Download fault-block mountains.

Deforming the Earth’s Crust
Faults and Folds
Chapter 7 Section 4
Deformation
• The process by which the shape of a
rock changes because of stress.
• There are two types of stress that
occur in rocks:
• Compression
• Tension
Compression
• Compression occurs when rock is
squeezed.
• Compression happens when two
plates collide at a convergent
boundary.
• Compression occurs and forms
large mountain ranges.
Compression/ Mountain Building
The Himalayas, for example, were raised by the compression that
accompanied collision of the Indian plate with the Eurasian plate. Another
example is Europe's Alps and Jura mountains which were also formed by
horizontal compression, generated in their case by collision with the African
plate and the Eurasian plate.
Tension
• Tension occurs when an object is stretched.
• Tension occurs when plates move away from
•
each other at plate boundaries.
At the Mid-Atlantic ridge the seafloor is
spreading at a rate of about 3cm per year. The
frequency of earthquakes at a mid-ocean ridge
will depend on how much tension is happening
at that point. The more tension means the more
seafloor spreading, resulting in a higher
frequency of earthquakes at a particular midocean ridge.
Folding
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Folding is the bending of rock layers due to
stress in the Earth’s crust.
Depending on how rock layers deform, different
types of folds occur:
Anticline
Syncline
Monocline
Anticline
• An anticline is an upward-arching fold.
• An anticline is formed when there is
horizontal stress on rock layers.
Horizontal stress
Syncline
• Synclines are downward folds.
• They are also caused by horizontal stress.
Horizontal Stress
Monocline
• Monoclines are rock layers that are folded
so that both ends of the fold are horizontal.
Faults
• Some rock layers break when stress is
applied to them.
• The surface along which rocks break is
called a fault.
• The blocks of crust on each side of the
fault are called fault blocks.
• A fault has a foot wall and a hanging
wall.
Footwall
Footwall
You could walk up this face of the fault, on foot, hence the
name footwall.
Hanging Wall
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You could hang from this wall.
Hanging Wall
This is a
normal fault.
Notice how the
rock layers are
the same at
the red lines.
Hanging wall and Footwall
3 Types of Faults
• Normal Fault
• Reverse Fault
• Slip-Strike Fault
Normal Fault
• Rocks are pulled apart because of tension.
Hanging wall
Footwall
In a normal Fault, the hanging wall slides down the
footwall.
Reverse Fault
In a reverse fault the hanging wall is
pushed upward due to compression.
Strike-Slip Fault
Opposing forces cause rocks to
move horizontally. Earthquakes
occur along these faults.
San Andreas Fault, California
Strike-Slip Fault
3 Most Common Types of
Mountains
• Mountains exist because tectonic plates
are continually moving around and
colliding with each other.
• There are 3 types of mountains, named for
how they form:
• Folded Mountains
• Fault-Block Mountain
• Volcanic Mountain
Folded Mountains
• Folding is a process in which the Earth's plates are pushed together
in a roller coaster like series of high points and low points. Folding
bends many layers of rocks without breaking them. The Appalachian
Mountains and Rocky Mountains of the United States, and the Alps
of Europe are examples of mountain ranges that were formed by
folding.
Folded Strata (Layers)
Fault- Block Mountains
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Mountains sometimes form when many layers of the Earth's crust are
moved vertically upward at fault lines by pressures caused by plates
colliding. Fault lines are great cracks in the crust. The mountains that are
formed in this way are called fault-block mountains. The Sierra Nevada
mountains in California and Nevada, and the Grand Teton range of
Wyoming are examples of fault-block mountains.
Fault block mountains form when
tension causes large blocks of
crust to drop down relative to other
blocks.
Volcanic Mountains
• Volcanic mountains are forms when
magma erupts from a divergent boundary
and hardens.
• Many volcanic mountains exist under the
sea.
• Some volcanic mountains rise above the
surface of the ocean to from islands,
Hawaii for example.
Hawaiian Islands