Download 7.1 * Forces in Earth*s Crust

7.1 – Forces in Earth’s Crust

Essential Questions:
1.
2.
3.
How Does Stress Change Earth’s Crust?
How Do Faults Form?
How Does Plate Movement Create New Landforms?
How Does Stress Change Earth’s Crust?

Stress is a force that acts on rocks to change its
shape or volume.
 Force

per unit area.
Tension, compression, and shear are types of stress
that work over millions of years to change the
shape and volume of rock.
Types of Stress

Tension: Stress that pulls rock in opposite directions.
 Divergent
Boundaries
Types of Stress

Compression: The stress force that squeezes rock
together.
 Convergent
Boundaries
Types of Stress

Shear: Stress that pushes a rock in two opposite
directions.
 Transform
Boundaries
How Do Faults Form?
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

A fault is a break in the Earth’s crust.
Most faults occur along plate
boundaries.
When enough stress builds up in rock,
the rock breaks, creating a fault.
 There
are three types of faults.
Normal Fault

In a normal fault, the fault cuts the rock at an
angle, so one block sits over the fault (hanging wall)
and the other lies under the fault (footwall).
 Forms
where two plates move apart, or diverge.
Reverse Fault

A reverse fault has the same structure as a normal
fault, but the blocks move in the reverse direction.
 The
hanging wall moves up and the footwall moves down.
 Caused
by compression, or convergence.
Strike-Slip Fault

In a strike-slip fault, the rocks on either side of the
fault slip past each other sideways, with little up or
down motion.
 Forms
where two plates slide past one another.
 Transform
boundary.
How Does Plate Movement Create
New Landforms?

Over millions of years, the forces of plate
movement can change a flat plain into features such
as anticlines and synclines, folded mountains, faultblock mountains, and plateaus.
Anticlines and Synclines

Formed by compression.
Folded Mountains

Also formed by
compression.
Zagros mountain range,
seen from space.
Stretching Earth’s Crust

Fault-block mountains form where Earth’s crust is
stretched.
Uplifting Earth’s Crust

A plateau is a large area of flat land elevated
high above sea level.