Deforming the Earth’s Crust Faults and Folds Chapter 7 Section 4.
Deforming the Earth’s Crust Faults and Folds
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Transcript of Deforming the Earth’s Crust Faults and Folds
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Deforming the Earth’s Deforming the Earth’s CrustCrust
Faults and FoldsFaults and FoldsChapter 7 Section 4Chapter 7 Section 4
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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
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Compression • Compression occurs when rock
is squeezed.
• Compression happens when two plates collide at a convergent boundary.
• Compression occurs and forms large mountain ranges.
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Compression/ Mountain BuildingCompression/ Mountain BuildingThe 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.
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TensionTension• Tension occurs when an Tension occurs when an object is stretchedobject is stretched..• Tension Tension occurs when plates move away fromoccurs when plates move away from
each othereach other at plate boundaries. at plate boundaries.• At the Mid-Atlantic ridge the seafloor is At the Mid-Atlantic ridge the seafloor is
spreading at a rate of about 3cm per year. spreading at a rate of about 3cm per year. The frequency of earthquakes at a mid-The frequency of earthquakes at a mid-ocean ridge will depend on how much ocean ridge will depend on how much tension is happening at that point. The more tension is happening at that point. The more tension means the more seafloor spreading, tension means the more seafloor spreading, resulting in a higher frequency of resulting in a higher frequency of earthquakes at a particular mid-ocean ridge. earthquakes at a particular mid-ocean ridge.
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FoldingFolding Folding is the Folding is the bending of rock layers bending of rock layers
due todue to stressstress in the Earth’s crust. in the Earth’s crust. Depending on how rock layers Depending on how rock layers
deform, different deform, different types of foldstypes of folds occur:occur:
AnticlineAnticline SynclineSyncline MonoclineMonocline
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Anticline
• An anticline is an upward-arching fold.• An anticline is formed when there is
horizontal stress on rock layers.
Horizontal stress
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Syncline
• Synclines are downward folds.• They are also caused by horizontal stress.
Horizontal Stress
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Monocline
• Monoclines are rock layers that are folded so that both ends of the fold are horizontal.
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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.
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FootwallFootwall
Footwall
You could walk up this face of the fault, on foot, hence the name footwall.
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Hanging WallHanging Wall You could hang from this wall.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.
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Hanging wall and FootwallHanging wall and Footwall
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3 Types of Faults• Normal Fault• Reverse Fault• Slip-Strike Fault
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Normal Fault
• Rocks are pulled apart because of tension.
In a normal Fault, the hanging wall slides down the footwall.
FootwallHanging wall
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Reverse Fault
In a reverse fault the hanging wall is pushed upward due to compression.
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Strike-Slip Fault
Opposing forces cause rocks to move horizontally. Earthquakes occur along these faults.
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San Andreas Fault, CaliforniaStrike-Slip Fault
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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
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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)
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Fault- Block Mountains• 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.
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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.
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Hawaiian Islands