Volcanoes
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Learning objectives
What is a volcano?
Formation of volcanoes
Types of volcanoes
Types of volcanic eruptions
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What is a volcano?
A volcano is an opening or vent in the earth’s surface
through which molten material erupts and solidifies as lava.
Volcanic vent
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Label this cross section of a volcano
Magma
Magma chamber
Secondary cone
Crater
Main vent
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Cross section of a volcano
Crater – this is the Main Vent – the
depression at the top pipe up the middle
of the vent. of the volcano
Magma –
molten rock
underneath the
Earth’s crust
Secondary
Magma Cone – also
Chamber – known as
source of the parasitic
molten rocks cone.
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Volcanic emissions
Pyroclastic flow – hot
Volcanic Bombs – gases and steam that
airborne material flow from a volcano
from the volcano; it
can be a water, ash,
gas clouds, and
more. Lahars – mudflows
caused by the
combination of
volcanic materials and
Lava – molten
water
rock that flows
down the
volcano sides
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What is a volcanism?
Volcanism refers to any phenomenon of eruption of molten
lava onto the surface, whether from a tall volcano or simply
from magma that rises through a crack on a planet’s
lithosphere. Volcanism happens when underground molten
rocks called magma find a path through the lithosphere to
the surface.
Volcanic vent
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Learning objectives
What is a volcano?
Formation of volcanoes
Types of volcanoes
Types of volcanic eruptions
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Destructive Plate Boundary
A destructive plate boundary is found where a
continental plate meets an oceanic plate.
The oceanic plate descends under the continental plate
because it is denser. As the plate descends it starts to
melt due to the friction caused by the movement between
the plates. This melted plate is now hot, liquid rock
(magma). The magma rises through the gaps in the
continental plate. If it reaches the surface, the liquid rock
forms a volcano.
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Destructive Plate Boundary
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Destructive Plate Boundary
At destructive plate boundaries the lava is viscous (thick
like treacle) and it cannot flow very far from the volcano’s
vent. This makes the volcano steep sided.
Mayon Volcano
(Albay)
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Constructive Plate Boundary
At a constructive plate boundary, two plates move apart.
As the two plates move apart, magma rises up to fill the
gap. This causes volcanoes. However, since the magma
can escape easily at the surface, the volcano does not
erupt with much force.
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Constructive Plate Boundary
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Constructive Plate Boundary
At constructive plate boundaries the
lava is runny and it can flow far away
from the volcano’s vent. This makes the
volcano gentle sided.
Mauna Loa
(Hawaii)
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Hot Spots
A volcanic "hotspot" is an area in the mantle from which heat
rises as a thermal plume from deep in the Earth. High heat and
lower pressure at the base of the lithosphere (tectonic plate)
facilitates the melting of the rock. This melt, called magma, rises
through cracks and erupts to form volcanoes. As the tectonic
plate moves over the stationary hot spot, the volcanoes are
rafted away and new ones form in their place.
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Hot Spots
This results in chains of volcanoes, such as the Hawaiian
Islands.
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Learning objectives
What is a volcano?
Formation of volcanoes
Types of volcanoes
Types of volcanic eruptions
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Volcano Shapes
Composite Volcanoes – produced when
viscous lava of andesitic composition flows out for a
long time. This builds a steep-sided mound of
cinders. The mound is built of alternating layers of
lava and pyroclastic materials. They occur in
destructive plate boundaries. Mayon Volcano
Cinder Cones – built from ejected lava fragments.
They are small, usually, less than 300 m high, and
are formed near or inside large volcanoes. They
frequently occur in groups. Taal Volcano
Extinct volcano – formed by less viscous
basaltic lava flows. Since lava composed of basalt is
free to flow, the volcanoes formed have a very wide
base. They are also slightly domes. They occur in
constructive plate boundaries. Mauna Loa
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Do all volcanoes erupt?
Active volcano – liable to erupt. Example: Mt. Mayon
(Albay), Eruptions were recorded from 1616 to 2013.
Permanently monitored. The most recent major volcanic
activity occurred in 2020 (ongoing).
Dormant (sleeping) volcano – a volcano which
has not erupted for many years. For example, Mt
Pinatubo erupted in 1991 after 500 years of dormancy.
Extinct volcano – a volcano which has not
erupted for many thousands or millions of years
e.g. Edinburgh.
However, it is often very difficult to tell whether a volcano will erupt
again…El Chichon, Mexico erupted in 1982 after being dormant for
approximately 1200 years!
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Learning objectives
What is a volcano?
Formation of volcanoes
Types of volcanoes
Types of volcanic eruptions
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Phreatic
It occurs when magma heat groundwater or surface water. The
extreme temperature of the magma causes near-instantaneous
evaporation of water to steam, resulting in an explosion of steam,
water, ash, rock, and volcanic bombs. It typically includes steam and
rock fragments; the inclusion of liquid lava is unusual.
Phreatic eruption of Taal (January 12, 2020)
https://upload.wikimedia.org/wikipedia/commons/e/ef/Phreatic_eruption_of_Taal_Volcano%2C_12_
January_2020_%28reduced%29.gif
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Vulcanian
An eruption resulting from the release of large quantities of
accumulated magmatic gas which lifts fine ash with great force high
into the air forming voluminous cauliflower clouds
https://tenor.com/view/volcano-
eruption-erupting-gif-8869210
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Strombolian
A weak to violent eruption characterized by lava fountains and
outburst of molten lava. Typical materials ejected are egg-shaped.
Ash is relatively minor in amount and the eruption cloud is generally
yellowish to white
https://media3.giphy.com/media/TD
mjb6HBDbSVy/giphy.gif
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Pelean
It is associated with explosive outbursts
that generate pyroclastic flows, dense
mixtures of hot volcanic fragments, and
gas described as a section of lava, gas,
and other hazards. The fluidized slurries
produced by these eruptions are heavier
than air but are of low viscosity and pour
down valleys and slopes at great
velocities. As a result, they are extremely
destructive
https://i.pinimg.com/originals/9f/f1/d6/9ff1d
656c55ac89b7c59f3737eeb0367.gif
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Phreatomagmatic
An eruption resulting from the interaction of new magma or lava with
water and can be very explosive. The eruptions from a high eruption
column with a radially spreading ring-shaped horizontal cloud at the
base due to the peeling of the crater lip or deflection in the rise of
later ejections caused by the pressure of falling pyroclastic materials
https://i.pinimg.com/originals/a0/7d/0a/a07d0abc47fdb35d01c
b66bb64dd9007.jpg
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Plinian
A violent explosion characterized by
voluminous ejections of pumice and by
ash flows. The extrusion of gas-rich
siliceous magma is commonly
accompanied by the collapse of the top
of the volcanic cone forming a caldera,
or by the collapse of a broader region,
forming a volcano-tectonic depression
https://media2.giphy.com/media/1
0gNBUWwKk44LK/giphy.gif
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Taal Volcano Eruption (2020)
BEFORE DURING AFTER
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What damage did the eruption cause?
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Why do people live in volcanic areas?
This lava is
weathered (broken
down) to form a fertile
soil,
Can you think of any other reasons?
Tourists are attracted to Geothermal energy
areas of volcanic activity. (heat from the earth)
can be produced in
many volcanic areas.
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