VOLCANOES
By Caleb Pothier and Bonita Sanford

VOLCANOES

~An opening in the earth's crust through
which molten lava, ash, and gases are
ejected.
~A similar opening on the surface of another
planet.
~A mountain formed by the materials ejected
from a volcano.
What is A Volcano?
http://dictionary.reference.com/search?q=volcano

What is a volcano?
• A volcano
connects molten
rock (magma)
from within the
Earth’s crust to
the Earth's
surface.
• The volcano
includes the
surrounding cone
of erupted
material.
vent
cone
magma
chamber
conduit

The types Of Volcanoes
~ Shield Volcano
~ Cinder Cone Volcano
~ Composite Volcano
~ Caldera Volcano
~ Fissure Volcano

TYPES OF ERUPTIONS
ERUPTIONS FALL INTO 2 CATEGORIES
Violent(explosive) eruptions
destroy the volcano
Non-Violent (calm or quiet)
eruptions build up the
volcano

Shield volcanoes can span across hundreds of miles.
Shield volcanoes have a gentle slope and consist of
frozen lava after it is hardened. Shield volcanoes
almost always have large craters at their summit.
Gentle slopes = non-violent eruptions
Hot spots!
http://www.cotf.edu/ete/modules/volcanoes/vtypesvolcan1.html

Cinder cone volcanoes consist of mostly loose,
grainy cinders and have very little to no lava.
Cinder cone volcanoes are normally small about a
miles span and about one thousand feet vertically.
Cinder cone volcanoes have fairly steep slopes and
normally have a small crater at the top.
Steep slopes = explosive or violent eruptions
http://www.cotf.edu/ete/modules/volcanoes/vtypesvolcan1.html

Composite volcanoes have another name called
“Strato Volcanoes.” Composite volcanoes consist of
lava that is mixed with sand or gravel which in turn
creates cinders or volcanic ash.
Steep slopes = explosive or violent eruptions
http://www.cotf.edu/ete/modules/volcanoes/vtypesvolcan1.html

Caldera volcanoes are circular depressions in the
ground over a magma chamber. Sometimes the
depression in Caldera volcanoes are covered in
with lava and volcanic ash making it hard to
recognize. This type of volcano is easier noticed
from space due to the distance and view point.
When this volcano erupts it can spew volcanic
rocks for miles and miles.
http://www.cotf.edu/ete/modules/volcanoes/vtypesvolcan1.html

Fissure volcanoes are also hard to recognize from
the ground and sometimes from space. Fissure
volcanoes have no main crater, the ground just
splits and lava pours out through the cracks. After
a fissure volcano erupts and has cooled because it’s
a solid it will look mainly like the plains.
http://www.cotf.edu/ete/modules/volcanoes/vtypesvolcan1.html

Types Of Magma
Granite magma consist of light-colored rock and is
not as heavy as basalt magma. Granite magma is
very sticky and flows rather slowly.
Basalt magma consist of dark-colored rocks and is
much heavier then granite magma. It flows more
fluidly then molten granite.

Volcano Environments
~In an island-arc environment, volcanoes lie
along the crest of an arcuate.
~In an oceanic environment, volcanoes are
aligned along the crest of a broad ridge that
marks an active fracture system in the
oceanic crust.
~In the continental environment, volcanoes
are located unstable, mountainous belts that
have thick roots of granite or granite like
rock.

Where are volcanoes likely to
occur?
Volcanoes occur in weak spots in the earth’s crust
There are many volcanoes along the Pacific Ocean.
Many islands in the Pacific Ocean are actually
volcanoes. They form a ring around the ocean
which is called the “Pacific Belt of Fire.”
Although there are some other “belts of fire”, the
“Pacific Belt of Fire” is the biggest.
There are approximately five hundred active
volcanoes, that are known, lying in these belts.

Volcanoes In Other Places
Volcanoes aren’t just a thing from earth they also
happen on other planets as seen in this picture. But
while on other planets there is no destruction as we
have seen from volcanoes on earth.
Mariner 9 imagery of
Olympus Mons volcano
on Mars

VOLCANO FORMATION:
HOT SPOTS
 A fixed source of
magma rising beneath
a plate forming
volcanic islands
 Magma can be
basaltic or granitic –
so eruptions can be
explosive or “quiet”

When and how do eruptions occur?
Steam and gases from magma in the earth create
bubbles that expand and burst when the pressure
above them is lessened. These bubbles usually burst
with a tremendous force that along with escaping
gas comes magma too. In some cases, it takes years
for the magma to break through the surface of the
earth.

Why do eruptions occur?
Eruptions occur when underground pressure is
released when blocks of the earth’s crust shift.
For example, earthquakes.

Direct
measurements of
pyroclastic flows
are extremely
dangerous!!!

Effusive Eruptions
• Effusive eruptions are
characterised by outpourings
of lava on to the ground.
Hawaii
Courtesy of www.swisseduc.ch

Damages
The most devastating destruction from volcanoes
is the tremendous loss of life. Following an
eruption in 1815, there were 56 000 people killed by
a tidal wave from a eruption. Lava from the
volcano is hot enough to catch everything in its path
on fire, even the ash from a volcano is hot enough
to start fires. Lahar can wash away houses and
uproot trees. Magma can give off poisonous gases
such as carbon monoxide. Damages from
volcanoes are very expensive to repair or replace.

No
Yes (Cinder
Cone)
No
Yes (Shield)
No (These are
the Catskills)
No
Yes
(Composite)
No
Which of these are volcanoes?