Transcript Forces in Earth’s Crust

Forces in
Earth’s Crust
Chapter 5 Section 1
But First, a Bit of Review on
Continental Drift!
 http://www.youtube.com/watch?v=wW2
3Z94yf24&list=PLVortxm_jTVgeSqPtPmh3o
OeQj8dcPcqu
Key Terms
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Stress
Tension
Compression
Shearing
Normal Fault
Hanging Wall
Footwall
Reverse Fault
Strike-Slip Fault
Plateau
Types of Stress
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Stress: a force that acts on an area of rock to change its
shape or volume
3 kinds of stress: tension, compression, and shearing
Tension, compression, and shearing work over millions of
years to change the shape and volume of rock.
Tension: 2 plates move apart, pull on the rock, and
stretch the rock out
Compression: pushes rock together
to squeeze it until it folds or breaks
Shearing: pushes a mass of rock in
2 different directions, which breaks
the rock or changes its shape.
http://www.youtube.com/watch?v=ib2Ox9U_nMQ
Kinds of Faults
A
fault is a break in the rock of the crust where rock
surfaces slip past each other.
 Most faults occur along plate boundaries, what the
forces of plate motion push or pull the crust so
much that the crust breaks.
 There are three main types of faults: normal faults,
reverse faults, and strike-slip faults.
Normal Faults
 Normal
faults: occur where tension in the crust pulls
rock apart
 The fault is at an angle, so one block of rick lies
above the other block of rock.
 Hanging wall: the rock that lies above and slips
downward
 Footwall: the rock that lies below
 http://www.youtube.com/watch?v=pjefNn9jQ5c
Reverse Faults
 Reverse
fault: rock of the crust is being pushed
together by compression
 Looks just like a normal fault, but the blocks move in
the opposite direction.
 The hanging wall moves upward rather than
downward.
 http://www.youtube.com/watch?v=Xy0f_rubZJI
Strike-Slip Faults
 Strike-slip
fault: the rocks on either side of
the fault slip past each other sideways
 The plates move past each other along a
sliding boundary.
 http://www.youtube.com/watch?v=4idd
OA95xp4
Changing Earth’s Surface
 Over
millions of years, the forces of plate movement
can change a flat plain into landforms produced
by folding, stretching, and uplifting the earth’s crust.
 These landforms include anticlines and synclines,
folded mountains, fault-block mountains, and
plateaus.
Folding Earth’s Crust
 Sometimes
plate movement causes the crust to
fold.
 Folds are bends in rock that form when compression
shortens and thickens part of the earth’s crust.
 A fold in rock that bends upward into an arch is
called an anticline.
 A fold that bends downward into a valley is called a
syncline
Stretching Earth’s Crust
 When
2 normal faults cut through a block of rock, a
fault-block mountain forms.
 2 normal faults form next to each other with rock in
between them.
 As the hanging walls on each normal fault move
downward, the rock in between moves upward to
form the
 fault-block mountain.
Uplifting Earth’s Crust
 Plateaus:
a large area of flat land elevate high
above sea level
 Some plateaus form when forces in the earth’s crust
push up a large, flat block of rock.
 Plateaus consist of many different layers of rock,
and is wider than it is tall.