of erupting again.
Examples of active volcanoes:
Mount Etna, Kīlauea, Mount Stromboli, Mt. Mayon
73. Dormant/Inactive Volcanoes
These are volcanoes that have no record of eruption for
the last 10,000 years . The long period of dormancy is manifested
by the weathering and erosion of deep and long valeys.
Although dormant volcanoes haven’t erupted for quite a
long time, they can explode in the future.
Examples:
Mount Fuji (Japan), and
Mount Kilimanjaro (Tanzania)
Balo Dome in South Cotabato.
74.
75. Extinct Volcanoes
It has not erupted or no proof of eruption in historical
times.
Example:
Kyushu-Palau Ridge in the Philippine Sea
76. Extinct Volcanoes
Extinct Volcanoes have minimal chance of eruption in
the future. A volcano is considered extinct if there has been no
eruption for thousands of years.
However, there is no guarantee that an extinct volcano may not
wake up and become active someday.
Examples:
Mount Thielsen, Oregon, US, and
Mount Slemish, Antrim.
77.
78. QUIZ;
1. _____________are elevated structures in the Earth’s surface, it is formed due to the magma
moving to the surface.
2. A type of volcano that has no central crater at all. It looks like a giant cracks open in the ground
and expel vast quantities of lava.
3. The simplest type of volcanoes. Has a single opening, wide crater and has a short and steep
slope.
4. They look like low, broad, dome shaped mountains. Almost flat like a warrior’s shield. Has wide
gentle slopes.
79. What are the Different Types of Volcanic
Eruptions?
Volcanoes can also be characterized by the kind of eruption that occurs from them. Based
on eruptions, volcanoes can be divided into six types;
• Hawaiian Eruptions
• Strombolian Eruptions
• Vulcan-type Eruptions
• Vesuvian Eruptions
• Plinian Eruptions
• Ultra Plinian Eruptions
80.
81. •Hawaiian eruptions are characterized by quiet
outpourings of lava without strong shocks or explosions.
•Lava coming out of Hawaiian eruptions is very fluid and
could travel kilometers.
•Gasses trapped in lava are released smoothly; therefore,
the lava forms a smooth surface.
82.
83. •Volcanoes with Strombolian eruptions are characterized
by effusive eruptions forming lava fountains.
•The Strombolian-type eruptions are regularly and
moderately explosive.
•Lava effusions form layers of solidified material and give
rise to stratovolcanoes.
84.
85. •Vulcun-type eruptions are marked by violent explosions
often destroying the cone they came from.
•The explosion involves, emission of volcanic bombs, gas
clouds, and large quantities of ash.
•The emissions consist of very viscous lava, rich in silica
and large quantities of gas.
Vesuvian Eruptions
•Vesuvian eruptions are similar to Vulcan-type eruptions;
however, they are characterized by a very heavy initial
explosion that empties the magma chamber completely.
•The eruptive material can reach 20-25 km in height
86.
87. •The name Plinian eruption is derived from the Pelée
volcano in Martinique, which erupted very violently in
1902.
•The eruption occurs under a “plug” formed by
solidification in the volcanic duct. The magma is very
acidic and, therefore, extremely viscous.
•The eruption is quite explosive, forming a river of
expelled materials.
Ultra Plinian Eruptions
•The explosion in Ultra Plinian Eruption exceeds even
Plinian eruptions in intensity.
•The eruption is so explosive it disintegrates the entire
volcanic structure.
•The volume of expelled material is staggering. The
escaping gasses could even impact the global climate.
88. Conclusion
Volcanoes are one of the most majestic yet violent structures on a planet. On Earth, different types of
volcanoes constantly shape the planet’s surface and depth of the ocean, destroying the old and giving rise to
new structures. A gateway connecting the blazing depth of Earth’s mantle to the surface, volcanoes bring
essential minerals to the surface, making it possible for life to thrive.
