Download 1-4 Notes: Convergent and Transform Boundaries Think About… • If

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.
 Because the plates are pushing together, crust is either folded or _____________________.
 When one plate ___________________ beneath another, it is called subduction.
 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 __________________________ plates meet, it is
called continental-continental collision.
 Because both crusts have the same ______________________,
neither plate will sink below the other.
 If the plates keep moving, their edges will eventually
 ___________________________and fold.
 Sometimes, the folded crust pushes up to create
_____________________________.
Oceanic-Oceanic Subduction
 When one plate with oceanic plate sinks under another oceanic
plate it is called oceanic-oceanic subduction.
 The ____________________ plate sinks because it is colder and
more dense than the younger plate.
 As the older crust sinks into the asthenosphere, it
__________________ , getting destroyed and reabsorbed into
the mantle.
 There are two features that form at oceanic-oceanic
subduction zones:
o Deep-Ocean ________________________:
 Deep __________________________ on the ocean floor that form as the plate sinks.
 The Marianas Trench is the deepest trench in the world at _______________ m (36,000 ft)
o Island Arcs
 Form on the top plate, ________________________ to the ocean trench.
 As the sinking plate melts, magma rises up through the top plate to build a series of islands.
 Example: Aleutian Islands of Alaska
 Example: Philippines
Oceanic-Continental Subduction
 When ocean crust sinks under __________________________
crust, it is called oceanic-continental subduction.
 The oceanic crust will sink because it is ___________________
and denser than the continental crust.
 There are 2 features that form at oceanic-continental subduction
zones.
p. 115
o Deep-Ocean ______________________
 Form as oceanic crust sinks under continental crust.
o Coastal __________________________
 As oceanic crust sinks, the continental crust ___________________________ to form a range of
mountains.
 Some of these mountains are __________________________.
 The Cascade Mountains in Oregon and Washington is a coastal mountain range.
 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.
 As the plates move, their edges _____________________ against each other.
 Most transform boundaries occur on the sea floor, but they also occur on __________________.
 The San Andreas Fault in California is a transform boundary.
 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 helps geologists explain Earth’s past and predict
what might happen in the _____________________.
 Studying rock layers allows us to see what geologic events occurred
in the ______________.
 Example: The Appalachian Mountains are evidence of a past
___________________________ boundary.
 They match mountains in Africa, which tells us that the U.S. was once
next to modern day _________________.
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
____2. Which type of landform is created from converging oceanic and continental plates?
A. Rift Valley
C. Mid-Ocean Ridge
B. Islands
D. Ocean Trench
____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