How Rocks Deal With Stress
Chapter 7: Plate Tectonics
Types of Stress
• Just like people, the rocks of the crust can get
stressed out too!
• 3 types of stress
1. Compression: squeezes rocks (convergent
boundary)
2. Tension: stretches and elongates rocks (divergent
boundary)
3. Shear: allows rocks to slip and grind past one
another (transform or strike-slip boundary)
• When rocks can’t take on any more stress, they
have reached their elastic limit! At that point
they can break or deform.
Let’s Deform!
• When stress acts on rocks
in the crust, they can do
one of two things: fold or
break.
• The compression stress is
what creates folds in
rocks, which is the
bending of rock layers.
• 3 types of folds:
1. Anticline: horizontal stress
bends rock layers upward
2. Syncline: horizontal stress
bends rock layers downward
3. Monocline: vertical stress
bends the rock layers in the
center
It Isn't My Fault!
• As a result of stress in the
crust, sometimes instead of
folding, the layers of rock
break.
• A fault is a break in the
crust along which blocks of
rock slide past each other.
• The blocks on either side of
the fault are called the
hanging wall and footwall.
• Easy way to remember which
is which: you can HANG off
the hanging wall and walk
with your FOOT up the
footwall.
Who’s At Fault?
• 3 types of faults
1. Normal: rock layers are
pulled apart
horizontally by tension,
hanging wall down
2. Reverse: rock layers are
pressed together due
to compression,
hanging wall up
3. Strike-slip: shear stress
pushes the fault blocks
in opposite directions,
no hanging wall