Transcript Tour of Plate Boundaries

The Relationships
Between Plate Boundaries
and Tectonic Landforms
The earth’s surface is covered with a variety of wonderful
and interesting landforms…
Island arcs
Volcanoes
Mountains
And valleys bordered
by steep cliffs,
Just to name a few!
How did these landforms originate?
How does it relate to our dynamic,
changing earth?
…These are questions that curious and analytical
scientific minds have only really been able to
answer in the last 40-50 years!
Courtesy of pictures from NASA’s website:
“Earth from Space”
http://earth.jsc.nasa.gov/land.html
We are going to take a “Virtual Tour” of the Earth to
explore these Tectonic Landscapes and put into “realworld” context what we have learned in class.
But first a review…
An important modern theory about the forces
that drive plate tectonics is that the plastic,
partially melted asthenosphere is undergoing
convection.
This movement of materials below the earth’s
lithosphere is thought to be causing the plates
of the earth’s lithosphere to move too!
As you have learned, where there is upwelling of the
asthenosphere, the crust above spreads apart, and new
material from below bulges up into ridges. Where there is
subsidence of the asthenosphere, the crust is being pulled
down along with it to form depressions, or trenches. This
can be visualized superbly in this diagram.
This
movement
of the
asthenosphere
causes the
lithosphere
plates to be
pulled apart
or pushed
together!
This creates
the different
plate
boundaries,
which in
turn creates
the
landscapes
we see on
earth today!
Let’s review the 3 types of plate
boundaries we have discussed so
we can better understand the
pictures we are about to see.
Plate Boundaries
1. Divergent:
Where tension forces are pulling the
earth’s plates apart.
(where plates move away from each other)
2. Convergent:
Where compression forces push
the earth’s plates together
(where plates crash into each other)
3. Transform:
Where shearing forces cause the
earth’s plates to slide past each other.
(where plates rub against each other in opposite directions)
How do scientists know where
plate boundaries are, and of what
type?
By studying where the earth is
under stress.
How do scientists know where
the earth is under stress?
By identifying where earthquakes
are and how deep they are!
Shallow earthquakes are found along divergent, transform, and rift
boundaries, and where continental crust is colliding.
Deep earthquakes are found along what kind of zones?!
*
*
O.K.! Enough Review! Let’s take off and look at
some real-life landforms!
Our first stops will take us to CONVERGENT boundaries.
Stop 1: Oceanic crust colliding into oceanic crust
COUNTDOWN….
5
4
3
2
1
LIFTOFF!!!!
We are going to fly over Alaska and
the Aleutian Islands
What features should we be looking for?
Aleutian
Islands
Unimak Island
Unimak Island
Turn to page 5 in your Earth
Science Reference Tables…
What tectonic feature do you
see associated with the
Aleutian Islands?
Volcanic Island Arcs are associated with trenches!
Why is this so?!
Stops 2&3: Oceanic crust colliding with continental crust
We will be visiting the
state of Washington
in order to view plate
tectonic features that
resulted when the
Juan de Fuca Plate
(oceanic crust)
collided with the
North American Plate
(continental crust.)
Based on the map to
the right, and in the
next slide, what
features should we be
looking for?
Cascade Range, Washington
Mount Rainier
Mount Saint Helens
A similar situation
exists in western
South America, but
the plates involved
are different.
What plates are
involved in this
collision between
oceanic and
continental
crust?
Now we’re off to Chile and Peru to
check out the landforms there!
Stop 3: South America
Chile
Look at your reference table again. What feature do you see on
the west side of South America that is associated with
convergent boundaries and the subduction that results?
What is probably happening to the asthenosphere here?
Stop 4: Continental crust colliding with
continental crust
What features do we expect to find here?
We’re off to Southeastern Asia, one of the best
places to observe this type of plate boundary!
China
India
Nepal
Himalayas
India
China
Mount Everest
29,035 feet tall! (8850 meters)
Use your reference table to
determine what plates are colliding
to form the Himalayas.
Now we have reached the
second part of our journey:
Stops 5&6:
Exploring DIVERGENT boundaries…
A flight over part of Africa’s Rift Valley
will demonstrate this.
First, find the East African
Rift on your reference table
and determine what plate the
rift is found on.
Here are some
volcanoes from
the Rift Valley.
Knowing this is
a divergent
zone, what type
of lava will
extrude from
them?
Lengai Volcano
Steep cliff of
rift valley
And here are some dramatic pictures of the lava
from these volcanoes!
…And now to explain how
rifting can form volcanoes
AND large lakes…
The uprising
asthenosphere here
has caused tension
forces which have
pulled apart the
continental crust.
The brittle crust has
fractured and a
section in the middle
has downfaulted into
the developing gap
(rift.)
Water filled into
the gap, creating a
freshwater lake.
There are two
stunning
examples of this
in Africa!
..and magma coming from the spreading center can form volcanoe
Stop 5: Malawi, Africa
Lake Malawi
And next to Tanzania…
Lake Tanganyika
And the last part of our journey…
Stop 7: A TRANSFORM BOUNDARY
We’re still in Africa—Zimbabwe this time!
Movement that occurs along a transform boundary:
Transform
Where is the evidence for a
transform fault in this area
of Zimbabwe?
And our final stop…
A PASSIVE CONTINETNAL
MARGIN
Greenlawn
In Summary…
Wait a second…I’m tired from all this running
around and being a tour guide…you do it!!!
1. What are the three main plate boundaries?
Describe the movement at each.
2. How does each plate boundary affect what
type of landscape results? Give specific
examples for each one!
3. Explain how the asthenosphere drives plate
tectonics.