Transcript plates - Geography

Plates on the Move
 Three kinds of boundaries between plates
 “Divergent” – pulling part
 “Convergent – pushed together
 “Transform fault” – slide past each other
Divergent Boundaries
 Plates pull apart &
leave a gap
 Magma fills gap, cools
and hardens
 Examples:
 Mid – Atlantic Ridge
(beneath ocean)
 Rift between North
American plate and the
Eurasian plate in
Thingvellir Iceland
Convergent Boundaries
 Plates ram into each
other
 Subduction process
 One plate cycles under
other
 Recycles earth’s crust
Oceanic plate converging with
Continental Plate
 Result: Oceanic plate is
“subducted” under the
continental plate
 Example: Juan de Fuca
plate pushing under
NA plate
Oceanic plate converging with
another Oceanic plate
 Result: form a “trench”
where one oceanic
plate slips under
another
 Example: Mariana
trench
 Convergence between
Pacific plate and
Phillipine plate
Continental Plate converging with
Continental Plate
 When two continental
plates meet do not
subduct
 Instead crust buckles
upwards forming
 Mountains (peak)
 Plateaus (flat)
 Eg. Tibetan Plateau
Transform Fault Boundary
 Two plates slide by
each other
 Most under ocean
 San Andreas Fault
 Few land based TF
 Pacific Plate sliding past
North American plate
Complete the missing
information
Place on
Earth
Type of
Boundary
Thingvellir Rift
Juan de Fuca Plate
(oceanic plate)
NA plate pulling away from the
Eurasian plate
Convergent Boundary
(Oceanic + Continental)
Tibetan Plateau
San Andreas Fault
Description of
Plate Movement
Indian plate pushing up
Eurasian plate
Transform Fault Boundary
Answers
Place on
Earth
Type of
Boundary
Description of
Plate Movement
Thingvellir Rift
Divergent Boundary
NA plate pulling away from the
Eurasian plate
Juan de Fuca Plate
(oceanic plate)
Convergent Boundary
(Oceanic + Continental)
Oceanic plate subducting
beneath NA Plate
Tibetan Plateau
Convergent Boundary
(Continental + Continental)
Indian plate pushing up
Eurasian plate
San Andreas Fault
Transform Fault Boundary
Pacific Plate sliding past NA
Plate
 At a Divergent boundary the plates are moving
apart. The plates move apart due to convection
currents inside the Earth.

 As the plates move apart (very slowly), magma rises
from the mantle. The magma erupts to the surface of
the earth. This is also accompanied by earthquakes.
 When the magma reaches the surface, it cools and
solidifies to form a new crust made up of igneous
rock. This process is repeated many times, over a
long period of time.
 Eventually the new rock builds up to form a volcano.
Divergent Boundaries tend to be found under the
sea, e.g. the Mid-Atlantic Ridge. Here, chains of
underwater volcanoes have formed along the plate
boundary. One of these volcanoes may become so
large that it erupts out of the sea to form a volcanic
island, e.g. Surtsey and the Westman Islands near
Iceland.
 At a convergent boundary the plates are moving
towards each other. This usually involves a
continental plate and an oceanic plate.
 The oceanic plate is denser than the continental
plate so, as they move together, the oceanic plate is
forced underneath the continental plate. The point at
which this happens is called the subduction zone.
As the oceanic plate is forced below the continental
plate it melts to form magma and earthquakes are
triggered. The magma collects to form a magma
chamber. This magma then rises up through cracks
in the continental crust. As pressure builds up, a
volcanic eruption may occur.