Geography 12
Plate Tectonics
Ms. Inden
Take a look at this picture of the Ring of Fire!
The area that we are discussing is the darker
peachy-pink area that surrounds the Pacific
Ocean.
The Ring of
Fire is where a
lot of volcanoes
and
earthquakes
occur. WHY
HERE??
The Structure of the Earth
The earth’s crust
• The outer crust of
the Earth is a thin
layer, like the shell
of an egg.
• Continental crust is
called SIAL
• Under it, and also
the ocean floor is
called SIMA
Sima – See
many fish
Sial – See
alpine
meadows
Plate Tectonics
• The crust is broken into pieces, or
plates
• At the edges of these plates, you will
find most of the world’s volcanoes and
earthquakes
• The reason is that these plates are
MOVING! (more on that in a few slides)
This is a
map of the
Earth – Can
you see it?
You are
here!
Atlantic Ocean
Pacific Ocean
Africa
Remember that the earth
is made up of broken
plates of crust?
Edges of the plates are in
yellow, Earthquakes of the last
100 years are in red
The area surrounding the Pacific Ocean is known as the
Ring of Fire, because of the volcanoes that occur around
its edges – mainly because of the type of plate boundary –
subduction – we’ll learn more about that.
Ring of
Fire
Here it is again, without the
plates
Volcanoes also happen over hotspots – not just
where plates come together .
These places are called hot spots – like Hawaii
and the Galapagos Islands.
RED DOTS ARE HOT SPOTS
Here are the Earth’s Plates on a
map of the world
What plates are next to the British Columbia and the rest of
North America (i.e., next to California and the San Andreas Fault?)
Remember that these plates are
moving? How?
• Idea: Convection Currents:
Cooled material
sinks back down,
heats and rises
again.
So, these currents of rising and
then sinking molten rock
(moving very slowly) acts like
conveyor belts that move the
plates around – this is the
theory of plate tectonics
Because the plates move, they
create mountains, trenches,
volcanoes, earthquakes
Here, one plate dives under the
other, which creates fold
mountains and volcanoes like Mt.
St. Helen’s, Mt. Baker, Mt.
Bachelor – a row, or arc of
volcanoes.
Here, plates slide past
each other, creating the
San Andreas Fault.
Here are pictures showing the North American
land forms we just looked at:
San Andreas
Transform Fault
Mt. Bachelor
Mt. St. Helen’s
Mt. Hood
These faults, occurring at plate
boundaries, or cracks in the
earth, come in three different
types:
• Diverge means to pull apart
• Converge – means to come together
• Transform faults slide past each other
3 types of faults
• Diverge means
• Converge means
• Transform –
When plates pull apart this creates a
ridge – because magma wells up
• One major diverging
plate is the midAtlantic Ridge
• Mid means middle,
and the Atlantic is
the ocean, right?
• So, this mountain
ridge is in the middle
of the Atlantic
Mid-Atlantic Ridge –another look
Can you see the plates that
create the Mid-Atlantic Ridge?
Transform Faults – plates or
faults sliding past each other
• The big one is the
San Andreas Fault in
California
Two types of land forms occur when
plates converge: 1. Subduction Zone
•
Remember that converge means to come
together
• Called subduction:–
where an ocean plate
dives under a
continental plate
• Creates a trench –
like along the Andes
Mountains, and helps
build the mountains
• See how it creates volcanoes
there – like Mt. St. Helens,
Mt. Bachelor, Mt. Baker, Mt.
Hood
Two types of land forms occur when
plates converge: 2. Fold Mountains
•
Remember that converge means to come
together
• Sometimes this
creates mountains –
like the Rockies, and
the Himalayas
This is how BC was formed
and we live on a high
plateau ourselves
Here is another look at the 3
types
Terms for Volcanoes
• Molten or melted
rock that is below
the surface is called
magma
• Molten or melted
rock at the earth’s
surface is called lava
• Volcanic ash also
comes out of the
volcano
When Mt. St. Helens erupted in
1980, ash and light rock was blown
north and west as far as the
Manitoba/Ontario border
What is an earthquake?
• Earthquakes happen when the earth
(rock masses) moves suddenly along a
crack or fault in the earth’s crust
• Faults - cracks or breaks in the earth’s
surface
• The movements of the earth can be up
and down, and side to side
• Take a look for the fault – the broken line of
earth
• An earthquake occurs at the focus,
underground
• The epicenter of the earthquake is right
above it at the surface