Download Section 11-3

Section 11-3
• What is the theory of plate tectonics?
• Describe the lithosphere and the asthenosphere.
• Review the difference between divergent and
convergent plate boundaries.
• Explain the three types of convergent plate
boundaries and define subduction zone.
• What is a transform fault boundary?
• Define convection current.
• What are the causes and effects of plate
tectonics?
• Plate tectonics is the theory that Earth’s crust
and upper mantle are broken into sections
called plates, that slowly move around on the
mantle.
• The lithosphere is the rigid, outermost layer of
Earth composed of the crust and upper
mantle. It is about 100 kilometers thick.
• The asthenosphere is the plastic-like layer
below the lithosphere in Earth’s mantle.
• The less dense lithosphere floats around on
the denser asthenosphere.
Plate Boundaries
• Divergent boundaries occur when two plates
are diverging, or moving away from each
other. Rifts and valleys can form.
• Convergent boundaries occur when two
plates are converging, or moving toward each
other. There are three types of convergent
boundaries.
• The first type of convergent boundary occurs
when an ocean-floor plate collides with a
continental plate and the denser ocean plate
sinks under the less dense continental plate.
• This is known as a subduction zone, an area
where an ocean plate descends into the upper
mantle.
• Volcanoes occur at subduction zones.
• The second type of convergent plate occurs
when two ocean plates collide.
• This also causes a subduction zone.
• The third type of convergent plate occurs
when two continental plates collide.
• No subduction zone usually occurs here.
• The collision forms mountain ranges or causes
earthquakes.
• A transform fault boundary occurs between
two plates that are sliding past one another
horizontally in opposite directions, or in the
same direction but at different speeds.
• The San Andreas fault is a transform fault
boundary.
• Earthquakes occur at this fault boundary.
• Convection currents cause plate tectonic
movement.
• A convection current is the cycle of heating,
rising, cooling, and sinking of matter.
• The formation of different landforms is the
effect of plate tectonics.
• Diverging boundaries result in fault-block
mountains, rift valleys, and mid-ocean
ridges.
• Converging boundaries result in folded
mountains, island arcs, volcanoes, and
earthquakes.
• Transform boundaries result in earthquakes
from strike-slip faults.
Rift Valley – a lowland created by the
action of a rift