Transcript Folded Mountains

Unit 1: Land & Water Forms
World Geography 3200/3202
Intro
 In this lesson you will:
 1.1.4 Explain how compressional forces create fold
mountains. (k)
 1.1.5 Differentiate between the terms anticline and
syncline. (k)
 The basis for today’s lesson will be page 13 in your text.
The main ideas in this presentation will be taken from
material outlined there.
 First a review from Friday……
Mountain Building
 Q. Generally, most mountain ranges are on the
margins of the continents. Why??
 A. Continental plates lie alongside oceanic plates & are
compressed against them (rock layers are squeezed
upward as a result, producing a mountain)
 Geologists study three main methods used to create
mountains from the Earth’s rocky crust
1. Folded Mountains
 Most major mountain ranges were formed by folding:
a process in which the Earth's plates are pushed
together in a roller coaster like series of high points &
low points
 With folding, the continental plates collide causing
the thin crust (lithosphere) to bend.
 The Appalachian Mountains and the Atlas Mountains
were formed by folding when North America & Africa
collided 400 million years ago.
Folded Mountains
 All rock that is put under extreme pressure for long
periods of time (thousands or millions of years) will
fold like clay.
 Folding bends many layers of rocks without breaking
them.
 The peaks are known as anticlines while the valleys
are known as synclines.
Folded Mountains
 The Rocky Mountains are a prime examples of Folded
Mountains
 How Stuff Works Video
 Assigned reading p. 13.
Folded Mountains Review
 Q. What type of tectonic force is required to create
folded mountains?
 A. Compressional
 Q. What name is given to the peaks created in folded
mountains?
 A. Anticline
 Q. What term is given to the valleys created in folded
mountains?
 A.Syncline
Folded Mountains Review
 Q. Are many of the worlds mountains formed by
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folding?
A. MOST
Q. How long does it take for folded mountains to
form?
A. 1000s of years
Q. At which type of tectonic zone would you find
folded mountains? (ridge, transform or subduction)
A. SUBDUCTION
Unit 1: Land & Water Forms
World Geography 3200/3202
 In this lesson you will:
 1.1.6 Explain how tensional forces create a normal fault.
(k)
 1.1.7 Explain how compressional forces create reverse
and overthrust faults. (k)
 This lesson corresponds to the information contained
in the "Mountains Formed by Faulting" section found
on page 14 of your text.
Fault Lines
 Fault lines are basically great cracks in the earth’s crust
created when plates are
compressed against each
other.
 The break or crack may
be slight or may run deep
into the Earth’s crust
 The length of the fault may
be short or may extend
hundreds of kms.
Faulting
 Faulting is instrumental in mountain building
 Geologists have analyzed the precise ways in which
plates are changed by faulting & have developed four
main types of mountains
1. Normal Fault Mountains
 Caused by: tensional forces.
 Occurs when: A plate on one side of the fault drops
down lower than the plate on the other side
Fault Block Mountains
 Sometimes two normal faults occur parallel to each
other
 In some cases the broken plate between the faults
drops as the broken plates move away from each other
forming a rift valley
 In case when many layers of the Earth's crust are
moved vertically upward between two parallel fault
lines, Fault Block Mountains result.
 The vertical force is caused by the Earth's internal
pressure.
Reverse Fault Mountains
 If simple rock layers around a fault push
against each other instead of pulling
away, one block can be pushed up over
the other
 This results in the creation of a Reverse
Fault Mountain caused by
compressional forces where plates move
together at the fault.
Overthrust Faults
 If the plate that suffers the fault has already undergone
folding, & its folded layers are then push up & thrust
over layers on the fault’s other side, an Overthrust
Fault occurs.
Faulting: A Review
 Q. What name is given to large cracks in the earth's crust?
 A. FAULT LINES
 Q. What name is given to faults formed by tensional forces?
 A.NORMAL FAULTS
 Q. What name is given to faults formed by compressional forces?
 A. REVERSE FAULTS
 Q. How do overthrust faults differ from regular reverse faults?
 A. THEY WERE FOLDED BEFORE FAULTING