The Theory of Plate Tectonics Tectonic comes from the Greek word tekton which means building. The actions of the plates are responsible for building the structures of the earth’s surface as we know it. Structures like mountains, volcanoes, and deep ocean trenches. * Now let’s look at the boundaries between the plates (the purple lines) more closely. * There are 3 kinds of plate boundaries. 1. Divergent – where plates are moving apart 2. Convergent- where plates are moving together 3. Transform – where plates are sliding past one another Divergent Boundaries Where ocean floor is ripping apart 2. Where continents are ripping apart Where ocean floor is ripping apart These pictures show you how a mid-ocean ridge forms. A mid ocean ridge is the boundary between 2 oceanic plates. * Mid-ocean ridge - a continuous mountain ridge on the floor of the ocean that is the boundary of two diverging oceanic plates. This is the Mid-Atlantic Ridge in the middle of the picture. It is a mid oceanic ridge in the middle of the Atlantic. * * The Mid Atlantic Ridge is just one of a series of mid ocean ridges, seen in red. Some sort of convective activity in the mantle is causing the two plates to separate. * Sea Floor Spreading - the process of producing new sea floor between 2 diverging oceanic plates Look at where Iceland is. (I circled it.) It is part of the Mid Atlantic Ridge; the part where the ridge is above sea level. * * The Mid Atlantic Ridge goes right through Iceland. Now look for Thingvellir National Park (just above Reykjavik). This is a map of Thingvellir National Park. The yellow on the left is the North American Plate going in the direction of the arrow I put there. The yellow on the right is the Eurasian Plate, going in the direction of the arrow I wrote there. The green represents the valley between the 2 plates. * These people are standing on the North American plate looking at the valley between the 2 plates. * This is a picture of the valley taken from the North American plate. The mountains in the back are the Eurasian plate. The valley has gotten about 240 feet wider over the last 10,000 years. * More valley * Where continents are ripped apart ? Which continent is being ripped apart? * Africa! The “crack” where it is being ripped apart is called The Great Rift Valley. * Rift valley - a region of the earth’s crust where divergence of a continent is taking place The first two pictures here show you how a rift valley forms. * Here it is from space. * Convective activity from the mantle causes the two plates to go in opposite direction. * This and the next 2 pictures are of the Great Rift Valley, which can be anywhere from 18-60 miles wide. * An earthquake in remote and desolate Boina, Ethiopia, about 270 miles northeast of the capital, Addis Ababa, split o.

1. The Theory of Plate Tectonics
Tectonic comes from the Greek word tekton which means
building. The actions of the plates are responsible for building
the structures of the earth’s surface as we know it. Structures
like mountains, volcanoes, and deep ocean trenches.
*
Now let’s look at the boundaries between the plates (the purple
lines) more closely.
*
There are 3 kinds of plate
boundaries.
1. Divergent – where plates are moving apart
2. Convergent- where plates are moving
together
3. Transform – where plates are sliding past
one another
Divergent Boundaries
Where ocean floor is ripping apart

2. 2. Where continents are ripping apart
Where ocean floor is ripping apart
These pictures show you how a mid-ocean ridge forms. A mid
ocean ridge is the boundary between 2 oceanic plates.
*
Mid-ocean ridge - a continuous
mountain ridge on the floor
of the ocean that is the
boundary of two diverging
oceanic plates.
This is the Mid-Atlantic Ridge in the middle of the picture. It
is a mid oceanic ridge in the middle of the Atlantic.
*
*
The Mid Atlantic Ridge is just one of a series of mid ocean
ridges, seen in red.

3. Some sort of convective activity in the mantle is causing the
two plates to separate.
*
Sea Floor Spreading - the
process of producing new
sea floor between 2
diverging oceanic plates
Look at where Iceland is. (I circled it.) It is part of the Mid
Atlantic Ridge; the part where the ridge is above sea level.
*
*
The Mid Atlantic Ridge goes right through Iceland. Now look
for Thingvellir National Park (just above Reykjavik).
This is a map of Thingvellir National Park. The yellow on the
left is the North American Plate going in the direction of the
arrow I put there. The yellow on the right is the Eurasian Plate,
going in the direction of the arrow I wrote there. The green
represents the valley between the 2 plates.
*

4. These people are standing on the North American plate looking
at the valley between the 2 plates.
*
This is a picture of the valley taken from the North American
plate. The mountains in the back are the Eurasian plate. The
valley has gotten about 240 feet wider over the last 10,000
years.
*
More valley
*
Where continents are ripped apart
?
Which continent is being ripped apart?
*

5. Africa! The “crack” where it is being ripped apart is called
The Great Rift Valley.
*
Rift valley - a region of
the earth’s crust where
divergence of a continent
is taking place
The first two pictures here show you how a rift valley forms.
*
Here it is from space.
*
Convective activity from the mantle causes the two plates to go
in opposite direction.
*
This and the next 2 pictures are of the Great Rift Valley, which

6. can be anywhere from 18-60 miles wide.
*
An earthquake in remote and desolate Boina, Ethiopia, about
270 miles northeast of the capital, Addis Ababa, split open a
crack in the Earth 37 miles long, according to an Associated
Press report. Over the next three weeks, the fissure in Boina
widened to a gap of 134 feet, and it continues to spread
today….”
It is believed that this is the latest development in the East
African Rift doing its thing.
*
A close up of the last slide
*
.
The blue dot is where that crack developed.
*

7. *
The map to the right shows how the Red Sea shore-lines may
have looked during the early phase of the Africa-Arabia Rift
Valley breakup.
Convergent BoundariesWhere continents collide with continents
Where continents collide with ocean floor
Where ocean floor collides with ocean floor
Where continents collide with continents
*
Notice where India is. I colored it red.
*
Over tens of millions of years, India would migrate northward

8. and collide with the Eurasian Plate. The land scrunched and
this formed the Himalayas. Collide is present tense because it
is still happenning. In fact, the Himalayas are getting an inch or
two taller every year. (see the next 3 slides)
*
Here are the Himalayas from space.
*
The Himalayas.
*
*
The Alps arose as a result of the pressure exerted on sediments
of the Tethys Ocean basin as its Mesozoic and early
Cenozoicstrata were pushed against the stable Eurasian
landmass by the northward-moving African landmass.
As Africa pushed northward, it scrunched the area in red. This
“scrunching” created the Alps in lower Eupore.

9. The Alps
*
Where continents and
ocean floor collide
Subduct - to go under
Subduction zone - where
one plate goes underneath
another
Look for the Juan de Fuca Plate. Notice it an oceanic plate
subducting under NW USA.
*
The Juan de Fuca Plate
is subducting the
Northwest USA.

10. Notice it an oceanic plate subducting under NW USA.
*
The ocean floor is made of basalt. The continents are made of
granite. Basalt is more dense than the granite. For this reason,
when the two collide, the ocean floor subducts the continent.
*
As it grinds past the continent, the heat and friction cause the
subducted ocean floor to liquify. The liquid blobs migrate
upward and form volcanoes, like Mt. St. Helens.
*
This is why the NW USA is littered with volcanoes.
*
Mt St Helens has easily been the most active over the last 4000
years.
*
When ocean floor collides

11. with ocean floor.
When 2 ocean plates collide, one will subduct the other. The
grinding motion will create a series of volcanoes in the ocean
called an island arc.
*
Aleutian Islands
The Aleutian Islands are an example of an island arc.
*
The Aleutians are at the SW tip of Alaska.
*
Look where they are from this perspective. Here the Pacific
Plate is subducting the North American Plate.
*
Island arc - a chain of
volcanoes formed when
one oceanic plate
subducts another oceanic

12. plate
Look at the yellow v I drew. This is a trench. Anytime one plate
of any kind subducts another, a trench will form.
*
Probably the most famous trench is the Mariana Trench. It is the
deepest trench in the world.
*
*
It is where the yellow Pacific Plate is subducting the pink
Phillippine plate.
It is about 7 miles deep at its deepest point, called the
Challenger Deep.
*
Transform Boundaries
Where plates slide past one another
*

13. Notice how North America is up against the Pacific Plate.
*
Actually part of North America (shown in green) is ON the
Pacific Plate.
*
Part of California is going in NE direction and the rest in
moving in a SE direction. The line that divides the two is
called the San Andreas Fault.
*
The San Andreas Fault can actually be seen if you fly over it.
*
That part of CA will break off someday and collide with
Alaska!

14. *
Tectonic comes from the Greek word tekton which means
building. The actions of the plates are responsible for building
the structures of the earth’s surface as we know it. Structures
like mountains, volcanoes, and deep ocean trenches.
*
Now let’s look at the boundaries between the plates (the purple
lines) more closely.
*
These pictures show you how a mid-ocean ridge forms. A mid
ocean ridge is the boundary between 2 oceanic plates.
*
This is the Mid-Atlantic Ridge in the middle of the picture. It
is a mid oceanic ridge in the middle of the Atlantic.
*
*
The Mid Atlantic Ridge is just one of a series of mid ocean
ridges, seen in red.
Some sort of convective activity in the mantle is causing the
two plates to separate.
*
Look at where Iceland is. (I circled it.) It is part of the Mid
Atlantic Ridge; the part where the ridge is above sea level.
*
*
The Mid Atlantic Ridge goes right through Iceland. Now look
for Thingvellir National Park (just above Reykjavik).
This is a map of Thingvellir National Park. The yellow on the
left is the North American Plate going in the direction of the
arrow I put there. The yellow on the right is the Eurasian Plate,
going in the direction of the arrow I wrote there. The green
represents the valley between the 2 plates.
*
These people are standing on the North American plate looking
at the valley between the 2 plates.

15. *
This is a picture of the valley taken from the North American
plate. The mountains in the back are the Eurasian plate. The
valley has gotten about 240 feet wider over the last 10,000
years.
*
More valley
*
Which continent is being ripped apart?
*
Africa! The “crack” where it is being ripped apart is called
The Great Rift Valley.
*
The first two pictures here show you how a rift valley forms.
*
Here it is from space.
*
Convective activity from the mantle causes the two plates to go
in opposite direction.
*
This and the next 2 pictures are of the Great Rift Valley, which
can be anywhere from 18-60 miles wide.
*
An earthquake in remote and desolate Boina, Ethiopia, about
270 miles northeast of the capital, Addis Ababa, split open a
crack in the Earth 37 miles long, according to an Associated
Press report. Over the next three weeks, the fissure in Boina
widened to a gap of 134 feet, and it continues to spread
today….”
It is believed that this is the latest development in the East
African Rift doing its thing.
*
A close up of the last slide
*
The blue dot is where that crack developed.

16. *
*
The map to the right shows how the Red Sea shore-lines may
have looked during the early phase of the Africa-Arabia Rift
Valley breakup.
*
Notice where India is. I colored it red.
*
Over tens of millions of years, India would migrate northward
and collide with the Eurasian Plate. The land scrunched and
this formed the Himalayas. Collide is present tense because it
is still happenning. In fact, the Himalayas are getting an inch or
two taller every year. (see the next 3 slides)
*
Here are the Himalayas from space.
*
The Himalayas.
*
*
The Alps arose as a result of the pressure exerted on sediments
of the Tethys Ocean basin as its Mesozoic and early
Cenozoicstrata were pushed against the stable Eurasian
landmass by the northward-moving African landmass.
As Africa pushed northward, it scrunched the area in red. This
“scrunching” created the Alps in lower Eupore.
The Alps
*
Look for the Juan de Fuca Plate. Notice it an oceanic plate
subducting under NW USA.
*
Notice it an oceanic plate subducting under NW USA.
*
The ocean floor is made of basalt. The continents are made of

17. granite. Basalt is more dense than the granite. For this reason,
when the two collide, the ocean floor subducts the continent.
*
As it grinds past the continent, the heat and friction cause the
subducted ocean floor to liquify. The liquid blobs migrate
upward and form volcanoes, like Mt. St. Helens.
*
This is why the NW USA is littered with volcanoes.
*
Mt St Helens has easily been the most active over the last 4000
years.
*
When 2 ocean plates collide, one will subduct the other. The
grinding motion will create a series of volcanoes in the ocean
called an island arc.
*
The Aleutian Islands are an example of an island arc.
*
The Aleutians are at the SW tip of Alaska.
*
Look where they are from this perspective. Here the Pacific
Plate is subducting the North American Plate.
*
Look at the yellow v I drew. This is a trench. Anytime one plate
of any kind subducts another, a trench will form.
*
Probably the most famous trench is the Mariana Trench. It is the
deepest trench in the world.
*
*
It is where the yellow Pacific Plate is subducting the pink
Phillippine plate.
It is about 7 miles deep at its deepest point, called the
Challenger Deep.
*
Where plates slide past one another

18. *
Notice how North America is up against the Pacific Plate.
*
Actually part of North America (shown in green) is ON the
Pacific Plate.
*
Part of California is going in NE direction and the rest in
moving in a SE direction. The line that divides the two is
called the San Andreas Fault.
*
The San Andreas Fault can actually be seen if you fly over it.
*
That part of CA will break off someday and collide with
Alaska!
*