Plate Tectonics – Boundaries
Lithospheric Plates– the layer of crust that is made of
rocks
 Earth’s crust is broken up into 13 plates
which move because of activity at the plate
boundaries.(7 major, 6 minor)
 Convection cells– provide the energy for plate
tectonics to occur. Heat from the hot magma
causes the plates to move like they are on a
conveyor belt.
Plate Movement
Convection
Cell
The Core
Types of Crust
Why does the oceanic crust sit below the continental crust?
Continental Crust
Oceanic Crust
Types of Boundaries
1. Convergent – plates move towards each other
2. Divergent – plates move away from each other
3. Transform Fault – plates move in sideways against each other
Divergent Plate Boundary – Oceanic
Also known as Seafloor Spreading
Example – Mid-Atlantic Ridge
Picture –
Ridges
Oceanic Plate 1
Effects –
Plate Movement
Rift Valley
Ridges
Oceanic Plate 2
Magma
1. Plates spread apart and create an opening (rift valley)
2. Magma is released to the surface
3. Creates underwater mountains (ridges) – birthplace of “new oceanic rocks”
4. “Ridge Push” occurs from the thickening of the lithosphere when moving away from the ridge.
a. This creates a slope of the asthenosphere underneath leading to the sliding down of the lithosphere away from the ridge
b. Causes earthquakes
Divergent Plate Boundary – Continental
Example – East African Rift (Ethiopian Mountains)
Picture –
Effects –
1. Plates spread apart and create an opening (rift valley)
2. Magma is released to the surface
3. Creates mountains (ridges) around the valley – birthplace of “new continental rocks”
CONVERGENT PLATE BOUNDARY – OCEANIC/CONTINENTAL
Example – Mariana Trench (South Asian Coast) & Peru-Chile Trench (western coast of S. America)
Picture –
Volcano
Mountain
Range
Continental Plate
Oceanic Plate
Ocean Trench
Effects –
1.
2.
3.
4.
Two plates collide together – ocean plate subducts (sinks) under the continental plate
Oceanic plate melts back into magma creating a volcano on the continental plate
Creates an ocean trench and continental mountains from the 2 plates colliding
“Slab Pull” occurs when the lithosphere becomes denser after cooling and when moving away from the ocean ridge.
a. The weight of the lithosphere causes the lithosphere to sink at a subduction zone and help pull the remaining
plate down with it.
CONVERGENT PLATE BOUNDARY – OCEANIC/OCEANIC
Example – Aleutian Islands (Island Chain off of Alaska)
Picture –
Oceanic Plate 1
Ocean Trench
Effects –
1. Denser oceanic plate sinks below the less dense oceanic plate
2. Subducting plate melts into magma, creating volcanoes &
mountains
Oceanic Plate 2
CONVERGENT PLATE BOUNDARY – CONTINENTAL /CONTINENTAL
Example – Himalayan Mountains (between the Indian and Asian continents)
Picture –
Effects –
1. Plates collide together
2. Plates get pushed upward
3. Creates mountains
Transform Fault Boundary
Example – San Andreas Fault (California)
Picture –
Effects –
1. Land is being pulled in opposite directions
2. Earthquakes produced from plates rubbing together
Questions –
Name
Period
Answer Key
1 2
3 4
Grade ________%
February 25, 2014
Score _______/24
1. How many types of boundaries
are there for each category?
a. Convergent 3
b. Divergent 2
c. Transform Fault 1
2. Why are mountains created by oceanic/oceanic and oceanic/continental boundaries even
though one plate is subducting under the other plate? The subduction of the ocean plate
pushes upward on the other plate creating the mountains
3. Why are ocean trenches formed by oceanic/oceanic and oceanic/continental boundaries?
There is a gap created where the 2 plates meet. The trench is formed because the
subducting plate is being bent down and the other plate is being pushed up
4. What forms the ridges (mountains) at a divergent plate boundary?
Pressure from
rising magma on the end of each plate
5. What will eventually happen to the West Coast of California? It will break off of
California and move out into the Pacific Ocean
6. What is happening to the size of the Atlantic Ocean? It is getting bigger
7. What is happening to the size of the Pacific Ocean? It is getting smaller
8. Look at the map below. What do you notice about the locations of earthquakes/volcanoes
and plate boundaries?
Earthquakes and volcanoes are created mostly at plate boundaries
9. Why is the Pacific Plate (under most of the Pacific Ocean) referred to as the “Ring of Fire”?
The Pacific Ocean is surrounded by plate boundaries that create volcanoes (referred to as
the “ring”). These erupting volcanoes are referred to as the “fire”.
10. How are the Hawaiian Islands different from other volcanic island chains? Hawaii is
located over a hot spot under the middle of the plate; it is not located at a plate boundary
like other volcanic island chains.
11. Create a chart (see below) that contrasts the differences between each type of plate
boundary.
Differences: (Come up with at least 3 differences for each Boundary Type)
Divergent Plate Boundaries
Convergent Plate Boundaries Transform Fault Boundaries
1. Moving apart
1. Moving together
2. Creates new rocks
1. Moving side by side
2. Creates volcanoes
3. Creates mountain chains
2. Causes most earthquakes
3. Creates trenches
3. Creates a fault zone
under water
Similarities: (Come up with at least 3 similarities for the boundaries)
1. Involves plate movements
2. Involve at least 2 plates
3. Slow, constant movements