Transcript Plate Movement and Geological Events

BELLWORK
• Name the 3 types of plate
boundaries and an example of
each.
Deforming the
Earth’s Crust
Moving Continents
•
http://www.suu.edu/faculty/colberg/hazards/platetectonics/18_Pangaea.html
Tracking Tectonic Plates
Scientists use GPS
to track plate
movement.
Radio waves are
beamed from
satellites to GPS
ground stations
which record their
position.
3 Possible Driving Forces
• Convection Currents
• Ridge Push and Slab Pull
–
Ridge Push – At mid-ocean ridges, the oceanic lithosphere is higher than it is where it sinks
into the asthenosphere. Because of ridge push, the oceanic lithosphere slides downhill
under the force of gravity.
–
Slab Pull – Because oceanic lithosphere is denser than the asthenosphere, the edge of the
tectonic plate that contains oceanic lithosphere sinks and pulls the rest of the tectonic plate
with it in a process called slab pull.
• Plate movement causes
geological events such as
mountain formation,
volcanic eruptions, and
earthquakes.
Deformation
• The process by which the shape of a rock
changes because of stress.
– Stress is the amount of force per unit area on a given
material.
• Different things happen to rock when different
types of stress are applied.
– Rock layers bend when stress is placed on them.
– When enough stress is placed on rocks, they can
reach their elastic limit and break.
Compression
• The type of stress that occurs when an
object is squeezed, such as when two
tectonic plates collide.
• When compression occurs at a convergent
boundary, large mountain ranges can
form.
Tension
• Stress that occurs when forces act to
stretch an object
• Tension occurs at divergent plate
boundaries, such as mid-ocean ridges,
when two tectonic plates pull away from
each other.
Folding
• The bending of rock layers because of
stress in the Earth’s crust.
• Types of Folds – depends on how the rock
layers deform:
– Anticlines
– Synclines
– Monoclines
Anticline
• Upwardarching folds.
• Caused by
horizontal
stress.
Syncline
• Downward,
troughlike
folds.
• Caused by
horizontal
stress.
Monocline
• Fold where
both ends are
horizontal.
• Cause by
vertical stress.
Faulting
• The surface along which rocks break and
slide past each other.
– Some rock layers break when stress is
applied
– The blocks of crust on each side of the fault
are called fault blocks.
Footwall & Hanging Wall
• When a fault is not vertical, its two sides are
either a hanging wall or a footwall.
Normal Fault
• When a normal
fault moves, it
causes the
hanging wall to
move down
relative to the
footwall.
• Caused by rocks
being pulled apart
(tension).
Normal Fault
Reverse Fault
• When a reverse
fault moves, it
causes the
hanging wall to
move up
relative to the
footwall.
• Caused when
rocks are
pushed together
(compression).
Reverse Fault
Strike-Slip Fault
• When opposing
forces cause
rock to break
and move
horizontally.
Mountain Building
• When tectonic plates undergo
compression or tension, they can
form mountain ranges in several
ways.
Folded Mountains
• The highest mountains in the world are
formed when rock layers are squeezed
together and pushed upwards to form
folds.
– This occurs at convergent
boundaries where plates collide.
– The plates buckle and thicken.
– The continental crust is pushed
upward, forming mountains.
Examples of Folded Mountains
• Himalayas
• Alps
In central
Europe
• Ural
Mountains
in Russia
• Great
Smoky
Mountains
Fault-Block Mountains
• Form when large blocks of the Earth’s crust drop
down relative to other blocks.
• Tension produces mountains that have sharp,
jagged peaks.
Examples of Fault-Block Mountains
• Teton Range
in Wyoming.
• Sierra Nevada
mountain
range in
California
• Harz
Mountains in
Germany
Volcanic Mountains
• Form when magma rises to
the Earth’s surface and erupts.
Examples of Volcanic Mountains
• Mount
St. Helens in
Washington
• Mount
Pinatubo in
the
Phillipines
Uplift and Subsidence
• Uplift is the rising of regions of the Earth’s
crust to higher elevations.
– Rebound – When the crust slowing springs
back to its previous elevation, as when a
glacier melts.
• Subsidence is the sinking of regions of
the Earth’s crust to lower elevations.
– Rocks that are hot take up more space than
cooler rocks.
Tectonic Letdown
• Subsidence can also occur when the
lithosphere becomes stretched in rift
zones.
Quiz
1. Name the 3 types of faults.
2. Name the 3 types of folds.
3. What is compression?
4. What is tension?
5. Would you find a folded mountain at a
mid-ocean ridge? Why or why not?