Transcript 7.4 Forces that move plates.

7.4 Forces that move plates.
Focus

Write a description of each example and suggest
how each might have formed.
Review





Continental – Continental - Convergent
Oceanic – Oceanic - Convergent
Continental – Oceanic – Convergent
Divergent
Transform
Deformation

Deformation – the process by which the shape of a
rock changes because of stress.
 Rock
layers bend when stress is placed on them.
 If enough stress is applied the rocks will break.
Compression

Compression – the type of stress that occurs when
an object is squeezed.
 Causes
the formation of large mountains.
Tension

Tension – is stress that occurs when forces act to
stretch an object.
 Occurs
 Ex.
at divergent plate boundaries.
Mid-ocean ridges.
Shear

A stress in which tension is usually created by
sliding.
 Earthquakes
are common due to these forces.
Folding

Folding – the bending of rock layers due to stress.
 We
assume that all rock layers start out as horizontal
layers.
 When you see a fold deformation must have occurred.
Types of Folds

Anticlines – upward-arching folds.

Synclines – downward, trough like folds.
Faulting


Fault – a break in a body of rock along which one
block slides relative to another.
Fault blocks – the blocks of crust on each side of the
fault.
Faulting

Hanging wall – a wall that you could not physically
stand on.
Faulting

Footwall – the wall that you could walk on.
Normal Faults

Normal fault – When the fault moves, it causes the
hanging wall to move down relative to the footwall.
 Occurs
where there is tension that pulls rocks apart.
Reverse Faults

Reverse Fault – when it moves it causes the hanging
wall to move up relative to the footwall.
 Happens
together.
when forces are compressed pushing rocks
Strike Slip Faults

Strike-slip Fault – form when opposing forces cause
rock to break and move horizontally.
 Ex.
San Andreas
Output: Diagram

Draw a diagram showing the three different types
of faults and the stress that is used to create those
faults boundaries.
Folded Mountains

Form at convergent boundaries when continents
have collided.
 Rock
layers are squeezed together and pushed
upward.
 Ex.
Appalachian Mountains
Fault-Block Mountains

Fault-Block Mountains – form when the tension
causes large block of the Earth’s crust to drop down
relative to other block.
 Normally
have sharp jagged edges.
 Tetons in Wyoming
Volcanic Mountains

1.
2.
Form when:
oceanic plates subduct below each other
continental and oceanic plates subduct below each
other.
 Some
of the most famous volcanic mountains are
located around the rim which has become known as the
ring of fire.
Ring of Fire
Uplift and Subsidence


Uplift – the rising of regions of Earth’s crust to
higher elevations.
Subsidence – the sinking of regions of the Earth’s
crust to lower elevations.
Uplifting of Depressed Rocks

Rebound – the process of land rising without
deformation.
 The
crust of the Earth slowly springs back to its previous
elevation.
 Occurs
normally when weight is removed from the crust.
Subsidence of Cooler Rocks



Hot rocks take up more space than cooler rocks.
Because of this, rocks near mid-ocean ridges tend to
be higher up than those that are father away.
As you move farther away from the mid-ocean
ridge rocks tend to subside.
Tectonic Letdown


Rift-zone – a set of deep cracks that forms between
two tectonic plates that are pulling away from each
other.
Pg 212.