What are the three
types of volcanoes and
what type of
eruptions does each
volcano have?
What do you know
about volcanoes?
And…
Do you know of any
famous volcanoes?
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.
Where do volcanoes erupt?
There are three places…
• Convergent plate boundaries – where two of
Earth’s plates join together
• Divergent plate boundaries – where two of
Earth’s plates move apart RING OF FIRE!!
• Hot spots – active areas below the earths
crust
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
• 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
Stages of a Volcano
• Magma chamber- the chamber below the volcano that
stores the magma.
• Without a magma chamber attached to the volcano it
will be come extinct. With it, it is still considered
active.
• If the volcano is still attached to its magma chamber
but hasn’t erupted recently (100 years) it is
considered to be dormant. It can still erupt at
anytime!!
Types of Volcanoes
There are three major types of volcanoes:
Shield volcanoes
Composite volcanoes
Cinder cone volcanoes
But there is also a fourth major volcanoe
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 and magnesium
and is very fluid (low viscosity).
Shield Volcanoes
• They have mild Eruptions that can occur
several times.
• Mauna Loa and Kilaeua in Hawaii are
examples of a shield volcanoes.
Mauna Loa (Shield Volcano)
Kilauea Caldera
Kilauea Crater
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 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
Thermal Imaging
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).
• The magma inside a cinder cone volcano has large
amounts of silica (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.
Cinder Cone Volcanoes
• Violent and explosive eruptions because
of all the gas trapped in the magma.
• 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.
Mount Vesuvius
What do you notice in this picture?
Mount Vesuvius
Thermal Imaging
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!
Pyroclastic Flows can even
travel across water!
Ash and
Pumice
distribution
People of Pompeii
Animals of Pompeii
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
Lava
• Lava is molten rock expelled by a volcano
during an eruption.
• Lava is a liquid at temperatures ranging
from 1,300 °F to 2,200 °F.
• Although lava is about 100,000 times the
viscosity of water, it can flow great
distances before cooling and solidifying.
• Dangerous because…
• Lava can kill people, animals, and destroy
property and even bury entire towns!
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 Lava
• Aa flows are
chunky and
slow moving
lava flows
• Has a high
silica content
Kona Lava Fields
Lava Tubes
Thurston’s Lava Tube