Download Plate Boundaries

Plate Boundaries
3 types of plate boundaries: •  Divergent (divide)
•  Convergent (collide)
•  Transform (slide past)
Remember the plates are in
motion….
•  When plates move ,
they can either:
•  A) converge (collide)
B) pull apart (divide)
C) slide along past
one another
Either way, changes will
occur along the
“boundaries” of the
plates.
#1) Divergent Boundaries
•  Are boundaries
between two plates
that are moving
apart (dividing) or
“rifting”
ß à
•  RIFTING causes
SEAFLOOR
SPREADING
Divergent Boundaries..
•  Most occur at the
mid-ocean ridges
•  Divergent
boundaries that
occur on land are
called rift valleys
•  (ex: Great Rift
valley in Africa)
What is a rift valley? How are rift
valleys formed?
•  A rift valley is a deep valley that forms
along a divergent boundary on land
•  Rift valleys form as two slabs of Earth’s
crust slide apart
What could eventually happen at the
Great Rift Valley in Africa?
•  The rift may someday split the eastern
part of Africa away from the rest of the
continent
Volcanic fissures
•  Divergent boundaries
also cause volcanic
fissures!!!
•  This is a vent through
which lava erupts, but
there is usually no
explosive activity.
#2) Convergent Boundaries
•  Boundaries between two plates that
are colliding
à ß
•  There are 3 types…
Convergent Boundaries
•  A plate boundary where two plates
move toward each other
•  Collisions can occur between:
–  oceanic crust and oceanic crust
–  oceanic crust and continental crust
–  continental crust and continental crust
When two plates collide, the ______ of the
plates determines which one comes out on
the top.
•  density
Type 1
•  Ocean plate colliding
with a less dense
continental plate
•  And meet at a
Subduction Zone:
(where the more
dense plate slides
under the less dense
plate)
•  VOLCANOES occur
at subduction zones
How do these volcanoes form?
•  High temperature
from the magma
causes the rocks to
melt along the
subduction slab as it
goes under the other
plate.
•  Magma seeps up
along the plate
boundary forming
volcanoes.
•  Ex: St. Andes mtns
along the Nazca plate
and S. American plate
boundary:
Type 2
•  When one oceanic
plate collides with
another oceanic
plate, the more
dense plate slides
under the less
dense plate creating
a subduction zone
called a TRENCH
Type 3
•  A continental plate
colliding with another
continental plate
•  Have Collision Zones:
– a place where
mountains will
form
Continental/Continental cont’d
•  Because the plates are less dense than
the material in the asthensosphere, the
two plates collide and crumble up forming
mountain ranges.
•  There is little or no subduction here, so volcanoes do not
form.
Result of the Eurasian and the IndianAustralian Plates Colliding
The Himalayas
Where are the Himalayas?
Quick Check #1:
What occurs when plates carrying oceanic
crust collide?
•  The more dense plate dives back into
the mantle (subduction)
•  The collision between oceanic plates
causes deep-ocean trenches
#2 What occurs when plates carrying
oceanic and continental crust collide?
•  The more dense oceanic crust sinks
and plunges (subducts) beneath the
less dense continental crust
•  The collision between oceanic plates
and continental plates can cause a
volcanic eruption
#3 What occurs when plates carrying
continental crust collide?
•  Plates crash head-on causing mighty
mountain ranges.
#3) Transform Fault
Boundaries
•  Boundary between
two plates that are
sliding past each
other
•  Crust is neither
created nor destroyed
What is a Fault?
•  Is a break in the
Earth’s crust where
slabs of rock slip past
each other
•  Ex: San Andreas
Fault where many
Earthquakes occur:
What Earth-changing event occurs on a
transform boundary?
•  Earthquakes frequently occur at
transform boundaries
Video Review of plate tectonics and
boundaries…..
•  Watch lesson one of the video review from
the link below. Be prepared to answer
questions after the video!!!
•  Video clip : Lesson 1 "Plate Tectonics"
Review Questions...
•  What are the three types of
boundaries?
•  What direction do the plates go
for each type?
•  Which boundary has a subduction
zone…what occurs at a
subduction zone?
So What Causes Plate
Tectonics?
(The continent’s slow dance)
Convection Currents
•  Hot magma in the
Earth moves toward
the surface, cools,
then sinks again.
•  Creates convection
currents beneath the
plates that cause the
plates to move.
What causes plates to move?
•  Because there is an unequal distribution of
heat, hot plastic-like rock is forced to the
top of the surface where it will cool,
thicken (denser), and sink.
•  It’s the transfer of heat inside the Earth
that provides the energy to move the
plates and causes many of our surface
features to form.
Plates move at a rate of between ____
and ____ centimeters per year.
•  one
•  ten
The North American and Eurasian plates
float away from each other at a rate of
fingernail growth. This is a rate of ____ per
year.
•  2.5 centimeters
Figure 29: Posing Questions
What questions would you need to
answer in order to predict where the
continents will be in 50 million years?
•  You would need
answers to how fast
and in what direction
each plate is moving
Review Questions...
•  What causes plates to move?
•  How is a convection current
formed?
How do we know the plates are
really moving?
•  1) We can feel it in the form of
seismic waves from earthquakes!!
•  2) We can see it as volcanoes erupt!
•  3) We can see it from how our land
changes from the volcanoes and
earthquakes!!!
Bellwork 10/31/13 •  Retake this pre-­‐test and see how much you have learned!! If you change an answer, rewrite it BESIDE your original answer. Practice
Unscramble the following words:
-  gneivdret - boundary where two plates pull apart
-  areinmls - a non-living, inorganic solid
-  sarfmrotn - where plates slide past each other;
earthquakes occur
-  utalf - a break in the Earth’s crust