Download earths crust in motion ppt

Earth’s Crust in Motion
EQ: How do stress forces affect
rock?
Earthquakes
• Earthquake: The shaking that results
from the movement of rock beneath
Earth’s surface
EQ: How do stress forces affect rock?
• Two powerful forces that change rock in
the Earth’s crust:
– Stress
– Friction
Stress
• Stress: A force that acts on rock to
change its shape or volume
EQ: How do stress forces affect
rock?
What is Volume?
• The amount of space an object takes up
EQ: How do stress
forces affect rock?
Energy is stored in rock until the rock
either breaks or changes shape
EQ: How do stress forces affect rock?
Shearing
• Shearing: Stress that pushes a mass of
a rock in opposite, horizontal directions
EQ: How do stress forces affect rock?
Tension
• Tension: Stress that stretches rocks
so that it becomes thinner in the
middle
EQ: How do stress forces
affect rock?
Compression
• Stress that squeezes rock until it
folds or breaks
EQ: How do stress
forces affect rock?
Figure 2: If shearing continues
to tug at the slab of rock in B,
what will happen to the rock?
• The rock will
break; the two
parts will move in
opposite directions
EQ: How do stress
forces affect rock?
Deformation
• Deformation: A change in the volume or
shape of Earth’s crust
• Most changes in the crust occur so
slowly that they can not be observed
directly
EQ: How do
stress forces
affect rock?
Checkpoint (Page 55): How
does deformation change
Earth’s surface?
• It causes it to:
•
•
•
•
•
•
Bend
Stretch
Break
Tilt
Fold
Slide
Guide For Reading: How does
stress forces affect rock?
• The three kinds of forces that
affect rock are:
• Shearing
– The rocks break and slip apart
• Tension
– The rock stretches and becomes thin in the
middle
• Compression
– The rock squeezes until it folds or breaks
• These stresses work over millions of
years to change the shape and volume
of rock
EQ: How do stress
forces affect rock?
Faults
• A break in the Earth’s crust where
slabs of rock slip past each other
• Faults occur when enough stress
builds up in rock
• Rocks on both sides of the fault can
move up or down, or sideways
Strike-Slip Faults
EQ: How
do stress
forces
affect
rock?
• A type of fault where rocks on either
side move past each other sideways
with little up-or down motion.
• Shearing causes these types of faults
Normal Faults
• A type of fault where the hanging
wall slides downward
• Tension forces cause normal faults
EQ: How do stress forces affect rock?
Hanging Wall & Footwall
• Hanging wall: The block of rock that
forms the upper half of a fault
• Footwall: The block of rock that
forms the lower half of a fault
EQ: How do stress forces affect rock?
Reverse Faults
• A type of fault where the hanging
wall slides up
• Compression forces cause reverse
faults
EQ: How do stress
forces affect rock?
Checkpoint (Page 57): What are
the three types of fault? What
force of deformation produce
each?
• Strike-slip faults
• Produced by shearing
• Normal faults
• Produced by tension
• Reverse faults
• Produced by compression
Why do faults form and where do
they occur?
• Plate move and they compress, pull or
shear the crust so much it breaks
• Faults occur along plate boundaries
EQ: How do stress
forces affect rock?
Which half of the reverse fault
slid up and across to form this
mountain, hanging wall or the
footwall? Explain.
• The hanging wall
slipped up and
across. If the
footwall had moved
up, the fault would
be called a normal
fault
EQ: How do stress forces affect
rock?
What is friction?
• A force that opposes the motion of one
surface as it moves across another
surface
• It exists because rocks are not
perfectly smooth
EQ: How do stress forces affect
rock?
Describe what occurs when
the friction along a fault line
is low.
• The rocks on both sides of the fault
slide by each other without much
sticking
EQ: How do stress
forces affect rock?
Describe what occurs when
the friction along a fault line
is moderate.
• The sides of the fault jam together
• From time to time they jerk free
• Small earthquakes occur
EQ: How do
stress forces
affect rock?
Describe what occurs when
the friction along a fault line
is high.
• Both sides of the fault lock together and
do not move
• The stress increases until it is strong
enough to overcome the force of friction
• Larger and/or more frequent earthquakes
will occur
EQ: How do stress
EQ: How
do stress
forces
affect
rock?
Fault-Block Mountain
• A mountain that forms where a
normal fault uplifts a block of rock
How does the process of a
fault-block mountain begin?
EQ: How do
stress forces
affect rock?
• Where two plates move away from each
other, tension forces create many normal
faults
• When two of these normal faults form
parallel to each other, a block of rock is
left lying between them
• As the hanging wall of each normal fault
slips downward, the block in between moves
upward
• When a block of rock lying between two
normal faults slides downward, a valley
forms
EQ: How do stress
forces affect rock?
Folds
• A bend in rock that forms where part
of Earth’s crust is compressed
How does the compression of two
plates cause an earthquake?
• The collisions of two plates can cause
compression and folding of the crust
• Such plate collisions also lead to
earthquakes, because folding rock can
fracture and produce faults
EQ: How do stress
forces affect rock?
Anticline
• Anticline: An upward fold in rock
formed by compression of Earth’s
crust
EQ: How do stress forces affect
rock?
EQ: How do stress
forces affect rock?
Syncline
• Syncline: A
downward fold in
rock formed by
tension in Earth’s
crust
Plateaus
• A large area of flat land elevated high
above sea level
EQ: How do stress forces
affect rock?
Guide For Reading: How does
movement along faults
change Earth’s surface?
• Over millions of years, fault
movement can change a flat plain into
a towering mountain range
• Mountain ranges can form from:
•
•
•
•
Fault – block mountain
Folding
Anticlines & Synclines
Plateaus