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Volcanoes
Geography 12
Ms. Inden
Volcanology; volcanologist
The study of the ways solid, liquid or
gaseous materials are forced into the
earth's crust or ejected onto the
surface; a person who does this
studying
A few terms
• Molten – melted
• Magma – molten
rock when it is
still underground
• Lava – magma
that has reached
the surface
http://www1.moe.edu.sg/learn@/Quest/winners/primary/yu_neng_pri_volcano_nc/qpixa.jpg
Where does magma come
from?
• Radioactive
decay or
uranium and
thorium
• Friction
created by the
movement of
plates
• The magma
develops in a
magma
chamber
below the
earth
http://www.georesources.co.uk/volgen.htm
Ka-boom!
• The rock expands as the temperature
rises, and also gas is produced
• This causes pressure underground
• The magma will erupt (now lava), along
with gasses, steam, ash, volcanic bombs
and rock fragments
• The eruption, and the violence involved
depends on the sort of volcano the type of
rock involved (more on this later)
Animation of a strata volcano
• http://www.pbs.org/wnet/savageearth/
animations/volcanoes/index.html
Extrusive
• When lava or
other materials
reach the surface
they are called
extrusive
• Form extrusive
igneous rock
when cooled
Intrusive
• When magma is
injected into the crust
(never reaching the
surface), it is called
intrusive
• Form intrusive
igneous rock when
cooled
• Sometimes exposed
through erosion
You need to know batholith,
laccolith, sill and dike
Which
landforms on
this image are
intrusive, and
which are
extrusive?
What would
cause a
batholith to be
exposed?
http://www.indiana.edu/~geol105/images/gaia_chapter_5/dike&sill.jpg
Intrusive landforms
• Most magma is intruded
• Intrusive igneous rock has bigger crystals than
lava which is cooled quickly at the surface
• Batholith – at least 100 km, magma cools slowly
• Sill – horizontal intrusion
• Dikes – cuts through bedding planes vertically
• Laccolith – smaller than batholith - fills up a
chamber or cavern
• This volcanic
flow probably ran
into a glacier, or
possibly a cliff –
this part of the
lava cooled
quicker, creating
these columns
• Look for columns
like this on the
highway toward
Vancouver –
south of Quesnel
• Giant’s
Causeway
in
Northern
Ireland
http://www.geolsoc.org.uk/webdav/site/GSL/shared/images/geoscientist/GiantsCausewayrersized.jpg