2. FFoollddss
• A fold is when the earth’s crust is pushed up from its sides. There
are six types of folds that may occur:
• Anticline
• Syncline
• Tight Fold
• Overfold
• Recumbent Fold
• Nappe Fold
3. AAnnttiicclliinnee
• An anticline occurs when a
tectonic plate is compressed by
movement of other plates. This
causes the center of the
compressed plate to bend in an
upwards motion.
• Fold mountains are formed when
the crust is pushed up as tectonic
plates collide. When formed,
these mountains are usually
enormous like the newly formed
Rocky Mountains in Western
Canada and the United States
• To the top right is a picture of an
anticline. Beneath is a picture of
the Rocky Mountains.
4. SSyynncclliinnee
• A syncline is similar to an
anticline, in that it is formed by
the compression of a tectonic
plate. However, a syncline
occurs when the plate bends in
a downward motion.
• The lowest part of the syncline
is known as the trough.
• To the top right is a diagram of
a syncline fold (The bottom of
the fold center is the trough).
Beneath, is an example of a
syncline in California. Can you
distinguish the trough in this
picture?
5. TTiigghhtt FFoolldd
• A tight fold is a sharp peaked
anticline or syncline.
• It is just a regular anticline or
syncline, but was compressed
with a greater force causing
the angle to be much smaller.
• Folds such as these occur to
form steep mountain slopes
like those in Whistler, British
Columbia.
• To the left is a photo of a tight
fold formed by extreme
pressure on these rocks.
6. OOvveerrffoolldd
• An overfold takes place when folding rock becomes bent
or warped.
• Sometimes the folds can become so disfigured that they
may even overlap each other.
• An example of overfolding is shown in the diagram
below.
7. RReeccuummbbeenntt FFoolldd
• This type of fold is
compressed so much that
it is no longer vertical.
• There is a large extent of
overlapping and it can
take the form of an “s”.
• To the right is a diagram
that shows the process of
recumbent folding.
8. NNaappppee FFoollddiinngg
• This fold is similar to a
recumbent fold because
of the extent of folding
and overlapping.
However, nappe folding
becomes so overturned
that rock layers become
fractured.
• To the right is a picture of
someone standing under
a fractured fold.
9. FFaauullttss
• A fault is when tension and compression associated with plate movement
is so great that blocks of rock fracture or break apart. This process can
occur very rapidly, in the form of earthquakes. The damage caused by
this event can be very destructive and cause severe changes to the
earths surface. There are five types of faults that can occur:
• Normal Fault
• Reverse Fault
• Tear Fault
• Rift Valley
• Horst Fault
10. NNoorrmmaall FFaauulltt
• This occurs when rocks move
away from each other due to
the land moving apart.
• When the rocks move apart,
the side with the less stable
tectonic plate drops below the
side with the more stable plate.
• On the top right is the
movement of a normal fault. A
picture is also shown below.
Notice the displacement of the
different types of rock on each
side of the fault.
11. RReevveerrssee FFaauulltt
• Reverse faults are the opposite of
normal faults. Rocks are
compressed such that one plate
moves up while the other
descends below it.
• When plates compress and crack,
usually the more dense one is
forced under the less dense one.
This is similar to the action of the
continental crust colliding with the
oceanic crust. Here the more
dense crust, being the oceanic
crust is forced under the
continental crust.
• To the right is an animation of a
reverse fault. Below that is a real
picture of what a reverse fault
looks like.
12. TTeeaarr FFaauulltt
• A tear fault, also known as a transform fault, occurs when two
tectonic plates slide in a lateral motion past each other.
• This type of fault causes the most severe earthquakes because they
grind against each other. These earthquakes can either be shallow
or deep and cause tremors over a short or long period of time.
• Tear faults can occur frequently, especially along the coast of
California.
13. RRiifftt VVaalllleeyy
• A rift valley is when two normal
faults occur parallel to each
other and the land sinks
between the faults.
• There are two major examples
of this. One being the Great
Rift Valley in North Africa and
the other, the San Andreas
Fault in California.
• The top right picture is San
Andreas Fault and on the
bottom right is a diagram of
what a rift valley looks like.
14. HHoorrsstt FFaauulltt
• A Horst is the opposite of
a rift valley. The land
between the parallel
faults is forced upward
because the two faults
are being pushed
together.
• This process can take a
long time to occur
because the average
plate movement is one
inch per year.
• There are examples of
horst faults on the left.
15. SSuummmmaarryy
• Folding and faulting has a major influence
on the way the earth looks. Mountains
form and disappear over time, as well as
large rift valleys and other features. This
has an impact on where and how we live.
