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Plate Boundaries
Plate Boundaries
• 3 Main Types:
– 1. Divergent Boundaries
• Plates moving AWAY from
each other
– 2. Convergent Boundaries
• Plates moving TOWARD
each other
• Three Main Types:
– Oceanic to Continental
– Oceanic to Oceanic
– Continental to
Continental
– 3. Transform Boundaries
• Plates slide past each
other
Divergent Boundary
Divergent Boundaries
• Where plates are moving away
from one another.
• Characteristics:
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–
–
–
–
Lengthening
Thinning of Lithosphere
Shallow Earthquakes
Fissure Volcanoes
Rift Valleys
• Locations:
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–
–
–
Oceanic Ridges
Mid-Atlantic Ridge
East-African Rift
Formation of Basalt
• Results in:
– Sea floor spreading
Divergent Boundary
• Oceanic
– Occurs above rising convection
currents that lift up the plate
– The plate travels in direction of
flow.
– The plate is stretched thin,
breaks and pulls apart.
– The magma flows into the
fissure, solidifies and the process
repeats itself.
• Continental:
– Two plates pull apart, faults
develop on both sides of the rift;
the central blocks slide
downwards.
– Earthquakes occur.
– Streams and rivers flow into the
rift and form a lake.
Convergent Boundary
Continental/Oceanic
Convergent: Continental to Oceanic
• As they collide, the less dense • Characteristics:
continental plate overrides the
– Coastal Mountain Ranges
oceanic plate.
– Continental Volcanic Arcs
– Oceanic plate is forced down;
temperature increases; plate
becomes magma in convection
current
• Subduction Zone:
– Where less dense crust
slides under the more
dense crust
– Location of Volcanoes
and Seafloor Trenches
• Andes, Cascades
– Formation of Volcanic Island
Arcs
• Japan, Philippines
Andes Mountains,
South America
Convergent Boundary
Oceanic/Oceanic
Convergent: Oceanic to Oceanic
• Two oceanic plates collide.
– The older (most dense) plate will
subduct beneath the younger plate.
• Subduction Zone Results in:
–
–
–
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Trenches
Island Arcs
Chain of Volcanic Isands
Deeper Earthquakes
• Examples:
– Japan
– The Caribbean Islands
Convergent Boundary
Continental/Continental
Convergent: Continental to
Continental
• Two thick continental
plates collide
– Both have a density that is
much lower than the
mantle, which prevents
subduction.
• Example:
– Himalaya Mountain Range
– Alps
Transform Fault Boundaries
• Boundary between
two plates that are
sliding past each other
• Earthquakes appear along
fault lines
• Example:
– San Andreas Fault
San Andreas Fault, CA
Questions...
•What are the three types of
boundaries?
•What direction do plates go for each?
•Which boundary has a subduction
zone…what occurs at a subduction
zone?
C. Why do the plates move?
1. Due to tremendous heat, rock in the
asthenosphere is like hot taffy
2. This allows plates to ride on top of hot,
flowing rock.
3. Plates move because heat is being
released from deep inside the earth.
4. Convection currents causes hot material
to rise and expand (plates diverge) and
cooler material to sink and contract
(plates converge).
Questions...
• What causes plates to move?
• How is a convection current formed?