Volcanoes form when tectonic plates collide and magma rises up through the crust. The document discusses the Ring of Fire around the Pacific Ocean which has many active volcanoes. It also defines key volcanic terms and describes the three main types of volcanoes: shield, composite, and cinder cone volcanoes. The effects of volcanic eruptions on humans and the environment are also summarized.

2. PRESENTED BY
GOWRI V PRABHU

3.  Volcano refer to the eruption of hot molten lava
from below the surface of earth.
A volcano is a vent in the earth’s crust through
which Lava, Steam, ashes etc. are expelled.

4. RING OF FIRERING OF FIRE
A zone along the edge of Pacific Ocean that has
many Volcanoes and Earthquakes.
The horseshoe shaped 40,000 kilometre long
belt is characterized by higher volcanic activity.
 The Ring of Fire is a string of volcanoes that
runs around the edge of the Pacific Ocean.

5. •A string of 452 volcanoes stretches from the southern
tip of South America, up along the coast of North
America, across the Bering Strait, down through Japan,
and into New Zealand

6. HOW ARE THEY FORMED ?
• When tectonic plates collide and go through the
process of subduction, it sets the foundation for a
volcano. The overlapping of the tectonic plates causes
the magma to break through the crust, which is the
cause of a volcanoes' birth.
• When temperature and pressure rises, the rock melts
and moves through the surface and crust, and releases
gases and magma, volcanic eruption occurs.

7. The narrow opening of a volcano is called
Vent. The upper part of vent is a cup
shaped depression called Crater.
The rock material ejected during volcanic
activity is deposited on surface of Earth. It is
called Lava.

8. Pyroclastic Flow is fluidized mixture of solid to
semi-solid fragments.
It is characterized by hot expanding gases that
flows down the flank of volcanic edifice.

9. • Pyroclastic flows are
mixtures of hot gas,
ash and other
volcanic rocks
travelling very
quickly down the
slopes of volcanoes.
They are one of the
most dangerous
hazards posed by
volcanoes.

10. Viscosity - the property of a fluid that resists the
force tending to cause the fluid to flow
Magma - molten material beneath or within the
earth's crust, from which igneous rock is formed
Lava - the molten, fluid rock that issues from a
volcano or volcanic vent
Ash - the powdery residue of matter that remains
after burning
Caldera - A large crater formed by volcanic
explosion or by collapse of a volcanic cone.
DEFINITIONSDEFINITIONS

11. VOLCANOES CAN BE IN ONE OF THREE PHASES:
ACTIVE, DORMANT, AND EXTINCT.

Active volcanoes are ones that have erupted in the
past 10,000 years, and that are likely to erupt again.
An example is Mt. Saint Helens in U.S.A.

Dormant volcanoes are ones that have not erupted in
the past 10,000 years, but still have the possibility,
though unlikely. An example is Mt. Rainier in the
U.S.A.

Extinct volcanoes are one which no eruption has
occurred within historic times and future occurrences
are highly improbable . An example is Mt. Ashitaka in
Japan.

12. HOTSPRINGS AND GEYSERSHOTSPRINGS AND GEYSERS
•A natural spring of mineral water at a
temperature of 21°C (70°F) or above, found in
areas of volcanic activity is called Hotspring.
• A hot spring that intermittently sends up
fountain like jets of water and steam into the air
is known as a Geyser.

15. There are three major types of volcanoes:
 Shield volcanoes
Composite volcanoes
 Cinder cone volcanoes

16. SHIELD VOLCANOES
• The magma inside a shield volcano is rich in
iron and magnesium and is very fluid.
• Since the magma is very fluid, the lava coming
out of the volcano tends to flow great
distances.
• When shield volcanoes erupt, the flowing lava
gives the volcano the shape of a gently sloping
mountain.

17. COMPOSITE VOLCANOES
• The magma inside a composite volcano is rich
in silica and much thicker than magma from a
shield volcano.
• Gases get trapped inside this thicker magma.
• Eruptions from composite volcanoes can be
flowing lava or explosions. The explosive
eruptions come from the trapped gases and
produce cinders and ash.

18. CINDER CONE VOLCANOES
• The magma inside a cinder cone volcano has
large amounts of gas trapped in it.
• Eruptions from cinder cone volcanoes are
violent and explosive because of all the gas
trapped in the magma.
• The large amounts of hot ash and lava thrown
out of the vent fall to the ground forming the
cone shape that these volcanoes have.

19. CAUSES OF VOLCANIC ACTIVITYCAUSES OF VOLCANIC ACTIVITY
•When a part of the earth's upper mantle or
lower crust melts, magma forms. A volcano is
essentially an opening or a vent through
which this magma and the dissolved gases it
contains are discharged.

20. SEVERAL PROCESSES ASSOCIATEDSEVERAL PROCESSES ASSOCIATED
WITH MECHANISM OF VOLCANISMWITH MECHANISM OF VOLCANISM
• A gradual increase of temperature with increasing
depth at the rate of one deg. Celsius for every 32
minutes.
• Gases and Vapours are formed due to heating of water,
which reaches underground through percolation.
• The ascent of magma forced by vast volume of gases
and water vapour.
• The occurrence of Volcanic Eruption

21. EFFECTS OF VOLCANIC ERUPTIONSEFFECTS OF VOLCANIC ERUPTIONS
•The effects of volcanic eruptions can be divided
into primary and secondary effects.
•The primary effects are immediate and come from the
eruption itself.
•The secondary effects result from the primary effects.

22. Volcanic gases: All magma contains dissolved
gases. These gases are mainly steam, carbon
dioxide and compounds of sulphur and
chlorine.
Lava flows: These are streams of molten rock.
Pyroclastic flows - These are high speed
avalanches of hot ash, rock fragments and gas
which move down the sides of a volcano.
These flows occur when the vent area or ash
column collapses.

23. Lahars - These are
mixtures of water,
rock, ash, sand and
mud that originate
from the slopes of a
volcano. Lahars often
happen because of
heavy rainfall eroding
volcanic deposits.

24. Landslides - Heat from cooling magma can
cause hydrothermal alteration of the rocks,
turning sections of them into clay. This
weakens the rocks and increases the risk of
slope failures.
Flooding - Explosive eruptions can change
the surface areas around a volcano and
disrupt drainage patterns, leading to long-
term flooding.

25. Other secondary effects include:
Food / water supply interrupted.
Homelessness.
Businesses forced to close.
Cost of insurance claims.
Unemployment.
Long-term issues with the tourism
industry.

26. •Volcanoes are caused when molten rock (magma) flows out onto
the earth’s surface through fissures that are caused due to the
movement of plates
•Though volcanic eruptions are threats to human life, the areas
where the eruptions have taken place are useful too. They have
helped to create beautiful Hawaiian Islands.
•These areas are rich in minerals.
• Volcanic Eruption cause heavy damage to human life and
property.