A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.

1.  A volcano is a rupture in the crust of a planetary-
mass object, such as Earth, that allows
hot lava, volcanic ash, and gases to escape from
a magma chamber below the surface.
A volcano is a rupture in the crust of
a planetary-mass object, such as Earth,
that allows hot lava, volcanic ash,
and gases to escape from a magma
chamber below the surface.

2.  A volcanic eruption occurs when hot materials
are thrown out of a volcano. Lava, rocks, dust,
and gas compounds are some of these are call as
"ejecta".
 Eruptions can come from side branches or from
the top of the volcano. Some eruptions are
terrible explosions that throw out huge amounts
of rock and volcanic ash and kill many people.
Some are quiet outflows of hot lava.

3.  Several more complex types of volcanic eruptions
have been described by volcanologists. Some
volcanoes may show only one type of eruption during
a period of activity, while others may show a range of
types in a series.
 The Earth's crust is made up of huge slabs called
plates, which fit together like a jigsaw puzzle. These
plates sometimes move. The friction causes
earthquakes and volcanic eruptions near the edges of
the plates. The theory that explains this process is
called plate tectonics.

4.  In geology, the crust is the outermost solid shell of
a rocky planet, dwarf planet, or natural satellite. It is
usually distinguished from the underlying mantle by
its chemical makeup; however, in the case of icy
satellites, it may be distinguished based on its phase
(solid crust vs. liquid mantle).
 Earth's crust is Earth's hard outer layer. It is less
than 1% of Earth's volume. The crust is made up of
different types of rocks: igneous, metamorphic,
and sedimentary rocks.

6.  The crust is of two different types. One is
the continental crust (under the land) and the other is
the oceanic crust (under the ocean). The continental
crust is thicker, and the oceanic crust is thinner. The
thickness of the crust varies from 5 to 80 kilometres.
 The temperature of the crust increases with depth
because of geothermal energy. Where the crust meets
the mantle the temperatures can be between 200 °C
(392 °F) to 400 °C (752 °F). The crust is the coldest
layer because it is exposed to the atmosphere.

7. CONTINENTAL PLATES OCEANIC PLATES
 They are made of older
rocks of more than 1500
yrs.
 They are composed of
granite, therefore light in
weight.
 The plates cannot sink in
the mantle and thus float.
 The continental plates are
permanent.
 They are made of younger
rocks of less than 200
million years.
 They are made of basalt,
therefore heavier in weight.
 The oceanic plates have a
tendency to sink in the
mantle.
 The oceanic plates are
temporary, as constantly
destroyed and replaced.

9.  A volcano is a rupture in the crust of a planetary-
mass object, such as Earth, that allows
hot lava, volcanic ash, and gases to escape from
a magma chamber below the surface. A volcano is a
mountain that opens downward to a pool of molten
rock below the surface of the earth. When pressure
builds up, eruptions occur. Gases and rock shoot up
through the opening and spill over or fill the air with
lava fragments.

10.  LAHAR: Lahar is a mixture of water and rock
fragments that flow down the sides of a volcano.
 TEPHRA: Pieces of volcanic rocks and lava that erupt
out of the vent of volcano in the form of an explosion.
 VOLCANIC GASES: Volcanic gases are the dissolved
gases in the magma composed of Sulphur dioxide,
Corbondioxide, hydrogen Fluoride, Water vapour,
hydrogen, carbonmonoixde, hydrogen sulphide.

11.  Volcanoes form when magma reaches the
Earth's surface, causing eruptions of lava and
ash. They occur at destructive (compressional)
and constructive (tensional) plate boundaries.
 The immediate effects of volcanic eruptions
can be devastating, but they may be beneficial
in the long term.

12.  A volcano is formed by eruptions of lava and
ash.
 Volcanoes are usually cone shaped mountains
or hills.
 When magma reaches the Earth's surface it is
called lava. When the lava cools, it forms rock.
 Some volcanoes happen underwater, along the
seabed or ocean floor.

13.  Magma rises through cracks or weaknesses in the
Earth's crust.
 Pressure builds up inside the Earth.
 When this pressure is released, eg as a result of plate
movement, magma explodes to the surface causing a
volcanic eruption.
 The lava from the eruption cools to form new crust.
 Over time, after several eruptions, the rock builds up
and a volcano forms.

16.  The magma chamber is a collection of magma inside
the Earth, below the volcano.
 The main vent is the main outlet for the magma to
escape.
 Secondary vents are smaller outlets through which
magma escapes.
 The crater is created after an eruption blows the top off
the volcano.
 An eruption occurs when pressure in the magma
chamber forces magma up the main vent, towards the
crater at the top of the volcano. Some magma will also
be forced out of the secondary vent at the side of the
volcano.

17.  Scientists have categorized volcanoes into three
main categories: active, dormant, and extinct.
1. An active volcano is one which has recently
erupted and there is a possibility that it may
erupt soon.
2. A dormant volcano is one which has not erupted
in a long time but there is a possibility it can
erupt in the future.
3. An extinct volcano is one which has erupted
thousands of years ago and there’s no possibility
of eruption.

18. Volcanoes are grouped into four types:
 Cinder cones
 Composite volcanoes
 Shield volcanoes and
 Lava volcanoes

19.  Cinder cones are circular or oval cones made
up of small fragments of lava from a single
vent that have been blown into the air, cooled
and fallen around the vent.

20.  Composite volcanoes are made up of alternating layers
of lava and ash (other volcanoes just consist of lava).
 They are usually found at destructive or compressional
boundaries.
 The eruptions from these volcanoes may be a
pyroclastic flow rather than a lava flow. A pyroclastic
flow is a mixture of hot steam, ash, rock and dust.
 A pyroclastic flow can roll down the sides of a volcano
at very high speeds and with temperatures of over
400°C.

21.  Composite volcanoes are steep-sided volcanoes
composed of many layers of volcanic rocks, usually
made from high-viscosity lava, ash and rock debris.

22.  A shield volcano is a type of volcano usually built
almost entirely of fluid lava flows. Shield volcanoes
are volcanoes shaped like a bowl or shield in the
middle with long gentle slopes made by basaltic lava
flows. Basalt lava flows from these volcanoes are
called flood basalts.

23.  Lava domes are formed when erupting lava is too thick to flow
and makes a steep-sided mound as the lava piles up near the
volcanic vent. The eruption of Mount St. Helens in 1980 was
caused in part by a lava dome shifting to allow explosive gas
and steam to escape from inside the mountain.

24. A supervolcano is a volcano on a massive scale. It
is different from a volcano because:
 it erupts at least 1,000 km3 of material (a large volcano
erupts around 1 km3)
 it forms a depression, called a caldera (a volcano forms
a cone shape)
 a supervolcano often has a ridge (chain of mountains)
of higher land around it
 a supervolcano erupts less frequently - eruptions are
hundreds of thousands of years apart

25. Stage 1:-
 Magma cannot escape to the surface and
collects under the lower crust.

26.  An 'uplifted bulge' begins to form under the lower
crust as the magma chamber enlarges.

27.  Cracks appear on the surface. Gas and ash erupt from
the magma chamber through these cracks.

28.  The magma chamber collapses and a depression is
formed. This is called a caldera.

29.  Yellowstone is one example of a supervolcano.
Yellowstone is one of the three huge eruptions have
happened in the last 3 million years, and was 1,000
times bigger than the Mount St Helens eruption in
1980.
 The large volume of material from the last Yellowstone
eruption caused the ground to collapse, creating a
depression called a caldera. The caldera is 55 km by 80
km wide.
 The supervolcano at Yellowstone is formed because of
a volcanic hotspot.

31.  Acid rains
 Corbondioxide emission
 Loss of life
 Loss of property
 The corbondioxide releases from the volcanic
emission is more than 130 million tonnes into the
atmosphere.

32.  Volcanic eruptions can have a devastating effect on
people and the environment.
 However, unlike earthquakes, volcanoes can also
have a positive impact on an area. These positive
impacts can help to explain why people choose to
live near volcanoes.

33. POSITIVE NEGATIVE
 The dramatic scenery
created by volcanic
eruptions attracts tourists.
This brings income to an
area.
 The lava and ash deposited
during an eruption breaks
down to provide valuable
nutrients for the soil. This
creates very fertile soil
which is good for
agriculture
 Many lives can be lost as
a result of a volcanic
eruption.
 If the ash and mud from a
volcanic eruption mix
with rain water or melting
snow, fast moving
mudflows are created.
These flows are called
lahars.

34. POSITIVE NEGATIVE
 The high level of heat
and activity inside the
Earth, close to a
volcano, can provide
opportunities for
generating geothermal
energy.
 Lava flows and lahars
can destroy settlements
and clear areas of
woodland or
agriculture.
 Human and natural
landscapes can be
destroyed and changed
forever.

35. There are more than 1500 active volcanoes on the
Earth. We currently know of 80 or more which are
under the oceans. Active volcanoes in INDIA are:
 Barren Island(Andaman Nicobar Islands)
 Deccan Traps (West Central India)
 Baratang(Andaman Nicobar Islands)
 Dhinodhar Hills (Gujarat)
 Dhosi Hill (Haryana)
 Tosham Hills (Aravalli mountain range near delhi).

36.  Pumice is a light, porous volcanic rock that forms
during explosive eruptions. It resembles a sponge
because it consists of a network of gas bubbles frozen
amidst fragile volcanic glass and minerals. All types
of magma will form pumice.

37.  The Pacific Ring of Fire is an area of frequent
earthquakes and volcanic eruptions encircling
the basin of the Pacific Ocean. The Ring of
Fire has 452 volcanoes and is home to over
50% of the world's active and dormant
volcanoes. Ninety percent of the world's
earthquakes and 81% of the world's largest
earthquakes occur along the Ring of Fire.

40.  The Earth's crust is broken up into pieces called plates.
Heat rising and falling inside the mantle
creates convection currents generated by radioactive
decay in the core.
 The convection currents move the plates. Where
convection currents diverge near the Earth's crust,
plates move apart. Where convection currents
converge, plates move towards each other. The
movement of the plates, and the activity inside the
Earth, is called plate tectonics.

41.  Plate tectonics cause earthquakes and volcanoes. The
point where two plates meet is called a plate
boundary. Earthquakes and volcanoes are most
likely to occur either on or near plate boundaries.
 The map shows the world's tectonic plates and the
distribution of earthquakes and volcanoes.

42.  At a tensional, constructive or divergent
boundary the plates move apart. At a compressional,
destructive or convergent boundary the plates move
towards each other.
 At a conservative or transform boundary the plates
slide past each other.

43.  At a tensional or constructive boundary, the plates are
moving apart. The plates move apart due to convection
currents inside the Earth.
 As the plates move apart (very slowly), magma rises
from the mantle. The magma erupts to the surface of
the Earth. This is also accompanied by earthquakes.
 When the magma reaches the surface, it cools and
solidifies to form a new crust of igneous rock. This
process is repeated many times, over a long period of
time.

44.  Eventually the new rock builds up to form a
volcano. Constructive boundaries tend to be found
under the sea, eg the Mid Atlantic Ridge. Here,
chains of underwater volcanoes have formed along
the plate boundary. One of these volcanoes may
become so large that it erupts out of the sea to form a
volcanic island, eg Surtsey and the Westman Islands
near Iceland.

45.  The diagram below to see how magma pushes up
between the two plates, causing a chain of volcanoes
along the constructive plate boundary.

46.  At a compressional or destructive boundary the plates
are moving towards each other. This usually involves
a continental plate and an oceanic plate.
 The oceanic plate is denser than the continental plate
so, as they move together, the oceanic plate is forced
underneath the continental plate. The point at which
this happens is called the sub-duction zone
 As the oceanic plate is forced below the continental
plate it melts to form magma and earthquakes are
triggered. The magma collects to form a magma
chamber.

47.  This magma then rises up through cracks in the
continental crust. As pressure builds up, a volcanic
eruption may occur.
 The diagram below shows how the oceanic plate is
pushed underneath the continental plate, causing
mountains and possibly volcanoes to form along the
destructive plate boundary.

48.  As the plates push together, the continental crust is
squashed together and forced upwards. This is called
folding. The process of folding creates fold mountains.
 Fold mountains can also be formed where two
continental plates push towards each other. This is how
mountain ranges such as the Himalayas and
the Alpswere formed.