Movement Of The Earth’S Crust

notes on earths crust movement

1. Movement of the Earth’s Crust
Dynamic Earth
Chapter 1
Mr. McKay

2. Earth’s Changing Surface
Stress in the Earth’s crust is
caused by forces pushing and
pulling on it
Crust: the surface or
outermost layer of the Earth
Continental crust makes up the
land masses
Between 32 to up to 70 km thick
Oceanic crust lies beneath the
oceans
Around 8 km thick
How do we know about the interior of the Earth?
Convection Currents in the Mantle

3. Types of Stress
The forces of stress change the shape and volume of
the crust and can cause it to move
Deformation: The Breaking, Tilting, and Folding of rocks
Prefix de = undo
Form = shape or configuration

4. Compression
Compression
occurs when the
rocks are pushed
together
Causes the rocks
to become denser
and smaller in
volume
Rocks are pushed
higher up and
deeper down

5. Tension
Tension pulls on
the rocks causing
them to stretch out
This causes the
rocks to be thinner
so they increase in
volume but
decreases in
density

6. Shearing
Shearing pushes the rocks in
opposite directions
Causes the rocks to twist or
break apart
Examples of deformation
San Andreas Fault
Earth's Landmass Formation

7. Fracture: the cracking or
rocks from stress
Where rocks fracture along
flat surfaces without
moving they are called
joints
Blocks form where the
different sets of joints cross
one another

8. Faulting
Fault: a break or
crack along which
rocks move
Hanging wall: the
block of rock above
the fault plane
Foot wall: the block
of rock below the
fault plane
Faulting Lecture
Faulting Demonstration

9. Normal Fault
Normal Fault: when tension causes the hanging
wall to move down to the foot wall
Vertical fault

10. Reverse Faults
Reverse fault: when
compression causes the the
hanging wall to move up relative
to the foot wall
Vertical fault
This fault has the same setup
as a normal fault, but reversed,
which explains it’s name
Just like the normal fault, one
side of the reverse fault is at
an angle of the other
This fault produced part of
the Appalachian Mountains in
the eastern United States

11. Thrust Faults
Thrust fault: when
compression causes
the hanging wall to
slide over the foot
wall
Horizontal fault
Mixes up the layers
of rock and carries
them miles away
from their original
home

12. Lateral (Strike-Slip) Fault
One block moves to the right or left in relation to
the other block
Horizontal movement
Shearing

13. Faulted Mountains
Fault-Block Mountains:
mountains formed by
blocks of rock uplifted by
normal faults
Several normal faults in one
area can cause mountain
ranges
Found along the west coast
from Mexico into Oregon

14. How Do Mountains
Form?
The forces of plate
movement can build up
Earth's surface, so over
millions of years,
movement of faults can
change a perfectly flat
plain into a gigantic
mountain range
Sometimes, a normal
fault uplifts a block of
rock, so a fault-block
mountain forms
When a piece of rock
between two normal
faults slips down, a
valley is created
Mountain Formation
Mountain Animation

15. Mountains Formed by Folding

Sometimes, under current
conditions, plate movement
causes the crust to fold
Folds are bends in rock
that form when
compression shortens and
thickens part of Earth's
crust
Folds can be microscopic or
huge
The Appalachian Mountains are
formed from folds
Some folds are hidden
underneath other layers of
rocks, hills, etc.
These plate collisions can
produce earthquakes
because rock folding can
fracture and lead to faults

16. Anticlines and Synclines
Geologists use the terms
syncline and anticline to
describe downward and
upward folds in rock
An anticline is a fold in a
rock that arcs upward
A syncline is a fold in a
rock that arcs downward
These folds in rocks are
found on many parts of
the earths surface where
compression forces have
folded the crust

17. What determines faulting or folding?
Temperature: higher temps during compression
result in folding rather than faulting
Pressure: the higher the pressure the more likely
they are to fold
Rock Type: brittle versus ductile (able to be
stretched or bend)
How the Stress is Applied: the more gradually
stress is applied the more likely the rocks will fold

18. Faulted Valleys
Rift Valleys: valleys
formed when the block of
land between two normal
faults slides downward.
Death Valley, CA

19. Plateaus
The forces that
elevate mountains
can also raise
plateaus, a large
area of flat land
elevated high above
sea level
Some form when a
vertical fault pushes
up a large flat piece
of rock
Like a lasagna, a
plateau consists of
many layers, so it is
wider than it is tall

May be formed by:
a flat-topped fold
vertical faulting
a series of molten rock
flows
Magma reaches the
surface through cracks
in the ground

20. Domes
Dome: uplifted area
created by rising magma
The magma underneath
doesn’t rise to the surface
but pushes the layers of
rock above up
Black Hills, SD

21. The Floating
Crust
Mantle: layer of the Earth
beneath the crust
2900 km thick
Made up very dense
flowing rock
The less dense crust floats
on top
Isostasy: The balance
between the downward
force of the crust and the
upward force of the mantle
If material is lost or added to
the crust it will float higher or
lower in the mantle allowing
the crust to rise or sink in areas
In northern areas where massive
amounts of ice have thawed the
crust has risen due to a loss in
material
Think about Antarctica
The Mississippi river basin has
dumped millions of tons of mud
into the Gulf of Mexico but
instead of piling up the weight
has caused the crust to sink so
the depth of the water has not
changed