Download Results of Stress

Chapter 5.2
1.Rock Deformation
a.Caused by the high temperatures and
pressures of geologic stress.
b.It is possible for the rock to return to
its original shape if the force (stress) is
applied and removed slowly.
c.When the stress passes the limits of the
rock, the rock can be deformed
permanently and may break.
1.Folding
a.When rock responds to stress by
becoming permanently deformed
without breaking.
b.Folding can be easily observed where
the rocks are compressed inward and
the layers of the rock move into new
positions without breaking. (Cracks
may appear, but the rock layers remain
intact.)
a.Size of folds can vary greatly.
i.Some rock folds can be found within
a small hand-size rock while others
span of thousands of miles and must
be seen from air.
a.There are three types of rock folding:
Anticline, Syncline, & Monocline.
i.An anticline fold is an up-curved fold in
which the oldest layer is in the center of
the fold.
1.Mountain ridges are generally found along
anticlines.
ii. A syncline fold is a down-curved
fold in which the youngest layer is in
the center.
1.Valleys are generally found along
synclines.
iii. A monocline fold is a fold in
which both sections remain
horizontal.
1.Faulting & Fracturing
a.Rocks do not always respond to stress by
folding. Under certain conditions rocks will
actually break when stress is applied.
b.Faulting & Fracturing of rocks generally
occurs nearer to the Earth’s surface where
the rocks are cooler and under less pressure.
c.A fracture is a break in rock where there is
no rock movement on either side of the
break.
a.A fault is a break in rock along
which rocks on either side of the
break move.
i.A fault plane is the surface of a fault
along which any motion occurs.
ii.The hanging wall is the rock above
the fault plane.
iii.The footwall is the rock below the
fault plane.
a.There are four types of faults: Normal
Faults, Reverse Faults, Thrust Faults, and
Strike-Slip Faults.
i.A normal fault is a fault in which the
hanging wall moves down relative to the
footwall.
1.These faults generally form along
divergent boundaries where the crust is
being pulled apart.
i.A reverse fault forms when
compression causes the hanging wall to
move up relative to the footwall.
ii.A thrust fault is a reverse fault where
the fault plane is nearly horizontal.
iii.A strike-slip fault is a fault where the
rock on either side of the fault plane
slide horizontally past each other.