Transcript Plate Tectonics - THS Aquatic Science

Plate Tectonics
Evolution of the Earth
Cracks in the Earth’s Crust
• The crust, when it is solid, acts as a heat
insulator for the hot interior of the Earth.
• The molten material in the mantle, magma, below
the crust builds up tremendous heat and
pressure.
• The magma creates convection currents and
rises to the surface.
• These currents can crack the crust (both oceanic
and continental)!
Tectonic Plates
• These cracks separate the crust into plates
(huge sections of the Earth that moves
relative to each other).
• Lithosphere is responsible for tectonic plates
because it adheres the crust to the mantle.
Plate Boundaries
•
Convergent Boundaries
– Subduction – when one oceanic
plate plunges beneath another
• Crust enters mantle, pressure
cracks crust
– Volcanoes
– Ocean trenches
– Continental Collision - continental
plates move toward one another
• The crust moves upward, folds and
buckles and breaks
– mountains
•
Divergent Boundaries – plates move
away from each other
– Seafloor spreading
• Mid-ocean ridges
•
Transform fault – plate moves sideways
from each other, slide past each other
–
earthquakes
Subduction
Convergent Plates
Convergent Plates
Seafloor Spreading
• Magma rises to the oceanic crustal surface
– forms mid ocean ridges.
• As the lava cools, it forms new seafloor and
features: rift valleys; seamounts; abyssal hills
(volcanic peaks)
• As new material reaches the surface, the plates
are pushed apart
Seafloor Spreading cont.
•
Earth’s longest mountain chain
– 47,000 miles long running down the middle of the Atlantic Ocean (surfacing at
Iceland), around Africa, through the Indian Ocean, between Australia and
Antarctica, and north through the Pacific Ocean.
•
Running along the top of this chain of mountains is a deep crack, called a rift valley. It
is here that new ocean floor is continuously created.
•
As the two sides of the mountain move away from each other, magma wells up from
the Earth's interior. It then solidifies into rock as it is cooled by the sea, creating new
ocean floor.
•
The mapping of the seafloor also revealed that these huge underwater mountain
ranges have a deep trench which bisects the length of the ridges and in places is
more than 2000 meters deep.
•
Seismic studies show that the mid-oceanic ridges experience an elevated number of
earthquakes. All these observations indicate intense geological activity at the midoceanic ridges.
•
The speed at which new ocean floor is created varies from one location on the ocean
ridge to another.
– Between North America and Europe, the rate is about 2.2 inches/year
– At the East Pacific rise, which is pushing a plate into the west coast of South
America, the rate is 12.6 inches/year
Transform Plates
Transform Plates
San Andreas
Fault
Why do the Plates Move?
• No single idea explains everything but we can
identify several forces that contribute to the
movement of the plates.
– Slab pull
• The sinking of the cooled dense oceanic plates pulls on the
rest of the plate
– Ridge rises
• The material deposited on the top of the ridge slides downs
from the rise pushing on the plate
– Convection
• Movement within the mantle could be part of the driving force
behind the motion of the plates.
Tectonic Plates
• Earth’s crust is broken into about 19 pieces
Earthquakes
Tidal waves or Tsunamis result when a large section of the sea floor
suddenly moves and therefore displaces a massive amount of water.
Earthquakes
Location of worldwide earthquakes
Tectonic Plates
Tectonic Plates
Volcanoes
Pangea
• What is Pangaea?
– Pangaea was a super continent at one time.
– 200 mill years ago, plates shifted enough to cause
movement.
– Scientists use the similarity of rock types and fossil types
that date to the same age to support their theory that the
continents were connected to form a super continent.
Pangea
Pangea
The break up
of Pangea
Where are we going?
We appear to be headed for another super
continent as North America, South America,
Asia and Australia converge in the
ever shrinking Pacific Ocean