Transcript Tectonic Plate Boundaries

Geology 12
Divergent Boundary
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Plates move apart.
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The crust cracks and
magma bubbles between
the plates, rises up to
form ridges and solidifies.
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This is known as seafloor
spreading.
Divergent Boundary
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When two continental plates
diverge, a valleylike rift develops.
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This rift is a dropped zone where
the plates are pulling apart.
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As the dropped zone widens and
thins, valleys and volcanoes form.
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Early in the rift formation, streams
and rivers flow into the low
valleys and long, narrow lakes
can be created
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Eventually, the crust may become
thin enough that a piece of the
continent breaks off, forming a
new tectonic plate.
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At this point, water from the
ocean will rush in, forming a new
sea or ocean basin in the rift
zone.
Convergent Boundary – Type 1
Oceanic Plates meets Continental Plate
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Oceanic crust tends to be denser
and thinner than continental
crust.
The oceanic crust gets pushed
under the continental crust. This
is called “subduction”.
This forms a subduction zone.
The sinking crust creates a deep
oceanic trench, or valley, at the
edge of the continent.
The crust continues to be forced
deeper into the earth, where high
heat and pressure the crust to
melt & then rise.
When this magma finds its way to
the surface through a vent in the
crust, the volcano erupts.
An example of this is the band of
active volcanoes that encircle the
Pacific Ocean, often referred to
as the Ring of Fire.
Type 1 Convergent Boundary
Convergent Boundary – Type 2
Two Oceanic Plates Meet
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When two oceanic plates
collide, the older plate is
forced below the younger
plate.
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This creates another
subduction zones.
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This creates a chain of
volcanic islands known as
island arcs.
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Examples include the Mariana
Islands in the western Pacific
Ocean and the Aleutian
Islands, off the coast of
Alaska.
Colliding Plates – Tsunami Makers
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The collision and subduction
of plates creates large,
powerful earthquakes.
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Earthquakes generated in a
subduction zone can also
give rise to tsunamis.
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A tsunami is a huge ocean
wave caused by a sudden
shift on the ocean floor.
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If the wave reaches land, it
can cause incredible
destruction, like the Asian
Tsunami, which killed more
than 200,000 people in 11
countries across the Indian
Ocean region in December
2004.
Convergent Boundary – Type 3
Two Continental Plates Meet
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A collision between two continental
plates crunches and folds the rock at
the boundary, lifting it up and leading
to the formation of mountains and
mountain ranges.
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An example of this mountain-building
process is the Himalayan range in
southern Asia.
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The Himalayas were formed by the
collision of the Indian and Eurasian
Plates.
Its best known peaks, Mount Everest
and K2, are among several
mountains that measure over 8,000
meters high at their summits.
Since the Indian Plate is continuing in
its northward movement into Asia, the
Himalayas continue to grow higher
each year by small amounts (5 to 20
mm or 1 inch per year).
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Transform Boundary
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Two tectonic plates grind past each
other in a horizontal direction.
This kind of boundary results in a
fault — a crack or fracture in the
earth's crust that is associated with
this movement.
Faults and Earthquakes
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Faults produce many earthquakes.
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As the plates grind past each other,
the jagged edges "lock" together for
a time.
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Stress builds up at the fault line.
A lot of energy is released when the
plates suddenly slip into new
positions.
The sudden movement is what we
feel as the shaking and trembling of
an earthquake.
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Transform Boundary
To recap:
Boundary Types
Geological Phenomenon
1
Divergent Boundary
New crust formation
In Oceanic Crust Sea-floor spreading
2
Divergent Boundary
Rift valley, volcanic activity
In Continental Crust New ocean if plate portion breaks away
3
Convergent Boundary
Subduction Zone – Deep sea trench
Oceanic meets Continental Volcanoes in mountain range
4
Deep sea trench at subduction zone
Convergent Boundary
Volcanic Island arcs
2 Oceanic Plates
Tsunamis (due to underwater earthquakes)
5
Convergent Boundary
Mountain range
2 Continental Plates
6
Transform Boundary
Faults & Earthquakes