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Volcanoes
The cause of it all…
• What do you think causes volcanoes to
erupt?
• The shift in the Earth’s plates are what
causes volcanoes to form and erupt.
• As the plates join or separate some of the
molten rock is exposed.
Volcanoes of the World
Structure of a Volcano
• Magma – the molten, or liquid-like, rock
within the
Earth
• Lava – magma that reaches Earth’s surface and is exposed
to O2 (two types of lava are Pahoehoe and Aa)
• Viscosity~ •(thickness), resistance of a liquid to flow.
Low viscosity = water high viscosity = maple syrup
• Vent – an opening through which molten (liquid-like) rock
flows onto Earth’s surface. Volcanoes will have many side
vents through which lava will flow out of!
• Crater- the central opening at the top or summit of volcano.
• Volcanoes always have one central vent, but can also have
several smaller side vents.
Structure of a Volcano
ash cloud
lava
central
vent
side vent
old layers
of lava
magma
Earth’s crust
Types of Volcanoes
There are three major types of volcanoes:
Shield volcanoes
Composite volcanoes
Cinder cone volcanoes
But there is also a fourth major volcano
Lava domes
Shield Volcanoes
• The flowing lava gives the volcano gently
sloping sides.
• They have mild Eruptions that can occur
several times.
• The lava tends to flow great distances.
• The magma rich in iron (Fe) and
magnesium (Mg) and is very fluid (low
viscosity).
Shield Volcanoes
• Mauna Loa and Kilauea in Hawaii are
examples of a shield volcanoes.
Composite Volcanoes
• They have much steeper slopes than shield
volcanoes.
• They have alternating layers of lava and
cinders.
• Eruptions can be flowing lava or explosions.
Explosive eruptions come from the trapped
gases and produce cinders and ash.
Composite Volcanoes
• The magma is rich in silica (Si) and much
thicker than magma from a shield volcano.
• Gases get trapped inside this thicker magma.
• Mount Fuji in Japan and Mount St. Helens in
Washington State in the US are examples of
composite volcanoes.
Mt. Fuji (Composite Volcano)
• Stands over 13,000 ft.
tall
• Surrounded by 5 lakes
• Last erupted in 1707-08.
Mount St. Helen’s
Composite Volcano
Mount St. Helen’s
before and after eruption
1979
1980
Cinder Cone Volcanoes
• Cinder Cones have very steep sides!
• Usually only active for a short time and then
become dormant (inactive).
• ***Most Dangerous type of Volcano!***
• Violent and explosive eruptions because of all
the gas trapped in the magma.
Cinder Cone Volcanoes
• The magma inside a cinder cone volcano
has large amounts of silica (Si) (63%)
and gas trapped in it.
• 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.
• Paricutin in Mexico and Mount Vesuvius
in Italy are examples of a cinder cone
volcanoes.
Paricutin Volcano (Cinder Cone)
• Grew over 5 stories
in the first week
• Continued to erupt
for 8 years reaching
a height of over
1,300 ft.
Volcanic Dangers
•
•
•
•
•
Pyroclastic flows
Lahars
Lava
Volcanic ash
Volcanic gas
Which volcanic
danger kills most
people? Volcanic Ash
Pyroclastic flows
• Pyroclastic flows mixtures
of hot gases, ash and rocks
that travel about 450mi/hr
down the sides of
volcanoes.
• Dangerous because…
• The poisonous gases can be
as hot as 1,000 degrees.
• They destroy anything in
its path!
• They are rare and don’t
happen in every eruption!
Lahars
• Lahars are mudflows
formed by the mixing
of volcanic particles
and water.
• Dangerous because…
• Carry large boulders
and logs down the side
of a volcanoes.
• Can easily crush or
shear off anything in
its path!
Damage caused from
Lahars
Types of Lava
• Pahoehoe lava is
runny and fast
moving (up to 50
km/h).
• Has high iron
content.
Pahoehoe Lava
Types of Lava
• Aa flows are
chunky and
slow moving
lava flows
• Has a high
silica content
Aa Lava
Lava Composition
Which element is
found most in lava?
Silicon!
• Lava is about 50% Silicon.
• Silicon makes lava thick
(high viscosity).
• The more silicon you have
in lava the more explosive
the eruptions will be in a
volcano.
• What is building up?
• Gas and pressure build up
under the thick magma.
Then Dangers of Lava!
Lava at Night!
Technology in Science
• Using infrared, scientists
were able to identify
specific warning signs before
the eruption of the nearby
Bezymianny volcano (Russia)
in December 2006.
• Flowing lava shows up as
bright yellow in an infrared
image (top) of Russia's
Klyuchevskoy volcano.
Volcanic ash
• Volcanic ash- small sharp
glass-particles that
damage anything they
come across.
• Volcanic ash exploded
from a vent in fragments
less than 2mm in size.
• Dangerous because…
• Can cause houses and
buildings to collapse.
• People and animals may
die from lack of oxygen.
• *kills most people
Volcanic gas
• Volcanic gas is gases
contained within magma.
• * Water Vapor is the gas
that is released the most
• Other gases include
carbon dioxide (CO2),
*sulfur dioxide (SO2), and
hydrogen sulfide (H2S).
• Dangerous because…
• These gases can kill
people and animals and
cause acid rain and
contribute to greenhouse
effects.
Volcanoes are the largest natural polluters!
Global Impact
• When a volcano erupts it
throws out a lot of
ash. At short notice this
ash can be very harmful
to the environment by
killing plants and animals.
• However, over a long
period of time, the ash
layer contains many
useful minerals, that
are converted into
fertile soil.
• Volcanoes provide
resources for energy
extraction, also called
geothermal energy.
• Heat from the earth's
crust is being converted
to energy. Advantages to
geothermal energy are
that it is very clean and
the resources are nearly
inexhaustible.
Positives and Negatives of
Volcanoes
Positives
• Lava flows create
extremely fertile soil for
crops and plants.
• Creates new beautiful land
(over long periods of time)•
• Emits water vapor into
atmosphere
• Create Geothermal energy
• Help us understand past
civilizations (Pompeii) and
cultures and even the
Earth itself!
Negatives
• Getting caught in volcanic
dangers (blasts, lava flows,
pyroclastic flows, lahars, and
ash clouds) is deadly.
Destroys anything in their path.
• Puts out large amounts of
carbon dioxide (greenhouse gas)
and sulfur dioxide.
• SO2 is a cooling gas that can
drop global temperatures after
a large eruption.
• SO2 also causes acid rain