Transcript Day 69 Pangaea and boundaries review

Plate Tectonics
• Earth’s Interior
• Pangaea
• Plate Movement
• Plate Boundaries
Pangaea
• Theory stating all of the continents were once joined
as a “super-continent”
• Alfred Wegener proposed this idea
• Looked at specific evidence (fossils/rock record/fit)
from one continent to the next.
• Proposed all continents once fit together, then broke
apart. Hence the term, Continental Drift.
Plate Movement
• Plates move because the Asthenosphere
– a layer of partially melted rock that is able to
flow (like silly putty) with the aid of convection
currents (“heat currents”)
– Convection currents slowly move the ridged
crust in a specific direction
– Movement per year is about the same as how
long your fingernails grow per year (how
much is that!?)
Plate Movement
• When plates move, they collide with one
another’s boundaries.
• Three main types of boundaries
-Convergent
-Divergent
-Transform
Plate Boundaries
• Type of Boundary
• Convergent
– Oceanic-oceanic
– Oceanic-continental
– Continentalcontinental
• Divergent
• Transform
• Result of Boundary
• Plates come together
– Subduction zone/
volcanic islands
– Subduction zone/
volcanic mountains
– Non-volcanic
mountains
• Plates moving away
from one another,
creates new sea floor
• Plates sliding past one
another, creates
earthquakes
Convergent Boundaries
• Oceanic-Oceanic
Boundary
• Plates converge creating a
subduction zone—one plate
slides underneath the other
plate creating a volcanic arc
(volcanic islands)
• This will also create a trench
in the ocean
Convergent Boundaries
• Oceanic-Continental Boundary
• Subduction zone—oceanic plate slides under
continental plate because it is more dense.
• The oceanic plate breaks off and melts once it is
heated in the mantle.
• The melted plate then comes through the
continental plate to create volcanoes on the
continental plate
• Additionally, this will create an oceanic trench
Convergent Boundaries
• Continental-Continental
• When two continental
plates come together, the
two plates “crumple”
much like a piece of
paper
• This creates huge
mountain ranges, e.g.
Himalayans & Mt.
Everest
Divergent Boundaries
• If two continental
plates diverge, the
continent would
stretch much like a
rubber band getting
thinner and thinner
with each stretch
Divergent Boundaries
• Occur mainly on the sea floor between oceanic
plates
• When the sea floor spreads, it splits, thus creating
a way for the mantle to rise through the crust,
creating new sea floor.
• Example: Mid-Atlantic Ridge.
Transform Boundary
• Transform boundaries slide past one
another laterally
• Can slide uniformly or they can get
“stuck” at a particular point until there
is enough pressure to move past the
“stuck” point
• When there is enough pressure to
move beyond this point, we may feel
the movement as an earthquake
depending on the intensity
• An example of a transform boundary is
the San Andres Fault in California
Hot Spots
• There are several volcanoes caused by “hot spots”
• A hot spot is a point in the mantle where a plume of
hot material rises to the surface causing an area of
geo-thermal activity.
• Hot spot does not move, the plate does
• Examples of hot spots include: the Hawaiian Island
Chain and Yellowstone National Park
• One theory indicates hot spots as
the reason for the break up of
Pangaea