Forces in Earth’s Crust
Stress
• A force that acts on an area of rock to
change its shape or volume.
There are 3 types of stress
• Tension stretches
rocks
• Compression
pushes rock together
• Shearing pushes
the rock in two
opposite directions
Questions
• What type of landforms results from
tension?
• What type of landform results from
compression?
Faults
• When enough stress builds up in rock, the
rock breaks, creating a fault.
• Most faults occur along plate boundaries
There are 3 kinds of faults
• Normal Faults - Tension in crust pulls
rock apart.
• Reverse Faults - Compression pushes
rock together
• Strike-Slip Faults – Shearing causes
rocks to slip past each other
Mrs. Brown’s Fault Movie
• http://youtu.be/hfir5KQpu6c
• Hanging Wall – The block of rock that is above
the fault plane
• Footwall – The block of rock that is below the
fault plane.
• In a normal fault, the hanging wall slips down
relative to the footwall
• In a reverse fault, the hanging wall moves up
relative to the footwall
• San Andreas fault is a strike-slip fault with little
up or down motion
• The forces of plate movement can
change a flat plain into anticlines,
synclines, folded mountains, fault-block
mountains, and plateau.
Fault Block Mountain
• When two normal faults cut through a
block of rock, a fault block mountain forms.
• Q: Where in California are there fault-block
mountains?
A: The Sierra Nevada and Mojave Desert
regions.
Plateau
• A large area of flat land elevated high
above sea level without much folding or
faulting.