Reference Book: Fundamentals of Physical Geology, Sreepat Jain. The slides were prepared keeping focus on FY BSc Geology students.

1. Volcano
Mr. Chinmay U. Dongare
Assistant Professor (Temp.)
Department of Geology, The Maharaja Sayajirao University of Baroda,
Vadodara-02
MSUB_CUD

2. Introduction
• A volcano is an opening in the earth’s surface from which molten lava,
rock fragments, and other gases erupt.
• When hot material (Lava) comes out from a volcano, it is called a volcanic
eruption.
• Magma is an extremely hot liquid (850°C - 1400°C) that is generated inside
the earth, usually at depths from 10 to 200 km.
• Often magma starts building pressure and moves up to the surface.
• This pressure buckles the surface of the earth and eventually forms a
mountain.
• If this liquid comes out to the surface of the earth, then, a Volcano is born.
• The word volcano comes from the little island of Vulcano in the
Mediterranean Sea off the coast of Sicily.
MSUB_CUD

3. MSUB_CUD

4. Components of Volcano
MSUB_CUD
•The volcanic material that is emitted on the
earth’s surface through an opening is
called a Volcanic vent.
• Main conduit through which magma moves
upward to the surface is called a Central
vent.
• It is connected to a magma chamber (a
reservoir) at depth, the main storage area
for the eruptive material.
• Side vents are found on the sides of some
volcanoes where lava is extruded and
secondary cones are formed.

5. MSUB_CUD
Magma Types

6. MSUB_CUD
Distribution of Volcanoes
 Volcanoes occur on divergent and convergent plate
boundaries.
 90 % of them encircle the Pacific Ocean as a Ring of Fire.
 volcanic eruptions can also occur in the middle of plates
and are called Intra-plate volcanoes or Hotspot .
 On an average, there are about 5–10 volcanoes erupting
every month (~ 50/year).
 So far, ~ 262,000 people have been killed by volcanoes
since 1600 A.D.

7. MSUB_CUD
Convergent Plate Margin
 These boundaries are often associated with intense
volcanism.
 As plates collide, heavier plates slide under lighter ones
and melt as they move down into the hot mantle.
 All around the Pacific Ocean is a zone called the
Pacific Ring of Fire.
 This ring occurs as most of the margins of the Pacific
ocean coincides with converging margins along which
subduction continuously occurs.
 The subduction-related volcanism is of two types:
1. Ocean - Ocean Convergence
2. Ocean – Continent Convergence

8. MSUB_CUD

9. MSUB_CUD
Ocean–Ocean Convergence
Here oceanic lithosphere is subducted beneath oceanic lithosphere.
The subsequent volcanism is expressed on the surface as chains of islands referred to
as Island arcs
Examples: Caribbean Arc, Aleutian Arc, Kurile Kamachatka Arc, Japan, Philippines,
South Sandwich Arc, Indonesian Arc, Marianas, Fiji, and Solomon Islands.
Ocean–Continent Convergence
Here the oceanic lithosphere is subducted beneath continental lithosphere and
volcanism occurs as chains of volcanoes near the continental margin, called the
Continental margin arc.
 examples include the Andes Mountains, Central American Volcanic Belt, Mexican
Volcanic Belt, the Cascades, the part of the Aleutian arc on Continental crust, and
the North Island of New Zealand.

10. MSUB_CUD
Divergent Plate Margins
The Oceanic Ridges or spreading centers are sites of active
volcanism along diverging plate margin.
However, most of this volcanism is submarine and often
does not pose any threat to humans.
One of the only places where an oceanic ridge reaches
above sea level is at Iceland, along the Mid-Atlantic Ridge.
Here, most eruptions are basaltic and are explosive in
nature belonging to the Strombolian types.

11. MSUB_CUD
Volcano
Continuity
of Eruption
Nature of
Eruption
Mode of
Eruption
Classification of Volcanoes

12. MSUB_CUD
Continuity of Eruption
Active Dormant Extinct

13. MSUB_CUD
 An active volcano is one that erupts either continually or
periodically. In precise terms, an active volcano is defined as
having erupted within the last 10,000 years.
There are approximately 1,500 active volcanoes in the world
today and 75 % of them are located in the ‘‘Pacific Ring of
Fire’’.
 A volcano that has not been known to erupt within modern
times and is now inactive is classified as a dormant, or a
sleeping volcano.
 A volcano not known to have erupted within recent history is
classified as an extinct volcano.
 Truly extinct volcanoes to be those that have been worn
away almost to the level of their magma chamber.

14. MSUB_CUD
Nature of Eruption
Quite Intermediate Violent
Quite type merely discharge steam and other gases.
 Intermediate eruptions quietly extrude quantities of lava
The most spectacular eruptions consist of violent explosions that
blast great clouds of gas-laden debris into the atmosphere
(Violent type).

15. MSUB_CUD
Mode of Eruption
 If the lava is not viscous, the gases escape easily.
But if the lava is thick and highly viscous, the gases will not
move freely but will build up enormous pressure, and
ultimately escape with a sudden expansion, causing
violent explosions that throw out great masses of solid rocks,
lava, dust and ashes.
 Such types of volcanic eruptions are often labeled with the
name of a well-known volcano where their characteristic
behavior is noted.

16. MSUB_CUD

18. MSUB_CUD

19. • It is a magnitude scale as there is not any singular feature
that determines the ‘‘bigness’’ of a volcano.
Volcanic Explosivity Index

20. MSUB_CUD
Types of Volcanoes

21. MSUB_CUD
Fissure Volcanoes are extremely massive outpourings of low viscosity
basaltic magma from fissure vents. The basalts spread in huge areas
of relatively low slope and builds up plateaus.
 Shield Volcanoes are large volcanic forms with broad summit areas
and low, sloping side.
 Cinder cones are the simplest of the volcano types, they expel ash
and cinders and have a cone-shaped peak that is associated with a
lava-spewing Strombolian type eruption.
 Strato-volcano shows well marked stratification or alternate layers of
pyroclastic material and solidifed lava-flows.
 Lava Domes (Volcanic Domes) are steep-sided, dome- or spine-
shaped masses of volcanic rock formed from viscous lavas that
solidifies in or immediately above a volcanic vent.

22. MSUB_CUD
Calderas are formed when an erupting volcano empties a
shallow-level magma chamber; the edifice of the volcano
collapses into the voided reservoir, thus, forming a steep,
bowl-shaped depression.
 Calderas are a volcanic depression much larger than the
original crater, having a diameter of at least 1 km and
may range to 100km.

23. Effects on Mankind
MSUB_CUD

24. Volcanic Hazards
MSUB_CUD
Volcanic hazards include the primary effects of volcanic activity
that are the direct results of the eruption.
 secondary effects, which may be caused by the primary
effects.
Primary Effects: Lava Flow, Pyroclastic activity, ash fall, ash flow,
Release of poisonous gases.
 Secondary Effects: Debris flow, mud flow, landslide or debris
avalanches, floods and fires.
 At the planetary level, large eruptions can cause global cooling
of the atmosphere for a year or so.

25. MSUB_CUD

26. MSUB_CUD

27. MSUB_CUD
Methods to Control Lava flows
1. Hydraulic Chilling: Water is used to chill and control the
lava flow.
2. Wall Construction: Walls used to redirect the lava flow.