Transcript Deforming the Earth`s Crust

Deforming the Earth’s
Crust
Deformation
• Stress is the amount of force
per unit area on a given
material
• The process by which the
shape of a rock changes
because of stress is called
deformation
Deformation
• Two types of deformation can
occur to rocks under stress
–Layers can bend when stress
is applied to them
–When too much stress is
applied, they can reach their
elastic limit and break
Compression & Tension
• Compression is the type of
stress that occurs when an object
is squeezed
• Tension is stress that occurs
when forces act to stretch an
object such
Folding
• Folding is the bending of rock
layers because of stress in the
Earth’s crust
• Scientists assume that all rock
layers start off horizontal
• So when scientists see a fold, they
know deformation has occurred
Types of Folds
• There are two main types of folds
–Anticlines, upward, arching
fold
–Synclines, downward, troughlike folds
Anticline
Syncline
Faulting
• Some rock layers break
when too much stress is
applied to them.
• The surface along which a
rocks break and slide past
each other is called a fault
Faulting
• The two sides of a fault are
known as the hanging wall
and the footwall
• The type of fault that forms
is dependent on where the
hanging and footwall are
located
Types of Faulting
• There are three types of
faults that occur
–Normal Faults
–Reverse Faults
–Strike-Slip Faults
Normal Faults
• When rocks are pulled apart
because of Tension, Normal
faults often form
• When a normal fault moves, it
causes the hanging wall to
move down relative to the
footwall
Hanging wall
Footwall
Hanging wall
Reverse Fault
• When rocks are pushed together by
Compression, reverse faults often form
• When a reverse fault moves, it causes the
hanging wall to move up relative to the
footwall
• Special type of reverse fault occurs
when the hanging walls continues to be
pushed over top of footwall called a
“thrust fault”
Reverse Fault
Hanging
wall
Footwall
Strike-Slip Fault
• Forms when opposing forces
‘Shearing’ cause rock to break
and moves horizontally
• If you were standing on one side
of the fault when it moved, the
ground on the other side would
appear to move to your left or
right
Plate Tectonics & Mountain
Building
• When tectonic plates collide, land
features that start as folds and
faults, can eventually become
large mountain ranges
• When tectonic plates undergo
compression and tension, they
can form mountains in several
ways
Folded Mountains
• Form when rock layers are
squeezed together and
pushed upward
• These mountains form at
convergent plate boundaries
• Appalachian Mountains 390
million years ago
Fault-Block Mountains
• When tectonic forces put enough
tension on the Earth’s crust, a large
number of normal faults can occur
• Fault-Block mountains form when
tension (Divergenence) causes
large blocks of the Earth’s crust to
drop down relative to other blocks
• Often leaves sharp, jagged peaks
Volcanic Mountains
• Located at convergent plate
boundaries where oceanic crust
sinks into the asthenosphere at
subduction zones
• The rock that is melted at
subduction zones forms magma
which rises to the surface and
erupts
Volcanic Mountains
• Sometimes these mountains can
rise above the sea and become
islands
• A majority of the tectonically
active volcanic mountains have
formed around the Pacific Plate
which is known as the Ring of
Fire
Uplift and Subsidence
• Uplift is the rising of regions
of Earth’s crust to higher
elevations
• Subsidence is known as
the sinking of Earth’s crust
to lower regions
Uplifting of Depressed Rock
• One way areas rise without deforming
is a process known as rebound
• Rebound occurs when the crust
slowly springs back to its previous
elevation
• Rebound happens when a weight is
removed from a region ( glacial
melting)
Tectonic Letdown
• Subsidence can occur when the
lithosphere becomes stretched
• A rift zone is a set of deep cracks
that forms at a divergent plate
boundary
• As the plates move apart, the rift
zone begins to subside between
the plates
Question 1
• What are two types of
deformation?
Answer
• Layers of rock can bend when
stress is applied to them and if
too much pressure is applied then
the layers can break
Question 2
• What type of fold has an upward,
arching fold that looks like the
letter ‘A’?
A. Syncline
B. Monocline
C. Anticline
Answer
• The answer is C. An anticline has
an upward, arching fold
Question 3
• What type of fault forms when
opposing forces cause rock to
break and move horizontally?
A. Normal Fault
B. Reverse Fault
C. Strike-Slip Fault
Answer
• The answer is C. A strike-slip
fault is formed when opposing
forces cause the rock to break
and move horizontally.