Earth’s Crust in Motion
I.
Stress in the Crust
A. Earthquake: shaking and
trembling that results
from
movement of rock below Earth’s
surface
B. Stress
1. Caused by the movement
of Earth’s plates
2. Powerful forces that
squeeze or pull the rock
in
the crust
3. Changes the shape or
volume of the rock
that it
acts upon
II. Types of Stress
A. Shearing
1. Pushes a mass of rock in
two opposite
directions
2. Effect: rock can break
and slip apart or
change
its shape
B. Tension
1. Pulls on the crust;
moving apart
2. Effect: The middle
becomes thinner
C. Compression
1. Rocks squeeze together
2. Effect: Crust breaks or
folds
D. Shearing, tension, and
compression work over
millions
of years to change the shape and
volume of rock.
E. Deformation
1. any change in the crust
2. Examples
a. bend
b. break
c. tilt
d. fold
e. stretch
III. Kinds of Faults
A. Fault: caused when enough
stress builds up in
rock and
the rock breaks
B. A break in the Earth’s
crust where slabs of crust slip
past each other
C. Usually occur along plate
boundaries, where the
forces
of plate motion compress, pull,
or shear the crust so much that
the crust breaks
D. Strike-Slip Faults
1. Created when the rocks
on each side of the
fault
slide past each other, with
little up-ordown motion.
2. Forms at transform
boundaries
3. San Andreas fault in
California is an example
of strike-slip fault that is
a transform boundary
E. Normal Faults
1. Fault is at an angle,
one block of rock lies
above the fault, while the
other lies below the
fault
a. HANGING WALL- half
that lies ABOVE the
fault
b. FOOT WALL- half that
lies BELOW the
fault
2. When movement occurs,
the hanging wall
slips
downward
3. Forms at divergent
boundaries
4. Rio Grande Rift Valley
is an example of a
normal fault that is
occurring at a divergent
boundary
F. Reverse Fault
1. Fault is at an angle,
same as a normal fault.
2. When movement occurs,
the hanging wall
slips
upward
3. Form at convergent
boundaries
4. The majestic peaks in
Glacier national Park
are an example of a reverse
fault occurring at a
convergent boundary.
IV. Friction Along Faults
A. Force that opposes the motion
of one surface as it
moves
across another surface.
1. When friction is lowrocks slide by each other
without much sticking
2. When friction is moderatesides of the fault jam
together (from time to time they
jerk free producing
small
earthquakes)
3. When friction is high- the
rocks lock together and
do
not move (stress increases until an
earthquake
releases the
stress)
V.
Mountain Building
A. Over millions of years,
fault movement can change a
flat plain into a towering
mountain range.
B. Mountains Formed by Faulting
1. Fault-block mountain forms
when normal faults
uplift a
block of rock.
2. When two normal faults
form parallel to each
other, and a block of rock is
left lying in the middle.
3. When the hanging wall of
each normal fault moves
downward, the block in between
moves upward.
C. Mountains Formed by Folding
1. Folds are bends in rocks
that form when
compression shortens or thickens
part of Earth’s
crust
2. When two plates collide,
compression causes
Earth’s
crust to fold.
3. Himalayas in Asia are an
example of fold
mountains.
4. These plate collisions can
also cause
earthquakes, because folding
rock can crack and
produce
cracks.
D. Anticlines and Synclines
1. Describe the upward and
downward folds in rock.
a. anticline- upward
b. syncline- downward
2. Found where compression
forces have folded the
crust.
3. May see a syncline where a
valley dips between
two
hills.
E. Plateaus
1. Large area of flat land
elevated high above sea
level.
2. Form when vertical faults
push up a large flat
block
of rock.
3. Consists of many different
flat layers.