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VOLCANOES
Types of Volcanoes &
Volcanic Landforms
TYPES OF VOLCANOES
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There are three
basic types of
volcanoes:
– Shield Volcano
– Cinder Cone
– Composite Cone
(Stratovolcano)
This diagram shows the
relative sizes of the three
types of volcanoes
Types of Volcanoes
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Shield Volcano
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Large broad domes
Mostly basaltic lava
Shallow slopes
Very little pyroclastics
Examples are Mona Loa &
Kilauea on Hawaii
– Mona Loa is over 4000m
above sea level & 9000m
total from sea floor to
summit
Top: With a Pahoehoe lava flow in
the foreground, Mona Loa is shown
towering in the background
Bottom: Active Kilauea crater is the
summit of shield volcano
Types of Volcanoes
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Cinder Cone
– Small individual peaks reaching
maximum height of 300 m
– Made up of ejected pyroclastics
– Steep, high angle slopes
– Very little lava erupted
– Examples are Sunset Crater (AZ),
Mt. Capulin (NM), & Mt. Paracutin
(Mexico)
– Cinder cones usually have a very
short life span & form in clusters
Top: Sunset
Crater, AZ
Right: The summit
of Mt. Capulin can
be reached by car
Left: Diagram
showing a typical
cinder cone
Types of Volcanoes
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Composite Volcano (Stratovolcano)
– Large symmetrical mountainous cones
– Made of alternating lava and pyroclastics
High angle slopes ~ 35°, can reach
heights of 3000 m
– Some examples are Mt. Fuji, Mt. St.
Helens, Mt. Pinatubo, Mt. Shasta, Mt.
Rainer, Mt. Vesuvius, & Mt. Etna
– These are the dangerous, explosive,
“Ring of Fire” volcanoes
Top: Pinatubo
explodes in 1991
Right: Mt. Shasta is
the most southern
volcano in the
Cascade range
Left: Mt. Rainer of
the Cascades looms
over nearby Seattle
Examples of U.S.
Composite Cones
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The entire Cascade Range in the
Pacific Northwest is made up of a
dozen active strato-volcanoes
These volcanoes are explosive
because of the type of magma
that erupts out of them
The subducting oceanic Juan de
Fuca plate has a high amount of
water dissolved in it
It melts and rises up through the
continental crust and becomes
more granitic (thicker, higher gas
content, more viscous, etc…)
That change gives the magma
the potential to be very explosive
Compare the three again
Cinder cones are the smallest and
are made of pyroclastic eruptions
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Shield volcanoes are the largest
and are made of lava flows
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Composite volcanoes are the most
dangerous and are made up of both
lava flows and pyroclastic eruptions
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Types of Volcanoes
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All volcanoes can be
characterized into one of
three groups:
– Active – the volcano has
erupted in recent times and is
expected to erupt again
– Dormant – the volcano has
erupted in historical times
and there is evidence that it
may erupt again
– Extinct – the volcano has not
erupted in historical times
and there is no evidence that
it will ever erupt again
All volcanoes have a life cycle, and
some will live much longer than
others depending upon the energy
contained within the magma
Once the magma source beneath the
cone has been completely depleted,
the volcano will be come extinct
Extra-Terrestrial Volcanism
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Earth is not the only planet in our solar system with
volcanoes
Both Mars and Venus have large extinct volcanoes
The Jovian moon IO, is the only other planetary body to
have active volcanism
Left: Olympus Mons
is the massive shield
volcano on Mars
which reaches a
height of 27km;
compare Mt. Everest
at a height of 8.8km
Right: IO is Jupiter’s
innermost moon
which has dozens of
active volcanoes
ejecting hot gases
into its atmosphere
Volcanic Destruction
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Nuee Ardente
This is the other name for a
pyroclastic flow
A cloud of superheated gas,
ash, and dust reaching speeds
of 200 km/hr
Races down mountain with
temps. exceeding 300°C
Large nuee ardentes may travel
up to 100 km or more and will
incinerate everything in its path
Top: A nuee ardente roars down the
slope of this Columbian volcano
Bottom: Click on the picture to see a
nuee ardente on an island arc volcano
More Death & Destruction
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Lahar
A large mudflow that
washes away and buries
anything in its wake
Triggered by an eruption
that melts the ice and
snow found the summit
of a volcano
Very dangerous and
quite unstoppable
Top: The awesome force of lahars is evident by
the burying of this car
Bottom: Click window to see video of a mini-lahar;
note the muddy consistency of the water
VOLCANIC LANDFORMS
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Caldera - a large crater (1 km
or more across) formed when
a volcano erupts, & collapses
in on itself
Examples are:
– Crater Lake, OR.
– Pinatubo Caldera
– Kilauea Caldera
Top: Diagram
depicts the
formation of
Crater Lake
Right: Arial photo
shows the 6 km
wide Caldera of
Crater Lake, OR
Left: The remnant
of Mt. Pinatubo
More Volcanic Landforms
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Volcanic Plug (neck)
When an extinct
volcano erodes and
leaves behind the
solidified magma
chamber
It is the ancient
crystallized core of a
volcano
Shiprock in NW New Mexico is a very
famous example of a volcanic plug
Notice the long ridge that extends from the
ancient heart; this is an igneous dike
More Volcanic Landforms
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Fissure Eruptions
When very low viscosity
lava pours from long
narrow cracks in the crust
it will form extensive rivers
and seas of lava
These are made from
basaltic, non-explosive
lavas, and can flow for 10s
– 100s of km
Examples of what we call
flood basalts can be found
in the Pacific NW
More Volcanic Landforms
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Pyroclastic Flow
Deposits – when a
nuee ardente
completes its fiery
destruction, the
fragments leave a
very distinct deposit
Top: a pyroclastic flow
deposit of large block and
bomb sized particles
Bottom: Note the bedding
planes from the fine ash
To Review:
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Volcanoes can come in three
varieties: shield volcano, cinder
cone, & composite volcano
Examples of Cinder cones:
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– Sunset Crater, Mt. Capulin, and
Mt. Paracutin
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Examples of Shield volcanoes:
– Mona Loa, Kilauea, and
Olympus Mons (Mars)
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Examples of Composite
volcanoes:
– Mt. St. Helens, Mt. Rainer, Mt.
Shasta, Mt. Vesuvius, Mt. Fuji,
Mt. Pinatubo, and Krakatau
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Volcanoes can be classified
as either active, dormant, or
extinct
Most death and destruction
from volcanic eruptions does
not come lava, but from
pyroclastic flows and lahars
Volcanic landforms take on
four basic types:
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Caldera craters
Volcanic plugs
Flood basalt deposits
Pyroclastic flow deposits