Transcript 1-4 Notes.pps

1-4 Notes
Convergent and Transform
Boundaries
Think About…
If
new crust is created at
divergent boundaries, why
does the total amount of
crust on Earth stay the
same?
Convergent Boundaries
Convergent
boundary: where
plates push
together.
Convergent Boundaries
Because
the plates are pushing together,
crust is either folded or destroyed.
Convergent Boundaries
When
one plate
sinks beneath
another, it is
called subduction.
Convergent Boundaries
There
are 3 types of convergent
boundaries…
1. Two continental plates
2. Two oceanic plates
3. An oceanic plate and a
continental plate
Continental-Continental Collision
When
two
continental plates
meet, it is called
continentalcontinental
collision.
Continental-Continental Collision
Because
both crusts
have the same
density, neither
plate will sink below
the other.
Continental-Continental Collision
If
the plates keep
moving, their edges
will eventually
crumple and fold.
Continental-Continental Collision
Sometimes,
the
folded crust
pushes up to
create mountains.
Oceanic-Oceanic Subduction
When
one oceanic plate
sinks under another
oceanic plate it is
called oceanic-oceanic
subduction.
Oceanic-Oceanic Subduction
The
older plate sinks
because it is colder
and more dense than
the younger plate.
Oceanic-Oceanic Subduction
As
the older crust sinks
into the asthenosphere
it melts, getting
destroyed and
reabsorbed into the
mantle.
Oceanic-Oceanic Subduction
There
are two features that form
at oceanic-oceanic subduction
zones:
Oceanic-Oceanic Subduction
Deep-Ocean
Deep
Trenches:
canyons on the
ocean floor that form as
the plate sinks.
The Marianas Trench is the
deepest trench in the
world at 11,000 m (36,000
ft)
Oceanic-Oceanic Subduction
Island
Arcs
Form
on the top plate,
parallel to the trench.
As the sinking plate
melts, magma rises up
through the top plate to
build a series of islands.
Oceanic-Oceanic Subduction
Example:
Aleutian Islands of Alaska
Oceanic-Oceanic Subduction
 Example:
Philippines
Oceanic-Continental Subduction
When
ocean crust sinks
under continental
crust, it is called
oceanic-continental
subduction.
Oceanic-Continental Subduction
The
oceanic crust will
sink because it is
colder and denser
than the continental
crust.
Oceanic-Continental Subduction
There
are 2 features that form at
oceanic-continental subduction zones.
Oceanic-Continental Subduction
Deep-Ocean
Form
Trenches
as oceanic crust
sinks under continental
crust.
Oceanic-Continental Subduction
 Coastal
Mountains
As
oceanic crust sinks,
the continental crust
crumples to form a range
of mountains.
Some
of these mountains
are volcanoes.
Oceanic-Continental Subduction
The
Cascade Mountains in Oregon and
Washington is a coastal mountain
range.
Oceanic-Continental Subduction
Mt.
St. Helens is an active volcano
that is part of the Cascade
mountains.
Transform Boundaries
 At
transform
boundaries, two plates
move past each other.
 Crust is neither
created nor destroyed.
Transform Boundaries
As
the plates move,
their edges scrape
against each other.
Transform Boundaries
Most
transform
boundaries occur on
the sea floor, but
they also occur on
land.
Transform Boundaries
The
San Andreas
fault in
California is a
transform
boundary.
Transform Boundaries
If
the Pacific and
North American Plates
keep moving, Los
Angeles may be next
to San Francisco in as
little as 10 million
years!
Geologists Today
Plate
tectonics help
geologists explain
Earth’s past and
predict what might
happen in the
future.
Geologists Today
Studying
rock
layers allows us
to see what
geologic events
occurred in the
past.
Geologists Today
 Example:
The Appalachian
Mountains are evidence of a
past convergent boundary.
 They match mountains in
Africa, which tells us that the
U.S. was once next to modern
day Africa.
Review
1. At
an oceanic-oceanic convergent
boundary,
A.crust is created
B.crust is subducted
C.crust is deformed or fractured
D.plates slide past one another
Review
2. Which type of landform is created from
converging oceanic and continental plates?
A. Rift
Valley
B. Islands
C. Mid-Ocean
D. Ocean
Ridge
Trench
Review
3. At transform boundaries, two
plates
A.Pull away from each other
B.Push against each other
C.Scrape past each other
D.Do not move in any direction